Neuropharmacology of the Neuropsychiatric Symptoms of Dementia and Role of Pain: Essential Oil of Bergamot as a Novel Therapeutic Approach

Abstract

Imaging studies revealed that BPSDs are associated with lower metabolism and perfusion in the frontal and temporal lobes. [...]a large amount of neurofibrillary tangles has been found concurrently with agitation and psychosis (see reference [20]). Neuropsychiatric symptoms were related to hypometabolism of different regions: e.g., psychosis to frontal cortical, agitation/disinhibition to temporal cortical and anxiety/depression to parietal cortical, respectively [21,22]. [...]the pathophysiological features differ based on the type of NPS: for instance, disinhibition, apathy, and frontal dysfunction in AD are linked to excess of neurofibrillary tangles in the frontal lobes, while visual hallucinations and delusions often occur in dementia with Lewy bodies [23]. According to analysis of the dorso-lateral prefrontal cortex (Brodmann area 9—BA9), anterior cingulate gyrus (BA24) and parietal cortex (BA40) delusions and agitation results are significantly linked to Tau tangle pathology and negatively correlated with the levels of the synaptic vesicle zinc transporter ZnT3 [24]. According to the results: - patients affected by AD showed a positive correlation of the ratio homovanillic acid/5-hydroxyindoleacetic acid with the cluster anxieties/phobias as assessed through the BEHAVE-AD; - patients with dementia with Lewy bodies were found to show a negative correlation between homovanillic acid and the cluster hallucinations at BEHAVE-AD; - taurine was inversely correlated with the Cornell Scale for Depression and BEHAVE-AD; - patients suffering from frontotemporal dementia presented an inverse correlation of glutamate with the cluster verbally agitated behavior at the Cohen–Mansfield Agitation Inventory [44].

1. Introduction: Neuropsychiatric Symptoms of Dementia

The global impact of dementia is very serious, since 50 million people all over the world are affected and this figure is expected to triple within 2050 [1]. Among the different forms of dementia, Alzheimer’s disease (AD) is the most common and accounts for about two thirds of all cases [1]. The current AD pipeline includes 112 agents [2] and, while waiting for the discovery of disease-modifying drugs, the treatment of these patients is a very complex issue. Dementia is characterized by progressive deficits of memory, thinking, orientation, comprehension and communication, which are the main targets of the pharmacological action towards AD. Interestingly, quality of life (QoL) of patients is remarkably affected by disturbances of behavior, mood, thought content and perception [3,4,5,6,7]. This latter cluster of symptoms is known as Behavioral and Psychological Symptoms of Dementia (BPSDs) or Neuropsychiatric Symptoms (NPSs), early hallmarks of AD remarkably reducing the quality of life and affecting some 97% of demented patients, who experiences at least one of these fluctuating symptoms over the course of the disease, as assessed in the Cache County Study [8]. There are several syndromes according to the experienced NPSs that can include irritability, anxiety, depression, apathy, agitation, aggression, psychotic symptoms as hallucination, aberrant motor behavior, disinhibition, elation etc. The occurrence of NPSs can be prodromal to the onset of dementia and often induces institutionalization. The time course of these syndromes was studied in volunteers at National Institute on Aging–funded Alzheimer’s Disease Centers [9]. It has been shown that NPSs occur earlier than dementia in most cases for all types of dementia and mild cognitive impairment (MCI). The 5-year longitudinal cohort study “Dementia Study of Western Norway (Demvest)” reported a mean decline of the Mini-Mental State Examination (MMSE) by 2.1 points/year and, in contrast, a median slight increase of the Neuropsychiatric Inventory (NPI) score from 15 at baseline to 17 at year 5 [10]. The symptoms most likely present in cognitive decline were delusions, hallucinations, agitation, apathy and aberrant motor behavior in NPI [10]. Interestingly, the 97% (i.e., almost the whole sample) displayed an NPI total score ≥16 ever and the 49% had ≥36 ever, which stands for need of pharmacological antipsychotic treatment in trials [10]. Agitation is one of the most challenging symptoms of which the principal features are excessive motor activity or verbal or physical aggression [11]. It is predictive of worse prognosis and increased risk of injury. The prevalence of agitation/aggression in AD was observed to be 47.38% [12]. Growing evidence suggests that these symptoms do not depend on cognitive impairment exclusively, since they could be due to peculiar neurotransmitter dysfunctions [13,14].

2. Neuropharmacology of NPSs

The diverse NPSs are characterized by macroscopic and microscopic neuropathological lesions typical of dementia in different anatomic areas, thus a comprehension of this pathogenesis is needed [15]. Neurofibrillary tangles were extensively found in amygdala [16], basal nucleus of Meynert [17], dorsal raphe nucleus [18] and locus coeruleus with following neurodegeneration of the originating noradrenergic projections [19]. Imaging studies revealed that BPSDs are associated with lower metabolism and perfusion in the frontal and temporal lobes. Moreover, a large amount of neurofibrillary tangles has been found concurrently with agitation and psychosis (see reference [20]). Neuropsychiatric symptoms were related to hypometabolism of different regions: e.g., psychosis to frontal cortical, agitation/disinhibition to temporal cortical and anxiety/depression to parietal cortical, respectively [21,22]. Moreover, the pathophysiological features differ based on the type of NPS: for instance, disinhibition, apathy, and frontal dysfunction in AD are linked to excess of neurofibrillary tangles in the frontal lobes, while visual hallucinations and delusions often occur in dementia with Lewy bodies [23]. Despite these associations, not all the patients affected by a specific form of dementia develop the same NPSs [23]. According to analysis of the dorso-lateral prefrontal cortex (Brodmann area 9—BA9), anterior cingulate gyrus (BA24) and parietal cortex (BA40) delusions and agitation results are significantly linked to Tau tangle pathology and negatively correlated with the levels of the synaptic vesicle zinc transporter ZnT3 [24].

Several neurotransmitters have been implicated in the development of these behavioral neuropsychiatric syndromes. A variable lack of balance among the several neurotransmissions may be involved in NPSs development and could explain the fluctuant nature of these syndromes [25].

