Amitifadine, a triple reuptake inhibitor, reduces self-administration of the opiate remifentanil in rats

Endogenous opiates and behavior: 2020

This paper is the forty-third consecutive installment of the annual anthological review of research concerning the endogenous opioid system, summarizing articles published during 2020 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides and receptors as well as effects of opioid/opiate agonists and antagonists. The review is subdivided into the following specific topics: molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors (1), the roles of these opioid peptides and receptors in pain and analgesia in animals (2) and humans (3), opioid-sensitive and opioid-insensitive effects of nonopioid analgesics (4), opioid peptide and receptor involvement in tolerance and dependence (5), stress and social status (6), learning and memory (7), eating and drinking (8), drug abuse and alcohol (9), sexual activity and hormones, pregnancy, development and endocrinology (10), mental illness and mood (11), seizures and neurologic disorders (12), electrical-related activity and neurophysiology (13), general activity and locomotion (14), gastrointestinal, renal and hepatic functions (15), cardiovascular responses (16), respiration and thermoregulation (17), and immunological responses (18).

Remifentanil self-administration in mice promotes sex-specific prefrontal cortex dysfunction underlying deficits in cognitive flexibility

Opioid-based drugs are frequently used for pain management in both males and females despite the known risk of prefrontal cortex dysfunction and cognitive impairments. Although poorly understood, loss of cognitive control following chronic drug use has been linked to decreased activation of frontal cortex regions. Here, we show that self-administration of the potent opioid, remifentanil, causes a long-lasting hypoactive basal state evidenced by a decrease in ex vivo excitability that is paralleled by an increase in firing capacity of layer 5/6 pyramidal neurons in the prelimbic, but not infralimbic region of the medial prefrontal cortex. This phenomenon was observed in females after as few as 5 days and up to 25-30 days of self-administration. In contrast, pyramidal neurons in males showed increased excitability following 10-16 days of self-administration, with hypoactive states arising only following 25-30 days of self-administration. The emergence of a hypoactive, but not hyperactive basal state following remifentanil self-administration aligned with deficits in cognitive flexibility as assessed using an operant-based attentional set-shifting task. In females, the hypoactive basal state is driven by a reduction in excitatory synaptic transmission mediated by AMPA-type glutamate receptors. Alternatively, hyper- and hypoactive states in males align selectively with decreased and increased GABA_B signaling, respectively. Chemogenetic compensation for this hypoactive state prior to testing restored cognitive flexibility, basal hypoactive state, and remifentanil-induced plasticity. These data define cellular and synaptic mechanisms by which opioids impair prefrontal function and cognitive control; indicating that interventions aimed at targeting opioid-induced adaptations should be tailored based on biological sex.

Differential behavioral functioning in the offspring of rats with high vs. low self-administration of the opioid agonist remifentanil

Opioid use disorder (OUD) has a variety of adverse effects on both the users and their offspring. In the current study, a random group of Sprague-Dawley rats (25 females and 15 males) were tested for intravenous self-administration of the opioid agonist remifentanil to determine the range of acquisition for opioid. One-month after the end of self-administration of remifentanil, rats with the highest intake were mated together and rats with lowest intake were mated together. Then, the offspring of the two groups were tested for anxiety-like behavior, locomotor activity, nociception and intravenous remifentanil self-administration. The parents showed a range of remifentanil self-administration, especially in the female rats. The offspring of the parents with low and high remifentanil self-administration showed significant differences in specific behavioral functions. On the hotplate test of nociception, the female offspring parents with high remifentanil self-administration had significantly longer hotplate latencies, indicating reduced nociception, than the female offspring of parents with low remifentanil-self-administration, whereas there was no difference in the male offspring of low and high responding parents. In the elevated plus maze test of anxiety-like behavior, the offspring of the parents with high remifentanil intake showed more anxiety-like behavior than the offspring of the parents with low remifentanil intake regardless of sex. Locomotor activity was not significantly different. Interestingly, no significant differences in remifentanil self-administration in the offspring of parents with low and high remifentanil self-administration were detected. Overall, our data suggest a considerable range in remifentanil self-administration in rats and the offspring of rats with high opioid self-administration exhibit different behaviors vs offspring of rats with low opioid self-administration.