Parvalbumin interneuron alterations in stress-related mood disorders: A systematic review

Response of parvalbumin interneurons and perineuronal nets in rat medial prefrontal cortex and lateral amygdala to stressor controllability

Behavioral control over a stressor limits the impact of the stressor being experienced and produces enduring changes that reduce the effects of future stressors. In rats, these stress-buffering effects of control (escapable stress, ES) require activation of the medial prefrontal cortex (mPFC) and prevent the typical amygdala-dependent behavioral outcomes of uncontrollable stress (inescapable stress, IS). Parvalbumin (PV) interneurons regulate output of excitatory neurons, and most mPFC PV neurons are surrounded by perineuronal nets (PNNs), which regulate firing. We exposed male rats to a single session of ES, IS, or no stress and measured c-Fos expression within PV/PNN-containing cells in mPFC subregions (prelimbic, PL; infralimbic, IL) and in the lateral amygdala. We also measured the number and intensity of PNNs. Within PL and IL PV/PNN cells, both ES and IS increased c-Fos intensity in PV/PNN, non-PV, and non-PNN cells. Within the IL, only ES increased the number of c-Fos-expressing PV/PNN-labeled cells. In the lateral amygdala, only ES increased c-Fos intensity within PV cells and PV/PNN cells. Thus, PV neurons in the IL and lateral amygdala may represent an important substrate by which behavioral control buffers against the amygdala-dependent behavioral outcomes typically observed after uncontrollable stress.

The impact of limited sucrose intake on perineuronal nets of parvalbumin interneurons in the basolateral amygdala: A potential role in stress resilience

Natural rewards like regular sucrose consumption can buffer physiological and behavioral stress responses, likely mediated, at least in part, by increased plasticity in parvalbumin-positive (PV+) interneurons in the basolateral amygdala (BLA). As PV+ interneuron plasticity is tightly regulated by specialized extracellular matrix structures called perineuronal nets (PNNs), this study investigated the impact of regular sucrose consumption vs. repetitive stress on the PNNs that surround PV+ interneurons in the BLA, as well as the number of glutamatergic (vGLUT1) and GABAergic (vGAT) appositions that PV+ cells receive. Male rats were given an established limited sucrose intake (LSI) feeding paradigm (vs. water-fed controls) and were co-exposed to a brief restraint stress (vs. no stress controls), daily for 14 days. Sucrose consumption increased the proportion of PV+ cells that were surrounded by PNNs, independent of stress exposure. PV+ cells with PNNs had more vGLUT1-positive and fewer vGAT-positive appositions compared to those lacking PNNs. Additionally, sucrose consumption increased the ratio of excitatory/inhibitory appositions onto PV+ cells, suggesting the possibility of elevated PV+ interneuron tone, leading to greater inhibition of the BLA's stress-excitatory output. These findings indicate that sucrose consumption influences PNN formation and structural plasticity on PV+ interneurons in the BLA, which has implications for understanding the neurological mechanisms underlying stress resilience by natural rewards.

Parvalbumin interneuron mGlu5 receptors govern sex differences in prefrontal cortex physiology and binge drinking

Despite established sex differences in the prevalence and presentation of psychiatric disorders, little is known about the cellular and synaptic mechanisms that guide these differences under basal conditions. The proper function of the prefrontal cortex (PFC) is essential for the top-down regulation of motivated behaviors. The activity of the PFC is tightly controlled by parvalbumin-expressing interneurons (PV-INs), a key subpopulation of fast-spiking GABAergic cells that regulate cortical excitability through direct innervations onto the perisomatic regions of nearby pyramidal cells. Recent rodent studies have identified notable sex differences in PV-IN activity and adaptations to experiences such as binge drinking. Here, we investigated the cellular and molecular mechanisms that underlie sex-specific regulation of PFC PV-IN function. Using whole-cell patch-clamp electrophysiology and selective pharmacology, we report that PV-INs from female mice are more excitable than those from males. Moreover, we find that mGlu1 and mGlu5 metabotropic glutamate receptors regulate cell excitability, excitatory drive, and endocannabinoid signaling at PFC PV-INs in a sex-dependent manner. Genetic deletion of mGlu5 receptors from PV-expressing cells abrogates all sex differences observed in PV-IN membrane and synaptic physiology. Lastly, we report that female, but not male, PV-mGlu5-/- mice exhibit decreased voluntary drinking on an intermittent access schedule, which could be related to changes in ethanol's stimulant properties. Importantly, these studies identify mGlu1 and mGlu5 receptors as candidate signaling molecules involved in sex differences in PV-IN activity and behaviors relevant to alcohol use.

Is the antidepressant effect of ketamine separate from its psychotomimetic effect? A review of rodent models

Ketamine is an NMDA (N-methyl-d-aspartate) glutamate receptor antagonist, which has a myriad of dose-dependent pharmacological and behavioral effects, including anesthetic, sedative, amnestic, analgesic, and anti-inflammatory properties. Intriguingly, ketamine at subanesthetic doses displays a relevant profile both in mimicking symptoms of schizophrenia and also as the first fast-acting treatment for depression. Here, we present an overview of the state-of-the-art knowledge about ketamine as an antidepressant as well as a pharmacological model of schizophrenia in animal models and human participants. Ketamine's dual effect appears to arise from its mechanism of action involving NMDA receptors, with both immediate and downstream consequences being triggered as a result. Finally, we discuss the feasibility of a unified approach linking the glutamatergic hypothesis of schizophrenia to the promising preclinical and clinical success of ketamine in the treatment of refractory depression.

A Mouse Model of Temporal Lobe Contusion

Trauma to the brain can induce a contusion characterized by a discrete intracerebral or diffuse interstitial hemorrhage. In humans, "computed tomography-positive," that is, hemorrhagic, temporal lobe contusions (tlCont) have unique sequelae. TlCont confers significantly increased odds for moderate or worse disability and the inability to return to baseline work capacity compared to intra-axial injuries in other locations. Patients with tlCont are at elevated risks of memory dysfunction, anxiety, and post-traumatic epilepsy due to involvement of neuroanatomical structures unique to the temporal lobe including the amygdala, hippocampus, and ento-/perirhinal cortex. Because of the relative inaccessibility of the temporal lobe in rodents, no preclinical model of tlCont has been described, impeding progress in elucidating the specific pathophysiology unique to tlCont. Here, we present a minimally invasive mouse model of tlCont with the contusion characterized by a traumatic interstitial hemorrhage. Mortality was low and sensorimotor deficits (beam walk, accelerating rotarod) resolved completely within 3-5 days. However, significant deficits in memory (novel object recognition, Morris water maze) and anxiety (elevated plus maze) persisted at 14-35 days and nonconvulsive electroencephalographic seizures and spiking were significantly increased in the hippocampus at 7-21 days. Immunohistochemistry showed widespread astrogliosis and microgliosis, bilateral hippocampal sclerosis, bilateral loss of hippocampal and cortical inhibitory parvalbumin neurons, and evidence of interhemispheric connectional diaschisis involving the fiber bundle in the ventral corpus callosum that connects temporal lobe structures. This model may be useful to advance our understanding of the unique features of tlCont in humans.

