Anorexia in rats infected with the nematode, Nippostrongylus brasiliensis:experimental manipulations

Nippostrongylus brasiliensis induces a biphasic anorexia in laboratory rats , the first phase coincident with lung invasion (ca day 2) and the second w hen the worms mature in the intestine (ca day 8). Using the anthelminthic, mebendazole (MBZ), N. brasiliensis infections of the rat were eliminated be tween the first and second anorexic episodes. This intervention prevented t he expression of the second phase of anorexia. Rats exposed to a second inf ection with N. brasiliensis, 3 weeks after the primary infection, exhibited only a first phase anorexic response which was not influenced by MBZ termi nation of the primary infection. The lower cumulative food intake and weigh t gain of all infected rats after 8 days of infection were accompanied by e levated plasma insulin and, in some individuals, by elevated plasma leptin, compared with uninfected controls and previously-infected MBZ-treated rats . Messenger RNA levels for neuropeptide Y were higher in the hypothalamic a rcuate nucleus of 8-day infected rats than in recovering MBZ-treated animal s. Inoculation of rats with heat-killed N. brasiliensis larvae failed to in duce anorexia and did not alter the severity of biphasic anorexia on subseq uent injection of viable larvae. The first anorexic episode is therefore de pendent upon viable migrating larvae. The second phase of anorexia clearly requires the continuing presence of the parasite beyond the lung phase. Via ble migrating larvae are also required to confer 'resistance' to reinfectio n.