Heroin self-administration as a function of time of day in rats

A Complex Relationship Among the Circadian Rhythm, Reward Circuit and Substance Use Disorder (SUD)

The human brain not only controls the various physiological functions but is also the prime regulator of circadian rhythms, rewards, and behaviors. Environmental factors, professional stress, and social disintegration are regarded as the initial causative factors of addiction behavior. Shift work, artificial light exposure at night, and chronic and acute jet lag influence circadian rhythm dysfunction. The result is impaired neurotransmitter release, dysfunction of neural circuits, endocrine disturbance, and metabolic disorder, leading to advancement in substance use disorder. There is a bidirectional relationship between chronodisruption and addiction behavior. Circadian rhythm dysfunction, neuroadaptation in the reward circuits, and alteration in clock gene expression in the mesolimbic areas influence substance use disorder (SUD), and chronotherapy has potential benefits in the treatment strategies. This review explores the relationship among the circadian rhythm dysfunction, reward circuit, and SUD. The impact of chronotherapy on SUD has also been discussed.

Neuroimaging of the effects of drug exposure or self-administration in rodents: A systematic review

A systematic review of functional neuroimaging studies on drug (self-) administration in rodents is lacking. Here, we summarized effects of acute or chronic drug administration of various classes of drugs on brain function and determined consistency with human literature. We performed a systematic literature search and identified 125 studies on in vivo rodent resting-state functional magnetic resonance imaging (n = 84) or positron emission tomography (n = 41) spanning depressants (n = 27), opioids (n = 23), stimulants (n = 72), and cannabis (n = 3). Results primarily showed alterations in the striatum, consistent with the human literature. The anterior cingulate cortex and (nonspecific) prefrontal cortex were also frequently implicated. Upregulation was most often found after shorter administration and downregulation after long chronic administration, particularly in the striatum. Importantly, results were consistent across study design, administration models, imaging method, and animal states. Results provide evidence of altered resting-state brain function in rodents upon drug administration, implicating the brain's reward network analogous to human studies. However, alterations were more dynamic than previously known, with dynamic adaptation depending on the length of drug administration.

Disrupted Circadian Rhythms and Substance Use Disorders: A Narrative Review

Substance use disorder is a major global health concern, with a high prevalence among adolescents and young adults. The most common substances of abuse include alcohol, marijuana, cocaine, nicotine, and opiates. Evidence suggests that a mismatch between contemporary lifestyle and environmental demands leads to disrupted circadian rhythms that impair optimal physiological and behavioral function, which can increase the vulnerability to develop substance use disorder and related problems. The circadian system plays an important role in regulating the sleep-wake cycle and reward processing, both of which directly affect substance abuse. Distorted substance use can have a reciprocal effect on the circadian system by influencing circadian clock gene expression. Considering the detrimental health consequences and profound societal impact of substance use disorder, it is crucial to comprehend its complex association with circadian rhythms, which can pave the way for the generation of novel chronotherapeutic treatment approaches. In this narrative review, we have explored the potential contributions of disrupted circadian rhythms and sleep on use and relapse of different substances of abuse. The involvement of circadian clock genes with drug reward pathways is discussed, along with the potential research areas that can be explored to minimize disordered substance use by improving circadian hygiene.

Renewal of cocaine seeking using social and nonsocial contextual stimuli

RATIONALE

Various nonsocial cues have been used as stimuli to examine the contextual control of drug seeking behavior, but little is known about the role of social stimuli.

OBJECTIVES

This study determined if renewal of cocaine seeking is differentially controlled using a context consisting of either a social peer and/or house light illumination.

METHODS

In Experiment 1, male and female rats trained to self-administer cocaine in the presence of a same-sex social peer and house light illumination (context A). Following self-administration, rats were randomly assigned to either an AAA (control) or ABA (renewal) group for extinction. For AAA rats, extinction consisted of the same context A as self-administration; for ABA rats, extinction occurred without the peer or house light (context B). Following extinction, renewal of cocaine seeking occurred by testing the peer alone, house light alone, and the peer + house light combination. Experiment 2 was conducted to ensure that the house light alone was sufficiently salient to produce renewal.