Evaluation of TRPM2 Channel-Mediated Autophagic Signaling Pathway in Hippocampus and Cortex Tissues of Rat Offspring Following Prenatal Exposure to Elevated Alcohol Levels

Fetal alcohol syndrome (FAS) can occur because of high amount of alcohol intake during pregnancy and is characterized by both physical and neurological problems. Children diagnosed with FAS have difficulties in learning, memory, and coordination. Hippocampus has a major role in memory and learning. We aimed to determine whether alcohol exposure during pregnancy had any effect on offspring by evaluating learning ability as well as oxidative stress and autophagy in the hippocampus and cortex tissues of litters. Attention was also paid to sex differences. To do so, TRPM2, Beclin1, p62, LC3B, IBA1, parvalbumin, GAD65, and mGluR5 expression levels were evaluated by immunohistochemistry. Lactate dehydrogenase (LDH), and malondialdehyde (MDA) levels, as well as total oxidant (TOS) and total antioxidant (TAS) status were determined by ELISA. Learning experiments were evaluated by the Morris water maze (MWM) test. Our findings demonstrated that IBA1, LC3B, GAD65, and mGluR5 expression levels were higher in female rats of the chronic alcohol exposure (CAE) model. Our IHC results revealed that TRPM2 expression levels were significantly increased in both males and females in the CAE group. Likewise, TAS was lower, and TOS was higher in CAE animals. Moreover, MWM outcomes supported a learning deficiency in CAE litters compared to controls and indicated that female offspring outperformed males in learning experiments. Therefore, our results revealed the detrimental effects of alcohol exposure during pregnancy on autophagy signaling in the hippocampus and cortex tissue of litters, which could affect the learning ability of animals.

Long term effects of peripubertal stress on the thalamic reticular nucleus of female and male mice

Adverse experiences during infancy and adolescence have an important and enduring effect on the brain and are predisposing factors for mental disorders, particularly major depression. This impact is particularly notable in regions with protracted development, such as the prefrontal cortex. The inhibitory neurons of this cortical region are altered by peripubertal stress (PPS), particularly in female mice. In this study we have explored whether the inhibitory circuits of the thalamus are impacted by PPS in male and female mice. This diencephalic structure, as the prefrontal cortex, also completes its development during postnatal life and is affected by adverse experiences. The long-term changes induced by PPS were exclusively found in adult female mice. We have found that PPS increases depressive-like behavior and induces changes in parvalbumin-expressing (PV+) cells of the thalamic reticular nucleus (TRN). We observed reductions in the volume of the TRN, together with those of parameters related to structures/molecules that regulate the plasticity and connectivity of PV+ cells: perineuronal nets, matricellular structures surrounding PV+ neurons, and the polysialylated form of the neural cell adhesion molecule (PSA-NCAM). The expression of the GluN1, but not of GluN2C, NMDA receptor subunit was augmented in the TRN after PPS. An increase in the fluorescence intensity of PV+ puncta was also observed in the synaptic output of TRN neurons in the lateral posterior thalamic nucleus. These results demonstrate that the inhibitory circuits of the thalamus, as those of the prefrontal cortex, are vulnerable to the effects of aversive experiences during early life, particularly in females. This vulnerability is probably related to the protracted development of the TRN and might contribute to the development of psychiatric disorders.

Differential Impact of Adolescent or Adult Stress on Behavior and Cortical Parvalbumin Interneurons and Perineuronal Nets in Male and Female Mice

BACKGROUND

Stress has become a common public health concern, contributing to the rising prevalence of psychiatric disorders. Understanding the impact of stress considering critical variables, such as age, sex, and individual differences, is of the utmost importance for developing effective intervention strategies.

METHODS

Stress effects (daily footshocks for 10 days) during adolescence (postnatal day [PND] 31-40) and adulthood (PND 65-74) were investigated on behavioral outcomes and parvalbumin (PV)-expressing GABAergic interneurons and their associated perineuronal nets (PNNs) in the prefrontal cortex of male and female mice 5 weeks post stress.

RESULTS

In adulthood, adolescent stress induced behavioral alterations in male mice, including anxiety-like behaviors, social deficits, cognitive impairments, and altered dopamine system responsivity. Applying integrated behavioral z-score analysis, we identified sex-specific differences in response to adolescent stress, with males displaying greater vulnerability than females. Furthermore, adolescent-stressed male mice showed decreased PV+ and PNN+ cell numbers and PV+/PNN+ colocalization, while in females, adolescent stress reduced prefrontal PV+/PNN+ colocalization in the prefrontal cortex. Further analysis identified distinct behavioral clusters, with certain females demonstrating resilience to adolescent stress-induced deficits in sociability and PV+ cell number. Adult stress in male and female mice did not cause long-lasting changes in behavior and PV+ and PNN+ cell number.

CONCLUSION

Our findings indicate that the timing of stress, sex, and individual variabilities seem to be determinants for the development of behavioral changes associated with psychiatric disorders, particularly in male mice during adolescence.

Neurobiological mechanisms of electroconvulsive therapy for depression: Insights into hippocampal volumetric increases from clinical and preclinical studies

Depression is a highly prevalent and disabling psychiatric disorder. The hippocampus, which plays a central role in mood regulation and memory, has received considerable attention in depression research. Electroconvulsive therapy (ECT) is the most effective treatment for severe pharmacotherapy-resistant depression. Although the working mechanism of ECT remains unclear, recent magnetic resonance imaging (MRI) studies have consistently reported increased hippocampal volumes following ECT. The clinical implications of these volumetric increases and the specific cellular and molecular significance are not yet fully understood. This narrative review brings together evidence from animal models and human studies to provide a detailed examination of hippocampal volumetric increases following ECT. In particular, our preclinical MRI research using a mouse model is consistent with human findings, demonstrating a marked increase in hippocampal volume following ECT. Notable changes were observed in the ventral hippocampal CA1 region, including dendritic growth and increased synaptic density at excitatory synapses. Interestingly, inhibition of neurogenesis did not affect the ECT-related hippocampal volumetric increases detected on MRI. However, it remains unclear whether these histological and volumetric changes would be correlated with the clinical effect of ECT. Hence, future research on the relationships between cellular changes, ECT-related brain volumetric changes, and antidepressant effect could benefit from a bidirectional translational approach that integrates human and animal models. Such translational research may provide important insights into the mechanisms and potential biomarkers associated with ECT-induced hippocampal volumetric changes, thereby advancing our understanding of ECT for the treatment of depression.

