NMDA receptor blockade in the prelimbic cortex activates the mesolimbic system and dopamine-dependent opiate reward signaling

Dissociable Roles of the mPFC-to-VTA Pathway in the Control of Impulsive Action and Risk-Related Decision-Making in Roman High- and Low-Avoidance Rats

BACKGROUND

Impulsive action and risk-related decision-making (RDM) are associated with various psychiatric disorders, including drug abuse. Both behavioral traits have also been linked to reduced frontocortical activity and alterations in dopamine function in the ventral tegmental area (VTA). However, despite direct projections from the medial prefrontal cortex (mPFC) to the VTA, the specific role of the mPFC-to-VTA pathway in controlling impulsive action and RDM remains unexplored.

METHODS

We used positron emission tomography with [18F]-fluorodeoxyglucose to evaluate brain metabolic activity in Roman high- (RHA) and low-avoidance (RLA) rats, which exhibit innate differences in impulsive action and RDM. Notably, we used a viral-based double dissociation chemogenetic strategy to isolate, for the first time to our knowledge, the role of the mPFC-to-VTA pathway in controlling these behaviors. We selectively activated the mPFC-to-VTA pathway in RHA rats and inhibited it in RLA rats, assessing the effects on impulsive action and RDM in the rat gambling task.

RESULTS

Our results showed that RHA rats displayed higher impulsive action, less optimal decision-making, and lower cortical activity than RLA rats at baseline. Chemogenetic activation of the mPFC-to-VTA pathway reduced impulsive action in RHA rats, whereas chemogenetic inhibition had the opposite effect in RLA rats. However, these manipulations did not affect RDM. Thus, by specifically targeting the mPFC-to-VTA pathway in a phenotype-dependent way, we reverted innate patterns of impulsive action but not RDM.

CONCLUSION

Our findings suggest a dissociable role of the mPFC-to-VTA pathway in impulsive action and RDM, highlighting its potential as a target for investigating impulsivity-related disorders.

Ketamine and hydroxynorketamine as novel pharmacotherapies for the treatment of Opioid-Use Disorders

Opioid use disorder (OUD) has reached epidemic proportions, with many countries facing high opioid use and related fatalities. Although currently-prescribed medications for OUD (MOUD) are considered life-saving, they inadequately address negative affect and cognitive impairment, resulting in high relapse rates to non-medical opioid use, even years after drug cessation (protracted abstinence). Evidence supports the notion that ketamine, an anesthetic and rapid-acting antidepressant drug, holds promise as a candidate for OUD treatment, including the management of acute withdrawal somatic symptoms, negative affect during protracted opioid abstinence and prevention of re-taking non-medical opioids. In this review, we comprehensively discuss preclinical and clinical research evaluating ketamine and its metabolites as potential novel therapeutic strategies for treating OUDs. We further examine evidence supporting the relevance of the molecular targets of ketamine and its metabolites in relation to their potential effects and therapeutic outcomes in OUDs. Overall, existing evidence demonstrates that ketamine and its metabolites can effectively modulate pathophysiological processes affected in OUD, suggesting their promising therapeutic role in the treatment of OUD and the prevention of return to opioid use during abstinence.

