Search

The effects of s.c. capsaicin treatment on the thoracic spinal cord contents of immunoreactive substance P (ISP), norepinephrine (NE) and serotonin (5-HT) were investigated in adult male Wistar-Kyoto (WKY) and spontaneously hypertensive (SHR) rats. Capsaicin administered s.c. significantly reduced the concentration of ISP in the thoracic spinal cords from rats of both the WKY and SHR strains. The s.c. administration of capsaicin significantly increased the NE contents of the thoracic spinal cords in rats of both the WKY and SHR strains, and both vehicle- and capsaicin-treated SHR animals exhibited significantly greater thoracic spinal cord NE concentrations than did rats from the corresponding WKY treatment groups. In contrast, s.c. capsaicin treatment significantly increased the concentration of 5-HT only in the thoracic spinal cords of SHR subjects. These results strongly suggest that the neurochemical effects of s.c. capsaicin administration on the spinal cord were not specific to ISP-containing neurons since significant changes in the concentrations of NE and 5-HT were also produced by capsaicin treatment. These capsaicin induced changes in the concentrations of putative neurotransmitter substances in the spinal cord are related to previously reported alterations in nociception and cardiovascular regulation produced by s.c. capsaicin administration. Physiological and pharmacological mechanisms possibly relating the neurochemical changes produced by capsaicin to the behavioral and cardiovascular effects of the drug previously reported are advanced and discussed.

The effects of s.c. capsaicin treatment on the contents of immunoreactive substance P (ISP) in several peripheral and central nervous system tissues were examined in normotensive Wistar-Kyoto (WKY) and spontaneously hypertensive (SHR) rats. Significant differences between vehicle-treated subjects of the WKY and SHR strains were observed in the ISP contents of both superior cervical and celiac sympathetic ganglia. Capsaicin pretreatment significantly reduced the ISP contents of both sympathetic ganglia in both strains. Capsaicin pretreatment significantly elevated the ISP contents of adrenal medullae only in rats of the SHR strain. The effects of s.c. capsaicin administration on the ISP contents of several selected isolated brain nuclei were also examined. No statistically significant strain or treatment differences in the SIP contents of the nucleus tractus solitarii nucleus locus ceruleus and periaqueductal central gray were observed. The ISP contents of the nucleus raphe magnus, periventricular preoptic area, and nucleus amygdaloideus medialis were significantly greater in vehicle-treated SHR rats than in vehicle-treated WKY animals. Capsaicin pretreatment significantly increased the ISP contents of both the periventricular preoptic area and nucleus amygdaloideus medialis in SHR rats. These results indicate that the effects of capsaicin treatment of the ISP contents of nervous systems tissues vary with both the tissues examined and the strain of rat. In addition, the previously reported long-lasting hypotensive effect produced by capsaicin in both the WKY and SHR strains may be related to the significant depletion of the ISP contents in peripheral sympathetic ganglia in both strains.

Effects of s.c. capsaicin pretreatment on nociception, mean systemic arterial blood pressure, and dose-response curves for depressor effects of substance P (SP) and pressor effects of angiotension II (AII) and norepinephrine (NE) were examined in normotensive Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR). Capsaicin pretreatment significantly elevated hot plate and tail flick latencies in SHR subjects but was without effect in WKY rats. Capsaicin pretreatment significantly reduced mean systemic arterial blood pressure in rats of both strains. Both vehicle- and capsaicin-treated WKY subjects exhibited greater depressor responses than did subjects of the corresponding SHR groups after i.v. SP administration. Vehicle-treated SHR subjects exhibited greater pressor responses to both AII and NE than did rats of the vehicle-treated WKY group. Capsaicin treatment decreased the sensitivity of WKY rats to the pressor effects of both AII and NE. Strain differences involving nociception, cardiovascular regulation, and responses to capsaicin may underly the results reported.