Greater Splanchnic Nerve Activity Research Articles

Wogonin attenuates the deleterious effects of traumatic brain injury in anesthetized Wistar rats

Wogonin, a flavonoid (5,7-dihydroxy-8-methoxyflavone) with reported neuroprotective properties, is widely used in treating inflammatory diseases. The main goal of this study was to explore the role of wogonin in preventing deleterious cardiovascular effects of traumatic brain injury (TBI). Experiments were carried out in adult male urethane-anesthetized, artificially ventilated, Wistar rats, weighing 300–350 gm. TBI was produced by fluid percussion injury (FPI). A significant decrease in blood pressure (BP), heart rate (HR) and greater splanchnic nerve activity (GSNA), which lasted for up to 4 h, was observed after the application of moderate FPI. Intravenous (i.v.) and intracerebroventricular (i.c.v.) administration of wogonin before and after the moderate FPI significantly attenuated the decreases in BP, HR, and GSNA elicited by FPI. Administration of wogonin also prevented the attenuation of baroreflex-induced bradycardia elicited by FPI. Based on these results, it was concluded that administration of wogonin attenuates the deleterious effects of moderate FPI.

Attenuation of angiotensin type 2 receptor function in the rostral ventrolateral medullary pressor area of the spontaneously hypertensive rat

We hypothesized that blockade of angiotensin II type 2 receptors (AT2Rs) in the rostral ventrolateral medullary pressor area (RVLM) may elicit sympathoexcitatory responses which are smaller in hypertensive rats compared to normotensive rats. This hypothesis was tested in urethane-anesthetized, artificially ventilated male 14-week-old spontaneously hypertensive rats (SHR). Age-matched male Wistar–Kyoto rats (WKY) and Wistar rats were used as controls. PD123319 (AT2R antagonist) was microinjected into the RVLM and mean arterial pressure (MAP), heart rate (HR) and greater splanchnic nerve activity (GSNA) were recorded. Increases in MAP, HR and GSNA elicited by unilateral microinjections of PD123319 into the RVLM were significantly smaller in SHR when compared with those in WKY and Wistar rats. Unilateral microinjections of l-glutamate (l-Glu) into the RVLM elicited greater increases in MAP and GSNA in SHR compared to those in WKY. AT2R immunoreactivity was demonstrated in the RVLM neurons which were retrogradely labeled from the intermediolateral cell column (IML) of the spinal cord. These results indicate that AT2Rs are present on the RVLM neurons projecting to the IML and their blockade results in sympathoexcitatory responses. Activation of AT2Rs has an inhibitory influence in the RVLM and these receptors are tonically active. Attenuation of the function of AT2Rs in the RVLM may play a role in genesis and/or maintenance of hypertension in SHR.

GABA(A) receptor overexpression in the lateral hypothalamic area attenuates gastric ischemia‑reperfusion injury in rats.

Excessive activation of the greater splanchnic nerve (GSN) has previously been determined to contribute to the progression of gastric ischemia‑reperfusion (GI‑R) injury. The present study was designed to estimate the protective effects of GABAA receptor (GABA(A)R) overexpression in the lateral hypothalamic area (LHA) against GI‑R injury. The GI‑R injury model was induced in rats by clamping the celiac artery for 30 min and then reperfusing for 1 h. Microinjection of recombinant adenoviral vectors overexpressing GABA(A)R (Ad‑GABA(A)R) or control adenoviral vectors (Ad‑Con) into the LHA was conducted in GI‑R and normal control rats. Significant protective effects were observed on day 2 after Ad‑GABA(A)R treatment in the GI‑R injury rats. Ad‑GABA(A)R treatment reduced plasma norepinephrine levels, plasma angiotensin II levels and peripheral GSN activity, but increased the gastric mucosal blood flow, as compared with Ad‑Con treatment. These results indicate that adenoviral vector‑induced GABA(A)R overexpression in the LHA blunts GSN activity and subsequently alleviates the effects of gastric injury in GI‑R rats.

