Mia Ericson

Background and Purpose: Nicotine dependence remains one of the leading causes of morbidity and mortality worldwide, with high relapse rates and post‐cessation weight gain representing persistent barriers to sustained abstinence. The incretin hormones glucose‐dependent insulinotropic polypeptide (GIP) and glucagon‐like peptide‐1 (GLP‐1) have emerged as novel treatment targets, as they appear to influence both reward‐related behaviours associated with addictive substances and body weight regulation. Whether recently developed multi‐receptor incretin agonists such as tirzepatide, a long‐acting dual GIP/GLP‐1 receptor agonist, affect nicotine‐induced behaviours remains unstudied. Experimental Approach: We investigated whether tirzepatide affects nicotine‐induced behaviours (locomotor stimulation and expression of locomotor sensitisation, expression and reinstatement of conditioned place preference) and related neurochemistry (in vivo microdialysis and ex vivo tissue neurochemical analysis) in male mice. Key Results: Tirzepatide attenuated nicotine‐induced locomotor stimulation in a dose‐related manner, and reduced nicotine‐induced place preference, and in vivo accumbal dopamine release. Furthermore, tirzepatide suppressed reinstatement of nicotine place preference and prevented the expression of locomotor sensitisation, indicating effects beyond acute reward processing. Ex vivo neurochemical analysis of addiction‐related brain regions in nicotine‐sensitised mice revealed that tirzepatide blocked nicotine‐induced dopamine elevations in the nucleus accumbens, ventral tegmental area and lateral septum. Furthermore, tirzepatide restored levels of multiple neurotransmitter systems, such as GABA, in a brain region‐specific manner, suggesting possible effects beyond dopaminergic signalling alone. Conclusions and Implications: Collectively, these findings indicate that tirzepatide attenuates nicotine‐induced locomotor stimulation and dopamine release, as well as the expression and reinstatement of place preference, and the expression of locomotor sensitisation, in mice.

Background: Glycinergic neurotransmission has been suggested as a tentative pharmacological treatment target for Alcohol Use Disorder (AUD), a devastating brain disease with limited treatment options that involves reduced dopamine (DA) activity in the nucleus Accumbens (nAc) and loss of control of alcohol intake. Glycine receptors (GlyRs) in the nAc, a pivotal part of the brain reward circuitry, are involved in regulating basal and alcohol‐induced accumbal DA levels as well as voluntary alcohol intake in rats. Methods: This study in rats examined if inhibition of the glycine transporter 2 (GlyT‐2, SLC6A5), present within glycinergic synapses, alters (1) accumbal DA and glycine content as measured by in vivo microdialysis coupled to HPLC and (2) the alcohol deprivation effect (ADE) in a two‐bottle‐choice alcohol consumption paradigm. Finally, (3) the presence of GlyT2‐expressing fibers and GlyRs in the nAc was examined by immunohistochemistry (IHC). Results: In brief, the two partial GlyT2‐inhibitors N‐Arachidonyl‐Glycine (NAGly, 10 mg/kg i.p.) and Opiranserin (20 mg/kg i.p.), but not the full GlyT2‐inhibitor Org 25543, slightly elevated accumbal DA levels, while no effects on extrasynaptic glycine levels were observed. The reversible GlyT1‐inhibitor Bitopertin (10 mg/kg p.o.) produced a pronounced glycine and DA elevation but combined GlyT1‐ and GlyT2 inhibition did not yield any statistically significant additive effects. In the alcohol consumption study, NAGly abolished the ADE as compared to placebo treatment. Finally, histology confirmed the presence of GlyT2 and GlyR in the nAc, although with a higher signal for GlyT2 in, for example, septal and basal forebrain regions. Conclusions: Overall, this study indicates that synaptic GlyRs are involved in regulating nAc DA levels and alcohol intake in rats, but probably to a lesser extent than extrasynaptic GlyRs. Further studies that specifically target GlyT2 in, for example, the nAc and septal regions and that utilize refined techniques for measuring synaptic glycine levels are warranted to better characterize the role of glycinergic innervation in the reward circuitry and for regulating alcohol intake.

