Nucleus Accumbens Core Research Articles

Incubation of cocaine craving coincides with changes in dopamine terminal neurotransmission

Relapse to drug use is one of the major challenges in treating substance use disorders. Exposure to drug-related cues and contexts triggers drug craving, which drives cocaine seeking, and increases the probability of relapse. Clinical and animal studies have shown a progressive intensification of cocaine seeking and craving that develops over the course of abstinence, a phenomenon commonly referred to as incubation of cocaine craving. Although the neurobiology underlying incubation of cocaine craving has been examined – particularly within the context of glutamate plasticity– the extent to which increased cocaine craving engenders mesolimbic dopamine (DA) changes has received relatively little attention. To assess whether incubation of cocaine craving is associated with alterations in DA terminal neurotransmission in the nucleus accumbens core (NAc), we used ex vivo fast scan cyclic voltammetry in female and male rats to assess DA dynamics following short access, long access, or intermittent access to cocaine self-administration followed by 28 days of abstinence. Results indicated that both long access and intermittent access to cocaine produced robust incubation of cocaine craving, which was associated with increases in cocaine potency. In addition, intermittent access self-administration also produced a robust increase in DA uptake rate at baseline. In contrast, short access to cocaine did not engender incubation of cocaine craving, nor produce changes in DA neurotransmission. Together these observations indicate that incubation of cocaine craving coincides with changes in DA transmission, suggesting that underlying changes in mesolimbic DA signaling may contribute to the progressive intensification of drug craving that occurs across periods of abstinence.

A Novel and Selective Dopamine Transporter Inhibitor, (S)-MK-26, Promotes Hippocampal Synaptic Plasticity and Restores Effort-Related Motivational Dysfunctions.

Dopamine (DA), the most abundant human brain catecholaminergic neurotransmitter, modulates key behavioral and neurological processes in young and senescent brains, including motricity, sleep, attention, emotion, learning and memory, and social and reward-seeking behaviors. The DA transporter (DAT) regulates transsynaptic DA levels, influencing all these processes. Compounds targeting DAT (e.g., cocaine and amphetamines) were historically used to shape mood and cognition, but these substances typically lead to severe negative side effects (tolerance, abuse, addiction, and dependence). DA/DAT signaling dysfunctions are associated with neuropsychiatric and progressive brain disorders, including Parkinson’s and Alzheimer diseases, drug addiction and dementia, resulting in devastating personal and familial concerns and high socioeconomic costs worldwide. The development of low-side-effect, new/selective medicaments with reduced abuse-liability and which ameliorate DA/DAT-related dysfunctions is therefore crucial in the fields of medicine and healthcare. Using the rat as experimental animal model, the present work describes the synthesis and pharmacological profile of (S)-MK-26, a new modafinil analogue with markedly improved potency and selectivity for DAT over parent drug. Ex vivo electrophysiology revealed significantly augmented hippocampal long-term synaptic potentiation upon acute, intraperitoneally delivered (S)-MK-26 treatment, whereas in vivo experiments in the hole-board test showed only lesser effects on reference memory performance in aged rats. However, in effort-related FR5/chow and PROG/chow feeding choice experiments, (S)-MK-26 treatment reversed the depression-like behavior induced by the dopamine-depleting drug tetrabenazine (TBZ) and increased the selection of high-effort alternatives. Moreover, in in vivo microdialysis experiments, (S)-MK-26 significantly increased extracellular DA levels in the prefrontal cortex and in nucleus accumbens core and shell. These studies highlight (S)-MK-26 as a potent enhancer of transsynaptic DA and promoter of synaptic plasticity, with predominant beneficial effects on effort-related behaviors, thus proposing therapeutic potentials for (S)-MK-26 in the treatment of low-effort exertion and motivational dysfunctions characteristic of depression and aging-related disorders.

Reward versus motoric activations in nucleus accumbens core of rats during Pavlovian conditioning.

