Somatostatin and calcitonin gene-related peptide synergistically modulate spinal sensory and reflex mechanisms in the rat: behavioral and electrophysiological studies.

Using behavioral and electrophysiological techniques evidence was obtained that somatostatin (SOM) and calcitonin gene-related peptide (CGRP) synergistically increase spinal cord excitability. In the behavioral experiments 1 microgram SOM or 1 microgram SOM + 20 ng CGRP injected intrathecally (i.t.) elicited a biting/scratching response lasting about 20 min. One microgram SOM combined with 200 ng, 2 micrograms or 20 micrograms CGRP caused an increase in the duration of this response. CGRP by itself (20 micrograms i.t.) had no effect. In the physiological experiments 10 ng SOM or 100 ng CGRP i.t. caused a brief facilitation of the hamstring flexion reflex (1-5 min) whereas 10 ng SOM + 100 ng CGRP synergistically facilitated the reflex for 40-75 min. The results are qualitatively similar to those obtained with substance P + CGRP and further strengthen the role of SOM in sensory transmission involving C-afferents.