Lyn kinase regulates mesolimbic dopamine release: implication for alcohol reward

Unraveling pathogenesis and potential biomarkers for autism spectrum disorder associated with HIF1A pathway based on machine learning and experiment validation

BACKGROUND

Autism spectrum disorder (ASD) is a neurodevelopmental disorder with a high social burden and limited treatments. Hypoxic condition of the brain is considered an important pathological mechanism of ASD. HIF1A is a key participant in brain hypoxia, but its contribution to the pathophysiological landscape of ASD remains unclear.

METHODS

ASD-related datasets were obtained from GEO database, and HIF1A-related genes from GeneCards. Co-expression module analysis identified module genes, which were intersected with HIF1A-related genes to identify common genes. Machine learning identified hub genes from intersection genes and PPI networks were constructed to explore relationships among hub and HIF1A. Single-cell RNA sequencing analyzed hub gene distribution across cell clusters. ASD mouse model was created by inducing maternal immune activation (MIA) with poly(I:C) injections, verified through behavioral tests. Validation of HIF1A pathway and hub genes was confirmed through Western Blot, qPCR, and immunofluorescence in ASD mice and microglia BV-2 cells.

RESULTS

Using CEMiTool and GeneCards, 45 genes associated with ASD and HIF1A pathway were identified. Machine learning identified CDKN1A, ETS2, LYN, and SLC16A3 as potential ASD diagnostic markers. Single-cell sequencing pinpointed activated microglia as key immune cells. Behavioral tests showed MIA offspring mice exhibited typical ASD-like behaviors. Immunofluorescence confirmed the activation of microglia and HIF1A pathway in frontal cortex of ASD mice. Additionally, IL-6 contributed to ASD by activating JUN/HIF1A pathway, affecting CDKN1A, LYN, and SLC16A3 expression in microglia.

CONCLUSIONS

HIF1A-related genes CDKN1A, ETS2, LYN, and SLC16A3 are strong diagnostic markers for ASD and the activation of IL-6/JUN/HIF1A pathway in microglia contributes to the pathogenesis of ASD.

Dopamine Pharmacodynamics: New Insights

Dopamine is a key neurotransmitter involved in physiological processes such as motor control, motivation, reward, cognitive function, and maternal and reproductive behaviors. Therefore, dysfunctions of the dopaminergic system are related to a plethora of human diseases. Dopamine, via different circuitries implicated in compulsive behavior, reward, and habit formation, also represents a key player in substance use disorder and the formation and perpetuation of mechanisms leading to addiction. Here, we propose dopamine as a model not only of neurotransmission but also of neuromodulation capable of modifying neuronal architecture. Abuse of substances like methamphetamine, cocaine, and alcohol and their consumption over time can induce changes in neuronal activities. These modifications lead to synaptic plasticity and finally to morphological and functional changes, starting from maladaptive neuro-modulation and ending in neurodegeneration.

Regulation of Microglial Signaling by Lyn and SHIP-1 in the Steady-State Adult Mouse Brain

Chronic neuroinflammation and glial activation are associated with the development of many neurodegenerative diseases and neuropsychological disorders. Recent evidence suggests that the protein tyrosine kinase Lyn and the lipid phosphatase SH2 domain-containing inositol 5' phosphatase-1 (SHIP-1) regulate neuroimmunological responses, but their homeostatic roles remain unclear. The current study investigated the roles of Lyn and SHIP-1 in microglial responses in the steady-state adult mouse brain. Young adult Lyn-/- and SHIP-1-/- mice underwent a series of neurobehavior tests and postmortem brain analyses. The microglial phenotype and activation state were examined by immunofluorescence and flow cytometry, and neuroimmune responses were assessed using gene expression analysis. Lyn-/- mice had an unaltered behavioral phenotype, neuroimmune response, and microglial phenotype, while SHIP-1-/- mice demonstrated reduced explorative activity and exhibited microglia with elevated activation markers but reduced granularity. In addition, expression of several neuroinflammatory genes was increased in SHIP-1-/- mice. In response to LPS stimulation ex vivo, the microglia from both Lyn-/- and SHIP-1-/- showed evidence of hyper-activity with augmented TNF-α production. Together, these findings demonstrate that both Lyn and SHIP-1 have the propensity to control microglial responses, but only SHIP-1 regulates neuroinflammation and microglial activation in the steady-state adult brain, while Lyn activity appears dispensable for maintaining brain homeostasis.

