Vagus nerve damage increases alcohol intake and preference in a nonpreferring rat line: Relationship to vagal regulation of the hypothalamic-pituitary-adrenal axis

BACKGROUND

Clinical and preclinical research indicates that gastric weight loss surgeries, such as Roux-en-Y gastric bypass surgery, can induce alcohol use disorder (AUD). While numerous mechanisms have been proposed for these effects, one relatively unexplored potential mechanism is physical damage to the gastric branch of the vagus nerve, which can occur during bypass surgery. Therefore, we hypothesized that direct damage to the gastric branch of the vagus nerve, without altering other aspects of gastric anatomy, could result in increased alcohol intake.

METHODS

To test this hypothesis, we compared alcohol intake and preference in multiple models in male Sprague-Dawley rats that received selective gastric branch vagotomy (VX) with rats who underwent sham surgery. Because the vagus nerve regulates hypothalamic-pituitary-adrenal (HPA) axis function, and alterations to HPA function are critical to the escalation of non-dependent alcohol intake, we also tested the hypothesis that gastric VX increases HPA function.

RESULTS

We found that VX increases alcohol intake and preference in the every-other-day, two-bottle choice test and increases preference for 1 g/kg alcohol in the conditioned place preference test. The effects were selective for alcohol, as sucrose intake and preference were not altered by VX. We also found that VX increases corticotropin releasing factor (CRF) mRNA in the paraventricular nucleus of the hypothalamus (PVN), increases putative PVN CRF neuronal action potential firing, and increases corticosterone levels.

CONCLUSIONS

Overall, these findings suggest that the vagus nerve may play a critical role in regulating HPA axis function via modulation of PVN CRF mRNA expression and putative PVN CRF neuronal activity. Furthermore, disruptions to vagal regulation of HPA axis function may increase alcohol intake and preference.

Brain-specific serine/threonine-protein kinase 1 is a substrate of protein kinase C epsilon involved in sex-specific ethanol and anxiety phenotypes

Protein kinase C epsilon (PKCε) regulates behavioural responses to ethanol and plays a role in anxiety-like behaviour, but knowledge is limited on downstream substrates of PKCε that contribute to these behaviours. We recently identified brain-specific serine/threonine-protein kinase 1 (BRSK1) as a substrate of PKCε. Here, we test the hypothesis that BRSK1 mediates responses to ethanol and anxiety-like behaviours that are also PKCε dependent. We used in vitro kinase assays to further validate BRSK1 as a substrate of PKCε and used Brsk1-/- mice to assess the role of BRSK1 in ethanol- and anxiety-related behaviours and in physiological responses to ethanol. We found that BRSK1 is phosphorylated by PKCε at a residue identified in a chemical genetic screen of PKCε substrates in mouse brain. Like Prkce-/- mice, male and female Brsk1-/- mice were more sensitive than wild-type to the acute sedative-hypnotic effect of alcohol. Unlike Prkce-/- mice, Brsk1-/- mice responded like wild-type to ataxic doses of ethanol. Although in Prkce-/- mice ethanol consumption and reward are reduced in both sexes, they were reduced only in female Brsk1-/- mice. Ex vivo slice electrophysiology revealed that ethanol-induced facilitation of GABA release in the central amygdala was absent in male Brsk1-/- mice similar to findings in male Prkce-/- mice. Collectively, these results indicate that BRSK1 is a target of PKCε that mediates some PKCε-dependent responses to ethanol in a sex-specific manner and plays a role distinct from PKCε in anxiety-like behaviour.

Adolescent alcohol disrupts development of noradrenergic neurons in the nucleus of the tractus solitarius and enhances stress behaviors in adulthood in mice in a sex specific manner

