Autoradiographic localization of muscarinic cholinergic receptors at various segmental levels of the human spinal cord.

Muscarinic cholinergic receptors were localized autoradiographically at different segmental levels of the normal human spinal cord after in vitro labelling using [3H]quinuclidinylbenzilate. The highest densities of muscarinic receptors were found in laminae II (substantia gelatinosa) and IX (motor neurons) of the gray matter. Lower densities of receptors were present in the other laminae and no binding sites were found in the white matter. This pattern of distribution of muscarinic receptors was similar at the cervical, thoracic, lumbar and sacral levels of the cord. These data suggest that muscarinic receptors may not only take part in motor function but also in the processing of sensory information.