Alcohol-specific transcriptional dynamics of memory reconsolidation and relapse

Relapse, a critical issue in alcohol addiction, can be attenuated by disruption of alcohol-associated memories. Memories are thought to temporarily destabilize upon retrieval during the reconsolidation process. Here, we provide evidence for unique transcriptional dynamics underpinning alcohol memory reconsolidation. Using a mouse place-conditioning procedure, we show that alcohol-memory retrieval increases the mRNA expression of immediate-early genes in the dorsal hippocampus and medial prefrontal cortex, and that alcohol seeking is abolished by post-retrieval non-specific inhibition of gene transcription, or by downregulating ARC expression using antisense-oligodeoxynucleotides. However, since retrieval of memories for a natural reward (sucrose) also increased the same immediate-early gene expression, we explored for alcohol-specific transcriptional changes using RNA-sequencing. We revealed a unique transcriptional fingerprint activated by alcohol memories, as the expression of this set of plasticity-related genes was not altered by sucrose-memory retrieval. Our results suggest that alcohol memories may activate two parallel transcription programs: one is involved in memory reconsolidation in general, and another is specifically activated during alcohol-memory processing.

The Src-family Kinase Lyn in Immunoreceptor Signaling

Effective regulation of immune-cell activation is critical for ensuring that the immune response, and inflammation generated for the purpose of pathogen elimination, are limited in space and time to minimize tissue damage. Autoimmune disease can occur when immunoreceptor signaling is dysregulated, leading to unrestrained inflammation and organ damage. Conversely, tumors can coopt the tissue healing and immunosuppressive functions of hematopoietic cells to promote metastasis and evade therapy. The Src-family kinase Lyn is an essential regulator of immunoreceptor signaling, initiating both proinflammatory and suppressive signaling pathways in myeloid immune cells (eg, neutrophils, dendritic cells, monocytes, macrophages) and in B lymphocytes. Defects in Lyn signaling are implicated in autoimmune disease, but mechanisms by which Lyn, expressed along with a battery of other Src-family kinases, may uniquely direct both positive and negative signaling remain incompletely defined. This review describes our current understanding of the activating and inhibitory contributions of Lyn to immunoreceptor signaling and how these processes contribute to myeloid and B-cell function. We also highlight recent work suggesting that the 2 proteins generated by alternative splicing of lyn, LynA and LynB, differentially regulate both immune and cancer-cell signaling. These principles may also extend to other Lyn-expressing cells, such as neuronal and endocrine cells. Unraveling the common and cell-specific aspects of Lyn function could lead to new approaches to therapeutically target dysregulated pathways in pathologies ranging from autoimmune and neurogenerative disease to cancer.

Therapeutic targeting of Lyn kinase to treat chorea-acanthocytosis

Chorea-Acanthocytosis (ChAc) is a devastating, little understood, and currently untreatable neurodegenerative disease caused by VPS13A mutations. Based on our recent demonstration that accumulation of activated Lyn tyrosine kinase is a key pathophysiological event in human ChAc cells, we took advantage of Vps13a^−/− mice, which phenocopied human ChAc. Using proteomic approach, we found accumulation of active Lyn, γ-synuclein and phospho-tau proteins in Vps13a^−/− basal ganglia secondary to impaired autophagy leading to neuroinflammation. Mice double knockout Vps13a^−/− Lyn^−/− showed normalization of red cell morphology and improvement of autophagy in basal ganglia. We then in vivo tested pharmacologic inhibitors of Lyn: dasatinib and nilotinib. Dasatinib failed to cross the mouse brain blood barrier (BBB), but the more specific Lyn kinase inhibitor nilotinib, crosses the BBB. Nilotinib ameliorates both Vps13a^−/− hematological and neurological phenotypes, improving autophagy and preventing neuroinflammation. Our data support the proposal to repurpose nilotinib as new therapeutic option for ChAc patients.

