CHOLINERGIC GABAERGIC INTERACTION IN THE PRODUCTION OF EEG THETA-OSCILLATIONS IN RAT HIPPOCAMPAL-FORMATION IN-VITRO

The generation of EEC theta rhythm (RSA) in the hippocampal formation is a prime example of rhythmic activity involving central mechanisms o f oscillation and synchrony. Cholinergic nature of the in vitro and in vivo induced RSA has been undoubtedly established. Recently, we have demonstrated in vitro that the hippocampal formation theta rhythm resu lted from interaction between the cholinergic and GABAergic systems. I n the present study we have provided additional in vitro evidence that the hippocampal GABA-A receptors are actively involved in the mechani sm of theta production. Specifically, we demonstrated that bicuculline - GABA-A antagonist significantly augmented carbachol induced theta r esponse increasing amplitude and power of rhythmical slow waves. In se parate experiments the carbachol+bicuculline induced RSA were studied in the presence of muscarinic M1 and M2 antagonists - pirenzepine and gallamine (respectively) and GABA-A agonist - muscimol. Both pirenzepi ne and muscimol antagonized induced theta oscillations and gallamine w as found to be completely ineffective in blocking this EEG response. T he results provided evidence for M1 cholinergic/GABA-Aergic interactio n in mechanisms responsible for theta production.