Cholinergic deficits mainly in the fronto-temporal lobes are involved in diverse neuropsychiatric manifestations of dementia, like delusions of burglary and infidelity or misidentification, as well as of several psychotic conditions (see reference [26]). A role of the cholinergic system in agitation has been hypothesized since anticholinergic drugs increase agitation, while cholinergic agents reduce this symptom (see reference [26]). An α2-adrenergic receptor binding study reported a 70% increase of these receptors in AD patients suffering from agitation and aggression in comparison with the not aggressive patients [27]. Aggression and the treatment with antipsychotics in AD were found to be linked to increased α1-adrenergic receptors in the dorsolateral prefrontal cortex [28,29], where there is an enhanced binding to α2-adrenergic receptors, as well as in middle temporal gyrus [29,30].

Dopamine has been hypothesized to take part in the integration of some behavioral aspects via the meso-limbic system; aggression likely seems to be linked to impairment of dopaminergic pathways [31]. Decreased levels of dopamine were detected in the cingulate gyrus, amygdala, striatum, raphe nuclei and cerebrospinal fluid in AD [29,32,33]. Furthermore, a reduction of striatal D2 receptors in patients suffering from AD was associated with more severe BPSDs [22,34].

Also, serotonin (5-HT) reduction in AD has been implicated in the development of BPSDs. In particular, the different behavioral syndromes characteristic of each patient may be due to an imbalance of more neurotransmitter systems [31]. Cellular alterations of neurons in the raphe nuclei of AD brains were reported: frequent features shown were globose neurofibrillary tangles in the perikaryon and a significant decrease of nucleolar volume and cytoplasmic RNA in medial and lateral dorsal tegmental nucleus [35]. Reduced levels of 5-HT and of 5-hydroxyindoleacetic acid in temporal cortex mainly were highlighted (see reference [36]).

By contrast, the role of γ-aminobutyric acid (GABA) in the presentation of NPSs is not fully understood yet (see reference [36]). An imbalance between glutamatergic and GABAergic transmissions, in circuits already more susceptible because of acetylcholine deficiency, was tested as possibly being involved both in cognitive decline and in neuropsychiatric manifestations [14]. No significant differences in glutamate content in BA10 and BA20 of AD brains were demonstrated, while GABA concentrations were significantly reduced by 21%; although there was no correlation between glutamate content and BPSDs, the ratio glutamate/GABA resulted in the best predictor for the depression factor score in BA10 for AD patients [14]. Also, an imbalance between cholinergic and serotonergic systems is involved in NPSs: the best predictor of lowered ChAT and AChE levels both in BA10 and BA20 was the aggression score and the ratio AChE/5-HT was the best predictor for the psychotic factor, as demonstrated for women [37].

Another interesting finding is that SLC6A4, the gene encoding 5-HT transporter, is subjected to several polymorphisms affecting its expression. In particular, 5-HTTVNTR allele 10 was associated with BPSDs and aggression [38,39]. The 5-HT2A T102C polymorphism has been proposed as a predisposing factor to BPSDs in AD patients at the transcriptional or posttranslational level [40]. Furthermore, it seems to be correlated to a decrease of 5-HT2A receptors in the temporal cortex [41], thus impairing serotonergic modulation of the dopaminergic pathways and, likely, inducing the psychosis spectrum [42,43].

Glutamatergic Transmission and NPSs

The NPSs typical of dementia are characterized by neuropharmacological alterations of the main neurotransmissions, variously investigated but not completely unraveled. The neurochemical correlates of these behavioral syndromes in the cerebrospinal fluid were investigated through lumbar puncture: the sample was searched for the amino acids aspartate, glutamate, glutamine, glycine, taurine, and proline and for norepinephrine, dopamine, 3,4-dihydroxyphenylacetic acid and 5-hydroxyindoleacetic acid at ultraperformance liquid chromatography, whereas for homovanillic acid at high-performance liquid chromatography [44]. According to the results:

-

patients affected by AD showed a positive correlation of the ratio homovanillic acid/5-hydroxyindoleacetic acid with the cluster anxieties/phobias as assessed through the BEHAVE-AD;

-

patients with dementia with Lewy bodies were found to show a negative correlation between homovanillic acid and the cluster hallucinations at BEHAVE-AD;

-

taurine was inversely correlated with the Cornell Scale for Depression and BEHAVE-AD;

-

patients suffering from frontotemporal dementia presented an inverse correlation of glutamate with the cluster verbally agitated behavior at the Cohen–Mansfield Agitation Inventory [44].

Glutamate may play a fundamental role in dementia-related agitation and anxiety because it is the major excitatory neurotransmitter. A study conducted at the University of California, Los Angeles Alzheimer Disease Research Center (UCLA-ADRC) highlighted:

-

an increase of the binding affinity to glycine recognition site;

-

a reduction of NR2A subunits compared to NR2B of N-methyl-D-aspartate (NMDA) receptors in the postmortem orbitofrontal cortex of AD patient subgroups with higher anxiety [45].

An altered balance between the activity of synaptic and extrasynaptic NMDA receptors with over-activation of the extrasynaptic component in subgenual cingulate region BA25 area has been proposed as the mechanism at the root of glutamate-based depression [46]. The involvement of the extrasynaptic NMDA receptors, responsible for the activation of pathways prompting synaptic damage, is a key feature of AD. This is demonstrated by the use of memantine, which exerts neuroprotection via an uncompetitive/fast-off rate acting mainly on these extrasynaptic receptors [47].

Social isolation housing is a model of BPSD-like behavioral disturbances in rodents. The intracerebroventricular injection of β amyloid 1-42 in isolated 11 week-old mice induced aggressive behavior in the resident-intruder test and anxiety behavior in the plus-maze test, according to reduction of the time spent in open arms 3 weeks after injection [48]. Moreover, an increase of the serum levels of corticosterone and an enhancement of presynaptic activity in the Schaffer collateral-CA1 pyramidal cell and in the mossy fiber-CA3 pyramidal cell synapses exist [48]. The latter findings may stand for a corticosterone-induced increase of hippocampal glutamatergic activity, likely implicated in these NPS-like syndromes [48].

