OXYTOCIN AND VASOPRESSIN RELEASE IN THE OLFACTORY-BULB OF PARTURIENT EWES - CHANGES WITH MATERNAL EXPERIENCE AND EFFECTS ON ACETYLCHOLINE, GAMMA-AMINOBUTYRIC-ACID, GLUTAMATE AND NORADRENALINE RELEASE

Maternal behaviour and the ewe's ability to recognize her lamb depend on olfactory cues and parturition, and are facilitated by maternal exp erience. Parturition induces a variety of neurochemical changes in the brain and, in particular, oxytocin (OT) release. This peptide injecte d centrally induces maternal behaviour. Oxytocin release occurs in the olfactory bulb (OB) at parturition and yet this structure is involved in the process of selective bonding with lamb. The present study ther efore investigated the possibility that oxytocin release in the OB mig ht modulate the release of classical transmitters that are known to be important in controlling selective recognition and whether maternal e xperience has any effect on this. We have first used in vivo microdial ysis to measure OT release, as well as that of the related peptide, ar ginine-vasopressin (AVP), in the OB of maternally experienced and inex perienced ewes during parturition. While OT release significantly incr eased in both primiparous and multiparous ewes at parturition this inc rease was significantly greater in multiparous ewes. No significant ch ange of AVP release was observed in either group. However, vagino-cerv ical stimulation (VCS) performed at 6 h post-partum caused similar inc reases in OT but not AVP release in both primiparous and multiparous e wes suggesting that the first birth experience potentiates the ability of VCS to evoke OT release within 6 h of parturition. Using retrodial ysis, either OT (10 mu M) or AVP (10 mu M) were infused into the OB of multiparous and nulliparous ewes and their effects on modulating acet ylcholine (ACh), noradrenaline (NA), glutamate and gamma-aminobutyric acid (GABA) release were monitored. Both peptides produced an increase of ACh and NA in multiparous animals and this effect was either absen t or less pronounced in nulliparous animals. OT, but not AVP, also inc reased GABA release equivalently in nulliparous and multiparous animal s. Glutamate release was not altered in response to OT or AVP infusion . These results suggest that OT release in the OB at parturition may f acilitate the recognition of lamb odours by modulating NA, ACh and GAB A release which are of primary importance for olfactory memory. The re duced release of OT in the OB of primiparous ewes at parturition, toge ther with its reduced ability to modulate NA and ACh release, might al so partly explain why maternally inexperienced animals require a longe r period to selectively bond with their lambs.