Early Gene C-fos Research Articles

BDNF augmentation reverses cranial radiation therapy-induced cognitive decline and neurodegenerative consequences

Cranial radiation therapy (RT) for brain cancers is often associated with the development of radiation-induced cognitive dysfunction (RICD). RICD significantly impacts the quality of life for cancer survivors, highlighting an unmet medical need. Previous human studies revealed a marked reduction in plasma brain-derived neurotrophic factor (BDNF) post-chronic chemotherapy, linking this decline to a substantial cognitive dysfunction among cancer survivors. Moreover, riluzole (RZ)-mediated increased BDNF in vivo in the chemotherapy-exposed mice reversed cognitive decline. RZ is an FDA-approved medication for ALS known to increase BDNF in vivo. In an effort to mitigate the detrimental effects of RT-induced BDNF decline in RICD, we tested the efficacy of RZ in a cranially irradiated (9 Gy) adult mouse model. Notably, RT-exposed mice exhibited significantly reduced hippocampal BDNF, accompanied by increased neuroinflammation, loss of neuronal plasticity-related immediate early gene product, cFos, and synaptic density. Spatial transcriptomic profiling comparing the RT + Vehicle with the RT + RZ group showed gene expression signatures of neuroprotection of hippocampal excitatory neurons post-RZ. RT-exposed mice performed poorly on learning and memory, and memory consolidation tasks. However, irradiated mice receiving RZ (13 mg/kg, drinking water) for 6–7 weeks showed a significant improvement in cognitive function compared to RT-exposed mice receiving vehicle. Dual-immunofluorescence staining, spatial transcriptomics, and biochemical assessment of RZ-treated irradiated brains demonstrated preservation of synaptic integrity and mature neuronal plasticity but not neurogenesis and reduced neuroinflammation concurrent with elevated BDNF levels and transcripts compared to vehicle-treated irradiated brains. In summary, oral administration of RZ represents a viable and translationally feasible neuroprotective approach against RICD.

Synapse-to-nucleus ERK-CREB transcriptional signaling requires dendrite-to-soma Ca2+propagation mediated by L-type voltage-gated Ca2+ channels.

The cAMP-response element binding protein (CREB) transcription factor controls the expression of the neuronal immediate early genes c-Fos, Arc, and Bdnf and is essential for long-lasting synaptic plasticity underlying learning and memory. Despite this critical role, there is still ongoing debate regarding the synaptic excitation-transcription (E-T) coupling mechanisms mediating CREB activation in the nucleus. Here we employed optical uncaging of glutamate to mimic synaptic excitation of distal dendrites in conjunction with simultaneous imaging of intracellular Ca2+ dynamics and transcriptional reporter gene expression to elucidate CREB E-T coupling mechanisms in hippocampal neurons cultured from both male and female rats. Using this approach, we found that CREB-dependent transcription was engaged following dendritic stimulation of N-methyl, D-aspartate receptors (NMDARs) only when Ca2+ signals propagated to the soma via subsequent activation of L-type voltage-gated Ca2+ channels resulting in activation of Extracellular signal-Regulated Kinase (ERK) MAP kinase signaling to sustain CREB phosphorylation in the nucleus. In contrast, dendrite-restricted Ca2+ signals generated by NMDARs failed to stimulate CREB-dependent transcription. Furthermore, Ca2+-CaM-dependent kinase (CaMK)-mediated signaling pathways that may transiently contribute to CREB-phosphorylation following stimulation were ultimately dispensable for downstream CREB-dependent transcription and c-Fos induction. These findings emphasize the essential role that L-type Ca2+ channels play in rapidly relaying signals over long distances from synapses located on distal dendrites to the nucleus to control gene expression.Significance Statement The transcription factor CREB controls gene expression programs required for long-lasting synaptic plasticity and learning and memory, yet the synapse-to-nucleus signaling mechanisms mediating CREB activation are still unclear. Using glutamate uncaging to mimic synaptic input to dendrites, this study shows that Ca2+ signals propagated to the soma by L-type voltage-gated Ca2+ channels engage the ERK MAP kinase cascade to mediate CREB phosphorylation and CREB-dependent transcription. In contrast, dendrite-restricted Ca2+ signals generated primarily by NMDARs failed to effectively engage this signaling pathway or CREB-dependent transcription. In addition, we found that while ERK and CaMK pathways may both contribute to increased CREB phosphorylation immediately following neuronal stimulation, sustained ERK signaling to CREB was necessary to effectively drive CREB-dependent transcription.

