Rostral Ventrolateral Medulla Of Rats Research Articles

Regulation of the sympathetic nervous system by nitric oxide and oxidative stress in the rostral ventrolateral medulla: 2012 Academic Conference Award from the Japanese Society of Hypertension

Sympathoexcitation has an important role in the pathogenesis of hypertension. Previous studies have demonstrated that nitric oxide (NO) and/or oxidative stress in the brain are important for the regulation of the sympathetic nervous system. We have investigated the role of NO derived from an overexpression of endothelial NO synthase (eNOS) or oxidative stress in the rostral ventrolateral medulla (RVLM), which is known as a vasomotor center in the brainstem, on the regulation of the sympathetic nervous system. Our results indicated that NO derived from an overexpression of eNOS in the RVLM caused sympathoinhibition via an increase in γ-amino butyric acid and that angiotensin II type 1 receptor (AT1R)-induced oxidative stress in the RVLM caused sympathoexcitation. We also demonstrated that oxidative stress in the RVLM caused sympathoexcitation via interactions with NO, effects on the signal transduction or apoptosis of the astrocytes. Furthermore, several orally administered AT1R blockers have been found to cause sympathoinhibition via a reduction in oxidative stress through the blockade of AT1R in the RVLM of hypertensive rats. In conclusion, our studies suggest that the increase in AT1R-induced oxidative stress and/or the decrease in NO in the RVLM mainly cause sympathoexcitation in hypertension.

Repeated electroacupuncture attenuating of apelin expression and function in the rostral ventrolateral medulla in stress-induced hypertensive rats

Studies have revealed that apelin is a novel multifunctional peptide implicated both in blood pressure (BP) regulation and cardiac function control. Evidence shows that apelin and its receptor (APJ) in the rostral ventrolateral medulla (RVLM) may play an important role in central BP regulation; however, its role is controversial and very few reports have shown the relationship between acupuncture and apelin. Our study aims to both investigate the apelinergic system role in stress-induced hypertension (SIH) and determine whether acupuncture therapy effects on hypertension involve the apelinergic system in the RVLM. We established the stress-induced hypertensive rat (SIHR) model using electric foot-shock stressors with noise interventions. The expression of both apelin and the APJ receptor in the RVLM neurons was examined by immunohistochemical staining and Western blots. The results showed apelin expression increased remarkably in SIHR while APJ receptor expression showed no significant difference between control and SIHR groups. Microinjection of apelin-13 into the RVLM of control rats or SIHR produced pressor and tachycardic effects. Furthermore, effects induced by apelin-13 in SIHR were significantly greater than those of control rats. In addition, repetitive electroacupuncture (EA) stimulation at the Zusanli (ST-36) acupoint attenuated hypertension and apelin expression in the RVLM in SIHR; it also attenuated the pressor effect elicited by exogenous apelin-13 microinjection in SIHR. The results suggest that augmented apelin in the RVLM was part of the manifestations of SIH; the antihypertensive effects of EA might be associated with the attenuation of apelin expression and function in the RVLM, which might be a novel role for EA in SIH setting.

Tiron, a superoxide scavenger, suppresses fictive locomotionevoked sympathoexcitation in rats with heart failure

We have previously reported that fictive locomotion‐evoked sympathoexcitation in rats with heart failure was exaggerated and that this exaggeration was suppressed by Tempol, a superoxide dismutase mimetic, injected bilaterally into the rostral ventrolateral medulla (RVLM). It should be noted that Tempol also possess a property to open ATP‐sensitive and Ca2+‐activated K+ channels. In the present study, we tested if Tiron, which does not chemically relate to Tempol but has a similar superoxide scavenging activity, injected bilaterally into the RVLM of rats with heart failure would reduce fictive locomotion‐evoked sympathoexcitation. Heart failure was induced in rats by coronary artery ligation. Fictive locomotion was evoked in decerebrated and paralyzed rats by electrical stimulation of the mesencephalic locomotor region. In the rats with heart failure (N8, fractional shortening < 35%), Tiron mirrored the effect of Tempol; bilateral injection into the RVLM of Tiron (10 mM, 100 nl) significantly (P<0.05) reduced the renal sympathoexcitatory and pressor responses to fictive locomotion by 42% and 43%, respectively. The present data support the concept that oxidative stress in the medulla of heart failure plays a role in excessively amplifying central command‐mediated sympathoexcitation. Supported by Mitsui Life Social Welfare Foundation Research Grant (to S. Koba).

