Biology subjects

Glover, E. J.

Publications and source records attributed to Glover, E. J..

10 recordsLinked to original sources

bioRxiv2026

Neuronal and astrocytic adaptations in the lateral habenula during withdrawal from chronic ethanol

The lateral habenula (LHb) encodes aversive states and negative affect, positioning it as a candidate region for the negative reinforcement that drives alcohol withdrawal. However, little is known about how chronic ethanol exposure affects LHb neuronal function and glial biology during withdrawal. Here, we used chronic intermittent ethanol (CIE) vapor exposure, a well-established model of alcohol dependence that reliably produces somatic and affective signs of withdrawal, to examine LHb physiology and astrocytic markers during acute withdrawal in male and female rats. Whole-cell and cell-attached recordings revealed that withdrawal reduced evoked and spontaneous firing in LHb neurons, with rebound firing following a crossover pattern between males and females. Despite these excitability changes, the overall distribution of firing phenotypes was unchanged, suggesting a shift in gain rather than a reorganization of cell types. Immunofluorescence revealed increased Sox9+ and GFAP labeling in the LHb during withdrawal at the same time point when electrophysiology experiments uncovered impaired astrocytic regulation of glutamate clearance. Together, these findings reveal that withdrawal from chronic ethanol exposure produces neuronal and glial adaptations in the LHb, pointing to impaired glutamate regulation as a candidate mechanism relevant to the negative affective state of alcohol withdrawal. These findings position the LHb as a potential node linking astrocyte-neuron dynamics to withdrawal symptoms and relapse vulnerability in alcohol use disorder.

neuroscience↗

bioRxiv2026

Unpredictable intermittent access exacerbates loss of control over ethanol drinking

BackgroundLoss of control over drinking is a hallmark feature of alcohol use disorder (AUD) that is modeled preclinically through escalation of ethanol consumption and aversion-resistant drinking. Prior work with other reinforcers suggests that within-session unpredictable, intermittent access (uIntA) promotes these phenotypes. However, the effect of uIntA on voluntary ethanol consumption is unknown. MethodsMale and female Long-Evans rats (n=9-10/group) underwent seven weeks of daily voluntary ethanol (20% v/v) drinking sessions under either a continuous access (ContA) or uIntA schedule. Following four weeks of baseline, rats were rendered dependent using a two-week chronic intermittent ethanol vapor exposure procedure. Daily testing was maintained through one week into withdrawal from vapor exposure. On the final day of testing, ethanol was adulterated with quinine (30 mg/L) to assess aversion-resistant drinking. ResultsRats drinking under ContA and uIntA exhibited similar levels of average daily ethanol consumption at baseline. However, uIntA elicited a more robust dependence-induced escalation of ethanol consumption compared to ContA, with uIntA sustaining escalation through early withdrawal. Additionally, while rats with ContA to ethanol remained sensitive to quinine even after chronic ethanol vapor exposure, uIntA promoted aversion-resistant drinking in ethanol dependent rats. ConclusionsThese results demonstrate that, compared to ContA, uIntA maintains ethanol drinking and exacerbates dependence-induced escalation and aversion-resistant ethanol consumption. This work positions uIntA as a powerful tool to assess psychological and neurobiological factors that may underlie loss of control over drinking.

neuroscience↗

bioRxiv2026

Functional bipartition of medial prefrontal cortex into salience detection and movement gain

Reward prediction error (RPE) is a key function putatively realized by brain-wide neural states to drive learning and adaptive responding. The medial prefrontal cortex (mPFC) is among the many areas canonically implicated in RPE computation. Yet, whether mPFC RPE processing differs as a function of valence, value, and sign is not well-understood. Here, we performed in vivo mPFC calcium imaging in male and female rats engaged in an appetitive or aversive Pavlovian task designed to elicit RPE, along with continuous, unbiased behavioral monitoring. We found that short-latency bulk mPFC activity reports salience independent of valence, value, or RPE. Surprisingly, as subsequently validated with in vivo bidirectional optogenetics, we show that salience-null mPFC activity modulates generalized movement in a valence- and task-agnostic fashion. Together, these results challenge the pervasive notion of a unitary, region-wide representation of cognitive processes, including RPE signaling, by bulk mPFC activity, and instead, support a functional bipartition schema combining reactive detection of integrated salience and dynamic modulation of movement gain.

