Postnatal development of the geniculocortical projection in the cat: electrophysiological and morphological studies.

Using laminar field potential analysis, we examined responses elicited by both photic and optic nerve stimulations in 30 kittens of 0--65 days of age and in three adult cats. In adult cats, the response in the visual cortex on optic nerve stimulations is a wave complex which consists mainly of surface positive depth negative (sP-dN) potentials. By contrast, the response in neonates consists of two surface negative - depth positive (sN-dP) waves. In 2 weeks, preceding the sN-dP waves, an sP-dN wave appears. As age increases, the sP-dN wave becomes of higher voltage and the sN-dP waves become of lower voltage. Thus, the configuration of the response resembles that of adult cats in 3--4 weeks. Both photic and optic nerve stimulations elicit responses of the same configuration in the same area. The extent of the response area is exactly the same at any age as in adult cats. Using the orthograde HRP method, we examined terminals of the geniculocortical afferent in 23 kittens of 0--43 days of age. The density of labeled terminals in layer I is much higher in kittens before 1 week of age (n = 8) than in kittens after 1 month of age (n = 5), whereas the density of labeled terminals in layer IV is higher in the older kittens than in the younger kittens. These electrophysiological and morphological changes are correlated in reference to the maturation of the neuronal circuit in the visual cortex.