Segmental distribution of thyrotropin releasing hormone in rat spinal cord.

The segmental and laminar distribution of thyrotropin releasing hormone (TRH) was determined in the rat spinal cord using radioimmunoassay (RIA) and immunocytochemistry (ICC). Immunoreactive TRH was found in sensory, autonomic, and motor spinal columns. Dorsal horn TRH-containing fibers and cell bodies in lamina II and along the lamina II/III border were seen by ICC in all spinal cord segments. ICC showed dense TRH immunoreactivity in the sympathetic areas of the thoracic cord. Densely staining TRH-containing fibers were seen in the ventral horn of all spinal segments. RIA of whole segment extracts showed high concentrations in C6-T1 and T12-L6. Low levels were seen in C2-C4 and T5-T6. Other segments were intermediate in concentration. RIA and ICC results were comparatively evaluated.