Sex-specific role for serotonin 5-HT2A receptor in modulation of opioid-induced antinociception and reward in mice.

Opioids are among the most effective analgesics and the mainstay of pain management. However, concerns about safety and abuse liability have challenged their widespread use by the medical community. Opioid-sparing therapies include drugs that in combination with opioids have the ability to enhance analgesia while decreasing opioid requirement as well as their side effects. Sex differences in antinociceptive responses to opioids have received increasing attention in recent years. However, the molecular mechanisms underlying sex differences related to opioid-sparing adjuncts remain largely unexplored. Using warm water tail-withdrawal as a mouse model of acute thermal nociception, our data suggest that adjunctive administration of the serotonin 5-HT2A receptor (5-HT2AR) antagonist volinanserin dose-dependently enhanced potency of the opioid analgesic oxycodone in male, but not female, mice. This antinociceptive-like response induced by oxycodone was also augmented in 5-HT2AR knockout (5-HT2AR-/-) male, but not female mice; an effect that was reversed by Cre-loxP-mediated selective expression of 5-HT2AR in dorsal root ganglion (DRG) neurons of 5-HT2AR-/- littermates. Pharmacological inhibition with volinanserin or genetic deletion in 5-HT2AR-/- animals potentiated the ability of oxycodone to reduce DRG excitability in male mice. Adjunctive volinanserin did not affect oxycodone-induced conditioned place preference (CPP), whereas it reduced oxycodone-induced locomotor sensitization in male and female mice. Together, these results suggest that adjunctive volinanserin augments opioid-induced antinociception, but not abuse-related behavior, through a sex-specific signaling crosstalk mechanism that requires 5-HT2AR expression in mouse DRG neurons. Ultimately, our results may pave the way for the clinical evaluation of volinanserin as a potential sex-specific opioid adjuvant.

Racial/ethnic differences in opioid-involved overdose deaths across metropolitan and non-metropolitan areas in the United States, 1999-2017.

BACKGROUND: From 1999 to 2017, more than 400,000 Americans died from a drug overdose death involving an opioid. Early surveillance studies have observed large variations in opioid-involved overdose deaths among different geographic regions and racial/ethnic groups. The purpose of this study was to characterize trends in racial/ethnic opioid-involved overdose deaths across metropolitan and non-metropolitan areas in the United States from 1999 to 2017. METHODS: The analysis used National Vital Statistics System data from 1999 to 2017 that were accessed through the CDC WONDER online database. Drug overdose deaths involving any opioid were identified using the International Classification of Diseases, Tenth Revision, codes and were represented as age-adjusted rates per 100,000 population. Joinpoint regression was used to examine trends in opioid-involved overdose deaths among racial/ethnic groups (non-Hispanic white, non-Hispanic black, Hispanic, non-Hispanic other) by metropolitan and non-metropolitan status (large metropolitan areas, medium-small metropolitan areas, and non-metropolitan areas). RESULTS: The annual age-adjusted death rates for drug overdose deaths that involved any opioid significantly increased for all racial/ethnic groups in metropolitan and non-metropolitan areas from 1999 to 2017. The largest average annual increases in rates occurred among non-Hispanic whites in non-metropolitan areas (13.6% increase per year) and medium-small metropolitan areas (12.3% increase per year), followed by non-Hispanic blacks in medium-small metropolitan areas (11.3% increase per year). CONCLUSIONS: The variations in opioid-involved overdose deaths among different racial/ethnic groups across geographic regions support the existence of multiple sub-epidemics in the current opioid overdose crisis and provide directions for targeted intervention efforts.

Adjunctive effect of the serotonin 5-HT2C receptor agonist lorcaserin on opioid-induced antinociception in mice.

Opioid-sparing adjuncts are treatments that aim to reduce the overall dose of opioids needed to achieve analgesia, hence decreasing the burden of side effects through alternative mechanisms of action. Lorcaserin is a serotonin 5-HT2C receptor (5-HT2CR) agonist that has recently been reported to reduce abuse-related effects of the opioid analgesic oxycodone. The goal of our studies was to evaluate the effects of adjunctive lorcaserin on opioid-induced analgesic-like behavior using the tail-flick reflex (TFR) test as a mouse model of acute thermal nociception. We show that whereas subcutaneous (s.c.) administration of lorcaserin alone was inactive on the TFR test, adjunctive lorcaserin (s.c.) significantly increased the potency of oxycodone as an antinociceptive drug. This effect was prevented by the 5-HT2CR antagonist SB242084. A similar lorcaserin (s.c.)-induced adjunctive phenotype was observed upon administration of the opioid analgesics morphine and fentanyl. Remarkably, we also show that, opposite to the effects observed via s.c. administration, intrathecal (i.t.) administration of lorcaserin alone induced antinociceptive TFR behavior, an effect that was not prevented by the opioid receptor antagonist naloxone. This route of administration (i.t.) also led to a significant augmentation of oxycodone-induced antinociception. Lorcaserin (s.c.) did not alter the brain or blood concentrations of oxycodone, which suggests that its adjunctive effects on opioid-induced antinociception do not depend upon changes in opioid metabolism. Together, these data indicate that lorcaserin-mediated activation of the 5-HT2CR may represent a new pharmacological approach to augment opioid-induced antinociception. This article is part of the special issue entitled 'Serotonin Research: Crossing Scales and Boundaries'.

