OBJECTIVETo develop a system for automatically controlling carotid sinus pressure in the study on baroreceptors.

METHODSThe preparation containing carotid sinus with parts of the connected vessels and carotid sinus nerve (CS-CSN) were isolated and perfused. A critical pressure controlling component (PRE-U, Hoerbiger, Deutschland) dictated by a computer was integrated into the system to clamp the intrasinus pressure. The pressure command and the relevant intrasinus pressure were compared to evaluate the validity of the pressure controlling system.

RESULTSA variety of sinus pressure-controlling patterns, including pulsation, ramp and step pressures, could be achieved accurately by using the system, and the pressure-dependent discharge activities of sinus nerve were confirmed.

CONCLUSIONThis system for clamping carotid sinus pressure could realize multiple pressure-controlling patterns and is a useful and flexible pressure controlling method that could applied in the study on mechano-electric transduction of baroreceptors.

Animals ; Blood Pressure ; Carotid Sinus ; innervation ; physiology ; Nerve Fibers ; physiology ; Pressoreceptors ; physiology ; Rabbits

Mechanosensitive ion channels (MSCs) are key molecules in the mechano-electrical transduction of arterial baroreceptors. Among them, acid-sensing ion channel 2 (ASIC2) and transient receptor potential vanilloid subfamily member 1 (TRPV1) have been studied extensively and documented to play important roles. In this study, experiments using aortic arch-aortic nerve preparations isolated from rats revealed that both ASIC2 and TRPV1 are functionally necessary, as blocking either abrogated nearly all pressure-dependent neural discharge. However, whether ASIC2 and TRPV1 work in coordination remained unclear. So we carried out cell-attached patch-clamp recordings in HEK293T cells co-expressing ASIC2 and TRPV1 and found that inhibition of ASIC2 completely blocked stretch-activated currents while inhibition of TRPV1 only partially blocked these currents. Immunofluorescence staining of aortic arch-aortic adventitia from rats showed that ASIC2 and TRPV1 are co-localized in the aortic nerve endings, and co-immunoprecipitation assays confirmed that the two proteins form a compact complex in HEK293T cells and in baroreceptors. Moreover, protein modeling analysis, exogenous co-immunoprecipitation assays, and biotin pull-down assays indicated that ASIC2 and TRPV1 interact directly. In summary, our research suggests that ASIC2 and TRPV1 form a compact complex and function synergistically in the mechano-electrical transduction of arterial baroreceptors. The model of synergism between MSCs may have important biological significance beyond ASIC2 and TRPV1.
Acid Sensing Ion Channels/physiology* ; Animals ; HEK293 Cells ; Humans ; Pressoreceptors/physiology* ; Rats ; TRPV Cation Channels/physiology*

OBJECTIVETo observe the regulation of heart rate to cardiac pump function in the phase of negative force-frequency relationship and their possible mechanisms.

METHODSThe left ventricular pressure, aortic pressure, and cardiac output were measured in isolated working heart of rat from 240 to 300 beats/min of pacing rate.

RESULTSCardiac output of isolated working heart was decreased by a proximally 20% (P < 0.01) with the increase in the pacing rate from 240 to 300 beats/min. Left ventricular end-systolic pressure (LVESP) was declined by 4.8% (P < 0.05), but left ventricular end-diastolic pressure (LVEDP) was elevated by 139% (P < 0.01) with an increase in the pacing rate. Left atrium was enlarged at 300 beats/min of pacing rate. The time from peak to 75% relaxation in left ventricular pressure was shortened with the increased pacing rate. Pressure at aortic valve close was raised (P < 0.01) and ejection duration was shortened with the increased pacing rate (P < 0.01).

CONCLUSIONThose above results suggest that there are different mechanisms between the depressed cardiac output at higher heart rate and negative force-frequency relationship. The frequency-dependent acceleration of relaxation facilitates the decline of left ventricular pressure, and then may elevate the pressure of aortic valve close in the condition that the shape of aortic pressure curve stays the same. Therefore, the ejection duration is shortened at higher pacing rate. The shortened ejection duration may induce a decrease in stroke volume of the left ventricle. The increment of heart rate is not enough to compensate the decreased stroke volume. Finally, cardiac output shows a decrease at higher heart rate.

