Orienting-like reaction after ibotenic acid injections into the thalamic centre median nucleus in the cat.

Abstract

The excitotoxin ibotenic acid was injected bilaterally into the intralaminar centre median nucleus of chronically implanted cats in order to study the effects of early excitation of centre median population on electrographic correlates of behavioral states and to compare them to those induced by injection into intralaminar centralis lateralis nucleus, previously shown. Immediately and during the first 24h after injection, highly aroused behavior with electrocortical activation, myoclonic jerks, enhancement of ocular movements and ponto-geniculo-occipital waves were observed. Surprisingly, in contrast to the increase of REM sleep episodes in centralis lateralis cases, REM sleep was obliterated. The injection sites were histologically confirmed. The different connectional properties of the two intralaminar population may explain the differential results. 5. In conclusion, the present behavioral observations and electrographic findings taken together with the known afferent and efferent projections suggest that the caudal group of intralaminar nuclei is involved in orienting-like behavior.