Activation of locus coeruleus to rostromedial tegmental nucleus (RMTg) noradrenergic pathway blunts binge-like ethanol drinking and induces aversive responses in mice

The Mouse Inferior Colliculus Responds Preferentially to Non-Ultrasonic Vocalizations

The inferior colliculus (IC), the midbrain auditory integration center, analyzes information about social vocalizations and provides substrates for higher level processing of vocal signals. We used multichannel recordings to characterize and localize responses to social vocalizations and synthetic stimuli within the IC of female and male mice, both urethane anesthetized and unanesthetized. We compared responses to ultrasonic vocalizations (USVs) with other vocalizations in the mouse repertoire and related vocal responses to frequency tuning, IC subdivisions, and sex. Responses to lower frequency, broadband social vocalizations were widespread in IC, well represented throughout the tonotopic axis, across subdivisions, and in both sexes. Responses to USVs were much more limited. Although we observed some differences in tonal and vocal responses by sex and subdivision, representations of vocal responses by sex and subdivision were largely the same. For most units, responses to vocal signals occurred only when frequency response areas overlapped with spectra of the vocal signals. Since tuning to frequencies contained within the highest frequency USVs is limited (<15% of IC units), responses to these vocalizations are correspondingly limited (<5% of sound-responsive units). These results highlight a paradox of USV processing in some rodents: although USVs are the most abundant social vocalization, their representation and the representation of corresponding frequencies are less than lower frequency social vocalizations. We interpret this paradox in light of observations suggesting that USVs with lower frequency elements (<50 kHz) are associated with increased emotional intensity and engage a larger population of neurons in the mouse auditory system.

Sex-dependent, lateralized engagement of anterior insular cortex inputs to the dorsolateral striatum in binge alcohol drinking

How does alcohol consumption alter synaptic transmission across time, and do these alcohol-induced neuroadaptations occur similarly in both male and female mice? Previous work shows that anterior insular cortex (AIC) projections to the dorsolateral striatum (DLS) are uniquely sensitive to alcohol-induced neuroadaptations in male, but not female mice, and play a role in governing binge alcohol consumption in male mice. Here, by using high-resolution behavior data paired with in-vivo fiber photometry, we show how similar levels of alcohol intake are achieved via different behavioral strategies across sex, and how inter-drinking session thirst states predict future alcohol intakes in females, but not males. Further, we show how presynaptic calcium activity recorded from AIC synaptic inputs in the DLS across 3 weeks of water consumption followed by 3 weeks of binge alcohol consumption change across, fluid, time, sex, and brain circuit lateralization. By time-locking presynaptic calcium activity from AIC inputs to the DLS to peri-initiation of drinking events we also show that AIC inputs into the left DLS robustly encode binge alcohol intake behaviors relative to water consumption and AIC inputs into the right DLS in males, but not females. These findings suggest a fluid-, sex- and lateralization-dependent role for the engagement of AIC inputs into the DLS that encode binge alcohol consumption behaviors and further contextualize alcohol-induced neuroadaptations at AIC inputs to the DLS.

Basolateral amygdala neuropeptide Y system modulates binge ethanol consumption

Neuropeptide Y (NPY) signaling regulation of corticolimbic communication is known to modulate binge-like ethanol consumption in rodents. In this work we sought to assess the impact of intra-BLA NPY system modulation on binge-like ethanol intake and to assess the role of the NPY1R+ projection from the BLA to the mPFC in this behavior. We used "drinking-in-the-dark" (DID) procedures in C57BL6J mice to address these questions. First, the impact of intra-BLA administration of NPY on binge-like ethanol intake was assessed. Next, the impact of repeated cycles of DID intake on NPY1R expression in the BLA was assessed with use of immunohistochemistry (IHC). Finally, chemogenetic inhibition of BLA→mPFC NPY1R+ projections was assessed to determine if limbic communication with the mPFC was specifically involved in binge-like ethanol intake. Importantly, as both the BLA and NPY system are sexually dimorphic, both sexes were assessed in these studies. Intra-BLA NPY dose-dependently decreased binge-like ethanol intake in males only. Repeated DID reduced NPY1R expression in the BLA of both sexes. Silencing of BLA→mPFC NPY1R+ neurons significantly reduced binge-like ethanol intake in both sexes in a dose-dependent manner. We provide novel evidence that (1) intra-BLA NPY reduces binge-like ethanol intake in males; (2) binge-like ethanol intake reduces NPY1R levels in the BLA; and (3) chemogenetic inhibition of BLA→mPFC NPY1R+ neurons blunts binge-like drinking in male and female mice. These observations provide the first direct evidence that NPY signaling in the BLA, and specifically BLA communication with the mPFC, modulates binge-like ethanol consumption.

