Enhanced astroglial GABA uptake attenuates tonic GABAA inhibition of the presympathetic hypothalamic paraventricular nucleus neurons in heart failure

Mitochondria-targeted sonodynamic modulation of neuroinflammation to protect against myocardial ischemia‒reperfusion injury

Sympathetic hyperactivation and inflammatory responses are the main causes of myocardial ischemia‒reperfusion (I/R) injury and myocardial I/R-related ventricular arrhythmias (VAs). Previous studies have demonstrated that light-emitting diodes (LEDs) could modulate post-I/R neuroinflammation, thus providing protection against myocardial I/R injury. Nevertheless, further applications of LEDs are constrained due to the low penetration depth (<1 cm) and potential phototoxicity. Low-intensity focused ultrasound (LIFU), an emerging noninvasive neuromodulation strategy with deeper penetration depth (∼10 cm), has been confirmed to modulate sympathetic nerve activity and inflammatory responses. Sonodynamic therapy (SDT), which combines LIFU with sonosensitizers, confers additional advantages, including superior therapeutic efficacy, precise localization of neuronal modulation and negligible side effects. Herein, LIFU and SDT were introduced to modulate post-myocardial I/R neuroinflammation to protect against myocardial I/R injury. The results indicated that LIFU and SDT inhibited sympathetic neural activity, suppressed the activation of astrocytes and microglia, and promoted microglial polarization towards the M2 phenotype, thereby attenuating myocardial I/R injury and preventing I/R-related malignant VAs. These insights suggest that LIFU and SDT inspire a noninvasive and efficient neuroinflammatory modulation strategy with great clinical translation potential thus benefiting more patients with myocardial I/R in the future. STATEMENT OF SIGNIFICANCE: Myocardial ischemia-reperfusion (I/R) may cause I/R injury and I/R-induced ventricular arrhythmias. Sympathetic hyperactivation and inflammatory response play an adverse effect in myocardial I/R injury. Previous studies have shown that light emitting diode (LED) can regulate I/R-induced neuroinflammation, thus playing a myocardial protective role. However, due to the low penetration depth and potential phototoxicity of LED, it is difficult to achieve clinical translation. Herein, we introduced sonodynamic modulation of neuroinflammation to protect against myocardial I/R injury, based on mitochondria-targeted nanosonosensitizers (CCNU980 NPs). We demonstrated that sonodynamic modulation could promote microglial autophagy, thereby preventing myocardial I/R injury and I/R-induced ventricular arrhythmias. This is the first example of sonodynamic modulation of myocardial I/R-induced neuroinflammation, providing a novel strategy for clinical translation.

Glutamate Spillover Dynamically Strengthens Gabaergic Synaptic Inhibition of the Hypothalamic Paraventricular Nucleus

The hypothalamic paraventricular nucleus (PVN) is strongly inhibited by γ-aminobutyric acid (GABA) from the surrounding peri-nuclear zone (PNZ). Because glutamate mediates fast excitatory transmission and is substrate for GABA synthesis, we tested its capacity to dynamically strengthen GABA inhibition. In PVN slices from male mice, bath glutamate applied during ionotropic glutamate receptor blockade increased PNZ-evoked inhibitory postsynaptic currents (eIPSCs) without affecting GABA-A receptor agonist currents or single-channel conductance, implicating a presynaptic mechanism(s). Consistent with this interpretation, bath glutamate failed to strengthen IPSCs during pharmacological saturation of GABA-A receptors. Presynaptic analyses revealed that glutamate did not affect paired-pulse ratio, peak eIPSC variability, GABA vesicle recycling speed, or readily releasable pool (RRP) size. Notably, glutamate-GABA strengthening (GGS) was unaffected by metabotropic glutamate receptor blockade and graded external Ca2+ when normalized to baseline amplitude. GGS was prevented by pan- but not glial-specific inhibition of glutamate uptake and by inhibition of glutamic acid decarboxylase (GAD), indicating reliance on glutamate uptake by neuronal excitatory amino acid transporter 3 (EAAT3) and enzymatic conversion of glutamate to GABA. EAAT3 immunoreactivity was strongly localized to presumptive PVN GABA terminals. High bath K+ also induced GGS, which was prevented by glutamate vesicle depletion, indicating that synaptic glutamate release strengthens PVN GABA inhibition. GGS suppressed PVN cell firing, indicating its functional significance. In sum, PVN GGS buffers neuronal excitation by apparent "over-filling" of vesicles with GABA synthesized from synaptically released glutamate. We posit that GGS protects against sustained PVN excitation and excitotoxicity while potentially aiding stress adaptation and habituation.

