Estrogen as modulator of genes expression involved in control of reproduction

The hypothalamic neurons, pituitary and their target cells, as genetically programmed to respond specifically to gonadal steroids (GS) and seasonal photoperiodic stimuli, play a crucial role in regulation of target genes transcription and regulatory ligands are conserved throughout evolution. Memory of these cells, acquired through the advanced evolution and programmed genes expression, may be modulated, transitory or permanently, by GS and estrogen (E) is a key hormone of these steroids. Pituitary chromophobes (Chr) and prolactin (PRL) cells reactions of birds and rats to GS and seasonal photoperiod were used as a parameter for elucidation of hypothalamic neurons and regulation of the animals reproduction. As a result of proliferative rate of chromophobes and hypertrophy of PRL cells, pituitary gonadotropic hormone (GTH) cells differentiation and activities are decreased, retarded or even inhibited and vice versa. The inverse relationship between PRL and GTH play a crucial role in regulation of reproduction. Light absorbed by rodopsin in the photoreceptor cells are transmitted via specific hypothalamic neurons to pars tuberalis cells, which are sensitive to photoperiodic stimuli and neurohormones as regulators of PRL cells activities.