22 and 50 kHz rat ultrasonic vocalization playback reveals sex differences in behavior and cFos in brain regions associated with affective processing

Adult rats communicate using ultrasonic vocalization (USV) frequencies indicating negative (22 kHz) or positive (50 kHz) affective states. Playback of USVs can serve as an ethologically translational method to study affective processing in response to socially communicated states. However, few studies have examined behavioral and neural effects of USV playback in both male and female rats. Here, adult male and female Sprague-Dawley rats experienced a 20-min open field test (OFT) with either silence, 22 kHz, or 50 kHz recorded USV playback. Center exploration and locomotor activity were analyzed to characterize sex differences in playback effects. Results suggest that females display greater sensitivity to frequency-specific effects of USV playback in this paradigm compared to males. 50 kHz USV playback evoked an immediate increase in center exploration and locomotor activity in females, indicating the appetitive nature of 50 kHz USVs. Initially, 22 kHz playback inhibited center exploration in the OFT compared to 50 kHz. However, females exhibited a switch in behavioral strategy in response to 22 kHz following prolonged playback. Following OFT, neural activity was quantified via the immediate early gene cFos. Results from cFos quantification showed sex- and region-specific differences in neural recruitment in areas of the brain associated with affective processing, including the prefrontal cortex, amygdala, bed nucleus of the stria terminalis, and nucleus accumbens. Taken together, this work provides a normative baseline for understanding how sex influences behavioral and neural responses to USV playback, which can be leveraged to study anxiety, communication, and affect in an ethologically relevant assay.

Persistent threat avoidance following negative reinforcement is not associated with elevated state anxiety.

Obsessive-Compulsive Disorder (OCD) is a debilitating illness consisting of obsessions and compulsions. OCD severity and treatment response are correlated with avoidant behaviors thought be performed to alleviate obsession-related anxiety. However, little is known about either the role of avoidance in the development of OCD or the interplay between anxiety states and avoidance behaviors. We have developed an instrumental negative reinforcement (i.e. active avoidance) paradigm in which mice must lever-press to avoid upcoming foot shocks. We show that mice (both sexes) can learn this task with high acquisition rates (75%) and that this behavior is largely stable when introducing uncertainty and modifying task structure. Furthermore, mice continue to perform avoidance responses on trials where lever pressing is not reinforced and increase response rates as they are maintained on this paradigm. With this paradigm, we did not find a relationship between negative reinforcement history and anxiety-related behaviors in well-established anxiety assays. Finally, we performed exploratory analyses to identify candidate regions involved in well-trained negative reinforcement using expression of the immediate early gene c-Fos. We detected correlated c-Fos expression in 1) cortico-striatal regions which regulate active avoidance in other paradigms and 2) amygdala circuits known to regulate conditioned defensive behaviors.Significance Statement Studies in patients with OCD suggest that compulsions are performed to avoid perceived threats and modulate anxiety tied to obsessions and/or compulsions. The negative reinforcement of avoidance and alleviated anxiety could therefore be a key driver of compulsive behaviors. However, there are still outstanding questions concerning the relationship between these two behaviors and the neural circuits involved in mediating negative reinforcement. We have developed an operant negative reinforcement paradigm in mice with discrete avoid and escape behaviors that can be learned without prior reward training with high throughput (75% acquisition) with responding that persists during nonreinforced trials. However, no differences were observed between negative reinforcement vs. unshocked and inescapably shocked controls, suggesting that continued negative reinforcement did not impact anxiety.