Integrative Pharmacology in the Treatment of Substance Use Disorders

The detrimental physical, mental, and socioeconomic effects of substance use disorders (SUDs) have been apparent to the medical community for decades. However, it has become increasingly urgent in recent years to develop novel pharmacotherapies to treat SUDs. Currently, practitioners typically rely on monotherapy. Monotherapy has been shown to be superior to no treatment at all for most substance classes. However, many randomized controlled trials (RCTs) have revealed that monotherapy leads to poorer outcomes when compared with combination treatment in all specialties of medicine. The results of RCTs suggest that monotherapy frequently fails since multiple dysregulated pathways, enzymes, neurotransmitters, and receptors are involved in the pathophysiology of SUDs. As such, research is urgently needed to determine how various neurobiological mechanisms can be targeted by novel combination treatments to create increasingly specific yet exceedingly comprehensive approaches to SUD treatment. This article aims to review the neurobiology that integrates many pathophysiologic mechanisms and discuss integrative pharmacology developments that may ultimately improve clinical outcomes for patients with SUDs. Many neurobiological mechanisms are known to be involved in SUDs including dopaminergic, nicotinic, N-methyl-D-aspartate (NMDA), and kynurenic acid (KYNA) mechanisms. Emerging evidence indicates that KYNA, a tryptophan metabolite, modulates all these major pathophysiologic mechanisms. Therefore, achieving KYNA homeostasis by harmonizing integrative pathophysiology and pharmacology could prove to be a better therapeutic approach for SUDs. We propose KYNA-NMDA-α7nAChRcentric pathophysiology, the "conductor of the orchestra," as a novel approach to treat many SUDs concurrently. KYNA-NMDA-α7nAChR pathophysiology may be the "command center" of neuropsychiatry. To date, extant RCTs have shown equivocal findings across comparison conditions, possibly because investigators targeted single pathophysiologic mechanisms, hit wrong targets in underlying pathophysiologic mechanisms, and tested inadequate monotherapy treatment. We provide examples of potential combination treatments that simultaneously target multiple pathophysiologic mechanisms in addition to KYNA. Kynurenine pathway metabolism demonstrates the greatest potential as a target for neuropsychiatric diseases. The investigational medications with the most evidence include memantine, galantamine, and N-acetylcysteine. Future RCTs are warranted with novel combination treatments for SUDs. Multicenter RCTs with integrative pharmacology offer a promising, potentially fruitful avenue to develop novel therapeutics for the treatment of SUDs.

Decoupling Dopamine Synthesis from Impulsive Action, Risk-Related Decision-Making, and Propensity to Cocaine Intake: A Longitudinal [18F]-FDOPA PET Study in Roman High- and Low-Avoidance Rats

Impulsive action and risk-related decision-making (RDM) are two facets of impulsivity linked to a hyperdopaminergic release in the striatum and an increased propensity to cocaine intake. We previously showed that with repeated cocaine exposure, this initial hyperdopaminergic release is blunted in impulsive animals, potentially signaling drug-induced tolerance. Whether such dopaminergic dynamics involve changes in dopamine (DA) synthesis as a function of impulsivity is currently unknown. Here, we investigated the predictive value of DA synthesis for impulsive action, RDM, and the propensity to take cocaine in a rat model of vulnerability to cocaine abuse. Additionally, we assessed the effects of cocaine intake on these variables. Rats were tested sequentially in the rat Gambling Task (rGT) and were scanned with positron emission tomography and [18F]-FDOPA to respectively assess both impulsivity facets and striatal DA synthesis before and after cocaine self-administration (SA). Our results revealed that baseline striatal levels of DA synthesis did not significantly predict impulsive action, RDM, or a greater propensity to cocaine SA in impulsive animals. Besides, we showed that impulsive action, but not RDM, predicted higher rates of cocaine taking. However, chronic cocaine exposure had no impact on DA synthesis, nor affected impulsive action and RDM. These findings indicate that the hyper-responsive DA system associated with impulsivity and a propensity for cocaine consumption, along with the reduction in this hyper-responsive DA state in impulsive animals with a history of cocaine use, might not be mediated by dynamic changes in DA synthesis.

Neuronal activity of the medial prefrontal cortex, nucleus accumbens, and basolateral amygdala in conditioned taste aversion and conditioned place preference induced by different doses of morphine administrations in rats