Perineuronal Net Alterations Following Early-Life Stress: Are Microglia Pulling Some Strings?

The extracellular matrix plays a key role in synapse formation and in the modulation of synaptic function in the central nervous system. Recent investigations have revealed that microglia, the resident immune cells of the brain, are involved in extracellular matrix remodeling under both physiological and pathological conditions. Moreover, the dysregulation of both innate immune responses and the extracellular matrix has been documented in stress-related psychopathologies as well as in relation to early-life stress. However, the dynamics of microglial regulation of the ECM and how it can be impacted by early-life adversity have been understudied. This brief review provides an overview of the recent literature on this topic, drawing from both animal model and human post mortem studies. Direct and indirect mechanisms through which microglia may regulate the extracellular matrix-including perineuronal nets-are presented and discussed in light of the interactions with other cell types.

Gephyrin phosphorylation facilitates sexually dimorphic development and function of parvalbumin interneurons in the mouse hippocampus

The precise function of specialized GABAergic interneuron subtypes is required to provide appropriate synaptic inhibition for regulating principal neuron excitability and synchronization within brain circuits. Of these, parvalbumin-type (PV neuron) dysfunction is a feature of several sex-biased psychiatric and brain disorders, although, the underlying developmental mechanisms are unclear. While the transcriptional action of sex hormones generates sexual dimorphism during brain development, whether kinase signaling contributes to sex differences in PV neuron function remains unexplored. In the hippocampus, we report that gephyrin, the main inhibitory post-synaptic scaffolding protein, is phosphorylated at serine S268 and S270 in a developmentally-dependent manner in both males and females. When examining GphnS268A/S270A mice in which site-specific phosphorylation is constitutively blocked, we found that sex differences in PV neuron density in the hippocampal CA1 present in WT mice were abolished, coincident with a female-specific increase in PV neuron-derived terminals and increased inhibitory input onto principal cells. Electrophysiological analysis of CA1 PV neurons indicated that gephyrin phosphorylation is required for sexually dimorphic function. Moreover, while male and female WT mice showed no difference in hippocampus-dependent memory tasks, GphnS268A/S270A mice exhibited sex- and task-specific deficits, indicating that gephyrin phosphorylation is differentially required by males and females for convergent cognitive function. In fate mapping experiments, we uncovered that gephyrin phosphorylation at S268 and S270 establishes sex differences in putative PV neuron density during early postnatal development. Furthermore, patch-sequencing of putative PV neurons at postnatal day 4 revealed that gephyrin phosphorylation contributes to sex differences in the transcriptomic profile of developing interneurons. Therefore, these early shifts in male-female interneuron development may drive adult sex differences in PV neuron function and connectivity. Our results identify gephyrin phosphorylation as a new substrate organizing PV neuron development at the anatomical, functional, and transcriptional levels in a sex-dependent manner, thus implicating kinase signaling disruption as a new mechanism contributing to the sex-dependent etiology of brain disorders.

Thalamocortical mGlu8 Modulates Dorsal Thalamus Excitatory Transmission and Sensorimotor Activity

Metabotropic glutamate receptor 8 (mGlu8) is a heterogeneously expressed and poorly understood glutamate receptor with potential pharmacological significance. The thalamic reticular nucleus (TRN) is a critical inhibitory modulator of the thalamocortical-corticothalamic (TC-CT) network and plays a crucial role in information processing throughout the brain, is implicated in a variety of psychiatric conditions, and is also a site of significant mGlu8 expression. Using both male and female mice, we determined via fluorescent in situ hybridization that parvalbumin-expressing cells in the TRN core and shell matrices (identified by spp1+ and ecel1+ expression, respectively), as well as the cortical layers involved in CT signaling, express grm8 mRNA. We then assayed the physiological and behavioral impacts of perturbing grm8 signaling in the TC circuit through conditional (adeno-associated virus-CRE mediated) and cell-type-specific constitutive deletion strategies. We show that constitutive parvalbumin grm8 knock-out (PV grm8 knock-out) mice exhibited (1) increased spontaneous excitatory drive onto dorsal thalamus relay cells and (2) impaired sensorimotor gating, measured via paired-pulse inhibition, but observed no differences in locomotion and thigmotaxis in repeated bouts of open field test (OFT). Conversely, we observed hyperlocomotive phenotypes and anxiolytic effects of AAV-mediated conditional knockdown of grm8 in the TRN (TRN grm8 knockdown) in repeated OFT. Our findings underscore a role for mGlu8 in regulating excitatory neurotransmission as well as anxiety-related locomotor behavior and sensorimotor gating, revealing potential therapeutic applications for various neuropsychiatric disorders and guiding future research endeavors into mGlu8 signaling and TRN function.

A TrkB cleavage fragment in hippocampus promotes Depressive-Like behavior in mice

Decreased hippocampal tropomyosin receptor kinase B (TrkB) level is implicated in the pathophysiology of stress-induced mood disorder and cognitive decline. However, how TrkB is modified and mediates behavioral responses to chronic stress remains largely unknown. Here the effects and mechanisms of TrkB cleavage by asparagine endopeptidase (AEP) were examined on a preclinical murine model of chronic restraint stress (CRS)-induced depression. CRS activated IL-1β-C/EBPβ-AEP pathway in mice hippocampus, accompanied by elevated TrkB 1-486 fragment generated by AEP. Specifi.c overexpression or suppression of AEP-TrkB axis in hippocampal CaMKIIα-positive cells aggravated or relieved depressive-like behaviors, respectively. Mechanistically, in addition to facilitating AMPARs internalization, TrkB 1-486 interacted with peroxisome proliferator-activated receptor-δ (PPAR-δ) and sequestered it in cytoplasm, repressing PPAR-δ-mediated transactivation and mitochondrial function. Moreover, co-administration of 7,8-dihydroxyflavone and a peptide disrupting the binding of TrkB 1-486 with PPAR-δ attenuated depression-like symptoms not only in CRS animals, but also in Alzheimer's disease and aged mice. These findings reveal a novel role for TrkB cleavage in promoting depressive-like phenotype.

