A hypothalamomedullary network for physiological responses to environmental stresses.

Various environmental stressors, such as extreme temperatures (hot and cold), pathogens, predators and insufficient food, can threaten life. Remarkable progress has recently been made in understanding the central circuit mechanisms of physiological responses to such stressors. A hypothalamomedullary neural pathway from the dorsomedial hypothalamus (DMH) to the rostral medullary raphe region (rMR) regulates sympathetic outflows to effector organs for homeostasis. Thermal and infection stress inputs to the preoptic area dynamically alter the DMH → rMR transmission to elicit thermoregulatory, febrile and cardiovascular responses. Psychological stress signalling from a ventromedial prefrontal cortical area to the DMH drives sympathetic and behavioural responses for stress coping, representing a psychosomatic connection from the corticolimbic emotion circuit to the autonomic and somatic motor systems. Under starvation stress, medullary reticular neurons activated by hunger signalling from the hypothalamus suppress thermogenic drive from the rMR for energy saving and prime mastication to promote food intake. This Perspective presents a combined neural network for environmental stress responses, providing insights into the central circuit mechanism for the integrative regulation of systemic organs.

The retrotrapezoid nucleus and the neuromodulation of breathing.

Breathing is regulated by a host of arousal and sleep-wake state-dependent neuromodulators to maintain respiratory homeostasis. Modulators such as acetylcholine, norepinephrine, histamine, serotonin (5-HT), adenosine triphosphate (ATP), substance P, somatostatin, bombesin, orexin, and leptin can serve complementary or off-setting functions depending on the target cell type and signaling mechanisms engaged. Abnormalities in any of these modulatory mechanisms can destabilize breathing, suggesting that modulatory mechanisms are not overly redundant but rather work in concert to maintain stable respiratory output. The present review focuses on the modulation of a specific cluster of neurons located in the ventral medullary surface, named retrotrapezoid nucleus, that are activated by changes in tissue CO2/H+ and regulate several aspects of breathing, including inspiration and active expiration.

Functional organization and connectivity of the dorsal column nuclei complex reveals a sensorimotor integration and distribution hub.

The dorsal column nuclei complex (DCN-complex) includes the dorsal column nuclei (DCN, referring to the gracile and cuneate nuclei collectively), external cuneate, X, and Z nuclei, and the median accessory nucleus. The DCN are organized by both somatotopy and modality, and have a diverse range of afferent inputs and projection targets. The functional organization and connectivity of the DCN implicate them in a variety of sensorimotor functions, beyond their commonly accepted role in processing and transmitting somatosensory information to the thalamus, yet this is largely underappreciated in the literature. To consolidate insights into their sensorimotor functions, this review examines the morphology, organization, and connectivity of the DCN and their associated nuclei. First, we briefly discuss the receptors, afferent fibers, and pathways involved in conveying tactile and proprioceptive information to the DCN. Next, we review the modality and somatotopic arrangements of the remaining constituents of the DCN-complex. Finally, we examine and discuss the functional implications of the myriad of DCN-complex projection targets throughout the diencephalon, midbrain, and hindbrain, in addition to their modulatory inputs from the cortex. The organization and connectivity of the DCN-complex suggest that these nuclei should be considered a complex integration and distribution hub for sensorimotor information.

Proprioceptive thalamus receiving forelimb and neck muscle spindle inputs via the external cuneate nucleus in the rat.

