Parasite-induced anorexia in rodents : the role of hypothalamic neuropeptides
An investigation was made into the role of Neuropeptide Y (a powerful stimulant of feeding behaviour), Corticotropin-Releasing Factor (a powerful anorectic substance) and Galanin (a feeding stimulant) during anorexia induced by the nematode Nippostrongylus brasiliensis in the rat host. This anorexia can reduce food intake by 50% over the 10 day span of infection in the host. Measurements of gene expression using in situ hybridization, showed that the parasitized rat could detect its state of energy deficit during anorexia and increases production of NPY mRNA, this rise being detectable on day 8 infection. However, this increase in NPY mRNA is not accompanied by appropriate feeding behaviour until the host expels the parasite naturally approximately 10 days post infection. Levels of NPY mRNA remained elevated at day 16 p.i., well after the worms had been expelled. No changes were detected in CRF mRNA or GAL mRNA. Measurements of NPY concentration were made in the arcuate (ARC) and paraventricular (PVN) nuclei. Increases in the PVN were detected in rats showing anorexia on day 8 p.i. This indicated that synthesis of NPY was still occurring and that the peptide was being transported to the PVN. A manipulation of the host-parasite system was also made, with rats being treated with mebendazole, an anthelminthic, on either day 4 p.i. or day 6 p.i. This resulted in the rapid restoration of feeding behaviour in infected rats, as the worms were expelled. The main conclusion of the study was that the anorexia induced by N. brasiliensis in the rat is controlled by substance(s) outwith the NPYergic system.