Neurogenesis-independent mechanisms of MRI-detectable hippocampal volume increase following electroconvulsive stimulation

Electroconvulsive therapy (ECT) is one of the most effective psychiatric treatments but the underlying mechanisms are still unclear. In vivo human magnetic resonance imaging (MRI) studies have consistently reported ECT-induced transient hippocampal volume increases, and an animal model of ECT (electroconvulsive stimulation: ECS) was shown to increase neurogenesis. However, a causal relationship between neurogenesis and MRI-detectable hippocampal volume increases following ECT has not been verified. In this study, mice were randomly allocated into four groups, each undergoing a different number of ECS sessions (e.g., 0, 3, 6, 9). T2-weighted images were acquired using 11.7-tesla MRI. A whole brain voxel-based morphometry analysis was conducted to identify any ECS-induced brain volume changes. Additionally, a histological examination with super-resolution microscopy was conducted to investigate microstructural changes in the brain regions that showed volume changes following ECS. Furthermore, parallel experiments were performed on X-ray-irradiated mice to investigate the causal relationship between neurogenesis and ECS-related volume changes. As a result, we revealed for the first time that ECS induced MRI-detectable, dose-dependent hippocampal volume increase in mice. Furthermore, increased hippocampal volumes following ECS were seen even in mice lacking neurogenesis, suggesting that neurogenesis is not required for the increase. The comprehensive histological analyses identified an increase in excitatory synaptic density in the ventral CA1 as the major contributor to the observed hippocampal volume increase following ECS. Our findings demonstrate that modification of synaptic structures rather than neurogenesis may be the underlying biological mechanism of ECT/ECS-induced hippocampal volume increase.

1-Methyltryptophan treatment ameliorates high-fat diet-induced depression in mice through reversing changes in perineuronal nets

Depression and obesity are prevalent disorders with significant public health implications. In this study, we used a high-fat diet (HFD)-induced obese mouse model to investigate the mechanism underlying HFD-induced depression-like behaviors. HFD-induced obese mice exhibited depression-like behaviors and a reduction in hippocampus volume, which were reversed by treatment with an indoleamine 2,3-dioxygenase (IDO) inhibitor 1-methyltryptophan (1-MT). Interestingly, no changes in IDO levels were observed post-1-MT treatment, suggesting that other mechanisms may be involved in the anti-depressive effect of 1-MT. We further conducted RNA sequencing analysis to clarify the potential underlying mechanism of the anti-depressive effect of 1-MT in HFD-induced depressive mice and found a significant enrichment of shared differential genes in the extracellular matrix (ECM) organization pathway between the 1-MT-treated and untreated HFD-induced depressive mice. Therefore, we hypothesized that changes in ECM play a crucial role in the anti-depressive effect of 1-MT. To this end, we investigated perineuronal nets (PNNs), which are ECM assemblies that preferentially ensheath parvalbumin (PV)-positive interneurons and are involved in many abnormalities. We found that HFD is associated with excessive accumulation of PV-positive neurons and upregulation of PNNs, affecting synaptic transmission in PV-positive neurons and leading to glutamate-gamma-aminobutyric acid imbalances in the hippocampus. The 1-MT effectively reversed these changes, highlighting a PNN-related mechanism by which 1-MT exerts its anti-depressive effect.

Parvalbumin interneurons in human ventromedial prefrontal cortex: a comprehensive post-mortem study of myelination and perineuronal nets in neurotypical individuals and depressed suicides with and without a history of child abuse

Cortical parvalbumin interneurons (PV+) are major regulators of excitatory/inhibitory information processing, and their maturation is associated with the opening of developmental critical periods (CP). Recent studies reveal that cortical PV+ axons are myelinated, and that myelination along with perineuronal net (PNN) maturation around PV+ cells is associated with the closures of CP. Although PV+ interneurons are susceptible to early-life stress, their relationship between their myelination and PNN coverage remains unexplored. This study compared the fine features of PV+ interneurons in well-characterized human post-mortem ventromedial prefrontal cortex samples (n = 31) from depressed suicides with or without a history of child abuse (CA) and matched controls. In healthy controls, 81% of all sampled PV+ interneurons displayed a myelinated axon, while a subset (66%) of these cells also displayed a PNN, proposing a relationship between both attributes. Intriguingly, a 3-fold increase in the proportion of unmyelinated PV+ interneurons with a PNN was observed in CA victims, along with greater PV-immunofluorescence intensity in myelinated PV+ cells with a PNN. This study, which is the first to provide normative data on myelination and PNNs around PV+ interneurons in human neocortex, sheds further light on the cellular and molecular consequences of early-life adversity on cortical PV+ interneurons.

Parvalbumin interneuron mGlu5 receptors govern sex differences in prefrontal cortex physiology and binge drinking

Despite established sex differences in the prevalence and presentation of psychiatric disorders, little is known about the cellular and synaptic mechanisms that guide these differences under basal conditions. Proper function of the prefrontal cortex (PFC) is essential for the top-down regulation of motivated behaviors. Activity of the PFC is tightly controlled by parvalbumin-expressing interneurons (PV-INs), a key subpopulation of fast-spiking GABAergic cells that regulate cortical excitability through direct innervations onto the perisomatic regions of nearby pyramidal cells. Recent rodent studies have identified notable sex differences in PV-IN activity and adaptations to experiences such as binge drinking. Here, we investigated the cellular and molecular mechanisms that underlie sex-specific regulation of PFC PV-IN function. Using whole-cell patch clamp electrophysiology and selective pharmacology, we report that PV-INs from female mice are more excitable than those from males. Moreover, we find that mGlu1 and mGlu5 metabotropic glutamate receptors regulate cell excitability, excitatory drive, and endocannabinoid signaling at PFC PV-INs in a sex-dependent manner. Genetic deletion of mGlu5 receptors from PV-expressing cells abrogates all sex differences observed in PV-IN membrane and synaptic physiology. Lastly, we report that female, but not male, PV-mGlu5-/- mice exhibit decreased voluntary drinking on an intermittent access schedule, which could be related to changes in ethanol's stimulant properties. Importantly, these studies identify mGlu1 and mGlu5 receptors as candidate signaling molecules involved in sex differences in PV-IN activity and behaviors relevant for alcohol use.

