Acute intracranial hypertension increases gastric tonus in anesthetized rats

We studied the acute effect of intracranial hypertension (ICH) on gastric tonus of anesthetized rats. Brain ventricles were cannulated bilaterally for intracerebro-ventricular pressure (ICP) monitoring and ICH induction. Next, a balloon catheter was inserted at the proximal stomach and coupled to a barostat for gastric volume (GV) monitoring by plethysmography. Arterial pressure (AP) and heart rate (HR) were monitored continuously during 80-min. After a 20-min basal period, they were submitted to control or ICH protocols. In controls, the ICP varied spontaneously up to the end. Other rats were subjected to ICP rising to 10, 20, 40 or 60 mmHg and kept at these levels for 30-min. Another group was subjected after basal period to stepwise ICH (ICP rising to 20, 40 and 60 mmHg at every 10-min interval). Next, the ICH rats were monitored for further 30-min. Other rats, previously submitted to a subdiaphragmatic vagotomy, splanchnicectomy plus ganglionectomy or their respective sham surgery, were also studied under ICH. Each subset consisted of 5-6 rats. Data were compared to respective basal values after ANOVA and Bonferroni`s test. In controls, the CV, AP, HR values remained within stable levels. Besides inducing bradycardia and arterial hypertension, ICH10 mmHg decreased GV by 14.8% at the 50-min interval. In ICH20, 40 and 60 mmHg subsets, GV decreased 14.0, 24.5 and 30.6% at the 40-min interval, respectively. In stepwise ICH rats, GV decreased 10.2% and 12.7%, respectively under ICP of 40 and 60 mmHg. The GV values remained significantly lower than basal levels during the last 30-min of monitoring. Thus, ICH decreases the GV in an ICP-dependent pattern besides inducing Cushing`s reflex. (C) 2008 Published by Elsevier B.V.

Bed nucleus of the stria terminalis alpha(1)-adrenoceptor modulates baroreflex cardiac component in unanesthetized rats

The bed nucleus of stria terminalis (BST) has a tonic modulating role on the baroreflex parasympathetic component. In the present study, we verified that local BST-adrenoceptors modulate baroreflex-evoked bradycardiac responses in unanesthetized rats. Bilateral microinjection of the selective alpha(1)-adrenoceptor antagonist WB4101 (15 nmol/100 nL) into the BST increased the gain of reflex bradycardia in response to mean arterial pressure increases caused by intravenous (i.v.) infusion of phenylephrine, suggesting that BST alpha(1)-adrenoceptors modulate baroreflex bradycardiac response. Bilateral microinjection of either the selective alpha(2)-adrenoceptor antagonist RX821002 (15 nmol/100 nL) or the non-selective beta-adrenoceptor antagonist propranolol (15 nmol/100 nL) into the BST had not affected baroreflex bradycardia. Animals were pretreated intravenously with the cholinergic muscarinic receptor antagonist homatropine methyl bromide (HMB, 1.5 mg/Kg) to test the hypothesis that activation of alpha(1)-adrenoceptors in the BST would modulate the baroreflex parasympathetic component. Baroreflex bradycardiac responses evoked before and after BST treatment with WB4101 were no longer different when rats were pretreated with HMB. These results suggest that parasympathetic activation accounts for the effects saw after BST pharmacological manipulation and ruling out the possibility of a sympathetic withdraw. In conclusion, our data point out that local alpha(1)-adrenoceptors mediate the BST tonic influence on the baroreflex bradycardiac response modulating parasympathetic cardiac activity. (C) 2008 Elsevier B.V. All rights reserved.

Prelimbic but not infralimbic cortex is involved in the pressor response to chemoreflex activation in awake rats

The ventral portion of the medial prefrontal cortex comprises the prelimbic cortex (PL) and the infralimbic cortex (IL). Several studies have indicated that both the PL and the IL play an important role in cardiovascular control. Chemoreflex activation by systemic administration of potassium cyanide (KCN) evokes pressor and bradycardiac responses in conscious rats, in addition to an increase in respiratory frequency. We report here a comparison between the effects of pharmacological inhibition of PL and IL neurotransmission on blood pressure and heart rate responses evoked by chemoreflex activation using KCN (i.v.) in conscious rats. Bilateral microinjection of 200 nl of the unspecific synaptic blocker CoCl(2) (1 mm) into the PL evoked a significant attenuation of the pressor response, without affecting the chemoreflex-induced heart rate decrease. However, IL local synapse inhibition evoked no changes in cardiovascular responses induced by chemoreflex activation. Thus, our results suggest that the pressor but not the bradycardiac response to chemoreflex activation is, at least in part, mediated by local neurotransmission present in the PL cortex, without influence of the IL cortex.

