Neural pathway between the nucleus accumbens and the rostral ventrolateral medulla in a rat model of anorexia nervosa / 南方医科大学学报

OBJECTIVE@#To investigate the potential neural pathway connecting the nucleus accumbens (NAc) and the rostral ventrolateral medulla (RVLM), and whether the pathway participates in the regulation of cardiovascular function in a model rat of anorexia nervosa (AN).@*METHODS@#Rat models of AN were established by allowing voluntary activity in a running wheel with restricted feeding, with the rats having free access to normal chow without exercise as the control group. FluoroGold (FG) retrograde tracing method and multi-channel simultaneous recording technique were used to explore the possible pathway between the NAc and the RVLM.@*RESULTS@#The rats in AN group exhibited significantly reduced systolic blood pressure (SBP), mean arterial pressure (MAP) and heart rate (HR) with significantly increased discharge frequency of RVLM neurons in comparison with the control rats. After the injection of FG into the RVLM, retrograde labeled neurons were observed in the NAc of the rats in both the normal control and AN groups. In both groups, SBP and HR were significantly decreased in response to 400 μA electrical stimulation of the NAc accompanied by an obvious increase in the discharge frequency of the RVLM neurons; the diastolic blood pressure (DBP) and MAP were significantly lower in AN model rats than in the normal rats in response to the stimulation.@*CONCLUSIONS@#We successfully established a rat model of AN via hyperactivity and restricted feeding and confirm the presence of a neural pathway connecting the NAc and the RVLM. This pathway might participate in the regulation of cardiovascular function in AN model rats.

The inhibitory effect of α-lipoic acid on the high salt-induced hypertension rats / 重庆医学

Objective To investigate whether the excessive production of reactive oxygen species (ROS) in the mitochondria of the rostral ventrolateral medulla (RVLM) can inhibit the high salt-induced hypertension response.Methods A total off 32 male rats were divided into two groups:two groups were given normal salt diet (0.3％ NaCl) for 8 weeks (n=16) and high salt diet (8％ NaCl) for 8 weeks (n=16,induced hypertension model) respectively.The two groups were divided into four groups,two groups were given α-lipoic dissolving in 0.9％ normal saline (60 mg/kg),two groups were fed with saline for 9 weeks.There were ffour groups:the experimental group (n=8,the hypertension model sample fed α-lipoic acid),the model group (n=8,the hypertension model sample fed saline),the control group (n=8,normal salt diet sample fed α-lipoic acid) and the blank control group (n=8,normal salt diet sample ffed saline).Monitored the change of the arterial pressure and detected the expression off superoxide by immunofluorescence at the end of the experiment,measured the expression of NAD(P)H NOX2,NOX4 and Cu/Zn-SOD in RVLM by Western blot;determined the expression differences of oxidative stress related substances such as mitochondrial malondialdehyde(MDA)in RVLM by ELISA.Results The mean arterial pressure (MAP) in the experimental group was lower than that in the model group,the difference was statistically significant (P＜0.05);in the experimental group and the model group the intensities of fluorescent-labled dihydroethidium(DHE) were 60.2±3.1,99.1±3.8;the numbers of positive neurons in Cu/Zn-SOD were 20.8±1.1,6.9 ± 1.2;the numbers of NOX2 positive neurons were 12.3 ± 3.5,25.1 ±5.4;the numbers of NOX4 positive neurons were 10.1±2.2,13.3±4.1,the difference was statistically significant (P＜0.05).Western blot showed that the NOX2 levels of the experimental group and the model group were 78.9 ± 2.0,112.7 ± 3.8;the levels of NOX4 were 63.2± 2.1,99.4 ± 1.7.The levels of Cu/Zn-SOD in RVLM of the experimental group and the model group were 19.7 ±1.6,10.3± 1.2,the difference was statistically significant (P＜0.05);the levels of mitochondrial superoxide dismutase (SOD) were (33.1±3.8),(15.2±1.7)U/mg,the difference was statistically significant (P＜0.05).The levels of mitochondrial glutathione (GSH) in the experimental group and the model group were (5.2±0.9),(2.3±0.5)μmol/g;the levels of norepinephrine (NE) were (325.8 ± 7.3),(467.9 ± 6.1) pg/mL,the difference was statistically significant (P＜0.05).Conclusion α-lipoic acid could decrease the expression of NOX2,NOX4 and the bioenergy of mitochondria enzyme,and increase the intracellular antioxidant ability in the RVLM during the development of hypertension to inhibit the oxidative stress response in the development of hypertension.