Hippocampal parvalbumin and perineuronal nets: Possible involvement in anxiety-like behavior in rats

The excitatory-inhibitory imbalance has been considered an important mechanism underlying stress-related psychiatric disorders. In the present study, rats were exposed to 6 days of inescapable foot shock (IFS) to induce stress. The open field test and elevated plus maze test showed that IFS-exposed rats exhibited increased anxiety-like behavior. Immunofluorescence showed that IFS rats had a decreased density of GAD67-immunoreactive interneurons in the dorsal hippocampal CA1 region, while no significant change in the density of CaMKIIα-immunoreactive glutamatergic neurons was seen. We investigated the expression of different interneuron subtype markers, including parvalbumin (PV), somatostatin (SST), and calretinin (CR), and noted a marked decline in the density of PV-immunoreactive interneurons in the dorsal CA1 region of IFS rats. The perineuronal net (PNN) is a specialized extracellular matrix structure primarily around PV interneurons. We used Wisteria floribunda agglutinin lectin to label the PNNs and observed that IFS rats had an increased proportion of PNN-coated PV-positive interneurons in CA1. The number of PSD95-positive excitatory synaptic puncta on the soma of PNN-free PV-positive interneurons was significantly higher than that of PNN-coated PV-positive interneurons. Our findings suggest that the effect of IFS on the hippocampal GABAergic interneurons could be cell-type-specific. Loss of PV phenotype in the dorsal hippocampal CA1 region may contribute to anxiety in rats. The dysregulated PV-PNN relationship in CA1 after traumatic stress exposure might represent one of the neurobiological correlates of the observed anxiety-like behavior.

Enhanced anxiety-like behavior induced by chronic neuropathic pain and related parvalbumin-positive neurons in male rats

Anxiety commonly co-occurs with and exacerbates pain, but the interaction between pain progression and anxiety, and its underlying mechanisms remain unclear. Inhibitory interneurons play a crucial role in maintaining normal central nervous system function and are suggested to be involved in pain-induced anxiety. This study aimed to elucidate the time-dependent effects of neuropathic pain on the developmental anxiety-like behaviors and related inhibitory interneurons; parvalbumin (PV)- and cholecystokinin (CCK)-positive neurons in corticolimbic regions. Using an 8-week-old male Wistar rat model with partial sciatic nerve ligation (pSNL), anxiety-like behaviors were biweekly assessed post-surgery through open field (OF) and elevated plus maze (EPM) tests. From 4 weeks post-surgery, pSNL rats exhibited reduced OF center time, rearing, and initial activity, along with diminished EPM open-arm activities (time spent, head dips, movement, and rearing), which correlated with the paw withdrawal threshold. These effects were absent at 2 weeks post-surgery. At 8 weeks post-surgery, specific behaviors (decreased total rearing and increased inactive time in EPM) were observed in the pSNL group. Immunohistochemistry revealed changes in PV- and CCK-positive neurons in specific corticolimbic subregions of pSNL rats at 8 weeks post-surgery. Notably, PV-positive neuron densities in the basolateral amygdaloid complex (BLC) and hippocampal cornu ammonis areas 1 and 2 correlated with anxiety-like behavioral parameters. PV-positive neurons in the BLC of pSNL rats were predominantly changed in large-cell subtypes and were less activated. These findings indicate that anxiety-like behaviors emerge in the late phase of neuropathic pain and relate to PV-positive neurons in corticolimbic regions of pSNL rats.

Early life adversity drives sex-dependent changes in 5-mC DNA methylation of parvalbumin cells in the prefrontal cortex in rats

Early life adversity (ELA) can result in increased risk for developing affective disorders, such as anxiety or depression, later in life, with women showing increased risk. Interactions between an individual's genes and their environment play key roles in producing, as well as mitigating, later life neuropathology. Our current understanding of the underlying epigenomic drivers of ELA associated anxiety and depression are limited, and this stems in part from the complexity of underlying biochemical processes associated with how early experiences shapes later life behavior. Epigenetic alterations, or experience-driven modifications to DNA, can be leveraged to understand the interplay between genes and the environment. The present study characterized DNA methylation patterning, assessed via evaluation of 5-methylcytosine (5-mC), following ELA in a Sprague Dawley rat model of ELA induced by early caregiver deprivation. This study utilized maternal separation to investigate sex- and age-specific outcomes of ELA on epigenetic patterning in parvalbumin (PV)-containing interneurons in the prefrontal cortex (PFC), a subpopulation of inhibitory neurons which are associated with ELA and affective dysfunction. While global analysis of 5-mC methylation and CpG site specific pyrosequencing of the PV promoter, Pvalb, showed no obvious effects of ELA, when analyses were restricted to assessing 5-mC intensity in colocalized PV cells, there were significant sex and age dependent effects. We found that ELA leads sex-specific changes in PV cell counts, and that cell counts can be predicted by 5-mC intensity, with males and females showing distinct patterns of methylation and PV outcomes. ELA also produced sex-specific effects in corticosterone reactivity, with juvenile females showing a blunted stress hormone response compared to controls. Overall, ELA led to a sex-specific developmental shift in PV profile, which is comparable to profiles that are seen at a later developmental timepoint, and this shift may be mediated in part by epigenomic alterations driven by altered DNA methylation.

SYK-623, a δ Opioid Receptor Inverse Agonist, Mitigates Chronic Stress-Induced Behavioral Abnormalities and Disrupted Neurogenesis

The δ opioid receptor (DOR) inverse agonist has been demonstrated to improve learning and memory impairment in mice subjected to restraint stress. Here, we investigated the effects of SYK-623, a new DOR inverse agonist, on behavioral, immunohistochemical, and biochemical abnormalities in a mouse model of imipramine treatment-resistant depression. Male ddY mice received daily treatment of adrenocorticotropic hormone (ACTH) combined with chronic mild stress exposure (ACMS). SYK-623, imipramine, or the vehicle was administered once daily before ACMS. After three weeks, ACMS mice showed impaired learning and memory in the Y-maze test and increased immobility time in the forced swim test. SYK-623, but not imipramine, significantly suppressed behavioral abnormalities caused by ACMS. Based on the fluorescent immunohistochemical analysis of the hippocampus, ACMS induced a reduction in astrocytes and newborn neurons, similar to the reported findings observed in the postmortem brains of depressed patients. In addition, the number of parvalbumin-positive GABA neurons, which play a crucial role in neurogenesis, was reduced in the hippocampus, and western blot analysis showed decreased glutamic acid decarboxylase protein levels. These changes, except for the decrease in astrocytes, were suppressed by SYK-623. Thus, SYK-623 mitigates behavioral abnormalities and disturbed neurogenesis caused by chronic stress.

