A stimulus-control account of dysregulated drug intake

Drug discrimination learning: Interoceptive stimulus control of behavior and its implications for regulated and dysregulated drug intake

Drug discrimination research has generated rich evidence for the capacity of interoceptive drug stimuli to control behavior by serving as discriminative cues. Owing to its neuropharmacological specificity, drug discrimination learning has been widely used to characterize the stimulus effects and neuropharmacological underpinning of drugs. Apart from such utility, discriminative drug stimuli may help regulate drug use by disambiguating conditioned associations and post-intake outcomes. First, this review summarizes the evidence supporting interoceptive regulation of drug intake from the literature of exteroceptive discriminative control of drug-related behavior, effects of drug priming, and self-titration of drug intake. Second, an overview of interoceptive control of reward-seeking and the animal model of discriminated goal-tracking is provided to illustrate interoceptive stimulus control of the initiation and patterning of drug intake. Third, we highlight the importance of interoceptive control of aversion-avoidance in the termination of drug-use episodes and describe the animal model of discriminated taste avoidance that supports such a position. In bridging these discriminative functions of drug stimuli, we propose that interoceptive drug stimuli help regulate intake by disambiguating whether intake will be rewarding, nonrewarding, or aversive. The reflection and discussion on current theoretical formulations of interoceptive control of drug intake may further scientific advances to improve animal models to study the mechanisms by which interoceptive stimuli regulate drug intake, as well as how alterations of interoceptive processes may contribute to the transition to dysregulated drug use.

Serial feature positive and feature negative discrimination learning in a taste avoidance preparation: implications for interoceptive control of behavior

BACKGROUND

Psychoactive drugs produce interoceptive stimuli that can guide appropriate behaviors by initiating or inhibiting responding.

OBJECTIVE

The current study investigated whether an interoceptive morphine state produces similar patterns of serial feature positive (FP) and feature negative (FN) discrimination learning under comparable conditions in a taste avoidance design.

METHODS

Male Sprague-Dawley rats were trained under 10 cycles of FP or FN discrimination. In the FP task, morphine (10 mg/kg, IP) signaled that a saccharin solution was followed by LiCl (1.2 mEq, IP), while the vehicle (saline) signaled that the LiCl was withheld. In the FN task, the contingency was reversed.

RESULTS

The FP-trained rats acquired the discrimination after three training cycles, consuming significantly less saccharin on morphine, than on vehicle, sessions ( P  < 0.05). The FN-trained rats acquired the discrimination after six training cycles, consuming more on morphine than on vehicle sessions ( P < 0.05). However, FN-trained rats never recovered saccharin consumption to baseline levels and 40% of the rats continued to avoid saccharin (consuming 0 ml) on morphine sessions. Control rats that never received LiCl consumed high levels of saccharin on morphine and vehicle sessions, indicating that morphine did not produce unconditioned suppression of saccharin consumption.

CONCLUSION

The difficulty to acquire FN discrimination might reflect the limitations of learning about safety contingencies in the taste avoidance design. The rapidity of FP learning when a drug state signals an aversive contingency may have implications for the general role of interoceptive stimuli in the control of behavior.

Conditioned Taste Avoidance Drug Discrimination Procedure: Assessments and Applications

In the present chapter, we summarize much of the work on the taste avoidance drug discrimination procedure, presenting the logic for its initial introduction and the extension of the procedure in the investigation of the discriminative properties of various drugs. Results from these assessments parallel those from more traditional operant and maze designs in classifying and characterizing the discriminative properties of drug. At the same time, this design reveals a procedure that is sensitive in such assessments by indexing these stimulus properties more rapidly and at lower doses than in the more traditional procedures (in some cases for drugs heretofore resistant in their detection). Importantly, much remains to be learned about the taste avoidance procedure in that the nature of such learning remains unknown and the specific parameters under which it can be established and generalized and its neurochemical and neuroanatomical bases are largely unexplored. The application of drug discrimination learning to human drug abuse continues to be an important consideration for this specific design (as well as that of drug discrimination procedures in general), and recent parallels between drug use and food intake in terms of its regulation by interoceptive stimuli suggests a possible role of the loss of stimulus control in drug escalation and addiction (with possible therapeutic implications via the modulation of these interoceptive cues).

Effects of orbitofrontal cortex lesions on cocaine self-administration

Previous research has implicated limbic and prefrontal cortical areas in the control of drug-seeking behavior. The present study examined the effects of orbitofrontal-cortex (OFC) lesions on acquisition, dose-dependence, within-session patterning, and reinstatement of cocaine self-administration. Rats received OFC or sham lesions before or after acquisition (0.3 mg/kg/injection, paired with a visual stimulus), then were tested with a range of doses (0, 0.03, 0.1, 0.3 and 1). Compared to controls, rats lesioned before acquisition acquired the behavior sooner, responded more at low doses, and responded more on the first day of extinction. Rats that were lesioned after acquisition showed an even larger increase in responding (approximately 250%) at the lowest dose, and they also showed increased timeout responding and drug "loading" at low doses. Pre-acquisition lesions were tested and found to have no effect on cocaine-induced reinstatement. In parallel experiments examining effects of pre-acquisition OFC lesions on food-reinforced responding, lesions did not alter acquisition, maintenance, or reinstatement, but accelerated the course of extinction. The increased cocaine self-administration seen in OFC-lesioned rats did not resemble the dysregulated drug intake observed in long-access models of addiction but might be due to impaired response inhibition or impaired tracking of the reward value of drug-related cues.