Myoclonic and tonic seizures elicited by microinjection of cholinergic drugs into the inferior colliculus

The inferior colliculus (IC) is the initiation site in the neuronal network for the epileptic audiogenic seizure (AGS). The present study investigates the effects of alteration of IC cholinergic transmission on the elicitatio n of epileptic seizures. Unilateral microinjections of carbachol (3 and 6 m u g/0.2 mu l) into the IC elicited intense locomotor activity, contraversiv e rotations and myoclonic seizures. This result indicates that the IC is th e initiation site for the induction of myoclonic seizures and suggests that these myoclonic seizures may result from activation of mi muscarinic recep tors. Microinjections of the nicotinic-muscarinic antagonist, gallamine (2 and 6 mu g/0.2 mu l), into the IC induced AGS susceptibility. However, micr oinjections of muscarinic antagonists, atropine (15 mu g/0.2 mu l) and scop olamine (12 and 20 mu g/0.2 mu l), or the nicotinic antagonist, hexamethoni um (12 and 20 mu g/0.2 mu l), into the IC have no effect. Gallamine-induced AGS susceptibility may result from a selective blockade of m2 muscarinic r eceptors.