Nociceptin in rVLM mediates electroacupuncture inhibition of cardiovascular reflex excitatory response in rats.

Electroacupuncture (EA) at Neiguan-Jianshi acupoints through an opioid mechanism inhibits the cardiovascular pressor response induced by mechanical stimulation of the stomach. Because nociceptin also may regulate cardiovascular activity through its action in the brain stem, we hypothesized that this neuromodulator serves a role in the EA-related inhibitory effect. Blood pressure in ventilated male Sprague-Dawley rats (400-600 g) anesthetized by ketamine and alpha-chloralose was measured during balloon inflation of the stomach. Gastric distension with 6-8 ml of air induced consistent pressor reflexes of 26 +/- 1 mmHg that could be repeated every 10 min for 100 min. When nociceptin (10 nM) was microinjected into the rostral ventrolateral medulla (rVLM), the pressor response induced by gastric distension was inhibited by 68 +/- 6%. Thirty minutes of EA also decreased the reflex response by 75 +/- 11%; microinjection of saline into the rVLM did not alter the inhibitory effect of EA. In contrast, microinjection of a nociceptin receptor antagonist into the rVLM promptly reversed the EA response. Pretreatment with the opioid receptor antagonist naloxone did not influence the EA-like inhibitory effect of nociceptin on the distension-induced pressor reflex (22 +/- 1 to 8 +/- 2 mmHg). Furthermore, a mu-opioid receptor agonist microinjected into the rVLM after microinjection of a nociceptin receptor antagonist during EA promptly reversed the nociceptin receptor antagonist-related inhibition of the EA effect. Thus, in addition to the classical opioid system, nociceptin, through opioid receptor-like-1 receptor stimulation in the rVLM, participates in the modulatory influence of EA on reflex-induced increases in blood pressure.     

Excitatory projections from arcuate nucleus to ventrolateral periaqueductal gray in electroacupuncture inhibition of cardiovascular reflexes

We have shown that the modulatory effect of electroacupuncture (EA) on the blood pressure (BP) response induced by visceral organ stimulation is related to inhibition of cardiovascular neurons in the rostral ventrolateral medulla (rVLM) through a mechanism that involves opioids. This effect is long lasting and may involve a long-loop neural supraspinal pathway, including the arcuate nucleus (ARC), which is an important site of opioid neurotransmitter synthesis. Therefore, we evaluated the role of the hypothalamic ARC and its interaction with the midbrain ventrolateral periaqueductal gray (vlPAG) in the EA-BP response. The gallbladder of alpha-chloralose-anesthetized cats was stimulated to test for the influence of EA on splanchnic afferent-induced cardiovascular reflexes. Electrodes were placed around the splanchnic nerve (SN), and acupuncture needles were applied at P5-6 acupoints overlying the median nerve (MN). Electrophysiological recordings showed that spontaneous activity of ARC and vlPAG neurons was low (1.3 +/- 0.5 and 2.0 +/- 0.5 spikes/s, respectively). We observed a gradation of responses of ARC neurons to the stimulation of different acupoints, ranging from uniform responses of all neurons during stimulation of the P5-6, LI4-11, H5-6, and St2-G2 located over deep nerves to fewer responses during stimulation of LI6-7 and G37-39 located over superficial nerves. Microinjection of the excitatory amino acid dl-homocysteic acid (DLH 4 nM, 50 nl) into the ARC augmented the responses of vlPAG neurons, whereas microinjection of kainic acid (KA 1 mM, 50 nl) to deactivate neurons in the ARC decreased vlPAG responses to SN stimulation. Thirty minutes of EA at P5-6 increased the SN-evoked discharge of vlPAG neurons (7.0 +/- 1.2 to 14.3 +/- 3.0 spikes/30 stimuli), a response that was blocked by microinjection of KA into the ARC. Microinjection of DLH into the ARC, like EA, inhibited (30 min) the reflex increase in BP induced by application of bradykinin (BK) to the gallbladder, whereas microinjection of KA into the ARC blocked the inhibitory influence of EA at P5-6 on the BK-induced BP response. These results suggest that excitatory projections from the ARC to the vlPAG are essential to the EA inhibition of the reflex increase in BP induced by SN or gallbladder visceral afferent stimulation.     

