Neonatal capsaicin modifies morphine withdrawal signs in the rat.
Rats received injections of either capsaicin (50 mg/kg, s.c.) or the capsaicin vehicle at two days of age. When the animals were 90-120 days of age they were implanted with morphine or placebo pellets (s.c.) for 3 (one pellet) or 6 (3 pellets) days. Naloxone (0.4 mg/kg, s.c.) produced no effects in the placebo-pelleted groups but elicited salivation, lacrimation and rhinorrhea in the morphine-treated animals. These abstinence signs were less severe in the morphine-pelleted rats (3- and 6-day groups) that were treated as neonates with capsaicin. However, the neonatal capsaicin treatment increased the number of naloxone-precipitated wet-dog shakes in morphine-dependent rats. The increase was statistically significant in rats treated with morphine for 3 but not 6 days. Since capsaicin induces a long-lasting depletion of substance P and other peptides in peripheral and central neurons, it was concluded that substance P or other related peptides may be involved in the expression of some signs of opioid withdrawal.
D000818:Animals; D000831:Animals, Newborn; D002211:Capsaicin; D005260:Female; D008297:Male; D009020:Morphine / Q000009:adverse effects*; D009270:Naloxone; D009297:Nasal Mucosa / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D012472:Salivation; D013373:Substance P / Q000502:physiology*; D013375:Substance Withdrawal Syndrome / Q000503:physiopathology*; D013666:Tears / Q000378:metabolism
D013373:Substance P; D009270:Naloxone; D009020:Morphine; D002211:Capsaicin