Proprioceptive signals from body muscles have historically been considered to project to the rostrodorsal shell of the ventrobasal thalamic complex [the ventral posterolateral nucleus (VPL) and ventral posteromedial nucleus (VPM)]. However, we have recently found that proprioception from rat jaw-closing muscle spindles (JCMSs) is conveyed via the supratrigeminal nucleus to the caudo-ventromedial edge of the VPM, but not to the rostrodorsal shell of the VPM. Therefore, proprioception from other body muscles may also project to thalamic regions other than the rostrodorsal shell of the VPL. We thus examined the thalamic projection from the rat external cuneate nucleus (ECu), which receives proprioceptive inputs from forelimb and neck muscles. After injection of anterograde tracer into the ECu, axon terminals were contralaterally labeled in the ventromedial part (VPLvm) of the VPL, but not in the rostrodorsal shell of the VPL. After anterograde tracer injection into the cuneate nucleus (Cu), axon terminals were widely labeled in the contralateral VPL including the VPLvm. In the VPLvm, we electrophysiologically confirmed the proprioceptive inputs responsive to electrical stimulation of the ECu or median nerve and to the pressure of forelimb/neck muscles or wrist flexion. After retrograde tracer injection into the VPLvm, neurons were contralaterally labeled in the ECu and Cu. After retrograde tracer injection into the VPL where no such proprioceptive inputs were recorded, no ECu neurons were labeled. These findings indicate that proprioception from forelimb/neck muscle spindles and JCMSs is somatotopically transmitted to the ventromedial floor of the ventrobasal thalamic complex, but not to its rostrodorsal shell.

Direct evidence of bradycardic effect of omega-3 fatty acids acting on nucleus ambiguus.

Docosahexaenoic acid (DHA) an omega-3 polyunsaturated fatty acid, is an agonist of FFA1 receptor. DHA administration reduces the heart rate via unclear mechanisms. We examined the effect of DHA on neurons of nucleus ambiguus that provide the parasympathetic control of heart rate. DHA produced a dose-dependent increase in cytosolic Ca2+ concentration in cardiac-projecting nucleus ambiguus neurons; the effect was prevented by GW1100, a FFA1 receptor antagonist. DHA depolarized cultured nucleus ambiguus neurons via FFA1 activation. Bilateral microinjection of DHA into nucleus ambiguus produced bradycardia in conscious rats. Our results indicate that DHA decreases heart rate by activation of FFA1 receptor on cardiac-projecting nucleus ambiguus neurons.

Peroxisome proliferator-activated receptor-γ mediates the antihypertensive effects of acupuncture in spontaneously hypertensive rats.

We investigated a central antihypertensive effect of acupuncture in rostral ventrolateral medulla (RVLM) in spontaneously hypertensive rats (SHRs). In total, 56 rats were randomly divided into seven groups as follows: the SHR group, SHR+acupuncture (SHR+Acu) group, SHR+nonacupuncture (SHR+Non-acu) group, GW9662+acupuncture (GW9662+Acu) group, GW9662+GW1929 group, GW9662 group, and 2% DMSO group (n = 8 per group). The whole eight Wistar-Kyoto rats were assigned to the WKY group. The acupuncture treatment lasting for 14 days was performed at the Taichong acupoint (LR3) or at a nonacupoint (non-acu) once daily. The peroxisome proliferator-activated receptor (PPAR)-γ agonist GW1929 and the PPAR-γ inhibitor GW9662 were microinjected by the brain stereotactic technique. Blood pressure was measured by the tail-cuff method. Sympathetic vasomotor activity was determined by implanting in a telemetry electrocardiogram radio transmitter. The expression of PPARs in the RVLM of the rats was detected using Western blot. We demonstrated that acupuncture attenuated blood pressure, heart rate, and sympathetic vasomotor activity in SHRs. The protein expression of PPAR-γ was significantly increased in SHRs treated with acupuncture. The antihypertensive effects of acupuncture in SHRs were abrogated by microinjection bilaterally into RVLM of GW9662. Microinjection of GW1929 mimicked the antihypertensive effect of acupuncture. PPAR-γ expression was negatively correlated with blood pressure and sympathetic vasomotor activity in SHRs treated with acupuncture. These results suggested that acupuncture promoted a central antihypertensive effect by increasing the expression of PPAR-γ in RVLM of SHRs.

Effect of thermal preconditioning on Hsp70 expression in the medulla oblongata and on hemodynamics during passive hyperthermia.