Chemogenetic inhibition of locus coeruleus to rostromedial tegmental nucleus noradrenergic pathway increases light cycle ethanol drinking in male and female mice and blunts ethanol-induced CTA

We recently showed that chemogenetic activation of the locus coeruleus (LC) to the rostromedial tegmental nucleus (RMTg) noradrenergic (NE) pathway significantly blunted binge-like ethanol drinking and induced aversive-like behaviors in mice. The aim of the present study is to determine if silencing this TH + LC → RMTg noradrenergic pathway promotes increased levels of binge-like ethanol intake and reduced ethanol-induced conditioned taste aversion (CTA). To this end, both male and female TH-ires-cre mice on a C57BL/6 J background were cannulated in the RMTg and injected in the LC with rAVV viruses that encode cre-dependent Gi-expressing designer receptor exclusively activated by designer drugs (DREADDs), or its control, to directly control the activity of NE neurons. Inhibition of the LC to RMTg pathway had no effect on the binge-ethanol drinking in a "drinking-in-the-dark" (DID) paradigm. However, when using this paradigm during the light cycle, silencing of this circuit significantly increased ethanol intake without altering sucrose drinking. Moreover, we found that inhibition of this circuit significantly attenuated an ethanol-induced CTA. In addition, when compared to control animals, pairing RMTg-directed Clozapine N-oxide (CNO) with an i.p. injection of 1.5 g/kg ethanol reduced c-Fos activation in the LC, and increased c-Fos expression in the ventral tegmental area (VTA) in Gi-expressing mice. Our data show that inhibition of the TH + LC to the RMTg pathway significantly increased ethanol drinking as well as attenuated ethanol-induced CTA, supporting the involvement of the LC to RMTg noradrenergic circuit as an important protective mechanism against excessive ethanol consumption.

The Mouse Inferior Colliculus Responds Preferentially to Non-Ultrasonic Vocalizations

The inferior colliculus (IC), the midbrain auditory integration center, analyzes information about social vocalizations and provides substrates for higher level processing of vocal signals. We used multi-channel recordings to characterize and localize responses to social vocalizations and synthetic stimuli within the IC of female and male mice, both urethane-anesthetized and unanesthetized. We compared responses to ultrasonic vocalizations (USVs) with other vocalizations in the mouse repertoire and related vocal responses to frequency tuning, IC subdivisions, and sex. Responses to lower frequency, broadband social vocalizations were widespread in IC, well represented throughout the tonotopic axis, across subdivisions, and in both sexes. Responses to USVs were much more limited. Although we observed some differences in tonal and vocal responses by sex and subdivision, representations of vocal responses by sex and subdivision were largely the same. For most units, responses to vocal signals occurred only when frequency response areas overlapped with spectra of the vocal signals. Since tuning to frequencies contained within the highest frequency USVs is limited (< 15% of IC units), responses to these vocalizations are correspondingly limited (< 5% of sound-responsive units). These results highlight a paradox of USV processing in some rodents: although USVs are the most abundant social vocalization, their representation and the representation of corresponding frequencies is less than lower frequency social vocalizations. We interpret this paradox in light of observations suggesting that USVs with lower frequency elements (<50 kHz) are associated with increased emotional intensity and engage a larger population of neurons in the mouse auditory system.

SIGNIFICANCE STATEMENT

The inferior colliculus (IC) integrates multiple inputs to analyze information about social vocalizations. In mice, we show that the most common type of social vocalization, the ultrasonic vocalization or USV, was poorly represented in IC compared to lower frequency vocalizations. For most neurons, responses to vocal signals occurred only when frequency response areas overlapped with vocalization spectra. These results highlight a paradox of USV processing in some rodent auditory systems: although USVs are the most abundant social vocalization, their representation and representation of corresponding frequencies is less than lower frequency social vocalizations. These results suggest that USVs with lower frequency elements (<50 kHz)-associated with increased emotional intensity-will engage a larger population of neurons in the mouse auditory system.

Neural Circuitries and Alcohol Use Disorder: Cutting Corners in the Cycle

An implicit tenet of the alcohol use disorder (AUD) research field is that knowledge of how alcohol interacts with the brain is critical to the development of an understanding of vulnerability to AUD and treatment approaches. Gaining this understanding requires the mapping of brain function critical to specific components of this heterogeneous disorder. Early approaches in humans and animal models focused on the determination of specific brain regions sensitive to alcohol action and their participation in AUD-relevant behaviors. Broadly speaking, this research has focused on three domains, Binge/Intoxication, Negative Affect/Withdrawal, and Preoccupation/Anticipation, with a number of regions identified as participating in each. With the generational advances in technologies that the field of neuroscience has undergone over the last two decades, this focus has shifted to a circuit-based analysis. A wealth of new data has sharpened the field's focus on the specific roles of the interconnectivity of multiple brain regions in AUD and AUD-relevant behaviors, as well as demonstrating that the three major domains described above have much fuzzier edges than originally thought.In this chapter, we very briefly review brain regions previously implicated in aspects of AUD-relevant behavior from animal model research. Next, we move to a more in-depth overview of circuit-based approaches, and the utilization of these approaches in current AUD research.

