Corticotropin Releasing Factor (CRF): Origin and Course of Afferent Pathways to the Median Eminence (ME) of the Rat Hypothalamus

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Abstract
8–10 days after making various lesions in the rat hypothalamus, the presence of corticotropin releasing factor (CRF) immunoreactive neural structures was studied in paraffin and vibratome sections with CRF immunocytochemistry. (1) Bilateral anterolateral deafferentation of the medial basal hypothalamus (MBH) caused complete disappearance of CRF immunoreactivity from the median eminence (ME) in brains where the posterior edge of the cut reached the level of the pituitary stalk. A shorter cut resulted in positive immunostaining caudal to the caudal edge of the cut. (2) Unilateral deafferentation of the MBH caused significant decrease in CRF immunostaining in the ipsilateral ME. (3) Unilateral posterolateral deafferentation of the MBH caused no changes in CRF immunostaining in the rostral ME, while fewer CRF-containing processes were observed in the more caudal regions. (4) A horizontal cut ventral to the paraventricular nuclei (PVN) caused a slight decrease in the number of CRF-immunoreactive profiles in the ME. A wider and complete unilateral horizontal cut resulted in a significant decrease in CRF immunoreactivity on the operated side. Following various surgical interventions, hormone accumulation in cell bodies was detected in the paraventricular, periventricular preoptic, dorsomedial, periventricular, lateral and posterior hypothalamic, and premammillary nuclei. Fibers arising from most of these nuclei formed a fan-like projection to the ME. The majority of the CRF-fibers ran through the lateral tract of the fan, and reached the ME by the lateral-basal retrochiasmatic area (LBRCA). Scattered fibers were detected in the lateral-basal hypothalamus as far caudally as the level of the pituitary stalk. Unilateral anterolateral and horizontal cuts did not result in complete disappearance of CRF immunoreactivity from the ipsilateral ME, indicating the existence of CRF-fibers of contralateral origin in the ME.

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