The nucleus accumbens (NAc) core plays an important role in processing of events related to food reward, such as conditioned cues, approach or consumption. Nonetheless, there is lack of clarity regarding whether NAc core processes these separable events differently. We used the high temporal and spatial resolution of single unit recording with trial-by-trial video analysis to examine firing during three distinct categories termed cue, approach and consumption in a Pavlovian task. We had three goals. First, we sought to precisely define task-related behaviour in terms of distinct phases, in order to compare neural activity between motorically matched behaviours. We found that cue-evoked firing did not distinguish between trials on which animals initiated an approach versus ones on which they did not. Firing associated with consumption was greater than firing associated with motorically similar uncued head entry, indicating that previously reported decreases in NAc core firing during consumption relative to approach or baseline may reflect differences in motor behaviour. Secondly, we assessed changes in firing over the course of training. We found that NAc core neurons acquired a response to the tone cue within three sessions but did not change further across 10 total sessions. Thirdly, we correlated individual neuron firing during a given event with its firing during the same event on subsequent sessions. We found substantial variation in processing of cue and approach but not consumption, indicating that a given neuron may process certain events differently from session to session, while maintaining more stable processing of appetitive reward.

The effects of ninjin'yoeito on the electrophysiological properties of dopamine neurons in the ventral tegmental area/substantia nigra pars compacta and medium spiny neurons in the nucleus accumbens.

The ventral tegmental area (VTA), substantia nigra pars compacta (SNpc) and nucleus accumbens (NAc) are involved in the regulation of appetite and motivational behaviors. A traditional Japanese (Kampo) medicine, ninjin’yoeito (NYT), has been reported to improve decreased motivation and anorexia in patients with Alzheimer’s disease and apathy-like model mice. Thus, NYT may affect the activities of neurons in the VTA, SNpc and NAc. However, little is known about the underlying mechanisms of NYT. Here, we investigated the effects of NYT on the electrophysiological properties of dopaminergic neurons in the VTA and SNpc, as well as on those of medium spiny neurons (MSNs) in the NAc (core and shell subregions), by applying the patch-clamp technique in the brain slices. NYT reduced the resting membrane potential of VTA and SNpc dopaminergic neurons. In contrast, NYT increased the firing frequency of NAc MSNs accompanied by shortened first spike latency and interspike interval. Furthermore, NYT attenuated the inward rectification and sustained outward currents. In conclusion, NYT may directly influence the excitability of dopaminergic neurons in the VTA and SNpc, as well as MSNs in the NAc (core and shell). NYT may modulate dopamine signals in appetite and motivational behaviors.

Altered prefrontal-striatal theta-band oscillatory dynamics underlie working memory deficits in neuropathic pain rats.

Prelimbic medial prefrontal cortex (PL-mPFC) and nucleus accumbens core region (NAcc) play an important role in supporting several executive cognitive mechanisms, such as spatial working memory (WM). Recently, this circuit has been also associated with both sensory and affective components of pain. However, it is still unclear whether this circuit is endogenously engaged in neuropathic pain-related cognitive dysfunctions. To answer this question, we induced the expression of halorhodopsin in local PL-mPFC neurons projecting to NAcc, and then selectively inhibited the terminals of these neurons in the NAcc while recording neural activity during the performance of a delayed non-match to sample (DNMS) spatial WM task. Within-subject behavioural performance and PL-mPFC to NAcc circuit neural activity was assessed after the onset of a persistent rodent neuropathic pain model-spared nerve injury (SNI). Our results revealed that the induction of the neuropathy reduced WM performance, and altered the interplay between PL-mPFC and NAcc neurons namely in increasing the functional connectivity from NAcc to PL-mPFC, particularly in the theta-band spontaneous oscillations; in addition, these behavioural and functional perturbations were partially reversed by selective optogenetic inhibition of PL-mPFC neuron terminals into the NAcc during the DNMS task delay-period, without significant antinociceptive effects. Altogether, these results strongly suggest that the PL-mPFC excitatory output into the NAcc plays an important role in the deregulation of WM under pain conditions. Selective optogenetic inhibition of prefrontal-striatal microcircuit reverses pain-related working memory deficits but has no significant impact on pain responses. Neuropathic pain underlies an increase of functional connectivity between the nucleus accumbens core area and the prelimbic medial prefrontal cortex mediated by theta-band activity.