Comparison of electrophysiological properties of two types of pre-sympathetic neurons intermingled in the hypothalamic paraventricular nucleus

The hypothalamic paraventricular nucleus (PVN) contains two types of neurons projecting to either the rostral ventrolateral medulla (PVN(RVLM)) or the intermediolateral horn (IML) of the spinal cord (PVN(IML)). These two neuron groups are intermingled in the same subdivisions of the PVN and differentially regulate sympathetic outflow. However, electrophysiological evidence supporting such functional differences is largely lacking. Herein, we compared the electrophysiological properties of these neurons by using patch-clamp and retrograde-tracing techniques. Most neurons (>70%) in both groups spontaneously fired in the cell-attached mode. When compared to the PVN(IML) neurons, the PVN(RVLM) neurons had a lower firing rate and a more irregular firing pattern (p < 0.05). The PVN(RVLM) neurons showed smaller resting membrane potential, slower rise and decay times, and greater duration of spontaneous action potentials (p < 0.05). The PVN(RVLM) neurons received greater inhibitory synaptic inputs (frequency, p < 0.05) with a shorter rise time (p < 0.05). Taken together, the results indicate that the two pre-sympathetic neurons differ in their intrinsic and extrinsic electrophysiological properties, which may explain the lower firing activity of the PVN(RVLM) neurons. The greater inhibitory synaptic inputs to the PVN(RVLM) neurons also imply that these neurons have more integrative roles in regulation of sympathetic activity.

Role of hydrogen sulfide in central cardiovascular regulation / 第二军医大学学报

Hydrogen sulfide (H2S) is the third endogenous gaseous mediator following nitric oxide and carbon monoxide. It has been demonstrated that H2S plays important regulatory roles in modulating the physiological and pathophysiological processes of the nervous system, respiratory system, digestive system, and cardiovascular system. Recently, regulatory roles of H2S in cardiovascular system are widely focused and seem to be complex. Here we sum up the roles of H2S in mediating the cardiovascular regulation and illustrate its underlying mechanisms and perspectives.

Analysis of the Baroreceptor and Vestibular Receptor Inputs in the Rostral Ventrolateral Medulla following Hypotension in Conscious Rats

Input signals originating from baroreceptors and vestibular receptors are integrated in the rostral ventrolateral medulla (RVLM) to maintain blood pressure during postural movement. The contribution of baroreceptors and vestibular receptors in the maintenance of blood pressure following hypotension were quantitatively analyzed by measuring phosphorylated extracellular regulated protein kinase (pERK) expression and glutamate release in the RVLM. The expression of pERK and glutamate release in the RVLM were measured in conscious rats that had undergone bilateral labyrinthectomy (BL) and/or sinoaortic denervation (SAD) following hypotension induced by a sodium nitroprusside (SNP) infusion. The expression of pERK was significantly increased in the RVLM in the control group following SNP infusion, and expression peaked 10 min after SNP infusion. The number of pERK positive neurons increased following SNP infusion in BL, SAD, and BL+SAD groups, although the increase was smaller than seen in the control group. The SAD group showed a relatively higher reduction in pERK expression when compared with the BL group. The level of glutamate release was significantly increased in the RVLM in control, BL, SAD groups following SNP infusion, and this peaked 10 min after SNP infusion. The SAD group showed a relatively higher reduction in glutamate release when compared with the BL group. These results suggest that the baroreceptors are more powerful in pERK expression and glutamate release in the RVLM following hypotension than the vestibular receptors, but the vestibular receptors still have an important role in the RVLM.

Sympathetic nervous activity and hypertensive disorder complicating pregnancy / 第二军医大学学报

Hypertensive disorder complicating pregnancy is a commonly seen pregnancy complication that may pose serious problem to maternity and infant health, and is one of the major causes for morbidity and mortality in pregnant women and neonates, with the specific etiology and pathogenesis remain unclear. Recent studies have found that sympathetic nervous activity hyperthyroidism plays a role in the pathogenesis of hypertensive disorders in pregnancy. This review focused on the relationship between the sympathetic nerve activity and hypertensive disorder complicating pregnancy.