3. Novel Pharmacological Mechanisms for NPSs of Dementia Clinical Management: The Essential Oil of Bergamot

A treatment for dementia NPSs endowed with efficacy and safety still remains a serious challenge. An extrapolation of the effects of antipsychotics in the treatment of primary neuropsychiatric disturbances led to their off label use also in BPSDs, regardless of the differences likely occurring between primary and secondary disorders in terms of neuropsychopathology and, consequently, of effectiveness and safety of the drug [49]. Based on the most expressed NPS in the individual syndrome, other pharmacological agents include antidepressants, methylphenidate, benzodiazepines, zolpidem, Z-agents etc [49]. The atypical antipsychotics, such as risperidone, olanzapine, aripiprazole and quetiapine, are more used than the typical agents because of the improved pharmacodynamic profile useful for the treatment of schizophrenia, but the increased risk of death for cerebrocardiovascular side effects is a serious issue in demented patients. Risperidone is considered the safest in the management of NPSs for short-term with accurate review of the treatment [50].

Because of the involvement of multiple neurotransmissions in NPSs, a novel investigational drug, lumateperone tosylate, is a first-in-class agent under study along with several mechanisms for the treatment of agitation in dementia [51]:

-

antagonist at 5-HT2A receptors;

-

partial agonist at presynaptic D2 receptors, while antagonist at postsynaptic receptors;

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enhancer of NMDA and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor activity through the pathway of the mammalian target of rapamycin (mTOR).

Actually, pimavanserin, a selective 5-HT2A receptor inverse agonist and antagonist, is endowed with efficacy in psychosis associated to AD, though only up to the 6th week of treatment [52].

Aromatherapy, a specialized form of phytotherapy that uses essential oils, is a complementary treatment that has provided preliminary though promising evidence for the management of agitation in dementia [53]. A placebo-controlled trial on seventy-two care facilities residents suffering from dementia showed that massage applying Melissa officinalis essential oil reduces the score of agitation at the Cohen-Mansfield agitation inventory, without the occurrence of significant side effects [54]. Bergamot essential oil (BEO) was demonstrated to exert anxiolytic-like activity in animal behavioral tests [55]. In particular, BEO decreased grooming behavior in the open field test as diazepam and most of the anxiolyitic drugs, but without the loss of vigilance induced by diazepam [55]. This effect of BEO in the open field test was not significantly counteracted by flumazenil, hence it is not superimposable to the activity of benzodiazepines [56]. Indeed, BEO was observed to increase alpha electroencephalographic frequency of relaxation and beta brainwave activity of alert [57]. In support of the latter anxyolitic-like relaxant effect, BEO also increased the time spent in open arms in the elevated plus maze and immobility in the forced swimming test, a parameter that can suggest successful coping to stress in this task of evaluating antidepressant effects [55]. Therefore, aromatherapy using BEO can improve BPSDs and these effects could be due to the capability of this essential oil of increasing the levels of aspartate, glycine and taurine in a Ca²⁺-dependent manner after systemic administration and of synaptic glutamate and GABA in a Ca²⁺-independent manner through microdialysis in the hippocampus [58]. Moreover, BEO was demonstrated to foster the release of endogenous glutamate and pre-loaded [³H]D-aspartate concentration-dependently in hippocampal synaptosomes of rat, which was inhibited by the selective non-transportable inhibitor of excitatory amino acid transporters DL-threo-β-benzyloxyaspartic acid [58]. Hence, low concentrations of BEO can cause glutamate exocytosis, whereas high concentrations glutamate release via a carrier-mediated Ca²⁺-independent mechanism (Figure 1) [58].

Therefore, low concentrations of BEO may prompt the presynaptic exocytosis of glutamate, which can act on Gq-coupled group I metabotropic glutamate autoreceptors or heteroreceptors [59]. This mechanism can induce modulation of multiple neurotransmissions dysregulated in the neuropsychiatric symptoms of dementia and initiate retrograde endocannabinoid signaling responsible for disinhibition of the descending analgesic pathway acting on GABAergic interneurons [60].

Patients affected by dementia often present alteration of the nociceptive transduction and modulation pathways, as well as age-related comorbidities responsible for chronic pain often underdetected and mistreated because of their impaired communication skills [60]. Chronic non-cancer pain (i.e., low back pain, diabetic neuropathy, osteoarthritis and migraine), common in neurodegenerative disorders, represents a remarkable social burden [61]. For instance, migraine is often disabling because several following or concomitant stages of the disease can undergo chronification [62] and patients over 65 are not recommended for treatment with triptans [63]. The development of NPSs, and of agitation mainly, is linked to misdiagnosed [64,65] and unrelieved pain [66,67]. In fact, the demented patients who are provided with analgesic therapy are less common than the general population [68], thus supporting pain undertreatment that has been also highlighted in the local context [69,70]. It was demonstrated that a stepwise protocol for pain treatment significantly reduced agitation of the 17%, with an increase after withdrawal [71]. Therefore, aromatherapy using an essential oil endowed with strong analgesic properties could be even more useful in the management of BPSDs as agitation [72]. BEO has been proven to exert analgesic activity both in inflammatory [73,74,75] and in neuropathic [76,77] pain models, as well as via an inhalatory route of administration [78]. The analgesic properties of BEO are reported in Table 1.

It is important to underline that aromatherapy for inhalation would be effective by virtue of the systemic absorption of BEO eliciting its pharmacological action but not because of a psychological perception of the fragrance [78], since patients suffering from dementia may be anosmic [79]. Glutamatergic modulation can explain also the analgesic properties of BEO [60]. Glutamate at the first synapse is implicated in central sensitization, and in modulation of painful stimuli through the metabotropic receptors involved in the release of endogenous opioid peptides and endocannabinoids [60], able to activate type 1 vanilloid receptor TRPV1 and to modulate the release of different neurotransmitters [80]. Glutamate induced pain sensitization can implicate derangement of autophagy, a process subjected to derangement in neuropathic pain [81]. Indeed, modulation of autophagy induced by glutamate has been investigated in vitro [82]. Glutamate induced autophagy, was accompanied by an increase of signals of LC3-II, as NAADP (nicotinic acid adenine dinucleotide phosphate) [82], which has been hypothesized to be a second messenger of glutamate [82,83]. In particular, glutamate fostered the mobilization of Ca²⁺ in a manner that depends on NAADP-regulated channels [82]. Moreover, pre-treatment of cells with the antagonist of the lysosomal Ca²⁺-permeable two-pore channels, i.e., NED-19, failed to increase basal levels of LC3-II, while no further increase occurred with glutamate [82]. This suggests that induction of autophagy by glutamate is inhibited by NED-19 and induced through NAADP and the NAADP-sensitive Ca²⁺-permeable two-pore channels; accordingly, silencing of the latter channels prevented the glutamate-induced increase of autophagy in astrocytes and SH-SY5Y cells [82]. This glutamate-induced autophagic flux via NAADP has been suggested to be linked to AMP-activated protein kinase pathway, a Ca²⁺ and energy deprivation responsive upstream modulator of autophagy [82]. Incidentally, BEO-induced analgesia implicates the induction of basal and induced autophagy [84], as illustrated in Figure 2.