Nitric oxide inhibition in paraventricular nucleus on cardiovascular and autonomic modulation after exercise training in unanesthetized rats

It is well known that regular physical exercise alter cardiac function and autonomic modulation of heart rate variability (HRV). The paraventricular nucleus of hypothalamus (PVN) is an important site of integration for autonomic and cardiovascular responses, where nitric oxide (NO) plays an important role. The aim of our study was to evaluate the cardiovascular parameters and autonomic modulation by means of spectral analysis after nitric oxide synthase (NOS) inhibition in the PVN in conscious sedentary (S) or swimming trained (ST) rats. After swimming training protocol, adult male Wistar rats, instrumented with guide cannulas to PVN and femoral artery and vein catheters were submitted to mean arterial pressure (MAP) and heart rate (HR) recording. At baseline, the physical training induced a resting bradycardia (S: 374 +/- 5, ST: 346 +/- 1 bpm) and promoted adaptations in HRV characterized by an increase in high-frequency oscillations (HF; 26.43 +/- 6.91 to 88.96 +/- 244) and a decrease in low-frequency oscillations (LF; 73.57 +/- 6.91 to 11.04 +/- 2.44) in normalized units. The microinjection of N(omega)-nitro-L-arginine methyl ester (L-NAME) in the PVN of sedentary and trained rats promoted increase in MAP and HR. L-NAME in the PVN did not significantly alter the spectral parameters of HRV of sedentary animals, however in the trained rats increased LF oscillations (11.04 +/- 2.44 to 27.62 +/- 6.97) and decreased HF oscillations (88.96 +/- 2.44 to 72.38 +/- 6.97) in normalized units compared with baseline. Our results suggest that NO in the PVN may collaborate to cardiac autonomic modulation after exercise training. (c) 2010 Elsevier B.V. All rights reserved.

N-Methyl-D-aspartate glutamate receptors in the hypothalamic paraventricular nucleus modulate cardiac component of the baroreflex in unanesthetized rats

In the present study, we investigated the role played by the hypothalamic paraventricular nucleus (PVN) in the modulation of cardiac baroreflex activity in unanesthetized rats. Bilateral microinjections of the nonselective neurotransmission blocker CoCl(2) into the PVN decreased the reflex bradycardic response evoked by blood pressure increases, but had no effect on reflex tachycardia evoked by blood pressure decreases. Bilateral microinjections of the selective NMDA glutamate receptor antagonist LY235959 into the PVN caused effects that were similar to those observed after microinjections of CoCl(2), decreasing reflex bradycardia without affecting tachycardic response. The microinjection of the selective non-NMDA glutamate receptor antagonist NBQX into the PVN did not affect the baroreflex activity. Also, the microinjection of L-glutamate into the PVN increased the reflex bradycardia, an effect opposed to that observed after PVN treatment with CoCl(2) or LY235959, and this effect of L-glutamate was blocked by PVN pretreatment with LY235959. LY235959 injected into the PVN after iv. treatment with the selective beta(1)-adrenoceptor antagonist atenolol still decreased the reflex bradycardia. Taken together, our results suggest a facilitatory influence of the PVN on the bradycardic response of the baroreflex through activation of local NMDA glutamate receptors and a modulation of the cardiac parasympathetic activity. (C) 2010 Elsevier Ireland Ltd and the Japan Neuroscience Society. All rights reserved.

