Intraseptally injected opiate agents: Effects on morphine-induced behaviour of cats

Abstract

Behavioural effects of intraseptally administered opiate agents were analyzed in cats pretreated with an intraperitoneal injection of morphine. In this way, it became possible to investigate (1) the involvement of septal opiate receptors in the behavioural response of cats to systemic administration of morphine, and (2) the pharmacological character of septal opiate receptors. The following results were obtained with intraseptal injections 15–16 min after intraperitoneal morphine: (1) naloxone decreased frequencies of head and limb movements, and (2) morphine was ineffective. The following results were obtained with intraseptal injections 40–41 min after intraperitoneal morphine: (1) β-endorphin and, to a lesser extent, fentanyl increased frequencies of locomotor patterns, (2) morphine and Met-enkephalin were ineffective, (3) naloxone and naltrexone decreased frequencies of locomotor patterns in a dose-dependent way, (4) naloxone and naltrexone antagonized the effects of β-endorphin and fentanyl, and (5) morphine did not attenuate the effect of naloxone. The intraseptal injections affected only the frequencies of the systemically evoked behaviour patterns; the nature of the behaviour patterns remained unchanged. It is concluded that (1) systemically administered morphine does not affect behaviour via a direct action on septal opiate receptors, and (2) the receptors mediating the septally evoked effects are most probably ϵ-type opiate receptors. The hypothesis is put forward that systemic administration of morphine results in an increased release of β-endorphin from hypothalamo-septal neurons and, as a consequence, changes the β-endorphin activity at the ϵ-type opiate receptors in the septum.