Differential response of methionine-enkephalin in basal hypothalamus and preoptic area following hypothalamic deafferentation

Abstract

Following identification and characterization of naturally occurring opiate peptides from the brain and pituitary gland 4,5 several investigators have examined the precise distribution of fl-endorphin and enkephalin-like immunoreactivity in the neurons of the rat brain 1,9,11-13. Enkephalin-like immunoreactivity has been localized by radioimmunoassays and by immunocytochemical means in various nuclei of the diencephalon 11-13. Of particular significance are the demonstrations of enkephalin containing neurons in the preoptic-tuberal pathway 11-13, and the ability of methionine-enkephalin (Met-enkephalin) administration to influence LH and prolactin secretion in the rat 2,3,10. In this communication we report the effects of disruption by surgical means of the preoptic-tuberal pathway on the Met-enkephalin levels in the basal tuberal regions and the anterior hypothalamic-preoptic area (AHPOA). Adult Charles River (CD) rats were maintained in air-conditioned rooms (76 ° F) with controlled light/dark cycle (lights on between 0500 and 1900 h). The rats were ovaliectomized under pentabarbitol anesthesia (40 mg/kg, i.p.) and underwent hypothalamic deafferentation with the help of Halasz-type knife which was lowered 1.6 mm behind the bregma when the rats were held in a stereotaxic instrument with the nosebar 7 mm below the ear bar. Two types of deafferentations were performed 6,7; for anterior hypothalamic deafferentation (AHD, knife dimensions, width -2.8 mm and height --: 2.2 ram) the knife was lowered to the base of the brain and rotated 90 ° to either side to transect anterolateral inputs to the medial-basal hypothalamus (MBH) along the caudal border of optic-chiasm; for complete hypothalamic deafferentation (CHD) the MBH was isolated from the rest of the brain by rotating the knife (width 3 mm, height -2.5 mm) full 360 °. The cut extended anteriorly along the caudal border of the optic-chiasm and caudally through the mammillary bodies. In sham deafferentation controls the knife was lowered to the base of the brain and lifted up without