Mapping responses to focal injections of bicuculline in the lateral parafacial region identifies core regions for maximal generation of active expiration.

The lateral parafacial area (pFL) is a crucial region involved in respiratory control, particularly in generating active expiration through an expiratory oscillatory network. Active expiration involves rhythmic abdominal (ABD) muscle contractions during late-expiration, increasing ventilation during elevated respiratory demands. The precise anatomical location of the expiratory oscillator within the ventral medulla's rostro-caudal axis is debated. While some studies point to the caudal tip of the facial nucleus (VIIc) as the oscillator's core, others suggest more rostral areas. Our study employed bicuculline (a γ-aminobutyric acid type A [GABA-A] receptor antagonist) injections at various pFL sites (-0.2 mm to +0.8 mm from VIIc) to investigate the impact of GABAergic disinhibition on respiration. These injections consistently elicited ABD recruitment, but the response strength varied along the rostro-caudal zone. Remarkably, the most robust and enduring changes in tidal volume, minute ventilation, and combined respiratory responses occurred at more rostral pFL locations (+0.6/+0.8 mm from VIIc). Multivariate analysis of the respiratory cycle further differentiated between locations, revealing the core site for active expiration generation with this experimental approach. Our study advances our understanding of neural mechanisms governing active expiration and emphasizes the significance of investigating the rostral pFL region.

Brainstem Dbh+ neurons control allergen-induced airway hyperreactivity.

Exaggerated airway constriction triggered by repeated exposure to allergen, also called hyperreactivity, is a hallmark of asthma. Whereas vagal sensory neurons are known to function in allergen-induced hyperreactivity1-3, the identity of downstream nodes remains poorly understood. Here we mapped a full allergen circuit from the lung to the brainstem and back to the lung. Repeated exposure of mice to inhaled allergen activated the nuclei of solitary tract (nTS) neurons in a mast cell-, interleukin-4 (IL-4)- and vagal nerve-dependent manner. Single-nucleus RNA sequencing, followed by RNAscope assay at baseline and allergen challenges, showed that a Dbh+ nTS population is preferentially activated. Ablation or chemogenetic inactivation of Dbh+ nTS neurons blunted hyperreactivity whereas chemogenetic activation promoted it. Viral tracing indicated that Dbh+ nTS neurons project to the nucleus ambiguus (NA) and that NA neurons are necessary and sufficient to relay allergen signals to postganglionic neurons that directly drive airway constriction. Delivery of noradrenaline antagonists to the NA blunted hyperreactivity, suggesting noradrenaline as the transmitter between Dbh+ nTS and NA. Together, these findings provide molecular, anatomical and functional definitions of key nodes of a canonical allergen response circuit. This knowledge informs how neural modulation could be used to control allergen-induced airway hyperreactivity.

miR-193b-3p and miR-346 Exert Antihypertensive Effects in the Rostral Ventrolateral Medulla.

BACKGROUND: Rostral ventrolateral medulla (RVLM) neuron hyperactivity raises sympathetic outflow, causing hypertension. MicroRNAs (miRNAs) contribute to diverse biological processes, but their influence on RVLM neuronal excitability and blood pressure (BP) remains widely unexplored. METHODS AND RESULTS: The RVLM miRNA profiles in spontaneously hypertensive rats were unveiled using RNA sequencing. Potential effects of these miRNAs in reducing neuronal excitability and BP and underlying mechanisms were investigated through various experiments. Six hundred thirty-seven miRNAs were identified, and reduced levels of miR-193b-3p and miR-346 were observed in the RVLM of spontaneously hypertensive rats. Increased miR-193b-3p and miR-346 expression in RVLM lowered neuronal excitability, sympathetic outflow, and BP in spontaneously hypertensive rats. In contrast, suppressing miR-193b-3p and miR-346 expression in RVLM increased neuronal excitability, sympathetic outflow, and BP in Wistar Kyoto and Sprague-Dawley rats. Cdc42 guanine nucleotide exchange factor (Arhgef9) was recognized as a target of miR-193b-3p. Overexpressing miR-193b-3p caused an evident decrease in Arhgef9 expression, resulting in the inhibition of neuronal apoptosis. By contrast, its downregulation produced the opposite effects. Importantly, the decrease in neuronal excitability, sympathetic outflow, and BP observed in spontaneously hypertensive rats due to miR-193b-3p overexpression was greatly counteracted by Arhgef9 upregulation. CONCLUSIONS: miR-193b-3p and miR-346 are newly identified factors in RVLM that hinder hypertension progression, and the miR-193b-3p/Arhgef9/apoptosis pathway presents a potential mechanism, highlighting the potential of targeting miRNAs for hypertension prevention.

