Biology subjects

Richie, C. T.

Publications and source records attributed to Richie, C. T..

6 recordsLinked to original sources

bioRxiv2025

Generation and characterization of a tamoxifen-inducible, Cre driver rat for transgene expression in microglia

Microglia are the resident immune cells of the central nervous system (CNS) and display diverse functions under both physiological and pathological conditions. The past decade has seen burgeoning interest in microglia function, with a variety of transgenic tools developed for specific genetic manipulation of microglia in various injury, disease, and developmental models. Although the majority of models have been developed in mice, the ability to manipulate microglia in rats provides additional advantages to studying microglial function in the brain especially related to complex behavior. Using BAC transgenesis, our lab has created a transgenic rat (Cx3cr1-CreERT2) that expresses a tamoxifen inducible Cre recombinase (CreERT2) under control of the microglial/macrophage specific fractalkine C-X3-C Motif Chemokine Receptor 1 (Cx3cr1) promoter. In mice, CreERT2 and other transgenes have been expressed in microglia using the Cx3cr1 promoter, however, this is the first demonstration in rats. Importantly, these rats exhibit similar cognitive behaviors compared to their wildtype (WT) controls. Microglial specificity of inducible Cre expression was confirmed by breeding the novel Cx3cr1-CreERT2+/- rat with a previously reported double floxed inverse open reading frame (DIO)-mCherry+/- reporter rat to show tamoxifen inducible mCherry expression that colocalizes with the microglial marker Iba1. In addition, we utilize flow cytometry to demonstrate time and Cre dependent differences in recombination of Cx3cr1+ cells in the spleen, peripheral blood, and brain at two- and eight-weeks post-tamoxifen treatment. Overall, we have created a novel transgenic rat model for researchers to employ in understanding microglial and peripheral immune cell function in rats.

neuroscience↗

bioRxiv2025

Targeted gene transfer into developmentally defined cell populations of the primate brain

The primate brain possesses unique physiological and developmental features whose systematic investigation is hampered by a paucity of transgenic germline models and tools. Here, we present a minimally invasive method to introduce transgenes widely across the primate cerebral cortex using ultrasound-guided fetal intracerebroventricular viral injections (FIVI). This technique enables rapid-onset and long-lasting transgene expression following the delivery of recombinant adeno-associated viruses (rAAVs). By adjusting the gestational timing of injections, viral serotypes, and transcriptional regulatory elements, rAAV FIVI allows for systematic targeting of specific cell populations. We demonstrate the versatility of this method through restricted laminar expression in the cortex, Cre-dependent targeting of neurons, CRISPR-based gene editing, and labeling of peripheral somatosensory and retinal pathways. By mimicking key desirable features of germline transgenic models, this efficient and targeted method for gene transfer into the fetal primate brain opens new avenues for experimental and translational neuroscience across the lifespan.

neuroscience↗

bioRxiv2024

A Rapid Method for Producing Adeno-Associated Viral Vectors Suitable for Transducing Rodent Neurons in vitro and in vivo

The use of adeno-associated viral vectors for delivery of genetic information into the mammalian CNS remains popular but producing highly purified vectors for in vivo applications requires a significant investment of resources and time that can impede the development and testing of AAV vectors for experimentation. To address this issue, we have developed a simplified AAV packaging protocol that does not require large capital equipment (ultracentrifugation or chromatography machines) yet still produces virus in quantities that are sufficient for testing AAV prototypes in the rodent CNS. This protocol is serotype agnostic, and has been successful with AAV1, AAV9, AAV-DJ, and rAAV2-retro. Intracranial injection of AAV-EF1a-GFP-KASH into rats demonstrated that our "small scale" AAV preps produce patterns of transgene expression and inflammation that are similar to those produced by the same AAV vector purified by affinity column chromatography. Our protocol allows for multiple vectors to be packaged and processed in parallel, making it ideal for testing multiple variants, constructs, and prototypes simultaneously.

molecular biology↗

bioRxiv2023

Excitotoxic glutamate levels cause the secretion of resident endoplasmic reticulum proteins

