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-e rgic pathway(s) leaving the medial hypothalamus (MH) in anterior or po sterior directions immunoreactive ACTH and beta-endorphin (ir-ACTH and ir-beta E) were quantified in selected brain regions of the rat 7-8 d ays after placing anterolateral (ALC) or posterolateral (PLC) cut arou nd the MH. Retrograde accumulation of both peptides was observed in th e MH after ALC, but not after PLC. ALC resulted in dramatic decrease i n ir-ACTH/ir-beta E concentrations in all extra-MR brain regions teste d (extra-MR hypothalamus, septum, thalamus, hippocampus, amygdala, and medulla oblongata). In contrast, ir-ACM and ir-beta E levels decrease d only in the thalamus and in the medulla oblongata after PLC. The pre sent data indicate (a) ACTH- and beta E-like substances synthesized in the arcuate region of the hypothalamus are axonally transported to ex trahypothalamic brain regions by neuronal pathways leaving the MR prim arily anterolateral, anterodorsal, or anteromedial direction (even the fibers of certain posteromedial or posterolateral projections leave t he MR some anterior directions); (b) the posterior ACTH/beta E-ergic p rojections seem to be of minor importance except for the thalamus and the medulla oblongata where it contributes to about one-third of the p eptide content. Our biochemical study provide quantitative complementa ry data to the detailed immunohistochemical picture of the ACTH/beta E -ergic projections in the rat brain described by Khachaturian et al. [ 5]. (C) 1997 Elsevier Science Inc.