Michelle G Baladi1, Yvonne M Thomas, Charles P France. 1. Department of Pharmacology, University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Drive, San Antonio, TX 78229-3900, USA.
Abstract
RATIONALE: Feeding conditions modify sensitivity to indirect- and direct-acting dopamine receptor agonists as well as the development of sensitization to these drugs. OBJECTIVES: This study examined whether feeding condition affects acute sensitivity to apomorphine-induced yawning or changes in sensitivity that occur over repeated drug administration. Quinpirole-induced yawning was also evaluated to see whether sensitization to apomorphine confers cross-sensitization to quinpirole. METHODS: Drug-induced yawning was measured in different groups of male Sprague Dawley rats (n = 6/group) eating high (34.3%) fat or standard (5.7% fat) chow. RESULTS: Five weeks of eating high-fat chow rendered otherwise drug-naïve rats more sensitive to apomorphine- (0.01-1.0 mg/kg, i.p.) and quinpirole- (0.0032-0.32 mg/kg, i.p.) induced yawning, compared with rats eating standard chow. In other rats, tested weekly with apomorphine, sensitivity to apomorphine-induced yawning increased (sensitization) similarly in rats with free access to standard or high-fat chow; conditioning to the testing environment appeared to contribute to increased yawning in both groups of rats. Food restriction decreased sensitivity to apomorphine-induced yawning across five weekly tests. Rats with free access to standard or high-fat chow and sensitized to apomorphine were cross-sensitized to quinpirole-induced yawning. The hypothermic effects of apomorphine and quinpirole were not different regardless of drug history or feeding condition. CONCLUSIONS: Eating high-fat chow or restricting access to food alters sensitivity to direct-acting dopamine receptor agonists (apomorphine, quinpirole), although the relative contribution of drug history and dietary conditions to sensitivity changes appears to vary among agonists.
RATIONALE: Feeding conditions modify sensitivity to indirect- and direct-acting dopamine receptor agonists as well as the development of sensitization to these drugs. OBJECTIVES: This study examined whether feeding condition affects acute sensitivity to apomorphine-induced yawning or changes in sensitivity that occur over repeated drug administration. Quinpirole-induced yawning was also evaluated to see whether sensitization to apomorphine confers cross-sensitization to quinpirole. METHODS: Drug-induced yawning was measured in different groups of male Sprague Dawley rats (n = 6/group) eating high (34.3%) fat or standard (5.7% fat) chow. RESULTS: Five weeks of eating high-fat chow rendered otherwise drug-naïve rats more sensitive to apomorphine- (0.01-1.0 mg/kg, i.p.) and quinpirole- (0.0032-0.32 mg/kg, i.p.) induced yawning, compared with rats eating standard chow. In other rats, tested weekly with apomorphine, sensitivity to apomorphine-induced yawning increased (sensitization) similarly in rats with free access to standard or high-fat chow; conditioning to the testing environment appeared to contribute to increased yawning in both groups of rats. Food restriction decreased sensitivity to apomorphine-induced yawning across five weekly tests. Rats with free access to standard or high-fat chow and sensitized to apomorphine were cross-sensitized to quinpirole-induced yawning. The hypothermic effects of apomorphine and quinpirole were not different regardless of drug history or feeding condition. CONCLUSIONS: Eating high-fat chow or restricting access to food alters sensitivity to direct-acting dopamine receptor agonists (apomorphine, quinpirole), although the relative contribution of drug history and dietary conditions to sensitivity changes appears to vary among agonists.
Authors: Rajkumar J Sevak; Wouter Koek; William Anthony Owens; Aurelio Galli; Lynette C Daws; Charles P France Journal: Eur J Pharmacol Date: 2008-07-10 Impact factor: 4.432