Individual Differences in Ethanol Locomotor Sensitization Are Associated with Dopamine D1 Receptor Intra-Cellular Signaling of DARPP-32 in the Nucleus Accumbens

Abstract

In mice there are clear individual differences in the development of behavioral sensitization to ethanol, a progressive potentiation of its psychomotor stimulant effect. Variability in the behavioral responses to ethanol has been associated with alcohol preference. Here we investigated if the functional hyperresponsiveness of D1 receptors observed in ethanol sensitized mice leads to an increased activation of DARPP-32, a central regulatory protein in medium spiny neurons, in the nucleus accumbens - a brain region known to play a role in drug reinforcement. Swiss Webster mice received ethanol (2.2 g/kg/day) or saline i.p. administrations for 21 days and were weekly evaluated regarding their locomotor activity. From those treated with ethanol, the 33% with the highest levels of locomotor activity were classified as “sensitized” and the 33% with the lowest levels as "non-sensitized”. The latter presented similar locomotor levels to those of saline-treated mice. Different subgroups of mice received intra-accumbens administrations of saline and, 48 h later, SKF-38393, D1 receptor agonist 0.1 or 1 µg/side. Indeed, sensitized mice presented functional hyperresponsiveness of D1 receptors in the accumbens. Two weeks following the ethanol treatment, other subgroups received systemic saline or SKF 10 mg/kg, 20 min before the euthanasia. The nucleus accumbens were dissected for the Western Blot analyses of total DARPP-32 and phospho-Thr34-DARPP-32 expression. D1 receptor activation induced higher phospho-Thr34-DARPP-32 expression in sensitized mice than in non-sensitized or saline. The functionally hyperresponsiveness of D1 receptors in the nucleus accumbens is associated with an increased phospho-Thr34-DARPP-32 expression after D1 receptor activation. These data suggest that an enduring increase in the sensitivity of the dopamine D1 receptor intracellular pathway sensitivity represents a neurobiological correlate associated with the development of locomotor sensitization to ethanol.

Impact of Caffeine on Ethanol‐Induced Stimulation and Sensitization: Changes in ERK and DARPP‐32 Phosphorylation in Nucleus Accumbens

“…Thus, it would have been expected that an increase in DA levels induced by EtOH would lead to an increase in pDARPP‐32‐Thr75 in D 2 containing neurons. Consistent with models of striatal function and DA‐related signal transduction, EtOH (1.5 g/kg) in rats has shown to increase phosphorylation of DARPP‐32 at Thr34 in striatum (Nuutinen et al, 2011), and EtOH ‐sensitized mice have shown functional hyperresponsiveness of D 1 receptors in Acb, which induced higher pDARPP‐32(Thr34) in sensitized mice (Abrahao et al, 2014). However, in our study, pDARPP‐32(Thr75) was not affected by EtOH or by the EtOH plus caffeine combination.…”

A Mechanism Linking Two Known Vulnerability Factors for Alcohol Abuse: Heightened Alcohol Stimulation and Low Striatal Dopamine D2 Receptors

“…The protein analysis data show that ethanol exposure mimics exposure to a D1-like agonist in mice lacking D2Rs on medium spiny neurons. Previous work suggests a positive correlation between ethanol-induced stimulation and the sensitivity of D1Rs in the striatal pathway (Abrahao et al, 2014). We speculated that the D1R hypersensitivity in iMSN-Drd2KO mice could be the underlying mechanism driving the enhanced ethanol stimulation and ethanol preference.…”

Sex Differences in the Ventral Tegmental Area and Nucleus Accumbens Proteome at Baseline and Following Nicotine Exposure

“…Nicotine regulates multiple DARPP-32 phosphorylation sites in striatal slices as well as in vivo after nicotine abstinence (Hamada et al, 2004(Hamada et al, , 2005Abdolahi et al, 2010). These studies did not show alterations in total DARPP-32 protein levels, although other drug treatments such as alcohol, methylphenidate, and cocaine can regulate total DARPP-32 protein levels (Lynch et al, 2007;Souza et al, 2009;Abrahao et al, 2014). In the current study DARPP-32 was significantly increased in the VTA of MC vs. FC mice in both mouse strains, and in the NAc of MC vs. FC C3H/HeJ mice.…”