The antiopioid peptide, neuropeptide FF, enhances the effects of acute morphine on the cerebral monoamines in rats

The effects of neuropeptide FF (NPFF) on the changes induced by acute morphine in cerebral monoamines were studied in male Wistar rats. We measured the concentrations of noradrenaline (NA), 5-hydroxytryptamine (5-HT), dopamine and their main metabolites in the limbic area (LIM), hypothalamus (HYP) and lower brain stem (LBS). NPFF (10 mu gx3 at 20 min intervals, i.c.v., bilaterally) did not alter the concentrations of monoamines or their metabolites. Morphine (10 mg kg(-1), s.c., 1 h) did not alter NA or 5-HT or their metabolites in any brain area studied, but elevated 3,4-dihydroxyphenylacetic acid (DOPAC) and/or homovanillic acid (HVA) in LIM and HYP, Combination of morphine and NPFF decreased NA in LIM, elevated 3-methoxy-4-hydroxyphenylethylene glycol in HYP and LBS as well as 5-hydroxyindoleacetic acid in LIM and HYP. These responses are typical to morphine at doses larger than 10 mg kg(-1), and suggest a synergistic effect of the two compounds. Further, the morphine-induced elevations of DOPAC and HVA were potentiated by NPFF in LIM and HYP. In conclusion, our results suggest that NPFF does not attenuate but rather enhances the changes induced by acute morphine in the cerebral monoamines. (C) 1995 The Italian Pharmacological Society