The pressor effect of angiotensin-(1-7) in the rat rostral ventrolateral medulla involves multiple peripheral mechanisms

OBJECTIVE: In the present study, the peripheral mechanism that mediates the pressor effect of angiotensin-(1-7) in the rostral ventrolateral medulla was investigated. METHOD: Angiotensin-(1-7) (25 pmol) was bilaterally microinjected in the rostral ventrolateral medulla near the ventral surface in urethane-anesthetized male Wistar rats that were untreated or treated (intravenously) with effective doses of selective autonomic receptor antagonists (atenolol, prazosin, methyl-atropine, and hexamethonium) or a vasopressin V1 receptor antagonist [d(CH2)5 -Tyr(Me)-AVP] given alone or in combination. RESULTS: Unexpectedly, the pressor response produced by angiotensin-(1-7) (16 ± 2 mmHg, n = 12), which was not associated with significant changes in heart rate, was not significantly altered by peripheral treatment with prazosin, the vasopressin V1 receptor antagonist, hexamethonium or methyl-atropine. Similar results were obtained in experiments that tested the association of prazosin and atenolol; methyl-atropine and the vasopressin V1 antagonist or methyl-atropine and prazosin. Peripheral treatment with the combination of prazosin, atenolol and the vasopressin V1 antagonist abolished the pressor effect of glutamate; however, this treatment produced only a small decrease in the pressor effect of angiotensin-(1-7) at the rostral ventrolateral medulla. The combination of hexamethonium with the vasopressin V1 receptor antagonist or the combination of prazosin, atenolol, the vasopressin V1 receptor antagonist and methyl-atropine was effective in blocking the effect of angiotensin-(1-7) at the rostral ventrolateral medulla. CONCLUSION: These results indicate that angiotensin-(1-7) triggers a complex pressor response at the rostral ventrolateral medulla that involves an increase in sympathetic tonus, release of vasopressin and possibly the inhibition of a vasodilatory mechanism.

Additive Role of the Vestibular End Organ and Baroreceptors on the Regulation of Blood Pressure in Rats

Contribution of the vestibular end organ to regulation of arterial pressure was quantitatively compared with the role of baroreceptors in terms of baroreflex sensitivity and c-Fos protein expression in the rostral ventrolateral medulla (RVLM). Baroreflex sensitivity and c-Fos protein expression in the RVLM were measured in conscious rats that had undergone bilateral labyrinthectomy (BL) and/or baroreceptor unloading. BL attenuated baroreflex sensitivity during intravenous infusion of sodium nitroprusside (SNP), but did not significantly affect the sensitivity following infusion of phenylephrine (PE). Baroreflex sensitivity became positive following sinoaortic denervation (SAD) during infusion of PE and attenuated sensitivity during infusion of SNP. Baroreflex sensitivity also became positive following double ablation (BL+SAD) during infusion of PE, and attenuated sensitivity during infusion of SNP. c-Fos protein expression increased significantly in the RVLM in the sham group after SNP administration. However, the BL, SAD, and SAD+BL groups showed significant decreases in c-Fos protein expression compared with that in the sham group. The SAD group showed more reduced c-Fos protein expression than that in the BL group, and the SAD+BL group showed less expression than that in the SAD group. These results suggest that the vestibular system cooperates with baroreceptors to maintain arterial pressure during hypotension but that baroreceptors regulate arterial pressure during both hypotension and hypertension. Additionally, afferent signals for maintaining blood pressure from the vestibular end organs and the baroreceptors may be integrated in the RVLM.

Mechanism of the cardiovascular action of salusin-a within caudal ventrolateral medulla in rats / 中国药学杂志

OBJECTIVE: To determine the cardiovascular actions of salusin-α in the caudal ventrolateral medulla (CVLM) in anesthetized rats. METHODS: Sixty-one anesthetic male SD rats were employed in the present study. The dose-dependant effects of salusin-α (0.04-4 pmol) on blood pressure and heart rate in the CVLM were determined by unilateral microinjection of salusin-α or artificial cerebrospinal fluid (aCSF) into the CVLM in 25 rats. In the other 36 rats, a CSF, kynurenic acid (Kyn), atropine, hexametho-nium (Hex) in the CVLM or a CSF/muscimol in the RVLM were given in advance to determine the mechanism of the cardiovascular actions of intra-CVLM salusin-α. RESULTS: Unilateral microinjection of salusin-a into the CVLM produced a dose-dependent hypotension and bradycardia. Prior administration of Kyn (1 nmol) or Hex (120 pmol) into the CVLM did not alter the hypotension and bradycardia induced by intra-CVLM salusin-α (P>0.05). But prior administration of atropine into the CVLM or pretreatment with muscimol within RVLM almost completely abolished the hypotension and bradycardia evoked by intra-CVLM salusin-α (P<0.05). CONCLUSION: Microinjection of salusin-α into the CVLM produces significantly hypotension and bradycardia, which probably originates from suppressing the activities of presympathetic neurons in the RVLM.

