Sensitivity to apomorphine-induced yawning and hypothermia in rats eating standard or high-fat chow.
BACKGROUND
Feeding conditions modify sensitivity to indirect- and direct-acting dopamine receptor agonists as well as the development of sensitization to these drugs.


OBJECTIVE
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.
Department of Pharmacology, University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Drive, San Antonio, TX 78229-3900, USA.
Michelle G
MG
Baladi
Yvonne M
YM
Thomas
Charles P
CP
France
D000821:Animal Feed; D000818:Animals; D001058:Apomorphine / Q000008:administration & dosage / Q000494:pharmacology*; D059305:Diet, High-Fat; D004041:Dietary Fats; D018491:Dopamine Agonists / Q000008:administration & dosage / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004334:Drug Administration Schedule; D004435:Eating; D005508:Food Deprivation; D007035:Hypothermia / Q000139:chemically induced*; D008297:Male; D019257:Quinpirole / Q000008:administration & dosage / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D015000:Yawning / Q000187:drug effects*
D004041:Dietary Fats; D018491:Dopamine Agonists; D019257:Quinpirole; D001058:Apomorphine