Post-conditioning catecholaminergic antagonism fails to alter methamphetamine sensitization in mice.

Single injection sensitization studies model the early transition to compulsive drug-seeking behavior, independent of other biological processes (e.g., drug tolerance). This paper examined a) the temporal persistence of (Experiment 1), and b) the role of catecholaminergic-mediated post-conditioning memory processes (Experiments 2a and 2b), in conditioned hyperactivity and behavioral sensitization after a single methamphetamine injection in male, Swiss Webster mice. Mice received either a single injection (intraperitoneal, i.p.) of physiological saline (vehicle) or methamphetamine (2.0 mg/kg) prior to a 30-minute locomotor activity session (Conditioning). Tests for conditioned hyperactivity (CR Test) and behavioral sensitization (Methamphetamine Challenge Test) occurred after a delay of 2 and 3 days (Immediate), 6 and 7 days (Short), 14 and 15 days (Moderate), or 27 and 28 days (Long), respectively. To assess the role of catecholaminergic activity, specifically dopamine D2 receptors (Experiments 2a) or β-adrenergic receptors (Experiment 2b) on memory consolidation, and its subsequent effect of conditioned hyperactivity and behavioral sensitization, the dopamine D2 antagonist, haloperidol (40 μg/kg), or the non-selective β-adrenergic (β1/β2) antagonist, propranolol (16 and 32 mg/kg), was administered immediately or 2.5 h after methamphetamine conditioning. Conditioned hyperactivity and behavioral sensitization were detected at all time points (Experiment 1). Furthermore, post-conditioning administration of haloperidol or propranolol failed to alter conditioned hyperactivity or behavioral sensitization (Experiment 2a and 2b). Collectively, these results suggest that the 1) conditioned and pharmacological responses persisted unchanged for equal durations, and 2) targeting the catecholaminergic system during memory consolidation did not disrupt induction of either conditioning hyperactivity or sensitization.