A short-term episode of elevated core body temperature that induces Hsp70 expression (thermal preconditioning) may protect against heatstroke during subsequent hyperthermia. The protective effects of thermal preconditioning may involve several cellular and immunological mechanisms and improvements in baroreflex sensitivity. To substantiate the hypothesis that the protective effect of thermal preconditioning also occurs in conditions with intact thermoregulation, we examined the evolution of spontaneous cardiovagal baroreflex sensitivity and the protective effect of Hsp70 expression after thermal preconditioning in nonanesthetized Wistar-Kyoto rats with implanted telemetric transmitters. In the baroreflex centers of the medulla oblongata, thermal preconditioning induced Hsp70 in perineuronal and perivascular oligodendrocytes, microglia, and endothelial cells but not in neurons. The maximal Hsp70 expression was detected 4 h after preconditioning, but a significant number of Hsp70-positive cells was still present 72 h after preconditioning. Increased c-Fos expression in the neurons of baroreflex centers was detectable only 4 h after preconditioning. The mean values of cardiovagal baroreflex sensitivity did not show significant differences during the 72-hour follow-up period after thermal preconditioning. Similarly, cardiovascular variability measures of the autonomic nervous system activity were also not significantly affected by thermal preconditioning. During passive hyperthermia, thermal preconditioning had no statistically significant effect on thermoregulation and the onset of arterial pressure decline. Our data suggest that thermal preconditioning induces a glial type of Hsp70 expression in the baroreflex centers of the medulla oblongata. However, this response was not associated with cardiovagal baroreflex sensitization and protection against hemodynamic instability during passive hyperthermia.

Treatment of Medial Medullary Infarction Using a Novel iNems Training: A Case Report and Literature Review.

Objective. We describe the case of a 66-year-old Japanese male patient who developed medial medullary infarction along with severe motor paralysis and intense numbness of the left arm, pain catastrophizing, and abnormal physical sensation. We further describe his recovery using a new imagery neurofeedback-based multisensory systems (iNems) training method. Clinical Course and Intervention. The patient underwent physical therapy for the rehabilitation of motor paralysis and numbness of the paralyzed upper limbs; in addition, we implemented iNems training using EEG activity, which aims to synchronize movement intent (motor imagery) with sensory information (feedback visual information). Results. Considerable improvement in motor function, pain catastrophizing, representation of the body in the brain, and abnormal physical sensations was accomplished with iNems training. Furthermore, iNems training improved the neural activity of the default mode network at rest and the sensorimotor region when the movement was intended. Conclusions. The newly developed iNems could prove a novel, useful tool for neurorehabilitation considering that both behavioral and neurophysiological changes were observed in our case.

Effect of electro-acupuncture on regulating the swallowing by activating the interneuron in ventrolateral medulla (VLM).

Ventrolateral medulla(VLM) was one of the essential part of central pattern generator(CPG) in swallowing and electro-acupuncture(EA) was an important intervention in swallowing disorder. But the effect and mechanism of EA at acupoints on swallowing were unknown. The present aim to detect the effect of EA at Lianquan (CV23) on swallowing and swallowing-related(SR) interneuron in VLM. Thirty-six Sprague-Dawley rats were operated and the swallowing reflex was induced through Double distilled water (DDW) infusion. Simultaneously, the numbers of swallowing were recorded. Then EA was given at Lianquan and Neiguan (PC6) and the neuron discharges in VLM were detected. A total of 72 neurons were recorded, 60 of which were correctly recorded after histology identification. Two types of SR neurons were found and the numbers of swallowing increased after EA at CV23 and PC6 compared with no EA group. The neuron response rates were 78.3% and 50% for EA at CV23 and PC6 respectively with significant difference (P < 0.05). Meanwhile, the neuron spike patterns were changed after EA at CV23 and PC6. In addition, twenty-four rats were used for immunofluorescence after EA at CV23 and PC6. The results showed that c-fos positive cells in CV23 group were 20.63±2.35, while PC6 group was 14.13±1.78 and 6.88±1.42 in control group. There were significant difference between them (P < 0.05). These results indicated that EA could regulate the swallowing function via activating the SR interneurons in VLM under the physiological condition.

Acupuncture activates a direct pathway from the nucleus tractus solitarii to the rostral ventrolateral medulla.