BDNF augmentation reverses cranial radiation therapy-induced cognitive decline and neurodegenerative consequences.

Cranial radiation therapy (RT) for brain cancers is often associated with the development of radiation-induced cognitive dysfunction (RICD). RICD significantly impacts the quality of life for cancer survivors, highlighting an unmet medical need. Previous human studies revealed a marked reduction in plasma brain-derived neurotrophic factor (BDNF) post-chronic chemotherapy, linking this decline to a substantial cognitive dysfunction among cancer survivors. Moreover, riluzole (RZ)-mediated increased BDNF in vivo in the chemotherapy-exposed mice reversed cognitive decline. RZ is an FDA-approved medication for ALS known to increase BDNF in vivo . In an effort to mitigate the detrimental effects of RT-induced BDNF decline in RICD, we tested the efficacy of RZ in a cranially irradiated (9 Gy) adult mouse model. Notably, RT-exposed mice exhibited significantly reduced hippocampal BDNF, accompanied by increased neuroinflammation, loss of neuronal plasticity-related immediate early gene product, cFos, and synaptic density. Spatial transcriptomic profiling comparing the RT+Veh with the RT+RZ group showed gene expression signatures of neuroprotection of hippocampal excitatory neurons post-RZ. RT-exposed mice performed poorly on learning and memory, and memory consolidation tasks. However, irradiated mice receiving RZ (13 mg/kg, drinking water) for 6-7 weeks showed a significant improvement in cognitive function compared to RT-exposed mice receiving vehicle. Dual-immunofluorescence staining, spatial transcriptomics, and biochemical assessment of RZ-treated irradiated brains demonstrated preservation of synaptic integrity and neuronal plasticity but not neurogenesis and reduced neuroinflammation concurrent with elevated BDNF levels and transcripts compared to vehicle-treated irradiated brains. In summary, oral administration of RZ represents a viable and translationally feasible neuroprotective approach against RICD.

Proteomic Profile of Circulating Extracellular Vesicles in the Brain after Δ9-Tetrahydrocannabinol Inhalation.

Given the increasing use of cannabis in the US, there is an urgent need to better understand the drug's effects on central signaling mechanisms. Extracellular vesicles (EVs) have been identified as intercellular signaling mediators that contain a variety of cargo, including proteins. Here, we examined whether the main psychoactive component in cannabis, Δ9-tetrahydrocannabinol (THC), alters EV protein signaling dynamics in the brain. We first conducted in vitro studies, which found that THC activates signaling in choroid plexus epithelial cells, resulting in transcriptional upregulation of the cannabinoid 1 receptor and immediate early gene c-fos, in addition to the release of EVs containing RNA cargo. Next, male and female rats were examined for the effects of either acute or chronic exposure to aerosolized ('vaped') THC on circulating brain EVs. Cerebrospinal fluid was extracted from the brain, and EVs were isolated and processed with label-free quantitative proteomic analyses via high-resolution tandem mass spectrometry. Interestingly, circulating EV-localized proteins were differentially expressed based on acute or chronic THC exposure in a sex-specific manner. Taken together, these findings reveal that THC acts in the brain to modulate circulating EV signaling, thereby providing a novel understanding of how exogenous factors can regulate intercellular communication in the brain.

Comparative analysis of the excitatory and inhibitory hippocampal neurons activity during associative context memory retrieval