Voluntary Exercise Boosts Striatal Dopamine Release: Evidence for the Necessary and Sufficient Role of BDNF.

Physical exercise improves motor performance in individuals with Parkinson's disease and elevates mood in those with depression. Although underlying factors have not been identified, clues arise from previous studies showing a link between cognitive benefits of exercise and increases in brain-derived neurotrophic factor (BDNF). Here, we investigated the influence of voluntary wheel-running exercise on BDNF levels in the striatum of young male wild-type (WT) mice, and on the striatal release of a key motor-system transmitter, dopamine (DA). Mice were allowed unlimited access to a freely rotating wheel (runners) or a locked wheel (controls) for 30 d. Electrically evoked DA release was quantified in ex vivo corticostriatal slices from these animals using fast-scan cyclic voltammetry. We found that exercise increased BDNF levels in dorsal striatum (dStr) and increased DA release in dStr and in nucleus accumbens core and shell. Increased DA release was independent of striatal acetylcholine (ACh), and persisted after a week of rest. We tested a role for BDNF in the influence of exercise on DA release using mice that were heterozygous for BDNF deletion (BDNF+/-). In contrast to WT mice, evoked DA release did not differ between BDNF+/- runners and controls. Complementary pharmacological studies using a tropomyosin receptor kinase B (TrkB) agonist in WT mouse slices showed that TrkB receptor activation also increased evoked DA release throughout striatum in an ACh-independent manner. Together, these data support a causal role for BDNF in exercise-enhanced striatal DA release and provide mechanistic insight into the beneficial effects of exercise in neuropsychiatric disorders, including Parkinson's, depression, and anxiety.SIGNIFICANCE STATEMENT Exercise has been shown to improve movement and cognition in humans and rodents. Here, we report that voluntary exercise for 30 d leads to an increase in evoked DA release throughout the striatum and an increase in BDNF in the dorsal (motor) striatum. The increase in DA release appears to require BDNF, indicated by the absence of DA release enhancement with running in BDNF+/- mice. Activation of BDNF receptors using a pharmacological agonist was also shown to boost DA release. Together, these data support a necessary and sufficient role for BDNF in exercise-enhanced DA release and provide mechanistic insight into the reported benefits of exercise in individuals with dopamine-linked neuropsychiatric disorders, including Parkinson's disease and depression.

Positive Allosteric Modulation of mGlu1 Reverses Cocaine-Induced Behavioral and Synaptic Plasticity Through the Integrated Stress Response and Oligophrenin-1

BackgroundCue-induced cocaine craving progressively intensifies (incubates) during abstinence from cocaine self-administration. Expression of incubated cocaine craving depends on elevated calcium-permeable AMPA receptors (CP-AMPARs) on medium spiny neurons in the nucleus accumbens (NAc) core. After incubation has occurred, stimulation of NAc metabotropic glutamate 1 (mGlu1) receptors or systemic administration of mGlu1 positive allosteric modulators removes CP-AMPARs from NAc synapses via dynamin-dependent internalization (mGlu1 long-term depression [LTD]) and thereby reduces incubated cocaine craving. Because mGlu1 positive allosteric modulators are potential therapeutics for cocaine craving, it is important to further define the mechanism triggering this mGlu1-LTD. MethodsMale and female rats self-administered saline or cocaine (10 days) using a long access regimen (6 h/day). Following ≥40 days of abstinence, we assessed the ability of an mGlu1 positive allosteric modulator to inhibit expression of incubated craving and remove CP-AMPARs from NAc synapses under control conditions, after blocking the integrated stress response (ISR), or after knocking down oligophrenin-1, a mediator of the ISR that can promote AMPAR endocytosis. AMPAR transmission in NAc medium spiny neurons was assessed with ex vivo slice recordings. ResultsmGlu1 stimulation reduced cue-induced craving and removed synaptic CP-AMPARs. When the ISR was blocked prior to mGlu1 stimulation, there was no reduction in cue-induced craving, nor were CP-AMPARs removed from the synapse. Further, selective knockdown of oligophrenin-1 blocked mGlu1-LTD. ConclusionsOur results indicate that mGlu1-LTD in the NAc and consequently the reduction of cue-induced seeking occur through activation of the ISR, which induces translation of oligophrenin-1. We also demonstrate CP-AMPAR accumulation and mGlu1 reversal in female rats, as previously shown in male rats.

