Rapid Synaptogenesis in the Nucleus Accumbens Is Induced by a Single Cocaine Administration and Stabilized by Mitogen-Activated Protein Kinase Interacting Kinase-1 Activity

Wireless optogenetic stimulation on the prelimbic to the nucleus accumbens core circuit attenuates cocaine-induced behavioral sensitization

Behavioral sensitization is defined as the heightened and persistent behavioral response to repeated drug exposure as a manifestation of drug craving. Psychomotor stimulants such as cocaine can induce strong behavioral sensitization. In this study, we explored the effects of optogenetic stimulation of the prelimbic (PL) to the nucleus accumbnes (NAc) core on the expression of cocaine-induced behavioral sensitization. Using wireless optogenetics, we selectively stimulated the PL-NAc core circuit, and assessed the effects of this treatment on cocaine-induced locomotor activity and accompanying changes in neuronal activation and dendritic spine density. Our findings revealed that optogenetic stimulation of the PL-NAc core circuit effectively suppressed the cocaine-induced locomotor sensitization, accompanied by a reduction in c-Fos expression within the NAc core. Moreover, optogenetic stimulation led to reduction in dendritic spine density, particularly thin and mushroom spine densities, in the NAc core. This study demonstrates that cocaine-induced locomotor sensitization can be regulated by optogenetic stimulation of the PL-NAc core circuit, providing insights into the crucial role of this circuit in psychomotor stimulant addiction.

Astrocytic HIV-1 Nef expression decreases glutamate transporter expression in the nucleus accumbens and increases cocaine-seeking behavior in rats

Cocaine use disorder is an intersecting issue in populations with HIV-1, further exacerbating the clinical course of the disease, contributing to neurotoxicity and neuroinflammation. Cocaine and HIV neurotoxins play roles in neuronal damage during neuroHIV progression by disrupting glutamate homeostasis in the brain. Even with cART, HIV-1 Nef, an early viral protein expressed in approximately 1% of infected astrocytes, remains a key neurotoxin. This study investigates the relationship that exists between Nef, glutamate homeostasis, and cocaine in the NAc, a critical brain region associated with drug motivation and reward. Using a rat model, we compared the effects of astrocytic Nef and cocaine by molecular analysis of glutamate transporters in the NAc. We further conducted behavioral assessments for cocaine self-administration to evaluate cocaine-seeking behavior. Our findings indicate that both cocaine and Nef independently decrease the expression of the glutamate transporter GLT-1 in the NAc. Additionally, rats with astrocytic Nef expression exhibited increased cocaine-seeking behavior but demonstrated sex dependent molecular differences after behavioral paradigm. In conclusion, our results suggest the expression of Nef intensifies cocaine-induced alterations in glutamate homeostasis in the NAc, potentially underlying increased cocaine-seeking. Understanding these interactions better may inform therapeutic strategies for managing cocaine use disorder in HIV-infected individuals.

Sex-Specific ADNP/NAP (Davunetide) Regulation of Cocaine-Induced Plasticity

Cocaine use disorder (CUD) is a chronic neuropsychiatric disorder estimated to effect 1-3% of the population. Activity-dependent neuroprotective protein (ADNP) is essential for brain development and functioning, shown to be protective in fetal alcohol syndrome and to regulate alcohol consumption in adult mice. The goal of this study was to characterize the role of ADNP, and its active peptide NAP (NAPVSIPQ), which is also known as davunetide (investigational drug) in mediating cocaine-induced neuroadaptations. Real time PCR was used to test levels of Adnp and Adnp2 in the nucleus accumbens (NAc), ventral tegmental area (VTA), and dorsal hippocampus (DH) of cocaine-treated mice (15 mg/kg). Adnp heterozygous (Adnp +/-)and wild-type (Adnp +/-) mice were further tagged with excitatory neuronal membrane-expressing green fluorescent protein (GFP) that allowed for in vivo synaptic quantification. The mice were treated with cocaine (5 injections; 15 mg/kg once every other day) with or without NAP daily injections (0.4 µg/0.1 ml) and sacrificed following the last treatment. We analyzed hippocampal CA1 pyramidal cells from 3D confocal images using the Imaris x64.8.1.2 (Oxford Instruments) software to measure changes in dendritic spine density and morphology. In silico ADNP/NAP/cocaine structural modeling was performed as before. Cocaine decreased Adnp and Adnp2 expression 2 h after injection in the NAc and VTA of male mice, with mRNA levels returning to baseline levels after 24 h. Cocaine further reduced hippocampal spine density, particularly synaptically weaker immature thin and stubby spines, in male Adnp+/+) mice while increasing synaptically stronger mature (mushroom) spines in Adnp+/-) male mice and thin and stubby spines in females. Lastly, we showed that cocaine interacts with ADNP on a zinc finger domain identical to ketamine and adjacent to a NAP-zinc finger interaction site. Our results implicate ADNP in cocaine abuse, further placing the ADNP gene as a key regulator in neuropsychiatric disorders. Ketamine/cocaine and NAP treatment may be interchangeable to some degree, implicating an interaction with adjacent zinc finger motifs on ADNP and suggestive of a potential sex-dependent, non-addictive NAP treatment for CUD.

