Biology subjects

Stern, J. E.

Publications and source records attributed to Stern, J. E..

11 recordsLinked to original sources

bioRxiv2025

Hypovolemia Evokes Conserved Inverse Neurovascular Coupling in the Supraoptic Nucleus Independent of Heart Failure

Vasopressin (AVP) neurons in the hypothalamic supraoptic nucleus (SON) are activated by systemic challenges that threaten fluid balance. Beyond their classical activity-dependent release of their neuropeptide cargo into the systemic circulation, these neurons also release AVP somatodendritically, enabling local modulation of neuronal excitability and vascular tone. We previously showed that a systemic salt challenge triggers inverse neurovascular coupling (iNVC) in the SON, in which activity-dependent dendritic AVP release induces parenchymal arteriole vasoconstriction and local hypoxia. In rats with heart failure (HF), however, the polarity of this salt-evoked response is reversed: microglia-derived adenosine acting on A2A receptors overrides an enhanced AVP-mediated vasoconstriction, producing net vasodilation. Still, whether AVP activation by non-osmotic stimuli engages similar neurovascular mechanisms is unknown. Here, we examined whether hypovolemia induced by intraperitoneal polyethylene glycol (PEG) evokes comparable vascular responses in control and HF rats. PEG produced a sustained rise in plasma protein concentration and vasoconstriction of SON parenchymal arterioles in both control and sham rats. In HF rats, PEG still induced vasoconstriction at 60 min, but vascular diameters returned to baseline by 90 min despite persistent hypovolemia. These findings indicate that hypovolemia engages a conserved AVP-mediated iNVC program that remains largely intact in HF, and that the previously described polarity reversal during HF is stimulus-specific, emerging during osmotic but not hypovolemic activation of AVP neurons.

neuroscience↗

bioRxiv2025

Asymmetric blood flow within a shared capillary network links the nucleus of the solitary tract and area postrema

The nucleus of the solitary tract (NTS) and the area postrema (AP) form a tightly coupled dorsal medullary complex that integrates visceral and humoral signals governing autonomic and cardiometabolic regulation. While their neural interconnections are well characterized, the organization and functional significance of their shared vascular network remain poorly understood. Here, we used in vivo two-photon microscopy in rats, combined with fluorescent vascular labeling and retrograde neuronal tracing, to visualize and quantify blood flow within the AP-NTS microcirculation. We identified direct capillary connections between the two regions, confirming a continuous vascular network previously inferred from ex vivo studies. Analysis of red blood cell trajectories revealed that blood flow across these junctions is predominantly unidirectional, from the NTS toward the AP. Morphometric measurements showed that AP capillaries are nearly twice the diameter of those in the NTS, implying a lower local vascular resistance and providing a structural basis for this directionality. Despite these geometric differences, capillary flow velocities were similar between regions, consistent with active regulation that maintains stable perfusion dynamics. Together, these findings uncover a previously unrecognized, functionally asymmetric vascular pathway within the dorsal medulla. By enabling the directed transfer of diffusible neurohumoral signals from the NTS to the AP, this specialized microvascular network adds a novel layer of communication between two key brainstem autonomic centers and may represent an additional mechanism for the integration of visceral and circulating information.

neuroscience↗

bioRxiv2025

A common Iba1 antibody labels vasopressin neurons in mice

There are a wide variety of commercially available antibodies for labeling microglial cells based on different protein targets, as well as antibodies for the same protein target made in different species. While this array of targets and hosts allows for flexibility in immunohistochemical experiments, it is important to validate that different antibodies provide comparable and accurate immunodetection prior to experimental data collection. We found that a commercially available anti-Iba1 antibody, made in goat, produces irregular staining patterns in specific regions of the mouse brain, prompting a further investigation into the phenomenon. This Iba1-goat antibody displayed increased numbers of labeled cells when compared to expression of a CX3CR1-GFP reporter and IHC detection of P2RY12, two common microglial markers. Furthermore, immunodetection by other common anti-Iba1 antibodies made in rabbit and chicken did not display the excessive cell labeling when compared to the CX3CR1-GFP reporter. Upon further investigation, this Iba1-goat antibody was observed to highly colocalize with vasopressin neurons in the paraventricular nucleus of the hypothalamus (PVN) and the supraoptic nucleus of the hypothalamus (SON), the two main sites of vasopressin production in the brain. Other anti-Iba1 antibodies made in other species did not show this same colocalization with vasopressin. Finally, this effect was species-specific, as Wistar rats did not display erroneous cell labeling by the Iba1-goat antibody. In sum, the present study employs both qualitative and quantitative data to highlight the importance of validating antibody efficacy and specificity in a region- and species-specific manner. Significance StatementMicroglia are the primary immune cells of the brain and are involved in many neurodevelopmental, as well as neurodegenerative, processes, thus making the study of microglia an important area of neuroscience research. There is a wide array of antibodies available to label microglia. Specific detection of microglia using immunohistochemistry is crucial for understanding differences in cell density, morphology, and interactions with other cells in various contexts. In the present study, a common anti-Iba1 antibody made in goat was found to display erroneous labeling of vasopressin neurons in specific regions of the mouse brain, inconsistent with other microglial markers, which emphasizes the importance of validating antibody efficacy and specificity in a region- and species-specific manner prior to beginning experimental data collection.