Alcohol use disorders (AUDs) are common mental health issues worldwide and can lead to other chronic diseases. Stress is a major factor in the development and continuation of AUDs, and adolescent alcohol exposure can lead to enhanced stress-responsivity and increased risk for AUD development in adulthood. The exact mechanisms behind the interaction between adolescence, stress, and alcohol are not fully understood and require further research. In this regard, the nucleus of the tractus solitarius (NTS) provides dense norepinephrine projections to the extended amygdala, providing a key pathway for stress-related alcohol behaviors. While NTS norepinephrine neurons are known to be alcohol sensitive, whether adolescent alcohol disrupts NTS-norepinephrine neuron development and if this is related to altered stress-sensitivity and alcohol preference in adulthood has not previously been examined. Here, we exposed male and female C57Bl/6J mice to the commonly used adolescent intermittent ethanol (AIE) vapor model during postnatal day 28-42 and examined AIE effects on: 1) tyrosine hydroxylase (TH) mRNA expression in the NTS across various ages (postnatal day 21-90), 2) behavioral responses to acute stress in the light/dark box test in adulthood, 3) NTS TH neuron responses to acute stress and ethanol challenges in adulthood, and 4) ethanol conditioned place preference behavior in adulthood. Overall the findings indicate that AIE alters NTS TH mRNA expression and increases anxiety-like behaviors following acute stress exposure in a sex-dependent manner. These mRNA expression and behavioral changes occur in the absence of AIE-induced changes in NTS TH neuron sensitivity to either acute stress or acute alcohol exposure or changes to ethanol conditioned place preference.

Ethanol withdrawal-induced adaptations in prefrontal corticotropin releasing factor receptor 1-expressing neurons regulate anxiety and conditioned rewarding effects of ethanol

Prefrontal circuits are thought to underlie aberrant emotion contributing to relapse in abstinence; however, the discrete cell-types and mechanisms remain largely unknown. Corticotropin-releasing factor and its cognate type-1 receptor, a prominent brain stress system, is implicated in anxiety and alcohol use disorder (AUD). Here, we tested the hypothesis that medial prefrontal cortex CRF1-expressing (mPFCCRF1+) neurons comprise a distinct population that exhibits neuroadaptations following withdrawal from chronic ethanol underlying AUD-related behavior. We found that mPFCCRF1+ neurons comprise a glutamatergic population with distinct electrophysiological properties and regulate anxiety and conditioned rewarding effects of ethanol. Notably, mPFCCRF1+ neurons undergo unique neuroadaptations compared to neighboring neurons including a remarkable decrease in excitability and glutamatergic signaling selectively in withdrawal, which is driven in part by the basolateral amygdala. To gain mechanistic insight into these electrophysiological adaptations, we sequenced the transcriptome of mPFCCRF1+ neurons and found that withdrawal leads to an increase in colony-stimulating factor 1 (CSF1) in this population. We found that selective overexpression of CSF1 in mPFCCRF1+ neurons is sufficient to decrease glutamate transmission, heighten anxiety, and abolish ethanol reinforcement, providing mechanistic insight into the observed mPFCCRF1+ synaptic adaptations in withdrawal that drive these behavioral phenotypes. Together, these findings highlight mPFCCRF1+ neurons as a critical site of enduring adaptations that may contribute to the persistent vulnerability to ethanol misuse in abstinence, and CSF1 as a novel target for therapeutic intervention for withdrawal-related negative affect.

Corticotropin releasing factor and norepinephrine related circuitry changes in the bed nucleus of the stria terminalis in stress and alcohol and substance use disorders

Alcohol Use Disorder (AUD) affects around 14.5 million individuals in the United States, with Substance Use Disorder (SUD) affecting an additional 8.3 million individuals. Relapse is a major barrier to effective long-term treatment of this illness with stress often described as a key trigger for a person with AUD or SUD to relapse during a period of abstinence. Two signaling molecules, norepinephrine (NE) and corticotropin releasing factor (CRF), are released during the stress response, and also play important roles in reward behaviors and the addiction process. Within the addiction literature, one brain region in which there has been increasing research focus in recent years is the bed nucleus of the stria terminalis (BNST). The BNST is a limbic structure with numerous cytoarchitecturally and functionally different subregions that has been implicated in drug-seeking behaviors and stress responses. This review focuses on drug and stress-related neurocircuitry changes in the BNST, particularly within the CRF and NE systems, with an emphasis on differences and similarities between the major dorsal and ventral BNST subregions.