High‐fat diets increase nicotine self‐administration in male and female mice by impacting dopamine release in the nucleus accumbens core

Prior investigations focused on the impact of high‐fat diet (HFD) on nicotine reward and reinforcement have indicated that HFD exposure increases reward‐related and reinforcement‐related behaviors associated with nicotine. However, there has been no investigation into how nicotine‐related behaviors may be altered by HFD. To investigate the potential mechanisms of HFD on nicotine addiction‐related behaviors, we exposed adult male and female mice to HFD or a regular diet (RD) for 6 weeks. Following this, we trained mice in a nicotine e‐vape® self‐administration (EVSA) paradigm. Here mice, were trained to self‐administer 6 mg/mL nicotine on a fixed‐ratio 1 (FR1), FR3 and progressive‐ratio schedules. Following behavioral assays we anesthetized the mice and extracted brains for ex‐vivo fast‐scan cyclic voltammetry (FSCV) assays. We observed that both male and female mice exhibited an increase in nicotine intake on the FR1 schedule but had the same intake of nicotine as RD mice on a FR3 schedule. We also observed that both male and female mice exhibited a significantly lower breakpoint when assessed on a progressive ratio. Using FSCV, we observed that HFD mice exhibited a significant decrease in dopamine release in the nucleus accumbens core when compared to RD mice at both tonic and phasic stimulation frequencies. These data support the fact that HFD promotes nicotine intake at low‐effort schedules (FR1) and this may be due to decreased baseline dopamine release in the nucleus accumbens core.

Ovarian Hormones Regulate Nicotine Consumption and Accumbens Glutamatergic Plasticity in Female Rats.

Women report greater cigarette cravings during the menstrual cycle phase with higher circulating levels of 17β-estradiol (E2), which is metabolized to estrone (E1). Both E2 and E1 bind to estrogen receptors (ERs), which have been highly studied in the breast, uterus, and ovary. Recent studies have found that ERs are also located on GABAergic medium spiny neurons (MSNs) within the nucleus accumbens core (NAcore). Glutamatergic plasticity in NAcore MSNs is altered following nicotine use; however, it is unknown whether estrogens impact this neurobiological consequence. To test the effect of estrogen on nicotine use, we ovariectomized (OVX) female rats that then underwent nicotine self-administration acquisition and compared them to ovary-intact (sham) rats. The OVX animals then received either sesame oil (vehicle), E2, or E1+E2 supplementation for 4 or 20 d before nicotine sessions. While both ovary-intact and OVX females readily discriminated levers, OVX females consumed less nicotine than sham females. Further, neither E2 nor E1+E2 increased nicotine consumption back to sham levels following OVX, regardless of the duration of the treatment. OVX also rendered NAcore MSNs in a potentiated state following nicotine self-administration, which was reversed by 4 d of systemic E2 treatment. Finally, we found that E2 and E1+E2 increased ERα mRNA in the NAcore, but nicotine suppressed this regardless of hormone treatment. Together, these results show that estrogens regulate nicotine neurobiology, but additional factors may be required to restore nicotine consumption to ovary-intact levels.