Cardiovascular responses to microinjections of endomorphin-2 into the nucleus of the solitary tract are attenuated in the spontaneously hypertensive rat

Stimulation of µ1-opioid receptors (M1ORs) in the medial nucleus solitarius (mNTS) by endomorphin-2 (EM2) elicits decreases in mean arterial pressure (MAP), heart rate (HR) and greater splanchnic nerve activity (GSNA) in Wistar rats. We tested the hypothesis that EM2-induced responses in the mNTS may be attenuated in the spontaneously hypertensive rat (SHR). Experiments were carried out in urethane-anesthetized, artificially ventilated, adult male SHR and Wistar-Kyoto rats (WKY). Alterations in responses to chemical stimulation of the hypothalamic arcuate nucleus (ARCN) after bilateral blockade of M1ORs in the mNTS were also studied. In SHR, microinjections of EM2 into the mNTS elicited smaller decreases in MAP, HR and GSNA compared to those elicited in WKY; smaller cardiovascular responses in SHR can be explained by lower expression of M1OR mRNA in the NTS of SHR compared to WKY. Decreases in MAP and GSNA and increases in HR were elicited by microinjections of N-methyl-d-aspartic acid (NMDA) into the ARCN of WKY. Bilateral blockade of M1ORs in the mNTS attenuated the decreases in MAP and GSNA and exaggerated the increases in HR elicited by the ARCN stimulation in WKY but not in SHR. Tonic inhibitory activity of neuropeptide Y/gamma-aminobutyric acid (NPY/GABA) neurons in the ARCN is attenuated in SHR; this observation may explain increases in MAP, GSNA and HR elicited by microinjections of NMDA into the ARCN of SHR. These results demonstrate that attenuation of EM2-induced responses in the mNTS of SHR may contribute to the excitatory responses elicited by ARCN stimulation in SHR.

Cardiovascular effect of angiotensin-(1–12) in the caudal ventrolateral medullary depressor area of the rat

Angiotensin (ANG)-(1-12) excites neurons via ANG II type 1 receptors (AT1Rs), which are present in the caudal ventrolateral medullary depressor area (CVLM). We hypothesized that microinjections of ANG-(1-12) into the CVLM may elicit decreases in mean arterial pressure (MAP), heart rate (HR), and sympathetic nerve activity. This hypothesis was tested in urethane-anesthetized adult male Wistar rats. Microinjections of ANG-(1-12) into the CVLM elicited decreases in MAP, HR, and greater splanchnic nerve activity (GSNA). ANG-(1-12)-induced responses consisted of initial (first 1-8 min) and delayed (8-24 min) phases. Prior microinjections of losartan, A-779, and captopril into the CVLM blocked initial, delayed, and both phases of ANG-(1-12) responses, respectively. Blockade of GABA receptors in the rostral ventrolateral medullary pressor area (RVLM) attenuated cardiovascular responses elicited by microinjections of ANG-(1-12) into the ipsilateral CVLM. Microinjections of ANG-(1-12) into the CVLM potentiated the reflex decreases and attenuated the reflex increases in GSNA elicited by intravenous injections of phenylephrine and sodium nitroprusside, respectively. These results indicate that microinjections of ANG-(1-12) into the CVLM elicit decreases in MAP, HR, and GSNA. Initial and delayed phases of these responses are mediated via ANG II and ANG-(1-7), respectively; the effects of ANG II and ANG-(1-7) are mediated via AT1Rs and Mas receptors, respectively. Captopril blocked both phases of ANG-(1-12) responses, indicating that angiotensin-converting enzyme is important in mediating these responses. GABA receptors in the RVLM partly mediate the cardiovascular responses to microinjections of ANG-(1-12) into the CVLM. Microinjections of ANG-(1-12) into the CVLM modulate baroreflex responses.