Endothelin-1 Induces Contraction of Female Rat Internal Pudendal and Clitoral Arteries through ET(A) Receptor and Rho-Kinase Activation

Introduction. Endothelin-1 (ET-1), a potent vasoconstrictor peptide, acts mainly through the Gprotein-coupled ET(A) receptor (ET(A)R). Increased vascular ET-1 production and constrictor sensitivity have been observed in various cardiovascular diseases, including hypertension, as well as erectile dysfunction. The internal pudendal artery (IPA) supplies blood to the vagina and clitoris. Inadequate blood flow through the IPA may lead to insufficient vaginal engorgement and clitoral tumescence. Aim. Characterize the effects of ET-1 on the IPA and clitoral artery (CA). Methods. IPA and CA from female Sprague Dawley rats (225-250 g) were mounted in myograph chambers. Arterial segments were submitted to increasing concentrations of ET-1 (10-10-10-6 M). Segments were incubated with the ET(A)R antagonist, atrasentan (10-8 M) or the Rho-kinase inhibitor, Y-27632 (10-6 M) 30 minutes prior to agonist exposure. All E(max) values are expressed as % KCl-induced maximal contraction. ET(A)R, RhoA, and Rho-kinase expression from IPA was evaluated by Western blot. mRNA of preproET-1, ET(A)R, ET(B)R, RhoA, and Rho-kinase were measured by real time PCR. Main Outcome Measures. ET-1 constrictor sensitivity in IPA and CA, protein expression and messenger RNA levels of ET-1-mediated constriction components. Results. ET-1 concentration-dependently contracted IPA (% Contraction and pD2, respectively: 156 +/- 18, 8.2 +/- 0.1) and CA (163 +/- 12, 8.8 +/- 0.08), while ET(A)R antagonism reduced ET-1-mediated contraction (IPA: 104 +/- 23, 6.4 +/- 0.2; CA: 112 +/- 17, 6.6 +/- 0.08). Pretreatment with Y-27632 significantly shifted ET-1 pD2 in IPA (108 +/- 24, 7.9 +/- 0.1) and CA (147 +/- 58 and 8.0 +/- 0.25). Protein expression of ET(A)R, ET(B)R, RhoA, and Rho-kinase were detected in IPA. IPA and CA contained preproET-1, ET(A)R, ET(B)R, RhoA, and Rho-kinase message. Conclusion. We observed that the IPA and CA are sensitive to ET-1, signaling through the ET(A)R and Rho-kinase pathway. These data indicate that ET-1 may play a role in vaginal and clitoral blood flow and may be important in pathologies where ET-1 levels are elevated. Allahdadi KJ, Hannan JL, Tostes RC, and Webb RC. Endothelin-1 induces contraction of female rat internal pudendal and clitoral arteries through ETA receptor and Rho-kinase activation. J Sex Med 2010;7:2096-2103.

Dopamine microinjected into brainstem of awake rats affects baseline arterial pressure but not chemoreflex responses

Dopamine (DA) is a neuromodulator in the brainstem involved with the generation and modulation of the autonomic and respiratory activities. Here we evaluated the effect of microinjection of DA intracistema magna (icm) or into the caudal nucleus tractus solitarii (cNTS) on the baseline cardiovascular and respiratory parameters and on the cardiovascular and respiratory responses to chemoreflex activation in awake rats. Guide cannulas were implanted in cisterna magna or cNTS and femoral artery and vein were catheterized. Respiratory frequency (f(R)) was measured by whole-body plethysmography. Chemoreflex was activated with KCN (iv) before and after microinjection of DA icm or into the cNTS bilaterally while mean arterial pressure (MAP), heart rate (HR) and f(R) were recorded. Microinjection of DA icm (n = 13), but not into the cNTS (n = 8) produced a significant decrease in baseline MAP (-15 +/- 1 vs 1 +/- 1 mm Hg) and HR (-55 +/- 11 vs -11 +/- 17 bpm) in relation to control (saline with ascorbic acid, n = 9) but no significant changes in baseline f(R). Microinjection of DA icm or into the cNTS produced no significant changes in the pressor, bradycardic and tachypneic responses to chemoreflex activation. These data show that a) DA icm affects baseline cardiovascular regulation, but not baseline f(R) and autonomic and respiratory components of chemoreflex and b) DA into the cNTS does not affect either the autonomic activity to the cardiovascular system or the autonomic and respiratory responses of chemoreflex activation. (C) 2010 Elsevier B.V. All rights reserved.

