Acute Visceral Pain in Rats: Vagal Nerve Block Compared to Bupivacaine Administered Intramuscularly

BACKGROUND

Visceral and parietal peritoneum layers have different sensory innervations. Most visceral peritoneum sensory information is conveyed via the vagus nerve to the nucleus of the solitary tract (NTS). We already showed in animal models that intramuscular (i.m.) injection of local anesthetics decreases acute somatic and visceral pain and general inflammation induced by aseptic peritonitis. The goal of the study was to compare the effects of parietal block, i.m. bupivacaine, and vagotomy on spinal cord and NTS stimulation induced by a chemical peritonitis.

METHODS

We induced peritonitis in rats using carrageenan and measured cellular activation in spinal cord and NTS under the following conditions, that is, a parietal nerve block with bupivacaine, a chemical right vagotomy, and i.m. microspheres loaded with bupivacaine. Proto-oncogene c-Fos (c-Fos), cluster of differentiation protein 11b (CD11b), and tumor necrosis factor alpha (TNF-α) expression in cord and NTS were studied.

RESULTS

c-Fos activation in the cord was inhibited by nerve block 2 hours after peritoneal insult. Vagotomy and i.m. bupivacaine similarly inhibited c-Fos activation in NTS. Forty-eight hours after peritoneal insult, the number of cells expressing CD11b significantly increased in the cord (P = .010). The median difference in the effect of peritonitis compared to control was 30 cells (CI95, 13.5-55). TNF-α colocalized with CD11b. Vagotomy inhibited this microglial activation in the NTS, but not in the cord. This activation was inhibited by i.m. bupivacaine both in cord and in NTS. The median difference in the effect of i.m. bupivacaine added to peritonitis was 29 cells (80% increase) in the cord and 18 cells (75% increase) in the NTS. Our study underlines the role of the vagus nerve in the transmission of an acute visceral pain message and confirmed that systemic bupivacaine prevents noxious stimuli by inhibiting c-Fos and microglia activation.

CONCLUSIONS

In rats receiving intraperitoneal carrageenan, i.m. bupivacaine similarly inhibited c-Fos and microglial activation both in cord and in the NTS. Vagal block inhibited activation only in the NTS. Our study underlines the role of the vagus nerve in the transmission of an acute visceral pain message and confirmed that systemic bupivacaine prevents noxious stimuli. This emphasizes the effects of systemic local anesthetics on inflammation and visceral pain.

The role of astrocytes in the nucleus tractus solitarii in maintaining central control of autonomic function

The nucleus tractus solitarii (nTS) is the first central site for the termination and integration of autonomic and respiratory sensory information. Sensory afferents terminating in the nTS as well as the embedded nTS neurocircuitry release and utilize glutamate that is critical for maintenance of baseline cardiorespiratory parameters and initiating cardiorespiratory reflexes, including those activated by bouts of hypoxia. nTS astrocytes contribute to synaptic and neuronal activity through a variety of mechanisms, including gliotransmission and regulation of glutamate in the extracellular space via membrane-bound transporters. Here, we aim to highlight recent evidence for the role of astrocytes within the nTS and their regulation of autonomic and cardiorespiratory processes under normal and hypoxic conditions.

Pulmonary Edema in COVID19-A Neural Hypothesis

In COVID-19, lung manifestations present as a slowly evolving pneumonia with insidious early onset interstitial pulmonary edema that undergoes acute exacerbation in the late stages and microvascular thrombosis. Currently, these manifestations are considered to be only consequences of pulmonary SARS-CoV-2 virus infection. We are proposing a new hypothesis that neurogenic insult may also play a major role in the pathogenesis of these manifestations. SARS-CoV-2 mediated inflammation of the nucleus tractus solitarius (NTS) may play a role in the acute exacerbation of pulmonary edema and microvascular clotting in COVID-19 patients.

Autonomic Brain Centers and Pathophysiology of COVID-19

Accumulating data have now shown strong evidence that COVID-19 infection leads to the occurrence of neurological signs with different injury severity. Anosmia and agueusia are now well documented and included in the criteria list for diagnosis, and specialists have stressed that doctors screen COVID-19 patients for these two signs. The eventual brainstem dysregulation, due to the invasion of SARS CoV-2, as a cause of respiratory problems linked to COVID-19, has also been extensively discussed. All these findings lead to an implication of the central nervous system in the pathophysiology of COVID-19. Here we provide additional elements that could explain other described signs like appetite loss, vomiting, and nausea. For this, we investigated the role of brainstem structures located in the medulla oblongata involved in food intake and vomiting control. We also discussed the possible pathways the virus uses to reach the brainstem, i.e., neurotropic and hematogenous (with its two variants) routes.