In the present study, we analyzed the differential involvement of hippocampal interneurons and pyramidal neurons in the retrieval of associative aversive context memory. For this purpose, we used a model of associative learning in which the formation of a neutral context memory and the subsequent association of this memory with the footshock US during a brief reminder of the context were significantly separated in time. The activation of hippocampal neurons during associative context memory retrieval in this task was addressed by immunohistochemical detection of the immediate early gene c-fos protein. Retrieval of associative context memory was accompanied by an increase in the number of c-Fos-positive cells in the CA1 region, but not in the CA3 region and the dentate gyrus of the hippocampus. Next, a protein marker, the product of the homeobox-containing gene Emx1, was used to specifically identify excitatory neurons, and the marker glutamate decarboxylase, GAD, the product of the GAD1 and GAD2 genes, was used to specifically identify inhibitory neurons. The results of double staining for cell markers and c-Fos protein showed that during retrieval of associative aversive context memory in the CA1 region of the hippocampus, both Emx1-positive excitatory neurons and, less, GAD-positive inhibitory interneurons were activated. At the same time, regardless of the type of behavioral procedure (retrieval of associative context memory, non-associative context memory, or exploration of context, where animals previously received the footshock but did not remember it), the proportion of activated excitatory and inhibitory neurons remained constant, only the number of activated cells of each type changed. Altogether, our results indicate the specific role of hippocampal CA1 neurons in associative context memory and demonstrate that both excitatory and inhibitory neurons are involved in the encoding of such memory.

The role of FGF2 in stress-induced cFos expression

During periods of stress, organisms endocrine systems respond by releasing glucocorticoids which later get expressed through corticosterone, simplified as CORT. CORT is proved to express FGF2, proteins found in critical glial cells named astrocytes. Increased FGF2 expression leads to higher rate of cell proliferation - including neurons. Theres been discoveries that newborn neurons, specifically those who have been exposed to FGF2, led to early neuron activation and enhanced neuronal function. Whats unclear is whether FGF2 played a role in somehow newborn neurons having enhanced function and activating earlier than usual (by releasing the early activation gene cFos). An experiment has been outlined in order to test the hypothesis that FGF2 does indeed play a role in altering some neurons. Using nanoparticles containing the micro RNA of NUDT6 - a gene that suppresses FGF2 expression - to target FGF2 in adult male Sprague-Dawley rats would directly test if FGF2 played a role in enhanced neuron activation.

Sex differences in the effects of N-ethylpentylone in young CD1 mice: Insights on behaviour, thermoregulation and early gene expression.

New psychoactive substances such as N-ethylpentylone (NEP) are continuously emerging in the illicit drug market, and knowledge of their effects and risks, which may vary between sexes, is scarce. Our present study compares some key effects of NEP in male and female mice. Psychostimulant, rewarding and reinforcing effects were investigated by tracking locomotor activity, conditioned place preference (CPP) paradigm and through a self-administration (SA) procedure, respectively, in CD1 mice. Moreover, the expression of early genes (C-fos, Arc, Csnk1e, Pdyn, Pp1r1b and Bdnf in addiction-related brain areas) was assessed by qPCR. Finally, serum and brain levels of NEP were determined by UHPLC-MS/MS. NEP-treated males experimented locomotor sensitisation and showed higher and longer increases in locomotion as well as higher hyperthermia after repeated administration than females. Moreover, while preference score in the CPP was similar in both sexes, extinction occurred later, and reinstatement was more easily established for males. Female mice self-administered more NEP than males at a higher dose. Differences in early gene expression (Arc, Bdnf, Csnk1e and Ppp1r1b) were found, but the serum and brain NEP levels did not differ between sexes. Our results suggest that male mice are more sensitive to NEP psychostimulant and rewarding effects. These differences may be attributed to different early gene expression but not to pharmacokinetic factors. Moreover, males appear to be more vulnerable to the hyperthermic effects of NEP, while females might be more prone to NEP abuse.

Innate responses to numerousness reveal neural activation in different brain regions in newly-hatched visually naïve chicks

Whether non-symbolic encoding of quantity is predisposed at birth with dedicated hard-wired neural circuits is debated. Here we presented newly-hatched visually naive chicks with stimuli (flashing dots) of either identical or different numerousness (with a ratio 1:3) with their continuous physical appearance (size, contour length, density, convex hull) randomly changing. Chicks spontaneously tell apart the stimuli on the basis of the number of elements. Upon presentation of either fixed or changing numerousness chicks showed different expression of early gene c-fos in the visual Wulst, the hippocampal formation, the intermediate medial mesopallium, and the caudal part of the nidopallium caudolaterale. The results support the hypothesis that the ability to discriminate quantities does not require any specific instructive experience and involves a neural network with several populations of number-selective neurons. Evidence for innateness of non-symbolic numerical cognition have implications for both neurobiology and philosophy of mathematics.

