The preoptico-infundibular LH-RH tract of the rat.

Following partial or total deafferentation of the right side of the medial basal hypothalamus (MBH) of female rats, distribution of luteinizing hormone-releasing hormone (LH-RH) axons in and around the isolated area was studied. Accumulation of the hormone along the cut indicated the directions from which LH-RH axons arrived to the isolated hypothalamic area. A comparison of the intact side of the median eminence (ME) to the deafferented side indicated the areas where the transected LH-RH axons would have ended. It was concluded that: (i) LH-RH axons of the MBH of the rat originate from extrahypothalamic areas and approach the ME through the preoptico-infundibular LH-RH tract; (ii) axons from the lateral fascicles of this tract turn toward the ME under oblique angle, consequently, a paramedian sagittal cut causes primary degeneration of the LH-RH terminals only behind the rostral level of the cut, and diminution of these terminals will last even behind the caudal end of the cut; (iii) the tubero-infundibular tract of the rat does not contain LH-RH axons; and (iv) a certain percentage of the LH-RH axons in the ME originates from the contralateral side of the brain.