Substance use and spine density: a systematic review and meta-analysis of preclinical studies

The elucidation of synaptic density changes provides valuable insights into the underlying brain mechanisms of substance use. In preclinical studies, synaptic density markers, like spine density, are altered by substances of abuse (e.g., alcohol, amphetamine, cannabis, cocaine, opioids, nicotine). These changes could be linked to phenomena including behavioral sensitization and drug self-administration in rodents. However, studies have produced heterogeneous results for spine density across substances and brain regions. Identifying patterns will inform translational studies given tools that now exist to measure in vivo synaptic density in humans. We performed a meta-analysis of preclinical studies to identify consistent findings across studies. PubMed, ScienceDirect, Scopus, and EBSCO were searched between September 2022 and September 2023, based on a protocol (PROSPERO: CRD42022354006). We screened 6083 publications and included 70 for meta-analysis. The meta-analysis revealed drug-specific patterns in spine density changes. Hippocampal spine density increased after amphetamine. Amphetamine, cocaine, and nicotine increased spine density in the nucleus accumbens. Alcohol and amphetamine increased, and cannabis reduced, spine density in the prefrontal cortex. There was no convergence of findings for morphine's effects. The effects of cocaine on the prefrontal cortex presented contrasting results compared to human studies, warranting further investigation. Publication bias was small for alcohol or morphine and substantial for the other substances. Heterogeneity was moderate-to-high across all substances. Nonetheless, these findings inform current translational efforts examining spine density in humans with substance use disorders.

BDNF/TrkB pathway activation in D1 receptor-expressing striatal projection neurons plays a protective role against L-DOPA-induced dyskinesia

L-DOPA-induced dyskinesia (LID) is a frequent adverse side effect of L-DOPA treatment in Parkinson's disease (PD). Understanding the mechanisms underlying the development of these motor disorders is needed to reduce or prevent them. We investigated the role of TrkB receptor in LID, in hemiparkinsonian mice treated by chronic L-DOPA administration. Repeated L-DOPA treatment for 10 days specifically increased full-length TrkB receptor mRNA and protein levels in the dopamine-depleted dorsal striatum (DS) compared to the contralateral non-lesioned DS or to the DS of sham-operated animals. Dopamine depletion alone or acute L-DOPA treatment did not significantly increase TrkB protein levels. In addition to increasing TrkB protein levels, chronic L-DOPA treatment activated the TrkB receptor as evidenced by its increased tyrosine phosphorylation. Using specific agonists for the D1 or D2 receptors, we found that TrkB increase is D1 receptor-dependent. To determine the consequences of these effects, the TrkB gene was selectively deleted in striatal neurons expressing the D1 receptor. Mice with TrkB floxed gene were injected with Cre-expressing adeno-associated viruses or crossed with Drd1-Cre transgenic mice. After unilateral lesion of dopamine neurons in these mice, we found an aggravation of axial LID compared to the control groups. In contrast, no change was found when TrkB deletion was induced in the indirect pathway D2 receptor-expressing neurons. Our study suggests that BDNF/TrkB signaling plays a protective role against the development of LID and that agonists specifically activating TrkB could reduce the severity of LID.