Comparison of chronic restraint stress-and lipopolysaccharide-induced mouse models of depression: Behavior, c-Fos expression, and microglial and astrocytic activation

Depression is a mental disease that involves a variety of complex physiological mechanisms. A wide range of methods have therefore been used to establish mouse models of depression, and there are currently many ways to develop such mouse models. The present study aimed to compare the effects of various model induction methods and assesses their different effects. To this end, C57BL/6J mice were divided into three experimental groups: the chronic restraint stress (CRS) group received 6 hours of daily confinement within restraint tubes over a 3-week period; the chronic lipopolysaccharide (C-LPS) administration group received daily intraperitoneal injections of 0.5 mg/kg LPS for 1 week; and the acute LPS (A-LPS) administration group received a singular intraperitoneal injection of 0.83 mg/kg LPS. A corresponding control group was established for each experimental condition. Following mouse model establishment, depression-like behaviors were assessed through the forced swimming and tail suspension tests; anxiety-related behaviors were evaluated using the open field test and elevated plus maze. Furthermore, the expression of the immediate early gene c-Fos, ionized calcium-binding adapter molecule 1 (IBA1), and glial fibrillary acidic protein (GFAP) was examined via immunofluorescence. Longer immobility durations during the forced swimming and tail suspension tests were observed across all model groups (p < 0.05), indicating depression-like behaviors. Furthermore, the CRS and C-LPS group, but not the A-LPS group, showed significant anxiety-like behaviors in the elevated plus maze (p < 0.05). All model groups also exhibited significant increases in both time and distance explored within the central area of the open field test (p < 0.05). The activation of GFAP- and IBA1-positive cells in the cerebral cortex and hippocampus was also markedly pronounced in all experimental groups, suggesting the association of neuroinflammatory responses with induced depressive states. The present findings contribute to our understanding of the pathophysiology of stress-induced and neuroinflammatory-associated depression, and will help researchers to choose suitable depression models for their investigations.

Noncortical coding of biological motion in newborn chicks' brain.

Biological motion, the typical movement of vertebrates, is perceptually salient for many animal species. Newly hatched domestic chicks and human newborns show a spontaneous preference for simple biological motion stimuli (point-light displays) at birth prior to any visual learning. Despite evidence of such preference at birth, neural studies performed so far have focused on a specialized neural network involving primarily cortical areas. Here, we presented newly hatched visually naïve domestic chicks to either biological or rigid motion stimuli and measured for the first time their brain activation. Immediate Early Gene (c-Fos) expression revealed selective activation in the preoptic area of the hypothalamus and the nucleus taeniae of the amygdala. These results suggest that subpallial/subcortical regions play a crucial role in biological motion perception at hatching, paving the way for future studies on adult animals, including humans.

Exploring ketamine’s reinforcement, cue-induced reinstatement, and nucleus accumbens cFos activation in male and female long evans rats