Tonic γ-Aminobutyric Acid–ergic Activity in the Hypothalamic Arcuate Nucleus Is Attenuated in the Spontaneously Hypertensive Rat

We tested the hypothesis that tonic γ-aminobutyric acid–ergic activity in the hypothalamic arcuate nucleus (ARCN) modulates blood pressure control and attenuation of this inhibitory activity contributes to hypertension in the spontaneously hypertensive rats (SHR). Mean arterial pressure (MAP), heart rate (HR), and greater splanchnic nerve activity (GSNA) were recorded in urethane-anesthetized, artificially ventilated, adult male SHR and Wistar-Kyoto rats (WKY). Microinjections of gabazine into the ARCN elicited significantly smaller increases in MAP, HR, and GSNA in baroreceptor-intact SHR compared with baroreceptor-intact WKY. Attenuation of the responses to gabazine in SHR persisted, despite lowering of their baseline MAP to levels of WKY or barodenervation. Microinjections of N-methyl- d -aspartic acid (NMDA) into the ARCN elicited decreases in MAP and GSNA and increases in HR in baroreceptor-intact WKY. However, after microinjections of gabazine into the ARCN, microinjections of NMDA into the same nucleus elicited pressor responses in baroreceptor-intact WKY. In barodenervated WKY, increases in MAP and GSNA were elicited by ARCN stimulation by NMDA and the increases in HR were exaggerated. In baroreceptor-intact SHR, ARCN stimulation by NMDA elicited increases in MAP, GSNA, and HR which persisted, despite lowering of baseline MAP or barodenervation. Increases in MAP and GSNA elicited by ARCN stimulation by NMDA in barodenervated SHR were significantly greater than corresponding increases in barodenervated WKY. These results indicated that attenuated γ-aminobutyric acid–ergic activity in the ARCN and impaired baroreflex function may contribute to increases in blood pressure and sympathetic nerve activity after ARCN stimulation by NMDA and elevation of baseline blood pressure in SHR.

Baroreceptor unloading converts depressor responses elicited from the hypothalamic arcuate nucleus to pressor responses

The type of response elicited from the hypothalamic arcuate nucleus (ARCN) depends on the level of baroreceptor activity. It was hypothesized that baroreceptor unloading may determine the type of response elicited from the ARCN. This hypothesis was tested in urethane‐anesthetized adult male Wistar rats. Bilateral barodenervation converted decreases in mean arterial pressure (MAP) and greater splanchnic nerve activity (GSNA) elicited by chemical stimulation of the ARCN to increases in MAP and GSNA and exaggerated tachycardia. Microinjections of ionotropic glutamate receptor antagonists into the paraventricular nucleus (PVN) in barodenervated rats converted increases in MAP and GSNA elicited by the ARCN stimulation to decreases in MAP and GSNA and attenuated tachycardia. Microinjections of a melanocortin 3/4 receptor antagonist into the PVN in barodenervated rats attenuated increases in MAP, GSNA and heart rate elicited by the ARCN stimulation. ARCN neurons projecting to the PVN were immunoreactive for proopiomelanocortin, alphamelanocyte stimulating hormone (alpha‐MSH) and adrenocorticotropic hormone (ACTH).Conclusionincreases in MAP and GSNA and exaggeration of tachycardia elicited by the ARCN stimulation in barodenervated rats may be mediated via release of alpha‐MSH and/or ACTH and glutamate from the ARCN neurons projecting to the PVN. Support: NIH grants HL024347 and HL076248(HNS).

Effect of Barodenervation on Cardiovascular Responses Elicited from the Hypothalamic Arcuate Nucleus of the Rat

