Propensity to form conditioned taste aversions augments anorexia in obese (ob/ob) mice with B16 melanoma

Ob/ob mice (OB) with B16 melanoma become anorectic, but lean mice (LN) do not. Present studies suggest that this difference reflects a greater bent for OB to form conditioned taste aversions (CTA). In Exp 1, healthy OB formed stronger CTAs than LN to a saccharin taste paired with lithium chloride (LiCl, 3 mEq/kg ip). In Exp 2, the OB-LN difference of Exp 1 was decreased by giving naltrexone (10 mg/kg sc) before LiCl, which suggested opiate involvement. Exp 3 showed that OB tumor anorexia vanishes if foods dissociated from tumor growth are given: OB fed a constant diet became anorectic 16 days after B16 inoculation; giving a new diet on Day 16 delayed anorexia onset for 8 days; a second new diet on Day 32 abolished anorexia for 24 hr. LN with tumors ate all diets at nontumor control levels. OB survived melanoma longer than LN regardless of diet, but OB fed a varied diet died first; thus, anorexia may enhance OB survival.