Abstract

Kappa-opioids exert a more powerful analgesic effect in females than in male animals. In females, this is further enhanced close to and immediately post parturition. Learning behaviour is also altered in the female around this period. Recently it was demonstrated that changes in a brain receptor subunit (part of the glutamate NMDA receptor present in all mammalian brains), termed NR2B, accompanied these periods of apparent learning enhancement. In this paper, evidence is presented for a dependence of this increase in NR2B and learning ability on Kappa-opioid systems. Pharmacological antagonism of the Kappa-opioid system during the peri-parturient period prevents both an increase in NR2B and in learning behaviour. Application of Kappa-opioids at other periods increased NR2B numbers and learning behaviour in female animals and in male castrates co-treated with oestrogen. Intact males were unaffected. The data suggests a new concept linking pain perception and processing systems to reproductive state behaviours and learning abilities.

CJ, Cook

Proceedings of the New Zealand Society of Animal Production, Volume 62, Palmerston North, 368-371, 2002