Anita C. Hansson

Dynamic reorganization of striatal circuits during the acquisition and consolidation of a skill

The learning of new skills is characterized by an initial phase of rapid improvement in performance and a phase of more gradual improvements as skills are automatized and performance asymptotes. Using in vivo striatal recordings, we observed region-specific changes in neural activity during the different phases of skill learning, with the associative or dorsomedial striatum being preferentially engaged early in training and the sensorimotor or dorsolateral striatum being engaged later in training. Ex vivo recordings from medium spiny striatal neurons in brain slices of trained mice revealed that the changes observed in vivo corresponded to regional- and training-specific changes in excitatory synaptic transmission in the striatum. Furthermore, the potentiation of glutamatergic transmission observed in dorsolateral striatum after extensive training was preferentially expressed in striatopallidal neurons, rather than striatonigral neurons. These findings demonstrate that region- and pathway-specific plasticity sculpts the circuits involved in the performance of the skill as it becomes automatized.

Upregulation of Voluntary Alcohol Intake, Behavioral Sensitivity to Stress, and Amygdala Crhr1 Expression Following a History of Dependence

BACKGROUND A history of alcohol dependence recruits increased voluntary alcohol intake and sensitivity to stress. Corticotropin-releasing hormone (CRH) has been implicated in this transition, but underlying molecular mechanisms remain unclear. METHODS A postdependent state was induced using intermittent alcohol exposure. Experiments were carried out following > or =3 weeks of recovery to eliminate contributions of acute withdrawal. Voluntary alcohol consumption was assessed in a two-bottle, free choice procedure. Behavioral sensitivity to stress was examined using fear suppression of behavior in a punished drinking (Vogel) conflict test. Effects of forced swim stress on voluntary alcohol intake were examined as a function of exposure history. Expression of Crh, Crhr1, and Crhr2 transcripts was analyzed by in situ hybridization histochemistry. RESULTS Alcohol drinking was upregulated long-term following a history of dependence. Fear suppression of behavior was selectively potentiated in postdependent animals. This persisted 3 months after alcohol exposure and was reversed by the selective CRH-R1 antagonist 3-(4-Chloro-2-morpholin-4-yl-thiazol-5-yl)-8-(1-ethylpropyl)-2,6-dimethyl-imidazo[1,2-b]pyridazine (MTIP) (10 mg/kg). Forced swim stress increased alcohol intake in postdependent animals but not in control animals. Behavioral changes were paralleled by an upregulation of Crhr1 transcript expression within basolateral (BLA) and medial (MeA) amygdala and Crh messenger RNA (mRNA) in central amygdala (CeA). In contrast, Crhr2 expression was down in the BLA. CONCLUSIONS Neuroadaptations encompassing amygdala CRH signaling contribute to the behavioral phenotype of postdependent animals.

Genetic Impairment of Frontocortical Endocannabinoid Degradation and High Alcohol Preference

Endocannabinoid signaling has recently been implicated in ethanol-seeking behavior. We analyzed the expression of endocannabinoid-related genes in key brain regions of reward and dependence, and compared them between the alcohol-preferring AA (Alko Alcohol) and nonpreferring ANA (Alko Non-Alcohol) rat lines. A decreased expression of fatty acid amidohydrolase (FAAH), the main endocannabinoid-degrading enzyme, was found in prefrontal cortex (PFC) of AA rats, and was accompanied by decreased enzyme activity in this region. Binding of the endocannabinoid-cannabinoid 1 (CB1) receptor ligand 3[H]SR141716A, and [35S]GTPγS incorporation stimulated by the CB1 agonist WIN 55,212-2 were downregulated in the same area. Together, this suggests an overactive endocannabinoid transmission in the PFC of AA animals, and a compensatory downregulation of CB1 signaling. The functional role of impaired FAAH function for alcohol self-administration was validated in two independent ways. The CB1 antagonist SR141716A potently and dose-dependently suppressed self-administration in AA rats when given systemically, or locally into the PFC, but not in the striatum. Conversely, intra-PFC injections of the competitive FAAH inhibitor URB597 increased ethanol self-administration in nonselected Wistar rats. These results show for the first time that impaired FAAH function may confer a phenotype of high voluntary alcohol intake, and point to a FAAH both as a potential susceptibility factor and a therapeutic target.

