Muscarinic cholinergic receptors in the human spinal cord: differential localization of [H]pirenzepine and [H]quinuclidinylbenzilate binding sites

The localization of muscarinic cholinergic receptor subtypes was studied in the human spinal cord using in vitro labelling of cryostat sections with ³H]quinuclidinylbenzilate (QNB) and ³H]pirenzepine (PZ) followed by autoradiography. The highest densities of ³H]QNB binding were localized in laminae II (substantia gelatinosa) and IX (motor neurons); in contrast, the highest density of ³H]PZ binding was localized to lamina II where the binding density was 22—32% higher than in lamina IX. These results suggest that the M₁ and M₂ muscarinic cholinergic receptor subtypes may be differentially localized in sensory and motor regions of the human spinal cord.