RESULTS

Both experiments showed that rats acquired cocaine self-administration and extinguished lever pressing. In Experiment 1, the ABA group renewed cocaine seeking to the peer and peer + house light, but not to the house light alone. In Experiment 2, ABA rats renewed cocaine seeking to the house light alone, indicating it was sufficiently salient to produce renewal. The AAA group did not show renewal in either experiment.

CONCLUSION

Social peers serve as powerful stimuli that can overshadow nonsocial visual stimuli in the renewal of cocaine seeking.

Sleep is increased by liraglutide, a glucagon-like peptide-1 receptor agonist, in rats

INTRODUCTION

Sleep disturbances are prominent in drug use disorders, including those involving opioids in both humans and animals. Recent studies have shown that administration of liraglutide, a glucagon-like peptide-1 agonist, significantly reduces heroin taking and seeking in rats. In an effort to further understand the action of this substance on physiological functions and to evaluate safety issues for its potential clinical use, the aim of the present study was to determine whether the dose of liraglutide found effective in reducing responding for an opioid also could improve sleep in drug-naïve rats.

METHODS

Using a within-subjects design, adult male rats chronically implanted with EEG and EMG electrodes received subcutaneous injection of saline or 0.06, 0.10, 0.30 or 0.60 mg/kg liraglutide. The 0.10 and 0.30 mg/kg doses are known to be most effective in reducing responding for heroin in rats at light or dark onset during a 12:12 h light-dark cycle (0.10 mg/kg for taking and seeking, 0.30 mg/kg for seeking). EEG and EMG were recorded across the 24 h period following each injection.

RESULTS

After both dark and light onset injections, liraglutide dose-dependently decreased wakefulness and increased non-rapid eye movement (NREM) sleep except at the lowest dose. The bout length of wakefulness and NREM sleep were decreased and increased, respectively. Whether administered at light or dark onset, the above alterations occurred primarily during the dark period (i.e., during the active period). The animals' body weight was decreased after liraglutide treatments as expected since it is clinically used for the treatment of obesity.

CONCLUSION

These data indicate that liraglutide, at doses known to reduce responding for heroin and fentanyl, also increases NREM sleep, suggesting that the increase in sleep may contribute to the protective effects of liraglutide and may promote overall general health.

Circadian rhythm influences naloxone induced morphine withdrawal and neuronal activity of lateral paragigantocellularis nucleus

Investigations have shown that the circadian rhythm can affect the mechanisms associated with drug dependence. In this regard, we sought to assess the negative consequence of morphine withdrawal syndrome on conditioned place aversion (CPA) and lateral paragigantocellularis (LPGi) neuronal activity in morphine-dependent rats during light (8:00-12:00) and dark (20:00-24:00) cycles. Male Wistar rats (250-300 g) were received 10 mg/kg morphine or its vehicle (Saline, 2 mL/kg/12 h, s.c.) in 13 consecutive days for behavioral assessment tests. Then, naloxone-induced conditioned place aversion and physical signs of withdrawal syndrome were evaluated during light and dark cycles. In contrast to the behavioral part, we performed in vivo extracellular single-unit recording for investigating the neural response of LPGi to naloxone in morphine-dependent rats on day 10 of morphine/saline exposure. Results showed that naloxone induced conditioned place aversion in both light and dark cycles, but the CPA score during the light cycle was larger. Moreover, the intensity of physical signs of morphine withdrawal syndrome was more severe during the light cycle (rest phase) compare to the dark one. In electrophysiological experiments, results indicated that naloxone evoked both excitatory and inhibitory responses in LPGi neurons and the incremental effect of naloxone on LPGi activity was stronger in the light cycle. Also, the neurons with the excitatory response exhibited higher baseline activity in the dark cycle, but the neurons with the inhibitory response showed higher baseline activity in the light cycle. Interestingly, the baseline firing rate of neurons recorded in the light cycle was significantly different in response (excitatory/inhibitory) -dependent manner. We concluded that naloxone-induced changes in LPGi cellular activity and behaviors of morphine-dependent rats can be affected by circadian rhythm and the internal clock.

