Lesions of the hypothalamic arcuate nucleus modify discrete brain and pituitary pools of dynorphin in addition to beta-endorphin in the rat.

Radiofrequency destruction of the hypothalamic arcuate nucleus, the exclusive central location of beta-endorphin (beta-EP)-synthesizing neurones, greatly depressed levels of immunoreactive (ir)-beta-EP in the hypothalamus. However, the content of ir-dynorphin (DYN) therein was also decreased, in parallel with that of ir-beta-EP. Levels of ir-Met-enkephalin (ME) were, in contrast, unaffected. In the midbrain and septum, the content of ir-beta-EP was greatly depleted; in the former but not latter tissue, levels of ir-DYN were also diminished whilst levels of ir-ME were not affected in either of these structures. Further, in the neurointermediate pituitary, the content of ir-beta-EP was depressed while that of ir-DYN was not changed, whereas, in the anterior pituitary, levels of ir-beta-EP were not altered in contrast to those of ir-DYN which were decreased. Destruction of the arcuate nucleus is not, therefore, restricted to selective effects upon central beta-EP neurones: this finding is of importance for studies of the role of central beta-EP via lesioning techniques. The data suggest an interaction of the arcuate nucleus and, possibly, beta-EP with particular brain and pituitary pools of DYN.