Ketamine (KET), a non-competitive N-methyl-d-aspartate (NMDA) receptor antagonist, has rapid onset of antidepressant effects in Treatment-Resistant Depression patients and repeated infusions are required to sustain its antidepressant properties. However, KET is an addictive drug, and so more preclinical and clinical research is needed to assess the safety of recurring treatments in both sexes. Thus, the aim of this study was to investigate the reinforcing properties of various doses of KET (0-, 0.125-, 0.25-, 0.5 mg/kg/infusion) and assess KET’s cue-induced reinstatement and neuronal activation in both sexes of Long Evans rats. Neuronal activation was assessed using the protein expression of the immediate early gene cFos in the nucleus accumbens (Nac), an important brain area implicated in reward, reinforcement and reinstatement to most drug-related cues. Our findings show that KET has reinforcing effects in both male and female rats, albeit exclusively at the highest two doses (0.25 and 0.5 mg/kg/infusion). Furthermore, we noted sex differences, particularly at the highest dose of ketamine, with female rats displaying a higher rate of self-administration. Interestingly, all groups that self-administered KET reinstated to drug-cues. Following drug cue-induced reinstatement test in rats exposed to KET (0.25 mg/kg/infusion) or saline, there was higher cFos protein expression in KET-treated animals compared to saline controls, and higher cFos expression in the core compared to the shell subregions of the Nac. As for reinstatement, there were no notable sex differences reported for cFos expression in the Nac. These findings reveal some sex and dose dependent effects in KET’s reinforcing properties and that KET at all doses induced similar reinstatement in both sexes. This study also demonstrated that cues associated with ketamine induce comparable neuronal activation in the Nac of both male and female rats. This work warrants further research into the potential addictive properties of KET, especially when administered at lower doses which are now being used in the clinic for treating various psychopathologies.

Is the Serpin-Enzyme Complex Receptor an Orphan G-Protein Coupled Receptor?

Alpha-1 antitrypsin (α1-AT) is a member of serine proteinase inhibitors, collectively known as serpins, that inactivate their target enzymes by forming a stabilized serpin-enzyme complex. α1-AT molecules interact with elastase, forming biologically active complexes. It was suggested that the formation of α1-AT-elastase complex would expose a domain from α1-AT molecule that is recognized by a specific cell receptor. Thus, a synthetic peptide, called 105Y, was made based on the sequence of the exposed domain. The peptide binds specifically to human hepatoma HepG2 cells, human monocytes, human neutrophils, and rat pheochromocytoma cells (PC12). This binding is blocked by α1-AT-elastase complex and other serpin-enzyme complexes, suggesting an existence of a specific cell surface receptor, termed SEC receptor, that recognizes serpin enzyme complexes. However, the identity of SEC receptor is still unknown. Thus, we decided to use the Deductive Reasoning Strategy approach to investigate if the SEC receptor belongs to G-protein-coupled receptor (GPCR) family. We measured responsiveness of HepG2 cells as well as human neuroblastoma SHSY5Y cells to 105Y peptide by quantifying their expression of an early response gene c-Fos using real time quantitative polymerase chain reaction (qPCR) and measured their expression of orphan GPCRs using polymerase chain reaction (PCR) followed by gel electrophoresis. Our results indicate that the cells were responding to 105Y peptide and express certain orphan GPCRs. Our goal is to evaluate the necessity of these oGPCRs in 105Y peptide signaling in order to determine the best candidate(s) for the 105Y receptor. These results would shed light on the identity of the SEC receptor for better understanding of the molecular biology and physiology of the serpin-enzyme complexes and their receptors. National Institute of Health. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Dorsal CA3 overactivation mediates witnessing stress-induced recognition memory deficits in adolescent male mice.

Witnessing violent or traumatic events is common during childhood and adolescence and could cause detrimental effects such as increased risks of psychiatric disorders. This stressor could be modeled in adolescent laboratory animals using the chronic witnessing social defeat (CWSD) paradigm, but the behavioral consequences of CWSD in adolescent animals remain to be validated for cognitive, anxiety-like, and depression-like behaviors and, more importantly, the underlying neural mechanisms remain to be uncovered. In this study, we first established the CWSD model in adolescent male mice and found that CWSD impaired cognitive function and increased anxiety levels and that these behavioral deficits persisted into adulthood. Based on the dorsal-ventral functional division in hippocampus, we employed immediate early gene c-fos immunostaining after behavioral tasks and found that CWSD-induced cognition deficits were associated with dorsal CA3 overactivation and anxiety-like behaviors were associated with ventral CA3 activity reduction. Indeed, chemogenetic activation and inhibition of dorsal CA3 neurons mimicked and reversed CWSD-induced recognition memory deficits (not anxiety-like behaviors), respectively, whereas both inhibition and activation of ventral CA3 neurons increased anxiety-like behaviors in adolescent mice. Finally, chronic administration of vortioxetine (a novel multimodal antidepressant) successfully restored the overactivation of dorsal CA3 neurons and the cognitive deficits in CWSD mice. Together, our findings suggest that dorsal CA3 overactivation mediates CWSD-induced recognition memory deficits in adolescent male mice, shedding light on the pathophysiology of adolescent CWSD-induced adverse effects and providing preclinical evidence for early treatment of stress-induced cognitive deficits.

