Abstract
We recently showed that bilateral neurotoxic microlesions (6-OH-DA) of the ventral noradrenergic ascending bundle (VNAB-X) at stereotaxic coordinates that blocked corticotropic stress responses did not affect the ACTH surge after bilateral intra-paraventricular (i.PVN) injections of interleukin-1 beta (IL-1 beta), and that lesioning at these stereotaxic coordinates obliterated the dorsal axonal populations of the VNAB (dVNAB-X), but spared the bundle's most ventral axons (vVNAB). The present study compares the effects of IL-1 beta given i.PVN (2 x 5 ng) of intra-arterially (i.a.) (100 ng) on plasma ACTH in rats with bilateral 6-OH-DA microlesions placed in the dVNAB or the vVNAB, or in an intermediary central position (cVNAB-X). Unlike our previous results, in which dVNAB-X did not alter the biphasic ACTH response to i.PVN IL-1 beta, both vVNAB-X and cVNAB-X reduced by 50-75% the early and delayed ACTH surges which are typical of the i.PVN route. On the other hand the swift monophasic ACTH surge usually occurring after an i.a. injection of IL-1 beta was 65% smaller after dVNAB-X, but was doubled after vVNAB-X or cVNAB-X. Hence, the release of ACTH after both i.PVN or i.a. IL-1 beta requires brainstem afferences conveyed to the hypothalamus by the VNAB. However, the VNAB appears to include at least two functionally different subsets of axons, the roles of which in the ACTH response to IL-1 beta depend on the route by which the cytokine is given.