Prenatal intermittent hypoxia sensitizes the laryngeal chemoreflex, blocks serotoninergic shortening of the reflex, and reduces 5-HT3 receptor binding in the NTS in anesthetized rat pups

We tested the hypothesis that exposure to intermittent hypoxia (IH) during pregnancy would prolong the laryngeal chemoreflex (LCR) and diminish the capacity of serotonin (5-hydroxytryptamine; 5-HT) to terminate the LCR. Prenatal exposure to IH was associated with significant prolongation of the LCR in younger, anesthetized, postnatal day (P) rat pups age P8 to P16 compared to control, room air (RA)-exposed rat pups of the same age. Serotonin microinjected into the NTS shortened the LCR in rat pups exposed to RA during gestation, but 5-HT failed to shorten the LCR in rat pups exposed to prenatal IH. Given these observations, we tested the hypothesis that prenatal hypoxia would decrease binding to 5-HT3 receptors in the nucleus of the solitary tract (NTS) where 5-HT acts to shorten the LCR. Serotonin 3 receptor binding was reduced in younger rat pups exposed to IH compared to control, RA-exposed rat pups in the age range P8 to P12. Serotonin 3 receptor binding was similar in older animals (P18-P24) regardless of gas exposure during gestation. The failure of the 5-HT injected into the NTS to shorten the LCR was correlated with a developmental decrease in 5-HT3 receptor binding in the NTS associated with exposure to prenatal IH. In summary, prenatal IH sensitized reflex apnea and blunted processes that terminate reflex apneas in neonatal rat pups, processes that are essential to prevent death following apneas such as those seen in babies who died of SIDS.

Modulation of hypercapnic respiratory response by cholinergic transmission in the commissural nucleus of the solitary tract

The nucleus of the solitary tract (NTS) is an important area of the brainstem that receives and integrates afferent cardiorespiratory sensorial information, including those from arterial chemoreceptors and baroreceptors. It was described that acetylcholine (ACh) in the commissural subnucleus of the NTS (cNTS) promotes an increase in the phrenic nerve activity (PNA) and antagonism of nicotinic receptors in the same region reduces the magnitude of tachypneic response to peripheral chemoreceptor stimulation, suggesting a functional role of cholinergic transmission within the cNTS in the chemosensory control of respiratory activity. In the present study, we investigated whether cholinergic receptor antagonism in the cNTS modifies the sympathetic and respiratory reflex responses to hypercapnia. Using an arterially perfused in situ preparation of juvenile male Holtzman rats, we found that the nicotinic antagonist (mecamylamine, 5 mM), but not the muscarinic antagonist (atropine, 5 mM), into the cNTS attenuated the hypercapnia-induced increase of hypoglossal activity. Furthermore, mecamylamine in the cNTS potentiated the generation of late-expiratory (late-E) activity in abdominal nerve induced by hypercapnia. None of the cholinergic antagonists microinjected in the cNTS changed either the sympathetic or the phrenic nerve responses to hypercapnia. Our data provide evidence for the role of cholinergic transmission in the cNTS, acting on nicotinic receptors, modulating the hypoglossal and abdominal responses to hypercapnia.

Anti-neuroinflammation ameliorates systemic inflammation-induced mitochondrial DNA impairment in the nucleus of the solitary tract and cardiovascular reflex dysfunction

BACKGROUND

Decreased heart rate variability (HRV) leads to cardiovascular diseases and increased mortality in clinical studies. However, the underlying mechanisms are still inconclusive. Systemic inflammation-induced neuroinflammation is known to impair the autonomic center of cardiovascular regulation. The dynamic stability of blood pressure and heart rate (HR) is regulated by modulation of the reciprocal responses of sympathetic and parasympathetic tone by the baroreflex, which is controlled by the nucleus of the solitary tract (NTS).

METHODS

Systemic inflammation was induced by E. coli lipopolysaccharide (LPS, 1.2 mg/kg/day, 7 days) peritoneal infusion via an osmotic minipump in normotensive Sprague-Dawley rats. Systolic blood pressure (SBP) and HR were measured by femoral artery cannulation and recorded on a polygraph under anesthesia. The low-frequency (LF; 0.25-0.8 Hz) and high-frequency (HF; 0.8-2.4 Hz) components of SBP were adopted as the indices for sympathetic vasomotor tone and parasympathetic vasomotor tone, while the baroreflex effectiveness index (BEI) was adopted from the analysis of SBP and pulse interval (PI). The plasma levels of proinflammatory cytokines and mitochondrial DNA (mtDNA) oxidative damage were analyzed by ELISA. Protein expression was evaluated by Western blot. The distribution of oxidative mtDNA was probed by immunofluorescence. Pharmacological agents were delivered via infusion into the cisterna magna with an osmotic minipump.