We have previously reported that chemical stimulation of the hypothalamic arcuate nucleus (ARCN) in the rat elicited increases as well as decreases in blood pressure (BP) and sympathetic nerve activity (SNA). The type of response elicited from the ARCN (i.e., increase or decrease in BP and SNA) depended on the level of baroreceptor activity which, in turn, was determined by baseline BP in rats with intact baroreceptors. Based on this information, it was hypothesized that baroreceptor unloading may play a role in the type of response elicited from the ARCN. Therefore, the effect of barodenervation on the ARCN-induced cardiovascular and sympathetic responses and the neurotransmitters in the hypothalamic paraventricular nucleus (PVN) mediating the excitatory responses elicited from the ARCN were investigated in urethane-anesthetized adult male Wistar rats. Bilateral barodenervation converted decreases in mean arterial pressure (MAP) and greater splanchnic nerve activity (GSNA) elicited by chemical stimulation of the ARCN with microinjections of N-methyl-D-aspartic acid to increases in MAP and GSNA and exaggerated the increases in heart rate (HR). Combined microinjections of NBQX and D-AP7 (ionotropic glutamate receptor antagonists) into the PVN in barodenervated rats converted increases in MAP and GSNA elicited by the ARCN stimulation to decreases in MAP and GSNA and attenuated increases in HR. Microinjections of SHU9119 (a melanocortin 3/4 receptor antagonist) into the PVN in barodenervated rats attenuated increases in MAP, GSNA and HR elicited by the ARCN stimulation. ARCN neurons projecting to the PVN were immunoreactive for proopiomelanocortin, alpha-melanocyte stimulating hormone (alpha-MSH) and adrenocorticotropic hormone (ACTH). It was concluded that increases in MAP and GSNA and exaggeration of tachycardia elicited by the ARCN stimulation in barodenervated rats may be mediated via release of alpha-MSH and/or ACTH and glutamate from the ARCN neurons projecting to the PVN.

γ‐aminobutyric acid‐mediated neurotransmission in cerebellar–hypothalamic circuit attenuates gastric mucosal injury induced by ischemia‐reperfusion

Excessive greater splanchnic nerve (GSN) activation contributes to the progression of gastric ischemia-reperfusion (GI-R) injury. This study was designed to investigate the protective mechanism of cerebellar fastigial nucleus (FN) stimulation against GI-R injury. The GI-R injury model was induced in rats by clamping the celiac artery for 30 min, and then reperfusion for 30 min, 1, 3, 6, or 24 h, respectively. Microinjection of L-Glu (3, 6, 12 μg) into the FN dose-dependently attenuated GI-R injury and GSN activity. In addition, there was an enhancement of gastric mucosal blood flow in GI-R rats. Pretreatment with the glutamic acid decarboxylase antagonist into the FN, the GABAA receptor antagonist into the lateral hypothalamic area or lesion of superior cerebellar peduncle all reversed the protective effects of the FN stimulation. Furthermore, the FN stimulation reduced the TUNEL-positive gastric mucosal cell and Bax-positive gastric mucosal cell in GI-R rats. These results indicate that the protective effects of the FN stimulation against GI-R injury may be mediated by attenuation of the excessive GSN activation, gastric mucosal cell apoptosis, and Bax expression in GI-R rats.

The hypothalamic arcuate nucleus: a new site of cardiovascular action of angiotensin-(1–12) and angiotensin II

The hypothalamic arcuate nucleus (ARCN) has been reported to play a significant role in cardiovascular regulation. It has been hypothesized that the ARCN may be one of the sites of cardiovascular actions of angiotensins (ANGs). Experiments were carried out in urethane-anesthetized, artificially ventilated, adult male Wistar rats. The ARCN was identified by microinjections of N-methyl-d-aspartic acid (NMDA; 10 mM). Microinjections (50 nl) of ANG-(1-12) (1 mM) into the ARCN elicited increases in mean arterial pressure (MAP), heart rate (HR), and greater splanchnic nerve activity (GSNA). The tachycardic responses to ANG-(1-12) were attenuated by bilateral vagotomy. The cardiovascular responses elicited by ANG-(1-12) were attenuated by microinjections of ANG II type 1 receptor (AT(1)R) antagonists but not ANG type 2 receptor (AT(2)R) antagonist. Combined inhibition of ANG-converting enzyme (ACE) and chymase in the ARCN abolished ANG-(1-12)-induced responses. Microinjections of ANG II (1 mM) into the ARCN also increased MAP and HR. Inhibition of ARCN by microinjections of muscimol (1 mM) attenuated the pressor and tachycardic responses to intravenously administered ANG-(1-12) and ANG II (300 pmol/kg each). These results indicated that 1) microinjections of ANG-(1-12) into the ARCN elicited increases in MAP, HR, and GSNA; 2) HR responses were mediated via both sympathetic and vagus nerves; 3) AT(1)Rs, but not AT(2)Rs, in the ARCN mediated ANG-(1-12)-induced responses; 4) both ACE and chymase were needed to convert ANG-(1-12) to ANG II in the ARCN; and 5) ARCN plays a role in mediating the cardiovascular responses to circulating ANGs.