To re-examine the paradoxical effect hypothesis of abused drugs, the present study concerned whether different doses of morphine disparately affect neuronal activity and associations among the subareas of the medial prefrontal cortex (mPFC: cingulate cortex 1-Cg1, prelimbic cortex-PrL, infralimbic cortex-IL), the subregions of the nucleus accumbens (NAc; both core and shell), and the basolateral amygdala (BLA) following conditioned taste aversion (CTA) and conditioned place preference (CPP). All rats were given a 0.1% saccharin solution for 15-min, and they were intraperitoneally injected with saline or 20, 30, or 40 mg/kg morphine to form the aversive CTA learning. Later, half of the rats were tested for CPP (including the CTA and then CPP tests) for 30-min. Finally, the immunohistochemical staining with c-Fos was conducted after the behavioral test. After the CTA test, c-Fos (%) in the Cg1 and PrL (but not the IL) was more in 20-40 mg/kg of the morphine groups; c-Fos (%) in the NAc core, NAc shell, and BLA was more in the 30-40 mg/kg morphine group. After the CPP test, the Cg1, PrL, IL, and BLA showed more c-Fos (%) in 20 mg/kg morphine; the NAc core showed fewer in c-Fos (%) in the 30-40 mg/kg morphine groups. The mPFC subregions (e.g., Cg1, PrL, and IL), NAc subareas (e.g., NAc core and NAc shell), and BLA were involved in the different doses of morphine injections. The correlation analysis showed that a positive correlation was observed between PrL and IL with NAc core with low doses of morphine and with NAc shell with increasing doses of morphine after the CTA test. After the CPP, an association between PrL and NAc core and NAc shell at low doses and between IL and BLA and NAc shell with increasing doses of morphine. Therefore, different neural substrates and the neural connectivity are observed following different doses of morphine and after the CTA and CPP tests. The present data extend the paradoxical effect hypothesis of abused drugs.

Similar role of mPFC orexin-1 receptors in the acquisition and expression of morphine- and food-induced conditioned place preference in male rats

Self-control problems are a typical character of drug addiction and excessive food consumption and it has been shown that natural rewards and drugs of abuse share parts of the same neural substrate and reward processing in the brain. Different brain areas are involved in natural and drug reward processing including the mesolimbic pathway, amygdala, nucleus accumbens (NAc), and prefrontal cortex. Considering the important role of orexins in the addictive behavior and the presence of orexin-1 subtype receptors (Orx1R) in the medial prefrontal cortex (mPFC), this study investigated the role of mPFC in natural- and drug-reward seeking behaviors to deepen our understanding of possible similarities or differences. To induce food- or morphine-conditioned place preference (CPP), adult male Wistar rats underwent CPP testing and received intra-mPFC doses of SB334867 (3, 10, or 30 nM/0.5 μl DMSO 12%), as an Orx1R antagonist, during the acquisition or expression phases of the CPP test. Results indicated that microinjection of Orx1R antagonist into the mPFC had similar effects on both morphine- and food-induced CPP and attenuated CPP scores in the acquisition and expression phases of the CPP test. The data demonstrated that Orx1Rs in the mPFC regulate the reward-related effects of morphine- and food-induced reward.

Glutamatergic Systems and Memory Mechanisms Underlying Opioid Addiction

Glutamate is the main excitatory neurotransmitter in the brain and is of critical importance for the synaptic and circuit mechanisms that underlie opioid addiction. Opioid memories formed over the course of repeated drug use and withdrawal can become powerful stimuli that trigger craving and relapse, and glutamatergic neurotransmission is essential for the formation and maintenance of these memories. In this review, we discuss the mechanisms by which glutamate, dopamine, and opioid signaling interact to mediate the primary rewarding effects of opioids, and cover the glutamatergic systems and circuits that mediate the expression, extinction, and reinstatement of opioid seeking over the course of opioid addiction.

A Conantokin Peptide Con-T[M8Q] Inhibits Morphine Dependence with High Potency and Low Side Effects

N-methyl-D-aspartate receptor (NMDAR) antagonists have been found to be effective to inhibit morphine dependence. However, the discovery of the selective antagonist for NMDAR GluN2B with low side-effects still remains challenging. In the present study, we report a selective NMDAR GluN2B antagonist con-T[M8Q](a conantokin-T variant) that potently inhibits the naloxone-induced jumping and conditioned place preference of morphine-dependent mice at nmol/kg level, 100-fold higher than ifenprodil, a classical NMDAR NR2B antagonist. Con-T[M8Q] displays no significant impacts on coordinated locomotion function, spontaneous locomotor activity, and spatial memory mice motor function at the dose used. Further molecular mechanism experiments demonstrate that con-T[M8Q] effectively inhibited the transcription and expression levels of signaling molecules related to NMDAR NR2B subunit in hippocampus, including NR2B, p-NR2B, CaMKII-α, CaMKII-β, CaMKIV, pERK, and c-fos. The high efficacy and low side effects of con-T[M8Q] make it a good lead compound for the treatment of opiate dependence and for the reduction of morphine usage.

