Autoradiographic study of α1‐ and α2‐noradrenergic and serotonin1A receptors in the spinal cord of normal and chronically transected cats

Abstract

Serotoninergic and noradrenergic drugs have been shown to initiate and/or modulate locomotion in cats after spinal cord transection and in patients suffering from spinal cord injuries. To establish a firmer basis for locomotor pharmacotherapy, the distribution of α1- and α2-noradrenergic and serotonin1A (5-HT1A) receptors was examined in the spinal cord of control cats and of from animals with spinal cord transection at T13 some weeks or months previously. In control cats, the highest levels of α1-noradrenergic receptors, labeled with [3H]prazosin, were found in laminae II, IX, and X. The α2-noradrenergic receptors, labeled with [3H]idazoxan, were found mainly in laminae II, III, and X, with moderate densities in lamina IX. After spinal transection, both receptors did not change in segments above the lesion. At 15 and 30 days after spinal transection, binding significantly increased in laminae II, III, IV, and X for α2 and in laminae I, II, III, and IX for α1 receptors in lumbar segments. For longer survival times, binding densities returned to near control values. The 5-HT1A receptors, labeled with [3H]8-hydroxy-dipropylaminotetralin, were found mainly in laminae I–IV and X. After spinal transection, binding significantly increased only in laminae II, III, and X of lumbar segments at 15 and 30 days. Thereafter, binding returned to control values. The pronounced upregulation of different monoaminergic receptors observed in the lumbar region in the first month after spinal transection suggests that these receptors may be important during the period when cats normally recover functions such as locomotion of the hindlimbs. J. Comp. Neurol. 406:402–414, 1999. © 1999 Wiley-Liss, Inc.