Adolescent morphine exposure changes the endogenous vlPAG opioid response to inflammatory pain in rats

Adolescence is one of the most critical periods for brain development, and exposure to morphine during this period can have long-life effects on pain-related behaviors. The opioid system in the periaqueductal gray (PAG) is highly vulnerable to drug exposure. However, the impact of adolescent morphine exposure (AME) on the endogenous opioid system in the PAG is currently unknown. This study aims to investigate the long-lasting effects of AME on the endogenous opioid system and its involvement in altering nociceptive behaviors. Adolescent rats were given escalating doses of morphine (2.5-25 mg/kg, subcutaneous) or an equal volume of saline twice daily for 10 consecutive days (PND 31-40). After a 30-day washout period, adult rats underwent formalin tests following microinjection of morphine, naloxone, or saline into the ventrolateral PAG (vlPAG) region. The results indicated that morphine microinjection into the vlPAG of the adolescent morphine-treated group significantly reduced the nociceptive score. However, the analgesic response to morphine in this group was significantly lower compared to the saline-treated group during adolescence. Additionally, the nociceptive score significantly increased following naloxone but not saline microinjection into the vlPAG of the saline-treated group during adolescence, rather than the morphine-treated one. These findings indicate that AME has long-lasting effects on the endogenous opioid system in the vlPAG, which can consequently alter behaviors related to inflammatory pain in adulthood.

Development of anxiety-like behaviors during adolescence: Persistent effects of adolescent morphine exposure in male rats

Epidemiological studies show the prevalence of opioid use, misuse and abuse in adolescents, which imposes social and economic accountability worldwide. Chronic opioid exposure, especially in adolescents, may have lasting effects on emotional behaviors that persist into adulthood. The current experiments were therefore designed to study the effects of sustained opioid exposure during adolescence on anxiety-like behaviors. Adolescent male Wistar rats underwent increasing doses of morphine for 10 days (PNDs 31-40). After that the open field test (OFT) and elevated plus maze (EPM) test were performed over a 4-week postmorphine treatment from adolescence to adulthood. Moreover, the weight of the animals was measured at these time points. We found that chronic adolescent morphine exposure reduces the weight gain during the period of morphine treatment and 4 weeks after that. It had no significant effect on the locomotor activity in the animals. Moreover, anxiolytic-like behavior was observed in the rats exposed to morphine during adolescence evaluated by OFT and EPM test. Thus, long-term exposure to morphine during adolescence has the profound potential of altering the anxiety-like behavior profile in the period from adolescence to adulthood. The maturation of the nervous system can be affected by drug abuse during the developmental window of adolescence and these effects may lead to behaviorally stable alterations.

Adolescent nicotine exposure increases nociceptive behaviors in rat model of formalin test: Involvement of ventrolateral periaqueductal gray neurons

Among the major life-threatening factors, smoking tobacco is the leading cause of death worldwide. Adolescence is a sensitive stage of brain development, and smoking at this age is thought to be associated with neural and behavioral alterations. Currently the association between adolescent tobacco use and pain perception remained to be addressed. It is also important to consider that the periaqueductal gray (PAG) is a major component of the descending pain inhibitory system. The present study was performed to reveal the possible effects of adolescent nicotine consumption on pain-related behaviors and also the antinociceptive effect of a single dose of morphine administration besides the ventrolateral PAG (vlPAG) firing assessment in adulthood during formalin test. Adolescent male Wistar rats were administered with either a nicotine or saline injection (s.c.), and after 30 days of washout period, formalin test was performed. The vlPAG neuronal responses to formalin injection were recorded via in vivo extracellular single-unit recording. The results demonstrated that adolescent nicotine exposure enhances behavioral responses to pain. It also reduced morphine-induced antinociceptive behavior in the formalin test during adulthood. Moreover, adolescent nicotine exposure attenuates the extent of vlPAG inhibitory response to formalin. Our data provided a further conclusion that adolescent nicotine exposure may alter the pain modulatory systems and their subsequent response to painful stimuli.

Sex differences in the rodent hippocampal opioid system following stress and oxycodone associated learning processes

Over the past two decades, opioid abuse has risen especially among women. In both sexes hippocampal neural circuits involved in associative memory formation and encoding of motivational incentives are critically important in the transition from initial drug use to drug abuse/dependence. Opioid circuits, particularly the mossy fiber pathway, are crucial for associative memory processes important for addiction. Our anatomical studies, especially those utilizing electron microscopic immunocytochemistry, have provided unique insight into sex differences in the distribution of opioid peptides and receptors in specific hippocampal circuits and how these distributions are altered following stress and oxycodone-associative learning processes. Here we review the hippocampal opioid system in rodents with respect to ovarian hormones effects and baseline sex differences then sex differences following acute and chronic stress. Next, we review sex differences in the hippocampal opioid system in unstressed and chronically stressed rats following oxycodone conditioned place preference. We show that opioid peptides and receptors are distributed within hippocampal circuits in females with elevated estrogen states in a manner that would enhance sensitivity to endogenous and exogenous opioids. Moreover, chronic stress primes the opioid system in females in a manner that would promote opioid-associative learning processes. In contrast, chronic stress has limited effects on the opioid system in males and reduces its capacity to support opioid-mediated learning processes. Interestingly, acute stress appears to prime males for opioid associative learning. On a broader scale the findings highlighted in this review have important implications in understanding sex differences in opioid drug use and abuse.

