Biology subjects

Wallace, T.

Publications and source records attributed to Wallace, T..

8 recordsLinked to original sources

bioRxiv2025

Infralimbic prefrontal cortical projections to the autonomic brainstem: Quantification of inputs to cholinergic and adrenergic/noradrenergic nuclei

The ventromedial prefrontal cortex regulates both emotional and physiological processes. The infralimbic cortex (IL), a prefrontal subregion in rodents, integrates behavioral, neuroendocrine, and autonomic responses to stress. However, the organization of cortical inputs to brainstem nuclei that regulate homeostatic responses are not well defined. We hypothesized that IL projections differentially target pre-ganglionic parasympathetic neurons and adrenergic/noradrenergic nuclei. To quantify IL projections to autonomic brainstem nuclei in male rats, we utilized viral-mediated gene transfer to express yellow fluorescent protein (YFP) in IL glutamatergic neurons. YFP-positive projections to cholinergic and adrenergic/noradrenergic nuclei were then imaged and quantified. Cholinergic neurons were visualized by immunohistochemistry for choline acetyltransferase (ChAT), the enzyme responsible for the synthesis of acetylcholine. Adrenergic/noradrenergic neurons were visualized with immunohistochemistry for dopamine beta-hydroxylase (DBH) which converts dopamine to norepinephrine. Our results indicate that IL glutamate neurons innervated the cholinergic dorsal motor nucleus of the vagus with greater density than the nucleus ambiguus. Furthermore, numerous DBH-positive cell groups received IL inputs. The greatest density was to the C2 and A2 regions of the nucleus of the solitary tract with intermediate levels of input to A6 locus coeruleus and throughout the C1 and A1 regions of the ventrolateral medulla. Minimal input was present in the pontine A5. Additionally, IL projections targeted the local GABAergic neurons that regulate activity within preautonomic nuclei. Collectively, our results indicate that IL pyramidal neurons project to vagal preganglionic parasympathetic neurons, presympathetic neurons of the ventrolateral medulla, as well as diffuse homeostatic modulators the nucleus of the solitary tract and locus coeruleus. Ultimately, these findings provide a roadmap for determining circuit-level mechanisms for neural control of homeostasis and autonomic balance.