Midbrain vlPAG inhibits rVLM cardiovascular sympathoexcitatory responses during electroacupuncture

The periaqueductal gray (PAG) is an important integrative region in the regulation of autonomic outflow and cardiovascular function and may serve as a regulatory center as part of a long-loop pathway during somatic afferent stimulation with acupuncture. Because the ventrolateral PAG (vlPAG) provides input to the rostral ventrolateral medulla (rVLM), an important area for electroacupuncture (EA) regulation of sympathetic outflow, we hypothesized that the vlPAG plays a role in the EA-related modulation of rVLM premotor sympathetic neurons activated during visceral afferent stimulation and autonomic excitatory reflexes. Cats were anesthetized and ventilated, and heart rate and mean blood pressure were monitored. Stimulation of the splanchnic nerve by a pledget of filter paper soaked in bradykinin (BK, 10 mug/ml) every 10 min on the gallbladder induced consistent cardiovascular reflex responses. Bilateral stimulation with EA at acupoints over the pericardial meridian (P5-6) situated over the median nerve reduced the increases in blood pressure from 34 +/- 3 to 18 +/- 5 mmHg for a period of time that lasted for 60 min or more. Unilateral inactivation of neuronal activity in the vlPAG with 50-75 nl of kainic acid (KA, 1 mM) restored the blood pressure responses from 18 +/- 3 to 36 +/- 5 mmHg during BK-induced gallbladder stimulation, an effect that lasted for 30 min. In the absence of EA, unilateral microinjection of the excitatory amino acid dl-homocysteic acid (DLH, 4 nM) in the vlPAG mimicked the effect of EA and reduced the reflex blood pressure responses from 35 +/- 6 to 14 +/- 5 mmHg. Responses of 21 cardiovascular sympathoexcitatory rVLM neurons, including 12 that were identified as premotor neurons, paralleled the cardiovascular responses. Thus splanchnic nerve-evoked neuronal discharge of 32 +/- 4 spikes/30 stimuli in six neurons was reduced to 10 +/- 2 spikes/30 stimuli by EA, which was restored rapidly to 28 +/- 4 spikes/30 stimuli by unilateral injection of 50 nl KA into the vlPAG. Conversely, 50 nl of DLH in the vlPAG reduced the number of action potentials of 5 rVLM neurons from 30 +/- 4 to 18 +/- 4 spikes/30 stimuli. We conclude that the inhibitory influence of EA involves vlPAG stimulation, which, in turn, inhibits rVLM neurons in the EA-related attenuation of the cardiovascular excitatory response during visceral afferent stimulation.     

Effect of electroacupuncture on pressor reflex during gastric distension

The effect of electroacupuncture (EA) on the reflex cardiovascular response induced by mechanical distension of the stomach was studied in ventilated male Sprague-Dawley rats anesthetized by ketamine and alpha-chloralose. Repeated balloon inflation of the stomach to produce 20 mmHg tension on the gastric wall induced a consistent rise in mean arterial pressure, while heart rate (372 +/- 22 beats/min) was unchanged. This response was reversed by transection of the splanchnic nerves. Bilateral application of EA (1-2 mA, 2 Hz) at Neiguan-Jianshi acupoints (pericardial meridian, Pe 5-6) over the median nerve for 30 min significantly decreased the pressor response from 33 +/- 6 to 18 +/- 4 mmHg (n = 7, P < 0.05). This effect began after 10 min of EA and continued for 40 min after termination of EA. EA at Zusanli-Shangquxu acupoints (stomach meridian, St 36-37) over the deep peroneal nerve similarly inhibited the pressor response. The effect lasted for 10 min after EA was stopped (n = 6, P < 0.05), while EA at Guangming-Xuanzhong acupoints (gallbladder meridian, GB 37-39) over the superficial peroneal nerve did not inhibit the pressor response. Naloxone injected intravenously (n = 6) immediately after termination of EA or administered by microinjection into the rostral ventrolateral medulla (rVLM) 25 min after initiation of EA (n = 6) reversed the inhibition by EA, suggesting an opiate mechanism, including the rVLM, was involved.     

