Supraspinal FMRFamide antagonizes morphine-induced horizontal, but not vertical, locomotor activity.
Morphine and the molluscan neuropeptide Phe-Met-Arg-Phe-NH2 (FMRFamide) were administered to mice alone or in combination intracerebroventricularly (ICV) and the effect on locomotor activity was measured. Morphine given alone (0.5 micrograms) significantly increased horizontal locomotor activity compared to vehicle-treated controls. FMRFamide at low doses (0.01-10 micrograms) had no effect of its own, but blocked the morphine-induced increase in horizontal locomotor activity. Unlike the opiate antagonist naloxone (1.0 micrograms), FMRFamide (up to 10 micrograms) had no effect on morphine-induced decrease in vertical activity. These data further support a role for FMRFamide as a modulator of opiate action, but comparison to naloxone suggests that FMRFamide might not act as a pure competitive antagonist of this opiate effect.
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Department of Biological Research, Janssen Research Foundation, Spring House, PA 19477-0776.
D000818:Animals; D002552:Cerebral Ventricles / Q000187:drug effects / Q000502:physiology*; D019835:FMRFamide; D007276:Injections, Intraventricular; D008297:Male; D051379:Mice; D009020:Morphine / Q000008:administration & dosage / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D009043:Motor Activity / Q000187:drug effects*; D009270:Naloxone / Q000494:pharmacology; D009479:Neuropeptides / Q000008:administration & dosage / Q000494:pharmacology*; D012016:Reference Values
D009479:Neuropeptides; D009270:Naloxone; D019835:FMRFamide; D009020:Morphine