NF-κB mediated glucocorticoid response in the inner ear after acoustic trauma

The inner ear of humans and experimental animals demonstrate an abundance of glucocorticoid receptors (GR). Glucocorticoids (GC) are widely used to treat different hearing disorders; yet the mechanisms of GC action on the inner ear are unknown. We demonstrate how GR can directly modulate hearing sensitivity in response to a moderate acoustic trauma that results in a hearing loss (10–30 dB). The GC agonist (dexamethasone) and the drugs (metyrapone + RU 486) showed opposing effects on hearing threshold shifts. GC agonist (dexamethasone) decreased the hearing threshold whereas pre‐treatment with a GC synthesis inhibitor (metyrapone) in combination with a GR antagonist (RU 486) exacerbated auditory threshold shifts (25–60 dB) after acoustic trauma with statistically significant increase in GR mRNA and GR protein compared with the vehicle and acoustic trauma group. Acoustic trauma caused a significant increase in the nuclear transport of NF‐κB, whereas pre‐treatment with the drugs (metyrapone and RU 486) blocked NF‐κB nuclear transport into spiral ganglion nuclei. An NF‐κB inhibitor, pyrrolidine dithiocarbamate ammonium blocked the trauma‐induced translocation of NF‐κB and resulted in a hearing loss (45–60) dB. These results indicate that several factors define the responsiveness of the inner ear to GC, including the availability of ligand or receptor, and the nuclear translocation of GR and NF‐κB. These findings will further our understanding of individual GC responsiveness to steroid treatment, and will help improve the development of pharmaceuticals to selectively target GR in the inner ear for individuals with increased sensitivity to acoustic trauma.

Translating the neuroscience of alcoholism into clinical treatments : from blocking the buzz to curing the blues

Understanding the pathophysiology of addictive disorders is critical for development of new treatments. A major focus of addiction research has for a long time been on systems that mediate acute positively reinforcing effects of addictive drugs, most prominently the mesolimbic dopaminergic (DA) system and its connections. This research line has been successful in shedding light on the physiology of both natural and drug reward, but has not led to therapeutic breakthroughs. The role of classical reward systems is perhaps least clear in alcohol addiction. Here, recent work is summarized that points to some clinically important conclusions. First, important pharmacogenetic differences exist with regard to positively reinforcing effects of alcohol and the ability of this drug to activate classical reward pathways. This offers an opportunity for personalized treatment approaches in alcoholism. Second, brain stress and fear systems become pathologically activated in later stages of alcoholism and their activation is a major influence in escalation of alcohol intake, sensitization of stress responses, and susceptibility to relapse. These findings offer a new category of treatment mechanisms. Corticotropin-releasing hormone (CRH) signaling through CRH1 receptors is a major candidate target in this category, but recent data indicate that antagonists for substance P (SP) neurokinin 1 (NK1) receptors may have a similar potential.

Dysregulation of Nociceptin/Orphanin FQ Activity in the Amygdala Is Linked to Excessive Alcohol Drinking in the Rat

BACKGROUND Alcoholism is a complex behavioral disorder in which interactions between stressful life events and heritable susceptibility factors contribute to the initiation and progression of disease. Neural substrates of these interactions remain largely unknown. Here, we examined the role of the nociceptin/orphanin FQ (N/OFQ) system, with an animal model in which genetic selection for high alcohol preference has led to co-segregation of elevated behavioral sensitivity to stress (Marchigian Sardinian alcohol-preferring [msP]). METHODS The msP and Wistar rats trained to self-administer alcohol received central injections of N/OFQ. In situ hybridization and receptor binding assays were also performed to evaluate N/OFQ receptor (NOP) function in naïve msP and Wistar rats. RESULTS Intracerebroventricular (ICV) injection of N/OFQ significantly inhibited alcohol self-administration in msP but not in nonselected Wistar rats. The NOP receptor messenger RNA expression and binding was upregulated across most brain regions in msP compared with Wistar rats. However, in msP rats [(35)S]GTPgammaS binding revealed a selective impairment of NOP receptor signaling in the central amygdala (CeA). Ethanol self-administration in msP rats was suppressed after N/OFQ microinjection into the CeA but not into the bed nucleus of the stria terminalis or the basolateral amygdala. CONCLUSIONS These findings indicate that dysregulation of N/OFQ-NOP receptor signaling in the CeA contributes to excessive alcohol intake in msP rats and that this phenotype can be rescued by local administration of pharmacological doses of exogenous N/OFQ. Data are interpreted on the basis of the anti-corticotropin releasing factor (CRF) actions of N/OFQ and the significance of the CRF system in promoting excessive alcohol drinking in msP rats.

Neuroplasticity in brain reward circuitry following a history of ethanol dependence

Mitogen‐activated and extracellular regulated kinase (MEK) and extracellular signal‐regulated protein kinase (ERK) pathways may underlie ethanol‐induced neuroplasticity. Here, we used the MEK inhibitor 1,4‐diamino‐2,3‐dicyano‐1,4‐bis(2‐aminophenylthio)butadiene (UO126) to probe the role of MEK/ERK signaling for the cellular response to an acute ethanol challenge in rats with or without a history of ethanol dependence. Ethanol (1.5 g/kg, i.p.) induced expression of the marker genes c‐fos and egr‐1 in brain regions associated with both rewarding and stressful ethanol actions. Under non‐dependent conditions, ethanol‐induced c‐fos expression was generally not affected by MEK inhibition, with the exception of the medial amygdala (MeA). In contrast, following a history of dependence, a markedly suppressed c‐fos response to acute ethanol was found in the medial pre‐frontal/orbitofrontal cortex (OFC), nucleus accumbens shell (AcbSh) and paraventricular nucleus (PVN). The suppressed ethanol response in the OFC and AcbSh, key regions involved in ethanol preference and seeking, was restored by pre‐treatment with UO126, demonstrating a recruitment of an ERK/MEK‐mediated inhibitory regulation in the post‐dependent state. Conversely, in brain areas involved in stress responses (MeA and PVN), an MEK/ERK‐mediated cellular activation by acute ethanol was lost following a history of dependence. These data reveal region‐specific neuroadaptations encompassing the MEK/ERK pathway in ethanol dependence. Recruitment of MEK/ERK‐mediated suppression of the ethanol response in the OFC and AcbSh may reflect devaluation of ethanol as a reinforcer, whereas loss of an MEK/ERK‐mediated response in the MeA and PVN may reflect tolerance to its aversive actions. These two neuroadaptations could act in concert to facilitate progression into ethanol dependence.