Multi-effect of central nitric oxide on cardiovascular activity / 第二军医大学学报

Objective To observe the effect of nitric oxide(NO)on cardiovascular activities in the nucleus tractus solitarii (NTS) and the rostral ventrolateral medulla (RVLM), so as to understand the role of central NO in cardiovascular regulation. Methods The changes of blood pressure (BP), heart rate (HR), and renal sympathetic nerve activity (RSNA) were observed following treatments with increased or decreased NO in the NTS and RVLM of anaesthetized SD rats. Results Microinjection of the NO precusor L-arginine (L-Arg, 2 nmol in 50 nl) into the NTS, a key relay of cardiovascular reflex transmission, produced significant decreases in BP, HR, and RSNA (P<0. 05), and injection of NO synthase inhibitor NG-nitro-L-arginine methyl ester(L-NAME, 10 nmol in 50 nl) into the NTS produced significant increases in these cardiovascular parameters (P<0. 05). However, injection of L-Arg (2 nmol in 100 nl) into the RVLM, a key region controlling sympathetic outflow, significantly increased basal BP, HR, and RSNA (P<0. 05), and injection of L-NAME (10 nmol in 100 nl) into the RVLM showed a cardiovascular inhibition effect (P<0. 05). Conclusion NO exhibits different effects in different cardiovascular centers, suggesting that it plays a special role in maintaining the basal cardiovascular activity.

Angiotensin-II-induced reactive oxygen species along the SFO-PVN-RVLM pathway: implications in neurogenic hypertension

Neurogenic hypertension has been the subject of extensive research worldwide. This review is based on the premise that some forms of neurogenic hypertension are caused in part by the formation of angiotensin-II (Ang-II)-induced reactive oxygen species along the subfornical organ-paraventricular nucleus of the hypothalamus-rostral ventrolateral medulla pathway (SFO-PVN-RVLM pathway). We will discuss the recent contribution of our laboratory and others regarding the mechanisms by which neurons in the SFO (an important circumventricular organ) are activated by Ang-II, how the SFO communicates with two other important areas involved in sympathetic activity regulation (PVN and RVLM) and how Ang-II-induced reactive oxygen species participate along the SFO-PVN-RVLM pathway in the pathogenesis of neurogenic hypertension.

Differential brain angiotensin-II type I receptor expression in hypertensive rats

Blood-borne angiotensin-II (Ang-II) has profound effects in the brain. We tested the hypothesis that Ang-II-dependent hypertension involves differential Ang-II type I (AT1) receptors expression in the subfornical organ (SFO) and the rostral ventrolateral medulla (RVLM). Male Wistar rats were implanted with 14-day osmotic minipump filled with Ang-II (150 ng/kg/min) or saline. AT1 receptor mRNA levels were detected in the SFO and RVLM by reverse transcription-polymerase chain reaction (RT-PCR). Ang-II caused hypertension (134 +/- 10 mmHg vs. 98 +/- 9 mmHg, n = 9, p < 0.05). RT-PCR revealed that Ang-II infusion induced increased AT1 receptor mRNA levels in RVLM and decreased in SFO. Our data suggest that Ang-II-induced hypertension involves differential expression of brain AT1 receptors.

Role of the caudal pressor area in the regulation of sympathetic vasomotor tone

It is well known that the ventrolateral medulla contains neurons involved in the tonic and reflex control of the cardiovascular system. Two regions within the ventrolateral medulla were initially identified: the rostral ventrolateral medulla (RVLM) and the caudal ventrolateral medulla (CVLM). Activation of the RVLM raises arterial blood pressure and sympathetic nerve activity, and activation of the CVLM causes opposite effects. The RVLM premotor neurons project directly to sympathetic preganglionic neurons and are involved in the maintenance of resting sympathetic vasomotor tone. A significant proportion of tonic activity in the RVLM sympathetic premotor neurons is driven by neurons located in a third region of the ventrolateral medulla denominated caudal pressor area (CPA). The CPA is a pressor region located at the extreme caudal part of the ventrolateral medulla that appears to have an important role controlling the activity of RVLM neurons. In this brief review, we will address the importance of the ventrolateral medulla neurons for the generation of resting sympathetic tone related to arterial blood pressure control focusing on two regions, the RVLM and the CPA.

