SUBSTANCE-P IS A POSSIBLE NEUROTRANSMITTER IN THE RAT SPINOTHALAMIC TRACT

In order to shed some light on the neurotransmitters in the spinothala mic tract (STT), we examined, biochemically and immunohistochemically, the contents of various neurotransmitter candidates in the terminal f ield of the STT after cervical hemichordotomy (HC) and dorsal quadrant -chordotomy (dQC) in the rat. Substance P (SP), calcitonin gene-relate d peptide (CGRP), enkephalin, neuropeptide Y, neurotensin, oxytocin an d dynorphin A were analyzed immunohistochemically. The contents of neu ropeptides (SP, CGRP and cholecystokinin octapeptide) were measured by radioimmunoassay and those of amino acids (aspartic acid, glutamic ac id, gamma-aminobutyric acid (GABA) and glycine) and noradrenaline were determined using high-performance liquid chromatography. Cervical hem i-chordotomy, but not dQC, caused significant decreases of the SP-like immunoreactivity in and SP content of the ventral thalamus on the ips ilateral side, compared with that on the contralateral side and of rat s subjected to sham-operation. However, neither HC nor dQC resulted in any changes in the ventral thalamic contents of other putative neurot ransmitters examined. These results suggest that, in rats, the STT con tains SP and that SP-positive fibers run in the ventral half of the as cending spinal tract at the cervical level.