Long-term retention of tolerance to amphetamine hypophagia following cessation of drug injections and feeding tests

Tolerance to Amphetamine Hypophagia: A Real-Time Depiction of Learning to Suppress Stereotyped Movements in the Rat.

“…However, experiments in which the level of food deprivation was systematically manipulated have demonstrated that tolerance is not an artifact of increased hunger (Demellweek & Goudie, 1982, 1983a; see Wolgin, 1989, for a more detailed review of this evidence). Moreover, when saline controls are fed the amount of milk ingested by their amphetamine-treated counterparts during the chronic phase and then tested with various doses of amphetamine, either they show no tolerance at all (Hughes et al, 1998;Wolgin & Hughes, 2001) or they show it only at lower doses of the drug (0.5 and 1 mg/kg; Wolgin & Hughes, 1996, 1997). An alternative view is that increased hunger contributes to tolerance by increasing the motivation to suppress stereotyped movements when rats are given chronic injections of amphetamine and access to food.…”

“…Indeed, stereotyped movements undergo sensitization in the absence of food (Hughes, Popi, & Wolgin, 1998; Wolgin & Hughes, 1996; Wolgin & Kinney, 1992). Third, tolerance is retained over long periods of time in most rats (at least 31 weeks) when both drug injections and milk tests are suspended (Wolgin & Hughes, 2001), conditions that preclude the learning of new contingencies for obtaining reinforcement. Conversely, if tolerant rats are permitted to drink milk under conditions in which reinforcement (milk) is no longer contingent on suppressing stereotyped movements (e.g., following injections of saline [Poulos et al, 1981; Wolgin & Hughes, 1997] or following injections of amphetamine but with milk delivered intraorally [Hughes & Wolgin, 2002]), tolerance is lost within 3–4 weeks.…”

“…Conversely, if tolerant rats are permitted to drink milk under conditions in which reinforcement (milk) is no longer contingent on suppressing stereotyped movements (e.g., following injections of saline [Poulos et al, 1981;Wolgin & Hughes, 1997] or following injections of amphetamine but with milk delivered intraorally [Hughes & Wolgin, 2002]), tolerance is lost within 3-4 weeks. Indeed, a substantial loss of tolerance occurs within three trials (Wolgin & Jakubow, 2003b).…”