Effects of anterolateral and posterolateral cuts around the medial hypothalamus on the immunoreactive ACTH and beta-endorphin levels in selected brain regions of the rat.

To evaluate the relative weight of the ACTH-ergic and beta-endorphin-ergic pathway(s) leaving the medial hypothalamus (MH) in anterior or posterior directions immunoreactive ACTH and beta-endorphin (ir-ACTH and ir-betaE) were quantified in selected brain regions of the rat 7-8 days after placing anterolateral (ALC) or posterolateral (PLC) cut around the MH. Retrograde accumulation of both peptides was observed in the MH after ALC, but not after PLC. ALC resulted in dramatic decrease in ir-ACTH/ir-betaE concentrations in all extra-MH brain regions tested (extra-MH hypothalamus, septum, thalamus, hippocampus, amygdala, and medulla oblongata). In contrast, ir-ACTH and ir-betaE levels decreased only in the thalamus and in the medulla oblongata after PLC. The present data indicate (a) ACTH- and betaE-like substances synthesized in the arcuate region of the hypothalamus are axonally transported to extrahypothalamic brain regions by neuronal pathways leaving the MH primarily anterolateral, anterodorsal, or anteromedial direction (even the fibers of certain posteromedial or posterolateral projections leave the MH some anterior directions); (b) the posterior ACTH-/betaE-ergic projections seem to be of minor importance except for the thalamus and the medulla oblongata where it contributes to about one-third of the peptide content. Our biochemical study provide quantitative complementary data to the detailed immunohistochemical picture of the ACTH/betaE-ergic projections in the rat brain described by Khachaturian et al.