Vasopressin and central control of the cardiovascular system: A 40-year retrospective

In the 40 years since vasopressin (AVP) was reported to have a central action with respect to raising blood pressure, the finding has been repeatedly replicated using a variety of complimentary approaches. The role of AVP as a central neurotransmitter involved in control of the cardiovascular system is now textbook material. However, it is evident that brain AVP plays, at best, a minor role in regulation of normal blood pressure. However, it appears to be an important player in a several cardiovascular-associated pathologies, ranging from hypertension to neural changes associated with heart failure. There are many interventions that have been shown to affect neural function, many of which are associated with alterations in behaviour. Possible alterations in neuronal AVP actions relevant to cardiovascular control in the setting of chronic inflammatory disease, early-life stress and inflammation are suggested areas for future research.

NETs Lead to Sympathetic Hyperactivity After Traumatic Brain Injury Through the LL37-Hippo/MST1 Pathway

Background: Paroxysmal sympathetic hyperactivity (PSH) is one of the important reasons for the high mortality and morbidity of traumatic brain injury (TBI). We aim to explore the role of the neutrophil extracellular traps (NETs) in the pathogenesis of sympathetic hyperexcitability after TBI and the underlying mechanisms, providing evidence for clinical treatment.

Methods: Enzyme-linked immunosorbent assay was used to assess the plasma metanephrine and normetanephrine levels which represented the variation of the sympathetic system after TBI with rat diffuse axonal injury (DAI) model. NETs in the paraventricular nucleus (PVN) and circulating blood were examined using immunofluorescence and flow cytometry. Neutrophils-microglia co-culture system was established to further explore the effect of NETs on PSH and its mechanisms.

Results: After TBI, metanephrine and normetanephrine levels began to increase at 9 h and peaked at 72 h. After the injury, the level of NETs kept increasing at 24 and 72 h in the PVN. A positive correlation was found between the concentration of the PVN NETs and blood catecholamine. Flow cytometry of peripheral blood cells revealed that NETs level in the injury group was higher than that in the control group. Immunofluorescence results confirmed the presence of NETs in the PVN after TBI. The positive result of immunoprecipitation suggested a correlation effect between LL37 and P2 × 7. Peptidyl arginine deiminase-4 (PAD4) inhibitor could inhibit the expression levels of MST1, YAP, and IL-1β. The hippo/MST1 pathway inhibitor could inhibit the expression levels of YAP and IL-1β.

Conclusion: NETs formation in the PVN might be associated with sympathetic hyperactivity after TBI, which might relate to the activation of microglia cells and increased secretion of IL-1β via the hippo/MST1 pathway.

High Salt Intake Recruits Tonic Activation of NR2D Subunit-Containing Extrasynaptic NMDARs in Vasopressin Neurons