Sympathetic activity is not increased in L-NAME hypertensive rats

Santos FM, Dias DPM, Silva CAA, Fazan Jr R, Salgado HC. Sympathetic activity is not increased in L-NAME hypertensive rats. Am J Physiol Regul Integr Comp Physiol 298: R89-R95, 2010. First published November 4, 2009; doi:10.1152/ajpregu.00449.2009.-The role played by the sympathetic drive in the development of N(G)-nitro-L-arginine methyl ester (L-NAME)-induced hypertension is not firmly established. Therefore, the present study was undertaken in conscious rats in which hypertension was induced by treatment with L-NAME over the course of either 2 or 14 days. Mean arterial pressure (MAP) was measured via a catheter placed in the femoral artery, drugs were administered via a cannula placed in the femoral vein, and renal sympathetic nerve activity (RSNA) was monitored using an implanted electrode. Despite the remarkable increase in arterial pressure, heart rate did not change after treatment with L-NAME. RSNA was similar in L-NAME-induced hypertensive rats treated over the course of 2 or 14 days, as well as in normotensive rats. It was also demonstrated that L-NAME-induced hypertensive rats displayed a resetting of the baroreflex control of RSNA to hypertensive levels, with decreased sensitivity over the course of 2 or 14 days. Furthermore, the sympathetic-vagal balance examined in the time and frequency domain and the renal and plasma norepinephrine content did not differ between groups. In conclusion, the evaluation of the sympathetic drive in conscious rats demonstrated that the arterial hypertension induced by L-NAME treatment over the course of 2 and 14 days does not show sympathetic overactivity.

NO in the caudal NTS modulates the increase in respiratory frequency in response to chemoreflex activation in awake rats

The role of nitric oxide (NO) in the caudal NTS (cNTS) on baseline cardiovascular and respiratory parameters and on changes in respiratory frequency (fR) and cardiovascular responses to chemoreflex activation was evaluated in awake rats. Bilateral microinjections of L-NAME (200 nmoles/50 nL), a non-selective NO synthase (NOS) inhibitor, into the cNTS increased baseline arterial pressure, while microinjections of NPLA (3 pmoles/50 nL), a selective neuronal NOS (nNOS) inhibitor, did not. L-NAME or N-PLA microinjected into the cNTS reduced the increase in fR in response to chemoreflex activation but not cardiovascular responses. These data show that (a) NO produced by non-nNOS in the cNTS is involved in the baseline autonomic control and (b) NO produced by nNOS in the cNTS is involved in modulation of the increase in fR in response to chemoreflex activation but not in the cardiovascular responses. We conclude that NO produced by the neuronal and endothelial NOS play a different role in the cNTS neurons integral to autonomic and respiratory pathways. (C) 2009 Elsevier B.V. All rights reserved.

GABA and nitric oxide in the PVN are involved in arterial pressure control but not in the chemoreflex responses in rats

GABAergic, nitrergic and glutamatergic mechanisms in the PVN on the baseline mean arterial pressure (MAP), heart rate (HR) and on the cardiovascular responses to chemoreflex activation in awake rat were evaluated. Chemoreflex was activated with KCN before and after microinjections into the PVN. Bicuculline into the PVN increased baseline MAP (94+/-3 vs 113+/-5 mmHg) and HR (350+/-9 vs 439+/-18 bpm) but had no effect on the pressor (49+/-5 vs 47+/-6 mmHg) or bradicardic (-213+/-23 vs -256+/-42 bpm) responses (n=7). Kynurenic acid into the PVN (n=6) produced no significant changes in the MAP (98+/-3 vs 100+/-3 mmHg), HR (330+/-5 vs 339+/-12 mmHg) or in the pressor (50+/-4 vs 42+/-4 mmHg) and bradicardic (-252+/-4 vs -285+/-16 bpm) responses to chemoreflex. L-NAME into the PVN (n=8) produced increase in the MAP (94+/-3 vs 113+/-5 mmHg) and HR (350+/-9 vs 439+/-18 bpm) but had no effect on the pressor (52+/-5 vs 47+/-6 mmHg) or bradicardic (-253+/-19 vs -320+/-25 bpm) responses to chemoreflex. We conclude that GABA(A) and nitric oxide in the PVN are involved in the maintenance of the baseline MAP but not in the modulation of the responses to chemoreflex. The results also show that Glutamate receptors in the PVN are not involved in maintenance of the baseline MAP, HR or in the cardiovascular responses to chemoreflex in awake rats. (C) 2008 Elsevier B.V. All rights reserved.

