Autoradiographic study of alpha(1)- and alpha(2)-noradrenergic and serotonin(1A) receptors in the spinal cord of normal and chronically transected cats

Serotoninergic and noradrenergic drugs have been shown to initiate and/or m odulate locomotion in cats after spinal cord transection and in patients su ffering from spinal cord injuries. To establish a firmer basis for locomoto r pharmacotherapy, the distribution of alpha(1)- and alpha(2)-noradrenergic and serotonin(1A) (5-HT1A) receptors was examined in the spinal cord of co ntrol cats and of from animals with spinal cord transection at T13 some wee ks or months previously. In control cats, the highest levels of alpha(1)-no radrenergic receptors, labeled with [H-3]prazosin, were found in laminae II , IX, and X. The alpha(2)-noradrenergic receptors, labeled with [H-3]idazox an, were found mainly in laminae II, III, and X, with moderate densities in lamina IX. After spinal transection, both receptors did not change in segm ents above the lesion. At 15 and 30 days after spinal transection, binding significantly increased in laminae II, III, IV, and X for alpha(2) and in l aminae I, II, III, and IX for alpha(1) receptors in lumbar segments. For lo nger survival times, binding densities returned to near control values. The 5-HT1A receptors, labeled with [H-3]8-hydroxy-dipropylaminotetralin, were found mainly in laminae I-TV and X. After spinal transection, binding signi ficantly 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 r egion in the first month after spinal transection suggests that these recep tors may be important during the period when cats normally recover function s such as locomotion of the hindlimbs. (C) 1999 Wiley-Liss, Inc.