Cocaine-regulated trafficking of dopamine transporters in cultured neurons revealed by a pH sensitive reporter

Ovarian Hormones and Addictive Behaviour Vulnerability: Insights From Preclinical Studies

Substance use disorder constitutes a global health challenge. Preclinical investigations into addiction heavily rely on animal models to explore the underlying biological mechanisms of addictive disorders, with a particular emphasis on understanding the etiological factors influencing drug intake. Exploring sex differences across various phases of addiction has revealed a heightened vulnerability in females. This study systematically reviews the impact of ovarian hormones on the consumption of psychoactive substances in rodents, adhering to the PRISMA 2009 protocol. Our findings underscore the significant role of ovarian hormones, particularly oestrogen, in augmenting drug consumption among female rodents. Notably, with heroin, it was observed that progesterone, rather than oestrogen, facilitated increased consumption in female rodents. The susceptibility to addiction influenced by oestrogen is accentuated across distinct phases, and the molecular mechanisms form a complex interplay that significantly influences addictive behaviours. By bringing together these findings, we aim to establish a strong foundation for future studies. This work may guide clinical investigations in developing more effective prevention or treatment strategies that address the unique vulnerabilities of females to substance use disorders.

Incentive Cocaine-Seeking Habits and Their Compulsive Manifestation Emerge After a Downregulation of the Dopamine Transporter in Astrocytes Across Functional Domains of the Striatum

The development of compulsive cue-controlled-incentive drug-seeking habits is a hallmark of substance use disorder that is predicated on an intrastriatal shift in the locus of control over behaviour from a nucleus accumbens (Nac) core-dorsomedial striatum network to a Nac core-anterior dorsolateral striatum (aDLS) network. This shift is paralleled by drug-induced (including cocaine) dopamine transporter (DAT) alterations originating in the ventral striatum that spread eventually to encompass the aDLS. Having recently shown that heroin self-administration results in a pan-striatal reduction in astrocytic DAT that precedes the development of aDLS dopamine-dependent incentive heroin-seeking habits, we tested the hypothesis that similar adaptations occur following cocaine exposure. We compared DAT protein levels in whole tissue homogenates, and in astrocytes cultured from ventral and dorsal striatal territories of drug-naïve male Sprague-Dawley rats to those of rats with a history of cocaine taking or an aDLS dopamine-dependent incentive cocaine-seeking habit. Cocaine exposure resulted in a decrease in whole tissue and astrocytic DAT across all territories of the striatum. We further demonstrated that compulsive (i.e., punishment-resistant) incentive cocaine-seeking habits were associated with a reduction in DAT mRNA levels in the Nac shell, but not the Nac core-aDLS incentive habit system. Together with the recent evidence of heroin-induced downregulation of striatal astrocytic DAT, these findings suggest that alterations in astrocytic DAT may represent a common mechanism underlying the development of compulsive incentive drug-seeking habits across drug classes.

Dopamine transporter endocytic trafficking: Neuronal mechanisms and potential impact on DA-dependent behaviors

The dopamine (DA) transporter (DAT) is a major determinant of DAergic neurotransmission, and is a primary target for addictive and therapeutic psychostimulants. Evidence accumulated over decades in cell lines and in vitro preparations revealed that DAT function is acutely regulated by membrane trafficking. Many of these findings have recently been validated in vivo and in situ, and several behavioral and physiological findings raise the possibility that regulated DAT trafficking may impact DA signaling and DA-dependent behaviors. Here we review key DAT trafficking findings across multiple systems, and discuss the cellular mechanisms that mediate DAT trafficking, as well as the endogenous receptors and signaling pathways that drive regulated DAT trafficking. We additionally discuss recent findings that DAT trafficking dysfunction correlates to perturbations in DA signaling and DA-dependent behaviors.

Protocol for live neuron imaging analysis of basal surface fraction and dynamic availability of the dopamine transporter using DAT-pHluorin

Surface availability of the dopamine (DA) transporter (DAT) critically influences DA transmission. Here, we present a protocol that describes the preparation of mouse ventral midbrain neurons, the expression of a new optical sensor, DAT-pHluorin, and the utilization of this sensor to analyze the surface availability of DAT in live neurons via fluorescent microscopy. This approach allows quantitative measures of basal surface DAT fraction under genetic backgrounds of interest and live trafficking of DAT in response to psychoactive substances. For complete details on the use and execution of this protocol, please refer to Saenz et al.1.