INTERMITTENT ACTIVATION OF PERIPHERAL CHEMORECEPTORS IN AWAKE RATS INDUCES Fos EXPRESSION IN ROSTRAL VENTROLATERAL MEDULLA-PROJECTING NEURONS IN THE PARAVENTRICULAR NUCLEUS OF THE HYPOTHALAMUS

Despite the well-established sympathoexcitation evoked by chemoreflex activation, the specific sub-regions of the CNS underlying such sympathetic responses remain to be fully characterized. In the present study we examined the effects of intermittent chemoreflex activation in awake rats on Fos-immunoreactivity (Fos-ir) in various subnuclei of the paraventricular nucleus of the hypothalamus (PVN), as well as in identified neurosecretory preautonomic PVN neurons. In response to intermittent chemoreflex activation, a significant increase in the number of Fos-ir cells was found in autonomic-related PVN subnuclei, including the posterior parvocellular, ventromedial parvocellular and dorsal-cap, but not in the neurosecretory magnocellular-containing lateral magnocellular subnucleus. No changes in Fos-ir following chemoreflex activation were observed in the anterior PVN subnucleus. Experiments combining Fos immunohistochemistry and neuronal tract tracing techniques showed a significant increase in Fos-ir in rostral ventrolateral medulla (RVLM)-projecting (PVN-RVLM), but not in nucleus of solitarii tract (NTS)-projecting PVN neurons. In summary, our results support the involvement of the PVN in the central neuronal circuitry activated in response to chemoreflex activation, and indicate that PVN-RVLM neurons constitute a neuronal substrate contributing to the sympathoexcitatory component of the chemoreflex. Published by Elsevier Ltd on behalf of IBRO.

Glutamatergic and purinergic mechanisms on respiratory modulation in the caudal NTS of awake rats

In the present study we evaluated the role of ionotropic glutamate receptors and purinergic P2 receptors in the caudal commissural NTS (cNTS) on the modulation of the baseline respiratory frequency (fR), and on the tachypneic response to chemoreflex activation in awake rats. The selective antagonism of ionotropic glutamate receptors with kynurenic acid (2 nmol/50 nl) in the cNTS produced a significant increase in the baseline fR but no changes in the tachypneic response to chemoreflex activation. The selective antagonism of purinergic P2 receptors by PPADS (0.25 nmol/50 nl) in the cNTS produced no changes in the baseline fR or in the tachypneic response to chemoreflex activation. The data indicate that glutamate acting on ionotropic receptors in the cNTS plays a inhibitory role on the modulation of the baseline fR but had no effect on the tachypneic response to chemoreflex activation, while ATP acting on P2 receptors in the cNTS plays no major role in the modulation of the baseline fR or in the tachypneic response to chemoreflex activation. We suggest that neurotransmitters other than L-glutamate and ATP are involved in the processing of the tachypneic response of the chemoreflex at the cNTS level. (C) 2008 Elsevier B.V. All rights reserved.

Interaction of purinergic and nitrergic mechanisms in the caudal nucleus tractus solitarii of rats