Endogenous opiates and behavior: 2019

This paper is the forty-second consecutive installment of the annual anthological review of research concerning the endogenous opioid system, summarizing articles published during 2019 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).

Circadian rhythms and substance use disorders: A bidirectional relationship

The circadian system organizes circadian rhythms (biological cycles that occur around 24 h) that couple environmental cues (zeitgebers) with internal functions of the organism. The misalignment between circadian rhythms and external cues is known as chronodisruption and contributes to the development of mental, metabolic and other disorders, including cancer, cardiovascular diseases and addictive disorders. Drug addiction represents a global public health concern and affects the health and well-being of individuals, families and communities. In this manuscript, we reviewed evidence indicating a bidirectional relationship between the circadian system and the development of addictive disorders. We provide information on the interaction between the circadian system and drug addiction for each drug or drug class (alcohol, cannabis, hallucinogens, psychostimulants and opioids). We also describe evidence showing that drug use follows a circadian pattern, which changes with the progression of addiction. Furthermore, clock gene expression is also altered during the development of drug addiction in many brain areas related to drug reward, drug seeking and relapse. The regulation of the glutamatergic and dopaminergic neurocircuitry by clock genes is postulated to be the main circadian mechanism underlying the escalation of drug addiction. The bidirectional interaction between the circadian system and drug addiction seems to be mediated by the effects caused by each drug or class of drugs of abuse. These studies provide new insights on the development of successful strategies aimed at restoring/stabilizing circadian rhythms to reduce the risk for addiction development and relapse.

Analysis of Opioid-Seeking Behavior Through the Intravenous Self-Administration Reinstatement Model in Rats

The inability to maintain drug abstinence is often referred to as relapse and consists of a process by which an abstaining individual slips back into old behavioral patterns and substance use. Animal models of relapse have been developed over the last decades and significantly contributed to shed light on the neurobiological mechanisms underlying vulnerability to relapse. The most common procedure to study drug-seeking and relapse-like behavior in animals is the "extinction-reinstatement model." Originally elaborated by Pavlov and Skinner, the concepts of reinforced operant responding were applied to addiction research not before 1971 (Stretch et al., Can J Physiol Pharmacol 49:581-589, 1971), and the first report of a reinstatement animal model as it is now used worldwide was published only 10 years later (De Wit and Stewart, Psychopharmacology 75:134-143, 1981). According to the proposed model, opioids are typically self-administered intravenously, as humans do, and although rodents are most often employed in these studies, a variety of species including nonhuman primates, dogs, cats, and pigeons can be used. Several operant responses are available, depending on the species studied. For example, a lever press or a nose poke response typically is used for rodents, whereas a panel press response typically is used for nonhuman primates. In this chapter we describe a simple and easily reproducible protocol of heroin-seeking reinstatement in rats, which proved useful to study the neurobiological mechanisms underlying relapse to heroin and vulnerability factors enhancing the resumption of heroin-seeking behavior.

Timing of Morphine Administration Differentially Alters Paraventricular Thalamic Neuron Activity

The paraventricular thalamic nucleus (PVT) is a brain region involved in regulating arousal, goal-oriented behaviors, and drug seeking, all key factors playing a role in substance use disorder. Given this, we investigated the temporal effects of administering morphine, an opioid with strongly addictive properties, on PVT neuronal function in mice using acute brain slices. Here, we show that morphine administration and electrophysiological recordings that occur during periods of animal inactivity (light cycle) elicit increases in PVT neuronal function during a 24-h abstinence time point. Furthermore, we show that morphine-induced increases in PVT neuronal activity at 24-h abstinence are occluded when morphine administration and recordings are performed during an animals' active state (dark cycle). Based on our electrophysiological results combined with previous findings demonstrating that PVT neuronal activity regulates drug-seeking behaviors, we investigated whether timing morphine administration with periods of vigilance (dark cycle) would decrease drug-seeking behaviors in an animal model of substance use disorder. We found that context-induced morphine-seeking behaviors were intact regardless of the time morphine was administered (e.g., light cycle or dark cycle). Our electrophysiological results suggest that timing morphine with various states of arousal may impact the firing of PVT neurons during abstinence. Although, this may not impact context-induced drug-seeking behaviors.