AUTORADIOGRAPHIC DISTRIBUTION OF BINDING-SITES FOR THE NON-NMDA RECEPTOR ANTAGONIST [H-3] CNQX IN HUMAN MOTOR CORTEX, BRAIN-STEM AND SPINAL-CORD

The distribution of non-NMDA receptors in the normal human motor cortex, brainstem and spinal cord has been investigated using [H-3]CNQX. In the motor and premotor cortex, specific [H-3]CNQX binding was present in all cortical laminae with the highest density of binding sites in laminae I, II and the upper part of III. In the normal brainstem, non-NMDA receptors labelled by [H-3]CNQX had a heterogenous distribution. Brainstem motor nuclei subserving eye movements, which tend to be spared in motor neuron disease (MND), had a higher density of [H-3]CNQX binding sites compared to other cranial nerve motor nuclei (VII, X, XII) which tend to be affected. Specific [H-3]CNQX binding was present throughout the spinal grey Matter, the greatest density of binding being found in the substantia gelatinosa. Excitotoxicity at non-NMDA receptors has been implicated in chronic neurodegenerative diseases such as motor neuron disease. This study suggests that the density of non-NMDA receptors, labelled by [H-3]CNQX, does not account for selective vulnerability of motor neurons in this disorder.