Orexin receptor 2 agonist activates diaphragm and genioglossus muscle through stimulating inspiratory neurons in the pre-Bötzinger complex, and phrenic and hypoglossal motoneurons in rodents.

Orexin-mediated stimulation of orexin receptors 1/2 (OX[1/2]R) may stimulate the diaphragm and genioglossus muscle via activation of inspiratory neurons in the pre-Bötzinger complex, which are critical for the generation of inspiratory rhythm, and phrenic and hypoglossal motoneurons. Herein, we assessed the effects of OX2R-selective agonists TAK-925 (danavorexton) and OX-201 on respiratory function. In in vitro electrophysiologic analyses using rat medullary slices, danavorexton and OX-201 showed tendency and significant effect, respectively, in increasing the frequency of inspiratory synaptic currents of inspiratory neurons in the pre-Bötzinger complex. In rat medullary slices, both danavorexton and OX-201 significantly increased the frequency of inspiratory synaptic currents of hypoglossal motoneurons. Danavorexton and OX-201 also showed significant effect and tendency, respectively, in increasing the frequency of burst activity recorded from the cervical (C3-C5) ventral root, which contains axons of phrenic motoneurons, in in vitro electrophysiologic analyses from rat isolated brainstem-spinal cord preparations. Electromyogram recordings revealed that intravenous administration of OX-201 increased burst frequency of the diaphragm and burst amplitude of the genioglossus muscle in isoflurane- and urethane-anesthetized rats, respectively. In whole-body plethysmography analyses, oral administration of OX-201 increased respiratory activity in free-moving mice. Overall, these results suggest that OX2R-selective agonists enhance respiratory function via activation of the diaphragm and genioglossus muscle through stimulation of inspiratory neurons in the pre-Bötzinger complex, and phrenic and hypoglossal motoneurons. OX2R-selective agonists could be promising drugs for various conditions with respiratory dysfunction.

Swallowing-like activity elicited in neonatal rat medullary slice preparation.

Swallowing is induced by a central pattern generator in the nucleus tractus solitarius (NTS). We aimed to create a medullary slice preparation to elucidate the neural architecture of the central pattern generator of swallowing (Sw-CPG) and record its neural activities. Experiments were conducted on 2-day-old Sprague-Dawley rats (n = 46). The brainstem-spinal cord was transected at the pontomedullary and cervicothoracic junctions; the medulla was sliced transversely at thicknesses of 600, 700, or 800 µm. The rostral end of the slice was 100 µm rostral to the vagus nerve. We recorded hypoglossal nerve activity and electrically stimulated the vagus nerve or microinjected bicuculline methiodide (BIC) into the NTS. The 800-µm slices generated both rhythmic respiratory activity and electrically elicited neural activity. The 700-µm slices generated only respiratory activity, while the 600-µm slices did not generate any neural activity. BIC microinjection into the NTS in 800-µm slices resulted in the typical activity that closely resembled the swallowing activity reported in other experiments. This swallowing-like activity consistently lengthened the respiratory interval. Despite complete inhibition of respiratory activity, weak swallowing-like activity was observed under bath application of a non-NMDA receptor antagonist. Contrastingly, bath application of NMDA receptor antagonists resulted in a complete loss of swallowing-like activity and no change in respiratory activity. These results suggest that the 800-µm medullary slice preparation contains both afferent and efferent neural circuits and pattern generators of swallowing activity. Additionally, NMDA receptors may be necessary for generating swallowing activity. This medullary slice preparation can therefore elucidate Sw-CPG neural networks.