Investigating the Role of Corticostriatal Glutamate Signaling in Methamphetamine Reward and Reinforcement

Highly addictive amphetamine‐type stimulants, including methamphetamine (MA), pose significant health and socioeconomic issues, with an estimated 27 million users worldwide. Understanding the neurobiological changes underlying various stages of MA abuse is key to developing safe and effective therapies. While the majority of addiction research has implicated the dopamine system, the long‐term neuroplasticity that maintains MA Use Disorder also involves drug‐induced changes in glutamate signaling in reward regions of the brain like the nucleus accumbens (NAC) and prefrontal cortex (PFC). In order to further characterize the role of glutamate in MA reward and reinforcement, glutamate receptor scaffolding protein Homer2 expression in the NAC and activity in the glutamatergic projection PFC‐NAC were manipulated prior to place‐ and operant‐conditioning procedures. Together the results from these studies argue that while research of the functional neuroanatomy of addiction tends to focus on traditional dichotomies between the NAC core and shell or PFC prelimbic and infralimbic sub‐regions, the role of these circuits in drug abuse is more complex than the narrow scope of our experiments were able to probe. Other inputs upstream from our regions of interest may be able to compensate for our manipulations via neurobiological redundancy. This would suggest that as research technologies advance, targeting functional networks will be crucial for elucidating the neurobiological underpinnings of addiction and discovering potential therapeutics.

Choice-selective sequences dominate in cortical relative to thalamic inputs to NAc to support reinforcement learning.

SUMMARYHow are actions linked with subsequent outcomes to guide choices? The nucleus accumbens, which is implicated in this process, receives glutamatergic inputs from the prelimbic cortex and midline regions of the thalamus. However, little is known about whether and how representations differ across these input pathways. By comparing these inputs during a reinforcement learning task in mice, we discovered that prelimbic cortical inputs preferentially represent actions and choices, whereas midline thalamic inputs preferentially represent cues. Choice-selective activity in the prelimbic cortical inputs is organized in sequences that persist beyond the outcome. Through computational modeling, we demonstrate that these sequences can support the neural implementation of reinforcement-learning algorithms, in both a circuit model based on synaptic plasticity and one based on neural dynamics. Finally, we test and confirm a prediction of our circuit models by direct manipulation of nucleus accumbens input neurons.

Role of Cortical Dopamine circuits in regulating Striatal Dopamine dynamics during Reversal Learning

Dopamine is a catecholamine neuromodulator implicated in locomotion, motivation, learning and cognitive behaviors. Although striatal dopamine signaling and circuitry are well established, the role of cortical dopamine projection circuitry in regulating striatal dopamine dynamics and behavior is not clear. Glutamatergic pyramidal neurons in the prefrontal cortex (PFC) are topographically organized and dopamine D1 and D2 receptors are expressed on glutamatergic pyramidal neurons in the PFC. Using a retrograde adeno‐associated virus (AAVRG)‐based approach we show that D1R+ subpopulations in medial orbitofrontal or prelimbic regions project to nucleus accumbens core (NAcc) or dorsal striatum (dSTR), respectively. However, D2R+ subpopulations in medial orbitofrontal, or medial prelimbic PFC, project to NAcc or the midbrain (SNpc/VTA) but not dSTR, respectively. Additionally, D1R+ and D2R+ medial orbitofrontal subpopulations have indirect connections to the medial SNpc through the NAcc core. We next wanted to test which of these topographically organized circuits regulate striatal dopamine dynamics during reversal learning. We used fiber photometry to measure striatal dopamine dynamics in the dorsomedial striatum (DMS) during reversal learning. We were able to measure reward prediction error (RPE) like responses in the DMS during reversal learning. We will next use an intersectional genetic approach to specifically activate or inhibit dopamine receptor cortical projection circuits and test their effect on striatal dopamine dynamics and reversal learning. Our studies will identify previously unappreciated roles for cortical dopamine projection circuits and their regulation of striatal dopamine dynamics.