Role of glutamate in the rostral ventrolateral medulla in acupuncture-related modulation of visceral reflex sympathoexcitation

Visceral sympathoexcitatory reflexes induced by stimulation of the gallbladder with bradykinin (BK) are attenuated by electroacupuncture (EA) at Neiguan-Jianshi (P5-6) acupoints located over the median nerve. Previous studies have shown that neurons in the rostral ventrolateral medulla (rVLM) receive convergent input from visceral organs and somatic nerves (activated by EA). Glutamate (Glu), an important excitatory neurotransmitter in the rVLM, processes visceral sympathoexcitatory cardiovascular reflexes. In the present study, we determined the relation between EA-mediated opioidergic modulation of visceral cardiovascular responses and Glu. Reflex cardiovascular responses were evoked by application of BK to the gallbladder before and after EA in anesthetized cats. Glu concentrations ([Glu]) were measured by HPLC from samples collected by microdialysis probe(s) inserted unilaterally or bilaterally into the rVLM. BK-induced reflex responses and [Glu] were attenuated by 45% and 70%, respectively, after 30 min of EA (n = 6). EA alone did not change [Glu] in the rVLM (n = 6, P > 0.05). However, microdialysis of naloxone (100 mM) into the rVLM reversed EA-related inhibition of blood pressure and [Glu] (n = 5). Immunohistochemical visualization showed that delta-opioid receptors colocalized with, and were in close apposition to, vesicular Glu transporter 3- and c-Fos-double-labeled perikarya and processes of rVLM neurons after gallbladder stimulation with BK. These data suggest that EA attenuates BK-induced visceral sympathoexcitatory reflexes through opioid-mediated inhibition of Glu's action in the rVLM.     

Central and peripheral mechanisms underlying gastric distention inhibitory reflex responses in hypercapnic-acidotic rats

We have observed that in chloralose-anesthetized animals, gastric distension (GD) typically increases blood pressure (BP) under normoxic normocapnic conditions. However, we recently noted repeatable decreases in BP and heart rate (HR) in hypercapnic-acidotic rats in response to GD. The neural pathways, central processing, and autonomic effector mechanisms involved in this cardiovascular reflex response are unknown. We hypothesized that GD-induced decrease in BP and HR reflex responses are mediated during both withdrawal of sympathetic tone and increased parasympathetic activity, involving the rostral (rVLM) and caudal ventrolateral medulla (cVLM) and the nucleus ambiguus (NA). Rats anesthetized with ketamine and xylazine or α-chloralose were ventilated and monitored for HR and BP changes. The extent of cardiovascular inhibition was related to the extent of hypercapnia and acidosis. Repeated GD with both anesthetics induced consistent falls in BP and HR. The hemodynamic inhibitory response was reduced after blockade of the celiac ganglia or the intraabdominal vagal nerves with lidocaine, suggesting that the decreased BP and HR responses were mediated by both sympathetic and parasympathetic afferents. Blockade of the NA decreased the bradycardia response. Microinjection of kainic acid into the cVLM reduced the inhibitory BP response, whereas depolarization blockade of the rVLM decreased both BP and HR inhibitory responses. Blockade of GABA(A) receptors in the rVLM also reduced the BP and HR reflex responses. Atropine methyl bromide completely blocked the reflex bradycardia, and atenolol blocked the negative chronotropic response. Finally, α(1)-adrenergic blockade with prazosin reversed the depressor. Thus, in the setting of hypercapnic-acidosis, a sympathoinhibitory cardiovascular response is mediated, in part, by splanchnic nerves and is processed through the rVLM and cVLM. Additionally, a vagal excitatory reflex, which involves the NA, facilitates the GD-induced decreases in BP and HR responses. Efferent chronotropic responses involve both increased parasympathetic and reduced sympathetic activity, whereas the decrease in BP is mediated by reduced α-adrenergic tone.     

Medullary substrate and differential cardiovascular responses during stimulation of specific acupoints

