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28 June and 23 August 2017
Increased right cardiac sympathetic and parasympathetic nerve activity in type 2 diabetes
CT Bussey, Z Ashley, DO Schwenke, RR Lamberts
Department of Physiology, HeartOtago, School of Biomedical Sciences, University of Otago, Dunedin.
Heart function is regulated by sympathetic and parasympathetic nervous inputs, which are unbalanced in type 2 diabetes contributing to widespread cardiac dysfunction. Specifically, diabetes disturbs heart rate (HR) regulation, which is under control of the previously unstudied right cardiac sympathetic nerve activity (cSNA) and parasympathetic nerve activity (PSNA).
We measured right cSNA and PSNA in 20-week-old male Zucker type 2 diabetic fatty rats (DM, n=6-9) and non-diabetic littermates (ND, n=6-7). The right cardiac sympathetic and parasympathetic vagal nerves were placed uncut over bipolar platinum recording electrodes, during anaesthesia. Baseline cSNA and PSNA were recorded, followed by injection of ß-agonist isoproterenol (1pg/ kg) before and after ganglionic blockade with hexamethonium (1mg/kg). Data were expressed as mean ± standard error, with differences assessed via t-test.
Although HR was decreased, right integrated cSNA was increased in DM (ND 1.7±0.4 vs DM 6.0±2.1 pV/s, P<0.05), accompanied by increased vagal PSNA frequency (ND 2.3±1.1 vs DM 15.7±5.6 Hz, P<0.05). Diabetes reduced ßadrenergic-induced increases in HR and integrated cSNA (ND 21.0±5.9 vs DM 3.9±2.9% change, P<0.05). Disrupting transmission through nerve ganglia with hexamethonium indicated diabetes impaired ß-adrenergic-induced increases in signalling frequency from the heart to the brain (cSNA: ND 35.2±11.7 vs DM -2.2±14.4 Hz; PSNA: ND 109.0±37.2 vs DM 5.7±56.5 Hz; P<0.05).
Thus right cSNA and PSNA are increased in DM, with lower HR suggesting dominant PSNA changes are an underestimated therapeutic target. Reduced ß- adrenergic responsiveness of cSNA and PSNA was largely attributable to rarely studied peripheral signalling. Severe impairment of autonomic regulation is likely a key contributor to the burden of cardiac dysfunction in type 2 diabetes.
Low-intensity magnetic stimulation and excitability in the rodent neocortex as measured by local field potentials
M Sykes,1,2 A Tang,2 J Rodger,2 JNJ Reynolds1
1Department of Anatomy, University of Otago, Dunedin; 2Experimental and Regenerative Neuroscience, School of Animal Biology, University of Western Australia, Perth, Australia.
Repetitive transcranial magnetic stimulation is a technique used to alter cortical excitability in patients with depression or stroke, using strong (~1 tesla) magnetic pulses. Outside of the targeted, focal zone,...