Nucleus accumbens D1-receptors regulate and focus transitions to reward-seeking action

It is well established that dopamine transmission is integral in mediating the influence of reward expectations on reward-seeking actions. However, the precise causal role of dopamine transmission in moment-to-moment reward-motivated behavioral control remains contentious, particularly in contexts where it is necessary to refrain from responding to achieve a beneficial outcome. To examine this, we manipulated dopamine transmission pharmacologically as rats performed a Go/No-Go task that required them to either make or withhold action to gain either a small or large reward. D1R Stimulation potentiated cue-driven action initiation, including fast impulsive actions on No-Go trials. By contrast, D1R blockade primarily disrupted the successful completion of Go trial sequences. Surprisingly, while after global D1R blockade this was characterized by a general retardation of reward-seeking actions, nucleus accumbens core (NAcC) D1R blockade had no effect on the speed of action initiation or impulsive actions. Instead, fine-grained analyses showed that this manipulation decreased the precision of animals’ goal-directed actions, even though they usually still followed the appropriate response sequence. Strikingly, such “unfocused” responding could also be observed off-drug, particularly when only a small reward was on offer. These findings suggest that the balance of activity at NAcC D1Rs plays a key role in enabling the rapid activation of a focused, reward-seeking state to enable animals to efficiently and accurately achieve their goal.

CircTmeff-1 in the nucleus accumbens regulates the reconsolidation of cocaine-associated memory

Reconsolidation of drug memories is the process of restoring unstable memories after unconditioned (UCS; e.g., drugs) or conditioned stimulus (CS; e.g., drug-paired contexts), and provides promise for prevention of drug relapse. Circular RNAs (circRNAs) have important effects on the transcription and post-transcriptional regulation of gene expression. However, the role of circRNAs in the reconsolidation of drug memories is unclear. Here, we observed that cocaine-induced memory retrieval significantly increased circTmeff-1 level in the nucleus accumbens (NAc) core but not shell. Importantly, the disrupted expression of circTmeff-1 using virus in the NAc core damaged the reconsolidation of cocaine-associated memories. The knockdown of circTmeff-1 in the NAc shell or without UCS retrieval or 9 h after UCS retrieval had no such effects. Mechanistically, using bioinformatic analysis and loss- or gain- of function assays, we revealed that antagomiR-206 reversed the inhibitory effect of circTmeff-1 knockdown on the expression of brain-derived neurotrophic factor (BDNF) during the reconsolidation of cocaine-associated memories. Taken together, these results demonstrate the role of circTmeff-1 in the reconsolidation of cocaine-associated memory and that circTmeff-1 may function as a decoy for miR-206 to regulate the expression of BDNF.

Early life stress influences basal ganglia dopamine receptors and novel object recognition of adolescent and adult rats.

Environmental stimuli in early life are recognized to affect brain development and behavior. Mother-pup interaction constitutes a determinant stimulus during this critical period. It is known that the dopaminergic system undergoes significant reorganization during adolescence and that dopamine receptors are involved in recognition memory. Based on the above, we examined the effects of brief and prolonged maternal separation during the neonatal period (15 or 180 min daily) on basal ganglia dopamine receptors and on the behavior in the novel object recognition task of adolescent and adult male rats. Using the NOR task, we observed that the discrimination index (DI) was decreased in rats with brief maternal separations independent of age. Using receptor autoradiography, we observed that brief maternal separation induced decreases in D1, D2 and D4 receptor binding levels in adult basal ganglia nuclei, while prolonged maternal separation induced increases in D1 receptor binding levels in caudate - putamen (CPu) of adolescent rats. With immunoblotting experiments, we found decreases in D1 and increases in D2 total protein levels in CPu of adult rats with prolonged maternal separations. Α positive correlation was observed between DI and D1 binding levels in CPu, internal globus pallidus and substantia nigra, and D2 binding levels in nucleus accumbens core in adult rats, using the Pearson correlation coefficient. Our results indicate that the long-lasting effects of neonatal mother-offspring separation on dopamine receptors depend on the duration of maternal separation and age and that this early life experience impairs recognition memory in adolescent and adult rats. Furthermore, the present results suggest that modulation of striatal dopamine receptors might underlie the reduced recognition memory of adult rats with brief neonatal maternal separations.

The Toll-like receptor 7 agonist imiquimod increases ethanol self-administration and induces expression of Toll-like receptor related genes.

