Neuroimmunological regulation of α-MSH release in tilapia (Oreochromis mossambicus)

Abstract

This study describes the effects of IL-1 (interleukin 1) and LPS (bacterial endotoxin lipopolysaccharide) on the release of α-MSH (alpha melanocyte stimulating hormone) from the neurointermediate lobe (NIL) of the teleost Oreochromis mossambicus (tilapia). In vivo treatment of tilapia with IL-1 for 8 days led to a 49% inhibition of basal α-MSH release, measured by means of an in vitro micro-superfusion technique. The treatment did not affect the sensitivity of the tissue to TRH. In vitro, the release of α-MSH was inhibited by LPS in a dose dependent manner. In addition to its effects on the unstimulated release of the hormone, LPS also blunted the response to a TRH stimulation. Together with recent results obtained by others demonstrating the effects of (neuro-)peptides on immune parameters and the presence of cytokines in fish, the present data establish the bidirectional character of the communication between the immune and the (neuro-)endocrine systems in teleosts.

Bacterial lipopolysaccharide (LPS) modulates corticotropin-releasing hormone (CRH) content and release in the brain of juvenile and adult tilapia (Oreochromis mossambicus; Teleostei)

“…Basal in vitro CRH release by the telencephalon was not affected following 3·h of LPS treatment/superfusion. Previously, we showed in tilapia that concentrations between 1-50·µg·ml -1 of LPS in vitro applied in a similar superfusion set-up dose-dependently inhibited the basal release of α-MSH by the pituitary gland (Balm et al, 1993).…”

“…Previously we showed that in vitro LPS treatment alters the α-MSH release from pituitary melanotropes in tilapia (Balm et al, 1993(Balm et al, , 1995. Since there was no HPI-axis activation or difference in body colour between experimental groups, the α-MSH increases after LPS exposure may subserve immune related actions.…”

“…CRH and cortisol levels were determined by radioimmunoassays (RIA) validated for tilapia larvae (Pepels et al, 2002b,c). α-MSH was determined by RIA (Balm et al, 1993) in which serial dilutions of juvenile head homogenates displaced radiolabelled α-MSH from the antibody in a parallel fashion with dilutions of the α-MSH standard (not shown).…”

“…Plasma cortisol was assayed by RIA (Balm et al, 1994), plasma glucose was measured using a commercial kit (Boehringer Mannheim, Germany), and chloride was quantified by flame photometry. Plasma CRH, α-MSH (in pituitary and plasma) was assayed by RIA (Balm et al, 1993;Pepels et al, 2002b).…”

“…Previously, we showed that chronic treatment with LPS (Balm et al, 1995) or with murine Interleukin-1 (IL-1; Balm et al, 1993) altered the activity of the PI axis. For these reasons we treated tilapia chronically.…”