Electroacupuncture (EA) at P5-P6 acupoints overlying the median nerve reduces premotor sympathetic cardiovascular neuronal activity in the rostral ventral lateral medulla (rVLM) and visceral reflex pressor responses. In previous studies, we have noted different durations of influence of EA comparing P5-P6 and S36-S37 acupoints, suggesting that point specificity may exist. The purpose of this study was to evaluate the influence of stimulating P5-P6 (overlying the median nerve), LI4-L7 (overlying branches of the median nerve and the superficial radial nerve), LI6-LI7 (overlying the superficial radial nerve), LI10-LI11 (overlying the deep radial nerves), S36-S37 (overlying the deep peroneal nerves), or K1-B67 (overlying terminal branches of the tibial nerves) specific acupoints, overlying deep and superficial somatic nerves, on the excitatory cardiovascular reflex and rVLM responses evoked by stimulation of chemosensitive receptors in the cat's gallbladder with bradykinin (BK) or direct splanchnic nerve (SN) stimulation. We observed point-specific differences in magnitude and duration of EA inhibition between P5-P6 or LI10-LI11 and LI4-L7 or S36-S37 in responses to 30-min stimulation with low-frequency, low-current EA. EA at LI6-LI7 and K1-B67 acupoints as well as direct stimulation of the superficial radial nerve did not cause any cardiovascular or rVLM neuronal effects. Cardiovascular neurons in the rVLM, a subset of which were classified as premotor sympathetic cells, responded to brief (30 s) stimulation of the SN as well as acupoints P5-P6, LI10-LI11, LI4-L7, S36-S37, LI6-LI7, or K1-B67, or underlying somatic pathways in a fashion similar to the reflex responses. In fact, we observed a significant linear relationship (r(2) = 0.71) between the evoked rVLM response and reflex change in mean arterial blood pressure. In addition, EA stimulation at P5-P6 and LI4-L7 decreased rVLM neuronal activity by 41 and 12%, respectively, for >1 h, demonstrating that prolonged input into the medulla during stimulation of somatic nerves, depending on the degree of convergence, leads to more or less inhibition of activity of these cardiovascular neurons. Thus EA at acupoints overlying deep and superficial somatic nerves leads to point-specific effects on cardiovascular reflex responses. In a similar manner, sympathetic cardiovascular rVLM neurons that respond to both visceral (reflex) and somatic (EA) nerve stimulation manifest graded responses during stimulation of specific acupoints, suggesting that this medullary region plays a role in site-specific inhibition of cardiovascular reflex responses by acupuncture.     

安定降低家兔血压和减少刺激下丘脑诱发室性期前收缩的机制分析

家兔62只,用乌拉坦(700mg/kg)和氯醛醣(35mg/kg)静脉麻醉,三碘季铵酚制动,在人工呼吸下进行实验。用电刺激下丘脑近中线区的方法诱发室性期前收缩(HVE)。静脉注射安定(0.5mg/kg)可降低基础血压(BP),减弱刺激下丘脑引起升压反应(指收缩压峰值SBP_(max))和减少HVE。在双侧延髓腹外侧头端区(rVLM)微量注射氟安定(200μg溶于0.5μl中),γ-氨基丁酸(GABA)(6μg溶于0.5μl中)均能降低BP、SBP_(max)和减少HVE,若微量注射印防己毒素(7.5μg溶于0.5μl中)则可使BP上升并增多HVE。而于双侧延髓腹外侧尾端区(cVLM)微量注射同样剂量氟安定、GABA则无上述反应。安定降低BP、SBP_(max)和减少HVE的作用可被双侧rVLM区微量注射GABA受体拮抗剂荷包牡丹碱(3μg溶于0.5μl中)或印防己毒素所消除,但在双侧rVLM区微量注射甘氨酸受体拮抗剂士的宁(1μg溶于0.5μl中)、阿片受体拮抗剂纳洛酮(0.5μg溶于0.5μl中)、胆碱能阻断药阿托品(0.25μg溶于0.5μl中)、东莨菪碱(1.5μg溶于0.5μl中)后仍然存在。 上述结果提示,在双侧rVLM应用GABA受体拮抗剂可消除安定降低BP、SBP_(max)和减少HVE的作用,安定降低BP、SBP_(max)和减少HVE的作用可能通过GABA这一中间环节,而胆碱能受体、阿片受体、甘氨酸受体可能不起重要作用。     

Modulation of cardiovascular excitatory responses in rats by transcutaneous magnetic stimulation: role of the spinal cord.