In addition to producing a classical excitatory postsynaptic current via activation of synaptic NMDA receptors (NMDARs), glutamate in the brain also induces a tonic NMDAR current (I _NMDA) via activation of extrasynaptic NMDARs (eNMDARs). However, since Mg²⁺ blocks NMDARs in nondepolarized neurons, the potential contribution of eNMDARs to the overall neuronal excitatory/inhibitory (E/I) balance remains unknown. Here, we demonstrate that chronic (7 d) salt loading (SL) recruited NR2D subunit-containing NMDARs to generate an Mg²⁺-resistant tonic I _NMDA in nondepolarized [V _h (holding potential) -70 mV] vasopressin (VP; but not oxytocin) supraoptic nucleus (SON) neurons in male rodents. Conversely, in euhydrated (EU) and 3 d SL mice, Mg²⁺-resistant tonic I _NMDA was not observed. Pharmacological and genetic intervention of NR2D subunits blocked the Mg²⁺-resistant tonic I _NMDA in VP neurons under SL conditions, while an NR2B antagonist unveiled Mg²⁺-sensitive tonic I _NMDA but not Mg²⁺-resistant tonic I _NMDA In the EU group VP neurons, an Mg²⁺-resistant tonic I _NMDA was not generated by increased ambient glutamate or treatment with coagonists (e.g., d-serine and glycine). Chronic SL significantly increased NR2D expression but not NR2B expression in the SON relative to the EU group or after 3 d under SL conditions. Finally, Mg²⁺-resistant tonic I _NMDA selectively upregulated neuronal excitability in VP neurons under SL conditions, independent of ionotropic GABAergic input. Our results indicate that the activation of NR2D-containing NMDARs constitutes a novel mechanism that generates an Mg²⁺-resistant tonic I _NMDA in nondepolarized VP neurons, thus causing an E/I balance shift in VP neurons to compensate for the hormonal demands imposed by a chronic osmotic challenge.SIGNIFICANCE STATEMENT The hypothalamic supraoptic nucleus (SON) consists of two different types of magnocellular neurosecretory cells (MNCs) that synthesize and release the following two peptide hormones: vasopressin (VP), which is necessary for regulation of fluid homeostasis; and oxytocin (OT), which plays a major role in lactation and parturition. NMDA receptors (NMDARs) play important roles in shaping neuronal firing patterns and hormone release from the SON MNCs in response to various physiological challenges. Our results show that prolonged (7 d) salt loading generated a Mg²⁺-resistant tonic NMDA current mediated by NR2D subunit-containing receptors, which efficiently activated nondepolarized VP (but not OT) neurons. Our findings support the hypothesis that NR2D subunit-containing NMDARs play an important adaptive role in adult brain in response to a sustained osmotic challenge.

The role of the tripartite synapse in the heart: how glial cells may contribute to the physiology and pathophysiology of the intracardiac nervous system

One of the major roles of the intracardiac nervous system (ICNS) is to act as the final site of signal integration for efferent information destined for the myocardium to enable local control of heart rate and rhythm. Multiple subtypes of neurons exist in the ICNS where they are organized into clusters termed ganglionated plexi (GP). The majority of cells in the ICNS are actually glial cells; however, despite this, ICNS glial cells have received little attention to date. In the central nervous system, where glial cell function has been widely studied, glia are no longer viewed simply as supportive cells but rather have been shown to play an active role in modulating neuronal excitability and synaptic plasticity. Pioneering studies have demonstrated that in addition to glia within the brain stem, glial cells within multiple autonomic ganglia in the peripheral nervous system, including the ICNS, can also act to modulate cardiovascular function. Clinically, patients with atrial fibrillation (AF) undergoing catheter ablation show high plasma levels of S100B, a protein produced by cardiac glial cells, correlated with decreased AF recurrence. Interestingly, S100B also alters GP neuron excitability and neurite outgrowth in the ICNS. These studies highlight the importance of understanding how glial cells can affect the heart by modulating GP neuron activity or synaptic inputs. Here, we review studies investigating glia both in the central and peripheral nervous systems to discuss the potential role of glia in controlling cardiac function in health and disease, paying particular attention to the glial cells of the ICNS.

Vasopressin & Oxytocin in Control of the Cardiovascular System: An Updated Review

Since the discovery of vasopressin (VP) and oxytocin (OT) in 1953, considerable knowledge has been gathered about their roles in cardiovascular homeostasis. Unraveling VP vasoconstrictor properties and V1a receptors in blood vessels generated powerful hemostatic drugs and drugs effective in the treatment of certain forms of circulatory collapse (shock). Recognition of the key role of VP in water balance via renal V2 receptors gave birth to aquaretic drugs found to be useful in advanced stages of congestive heart failure. There are still unexplored actions of VP and OT on the cardiovascular system, both at the periphery and in the brain that may open new venues in treatment of cardiovascular diseases. After a brief overview on VP, OT and their peripheral action on the cardiovascular system, this review focuses on newly discovered hypothalamic mechanisms involved in neurogenic control of the circulation in stress and disease.

Postacute Delivery of GABAA α5 Antagonist Promotes Postischemic Neurological Recovery and Peri-infarct Brain Remodeling

Supplemental Digital Content is available in the text.

Background and Purpose—

Poststroke, neuronal excitability is tonically reduced in peri-infarct tissue via inhibitory influences of extrasynaptic GABA_A receptors. We hypothesized that GABA_A α5 blockade by the competitive antagonist S44819 enhances postischemic neurological recovery, brain remodeling, and neuroplasticity.