The rostromedial tegmental nucleus RMTg is not a critical site for ethanol-induced motor activation in rats

RATIONALE

Opioid drugs indirectly activate dopamine (DA) neurons in the ventral tegmental area (VTA) through a disinhibition mechanism mediated by mu opioid receptors (MORs) present both on the GABA projection neurons located in the medial tegmental nucleus/tail of the VTA (RMTg/tVTA) and on the VTA GABA interneurons. It is well demonstrated that ethanol, like opioid drugs, provokes VTA DA neuron disinhibition by interacting (through its secondary metabolite, salsolinol) with MORs present in VTA GABA interneurons, but it is not known whether ethanol could disinhibit VTA DA neurons through the MORs present in the RMTg/tVTA.

OBJECTIVES

The objective of the present study was to determine whether ethanol, directly microinjected into the tVTA/RMTg, is also able to induce VTA DA neurons disinhibition.

METHODS

Disinhibition of VTA DA neurons was indirectly assessed through the analysis of the motor activity of rats. Cannulae were placed into the tVTA/RMTg to perform microinjections of DAMGO (0.13 nmol), ethanol (150 or 300 nmol) or acetaldehyde (250 nmol) in animals pre-treated with either aCSF or the irreversible antagonist of MORs, beta-funaltrexamine (beta-FNA; 2.5 nmol). After injections, spontaneous activity was monitored for 30 min.

RESULTS

Neither ethanol nor acetaldehyde directly administered into the RMTg/tVTA were able to increase the locomotor activity of rats at doses that, in previous studies performed in the posterior VTA, were effective in increasing motor activities. However, microinjections of 0.13 nmol of DAMGO into the tVTA/RMTg significantly increased the locomotor activity of rats. These activating effects were reduced by local pre-treatment of rats with beta-FNA (2.5 nmol).

CONCLUSIONS

The tVTA/RMTg does not appear to be a key brain region for the disinhibiting action of ethanol on VTA DA neurons. The absence of dopamine in the tVTA/RMTg extracellular medium, the lack of local ethanol metabolism or both could explain the present results.

Chronic ethanol alters adrenergic receptor gene expression and produces cognitive deficits in male mice

Hyperkateifia and stress-induced alcohol cravings drive relapse in individuals with alcohol use disorder (AUD). The brain stress signal norepinephrine (also known as noradrenaline) tightly controls cognitive and affective behavior and was thought to be broadly dysregulated with AUD. The locus coeruleus (LC) is a major source of forebrain norepinephrine, and it was recently discovered that the LC sends distinct projections to addiction-associated regions suggesting that alcohol-induced noradrenergic changes may be more brain region-specific than originally thought. Here we investigated whether ethanol dependence alters adrenergic receptor gene expression in the medial prefrontal cortex (mPFC) and central amgydala (CeA), as these regions mediate the cognitive impairment and negative affective state of ethanol withdrawal. We exposed male C57BL/6J mice to the chronic intermittent ethanol vapor-2 bottle choice paradigm (CIE-2BC) to induce ethanol dependence, and assessed reference memory, anxiety-like behavior and adrenergic receptor transcript levels during 3-6 days of withdrawal. Dependence bidirectionally altered mouse brain α1 and β receptor mRNA levels, potentially leading to reduced mPFC adrenergic signaling and enhanced noradrenergic influence over the CeA. These brain region-specific gene expression changes were accompanied by long-term retention deficits and a shift in search strategy in a modified Barnes maze task, as well as greater spontaneous digging behavior and hyponeophagia. Current clinical studies are evaluating adrenergic compounds as a treatment for AUD-associated hyperkatefia, and our findings can contribute to the refinement of these therapies by increasing understanding of the specific neural systems and symptoms that may be targeted.