This study investigated the efficacy of magnetic stimulation on the reflex cardiovascular responses induced by gastric distension in anesthetized rats and compared these responses to those influenced by electroacupuncture (EA). Unilateral magnetic stimulation (30% intensity, 2 Hz) at the Jianshi-Neiguan acupoints (pericardial meridian, P 5-6) overlying the median nerve on the forelimb for 24 min significantly decreased the reflex pressor response by 32%. This effect was noticeable by 20 min of magnetic stimulation and continued for 24 min. Median nerve denervation abolished the inhibitory effect of magnetic stimulation, indicating the importance of somatic afferent input. Unilateral EA (0.3-0.5 mA, 2 Hz) at P 5-6 using similar durations of stimulation similarly inhibited the response (35%). The inhibitory effects of EA occurred earlier and were marginally longer (20 min) than magnetic stimulation. Magnetic stimulation at Guangming-Xuanzhong acupoints (gallbladder meridian, GB 37-39) overlying the superficial peroneal nerve on the hindlimb did not attenuate the reflex. Intravenous naloxone immediately after termination of magnetic stimulation reversed inhibition of the cardiovascular reflex, suggesting involvement of the opioid system. Also, intrathecal injection of delta- and kappa-opioid receptors antagonists, ICI174,864 (n=7) and nor-binaltorphimine (n=6) immediately after termination of magnetic stimulation reversed inhibition of the cardiovascular reflex. In contrast, the mu-opioid antagonist CTOP (n=7) failed to alter the cardiovascular reflex. The endogenous neurotransmitters for delta- and kappa-opioid receptors, enkephalins and dynorphin but not beta-endorphin, therefore appear to play significant roles in the spinal cord in mediating magnetic stimulation-induced modulation of cardiovascular reflex responses.     

Role of glutamate in a visceral sympathoexcitatory reflex in rostral ventrolateral medulla of cats

The rostral ventrolateral medulla (rVLM) is involved in processing visceral sympathetic reflexes. However, there is little information on specific neurotransmitters in this brain stem region involved in this reflex. The present study investigated the importance of glutamate and glutamatergic receptors in the rVLM during gallbladder stimulation with bradykinin (BK), because glutamate is thought to function as an excitatory neurotransmitter in this region. Stimulation of visceral afferents activated glutamatergic neurons in the rVLM, as noted by double-labeling with c-Fos and the cellular vesicular glutamate transporter 3 (VGLUT3). Visceral reflex activation significantly increased arterial blood pressure as well as extracellular glutamate concentrations in the rVLM as determined by microdialysis. Barodenervation did not alter the release of glutamate in the rVLM evoked by visceral reflex stimulation. Iontophoresis of glutamate into the rVLM enhanced the activity of sympathetic premotor cardiovascular rVLM neurons. Also, the responses of these neurons to visceral afferent stimulation with BK were attenuated significantly (70%) by blockade of glutamatergic receptors with kynurenic acid. Microinjection of either an N-methyl-D-aspartate (NMDA) receptor antagonist 2-amino-5-phosphonopentanate (25 mM, 30 nl) or an dl-alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA) receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (2 mM, 30 nl) into the rVLM significantly attenuated the visceral sympathoexcitatory reflex responses. These results suggest that glutamate in the rVLM serves as an excitatory neurotransmitter through a baroreflex-independent mechanism and that both NMDA and AMPA receptors mediate the visceral sympathoexcitatory reflex responses.     

Modulation of cardiopulmonary depressor reflex in nucleus ambiguus by electroacupuncture: roles of opioids and γ-aminobutyric acid

Stimulation of cardiopulmonary receptors with phenylbiguanide (PBG) elicits depressor cardiovascular reflex responses, including decreases in blood pressure and heart rate mediated in part by the brain stem parasympathetic cardiac neurons in the nucleus ambiguus (NAmb). The present study examined NAmb neurotransmitter mechanisms underlying the influence of electroacupuncture (EA) on the PBG-induced hypotension and bradycardia. We hypothesized that somatic stimulation during EA modulates PBG responses through opioid and γ-aminobutyric acid (GABA) modulation in the NAmb. Anesthetized and ventilated cats were studied during repeated stimulation with PBG or cardiac vagal afferents while low-frequency EA (2 Hz) was applied at P5-6 acupoints overlying the median nerve for 30 min and NAmb neuronal activity, heart rate, and blood pressure were recorded. Microinjection of kainic acid into the NAmb attenuated the PBG-induced bradycardia from -60 ± 11 to -36 ± 11 beats/min. Likewise, EA reduced the PBG-induced depressor and bradycardia reflex by 52 and 61%, respectively. Cardiac vagal afferent evoked preganglionic cellular activity in the NAmb was reduced by EA for about 60 min. Blockade of opioid or GABA(A) receptors using naloxone and gabazine reversed the EA-related modulation of the evoked cardiac vagal activity by 73 and 53%, respectively. Similarly, naloxone and gabazine reversed EA modulation of the negative chronotropic responses from -11 ± 5 to -23 ± 6 and -13 ± 4 to -24 ± 3 beats/min, respectively. Thus EA at P5-6 decreases PBG evoked hypotension and bradycardia as well as the NAmb PBG-sensitive preganglionic cardiac vagal outflow through opioid and GABA neurotransmitter systems.     