Region-specific down-regulation of Crhr1 gene expression in alcohol-preferring msP rats following ad lib access to alcohol.

Corticotropin‐releasing hormone 1 receptors (CRH‐R1) mediate increased behavioral sensitivity to stress and excessive alcohol self‐administration following a history of dependence. It was recently demonstrated that the genetically selected alcohol‐preferring msP rat line replicates many characteristics of the post‐dependent state, due to an innate up‐regulation of the Crhr1 transcript in several limbic areas related to alcohol drinking motivation. Here, we examined whether voluntary alcohol consumption might be able to down‐regulate Crhr1 transcript levels in msP rats in brain areas where elevated expression previously has been shown. Within central and medial amygdala (CeA, MeA), as well as the Nc. Accumbens, 2 weeks’ad lib access to alcohol led to a highly significant down‐regulation of the Crhr1 transcript. Alcohol‐induced Crhr1 down‐regulation was not seen in cingulate cortex. These data support that recruitment of CRH‐R1 signaling within components of the extended amygdala drives excessive alcohol intake, and that alcohol is voluntarily consumed in part for its ability to reduce CRH‐R1 activity in this region.

Long-term suppression of forebrain neurogenesis and loss of neuronal progenitor cells following prolonged alcohol dependence in rats

Alcohol dependence leads to persistent neuroadaptations, potentially related to structural plasticity. Previous work has shown that hippocampal neurogenesis is modulated by alcohol, but effects of chronic alcohol on neurogenesis in the forebrain subventricular zone (SVZ) have not been reported. Effects in this region may be relevant for the impairments in olfactory discrimination present in alcoholism. Here, we examined the effects of prolonged alcohol dependence on neurogenesis. Rats were sacrificed directly after 7 wk of intermittent alcohol vapour exposure, or 3, 7 or 21 d into abstinence. Proliferation was assessed using BrdU and Ki67 immunoreactivity, newly differentiated neurons (neurogenesis) as doublecortin-immunoreactivity (DCX-IR), and neural stem cells using the SOX2 marker. In the dentate gyrus, chronic dependence resulted in a pattern similar to that previously reported for acute alcohol exposure: proliferation and neurogenesis were suppressed by the end of exposure, rebounded on day 3 of abstinence, and returned to control levels by days 7 and 21. In the SVZ, proliferation was also suppressed at the end of alcohol exposure, followed by a proliferation burst 3 d into abstinence. However, in this area, there was a trend for reduced proliferation on days 7 and 21 of abstinence, and this was accompanied by significant suppression of DCX-IR, indicating a long-term suppression of forebrain neurogenesis. Finally, a decrease in the SOX2 stem cell marker was detected at days 7 and 21, suggesting long-term reduction of the SVZ stem cell pool. While suppression of hippocampal neurogenesis by alcohol dependence is transient, the suppression in the forebrain SVZ appears long-lasting.

Modulation of voluntary ethanol consumption by beta-arrestin 2

Beta‐arrestin 2 is a multifunctional key component of the G protein‐coupled receptor complex and is involved in μ‐opiate and dopamine D2 receptor signaling, both of which are thought to mediate the rewarding effects of ethanol consumption. We identified elevated expression of the beta‐arrestin 2 gene (Arrb2) in the striatum and the hippocampus of ethanol‐preferring AA rats compared to their nonpreferring counterpart ANA line. Differential mRNA expression was accompanied by different levels of Arrb2 protein. The elevated expression was associated with a 7‐marker haplotype in complete linkage disequilibrium, which segregated fully between the lines, and was unique to the preferring line. Furthermore, a single, distinct, and highly significant quantitative trait locus for Arrb2 expression in hippocampus and striatum was identified at the locus of this gene, providing evidence that genetic variation may affect a cis‐regulatory mechanism for expression and regional control of Arrb2. These findings were functionally validated using mice lacking Arrb2, which displayed both reduced voluntary ethanol consumption and ethanol‐induced psychomotor stimulation. Our results demonstrate that beta‐arrestin 2 modulates acute responses to ethanol and is an important mediator of ethanol reward.—Björk, K., Rimondini, R., Hansson, A. C., Terasmaa, A., Hyytiä, P., Heilig, M., Sommer, W. H. Modulation of voluntary ethanol consumption by beta‐arrestin 2. FASEB J. 22, 2552–2560 (2008)