neuroscience↗

bioRxiv2023

Angiotensin-II drives changes in microglia-vascular interactions in rats with heart failure

Activation of microglia, the resident immune cells of the central nervous system, leading to the subsequent release of pro-inflammatory cytokines, has been linked to cardiac remodeling, autonomic disbalance, and cognitive deficits in heart failure (HF). While previous studies emphasized the role of hippocampal Angiotensin II (AngII) signaling in HF-induced microglial activation, unanswered mechanistic questions persist. Evidence suggests significant interactions between microglia and local microvasculature, potentially affecting blood-brain barrier integrity and cerebral blood flow regulation. Still, whether the microglial-vascular interface is affected in the brain during HF remains unknow. Using a well-established ischemic HF rat model, we demonstrate increased vessel-associated microglia (VAM) in HF rat hippocampi, which showed heightened expression of AngII AT1a receptors. Acute AngII administration to sham rats induced microglia recruitment to the perivascular space, along with increased expression of TNFa. Conversely, administering an AT1aR blocker to HF rats prevented the recruitment of microglia to the perivascular space, normalizing their levels to those in healthy rats. These results highlight the critical importance of a rather understudied phenomenon (i.e., microglia-vascular interactions in the brain) in the context of the pathophysiology of a highly prevalent cardiovascular disease, and unveil novel potential therapeutic avenues aimed at mitigating neuroinflammation in cardiovascular diseases.

neuroscience↗

bioRxiv2023

Blood flow directionality establishes the SCN as source and OVLT as target within a new vascular portal pathway

The suprachiasmatic nucleus (SCN) is the locus of a brain clock that sets the phase of oscillation in cells throughout the brain and body. Anatomical evidence reveals a portal system linking the SCN and the OVLT (here termed SCN-OVLTp). This discovery begs the question of the direction of blood flow and the nature of diffusible signals that flow in this specialized vasculature. Here we show unequivocally that the direction of blood flow is from the SCN to the OVLT, that the rate of flow is under circadian regulation, and that vasopressin (AVP) is present in portal vessels following systemic injection. These findings highlight a previously unknown CNS communication pathway. It is well established that the SCN is required for circadian regulation of AVP in the CSF and that the OVLT bears AVP receptors. Specifically, SCN neurons are necessary for time-stamped signals such as the peptide AVP, that can travel via portal veins to a target in the OVLT. The OVLT, a circumventricular organ offering a "window to the brain," can relay neural and diffusible signals to broad brain areas via its efferent connections and via the CSF. We conclude that the SCN-OVLTp, like that of the pituitary portal system, discovered almost a century ago, allows neurosecretions to reach nearby specialized target sites, thereby avoiding dilution in the systemic blood. In both of these brain portal pathways, the target site, namely the pituitary and OVLT respectively, relay signals broadly, to both the brain and the rest of the body.

neuroscience↗

bioRxiv2022

Analysis of the hypothalamic oxytocin system and oxytocin receptor-expressing astrocytes in a mouse model of Prader-Willi syndrome