Exercise Training Lowers the Enhanced Tonically Active Glutamatergic Input to the Rostral Ventrolateral Medulla in Hypertensive Rats

It is well known that low-intensity exercise training (ExT) is beneficial to cardiovascular dysfunction in hypertension. The tonically active glutamatergic input to the rostral ventrolateral medulla (RVLM), a key region for control of blood pressure and sympathetic tone, has been demonstrated to be increased in hypertensive rats. The aim of this study was to determine the effect of ExT on the increased glutamatergic input to the RVLM in spontaneously hypertensive rat (SHR). Normotensive rats Wistar-Kyoto (WKY) and SHR were treadmill trained or remained sedentary (Sed) for 12 weeks and classed into four groups (WKY-Sed, WKY-ExT, SHR-Sed, and SHR-ExT). The release of glutamate in the RVLM and its contribution to cardiovascular activity were determined in WKY and SHR after treatment of ExT. Blood pressure and sympathetic tone were significantly reduced in SHR after treatment with ExT. Bilateral microinjection of the glutamate receptor antagonist kynurenic acid (2.7 nmol in 100 nL) into the RVLM significantly decreased resting blood pressure, heart rate, and renal sympathetic nerve activity in SHR-Sed but not in WKY groups (WKY-Sed and WKY-ExT). However, the degree of reduction in these cardiovascular parameters evoked by KYN was significantly blunted in SHR-ExT compared with SHR-Sed group. The concentration of glutamate and the protein expression of vesicular glutamate transporter 2 in the RVLM were significantly increased in SHR-Sed compared with WKY-Sed, whereas they were reduced after treatment with ExT. Our findings suggest that ExT attenuates the enhancement in the tonically acting glutamatergic input to the RVLM of hypertensive rats, thereby reducing the sympathetic hyperactivity and blood pressure.

Salusin-β in paraventricular nucleus increases blood pressure and sympathetic outflow via vasopressin in hypertensive rats

Salusin-β is a bioactive peptide with peripheral hypotensive, mitogenic and pro-atherosclerotic effects. The present study was designed to determine the roles of salusin-β in the paraventricular nucleus (PVN) and its relationship with arginine vasopressin (AVP) in hypertension and sympathetic activation. Renovascular hypertension was induced by two-kidney, one-clip (2K1C) in male Sprague-Dawley rats. Acute experiments were carried out 4 weeks after 2K1C or sham-operation under urethane and alpha-chloralose anaesthesia. Renal sympathetic nerve activity (RSNA), mean arterial pressure (MAP), and heart rate (HR) were recorded. Microinjection of salusin-β into the PVN increased the RSNA, MAP, and HR in a dose-related manner, whereas anti-salusin-β IgG in the PVN decreased the RSNA and MAP, and abolished the effects of salusin-β in 2K1C rats. However, either salusin-β or anti-salusin-β IgG in the PVN failed to cause any significant effects in sham-operated rats. The number of salusin-β-like immunopositive neurons in the PVN was significantly increased in 2K1C rats. Salusin-β in the PVN increased the plasma AVP and norepinephrine levels in 2K1C rats, but not in sham-operated rats. Iv injection of dTyr(CH2)5(Me)AVP (an AVP V1-receptor antagonist, AAVP) decreased RSNA and MAP, and abolished the effects of salusin-β in the PVN in 2K1C rats. Microinjection of AAVP into the rostral ventrolateral medulla (RVLM), but not into the PVN, abolished the effects of salusin-β on RSNA and HR. Salusin-β in the PVN increases blood pressure, heart rate, and sympathetic outflow via both circulating AVP and AVP in the RVLM in hypertensive rats.