Adolescent opioid abuse: Role of glial and neuroimmune mechanisms

Opioids are widely prescribed for pain management, and prescription opioid misuse in adolescents has become a major epidemic in the United States and worldwide. Emerging data indicate that adolescence represents a critical period of brain development, and exposure to opioids during adolescence may increase the risk of addiction in adulthood. There is growing evidence that disruptions in brain glial function may be implicated in numerous chronic neuropathologies. Evidence suggests that glial mechanisms have an important role in the development and maintenance of opioid abuse and the risk for addiction. This review will describe glial and neuroimmune mechanisms involved in opioid use disorders during adolescence, which may increase substance use disorder liability later in life. Moreover, this review will identify some important neuro-glial targets, involved in opioid abuse and addiction, to develop future preventions and treatment strategies.

Opioid use disorder: a neglected human immunodeficiency virus risk in American adolescents

In 2017 alone, 783 000 children aged 12-17 years misused opioids with 14 000 using heroin. Opioid misuse and opioid use disorder (OUD) in adolescents and young adults are significant barriers to ending the HIV epidemic. To address these synergistic scourges requires dedicated practitioners and improved access to life-saving evidence-based treatment. Adolescents and young adults make up over one in five new HIV diagnoses even though they are less likely to be tested or know they are infected. Adolescents and young adults living with HIV are less likely to be retained in care or achieve virological suppression. OUD further leads to increased rates of risky behaviours (like sex without condoms), deceased retention in HIV care and decreased rates of viral suppression in this vulnerable population. Medications for opioid use disorder (MOUD) are recommended for adolescents and young adults with severe OUD and help retain youth in HIV treatment and decrease risk of death. However, due to stigma and lack of experience prescribing MOUD in adolescents, MOUD is often perceived as a last line option. MOUD remains difficult to access for adolescents with a shortage of providers and decreased options for treatment as compared to adults. Addiction treatment is infection prevention, and integrated addiction and HIV services are recommended to improve health outcomes. A multipronged approach including patient education, provider training and policy changes to improve access to treatment and harm reduction are urgently needed confront the drug use epidemic in youth.

Review of addiction risk potential associated with adolescent opioid use

Adolescence is a critical period of development with robust behavioral, morphological, hormonal, and neurochemical changes including changes in brain regions implicated in the reinforcing effects of drugs such as opioids. Here we examine the preclinical and, where appropriate complementary clinical literature, for the behavioral and neurological changes induced by adolescent opioid exposure/use and their long-term consequences during adulthood. Adolescent opioid exposure results in a widened biphasic shift in reinforcement with increased impact of positive rewarding aspects during initial use and profound negative reinforcement during adulthood. Females may have enhanced vulnerability due to fast onset of antinociceptive tolerance and reduced severity of somatic withdrawal symptoms during adolescence. Overall, adolescent opioid exposure, be it legally prescribed protracted intake or illicit consumption, results in significant and prolonged consequences of increased opioid reward concomitant with reduced analgesic efficacy and exacerbated somatic withdrawal severity during opioid use/exposure in adulthood. These findings are highly relevant to physicians, parents, law makers, and the general public as adolescent opioid exposure/misuse results in heightened risk for substance use disorders.

Adolescent drug exposure: A review of evidence for the development of persistent changes in brain function

Over the past decade, many studies have indicated that adolescence is a critical period of brain development and maturation. The refinement and maturation of the central nervous system over this prolonged period, however, makes the adolescent brain highly susceptible to perturbations from acute and chronic drug exposure. Here we review the preclinical literature addressing the long-term consequences of adolescent exposure to common recreational drugs and drugs-of-abuse. These studies on adolescent exposure to alcohol, nicotine, opioids, cannabinoids and psychostimulant drugs, such as cocaine and amphetamine, reveal a variety of long-lasting behavioral and neurobiological consequences. These agents can affect development of the prefrontal cortex and mesolimbic dopamine pathways and modify the reward systems, socio-emotional processing and cognition. Other consequences include disruption in working memory, anxiety disorders and an increased risk of subsequent drug abuse in adult life. Although preventive and control policies are a valuable approach to reduce the detrimental effects of drugs-of-abuse on the adolescent brain, a more profound understanding of their neurobiological impact can lead to improved strategies for the treatment and attenuation of the detrimental neuropsychiatric sequelae.

Pediatric postoperative opioid prescribing and the opioid crisis

PURPOSE OF REVIEW

The purpose of this review is to explore the effects of the opioid crisis on pediatric patients in the postoperative setting and provide recommendations for well-tolerated opioid prescribing practices.

RECENT FINDINGS

Opioid overdoses have increased among all age groups, predominantly related to overprescribing and accessibility of opioids in the home. Adverse risks of prescribed opioids include respiratory depression, gastrointestinal distress, accidental ingestion, intentional misuse, new chronic use, diversion to another user, and overdose. Well-tolerated opioid prescribing practices include multimodal pain management; prescribing guided by patient need; risk assessment for potential misuse; and comprehensive patient and family education on risks, safe storage, and disposal practices. Evolving state laws will affect varying institutional policies; thus, providers must ensure their prescribing practices are current and compliant.

SUMMARY

All age groups have been affected by the opioid crisis, including children and adolescents. When managing postoperative pain, clinicians must balance appropriate pain management with well-tolerated opioid stewardship to minimize harm related to postoperative care.