There is growing evidence that immune signalling may be involved in both the causes and consequences of alcohol abuse. Toll‐like receptor (TLR) expression is increased by alcohol consumption and is implicated in AUD, and specifically TLR7 may play an important role in ethanol consumption. We administered the TLR7‐specific agonist imiquimod in male and female Long–Evans rats to determine (1) gene expression changes in brain regions involved in alcohol reinforcement, the nucleus accumbens core and anterior insular cortex, in rats with and without an alcohol history, and (2) whether TLR7 activation could modulate operant alcohol self‐administration. Interferon regulatory factor 7 (IRF7) was dramatically increased in both sexes at both 2‐ and 24‐h post‐injection regardless of alcohol history and TLR3 and 7 gene expression was increased as well. The proinflammatory cytokine TNFα was increased 24‐h post‐injection in rats with an alcohol self‐administration history, but this effect did not persist after four injections, suggesting molecular tolerance. Ethanol consumption was increased 24 h after imiquimod injections but did not occur until the third injection, suggesting adaptation to repeated TLR7 activation is necessary for increased drinking to occur. Notably, imiquimod reliably induced weight loss, indicating that sickness behaviour persisted across repeated injections. These findings show that TLR7 activation can modulate alcohol drinking in an operant self‐administration paradigm and suggest that TLR7 and IRF7 signalling pathways may be a viable druggable target for treatment of AUD.

Sex-specific neurobehavioural outcomes and brain stimulation pattern in adult offspring paternally exposed to methamphetamine.

Paternal methamphetamine (METH) exposure results in long-term behavioural deficits in the sub-generations with a sex difference. Here, we aim to investigate the sex-specific neurobehavioural outcomes in the first-generation offspring mice (F1 mice) paternally exposed to METH prior to conception and explore the underlying brain mechanisms. We found that paternal METH exposure increased anxiety-like behaviours and spatial memory deficits only in female F1 mice and caused depression-like behaviours in the offspring without sex-specific differences. In parallel, METH-sired F1 mice exhibited sex-specific brain activity pattern in response to mild stimulus (in water at room temperature for 3 min). Overall, paternal METH exposure caused a blunting phenomenon of prelimbic cortex (PrL), infralimbic cortex (IL) and nucleus accumbens (NAc) core in both male and female F1 mice, as indicated by the decreased c-Fos levels under mild stimulus. Of note, the activity of central nucleus of the amygdala (CeA) by mild stimulus was triggered in male but suppressed in female F1 mice, whereas the neurons of orbitofrontal cortex (OFC), cingulate cortex (Cg1), NAc shell, medial habenula (mHb), dorsal hippocampal CA1 (dCA1) and ventral hippocampal CA1 (vCA1) were only blunted in female F1 mice. Taken together, the distinct brain stimulation patterns between male and female F1 mice might contribute to the sex-specific behavioural outcomes by paternal METH exposure, which indicate that sex differences should be considered in the treatment of offspring paternally exposed drugs.

Pituitary adenylate cyclase-activating polypeptide type 1 receptor within the nucleus accumbens core mediates excessive alcohol drinking in alcohol-preferring rats

Alcohol use disorders (AUD) have a strong component of heritability; however, the neurobiological mechanisms mediating the propensity to consume excessive amounts of alcohol are still not well understood. Pituitary adenylate cyclase-activating polypeptide (PACAP), a highly conserved neuropeptide which exerts its effects mainly through the PAC1 receptor (PAC1R), has been suggested to be one of the mediators of the effects of drugs of abuse and alcohol. Here, we investigated the role of the PACAP/PAC1R system in excessive alcohol drinking in alcohol-preferring rats, an established animal model of AUD. Intracerebroventricular (i.c.v.) administration of the PAC1R antagonist PACAP(6–38) blocked excessive alcohol drinking and motivation to drink in Sardinian alcohol-preferring (Scr:sP) rats, without affecting water, saccharin, or sucrose intake. Notably, PACAP(6–38) did not affect ethanol responding in outbred Wistar rats. PACAP(6–38) also significantly reduced alcohol-seeking behavior under a second-order schedule of reinforcement. Using immunohistochemistry, a significant increase in the number of PAC1R positive cells was observed selectively in the nucleus accumbens (NAcc) Core of Scr:sP rats, compared to Wistar rats, following alcohol drinking. Finally, excessive drinking in Scr:sP rats was suppressed by intra-NAcc Core, but not intra-NAcc Shell, PACAP(6–38), as well as by virally-mediated PAC1R knockdown in the NAcc Core. The present study shows that hyperactivity of the PACAP/PAC1R system specifically in the NAcc Core mediates excessive drinking of alcohol-preferring rats, and indicates that this system may represent a novel target for the treatment of AUD.