The pressor effect of angiotensin-(1-7) in the rat rostral ventrolateral medulla involves multiple peripheral mechanisms

OBJECTIVE:In the present study, the peripheral mechanism that mediates the pressor effect of angiotensin-(1-7) in the rostral ventrolateral medulla was investigated.METHOD:Angiotensin-(1-7) (25 pmol) was bilaterally microinjected in the rostral ventrolateral medulla near the ventral surface in urethane-anesthetized male Wistar rats that were untreated or treated (intravenously) with effective doses of selective autonomic receptor antagonists (atenolol, prazosin, methyl-atropine, and hexamethonium) or a vasopressin V1 receptor antagonist [d(CH2)5 -Tyr(Me)–AVP] given alone or in combination.RESULTS:Unexpectedly, the pressor response produced by angiotensin-(1-7) (16±2 mmHg, n = 12), which was not associated with significant changes in heart rate, was not significantly altered by peripheral treatment with prazosin, the vasopressin V1 receptor antagonist, hexamethonium or methyl-atropine. Similar results were obtained in experiments that tested the association of prazosin and atenolol; methyl-atropine and the vasopressin V1 antagonist or methyl-atropine and prazosin. Peripheral treatment with the combination of prazosin, atenolol and the vasopressin V1 antagonist abolished the pressor effect of glutamate; however, this treatment produced only a small decrease in the pressor effect of angiotensin-(1-7) at the rostral ventrolateral medulla. The combination of hexamethonium with the vasopressin V1 receptor antagonist or the combination of prazosin, atenolol, the vasopressin V1 receptor antagonist and methyl-atropine was effective in blocking the effect of angiotensin-(1-7) at the rostral ventrolateral medulla.CONCLUSION:These results indicate that angiotensin-(1-7) triggers a complex pressor response at the rostral ventrolateral medulla that involves an increase in sympathetic tonus, release of vasopressin and possibly the inhibition of a vasodilatory mechanism.

Brain sources of inhibitory input to the rat rostral ventrolateral medulla

The rostral ventrolateral medulla (RVLM) contains neurons critical for cardiovascular, respiratory, metabolic, and motor control. The activity of these neurons is controlled by inputs from multiple identified brain regions; however, the neurochemistry of these inputs is largely unknown. Gamma-aminobutyric acid (GABA) and enkephalin tonically inhibit neurons within the RVLM. The aim of this study was to identify all brain regions that provide GABAergic or enkephalinergic input to the rat RVLM. Neurons immunoreactive for cholera toxin B (CTB-ir), retrogradely transported from the RVLM, were assessed for expression of glutamic acid decarboxylase (GAD67) or preproenkephalin (PPE) mRNA using in situ hybridization. GAD67 mRNA was expressed in CTB-ir neurons in the following regions: the nucleus of the solitary tract (NTS, 6% of CTB-ir neurons), area postrema (AP, 8%), caudal ventrolateral medulla (17%), midline raphe (40%), ventrolateral periaqueductal gray (VLPAG, 15%), lateral hypothalamic area (LHA, 25%), central nucleus of the amygdala (CeA, 77%), sublenticular extended amygdala (SLEA, 86%), interstitial nucleus of the posterior limb of the anterior commissure (IPAC, 56%), bed nucleus of the stria terminals (BNST, 59%), and medial preoptic area (MPA, 53%). PPE mRNA was expressed in CTB-ir neurons in the following regions: the NTS (14% of CTB-ir neurons), midline raphe (26%), LHA (22%), zona incerta (ZI, 15%), CeA (5%), paraventricular nucleus (PVN, 13%), SLEA (66%), and MPA (26%). Thus, limited brain regions contribute GABAergic and/or enkephalinergic input to the RVLM. Multiple neurochemically distinct pathways originate from these brain regions projecting to the RVLM.