Clinical benefits and risks of N-methyl-d-aspartate receptor antagonists to treat severe opioid use disorder: A systematic review

BACKGROUND

Demand for treatments for severe opioid use disorder is increasing worldwide. The current pharmacotherapy is mainly focused on opioid and adrenergic receptors. The N-methyl-d-aspartate receptor (NMDAR) is among other receptors that can also be targeted to treat the disease. Findings from randomized controlled trials (RTCs) on NMDAR antagonists to treat severe opioid use disorder amply varied. This study aimed to evaluate the clinical benefits and assess the potential risks for adverse events or side effects of NMDAR antagonists that were investigated for the treatment of severe opioid use disorder.

METHODS

Articles were searched in PubMed, Scopus, Google Scholar, Proquest. Cochrane Review Database, Medline Ovid, and EMBASE from their inception to March 2019. RTCs on NMDAR antagonists for the treatment of severe opioid use disorder were independently screened and assessed by two authors. The results were synthesized qualitatively.

RESULTS

Nineteen RTCs of 1459 participants met the inclusion criteria. There is moderate evidence suggesting that ketamine, memantine, amantadine, and dextromethorphan may be able to manage opioid withdrawal symptoms. There is little evidence suggesting that memantine may be able to reduce methadone maintenance dose in participants on methadone, reduce opioid use, and reduce craving. Dropout is noticeable among dextromethorphan's participants. Safety concerns are more likely associated with dextromethorphan and ketamine.

CONCLUSIONS

NMDAR antagonists have the potentiality to treat severe opioid use disorder. There is insufficient evidence to recommend them for the treatment of severe opioid use disorder due to several limitations inherent to the RCTs reviewed. Further exploration is needed.

Conduct Disorder Symptoms and Illicit Drug Use in Juvenile Justice Involved Youth: The Reciprocal Relationship Between Positive Illicit Drug-Use Attitudes and Illicit Drug Use

Conduct disorder (CD) symptoms cooccur at high rates with illicit drug use in juvenile justice involved youth, which results in poorer outcomes; however, research has not identified where best to intervene in this relationship, limiting the identification of modifiable risk factors to reduce negative effects of CD symptoms. Two mediation models were examined to investigate the potential for CD symptoms to influence a reciprocal relationship between illicit drug use and positive drug attitudes, controlling for age, gender, and race. Data were examined for 245 juvenile justice involved youth (mean age = 15.46, SD = 1.30, range 12-18, 64.9% Black, 80.4% male) who completed court-ordered psychological assessments. Findings indicate: (1) Positive attitudes toward illicit drug use significantly mediated the relationship between CD symptoms and illicit drug use (β = 0.16, CI 0.09-0.27; test for indirect effect z = 4.17, p < .001) and (2) illicit drug use significantly mediated the relationship between CD symptoms and positive attitudes toward illicit drug use (β = 0.20, CI 0.12-0.32; test for indirect effect z = 4.87, p < .001). Overall, the present study suggests that CD symptoms impart risk for illicit drug use both indirectly, through more positive attitudes toward illicit drug use, and directly, which further strengthens positive attitudes toward illicit drug use.

