COLOCALIZATION OF MUSCARINIC ACETYLCHOLINE-RECEPTORS AND PROTEIN KINASE-C-GAMMA IN RAT PARIETAL CORTEX

The present investigation analyzes the cellular distribution of muscarinic acetylcholine receptors (mAChRs) and the gamma isoform of protein kinase C (PKC) in the rat parietal cortex employing the monoclonal antibodies M35 and 36G9, respectively. Muscarinic cholinoceptive neurons were most present in layers 2, 3 and 5, whereas most PKCgamma-positive cells were found in layers 2, 5 and 6. Under normal, non-stimulated conditions, approximately 58% of all muscarinic cholinoceptive neurons were immunoreactive for PKCgamma. Conversely, nearly all PKCgamma-positive neurons were M35-immunoreactive. Although both pyramidal and nonpyramidal neurons express the two types of protein, the pyramidal cell type represents the vast majority. Of all cortical neurons, the large (15-25 mu m in diameter) muscarinic cholinoceptive pyramidal neurons in layer 5 express the gamma isoform of PKC most abundantly and most frequently. Approximately 96% of these cells are immunoreactive for PKCgamma. Stimulation of mAChRs by the cholinergic agonist carbachol resulted in a pronounced increase in the intensity of 36G9 immunoreactivity, which may suggest that the mAChRs are functionally linked to the colocalized PKCgamma. No change was found in the number of 36G9-immunoreactive neurons. In contrast, the number of immunocytochemically detectable muscarinic cholinoceptive neurons increased by approximately 38% after carbachol stimulation. The high degree of codistribution in cortical neurone of both transduction proteins suggests a considerable cholinergic impact upon the regulation of PKCgamma, a candidate key enzyme in cortical learning and memory mechanisms