Distinct mechanisms of allopregnanolone and diazepam underlie neuronal oscillations and differential antidepressant effect

The rapid relief of depressive symptoms is a major medical requirement for effective treatments for major depressive disorder (MDD). A decrease in neuroactive steroids contributes to the pathophysiological mechanisms associated with the neurological symptoms of MDD. Zuranolone (SAGE-217), a neuroactive steroid that acts as a positive allosteric modulator of synaptic and extrasynaptic δ-subunit-containing GABAA receptors, has shown rapid-onset, clinically effective antidepressant action in patients with MDD or postpartum depression (PPD). Benzodiazepines, on the other hand, act as positive allosteric modulators of synaptic GABAA receptors but are not approved for the treatment of patients with MDD. It remains unclear how differences in molecular mechanisms contribute to the alleviation of depressive symptoms and the regulation of associated neuronal activity. Focusing on the antidepressant-like effects and neuronal activity of the basolateral amygdala (BLA) and medial prefrontal cortex (mPFC), we conducted a head-to-head comparison study of the neuroactive steroid allopregnanolone and the benzodiazepine diazepam using a mouse social defeat stress (SDS) model. Allopregnanolone but not diazepam exhibited antidepressant-like effects in a social interaction test in SDS mice. This antidepressant-like effect of allopregnanolone was abolished in extrasynaptic GABAA receptor δ-subunit knockout mice (δko mice) subjected to the same SDS protocol. Regarding the neurophysiological mechanism associated with these antidepressant-like effects, allopregnanolone but not diazepam increased theta oscillation in the BLA of SDS mice. This increase did not occur in δko mice. Consistent with this, allopregnanolone potentiated tonic inhibition in BLA interneurons via δ-subunit-containing extrasynaptic GABAA receptors. Theta oscillation in the mPFC of SDS mice was also increased by allopregnanolone but not by diazepam. Finally, allopregnanolone but not diazepam increased frontal theta activity in electroencephalography recordings in naïve and SDS mice. Neuronal network alterations associated with MDD showed decreased frontal theta and beta activity in depressed SDS mice. These results demonstrated that, unlike benzodiazepines, neuroactive steroids increased theta oscillation in the BLA and mPFC through the activation of δ-subunit-containing GABAA receptors, and this change was associated with antidepressant-like effects in the SDS model. Our findings support the notion that the distinctive mechanism of neuroactive steroids may contribute to the rapid antidepressant effects in MDD.

Molecular neurobiology of loss: a role for basolateral amygdala extracellular matrix

Psychological loss is a common experience that erodes well-being and negatively impacts quality of life. The molecular underpinnings of loss are poorly understood. Here, we investigate the mechanisms of loss using an environmental enrichment removal (ER) paradigm in male rats. The basolateral amygdala (BLA) was identified as a region of interest, demonstrating differential Fos responsivity to ER and having an established role in stress processing and adaptation. A comprehensive multi-omics investigation of the BLA, spanning multiple cohorts, platforms, and analyses, revealed alterations in microglia and the extracellular matrix (ECM). Follow-up studies indicated that ER decreased microglia size, complexity, and phagocytosis, suggesting reduced immune surveillance. Loss also substantially increased ECM coverage, specifically targeting perineuronal nets surrounding parvalbumin interneurons, suggesting decreased plasticity and increased inhibition within the BLA following loss. Behavioral analyses suggest that these molecular effects are linked to impaired BLA salience evaluation, leading to a mismatch between stimulus and reaction intensity. These loss-like behaviors could be rescued by depleting BLA ECM during the removal period, helping us understand the mechanisms underlying loss and revealing novel molecular targets to ameliorate its impact.

Altered regulation of oligodendrocytes associated with parvalbumin neurons in the ventral hippocampus underlies fear generalization in male mice

Fear generalization is a neurobiological process by which an organism interprets a novel stimulus as threatening because of its similarity to previously learned fear-inducing stimuli. Because recent studies have suggested that the communication between oligodendrocyte precursor cells (OPCs) and parvalbumin (PV)-expressing GABAergic neurons (PV neurons) may play critical roles in stress-related disorders, we examined the involvement of these cells in fear generalization. We first tested the behavioral characteristics of mouse models for conventional fear conditioning (cFC) and modified FC (mFC) with severe electric foot shocks and found that fear generalization was observed in mice treated with mFC but not in mice treated with cFC. The expression levels of genes related to OPCs, oligodendrocytes (OLs), and myelin in the ventral hippocampus were lower in mFC mice than in cFC mice. The densities of OPCs and OLs were decreased in the ventral hippocampus of mFC mice compared to cFC mice. The myelination ratios of PV neurons in the ventral hippocampus were lower in mFC mice than in cFC mice. The chemogenetic activation of PV neurons in the ventral hippocampus of mFC mice reduced fear generalization. The expression levels of genes related to OPCs, OLs, and myelin were recovered following the activation of PV neurons. Finally, the myelination ratios of PV neurons were increased after the activation of PV neurons. Our results suggest that altered regulation of OLs specifically associated with axons of PV neurons in the ventral hippocampus may underlie the generalization of remote fear memory following severe stress exposure.

A tale of two receptors: simultaneous targeting of NMDARs and 5-HT 4 Rs exerts additive effects against stress

BACKGROUND

Serotonin (5-HT) receptors and N -methyl-D-aspartate receptors (NMDARs) have both been implicated in the pathophysiology of depression and anxiety disorders. Here, we evaluated whether targeting both receptors through combined dosing of ( R , S )-ketamine, an NMDAR antagonist, and prucalopride, a serotonin type IV receptor (5-HT 4 R) agonist, would have additive effects, resulting in reductions in stress-induced fear, behavioral despair, and hyponeophagia.

METHODS

A single injection of saline (Sal), ( R , S )-ketamine (K), prucalopride (P), or a combined dose of ( R , S )-ketamine and prucalopride (K+P) was administered before or after contextual fear conditioning (CFC) stress in both sexes. Drug efficacy was assayed using the forced swim test (FST), elevated plus maze (EPM), open field (OF), marble burying (MB), and novelty-suppressed feeding (NSF). Patch clamp electrophysiology was used to measure the effects of combined drug on neural activity in hippocampal CA3. c-fos and parvalbumin (PV) expression in the hippocampus (HPC) and medial prefrontal cortex (mPFC) was examined using immunohistochemistry and network analysis.

RESULTS

We found that a combination of K+P, given before or after stress, exerted additive effects, compared to either drug alone, in reducing a variety of stress-induced behaviors in both sexes. Combined K+P administration significantly altered c-fos and PV expression and network activity in the HPC and mPFC.

