Hypothalamic and extrahypothalamic mediation of pulsatile discharges of luteinizing hormone in the ovariectomized rat

Various hypothalamic lesions were placed in long term ovariectomized rats, and their effects on pulsatile discharges of LH were noted in order to determine which neural regions are involved in the control of this mode of LH secretion. Complete hypothalamic deafferentiation did not affect pulsatile patterns of LH secretion unless the anterior portion of the cut also lesioned the anterior portion of the arcuate nuclei, in which case pulsatile LH discharges were completely blocked. Pulsatile LH secretion was not blocked by bilateral electrolytic lesions placed in ventromedial, paraventricular, or suprachiasmatic nuclei or anterior or posterior portions of the arcuate nuclei, although the nuclei were not completely destroyed by the lesions. When bilateral electrolytic lesions of the anterior portions of the arcuate nuclei were combined with anterior hypothalamic deafferentation, however, pulsatile discharges of LH were completely blocked. These results suggest that two pathways can stimulate the pulsatile mode of LH secretion independently of each other. One of these pathways involves the arcuate nuclei and possibly nearby structures, while the other appears to include extrahypothalamic structures and to enter the hypothalamus anteriorly.