Effect of sympathectomy on the expression of NMDA receptors in the spinal cord

The expression of NMDA receptors in the intermediolateral (IML) region of t he upper thoracic spinal cord, was studied in 3 week old rats. The effect o f section of the cervical sympathetic nerve on neuronal cell number and rec eptor expression was examined up to two weeks after the operation. Age-matc hed sham-operated and unoperated animals were used as controls. It was show n using quantitative autoradiography with the NMDA receptor antagonist [H-3 ]MK-801 (dizocilpine maleate), that there was a marked downregulation of re ceptors in all groups of animals, beginning at approximately 4 weeks of age . However after sympathectomy, which resulted in the death of 44% of neuron es in the IML by 7 days, there was a significant increase in receptor densi ty per neurone compared to sham-operated controls. In the control animals t here was a significant increase in the Kd value of the binding between 21 a nd 24 days after birth indicating an increased expression of a low affinity receptor, but no such increase was seen after axotomy. The results are con sistent with two populations of NMDA receptors being transiently expressed in the IML in developing animals, and the higher affinity receptor being do wn-regulated between 4 and 5 weeks of age. The presence of the high affinit y receptor subtype may predispose neurones to die after axotomy. (C) 1999 E lsevier Science B.V. All rights reserved.