Blockade of prelimbic glutamate receptor reduces the reinforcing effect of morphine

The prelimbic cortex (PrL) as a part of the medial prefrontal cortex (mPFC) plays a crucial role in drug addiction. Previous studies have shown that glutamatergic transmission through the NMDA and AMPA receptors plays an important role in morphine rewarding properties. In this study, we evaluated the effect of glutamate receptors blockade within the PrL on morphine self-administration. Male Wistar rats were randomly selected and divided into 7 groups. Trained rats were placed in self-administration apparatus, where they pressed an active lever for receiving morphine (5 mg/mL) in test groups and saline in saline group during 11 consecutive days for 2 h per session. The effects of intra-prelimbic AMPA receptor antagonist (CNQX; 0.5 and 2.5 μg/0.5 μL) and the NMDA antagonist (AP5; 0.1 and 1 μg/0.5 μL) on self-administration were tested. Our results demonstrated that intra-prelimbic injection of different doses of CNQX and AP5, and co-administration of these 2 drugs before self-administration significantly decreased active lever pressing compared with morphine group (p < 0.001). Also, the number of self-infusion significantly decreased in test groups compared with morphine group (p < 0.001). These findings suggest that a reduction in PrL glutamatergic output can modulate morphine reinforcement.

NMDA receptors in the dorsal hippocampal area are involved in tramadol state-dependent memory of passive avoidance learning in mice

The precise neurobiological mechanisms of tramadol abuse underlying the cognitive function are still unknown. The aim of the present study was to examine the possible effects of intra-CA1 injections of N-methyl-d-aspartate (NMDA), a glutamate NMDA receptor (NMDAR) agonist, and d,l-2-amino-5-phosphonopentanoic acid (DL-AP5), a competitive NMDAR antagonist, on tramadol state-dependent memory. A single-trial step-down passive avoidance task was used for the assessment of memory retrieval in adult male NMRI mice. Post-training i.p. administration of an atypical μ-opioid receptor agonist, tramadol (2.5 and 5 mg/kg), dose-dependently induced impairment of memory retention. Pre-test injection of tramadol (2.5 and 5 mg/kg) induced state-dependent retrieval of the memory acquired under post-training administration of tramadol (5 mg/kg) influence. Pre-test intra-CA1 injection of NMDA (10−5 and 10−4 μg/mouse) 5 min before the administration of tramadol (5 mg/kg, i.p.) dose-dependently inhibited tramadol state-dependent memory. Pre-test intra-CA1 injection of DL-AP5 (0.25 and 0.5 μg/mouse) reversed the memory impairment induced by post-training administration of tramadol (5 mg/kg). Pre-test administration of DL-AP5 (0.25 and 0.5 μg/mouse) with an ineffective dose of tramadol (1.25 mg/kg) restored the retrieval and induced tramadol state-dependent memory. It can be concluded that dorsal hippocampal NMDAR mechanisms play an important role in the modulation of tramadol state-dependent memory.

The Role of Dopamine D1 and D3 Receptors in N-Methyl-D-Aspartate (NMDA)/GlycineB Site-Regulated Complex Cognitive Behaviors following Repeated Morphine Administration

BACKGROUND

Opiate addiction is associated with complex cognitive impairment, which contributes to the development of compulsive drug use and relapses. Dopamine and N-methyl-D-aspartate receptors play critical roles in opiate-induced cognitive deficits. However, the roles of D1 and D3 receptors in the N-methyl-D-aspartate/glycineB receptor-regulated cognitive behaviors induced by morphine remain unknown.

METHODS

The 5-choice serial reaction time task was used to investigate the cognitive profiles associated with repeated morphine administration in D1 (D1-/-)- and D3 (D3-/-)-receptor knockout mice. The expression of phosphorylated NR1, Ca2+/calmodulin-dependent protein kinase II (CaMKII), and cAMP response element-binding protein (CREB) in the brain was examined by western blotting. D1-/- and D3-/- mice were treated with the N-methyl-D-aspartate/glycineB site agonist l-aminocyclopropanecarboxylic acid and the antagonist L-701,324 to chronically disrupt N-methyl-D-aspartate receptor function and investigate their effects on morphine-induced cognitive changes.

RESULTS

Repeated morphine administration impaired attentional function and caused impulsive and compulsive behaviors. D1-/- mice exhibited hardly any premature nosepokes. D3-/- mice showed robustly increased morphine-induced impulsive behavior. The numbers of premature responses were decreased by L-701,324 administration and increased by ACPC administration; these effects were completely abolished in D1-/- mice due to their inability to perform reward-based tasks. In contrast, the inhibitory effects of L-701,324 on impulsive behavior were significantly augmented in D3-/- mice.