neuroscience↗

bioRxiv2024

Presence of distinct operant phenotypes and transient withdrawal-induced escalation of operant ethanol intake in female rats

Operant self-administration is frequently used to investigate the neurobiological mechanisms underlying alcohol seeking and drinking and to test the efficacy of drugs under development for the treatment of alcohol use disorder (AUD). Although widely used by the research community, there is a paucity of operant ethanol self-administration studies that include female subjects. The current study characterizes home cage drinking and operant ethanol self-administration in female Sprague Dawley, Long Evans, and Wistar rats. Rats underwent three weeks of intermittent-access two-bottle choice home cage drinking before being trained to lever press for ethanol in standard operant chambers equipped with contact lickometers. After capturing baseline operant performance, rats were chronically exposed to control or ethanol liquid diet using the Lieber-DeCarli method. Operant ethanol self-administration was re-evaluated after chronic liquid diet exposure to determine whether female rats exhibit similar withdrawal-induced escalation of ethanol intake as is regularly observed in male rats. Our findings reveal the presence of three distinct operant phenotypes (Drinker, Responder, Nonresponder), the prevalence of which within each strain is strikingly similar to our previous observations in males. Within a given phenotype, rats of each strain performed similarly during operant testing. Ethanol intake during home cage drinking was unable to predict future operant phenotype. Relative to controls, Drinkers chronically exposed to ethanol liquid diet exhibited a significant, but transient, escalation in consummatory, but not appetitive, responding during acute withdrawal. Collectively, these data closely parallel many of our previous observations in males while also highlighting potential sex differences in drinking strategies following dependence. The presence of the Responder phenotype reinforces the importance of using direct measures of ethanol consumption. Our findings provide new insight into similarities and differences in operant ethanol self-administration between males and females and emphasize the importance of including females in future studies of ethanol drinking and dependence.

neuroscience↗

bioRxiv2024

Modelling alcohol consumption in rodents using two-bottle choice home cage drinking and optional lickometry-based microstructural analysis

Two-bottle choice home cage drinking is one of the most widely used paradigms to study ethanol consumption in rodents. In its simplest form, animals are provided with access to two drinking bottles, one of which contains regular tap water and the other ethanol, for 24 hr/day with daily intake measured via change in bottle weight over the 24 hr period. Consequently, this approach requires no specialized laboratory equipment. While such ease of implementation is likely the greatest contributor to its widespread adoption by preclinical alcohol researchers, the resolution of drinking data acquired using this approach is limited by the number of times the researcher measures bottle weight (e.g., once daily). However, the desire to examine drinking patterns in the context of overall intake, pharmacological interventions, and neuronal manipulations has prompted the development of home cage lickometer systems that can acquire data at the level of individual licks. Although a number of these systems have been developed recently, the open-source system, LIQ HD, has garnered significant attention in the field for its affordability and user friendliness. Although exciting, this system was designed for use in mice. Here, we review appropriate procedures for standard and lickometer-equipped two-bottle choice home cage drinking. We also introduce methods for adapting the LIQ HD system to rats including hardware modifications to accommodate larger cage size and a redesigned 3D printed bottle holder compatible with standard off-the-shelf drinking bottles. Using this approach, researchers can examine daily drinking patterns in addition to levels of intake in many rats in parallel thereby increasing the resolution of acquired data with minimal investment in additional resources. These methods provide researchers with the flexibility to use either standard bottles or a lickometer-equipped apparatus to interrogate the neurobiological mechanisms underlying alcohol drinking depending on their precise experimental needs. SUMMARYThis protocol describes a standard intermittent-access two-bottle choice home cage drinking paradigm to model alcohol consumption in rats. In addition, it provides step-by-step instructions to augment the standard protocol with a DIY lickometer system that enables microstructural analysis of drinking behavior.

neuroscience↗

bioRxiv2024

Chronic ethanol exposure produces long-lasting, subregion-specific physiological adaptations in RMTg-projecting mPFC neurons