Animals ; Blood Pressure ; Cardiac Output ; Heart Rate ; physiology ; Male ; Pressoreceptors ; Rats ; Rats, Sprague-Dawley

The changes in carotid sinus baroreceptor reflex (CSR) performance induced by intracerebroventricular injection (i.c.v.) of histamine (HA) were investigated. The effects of pretreatment with HA receptors antagonists into the cerebroventricle or nucleus of solitary tract (NTS) on the responses of CSR to HA were also examined. Intracarotid sinus pressure (ISP)-mean arterial pressure (MAP) relationship curve was constructed by fitting to the logistic function with five parameters in 50 Wistar rats anesthetized with pentobarbital sodium. The left and right carotid sinus regions were isolated from the systemic circulation and the ISP was altered in a stepwise manner. The main results obtained are as follows. (1) i.c.v. injection of HA (100 ng) significantly shifted the ISP-MAP relationship curve upwards and moved the middle part of ISP-Gain relationship curve downwards, and reduced the MAP range and maximum gain (G(max)), but increased the threshold pressure (TP), saturation pressure (SP) and ISP at G(max) (ISP (Gmax)). (2) The pretreatment with H(1) or H(2) receptors antagonist, chlorpheniramine (CHL, 5 microg) or cimetidine (CIM, 15 microg), could obviously diminish the above-mentioned changes in CSR performance induced by HA, but the effect of CIM was less remarkable than that of CHL. (3) The pretreatment with both CHL and CIM (5 microg and 15 microg) at the same time abolished the responses of CSR performance to HA completely. (4) After microinjection of CHL (0.5 microg) or CIM (1.5 microg) into the NTS, the responses of CSR to HA were similar to those after i.c.v. CHL or CIM, but the change in TP was significantly decreased. These findings suggest that the intracerebroventricular administration of HA results in a rapid resetting of CSR and a decrease in reflex sensitivity. The response of CSR to HA might be mediated by both central H(1) and H(2) receptors, especially by H(1) receptors. The effects of the central HA on CSR might be related to a histaminergic descending pathway from the hypothalamus to NTS. It is suggested that the HA receptors in the NTS play an important role in the responses of CSR to HA.
Animals ; Baroreflex ; drug effects ; physiology ; Carotid Sinus ; physiology ; Histamine ; administration & dosage ; pharmacology ; Lateral Ventricles ; Male ; Pressoreceptors ; physiology ; Rats ; Rats, Wistar

To investigate the eletrophysiological effect of rat adrenomedullin (rADM) on barosensitive neurons in the rostral ventrolateral medulla (rVLM) and its potential mechanisms, the extracellular recording and multi-barrel iontophoresis methods were used. Of the 29 barosensitive neurons in the rVLM, 20 neurons demonstrated excitatory response to iontophoretically applied rADM and increased the firing rate from (10.8 +/- 2.7) spikes/s to (14.6 +/- 3.6), (19.8 +/- 4.7) and (31.9 +/- 6.4) spikes/s (P<0.05, n=20) at the current of 30, 60 and 90 nA, respectively. Application of human adrenomedullin (22-52) [hADM (22-52)], a specific antagonist of rADM receptor, distinctly attenuated the augmentation of firing rate induced by rADMjthe firing rate was increased by 15.4% [(11.4 +/- 2.5) spikes/s, P<0.05, n=10]. Another antagonist, human calcitonin gene-related peptide (8-37) [hCGRP (8-37)] had no significant effect on rADM-induced excitation. Other 23 barosensitive neurons were recorded to test the influence of nitric oxide synthase (NOS) inhibitors on the excitatory effect of rADM. In 10 neurons, 7-NiNa (neuronal NOS inhibitor) decreased the firing rate from (10.1 +/- 3.5) spikes/s to (7.5 +/- 2.5), (5.3 +/- 2.1) and (3.1 +/- 1.4) spikes/s (P<0.05, n=10) at the current of 10, 20 and 40 nA, respectively. The excitatory effect of rADM (60 nA, 30 s) during 7-NiNa application was nearly eliminated and the magnitude of firing rate was increased only by 17% of the basal level (6.2 +/- 1.9) spikes/s (P<0.05, n=7). While aminoguanidine (AG, iNOS inhibitor) increased the firing rate at the resting level from (11.5 +/- 5.1) spikes/s to (17.8 +/- 5.6), (22.5 +/- 6.3) and (29.1 +/- 6.4) spikes/s (P<0.05, n=8) at the current of 10, 20 and 40 nA in 8 barosensitive neurons, respectively. When rADM (60 nA, 30 s) was delivered during AG iontophoresis period, the firing rate significantly increased by 60% of the basal level [(22.5 +/- 6.3) spikes/s, n=5]. These results indicate that rADM activates the barosensitive neurons in the rVLM directly and acts as a cardiovascular regulator, and that this function might be mediated by its specific receptor. NO, mainly neuronal NOS-originated might be involved in the excitatory effect of rADM in the rVLM.
Adrenomedullin ; physiology ; Animals ; Electrophysiological Phenomena ; Male ; Medulla Oblongata ; physiology ; Neurons ; physiology ; Nitric Oxide ; physiology ; Nitric Oxide Synthase Type I ; physiology ; Pressoreceptors ; physiology ; Rats ; Rats, Sprague-Dawley