Face validity of a pre-clinical model of operant binge drinking: just a question of speed

Binge drinking (BD) is often defined as a large amount of alcohol consumed in a 'short' period of time or 'per occasion'. In clinical research, few researchers have included the notion of 'speed of drinking' in the definition of BD. Here, we aimed to describe a novel pre-clinical model based on voluntary operant BD, which included both the quantity of alcohol and the rapidity of consumption. In adult Long-Evans male rats, we induced BD by regularly decreasing the duration of ethanol self-administration from 1-hour to 15-minute sessions. We compared the behavioral consequences of BD with the behaviors of rats subjected to moderate drinking or heavy drinking (HD). We found that, despite high ethanol consumption levels (1.2 g/kg/15 minutes), the total amounts consumed were insufficient to differentiate HD from BD. However, consumption speed could distinguish between these groups. The motivation to consume was higher in BD than in HD rats. After BD, we observed alterations in locomotor coordination in rats that consumed greater than 0.8 g/kg, which was rarely observed in HD rats. Finally, chronic BD led to worse performance in a decision-making task, and as expected, we observed a lower stimulated dopaminergic release within nucleus accumbens slices in poor decision makers. Our BD model exhibited good face validity and can now provide animals voluntarily consuming very rapidly enough alcohol to achieve intoxication levels and thus allowing the study of the complex interaction between individual and environmental factors underlying BD behavior.

Nonphosphorylatable Src Ser75 Mutation Increases Ethanol Preference and Consumption in Mice

Src is highly expressed in CNS neurons and contributes not only to developmental proliferation and differentiation but also to high-order brain functions, such as those contributing to alcohol consumption. Src knock-out mice exhibit no CNS abnormalities, presumably due to compensation by other Src family kinases (SFKs), but have a shortened lifespan and osteopetrosis-associated defects, impeding investigations of the role of Src on behavior in adult mice. However, the Unique domain of Src differs from those in other SFKs and is phosphorylated by cyclin-dependent kinase 1 (Cdk1) and Cdk5 at Ser75, which influences its postmitotic function in neurons. Therefore, ethanol consumption in mice harboring nonphosphorylatable (Ser75Ala) or phosphomimetic (Ser75Asp) Src mutants was investigated. Mice harboring the Ser75Ala Src mutant, but not the Ser75Asp mutant, had a higher preference for and consumption of solutions containing 5% and 10% ethanol than wild-type mice. However, plasma ethanol concentrations and sensitivities to the sedative effects of ethanol were not different among the groups. In mice harboring the Ser75Ala Src mutant, the activity of Rho-associated kinase (ROCK) in the striatum was significantly lower and Akt Ser473 phosphorylation was significantly higher than in wild-type mice. These results suggest that Src regulates voluntary ethanol drinking in a manner that depends on Ser75 phosphorylation.

Modulation of ethanol reward sensitivity by nicotinic acetylcholine receptors containing the α6 subunit

The prevalent co-abuse of nicotine and alcohol suggests a common neural mechanism underlying the actions of the two drugs. Nicotine, the addictive component of tobacco, activates nicotinic acetylcholine receptors (nAChRs) containing the α6 subunit (α6* nAChRs) in dopaminergic (DAergic) neurons of the ventral tegmental area (VTA), a region known to be crucial for drug reward. Recent evidence suggests that ethanol may potentiate ACh activation of these receptors as well, although whether α6* nAChR expression is necessary for behavioral effects of acute ethanol exposure is unknown. We compared binge-like ethanol consumption and ethanol reward sensitivity between knockout (KO) mice that do not express chrna6 (the gene encoding the α6 nAChR subunit, the α6 KO line) and wild-type (WT) littermates using the Drinking-in-the-Dark (DID) and Conditioned Place Preference (CPP) assay, respectively. In the DID assay, α6 KO female and male mice consumed ethanol similarly to WT mice at all concentrations tested. In the CPP assay, 2.0-g/kg and 3.0-g/kg, but not 0.5-mg/kg, ethanol conditioned a place preference in WT female and male mice, whereas only 2.0-g/kg ethanol conditioned a place preference in α6 KO mice. Acute challenge with ethanol reduced locomotor activity, an effect that developed tolerance with repeated injections, similarly between genotypes in both female and male mice. Together, these data indicate that expression of α6* nAChRs is not required for binge-like ethanol consumption and reward, but modulate sensitivity to the rewarding properties of the drug.