Parotid hypersalivation after inferior salivatory nucleus glutamate/NMDA receptor excitation in the rat.

Although salivation is essential during eating behavior, little is known about the brainstem centers that directly control the salivary glands. With regard to the inferior salivatory nucleus (ISN), the site of origin of the parasympathetic preganglionic cell bodies that innervate the parotid glands, previous anatomical studies have located it within the rostrodorsal medullary reticular formation. However, to date there is no functional data that shows the secretory nature of the somas grouped in this region. To activate only the somas and rule out the activation of the efferent fibers from and the afferent fibers to the ISN, in exp. 1, NMDA neurotoxin was administered to the rostrodorsal medullary region and the secretion of saliva was recorded during the following hour. Results showed an increased secretion of parotid saliva but a total absence of submandibular-sublingual secretion. In exp. 2, results showed that the hypersecretion of parotid saliva after NMDA microinjection was completely blocked by the administration of atropine (a cholinergic blocker) but not after administration of dihydroergotamine plus propranolol (α and ß-adrenergic blockers, respectively). These findings suggest that the somata of the rostrodorsal medulla are secretory in nature, controlling parotid secretion via a cholinergic pathway. The data thus functionally supports the idea that these cells constitute the ISN.

Inputs to the locus coeruleus from the periaqueductal gray and rostroventral medulla shape opioid-mediated descending pain modulation.

The supraspinal descending pain modulatory system (DPMS) shapes pain perception via monoaminergic modulation of sensory information in the spinal cord. However, the role and synaptic mechanisms of descending noradrenergic signaling remain unclear. Here, we establish that noradrenergic neurons of the locus coeruleus (LC) are essential for supraspinal opioid antinociception. While much previous work has emphasized the role of descending serotonergic pathways, we find that opioid antinociception is primarily driven by excitatory output from the ventrolateral periaqueductal gray (vlPAG) to the LC. Furthermore, we identify a previously unknown opioid-sensitive inhibitory input from the rostroventromedial medulla (RVM), the suppression of which disinhibits LC neurons to drive spinal noradrenergic antinociception. We describe pain-related activity throughout this circuit and report the presence of prominent bifurcating outputs from the vlPAG to the LC and the RVM. Our findings substantially revise current models of the DPMS and establish a supraspinal antinociceptive pathway that may contribute to multiple forms of descending pain modulation.

Estrogen dampens central cannabinoid receptor 1-mediated neuroexcitation and pressor response in conscious female rats.

Activation of the rostral ventrolateral medulla (RVLM) cannabinoid receptor-1 (CB1R) causes neuronal nitric oxide synthase (nNOS)-dependent increases in sympathetic activity, blood pressure (BP) and heart rate (HR) in male rats. However, it remains unknown if the CB1R-mediated neurochemical and cardiovascular responses are influenced by the ovarian sex hormones, particularly estrogen (E2). Therefore, we studied the effects of intra-RVLM CB1R activation (WIN 55,212-2) on BP and HR in conscious female rats under the following hormonal states: (1) highest E2 level (proestrus sham-operated, SO); (2) E2-deprivation (ovariectomized, OVX); (3) OVX with E2 replacement (OVXE2). Intra-RVLM WIN55,212-2 elicited dose (100-400 pmol) dependent pressor and tachycardic responses, in OVX rats, which replicated the reported responses in male rats. However, in SO and OVXE2 rats, the CB1R-mediated pressor response was attenuated and the tachycardic response reverted to bradycardic response. The neurochemical findings suggested a key role for the upregulated RVLM sympathoexcitatory molecules phosphorated protein kinase B, phosphorated nNOS and reactive oxygen species in the exaggerated CB1R-mediated BP and HR responses in OVX rats, and an E2-dependent dampening of these responses. The intra-RVLM WIN55212-2-evoked cardiovascular and neurochemical responses were CB1R-mediated because they were attenuated by prior CB1R blockade (AM251). Our findings suggest that attenuation of RVLM neuroexcitation and oxidative stress underlies the protection conferred by E2, in female rats, against the CB1R-mediated adverse cardiovascular effects.

