The present study was undertaken to determine whether changes in receptor binding of substance P (SP) and 5-hydroxytryptamine (5-HT) occur in lumbar spinal cord laminae 2, 3, 4 and 10 following interruption of descending SP and 5-HT input. These transmitters and spinal cord regions have been implicated in nociceptive and visceral functions. Quantitative receptor binding autoradiography was used to assess the binding of 2 nM [3H]SP and 2 nM [3H]5-HT to lumbar spinal cord sections taken from normal rats and rats with unilateral thoracic dorsolateral funiculus (DLF) lesions. Postoperative survival times ranged from 1 to 28 days. Substance P binding was above normal in laminae 2 and 3 ipsilateral to the lesion and in contralateral lamina 2 at 1 day postoperatively (DPO), and declined thereafter, reaching below normal levels by 28 DPO. Substance P binding in lamina 10 was significantly above normal at 7 and 14 DPO, but not at 1 or 28 DPO. Binding of 5-HT was above normal at 7 DPO in lamina 2 ipsilateral to the lesion, lamina 3 contralaterally, and lamina 10 bilaterally. These increases were not sustained, however, and at 28 DPO 5-HT binding was significantly below normal in laminae 2-4 bilaterally. The bilateral effects seen in the present study are consistent with the bilaterality of descending thoracic DLF projections demonstrated by the Fink-Heimer method.(ABSTRACT TRUNCATED AT 250 WORDS)