Influence of Chronic Electroconvulsive Seizures on Plasticity-Associated Gene Expression and Perineuronal Nets Within the Hippocampi of Young Adult and Middle-Aged Sprague-Dawley Rats.

BACKGROUND: Electroconvulsive seizure therapy is often used in both treatment-resistant and geriatric depression. However, preclinical studies identifying targets of chronic electroconvulsive seizure (ECS) are predominantly focused on animal models in young adulthood. Given that putative transcriptional, neurogenic, and neuroplastic mechanisms implicated in the behavioral effects of chronic ECS themselves exhibit age-dependent modulation, it remains unknown whether the molecular and cellular targets of chronic ECS vary with age. METHODS: We subjected young adult (2-3 months) and middle-aged (12-13 months), male Sprague Dawley rats to sham or chronic ECS and assessed for despair-like behavior, hippocampal gene expression, hippocampal neurogenesis, and neuroplastic changes in the extracellular matrix, reelin, and perineuronal net numbers. RESULTS: Chronic ECS reduced despair-like behavior at both ages, accompanied by overlapping and unique changes in activity-dependent and trophic factor gene expression. Although chronic ECS had a similar impact on quiescent neural progenitor numbers at both ages, the eventual increase in hippocampal progenitor proliferation was substantially higher in young adulthood. We noted a decline in reelin⁺ cell numbers following chronic ECS only in young adulthood. In contrast, an age-invariant, robust dissolution of perineuronal net numbers that encapsulate parvalbumin⁺ neurons in the hippocampus were observed following chronic ECS. CONCLUSION: Our findings indicate that age is a key variable in determining the nature of chronic ECS-evoked molecular and cellular changes in the hippocampus. This raises the intriguing possibility that chronic ECS may recruit distinct, as well as overlapping, mechanisms to drive antidepressant-like behavioral changes in an age-dependent manner.

Serotonin regulates mitochondrial biogenesis and function in rodent cortical neurons via the 5-HT2A receptor and SIRT1-PGC-1α axis.

Mitochondria in neurons, in addition to their primary role in bioenergetics, also contribute to specialized functions, including regulation of synaptic transmission, Ca2+ homeostasis, neuronal excitability, and stress adaptation. However, the factors that influence mitochondrial biogenesis and function in neurons remain poorly elucidated. Here, we identify an important role for serotonin (5-HT) as a regulator of mitochondrial biogenesis and function in rodent cortical neurons, via a 5-HT2A receptor-mediated recruitment of the SIRT1-PGC-1α axis, which is relevant to the neuroprotective action of 5-HT. We found that 5-HT increased mitochondrial biogenesis, reflected through enhanced mtDNA levels, mitotracker staining, and expression of mitochondrial components. This resulted in higher mitochondrial respiratory capacity, oxidative phosphorylation (OXPHOS) efficiency, and a consequential increase in cellular ATP levels. Mechanistically, the effects of 5-HT were mediated via the 5-HT2A receptor and master modulators of mitochondrial biogenesis, SIRT1 and PGC-1α. SIRT1 was required to mediate the effects of 5-HT on mitochondrial biogenesis and function in cortical neurons. In vivo studies revealed that 5-HT2A receptor stimulation increased cortical mtDNA and ATP levels in a SIRT1-dependent manner. Direct infusion of 5-HT into the neocortex and chemogenetic activation of 5-HT neurons also resulted in enhanced mitochondrial biogenesis and function in vivo. In cortical neurons, 5-HT enhanced expression of antioxidant enzymes, decreased cellular reactive oxygen species, and exhibited neuroprotection against excitotoxic and oxidative stress, an effect that required SIRT1. These findings identify 5-HT as an upstream regulator of mitochondrial biogenesis and function in cortical neurons and implicate the mitochondrial effects of 5-HT in its neuroprotective action.

Altered Membrane Mechanics Provides a Receptor-Independent Pathway for Serotonin Action.