Chronic ethanol exposure produces neuroadaptations in the medial prefrontal cortex (mPFC) which facilitate the maladaptive behaviors interfering with recovery from alcohol use disorder. Despite evidence that different cortico-subcortical projections play distinct roles in behavior, few studies have examined the physiological effects of chronic ethanol at the circuit level. The rostromedial tegmental nucleus (RMTg) is a GABAergic midbrain region involved in aversive signaling and is functionally altered by chronic ethanol exposure. Our recent work identified a dense input from the mPFC to the RMTg, yet the effects of chronic ethanol exposure on this circuitry is unknown. In the current study, we examined physiological changes after chronic ethanol exposure in prelimbic (PL) and infralimbic (IL) mPFC neurons projecting to the RMTg. Adult male Long-Evans rats were injected with fluorescent retrobeads into the RMTg and rendered dependent using a 14-day chronic intermittent ethanol (CIE) vapor exposure paradigm. Whole-cell patch-clamp electrophysiological recordings were performed in fluorescently-labeled (RMTg-projecting) and -unlabeled (projection-undefined) layer 5 pyramidal neurons 7-10 days following ethanol exposure. CIE significantly increased intrinsic excitability as well as excitatory and inhibitory synaptic drive in RMTg-projecting IL neurons. In contrast, no lasting changes in excitability were observed in RMTg-projecting PL neurons, although a CIE-induced reduction in excitability was observed in projection-undefined PL neurons. CIE also increased excitatory synaptic drive in RMTg-projecting PL neurons. These data uncover novel subregion- and circuit-specific neuroadaptations in the mPFC following chronic ethanol exposure and reveal that the IL mPFC-RMTg projection is uniquely vulnerable to long-lasting effects of chronic ethanol.

neuroscience↗

bioRxiv2024

Variables affecting acquisition and maintenance of operant ethanol self-administration in male and female Long-Evans rats

AimsThe goal of the present study was to determine the effect of prior experience with ethanol drinking and changes in session duration on the acquisition and maintenance of operant ethanol self-administration. MethodsAdult male and female Long-Evans rats were trained to operantly self-administer ethanol. A subset of male rats underwent intermittent-access two-bottle choice drinking in the home cage prior to operant training. Controls were given access to two bottles of water. Once fully trained in 30-min operant sessions, session duration was reduced to 15 min for all male and female rats. Differences between 30- and 15-min sessions were also assessed in a separate group of male and female rats trained to self-administer sucrose. ResultsNo differences were observed in acquisition rates, the magnitude of responding for ethanol, or total ethanol consumed between male rats allowed to drink ethanol in the home cage and those that remained ethanol naive prior to operant training. A significant decrease in appetitive and consummatory behaviors was observed in males trained to lever press for either ethanol or sucrose. Females exhibited a similar decrease in operant performance for sucrose, but their behavior was largely unchanged in response to changes in session duration when ethanol was the reinforcer. ConclusionsThese data suggest that the use of prior home cage ethanol drinking as an initiation procedure offers little advantage over no initiation procedure at all. Moreover, reducing operant session duration from 30-min to 15-min has the potential to decrease, rather than increase, levels of ethanol intake. Short summaryIntermittent-access two-bottle choice ethanol drinking offers no advantage as an initiation procedure for operant ethanol self-administration over animals that are ethanol-naive prior to training. In addition, shortening the operant session duration does not increase overall intake or promote binge-like patterns of intake for either ethanol or sucrose reinforcer.

neuroscience↗

bioRxiv2023

Attenuated incubation of ethanol-induced conditioned taste aversion in a model of dependence

RationalePreclinical studies report attenuated ethanol-induced conditioned taste aversion (CTA) following chronic ethanol exposure, suggesting that tolerance develops to the aversive properties of ethanol. However, these studies are confounded by pre-exposure to the unconditioned stimulus (US; ethanol), which is well known to hinder conditioning. ObjectivesThis study was designed to determine whether chronic ethanol exposure produces tolerance to the aversive properties of ethanol in the absence of a US pre-exposure confound. MethodsCTA was performed in adult male and female Long-Evans rats by pairing 0.1% ingested saccharin with an intraperitoneal injection of ethanol (1.5 or 2.0 g/kg) or saline. Rats were then rendered ethanol dependent using chronic intermittent ethanol (CIE) vapor exposure. Controls were exposed to room air (AIR). The effect of chronic ethanol on CTA expression and reconditioning were examined following vapor exposure. ResultsPrior to vapor exposure, both sexes developed CTA to a comparable degree with 2.0 g/kg producing greater CTA than 1.5 g/kg ethanol. Following vapor exposure, AIR controls exhibited an increase in CTA magnitude compared to pre-vapor levels. This effect was absent in CIE-exposed rats. These group differences were eliminated upon re-conditioning after vapor exposure. ConclusionsThese data suggest that chronic ethanol does not facilitate tolerance to the aversive properties of ethanol but rather, attenuates incubation of ethanol-induced CTA. Loss of CTA incubation suggests that CIE exposure disrupts circuits encoding aversion.

