Procedures affecting maintenance and loss of tolerance to amphetamine-induced anorexia and cross-tolerance to haloperidol-induced catalepsy

Abstract

Procedures affecting the maintenance and loss of tolerance to amphetamine anorexia were investigated. Following a period in which rats acquired tolerance to amphetamine-induced anorexia via the contingent- tolerance procedure, a variety of manipulations were investigated to determine which effected a loss of tolerance. The procedures included: continued milk availability or its absence, saline injections or no injections and a switch to non-contingent amphetamine injections. These procedures were each investigated while animals continued to be food-deprived or were maintained at their ad libitum weights. The animals maintained at 100% ad lib. lost tolerance whereas tolerance was maintained by the 85% groups, regardless of what other manipulations were given. Subsequently all animals were tested for catalepsy induced by 1.25 mg/kg haloperidol. Animals that had maintained tolerance to amphetamine anorexia (85% groups) were significantly less cataleptic than the animals that had lost tolerance to amphetamine anorexia (100% groups). The finding that tolerance to amphetamine anorexia is lost in animals that have ad lib. access to food indicates that a homeostatic imbalance caused by food-deprivation is perhaps the most important factor in the maintenance of tolerance to amphetamine anorexia.