GABA INHIBITION OF LATERAL HYPOTHALAMIC NEURONS - ROLE OF RETICULAR THALAMIC AFFERENTS

GABA and reticular thalamic (RT) stimulation induced inhibition of lat eral hypothalamic (LH) neuronal activity was studied to determine if R T inhibitory input to the LH is mediated by stimulation of GABA recept ors. Seven barrel electrodes were utilized to record simultaneously fr om the LH during microiontophoretic application of GABA, glycine, bicu culline, picrotoxin, and electrical stimulation of the RT. GABA produc ed an ejection current-related decrease in LH neuronal activity that w as antagonized, in a dose-related manner, by the simultaneous administ ration of picrotoxin or bicuculline. LH neurons were much less sensiti ve to glycine inhibition which also was relatively insensitive to the GABA receptor antagonists. RT electrical stimulation provided a short latency inhibitory input to LH neurons that was mimicked by the microi ontophoretic administration of GABA. In addition, the microiontophoret ic application of picrotoxin or bicuculline blocked the RT stimulation induced inhibition of LH neuronal activity. These data indicate that the inhibitory effects of both GABA and RT synaptic inputs onto LH neu rons are mediated by stimulation of GABA, receptors and substantiates the involvement of GABA as the inhibitory transmitter of thalamic to h ypothalamic projections.