DEVELOPMENT OF GONADOTROPIN-RELEASING-HORMONE (GNRH) NEURON REGULATION IN THE FEMALE RAT

1. After reaching its final destination the GnRH neuronal network deve lops under the influence of both excitatory and inhibitory inputs. 2. In the first 2 weeks of life, the immaturity of the GnRH neuronal syst em is reflected in sporadic unsynchronized bursts of the decapeptide, which determine the pattern of serum gonadotropin levels observed in f emale rats: high FSH levels and transient bursts of LH. The main inhib itory neuronal systems that operate in this period are the opioid and dopaminergic systems. A decrease in their inhibitory effectiveness may not be sufficient correctly to activate and synchronize the GnRH neur onal system. 3. There is a concomitant increase in excitatory inputs, mainly noradrenaline, excitatory amino acids, and NPY, which increase the synthesis and release of GnRH at the beginning of the juvenile per iod and participate in the coupling of GnRH neural activity to the ong oing rhythmic activity of a hypothalamic circadian oscillator. 4. The morphological changes of GnRH neurons which take place during the thir d and fourth weeks of life, and which are probably related to increasi ng estradiol levels, reflects the increasing complexity of the GnRH ne uronal network, which establishes synaptic contacts to enable the expr ession of pulsatility and of the positive feedback of estradiol, both necessary components for the occurrence of puberty.