THETA-LIKE ACTIVITY IN HIPPOCAMPAL-FORMATION SLICES - THE EFFECT OF STRONG DISINHIBITION OF GABA(A) AND GABA(B) RECEPTORS

The involvement of GABA(A) and GABA(B) receptors in neural mechanisms responsible for the production of theta rhythms in hippocampal formati on (HPC) slices is addressed in the present study. In a number of pape rs published in the last decade, we have demonstrated that theta-like activity can be successfully recorded in the limbic cortex maintained in vitro when the cholinergic agonists, acetylcholine, carbachol or mu scarine, were added to the bath. Recently, we have also shown a strong GABA(A) modulation of the cholinergic-induced in vitro theta-like act ivity. This study presents a report of the first demonstration of in v itro theta-like field responses induced as a consequence of simultaneo usly inhibiting hippocampal GABA(A) and GABA(B) receptors. HPC slices (350 mu m) were maintained in a gas-liquid interface chamber (35 degre es C). Theta-like activity was induced in the presence of bath perfusi on of bicuculline (GABA(A) antagonist) and 2-hydroxysaclophen (GABA(B) antagonist). This in vitro induced field response was antagonized bot h by muscimol (GABA(A) agonist) and baclophen (GABA(B) agonist). Tn ad dition, the experiments presented hen revealed that bicuculline/2-hydr oxysaclophen-induced in vitro theta-like activity also had a strong ch olinergic M-1 involvement: it was abolished by hemicholinium-3 (cholin e transport blocker) and pirenzepine (specific antagonist of M-1 recep tor), but not by gallamine (specific antagonist of M-2 receptor). The results of the present study provided further evidence for a strong GA BAergic/cholinergic interaction in the neural mechanism responsible fo r production of theta-like activity in the hippocampal formation slice s. (C) 1997 Elsevier Science B.V.