Exploratory studies in sensory reinforcement in male rats: Effects of methamphetamine.

Abstract

Understanding sensory reinforcement and the effects of stimulant drugs on sensory reinforcers is potentially important for understanding their influence on addiction processes. Experiment 1 explored the reinforcing properties of a visual stimulus and the effects of methamphetamine (METH) on responding maintained by a visual reinforcer (VRF) in male rats. Snout poke responses to the active alternative produced the VRF according to variable interval (VI) schedules of reinforcement, and responses to an inactive alternative had no programmed effect. Experiment 2 explored the effects of METH on choice between the VRF and a water reinforcer (H2ORF) using concurrent VI schedules in male rats. In Experiment 1, response-contingent onset of the VRF produced an increase in both the relative frequency and absolute rate of active responding. The rate of both active and inactive responding declined across the 40-min test sessions. METH did not differentially enhance active responding for the VRF. Instead, METH nondifferentially increased the rate of responding and attenuated the within-session decline of responding. In Experiment 2, METH differentially increased the rate of responding for the VRF relative to the H2ORF. The results of these exploratory experiments indicate that the reinforcing effects of the VRF were weak and transient. In addition, METH treatment increased responding, and the specificity of the enhancement of METH was dependent upon the testing conditions. Potential explanations of these differences, such as novelty and reinforcer type, are discussed.

Chronic variable stress and intravenous methamphetamine self-administration – Role of individual differences in behavioral and physiological reactivity to novelty

“…These findings are consistent with the existing literature indicating that high responders (i.e., rats demonstrating high locomotor activity in a novel open field environment) exhibit increased operant self-administration for psychostimulants compared to low responders (Piazza et al, 1989, Pierre and Vezina, 1997, Marinelli and White, 2000, Piazza et al, 2000, Cain et al, 2006, Davis et al, 2008, Gancarz et al, 2011). In addition, Gancarz et al ( 2011, 2012) found that rats with higher locomotor reactivity exhibited increased operant responding for methamphetamine reinforcement in combination with a visual stimulus compared to rats with lower reactivity. While the present study used a higher unit dose of methamphetamine reinforcement (0.05 mg/kg/infusion) as compared to that utilized by Gancarz et al (2011, 2012) who used 0.025 mg/kg/infusion, collectively these observations suggest that a range of doses can be used to detect the effects of individual differences on intravenous methamphetamine self-administration.…”

“…In addition, Gancarz et al ( 2011, 2012) found that rats with higher locomotor reactivity exhibited increased operant responding for methamphetamine reinforcement in combination with a visual stimulus compared to rats with lower reactivity. While the present study used a higher unit dose of methamphetamine reinforcement (0.05 mg/kg/infusion) as compared to that utilized by Gancarz et al (2011, 2012) who used 0.025 mg/kg/infusion, collectively these observations suggest that a range of doses can be used to detect the effects of individual differences on intravenous methamphetamine self-administration.…”

Habituation of reinforcer effectiveness

“…We have shown for both nicotine (Lloyd et al, in press) and methamphetamine (Gancarz et al, 2012a; Lloyd et al, in press) that the drug-induced increases in responding for sensory reinforcers are accompanied by a decrease in HRE. Figure 4A illustrates our findings in rats administered 0.4 mg/kg nicotine, and Figure 4B illustrates the effects of 0.25 and 1.0 mg/kg doses of methamphetamine.…”

Nicotine and methamphetamine disrupt habituation of sensory reinforcer effectiveness in male rats.

“…For example, exploratory activity is high when a rat is first placed into a novel locomotor chamber and then decreases within the same session. Similarly, operant responding for novel light-onset is initially high at the start of a test session and then shows a within-session decline (Gancarz, Ashrafioun, et al, 2012; Gancarz, Robble, Kausch, Lloyd, & Richards, 2012). …”

“…We selected 0.75 mg/kg METH for this experiment because it was within the range of known effective doses (Gancarz, Ashrafioun, et al, 2012), and we selected the NIC dose of 0.4 mg/kg because this dose was found to effectively increase light reinforced responding (Palmatier et al, 2007). …”