THE INFLUENCE OF THALAMIC GABA TRANSMISSION ON THE SUSCEPTIBILITY OF ADULT-RATS TO FLUROTHYL INDUCED SEIZURES

There is considerable evidence that thalamic nuclei are involved in th e propagation and regulation of seizures. In the present study, we inv estigated the possible role in seizure mechanisms of GABAergic transmi ssion in two thalamic nuclei, the posterior nucleus (PO) and the ventr omedial nucleus (VM). Several GABAergic drugs were bilaterally microin fused into PO or VM of adult rats via chronically implanted cannulae, before testing the rats' susceptibility to seizures induced by fluroth yl. In PO, infusions of the GABA elevating agent gamma-vinyl-GABA (20 mug) or of the GABA(A) receptor agonist muscimol (100 ng) suppressed b oth clonic and tonic seizures. Infusions into PO of the GABA(A) recept or antagonist bicuculline (100 ng) facilitated both these seizure type s. Administration of the GABA(B) receptor agonist baclofen (200 ng) al so suppressed clonic seizure susceptibility. Drug infusions into VM, h owever, did not significantly modify the susceptibility to seizures. T hese findings lead us to conclude that GABAergic transmission in the v icinity of the PO, but perhaps not in VM, affects flurothyl seizure su sceptibility. We hypothesize that GABA synapses in PO may be part of a seizure propagation or control circuit including striatum, substantia nigra, and superior colliculus.