Distinctive properties of biological neural networks and recent advances in bottom-up approaches toward a better biologically plausible neural network

Although it may appear infeasible and impractical, building artificial intelligence (AI) using a bottom-up approach based on the understanding of neuroscience is straightforward. The lack of a generalized governing principle for biological neural networks (BNNs) forces us to address this problem by converting piecemeal information on the diverse features of neurons, synapses, and neural circuits into AI. In this review, we described recent attempts to build a biologically plausible neural network by following neuroscientifically similar strategies of neural network optimization or by implanting the outcome of the optimization, such as the properties of single computational units and the characteristics of the network architecture. In addition, we proposed a formalism of the relationship between the set of objectives that neural networks attempt to achieve, and neural network classes categorized by how closely their architectural features resemble those of BNN. This formalism is expected to define the potential roles of top-down and bottom-up approaches for building a biologically plausible neural network and offer a map helping the navigation of the gap between neuroscience and AI engineering.

Effects of acid-sensing ion channel-1A (ASIC1A) on cocaine-induced synaptic adaptations

Chronic drug abuse is thought to induce synaptic changes in nucleus accumbens medium spiny neurons (MSNs) that promote subsequent craving and drug-seeking behavior. Accumulating data suggest acid-sensing ion channels (ASICs) may play a critical role. In drug naïve mice, disrupting the ASIC1A subunit produced a variety of synaptic changes reminiscent of wild-type mice following cocaine withdrawal, including increased AMPAR/NMDAR ratio, increased AMPAR rectification, and increased dendrite spine density. Importantly, these changes in Asic1a -/- mice were normalized by a single dose of cocaine. Here we sought to understand the temporal effects of cocaine exposure in Asic1a -/- mice and the cellular site of ASIC1A action. Six hours after cocaine exposure, there was no effect. However, 15 h, 24 h and 4 days after cocaine exposure there was a significant reduction in AMPAR/NMDAR ratio in Asic1a -/- mice. Within 7 days the AMPAR/NMDAR ratio had returned to baseline levels. Cocaine-evoked changes in AMPAR rectification and dendritic spine density followed a similar time course with significant reductions in rectification and dendritic spines 24 h after cocaine exposure in Asic1a -/- mice. To test the cellular site of ASIC1A action on these responses, we disrupted ASIC1A specifically in a subpopulation of MSNs. We found that effects of ASIC1A disruption were cell autonomous and restricted to neurons in which the channels are disrupted. We further tested whether ASIC1A disruption differentially affects MSNs subtypes and found AMPAR/NMDAR ratio was elevated in dopamine receptor 1-expressing MSNs, suggesting a preferential effect for these cells. Finally, we tested if protein synthesis was involved in synaptic adaptations that occurred after ASIC1A disruption, and found the protein synthesis inhibitor anisomycin normalized AMPAR-rectification and AMPAR/NMDAR ratio in drug-naïve Asic1a -/- mice to control levels, observed in wild-type mice. Together, these results provide valuable mechanistic insight into the effects of ASICs on synaptic plasticity and drug-induced effects and raise the possibility that ASIC1A might be therapeutically manipulated to oppose drug-induced synaptic changes and behavior.

Dendritic Spines in Learning and Memory: From First Discoveries to Current Insights

The central nervous system is composed of neural ensembles, and their activity patterns are neural correlates of cognitive functions. Those ensembles are networks of neurons connected to each other by synapses. Most neurons integrate synaptic signal through a remarkable subcellular structure called spine. Dendritic spines are protrusions whose diverse shapes make them appear as a specific neuronal compartment, and they have been the focus of studies for more than a century. Soon after their first description by Ramón y Cajal, it has been hypothesized that spine morphological changes could modify neuronal connectivity and sustain cognitive abilities. Later studies demonstrated that changes in spine density and morphology occurred in experience-dependent plasticity during development, and in clinical cases of mental retardation. This gave ground for the assumption that dendritic spines are the particular locus of cerebral plasticity. With the discovery of synaptic long-term potentiation, a research program emerged with the aim to establish whether dendritic spine plasticity could explain learning and memory. The development of live imaging methods revealed on the one hand that dendritic spine remodeling is compatible with learning process and, on the other hand, that their long-term stability is compatible with lifelong memories. Furthermore, the study of the mechanisms of spine growth and maintenance shed new light on the rules of plasticity. In behavioral paradigms of memory, spine formation or elimination and morphological changes were found to correlate with learning. In a last critical step, recent experiments have provided evidence that dendritic spines play a causal role in learning and memory.

