cAMP-Fyn signaling in the dorsomedial striatum direct pathway drives excessive alcohol use

Fyn kinase in the dorsomedial striatum (DMS) of rodents plays a central role in mechanisms underlying excessive alcohol intake. The DMS is comprised of medium spiny neurons (MSNs) that project directly (dMSNs) or indirectly (iMSNs) to the substantia nigra. Here, we examined the cell-type specificity of Fyn's actions in alcohol use. First, we knocked down Fyn selectively in DMS dMSNs or iMSNs of mice and measured the level of alcohol consumption. We found that downregulation of Fyn in dMSNs, but not in iMSNs, reduces excessive alcohol but not saccharin intake. D1Rs are coupled to Gαs/olf, which activate cAMP signaling. To examine whether Fyn's actions are mediated through cAMP signaling, DMS dMSNs were infected with GαsDREADD, and the activation of Fyn signaling was measured following CNO treatment. We found that remote stimulation of cAMP signaling in DMS dMSNs activates Fyn and promotes the phosphorylation of the Fyn substrate, GluN2B. In contract, remote activation of GαsDREADD in DLS dMSNs did not alter Fyn signaling. We then tested whether activation of GαsDREADD in DMS dMSNs or iMSNs alters alcohol intake and observed that CNO-dependent activation of GαsDREADD in DMS dMSNs but not iMSNs increases alcohol but not saccharin intake. Finally, we examined the contribution of Fyn to GαsDREADD-dependent increase in alcohol intake, and found that systemic administration of the Fyn inhibitor, AZD0503 blocks GαsDREADD-dependent increase in alcohol consumption. Our results suggest that the cAMP-Fyn axis in the DMS dMSNs is a molecular transducer of mechanisms underlying the development of excessive alcohol consumption.

Genetic inhibition of neurotransmission reveals role of glutamatergic input to dopamine neurons in high-effort behavior

Midbrain dopamine neurons are crucial for many behavioral and cognitive functions. As the major excitatory input, glutamatergic afferents are important for control of the activity and plasticity of dopamine neurons. However, the role of glutamatergic input as a whole onto dopamine neurons remains unclear. Here we developed a mouse line in which glutamatergic inputs onto dopamine neurons are specifically impaired, and utilized this genetic model to directly test the role of glutamatergic inputs in dopamine-related functions. We found that while motor coordination and reward learning were largely unchanged, these animals showed prominent deficits in effort-related behavioral tasks. These results provide genetic evidence that glutamatergic transmission onto dopaminergic neurons underlies incentive motivation, a willingness to exert high levels of effort to obtain reinforcers, and have important implications for understanding the normal function of the midbrain dopamine system.

Correction: Genetic inhibition of neurotransmission reveals role of glutamatergic input to dopamine neurons in high-effort behavior

In Figure 1e and f, "F4 control" should be "Cre/tdTomato" and "F4Cre KO" should be "F4Cre/tdTomato". In addition, in the Figure1f legend, the first sentence should end with "(Cre/tdTomato: n = 10, F4Cre/tdTomato: n = 14)".In the 'Materials and Methods' section, under 'Electrophysiology,' the n values for evoked action potential recordings were omitted. The sentence 'For high-frequency stimulus-induced action potentials, the stimulus electrode was placed in the rostral part of VTA and a train of 100 Hz stimuli (1 s) was applied' should end with '(Cre/tdTomato: n=10, F4Cre/tdTomato: n=14).'Later in the same paragraph, in 'For recording evoked EPSCs (Cre/tdTomato, n=13, F4Cre/tdTomato, n=15; AMPA EPSCs were recorded at -70  mV and NMDA EPSCs were recorded at +40 mV)', the phrase 'Cre/tdTomato, n=13, F4Cre/tdTomato, n=15' should be deleted; those n values should have appeared at the end of the later sentence beginning 'Miniature ESPCs...'. The complete, corrected sentence is 'Miniature EPSCs (mEPSCs) were acquired in the presence of 0.5-1 μM TTX and 100 μM picrotoxin and semiautomatically detected by offline analysis using in-house software in Igor Pro (Wavemetrics, Portland, OR, USA) (Cre/tdTomato, n=13, F4Cre/tdTomato, n=15).'Finally, in the 'Materials and Methods' section, third sentence under 'Immunohistochemistry,' information for one TH antibody was omitted. The list of antibodies should end with 'or Millipore MAB5280, 1:1000-1:2000.'

Prosapip1-Dependent Synaptic Adaptations in the Nucleus Accumbens Drive Alcohol Intake, Seeking, and Reward

The mammalian target of rapamycin complex 1 (mTORC1), a transducer of local dendritic translation, participates in learning and memory processes as well as in mechanisms underlying alcohol-drinking behaviors. Using an unbiased RNA-seq approach, we identified Prosapip1 as a novel downstream target of mTORC1 whose translation and consequent synaptic protein expression are increased in the nucleus accumbens (NAc) of mice excessively consuming alcohol. We demonstrate that alcohol-dependent increases in Prosapip1 levels promote the formation of actin filaments, leading to changes in dendritic spine morphology of NAc medium spiny neurons (MSNs). We further demonstrate that Prosapip1 is required for alcohol-dependent synaptic localization of GluA2 lacking AMPA receptors in NAc shell MSNs. Finally, we present data implicating Prosapip1 in mechanisms underlying alcohol self-administration and reward. Together, these data suggest that Prosapip1 in the NAc is a molecular transducer of structural and synaptic alterations that drive and/or maintain excessive alcohol use.

