Plasma corticosterone in the rat in response to nicotine and saline injections in a context previously paired or unpaired with nicotine

Abstract

Rationale: Following repeated injections with nicotine paired with a distinctive environment, some studies have reported that the distinctive context becomes a conditioned stimulus (CS) capable of eliciting conditioned corticosterone (CORT) release. Conversely, other studies have found that exposure to the CS results in conditioned attenuation of nicotine-induced CORT release.

Objective: The present study was designed to examine whether these sets of separate findings could be replicated in animals exposed to the same experimental procedures within the same study.

Methods: CORT assessments were conducted in a distinctive context after independent groups of animals were injected with either saline or nicotine (1 mg/kg, salt) after five or ten nicotine injections either explicitly paired or unpaired with a distinctive context. The design also included groups of nicotine-naïve rats exposed to the experimental procedures and assessed for CORT levels following either nicotine or saline injections during their first, and after their fifth and tenth context exposures.

Results: CORT levels were higher after nicotine than after saline, and higher in the paired than in the unpaired condition. Exposure to the context without nicotine produced conditioned CORT release and exposure to the context did not attenuate nicotine-induced CORT release.

Conclusions: The results supported the notion that a CS associated with nicotine effects elicit a conditioned response (CR) in the form of CORT release. Future research will be needed to examine whether conditioned CORT release can explain the context-dependent attenuations of nicotine-induced CORT.