neuroscience↗

bioRxiv2023

Cortical-brainstem circuitry attenuates stress reactivity

Exposure to stressful stimuli promotes multi-system biological responses to restore homeostasis. Catecholaminergic neurons in the rostral ventrolateral medulla (RVLM) facilitate sympathetic activity and promote physiological adaptations, including glycemic mobilization and corticosterone release. While it is unclear how brain regions involved in the cognitive appraisal of stress regulate RVLM neural activity, recent studies found that the rodent ventromedial prefrontal cortex (vmPFC) mediates stress appraisal and physiological stress responses. Thus, a vmPFC-RVLM connection could represent a circuit mechanism linking stress appraisal and physiological reactivity. The current study investigated a direct vmPFC-RVLM circuit utilizing genetically-encoded anterograde and retrograde tract tracers. Together, these studies found that stress-reactive vmPFC neurons project to catecholaminergic neurons throughout the ventrolateral medulla in male and female rats. Next, we utilized optogenetic terminal stimulation to evoke vmPFC synaptic glutamate release in the RVLM. Photostimulating the vmPFC-RVLM circuit during restraint stress suppressed glycemic stress responses in males, without altering the female response. However, circuit stimulation decreased corticosterone responses to stress in both sexes. Circuit stimulation did not modulate affective behavior in either sex. Further analysis indicated that circuit stimulation preferentially activated non-catecholaminergic medullary neurons in both sexes. Additionally, vmPFC terminals targeted medullary inhibitory neurons. Thus, both male and female rats have a direct vmPFC projection to the RVLM that reduces endocrine stress responses, likely through the recruitment of local RVLM inhibitory neurons. Ultimately, the excitatory/inhibitory balance of vmPFC synapses in the RVLM may regulate stress reactivity as well as stress-related health outcomes. First author profileSebastian Pace is a Ph.D. candidate in the laboratory of Brent Myers at Colorado State University. Before beginning his Ph.D., Sebastian completed his B.S. and M.S. at the University of Texas-El Paso. While completing his M.S. he worked in the Karine Fenelon Lab. Sebastians current research project focuses on understanding how corticolimbic inputs to the medullary brainstem regulate sympathetic and neuroendocrine stress responses. Key points summaryO_LIGlutamatergic efferents from the ventromedial prefrontal cortex target catecholaminergic neurons throughout the ventrolateral medulla. C_LIO_LIPartially segregated, stress-responsive ventromedial prefrontal cortex populations innervate the rostral and caudal ventrolateral medulla. C_LIO_LIStimulating ventromedial prefrontal cortex synapses in the rostral ventrolateral medulla decreases stress-induced glucocorticoid release in males and females. C_LIO_LIStimulating ventromedial prefrontal cortex terminals in the rostral ventrolateral medulla preferentially activates non-catecholaminergic neurons. C_LIO_LIVentromedial prefrontal cortex terminals target medullary inhibitory neurons. C_LI Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=105 SRC="FIGDIR/small/549781v2_ufig1.gif" ALT="Figure 1"> View larger version (35K): org.highwire.dtl.DTLVardef@c362acorg.highwire.dtl.DTLVardef@1830ca5org.highwire.dtl.DTLVardef@b3411borg.highwire.dtl.DTLVardef@779392_HPS_FORMAT_FIGEXP M_FIG C_FIG

neuroscience↗

bioRxiv2023

Sex-specific prefrontal-hypothalamic control of behavior and stress responding

Depression and cardiovascular disease are both augmented by daily life stress. Yet, the biological mechanisms that translate psychological stress into affective and physiological outcomes are unknown. Previously, we demonstrated that stimulation of the ventromedial prefrontal cortex (vmPFC) has sexually divergent outcomes on behavior and physiology. Importantly, the vmPFC does not innervate the brain regions that initiate autonomic or neuroendocrine stress responses; thus, we hypothesized that intermediate synapses integrate cortical information to regulate stress responding. The posterior hypothalamus (PH) directly innervates stress-effector regions and receives substantial innervation from the vmPFC. In the current studies, circuit-specific approaches examined whether vmPFC synapses in the PH coordinate stress responding. Here we tested the effects of optogenetic vmPFC-PH circuit stimulation in male and female rats on social and motivational behaviors as well as physiological stress responses. Additionally, an intersectional genetic approach was used to knock down synaptobrevin in PH-projecting vmPFC neurons. Our collective results indicate that male vmPFC-PH circuitry promotes positive motivational valence and is both sufficient and necessary to reduce sympathetic-mediated stress responses. In females, the vmPFC-PH circuit does not affect social or preference behaviors but is sufficient and necessary to elevate neuroendocrine stress responses. Altogether, these data suggest cortical regulation of stress reactivity and behavior is mediated, in part, by projections to the hypothalamus that function in a sex-specific manner.

neuroscience↗

bioRxiv2023

Epigenetic signature of human immune aging: the GESTALT study.

Age-associated DNA methylation in blood cells convey information on health status. However, the mechanisms that drive these changes in circulating cells and their relationships to gene regulation are unknown. We identified age-associated DNA methylation sites in six purified blood borne immune cell types (naive B, naive CD4+and CD8+ T cells, granulocytes, monocytes and NK cells) collected from healthy individuals interspersed over a wide age range. Of the thousand of age-associated sites, only 350 sites were differentially methylated in the same direction in all cell types and validated in an independent longitudinal cohort. Genes close to age-associated hypomethylated sites were enriched for collagen biosynthesis and complement cascade pathways, while genes close to hypermethylated sites mapped to neuronal pathways. In-silico analyses showed that in most cell types, the age-associated hypo- and hypermethylated sites were enriched for ARNT (HIF1{beta}) and REST transcription factor motifs respectively, which are both master regulators of hypoxia response. To conclude, despite spatial heterogeneity, there is a commonality in the putative regulatory role with respect to transcription factor motifs and histone modifications at and around these sites. These features suggest that DNA methylation changes in healthy aging may be adaptive responses to fluctuations of oxygen availability.