Orexin A regulates cardiovascular responses in stress-induced hypertensive rats

Several pieces of evidence indicate that the rostral ventrolateral medulla (RVLM) is probably one of the key neural structures mediating the pressor effects of orexins in the brain. Nitric oxide synthase/nitric oxide (NOS/NO) system in the RVLM modulates cardiovascular activities. Our experiments were designed to test the hypothesis that orexin-A (OXA) is involved in the mechanism of stress-induced hypertension (SIH) by adjusting NOS/NO system in the RVLM. The stress-induced hypertensive rats (SIHR) model was established by electric foot-shocks and noises. Here we examined the expression of OXA immunoreactive (OXA-IR) cells in the lateral hypothalamus (LH) and the protein level of orexin 1 receptor (OX1R) in the RVLM of SIHR, and we found that the expressions of OXA-IR and OX1R were higher than those of the control group. The double-staining immunohistochemical evidence showed that OX1R immunoreactive (OX1R-IR) cells and neuronal nitric oxide synthase (nNOS) or inducible nitric oxide synthase (iNOS) immunoreactive (IR) cells were co-localizated in the RVLM. Microinjection of OXA (10, 50, 100 pmol/100 nl) into the unilateral (right) RVLM of control rats or SIHR produced pressor and tachycardiac effects in a dose-dependent manner. SB-408124 (100 pmol/100 nl, an antagonist of OX1R) or TCS OX2 29 (100 pmol/100 nl, an antagonist of OX2R) partly abolished the cardiovascular effects of exogenously-administrated OXA into the RVLM of control rats and SIHR, and lowered the increased systolic blood pressure (SBP) and heart rate (HR) of SIHR, with no difference in statistical significance between the two antagonists' effects. Microinjection into the RVLM of both control and SIHR groups of 7-Ni (0.05 pmol/100 nl, nNOS inhibitor) or Methylene Blue [100 pmol/100 nl, an inhibitor of soluble guanylate cyclase (sGC)] suppressed the OXA-induced increase of SBP and HR, whereas microinjection of AG (1, 10, 100 pmol/100 nl) had no obvious effects on the OXA-induced increase of SBP and HR. Our results indicate that OXA in the RVLM may participate in the central regulation of cardiovascular activities in SIHR, and OX1R and OX2R both have important roles in it. The cardiovascular effects of OXA in the RVLM may be induced by nNOS-derived NO, which activated sGC-associated signaling pathway.

Sympathoinhibitory effects of telmisartan through the reduction of oxidative stress in the rostral ventrolateral medulla of obesity-induced hypertensive rats

Sympathetic nervous system (SNS) activity is critically involved in the development and progression of obesity-induced hypertension. Angiotensin II type 1 receptor (AT1R)-induced oxidative stress in the rostral ventrolateral medulla (RVLM), a vasomotor center in the brainstem, activates the SNS in hypertensive rats. The aim of the present study was to determine whether oral administration of an AT1R blocker (ARB) inhibits SNS activity via antioxidative effects in the RVLM of rats with dietary-induced obesity. Obesity-prone rats fed a high-fat diet were divided into groups treated with either telmisartan obesity-prone (TLM-OP), or losartan obesity-prone (LOS-OP), or vehicle obesity-prone (VEH-OP). SBP, SNS activity, and oxidative stress in the RVLM were significantly higher in obesity-prone rats than in obesity-resistant rats. Body weight, visceral fat, blood glucose, serum insulin, and plasma adiponectin concentrations were significantly lower in TLM-OP and LOS-OP than in VEH-OP, and plasma adiponectin concentrations were significantly higher in TLM-OP than in LOS-OP. Although SBP was reduced to similar levels both in TLM-OP and LOS-OP, both oxidative stress in the RVLM and SNS activity were significantly lower in TLM-OP than in LOS-OP or VEH-OP. Orally administered telmisartan inhibited SNS activity through antioxidative effects via AT1R blockade in the RVLM of obesity-prone rats. AT1R and oxidative stress in the RVLM might be novel treatment targets for obesity-induced hypertension through sympathoinhibition, and telmisartan might be preferable for obesity-induced hypertension.