Serotonin, an important signaling molecule in humans, has an unexpectedly high lipid membrane affinity. The significance of this finding has evoked considerable speculation. Here we show that membrane binding by serotonin can directly modulate membrane properties and cellular function, providing an activity pathway completely independent of serotonin receptors. Atomic force microscopy shows that serotonin makes artificial lipid bilayers softer, and induces nucleation of liquid disordered domains inside the raft-like liquid-ordered domains. Solid-state NMR spectroscopy corroborates this data at the atomic level, revealing a homogeneous decrease in the order parameter of the lipid chains in the presence of serotonin. In the RN46A immortalized serotonergic neuronal cell line, extracellular serotonin enhances transferrin receptor endocytosis, even in the presence of broad-spectrum serotonin receptor and transporter inhibitors. Similarly, it increases the membrane binding and internalization of oligomeric peptides. Our results uncover a mode of serotonin-membrane interaction that can potentiate key cellular processes in a receptor-independent fashion.

Early-life stress impairs postnatal oligodendrogenesis and adult emotional behaviour through activity-dependent mechanisms.

Exposure to stress during early life (infancy/childhood) has long-term effects on the structure and function of the prefrontal cortex (PFC), and increases the risk for adult depression and anxiety disorders. However, little is known about the molecular and cellular mechanisms of these effects. Here, we focused on changes induced by chronic maternal separation during the first 2 weeks of postnatal life. Unbiased mRNA expression profiling in the medial PFC (mPFC) of maternally separated (MS) pups identified an increased expression of myelin-related genes and a decreased expression of immediate early genes. Oligodendrocyte lineage markers and birthdating experiments indicated a precocious oligodendrocyte differentiation in the mPFC at P15, leading to a depletion of the oligodendrocyte progenitor pool in MS adults. We tested the role of neuronal activity in oligodendrogenesis, using designed receptors exclusively activated by designed drugs (DREADDs) techniques. hM4Di or hM3Dq constructs were transfected into mPFC neurons using fast-acting AAV8 viruses. Reduction of mPFC neuron excitability during the first 2 postnatal weeks caused a premature differentiation of oligodendrocytes similar to the MS pups, while chemogenetic activation normalised it in the MS animals. Bidirectional manipulation of neuron excitability in the mPFC during the P2-P14 period had long lasting effects on adult emotional behaviours and on temporal object recognition: hM4Di mimicked MS effects, while hM3Dq prevented the pro-depressive effects and short-term memory impairment of MS. Thus, our results identify neuronal activity as a critical target of early-life stress and demonstrate its function in controlling both postnatal oligodendrogenesis and adult mPFC-related behaviours.

Differential signaling signatures evoked by DOI versus lisuride stimulation of the 5-HT2A receptor.

The 5-HT2A receptor is a target for hallucinogenic and non-hallucinogenic ligands that evoke unique behavioral, electrophysiological and molecular consequences. Here, we explored the differential effects of distinct 5-HT2A receptor ligands on signaling pathways downstream to the 5-HT2A receptor. The hallucinogenic 5-HT2A receptor agonist DOI evoked an enhanced signaling response compared to the non-hallucinogenic 5-HT2A receptor agonist lisuride in human/rat 5-HT2AR-EGFP receptor expressing HEK293 cell lines and cortical neuronal cultures. We noted higher levels of phospho-PLC, pPKC, pERK, pCaMKII, pCREB, as well as higher levels of IP3 and DAG production following 5-HT2A receptor stimulation with DOI. Our study reveals distinct signaling signatures, differing in magnitude and kinetics at the 5-HT2A receptor in response to DOI versus lisuride.

Acute stress evokes sexually dimorphic, stressor-specific patterns of neural activation across multiple limbic brain regions in adult rats.

Stress enhances the risk for psychiatric disorders such as anxiety and depression. Stress responses vary across sex and may underlie the heightened vulnerability to psychopathology in females. Here, we examined the influence of acute immobilization stress (AIS) and a two-day short-term forced swim stress (FS) on neural activation in multiple cortical and subcortical brain regions, implicated as targets of stress and in the regulation of neuroendocrine stress responses, in male and female rats using Fos as a neural activity marker. AIS evoked a sex-dependent pattern of neural activation within the cingulate and infralimbic subdivisions of the medial prefrontal cortex (mPFC), lateral septum (LS), habenula, and hippocampal subfields. The degree of neural activation in the mPFC, LS, and habenula was higher in males. Female rats exhibited reduced Fos positive cell numbers in the dentate gyrus hippocampal subfield, an effect not observed in males. We addressed whether the sexually dimorphic neural activation pattern noted following AIS was also observed with the short-term stress of FS. In the paraventricular nucleus of the hypothalamus and the amygdala, FS similar to AIS resulted in robust increases in neural activation in both sexes. The pattern of neural activation evoked by FS was distinct across sexes, with a heightened neural activation noted in the prelimbic mPFC subdivision and hippocampal subfields in females and differed from the pattern noted with AIS. This indicates that the sex differences in neural activation patterns observed within stress-responsive brain regions are dependent on the nature of stressor experience.