Cardiovascular Responses to Hypothalamic Arcuate Nucleus Stimulation in the Rat

Experiments were carried out in urethane-anesthetized, artificially ventilated, adult male Wistar rats. Microinjections (50 nL) of N-methyl-d-aspartic acid (1, 5, and 10 mmol/L), but not artificial cerebrospinal fluid, into the hypothalamic arcuate nucleus (ARCN) elicited increases in mean arterial pressure (5.7+/-0.5, 13.2+/-1.4, and 17.3+/-1.1 mm Hg, respectively) and heart rate (24.3+/-4.3, 49.3+/-5.2, and 75.2+/-8.0 bpm, respectively). ARCN stimulation was accomplished by microinjections of a maximally effective concentration of N-methyl-d-aspartic acid (10 mmol/L). The tachycardic responses to the ARCN stimulation were significantly attenuated after bilateral vagotomy. Intrathecal injections of ionotropic glutamate receptor (iGLUR) antagonists completely blocked pressor responses to the ARCN stimulation, whereas the tachycardic responses were significantly attenuated but not abolished. Intrathecal injections of iGLUR antagonists at T9 to T10, combined with bilateral vagotomy, completely blocked the tachycardic responses to ARCN stimulation. ARCN stimulation with N-methyl-d-aspartic acid elicited increased activities of the greater splanchnic nerve (91.7+/-14.8%) and the renal nerve (109.3+/-13%). Intrathecal injections of iGLURs at T9 to T10 blocked the increase in the greater splanchnic nerve activity in response to ARCN stimulation. These results indicate the following: (1) the chemical stimulation of the ARCN elicits increases in mean arterial pressure, greater splanchnic nerve and renal nerve activity, and heart rate; (2) the increases in mean arterial pressure and sympathetic nerve activity are mediated via the activation of spinal cord iGLURs; and (3) the increases in heart rate are mediated via the activation of spinal cord iGLURs and decreases in vagal input to the heart.

Cold pressor test in the rat: medullary and spinal pathways and neurotransmitters

This study was designed to delineate the medullary and spinal pathways mediating the cardiovascular responses to cold pressor test (CPT) and to identify neurotransmitters in these pathways. Experiments were done in barodenervated, urethane-anesthetized, male Wistar rats. The CPT was performed by immersing the limbs and ventral half of the body of the rat in ice-cold water (0.5 degrees C) for 2 min. CPT elicited an immediate increase in mean arterial pressure (MAP), heart rate (HR), and greater splanchnic nerve activity (GSNA). Bilateral blockade of ionotropic glutamate receptors (iGLURs) in the rostral ventrolateral medullary pressor area (RVLM) significantly attenuated the CPT-induced responses. Bilateral blockade of gamma-aminobutyric acid (GABA) receptors, but not iGLURs, in the nucleus ambiguus (nAmb) significantly reduced the CPT-induced increases in HR, but not MAP. Blockade of spinal iGLURs caused a significant reduction in CPT-induced increases in MAP and GSNA, whereas the increases in HR were reduced to a lesser extent. Combination of the blockade of spinal iGLURs and bilateral vagotomy or intravenous atropine almost completely blocked CPT-induced tachycardia. Midcollicular decerebration significantly reduced CPT-induced increases in MAP and HR. These results indicated that: 1) CPT-induced increases in MAP, HR, and GSNA were mediated by activation of iGLURs in the RVLM and spinal cord, 2) activation of GABA receptors in the nAmb also contributed to the CPT-induced tachycardic responses, and 3) brain areas rostral to the brain stem also participated in the CPT-induced pressor and tachycardic responses.