Parkinson's disease gene, Synaptojanin1, dysregulates the surface maintenance of the dopamine transporter

Missense mutations of PARK20/SYNJ1 (synaptojanin1/Synj1) were found in complex forms of familial Parkinsonism. However, the Synj1-regulated molecular and cellular changes associated with dopaminergic dysfunction remain unknown. We now report a fast depletion of evoked dopamine and impaired maintenance of the axonal dopamine transporter (DAT) in the Synj1 haploinsufficient (Synj1+/-) neurons. While Synj1 has been traditionally known to facilitate the endocytosis of synaptic vesicles, we provide in vitro and in vivo evidence demonstrating that Synj1 haploinsufficiency results in an increase of total DAT but a reduction of the surface DAT. Synj1+/- neurons exhibit maladaptive DAT trafficking, which could contribute to the altered DA release. We showed that the loss of surface DAT is associated with the impaired 5'-phosphatase activity and the hyperactive PI(4,5)P2-PKCβ pathway downstream of Synj1 deficiency. Thus, our findings provided important mechanistic insight for Synj1-regulated DAT trafficking integral to dysfunctional DA signaling, which might be relevant to early Parkinsonism.

Haploinsufficiency of the Parkinson's disease gene synaptojanin1 is associated with abnormal responses to psychomotor stimulants and mesolimbic dopamine signaling

The synaptojanin-1 (SYNJ1) gene is known to be important for dopamine-related disorders. Recent evidence has demonstrated that Synj1 deficient mice (Synj1 +/-) have impairments in dopaminergic synaptic vesicular recycling. However, less is known about how Synj1 deficits affect the mesolimbic system, reward processing, and motivated behavior. To examine the role of the Synj1 gene in motivated behavior, we subjected male and female Synj1 +/- and Synj1 +/+ mice to a battery of behavioral tests evaluating hedonic responses, effortful responding, and responses to psychomotor stimulants. We observed that Synj1 +/- mice exhibit few differences in reward processing and motivated behavior, with normal hedonic responses and motivated responding for sucrose. However, male but not female Synj1 +/- demonstrated an attenuated conditioned place preference for cocaine that could not be attributed to deficits in spatial memory. To further understand the dopamine signaling underlying the attenuated response to cocaine in these mutant mice, we recorded nucleus accumbens dopamine in response to cocaine and observed that Synj1 +/- male and female mice took longer to reach peak dopamine release following experimenter-administered cocaine. However, female mice also showed slower decay in accumbens dopamine that appear to be linked to differences in cocaine-induced DAT responses. These findings demonstrate that SYNJ1 deficiencies result in abnormal mesolimbic DA signaling which has not previously been demonstrated. Our work also highlights the need to develop targeted therapeutics capable of restoring deficits in DAT function, which may be effective for reversing the pathologies associated with Synj1 mutations.

Neuronal DAMPs exacerbate neurodegeneration via astrocytic RIPK3 signaling

Astrocyte activation is a common feature of neurodegenerative diseases. However, the ways in which dying neurons influence the activity of astrocytes is poorly understood. Receptor interacting protein kinase-3 (RIPK3) signaling has recently been described as a key regulator of neuroinflammation, but whether this kinase mediates astrocytic responsiveness to neuronal death has not yet been studied. Here, we used the 1-methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine model of Parkinson's disease to show that activation of astrocytic RIPK3 drives dopaminergic cell death and axon damage. Transcriptomic profiling revealed that astrocytic RIPK3 promoted gene expression associated with neuroinflammation and movement disorders, and this coincided with significant engagement of damage-associated molecular pattern signaling. In mechanistic experiments, we showed that factors released from dying neurons signaled through receptor for advanced glycation endproducts to induce astrocytic RIPK3 signaling, which conferred inflammatory and neurotoxic functional activity. These findings highlight a mechanism of neuron-glia crosstalk in which neuronal death perpetuates further neurodegeneration by engaging inflammatory astrocyte activation via RIPK3.

Parkinson's disease gene, Synaptojanin1, dysregulates the surface maintenance of the dopamine transporter

Missense mutations of PARK20/SYNJ1 (synaptojanin1/Synj1) have been linked to complex forms of familial parkinsonism, however, the molecular and cellular changes associated with dopaminergic dysfunction remains unknown. We now report fast depletion of evoked dopamine (DA) and altered maintenance of the axonal dopamine transporter (DAT) in the Synj1+/- neurons. While Synj1 has been traditionally known to facilitate the endocytosis of synaptic vesicles, we demonstrated that axons of cultured Synj1+/- neurons exhibit an increase of total DAT but a reduction of the surface DAT, which could be exacerbated by neuronal activity. We revealed that the loss of surface DAT is specifically associated with the impaired 5'-phosphatase activity of Synj1 and the hyperactive downstream PI(4,5)P2-PKCβ pathway. Thus, our findings provided important mechanistic insight for Synj1-regulated DAT trafficking integral to dysfunctional DA signaling in early parkinsonism.