Nontranscriptional activation of PI3K/Akt signaling mediates hypotensive effect following activation of estrogen receptor β in the rostral ventrolateral medulla of rats

BackgroundEstrogen acts on the rostral ventrolateral medulla (RVLM), where sympathetic premotor neurons are located, to elicit vasodepressor effects via an estrogen receptor (ER)β-dependent mechanism. We investigated in the present study nontranscriptional mechanism on cardiovascular effects following activation of ERβ in the RVLM, and delineated the involvement of phosphatidylinositol 3-kinase (PI3K)/serine/threonine kinase (Akt) signaling pathway in the effects.MethodsIn male Sprague–Dawley rats maintained under propofol anesthesia, changes in arterial pressure, heart rate and sympathetic neurogenic vasomotor tone were examined after microinjection bilaterally into RVLM of 17β-estradiol (E2β) or a selective ERα or ERβ agonist. Involvement of ER subtypes and PI3K/Akt signaling pathway in the induced cardiovascular effects were studied using pharmacological tools of antagonists or inhibitors, gene manipulation with antisense oligonucleotide (ASON) or adenovirus-mediated gene transfection.ResultsSimilar to E2β (1 pmol), microinjection of ERβ agonist, diarylpropionitrile (DPN, 1, 2 or 5 pmol), into bilateral RVLM evoked dose-dependent hypotension and reduction in sympathetic neurogenic vasomotor tone. These vasodepressive effects of DPN (2 pmol) were inhibited by ERβ antagonist, R,R-tetrahydrochrysene (50 pmol), ASON against ERβ mRNA (250 pmol), PI3K inhibitor LY294002 (5 pmol), or Akt inhibitor (250 pmol), but not by ERα inhibitor, methyl-piperidino-pyrazole (1 nmol), or transcription inhibitor, actinomycin D (5 or 10 nmol). Gene transfer by microinjection into bilateral RVLM of adenovirus encoding phosphatase and tensin homologues deleted on chromosome 10 (5 × 108 pfu) reversed the vasodepressive effects of DPN.ConclusionsOur results indicate that vasodepressive effects following activation of ERβ in RVLM are mediated by nongenomic activation of PI3K/Akt signaling pathway. This study provides new insight in the intracellular signaling cascades involved in central vasodepressive functions of estrogen.

Sympathoinhibition caused by orally administered telmisartan through inhibition of the AT1 receptor in the rostral ventrolateral medulla of hypertensive rats

In patients and animals with hypertension, sympathetic nervous system (SNS) activation is present. We have demonstrated that angiotensin II type 1 receptor (AT₁R)-induced oxidative stress in the rostral ventrolateral medulla (RVLM), a vasomotor center in the brainstem, causes SNS activation in hypertensive rats. The aim of the present study was to determine whether orally administered AT₁R blockers (ARBs) inhibit SNS activation through an anti-oxidant effect via inhibition of AT₁R in the RVLM of hypertensive rats and, if so, whether the benefits are class effects of ARBs. Stroke-prone spontaneously hypertensive rats (SHRSPs), a hypertensive model with sympathoexcitation, were divided into four groups: SHRSPs treated with telmisartan (TLM), candesartan (CAN), or hydralazine (HYD) and a vehicle group (VEH). Although systolic blood pressure was reduced in the TLM, CAN and HYD groups to the same level, heart rate, SNS activation and oxidative stress in the RVLM were significantly lower in the TLM group only. The pressor effect caused by the microinjection of angiotensin II into the RVLM and the depressor effect caused by the microinjection of tempol, a superoxide dismutase mimetic, into the RVLM were both significantly smaller in TLM, but not in CAN or HYD. These results suggest that orally administered TLM inhibits SNS activation through an anti-oxidant effect via inhibition of AT₁R in the RVLM of SHRSPs; these results are also independent of depressor effects and are not class effects of ARBs.

