Subcortical serotonin 5HT2c receptor-containing neurons sex-specifically regulate binge-like alcohol consumption, social, and arousal behaviors in mice.

Binge alcohol consumption induces discrete social and arousal disturbances in human populations that promote increased drinking and accelerate the progression of Alcohol Use Disorder. Here, we show in a mouse model that binge alcohol consumption disrupts social recognition in females and potentiates sensorimotor arousal in males. These negative behavioral outcomes were associated with sex-specific adaptations in serotonergic signaling systems within the lateral habenula (LHb) and the bed nucleus of the stria terminalis (BNST), particularly those related to the receptor 5HT2c. While both BNST and LHb neurons expressing this receptor display potentiated activation following binge alcohol consumption, the primary causal mechanism underlying the effects of alcohol on social and arousal behaviors appears to be excessive activation of LHb5HT2c neurons. These findings may have valuable implications for the development of sex-specific treatments for mood and alcohol use disorders targeting the brain's serotonin system.

Acute engagement of Gq-mediated signaling in the bed nucleus of the stria terminalis induces anxiety-like behavior.

The bed nucleus of the stria terminalis (BNST) is a brain region important for regulating anxiety-related behavior in both humans and rodents. Here we used a chemogenetic strategy to investigate how engagement of G protein-coupled receptor (GPCR) signaling cascades in genetically defined GABAergic BNST neurons modulates anxiety-related behavior and downstream circuit function. We saw that stimulation of vesicular γ-aminobutyric acid (GABA) transporter (VGAT)-expressing BNST neurons using hM3Dq, but neither hM4Di nor rM3Ds designer receptors exclusively activated by a designer drug (DREADD), promotes anxiety-like behavior. Further, we identified that activation of hM3Dq receptors in BNST VGAT neurons can induce a long-term depression-like state of glutamatergic synaptic transmission, indicating DREADD-induced changes in synaptic plasticity. Further, we used DREADD-assisted metabolic mapping to profile brain-wide network activity following activation of Gq-mediated signaling in BNST VGAT neurons and saw increased activity within ventral midbrain structures, including the ventral tegmental area and hindbrain structures such as the locus coeruleus and parabrachial nucleus. These results highlight that Gq-mediated signaling in BNST VGAT neurons can drive downstream network activity that correlates with anxiety-like behavior and points to the importance of identifying endogenous GPCRs within genetically defined cell populations. We next used a microfluidics approach to profile the receptorome of single BNST VGAT neurons. This approach yielded multiple Gq-coupled receptors that are associated with anxiety-like behavior and several potential novel candidates for regulation of anxiety-like behavior. From this, we identified that stimulation of the Gq-coupled receptor 5-HT2CR in the BNST is sufficient to elevate anxiety-like behavior in an acoustic startle task. Together, these results provide a novel profile of receptors within genetically defined BNST VGAT neurons that may serve as therapeutic targets for regulating anxiety states and provide a blueprint for examining how G-protein-mediated signaling in a genetically defined cell type can be used to assess behavior and brain-wide circuit function.

Integrated circuits and molecular components for stress and feeding: implications for eating disorders.

Eating disorders are complex brain disorders that afflict millions of individuals worldwide. The etiology of these diseases is not fully understood, but a growing body of literature suggests that stress and anxiety may play a critical role in their development. As our understanding of the genetic and environmental factors that contribute to disease in clinical populations like anorexia nervosa, bulimia nervosa and binge eating disorder continue to grow, neuroscientists are using animal models to understand the neurobiology of stress and feeding. We hypothesize that eating disorder clinical phenotypes may result from stress-induced maladaptive alterations in neural circuits that regulate feeding, and that these circuits can be neurochemically isolated using animal model of eating disorders.

Developmental changes in the acute ethanol sensitivity of glutamatergic and GABAergic transmission in the BNST.

Glutamatergic and GABAergic transmission undergo significant changes during adolescence. Receptors for both of these transmitters (NMDAR, and GABAA) are known to be key targets for the acute effects of ethanol in adults. The current study set out to investigate the acute effects of ethanol on both NMDAR-mediated excitatory transmission and GABAergic inhibitory transmission within the bed nucleus of the stria terminalis (BNST) across age. The BNST is an area of the brain implicated in the negative reinforcing properties associated with alcohol dependence, and the BNST plays a critical role in stress-induced relapse. Therefore, assessing the developmental regulation of ethanol sensitivity in this key brain region is important to understanding the progression of ethanol dependence. To do this, whole-cell recordings of isolated NMDAR-evoked excitatory postsynaptic currents (eEPSCs) or evoked GABAergic inhibitory postsynaptic currents (eIPSCs) were performed on BNST neurons in slices from 4- or 8-week-old male C57BL/6J mice. Ethanol (50 mm) produced greater inhibition of NMDAR-eEPSCs in adolescent mice than in adult mice. This enhanced sensitivity in adolescence was not a result of shifts in function of the GluN2B subunit of the NMDAR, measured by Ro25-6981 inhibition and decay kinetics measured across age. Adolescent mice also exhibited greater ethanol sensitivity of GABAergic transmission, as ethanol (50 mm) enhanced eIPSCs in the BNST of adolescent but not adult mice. Collectively, this work illustrates that a moderate dose of ethanol produces greater inhibition of transmission in the BNST (through greater excitatory inhibition and enhancement of inhibitory transmission) in adolescents compared to adults. Given the role of the BNST in alcohol dependence, these developmental changes in acute ethanol sensitivity could accelerate neuroadaptations that result from chronic ethanol use during the critical period of adolescence.

