Somayeh Ahmadiantehrani

GDNF is an Endogenous Negative Regulator of Ethanol-Mediated Reward and of Ethanol Consumption After a Period of Abstinence

BACKGROUND We previously found that activation of the glial cell line-derived neurotrophic factor (GDNF) pathway in the ventral tegmental area (VTA) reduces ethanol-drinking behaviors. In this study, we set out to assess the contribution of endogenous GDNF or its receptor GFRalpha1 to the regulation of ethanol-related behaviors. METHODS GDNF and GFRalpha1 heterozygote mice (HET) and their wild-type littermate controls (WT) were used for the studies. Ethanol-induced hyperlocomotion, sensitization, and conditioned place preference (CPP), as well as ethanol consumption before and after a period of abstinence were evaluated. Blood ethanol concentration (BEC) was also measured. RESULTS We observed no differences between the GDNF HET and WT mice in the level of locomotor activity or in sensitization to ethanol-induced hyperlocomotion after systemic injection of a nonhypnotic dose of ethanol and in BEC. However, GDNF and GFRalpha1 mice exhibited increased place preference to ethanol as compared with their WT littermates. The levels of voluntary ethanol or quinine consumption were similar in the GDNF HET and WT mice, however, a small but significant increase in saccharin intake was observed in the GDNF HET mice. No changes were detected in voluntary ethanol, saccharin or quinine consumption of GFRalpha1 HET mice as compared with their WT littermates. Interestingly, however, both the GDNF and GFRalpha1 HET mice consumed much larger quantities of ethanol after a period of abstinence from ethanol as compared with their WT littermates. Furthermore, the increase in ethanol consumption after abstinence was found to be specific for ethanol as similar levels of saccharin intake were measured in the GDNF and GFRalpha1 HET and WT mice after abstinence. CONCLUSIONS Our results suggest that endogenous GDNF negatively regulates the rewarding effect of ethanol and ethanol-drinking behaviors after a period of abstinence.

Nucleus accumbens-derived glial cell line-derived neurotrophic factor is a retrograde enhancer of dopaminergic tone in the mesocorticolimbic system.

Spontaneous firing of ventral tegmental area (VTA) dopamine (DA) neurons provides ambient levels of DA in target areas such as the nucleus accumbens (NAc) and the prefrontal cortex (PFC). Here we report that the glial cell line-derived neurotrophic factor (GDNF), produced in one target region, the NAc, is retrogradely transported by DA neurons to the VTA where the growth factor positively regulates the spontaneous firing activity of both NAc- and PFC-projecting DA neurons in a mechanism that requires the activation of the mitogen-activated protein kinase (MAPK) pathway. We also show that the consequence of GDNF-mediated activation of the MAPK signaling cascade in the VTA is an increase in DA overflow in the NAc. Together, these results demonstrate that NAc-produced GDNF serves as a retrograde enhancer that upregulates the activity of the mesocorticolimbic DA system.

Cabergoline decreases alcohol drinking and seeking behaviors via glial cell line-derived neurotrophic factor.

BACKGROUND Cabergoline is an ergotamine derivative that increases the expression of glial cell line-derived neurotrophic factor (GDNF) in vitro. We recently showed that GDNF in the ventral tegmental area (VTA) reduces the motivation to consume alcohol. We therefore set out to determine whether cabergoline administration decreases alcohol-drinking and -seeking behaviors via GDNF. METHODS Reverse transcription polymerase chain reaction (RT-PCR) and Enzyme-Linked ImmunoSorbent Assay (ELISA) were used to measure GDNF levels. Western blot analysis was used for phosphorylation experiments. Operant self-administration in rats and a two-bottle choice procedure in mice were used to assess alcohol-drinking behaviors. Instrumental performance tested during extinction was used to measure alcohol-seeking behavior. The [35S]GTPgammaS binding assay was used to assess the expression and function of the dopamine D2 receptor (D2R). RESULTS We found that treatment of the dopaminergic-like cell line SH-SY5Y with cabergoline and systemic administration of cabergoline in rats resulted in an increase in GDNF level and in the activation of the GDNF pathway. Cabergoline treatment decreased alcohol-drinking and -seeking behaviors including relapse, and its action to reduce alcohol consumption was localized to the VTA. Finally, the increase in GDNF expression and the decrease in alcohol consumption by cabergoline were abolished in GDNF heterozygous knockout mice. CONCLUSIONS Together, these findings suggest that cabergoline-mediated upregulation of the GDNF pathway attenuates alcohol-drinking behaviors and relapse. Alcohol abuse and addiction are devastating and costly problems worldwide. This study puts forward the possibility that cabergoline might be an effective treatment for these disorders.