阿片受体在大鼠丘脑中央下核和顶盖前区前核介导电针镇痛中的不同作用

本文旨在研究阿片受体是否参与丘脑中央下核(nucleus submedius,Sm)和顶盖前区前核(anterior pretectal nucleus,APtN)所介导的不同强度电针的镇痛作用。以辐射热诱发甩尾(tail flick,TF)反射潜伏期为伤害性反应的指标,观察了Sm和APtN微量注射阿片受体拮抗剂纳洛酮对不同强度电针“足三里”穴(St．36)抑制大鼠TF反射的效应。结果表明,Sm给予纳洛酮(1．0μg,0．5μl)阻断强电针(5mA)对TF反射的抑制效应,而对弱电针(0．5mA)的效应无明显影响;相反,APtN给予纳洛酮阻断弱电针对TF反射的抑制效应,而对强电针的效应无明显影响;纳洛酮供给到Sm或APtN邻近其它脑区对强、弱电针的效应均无影响。这些结果提示,Sm内的阿片受体参与介导强电针兴奋细传入纤维(A-δ和C类)产生的镇痛,而APtN内的阿片受体则介导弱电针兴奋粗传入纤维(A-β类)产生的镇痛。     

GABA-mediated neurotransmission in the ventrolateral NTS plays a role in respiratory regulation in the rat

Our purpose was to determine whether endogenously released GABA in the ventrolateral nucleus of the solitary tract (vlNTS) of the rat influences respiration. Experiments were carried out in anesthetized, vagotomized and spontaneously breathing rats, and diaphragm electromyogram activity was measured while drugs affecting GABAergic neurotransmission were microinjected into the vlNTS and medial NTS (mNTS). Bilateral microinjection of nipecotic acid, 5 or 25 nmol, into the vlNTS (but not in the mNTS) produced dose-dependent increases in inspiratory duration (Ti) frequently culminating in apneustic breathing. Neither unilateral microinjection of bicuculline nor CGP-35348 (GABA(B) receptor antagonist) reversed this response; however, a combination of both GABA receptor antagonists effectively reversed apneustic breathing. Bilateral microinjection of either muscimol or baclofen into the vlNTS mimicked the effect of nipecotic acid. Microinjection of the bicuculline produced apnea, whereas microinjection of CGP-35348 produced a decrease in Ti and an increase in expiratory duration. Immunohistochemical analysis of the vlNTS region revealed GABA(A) receptors densely localized to processes, whereas GABA(B) immunoreactivity was localized to cell bodies. Our data indicate that GABA activity in the vlNTS is important for respiratory function.     

Rostral ventral medulla 5-HT1A receptors selectively inhibit the somatosympathetic reflex

The role of the 5-hydroxytryptamine (5-HT1A) receptors in the rostral ventrolateral medulla (RVLM) on somatosympathetic, baroreceptor, and chemoreceptor reflexes was examined in anesthetized rats. Microinjection of the selective 5-HT1A agonist 8-hydroxy-di-n-propylamino tetralin (8-OH-DPAT) decreased arterial blood pressure and splanchnic sympathetic nerve activity (SNA). Electrical stimulation of the hindlimb evoked early and late excitatory sympathetic responses. Bilateral microinjection in the RVLM of 8-OH-DPAT markedly attenuated both the early and late responses. This potent inhibition of the somatosympathetic reflex persisted even after SNA and arterial blood pressure returned to preinjection levels. Preinjection of the selective 5-HT1A antagonist NAN-190 in the RVLM blocked the sympathoinhibitory effect of 8-OH-DPAT and attenuated the inhibitory effect on the somatosympathetic reflex. 8-OH-DPAT injected in the RVLM did not affect baroreceptor or chemoreceptor reflexes. Our findings suggest that activation of 5-HT1A receptors in the RVLM exerts a potent, selective inhibition on the somatosympathetic reflex.     

