Persistence of one-trial cocaine-induced behavioral sensitization in young rats: regional differences in Fos immunoreactivity.
BACKGROUND
Unlike adult rats, young rats exhibit context-dependent and context-independent behavioral sensitization when assessed after a single pretreatment injection of cocaine.


OBJECTIVE
The purpose of this study was to determine whether: (1) the context-dependent and context-independent sensitization of young rats can be dissociated based on the persistence of the sensitized response and (2) the expression of behavioral sensitization is associated with region-specific increases in Fos immunoreactivity (Fos-IR).


METHODS
On postnatal day (PD) 19, rats were injected with either saline or cocaine (30 mg/kg) in a novel test chamber or the home cage. After 1, 3, 5, 7, 14, or 61 abstinence days, rats were challenged with 20 mg/kg cocaine and locomotor activity was measured for 60 min. In a separate experiment, rats pretreated on PD 19 were challenged with cocaine (10-30 mg/kg) on PD 80.


RESULTS
The sensitized responding of young rats persisted for the same length of time (5 days) regardless of whether cocaine pretreatment occurred in a novel environment or the home cage. Behavioral sensitization did not reemerge in adulthood. When assessed after three abstinence days (i.e., on PD 22), acute treatment with cocaine increased Fos-IR in various brain regions, but sensitized responding was associated with elevated Fos expression in only the caudate-putamen (CP) and prefrontal cortex (PFC).


CONCLUSIONS
Persistence of the sensitized response cannot be used to dissociate the one-trial context-dependent and context-independent sensitization of young rats. Fos data indicate that the CP and PFC may be involved in the mediation of short-term behavioral sensitization on PD 22.
McDougall
Sanders A
SA
Department of Psychology, California State University, San Bernardino, CA 92407, USA. smcdouga@csusb.edu
Charntikov
Sergios
S
Cortez
Anthony M
AM
Amodeo
Dionisio A
DA
Martinez
Cynthia E
CE
Crawford
Cynthia A
CA
D000375:Aging / Q000378:metabolism / Q000523:psychology; D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects*; D001921:Brain / Q000187:drug effects* / Q000378:metabolism; D000697:Central Nervous System Stimulants / Q000494:pharmacology*; D003042:Cocaine / Q000494:pharmacology*; D005260:Female; D007150:Immunohistochemistry; D008297:Male; D009043:Motor Activity / Q000187:drug effects*; D016760:Proto-Oncogene Proteins c-fos / Q000096:biosynthesis*; D051381:Rats; D017207:Rats, Sprague-Dawley
D000697:Central Nervous System Stimulants; D016760:Proto-Oncogene Proteins c-fos; D003042:Cocaine