Estrogen receptors observed at extranuclear neuronal sites and in glia in the nucleus accumbens core and shell of the female rat: Evidence for localization to catecholaminergic and GABAergic neurons.

Estrogens affect dopamine-dependent diseases/behavior and have rapid effects on dopamine release and receptor availability in the nucleus accumbens (NAc). Low levels of nuclear estrogen receptor (ER) α and ERβ are seen in the NAc, which cannot account for the rapid effects of estrogens in this region. G-protein coupled ER 1 (GPER1) is observed at low levels in the NAc shell, which also likely does not account for the array of estrogens' effects in this region. Prior studies demonstrated membrane-associated ERs in the dorsal striatum; these experiments extend those findings to the NAc core and shell. Single- and dual-immunolabeling electron microscopy determined whether ERα, ERβ, and GPER1 are at extranuclear sites in the NAc core and shell and whether ERα and GPER1 were localized to catecholaminergic or γ-aminobutyric acid-ergic (GABAergic) neurons. All three ERs are observed, almost exclusively, at extranuclear sites in the NAc, and similarly distributed in the core and shell. ERα, ERβ, and GPER1 are primarily in axons and axon terminals suggesting that estrogens affect transmission in the NAc via presynaptic mechanisms. About 10% of these receptors are found on glia. A small proportion of ERα and GPER1 are localized to catecholaminergic terminals, suggesting that binding at these ERs alters release of catecholamines, including dopamine. A larger proportion of ERα and GPER1 are localized to GABAergic dendrites and terminals, suggesting that estrogens alter GABAergic transmission to indirectly affect dopamine transmission in the NAc. Thus, the localization of ERs could account for the rapid effects of estrogen in the NAc.

Effects of dopamine modulation on chronic stress-induced deficits in reward learning.

Anhedonia is characteristically preceded by chronic stress, likely involving downstream effects of glucocorticoid alterations on dopamine (DA) function. To elucidate the neural underpinnings of this interaction, we examined whether acute pharmacological modulation of DA alters reward learning after chronic mild stress (CMS). Forty-eight male Wistar rats were exposed to a 21-day CMS regime (n = 48 nostress controls) before completing the probabilistic reward task (PRT), a well-validated cross-species test of reward learning. We first examined whether stress-induced reward dysfunction could be restored by systemic injections of low-dose amisulpride (AMI), which increases DA transmission via D2-like autoreceptor blockade. Then, we investigated region-specific effects through bilateral infusions of quinpirole (QUIN), a D2-like receptor agonist, into either the nucleus accumbens core (NAcc) or medial prefrontal cortex (mPFC). Blunted reward learning in CMS animals was reversed by acute AMI administration, but this treatment did not alter reward learning in the no stress group. Elevated adrenal gland weight, a proxy for stress reactivity, predicted lower reward learning in the untreated CMS group. This effect was extinguished following AMI treatment. These findings might be attributed to significantly higher D2 receptor density in the NAcc of high stress reactive animals. To this end, NAcc QUIN infusions potentiated reward learning relative to mPFC QUIN infusions in CMS rats, but there was no effect in no stress control rats. Collectively, these findings suggest that DA modulation reverses stress-induced reward dysfunction, even among the most stress-reactive animals. The effect might depend on D2-like receptor activation in the mesolimbic system.