Autonomic neurosurgery: from microvascular decompression to image guided stimulation

The paper reviews mechanisms underlying autonomic disorders, with a focus on cardiovascular dysfunction. Neurosurgical approaches are described for medically refractory hypertension and orthostatic hypotension. After review of microvascular decompression of the rostral ventrolateral medulla, stereotactic CT and MRI guided deep brain stimulation of the periaqueductal grey matter (PAG) is evaluated. Results are presented from patient studies showing reductions in blood pressure with ventral PAG stimulation and increases in blood pressure with dorsal PAG stimulation. A rationale for the treatment of autonomic disorders by neurosurgical intervention is discussed.

Relationship Between the Central Hypotensive Effect of Acupuncture or Melatonin and the Changes of Medullary Amino Acid Neurotransmitter / 针灸推拿医学（英文版）

To investigate whether changes of amino acid neurotransmitter releases in the rostral ventrolateral medulla (rVLM) were related to acupuncture and to the antihypertensive effect of melatonin (Mel) microinjected into the anterior hypothalamic area (AHA) of rats with stress-induced hypertension (SIH), as well as to compare and analyze the relationship between the both antihypertensive mechanisms of acupuncture and of Mel in the AHA. Methods: Animal model of SIHR was made by electric foot shocks combined with noises. Electroacupuncture (EA) was used and Zusanli acupoint of both side was selected. The technique of drug microinjection into the brain was used to observe the change of blood pressure (BP), and synchronously, brain microdialysis was performed for collecting dialysate samples, and then the concentration of amino acid neurotransmitters in the dialysate samples was determined by high performance liquid chromatography combined with fluorescent detection (HPLC-FD). Results: After the animal received stress treatment, the BP elevated, synchronously, the release of glutamate (Glu) in the rVLM increased, and when EA was performed, the elevated BP of the rats with SIH decreased,simultaneously, the release of Glu in the rVLM decreased also. After Mel was microinjected of into the AHA of the SIHR, the elevated BP attenuated, meanwhile, the release of Glu decreased,and those of γ-aminobutyric acid (GABA) and taurine (Tau) increased in the rVLM.Administration ofbicuculline, an antagonist of GABAA receptor, into the rVLM prior to microinjection of Mel into the AHA could partially block the depressor effect of Mel in the AHA. Conclusion: The decrease in the release of Glu in the rVLM contributes to the antihypertensive effect of both acupuncture and Mel in the AHA in the rats with SIH, and the increase in the release of GABA and Tau in the rVLM is also important to Mel in the AHA.

Role of the rostral ventrolateral medulla in pressor response of lateral hypothalamus-perifornical region to glutamate in rats / 中国康复理论与实践

@#ObjectiveTo investigate the effect and mechanisms of rostral ventrolateral medulla (RVL) on the pressor response of lateral hypothalamus-perifornical region (LH/PF) in rats.Methods30 healthy Wistar rats were randomly divided into four groups: the phentolamine group; propranolol group; atropine group and glutamate diethyl ester group, saline was as the control in every group. After microinjection of Glu into LH/PF, the blood pressure and heart rate were observed. Then phentolamine, propranolol, atropine and glutamate diethyl ester were microinjected into RVL and the blood pressure and heart rate changes induced by microinjection of Glu were observed again.ResultsMicroinjection of Glu into LH/PF can cause the blood pressure elevating and heart rate accelerating. The pressor response of Glu to excited LH/PF could be attenuated after response of phentolamine, propranolol, atropine and glutamate diethyl ester microinjected into RVL. The blood pressures of phentolamine group; propranolol group; atropine group and glutamate diethyl ester group reduced significantly different from those in the saline control group (P<0.01).ConclusionThe α-,β-,M- and Glu-receptors in the RVL induce the pressor response of LH/PF region.