A functional eEF2K-eEF2 pathway in the NAc is critical for the expression of cocaine-induced psychomotor sensitisation and conditioned place preference

Recent evidence links synaptic plasticity and mRNA translation, via the eukaryotic elongation factor 2 kinase (eEF2K) and its only known substrate, eEF2. However, the involvement of the eEF2 pathway in cocaine-induced neuroadaptations and cocaine-induced behaviours is not known. Knock-in (KI) mice and shRNA were used to globally and specifically reduce eEF2K expression. Cocaine psychomotor sensitization and conditioned place preference were used to evaluate behavioural outcome. Changes in eEF2 phosphorylation were determined by western blot analyses. No effect was observed on the AMPA/NMDA receptor current ratio in the ventral tegmental area, 24 h after cocaine injection in eEF2K-KI mice compared with WT. However, development and expression of cocaine psychomotor sensitization were decreased in KI mice. Phosphorylated eEF2 was decreased one day after psychomotor sensitization and returned to baseline at seven days in the nucleus accumbens (NAc) of WT mice, but not in eEF2K-KI mice. However, one day following cocaine challenge, phosphorylated eEF2 decreased in WT but not KI mice. Importantly, specific targeting of eEF2K expression by shRNA in the NAc decreased cocaine condition place preference. These results suggest that the eEF2 pathway play a role in cocaine-induced locomotor sensitization and conditioned place preference.

Cell-Type-Specific Adaptions in Striatal Medium-Sized Spiny Neurons and Their Roles in Behavioral Responses to Drugs of Abuse

Drug addiction is defined as a compulsive pattern of drug-seeking- and taking- behavior, with recurrent episodes of abstinence and relapse, and a loss of control despite negative consequences. Addictive drugs promote reinforcement by increasing dopamine in the mesocorticolimbic system, which alters excitatory glutamate transmission within the reward circuitry, thereby hijacking reward processing. Within the reward circuitry, the striatum is a key target structure of drugs of abuse since it is at the crossroad of converging glutamate inputs from limbic, thalamic and cortical regions, encoding components of drug-associated stimuli and environment, and dopamine that mediates reward prediction error and incentive values. These signals are integrated by medium-sized spiny neurons (MSN), which receive glutamate and dopamine axons converging onto their dendritic spines. MSN primarily form two mostly distinct populations based on the expression of either DA-D1 (D1R) or DA-D2 (D2R) receptors. While a classical view is that the two MSN populations act in parallel, playing antagonistic functional roles, the picture seems much more complex. Herein, we review recent studies, based on the use of cell-type-specific manipulations, demonstrating that dopamine differentially modulates dendritic spine density and synapse formation, as well as glutamate transmission, at specific inputs projecting onto D1R-MSN and D2R-MSN to shape persistent pathological behavioral in response to drugs of abuse. We also discuss the identification of distinct molecular events underlying the detrimental interplay between dopamine and glutamate signaling in D1R-MSN and D2R-MSN and highlight the relevance of such cell-type-specific molecular studies for the development of innovative strategies with potential therapeutic value for addiction. Because drug addiction is highly prevalent in patients with other psychiatric disorders when compared to the general population, we last discuss the hypothesis that shared cellular and molecular adaptations within common circuits could explain the co-occurrence of addiction and depression. We will therefore conclude this review by examining how the nucleus accumbens (NAc) could constitute a key interface between addiction and depression.