Clinical trials that are able to clear any doubt and to provide sound basis for the use of phytotherapeutic interventions with essential oils (i.e., aromatherapy) in the management of dementia are needed [85]. The evidence accumulated so far supports the need for a rigorous clinical trial in patients affected by dementia, in order to assess efficacy and safety of aromatherapy with BEO in the management of the several neuropsychiatric behavioral syndromes related to this neurodegenerative disorder [86].

Figure 1. Mechanism of BEO-induced increase of synaptic glutamate. BEO in low concentrations causes glutamate exocytosis, while in high concentrations it induces the release of glutamate through a carrier-mediated Ca2+-independent process [58].

Figure 2. Autophagy and analgesic activity of BEO. (A) LC3 expression in the hemi-cord contralateral (C) and ipsilateral (I) to the side of ligation, 7 days after Spinal Nerve Ligation (SNL), showing higher LC3-I expression in ipsilateral side of SNL mice and appearance of LC3-II, thus demonstrating a derangement of autophagy in this neuropathic pain model. The slight increase in LC3-I levels and the apparent formation of LC3-II well correlated with α2δ-1 upregulation (Sham: n = 5, SNL: n = 6; adapted with permission from reference [81]). (B) BEO-mediated concentration-dependent induction of autophagy in SH-SY5Y cells, demonstrated by immunoblot showing the conversion of LC3I to LC3II and reduced p62 levels. Histogram shows the densitometric analysis of p62 levels normalized on the values of GAPDH (used as loading control) expressed as percentage of vehicle from three independent experiments (mean ± SEM). * p <0.05, ** p <0.01, *** p <0.001 vs. 0.005% BEO (ANOVA followed by Tukey-Kramer multiple comparisons test; adapted with permission from reference [84]). (C) A daily dose of BEO (square; 1 mL/kg) subcutaneously administered for 7 days attenuated SNL-induced mechanical allodynia compared to vehicle (filled circles; *** p <0.001). Open circles indicate mechanical sensitivity of sham operated mice. Data are expressed as mean ± SEM of 50% of pain threshold and normalized to the basal value of each animal (n = 5-10 per group). Differences are evaluated using one way analysis of variance (ANOVA), followed by Tukey multiple comparisons test. Adapted with permission from reference [76].

Analgesic Effect	Pain Model	Route of Administration	Main Results of the Research	Study
Antinociceptive effect on licking/biting response	Capsaicin test [73,74]	Intraplantar [73]	BEO (5, 10 and 20 mg) exerted antinociceptive effect in the capsaicin test (50 µg) [73].	Sakurada et al., 2009 [73]
		Subcutaneous into the plantar surface [74]	BEO (20 μg) produced significant antinociception in capsaicin test (1.6 μg), only in the ipsilateral side, reverted by naloxone hydrochloride and methiodide, suggesting a role of peripheral opioid system [74]	Sakurada et al., 2011 [74]
	Formalin test [75,78].	Plantar subcutaneous [75]	BEO (10 μg) significantly inhibited the nociceptive response to 2% formalin, only in the ipsilateral side, and this effect was antagonized by naloxone hydrochloride and methiodide [75]	Katsuyama et al., 2015 [75]
		Inhalatory [78]	A filter paper disc soaked with different volumes of BEO (100, 200, 400, 800 μL) to the edge of the cage allowed inhalation of BEO in different experimental settings, showing its antinociceptive activity in formalin test (2%) in a volume and time of exposure dependent manner [78]	Scuteri et al., 2018 [78]
Antiallodynic effect	Spinal nerve ligation [76]	Subcutaneous into the plantar surface [76]	BEO (1 mL/kg) subcutaneously administered daily for 7 days attenuated mechanical allodynia [76]	Bagetta et al., 2010 [76]
	Partial sciatic nerve ligation [77]	Subcutaneous into the plantar surface [77]	On post-operative day 7, BEO (5.0, 10.0 and 20.0 μg) dose-dependently increased ipsilateral hindpaw withdrawal thresholds and blocked spinal ERK activation [77].	Kuwahata et al., 2013 [77]

Author Contributions

M.T.C., S.S., T.S., L.A.M., P.T. and G.B. conceived the study. D.S. and L.R. participated in the conceptualization of the study, collected the results, analyzed the literature, and wrote the manuscript. All authors read and approved the final manuscript.

Funding

This research received no external funding.

Acknowledgments

D.S. is a post-doc recipient of a research grant salary in the frame of a research project (Tutor: Giacinto Bagetta) on "Pharmacoepidemiology of drugs used in the treatment of neuropsychiatric symptoms and pain in aged (over 65) people with dementia" funded by Calabria Region (POR Calabria FESR-FSE 2014/2020-Linea B) Azione 10.5.12.

Conflicts of Interest

The authors declare no conflict of interest.

Abbreviations

AD Alzheimer's disease

AMPA α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid

BPSDs Behavioral and Psychological Symptoms of Dementia

BA Brodmann area

BEO Bergamot essential oil

CNS Central Nervous System

GABA γ-aminobutyric acid

mTOR mammalian target of rapamycin

MCI Mild cognitive impairment

MMSE Mini-Mental State Examination

NAADP Nicotinic acid adenine dinucleotide phosphate

NMDA N-methyl-D-aspartate

NPI Neuropsychiatric Inventory

NPSs Neuropsychiatric Symptoms

QoL Quality of life

5-HT Serotonin

ZnT3 Synaptic vesicle zinc transporter

TRPV1 Type 1 vanilloid receptor

UCLA-ADRC University of California, Los Angeles Alzheimer Disease Research Center

© 2019 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

References

1. Patterson, C. World Alzheimer Report 2018: The State of the Art of Dementia Research: New Frontiers; Alzheimer's Disease International (ADI): London, UK, 2018.