Loss of feedback inhibition via D2 autoreceptors enhances acquisition of cocaine taking and reactivity to drug-paired cues

A prominent aspect of drug addiction is the ability of drug-associated cues to elicit craving and facilitate relapse. Understanding the factors that regulate cue reactivity will be vital for improving treatment of addictive disorders. Low availability of dopamine (DA) D2 receptors (D2Rs) in the striatum is associated with high cocaine intake and compulsive use. However, the role of D2Rs of nonstriatal origin in cocaine seeking and taking behavior and cue reactivity is less understood and possibly underestimated. D2Rs expressed by midbrain DA neurons function as autoreceptors, exerting inhibitory feedback on DA synthesis and release. Here, we show that selective loss of D2 autoreceptors impairs the feedback inhibition of DA release and amplifies the effect of cocaine on DA transmission in the nucleus accumbens (NAc) in vitro. Mice lacking D2 autoreceptors acquire a cued-operant self-administration task for cocaine faster than littermate control mice but acquire similarly for a natural reward. Furthermore, although mice lacking D2 autoreceptors were able to extinguish self-administration behavior in the absence of cocaine and paired cues, they exhibited perseverative responding when cocaine-paired cues were present. This enhanced cue reactivity was selective for cocaine and was not seen during extinction of sucrose self-administration. We conclude that low levels of D2 autoreceptors enhance the salience of cocaine-paired cues and can contribute to the vulnerability for cocaine use and relapse.

Hippocampal infection with HSV-1-derived vectors expressing an NMDAR1 antisense modifies behavior

Herpes simplex virus-derived amplicon vectors simultaneously expressing the open reading frame encoding NR1 subunit of the NMDA receptor, either in sense or antisense orientation, as well as the open reading frame encoding the green fluorescent protein (GFP), as distinct transcription units, were constructed. Vector expression in cells was demonstrated by GFP-fluorescence, immunofluorescence, Western blots and RT-PCR. The vectors were inoculated into the dorsal hippocampus of adult male rats, which were then trained for habituation to an open field and for inhibitory avoidance to a foot-shock. Those animals injected with vectors expressing NR1 protein showed habituation to a new environment, and achieved the criteria for a step-down inhibitory avoidance to a foot-shock. In contrast, animals injected with vectors carrying the NR1 open reading frame in antisense position, showed neither habituation nor appropriate performance in the inhibitory avoidance task. There was no evidence for motor impairment or motivational disturbance, since all the animals exhibit similar behavior and performance in the training sessions. Hence, the impaired performance might be due to either amnesia or disability to record events. Transgene expression in brain, as revealed by GFP fluorescence, was mainly observed in pyramidal cells of CA1, but also in CA3. Therefore, our results strongly support the participation of hippocampal NR1 subunit in habituation to a new environment, but also in recording events for the inhibitory avoidance task. Hence, amplicon vectors appear to be useful tools to modify endogenous gene expression at a defined period, in restricted brain regions, and should allow investigating in vivo functions of genes.

Gene transfer of NMDAR1 subunit sequences to the rat CNS using herpes simplex virus vectors interfered with habituation

1. The aim is to study some roles of the hippocampal NMDA receptor, by modifying the expression of the essential NR1 subunit, with temporal and spatial restrictions in the central nervous system (CNS) of the rat. 2. Due to their neurotropism and the size of inserts they can accomodate, herpes simplex virus type-1 (HSV-1) derived amplicon vectors were used to transfer sequences, either in sense (+) or antisense (-) orientations, of the NR1 subunit gene, or of the green fluorescent protein (GFP) gene, into the CNS. 3. Vector expression in cell lines was followed by GFP autofluorescence, immunofluorescence and western blot. 4. The vectors were inoculated into the dorsal hippocampus of adult male Wistar rats, which were evaluated for habituation to an open field, and then, for expression of the transgenes, by autofluorescence and western blot; the expression mainly happened in pyramidal cells of CA1. 5. The animals injected with vectors carrying the NR1(+) transgene showed habituation to the new environment, as also happened with rats injected with vectors carrying only the GFP transgene. 6. In contrast, animals injected with vectors carrying NR1(-) sequence, did not show habituation. This might be retrograde amnesia or disability to record the trace, suggesting that the NR1 subunit in the dorsal hippocampus, is involved in habituation to a new environment. 7. HSV-1 derived amplicon vectors appear to be useful tools to modify endogenous gene expression, at a defined period, in restricted regions of the CNS.