CONCLUSIONS

N-methyl-D-aspartate/glycineB site functions may contribute to morphine-induced cognitive deficits, especially those related to impulsive behavior. D1 and D3 receptors may have contrasting effects with respect to modulating impulsive behavior. D3 receptors have inhibitory effects on impulsive behaviors, and these effects are clearly mediated by N-methyl-D-aspartate/glycineB receptor and μ-opioid receptor interactions.

Do specific NMDA receptor subunits act as gateways for addictive behaviors?

Addiction to alcohol and drugs is a major social and economic problem, and there is considerable interest in understanding the molecular mechanisms that promote addictive drives. A number of proteins have been identified that contribute to expression of addictive behaviors. NMDA receptors (NMDARs), a subclass of ionotropic glutamate receptors, have been of particular interest because their physiological properties make them an attractive candidate for gating induction of synaptic plasticity, a molecular change thought to mediate learning and memory. NMDARs are generally inactive at the hyperpolarized resting potentials of many neurons. However, given sufficient depolarization, NMDARs are activated and exhibit long-lasting currents with significant calcium permeability. Also, in addition to stimulating neurons by direct depolarization, NMDARs and their calcium signaling can allow strong and/or synchronized inputs to produce long-term changes in other molecules (such as AMPA-type glutamate receptors) which can last from days to years, binding internal and external stimuli in a long-term memory trace. Such memories could allow salient drug-related stimuli to exert strong control over future behaviors and thus promote addictive drives. Finally, NMDARs may themselves undergo plasticity, which can alter subsequent neuronal stimulation and/or the ability to induce plasticity. This review will address recent and past findings suggesting that NMDAR activity promotes drug- and alcohol-related behaviors, with a particular focus on GluN2B subunits as possible central regulators of many addictive behaviors, as well as newer studies examining the importance of non-canonical NMDAR subunits and endogenous NMDAR cofactors.

Inhibition of Reinforcing, Hyperalgesic, and Motor Effects of Morphine by Buspirone in Rats

Morphine and other opioids are among the most effective prescription medications for the treatment of pain. Addiction and hyperalgesia associated with their long-term use limits the clinical utility of these drugs. In view of a role of somatodendritic serotonin-1A receptors in addiction and analgesic effects of morphine, the present study concerns effects of co-use of buspirone, a partial agonist at the serotonin-1A receptor, on reinforcing, hyperalgesic, and motor effects of morphine in rats. A dose of morphine (7.5 mg/kg) producing moderate effects on motor activity and analgesia, and buspirone (doses of 0, 1.0, and 2.0 mg/kg) were injected intraperitoneally. Reinforcing effects were monitored in a conditioned place preference (CPP) paradigm and associated changes in motor activity were monitored during a drug conditioning phase. The hot plate test was used to monitor nociceptive response. Acute administration of morphine decreased motor activity and reduced pain perception. Repeated administration was reinforcing in the CPP paradigm and was associated with hyperalgesia and tolerance in motor depressant effects of morphine. These effects of repeated morphine administration were blocked in rats cotreated with buspirone. Pain perception was also slightly reduced in rats repeatedly treated with higher doses of buspirone. The findings are important for improving and extending therapeutic medications for pain.

PERSPECTIVE

The present study shows an important role of serotonin-1A receptors in morphine-induced hyperalgesia and addiction. It shows that buspirone, a prescription medicine for anxiety and depression can block addictive and hyperalgesic effects of morphine. Clinicians should consider buspirone as adjunctive therapy with morphine to improve therapeutic medications in pain.