Cell-type- and region-specific modulation of cocaine seeking by micro-RNA-1 in striatal projection neurons

The persistent and experience-dependent nature of drug addiction may result in part from epigenetic alterations, including non-coding micro-RNAs (miRNAs), which are both critical for neuronal function and modulated by cocaine in the striatum. Two major striatal cell populations, the striato-nigral and striato-pallidal projection neurons, express, respectively, the D1 (D1-SPNs) and D2 (D2-SPNs) dopamine receptor, and display distinct but complementary functions in drug-evoked responses. However, a cell-type-specific role for miRNAs action has yet to be clarified. Here, we evaluated the expression of a subset of miRNAs proposed to modulate cocaine effects in the nucleus accumbens (NAc) and dorsal striatum (DS) upon sustained cocaine exposure in mice and showed that these selected miRNAs were preferentially upregulated in the NAc. We focused on miR-1 considering the important role of some of its predicted mRNA targets, Fosb and Npas4, in the effects of cocaine. We validated these targets in vitro and in vivo. We explored the potential of miR-1 to regulate cocaine-induced behavior by overexpressing it in specific striatal cell populations. In DS D1-SPNs miR-1 overexpression downregulated Fosb and Npas4 and reduced cocaine-induced CPP reinstatement, but increased cue-induced cocaine seeking. In DS D2-SPNs miR-1 overexpression reduced the motivation to self-administer cocaine. Our results indicate a role of miR1 and its target genes, Fosb and Npas4, in these behaviors and highlight a precise cell-type- and region-specific modulatory role of miR-1, illustrating the importance of cell-specific investigations.

Astrocytes in Addictive Disorders

Astroglia are key regulators of synaptic function, playing central roles in homeostatic ion buffering, energy dynamics, transmitter uptake, maintenance of neurotransmitter pools, and regulation of synaptic plasticity through release of neuroactive chemicals. Given the myriad of crucial homeostatic and signaling functions attributed to astrocytes and the variety of neurotransmitter receptors expressed by astroglia, they serve as prime cellular candidates for establishing maladaptive synaptic plasticity following drug exposure. Initial studies on astroglia and addiction have placed drug-mediated disruptions in the homeostatic regulation of glutamate as a central aspect of relapse vulnerability. However, the generation of sophisticated tools to study and manipulate astroglia have proven that the interaction between addictive substances, astroglia, and relapse-relevant synaptic plasticity extends far beyond the homeostatic regulation of glutamate. Here we present astroglial systems impacted by drug exposure and discuss how changes in astroglial biology contribute to addiction biology.

Npas4 regulates medium spiny neuron physiology and gates cocaine-induced hyperlocomotion

We show here that the transcription factor Npas4 is an important regulator of medium spiny neuron spine density and electrophysiological parameters and that it determines the magnitude of cocaine-induced hyperlocomotion in mice. Npas4 is induced by synaptic stimuli that cause calcium influx, but not dopaminergic or PKA-stimulating input, in mouse medium spiny neurons and human iPSC-derived forebrain organoids. This induction is independent of ubiquitous kinase pathways such as PKA and MAPK cascades, and instead depends on calcineurin and nuclear calcium signalling. Npas4 controls a large regulon containing transcripts for synaptic molecules, such as NMDA receptors and VDCC subunits, and determines in vivo MSN spine density, firing rate, I/O gain function and paired-pulse facilitation. These functions at the molecular and cellular levels control the locomotor response to drugs of abuse, as Npas4 knockdown in the nucleus accumbens decreases hyperlocomotion in response to cocaine in male mice while leaving basal locomotor behaviour unchanged.

Disrupting D1-NMDA or D2-NMDA receptor heteromerization prevents cocaine's rewarding effects but preserves natural reward processing

Addictive drugs increase dopamine in the nucleus accumbens (NAc), where it persistently shapes excitatory glutamate transmission and hijacks natural reward processing. Here, we provide evidence, from mice to humans, that an underlying mechanism relies on drug-evoked heteromerization of glutamate N-methyl-d-aspartate receptors (NMDAR) with dopamine receptor 1 (D1R) or 2 (D2R). Using temporally controlled inhibition of D1R-NMDAR heteromerization, we unraveled their selective implication in early phases of cocaine-mediated synaptic, morphological, and behavioral responses. In contrast, preventing D2R-NMDAR heteromerization blocked the persistence of these adaptations. Interfering with these heteromers spared natural reward processing. Notably, we established that D2R-NMDAR complexes exist in human samples and showed that, despite a decreased D2R protein expression in the NAc, individuals with psychostimulant use disorder display a higher proportion of D2R forming heteromers with NMDAR. These findings contribute to a better understanding of molecular mechanisms underlying addiction and uncover D2R-NMDAR heteromers as targets with potential therapeutic value.

