Effect of muscarinic ligands on the electrical activity recorded from the hippocampus: a quantitative approach

Abstract

1 The electrical activity of the hippocampus was recorded from the CA 1 region in rats anaesthetized with halothane and the effects of compounds assessed following their intravenous injection. Quantification of the effects was achieved following on-line fast Fourier transformation of the signal. 2 The electrical activity recorded from the hippocampus of the halothane-anaesthetized rat demonstrated identical characteristics to that recorded from the freely-moving animal. 3 Three types of activity could be distinguished: rhythmical slow wave activity (RSA or theta); large amplitude slow wave activity (LIA); and small amplitude fast wave activity. 4 Muscarinic agonists induced RSA with a consequent reduction in power. The effects were dose-dependent and were reversibly antagonized by scopolamine, but not methyl-scopolamine, indicating that the effects are mediated centrally by muscarinic receptors. 5 The results show that, in halothane anaesthetized rats, a muscarinic RSA occurs which is unrelated to movement or behavioural arousal.