In pursuit of scientific excellence: sex matters

In pursuit of scientific excellence: sex matters

In pursuit of scientific excellence: sex matters

In pursuit of scientific excellence: sex matters

In pursuit of scientific excellence: sex matters

In pursuit of scientific excellence: sex matters

In pursuit of scientific excellence: sex matters

In pursuit of scientific excellence: sex matters

CARDIOVASCULAR EFFECTS AFTER GLUTAMATE MICROINJECTION INTO THE RVLM OF MSG OBESE CONSCIOUS RATS

Obesity is a precursor condition of several diseases, among them hypertension. The sympathoexcitatory neurons of the rostral ventrolateral medulla (RVLM), which directly innervate sympathetic preganglionic neurons in the intermediolateral cell columns of the spinal cord, are a possible target for cardiovascular modulation by obesity, and glutamatergic neurotransmission has an important role. Thus, the aim of this study was to determine the effect of glutamate microinjection into the RVLM in control and MSG obese rats. Obesity was induced by intradermal administration of 4 mg/g of monosodium glutamate (MSG) or hyperosmotic saline (control = CTR) in the first 5 days of life in male Wistar rats. At 90 days old, the animals were submitted to guide cannulae implantation to the RVLM for unilateral microinjection of L‐glutamate (5 nmol/100 nl) in conscious state for recording for mean arterial pressure (MAP) and heart rate (HR). There was no difference in MAP and HR at baseline among the experimental groups (CTR: 112 ± 2 mmHg, 362 ± 14 bpm; MSG: 106 ± 3 mmHg, 389 ± 13 bpm). Unilateral microinjection of l‐glutamate produced an increase in MAP in CTR and MSG groups, however, the magnitude of this response was higher in obese rats (CTR: 44 ± 3; MSG: 56 ± 2, p=0,02). The excitation of the RVLM with glutamate decreased HR to levels that were not statistically different between groups (CTR: −26 ± 19 bpm; MSG: −45 ± 37 bpm). The present results suggest that MSG obese rats may have elevated sympathetic nerve activity originated from the activity of RVLM neurons.

In pursuit of scientific excellence: sex matters

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Orexin A in rat rostral ventrolateral medulla is pressor, sympatho‐excitatory, increases barosensitivity and attenuates the somato‐sympathetic reflex

The rostral ventrolateral medulla (RVLM) maintains sympathetic nerve activity (SNA), and integrates adaptive reflexes. Orexin A-immunoreactive neurones in the lateral hypothalamus project to the RVLM. Microinjection of orexin A into RVLM increases blood pressure and heart rate. However, the expression of orexin receptors, and effects of orexin A in the RVLM on splanchnic SNA (sSNA), respiration and adaptive reflexes are unknown. The effect of orexin A on baseline cardio-respiratory variables as well as the somato-sympathetic, baroreceptor and chemoreceptor reflexes in RVLM were investigated in urethane-anaesthetized, vagotomized and artificially ventilated male Sprague-Dawley rats (n= 50). orexin A and its receptors were detected with fluorescence immunohistochemistry. Tyrosine hydroxylase-immunoreactive neurones in the RVLM were frequently co-localized with orexin 1 (OX(1) ) and orexin 2 (OX(2) ) receptors and closely apposed to orexin A-immunoreactive terminals. Orexin A injected into the RVLM was pressor and sympatho-excitatory. Peak effects were observed at 50 pmol with increased mean arterial pressure (42 mmHg) and SNA (45%). Responses to orexin A (50 pmol) were attenuated by the OX(1) receptor antagonist, SB334867, and reproduced by the OX(2) receptor agonist, [Ala(11) , D-Leu(15) ]orexin B. Orexin A attenuated the somato-sympathetic reflex but increased baroreflex sensitivity. Orexin A increased or reduced sympatho-excitation following hypoxia or hypercapnia respectively. Although central cardio-respiratory control mechanisms at rest do not rely on orexin, responses to adaptive stimuli are dramatically affected by the functional state of orexin receptors.

Differential Cardiorespiratory and Sympathetic Reflex Responses to Microinjection of Neuromedin U in Rat Rostral Ventrolateral Medulla