Our previous studies have shown that electroacupuncture (EA) at the Jianshi-Neiguan acupoints (P5-6, overlying the median nerve) attenuates sympathoexcitatory responses through its influence on neuronal activity in the rostral ventrolateral medulla (rVLM). The nucleus tractus solitarii (NTS) receives input from somatic nerve stimulation. Connections between the NTS and the rVLM during EA stimulation have not been investigated and thus were the focus of the present study. Seven to ten days after unilateral microinjection of a rhodamine-conjugated microsphere retrograde tracer (100 nl) into the rVLM, rats were subjected to EA or sham-EA without electrical stimulation. EA was performed for 30 min at the P5-6 acupoints bilaterally. Perikarya containing the microsphere tracer were found in the NTS of both groups. Compared to controls (needle placement without electrical stimulation, n = 7), c-Fos immunoreactivity and neurons double-labeled with c-Fos, an immediate early gene, and the tracer were significantly increased in the NTS of EA-treated rats (all P < 0.05; n = 8), particularly, in the medial and lateral subdivisions of NTS at subpostremal and obex levels. These results suggest that EA at the P5-6 acupoints activates NTS neurons. Furthermore, EA-activated NTS neurons directly project to the rVLM and likely influence the rVLM activity.

EA promotes swallowing via activating swallowing-related motor neurons in the nucleus ambiguus.

To observe the effect of electroacupuncture (EA) on swallowing and its underlying mechanism, 32 Sprague-Dawley (SD) rats were chose and the electrophysiology was used to detect the discharge of nucleus ambiguus (NA) after EA at CV23 (Lianquan), GV16 (Fengfu), and other acupoints. The swallowing-related motor neuron was identified by antidromic stimulation through recurrent laryngeal nerve. Meanwhile, the swallowing numbers were induced by Double-distilled water (DDW) and the neuron discharges were recorded before and after EA. Beside, 50 SD rats were used for testing the c-fos expressions in NA after EA at different acupoints and the other 80 SD rats were used for chemical damage through the microinjection to bilateral NA. 58 neurons provided complete data after histological identification. And two types of swallowing-related (SR) motor neurons were identified, named spontaneous and silent neurons. We found that the onset latency of the first swallow was shorter and the swallowing numbers were increased after EA at CV23 than the other acupoints (P < 0.01). The excitatory neuron response rates were 66.67%, 71.11%, 42.22% and 35.56% for CV23, GV16, PC6 (Neiguan), and ST36 (Zusanli), respectively. The c-fos expressions on CV23 and GV16 groups were significantly higher than the other groups (P < 0.05). After chemical damage, the swallowing numbers could not be regulated by EA, but could be regulated by EA after fake damage. The results of the present study demonstrate that EA at CV23 and GV16 could regulate swallowing function via activating swallowing-related motor neurons in NA.

Hunger and Satiety Signaling: Modeling Two Hypothalamomedullary Pathways for Energy Homeostasis.

The recent discovery of the medullary circuit driving "hunger responses" - reduced thermogenesis and promoted feeding - has greatly expanded our knowledge on the central neural networks for energy homeostasis. However, how hypothalamic hunger and satiety signals generated under fasted and fed conditions, respectively, control the medullary autonomic and somatic motor mechanisms remains unknown. Here, in reviewing this field, we propose two hypothalamomedullary neural pathways for hunger and satiety signaling. To trigger hunger signaling, neuropeptide Y activates a group of neurons in the paraventricular hypothalamic nucleus (PVH), which then stimulate an excitatory pathway to the medullary circuit to drive the hunger responses. In contrast, melanocortin-mediated satiety signaling activates a distinct group of PVH neurons, which then stimulate a putatively inhibitory pathway to the medullary circuit to counteract the hunger signaling. The medullary circuit likely contains inhibitory and excitatory premotor neurons whose alternate phasic activation generates the coordinated masticatory motor rhythms to promote feeding.

Apelin in the hypothalamic paraventricular nucleus improves cardiac function in surgical trauma rats.

