Effect of neuropeptide FMRFamide on immobile behavior in rats

In the forced swimming induced immobility test, neuropeptide FMRFamide (5-20 micrograms) administered via the intracerebroventricular (icv) route, prolonged immobilization period in rats. On the other hand, immunoneutralization of endogenous FMRFamide by its antiserum (1 microliter, icv) significantly reduced the duration of immobility. Intraperitoneal administration of amitriptyline (3 mg/kg), imipramine (5 mg/kg), fluoxetine (5 mg/kg) or amphetamine (0.5 mg/kg) attenuated FMRFamide-induced prolongation of immobility. Biochemical studies indicated that FMRFamide treatment had significant effects on rat brain monoamines. FMRFamide significantly lowered the brain levels of 5-hydroxytryptamine and norepinephrine in the doses that prolonged the immobility. These results that FMRFamide prolongs the duration of immobility, perhaps by modulating the release of neurotransmitters like 5-hydroxytryptamine and/or norepinephrine.