Hydrogen sulfide ameliorated preeclampsia via suppression of toll-like receptor 4-activated inflammation in the rostral ventrolateral medulla of rats.

This study aims to determine whether toll-like receptor 4 (TLR4)-mediated inflammation in rostral ventrolateral medulla (RVLM) causes sympathetic overactivity leading to preeclampsia (PE) and if TLR4 inhibition with hydrogen sulfide (H2S) would reduce PE severity. Thirty patients with PE and 30 pregnant controls were involved. PE in rats was induced through deoxycorticosterone acetate and normal saline. NaHS (donor of H2S), lipopolysaccharide (LPS) (TLR4 agonist), and TAK-242 (TLR4 inhibitor) were injected in lateral cerebral ventricle to investigate their effect on microglia-mediated inflammation in RVLM, sympathetic activation, and PE symptoms. In patients with PE, plasma levels of NE, TNF-α, and interleukin-1ß were high compared with those of controls, whereas levels of H2S were low. Rats with PE showed an increased amount of renal sympathetic nerve activity and plasma levels of NE, with decreased H2S levels in RVLM. Microglia-mediated inflammation was observed in the RVLM of PE rats. Central infusion of LPS in pregnant rats induced microglia-mediated inflammation, sympathetic nervous tension, and PE-like symptoms, whereas TAK-242 reduced PE symptoms. NaHS treatment lessened microglia-mediated inflammation in the RVLM, sympathetic tension, and symptoms of PE both in PE rats and LPS-treating pregnant rats.These results suggest that inflammation in the RVLM caused by microglial activation might contribute to the progression of PE via an overactive sympathetic system. H2S could reduce PE via inhibiting inflammation in the RVLM. These results might provide a new target for the treatment of PE.

Antioxidant therapy reverses sympathetic dysfunction, oxidative stress, and hypertension in male hyperadipose rats.

AIMS: The rostral ventrolateral medulla (RVLM) is the main sympathetic output of the central nervous system to control blood pressure. Reportedly, reactive oxygen species (ROS) can increase arterial pressure, leading to hypertension. As ROS increase the sympathetic tone in RVLM and obese animals present grater oxidative stress, it would be important to note this relationship. MAIN METHODS: Therefore, we evaluated the systemic and central effects (in the RVLM) of vitamin C (vit C, an antioxidant) on the redox balance and cardiovascular and autonomic profiles in hyperadipose male rats. We also evaluated the neurotransmission by L-glutamate (L-glu) and vit C in the RVLM of awake hyperadipose rats. KEY FINDINGS: Our study confirmed that hyperadipose rats were hypertensive and tachycardic, presented increased sympathetic and decreased parasympathetic modulation of the heart, and had increased plasma lipoperoxidation compared with the control rats (CTR). Oral vitamin C treatment reverted cardiovascular, autonomic, and plasma redox dysfunction. Hyperadipose rats presented a higher blood pressure increase after L-glu microinjection and a lower response to vit C in the RVLM compared with the CTR group. Biochemical analysis of redox balance in RVLM punches showed that hyperadipose rats have increased NBT and T-BARS, and after treatment with vit C, the oxidative profile decreased. The antioxidative activity of vit C reduced the amount of ROS in the RVLM area that might have resulted in lowered blood pressure and sympathetic modulation. SIGNIFICANCE: Our data suggest central and peripheral benefits of vit C treatment on cardiovascular, autonomic, and oxidative dysfunctions in hyperadipose animals.

The role of neuronal excitation and inhibition in the pre-Bötzinger complex on the cough reflex in the cat.

