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

Abstract

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 Parkinson’s disease.

Intermittent ethanol access schedule in rats as a preclinical model of alcohol abuse

“…The placement of the ethanol bottle is alternated each drinking session to control for side preferences. Drinking sessions can begin during the light cycle (Barak, Ahmadiantehrani, Kharazia, & Ron, 2011; Barak, Carnicella, Yowell, & Ron, 2011; Carnicella, Amamoto, et al, 2009; Carnicella et al, 2008) or the dark cycle (Li, Bian, Dave, & Ye, 2011; Simms et al, 2008). Fluid intake is recorded at various time points, usually 30–60 min and 24 h after the beginning of the session.…”

From Signaling Pathways to Behavior

“…It should be noted however, that although the responsiveness of the GDNF gene to alcohol is altered after chronic excessive drinking, the pathway itself appears to be unperturbed. The likelihood of this possibility is supported by the fact that infusion of exogenous GDNF protein into the VTA of chronically drinking rats causes a reliable and rapid decrease in both operant selfadministration (Barak, Carnicella, et al, 2011;Carnicella et al, 2008) and voluntary consumption of alcohol (Barak, Ahmadiantehrani, et al, 2011;Carnicella, Amamonto, et al, 2009). Interestingly, studies in humans have reported significantly reduced BDNF (Joe et al, 2007) and GDNF (Heberlein et al, 2010) levels in the blood serum of alcohol-dependent subjects, strongly corroborating the idea that the dysregulation of these protective signaling proteins is an evolutionarily conserved neuroadaptation to long-term, repeated cycles of excessive drinking and withdrawal.…”

“…In a series of recent studies, we found that the GDNF-mediated signaling pathway in the VTA is a potent negative regulator of excessive alcohol consumption and reinforcement. Specifically, infusion of the growth factor into the rat VTA, a region in which the GDNF receptors Ret and GFR1 are expressed, induced a rapid and robust activation of ERK1/2 and a corresponding decrease of excessive alcohol in a 2BC model of voluntary excessive drinking and operant self-administration (Barak, Ahmadiantehrani, Kharazia, & Ron, 2011;Carnicella, Kharazia, Jeanblanc, Janak, & Ron, 2008;. Furthermore, GDNF also blocked relapse to alcohol seeking (Carnicella et al, 2008) as well as acquisition and expression of conditioned place preference (CPP) for alcohol .…”

Opportunities for the Development of Neuroimmune Therapies in Addiction

“…Glial cell line-derived neurotrophic factor (GDNF) is a protein that is essential for the maintenance and survival of dopamine (DA) neurons (Boger et al, 2006) and can inhibit microglial activation (Rocha, Cristovão, Campos, Fonseca, & Baltazar, 2012). Additionally, preclinical evidence suggests that infusion of GDNF into the ventral tegmental area (VTA) blocks the acquisition and expression of alcohol-induced conditioned place preference (Barak, Ahmadiantehrani, Kharazia, & Ron, 2011;Barak, Carnicella, Yowell, & Ron, 2011), rapidly reduces alcohol intake (Carnicella, Ahmadiantehrani, Janak, & Ron, 2009, Carnicella, Amamoto, & Ron, 2009Carnicella, Kharazia, Jeanblanc, Janak, & Ron, 2008), and blocks alcohol reinstatement following extinction (Carnicella et al, 2008). Furthermore, endogenous levels of GDNF have been found to negatively regulate the rewarding effect of alcohol after a period of abstinence (Carnicella, Ahmadiantehrani, et al, 2009;Carnicella, Amamoto, et al, 2009).…”

“…In one human study, GDNF serum levels measured peripherally were found to be significantly reduced in alcohol-dependent patients versus healthy controls and to be negatively associated with measures of tolerance and withdrawal (Heberlein et al, 2010). It has been hypothesized that GDNF functions to reduce these alcohol-related behaviors in animal models by reversing an alcohol-induced allostatic DA deficiency in the mesolimbic system caused by prolonged excessive alcohol consumption and repeated withdrawal (Barak, Ahmadiantehrani, et al, 2011;Barak, Carnicella, et al, 2011). Furthermore, there is evidence that pharmacological inhibition of phosphodiesterase-4 (PDE4), an enzyme that hydrolyses cyclic adenosine monophosphate (cAMP), decreases alcohol intake in mice (Hu et al, 2011) and rat (Wen et al, 2012) models of alcoholism, as well as reduces neuroinflammation and neuronal death in rats .…”