Racial/Ethnic and Age Group Differences in Opioid and Synthetic Opioid-Involved Overdose Deaths Among Adults Aged ≥18 Years in Metropolitan Areas - United States, 2015-2017.

Among the 47,600 opioid-involved overdose deaths in the United States in 2017, 59.8% (28,466) involved synthetic opioids (1). Since 2013, synthetic opioids, particularly illicitly manufactured fentanyl (IMF), including fentanyl analogs, have been fueling the U.S. overdose epidemic (1,2). Although initially mixed with heroin, IMF is increasingly being found in supplies of cocaine, methamphetamine, and counterfeit prescription pills, which increases the number of populations at risk for an opioid-involved overdose (3,4). With the proliferation of IMF, opioid-involved overdose deaths have increased among minority populations including non-Hispanic blacks (blacks) and Hispanics, groups that have historically had low opioid-involved overdose death rates (5). In addition, metropolitan areas have experienced sharp increases in drug and opioid-involved overdose deaths since 2013 (6,7). This study analyzed changes in overdose death rates involving any opioid and synthetic opioids among persons aged ≥18 years during 2015-2017, by age and race/ethnicity across metropolitan areas. Nearly all racial/ethnic groups and age groups experienced increases in opioid-involved and synthetic opioid-involved overdose death rates, particularly blacks aged 45-54 years (from 19.3 to 41.9 per 100,000) and 55-64 years (from 21.8 to 42.7) in large central metro areas and non-Hispanic whites (whites) aged 25-34 years (from 36.9 to 58.3) in large fringe metro areas. Comprehensive and culturally tailored interventions are needed to address the rise in drug overdose deaths in all populations, including prevention strategies that address the risk factors for substance use across each racial/ethnic group, public health messaging to increase awareness about synthetic opioids in the drug supply, expansion of naloxone distribution for overdose reversal, and increased access to medication-assisted treatment.

CCR5 mediates HIV-1 Tat-induced neuroinflammation and influences morphine tolerance, dependence, and reward.

The HIV-1 regulatory protein, trans-activator of transcription (Tat), interacts with opioids to potentiate neuroinflammation and neurodegeneration within the CNS. These effects may involve the C-C chemokine receptor type 5 (CCR5); however, the behavioral contribution of CCR5 on Tat/opioid interactions is not known. Using a transgenic murine model that expresses HIV-1 Tat protein in a GFAP-regulated, doxycycline-inducible manner, we assessed morphine tolerance, dependence, and reward. To assess the influence of CCR5 on these effects, mice were pretreated with oral vehicle or the CCR5 antagonist, maraviroc, prior to morphine administration. We found that HIV-1 Tat expression significantly attenuated the antinociceptive potency of acute morphine (2-64 mg/kg, i.p.) in non-tolerant mice. Consistent with this, Tat attenuated withdrawal symptoms among morphine-tolerant mice. Pretreatment with maraviroc blocked the effects of Tat, reinstating morphine potency in non-tolerant mice and restoring withdrawal symptomology in morphine-tolerant mice. Twenty-four hours following morphine administration, HIV-1 Tat significantly potentiated (∼3.5-fold) morphine-conditioned place preference and maraviroc further potentiated these effects (∼5.7-fold). Maraviroc exerted no measurable behavioral effects on its own. Protein array analyses revealed only minor changes to cytokine profiles when morphine was administered acutely or repeatedly; however, 24 h post morphine administration, the expression of several cytokines was greatly increased, including endogenous CCR5 chemokine ligands (CCL3, CCL4, and CCL5), as well as CCL2. Tat further elevated levels of several cytokines and maraviroc pretreatment attenuated these effects. These data demonstrate that CCR5 mediates key aspects of HIV-1 Tat-induced alterations in the antinociceptive potency and rewarding properties of opioids.

Collagen-derived matricryptins promote inhibitory nerve terminal formation in the developing neocortex.

Inhibitory synapses comprise only ∼20% of the total synapses in the mammalian brain but play essential roles in controlling neuronal activity. In fact, perturbing inhibitory synapses is associated with complex brain disorders, such as schizophrenia and epilepsy. Although many types of inhibitory synapses exist, these disorders have been strongly linked to defects in inhibitory synapses formed by Parvalbumin-expressing interneurons. Here, we discovered a novel role for an unconventional collagen-collagen XIX-in the formation of Parvalbumin(+) inhibitory synapses. Loss of this collagen results not only in decreased inhibitory synapse number, but also in the acquisition of schizophrenia-related behaviors. Mechanistically, these studies reveal that a proteolytically released fragment of this collagen, termed a matricryptin, promotes the assembly of inhibitory nerve terminals through integrin receptors. Collectively, these studies not only identify roles for collagen-derived matricryptins in cortical circuit formation, but they also reveal a novel paracrine mechanism that regulates the assembly of these synapses.