A QUANTITATIVE AUTORADIOGRAPHIC STUDY OF [H-3] KAINATE BINDING-SITES IN THE NORMAL HUMAN SPINAL-CORD, BRAIN-STEM AND MOTOR CORTEX

The quantitative autoradiographic distribution of the kainate subtype of non-NMDA receptor in the normal human motor cortex, brainstem and spinal cord has been investigated using [H-3]kainate. In the motor cortex specific [H-3]kainate binding was present in all cortical laminae with the highest density in laminae and 11 and the upper part of III and lower densities in the middle and deep laminae. In the premotor cortex a band of high density was found in laminae V and VI as well as in the superficial laminae. In the normal brainstem kainate receptors had a heterogeneous distribution. Brainstem motor nuclei which tend to be affected in motor neuron disease (MND) had very low densities of binding sites, whereas the oculomotor nucleus had a higher density. Specific [H-3]kainate binding was found throughout the spinal grey matter, the greatest density being found in the substantia gelatinosa and much lower densities in the rest of the grey matter including the ventral horns. Excitotoxicity at non-NMDA receptors has been implicated in the pathogenesis of MND. This study shows that the motor neuron groups vulnerable in MND express a low density of [H-3]kainate binding sites and suggests that the density of kainate receptors does not account for selective vulnerability in this disorder.