Biology subjects

Hollon, N. G.

Publications and source records attributed to Hollon, N. G..

4 recordsLinked to original sources

bioRxiv2025

GABA-glutamate corelease is a mechanism for state-dependent neurotransmission

Ventral tegmental area neurons projecting to lateral habenula (LHb) corelease the main inhibitory and excitatory transmitters, GABA and glutamate (VTAGG). Yet the functional role of this synchronous signal remains unclear. We hypothesized that the sign of VTAGG action depends on postsynaptic state in LHb. Ex vivo, activating VTAGG terminals evoked excitatory and inhibitory responses in LHb that varied with postsynaptic membrane potential. In vivo, VTAGG inputs drove net inhibition and supported positive reinforcement that was dependent on GABA, but not glutamate, release. Using chemogenetics to bidirectionally modulate LHb, we found that LHb hyperpolarization shifted VTAGG effects toward excitation, abolishing positive reinforcement, whereas LHb depolarization enhanced net inhibition and positive reinforcement. Thus, the activity state of LHb neurons dictates whether GABA-glutamate corelease is functionally inhibitory or excitatory and can reverse the motivational valence of VTAGG input, supporting a homeostatic role for GABA-glutamate cotransmission with broad implications for disorders of imbalanced motivation.

neuroscience↗

bioRxiv2025

Parkinson's disease-vulnerable and -resilient dopamine neurons display opposite responses to excitatory input

Dopamine (DA) neurons of the substantia nigra (SN) are essential for motor control and selectively degenerate in Parkinsons disease (PD). However, DA neurons are molecularly heterogeneous, with some showing greater vulnerability and others resilience. Here, we show that the DA subtype marker Anxa1, identified in mice, labels PD-vulnerable DA neurons in human SN. Using mice, we found that excitatory inputs from subthalamic (STN) and pedunculopontine (PPN) nuclei evoked frequency-dependent excitation in SN GABA neurons, but complex multiphasic DA neuron responses, suggesting heterogeneous DA subtype responses. Indeed, excitatory inputs evoked differential DA responses in striatal subregions, an increase in caudal striatum, but inhibition followed by rebound in dorsolateral striatum. Additionally, PD-resilient Vglut2+ DA neurons were excited by STN/PPN input, while vulnerable Anxa1+ DA neurons were inhibited. These findings demonstrate that DA subtypes are embedded in distinct functional networks, suggesting that some therapeutic interventions may differentially impact vulnerable and resilient DA subtypes.

neuroscience↗

bioRxiv2021

Nigrostriatal Dopamine Signals Sequence-Specific Action-Outcome Prediction Errors

Dopamine has been suggested to encode cue-reward prediction errors during Pavlovian conditioning. While this theory has been widely applied to reinforcement learning concerning instrumental actions, whether dopamine represents action-outcome prediction errors and how it controls sequential behavior remain largely unknown. Here, by training mice to perform optogenetic intracranial self-stimulation, we examined how self-initiated goal-directed behavior influences nigrostriatal dopamine transmission during single as well as sequential instrumental actions. We found that dopamine release evoked by direct optogenetic stimulation was dramatically reduced when delivered as the consequence of the animals own action, relative to non-contingent passive stimulation. This action-induced dopamine suppression was specific to the reinforced action, temporally restricted to counteract the expected outcome, and exhibited sequence-selectivity consistent with hierarchical control of sequential behavior. Together these findings demonstrate that nigrostriatal dopamine signals sequence-specific prediction errors in action-outcome associations, with fundamental implications for reinforcement learning and instrumental behavior in health and disease.

neuroscience↗

bioRxiv2020

Optogenetic interrogation of the role of striatal patches in habit formation and inhibition of striatal dopamine

Habits are inflexible behaviors that can be maladaptive in diseases including drug addiction. The striatum is integral to habit formation, and interspersed throughout the striatum are patches, or striosomes, which are characterized by unique gene expression relative to the surrounding matrix. Recent work has indicated that patches are necessary for habit formation, but how patches contribute to habits remains partially understood. Here, using optogenetics, we modulated striatal patches in Sepw1-NP67 mice during habit formation. We find that patch activation during operant training impairs habit formation, and conversely, that acute patch stimulation after reward devaluation can drive habitual reward seeking. Patch stimulation invigorates general locomotion but is not inherently rewarding. Finally, we use fast-scan cyclic voltammetry to demonstrate that patch stimulation suppresses dopamine release in dorsal striatum in vivo. Overall, this work provides novel insight into the role of the patch compartment in habit formation, and potential interactions with dopamine signaling.

neuroscience↗