CONCLUSIONS

Our results indicate that combined K+P has additive benefits for combating stress-induced pathophysiology, both at the behavioral and neural level. Our findings provide preliminary evidence that future clinical studies using this combined treatment strategy may prove advantageous in protecting against a broader range of stress-induced psychiatric disorders.

microRNA-dependent regulation of gene expression in GABAergic interneurons

Information processing within neuronal circuits relies on their proper development and a balanced interplay between principal and local inhibitory interneurons within those circuits. Gamma-aminobutyric acid (GABA)ergic inhibitory interneurons are a remarkably heterogeneous population, comprising subclasses based on their morphological, electrophysiological, and molecular features, with differential connectivity and activity patterns. microRNA (miRNA)-dependent post-transcriptional control of gene expression represents an important regulatory mechanism for neuronal development and plasticity. miRNAs are a large group of small non-coding RNAs (21-24 nucleotides) acting as negative regulators of mRNA translation and stability. However, while miRNA-dependent gene regulation in principal neurons has been described heretofore in several studies, an understanding of the role of miRNAs in inhibitory interneurons is only beginning to emerge. Recent research demonstrated that miRNAs are differentially expressed in interneuron subclasses, are vitally important for migration, maturation, and survival of interneurons during embryonic development and are crucial for cognitive function and memory formation. In this review, we discuss recent progress in understanding miRNA-dependent regulation of gene expression in interneuron development and function. We aim to shed light onto mechanisms by which miRNAs in GABAergic interneurons contribute to sculpting neuronal circuits, and how their dysregulation may underlie the emergence of numerous neurodevelopmental and neuropsychiatric disorders.

Gene Expression has Distinct Associations with Brain Structure and Function in Major Depressive Disorder

Major depressive disorder (MDD) is associated with structural and functional brain abnormalities. MDD as well as brain anatomy and function are influenced by genetic factors, but the role of gene expression remains unclear. Here, this work investigates how cortical gene expression contributes to structural and functional brain abnormalities in MDD. This work compares the gray matter volume and resting-state functional measures in a Chinese sample of 848 MDD patients and 749 healthy controls, and these case-control differences are then associated with cortical variation of gene expression. While whole gene expression is positively associated with structural abnormalities, it is negatively associated with functional abnormalities. This work observes the relationships of expression levels with brain abnormalities for individual genes, and found that transcriptional correlates of brain structure and function show opposite relations with gene dysregulation in postmortem cortical tissue from MDD patients. This work further identifies genes that are positively or negatively related to structural abnormalities as well as functional abnormalities. The MDD-related genes are enriched for brain tissue, cortical cells, and biological pathways. These findings suggest that distinct genetic mechanisms underlie structural and functional brain abnormalities in MDD, and highlight the importance of cortical gene expression for the development of cortical abnormalities.

Reorganization of Brain Networks as a Substrate of Resilience: An Analysis of Cytochrome c Oxidase Activity in Rats

The unpredictable chronic mild stress (UCMS) model has been used to induce depressive-like symptoms in animal models, showing adequate predictive validity. Our work aims to evaluate the effects of environmental enrichment (EE) on resilience in this experimental model of depression. We also aim to assess changes in brain connectivity using cytochrome c oxidase histochemistry in cerebral regions related to cognitive-affective processes associated with depressive disorder: dorsal hippocampus, prefrontal cortex, amygdala, accumbens, and habenula nuclei. Five groups of rats were used: UCMS, EE, EE + UCMS (enrichment + stress), BG (basal level of brain activity), and CONT (behavioral tests only). We assessed the hedonic responses elicited by sucrose solution using a consumption test; the anxiety level was evaluated using the elevated zero maze test, and the unconditioned fear responses were assessed by the cat odor test. The behavioral results showed that the UCMS protocol induces elevated anhedonia and anxiety. But these responses are attenuated previous exposure to EE. Regarding brain activity, the UCMS group showed greater activity in the habenula compared to the EE + UCMS group. EE induced a functional reorganization of brain activity. The EE + UCMS and UCMS groups showed different patterns of connections between brain regions. Our results showed that EE favors greater resilience and could reduce vulnerability to disorders such as depression and anxiety, modifying metabolic brain activity.

Prepubertal ovariectomy confers resilience to stress-induced anxiety in adult female mice

The increased vulnerability to stress-induced neuropsychiatric disorders in women, including anxiety disorders, does not emerge until pubertal onset, suggesting a role for ovarian hormones in organizing sex-specific vulnerability to anxiety. Parvalbumin (PV) interneurons in the prefrontal cortex are a potential target for these ovarian hormones. PV+ interneurons undergo maturation during the adolescent period and have been shown to be sensitive to stress and to mediate stress-induced anxiety in female mice. To test the idea that ovarian hormones at puberty are necessary for the acquisition of sensitivity to stress, hypothetically driving the response of PV+ interneurons to stress, we performed ovariectomy or sham surgery before pubertal onset in female mice. These mice then were exposed to four weeks of unpredictable chronic mild stress in adulthood. We then assessed anxiety-like behavior and PV/FosB colocalization in the medial PFC. Additionally, we assessed stress-induced anxiety-like behavior in female mice following ovariectomy in adulthood to determine if puberty is a sensitive period for ovarian hormones in mediating vulnerability to stress. We found that prepubertal ovariectomy protects against the development of anxiety-like behavior in adulthood, an effect not found following ovariectomy in adulthood. This effect may be independent of ovarian hormones on prefrontal PV+ interneurons response to stress.

Sex- and exposure age-dependent effects of adolescent stress on ventral tegmental area dopamine system and its afferent regulators

Adolescent stress is a risk factor for schizophrenia. Emerging evidence suggests that age-dependent sensitive windows for childhood trauma are associated more strongly with adult psychosis, but the neurobiological basis and potential sex differences are unknown.Using in vivo electrophysiology and immunohistology in rats, we systematically compared the effects of two age-defined adolescent stress paradigms, prepubertal (postnatal day [PD] 21-30; PreP-S) and postpubertal (PD41-50; PostP-S) foot-shock and restraint combined stress, on ventral tegmental area (VTA) dopaminergic activity, pyramidal neuron activity in the ventral hippocampus (vHipp) and the basolateral amygdala (BLA), corticoamygdalar functional inhibitory control, and vHipp and BLA parvalbumin interneuron (PVI) impairments. These endpoints were selected based on their well-documented roles in the pathophysiology of psychosis.Overall, we found distinct sex- and exposure age-dependent stress vulnerability. Specifically, while males were selectively vulnerable to PreP-S-induced adult VTA dopamine neuron and vHipp hyperactivities, females were selectively vulnerable to PostP-S. These male selective PreP-S effects were correlated with stress-induced aberrant persistent BLA hyperactivity, dysfunctional prefrontal inhibitory control of BLA neurons, and vHipp/BLA PVI impairments. In contrast, female PostP-S only produced vHipp PVI impairments in adults, with the BLA structure and functions largely unaffected.Our results indicated distinct adolescent-sensitive periods during which stress can sex-dependently confer maximal risks to corticolimbic systems to drive dopamine hyperactivity, which provide critical insights into the neurobiological basis for sex-biased stress-related psychopathologies emphasizing but not limited to schizophrenia. Furthermore, our work also provides a framework for future translational research on age-sensitive targeted interventions.