2. Cummings, J.; Lee, G.; Ritter, A.; Zhong, K. Alzheimer's disease drug development pipeline: 2018. Alzheimer's Dement. 2018, 4, 195-214.

3. Huang, Y.J.; Lin, C.H.; Lane, H.Y.; Tsai, G.E. Nmda neurotransmission dysfunction in behavioral and psychological symptoms of alzheimer's disease. Curr. Neuropharmacol. 2012, 10, 272-285.

4. Burns, A.; Jacoby, R.; Levy, R. Psychiatric phenomena in alzheimer's disease. I: Disorders of thought content. Br. J. Psychiatry J. Ment. Sci. 1990, 157, 72-76.

5. Burns, A.; Jacoby, R.; Levy, R. Psychiatric phenomena in alzheimer's disease. II: Disorders of perception. Br. J. Psychiatry J. Ment. Sci. 1990, 157, 76-81.

6. Burns, A.; Jacoby, R.; Levy, R. Psychiatric phenomena in alzheimer's disease. III: Disorders of mood. Br. J. Psychiatry J. Ment. Sci. 1990, 157, 81-86.

7. Burns, A.; Jacoby, R.; Levy, R. Psychiatric phenomena in alzheimer's disease. IV: Disorders of behaviour. Br. J. Psychiatry J. Ment. Sci. 1990, 157, 86-94.

8. Steinberg, M.; Shao, H.; Zandi, P.; Lyketsos, C.G.; Welsh-Bohmer, K.A.; Norton, M.C.; Breitner, J.C.; Steffens, D.C.; Tschanz, J.T.; Cache County, I. Point and 5-year period prevalence of neuropsychiatric symptoms in dementia: The cache county study. Int. J. Geriatr. Psychiatry 2008, 23, 170-177.

9. Wise, E.A.; Rosenberg, P.B.; Lyketsos, C.G.; Leoutsakos, J.M. Time course of neuropsychiatric symptoms and cognitive diagnosis in national alzheimer's coordinating centers volunteers. Alzheimers Dement. (Amst) 2019, 11, 333-339.

10. Vik-Mo, A.O.; Giil, L.M.; Ballard, C.; Aarsland, D. Course of neuropsychiatric symptoms in dementia: 5-year longitudinal study. Int. J. Geriatr. Psychiatry 2018, 33, 1361-1369.

11. Cummings, J.; Mintzer, J.; Brodaty, H.; Sano, M.; Banerjee, S.; Devanand, D.P.; Gauthier, S.; Howard, R.; Lanctot, K.; Lyketsos, C.G.; et al. Agitation in cognitive disorders: International psychogeriatric association provisional consensus clinical and research definition. Int. Psychogeriatr. 2015, 27, 7-17.

12. Sennik, S.; Schweizer, T.A.; Fischer, C.E.; Munoz, D.G. Risk factors and pathological substrates associated with agitation/aggression in alzheimer's disease: A preliminary study using nacc data. J. Alzheimer's Dis. JAD 2017, 55, 1519-1528.

13. Esiri, M.M. The basis for behavioural disturbances in dementia. J. Neurol. Neurosurg. Psychiatry 1996, 61, 127-130.

14. Garcia-Alloza, M.; Tsang, S.W.; Gil-Bea, F.J.; Francis, P.T.; Lai, M.K.; Marcos, B.; Chen, C.P.; Ramirez, M.J. Involvement of the gabaergic system in depressive symptoms of alzheimer's disease. Neurobiol. Aging 2006, 27, 1110-1117.

15. Lanctot, K.L.; Amatniek, J.; Ancoli-Israel, S.; Arnold, S.E.; Ballard, C.; Cohen-Mansfield, J.; Ismail, Z.; Lyketsos, C.; Miller, D.S.; Musiek, E.; et al. Neuropsychiatric signs and symptoms of alzheimer's disease: New treatment paradigms. Alzheimer's Dement. 2017, 3, 440-449.

16. Kromer Vogt, L.J.; Hyman, B.T.; Van Hoesen, G.W.; Damasio, A.R. Pathological alterations in the amygdala in alzheimer's disease. Neuroscience 1990, 37, 377-385.

17. Sassin, I.; Schultz, C.; Thal, D.R.; Rub, U.; Arai, K.; Braak, E.; Braak, H. Evolution of alzheimer's disease-related cytoskeletal changes in the basal nucleus of meynert. Acta Neuropathol. 2000, 100, 259-269.

18. Grinberg, L.T.; Rub, U.; Ferretti, R.E.; Nitrini, R.; Farfel, J.M.; Polichiso, L.; Gierga, K.; Jacob-Filho, W.; Heinsen, H.; Brazilian Brain Bank Study Group. The dorsal raphe nucleus shows phospho-tau neurofibrillary changes before the transentorhinal region in alzheimer's disease. A precocious onset? Neuropathol. Appl. Neurobiol. 2009, 35, 406-416.

19. Grudzien, A.; Shaw, P.; Weintraub, S.; Bigio, E.; Mash, D.C.; Mesulam, M.M. Locus coeruleus neurofibrillary degeneration in aging, mild cognitive impairment and early alzheimer's disease. Neurobiol. Aging 2007, 28, 327-335.

20. McKeith, I.; Cummings, J. Behavioural changes and psychological symptoms in dementia disorders. Lancet Neurol. 2005, 4, 735-742.

21. Sultzer, D.L.; Mahler, M.E.; Mandelkern, M.A.; Cummings, J.L.; Van Gorp, W.G.; Hinkin, C.H.; Berisford, M.A. The relationship between psychiatric symptoms and regional cortical metabolism in alzheimer's disease. J. Neuropsychiatry Clin. Neurosci. 1995, 7, 476-484.

22. Hirao, K.; Pontone, G.M.; Smith, G.S. Molecular imaging of neuropsychiatric symptoms in alzheimer's and parkinson's disease. Neurosci. Biobehav. Rev. 2015, 49, 157-170.