The interaction of purinergic and nitrergic mechanisms was evaluated in the caudal nucleus tractus solitarii (cNTS) using awake animals and brainstem slices. In awake animals, ATP (1.25 nmol/50 nL) was microinjected into the cNTS before and after the microinjection of a selective neuronal nitric oxide synthase (nNOS) inhibitor N-propyl-L-arginine (NPLA, 3 pmoles/50 nL, n=8) or vehicle (saline, n=4), and cardiovascular and ventilatory parameters were recorded. In brainstem slices from a distinct group of rats, the effects of ATP on the NO concentration in the cNTS using the fluorescent dye DAF-2 DA were evaluated. For this purpose brainstem slices (150 pm) containing the cNTS were pre-incubated with ATP (500 mu M; n=8) before and during DAF-2 DA loading. Microinjection of ATP into the cNTS increases the arterial pressure (AP), respiratory frequency (f(R)) and minute ventilation (V(E)), which were significantly reduced by pretreatment with N-PLA, a selective nNOS inhibitor (AP: 39 +/- 3 vs 16 +/- 14 mm Hg; f(R): 75 +/- 14 vs 4 +/- 3 cpm; V(E): 909 159 vs 77 39 mL kg(-1) m(-1)). The effects of ATP in the cNTS were not affected by microinjection of saline. ATP significantly increased the NO fluorescence in the cNTS (62 +/- 7 vs 101 +/- 10 AU). The data show that in the cNTS: a) the NO production is increased by ATP; b) NO formation by nNOS is involved in the cardiovascular and ventilatory responses to microinjection of ATP. Taken together, these data suggest an interaction of purinergic and nitrergic mechanisms in the cNTS. (C) 2009 Elsevier B.V. All rights reserved.

Nitric oxide synthesis blockade reduced the baroreflex sensitivity in trained rats

Objective: The present study has investigated the effect of blockade of nitric oxide synthesis on cardiovascular autonomic adaptations induced by aerobic physical training using different approaches: 1) double blockade with methylatropine and propranolol; 2) systolic arterial pressure (SAP) and heart rate variability (HRV) by means of spectral analysis; and 3) baroreflex sensitivity. Methods: Male Wistar rats were divided into four groups: sedentary rats (SR); sedentary rats treated with N(omega)-nitro-L-arginine methyl ester (L-NAME) for one week (SRL); rats trained for eight weeks (TR); and rats trained for eight weeks and treated with L-NAME in the last week (TRL). Results: Hypertension and tachycardia were observed in SRL group. Previous physical training attenuated the hypertension in L-NAME-treated rats. Bradycardia was seen in TR and TRL groups, although such a condition was more prominent in the latter. All trained rats had lower intrinsic heart rates. Pharmacological evaluation of cardiac autonomic tonus showed sympathetic predominance in SRL group, differently than other groups. Spectral analysis of HRV showed smaller low frequency oscillations (LF: 0.2-0.75 Hz) in SRL group compared to other groups. Rats treated with L-NAME presented greater LF oscillations in the SAP compared to non-treated rats, but oscillations were found to be smaller in TRL group. Nitric oxide synthesis inhibition with L-NAME reduced the baroreflex sensitivity in sedentary and trained animals. Conclusion: Our results showed that nitric oxide synthesis blockade impaired the cardiovascular autonomic adaptations induced by previous aerobic physical training in rats that might be, at least in part, ascribed to a decreased baroreflex sensitivity. (C) 2009 Elsevier B.V. All rights reserved.

The effect of aerobic physical training on cardiac autonomic control of rats submitted to ovariectomy

Objective: To investigate the effect of aerobic physical training on cardiovascular autonomic control in ovariectomized rats using different approaches. Design: Female Wistar rats were divided into four groups: sedentary sham rats (group SSR), trained sham rats (group TSR), sedentary ovariectomized rats (group SOR), and trained ovariectomized rats (group TOR). Animals from the trained groups were submitted to a physical training protocol (swimming) for 12 weeks. Results: Pharmacological evaluation showed that animals from group TSR had an increase in their cardiac vagal tonus compared with the animals from groups SSR and SOR. The analysis of heart rate variability (HRV) showed that groups TSR and SOR had fewer low-frequency oscillations (0.20-0.75 Hz) compared with groups SSR and TOR. When groups TSR and SOR were compared, the former was found to have fewer oscillations. With regard to high-frequency oscillations (0.75-2.5 Hz), group SSR had a reduction compared with the other groups, whereas group TSR had the greatest oscillation compared with groups SOR and TOR, with all values expressed in normalized units. Analysis of HRV was performed after pharmacological blockade, and low-frequency oscillations were found to be predominantly sympathetic in sedentary animals, whereas there was no predominance in trained animals. Conclusion: Ovariectomy did not change the tonic autonomic control of the heart and, in addition, reduced the participation of sympathetic component in cardiac modulation. Physical training, on the other hand, increased the participation of parasympathetic modulation on the HRV, including ovariectomized rats.