NEURONS IN THE RAT OCCIPITAL CORTEX CO-EXPRESSING THE SUBSTANCE P-RECEPTOR AND GABA - A COMPARISON BETWEEN IN-VIVO AND ORGANOTYPIC CULTURES

The morphology and the distribution of neurons expressing the NK1-rece ptor (NK1R) and the co-expression of gamma-aminobutyric acid (GABA) in these neurons were studied in the rat occipital cortex and in organot ypic cultures (OTCs) derived from this structure. By employing immunoh istochemistry, we demonstrate that the NK1R-expressing neurons are non -pyramidal neurons and cc-express GABA. Some differences were noted be tween in vivo and OTCs. NK1R-expressing neurons in OTCs had larger som ata and longer dendrites and the proportion stained with an anti-GABA- antibody (similar to 50%) was smaller than in vivo (90%). The preferen tial location of NK1R-expressing neurons in layers II/III and VI, seen in vivo is not present in OTCs where these neurons distribute rather homogeneously through layers Il-VI. Our findings imply that in contras t to the cat and monkey, in the rat occipital cortex the effects of su bstance P are almost exclusively mediated via inhibitory interneurons.