Methods—

In an explorative study followed by a confirmation study, male C57Bl6/j mice were exposed to transient intraluminal middle cerebral artery occlusion. Starting 72 hours poststroke, vehicle or S44819 (3 or 10 mg/kg, BID) was delivered orally for 28 days. Neurological recovery, perilesional tissue remodeling, and contralesional pyramidal tract plasticity were evaluated for 42 days, that is, 14 days after completion of S44819 delivery.

Results—

S44819, delivered at 10 but not 3 mg/kg, persistently improved motor coordination and spatial memory in both studies. Striatal atrophy was reduced by 10 mg/kg S44819 at 42 days post-treatment onset, and neuronal long-term survival in the peri-infarct striatum was increased. Delayed neuroprotection was associated with reduced peri-infarct astrogliosis, increased peri-infarct brain capillary density, and increased neural precursor cell proliferation and differentiation in proximity to the ipsilesional subventricular zone. Contralesional pyramidal tract plasticity, evaluated by anterograde tract tracing at the level of the red nucleus, was not influenced by S44819. Concentrations of neurotrophic (brain-derived neurotrophic factor and glial cell line-derived neurotrophic factor) and angiogenic (vascular endothelial growth factor and basic fibroblast growth factor) growth factors were elevated by 10 mg/kg S44819 in peri-infarct but not contralesional brain tissue.

Conclusions—

Our data demonstrate that S44819 enhances neurological recovery and peri-infarct brain remodeling in the postacute stroke phase.

Exercise training normalizes elevated firing rate of hypothalamic presympathetic neurons in heart failure rats

Exercise training (ExT) normalizes elevated sympathetic nerve activity in heart failure (HF), but the underlying mechanisms are not well understood. In this study, we examined the effects of 3 wk of ExT on the electrical activity of the hypothalamic presympathetic neurons in the brain slice of HF rats. HF rats were prepared by ligating the left descending coronary artery. The electrophysiological properties of paraventricular nucleus neurons projecting to the rostral ventrolateral medulla (PVN-RVLM) were examined using the slice patch-clamp technique. The neuronal firing rate was elevated in HF rats, and ExT induced a reduction in the firing rate ( P < 0.01). This ExT-induced decrease in the firing rate was associated with an increased frequency of spontaneous and miniature inhibitory postsynaptic current (IPSCs; P < 0.05). There was no significant change in excitatory postsynaptic current. Replacing Ca²⁺ with Mg²⁺ in the recording solution reduced the elevated IPSC frequency in HF rats with ExT ( P < 0.01) but not in those without ExT, indicating an increase in the probability of GABA release. In contrast, ExT did not restore the reduced GABA_A receptor-mediated tonic inhibitory current in HF rats. A GABA_A receptor blocker (bicuculline, 20 μM) increased the firing rate in HF rats with ExT ( P < 0.01) but not in those without ExT. Collectively, these results show that ExT normalized the elevated firing activity by increasing synaptic GABA release in PVN-RVLM neurons in HF rats. Our findings provide a brain mechanism underlying the beneficial effects of ExT in HF, which may shed light on the pathophysiology of other diseases accompanied by sympathetic hyperactivation.

Comparison of electrophysiological properties of two types of pre-sympathetic neurons intermingled in the hypothalamic paraventricular nucleus

The hypothalamic paraventricular nucleus (PVN) contains two types of neurons projecting to either the rostral ventrolateral medulla (PVN_RVLM) or the intermediolateral horn (IML) of the spinal cord (PVN_IML). These two neuron groups are intermingled in the same subdivisions of the PVN and differentially regulate sympathetic outflow. However, electrophysiological evidence supporting such functional differences is largely lacking. Herein, we compared the electrophysiological properties of these neurons by using patch-clamp and retrograde-tracing techniques. Most neurons (>70%) in both groups spontaneously fired in the cell-attached mode. When compared to the PVN_IML neurons, the PVN_RVLM neurons had a lower firing rate and a more irregular firing pattern (p < 0.05). The PVN_RVLM neurons showed smaller resting membrane potential, slower rise and decay times, and greater duration of spontaneous action potentials (p < 0.05). The PVN_RVLM neurons received greater inhibitory synaptic inputs (frequency, p < 0.05) with a shorter rise time (p < 0.05). Taken together, the results indicate that the two pre-sympathetic neurons differ in their intrinsic and extrinsic electrophysiological properties, which may explain the lower firing activity of the PVN_RVLM neurons. The greater inhibitory synaptic inputs to the PVN_RVLM neurons also imply that these neurons have more integrative roles in regulation of sympathetic activity.

