Ontogenesis of ponto-geniculo-occipital activity in the lateral geniculate nucleus of the kitten

Abstract

In the adult cat, just before the onset of and throughout paradoxical sleep, sharp, monophasic waves appear in the pontine reticular formation, and are transmitted to the lateral geniculate nucleus and occipital cortex. This report describes a study of the appearance and maturation of these ponto-geniculo-occipital weves, or PGO “spikes,” in the lateral geniculate nucleus of the developing kitten. Thirty-nine implantations of the lateral geniculate nucleus were carried out in 34 kittens (ages 8–75 days). Electrodes were also placed for the recording of electrocorticograms, neck muscle activity, and eye movements. Despite the high proportion of paradoxical sleep, and the copious amount of peripheral phasic activity in the neonatal kitten, no PGO activity was found prior to Day 15. The average age of emergence of the activity was Day 21. The PGO waves, at initial appearance, were low in frequency as well as amplitude. However, during a 3- to 6-day sequence, the spikes increased in both frequency and amplitude, and an association developed progressively with the increasingly well-defined periods of paradoxical sleep. Adult PGO spike frequencies were reached by Day 35, though the temporal characteristics of their discharge continued to change for several weeks thereafter. The 3-week postbirth latency to the first appearance of the PGO spikes, as well as the ensuing rise in their recorded frequency and amplitude, seem to be basic characteristics of PGO development. Further, the ontogenesis of spontaneous PGO activity in the lateral geniculate nucleus of the kitten during paradoxical sleep parallels the pace of maturation of the sleep-wake pattern and of the neuroanatomical and neurochemical pathways that function in the mediation of the stages of sleep.