延髓头端腹外侧区血管升压素能机制在应激性高血粘度中的作用

观察延髓头端腹外侧区（ｒＶＬＭ）微量注射血管升压素（ＡＶＰ）能否影响正常大鼠的血压和血粘度,并分析ｒＶＬＭ内ＡＶＰ能机制在清醒大鼠经悬吊加束缚引起应激性升压反应和高血粘度中的影响。结果如下：⑴正常大鼠双侧ｒＶＬＭ微量注射ＡＶＰ（每侧０．５μｇ／０．５μｌ）,可引起血压和血粘度升高;此作用可被事先在同一位置微量注射ＡＶＰ－Ｖ１受体拮抗剂ｄ（ＣＨ２）５「Ｔｙｒ（Ｍｅ）＾２」ＡＶＰ（每侧０．１μｇ／０．     

Angiotensin II in dorsomedial hypothalamus modulates cardiovascular arousal caused by stress but not feeding in rabbits

The dorsomedial hypothalamus (DMH) is critically implicated in the cardiovascular response to emotional stress. This study aimed to determine whether the DMH is also important in cardiovascular arousal associated with appetitive feeding behavior and, if so, whether locally released angiotensin II and glutamate are important in this arousal. Emotional (air-jet) stress and feeding elicited similar tachycardic (+51 and +45 beats/min, respectively) and pressor (+16 and +9 mmHg, respectively) responses in conscious rabbits. Bilateral microinjection of GABA(A) agonist muscimol (500 pmol) into the DMH, but not nearby hypothalamic regions, attenuated pressor and tachycardic responses to air-jet by 56-63% and evoked anorexia. Conversely, stimulation of the DMH with the glutamate analog kainic acid (250 pmol) elicited hypertension (+25 mmHg) and tachycardia (+114 beats/min) and activated feeding behavior. Local microinjection of a glutamate receptor antagonist, kynurenic acid (10 nmol), decreased pressor responses to stress and eating by 46 and 72%, respectively, without affecting feeding behavior. Bilateral microinjection of a selective AT(1)-receptor antagonist, candesartan (500 pmol), into the DMH, but not nearby sites, attenuated pressor and tachycardic stress responses by 31 and 33%, respectively. Candesartan did not alter feeding behavior or circulatory response to feeding. These results indicate that, in addition to its role in mediating stress responses, the DMH may be important in regulating cardiovascular arousal associated with feeding. Local glutamatergic inputs appear to regulate cardiovascular response to both stress and feeding. Conversely, angiotensin II, acting via AT1 receptors, may selectively modulate, in the DMH, cardiovascular response to stress, but not feeding.     

Sympathoinhibitory pathway from caudal midline medulla to RVLM is independent of baroreceptor reflex pathway

Glutamate stimulation of the caudal midline medulla (CMM) causes profound sympathoinhibition due to GABAergic inhibition of presympathetic neurons in the rostral ventrolateral medulla (RVLM). We investigated whether the sympathoinhibitory pathway from CMM to RVLM, like the central baroreceptor reflex pathway, includes a glutamatergic synapse in the caudal ventrolateral medulla (CVLM). In pentobarbital sodium-anesthetized rats, the RVLM on one side was inhibited by a muscimol microinjection. Then the response evoked by glutamate microinjections into the CMM or by baroreceptor stimulation was determined before and after 1) microinjection of the GABA receptor antagonist bicuculline into the RVLM on the other side or 2) microinjections of the glutamate receptor antagonist kynurenate bilaterally into the CVLM. Bicuculline in the RVLM greatly reduced both CMM- and baroreceptor-evoked sympathoinhibition. Compared with the effect of vehicle solution, kynurenate in the CVLM greatly reduced baroreceptor-evoked sympathoinhibition, whereas its effect on CMM-evoked sympathoinhibition was not different from that of the vehicle solution. These findings indicate that the output pathway from CMM sympathoinhibitory neurons, unlike the baroreceptor and other reflex sympathoinhibitory pathways, does not include a glutamatergic synapse in the CVLM.     

Afferent mechanisms underlying stimulation modality-related modulation of acupuncture-related cardiovascular responses.

