Effects of (Des-Tyr1)-gamma-endorphin and alpha-endorphin as compared to haloperidol and amphetamine on nucleus accumbens self-stimulation

The β-endorphin fragment (Des-Tyr¹)-γ-endorphin (DTγE, β-LPH 62–77) attenuated self-stimulation behaviour associated with electrical stimulation of the nucleus accumbens area of rats. This effect was observed after subcutaneous (s.c.) injection of 2.5 and 25 μg of the neuropeptide and appeared to be dose-dependent. It was present only at current intensities in the neighbourhood of the threshold for eliciting the behaviour. Subcutaneous administration of haloperidol (5 μg) exerted a similar effect, but in addition affected the rate of responding at currents associated with maximal performance. Amphtamine (100 μg s.c.) enhanced responding at both low and high current intensities. α-Endorphin (β-LPH 61–76; 2.5 and 25 μg s.c.) did not influence nucleus accumbens self-stimulation behaviour.It is postulated that DTγE affects this behaviour by interfering with mesostriatal dopaminergic neuronal systems projecting to the nucleus accumbens, possibly via an action on synaptic membranes.