Co-expression of Fos immunoreactivity in protein kinase (PKC gamma)-positive neurones: quantitative analysis of a brain region involved in learning.

The expression of the gamma protein kinase C isoenzyme (PKC gamma) and of the c-fos immediate early gene protein product Fos in the intermediate and medial hyperstriatum ventrale (IMHV) of day-old chicks was determined immunocytochemically. Previous research has shown that (a) there is a learning-related increase in the expression of Fos in the IMHV of the chick after imprinting; (b) PKC gamma is expressed in neurones in most regions of the chick forebrain, including the IMHV. In the present study it was found that in imprinted chicks, 96.5% of neurones in the IMHV that expressed Fos also stained positively for PKC gamma. These results raise the possibility of a functional connection between PKC gamma activation and c-fos expression in neurones in general, and in particular in neurones in the IMHV that are involved in learning.