Biology subjects

Ostroumov, A.

Publications and source records attributed to Ostroumov, A..

3 recordsLinked to original sources

bioRxiv2026

Acute stress induces circuit-specific alterations in mesolimbic and nigrostriatal inhibitory transmission and potentiates operant learning

Acute stress can facilitate learning about stimuli that predict rewarding outcomes, yet whether stress similarly potentiates acquisition of reward-directed actions remains less well understood. Reward learning broadly depends on dopamine signaling within mesolimbic and nigrostriatal pathways. Dopamine transmission in the mesolimbic system is traditionally associated with cue-reward learning, whereas nigrostriatal dopamine signaling has been implicated in movement vigor and the acquisition of instrumental actions. Stress can alter dopamine transmission within these circuits and thereby influence reward learning. Previous work demonstrated that acute stress downregulates the potassium-chloride cotransporter KCC2 in ventral tegmental area GABA neurons. These stress-induced adaptations in inhibitory transmission enhance mesolimbic dopamine signaling and potentiate associative learning. Here, we show that prior exposure to acute restraint stress facilitates acquisition of operant sucrose self-administration in male and female rats. Enhanced learning was associated with increased temporal coincidence of GABA release events onto dopamine neurons and increased excitability of GABAergic inputs, alterations previously linked to enhanced dopamine signaling. These stress-induced adaptations exhibited marked circuit specificity within mesolimbic and nigrostriatal systems, selectively affecting inhibitory transmission onto dopamine neurons projecting to the nucleus accumbens lateral shell and dorsomedial striatum. Importantly, pharmacological enhancement of KCC2 function with CLP290 normalized inhibitory transmission within these pathways and attenuated stress-induced potentiation of operant learning. Together, these findings identify circuit-specific alterations in midbrain inhibitory signaling induced by acute stress that contribute to enhanced reward learning.

neuroscience↗

bioRxiv2025

Cocaine and Morphine Converge to Disrupt Chloride Homeostasis in Ventral Tegmental Area GABA Neurons

Identifying shared neural mechanisms influenced by diverse classes of drugs of abuse is essential for understanding addiction and for developing broad-spectrum treatments for substance use disorders. Previous studies indicate that many drugs of abuse increase dopamine output from the ventral tegmental area (VTA) by altering the balance of excitatory and inhibitory inputs onto dopamine neurons, thereby promoting maladaptive plasticity within reward circuits. Here, we demonstrate in rats that acute injections of morphine and cocaine, but not saline, disrupt chloride homeostasis in VTA GABA neurons. This disruption is characterized by a depolarized GABAA reversal potential, impaired chloride extrusion, and posttranslational downregulation of the potassium chloride cotransporter KCC2. Although previous studies linked drug-induced posttranslational downregulation of KCC2 in the VTA to glucocorticoid receptor activation, we found that a glucocorticoid receptor antagonist did not prevent cocaine- and morphine-induced disruption of chloride homeostasis. Instead, our data show that dopamine receptor activation is both necessary and sufficient for these alterations. Notably, chloride homeostasis remains impaired 30 days after volitional morphine self-administration, indicating long-lasting plasticity. These findings complement previous work on nicotine and alcohol, suggesting a shared mechanism of inhibitory plasticity in the VTA following drug exposure. Given that chloride dysregulation in VTA GABA neurons influences downstream circuit function and promotes maladaptive behaviors associated with drug use, we propose KCC2 as a promising therapeutic target for substance use disorders.

neuroscience↗

bioRxiv2024

Dynamic Changes in Chloride Homeostasis Coordinate Midbrain Inhibitory Network Activity during Reward Learning

The ability to associate environmental stimuli with positive outcomes is a fundamental form of learning. While extensive research has focused on the response profiles of midbrain dopamine neurons during associative learning, less is known about learning-mediated changes in the afferents that shape their responses. We demonstrate that during critical phases of learning, anion homeostasis in midbrain GABA neurons - a primary source of input to dopamine neurons - is disrupted due to downregulation of the chloride transporter KCC2. This alteration in GABA neurons preferentially impacted lateral mesoaccumbal dopamine pathways and was not observed after learning was established. At the network level, learning-mediated KCC2 downregulation was associated with enhanced synchronization between individual GABA neurons and increased dopamine responses to reward-related stimuli. Conversely, enhancing KCC2 function during learning reduced GABA synchronization, diminished relevant dopamine signaling, and prevented cue-reward associations. Thus, circuit-specific adaptations in midbrain GABA neurons are crucial for forming new reward-related behaviors.

neuroscience↗