C-FOS IMMUNOHISTOCHEMICAL LOCALIZATION OF NEURONS IN THE MESENCEPHALIC LOCOMOTOR REGION IN THE RAT-BRAIN

The projection from the limbic system via the subpallidal region to th e mesencephalic locomotor region is implicated in limbic-motor integra tion. The goal of this study was to visualize neurons of the mesenceph alic locomotor region which are active during locomotor activity induc ed by the disinhibition of the subpallidal region. The subpallidal reg ion was disinhibited by picrotoxin, which antagonizes the effects of G ABA. The unilateral injection of picrotoxin into the subpallidal regio n caused a significant increase in locomotor activity. Active tegmenta l neurons were subsequently visualized by immunocytochemical staining of c-Fos protein. There were significantly more immunostained neurons in the picrotoxin-injected animals than in the saline-treated rats. He avily stained neuronal nuclei, prevailing on the brain side ipsilatera l to the injection of picrotoxin, were localized within a narrow strip of tissue which stretched from the ventrolateral periaqueductal gray (including the dorsal raphe), the cuneiform nucleus, through the regio n of the dorsal tegmental bundle to the pedunculopontine nucleus. Ther e were 3.5 times more immunostained neurons in the cuneiform/pedunculo pontine region and 2.5 times more stained neurons in the periaqueducta l region of the picrotoxin-injected rats, as compared to the saline gr oup. This strip of immunostained cells represents neurons which are in volved in the initiation and maintenance of locomotor activity due to subpallidal activation (predominantly pedunculopontine and cuneiform n uclei), as well as neurons possibly involved in the inhibition of loco motor activity (ventrolateral periaqueductal gray) and other feedback regulations. This study will help identify the neuronal pool involved in coupling the motivational commands with the locomotor system for ex ecution of behaviour. Copyright (C) 1996 IBRO.