Electroacupuncture prevents cocaine-induced conditioned place preference reinstatement and attenuates ΔFosB and GluR2 expression

Acupuncture has been used for treating drug addiction since the 1970s, but little is known about the mechanisms by which acupuncture affects drug cue-induced relapse. The transcription factor delta-FosB (ΔFosB) plays a critical role in behavior and pathology after chronic use of cocaine. ΔFosB regulates glutamate receptor signaling and dendritic spine morphology in animal models. This experimental study compared the effects of electroacupuncture (EA) at acupoints LI4 and LI11 with those of another potentially beneficial intervention, gabapentin (GBP), alone or in combination, on reinstatement of cocaine-induced conditioned place preference (CPP) and levels of ΔFosB and glutamate receptor subunit 2 (GluR2) expression in the nucleus accumbens (NAc). EA at LI4 and LI11 significantly prevented cue-induced cocaine CPP reinstatement, whereas needle insertion without electrical stimulation at these acupoints had no such effect. EA also significantly attenuated cocaine-induced increases in ΔFosB and GluR2 expression in the NAc. Unexpectedly, these effects were reversed when GBP was combined with EA. Treatment with EA at LI4 and LI11 prevented cocaine-induced increases in dendritic spine density in the NAc core and shell. Our results suggest that EA at LI4 and LI11 may prevent cocaine relapse by modulating ΔFosB and GluR2 expression, as well as dendritic spine density.

Cocaine Triggers Astrocyte-Mediated Synaptogenesis

BACKGROUND

Synaptogenesis is essential in forming new neurocircuits during development, and this is mediated in part by astrocyte-released thrombospondins (TSPs) and activation of their neuronal receptor, α2δ-1. Here, we show that this developmental synaptogenic mechanism is utilized during cocaine experience to induce spinogenesis and the generation of AMPA receptor-silent glutamatergic synapses in the adult nucleus accumbens shell (NAcSh).

METHODS

Using multidisciplinary approaches including astrocyte Ca²⁺ imaging, genetic mouse lines, viral-mediated gene transfer, and operant behavioral procedures, we monitor the response of NAcSh astrocytes to cocaine administration and examine the role of astrocytic TSP-α2δ-1 signaling in cocaine-induced silent synapse generation as well as the behavioral impact of astrocyte-mediated synaptogenesis and silent synapse generation.

RESULTS

Cocaine administration acutely increases Ca²⁺ events in NAcSh astrocytes, while decreasing astrocytic Ca²⁺ blocks cocaine-induced generation of silent synapses. Furthermore, knockout of TSP2, or pharmacological inhibition or viral-mediated knockdown of α2δ-1, prevents cocaine-induced generation of silent synapses. Moreover, disrupting TSP2-α2δ-1-mediated spinogenesis and synapse generation in NAcSh decreases cue-induced cocaine seeking after withdrawal from cocaine self-administration and cue-induced reinstatement of cocaine seeking after drug extinction.

CONCLUSIONS

These results establish that silent synapses are generated by an astrocyte-mediated synaptogenic mechanism in response to cocaine experience and embed critical cue-associated memory traces that promote cocaine relapse.

Developmental Changes in Dendritic Spine Morphology in the Striatum and Their Alteration in an A53T α-Synuclein Transgenic Mouse Model of Parkinson's Disease

The aging process is accompanied by various neurophysiological changes, and the severity of neurodegenerative disorders such as Parkinson’s disease (PD) increases with aging. However, the precise neuroanatomical changes that accompany the aging process in both normal and pathologic conditions remain unknown. This is in part because there is a lack of high-resolution imaging tool that has the capacity to image a desired volume of neurons in a high-throughput and automated manner. In the present study, focused ion beam/scanning electron microscopy (FIB/SEM) was used to image striatal neuropil in both wild-type (WT) mice and an A53T bacterial artificial chromosome (BAC) human α-synuclein (A53T-BAC-SNCA) transgenic (Tg) mouse model of PD, at 1, 3, 6, and 22 months of age. We demonstrated that spine density gradually decreases, and average spine head volume gradually increases with age in WT mice, suggesting a homeostatic balance between spine head volume and spine density. However, this inverse relationship between spine head volume and spine density was not observed in A53T-BAC-SNCA Tg mice. Taken together, our data suggest that PD is accompanied by an abnormality in the mechanisms that control synapse growth and maturity.