Clinical trials and animal experimental studies have demonstrated an association of arterial baroreflex impairment with the prognosis and mortality of cardiovascular diseases and diabetes. As a primary part of the arterial baroreflex arc, the pressure sensitivity of arterial baroreceptors is blunted and involved in arterial baroreflex dysfunction in cardiovascular diseases and diabetes. Changes in the arterial vascular walls, mechanosensitive ion channels, and voltage-gated ion channels contribute to the attenuation of arterial baroreceptor sensitivity. Some endogenous substances (such as angiotensin II and superoxide anion) can modulate these morphological and functional alterations through intracellular signaling pathways in impaired arterial baroreceptors. Arterial baroreceptors can be considered as a potential therapeutic target to improve the prognosis of patients with cardiovascular diseases and diabetes.
Animals ; Baroreflex ; physiology ; Blood Pressure ; physiology ; Cardiovascular Diseases ; metabolism ; physiopathology ; Diabetes Mellitus ; metabolism ; physiopathology ; Humans ; Ion Channels ; metabolism ; Pressoreceptors ; metabolism

The carotid sinus baroreceptor reflex (CSR) is an important approach for regulating arterial blood pressure homeostasis instantaneously and physiologically. Activation of the central histaminergic or cholinergic systems results in CSR functional inhibitory resetting. However, it is unclear whether two systems at the nucleus tractus solitarius (NTS) level display cross interaction to regulate the CSR or not. In the present study, the left or right carotid sinus region was isolated from the systemic circulation in Sprague-Dawley rats (sinus nerve was reserved) anesthetized with pentobarbital sodium. Respective intubation was conducted into one side isolated carotid sinus and into the femoral artery for recording the intracarotid sinus pressure (ISP) and mean arterial pressure (MAP) simultaneously with pressure transducers connection in vivo. ISP was set at the level of 0 mmHg to eliminate the effect of initial internal pressure of the carotid sinus on the CSR function. To trigger CSR, the ISP was quickly elevated from 0 mmHg to 280 mmHg in a stepwise manner (40 mmHg) which was added at every step for over 4 s, and then ISP returned to 0 mmHg in similar steps. The original data of ISP and corresponding MAP were fitted to a modified logistic equation with five parameters to obtain the ISP-MAP, ISP-Gain relationship curves and the CSR characteristic parameters, which were statistically compared and analyzed separately. Under the precondition of no influence on the basic levels of the artery blood pressure, the effects and potential regulatory mechanism of preceding microinjection with different cholinoceptor antagonists, the selective cholinergic M1 receptor antagonist, i.e., pirenzepine (PRZ), the M2 receptor antagonist, i.e., methoctramine (MTR) or the N1 receptor antagonist, i.e., hexamethonium (HEX) into the NTS on the changes in function of CSR induced by intracerebroventricular injection (i.c.v.) of histamine (HA) in rats were observed. Meanwhile, the actions and possible modulatory mechanism of preceding microinjection with different histaminergic receptor antagonists, the selective histaminergic H1 receptor antagonist, i.e., chlorpheniramine (CHL) or the H2 receptor antagonist, i.e., cimetidine (CIM) into the NTS on the changes in function of CSR resulted from the i.c.v. cholinesterase inhibitor, physostigmine (PHY) were also examined in order to confirm and to analyze effects of cross interaction between central