GABA inhibition of lateral hypothalamic neurons: Role of reticular thalamic afferents

GABA and reticular thalamic (RT) stimulation induced inhibition of lateral hypothalamic (LH) neuronal activity was studied to determine if RT inhibitory input to the LH is mediated by stimulation of GABA receptors. Seven barrel electrodes were utilized to record simultaneously from the LH during microiontophoretic application of GABA, glycine, bicuculline, picrotoxin, and electrical stimulation of the RT. GABA produced an ejection current-related decrease in LH neuronal activity that was antagonized, in a dose-related manner, by the simultaneous administration of picrotoxin or bicuculline. LH neurons were much less sensitive 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 microiontophoretic administration of GABA. In addition, the microiontophoretic 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 neurons are mediated by stimulation of GABA_A receptors and substantiates the involvement of GABA as the inhibitory transmitter of thalamic to hypothalamic projections.