The effects of 5-hydroxytryptamine-depleting drugs on peptides in the ventral spinal cord.

The ventral spinal cord content of several neuronally localised peptides was measured after treatment with a number of drugs which deplete spinal cord monoamines. Reserpine and tetrabenazine, but not p-chlorophenylalanine caused a partial depletion of ventral spinal cord substance P (SP) and thyrotropin-releasing hormone (TRH). Two other peptides, methionine-enkephalin and somatostatin were not depleted by any of the drugs. The rates of loss and recovery of SP and TRH after reserpine and tetrabenazine were different from that of 5-hydroxytryptamine (5-HT), though in the ventral spinal cord these two peptides probably coexist with 5-HT in the terminals of bulbospinal neurones. The results are discussed in relation to the possible costorage of SP and TRH with 5-HT in the same vesicles in nerve terminals in the ventral spinal cord.