Apelin is a novel endogenous active peptide. The aim of this study is to investigate whether apelin in the paraventricular nucleus (PVN) can improve the cardiac function in rats subjected to thoracic surgery trauma, and whether it is involved in the protective effect of electro-acupuncture (EA). Sprague-Dawley rats were randomly divided into non-stressed group (control), thoracic surgical trauma stressed group (trauma) and bilateral Neiguan EA applied on thoracic surgical trauma stressed group (trauma + EA-PC 6). The mRNA expressions of apelin receptor (APJR) and apelin in the PVN were detected by real time-PCR. The exogenous apelin-13 (6 mmol/L, 0.1 µL) was microinjected into the rat PVN in the thoracic trauma group, and the effects of apelin-13 on the blood pressure (BP), heart rate (HR) and the discharge of rostral ventrolateral medulla (RVLM) neurons were observed through the simultaneous recording technology by polygraph. The results showed that the APJR mRNA expression was significantly decreased in the rats of trauma group as compared with that in the control group (P < 0.05), and a decline trend of apelin mRNA expression was also observed. EA application at bilateral Neiguan acupoints partially recovered the decline of APJR and apelin mRNA expression by the treatment of thoracic trauma. Both mean arterial pressure and HR in the thoracic surgical trauma group were significantly increased by the microinjection of exogenous apelin-13 into the PVN (P < 0.05), and the single-unit discharge rate of RVLM neurons also had an increasing trend. These results suggest that apelin in the PVN can improve the cardiac function of thoracic surgical trauma rats, and may be involved in the protective effects of EA.

Ventromedial medulla inhibitory neuron inactivation induces REM sleep without atonia and REM sleep behavior disorder.

Despite decades of research, there is a persistent debate regarding the localization of GABA/glycine neurons responsible for hyperpolarizing somatic motoneurons during paradoxical (or REM) sleep (PS), resulting in the loss of muscle tone during this sleep state. Combining complementary neuroanatomical approaches in rats, we first show that these inhibitory neurons are localized within the ventromedial medulla (vmM) rather than within the spinal cord. We then demonstrate their functional role in PS expression through local injections of adeno-associated virus carrying specific short-hairpin RNA in order to chronically impair inhibitory neurotransmission from vmM. After such selective genetic inactivation, rats display PS without atonia associated with abnormal and violent motor activity, concomitant with a small reduction of daily PS quantity. These symptoms closely mimic human REM sleep behavior disorder (RBD), a prodromal parasomnia of synucleinopathies. Our findings demonstrate the crucial role of GABA/glycine inhibitory vmM neurons in muscle atonia during PS and highlight a candidate brain region that can be susceptible to α-synuclein-dependent degeneration in RBD patients.

Cellular populations and thermosensing mechanisms of the hypothalamic thermoregulatory center.

Temperature affects all aspects of life down to the diffusion rates of biologically active molecules and reaction rates of enzymes. The reciprocal argument holds true as well and every biological process down to enzymatic reactions influences temperature. In order to assure biological stability, mammalian organisms possess the remarkable ability to maintain internal body temperature within a narrow range, which in humans and mice is close to 37 °C, despite wide environmental temperature variations and different rates of internal heat production. Nevertheless, body temperature is not a static property but adaptively regulated upon physiological demands and in the context of pathological conditions. The brain region that has been primarily associated with internal temperature regulation is the preoptic area and the anterior portion of the hypothalamus. Similar to a thermostat, this brain area detects deep brain temperature, integrates temperature information from peripheral body sensors, and-based on these inputs--controls body temperature homeostasis. Discovered more than a century ago, we still know comparatively little about the molecular and cellular make-up of the hypothalamic thermoregulatory center. After a brief historic outline that led to the discovery of the thermoregulatory center, we here review recent studies that have considerably advanced our understanding of hypothalamic thermoregulation. We touch upon proposed mechanisms of intrinsic deep brain temperature detection and focus on newly identified hypothalamic cell populations that mediate thermoregulatory responses and that provide novel entry points not only to shed light on the mechanistic underpinnings of the thermoregulatory center but also to probe its therapeutic value.

Central regulation of brown adipose tissue thermogenesis and energy homeostasis dependent on food availability.