GABAergic neurons in the rostromedial tegmental nucleus are essential for rapid eye movement sleep suppression

Rapid eye movement (REM) sleep disturbances are prevalent in various psychiatric disorders. However, the neural circuits that regulate REM sleep remain poorly understood. Here, we found that in male mice, optogenetic activation of rostromedial tegmental nucleus (RMTg) GABAergic neurons immediately converted REM sleep to arousal and then initiated non-REM (NREM) sleep. Conversely, laser-mediated inactivation completely converted NREM to REM sleep and prolonged REM sleep duration. The activity of RMTg GABAergic neurons increased to a high discharge level at the termination of REM sleep. RMTg GABAergic neurons directly converted REM sleep to wakefulness and NREM sleep via inhibitory projections to the laterodorsal tegmentum (LDT) and lateral hypothalamus (LH), respectively. Furthermore, LDT glutamatergic neurons were responsible for the REM sleep-wake transitions following photostimulation of the RMTg^GABA-LDT circuit. Thus, RMTg GABAergic neurons are essential for suppressing the induction and maintenance of REM sleep.

The role of anterior insular cortex inputs to dorsolateral striatum in binge alcohol drinking

How does binge drinking alcohol change synaptic function, and do these changes maintain binge consumption? The anterior insular cortex (AIC) and dorsolateral striatum (DLS) are brain regions implicated in alcohol use disorder. In male, but not female mice, we found that binge drinking alcohol produced glutamatergic synaptic adaptations selective to AIC inputs within the DLS. Photoexciting AIC→DLS circuitry in male mice during binge drinking decreased alcohol, but not water consumption and altered alcohol drinking mechanics. Further, drinking mechanics alone from drinking session data predicted alcohol-related circuit changes. AIC→DLS manipulation did not alter operant, valence, or anxiety-related behaviors. These findings suggest that alcohol-mediated changes at AIC inputs govern behavioral sequences that maintain binge drinking and may serve as a circuit-based biomarker for the development of alcohol use disorder.

Lateral habenula-projecting central amygdala circuits expressing GABA and NPY Y1 receptor modulate binge-like ethanol intake in mice

The central nucleus of the amygdala (CeA) is a critical brain region in the integration of emotional behaviors and is one of the major output areas of the amygdaloid complex. The CeA is composed of GABAergic interneurons and projection neurons which co-express a range of peptides including neuropeptide Y (NPY). Importantly, GABA and NPY signaling, via the NPY Y1 receptor (Y1R), in the CeA modulate binge-like ethanol intake in rodents and these systems undergo neuroplastic alterations following a history of ethanol consumption. Here we assessed the roles of GABAergic and Y1R+ circuits arising from the CeA and innervating the lateral habenula (LHb), a brain region that modulates the aversive properties of ethanol, in modulating binge-like ethanol intake in mice using "drinking in the dark" (DID) procedures. Using an anterograde cre-inducible reporter virus we established the CeA → LHb circuit in male and female vgat-ires-cre and NPY1r-cre mice. Next, we found that chemogenetic silencing of both the GABAergic or Y1R+ CeA → LHb circuit significantly blunted binge-like intake of a 20% ethanol solution but this same procedure failed to alter the consumption of a 3% sucrose solution. Finally, one, 4-day cycle of DID failed to alter basal or effects of ethanol or NPY on inhibitory transmission in Y1R+ CeA → LHb neurons. The present results suggest that blunting GABAergic tone in LHb-projecting CeA neurons may represent a new approach to preventing the development of AUDs. Drugs that target NPY Y1Rs are potential attractive targets.

Activation of the dorsal septum increases alcohol consumption in male C57BL/6J mice

Binge drinking is a common pattern of excessive alcohol consumption associated with Alcohol Use Disorder (AUD) and unraveling the neurocircuitry that promotes this type of drinking is critical to the development of novel therapeutic interventions. The septal region was once a focal point of alcohol research yet has seen limited study over the last decade in relation to binge drinking. Numerous studies point to involvement of the dorsal septum (dSep) in excessive drinking and withdrawal, but few studies have manipulated this region in the context of binge drinking behavior. The present experiments were primarily designed to determine the effect of chemogenetic manipulation of the dSep on binge-like alcohol drinking in male and female C57BL/6J mice. Mice received bilateral infusion of AAVs harboring hM4Di, hM3Dq, or mCherry into the dSep and subjects were challenged with systemic administration of clozapine-N-oxide (CNO) and vehicle in the context of binge-like alcohol consumption, locomotor activity, and sucrose drinking. CNO-mediated activation (hM3Dq) of the dSep resulted in increased binge-like alcohol consumption, locomotor activity, and sucrose intake in males. DSep activation promoted sucrose drinking in female mice, but alcohol intake and locomotor activity were unaffected. Conversely, silencing (hM4Di) of the dSep modestly decreased locomotor activity in males and did not influence alcohol or sucrose intake in either sex. These data support a role for the dSep in promoting binge-like drinking behavior in a sex-dependent fashion and suggests a broad role for the region in the modulation of general appetitive behaviors and locomotor activity.