CHOLINOCEPTIVE CELLS IN RAT CEREBRAL-CORTEX - SOMATODENDRITIC IMMUNOREACTIVITY FOR MUSCARINIC RECEPTOR AND CYTOSKELETAL PROTEINS

Adult rat telecephalon was surveyed for cells demonstrating immunoposi tivity for muscarinic receptor (M35 antibody), microtubule-associated proteins, neurofilaments, and brain-spectrin. Neurons immunostained fo r muscarinic receptor were found in frontal, parietal, temporal and oc cipital isocortex where they accounted for approximately 15-16% of all neurons. This labeling involved a large proportion of layer V pyramid al cells, some layer III pyramidal cells and a small proportion of non -pyramidal cells in layers II-VI. In the hippocampus, pyramidal cells, non-pyramidal cells and granular cells were immunoreactive, as were m any pyramidal cells in subicular and entorhinal cortices. In every cor tical region examined, cells demonstrating muscarinic receptor were mo rphologically identical to cells stained lightly to moderately for ace tylcholinesterase following pretreatment with diisopropylfluorophospha te, and they were found in similar numbers and in a similar laminar di stribution. These characteristics further corresponded to those of cel ls whose somatodendritic compartments were intensely immunostained by antibodies to microtubule-associated proteins (MAP): MAP-I, MAP-2, MAP -5; neurofilament proteins (NF): NF-68kD, NF-160kD, NF-200kD; and brai n-spectrin. Double immunostaining using a fluorescence method followed by an avidin-biotin staining procedure revealed that cortical cells w hich possessed immunoreactivity for muscarinic receptor demonstrated a n 80-85% overlap with cells that were immunoreactive for MAP-2 (and ta u) or NF-200kD. Following unilateral ibotenic acid lesions of the nucl eus basalis, MAP-2 immunostaining was reduced in the ipsilateral isoco rtex. This significant reduction was most evident in the parietal cort ex, exactly where maximal loss of acetylcholinesterase-containing fibe rs occurred. The same lesion produced no significant difference in imm unodensity of muscarinic receptor, MAP-I, MAP-5 NF-68kD, NF-160kD and NF-200kD. Thus, cortical cholinoceptive cells are enriched with cytosk eletal components and cholinergic afferents modulate cortical MAP-2.