Impairments in the early consolidation of spatial memories via group II mGluR agonism in the mammillary bodies

mGluR2 receptors are widely expressed in limbic brain regions associated with memory, including the hippocampal formation, retrosplenial and frontal cortices, as well as subcortical regions including the mammillary bodies. mGluR2/3 agonists have been proposed as potential therapeutics for neurological and psychiatric disorders, however, there is still little known about the role of these receptors in cognitive processes, including memory consolidation. To address this, we assessed the effect of the mGluR2/3 agonist, eglumetad, on spatial memory consolidation in both mice and rats. Using the novel place preference paradigm, we found that post-sample injections of eglumetad impaired subsequent spatial discrimination when tested 6 h later. Using the immediate early gene c-fos as a marker of neural activity, we showed that eglumetad injections reduced activity in a network of limbic brain regions including the hippocampus and mammillary bodies. To determine whether the systemic effects could be replicated with more targeted manipulations, we performed post-sample infusions of the mGluR2/3 agonist 2R,4R-APDC into the mammillary bodies. This impaired novelty discrimination on a place preference task and an object-in-place task, again highlighting the role of mGluR2/3 transmission in memory consolidation and demonstrating the crucial involvement of the mammillary bodies in post-encoding processing of spatial information.

Age dependent path integration deficit in 5xFAD mice

Alzheimer's disease (AD) is a severe neurodegenerative disorder and the most common form of dementia in elderly individuals, characterized by memory deficits, cognitive decline, and neuropathology. The identification of preclinical markers for AD remains elusive. We employed an ultrasound-evoked spatial memory assay to investigate path integration (PI) in wild type C57BL/6 J and 5xFAD mice. We observed significant recruitment of the mammillary bodies (MB) and subiculum (Sub) – core regions of the Papez circuit during PI, as indicated by increased expression of the immediate early gene c-Fos in C57BL/6 J mice. In 5xFAD mice, amyloid-beta (Aβ) vulnerability in the MB and Sub was evident at 3-months of age, preceding widespread pathology at 5-months of age. In parallel, we detected significant behavioral deficits in PI in the 5XFAD mice at 5- but not 3-months of age. Sex based analysis revealed a more profound deficit in males compared to females at 5-months of age. Our data suggest PI may be as an early indicator of AD, potentially associated with dysfunction within the Papez circuit.

Pramipexole restores behavioral inhibition in highly impulsive rats through a paradoxical modulation of frontostriatal networks

Impulse control disorders (ICDs), a wide spectrum of maladaptive behaviors which includes pathological gambling, hypersexuality and compulsive buying, have been recently suggested to be triggered or aggravated by treatments with dopamine D2/3 receptor agonists, such as pramipexole (PPX). Despite evidence showing that impulsivity is associated with functional alterations in corticostriatal networks, the neural basis of the exacerbation of impulsivity by PPX has not been elucidated. Here we used a hotspot analysis to assess the functional recruitment of several corticostriatal structures by PPX in male rats identified as highly (HI), moderately impulsive (MI) or with low levels of impulsivity (LI) in the 5-choice serial reaction time task (5-CSRTT). PPX dramatically reduced impulsivity in HI rats. Assessment of the expression pattern of the two immediate early genes C-fos and Zif268 by in situ hybridization subsequently revealed that PPX resulted in a decrease in Zif268 mRNA levels in different striatal regions of both LI and HI rats accompanied by a high impulsivity specific reduction of Zif268 mRNA levels in prelimbic and cingulate cortices. PPX also decreased C-fos mRNA levels in all striatal regions of LI rats, but only in the dorsolateral striatum and nucleus accumbens core (NAc Core) of HI rats. Structural equation modeling further suggested that the anti-impulsive effect of PPX was mainly attributable to the specific downregulation of Zif268 mRNA in the NAc Core. Altogether, our results show that PPX restores impulse control in highly impulsive rats by modulation of limbic frontostriatal circuits.