Protein interactions of the vesicular glutamate transporter VGLUT1

Exocytotic release of glutamate depends upon loading of the neurotransmitter into synaptic vesicles by vesicular glutamate transporters, VGLUTs. The major isoforms, VGLUT1 and 2, exhibit a complementary pattern of expression in synapses of the adult rodent brain that correlates with the probability of release and potential for plasticity. Indeed, expression of different VGLUT protein isoforms confers different properties of release probability. Expression of VGLUT1 or 2 protein also determines the kinetics of synaptic vesicle recycling. To identify molecular determinants that may be related to reported differences in VGLUT trafficking and glutamate release properties, we investigated some of the intrinsic differences between the two isoforms. VGLUT1 and 2 exhibit a high degree of sequence homology, but differ in their N- and C-termini. While the C-termini of VGLUT1 and 2 share a dileucine-like trafficking motif and a proline-, glutamate-, serine-, and threonine-rich PEST domain, only VGLUT1 contains two polyproline domains and a phosphorylation consensus sequence in a region of acidic amino acids. The interaction of a VGLUT1 polyproline domain with the endocytic protein endophilin recruits VGLUT1 to a fast recycling pathway. To identify trans-acting cellular proteins that interact with the distinct motifs found in the C-terminus of VGLUT1, we performed a series of in vitro biochemical screening assays using the region encompassing the polyproline motifs, phosphorylation consensus sites, and PEST domain. We identify interactors that belong to several classes of proteins that modulate cellular function, including actin cytoskeletal adaptors, ubiquitin ligases, and tyrosine kinases. The nature of these interactions suggests novel avenues to investigate the modulation of synaptic vesicle protein recycling.

Brain-derived neurotrophic factor mediates the suppression of alcohol self-administration by memantine

Brain-derived neurotrophic factor (BDNF) within the striatum is part of a homeostatic pathway regulating alcohol consumption. Memantine, a non-competitive antagonist of N-methyl-D-aspartate receptors, induces expression of BDNF in several brain regions including the striatum. We hypothesized that memantine could decrease ethanol (EtOH) consumption via activation of the BNDF signalling pathway. Effects of memantine were evaluated in Long-Evans rats self-administering moderate or high amounts of EtOH 6, 30 and 54 hours after an acute injection (12.5 and 25 mg/kg). Motivation to consume alcohol was investigated through a progressive ratio paradigm. The possible role for BDNF in the memantine effect was tested by blockade of the TrkB receptor using the pharmacological agent K252a and by the BDNF scavenger TrkB-Fc. Candidate genes expression was also assessed by polymerase chain reaction array 4 and 28 hours after memantine injection. We found that memantine decreased EtOH self-administration and motivation to consume EtOH 6 and 30 hours post-injection. In addition, we found that inhibition or blockade of the BDNF signalling pathway prevented the early, but not the delayed decrease in EtOH consumption induced by memantine. Finally, Bdnf expression was differentially regulated between the early and delayed timepoints. These results demonstrate that an acute injection of memantine specifically reduces EtOH self-administration and motivation to consume EtOH for at least 30 hours. Moreover, we showed that BDNF was responsible for the early effect, but that the delayed effect was BDNF-independent.