Energy homeostasis of mammals is maintained by balancing energy expenditure within the body and energy intake through feeding. Several lines of evidence indicate that brown adipose tissue (BAT), a sympathetically activated thermogenic organ, turns excess energy into heat to maintain the energy balance in rodents and humans, in addition to its thermoregulatory role for the defense of body core temperature in cold environments. Elucidating the central circuit mechanism controlling BAT thermogenesis dependent on nutritional conditions and food availability in relation to energy homeostasis is essential to understand the etiology of symptoms caused by energy imbalance, such as obesity. The central thermogenic command outflow to BAT descends through an excitatory neural pathway mediated by hypothalamic, medullary and spinal sites. This sympathoexcitatory thermogenic drive is controlled by tonic GABAergic inhibitory signaling from the thermoregulatory center in the preoptic area, whose tone is altered by body core and cutaneous thermosensory inputs. This circuit controlling BAT thermogenesis for cold defense also functions for the development of fever and psychological stress-induced hyperthermia, indicating its important role in the defense from a variety of environmental stressors. When food is unavailable, hunger-driven neural signaling from the hypothalamus activates GABAergic neurons in the medullary reticular formation, which then block the sympathoexcitatory thermogenic outflow to BAT to reduce energy expenditure and simultaneously command the masticatory motor system to promote food intake-effectively commanding responses to survive starvation. This article reviews the central mechanism controlling BAT thermogenesis in relation to the regulation of energy and thermal homeostasis dependent on food availability.

RETRACTED: Cerebral ischemia-induced elevation of hepatic inflammatory factors accompanied by glucose intolerance suppresses hypothalamic orexin-A-mediated vagus nerve activation.

This article has been retracted: please see Elsevier Policy on Article Withdrawal (https://www.elsevier.com/about/our-business/policies/article-withdrawal). This article has been retracted at the request of the authors following an investigation into data manipulation (Fig.3A-D and Fig.4A-F) by an Investigation Committee at Kobe Gakuin University. Namely: Fig.3A-D and Fig.4A-F ­ numerical disagreement (numbers removed) was found in some parts between the raw data and the article data, hence the significant difference illustrated in the published article was not obtained.

Effects of Single Administration of Bupropion on Carboxypeptidase E Activity in Structures of Rat Brain.

Depression is associated with changes in the levels of some neurotransmitters in various brain structures. Being the key enzyme of peptide processing, carboxypeptidase E regulates their levels in various structures of the nervous system. Single injection of bupropion induced long-lasting changes in carboxypeptidase E activity in all brain structures. The decrease in enzyme activity observed in 12 and 24 h after bupropion injection confirmed the inhibiting effect of the drug on the hypothalamic-pituitary-adrenal axis. Activation of the enzyme in the medulla oblongata, hypothalamus, and hippocampus observed in 72 h after bupropion administration probably leads to enhanced synthesis and secretion of regulatory peptides (reduced during stress and depression) and stimulation of neurogenesis. Changes in enzyme activity can be a mechanism regulating the level of bioactive peptides involved in the pathogenesis of depression.

Neural Transmission from Oropharyngeal Bitter Receptors to the Medulla is Partially or Completely Labelled-Line.

The ground breaking advances in taste cell receptor cell physiology over the last 20 years have established a functional basis which enables neural pathways to be mapped. There is.only one, or perhaps several, types of taste receptors for salt, sour, sweet and umami (meaty) tastes and stimulation of each receptor type elicits responses in different cognitive regions. These findings support the labelled-line neural pathway model. In contrast, there are 25 types of the bitter taste receptors which all produce the same cognitive sensation, a finding which supports the across-fiber pattern model. This paper compiles the findings.of several human studies investigating the impact of bitter tastants on postprandial hemodynamics, to demonstrate that diverse bitter tastants are capable of eliciting a range of characteristic reflex cephalic phase responses in the autonomic and cardiovascular systems. These findings indicate that neural pathways from the oropharyngeal bitter taste receptors to the nucleus of the solitary tract are either partially or completely labelled-line. Consequently, the hedonics of a bitter tastant are not an accurate indicator of the cephalic phase responses elicited by the tastant. The finding that secondary metabolites present in dietary condiments modulate autonomic activity and in particular postprandial hemodynamics is novel and adds a new dimension to our understanding of the ways in which humans are influenced by their diet, both in health and disease. These findings suggest that condiments play a role in food digestion, unrelated to their. hedonistic qualities. Consequently, condiments may be of significance to those with digestive disorders and especially for diabetics experiencing gastroparesis and/or postprandial hypotension. Additionally, the findings suggest a noninvasive method to assess the integrity of multiple neural pathways. For investigators exploring the effect of condiments on autonomic reflexes, traditional cuisines may be a valuable source as they are full of uncharted human recordings.

