Addiction neuroscience最新文献

Background

Methods

Results

Conclusions

Chronic social defeat stress (SDS) is a widely employed preclinical model of depression involving repeated exposure to physical defeats using a resident-intruder model in male mice. Exposure to SDS induces depressive-like phenotypes including anhedonia, social withdrawal, and increased drug and alcohol consumption. Previously, we found that expression of the neurokinin-1 receptor (NK1R) is increased in the nucleus accumbens (NAC) of mice that are sensitive to this stressor and increase their alcohol intake. The NK1R is the endogenous receptor for the neuropeptide substance P (SP) and plays a prominent role in stress, anxiety, and addiction. In the present study, we assessed changes in NK1R protein levels in the NAC shell and implemented viral vector strategies to demonstrate a functional role of the NK1R in sensitivity to SDS. Specifically, we found that NK1R protein levels were increased in the NAC shell following SDS exposure. Next, we found that NK1R overexpression in the NAC shell increased the sensitivity to SDS and stress-induced alcohol consumption. Together, these experiments provide evidence for a role of the NK1R in the NAC shell in the sensitivity to SDS and the subsequent escalation in alcohol intake.

Adolescence is a period of increased risk taking, including increased alcohol and drug use. Multiple clinical studies report a positive relationship between adolescent alcohol consumption and risk of developing an alcohol use disorder (AUD) in adulthood. However, few preclinical studies have attempted to tease apart the biological contributions of adolescent alcohol exposure, independent of other social, environmental, and stress factors, and studies that have been conducted show mixed results. Here we use several adolescent voluntary consumption of alcohol models, conducted across four labs in three institutes and with two rodent species, to investigate the ramifications of adolescent alcohol consumption on adulthood alcohol consumption in controlled, pre-clinical environments. We consistently demonstrate a lack of robust increases in adulthood alcohol consumption. This work highlights that risks seen in both human datasets and other murine drinking models may be due to unique social and environmental factors – some of which may be unique to humans.

The ventral pallidum (VP) has emerged as a critical node in the mesolimbic reward system. Modulating the VP can impact the subjective valuation of rewards, reward motivation, and reward seeking under conflict, making it an attractive target for clinical neuromodulation therapies that manage substance use disorders. To understand how to rationally modulate the VP, we need a better understanding of the electrophysiological properties of VP neurons and the molecular and biophysical determinants of these properties. Here, we used patch-clamp electrophysiology to characterize the intrinsic properties of glutamatergic VP (VP_Glu) neurons and observed two distinct electrophysiological profiles: VP_Glu neurons that undergo depolarization block in response to progressively increasing current injection amplitudes and those that were resistant to depolarization block. To explore the mechanisms that could contribute to these distinct profiles, we used targeted ribosome affinity purification to identify ion channel subunits and regulatory proteins by isolating actively transcribed mRNA selectively from VP_Glu neurons. We then used this transcriptomic information to implement a Markov Chain Monte Carlo method to parameterize a large population of biophysically distinct multicompartment models of VP_Glu neurons conforming to either subpopulation. Based on prior literature suggesting parvalbumin (PV) is expressed in a subset of VP_Glu neurons, and that PV expression governs the firing properties of those neurons, we tested the hypothesis that PV expression accounted for differences in subgroups, by increasing the maximal firing frequency and conferring resistance to depolarization block. In contrast, our model determined that PV expression at physiological levels had no effect on maximum firing rate. However, supraphysiological expression levels of PV appeared to induce a depolarization block in previously depolarization block-resistant neuron models, suggesting that other intracellular calcium-binding proteins could play a role in determining the firing phenotype of VP_Glu neurons. We corroborated this result with single-cell patch-clamp RT-PCR, which confirmed that PV expression did not distinguish the two electrophysiologically distinct subpopulations. Together, these findings establish that VP_Glu neurons are composed of biophysically distinct subpopulations that have not been appreciated in prior studies interrogating the function of this population. With the advent of novel tools for cell-type specific pharmacology and targeted neurostimulation, this understanding will be critical for developing strategies to rationally modulate VP_Glu cells to treat disorders characterized by maladaptive reward seeking.