Glia and central cardiorespiratory pathology

Respiration and blood pressure are primarily controlled by somatic and autonomic motor neurones, respectively. Central cardiorespiratory control is critical in moment-to-moment survival, but it also has a role in the development and maintenance of chronic pathological conditions such as hypertension. The glial cells of the brain are non-neuronal cells with metabolic, immune, and developmental functions. Recent evidence shows that glia play an active role in supporting and regulating the neuronal circuitry which drives the cardiorespiratory system. Here we will review the activities of two key types of glial cell, microglia and astrocytes, in assisting normal central cardiorespiratory control and in pathology.

Differential electrophysiological properties of D1 and D2 spiny projection neurons in the mouse nucleus accumbens core

The striatum consists of the dorsal (caudate/putamen) and the ventral (nucleus accumbens) regions. The nucleus accumbens is further divided into a core and shell. Both the dorsal and ventral striatum contain populations of spiny projection neurons, which make up 95% of the neurons within the striatum. SPNs are canonically categorized into those that express the D1-type dopamine receptor (D1 SPNs) and those that express the D2-type dopamine receptor (D2 SPNs). D1 and D2 SPNs differ with respect to both synaptic inputs and projection targets. In the dorsal striatum, it is well established that these populations of SPNs differ in terms of their electrophysiological and morphological properties. However, there remains a gap in our knowledge of the electrophysiological properties of SPNs in the nucleus accumbens core. To evaluate the differential properties of these SPNs, we performed whole-cell recordings from D1 and D2 SPNs in BAC transgenic mice in which D1 SPNs fluoresce red and D2 SPNs fluoresce green. The two SPN subtypes did not differ in terms of their time constant, capacitance, resting membrane potential, or tonic current. However, D2 SPNs displayed heightened inhibitory postsynaptic current (IPSC) and miniature excitatory PSC frequency as compared with D1 SPNs. Furthermore, D2 SPNs displayed decreased rheobase, increased excitability as measured by firing rates to depolarizing current injections, increased inward rectification, increased input resistance, and decreased dendritic complexity compared to D1 SPNs. Our results demonstrate a dichotomy in the electrophysiological properties of D1 and D2 SPNs in the nucleus accumbens core, which contributes to our knowledge of ventral striatal circuitry.

Balancing tonic and phasic inhibition in hypothalamic corticotropin-releasing hormone neurons

KEY POINTS

GABA transporter (GAT) blockade recruits extrasynaptic GABA_A receptors (GABA_A Rs) and amplifies constitutive presynaptic GABA_B R activity. Extrasynaptic GABA_A Rs contribute to a tonic current. Corticosteroids increase the tonic current mediated by extrasynaptic GABA_A Rs.

ABSTRACT

Corticotropin-releasing hormone (CRH) neurons in the paraventricular nucleus of the hypothalamus (PVN) are integratory hubs that regulate the endocrine response to stress. GABA inputs provide a basal inhibitory tone that constrains this system and circulating glucocorticoids (CORT) are important feedback controllers of CRH output. Surprisingly little is known about the direct effects of CORT on GABA synapses in PVN. Here we used whole-cell patch clamp recordings from CRH neurons in mouse hypothalamic brain slices to examine the effects of CORT on synaptic and extrasynaptic GABA signalling. We show that GABA transporters (GATs) limit constitutive activation of presynaptic GABA_B receptors and ensure high release probability at GABA synapses. GATs in combination with GABA_B receptors also curtail extrasynaptic GABA_A R signalling. CORT has no effect on synaptic GABA signalling, but increases extrasynaptic GABA tone through upregulation of postsynaptic GABA_A receptors. These data show that efficient GABA clearance and autoinhibition control the balance between synaptic (phasic) and extrasynaptic (tonic) inhibition in PVN CRH neurons. This balance is shifted towards increased extrasynaptic inhibition by CORT.