23. Cummings, J.L. Toward a molecular neuropsychiatry of neurodegenerative diseases. Ann. Neurol. 2003, 54, 147-154.

24. Whitfield, D.R.; Francis, P.T.; Ballard, C.; Williams, G. Associations between znt3, tau pathology, agitation, and delusions in dementia. Int. J. Geriatr. Psychiatry 2018, 33, 1146-1152.

25. Cummings, J.L.; Back, C. The cholinergic hypothesis of neuropsychiatric symptoms in alzheimer's disease. Am. J. Geriatr. Psychiatry Off. J. Am. Assoc. Geriatr. Psychiatry 1998, 6, S64-S78.

26. Cummings, J.L.; Kaufer, D. Neuropsychiatric aspects of alzheimer's disease: The cholinergic hypothesis revisited. Neurology 1996, 47, 876-883.

27. Russo-Neustadt, A.; Cotman, C.W. Adrenergic receptors in alzheimer's disease brain: Selective increases in the cerebella of aggressive patients. J. Neurosci. Off. J. Soc. Neurosci. 1997, 17, 5573-5580.

28. Sharp, S.I.; Ballard, C.G.; Chen, C.P.; Francis, P.T. Aggressive behavior and neuroleptic medication are associated with increased number of alpha1-adrenoceptors in patients with alzheimer disease. Am. J. Geriatr. Psychiatry Off. J. Am. Assoc. Geriatr. Psychiatry 2007, 15, 435-437.

29. Trillo, L.; Das, D.; Hsieh, W.; Medina, B.; Moghadam, S.; Lin, B.; Dang, V.; Sanchez, M.M.; De Miguel, Z.; Ashford, J.W.; et al. Ascending monoaminergic systems alterations in alzheimer's disease. Translating basic science into clinical care. Neurosci. Biobehav. Rev. 2013, 37, 1363-1379.

30. Matthews, K.L.; Chen, C.P.; Esiri, M.M.; Keene, J.; Minger, S.L.; Francis, P.T. Noradrenergic changes, aggressive behavior, and cognition in patients with dementia. Biol. Psychiatry 2002, 51, 407-416.

31. Lanari, A.; Amenta, F.; Silvestrelli, G.; Tomassoni, D.; Parnetti, L. Neurotransmitter deficits in behavioural and psychological symptoms of alzheimer's disease. Mech. Ageing Dev. 2006, 127, 158-165.

32. Storga, D.; Vrecko, K.; Birkmayer, J.G.; Reibnegger, G. Monoaminergic neurotransmitters, their precursors and metabolites in brains of alzheimer patients. Neurosci. Lett. 1996, 203, 29-32.

33. Tohgi, H.; Ueno, M.; Abe, T.; Takahashi, S.; Nozaki, Y. Concentrations of monoamines and their metabolites in the cerebrospinal fluid from patients with senile dementia of the alzheimer type and vascular dementia of the binswanger type. J. Neural Transm. Park. Dis. Dement. Sect. 1992, 4, 69-77.

34. Tanaka, Y.; Meguro, K.; Yamaguchi, S.; Ishii, H.; Watanuki, S.; Funaki, Y.; Yamaguchi, K.; Yamadori, A.; Iwata, R.; Itoh, M. Decreased striatal d2 receptor density associated with severe behavioral abnormality in alzheimer's disease. Ann. Nuclear Med. 2003, 17, 567-573.

35. Mann, D.M.; Yates, P.O. Serotonin nerve cells in alzheimer's disease. J. Neurol. Neurosurg. Psychiatry 1983, 46, 96.

36. Lanctot, K.L.; Herrmann, N.; Mazzotta, P. Role of serotonin in the behavioral and psychological symptoms of dementia. J. Neuropsychiatry Clin. Neurosci. 2001, 13, 5-21.

37. Garcia-Alloza, M.; Gil-Bea, F.J.; Diez-Ariza, M.; Chen, C.P.; Francis, P.T.; Lasheras, B.; Ramirez, M.J. Cholinergic-serotonergic imbalance contributes to cognitive and behavioral symptoms in alzheimer's disease. Neuropsychologia 2005, 43, 442-449.

38. Ueki, A.; Ueno, H.; Sato, N.; Shinjo, H.; Morita, Y. Serotonin transporter gene polymorphism and bpsd in mild alzheimer's disease. J. Alzheimer's Dis. JAD 2007, 12, 245-253.

39. Galimberti, D.; Scarpini, E. Behavioral genetics of neurodegenerative disorders. Curr. Top. Behav. Neurosci. 2012, 12, 615-631.

40. Norton, N.; Owen, M.J. Htr2a: Association and expression studies in neuropsychiatric genetics. Ann. Med. 2005, 37, 121-129.

41. Polesskaya, O.O.; Sokolov, B.P. Differential expression of the "c" and "t" alleles of the 5-ht2a receptor gene in the temporal cortex of normal individuals and schizophrenics. J. Neurosci. Res. 2002, 67, 812-822.

42. Serretti, A.; Drago, A.; De Ronchi, D. Htr2a gene variants and psychiatric disorders: A review of current literature and selection of snps for future studies. Curr. Med. Chem. 2007, 14, 2053-2069.

43. Flirski, M.; Sobow, T.; Kloszewska, I. Behavioural genetics of alzheimer's disease: A comprehensive review. Arch. Med. Sci. AMS 2011, 7, 195-210.

44. Vermeiren, Y.; Le Bastard, N.; Van Hemelrijck, A.; Drinkenburg, W.H.; Engelborghs, S.; De Deyn, P.P. Behavioral correlates of cerebrospinal fluid amino acid and biogenic amine neurotransmitter alterations in dementia. Alzheimer's Dement. J. Alzheimer's Assoc. 2013, 9, 488-498.

45. Tsang, S.W.; Vinters, H.V.; Cummings, J.L.; Wong, P.T.; Chen, C.P.; Lai, M.K. Alterations in nmda receptor subunit densities and ligand binding to glycine recognition sites are associated with chronic anxiety in alzheimer's disease. Neurobiol. Aging 2008, 29, 1524-1532.

46. McCarthy, D.J.; Alexander, R.; Smith, M.A.; Pathak, S.; Kanes, S.; Lee, C.M.; Sanacora, G. Glutamate-based depression gbd. Med. Hypotheses 2012, 78, 675-681.

