Browsing by Author "Richard, Jocelyn"

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    Exploration of Projection Targets of Caudal GABAergic Ventral Pallidum Neurons for Basis of Functional Heterogeneity
    (2024-04-18) Muruganandan, Preethi; Newell, Bailey; Lortie, Margot; Sood, Ankit; Richard, Jocelyn
    The ventral pallidum is a brain region known to play a major role in mesocorticolimbic circuits underlying learning, motivation, and reward-evoked behavior. It is known that the ventral pallidum is a structure heterogeneous in nature, but the extent of its heterogeneity in projection targets is yet to be explored thoroughly. Experiments targeting the ventral pallidum speculate the existence of hotspots, defined sites known to modulate specific behavioral responses to stimuli, within this area of the basal ganglia. The caudal ventral pallidum was found to be a hedonic hotspot, enhancing liking reactions to sucrose following both opioid and orexin injections. This project aims to explore the extent of heterogeneity within the caudal ventral pallidum on the basis of projection regions. As the ventral pallidum signals primarily with GABA, a dual viral mixture was unilaterally injected in rat models to target VP GABAergic neurons and identify their downstream projections. Fluorescent microscopy and image processing were then used to quantify these projection signals in the lateral habenula, lateral hypothalamus, and subthalamic nucleus. Degree of viral expression in the aforementioned projections was compared among rats receiving either a caudal- or central-VP injection. Greater knowledge of this subregional heterogeneity could help develop targeted medications and uncover specialized treatments in the cases of addiction and relapse, highlighting the need for understanding the circuit differences between the ventral pallidal subregions.
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    Investigating GABAergic Projections of the Ventral Pallidum’s Hedonic Hotspot Using a Dual-Virus Approach
    (2025-04-15) Muruganandan, Preethi; Newell, Bailey; Sood, Ankit; Lortie, Margot; Richard, Jocelyn
    The ventral pallidum (VP) is a brain region implicated in reward-related behaviors, motivation, and addiction. The posterior half of the VP is coined as the “hedonic hotspot”, a subregion that amplifies liking reactions in response to palatable stimuli. The feature does not remain true for the anterior half of the VP, indicating a divergence in functionality. The extent of the VP’s heterogeneity with respect to circuit-level connections is yet to be explored fully. This project aimed to distinguish the difference in downstream projection targets between the anterior and posterior VP that give rise to the hedonic hotspot. A fluorescent tracer virus was injected into either the anterior or posterior VP in rats to specifically target GABAergic neurons. Post-mortem brain tissue processing and imaging was performed for visualization of projections. Quantification data showed that the posterior VP projects more robustly to the lateral habenula and lateral hypothalamus than the anterior VP. This finding suggests that certain hedonic hotspot neurons may wire together to these 2 regions. This synaptic connection could be a potential target for pharmacological modulation in cases of substance use disorders. Further elucidation of VP inputs and outputs will allow us to better understand the mechanisms that underlie reward pursuit, addiction and relapse.