Developmental changes in GABAA tonic inhibition are compromised by multiple mechanisms in preadolescent dentate gyrus granule cells

The sustained tonic currents (I_tonic) generated by γ-aminobutyric acid A receptors (GABA_ARs) are implicated in diverse age-dependent brain functions. While various mechanisms regulating I_tonic in the hippocampus are known, their combined role in I_tonic regulation is not well understood in different age groups. In this study, we demonstrated that a developmental increase in GABA transporter (GAT) expression, combined with gradual decrease in GABA_AR α₅ subunit, resulted in various I_tonic in the dentate gyrus granule cells (DGGCs) of preadolescent rats. Both GAT-1 and GAT-3 expression gradually increased at infantile (P_6-8 and P_13-15) and juvenile (P_20-22 and P_27-29) stages, with stabilization observed thereafter in adolescents (P_34-36) and young adults (P_41-43). I_tonic facilitation of a selective GAT-1 blocker (NO-711) was significantly less at P_6-8 than after P_13-15. The facilitation of I_tonic by SNAP-5114, a GAT-3 inhibitor, was negligible in the absence of exogenous GABA at all tested ages. In contrast, I_tonic in the presence of a nonselective GAT blocker (nipecotic acid, NPA) gradually decreased with age during the preadolescent period, which was mimicked by I_tonic changes in the presence of exogenous GABA. I_tonic sensitivity to L-655,708, a GABA_AR α₅ subunit inverse agonist, gradually decreased during the preadolescent period in the presence of NPA or exogenous GABA. Finally, Western blot analysis showed that the expression of the GABA_AR α₅ subunit in the dentate gyrus gradually decreased with age. Collectively, our results suggested that the I_tonic regulation of altered GATs is under the final tune of GABA_AR α₅ subunit activation in DGGCs at different ages.

Effect of the changes of NMDA receptor in hypothalamic paraventricular nucleus on cardiac function and sympathetic nervous activity in rats with heart failure

OBJECTIVE

To observe the effect of the changes of n-methyl-d-aspartate receptor 1 (NMDAR1), tyrosine hydroxylase (TH), and glutamic acid decarboxylase 67 (GAD67) in the hypothalamic paraventricular nucleus (PVN) on cardiac function and sympathetic nervous activity in rats with heart failure (HF).

METHODS

Thirty-six adult male SD rats were randomly divided into the heart failure group (HF), the heart failure + NMDA receptors agonist AP5 intervention group (HF-AP5), and the Sham-operation group (SO) (n = 12). HF model in SD rats was induced by ligation of left coronary artery. AP5 (0.02 μg/h) was administrated by the paraventricular nucleus subsequently for 4 weeks. The cardiac function, renal sympathetic nerve activity (RSNA), lung/body weight ratio (L/BW), and right ventricle/body weight ratio (RV/BW), as well as the plasma noradrenaline (NE) and Angiotensin II (Ang II) level and the expressions of NMDAR1, GAD67, and TH in PVN, in different groups were recorded 4 weeks after the establishment of HF model.

RESULTS

After the coronary artery was ligated, LVEDP was increased, ±dp/dt max and LVEF were decreased, lung/BW and RV/BW were raised. RSNA, Ang II and NE were raised. Expression of NMDAR1 and TH were increased, but GAD67 was decreased. The levels of LVEDP, lung/BW, and RV/BW in group HF-AP5 were reduced while ± dp/dtmax was increased after the treatment. The blood Ang II and NE content was decreased, RSNA was reduced, expression of NMDAR1 and TH were downregulated, but GAD67 was upregulated.

CONCLUSIONS

NMDAR1 is significantly activated in PVN of HF rats, the activity of TH is increased, GAD67 is downregulated, RSNA is increased, and the heart function is decreased. NMDA receptor blockers can alleviate HF.

Systemic Sympathoexcitation Was Associated with Paraventricular Hypothalamic Phosphorylation of Synaptic CaMKIIα and MAPK/ErK