Dysregulation of synaptic glutamate levels can lead to excitotoxicity such as that observed in stroke, traumatic brain injury, and epilepsy. The role of increased intracellular calcium (Ca2+) in the development of excitotoxicity is well established. However, less is known regarding the impact of glutamate on endoplasmic reticulum (ER)-Ca2+-mediated processes such as proteostasis. To investigate this, we expressed a secreted ER Ca2+ modulated protein (SERCaMP) in primary cortical neurons to monitor exodosis, a phenomenon whereby ER calcium depletion causes the secretion of ER resident proteins that perform essential functions to the ER and the cell. Activation of glutamatergic receptors (GluRs) led to an increase in SERCaMP secretion indicating that normally ER resident proteins are being secreted in a manner consistent with ER Ca2+ depletion. Antagonism of ER Ca2+ channels attenuated the effects of glutamate and GluR agonists on SERCaMP release. We also demonstrate that endogenous proteins containing an ER retention sequence (ERS) are secreted in response to GluR activation supporting that neuronal activation by glutamate promotes ER exodosis. Ectopic expression of KDEL receptors attenuated the secretion of ERS-containing proteins caused by GluR agonists. Taken together, our data indicate that excessive GluR activation causes disruption of neuronal proteostasis by triggering the secretion of ER resident proteins through ER Ca2+ depletion and describes a new facet of excitotoxicity. SignificanceDuring excitotoxicity, the excessive activation of glutamate receptors causes elevated intracellular calcium (Ca2+) that promotes cellular dysfunction and death. While the role of cytosolic Ca2+ in excitotoxicity has been well-studied, the consequences of changes in endoplasmic reticulum (ER) Ca2+ during excitotoxicity remains unclear. The relatively high concentration of calcium in the ER is necessary for ER resident proteins to function prop out essential functions and maintain cellular proteostasis. We show here that excitotoxic conditions destabilize the ER proteome by triggering ER resident protein secretion. Stabilizing ER Ca2+ or overexpressing receptors that interact with ER resident proteins can prevent disruption of proteostasis associated with excitotoxicity. The present study provides a new link between excitotoxicity, ER Ca2+ homeostasis, and the ER proteome.

neuroscience↗

bioRxiv2023

Nucleus Accumbens Local Circuit for Cue-Dependent Aversive Learning

Response to threatening environmental stimuli requires detection and encoding of important environmental features that dictate threat. Aversive events are highly salient which promotes associative learning about stimuli that signal this threat. The nucleus accumbens is uniquely positioned to process this salient, aversive information and promote motivated output, through plasticity on the major projection neurons in the brain area. We uncovered a nucleus accumbens core local circuit whereby excitatory plasticity facilitates learning and recall of discrete aversive cues. We demonstrate that putative nucleus accumbens substance P release and long-term excitatory plasticity on dopamine 2 receptor expressing projection neurons is required for cue-dependent fear learning. Additionally, we found fear learning and recall were dependent on distinct projection-neuron subtypes. Our work demonstrates a critical role for Nucleus Accumbens substance P in cue-dependent aversive learning.

neuroscience↗

bioRxiv2022

Effect of selective lesions of nucleus accumbens μ-opioid receptor-expressing cells on heroin self-administration in male and female rats: a study with novel Oprm1-Cre knock-in rats

The brain {micro}-opioid receptor (MOR) is critical for the analgesic, rewarding, and addictive effects of opioid drugs. However, in rat models of opioid-related behaviors, the circuit mechanisms of MOR-expressing cells are less known because of a lack of genetic tools to selectively manipulate them. We introduce a CRISPR-based Oprm1-Cre knock-in transgenic rat that provides cell-type specific genetic access to MOR-expressing cells. After performing anatomical and behavioral validation experiments, we used the Oprm1-Cre knock-in rats to study the role of nucleus accumbens (NAc) MOR-expressing cells in heroin self-administration in male and female rats. Using RNAscope, autoradiography, and fluorescence in situ hybridization chain reaction (HCR-FISH), we found no differences in Oprm1 expression in NAc, dorsal striatum (DS), and dorsal hippocampus, or MOR receptor density (except DS) or function between Oprm1-Cre knock-in rats and wildtype littermates. HCR-FISH assay showed that iCre is highly co-expressed with Oprm1 (95-98%). There were no genotype differences in pain responses, morphine analgesia and tolerance, heroin self-administration, and relapse-related behaviors. We used the Cre-dependent vector AAV1-EF1a-Flex-taCasp3-TEVP to lesion NAc MOR-expressing cells and report sex-specific effects: the lesions decreased acquisition of heroin self-administration in male Oprm1-Cre rats and had a stronger inhibitory effect on the effort to self-administer heroin in female Oprm1-Cre rats. The validation of an Oprm1-Cre knock-in rat enables new strategies for understanding the role of MOR-expressing cells in rat models of opioid addiction, pain-related behaviors, and other opioid-mediated functions. Our initial mechanistic study with these rats suggests a sex-specific role of NAc MOR-expressing cells in heroin self-administration. Significance statementThe brain {micro}-opioid receptor (MOR) is critical for the analgesic, rewarding, and addictive effects of opioid drugs. However, in rat models of opioid-related behaviors, the circuit mechanisms of MOR-expressing cells are less known because of a lack of genetic tools to selectively manipulate them. We introduce a CRISPR-based Oprm1-Cre knock-in transgenic rat that provides cell-type specific genetic access to brain MOR-expressing cells. After performing anatomical and behavioral validation experiments, we used the Oprm1-Cre knock-in rats to show a potential sex-specific role of nucleus accumbens MOR-expressing cells in heroin self-administration. The new Oprm1-Cre rats can be used to study both the general and sex-specific role of brain MOR-expressing cells in animal models of opioid addiction, pain-related behaviors, and other opioid-mediated functions.

neuroscience↗