Opioid use disorder involves disruptions to glutamate homeostasis and dendritic spine density in the reward system. PKMζ is an atypical isoform of protein kinase C that is expressed exclusively in neurons and plays a role in postsynaptic glutamate signaling and dendritic spine maturation. As opioid use leads to alterations in glutamate transmission and dendritic spine density, we hypothesized that PKMζ deletion would alter opioid-taking behaviors. The current study examined two doses of oxycodone self-administration in male and female mice with constitutive deletion of PKMζ compared to wildtype controls. At a dose of 0.25 mg/kg/infusion, PKMζ deletion significantly potentiated oxycodone self-administration in both male and female mice. However, increases in motivation for oxycodone, as indicated by increased breakpoint on a progressive ratio schedule, were only seen in male PKMζ knockout mice and not females. When we examined a lower dose of oxycodone, 0.125 mg/kg/infusion, PKMζ knockout led to increases in oxycodone self-administration only in female mice. Additionally, female PKMζ knockout mice exhibited higher breakpoints on a progressive ratio schedule at this dose compared to all other groups. In addition to the self-administration studies, we also examined locomotor sensitization in response to experimenter administered oxycodone. PKMζ KO decreased oxycodone induced locomotion in males and potentiated oxycodone sensitization in females. Together, these results suggest that PKMζ acts to dampen oxycodone taking in both sexes, but females may be more sensitive to its effects.

Following opioid cessation, patients with opioid use disorder experience physical and psychological withdrawal symptoms. Prolonged negative affect, including anxiety and heightened stress reactivity, continues after physical withdrawal symptoms subside, contributing to the high relapse rates. The nitric oxide system plays a role in synaptic plasticity downstream of the mu opioid receptor pathway, and nitric oxide synthase inhibitors attenuate physical opioid withdrawal signs. We hypothesized that N(gamma)-nitro-l-arginine methyl ester (L-NAME), a nitric oxide synthase inhibitor, would reduce negative affect after protracted opioid withdrawal. Therefore, we first modeled withdrawal in male and female mice using 5 days of morphine injections followed by behavioral tests after one week of forced abstinence from morphine. One week of morphine withdrawal caused altered responses to tests of affective behavior in both male and female mice. There were, however, both subtle and significant sex differences among many of the behavioral measures of negative affect. Males and females had differences in immobility during the tail suspension test during morphine withdrawal, while only females had altered grooming in the sucrose splash test. Forced l-NAME in the animals’ drinking water during withdrawal attenuated all physical and affective measures of withdrawal in males and females but there were subtle differences. Together, these results suggest that the nitric oxide system may be a target to ameliorate the different behavioral manifestations of negative affect in males and females.

The Special Issue on Stress and Addiction is concerned with interrelationships between environmental stimuli such as stress and endogenous opioid systems that lead to addiction and other behaviors. Stress can have a profound effect on pain that is mediated in part through endogenous opioids. Here we briefly summarize investigation pertaining to the involvement of endogenous opioids in stress-induced analgesia, and their mediation by hypothalamo-pituitary-adrenal systems. Subsequent studies of the contribution of opioid receptor subtypes mediating supraspinal pain-inhibitory systems are examined using selective agonists and antagonists largely developed by Dr. Philip Portoghese. Because of the ongoing opioid epidemic yet the need to discover effective analgesics, we conclude with a discussion of several approaches to manage pain effectively without such serious side effects as tolerance and addiction, associated with traditional opioid use. These include opioid analgesic synergy, biased opioid agonism, and targeting of opioid receptor heteromers with bivalent ligands.

Individuals who initiate drug use before 14 years of age are at increased risk of developing a lifelong addiction. Risk behaviors associated with drug use in adult animals include novel reactivity, novelty preferences, and sucrose preferences. Whether those same behaviors predict drug use in young populations is not well-studied. We determined how these risk behaviors i) change across development in Sprague-Dawley male and female rats and ii) predict adolescent cocaine self-administration when risk is assessed in juveniles. A longitudinal design characterized the behavioral trajectory of rats at the ages of 21 (juvenile), 56 (adolescent), and 96 (adult) days of age. Novel reactivity and sucrose preferences increased with maturation, with females having higher reactivity levels than males. Sucrose preferences predicted increased cocaine intake in both sexes, an effect primarily driven by males. Novelty preferences, especially in males, predicted less cocaine intake. Segregation of the data into high and low tertiles (risk and resilience) revealed that high sucrose preference predicted cocaine infusions. Low levels of novel reactivity in females significantly correlated with presses on the active lever for cocaine. The number of days to acquire stable intake was the only metric to classify a group with more overall cocaine consumption. Juvenile rats are either too immature to demonstrate predictive behavior related to novelty or, alternatively, a more extreme phenotype may be necessary to identify addiction risk.