neuroscience↗

bioRxiv2023

A translational rodent model of individual differences in sensitivity to the aversive properties of ethanol

BackgroundA strong relationship exists between individual sensitivity to the aversive properties of ethanol and risk for alcohol use disorder (AUD). Despite this, our understanding of the neurobiological mechanisms underlying subjective response to ethanol is relatively poor. A major contributor to this is the absence of preclinical models that enable exploration of this individual variability similar to studies performed in humans. MethodsAdult male and female Long-Evans rats were trained to associate a novel tastant (saccharin) with acute exposure to either saline or ethanol (1.5 g/kg or 2.0 g/kg i.p.) over three conditioning days using a standard conditioned taste aversion (CTA) procedure. Variability in sensitivity to ethanol-induced CTA was phenotypically characterized using a median split across the populations studied. ResultsWhen examining group averages, both male and female rats that had saccharin paired with either dose of ethanol exhibited reduced saccharin intake relative to saline controls of ethanol-induced CTA. Examination of individual data revealed a bimodal distribution of responses uncovering two distinct phenotypes present in both sexes. CTA-sensitive rats exhibited a rapid and progressive reduction in saccharin intake with each successive ethanol pairing. In contrast, saccharin intake was unchanged or maintained after an initial decrease from baseline levels in CTA-resistant rats. While CTA magnitude was similar between male and female CTA-sensitive rats, CTA-resistant females were more resistant to the development of ethanol-induced CTA than their male counterparts. Phenotypic differences were not driven by differences in baseline saccharin intake. CTA sensitivity correlated with behavioral signs of intoxication in only a subset of rats. ConclusionsThese data parallel work in humans by revealing individual differences in sensitivity to the aversive properties of ethanol that emerge immediately after initial exposure to ethanol in both sexes. This model can be leveraged in future studies to investigate the neurobiological mechanisms that confer risk for AUD.

neuroscience↗

bioRxiv2021

Dense cortical input to the rostromedial tegmental nucleus mediates aversive signaling

AO_SCPLOWBSTRACTC_SCPLOWThe rostromedial tegmental nucleus (RMTg) encodes negative reward prediction error (RPE) and plays an important role in guiding behavioral responding to aversive stimuli. While initial studies describing the RMTg revealed the presence of cortical afferents, the density and distribution of this input has not been explored in detail. In addition, the functional consequences of cortical modulation of RMTg signaling are only just beginning to be investigated. The current study anatomically and functionally characterizes cortical input to the RMTg in rats. Findings from this work reveal dense input spanning the entire medial prefrontal cortex (PFC) as well as the orbitofrontal cortex and anterior insular cortex. Afferents were most dense in the dorsomedial subregion of the PFC (dmPFC), an area which has also been implicated in both RPE signaling and aversive responding. RMTg-projecting dmPFC neurons originate in layer V and collateralize extensively throughout the brain. In-situ mRNA hybridization further revealed that neurons in this circuit are predominantly D1 receptor-expressing with a high degree of D2 receptor colocalization. Optogenetic stimulation of dmPFC terminals in the RMTg drives avoidance, and cFos expression is enhanced in this neural circuit during exposure to aversive stimuli. Exposure to such aversive stimuli results in significant physiological and structural plasticity suggestive of a loss of top-down modulation of RMTg-mediated signaling. Altogether, these data reveal the presence of a prominent cortico-subcortical projection involved in adaptive behavioral responding and provide a foundation for future work aimed at exploring alterations in circuit function in diseases characterized by deficits in cognitive control over the balance between reward and aversion.

neuroscience↗