Acute and Chronic Electroconvulsive Seizures (ECS) Differentially Regulate the Expression of Epigenetic Machinery in the Adult Rat Hippocampus.

BACKGROUND: Electroconvulsive seizure treatment is a fast-acting antidepressant therapy that evokes rapid transcriptional, neurogenic, and behavioral changes. Epigenetic mechanisms contribute to altered gene regulation, which underlies the neurogenic and behavioral effects of electroconvulsive seizure. We hypothesized that electroconvulsive seizure may modulate the expression of epigenetic machinery, thus establishing potential alterations in the epigenetic landscape. METHODS: We examined the influence of acute and chronic electroconvulsive seizure on the gene expression of histone modifiers, namely histone acetyltransferases, histone deacetylases, histone methyltransferases, and histone (lysine) demethylases as well as DNA modifying enzymes, including DNA methyltransferases, DNA demethylases, and methyl-CpG-binding proteins in the hippocampi of adult male Wistar rats using quantitative real time-PCR analysis. Further, we examined the influence of acute and chronic electroconvulsive seizure on global and residue-specific histone acetylation and methylation levels within the hippocampus, a brain region implicated in the cellular and behavioral effects of electroconvulsive seizure. RESULTS: Acute and chronic electroconvulsive seizure induced a primarily unique, and in certain cases bidirectional, regulation of histone and DNA modifiers, and methyl-CpG-binding proteins, with an overlapping pattern of gene regulation restricted to Sirt4, Mll3, Jmjd3, Gadd45b, Tet2, and Tet3. Global histone acetylation and methylation levels were predominantly unchanged, with the exception of a significant decline in H3K9 acetylation in the hippocampus following chronic electroconvulsive seizure. CONCLUSIONS: Electroconvulsive seizure treatment evokes the transcriptional regulation of several histone and DNA modifiers, and methyl-CpG-binding proteins within the hippocampus, with a predominantly distinct pattern of regulation induced by acute and chronic electroconvulsive seizure.

Early stress evokes dysregulation of histone modifiers in the medial prefrontal cortex across the life span.

Early stress has been hypothesized to recruit epigenetic mechanisms to mediate persistent molecular, cellular, and behavioral changes. Here, we have examined the consequence of the early life stress of maternal separation (ES) on the gene expression of several histone modifiers that regulate histone acetylation and methylation within the medial prefrontal cortex (mPFC), a key limbic brain region that regulates stress responses and mood-related behavior. ES animals exhibit gene regulation of both writer (histone acetyltransferases and histone methyltransferases) and eraser (histone deacetylases and histone lysine demethylases) classes of histone modifiers. While specific histone modifiers (Kat2a, Smyd3, and Suv420h1) and the sirtuin, Sirt4 were downregulated across life within the mPFC of ES animals, namely at postnatal Day 21, 2 months, and 15 months of age, we also observed gene regulation restricted to these specific time points. Despite the decline noted in expression of several histone modifiers within the mPFC following ES, this was not accompanied by any change in global or residue-specific H3 acetylation and methylation. Our findings indicate that ES results in the regulation of several histone modifiers within the mPFC across life, and suggest that such perturbations may contribute to the altered prefrontal structural and functional plasticity observed following early adversity.

Perspectives on thyroid hormone action in adult neurogenesis.