[Does the Nucleus Ambiguus-Vague Nerve Mediate Anti-myocardial Ischemic Effect of Electroacupuncture of "Neiguan" (PC 6)-"Jianshi" (PC 7) in Myocardial Ischemia Rats].

OBJECTIVE: To observe the effect of electroacupuncture (EA) stimulation of "Neiguan" (PC 6)-"Jianshi" (PC 7) on ischemic myocardial injury in myocardial ischemic (MI) rats, so as to explore its mechanism underlying improvement of MI. METHODS: A total of 48 male Wistar rats were randomly divided into normal, MI model, PC 6-PC 7, Sanyinjiao-Diji (SP 6-SP 8) groups (n=8 in each group for physiological experiments, n=4 in each group for immunoflorescence stain). The MI model was established by occlusion of the anterior descending branch of the left coronary artery. Electrocardiogram (ECG) of the neck-thoracic lead was recorded and the heart rate variability (HRV) analyzed by using a physiological signal collecting system (MP 150) and PowerLab software. EA (2 Hz/15 Hz, 0.5 mA) was applied to bilateral PC 6-PC 7 or SP 6-SP 8 for 30 min every time, on the 1,2,3 day after modeling. Serum creatine kinase-MB isoenzyme (CK-MB) and lactate dehydrogenase-1 (LDH 1) and endothelin (ET) contents were assayed by ELISA. The expression of choline acetyltransferase (ChAT) and vesicular acetylcholine transporter (VAChT) and c-fos proteins in the nucleus ambiguus (NA) region of the medulla oblongata was detected by immunofluo-rescence stain. RESULTS: Compared with the normal group, the ECG J-point height (1 h), serum CK-MB, LDH 1 and ET contents (1 d and 3 d), HR (1 h and 1 d) and LF/HF levels of HRV (1 h, 1 d and 3 d) and the number of c-fos positive neurons (3 d) in the NA region were significantly increased in the model group (P<0.01, P<0.05), while HF levels (1 h, 1 d and 3 d) and ECG J-point height (1 d and 3 d) were considerably decreased after MI. After EA intervention, the ECG J-point height 3 d after MI was close to zero in both PC 6-PC 7 and SP 6-SP 8 groups, being better than that (negative value) of the model group, and serum CK-MB, LDH 1 and ET contents (1 d, 3 d) of both EA groups, and HR (1 d) and LF/HF (3 d) of the PC 6-PC 7 group were obviously down-regulated (P<0.01, P<0.05), and the decreased HF 3 d post-MI and the increased number of c-fos positive neurons were significantly up-regulated in the PC 6-PC 7 group (P<0.01). No significant differences were found between the two EA groups in raising J-point height and in down-regulating serum CK-MB, LDH 1 and ET contents (P>0.05). Compared with the model group, no significant changes were found in HR 1 d post-MI of the SP 6-SP 8 group, 3 d post-MI of both EA groups, in HF 3 d post-MI of the SP 6-SP 8 group, in LF/HF 1 d post-MI of both EA groups and 3 d post-MI of the SP 6-SP 8 group, in the number of c-fos positive neurons of the SP 6-SP 8 group, and ChAT and VAChT positive neurons of both EA groups (P>0.05). CONCLUSIONS: EA intervention may improve ischemic myocardial injury in MI rats, probably by activating neurons in the NA region, and enhancing the cardiac parasympathetic tension, and balancing cardiac sympathetic/parasympathetic nerve activities, but the effect of cholinergic neurons of NA needs being studied further.