Schedule of passive ethanol exposure affects subsequent intragastric ethanol self-infusion.
BACKGROUND
Many studies have shown that chronic ethanol exposure can enhance later self-administration of ethanol, but only a few studies have identified critical parameters for such exposure. The present studies examined temporal and other parameters of chronic ethanol exposure on subsequent intragastric (IG) self-infusion of ethanol.


METHODS
Sprague-Dawley rats implanted with IG catheters were passively infused with ethanol for 5 to 6 days and then allowed to self-infuse ethanol or water using a procedure in which infusions were contingent upon licking fruit-flavored solutions. Experiment 1 examined the time interval between consecutive periods of passive infusion (Massed Group: 12 hours vs. Spaced Group: 36 hours). Experiment 2 studied the interval between the final passive infusion and onset of self-infusion (12 vs. 36 hours). Finally, Experiment 3 tested the effect of inserting self-infusion days within the passive infusion phase.


RESULTS
Passive ethanol exposure on consecutive days induced relatively large amounts of ethanol self-infusion (4.1 to 7.9 g/kg/d). Increasing the duration of the ethanol-free interval between periods of passive exposure to 36 hours significantly reduced ethanol self-infusion (2.2 g/kg/d; Exp. 1). The time delay between the last passive ethanol exposure and onset of self-infusion had no effect on self-infusion (Exp. 2). Moreover, inserting no-choice self-infusion days between the last few passive exposure days did not increase self-infusion (Exp. 3).


CONCLUSIONS
Measurement of withdrawal signs indicated that Massed passive exposure produced stronger dependence than Spaced passive exposure, suggesting that enhanced ethanol self-infusion in Massed Groups might be explained by the opportunity for greater negative reinforcement by ethanol. Although enhanced negative reinforcement might also explain why the Massed Group showed a weaker aversion for the ethanol-paired flavor than the Spaced Group, this observation could also be explained by the development of greater tolerance to ethanol's aversive pharmacological effects in the Massed Group.
Fidler
Tara L
TL
Department of Behavioral Neuroscience and Portland Alcohol Research Center, Oregon Health & Science University, Portland, OR 97239-3098, USA. fidlert@ohsu.edu
Oberlin
Brandon G
BG
Struthers
Amanda M
AM
Cunningham
Christopher L
CL
D000428:Alcohol Drinking / Q000523:psychology*; D000435:Alcoholic Intoxication / Q000523:psychology; D000818:Animals; D002492:Central Nervous System Depressants / Q000008:administration & dosage / Q000097:blood / Q000494:pharmacology*; D003213:Conditioning, Psychological / Q000502:physiology; D004305:Dose-Response Relationship, Drug; D000431:Ethanol / Q000008:administration & dosage / Q000097:blood / Q000494:pharmacology*; D007441:Intubation, Gastrointestinal; D051381:Rats; D017207:Rats, Sprague-Dawley; D012646:Self Administration; D013375:Substance Withdrawal Syndrome / Q000523:psychology
D002492:Central Nervous System Depressants; D000431:Ethanol