• colocalizations;
  • immunohistochemistry;
  • inhibitory interneurons;
  • neocortex;
  • tachykinin receptor


The morphology and the distribution of neurons expressing the NK1-receptor (NK1R) and the co-expression of γ-aminobutyric acid (GABA) in these neurons were studied in the rat occipital cortex and in organotypic cultures (OTCs) derived from this structure. By employing immunohistochemistry, we demonstrate that the NK1R-expressing neurons are non-pyramidal neurons and co-express GABA. Some differences were noted between in vivo and OTCs. NK1 R-expressing neurons in OTCs had larger somata and longer dendrites and the proportion stained with an anti-GABA-antibody (∼50%) was smaller than in vivo (90%). The preferential location of NK1 R-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 contrast to the cat and monkey, in the rat occipital cortex the effects of substance P are almost exclusively mediated via inhibitory interneurons.