Roles of NMDA receptors in arterial baroreceptor reflex in rostral ventrolateral medulla of rats / 第二军医大学学报

Objective: To study the roles of N methyl D aspartate acid (NMDA) receptors of glutamate in mediating the arterial baroreceptor reflex (ABR)in rostral ventrolateral medulla (RVLM) in rats. Methods: The blood pressure, heart rates and ABR were observed after the bilateral microinjection of 0.1 ?l 50 mmol/L ketamine into RVLM of ureth anesthetized rats. Results: Bilateral microinjection of ketamine into RVLM induced decrease of the blood pressure and heart rate ( P

Cholinergic activity related to cardiovascular regulation in rostral ventrolateral medulla of spontaneously hypertensive rats

The hyperactivity of cholinergic system in the RVLM of spontaneously hypertensive rats (SHR) may contribute to the sustained elevation of blood pressure. However, the hyperactivity mechanisms of cholinergic system are controversial. Thus, to clarify the mechanisms of cholinergic hyperactivity in RVLM of the SHR, we studied the activities of enzymes that participate in the biosynthesis and degradation of acetylcholine (ACh) and the density of muscarinic receptors in RVLM of the 14- to 18-week-old SHR and age-marched Wistar Kyoto rats (WKY). Choline acetyltransferase activity was far greater in RVLM of SHR than that of WKY. (3H)ACh release from RVLM was also greater in SHR than in WKY. Acetylcholinesterase activity and (3H)NMS binding of RVLM slice of SHR were not significantly different from that of WKY. These results suggest that the enhanced cholinergic mechanisms in the RVLM of SHR is due to the enhanced presynaptic cholinergic tone rather than the altered postsynaptic mechanisms.

DISTRIBUTION OF SEROTONIN, PHENYLETHANOLAMINE-N-METHYLTRANSFERASE SUBSTANCE P AND LEU-ENKEPHALIN IMMUNOREACTIVE NEURONS IN THE ROSTRAL VENTROLATERAL MEDULLA OF THE CAT / 解剖学报

The distribution of serotonin(5-HT), phenylethanolamine-N-methyltransferase (PNMT), substance P(SP) and leu-enkephalin(L-ENK) immunoreactive neurons in the rostral ventrolateral medulla (RVL) of the cat was studied with the immunohistochemical ABC technique, and the projection of 5-HT, SP and L-ENK positive neurons of the RVL into the thoracic cord was preliminarily investigated by a combined fluorescent retrograde transport and immunofluorescence method. The results indicate that 5-HT, PNMT, SP and L-ENK immunoreactive neurons mentioned above were localized primarily in the caudal part of nucleus paragigantocellularis lateralis and the rostral part of nucleus lateralis reticularis. SP positive cell bodies in the reticular formation close ventrolateral to nucleus ambiguus were also found. Some 5-HT, SP and L-ENK positive cells were situated in the area near the pia mater. In the most area of the RVL, 5-HT, PNMT, SP and L-ENK immunoreactive cell bodies had an overlapping distribution. 5-HT or PNMT or L-ENK positive neurons crowded, intertwined each other with their processes in the region at the levels 1.0-3.5mm caudal to trapezoid body, about 3.3mm lateral to the midline and about 0.8mm from the ventral surface of the medulla, and formed a longer or shorter continuous cell column which ran in the rostrocaudal direction. These three columns nearly coincided with each other at the level 1.5-2.5mm caudal to trapezoid body. Part of 5-HT, SP and L-ENK positive neurons in the RVL projected into the thoracic cord. The functional significance of these substances in the RVL was also discussed.

THE EFFERENT PROJECTIONS OF THE ROSTRAL VENTROLATERAL MEDULLA TO THE HYPOTHALAMIC PARAVENTRICULAR NUCLEUS AND THE THORACIC CORD IN THE CAT / 解剖学报

The efferent projections of the rostral ventrolateral medulla(RVL) to the hypothalamic paraventricular nucleus(Pa) and the thoracic cord were studied in the adult cat by using WGA-HRP or fluorescent retrograde tract-tracing method. After injection of WGA-HRP or fluorescent tracer Fast blue(FB) into one side of the Pa, retrogradely labelled cells were found in bilateral RVL, with an ipsilateral predominance. The labelled cells decreased in number from the caudal to the rostral level. After injection of FB into one side of the thoracic cord at T_2-T_3 segments, retrogradely labelled cells in the RVL were observed which increased in number from the caudal to the rostral level and reached the peak at 1.0-1.5mm caudal to the trapezoid body. Most of these cells were distributed in the ipsilateral RVL, and clustered in the region 0.0-1.0mm from the ventral surface of the medulla. After Diamino yellow 2HC1 and FB were injected into the Pa and the thoracic cord respectively, only single labelled cells were detected in the RVL, no double labelled cells were found. The above results suggest that the Pa and the thoracic cord receive separate fiber projections from different cells of the RVL.