Generalization of a positive-feature interoceptive morphine occasion setter across the rat estrous cycle.

Introduction: Interoceptive stimuli elicited by drug administration acquire conditioned modulatory properties of the induction of conditioned appetitive behaviours by exteroceptive cues. This effect may be modeled using a drug discrimination task in which the drug stimulus is trained as a positive-feature (FP) occasion setter (OS) that disambiguates the relation between an exteroceptive light conditioned stimulus (CS) and a sucrose unconditioned stimulus (US). We previously reported that females are less sensitive to generalization of a FP morphine OS than males, so we investigated the role of endogenous ovarian hormones in this difference.

Disruption of positive- and negative-feature morphine interoceptive occasion setters by dopamine receptor agonism and antagonism in male and female rats.

Rationale: Internally perceived stimuli evoked by morphine administration can form Pavlovian associations such that they can function as occasion setters (OSs) for externally perceived reward cues in rats, coming to modulate reward-seeking behaviour. Though much research has investigated mechanisms underlying opioid-related reinforcement and analgesia, neurotransmitter systems involved in the functioning of opioids as Pavlovian interoceptive discriminative stimuli remain to be disentangled despite documented differences in the development of tolerance to analgesic versus discriminative stimulus effects.

Objectives: Dopamine has been implicated in many opioid-related behaviours, so we aimed to investigate the role of this neurotransmitter in expression of morphine occasion setting.

Regulation of cocaine-related behaviours by estrogen and progesterone.

Women are more sensitive to cocaine craving elicited by stimuli associated with relapse. Ovarian hormones modulate cocaine craving and may therefore function as risk factors or therapeutic agents for the development and treatment of cocaine use disorder, respectively. We review herein the neuropharmacological effects of the steroid hormones 17ß-estradiol, progesterone, and allopregnanolone, a progesterone metabolite, in relation to their effects on cocaine-induced locomotion, behavioural sensitization, conditioned place preference, and reinstatement of cocaine seeking.