47. Scuteri, D.; Rombolà, L.; Berliocchi, L.; Corasaniti, M.T.; Bagetta, G.; Morrone, L.A. Aging brain: In search for better neurotherapeutics. Confin. Cephalalalgica Neurol. 2017, 27, 65-71.

48. Tamano, H.; Ide, K.; Adlard, P.A.; Bush, A.I.; Takeda, A. Involvement of hippocampal excitability in amyloid beta-induced behavioral and psychological symptoms of dementia. J. Toxicol. Sci. 2016, 41, 449-457.

49. Forlenza, O.V.; Loureiro, J.C.; Pais, M.V.; Stella, F. Recent advances in the management of neuropsychiatric symptoms in dementia. Curr. Opin. Psychiatry 2017, 30, 151-158.

50. Ballard, C.; Corbett, A. Agitation and aggression in people with alzheimer's disease. Curr. Opin. Psychiatry 2013, 26, 252-259.

51. Kumar, B.; Kuhad, A.; Kuhad, A. Lumateperone: A new treatment approach for neuropsychiatric disorders. Drugs Today 2018, 54, 713-719.

52. Ballard, C.; Banister, C.; Khan, Z.; Cummings, J.; Demos, G.; Coate, B.; Youakim, J.M.; Owen, R.; Stankovic, S.; Investigators, A.D.P. Evaluation of the safety, tolerability, and efficacy of pimavanserin versus placebo in patients with alzheimer's disease psychosis: A phase 2, randomised, placebo-controlled, double-blind study. Lancet Neurol. 2018, 17, 213-222.

53. Ballard, C.G.; Gauthier, S.; Cummings, J.L.; Brodaty, H.; Grossberg, G.T.; Robert, P.; Lyketsos, C.G. Management of agitation and aggression associated with alzheimer disease. Nat. Rev. Neurol. 2009, 5, 245-255.

54. Ballard, C.G.; O'Brien, J.T.; Reichelt, K.; Perry, E.K. Aromatherapy as a safe and effective treatment for the management of agitation in severe dementia: The results of a double-blind, placebo-controlled trial with melissa. J. Clin. Psychiatry 2002, 63, 553-558.

55. Rombola, L.; Tridico, L.; Scuteri, D.; Sakurada, T.; Sakurada, S.; Mizoguchi, H.; Avato, P.; Corasaniti, M.T.; Bagetta, G.; Morrone, L.A. Bergamot essential oil attenuates anxiety-like behaviour in rats. Molecules 2017, 22, 614.

56. Rombolà, L.; Scuteri, D.; Adornetto, A.; Straface, A.; Sakurada, T.; Sakurada, S.; Mizoguchi, H.; Corasaniti, M.T.; Bagetta, G.; Tonin, P.; et al. Anxiolytic-like effects of bergamot essential oil are insensitive to flumazenil in rat. Evid. Based Complement. Altern. Med. 2019. submitted.

57. Rombola, L.; Corasaniti, M.T.; Rotiroti, D.; Tassorelli, C.; Sakurada, S.; Bagetta, G.; Morrone, L.A. Effects of systemic administration of the essential oil of bergamot (BEO) on gross behaviour and eeg power spectra recorded from the rat hippocampus and cerebral cortex. Funct. Neurol. 2009, 24, 107-112.

58. Morrone, L.A.; Rombola, L.; Pelle, C.; Corasaniti, M.T.; Zappettini, S.; Paudice, P.; Bonanno, G.; Bagetta, G. The essential oil of bergamot enhances the levels of amino acid neurotransmitters in the hippocampus of rat: Implication of monoterpene hydrocarbons. Pharmacol. Res. 2007, 55, 255-262.

59. Pittaluga, A. Presynaptic release-regulating mglu1 receptors in central nervous system. Front. Pharmacol. 2016, 7, 295.

60. Scuteri, D.; Rombola, L.; Tridico, L.; Mizoguchi, H.; Watanabe, C.; Sakurada, T.; Sakurada, S.; Corasaniti, M.T.; Bagetta, G.; Morrone, L.A. Neuropharmacological properties of the essential oil of bergamot for the clinical management of pain-related bpsds. Curr. Med. Chem. 2018.

61. Morrone, L.A.; Scuteri, D.; Rombola, L.; Mizoguchi, H.; Bagetta, G. Opioids resistance in chronic pain management. Curr. Neuropharmacol. 2017, 15, 444-456.

62. Scuteri, D.; Adornetto, A.; Rombola, L.; Naturale, M.D.; Morrone, L.A.; Bagetta, G.; Tonin, P.; Corasaniti, M.T. New trends in migraine pharmacology: Targeting calcitonin gene-related peptide (cgrp) with monoclonal antibodies. Front. Pharmacol. 2019, 10, 363.

63. Scuteri, D.; Adornetto, A.; Rombolà, L.; Naturale, M.D.; De Francesco, A.E.; Esposito, S.; Zito, M.; Morrone, L.A.; Bagetta, G.; Tonin, P.; et al. Pattern of prescription of triptans in calabria region. Front. Neurol. 2019. submitted.

64. Sengstaken, E.A.; King, S.A. The problems of pain and its detection among geriatric nursing home residents. J. Am. Geriatr. Soc. 1993, 41, 541-544.

65. Sampson, E.L.; White, N.; Lord, K.; Leurent, B.; Vickerstaff, V.; Scott, S.; Jones, L. Pain, agitation, and behavioural problems in people with dementia admitted to general hospital wards: A longitudinal cohort study. Pain 2015, 156, 675-683.

66. Scherder, E.; Herr, K.; Pickering, G.; Gibson, S.; Benedetti, F.; Lautenbacher, S. Pain in dementia. Pain 2009, 145, 276-278.

67. Husebo, B.S.; Ballard, C.; Aarsland, D. Pain treatment of agitation in patients with dementia: A systematic review. Int. J. Geriatr. Psychiatry 2011, 26, 1012-1018.

68. Ballard, C.; Smith, J.; Husebo, B.; Aarsland, D.; Corbett, A. The role of pain treatment in managing the behavioural and psychological symptoms of dementia (BPSD). Int. J. Palliat. Nurs. 2011, 17, 420-424.