Cortical activation of accumbens hyperpolarization-active NMDARs mediates aversion-resistant alcohol intake

Compulsive drinking despite serious adverse medical, social and economic consequences is a characteristic of alcohol use disorders in humans. Although frontal cortical areas have been implicated in alcohol use disorders, little is known about the molecular mechanisms and pathways that sustain aversion-resistant intake. Here, we show that nucleus accumbens core (NAcore) NMDA-type glutamate receptors and medial prefrontal (mPFC) and insula glutamatergic inputs to the NAcore are necessary for aversion-resistant alcohol consumption in rats. Aversion-resistant intake was associated with a new type of NMDA receptor adaptation, in which hyperpolarization-active NMDA receptors were present at mPFC and insula but not amygdalar inputs in the NAcore. Accordingly, inhibition of Grin2c NMDA receptor subunits in the NAcore reduced aversion-resistant alcohol intake. None of these manipulations altered intake when alcohol was not paired with an aversive consequence. Our results identify a mechanism by which hyperpolarization-active NMDA receptors under mPFC- and insula-to-NAcore inputs sustain aversion-resistant alcohol intake.

Nicotinic acetylcholine receptors containing the α4 subunit modulate alcohol reward

BACKGROUND

Nicotine and alcohol are the two most co-abused drugs in the world, suggesting a common mechanism of action might underlie their rewarding properties. Although nicotine elicits reward by activating ventral tegmental area dopaminergic (DAergic) neurons via high-affinity neuronal nicotinic acetylcholine receptors (nAChRs), the mechanism by which alcohol activates these neurons is unclear.

METHODS

Because most high-affinity nAChRs expressed in ventral tegmental area DAergic neurons contain the α4 subunit, we measured ethanol-induced activation of DAergic neurons in midbrain slices from two complementary mouse models, an α4 knock-out (KO) mouse line and a knock-in line (Leu9'Ala) expressing α4 subunit-containing nAChRs hypersensitive to agonist compared with wild-type (WT). Activation of DAergic neurons by ethanol was analyzed with both biophysical and immunohistochemical approaches in midbrain slices. The ability of alcohol to condition a place preference in each mouse model was also measured.

RESULTS

At intoxicating concentrations, ethanol activation of DAergic neurons was significantly reduced in α4 KO mice compared with WT. Conversely, in Leu9'Ala mice, DAergic neurons were activated by low ethanol concentrations that did not increase activity of WT neurons. In addition, alcohol potentiated the response to ACh in DAergic neurons, an effect reduced in α4 KO mice. Rewarding alcohol doses failed to condition a place preference in α4 KO mice, paralleling alcohol effects on DAergic neuron activity, whereas a sub-rewarding alcohol dose was sufficient to condition a place preference in Leu9'Ala mice.

CONCLUSIONS

Together, these data indicate that nAChRs containing the α4 subunit modulate alcohol reward.

Dopamine D2 receptor activation leads to an up-regulation of glial cell line-derived neurotrophic factor via Gβγ-Erk1/2-dependent induction of Zif268

Glial cell line-derived neurotrophic factor (GDNF) is a potent growth factor essential to the development, survival, and function of dopaminergic neurons (Airaksinen and Saarma 2002). The molecular mechanisms underlying GDNF expression remain elusive; thus, we set out to identify a signaling pathway that governs GDNF levels. We found that treatment of both differentiated dopaminergic-like SH-SY5Y cells and rat midbrain slices with the dopamine D2 receptor (D2R) agonist, quinpirole, triggered an increase in the expression of GDNF that was temporally preceded by an increase in the levels of zinc-finger protein 268 (Zif268), a DNA-binding transcription factor encoded by an immediate-early gene. Moreover, the D2R inhibitor raclopride blocked the increase of both GDNF and Zif268 expression following potassium-evoked dopamine release in SH-SY5Y cells. We used adenoviral delivery of small hairpin RNA (shRNA) targeting Zif268 to down-regulate its expression and found that Zif268 is specifically required for the D2R-mediated up-regulation of GDNF. Furthermore, the D2R-mediated induction of GDNF and Zif268 expression was dependent on Gβγ-mediated signaling and activation of extracellular signal-regulated kinase 1/2. Importantly, using chromatin immunoprecipitation assay, we identified a direct association of Zif268 with the GDNF promoter. These results suggest that D2R activation induces a Gβγ- and extracellular signal-regulated kinase 1/2-dependent increase in the level of Zif268, which functions to directly up-regulate the expression of GDNF.

