Molecular, Circuit, and Stress Response Characterization of Ventral Pallidum Npas1-Neurons

Abstract

Altered activity of the ventral pallidum (VP) underlies disrupted motivation in stress and drug exposure. The VP is a very heterogeneous structure composed of many neuron types with distinct physiological properties and projections. Neuronal PAS 1-positive (Npas1+) VP neurons are thought to send projections to brain regions critical for motivational behavior. While Npas1+neurons have been characterized in the globus pallidus external, there is limited information on these neurons in the VP. To address this limitation, we evaluated the projection targets of the VP Npas1+neurons and performed RNA-sequencing on ribosome-associated mRNA from VP Npas1+neurons to determine their molecular identity. Finally, we used a chemogenetic approach to manipulate VP Npas1+neurons during social defeat stress (SDS) and behavioral tasks related to anxiety and motivation in Npas1-Cre mice. We used a similar approach in females using the chronic witness defeat stress (CWDS). We identified VP Npas1+projections to the nucleus accumbens, ventral tegmental area, medial and lateral habenula, lateral hypothalamus, thalamus, medial and lateral septum, and periaqueductal gray area. VP Npas1+neurons displayed distinct translatome representing distinct biological processes. Chemogenetic activation of hM3D(Gq) receptors in VP Npas1+neurons increased susceptibility to a subthreshold SDS and anxiety-like behavior in the elevated plus maze and open field while the activation of hM4D(Gi) receptors in VP Npas1+neurons enhanced resilience to chronic SDS and CWDS. Thus, the activity of VP Npas1+neurons modulates susceptibility to social stressors and anxiety-like behavior. Our studies provide new information on VP Npas1+neuron circuitry, molecular identity, and their role in stress response.SIGNIFICANCE STATEMENTThe ventral pallidum (VP) is a structure connected to both reward-related and aversive brain centers. It is a key brain area that signals the hedonic value of natural rewards. Disruption in the VP underlies altered motivation in stress and substance use disorder. However, VP is a very heterogeneous area with multiple neuron subtypes. This study characterized the projection pattern and molecular signatures of VP Neuronal PAS 1-positive (Npas1+) neurons. We further used tools to alter receptor signaling in VP Npas1+neurons in stress to demonstrate a role for these neurons in stress behavioral outcomes. Our studies have implications for understanding brain cell type identities and their role in brain disorders, such as depression, a serious disorder that is precipitated by stressful events.

Ventral pallidal GABAergic neuron calcium activity encodes cue-driven reward-seeking and persists in the absence of reward delivery

“…VP GABA neurons may differ in their encoding and functional contributions based on more specific cell-type subdivisions or output pathways. For instance, some work points to parvalbumin neurons being a subset of VP GABA neurons involved in cue-evoked behaviors (Prasad et al, 2020), whereas PAS 1-positive VP GABA neurons may contribute to stress and anxiety-related behaviors (Morais-Silva et al, 2022). Additionally, VP GABA neurons have many projection targets that have varied roles in appetitive behavior (Covelo et al, 2014; Mahler et al, 2014; Leung and Balleine, 2015; Root et al, 2015; Prasad and McNally, 2016; Farrell et al, 2021; Vachez et al, 2021; Morais-Silva et al, 2022).…”

“…For instance, some work points to parvalbumin neurons being a subset of VP GABA neurons involved in cue-evoked behaviors (Prasad et al, 2020), whereas PAS 1-positive VP GABA neurons may contribute to stress and anxiety-related behaviors (Morais-Silva et al, 2022). Additionally, VP GABA neurons have many projection targets that have varied roles in appetitive behavior (Covelo et al, 2014; Mahler et al, 2014; Leung and Balleine, 2015; Root et al, 2015; Prasad and McNally, 2016; Farrell et al, 2021; Vachez et al, 2021; Morais-Silva et al, 2022). Probing a more specific subset of VP GABA cells (cell-type or projection-specific) may reveal greater, or lack of, reward-predictive cue encoding and latency correlations.…”

Ventral pallidal regulation of motivated behaviors and reinforcement

“…For instance, while GP Npas1 neurons preferentially innervate the striatum and cortex (Hernandez et al, 2015 ; Abecassis et al, 2020 ), VP Npas1 neurons provide only sparse inputs to the NAc and do not innervate the cortex. Instead, VP Npas1 neurons densely innervate the MD, lateral habenula (lHb), and lateral hypothalamus (LH; Morais-Silva et al, 2022 ). Furthermore, VP Npas1 neurons are not an exclusively GABAergic population and express genes for glutamatergic neurotransmission (Morais-Silva et al, 2022 ).…”

“…Instead, VP Npas1 neurons densely innervate the MD, lateral habenula (lHb), and lateral hypothalamus (LH; Morais-Silva et al, 2022 ). Furthermore, VP Npas1 neurons are not an exclusively GABAergic population and express genes for glutamatergic neurotransmission (Morais-Silva et al, 2022 ). The VP also contains neuropeptide Y, somatostatin, and galanin neurons, which are likely GABAergic (Johansson et al, 1984 ; Perez et al, 2001 ; Zaborszky et al, 2012 ).…”

“…However, optogenetic or chemogenetic stimulation of VP GABA produces mixed results in anxiety tests with either no effects or increased anxiety in the EPM (Zhu et al, 2017 ; Li et al, 2021 ; Roman-Ortiz et al, 2021 ), or no effects or reduced anxiety in OF and light-dark box tests (Zhu et al, 2017 ; Li et al, 2021 ). By contrast, chemogenetic stimulation of VP Npas1 neurons augments anxiety in the EPM (Morais-Silva et al, 2022 ). Given that VP Npas1 neurons are capable of releasing glutamate, these effects may in part be mediated by glutamate released in downstream target structures.…”