Capsaicin Does Not Change Tissue Levels of Glutamic Acid, Its Uptake, or Release in the Rat Spinal Cord

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Abstract
Capsaicin treatment (50 mg/kg, s.c.) of newborn rats resulted in a 75% decrease of substance P immunoreactivity in the dorsal spinal cord of the adult animal, but failed to affect levels of the proposed sensory neurotransmitter glutamic acid or to alter high-affinity uptake of [3H]glutamic acid into synaptosomes of the same tissue. Furthermore, capsaicin (30 .mu.M) in vitro had no influence on the release of [3H]glutamic acid from spinal cord P2 fractions of untreated adult rats, but induced a marked release of substance P. In contrast to substance P fibers, neurons containing glutamic acid are not sensitive to capsaicin. Eleven other neurochemical parameters measured in the spinal cord did not appear to be changed by the treatment with capsaicin, suggesting a considerable neurochemical selectivity of the lesion.