Signaling pathways mediating alcohol effects

Ethanol's effects on intracellular signaling pathways contribute to acute effects of ethanol as well as to neuroadaptive responses to repeated ethanol exposure. In this chapter we review recent discoveries that demonstrate how ethanol alters signaling pathways involving several receptor tyrosine kinases and intracellular tyrosine and serine-threonine kinases, with consequences for regulation of cell surface receptor function, gene expression, protein translation, neuronal excitability and animal behavior. We also describe recent work that demonstrates a key role for ethanol in regulating the function of scaffolding proteins that organize signaling complexes into functional units. Finally, we review recent exciting studies demonstrating ethanol modulation of DNA and histone modification and the expression of microRNAs, indicating epigenetic mechanisms by which ethanol regulates neuronal gene expression and addictive behaviors.

MLR-1023 is a potent and selective allosteric activator of Lyn kinase in vitro that improves glucose tolerance in vivo

2(1H)-pyrimidinone,5-(3-methylphenoxy) (MLR-1023) is a candidate for the treatment of type 2 diabetes. The current studies were aimed at determining the mechanism by which MLR-1023 mediates glycemic control. In these studies, we showed that MLR-1023 reduced blood glucose levels without increasing insulin secretion in vivo. We have further determined that MLR-1023 did not activate peroxisome proliferator-activated α, δ, and γ receptors or glucagon-like peptide-1 receptors or inhibit dipeptidyl peptidase-4 or α-glucosidase enzyme activity. However, in an in vitro broad kinase screen MLR-1023 activated the nonreceptor-linked Src-related tyrosine kinase Lyn. MLR-1023 increased the V(max) of Lyn with an EC(50) of 63 nM. This Lyn kinase activation was ATP binding site independent, indicating that MLR-1023 regulated the kinase through an allosteric mechanism. We have established a link between Lyn activation and blood glucose lowering with studies showing that the glucose-lowering effects of MLR-1023 were abolished in Lyn knockout mice, consistent with existing literature linking Lyn kinase and the insulin-signaling pathway. In summary, these studies describe MLR-1023 as a unique blood glucose-lowering agent and show that MLR-1023-mediated blood glucose lowering depends on Lyn kinase activity. These results, coupled with other results (J Pharmacol Exp Ther 342:23-32, 2012), suggest that MLR-1023 and Lyn kinase activation may be a new treatment modality for type 2 diabetes.

Genome-wide analysis of familial dysautonomia and kinetin target genes with patient olfactory ecto-mesenchymal stem cells

Familial dysautonomia (FD) is a rare inherited neurodegenerative disorder. The most common mutation is a c.2204+6T>C transition in the 5' splice site (5'ss) of IKBKAP intron 20, which causes a tissue-specific skipping of exon 20, resulting in lower synthesis of IKAP/hELP1 protein. To better understand the specificity of neuron loss in FD, we modeled the molecular mechanisms of IKBKAP mRNA splicing by studying human olfactory ecto-mesenchymal stem cells (hOE-MSCs) derived from FD patient nasal biopsies. We explored how the modulation of IKBKAP mRNA alternative splicing impacts the transcriptome at the genome-wide level. We found that the FD transcriptional signature was highly associated with biological functions related to the development of the nervous system. In addition, we identified target genes of kinetin, a plant cytokinin that corrects IKBKAP mRNA splicing and increases the expression of IKAP/hELP1. We identified this compound as a putative regulator of splicing factors and added new evidence for a sequence-specific correction of splicing. In conclusion, hOE-MSCs isolated from FD patients represent a promising avenue for modeling the altered genetic expression of FD, demonstrating a methodology that can be applied to a host of other genetic disorders to test the therapeutic potential of candidate molecules.