Systemic administration of adrenergic agonist (Isoproterenol; ISOP) is known to facilitate cardiovascular changes associated with heart failure through an upregulation of cardiac toll-like receptor 4 (TLR4). Furthermore, previous studies have shown that cardiac tissue-specific deletion of TLR4 protects the heart against such damage. Since the autonomic regulation of systemic cardiovascular function originates from pre-autonomic sympathetic centers in the brain, it is unclear how a systemically driven sympathetic change may affect the pre-autonomic paraventricular hypothalamic nuclei (PVN) TLR4 expression. Here, we examined how change in PVN TLR4 was associated with alterations in the neurochemical cytoarchitecture of the PVN in systemic adrenergic activation. After 48 h of intraperitoneal 150 mg/kg ISOP treatment, there was a change in PVN CaMKIIα and MAPK/ErK expression, and an increase in TLR4 in expression. This was seen as an increase in p-MAPK/ErK, and a decrease in synaptic CaMKIIα expression in the PVN (p < 0.01) of ISOP treated mice. Furthermore, there was an upregulation of vesicular glutamate transporter (VGLUT 2; p < 0.01) and a decreased expression of GABA in the PVN of Isoproterenol (ISOP) treated WT mice (p < 0.01). However, after a PVN-specific knockdown of TLR4, the effect of systemic administration of ISOP was attenuated, as indicated by a decrease in p-MAPK/ErK (p < 0.01) and upregulation of CaMKIIα (p < 0.05). Additionally, loss of inhibitory function was averted while VGLUT2 expression decreased when compared with the ISOP treated wild type mice and the control. Taken together, the outcome of this study showed that systemic adrenergic activation may alter the expression, and phosphorylation of preautonomic MAPK/ErK and CaMKIIα downstream of TLR4. As such, by outlining the roles of these kinases in synaptic function, we have identified the significance of neural TLR4 in the progression, and attenuation of synaptic changes in the pre-autonomic sympathetic centers.

Thalamic dopaminergic neurons projects to the paraventricular nucleus-rostral ventrolateral medulla/C1 neural circuit

Paraventricular nuclei (PVN) projections to the rostral ventrolateral medulla (RVLM)/C1 catecholaminergic neuron group constitute the pre-autonomic sympathetic center involved in the neural control of systemic cardiovascular function. However, the role of extra-hypothalamic and thalamic dopaminergic (DA) inputs in this circuit remains underexplored. Using retrograde neuroanatomical tracing and high contrast confocal imaging methods, we investigated the projections and morphology of the discrete thalamic DA neuron groups in the dorsal hypothalamic area and their contribution to the PVN-RVLM neural circuit. We found that DA neuron subgroups in the Zona Incerta (Zi; 60%) and Reuniens thalamic nuclei (Re; 40%) were labeled comparably to the PVN (85%) after a retrograde tracer was injected into the RVLM/C1 (P < 0.01 mean ± SEM). The Re/Zi DA neuron subgroups were characterized by angulated cell bodies, superiomedial and inferiomedial projections reaching the contralateral Re/Zi and ipsilateral PVN DA neurons respectively. Ultimately, we deduced that the DA projections of the Re/Zi to the PVN contribute to the PVN-RVLM/C1 neural circuit. As a result of these connections, the Re/Zi DA neuron groups may regulate preautonomic sympathetic events associated with the PVN-RVLM pathway. Anat Rec, 300:1307-1314, 2017. © 2016 Wiley Periodicals, Inc.

c-Jun N-terminal Kinase mediates prostaglandin-induced sympathoexcitation in rats with chronic heart failure by reducing GAD1 and GABRA1 expression

AIM

Prostaglandin E2 mediates sympathoexcitation in chronic heart failure (CHF) through EP3 receptors (PTGER3) in the paraventricular nucleus (PVN). The aim of this study was to investigate the role of c-Jun N-terminal kinase (JNK) in expressional regulation of gamma-aminobutyric acid signalling in PVN in CHF rats.

METHODS

Chronic heart failure was induced by left coronary ligation in Wistar rats. Renal sympathetic nerve discharge (RSND) and mean arterial pressure (MAP) responses to the PVN infusion were determined in anaesthetized rats. Osmotic minipumps were used for chronic PVN infusion. PTGER3 expression was examined with immunofluorescence staining, quantitative real-time PCR and Western blot.

RESULTS

Chronic heart failure rats had increased JNK activation and decreased glutamate decarboxylase 1 (GAD1) and GABA_A receptor alpha 1 subunit (GABRA1) expression in the PVN. PVN infusion of the PTGER3 agonist SC-46275 caused sympathoexcitation in sham-operated control (Sham) rats and increased it further in CHF. The PTGER3 antagonist L798106 reduced sympathoexcitation and cardiac dysfunction in CHF. PVN infusion of EP1 receptor antagonist SC-19220, EP2 receptor antagonist AH6809 or EP4 receptor antagonist L-161982 had no effect on sympathoexcitation. The JNK inhibitor SP600125 normalized sympathoexcitation and GAD1 and GABRA1 expression in PVN in CHF rats. Both the p44/42 and p38 mitogen-activated protein kinase inhibitors PD98059 and SB203580 could not prevent the downregulation of GAD1 and GABRA1 expression in PVN in CHF. PTGER3 agonist activated JNK but downregulated GAD1 and GABRA1 expression in NG108 neuronal cells.