histaminergic and cholinergic systems on CSR. The main results obtained are as follows. (1) Standalone microinjection of different selective cholinergic receptor antagonists (PRZ, MTR or HEX) or different selective histaminergic receptor antagonists (CHL or CIM) into the NTS with each given dose had no effects on the CSR function and on the basic levels of the artery blood pressure, respectively (P > 0.05). (2) The pretreatment of PRZ or MTR into the NTS with each corresponding dose could attenuate CSR resetting resulted from i.c.v. HA in some degrees, which remarkably moved the posterior half range of ISP-MAP relationship curve downwards (P < 0.05), shifted the middle part of ISP-Gain relationship curve upwards (P < 0.05), and increased reflex parameters such as the MAP range and maximum gain (P < 0.05), but decreased parameters such as saturation pressure and intracarotid sinus pressure at maximum gain (P < 0.05). The catabatic effects of pretreatment with MTR into the NTS on CSR resetting induced by i.c.v. HA were more obvious than those with PRZ (P < 0.05), but pretreatment of HEX with given dose into the NTS had no effects on CSR resetting induced by i.c.v. HA (P > 0.05). (3) The effects of pretreatment of CHL or CIM into the NTS with each corresponding dose on CSR resetting made by i.c.v. PHY were similar to those of pretreatment of PRZ or MTR into the NTS on CSR resetting resulted from i.c.v. HA, and the decreasing effects of pretreatment with CHL into the NTS on CSR resetting induced by i.c.v. PHY were more remarkable than those with CIM (P < 0.05). These findings suggest that CSR resetting resulted from either HA or PHY into the lateral ventricle may partly involve the descending histaminergic or cholinergic pathway from the hypothalamus to NTS, which might evoke a cross activation of the cholinergic system in the NTS, via cholinergic M1 and M2 receptors mediation, especially the M2 receptors showing actions, or trigger another cross activation of the histaminergic system in the NTS, by histaminergic H1 and H2 receptors mediation, especially the H1 receptors displaying effects.
Animals ; Baroreflex ; Carotid Sinus ; physiology ; Chlorpheniramine ; pharmacology ; Cholinergic Antagonists ; pharmacology ; Cimetidine ; pharmacology ; Histamine ; pharmacology ; Pressoreceptors ; physiology ; Rats ; Rats, Sprague-Dawley ; Solitary Nucleus ; physiology

OBJECTIVETo investigate the role of the dorsal column (DC) in the inhibitory effect of somatic afferent inputs on the central pressor response.

METHODSThe femoral arterial pressure, mean arterial pressure (MAP), electrocardiogram (ECG) and heart rate (HR) of the male SD rats were recorded when the hypothalamic paraventricular nucleus (PVN) was electrically stimulated with or without destruction of DC. The inhibitory effect of the deep peroneal nerve (DPN) on the pressor response induced by stimulation of PVN was observed 20 min or 5 d after ipsilateral DC destruction.

RESULTSStimulating DPN inhibited the pressor response elicited by electrical stimulation of PVN with an inhibitory rate of 43.29%. Twenty minutes after destroying the right DC, stimulation of the right or left DPN could inhibit the pressor response with an inhibitory rate of 38.64% and 39.97%, respectively (P>0.05); five days later the inhibitory rates remained as 33.87% and 36.86% respectively (P>0.05). The pain responses of both hindlimbs in the rats with the right DC destroyed showed no significant difference compared with the intact rats.

CONCLUSIONDC is not involved in the inhibitory effect of DPN on the pressor response induced by PVN stimulation.

