2nd Institute of Human Physiology University of Milan, Italy
n order to investigate the role of intralaminar, mediodorsal and reticular thalamic nuclei in sleep control, ibotenic acid has been injected into these different nuclei in free-moving cats and rats.
The following results have been obtained:
a) Centralis lateralis (Cl) neurons in the cat control EEG desyncronization and behavioral arousal. When stimulated they induce saccadic ocular movements and PGO waves. They also facilitate REM sleep by enhancing the number of REM episodes.
b) Centrum Medianum (CM) neurons in the cat, have the same effect as CL, as far as EEG, eye movements and PGO waves were concerned. REM sleep, on the contrary was completely obliterated for 24 hours after the injection.
c) Medialis dorsalis (MD) neurons in the cat are involved in EEG synchronization and sleep. They do not participate in REM organization.
d) Bilateral stimulation of n. Reticularis (RE) rostal pole in the cat increases EEG spindles and behavioral sleep. Its ablation abolishes the spindles which are substituted by delta/theta activity.
e) Unilateral lesion of RE rostral pole in the rat induces on the contrallateral cortex a parossistic activity characterised by spikes and spike-waves complexes with a motor behavior which resembled petit-mal epilepsy in humans.
f) Bilateral lesion of RE rostral pole in the rat abolishes both parossistic and normal spindles activity. It induces a dramatic and persistent (up to 48 hours) insomnia with an exploratory behavior accompanied by a monotonous delta-theta diffuse EEG activity.
The results suggest a different control of CL and CM nuclei on REM sleep which mediodorsal neurons are mainly involved in synchronous sleep. RE nuclei, at least in rats, have a role in controlling parossistic activity and seem necessary for sleep induction and maintenance.