Thyroid hormone exhibits profound effects on neural progenitor turnover, survival, maturation, and differentiation during perinatal development. Studies over the past decade have revealed that thyroid hormone continues to retain an important influence on progenitors within the neurogenic niches of the adult mammalian brain. The focus of the current review is to critically examine and summarize the current state of understanding of the role of thyroid hormone in regulating adult neurogenesis within the major neurogenic niches of the subgranular zone in the hippocampus and the subventricular zone lining the lateral ventricles. We review in depth the studies that highlight a role for thyroid hormone, in particular the TRα1 receptor isoform, in regulating progenitor survival and commitment to a neuronal fate. We also discuss putative models for the mechanism of action of thyroid hormone/TRα1 on specific stages of subgranular zone and subventricular zone progenitor development, and highlight potential thyroid hormone responsive target genes that may contribute to the neurogenic effects of thyroid hormone. The effects of thyroid hormone on adult neurogenesis are discussed in the context of a potential role of these effects in the cognitive- and mood-related consequences of thyroid hormone dysfunction. Finally, we detail hitherto unexplored aspects of the effects of thyroid hormone on adult neurogenesis that provide impetus for future studies to gain a deeper mechanistic insight into the neurogenic effects of thyroid hormone. Thyroid hormone regulation of adult neurogenesis in the mammalian brain exhibits both unique and overlapping effects within distinct neurogenic niches. Thyroid hormone regulates hippocampal subgranular zone (SGZ) progenitor survival and neuronal cell fate acquisition and influences subventricular zone (SVZ) progenitor cell turnover, cell cycle exit, and neuronal cell fate acquisition. In this review, we summarize, critically discuss and highlight open questions in regard to thyroid hormone regulation of adult neurogenesis.

The adaptive and maladaptive continuum of stress responses - a hippocampal perspective.

Exposure to stressors elicits a spectrum of responses that span from potentially adaptive to maladaptive consequences at the structural, cellular and physiological level. These responses are particularly pronounced in the hippocampus where they also appear to influence hippocampal-dependent cognitive function and emotionality. The factors that influence the nature of stress-evoked consequences include the chronicity, severity, predictability and controllability of the stressors. In addition to adult-onset stress, early life stress also elicits a wide range of structural and functional responses, which often exhibit life-long persistence. However, the outcome of early stress exposure is often contingent on the environment experienced in adulthood, and could either aid in stress coping or could serve to enhance susceptibility to the negative consequences of adult stress. This review comprehensively examines the consequences of adult and early life stressors on the hippocampus, with a focus on their effects on neurogenesis, neuronal survival, structural and synaptic plasticity and hippocampal-dependent behaviors. Further, we discuss potential factors that may tip stress-evoked consequences from being potentially adaptive to largely maladaptive.

Early stress evokes temporally distinct consequences on the hippocampal transcriptome, anxiety and cognitive behaviour.

The early stress of maternal separation (ES) exerts long-lasting effects on cognition and anxiety. Recent evidence indicates enhanced hippocampus-dependent spatial learning in young adult ES animals, which shifts towards a decline in long-term memory in middle-aged life. Further, we find that ES animals exhibit enhanced anxiety in young adulthood that does not persist into middle-aged life. Here, we demonstrate unique, predominantly non-overlapping, hippocampal transcriptomes in young adult and middle-aged ES animals that accompany the temporally-specific behavioural consequences. Strikingly, the extent of gene dysregulation in middle-aged ES animals was substantially higher than in young adulthood. Functional analysis revealed distinct biological processes enriched at the two ages, highlighting the temporal shift in ES-evoked gene regulation. Our results suggest that ES history interacts with aging to exacerbate age-associated transcriptional changes and cognitive decline. qPCR profiling of histone deacetylases (Hdacs) and histone methyltransferases (HMTs) revealed an age-dependent, opposing regulation with decreased expression noted in young adult ES animals (Hdac 2, 7, 8, 9 and Suv39h1) and enhanced levels in middle-aged life (Hdac 2, 6, 8 and Suv39h1). While altered expression of histone modifying enzymes did not translate into global histone acetylation or methylation changes, we noted differential enrichment of histone acetylation and methylation modifications at the promoters of multiple genes regulated in the hippocampi of young adult and middle-aged ES animals. Our results highlight the differential molecular and behavioural consequences of ES across a life-span, and suggest a possible role for epigenetic mechanisms in contributing to the temporally-specific transcriptional changes following ES.

Single episode of mild murine malaria induces neuroinflammation, alters microglial profile, impairs adult neurogenesis, and causes deficits in social and anxiety-like behavior.