From Signaling Molecules to Circuits and Behaviors: Cell-Type-Specific Adaptations to Psychostimulant Exposure in the Striatum

Addiction is characterized by a compulsive pattern of drug seeking and consumption and a high risk of relapse after withdrawal that are thought to result from persistent adaptations within brain reward circuits. Drugs of abuse increase dopamine (DA) concentration in these brain areas, including the striatum, which shapes an abnormal memory trace of drug consumption that virtually highjacks reward processing. Long-term neuronal adaptations of gamma-aminobutyric acidergic striatal projection neurons (SPNs) evoked by drugs of abuse are critical for the development of addiction. These neurons form two mostly segregated populations, depending on the DA receptor they express and their output projections, constituting the so-called direct (D₁ receptor) and indirect (D₂ receptor) SPN pathways. Both SPN subtypes receive converging glutamate inputs from limbic and cortical regions, encoding contextual and emotional information, together with DA, which mediates reward prediction and incentive values. DA differentially modulates the efficacy of glutamate synapses onto direct and indirect SPN pathways by recruiting distinct striatal signaling pathways, epigenetic and genetic responses likely involved in the transition from casual drug use to addiction. Herein we focus on recent studies that have assessed psychostimulant-induced alterations in a cell-type-specific manner, from remodeling of input projections to the characterization of specific molecular events in each SPN subtype and their impact on long-lasting behavioral adaptations. We discuss recent evidence revealing the complex and concerted action of both SPN populations on drug-induced behavioral responses, as these studies can contribute to the design of future strategies to alleviate specific behavioral components of addiction.

S-Ketamine Reverses Hippocampal Dendritic Spine Deficits in Flinders Sensitive Line Rats Within 1 h of Administration

When administered as a single subanesthetic dose, the N-methyl-D-aspartate (NMDA) receptor antagonist, ketamine, produces rapid (within hours) and relatively sustained antidepressant actions even in treatment-resistant patients. Preclinical studies have shown that ketamine increases dendritic spine density and synaptic proteins in brain areas critical for the actions of antidepressants, yet the temporal relationship between structural changes and the onset of antidepressant action remains poorly understood. In this study, we examined the effects of a single dose of S-ketamine (15 mg/kg) on dendritic length, dendritic arborization, spine density, and spine morphology in the Flinders Sensitive and Flinders Resistant Line (FSL/FRL) rat model of depression. We found that already 1 h after injection with ketamine, apical dendritic spine deficits in CA1 pyramidal neurons of FSL rats were completely restored. Notably, the observed increase in spine density was attributable to regulation of both mushroom and long-thin spines. In contrast, ketamine had no effect on dendritic spine density in FRL rats. On the molecular level, ketamine normalized elevated levels of phospho-cofilin and the NMDA receptor subunits GluN2A and GluN2B and reversed homer3 deficiency in hippocampal synaptosomes of FSL rats. Taken together, our data suggest that rapid formation of new spines may provide an important structural substrate during the initial phase of ketamine's antidepressant action.

Cocaine addicted to cytoskeletal change and a fibrosis high

Cocaine is one of the most widely abused illicit drugs due to its euphoric and addictive properties. Cocaine-mediated cognitive impairments are the result of dynamic cytoskeletal rearrangements involved in mediating structural and behavioural plasticity. Cytoskeletal changes initiated following cocaine abuse are regulated by the Rho family of GTPases with significant downstream activity in key actin binding proteins. Moreover, signalling via the endoplasmic reticulum chaperone protein, sigma-1 receptor has highlighted the possibility of cocaine regulated pathology in other organ systems. However, the question of whether upstream stimulation of such a high affinity binding receptor is directly involved in cocaine-mediated cytoskeletal changes at present remains unknown. In this review, we describe the functional role of key cytoskeletal regulators in response to cocaine-induced signalling cues. In addition, we ascertain the extent of whether global cytoskeletal modulators involved in cocaine-induced neurological stimulation can be used as a platform for future studies into elucidating its fibrotic potential within the hepatic microenvironment. A focus on aspects still poorly understood relating to the nonneuronal pathological impact of cocaine is discussed in the sphere of hepatic dysregulation. Lastly, we suggest that cocaine may mediate its pathological capacity via the sigma1 receptor in regulating hepatoxicity, hepatic stellate cells activity, cytoskeletal dynamics, and the transcriptional regulation of key hepato-fibrogenic modulators.