CONCLUSION

Prostaglandin signalling through upregulated PTGER3 activates JNK which reduces GAD1 and GABRA1 expression in the PVN, and contributes to sympathoexcitation in CHF.

The anti-inflammatory role of extranuclear apurinic/apyrimidinic endonuclease 1/redox effector factor-1 in reactive astrocytes

Apurinic/apyrimidinic endonuclease 1 (APE1), a ubiquitous multipurpose protein, is also known as redox effector factor-1 (Ref-1). It is involved in DNA repair and redox signaling and, in turn, oxidative stress-induced neurodegeneration. Although previous studies have demonstrated that APE1/Ref-1 functions as a negative regulator of inflammatory response via several mechanisms in neuronal cells, little is known about the roles of APE1/Ref-1 in glial cells. In this study, we found that cytoplasmic APE1/Ref-1 expression was upregulated in reactive astrocytes of the kainic acid- or lipopolysaccharide (LPS)-injected hippocampus. Analysis of the inflammatory response induced by extranuclear APE1/Ref-1 (ΔNLS-Ref-1) in cultured primary astrocytes revealed that it markedly suppressed inducible nitric oxide synthase (iNOS) expression and tumor necrosis factor-α (TNF-α) secretion induced by LPS to a similar extent as did wild type APE1/Ref-1 (WT-Ref-1), supporting the concept an anti-inflammatory role of extranuclear APE1/Ref-1 in astrocytes. Additionally, overexpression of WT- and ΔNLS-Ref-1 suppressed the transcriptional activity of nuclear factor-κB (NF-κB), although it effectively enhanced activator protein 1 (AP-1) activity. The blunting effect of APE1/Ref-1 on LPS-induced NF-κB activation was not mediated by IκB kinase (IKK) activity. Instead, APE1/Ref-1 inhibited p300-mediated acetylation of p65 by suppressing intracellular reactive oxygen species (ROS) levels following LPS treatment. Taken together, our results showed that altered expression and/or subcellular distribution of APE1/Ref-1 in activated astrocytes regulated the neuroinflammatory response to excitotoxin and endotoxin insults used in model of neurodegenerative brain diseases.

Facilitation of AMPA receptor-mediated steady-state current by extrasynaptic NMDA receptors in supraoptic magnocellular neurosecretory cells

In addition to classical synaptic transmission, information is transmitted between cells via the activation of extrasynaptic receptors that generate persistent tonic current in the brain. While growing evidence supports the presence of tonic NMDA current (I_NMDA) generated by extrasynaptic NMDA receptors (eNMDARs), the functional significance of tonic I_NMDA in various brain regions remains poorly understood. Here, we demonstrate that activation of eNMDARs that generate I_NMDA facilitates the α-amino-3-hydroxy-5-methylisoxazole-4-proprionate receptor (AMPAR)-mediated steady-state current in supraoptic nucleus (SON) magnocellular neurosecretory cells (MNCs). In low-Mg²⁺ artificial cerebrospinal fluid (aCSF), glutamate induced an inward shift in I_holding (I_GLU) at a holding potential (V_holding) of –70 mV which was partly blocked by an AMPAR antagonist, NBQX. NBQX-sensitive I_GLU was observed even in normal aCSF at V_holding of –40 mV or –20 mV. I_GLU was completely abolished by pretreatment with an NMDAR blocker, AP5, under all tested conditions. AMPA induced a reproducible inward shift in I_holding (I_AMPA) in SON MNCs. Pretreatment with AP5 attenuated I_AMPA amplitudes to ~60% of the control levels in low-Mg²⁺ aCSF, but not in normal aCSF at V_holding of –70 mV. I_AMPA attenuation by AP5 was also prominent in normal aCSF at depolarized holding potentials. Memantine, an eNMDAR blocker, mimicked the AP5-induced I_AMPA attenuation in SON MNCs. Finally, chronic dehydration did not affect I_AMPA attenuation by AP5 in the neurons. These results suggest that tonic I_NMDA, mediated by eNMDAR, facilitates AMPAR function, changing the postsynaptic response to its agonists in normal and osmotically challenged SON MNCs.