Interrelationships of gabaergic, serotoninergic and excitatory amino acid systems in its regulatory effect on prolactin secretion in prepubertal rats

GABAergic, serotoninergic and excitatory amino acid systems (EAAs) regulate the prolactin (PROL) secretion in prepubertal female rats. The aim of the present paper was to determine the interrelationships of these systems on t he control of this pituitary hormone. It was carried out through the follow ing scheme: 1. The participation of the EAAs and serotonin in the effect of GABAergic system on PROL release, determined by evaluating the GABA A and GABA B receptor agonists. It was carried out on animals that were previousl y treated with AAEs receptor antagonist or p-chiorophenylamphetamine (PCA), this one depleting serotonin in the hypothalamus. 2. The participation of GABAergic system in the effect of serotonin and EAAs systems, determined by the evaluation of the effects of EAAs receptor agonists and of 5-HTP, a se rotonin precursor. With this purpose the rats were previously treated with GABA A and GABA B receptor antagonists. 3. The interrelationships between t he EAAs and the serotoninergic systems in the control of PROL secretion, de termined (a) by using EAAs agonists tin rats depleted of serotonin by (PCA) and (b) using EAAs antagonists (in rats treated with 5-HTP, a serotonin pr ecursor). The administration of GABAergic agonists significantly increased PROL secretion in prepubertal female rats. Neither EAAs antagonists nor the depletion of serotonin in the brain, modified the stimulatory effects of t he GABAergic system on PROL levels. This is a clear indication that the act ivity of the GABAergic system is independent of the serotoninergic and of t he EAAs system effects on the pituitary hormone. The EAAs neurotransmitter system agonists significantly increase PROL levels. This effect was blocked by the GABAergic system antagonists but was not modified by serotonin depl etion. Taking into account these facts it may be considered that the GABAer gic system is involved in the stimulatory effect of EAAs on PROL secretion, this effect being independent of the serotoninergic system. 5-HTP signific antly increased PROL plasma levels, and this effect was modified neither by the GABAergic nor by the EAAs receptor antagonists. These results indicate that the stimulatory effect of serotonin on PROL release is independent of the GABAergic and EAAs systems. In conclusion it may be considered that in prepubertal female rats, the GABAergic and serotoninergic systems stimulat e PROL secretion by independent mechanisms that do not include EAAs. On the other hand, the effects of EAAs neurotransmission are exerted via the GABA ergic system.