Cerebral malaria is associated with cerebrovascular damage and neurological sequelae. However, the neurological consequences of uncomplicated malaria, the most prevalent form of the disease, remain uninvestigated. Here, using a mild malaria model, we show that a single Plasmodium chabaudi adami infection in adult mice induces neuroinflammation, neurogenic, and behavioral changes in the absence of a blood-brain barrier breach. Using cytokine arrays we show that the infection induces differential serum and brain cytokine profiles, both at peak parasitemia and 15days post-parasite clearance. At the peak of infection, along with the serum, the brain also exhibited a definitive pro-inflammatory cytokine profile, and gene expression analysis revealed that pro-inflammatory cytokines were also produced locally in the hippocampus, an adult neurogenic niche. Hippocampal microglia numbers were enhanced, and we noted a shift to an activated profile at this time point, accompanied by a striking redistribution of the microglia to the subgranular zone adjacent to hippocampal neuronal progenitors. In the hippocampus, a distinct decline in progenitor turnover and survival was observed at peak parasitemia, accompanied by a shift from neuronal to glial fate specification. Studies in transgenic Nestin-GFP reporter mice demonstrated a decline in the Nestin-GFP(+)/GFAP(+) quiescent neural stem cell pool at peak parasitemia. Although these cellular changes reverted to normal 15days post-parasite clearance, specific brain cytokines continued to exhibit dysregulation. Behavioral analysis revealed selective deficits in social and anxiety-like behaviors, with no change observed in locomotor, cognitive, and depression-like behaviors, with a return to baseline at recovery. Collectively, these findings indicate that even a single episode of mild malaria results in alterations of the brain cytokine profile, causes specific behavioral dysfunction, is accompanied by hippocampal microglial activation and redistribution, and a definitive, but transient, suppression of adult hippocampal neurogenesis.

Induction of the plasticity-associated immediate early gene Arc by stress and hallucinogens: role of brain-derived neurotrophic factor.

Exposure to stress and hallucinogens in adulthood evokes persistent alterations in neurocircuitry and emotional behaviour. The structural and functional changes induced by stress and hallucinogen exposure are thought to involve transcriptional alterations in specific effector immediate early genes. The immediate early gene, activity regulated cytoskeletal-associated protein (Arc), is important for both activity and experience dependent plasticity. We sought to examine whether trophic factor signalling through brain-derived neurotrophic factor (BDNF) contributes to the neocortical regulation of Arc mRNA in response to distinct stimuli such as immobilization stress and the hallucinogen 2,5-dimethoxy-4-iodoamphetamine (DOI). Acute exposure to either immobilization stress or DOI induced Arc mRNA levels within the neocortex. BDNF infusion into the neocortex led to a robust up-regulation of local Arc transcript expression. Further, baseline Arc mRNA expression in the neocortex was significantly decreased in inducible BDNF knockout mice with an adult-onset, forebrain specific BDNF loss. The induction of Arc mRNA levels in response to both acute immobilization stress or a single administration of DOI was significantly attenuated in the inducible BDNF knockout mice. Taken together, our results implicate trophic factor signalling through BDNF in the regulation of cortical Arc mRNA expression, both under baseline conditions and following stress and hallucinogen exposure. These findings suggest the possibility that the regulation of Arc expression via BDNF provides a molecular substrate for the structural and synaptic plasticity observed following stimuli such as stress and hallucinogens.

Thyroid hormone regulation of adult hippocampal neurogenesis: Putative molecular and cellular mechanisms.

Adult hippocampal neurogenesis is sensitive to perturbations in thyroid hormone signaling, with evidence supporting a key role for thyroid hormone and thyroid hormone receptors (TRs) in the regulation of postmitotic progenitor survival and neuronal differentiation. In this book chapter we summarize the current understanding of the effects of thyroid hormone signaling on adult hippocampal progenitor development, and also critically address the role of TRs in regulation of distinct aspects of stage-specific hippocampal progenitor progression. We highlight actions of thyroid hormone on thyroid hormone responsive target genes, and the implications for hippocampal progenitor regulation. Given the influence of thyroid hormone on both mitochondrial and lipid metabolism, we discuss a putative role for regulation of metabolism in the effects of thyroid hormone on adult hippocampal neurogenesis. Finally, we highlight specific ideas that require detailed experimental investigation, and the need for future studies to obtain a deeper mechanistic insight into the influence of thyroid hormone and TRs in the developmental progression of adult hippocampal progenitors.

Early Adversity and Accelerated Brain Aging: A Mini-Review.

Early adversity is an important risk factor that influences brain aging. Diverse animal models of early adversity, including gestational stress and postnatal paradigms disrupting dam-pup interactions evoke not only persistent neuroendocrine dysfunction and anxio-depressive behaviors, but also perturb the trajectory of healthy brain aging. The process of brain aging is thought to involve hallmark features such as mitochondrial dysfunction and oxidative stress, evoking impairments in neuronal bioenergetics. Furthermore, brain aging is associated with disrupted proteostasis, progressively defective epigenetic and DNA repair mechanisms, the build-up of neuroinflammatory states, thus cumulatively driving cellular senescence, neuronal and cognitive decline. Early adversity is hypothesized to evoke an "allostatic load" via an influence on several of the key physiological processes that define the trajectory of healthy brain aging. In this review we discuss the evidence that animal models of early adversity impinge on fundamental mechanisms of brain aging, setting up a substratum that can accelerate and compromise the time-line and nature of brain aging, and increase risk for aging-associated neuropathologies.