Design of Ultrapotent Genetically Encoded Inhibitors ofKv4.2 for Gating Neural Plasticity.

The Kv4.2 potassium channel plays established roles in neuronal excitability, while also being implicated in plasticity. Current means to study the roles of Kv4.2 are limited, motivating us to design a genetically encoded membrane tethered Heteropodatoxin-2 (MetaPoda). We find that MetaPoda is an ultrapotent and selective gating-modifier of Kv4.2. We narrow its site of contact with the channel to two adjacent residues within the voltage sensitive domain (VSD) and, with docking simulations, suggest that the toxin binds the VSD from within the membrane. We also show that MetaPoda does not require an external linker of the channel for its activity. In neurons (obtained from female and male rat neonates), MetaPoda specifically, and potently, inhibits all Kv4 currents, leaving all other A-type currents unaffected. Inhibition of Kv4 in hippocampal neurons does not promote excessive excitability, as is expected from a simple potassium channel blocker. We do find that MetaPoda's prolonged expression (1 week) increases expression levels of the immediate early gene cFos and prevents potentiation. These findings argue for a major role of Kv4.2 in facilitating plasticity of hippocampal neurons. Lastly, we show that our engineering strategy is suitable for the swift engineering of another potent Kv4.2-selective membrane-tethered toxin, Phrixotoxin-1, denoted MetaPhix. Together, we provide two uniquely potent genetic tools to study Kv4.2 in neuronal excitability and plasticity.

Bed Nucleus of the Stria Terminalis (BNST) neurons containing the serotonin 5HT2c receptor modulate operant alcohol self-administration behavior in mice.

The serotonin 5HT2c receptor has been widely implicated in the pathophysiology of alcohol use disorder (AUD), particularly alcohol seeking and the affective consequences of chronic alcohol consumption. However, little is known about the brain sites in which 5HT2c exerts its effects on specific alcohol-related behaviors, especially in females. Here, we investigated the effects of site-specific manipulation of the 5HT2c receptor system in the BNST on operant alcohol self-administration behaviors in adult mice of both sexes, including the acquisition and maintenance of fixed-ratio responding, motivation for alcohol (progressive ratio), and quinine-adulterated responding for alcohol on a fixed-ratio schedule (punished alcohol seeking). Knockdown of 5HT2c in the BNST did not affect the acquisition or maintenance of operant alcohol self-administration, nor did it affect progressive ratio responding for alcohol. This manipulation had only a subtle effect on responding for quinine alcohol selectively in females. On the other hand, chemogenetic inhibition of BNST 5HT2c-containing neurons (BNST5HT2c) increased operant alcohol self-administration behavior in both sexes on day 2, but not day 9, of testing. It also increased operant responding for 1000 μM quinine-adulterated alcohol selectively in males. Importantly, chemogenetic inhibition of BNST5HT2c did not alter operant sucrose responding or motivation for sucrose in either sex. We then performed cell-type specific anterograde tracing, which revealed that BNST5HT2c project to similar regions in males and females, many of which have been previously implicated in AUD. We next used chemogenetics and quantification of the immediate early gene cFos to characterize the functional influence of BNST5HT2c inhibition on vlPAG activity. We show that chemogenetic inhibition of BNST5HT2c reduces vlPAG cFos in both sexes, but that this reduction is more robust in males. Together these findings suggest that BNST5HT2c neurons, and to a small extent the BNST 5HT2c receptor, serve to promote aversive responses to alcohol consumption, potentially through sex-dependent disinhibition of vlPAG neurons.