The rostral ventrolateral medulla (RVLM) regulates sympathetic vasomotor outflow and reflexes. Intracerebroventricular neuromedin U (NMU) increases sympathetic nerve activity (SNA), mean arterial pressure (MAP), and heart rate (HR), but the central nuclei that mediate these effects are unknown. In urethane-anesthetized, vagotomized, and artificially ventilated male Sprague-Dawley rats (n = 36) the effects of bilateral microinjection of NMU (50 nl, each side) into RVLM on cardiorespiratory variables, somatosympathetic reflex, arterial baroreflex, and chemoreflex were investigated. Microinjection of NMU into RVLM elicited a hypertension, tachycardia, and an increase in splanchnic SNA (SSNA) and lumbar SNA (LSNA) at lower doses (25 and 50 pmol). At higher dose (100 pmol), NMU caused a biphasic response, a brief hypertension and sympathoexcitation followed by prolonged hypotension and sympathoinhibition. The peak excitatory and inhibitory response was found at 100 pmol NMU with an increase in MAP, HR, SSNA, and LSNA of 36 mm Hg, 20 beats per minute, 34%, and 89%, respectively, and a decrease of 33 mm Hg, 25 beats per minute, 42%, and 52%, respectively, from baseline. NMU, in the RVLM, also increased phrenic nerve amplitude and the expiratory period and reduced the inspiratory period. NMU (100 pmol) attenuated the somatosympathetic reflex and the sympathoexcitatory and respiratory responses to hypoxia and hypercapnia. After NMU injection in RVLM, the maximum gain of the SSNA baroreflex function curve was increased, but that of the LSNA was reduced. The present study provides functional evidence for a complex differential modulatory activity of NMU on the cardiovascular and reflex responses that are integrated in the RVLM.

Pro-life role for c-Jun N-terminal kinase and p38 mitogen-activated protein kinase at rostral ventrolateral medulla in experimental brain stem death

BackgroundBased on an experimental brain stem death model, we demonstrated previously that activation of the mitogen-activated protein kinase kinase 1/2 (MEK1/2)/extracellular signal-regulated kinase 1/2 (ERK1/2)/ mitogen-activated protein kinase signal-interacting kinase 1/2 (MNK1/2) cascade plays a pro-life role in the rostral ventrolateral medulla (RVLM), the origin of a life-and-death signal detected from systemic arterial pressure, which sequentially increases (pro-life) and decreases (pro-death) to reflect progressive dysfunction of central cardiovascular regulation during the advancement towards brain stem death in critically ill patients. The present study assessed the hypothesis that, in addition to ERK1/2, c-Jun NH2-terminal kinase (JNK) and p38 mitogen-activated protein kinase (p38MAPK), the other two mammalian members of MAPKs that are originally identified as stress-activated protein kinases, are activated specifically by MAPK kinase 4 (MAP2K4) or MAP2K6 and play a pro-life role in RVLM during experimental brain stem death. We further delineated the participation of phosphorylating activating transcriptional factor-2 (ATF-2) and c-Jun, the classical transcription factor activated by JNK or p38MAPK, in this process.ResultsAn experimental model of brain stem death that employed microinjection of the organophosphate insecticide mevinphos (Mev; 10 nmol) bilaterally into RVLM of Sprague–Dawley rats was used, alongside cardiovascular, pharmacological and biochemical evaluations. Results from ELISA showed that whereas the total JNK, p38MAPK, MAP2K4 and MAP2K6 were not affected, augmented phosphorylation of JNK at Thr183 and Tyr185 and p38MAPK at Thr180 and Tyr182, accompanied by phosphorylation of their upstream activators MAP2K4 at Ser257 and Thr261 and MAP2K6 at Ser207 and Thr211 in RVLM occurred preferentially during the pro-life phase of experimental brain stem death. Moreover, the activity of transcription factors ATF-2 at Thr71 and c-Jun at Ser73, rather than Elk-1 at Ser383 in RVLM were also augmented during the pro-life phase. Furthermore, pretreatment by microinjection into the bilateral RVLM of specific JNK inhibitors, JNK inhibitor I (100 pmol) or SP600125 (5 pmol), or specific p38MAPK inhibitors, p38MAPK inhibitor III (500 pmol) or SB203580 (2 nmol), exacerbated the depressor effect and blunted the augmented life-and-death signal exhibited during the pro-life phase. On the other hand, pretreatment with the negative control for JNK or p38MAPK inhibitor, JNK inhibitor I negative control (100 pmol) or SB202474 (2 nmol), was ineffective in the vehicle-controls and Mev-treatment groups.ConclusionsOur results demonstrated that activation of JNK or p38MAPK in RVLM by their upstream activators MAP2K4 or MAP2K6 plays a preferential pro-life role by sustaining the central cardiovascular regulatory machinery during experimental brain stem death via phosphorylation and activation of nuclear transcription factor ATF-2 or c-Jun.