Prader-Willi syndrome (PWS) is a neurodevelopmental disorder characterized by hyperphagia, obesity, developmental delay and intellectual disability. Studies suggest dysfunctional signaling of the neuropeptide oxytocin as one of the key mechanisms in PWS, and administration of oxytocin via intranasal or systemic routes yielded promising results in both humans and mouse models. However, a detailed assessment of the oxytocin system in mouse models of PWS such as the Magel2-deficient Magel2tm1.Stw mouse, is lacking. In this study, we performed an automated counting of oxytocin cells in the entire paraventricular nucleus of the hypothalamus of Magel2tm1.Stw and wild-type control mice and found a significant reduction in the caudal part, which represents the parvocellular subdivision. In addition, based on the recent discovery that some astrocytes express the oxytocin receptor (OTR), we performed detailed analysis of astrocyte numbers and morphology in various brain regions, and assessed expression levels of the astrocyte marker GFAP, which was significantly decreased in the hypothalamus, but not other brain regions in Magel2tm1.Stw mice. Finally, we analyzed the number of OTR-expressing astrocytes in various brain regions and found a significant reduction in the nucleus accumbens of Magel2tm1.Stw mice, as well as a sex-specific difference in the lateral septum. This study suggests a role for caudal PVN OT neurons as well as OTR-expressing astrocytes in a mouse model of PWS, provides novel information about sex-specific expression of astrocytic OTRs, and presents several new brain regions containing OTR-expressing astrocytes in the mouse brain.

neuroscience↗

bioRxiv2022

Altered PVN-to-CA2 hippocampal oxytocin pathway and reduced number of oxytocin-receptor expressing astrocytes in heart failure rats

Oxytocinergic actions within the hippocampal CA2 are important for neuromodulation, memory processing and social recognition. However, the source of the OTergic innervation, the cellular targets expressing the OT receptors (OTRs) and whether the PVN-to-CA2 OTergic system is altered during heart failure (HF), a condition recently associated with cognitive and mood decline, remains unknown. Using immunohistochemistry along with retrograde monosynaptic tracing, RNAscope and a novel OTR-Cre rat line, we show that the PVN (but not the supraoptic nucleus) is an important source of OTergic innervation to the CA2. These OTergic fibers were found in many instances in close apposition to OTR expressing cells within the CA2. Interestingly, while only a small proportion of neurons were found to express OTRs ([~]15%), this expression was much more abundant in CA2 astrocytes ([~]40%), an even higher proportion that was recently reported for astrocytes in the central amygdala. Using an established ischemic rat heart failure (HF) model, we found that HF resulted in robust changes in the PVN-to-CA2 OTergic system, both at the source and target levels. Within the PVN, we found an increased OT immunoreactivity, along with a diminished OTR expression in PVN neurons. Within the CA2 of HF rats, we observed a blunted OTergic innervation, along with a diminished OTR expression, which appeared to be restricted to CA2 astrocytes. Taken together, our studies highlight astrocytes as key cellular targets mediating OTergic PVN inputs to the CA2 hippocampal region. Moreover, provides the first evidence for an altered PVN-to-CA2 OTergic system in HF rats, which could potentially contribute to previously reported cognitive and mood impairments in this animal model.

neuroscience↗

bioRxiv2022

Hypothalamic astrocyte control systemic glucose metabolism and energy balance via regulation of extra-synaptic glutamate signaling

The hypothalamus is key in the control of energy balance. However, to this day strategies targeting hypothalamic neurons failed to provide viable option to treat most metabolic diseases. Conversely, the role of astrocytes in systemic metabolic control has remained largely unexplored. Here we show that obesity promotes anatomically restricted remodeling of hypothalamic astrocyte activity. In the paraventricular nucleus (PVN) of the hypothalamus, chemogenetic manipulation of astrocytes results in bidirectional control of neighboring neuron activity, autonomic outflow, glucose metabolism and energy balance. Such process recruits a mechanism involving the astrocytic control of ambient glutamate levels, which becomes defective in obesity. Positive or negative chemogenetic manipulation of PVN astrocyte Ca2+ signals respectively worsen or improves metabolic status of diet-induced obese mice. Collectively, these findings highlight a yet unappreciated role for astrocyte in the direct control of systemic metabolism and suggest potential targets for anti-obesity strategy.

physiology↗

bioRxiv2021

Angiotensin II Inhibits the A-type K+ Current of Hypothalamic Paraventricular Nucleus Neurons in Rats with Heart Failure: Role of MAPK-ERK1/2 Signaling