Brainstem respiratory neuronal network significantly contributes to cough motor pattern generation. Neuronal populations in the pre-Bötzinger complex (PreBötC) represent a substantial component for respiratory rhythmogenesis. We studied the role of PreBötC neuronal excitation and inhibition on mechanically induced tracheobronchial cough in 15 spontaneously breathing, pentobarbital anesthetized adult cats (35 mg/kg, iv initially). Neuronal excitation by unilateral microinjection of glutamate analog d,l-homocysteic acid resulted in mild reduction of cough abdominal electromyogram (EMG) amplitudes and very limited temporal changes of cough compared with effects on breathing (very high respiratory rate, high amplitude inspiratory bursts with a short inspiratory phase, and tonic inspiratory motor component). Mean arterial blood pressure temporarily decreased. Blocking glutamate-related neuronal excitation by bilateral microinjections of nonspecific glutamate receptor antagonist kynurenic acid reduced cough inspiratory and expiratory EMG amplitude and shortened most cough temporal characteristics similarly to breathing temporal characteristics. Respiratory rate decreased and blood pressure temporarily increased. Limiting active neuronal inhibition by unilateral and bilateral microinjections of GABAA receptor antagonist gabazine resulted in lower cough number, reduced expiratory cough efforts, and prolongation of cough temporal features and breathing phases (with lower respiratory rate). The PreBötC is important for cough motor pattern generation. Excitatory glutamatergic neurotransmission in the PreBötC is involved in control of cough intensity and patterning. GABAA receptor-related inhibition in the PreBötC strongly affects breathing and coughing phase durations in the same manner, as well as cough expiratory efforts. In conclusion, differences in effects on cough and breathing are consistent with separate control of these behaviors.NEW & NOTEWORTHY This study is the first to explore the role of the inspiratory rhythm and pattern generator, the pre-Bötzinger complex (PreBötC), in cough motor pattern formation. In the PreBötC, excitatory glutamatergic neurotransmission affects cough intensity and patterning but not rhythm, and GABAA receptor-related inhibition affects coughing and breathing phase durations similarly to each other. Our data show that the PreBötC is important for cough motor pattern generation, but cough rhythmogenesis appears to be controlled elsewhere.

Regularly swimming exercise modifies opioidergic neuromodulation in rostral ventrolateral medulla in hypertensive rats.

Moderate exercise reduces arterial pressure (AP) and heart rate (HR) in spontaneously hypertensive rats (SHR) and changes neurotransmission in medullary areas involved in cardiovascular regulation. We investigated if regularly swimming exercise (SW) affects the cardiovascular adjustments mediated by opioidergic neuromodulation in the RVLM in SHR and Wistar-Kyoto (WKY) rats. Rats were submitted to 6 wks of SW. The day after the last exercise bout, α-chloralose-anesthetized rats underwent a cannulation of the femoral artery for AP and HR recordings, and Doppler flow probes were placed around the lower abdominal aorta and superior mesenteric artery. Bilateral injection of endomorphin-2 (EM-2, 0.4 mmol/L, 60 nL) into the RVLM increased MAP in SW-SHR (20 ± 4 mmHg, N = 6), which was lower than in sedentary (SED)-SHR (35 ± 4 mmHg, N = 6). The increase in MAP in SW-SHR induced by EM-2 into the RVLM was similar in SED- and SW-WKY. Naloxone (0.5 mmol/L, 60 nL) injected into the RVLM evoked an enhanced hypotension in SW-SHR (-66 ± 8 mmHg, N = 6) compared to SED-SHR (-25 ± 3 mmHg, N = 6), which was similar in SED- and SW-WKY. No significant changes were observed in HR after EM-2 or naloxone injections into the RVLM. Changes in hindquarter and mesenteric conductances evoked by EM-2 or naloxone injections into the RVLM in SW- or SED-SHR were not different. Mu Opioid Receptor expression by Western blotting was reduced in SW-SHR than in SED-SHR and SW-WKY. Therefore, regularly SW alters the opioidergic neuromodulation in the RVLM in SHR and modifies the mu opioid receptor expression in this medullary area.

Systemic 8-OH-DPAT challenge causes hyperventilation largely via activating pre-botzinger complex 5-HT1A receptors.

