The role of the retrochiasmatic area in the control of pineal metabolism

The aim of the present investigation was to study the effect of neurotoxic ibotenic acid lesion of the retrochiasmatic area on the daily profile of pi neal N-acetylserotonin and melatonin synthesis and on the pineal metabolic reactivity to nocturnal short-term retinal photostimulation. Groups of rats were killed 6 h after lights off either in the dark of immediately after b eing photostimulated for 1 or 15 min. Additionally, groups of rats were sac rificed at six different time points throughout the 24-hour light-dark cycl e. The results suggested the presence of two functionally distinct territor ies in the retrochiasmatic area. The basal retrochiasmatic area, an area si tuated immediately ventral to the third ventricle, behind the suprachiasmat ic nuclei and in front of the arcuate nucleus, is implicated in the nocturn al inhibitory process induced by short-term retinal photostimulation. The l ateral retrochiasmatic area, which is situated immediately lateral to the a nterior periventricular nucleus, below the anterior hypothalamic nucleus an d in front of the ventromedial hypothalamic nucleus, is importantly involve d in the control of the peak amplitude of the daily production of N-acetyls erotonin and melatonin by the pineal gland.