Chronic hM3Dq-DREADD-mediated chemogenetic activation of parvalbumin-positive inhibitory interneurons in postnatal life alters anxiety and despair-like behavior in adulthood in a task- and sex-dependent manner.

Animal models of early adversity or neurodevelopmental disorders are associated with altered parvalbumin (PV)-positive inhibitory interneuron number and function, correlated with a dysregulated excitation-inhibition (E/I) balance that is implicated in the pathophysiology of neuropsychiatric disorders. We sought to address whether altering neuronal activity of PV-positive interneurons during the postnatal developmental window influences the emergence of anxio-depressive behaviors in adulthood, which are known to be perturbed in models of early adversity and neurodevelopmental disorders. We used a PV-Cre::hM3Dq-DREADD bigenic mouse line that selectively expresses the hM3Dq-DREADD receptor in PV-positive interneurons, and chemogenetically enhanced Gq signaling in PV-positive interneurons during the postnatal window via administration of the DREADD agonist, clozapine-N-oxide. Immunofluorescence studies have indicated the selective expression of hM3Dq-DREADD in PV-positive interneurons in limbic circuits, and have revealed a reduction in expression of the neuronal activity marker, c-Fos, in these circuits, following chemogenetic hM3Dq-DREADD-mediated activation of PV-positive inhibitory interneurons. We noted no change in either growth or sensorimotor reflex milestones following chronic hM3Dq-DREADD-mediated chemogenetic activation of PV-positive inhibitory interneurons in postnatal life. Adult male and female PV-Cre::hM3DqDREADD bigenic mice with a history of postnatal chemogenetic activation of PV-positive interneurons exhibited a reduction in anxiety and despair-like behavior in adulthood, which was noted in both a behavioral task- and sex-dependent manner. These results indicate that altering neuronal activity within PV-positive interneurons during the critical postnatal developmental window can shape the emergence of anxio-depressive behaviors in adulthood, with sex as a variable playing a key role in determining behavioral outcomes.

Chronic hM4Di-DREADD-Mediated Chemogenetic Inhibition of Forebrain Excitatory Neurons in Postnatal or Juvenile Life Does Not Alter Adult Mood-Related Behavior.

G-protein-coupled receptors (GPCRs) coupled to Gi signaling, in particular downstream of monoaminergic neurotransmission, are posited to play a key role during developmental epochs (postnatal and juvenile) in shaping the emergence of adult anxiodepressive behaviors and sensorimotor gating. To address the role of Gi signaling in these developmental windows, we used a CaMKIIα-tTA::TRE hM4Di bigenic mouse line to express the hM4Di-DREADD (designer receptor exclusively activated by designer drugs) in forebrain excitatory neurons and enhanced Gi signaling via chronic administration of the DREADD agonist, clozapine-N-oxide (CNO) in the postnatal window (postnatal days 2-14) or the juvenile window (postnatal days 28-40). We confirmed that the expression of the HA-tagged hM4Di-DREADD was restricted to CaMKIIα-positive neurons in the forebrain, and that the administration of CNO in postnatal or juvenile windows evoked inhibition in forebrain circuits of the hippocampus and cortex, as indicated by a decline in expression of the neuronal activity marker c-Fos. hM4Di-DREADD-mediated inhibition of CaMKIIα-positive forebrain excitatory neurons in postnatal or juvenile life did not impact the weight profile of mouse pups, and also did not influence the normal ontogeny of sensory reflexes. Further, postnatal or juvenile hM4Di-DREADD-mediated inhibition of CaMKIIα-positive forebrain excitatory neurons did not alter anxiety- or despair-like behaviors in adulthood and did not impact sensorimotor gating. Collectively, these results indicate that chemogenetic induction of Gi signaling in CaMKIIα-positive forebrain excitatory neurons in postnatal and juvenile temporal windows does not appear to impinge on the programming of anxiodepressive behaviors in adulthood.