molecular biology↗

bioRxiv2022

Prefrontal representation of affective stimuli: importance of stress, sex, and context

Major depressive disorder diminishes health-related quality-of-life and disproportionality impacts females. Negative life events predict the onset of depressive symptoms including negative mood, anhedonia, and social withdrawal. While the neurobiology of affective illness is not completely understood, structural and functional changes in the ventromedial prefrontal cortex (vmPFC) associate with mood and anxiety disorders. Rodent studies have investigated the prefrontal impact of chronic stress, a preclinical model of mood disruption. However, ex vivo slice and postmortem histological studies have focused largely on males and yielded mixed results. Although genetically-defined recordings in behaving animals of both sexes have not been reported. Here, we hypothesized that chronic variable stress (CVS) would reduce the neural processing of affective stimuli in the infralimbic region of rodent vmPFC region. To test this hypothesis, we targeted expression of a fluorescent calcium indicator, GCaMP6s, to infralimbic pyramidal cells. In males, CVS reduced infralimbic responses to social interaction and restraint stress but increased responses to novel objects and food reward. In contrast, females did not have CVS-induced changes in infralimbic activity, which was partially dependent on ovarian status. Collectively, these results indicate that both male and female vmPFC pyramidal cells encode social, stress, and reward stimuli. However, chronic stress effects are sex-dependent and behavior-specific. Ultimately, these findings extend the understanding of chronic stress-induced prefrontal dysfunction and indicate that sex is a critical factor for cortical processing of affective stimuli. SignificanceMood disorders are often preceded by stressful experiences and exhibit sex differences in prevalence. Further, affective illness is frequently accompanied by changes in prefrontal cortical function. However, the neurobiology that underlies sex-specific cortical processing of affective stimuli is poorly understood. Therefore, the current studies employ cell type-specific calcium photometry to determine the effects of chronic stress on ventromedial prefrontal cortex (vmPFC) activity in male and female rats. Our results indicate that chronic stress exposure differentially alters vmPFC encoding of social, stress, and reward stimuli. Moreover, the sex-specific effects of chronic stress are partially mediated by ovarian hormones. Ultimately, our results indicate that prolonged stress alters vmPFC function in a context-dependent and sex-specific manner, contributing to the biological bases for sex differences in emotional processing.

neuroscience↗

bioRxiv2022

Single-cell analysis of skeletal muscle macrophages reveals age- associated functional subpopulations

Tissue-resident macrophages represent a group of highly responsive innate immune cells that acquire diverse functions by polarizing towards distinct subgroups. The subgroups of macrophages that reside in skeletal muscle (SKM) and their changes during aging are poorly characterized. By single-cell transcriptomic analysis, we found that mouse SKM macrophages primarily comprise two large populations, "healing" LYVE1+ and "proinflammatory" LYVE1-macrophages. SKM macrophages were further classified into four functional subgroups based on the expression levels of another cell-surface marker, MHCII: LYVE1+/MHCII-lo (similar to alternatively activated M2), LYVE1-/MHCII-hi (similar to classically activated M1), and two new subgroups, LYVE1+/MHCII-hi and LYVE1-/MHCII-lo. Notably, the new subgroup LYVE1+/MHCII-hi had traits of both M2 and M1 macrophages, while the other new subgroup, LYVE1-/MHCII-lo, expressed high levels of mRNAs encoding cytotoxicity proteins. Flow cytometric analysis validated the presence of the four macrophage subgroups in SKM. In old SKM, LYVE1-macrophages were more abundant than LYVE1+ macrophages. Furthermore, complementary unsupervised classification revealed the emergence of specific macrophage subclusters expressing abundant proinflammatory markers, including S100a8 and S100a9 in aged SKM. In sum, our study has identified dynamically polarized mouse SKM macrophages and further uncovered the contribution of specific macrophage subpopulations to the proinflammatory status in old SKM.