Background: Alcohol use disorder (AUD) has limited treatment options and glycine receptors (GlyRs) in brain reward regions have emerged as tentative targets for pharmacotherapy. The rationale derives from studies showing that glycine, an endogenous GlyR agonist, alters dopamine (DA) transmission and reduces alcohol intake in rats. This study sought to translate these findings to individuals with AUD by examining whether glycine treatment reduces craving for alcohol and laboratory alcohol intake. Methods: Individuals with AUD were randomized to oral glycine (0.12 g/kg) or placebo treatment for 5 days. Thereafter, 48 participants completed an alcohol challenge including priming for alcohol followed by self‐administration of up to four drinks of 12 g alcohol. Alcohol craving and subjective effects of alcohol were measured throughout the study. Results: Glycine treatment raised serum glycine levels by 125%. Neither alcohol intake nor craving or subjective effects of alcohol differed between treatment groups, except for peak stimulatory effects, which were slightly higher in the glycine‐treated group. The relationships between craving for alcohol or “wanting more” on the Drugs Effects Questionnaire and laboratory alcohol intake were dissociated in the glycine‐treated group. In the full sample, serum glycine levels at baseline were inversely associated with recent drinking history. Conclusion: Glycine treatment does not reduce craving or laboratory alcohol consumption in individuals with AUD per se, but results are equivocal as the association between alcohol‐induced craving or “wanting more” and the ensuing self‐administration of alcohol was abolished in the glycine‐treated group. The inverse association observed between glycine levels at baseline and self‐reported recent drinking could be a consequence of alcohol intake or support a protective role for glycine activity in limiting alcohol intake. Further studies are warranted to delineate how GlyR activity is linked to alcohol consumption in humans and to establish whether targeting this system may constitute a new treatment concept for AUD.

Introduction: Alcohol use disorder (AUD) causes significant morbidity and mortality globally. Ethanol’s rewarding and reinforcing effects are attributed to activation of the mesolimbic dopamine system, increasing accumbal dopamine release. While activation of accumbal glycine receptors (GlyRs) is a prerequisite for ethanol-induced dopamine signaling, multiple transmitter systems may be involved; recent research implicates the GABA-rho receptor as a prominent target. Considering the structural and functional similarities between GlyRs and GABA-rho receptors, this study aimed to define the role of GlyRs and GABA-rho receptors in regulating baseline dopamine signalling and ethanol-induced elevation of extracellular dopamine and GlyR agonists, as well as to determine their involvement in the action of the ethanol relapse-preventing drug acamprosate. Methods: To investigate this, in vivo microdialysis was conducted in male Wistar rats. Results and discussion: Local perfusion with either the GABA-rho receptor antagonist TPMPA or the GlyR antagonist strychnine prior to ethanol administration significantly reduced the ethanol-induced increase in dopamine levels. These findings suggest that both GlyRs and GABA-rho receptors are involved in mediating the dopamine-elevating effect of ethanol. In addition, a significant attenuation of the ethanol-induced glycine and taurine elevation was observed following both pretreatment with TPMPA and strychnine, whilst only GlyR blockade inhibited the acamprosate-induced increase of dopamine. Unlike strychnine, TPMPA alone did not alter dopamine levels, suggesting that GABA-rho receptors display features that distinguish them from GlyR. In conclusion, GABA-rho receptors regulate ethanol-induced dopamine and glycine/taurine levels within the nAc without affecting basal dopamine neurotransmission, suggesting their potential as a pharmacological target for the treatment of AUD.

