Improvement of memory impairment by (+)- and (-)-pentazocine via sigma, but not kappa opioid receptors
by
Hiramatsu M, Hoshino T.
Laboratory of Neuropsychopharmacology,
Graduate School of Environmental and Human Sciences,
Tenpaku-ku, Nagoya 468-8503, Japan;
Department of Chemical Pharmacology,
Faculty of Pharmaceutical Sciences,
Meijo University, Tenpaku-ku,
Nagoya 468-8503, Japan.
Brain Res. 2005 Aug 25

ABSTRACT

(+/-)-Pentazocine is widely used clinically to treat mild to moderate pain as a racemic compound. Although it is known that (-)-pentazocine acts as a kappa opioid receptor agonist to exhibit analgesic actions and (+)-pentazocine acts as a sigma receptor agonist without analgesic effects, their combined effect on memory has not been investigated in detail. In this study, the effect of (+)- and/or (-)-pentazocine on scopolamine-induced memory impairment in mice was investigated using spontaneous alternation performance in a Y-maze. (+)-Pentazocine (0.35 mumol/kg, s.c.) administered 30 min before behavioral testing significantly improved the impairment of spontaneous alternation induced by scopolamine. A higher dose of (-)-pentazocine (3.50 mumol/kg, s.c.) also reversed the scopolamine-induced impairment of alternation performance. Interestingly, the ameliorating effects of not only (+)-pentazocine, but also (-)-pentazocine were antagonized by a selective sigma receptor antagonist, N,N-dipropyl-2-[4-methoxy-3-(2-phenylenoxy)-phenyl]-ethylamine monohydrochloride (NE-100) (2.6 mumol/kg, i.p.). However, those effects were not antagonized by a selective kappa opioid receptor antagonist, nor-binaltorphimine (4.9 nmol/mouse, i.c.v.). Coadministration of (+)- and (-)-pentazocine (0.35 or 3.50 mumol/kg each) did not have any additive or antagonizing effects on the percent alternation. An antinociceptive effect was observed only with (-)-pentazocine (3.50 mumol/kg, s.c.), and was antagonized by nor-binaltorphimine (4.9 nmol/mouse, i.c.v.), but not by NE-100 (2.6 mumol/kg, i.p.). These results suggest that although the analgesic effect of pentazocine was mediated via kappa opioid receptors, the ameliorating effect on scopolamine-induced impairment of spontaneous alternation was mediated via sigma receptors, not via kappa opioid receptors.

Mu
Pain
Tramadol
Tolerance
Pentazocine
Endomorphins
Opioids and depression
Depression, opioids and the HPA
Kappa opioids and cocaine addiction
Kappa receptors, dopamine d3, and cocaine

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