Resumo

ARROYO LEDEZMA, Jaime; GALLEGOS-SANCHEZ, Jaime; VILLA GODOY, Alejandro  e  VALENCIA MENDEZ, Javier. FEEDBACK NEURAL SYSTEMS OPERATING DURING THE CIRCANNUAL REPRODUCTIVE CYCLE OF THE EWE. INCI [online]. 2006, vol.31, n.1, pp.8-15. ISSN 0378-1844.

The annual reproductive cycle in the ewe is controlled by the changes in the amplitud of photoperiod. The light stimulus is converted into a hormonal signal: the circadian rhytm of melatonin secretion. Short days are inductive whereas long days inhibits the ovulatory activity. During the reproductive season, progesterone regulates the estrous cycle of the ewe inhibiting the GnRH pulsatil secretion. Progesterone exerts its action on the preoptic area of the hypothalamus indirectly, possibly via the gamma aminobutiric acid and the endogeneous opiod peptides. Estradiol (E₂) increases the GnRH pulsatile secretion by a positive feedback effect. Increments in GnRH pulses induce the preovulatory peak of LH evoking estrous behaviour and ovulation. During the seasonal anestrus, the secretion pattern of melatonin increases the sensivity of the hypothalamus to the negative effect of E₂, then estradiol inhibits the pulsatil secretion of GnRH, acting in the A-15 dopaminergic nucleous of the retrochiasmatic lateral area of the hypothalamus; in this mechanism the dopaminergic system mediates the effect of estradiol on the GnRHergic neurons.

Palavras-chave : Actividad Reproductiva ; Anestro Estacional ; Estro ; Neuroendocrinología ; Oveja .