Despite the use of acupuncture to treat a number of heart diseases, little is known about the mechanisms that underlie its actions. Therefore, we examined the influence of acupuncture on sympathoexcitatory cardiovascular responses to gastric distension in anesthetized Sprague-Dawley rats. Thirty minutes of low-current, low-frequency, (0.3-0.5 mA, 2 Hz) electroacupuncture (EA), at P 5-6, S 36-37, and H 6-7 overlying the median, deep peroneal, and ulnar nerves significantly decreased reflex pressor responses by 40, 39, and 44%, respectively. In contrast, sham acupuncture involving needle insertion without stimulation at P 5-6 or 30 min of EA at LI 6-7 acupoints overlying the superficial radial nerve did not attenuate the reflex. Similarly, EA at P 5-6 using 40- or 100-Hz stimulation frequencies did not inhibit the reflex. Compared with EA at P 5-6, EA at two sets of acupoints, including P 5-6 and S 36-37, did not lead to larger inhibition of the reflex. Two minutes of manual acupuncture (MA; 2 Hz) at P 5-6 every 10 min for 30 min inhibited the reflex cardiovascular pressor response by 33%, a value not significantly different from 2-Hz EA at P 5-6. Single-unit afferent activity was not different between electrical stimulation (ES) and manual stimulation. However, 2-Hz ES activated more somatic afferents than 10- or 20-Hz ES. These data suggest that, although the location of acupoint stimulation and the frequency of stimulation determine the extent of influence of EA, there is little difference between low-frequency EA and MA at P 5-6. Furthermore, simultaneous stimulation using two acupoints that independently exert strong effects did not lead to an additive or a facilitative interaction. The similarity of the responses to EA and MA and the lack of cardiovascular response to high-frequency EA appear to be largely a function of somatic afferent responses.     

头端延髓腹外侧区注射5—羟色胺对应激性高血粘度...

Experiments were carried out on 62 wistar rats. The hyperviscosity and elevation of blood pressure were induced by hanging and restraining the rats with their four limbs tied on a frame. It was found that microinjection of 5-HT (25 micrograms/10 microliters) into the 4th ventricle of the brain or bilateral microinjection of 5-HT (4 micrograms/0.5 microliters/site) into rostral ventrolateral medulla (rVLM) reduced stress-induced hyperviscosity (p < 0.01) and elevation of blood pressure (p < 0.01). The effect of 5-HT injected into the 4th ventricle or rVLM was blocked by bilateral microinjection of cinanserine (4 micrograms/0.5 microliter/site) into rVLM. These results suggest that microinjection of 5-HT into 4th ventricle and rVLM could reduce stress-induced hyperviscosity and elevation of blood pressure and these effects were probably mediated via 5-HT receptors in the rVLM.     

Brain stem mechanisms underlying acupuncture modality-related modulation of cardiovascular responses in rats.

The present study was designed to investigate brain stem responses to manual acupuncture (MA) and electroacupuncture (EA) at different frequencies at pericardial P (5-6) acupoints located over the median nerve. Activity of premotor sympathetic cardiovascular neurons in the rostral ventral lateral medulla (rVLM) was recorded during stimulation of visceral and somatic afferents in ventilated anesthetized rats. We stimulated either the splanchnic nerve at 2 Hz (0.1-0.4 mA, 0.5 ms) or the median nerve for 30 s at 2, 10, 20, 40, or 100 Hz using EA (0.3-0.5 mA, 0.5 ms) or at approximately 2 Hz with MA. Twelve of 18 cells responsive to splanchnic and median nerve stimulation could be antidromically driven from the intermediolateral columns of the thoracic spinal cord, T2-T4, indicating that they were premotor sympathetic neurons. All 18 neurons received baroreceptor input, providing evidence of their cardiovascular sympathoexcitatory function. Evoked responses during stimulation of the splanchnic nerve were inhibited by 49 +/- 6% (n = 7) with EA and by 46 +/- 4% (n = 6) with MA, indicating that the extent of inhibitory effects of the two modalities were similar. Inhibition lasted for 20 min after termination of EA or MA. Cardiovascular premotor rVLM neurons responded to 2-Hz electrical stimulation at P 5-6 and to a lesser extent to 10-, 20-, 40-, and 100-Hz stimulation (53 +/- 10, 16 +/- 2, 8 +/- 2, 2 +/- 1, and 0 +/- 0 impulses/30 stimulations, n = 7). These results indicate that rVLM premotor sympathetic cardiovascular neurons that receive convergent input from the splanchnic and median nerves during low-frequency EA and MA are inhibited similarly for prolonged periods by low-frequency MA and EA.