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(Accepted March 15, 2001)
To evaluate the influence of light and darkness on brain pyroglutamyl-peptidase I (pGluPI) activity, four experimental groups of rats were compared at the same time-point (10.00 h). Two groups were designed with a standard 12-12 h light-dark cycle: In group A, the lights were on from 7.00 h to 19.00 h, and the experiment was done under light conditions; in group B, the lights were on from 19.00 h to 7.00 h, and the experiment was done under darkness conditions. Two additional groups were designed with nonstandard light-dark conditions: In group C, the animals were subjected to constant light, and the experiment was done under light conditions. In group D, animals were subjected to constant darkness, and the experiment was done under darkness conditions. Light (vs darkness) and standard (vs nonstandard) conditions produced significant changes on pGluPI activity in specific structures; the data suggested that endogenous substrates of pGluPI such as thyrotropin-releasing hormone and gonadotropin-releasing hormone, might be modified in parallel. There was left predominance in the retina under light conditions on a standard schedule (group A). The regional pattern of distribution of activity was similar in groups on a standard schedule (A vs B) and in groups tested under constant light-dark conditions (C vs D). However, this pattern differed between groups subjected to standard vs constant light-dark conditions (A and B vs C and D). These results support an influence of environmental light and darkness on pGluPI activity, which may reflect concomitant changes in its susceptible substrates and consequently in their functions.
KEY WORDS: Pyroglutamyl-peptidase I; light; darkness; rats; brain.
INTRODUCTION
Environmental light generates important neuromorphological (1), behavioural (2,3), neurochemical (1,4) and neuroendocrine changes (5,6). We report significant modifications in a neuropeptide-degrading peptidase activity in serum and several photoneuroendocrine structures under standard and nonstandard light-dark conditions.
The neural pathway by which photoperiodic information reaches the pineal gland involves a photoneuroendocrine circuit related to the melatonin rhythmgenerating system and other neuroendocrine rhythms. Nerve impulses generated in the retina first reach the suprachiasmatic nuclei (SCN) of the anterior hypothalamus (Ht), and then the paraventricular nuclei (7), via the retinohypothalamic tract. Through the medial forebrain bundle and reticular formation, these nuclei project to the intermediolateral nucleus of the spinal cord, from which...