69. Scuteri, D.; Piro, B.; Morrone, L.A.; Corasaniti, M.T.; Vulnera, M.; Bagetta, G. The need for better access to pain treatment: Learning from drug consumption trends in the USA. Funct. Neurol. 2017, 22, 229-230.

70. Scuteri, D.; Garreffa, M.R.; Esposito, S.; Bagetta, G.; Naturale, M.D.; Corasaniti, M.T. Evidence for accuracy of pain assessment and painkillers utilization in neuropsychiatric symptoms of dementia in calabria region, italy. Neural Regen. Res. 2018, 13, 1619-1621.

71. Husebo, B.S.; Ballard, C.; Sandvik, R.; Nilsen, O.B.; Aarsland, D. Efficacy of treating pain to reduce behavioural disturbances in residents of nursing homes with dementia: Cluster randomised clinical trial. BMJ 2011, 343, d4065.

72. Scuteri, D.; Morrone, L.A.; Rombola, L.; Avato, P.R.; Bilia, A.R.; Corasaniti, M.T.; Sakurada, S.; Sakurada, T.; Bagetta, G. Aromatherapy and aromatic plants for the treatment of behavioural and psychological symptoms of dementia in patients with alzheimer's disease: Clinical evidence and possible mechanisms. Evid.-Based complement. Altern. Med. eCAM 2017, 2017, 9416305.

73. Sakurada, T.; Kuwahata, H.; Katsuyama, S.; Komatsu, T.; Morrone, L.A.; Corasaniti, M.T.; Bagetta, G.; Sakurada, S. Intraplantar injection of bergamot essential oil into the mouse hindpaw: Effects on capsaicin-induced nociceptive behaviors. Int. Rev. Neurobiol. 2009, 85, 237-248.

74. Sakurada, T.; Mizoguchi, H.; Kuwahata, H.; Katsuyama, S.; Komatsu, T.; Morrone, L.A.; Corasaniti, M.T.; Bagetta, G.; Sakurada, S. Intraplantar injection of bergamot essential oil induces peripheral antinociception mediated by opioid mechanism. Pharmacol. Biochem. Behav. 2011, 97, 436-443.

75. Katsuyama, S.; Otowa, A.; Kamio, S.; Sato, K.; Yagi, T.; Kishikawa, Y.; Komatsu, T.; Bagetta, G.; Sakurada, T.; Nakamura, H. Effect of plantar subcutaneous administration of bergamot essential oil and linalool on formalin-induced nociceptive behavior in mice. Biomed. Res. 2015, 36, 47-54.

76. Bagetta, G.; Morrone, L.A.; Rombola, L.; Amantea, D.; Russo, R.; Berliocchi, L.; Sakurada, S.; Sakurada, T.; Rotiroti, D.; Corasaniti, M.T. Neuropharmacology of the essential oil of bergamot. Fitoterapia 2010, 81, 453-461.

77. Kuwahata, H.; Komatsu, T.; Katsuyama, S.; Corasaniti, M.T.; Bagetta, G.; Sakurada, S.; Sakurada, T.; Takahama, K. Peripherally injected linalool and bergamot essential oil attenuate mechanical allodynia via inhibiting spinal erk phosphorylation. Pharmacol. Biochem. Behav. 2013, 103, 735-741.

78. Scuteri, D.; Crudo, M.; Rombola, L.; Watanabe, C.; Mizoguchi, H.; Sakurada, S.; Sakurada, T.; Greco, R.; Corasaniti, M.T.; Morrone, L.A.; et al. Antinociceptive effect of inhalation of the essential oil of bergamot in mice. Fitoterapia 2018, 129, 20-24.

79. Vance, D. Considering olfactory stimulation for adults with age-related dementia. Percept. Motor Skills 1999, 88, 398-400.

80. Gratteri, S.; Scuteri, D.; Gaudio, R.M.; Monteleone, D.; Ricci, P.; Avato, F.M.; Bagetta, G.; Morrone, L.A. Benefits and risks associated with cannabis and cannabis derivatives use. Confin. Cephalalalgica Neurol. 2017, 27, 109-116.

81. Berliocchi, L.; Russo, R.; Maiaru, M.; Levato, A.; Bagetta, G.; Corasaniti, M.T. Autophagy impairment in a mouse model of neuropathic pain. Mol. Pain 2011, 7, 83.

82. Pereira, G.J.; Antonioli, M.; Hirata, H.; Ureshino, R.P.; Nascimento, A.R.; Bincoletto, C.; Vescovo, T.; Piacentini, M.; Fimia, G.M.; Smaili, S.S. Glutamate induces autophagy via the two-pore channels in neural cells. Oncotarget 2017, 8, 12730-12740.

83. Pandey, V.; Chuang, C.C.; Lewis, A.M.; Aley, P.K.; Brailoiu, E.; Dun, N.J.; Churchill, G.C.; Patel, S. Recruitment of naadp-sensitive acidic Ca2+ stores by glutamate. Biochem. J. 2009, 422, 503-512.

84. Russo, R.; Cassiano, M.G.; Ciociaro, A.; Adornetto, A.; Varano, G.P.; Chiappini, C.; Berliocchi, L.; Tassorelli, C.; Bagetta, G.; Corasaniti, M.T. Role of d-limonene in autophagy induced by bergamot essential oil in sh-sy5y neuroblastoma cells. PLoS ONE 2014, 9, e113682.

85. Zucchella, C.; Sinforiani, E.; Tamburin, S.; Federico, A.; Mantovani, E.; Bernini, S.; Casale, R.; Bartolo, M. The multidisciplinary approach to alzheimer's disease and dementia. A narrative review of non-pharmacological treatment. Front. Neurol. 2018, 9, 1058.

86. Scuteri, D.; Rombolà, L.; Morrone, L.A.; Monteleone, D.; Corasaniti, M.T.; Sakurada, T.; Sakurada, S.; Bagetta, G. Exploitation of aromatherapy in dementia-Impact on pain and neuropsychiatric symptoms. In The Neuroscience of Dementia: Diagnosis and Management; Preedy, V.R., Martin, C.R., Eds.; Academic Press: San Diego, CA, USA, 2019; in press.