Dopamine and addiction: what have we learned from 40 years of research

Among the neurotransmitters involved in addiction, dopamine (DA) is clearly the best known. The critical role of DA in addiction is supported by converging evidence that has been accumulated in the last 40 years. In the present review, first we describe the dopaminergic system in terms of connectivity, functioning and involvement in reward processes. Second, we describe the functional, structural, and molecular changes induced by drugs within the DA system in terms of neuronal activity, synaptic plasticity and transcriptional and molecular adaptations. Third, we describe how genetic mouse models have helped characterizing the role of DA in addiction. Fourth, we describe the involvement of the DA system in the vulnerability to addiction and the interesting case of addiction DA replacement therapy in Parkinson's disease. Finally, we describe how the DA system has been targeted to treat patients suffering from addiction and the result obtained in clinical settings and we discuss how these different lines of evidence have been instrumental in shaping our understanding of the physiopathology of drug addiction.

Biphasic effect of abstinence duration following cocaine self-administration on spine morphology and plasticity-related proteins in prelimbic cortical neurons projecting to the nucleus accumbens core

Cocaine self-administration (SA) in rats dysregulates glutamatergic signaling in the prelimbic (PrL) cortex and glutamate release in the nucleus accumbens (NA) core, promoting cocaine seeking. PrL adaptations that affect relapse to drug seeking emerge during the first week of abstinence, switching from an early (2 h) hypoglutamatergic state to a later (7 days) hyperglutamatergic state. Different interventions that normalize glutamatergic signaling in PrL cortex at each timepoint are necessary to suppress relapse. We hypothesized that plasticity-related proteins that regulate glutamatergic neurotransmission as well as dendritic spine morphology would be biphasically regulated during these two phases of abstinence in PrL cortical neurons projecting to the NA core (PrL-NA core). A combinatorial viral approach was used to selectively label PrL-NA core neurons with an mCherry fluorescent reporter. Male rats underwent 2 weeks of cocaine SA or received yoked-saline infusions and were perfused either 2 h or 7 days after the final SA session. Confocal microscopy and 3D reconstruction analyses were performed for Fos and pCREB immunoreactivity (IR) in the nucleus of layer V PrL-NA core neurons and GluA1-IR and GluA2-IR in apical dendritic spines of the same neurons. Here, we show that cocaine SA decreased PrL-NA core spine head diameter, nuclear Fos-IR and pCREB-IR, and GluA1-IR and GluA2-IR in putative mushroom-type spines 2 h after the end of cocaine SA, whereas the opposite occurred following 1 week of abstinence. Our findings reveal biphasic, abstinence duration-dependent alterations in structural plasticity and relapse-related proteins in the PrL-NA core pathway after cocaine SA.

Effects of location and extent of spine clustering on synaptic integration in striatal medium spiny neurons-a computational study

The nucleus accumbens (NAc) is known widely for its role in the reward circuit, which is dysregulated in a number of psychological disorders. Recent evidence also suggests the contribution of this structure in spatial and gustatory memories. Because of its role in different types of memories, similar to the hippocampus, we assumed the formation of spine clusters, which are engrams of memory, to be present on dendrites of medium spiny neurons (MSNs). We found that the activation of clustered inputs resulted in sublinear summation when clusters were present on the same branch and also when inputs were distributed on different branches. The size, as well as the location of clusters, was found to affect the summation. With an increase in cluster size and distance from soma, the summation was increasingly sublinear. When the temporal integration window was measured for clustered spines, it was found to be narrower as compared to that for a single spine. Also, distally located clusters resulted in a wider temporal window, as compared to proximal clusters. Our results suggest that depending on the location of clusters, the modes of integration will differ in MSNs possessing clustered spines.