Endorphin-Monoamine Interaction and Steroid-Dependent Behaviour
The discovery of endogenous neuropeptides, which in pharmacological experiments produced behavioural effects, led to the assumption that neuropeptides may participate in central nervous transmittor processes. Apparently for some steroid dependent behaviour responses we should consider three classes of agents which may participate in the cerebral chemical communication processes; besides the steroid hormones, neuropeptides and the ‘classical’ neurotransmittors such as monoamines. The question arises whether there exists a close relationship and interaction between these factors. In the present study we focus on the effets of β-endorphin (β-END) on copulatory behaviour in the male rat. The significance of testosterone for this behaviour is since long established. Psychopharmacological studies have demonstrated that copulatory behaviour in the male rat is facilitated by increased dopaminergic activity (Malmnäs 1973, Meyerson and Malmnäs 1978). A stimulatory effect is also obtained after decreased serotonergic neuronal activity, e.g., achieved by treatment with the inhibitor of serotonin biosynthesis, p-chloropehnylalanine (PCPA) (for references see Meyerson and Malmnäs 1978). Intracerebroventricular (i.c.v.) infusion of β-END inhibits the copulatory response in intact and testosterone treated castrated male rats (Meyerson and Terenius 1977, Meyerson 1981). Evidence were provided that this effect was specific and not achieved by a general inability to behave in a sexual situation as other social behaviours were not influenced or even stimulated. Also neonatal β-END treatment of male rats has recently been reported to influence sexual responses in the adult animal (Meyerson 1982a,b).
KeywordsCage Propionate Morphine Serotonin Testosterone
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