Propranolol Administration Modulates Neural Activity in the Hippocampal Hilus During Fear Retrieval

Altered fear learning is a strong behavioral component of anxiety disorders such as post-traumatic stress disorder (PTSD). Recent efforts have attempted to combine exposure therapies with drugs that target fear memory retrieval and memory reconsolidation, in order to improve treatment efficacy. The noradrenergic (NA) signaling system is of particular interest, due to its role in regulating the stress response and its involvement in fear and learning processes. Importantly, propranolol (P), a non-selective β-adrenergic antagonist, has shown the potential in decreasing exaggerated fear in both humans and animal models. In a previous study, we utilized an activity-dependent tagging murine model to determine the neural mechanisms by which propranolol attenuates learned fear. We found that propranolol acutely decreased memory trace reactivation specifically in the dorsal dentate gyrus (dDG), but not in CA3 or CA1. Here, we extended our previous study by investigating whether propranolol additionally altered activity in the hilus, a polymorphic layer that consists of neurons, mossy cells, and GABAergic interneurons. We found that propranolol acutely reduced overall hilar activity in both the dorsal and ventral hilus. Moreover, we report that propranolol significantly altered the activity of parvalbumin (PV)⁺ cells in the ventral (vDG), but not dorsal DG (dDG). Together, these results suggest that a β-adrenergic blockade may affect the activity of excitatory and inhibitory cell types in the hilar layer of the DG, and that these alterations may contribute to manipulating fear memory traces.

Scoping review on environmental enrichment: Are critical periods and sex differences adequately studied?

BACKGROUND

Decades of research have shown the robust behavioral, structural, and molecular effects of environmental enrichment (EE) which predominantly improves neuropathological conditions. However, systematic examination of age and sex influences in response to EE is limited.

OBJECTIVE

Examine the use of EE and evaluate where sex differences (or similarities) are described and whether critical developmental periods are addressed. A critical examination of review articles about EE will establish a framework for the context of the findings of EE-induced effects, improve the impact of future EE studies and improve translatability.

ELIGIBILITY CRITERIA

Narrative, systematic reviews (not original reports) and meta-analyses of any animal species published during 2011 to 2021. Clinical and farming studies were excluded.

SOURCES OF EVIDENCE

Indexed review articles in Pubmed and Psychinfo.

RESULTS

Most studies examine EE during adulthood such as following an injury or following repeated addictive drug exposure. However, in various genetic models of disease states, little attention is paid to effects of EE at different ages. Only some reviews acknowledge that sex differences exist even when the disease state under study is known to be sexually dimorphic. Identified issues include lack of systematic reporting; status of the "control group" (i.e., isolation or pair housing); the use and reporting of proper statistical analyses.

CONCLUSION

Reviews have concluded that EE is most effective when administered early in life but that EE during adulthood is certainly effective. Too few review studies have compared sexes for the effects of EE to make a statement about sex differences. Overall, articles reflect a lack of integration of information on age and sex differences in response to EE. Future studies of EE should examine both sexes and consider critical periods of the lifespan in the experimental models to facilitate the adequate translation of EE as a non-pharmaceutical intervention.

Impact of stress on inhibitory neuronal circuits, our tribute to Bruce McEwen

This manuscript is dedicated to the memory of Bruce S. McEwen, to commemorate the impact he had on how we understand stress and neuronal plasticity, and the profound influence he exerted on our scientific careers. The focus of this review is the impact of stressors on inhibitory circuits, particularly those of the limbic system, but we also consider other regions affected by these adverse experiences. We revise the effects of acute and chronic stress during different stages of development and lifespan, taking into account the influence of the sex of the animals. We review first the influence of stress on the physiology of inhibitory neurons and on the expression of molecules related directly to GABAergic neurotransmission, and then focus on specific interneuron subpopulations, particularly on parvalbumin and somatostatin expressing cells. Then we analyze the effects of stress on molecules and structures related to the plasticity of inhibitory neurons: the polysialylated form of the neural cell adhesion molecule and perineuronal nets. Finally, we review the potential of antidepressants or environmental manipulations to revert the effects of stress on inhibitory circuits.

Behavioral and Neuroanatomical Consequences of Cell-Type Specific Loss of Dopamine D2 Receptors in the Mouse Cerebral Cortex

Developmental dysregulation of dopamine D2 receptors (D2Rs) alters neuronal migration, differentiation, and behavior and contributes to the psychopathology of neurological and psychiatric disorders. The current study is aimed at identifying how cell-specific loss of D2Rs in the cerebral cortex may impact neurobehavioral and cellular development, in order to better understand the roles of this receptor in cortical circuit formation and brain disorders. We deleted D2R from developing cortical GABAergic interneurons (Nkx2.1-Cre) or from developing telencephalic glutamatergic neurons (Emx1-Cre). Conditional knockouts (cKO) from both lines, Drd2^fl/fl, Nkx2.1-Cre⁺ (referred to as GABA-D2R-cKO mice) or Drd2^fl/fl, Emx1-Cre⁺ (referred to as Glu-D2R-cKO mice), exhibited no differences in simple tests of anxiety-related or depression-related behaviors, or spatial or nonspatial working memory. Both GABA-D2R-cKO and Glu-D2R-cKO mice also had normal basal locomotor activity, but GABA-D2R-cKO mice expressed blunted locomotor responses to the psychotomimetic drug MK-801. GABA-D2R-cKO mice exhibited improved motor coordination on a rotarod whereas Glu-D2R-cKO mice were normal. GABA-D2R-cKO mice also exhibited spatial learning deficits without changes in reversal learning on a Barnes maze. At the cellular level, we observed an increase in PV+ cells in the frontal cortex of GABA-D2R-cKO mice and no noticeable changes in Glu-D2R-cKO mice. These data point toward unique and distinct roles for D2Rs within excitatory and inhibitory neurons in the regulation of behavior and interneuron development, and suggest that location-biased D2R pharmacology may be clinically advantageous to achieve higher efficacy and help avoid unwanted effects.