Systemic 8-OH-DPAT (a 5-HT1A receptor agonist) challenge evokes hyperventilation independent of peripheral 5-HT1A receptors. Though the pre-Botzinger Complex (PBC) is critical in generating respiratory rhythm and activation of local 5-HT1A receptors induces tachypnea via disinhibition of local GABAA neurons, its role in the respiratory response to systemic 8-OH-DPAT challenge is still unclear. In anesthetized rats, 8-OH-DPAT (100 µg/kg, iv) was injected twice to confirm the reproducibility of the evoked responses. The same challenges were performed after bilateral microinjections of (S)-WAY-100135 (a 5-HT1A receptor antagonist) or gabazine (a GABAA receptor antagonist) into the PBC. Our results showed that: 1) 8-OH-DPAT caused reproducible hyperventilation associated with hypotension and bradycardia; 2) microinjections of (S)-WAY-100135 into the PBC attenuated the hyperventilation by ˜60 % without effect on the evoked hypotension and bradycardia; and 3) the same hyperventilatory attenuation was also observed after microinjections of gabazine into the PBC. Our data suggest that PBC 5-HT1A receptors play a key role in the respiratory response to systemic 8-OH-DPAT challenge likely via disinhibiting local GABAergic neurons.

Thymoquinone has a neuroprotective effect against inflammation, oxidative stress, and endoplasmic reticulum stress in the brain cortex, medulla, and hippocampus due to doxorubicin.

Although doxorubicin (DOX) is used in many cancer treatments, it causes neurotoxicity. In this study, the effect of thymoquinone (THQ), a powerful antioxidant, on DOX-induced neurotoxicity was evaluated. In total, 40 rats were used and 5 groups were formed. Group I: control group (n = 8); Group II: olive oil group (n = 8); Group III: the THQ group (n = 8); THQ 10 mg/kg per day was given intraperitoneally (i.p.) throughout the experiment; group IV: DOX group (n = 8); On Day 7 of the experiment, a single dose of 15 mg/kg intraperitoneally DOX injected; group V: DOX + THQ group (n = 8); Throughout the experiment, 10 mg/kg THQ per day and intraperitoneally 15 mg/kg DOX on Day 7 were injected. Immunohistochemically, tumor necrosis factor-α (TNF-α), interleukin-17 (IL-17), hypoxia-inducible factor 1α (HIF1-α), glucose regulatory protein 78 (GRP78), and the gene inducible by growth arrest and DNA damage 153 (GADD153) proteins were evaluated in the brain cortex, medulla, and hippocampus regions. Total oxidant status (TOS) levels and total antioxidant status (TAS) in the brain tissue were measured. TNF-α, IL-17, HIF1-α, GRP78, and GADD153 immunoreactivities significantly increased in the DOX group in the study. THQ significantly reduced these values. THQ increased the TAS level significantly and decreased the TOS level significantly compared to the DOX group. THQ may play a role as a neuroprotective agent in DOX-induced neurotoxicity in the cortex, medulla, and hippocampus regions of the brain.

Neural mechanisms underlying respiratory regulation within the preBötzinger complex of the rabbit.

The preBötzinger complex (preBötC) is a medullary area essential for normal breathing and widely recognized as necessary and sufficient to generate the inspiratory phase of respiration. It has been studied mainly in rodents. Here we report the main results of our studies revealing the characteristics of the rabbit preBötC identified by means of neuronal recordings, D,L-homocysteic acid microinjections and histological controls. A crucial role in the respiratory rhythmogenesis within this neural substrate is played by excitatory amino acids, but also GABA and glycine display important contributions. Increases in respiratory frequency are induced by microinjections of neurokinins, somatostatin as well by serotonin (5-HT) through an action on 5-HT1A and 5-HT3 receptors or the disinhibition of a GABAergic circuit. Respiratory depression is observed in response to microinjections of the µ-opioid receptor agonist DAMGO. Our results show similarities and differences with the rodent preBötC and emphasize the importance of comparative studies on the mechanisms underlying respiratory rhythmogenesis in different animal species.

Circadian rhythm influences naloxone induced morphine withdrawal and neuronal activity of lateral paragigantocellularis nucleus.