Alcohol use disorder (AUD) is a relapsing brain disorder involving major neurobiological changes. Upon alcohol exposure, dopamine (DA) levels increase in the nucleus accumbens (nAc), a key region of the mesolimbic DA system involved in reward and reinforcement. A concomitant increase in extracellular taurine within the nAc has been shown to be important for the alcohol-induced DA increase. Sex differences in alcohol consumption and in the development of AUD have previously been shown. However, knowledge regarding sex differences in alcohol-induced DA and concomitant taurine release is limited. The aim of this study was to examine potential sex differences in alcohol-induced increases of extracellular levels of DA and taurine within the nAc, following local and systemic alcohol administration. To this end, in vivo microdialysis was performed using male and female Wistar rats. Following systemic alcohol administration, both male and female rats displayed a significant increase of both DA and taurine within the nAc, with no observed sex differences. In contrast, males displayed a significant increase in both DA and taurine following alcohol administration locally into the nAc whilst female rats displayed a blunted DA response and an attenuated taurine increase. Basal levels of DA or taurine did not differ significantly between males and females. The results presented here suggest that local accumbal mechanisms contribute to a greater extent to the alcohol-induced DA increase in male compared to female rats, whilst the response to systemic alcohol administration is similar between sexes.

Alcohol use disorder is a severe mental health condition causing medical consequences and preterm death. Alcohol activates the mesolimbic dopamine system leading to an increase of extracellular dopamine (DA) in the nucleus accumbens, an event that is associated with the reinforcing effects of alcohol. Cholinergic interneurons (CIN) are important modulators of accumbal DA signalling, and depletion of accumbal CIN attenuates the alcohol‐induced increase in extracellular DA. The aim of this study was to explore the functional role of accumbal CIN in alcohol‐related behaviour. To this end, ablation of CIN was induced by local administration of anticholine acetyltransferase‐saporin bilaterally into the nucleus accumbens of male Wistar rats. Alcohol consumption in ablated and sham‐treated rats was studied using a two‐bottle‐choice intermittent alcohol consumption paradigm. Rats with depleted CIN consumed significantly less alcohol than sham‐treated controls. No differences in sucrose preference, motor activity, water intake or weight gain were noted between treatment groups, suggesting that the ablation selectively affected alcohol‐related behaviour. In conclusion, this study further supports a role for accumbal CIN in regulating alcohol‐consummatory behaviour.

Astrocytes are pivotal for synaptic transmission and may also play a role in the induction and expression of synaptic plasticity, including endocannabinoid-mediated long-term depression (eCB-LTD). In the dorsolateral striatum (DLS), eCB signaling plays a major role in balancing excitation and inhibition and promoting habitual learning. The aim of this study was to outline the role of astrocytes in regulating eCB signaling in the DLS. To this end, we employed electrophysiological slice recordings combined with metabolic, chemogenetic and pharmacological approaches in an attempt to selectively suppress astrocyte function. High-frequency stimulation induced eCB-mediated LTD (HFS-LTD) in brain slices from both male and female rats. The metabolic uncoupler fluorocitrate (FC) reduced the probability of transmitter release and depressed synaptic output in a manner that was independent on cannabinoid 1 receptor (CB1R) activation. Fluorocitrate did not affect the LTD induced by the CB1R agonist WIN55,212-2, but enhanced CB1R-dependent HFS-LTD. Reduced neurotransmission and facilitated HFS-LTD were also observed during chemogenetic manipulation using Gi-coupled DREADDs targeting glial fibrillary acidic protein (GFAP)-expressing cells, during the pharmacological inhibition of connexins using carbenoxolone disodium, or during astrocytic glutamate uptake using TFB-TBOA. While pretreatment with the N-methyl-D-aspartate (NMDA) receptor antagonist 2-amino-5-phosphonopentanoic acid (APV) failed to prevent synaptic depression induced by FC, it blocked the facilitation of HFS-LTD. While the lack of tools to disentangle astrocytes from neurons is a major limitation of this study, our data collectively support a role for astrocytes in modulating basal neurotransmission and eCB-mediated synaptic plasticity.