ANGII-mediated sympathohumoral activation constitutes a key pathophysiological mechanism in heart failure (HF). While the hypothalamic paraventricular nucleus (PVN) is recognized as a major site mediating ANGII effects in HF, the precise mechanisms by which ANGII influences sympathohumoral outflow from the PVN remain unknown. ANGII activates the ubiquitous intracellular MAPK signaling cascades and recent studies revealed a key role for ERK1/2 MAPK signaling in ANGII-mediated sympathoexcitation in HF rats. Importantly, ERK1/2 was reported to inhibit the transient outward potassium current (IA) in hippocampal neurons. Given that IA is a critical determinant of the PVN neuronal excitability, and that downregulation of IA in the brain has been reported in cardiovascular disease states, including HF, we investigated here whether ANGII modulates IA in PVN neurons via the MAPK-ERK pathway, and, whether these effects are altered in HF rats. Patch-clamp recordings from identified magnocellular neurosecretory (MNNs) and presympathetic (PS) PVN neurons revealed that ANGII inhibited IA in both PVN neuronal types, both in sham and HF rats. Importantly, ANGII effects were blocked by inhibiting MAPK-ERK signaling as well as by inhibiting EGFR, a gateway to MAPK-ERK signaling. While no differences in basal IA magnitude were found between sham and HF rats under normal conditions, MAPK-ERK blockade resulted in significantly larger IA in both PVN neuronal types in HF rats. Taken together, our studies show that ANGII-induced ERK1/2 activity inhibits IA and increases the excitability of presympathetic and neuroendocrine PVN neurons, contributing to the neurohumoral overactivity than promotes progression of the HF syndrome. GRAPHICAL ABSTRACT O_FIG O_LINKSMALLFIG WIDTH=184 HEIGHT=200 SRC="FIGDIR/small/459939v1_ufig1.gif" ALT="Figure 1"> View larger version (18K): org.highwire.dtl.DTLVardef@1e4ec4org.highwire.dtl.DTLVardef@1c54be0org.highwire.dtl.DTLVardef@1f86529org.highwire.dtl.DTLVardef@b98aa2_HPS_FORMAT_FIGEXP M_FIG C_FIG

neuroscience↗

bioRxiv2020

A Multi-Gene Synaptic Plasticity Array Identifies Candidate Molecular Underpinnings Of Cognitive And Mood Deficits In Rats With Heart Failure

Chronic heart failure (HF) is a serious disorder that afflicts more than 26 million patients worldwide. HF is comorbid with depression, anxiety and memory deficits that have serious implications for quality of life and self-care in patients who have HF. Despite evidence that cognitive performance is worse in HF patients with reduced ejection fraction than in HF patients with preserved cardiac function, there are few studies that have assessed the effects of severely reduced ejection fraction ([≤]40%) on cognition in non-human animal models. Moreover, very limited information is available regarding the effects of HF on genetic markers of synaptic plasticity in brain areas critical for memory and mood regulation. We induced HF in male rats and tested mood and anxiety (sucrose preference and elevated plus maze) and memory (spontaneous alternation and inhibitory avoidance) and measured the simultaneous expression of 84 synaptic plasticity-associated genes in dorsal (DH) and ventral hippocampus (VH), basolateral (BLA) and central amygdala (CeA,) and prefrontal cortex (PFC). We also included the hypothalamic paraventricular nucleus (PVN), which has been implicated in neurohumoral activation in HF. Our results show that rats with severely reduced ejection fraction displayed signs of polydipsia, anhedonia, increased anxiety, and impaired memory in both tasks. HF also produced a drastic downregulation of synaptic-plasticity genes in PFC and PVN, moderate decreases in DH and CeA and minimal effects in BLA and VH. Collectively, these findings identify candidate brain areas and molecular mechanisms underlying HF-induced disturbances in mood and memory.

neuroscience↗

bioRxiv2020

Oxytocin Acts on Astrocytes in the Central Amygdala to Promote a Positive Emotional State

Oxytocin orchestrates social and emotional behaviors through modulation of neural circuits in brain structures such as the central amygdala (CeA). The long-standing dogma is that oxytocin signaling in the central nervous system occurs exclusively via direct actions on neurons. However, several findings over the last decades showed that astrocytes actively participate in the modulation of neuronal circuits. Here, we investigate the degree of astrocytes involvement in oxytocin functions. Using astrocyte specific gain and loss of function approaches, we demonstrate that CeA astrocytes not only directly respond to oxytocin, but are actually necessary for its effects on neuronal circuits and ultimately behavior. Our work identifies astrocytes as a crucial cellular substrate underlying the promotion of a positive emotional state by oxytocin. These results further corroborate that astrocytes are key regulators of neuronal circuits activity by responding to specific neuropeptidergic inputs, and opens up new perspectives to understand how neuromodulators gate brain functions.

neuroscience↗