ROLE OF EFFERENT AND AFFERENT VAGAL NERVE ACTIVITY DURING REPRODUCTION - INTEGRATING FUNCTION OF OXYTOCIN ON METABOLISM AND BEHAVIOR

The vagal nerves convey information between the brain and the gastroin testinal tract in both afferent and efferent direction. The efferent v agal nerves regulate gastrointestinal secretory and motor function and also the activity in the endocrine system of the gut. Gastrointestina l function and anabolic metabolism is optimized during gestation and l actation as a means of saving energy for this calorie-demanding proces s. This enhanced activity seems to involve central oxytocinergic trans mission which increases efferent vagal nerve activity as reflected by altered levels of gastrointestinal hormones in plasma. In parallel a b ehaviour pattern characterized by sedation is induced. In addition, va gal afferents transfer information from the gut to the brain, e.g. as to the presence or absence of calories in the gastrointestinal tract. It is well known that satiety and sedation following a meal is in part caused by an activation of vagal afferents in response to food intake . Cholecystokinin released from the intestine is one of the factors th at triggers the afferent vagal nerve activity. Also reproductive ''int eractive behaviours'' such as milk ejection and maternal behaviour can be induced by CCK via afferent activation of vagal nerves. In contras t, when no food reaches the gut, milk production and ejection is block ed, Parts of these effects are vagally mediated, since they can be obs erved in vagotomized rats receiving full amounts of calories.