Investigations have shown that the circadian rhythm can affect the mechanisms associated with drug dependence. In this regard, we sought to assess the negative consequence of morphine withdrawal syndrome on conditioned place aversion (CPA) and lateral paragigantocellularis (LPGi) neuronal activity in morphine-dependent rats during light (8:00-12:00) and dark (20:00-24:00) cycles. Male Wistar rats (250-300 g) were received 10 mg/kg morphine or its vehicle (Saline, 2 mL/kg/12 h, s.c.) in 13 consecutive days for behavioral assessment tests. Then, naloxone-induced conditioned place aversion and physical signs of withdrawal syndrome were evaluated during light and dark cycles. In contrast to the behavioral part, we performed in vivo extracellular single-unit recording for investigating the neural response of LPGi to naloxone in morphine-dependent rats on day 10 of morphine/saline exposure. Results showed that naloxone induced conditioned place aversion in both light and dark cycles, but the CPA score during the light cycle was larger. Moreover, the intensity of physical signs of morphine withdrawal syndrome was more severe during the light cycle (rest phase) compare to the dark one. In electrophysiological experiments, results indicated that naloxone evoked both excitatory and inhibitory responses in LPGi neurons and the incremental effect of naloxone on LPGi activity was stronger in the light cycle. Also, the neurons with the excitatory response exhibited higher baseline activity in the dark cycle, but the neurons with the inhibitory response showed higher baseline activity in the light cycle. Interestingly, the baseline firing rate of neurons recorded in the light cycle was significantly different in response (excitatory/inhibitory) -dependent manner. We concluded that naloxone-induced changes in LPGi cellular activity and behaviors of morphine-dependent rats can be affected by circadian rhythm and the internal clock.

G protein-coupled estrogen receptor in the rostral ventromedial medulla contributes to the chronification of postoperative pain.

AIMS: Chronification of postoperative pain is a common clinical phenomenon following surgical operation, and it perplexes a great number of patients. Estrogen and its membrane receptor (G protein-coupled estrogen receptor, GPER) play a crucial role in pain regulation. Here, we explored the role of GPER in the rostral ventromedial medulla (RVM) during chronic postoperative pain and search for the possible mechanism. METHODS AND RESULTS: Postoperative pain was induced in mice or rats via a plantar incision surgery. Behavioral tests were conducted to detect both thermal and mechanical pain, showing a small part (16.2%) of mice developed into pain persisting state with consistent low pain threshold on 14 days after incision surgery compared with the pain recovery mice. Immunofluorescent staining assay revealed that the GPER-positive neurons in the RVM were significantly activated in pain persisting rats. In addition, RT-PCR and immunoblot analyses showed that the levels of GPER and phosphorylated µ-type opioid receptor (p-MOR) in the RVM of pain persisting mice were apparently increased on 14 days after incision surgery. Furthermore, chemogenetic activation of GPER-positive neurons in the RVM of Gper-Cre mice could reverse the pain threshold of pain recovery mice. Conversely, chemogenetic inhibition of GPER-positive neurons in the RVM could prevent mice from being in the pain persistent state. CONCLUSION: Our findings demonstrated that the GPER in the RVM was responsible for the chronification of postoperative pain and the downstream pathway might be involved in MOR phosphorylation.

Chronic stimulation of group II metabotropic glutamate receptors in the medulla oblongata attenuates hypertension development in spontaneously hypertensive rats.

Baroreflex dysfunction is partly implicated in hypertension and one responsible region is the dorsal medulla oblongata including the nucleus tractus solitarius (NTS). NTS neurons receive and project glutamatergic inputs to subsequently regulate blood pressure, while G-protein-coupled metabotropic glutamate receptors (mGluRs) play a modulatory role for glutamatergic transmission in baroreflex pathways. Stimulating group II mGluR subtype 2 and 3 (mGluR2/3) in the brainstem can decrease blood pressure and sympathetic nervous activity. Here, we hypothesized that the chronic stimulation of mGluR2/3 in the dorsal medulla oblongata can alleviate hypertensive development via the modulation of autonomic nervous activity in young, spontaneously hypertensive rats (SHRs). Compared with that in the sham control group, chronic LY379268 application (mGluR2/3 agonist; 0.40 µg/day) to the dorsal medulla oblongata for 6 weeks reduced the progression of hypertension in 6-week-old SHRs as indicated by the 40 mmHg reduction in systolic blood pressure and promoted their parasympathetic nervous activity as evidenced by the heart rate variability. No differences in blood catecholamine levels or any echocardiographic indices were found between the two groups. The improvement of reflex bradycardia, a baroreflex function, appeared after chronic LY379268 application. The mRNA expression level of mGluR2, but not mGluR3, in the dorsal medulla oblongata was substantially reduced in SHRs compared to that of the control strain. In conclusion, mGluR2/3 signaling might be responsible for hypertension development in SHRs, and modulating mGluR2/3 expression/stimulation in the dorsal brainstem could be a novel therapeutic strategy for hypertension via increasing the parasympathetic activity.