Cardiovascular function of a glutamatergic projection from the hypothalamic paraventricular nucleus to the nucleus tractus solitarius in the rat

Experiments were done in urethane-anesthetized, barodenervated, male Wistar rats. Chemical stimulation of the hypothalamic paraventricular nucleus (PVN) by unilateral microinjections of N-methyl- d-aspartic acid (NMDA) elicited increases in mean arterial pressure (MAP) and greater splanchnic nerve activity (GSNA). The increases in the MAP and GSNA induced by chemical stimulation of the PVN were significantly exaggerated by bilateral microinjections of d(−)-2-amino-7-phosphono-heptanoic acid ( d-AP7) and 2,3-dioxo-6-nitro-1,2,3,4-tetrahydro-benzo[f]quinoxaline-7-sulfonamide disodium (NBQX) (ionotropic glutamate receptor antagonists) into the medial subnucleus of the nucleus tractus solitarius (mNTS). These results were confirmed by single unit recordings; i.e. excitation of mNTS barosensitive neurons caused by chemical stimulation of the ipsilateral PVN was blocked by application of d-AP7 and NBQX to these neurons. Bilateral microinjections of d-AP7 and NBQX into the mNTS elicited pressor responses which were significantly attenuated by inhibition of PVN neurons by bilateral microinjections of muscimol. Unilateral microinjections of fluorogold into the mNTS resulted in bilateral retrograde labeling of the PVN neurons. Unilateral microinjections of biotinylated dextran amine into the PVN resulted in anterograde labeling of axons and terminals in the mNTS bilaterally and the labeled terminals exhibited vesicular glutamate transporter-2 immunoreactivity. These results indicated that 1) a tonically active glutamatergic bilateral projection from the PVN to the mNTS exists; 2) bilateral blockade of ionotropic glutamate receptors in the mNTS exaggerates the increases in MAP and GSNA, but not heart rate, to the chemical stimulation of the PVN; and 3) this projection may serve as a restraint mechanism for excitatory cardiovascular effects of PVN stimulation.

Differential regulation of regional vascular resistance by the rostral and caudal ventrolateral medulla in the rat

Regional vascular resistance changes were determined following chemical excitation and inhibition of the rostral vasopressor (RVLM) and caudal vasodepressor (CVLM) areas in the ventrolateral medulla. Mesenteric, renal and hindquarter vascular resistances were assessed in paralyzed and artificially ventilated urethane-anesthetized rats instrumented with pulsed Doppler flow probes. Microinjection of the excitatory amino acid λ-glutamate in the RVLM elicited a significant dose-related transient increase in blood pressure, heart rate and resistance of mesenteric, renal and hindquarter vascular beds. A similar dose-related hemodynamic profile was obtained following microinjection of muscimol, a GABAmimetic, in the CVLM. In contrast, significant dose-related decrease in blood pressure, heart rate and resistance in mesenteric and hindquarter vascular beds was observed following glutamate-induced excitation of the CVLM and muscimol-induced inhibition of the RVLM. Changes in renal vascular resistance were inconsistent in this second hemodynamic profile. Intravenous administration of the α 1 adrenergic antagonist, prazosin, abolished all of the hemodynamic effects elicited by excitation of the RVLM except the tachycardia. Intravenous atropine methylnitrate blocked the bradycardia associated with excitation of the CVLM but did not alter the vascular resistance changes. These results indicate that the changes in heart rate did not contribute significantly to the resistance profiles described. The changes in vascular resistance elicited by excitation and inhibition of the RVLM were correlated with increase and decrease in the greater splanchnic nerve activity, respectively. In conclusion, neuron pools in the RVLM and CVLM exert differential effects upon resistance in different vascular beds via changes in sympathetic outflow. The relative balance between the opposing cardiovascular control exerted by the RVLM and CVLM is instrumental in determining basal vascular resistance and the distribution of cardiac output.