Behavioral characterization of a novel Cisd2 mutant mouse

Wolfram syndrome (WFS) is a rare autosomal recessive disorder characterized by diabetes mellitus and insipidus, progressive optic atrophy and sensorineural deafness. An increased incidence of psychiatric disorders has also been reported in WFS patients. There are two subtypes of WFS. Type 1 (WFS1) is caused by mutations in the WFS1 gene and type 2 (WFS2) results from mutations in the CISD2 gene. Existing Wfs1 knockout mice exhibit many WFS1 cardinal symptoms including diabetic nephropathy, metabolic disruptions and optic atrophy. Far fewer studies have examined loss of Cisd2 function in mice. We identified B6.DDY-Cisd2^m1Lmt, a mouse model with a spontaneous mutation in the Cisd2 gene. B6.DDY-Cisd2^m1Lmt mice were initially identified based on the presence of audible sonic vocalizations as well as decreased body size and weight compared to unaffected wildtype littermates. Although Wfs1 knockout mice have been characterized for numerous behavioral phenotypes, similar studies have been lacking for Cisd2 mutant mice. We tested B6.DDY-Cisd2^m1Lmt mice in a battery of behavioral assays that model phenotypes related to neurological and psychiatric disorders including anxiety, sensorimotor gating, stress response, social interaction and learning and memory. B6.DDY-Cisd2^m1Lmt mice displayed hypoactivity across several behavioral tests, exhibited increased stress response and had deficits in spatial learning and memory and sensorimotor gating compared to wildtype littermates. Our data indicate that the B6.DDY-Cisd2^m1Lmt mouse strain is a useful model to investigate potential mechanisms underlying the neurological and psychiatric symptoms observed in WFS.

Chronic Intermittent Ethanol and Acute Stress Similarly Modulate BNST CRF Neuron Activity via Noradrenergic Signaling

BACKGROUND

Relapse is a critical barrier to effective long-term treatment of alcoholism, and stress is often cited as a key trigger to relapse. Numerous studies suggest that stress-induced reinstatement to drug-seeking behaviors is mediated by norepinephrine (NE) and corticotropin-releasing factor (CRF) signaling interactions in the bed nucleus of the stria terminalis (BNST), a brain region critical to many behavioral and physiologic responses to stressors. Here, we sought to directly examine the effects of NE on BNST CRF neuron activity and determine whether these effects may be modulated by chronic intermittent EtOH (CIE) exposure or a single restraint stress.

METHODS

Adult male CRF-tomato reporter mice were treatment-naïve, or either exposed to CIE for 2 weeks or to a single 1-hour restraint stress. Effects of application of exogenous NE on BNST CRF neuron activity were assessed via whole-cell patch-clamp electrophysiological techniques.

RESULTS

We found that NE depolarized BNST CRF neurons in naïve mice in a β-adrenergic receptor (AR)-dependent mechanism. CRF neurons from CIE- or stress-exposed mice had significantly elevated basal resting membrane potential compared to naïve mice. Furthermore, CIE and stress individually disrupted the ability of NE to depolarize CRF neurons, suggesting that both stress and CIE utilize β-AR signaling to modulate BNST CRF neurons. Neither stress nor CIE altered the ability of exogenous NE to inhibit evoked glutamatergic transmission onto BNST CRF neurons as shown in naïve mice, a mechanism previously shown to be α-AR-dependent.

CONCLUSIONS

Altogether, these findings suggest that stress and CIE interact with β-AR signaling to modulate BNST CRF neuron activity, potentially disrupting the α/β-AR balance of BNST CRF neuronal excitability. Restoration of α/β-AR balance may lead to novel therapies for the alleviation of many stress-related disorders.

Using kaon regeneration to probe the quark mixing parameter cos2beta in B --> psiK decays

We suggest a novel method to determine the sign of cos2beta in the decays B --> psiK, by creating interference between K(L) and K(S) final states via "regeneration," that is propagation through a matter target region to convert some K(L) to K(S). The determination of this quantity resolves an ambiguity between beta and 90 degrees -beta that remains after the standard measurements of sin2beta and may turn out to be important in resolving whether the result is in agreement with standard model predictions or indicates the presence of new physics. We find the measurement is feasible at a B factory, but requires several years of high-luminosity running with a regeneration target affecting a significant fraction of the detector.