Evidence for two populations of N-methyl- d-aspartate receptors in neonatal rat spinal cord. The effect of peripheral nerve axotomy

Abstract

Quantitative autoradiography was used to characterise the binding of the N-methyl- d-aspartate (NMDA) receptor antagonist [ 3H]dizocilpine maleate (MK801) in the white matter and dorsal, intermediate and ventral subregions of the grey matter in the lumbar spinal cord of neonatal rats. The effect on the binding of unilateral sciatic nerve section on the day of birth was examined. In unoperated animals the B max and K d of the binding had decreased in all subregions by two weeks, when the values were similar to those in the adult. After axotomy the B max values declined during the first 14 days in all subregions although the density appeared higher in the grey matter in the ventral horn compared to sham operated control. In the axotomised animals, the K d values for the white matter and ventral horn grey matter had declined by two weeks but in the dorsal and intermediate subregions of the grey matter the values remained elevated. The results are consistent with the presence of two populations of NMDA receptor at birth. In the normal animals the lower affinity receptor disappears in all subregions, but after axotomy it is retained in the dorsal and intermediate subregions for at least 2 weeks.