Afferent Pathways ; physiology ; Animals ; Blood Pressure ; physiology ; Electric Stimulation ; Male ; Paraventricular Hypothalamic Nucleus ; physiology ; Peroneal Nerve ; physiology ; Pressoreceptors ; physiology ; Random Allocation ; Rats ; Rats, Sprague-Dawley ; Spinal Cord ; physiology ; Spinothalamic Tracts ; physiology

OBJECTIVETo investigate the cardiovascular responses induced by activation of the paraventricular nucleus of hypothalamus (PVN) and the roles of the central nucleus of amygdala (CeA) on this effect.

METHODSThe PVN was activated by microinjection of L-glutamate or electrical stimulation. The CeA was injected with L-glutamate or Kainic acid (KA). The femoral arterial pressure, mean arterial pressure (MAP), electrocardiogram (ECG) and heart rate (HR) of the male SD rats were recorded when the PVN was electrically stimulated.

RESULTThe blood pressure increased when the PVN was activated either by electrical current or by L-glutamate. The blood pressure increased for (10.27+/-1.80)mmHg and the change of heart rate was -10.66 +/- 8.11 beat/min after L-Glu (100 nl) was injected into the ipsilateral CeA. The pressor response of PVN stimulation could still be evoked by electrical stimulation of (13.78 +/- 3.18)mmHg 10 min after kainic acid (100 nl) was injected into the ipsilateral CeA. But this pressor response decreased of 6.57 mmHg compared to that before injection of KA (P <0.05). The locations of the electrode tips and termination of the injector tracts were identified according to the atlas after the recording.

CONCLUSIONStimulating the PVN elicits pressor response in rats. The CeA mediates partly the pressor response elicited by activation of the PVN.

Amygdala ; physiology ; Animals ; Blood Pressure ; physiology ; Cardiovascular Physiological Phenomena ; Electric Stimulation ; Glutamic Acid ; Heart Rate ; physiology ; Kainic Acid ; Male ; Paraventricular Hypothalamic Nucleus ; physiology ; Pressoreceptors ; physiology ; Rats ; Rats, Sprague-Dawley

OBJECTIVETo assess the inhibitory modulation of blood pressure by stimulation of the deep peroneal nerve (DPN) and to determine the involvement of nociceptive fibers in the modulation.

METHODSAll the animals were divided into six groups (A-F). The rats in groups A and B received no pretreatment. The rats in groups C and D received subcutaneous injection of capsaicin or control vehicle, respectively, near the DPN for 2 days. Those in groups E and F had the DPN exposed to capsaicin or control vehicle, respectively, for 20 min. Subsequently, pressor responses were induced by stimulation of paraventricular nucleus (PVN) either electrically (groups A and C C-F) or chemically via injection of glutamate (group B). After two stable pressor responses (baseline), all groups were subject to 5-min DPN stimulation followed by PVN stimulation for 10 s. Arterial blood pressure, heart rate, and electrocardiogram were recorded. The pressor response was calculated as the difference in the mean arterial pressure (MAP) before and after PVN stimulation, and changes from baseline in pressor response after DPN stimulation were compared between the groups.

RESULTSIncreases of MAP of 22.88±2.18 mm Hg and 20.32±5.25 mm Hg were induced by electrical (group A) or chemical (group B) stimulation of the PVN, respectively. These pressor responses were inhibited by stimulation of the DPN, and the MAP was reduced to 12.00±2.10 mm Hg in group A (n=6, P<0.01) and 7.00±2.85 mm Hg in group B (n=6, P<0.01). Subcutaneous injection of capsaicin (125 mg/kg) near the DPN in group C (n=7) had no effect on the inhibitory effect of DPN stimulation compared with the group D (n=9), and neither did blockade of nociceptive fibers with capsaicin in group E (n=6) compared with group F (n=8).

CONCLUSIONStimulation of the DPN mimicking acupuncture has an inhibitory effect on the pressor response, and the effect is mediated by capsaicin-insensitive afferent fibers in the DPN.

Acupuncture Therapy ; Anesthesia ; Animals ; Blood Pressure ; drug effects ; Capsaicin ; administration & dosage ; pharmacology ; Electric Stimulation ; Injections, Subcutaneous ; Male ; Paraventricular Hypothalamic Nucleus ; cytology ; drug effects ; Peroneal Nerve ; drug effects ; physiology ; Pressoreceptors ; drug effects ; physiology ; Rats ; Rats, Sprague-Dawley