Compartment-specific localization of cannabinoid 1 (CB1) and mu-opioid receptors in rat nucleus accumbens.

Interactions between cannabinoid and opioid systems have been implicated in reward and drug seeking behaviors involving neuronal circuitry in the nucleus accumbens (Acb) shell and core. To determine the relevant sites, we examined the electron microscopic localization of cannabinoid type-1 (CB1) receptors and mu-opioid receptors in each Acb compartment in rat brain. CB1 receptor immunogold labeling was seen on the plasma membrane and within the cytoplasm of neuronal and glial profiles throughout the Acb. These neuronal profiles included somata and dendrites as well as axon terminals, many of which formed excitatory-type, asymmetric synapses with notable perforations that are often associated with synaptic plasticity. The number of CB1-labeled terminals within the neuropil of the Acb shell was significantly greater than in the core. Mu-opioid receptors were also detected in axonal and dendritic profiles. These dendrites were most prevalent in the Acb shell, where mu-receptors also were located in 21% of the dendritic profiles and 3% of the axon terminals containing CB1 receptors. More of the CB1-labeled terminals contacted dendrites expressing mu-opioid receptors in the shell (19%) compared with the core (13%). Conversely, of the synaptic mu-labeled terminals, 20% in the shell and 10% in the core contacted dendrites containing CB1 receptors. These findings provide ultrastructural evidence that cannabinoid-opioid interactions are mediated by activation of CB1 and mu-opioid receptors within the same or synaptically linked neurons in the Acb shell and core. They also suggest a particularly important role for presynaptic CB1 receptors in the reward circuit of the Acb shell.

Structural elements involved in activation of the gamma-aminobutyric acid type A (GABAA) receptor.

Ligand-gated ion channels function as rapid signal transducers, converting chemical signals (in the form of neurotransmitters) into electrical signals in the postsynaptic neuron. This is achieved by the recognition of neurotransmitter at its specific-binding sites, which then triggers the opening of an ion channel ('gating'). For this to occur rapidly (< 1 ms), there must be an efficient coupling between the agonist-binding site and the gate, located more than 30 angstroms (1 angstroms = 0.1 nm) away. Whereas a great deal of progress has been made in elucidating the structure and function of both the agonist-binding site and the ion permeation pathway in ligand-gated ion channels, our knowledge of the coupling mechanism between these domains has been limited. In this review, we summarize recent studies of the agonist-binding site and the ion channel in the gamma-aminobutyric acid type A receptor, and discuss those structural elements that may mediate coupling between them. We will also consider some possible molecular mechanisms of receptor activation.

Effect of amphetamine-induced dopamine release on radiotracer binding to D1 and D2 receptors in rat brain striatal slices.

The in vivo binding of positron emission tomography (PET) and single photon emission computer tomography (SPECT) radiotracers to dopamine D2 receptors in the striatum can be influenced by competition with endogenous dopamine. The present study was undertaken to determine if a similar inhibition of radiotracer binding to dopamine receptors could be observed following pharmacologically-evoked dopamine release in rat brain striatal slices. Striatal slices were incubated in a large volume of oxygenated Krebs saline and exposed to amphetamine or methamphetamine to evoke dopamine release within the slice. Amphetamine and methamphetamine, at concentrations up to 30 microM, reduced [3H]raclopride binding in the slices by 77% and 86%, respectively, with 50% inhibition at 1.6 microM amphetamine or 3.0 microM methamphetamine. Neither drug produced a significant effect on binding of [3H]SCH 23390 in the slices. This suggests that dopamine was able to interfere with radiotracer binding to D2 but not D1 receptors. The dopamine uptake blockers, cocaine and methylphenidate, had relatively little effect by themselves on [3H]raclopride binding but, by inhibiting amphetamine-induced dopamine release, significantly reduced inhibition of [3H]raclopride binding by a low (3 microM) amphetamine concentration. At a higher (30 microM) amphetamine concentration the inhibition of [3H]raclopride binding was not antagonized by uptake blockers and data obtained from homogenate binding experiments indicated a direct displacement of [3H]raclopride binding by amphetamine at this concentration. In conclusion the data obtained in the present study demonstrate that the effects of amphetamine on striatal radiotracer accumulation observed in PET and SPECT can also be observed in brain slices in vitro and, at least at low amphetamine concentrations, are mediated by competition with released dopamine.