Brain Reward Circuits in Morphine Addiction

Morphine is the most potent analgesic for chronic pain, but its clinical use has been limited by the opiate's innate tendency to produce tolerance, severe withdrawal symptoms and rewarding properties with a high risk of relapse. To understand the addictive properties of morphine, past studies have focused on relevant molecular and cellular changes in the brain, highlighting the functional roles of reward-related brain regions. Given the accumulated findings, a recent, emerging trend in morphine research is that of examining the dynamics of neuronal interactions in brain reward circuits under the influence of morphine action. In this review, we highlight recent findings on the roles of several reward circuits involved in morphine addiction based on pharmacological, molecular and physiological evidences.

GABA-Mediated Inactivation of Medial Prefrontal and Agranular Insular Cortex in the Rat: Contrasting Effects on Hunger- and Palatability-Driven Feeding

A microanalysis of hunger-driven and palatability-driven feeding was carried out after muscimol-mediated inactivation of two frontal regions in rats, the agranular/dysgranular insular cortex (AIC) and the ventromedial prefrontal cortex (vmPFC). Food and water intake, feeding microstructure, and general motor activity were measured under two motivational conditions: food-deprived rats given standard chow or ad libitum-fed rats given a palatable chocolate shake. Muscimol infusions into the AIC diminished intake, total feeding duration, and average feeding bout duration for the palatable-food condition only but failed to alter exploratory-like behavior (ambulation or rearing). In contrast, intra-vmPFC muscimol infusions did not alter the overall intake of chow or chocolate shake. However, these infusions markedly increased mean feeding bout duration for both food types and produced a modest but significant reduction of exploratory-like behavior. The lengthening of feeding-bout duration and reduction in rearing were mimicked by intra-vmPFC blockade of AMPA-type but not NMDA-type glutamate receptors. Neither water consumption nor the microstructure of water drinking was affected by inactivation of either site. These results indicate a regional heterogeneity in frontal control of feeding behavior. Neural processing in AIC supports palatability-driven feeding but is not necessary for intake of a standard food under a food-restriction condition, whereas ventromedial prefrontal cortex, and AMPA signaling therein, modulates the duration of individual feeding bouts regardless of motivational context. Results are discussed in the context of regionally heterogeneous frontal modulation of two distinct components of feeding behavior: reward valuation based upon taste perception (AIC) vs switching between ingestive and non-ingestive (eg, exploratory-like) behavioral repertoires (vmPFC).

Endogenous opiates and behavior: 2014

This paper is the thirty-seventh consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2014 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (endogenous opioids and receptors), and the roles of these opioid peptides and receptors in pain and analgesia (pain and analgesia); stress and social status (human studies); tolerance and dependence (opioid mediation of other analgesic responses); learning and memory (stress and social status); eating and drinking (stress-induced analgesia); alcohol and drugs of abuse (emotional responses in opioid-mediated behaviors); sexual activity and hormones, pregnancy, development and endocrinology (opioid involvement in stress response regulation); mental illness and mood (tolerance and dependence); seizures and neurologic disorders (learning and memory); electrical-related activity and neurophysiology (opiates and conditioned place preferences (CPP)); general activity and locomotion (eating and drinking); gastrointestinal, renal and hepatic functions (alcohol and drugs of abuse); cardiovascular responses (opiates and ethanol); respiration and thermoregulation (opiates and THC); and immunological responses (opiates and stimulants). This paper is the thirty-seventh consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2014 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (endogenous opioids and receptors), and the roles of these opioid peptides and receptors in pain and analgesia (pain and analgesia); stress and social status (human studies); tolerance and dependence (opioid mediation of other analgesic responses); learning and memory (stress and social status); eating and drinking (stress-induced analgesia); alcohol and drugs of abuse (emotional responses in opioid-mediated behaviors); sexual activity and hormones, pregnancy, development and endocrinology (opioid involvement in stress response regulation); mental illness and mood (tolerance and dependence); seizures and neurologic disorders (learning and memory); electrical-related activity and neurophysiology (opiates and conditioned place preferences (CPP)); general activity and locomotion (eating and drinking); gastrointestinal, renal and hepatic functions (alcohol and drugs of abuse); cardiovascular responses (opiates and ethanol); respiration and thermoregulation (opiates and THC); and immunological responses (opiates and stimulants).