Alterations in brain and pituitary beta-endorphin content in genetically epilepsy-prone rats.

We measured beta-endorphin concentrations in the anterior and neurointermediate lobes of the pituitary gland and in microdissected brain regions of moderate-seizure genetically epilepsy-prone rats (GEPR-3), severe-seizure GEPR-9s and Sprague-Dawley non-epileptic control rats. Plasma concentrations of beta-endorphin and beta-melanocyte-stimulating hormone (alpha-MSH) were also measured as indicators of pituitary POMC-peptide secretion. Concentrations of beta-endorphin in the anterior lobe of GEPR-3s were 53% higher compared to controls and 57% higher compared to GEPR-9s. There were no differences in neurointermediate lobe beta-endorphin concentrations between control and either GEPR strain. Plasma beta-endorphin concentrations were significantly lower in GEPR-9s than controls. Plasma levels of alpha-MSH did not differ between control and GEPRs. In the hypothalamus of GEPR-9s beta-endorphin concentrations in the arcuate nucleus were significantly greater than in GEPR-3s. Concentrations of beta-endorphin in the central amygdala of GEPR-9s were two- to threefold greater than in control or GEPR-3s. Beta-Endorphin concentrations in the central gray of GEPR-3s were 58% lower than control or GEPR-9s. These data suggest that anterior lobe beta-endorphin secretion is reduced in GEPR-9s. Furthermore, brain endorphinergic pathways appear to be differentially altered in GEPR-3s and GEPR-9s. Alterations in pituitary beta-endorphin secretion and brain endorphinergic systems may contribute to seizure susceptibility in GEPRs and to differences in seizure severity between GEPR-3s and GEPR-9s.