Positive autoregulation of GDNF levels in the ventral tegmental area mediates long-lasting inhibition of excessive alcohol consumption

Glial cell line-derived neurotrophic factor (GDNF) is an essential growth factor for the survival and maintenance of the midbrain dopaminergic (DA-ergic) neurons. Activation of the GDNF pathway in the ventral tegmental area (VTA), where the GDNF receptors are expressed, produces a long-lasting suppression of excessive alcohol consumption in rats. Previous studies conducted in the DA-ergic-like cells, SHSY5Y, revealed that GDNF positively regulates its own expression, leading to a long-lasting activation of the GDNF signaling pathway. Here we determined whether GDNF activates a positive autoregulatory feedback loop in vivo within the VTA, and if so, whether this mechanism underlies the long-lasting suppressive effects of the growth factor on excessive alcohol consumption. We found that a single infusion of recombinant GDNF (rGDNF; 10 μg) into the VTA induces a long-lasting local increase in GDNF mRNA and protein levels, which depends upon de novo transcription and translation of the polypeptide. Importantly, we report that the GDNF-mediated positive autoregulatory feedback loop accounts for the long-lasting inhibitory actions of GDNF in the VTA on excessive alcohol consumption. Specifically, the long-lasting suppressive effects of a single rGDNF infusion into the VTA on excessive alcohol consumption were prevented when protein synthesis was inhibited, as well as when the upregulation of GDNF expression was prevented using short hairpin RNA to focally knock down GDNF mRNA in the VTA. Our results could have implications for the development of long-lasting treatments for disorders in which GDNF has a beneficial role, including drug addiction, chronic stress and Parkinsons disease.

GDNF is a novel ethanol‐responsive gene in the VTA: implications for the development and persistence of excessive drinking

Glial cell line‐derived neurotrophic factor (GDNF) is a potent inhibitor of ethanol consumption and relapse, and GDNF heterozygous knockout mice display increased reward sensitivity to ethanol and consume more ethanol after a period of abstinence than their wild‐type littermates. Here, we tested whether ethanol alters GDNF expression in the ventral tegmental area (VTA; GDNFs site of action) and/or the nucleus accumbens (NAc; the main source of GDNF), and if so, determine the role of the endogenous growth factor in the regulation of ethanol consumption. Systemic administration of ethanol increased GDNF expression and protein levels in the VTA, but not the NAc. Additionally, GDNF levels were elevated after an ethanol‐drinking session in rats that consumed ethanol in the intermittent‐access two‐bottle choice procedure for 1 week, but not 7 weeks. Deprivation following 7 weeks of excessive ethanol intake reduced GDNF levels, while a short ethanol binge drinking period following deprivation upregulated GDNF expression. Importantly, knockdown of GDNF within the VTA using adenovirus expressing short hairpin RNA facilitated the escalation of ethanol drinking by ethanol‐naïve rats, but not by rats with a history of excessive ethanol consumption. These results suggest that during initial ethanol‐drinking experiences, GDNF in the VTA is increased and protects against the development of excessive ethanol intake. However, the growth factors protective response to ethanol breaks down after protracted excessive ethanol intake and withdrawal, resulting in persistent, excessive ethanol consumption.

Glial cell line-derived neurotrophic factor (GDNF) is an endogenous protector in the mesolimbic system against excessive alcohol consumption and relapse.

Moderate social consumption of alcohol is common; however, only a small percentage of individuals transit from social to excessive, uncontrolled alcohol drinking. This suggests the existence of protective mechanisms that prevent the development of alcohol addiction. Here, we tested the hypothesis that the glial cell line‐derived neurotrophic factor (GDNF) in the mesolimbic system [e.g. the nucleus accumbens (Acb) and ventral tegmental area (VTA)] is part of such a mechanism. We found that GDNF knockdown, by infecting rat Acb neurons with a small hairpin RNA (shRNA) targeting the GDNF gene, produced a rapid escalation to excessive alcohol consumption and enhanced relapse to alcohol drinking. Conversely, viral‐mediated overexpression of the growth factor in the mesolimbic system blocked the escalation from moderate to excessive alcohol drinking. To access the mechanism underlying GDNFs actions, we measured the firing rate of dopaminergic (DAergic) neurons in the VTA after a history of excessive alcohol intake with or without elevating GDNF levels. We found that the spontaneous firing rate of DAergic neurons in the VTA was reduced during alcohol withdrawal and that GDNF reversed this alcohol‐induced DA deficiency. Together, our results suggest that endogenous GDNF in the mesolimbic system controls the transition from moderate to excessive alcohol drinking and relapse via reversal of alcohol‐dependent neuro‐adaptations in DAergic VTA neurons.

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.

From Signaling Pathways to Behavior: The Light and Dark Sides of Alcohol

Abstract Understanding the mechanism of action of drugs of abuse, including alcohol, is central for the development of treatments for addiction. Most drugs of abuse possess very specific modes of action, that is, binding to discrete receptors in certain subsets of neurons to precipitate a singular, defined effect. Alcohol, on the other hand, exerts a multitude of effects on various receptors and signaling pathways. As a result, instead of discovering a simple mode of action, exploration into alcohol’s biological influence has unveiled an intriguing dichotomy in this drug’s effects. Although some signaling pathways altered by alcohol underlie the adverse phenotypes associated with alcohol-use disorders (what we term the “dark side” of alcohol), others serve to protect and/or delay the development of alcohol-abuse disorders (what we term the “light side” of alcohol). A better understanding of these opposing forces and the implied balancing act between them is a much-needed step towards an effective treatment for alcohol-use disorders. Because alcohol’s action on signaling has recently been reviewed in detail, this review focuses on the bridge between the molecular actions of alcohol and behavior. Recently published findings on the acute and long-term molecular adaptations that occur following the exposure of awake, behaving vertebrates and invertebrates to alcohol are described. The signaling cascades described herein are activated in response to alcohol in specific brain regions, resulting in synaptic plasticity events and/or changes in transcription and translation as well as epigenetic modifications that mediate either the dark or light sides of this drug.