Increased consumption but not operant self-administration of ethanol in mice lacking the RIIbeta subunit of protein kinase A.
BACKGROUND
Accumulating evidence indicates that adenosine monophosphate (cAMP)-dependent protein kinase A (PKA) is involved in the neurobiological responses to ethanol. Previous reports indicate that mice lacking the RIIbeta subunit of PKA (RIIbeta(-/-)) voluntarily consume more ethanol than wild-type controls (RIIbeta(+/+)) using 2-bottle testing procedures. Although such procedures primarily measure consummatory behavior, operant self-administration procedures allow analysis of consummatory as well as appetitive or "ethanol-seeking" behavior (i.e., lever pressing is required to gain access to the ethanol solution). Therefore, we determined whether the high ethanol consumption characteristic of RIIbeta(-/-) mice would be complemented by increased appetitive ethanol-seeking behavior in an operant paradigm.


METHODS
RIIbeta(-/-) (n=8) and RIIbeta(+/+) (n=8) mice were initially sucrose-faded until they were lever responding for nonsweetened ethanol (10, 14, and 18%). Following the self-administration testing, RIIbeta(+/+) and RIIbeta(-/-) mice were given access to 2 bottles, one containing water and the other ethanol to replicate the voluntary ethanol drinking data previously from our laboratory. Finally, immediately after voluntary consumption all mice were again tested for self-administration of 10% ethanol. Alterations in the reinforcement schedule were also explored as RIIbeta(+/+) and RIIbeta(-/-) mice were tested for self-administration of 10% ethanol at FR-3 and FR-5 schedules.


RESULTS
The RIIbeta(-/-) mice displayed lower operant responding for ethanol and food reinforcement compared with RIIbeta(+/+) controls. However, this effect was driven by a significant increase in lever responses made by female RIIbeta(+/+) mice. When the excessive lever responses of the female RIIbeta(+/+) mice are accounted for, the RIIbeta(-/-) mice show ethanol lever responses comparable to controls. Following operant self-administration testing, RIIbeta(-/-) mice of both sexes consumed more ethanol solution compared with RIIbeta(+/+) mice during 2-bottle testing.


CONCLUSIONS
Increased ingestion of ethanol by RIIbeta(-/-) mice is likely the result of altered PKA activity within neuronal pathways that control ethanol-consummatory behaviors. Conversely, the RIIbeta subunit of PKA appears not to play a critical role in neuronal pathways that regulate appetitive behaviors directed at obtaining ethanol. Finally, increased operant self-administration of food and ethanol by female wild-type mice was absent in female RIIbeta(-/-) mice, suggesting that normal PKA signaling may be part of a general, and sex-dependent, mechanism involved with reinforcement-seeking behavior.
Ferraro
Frank M
FM
Department of Psychology, University of North Carolina, Chapel Hill 27599-3270, USA. ferraro@unc.edu
Sparta
Dennis R
DR
Knapp
Darin J
DJ
Breese
George R
GR
Thiele
Todd E
TE
D000428:Alcohol Drinking; D000818:Animals; D001070:Appetitive Behavior; D003259:Consummatory Behavior; D054757:Cyclic AMP-Dependent Protein Kinase RIIbeta Subunit; D017868:Cyclic AMP-Dependent Protein Kinases / Q000737:chemistry / Q000172:deficiency / Q000502:physiology*; D004326:Drinking; D000431:Ethanol / Q000008:administration & dosage*; D005260:Female; D005502:Food; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D012646:Self Administration; D012727:Sex Characteristics; D012996:Solutions; D013395:Sucrose / Q000008:administration & dosage
D054757:Cyclic AMP-Dependent Protein Kinase RIIbeta Subunit; C517838:Prkar2b protein, mouse; D012996:Solutions; D000431:Ethanol; D013395:Sucrose; D017868:Cyclic AMP-Dependent Protein Kinases