Potentiation of electroencephalographic spindles by ibotenate microinjections into nucleus reticularis thalami of cats

It is found that, in cats, spindle density was dramatically increased following infusion of ibotenic acid into the rostral pole of the nucleus, supporting the role of this sector in spindle-related rhythmicity.

Abstract

It is well known that the electroencephalogram of the cat in the early stages of slow wave sleep is mainly characterized by rhythmic wave activity at 7-14 Hz, termed spindles, which recur periodically with a slow rhythm of 0.1-0.2 Hz. From early stimulation, decortication and transection studies (see Ref. 14), spindle oscillations were thought to originate in the thalamus. The search for the anatomical substrate of thalamic spindling, however, moved from medial (intralaminar nuclei) to lateral thalamic nuclei, and recently focused on the extreme shell-shaped collection of GABA-ergic cells, the nucleus reticularis thalami. This proposition was based on its structural, hodological, and physiological aspects. There is accumulating evidence that the nucleus reticularis may act as a conditional pacemaker, synchronizing the activity of cortically projecting thalamic neurons. The introduction of glutamate analogues with excitotoxic properties such as ibotenic acid provided the opportunity of studying the immediate effects of chemical excitation of this nucleus on synchronized electroencephalographic activity. We found that, in cats, spindle density was dramatically increased following infusion of ibotenic acid into the rostral pole of the nucleus, supporting the role of this sector in spindle-related rhythmicity.