Exercise training rescues the electrical activity of liver-projecting DMNV neurones in response to oxytocin in spontaneously hypertensive rats.

A neural circuit between the paraventricular nucleus of the hypothalamus (PVN) and the dorsal motor nucleus of the vagus (DMNV) constitutes part of an important parasympathetic autonomic pathway that controls hepatic glucose production. Intracerebroventricular injection of insulin activates oxytocinergic neurones in the PVN and elicits the release of oxytocin into the circulation, which plays an important role in the metabolism of glucose. Moreover, the central action of insulin can reduce the concentration of glucose in blood taken from the hepatic vein of Wistar rats via activation of vagal efferent nerves to the liver. This mechanism is impaired in sedentary spontaneously hypertensive rats (SHR). Because aerobic exercise increases vagal tone, partly mediated by increasing the oxytocinergic connections between the PVN and DMNV, we hypothesised that oxytocin (OT) might alter the excitability of liver-projecting DMNV neurones. Thus, we investigated the effects of OT on electrical properties of the liver-projecting DMNV neurones from Wistar, SHR subjected to 4 weeks of exercise training, as well sedentary controls, using whole cell patch-clamping. The results show that OT increased the resting membrane potential of DMNV neurones in Wistar rats, as well as the firing frequency of these cells, but not in sedentary SHR. However, in SHR subjected to 4 weeks of exercise training, the effects of OT on liver-projecting DMNV neurones of were similar to those seen in Wistar rats. These findings show that OT elicits similar changes in the electrophysiological properties of liver-projecting DMNV neurones of Wistar and exercise-trained but not sedentary SHR. These results indicate that exercise training can restore the sensitivity of liver-projecting DMNV neurones of exercise-trained SHR to OT.

Sexual dimorphism in rats exposed to maternal high fat diet: alterations in medullary sympathetic network.

Exposure to high fat diet during perinatal period (PHFD) leads to neuroplastic changes in autonomic circuits, however, the role of gender has been incompletely understood. This study aims to investigate (i) short, and (ii) long-term effects of PHFD on autonomic outflow, and (iii) sexual dimorphic variations emerge at adulthood. Male and female rats were fed a control diet (13.5 % kcal from fat) or PHFD (60 % kcal from fat) from embryonic day-14 to postnatal day-21. To assess changes in autonomic outflow, heart rate variability (HRV) was analyzed at 10- and 20-week-old ages. Expressions of tyrosine hydroxylase (TH), metabotropic glutamate2/3 receptor (mGlu2/3R), N-methyl-D-aspartate1 receptor (NMDA1R), and gamma aminobutyric acidA receptor (GABAAR) were evaluated by immunohistochemistry. PHFD did not affect the body weight of 4-, 10-or 20-week-old male or female offsprings. PHFD significantly increased the sympathetic marker low frequency (LF) component, and sympatho-vagal balance (LF:HF) only in 10-week-old PHFD males. Compared with control, the propranolol-induced (4 mg·kg- 1, ip) decline in LF was observed more prominently in PHFD rats, however, these changes were found to be restored at the age of 20 weeks. In caudal ventrolateral medulla and nucleus tractus solitarius, expression of mGlu2/3R was downregulated in PHFD males, whereas no change was detected in NMDA1R. The number of GABAAR-expressing TH-immunoreactive cells was decreased in rostral ventrolateral medulla of PHFD males. The findings of this study suggest that exposure to maternal high-fat diet could lead to autonomic imbalance with increased sympathetic tone in the early adulthood of male offspring rats without developing obesity.