[Surface negative waves in penicillin-induced epileptogenesis in cats].
The "surface negative (SN) wave" produced by pyramidal tract stimulation and recorded at the cortical surface has been identified as a reflection of postsynaptic potentials generated through recurrent inhibitory pathways (Humphrey, et al.). We studied changes in SN wave in an attempt to examine inhibitory mechanisms underlying epileptogenesis in immobilized cats. 1) A single shock applied to the cerebral peduncle evoked alpha and beta wave at the surface of ipsilateral anterior sigmoid gyrus (Fig.1 A). A train of 4 shocks with 4 msec shock-interval elicited SN wave which had a peak latency of 20 msec and decayed in 60-80 msec (Fig. 1 B,C,D). 2) The spindle-like after-discharges elicited by direct cortical shock were markedly suppressed with conditioning stimulation of the ipsilateral pyramidal tract (Fig. 2). Spike-and-wave complexes and other ECoG paroxysms produced by intramuscular administration of penicillin (Pc) were also depressed by repeated stimulation of the cerebral peduncle (Fig. 3). These facts revealed that the inhibitory effects of pyramidal tract stimulation caused to suppress the occurrence of epileptic discharges. 3) SN wave gradually diminished in amplitude after topical application of Pc at the anterior sigmoid gyrus (Fig. 4 A-D). It disappeared completely when tonic-clonic sustained paroxysms occurred at the focus (Fig. 4 E). These effects are due presumably to depression of recurrent postsynaptic inhibition caused by topical penicillin. 4) SN wave observed at the contralateral secondary focus was almost unchanged during interictal and ictal stage (Fig. 5).(ABSTRACT TRUNCATED AT 250 WORDS)
D000287:Administration, Topical; D000818:Animals; D002415:Cats; D004569:Electroencephalography; D004828:Epilepsies, Partial / Q000139:chemically induced / Q000503:physiopathology*; D005071:Evoked Potentials; D007273:Injections, Intramuscular; D010406:Penicillins / Q000008:administration & dosage*
D010406:Penicillins