The regulation of N-methyl-D-aspartate receptors by Src kinase

Src family kinases (SFKs) play critical roles in the regulation of many cellular functions by growth factors, G-protein-coupled receptors and ligand-gated ion channels. Recent data have shown that SFKs serve as a convergent point of multiple signaling pathways regulating N-methyl-d-aspartate (NMDA) receptors in the central nervous system. Multiple SFK molecules, such as Src and Fyn, closely associate with their substrate, NMDA receptors, via indirect and direct binding mechanisms. The NMDA receptor is associated with an SFK signaling complex consisting of SFKs; the SFK-activating phosphatase, protein tyrosine phosphatase α; and the SFK-inactivating kinase, C-terminal Src kinase. Early studies have demonstrated that intramolecular interactions with the SH2 or SH3 domain lock SFKs in a closed conformation. Disruption of the interdomain interactions can induce the activation of SFKs with multiple signaling pathways involved in regulation of this process. The enzyme activity of SFKs appears 'graded', exhibiting different levels coinciding with activation states. It has also been proposed that the SH2 and SH3 domains may stimulate catalytic activity of protein tyrosine kinases, such as Abl. Recently, it has been found that the enzyme activity of neuronal Src protein is associated with its stability, and that the SH2 and SH3 domain interactions may act not only to constrain the activation of neuronal Src, but also to regulate the enzyme activity of active neuronal Src. Collectively, these findings demonstrate novel mechanisms underlying the regulation of SFKs.

Src family kinases: modulators of neurotransmitter receptor function and behavior

Src family kinases (SFKs) are non-receptor-type protein tyrosine kinases that were originally identified as the products of proto-oncogenes and were subsequently implicated in the regulation of cell proliferation and differentiation in the developing mammalian brain. Recent studies using transgenic mouse models have demonstrated that SFKs that are highly expressed in the adult brain regulate neuronal plasticity and behavior through tyrosine phosphorylation of key substrates such as neurotransmitter receptors. Here, we provide an overview of these recent studies, as well as discussing how modulation of the endocytosis of neurotransmitter receptors by SFKs contributes, in part, to this regulation. Deregulation of SFK-dependent tyrosine phosphorylation of such substrates might underlie certain brain disorders.

Glial cell line-derived neurotrophic factor reverses alcohol-induced allostasis of the mesolimbic dopaminergic system: implications for alcohol reward and seeking

We previously showed that infusion of glial cell line-derived neurotrophic factor (GDNF) into the ventral tegmental area (VTA) rapidly reduces alcohol intake and relapse (Carnicella et al., 2008, 2009a), and increases dopamine (DA) levels in the nucleus accumbens (NAc) of alcohol-naive rats (Wang et al., 2010). Withdrawal from excessive alcohol intake is associated with a reduction in NAc DA levels, whereas drug-induced increases in NAc DA levels are associated with reward. We therefore tested whether GDNF in the VTA reverses alcohol withdrawal-associated DA deficiency and/or possesses rewarding properties. Rats were trained for 7 weeks to consume high levels of alcohol (5.47 ± 0.37 g/kg/24 h) in intermittent access to 20% alcohol in a two-bottle choice procedure. Using in vivo microdialysis, we show that 24 h withdrawal from alcohol causes a substantial reduction in NAc DA overflow, which was reversed by intra-VTA GDNF infusion. Using conditioned place preference (CPP) paradigm, we observed that GDNF on its own does not induce CPP, suggesting that the growth factor is not rewarding. However, GDNF blocked acquisition and expression of alcohol-CPP. In addition, GDNF induced a downward shift in the dose-response curve for operant self-administration of alcohol, further suggesting that GDNF suppresses, rather than substitutes for, the reinforcing effects of alcohol. Our findings suggest that GDNF reduces alcohol-drinking behaviors by reversing an alcohol-induced allostatic DA deficiency in the mesolimbic system. In addition, as it lacks abuse liability, the study further highlights GDNF as a promising target for treatment of alcohol use/abuse disorders.