cell biology↗

bioRxiv2020

Sexually divergent cortical control of affective-autonomic integration

Depression and cardiovascular disease reduce quality of life and increase mortality risk. These conditions commonly co-occur with sex-based differences in incidence and severity. However, the biological mechanisms linking the disorders are poorly understood. In the current study, we hypothesized that the infralimbic (IL) prefrontal cortex integrates mood-related behaviors with the cardiovascular burden of chronic stress. In a rodent model, we utilized optogenetics during behavior and in vivo physiological monitoring to examine how the IL regulates affect, social motivation, neuroendocrine-autonomic stress reactivity, and the cardiac consequences of chronic stress. Our results indicate that IL glutamate neurons increase socio-motivational behaviors specifically in males. IL activation also reduced endocrine and cardiovascular stress responses in males, while increasing reactivity in females. Moreover, prior IL stimulation protected males from subsequent chronic stress-induced sympatho-vagal imbalance and cardiac hypertrophy. Our findings suggest that cortical regulation of behavior, physiological stress responses, and cardiovascular outcomes fundamentally differ between sexes.

neuroscience↗

bioRxiv2020

Infralimbic cortical glutamate output is necessary for the neural and behavioral consequences of chronic stress

Exposure to prolonged stress is a major risk-factor for psychiatric disorders such as generalized anxiety and major depressive disorder (MDD). Human imaging studies have identified structural and functional abnormalities in the prefrontal cortex of MDD patients, particularly Brodmanns area 25 (BA25). Further, deep brain stimulation of BA25 reduces symptoms of treatment-resistant depression. The rat homolog of BA25 is the infralimbic cortex (IL), which is critical for cognitive appraisal, executive function, and physiological stress reactivity. Previous studies indicate that the IL undergoes stress-induced changes in excitatory/inhibitory balance culminating in reduced activity of glutamate output neurons. However, the regulatory role of IL glutamate output in mood-related behaviors after chronic variable stress (CVS) is unknown. Here, we utilized a lentiviral-packaged small-interfering RNA to reduce translation of vesicular glutamate transporter 1 (vGluT1 siRNA), thereby constraining IL glutamate output. This viral-mediated gene transfer was used in conjunction with a quantitative anatomical analysis of cells expressing the stable immediate-early gene product {Delta}FosB, which accumulates in response to repeated neural activation. Through assessment of {Delta}FosB-expressing neurons across the frontal lobe in adult male rats, we mapped regions altered by chronic stress and determined the coordinating role of the IL in frontal cortical plasticity. Specifically, CVS-exposed rats had increased density of {Delta}FosB-expressing cells in the IL and decreased density in the anterior insula. The later effect was dependent on IL glutamate output. Next, we examined the interaction of CVS and reduced IL glutamate output in behavioral assays examining coping, anxiety-like behavior, associative learning, and nociception. IL glutamate knockdown decreased immobility during the forced swim test compared to GFP controls, both in rats exposed to CVS as well as rats without previous stress exposure. Further, vGluT1 siRNA prevented CVS-induced avoidance behaviors, while also reducing risk aversion and passive coping. Ultimately, this study identifies the necessity of IL glutamatergic output for regulating frontal cortical neural activity and behavior following chronic stress. These findings also highlight how disruption of excitatory/inhibitory balance within specific frontal cortical cell populations may impact neurobehavioral adaptation and lead to stress-related disorders.

neuroscience↗