RESULTS

The suppression of baroreflex sensitivity was concurrent with increased SBP and decreased HR. Neuroinflammatory factors, including TNF-α, CD11b, and Iba-1, were detected in the NTS of the LPS group. Moreover, indices of mtDNA damage, including 8-OHdG and γ-H2AX, were significantly increased in neuronal mitochondria. Pentoxifylline or minocycline intracisternal (IC) infusion effectively prevented mtDNA damage, suggesting that cytokine and microglial activation contributed to mtDNA damage. Synchronically, baroreflex sensitivity was effectively protected, and the elevated blood pressure was significantly relieved. In addition, the mtDNA repair mechanism was significantly enhanced by pentoxifylline or minocycline.

CONCLUSION

These results suggest that neuronal mtDNA damage in the NTS induced by neuroinflammation could be the core factor in deteriorating baroreflex desensitization and subsequent cardiovascular dysfunction. Therefore, the enhancement of base excision repair (BER) signaling in mitochondria could be a potential therapeutic strategy for cardiovascular reflex dysregulation.

Nucleus tractus solitarius mediates hyperalgesia induced by chronic pancreatitis in rats

BACKGROUND

Central sensitization plays a pivotal role in the maintenance of chronic pain induced by chronic pancreatitis (CP). We hypothesized that the nucleus tractus solitarius (NTS), a primary central site that integrates pancreatic afferents apart from the thoracic spinal dorsal horn, plays a key role in the pathogenesis of visceral hypersensitivity in a rat model of CP.

AIM

To investigate the role of the NTS in the visceral hypersensitivity induced by chronic pancreatitis.

METHODS

CP was induced by the intraductal injection of trinitrobenzene sulfonic acid (TNBS) in rats. Pancreatic hyperalgesia was assessed by referred somatic pain via von Frey filament assay. Neural activation of the NTS was indicated by immunohistochemical staining for Fos. Basic synaptic transmission within the NTS was assessed by electrophysiological recordings. Expression of vesicular glutamate transporters (VGluTs), N-methyl-D-aspartate receptor subtype 2B (NR2B), and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor subtype 1 (GluR1) was analyzed by immunoblotting. Membrane insertion of NR2B and GluR1 was evaluated by electron microscopy. The regulatory role of the NTS in visceral hypersensitivity was detected via pharmacological approach and chemogenetics in CP rats.

RESULTS

TNBS treatment significantly increased the number of Fos-expressing neurons within the caudal NTS. The excitatory synaptic transmission was substantially potentiated within the caudal NTS in CP rats (frequency: 5.87 ± 1.12 Hz in CP rats vs 2.55 ± 0.44 Hz in sham rats, P < 0.01; amplitude: 19.60 ± 1.39 pA in CP rats vs 14.71 ± 1.07 pA in sham rats; P < 0.01). CP rats showed upregulated expression of VGluT2, and increased phosphorylation and postsynaptic trafficking of NR2B and GluR1 within the caudal NTS. Blocking excitatory synaptic transmission via the AMPAR antagonist CNQX and the NMDAR antagonist AP-5 microinjection reversed visceral hypersensitivity in CP rats (abdominal withdraw threshold: 7.00 ± 1.02 g in CNQX group, 8.00 ± 0.81 g in AP-5 group and 1.10 ± 0.27 g in saline group, P < 0.001). Inhibiting the excitability of NTS neurons via chemogenetics also significantly attenuated pancreatic hyperalgesia (abdominal withdraw threshold: 13.67 ± 2.55 g in Gi group, 2.00 ± 1.37 g in Gq group, and 2.36 ± 0.67 g in mCherry group, P < 0.01).

CONCLUSION

Our findings suggest that enhanced excitatory transmission within the caudal NTS contributes to pancreatic pain and emphasize the NTS as a pivotal hub for the processing of pancreatic afferents, which provide novel insights into the central sensitization of painful CP.

TRPV1 channels contribute to spontaneous glutamate release in nucleus tractus solitarii following chronic intermittent hypoxia

Chronic intermittent hypoxia (CIH) reduces afferent-evoked excitatory postsynaptic currents (EPSCs) but enhances basal spontaneous (s) and asynchronous (a) EPSCs in second-order neurons of nucleus tractus solitarii (nTS), a major area for cardiorespiratory control. The net result is an increase in synaptic transmission. The mechanisms by which this occurs are unknown. The N-type calcium channel and transient receptor potential cation channel TRPV1 play prominent roles in nTS sEPSCs and aEPSCs. The functional role of these channels in CIH-mediated afferent-evoked EPSC, sEPSC, and aEPSC was tested in rat nTS slices following antagonist inhibition and in mouse nTS slices that lack TRPV1. Block of N-type channels decreased aEPSCs in normoxic and, to a lesser extent, CIH-exposed rats. sEPSCs examined in the presence of TTX (miniature EPSCs) were also decreased by N-type block in normoxic but not CIH-exposed rats. Antagonist inhibition of TRPV1 reduced the normoxic and the CIH-mediated increase in sEPSCs, aEPSCs, and mEPSCs. As in rats, in TRPV1+/+ control mice, aEPSCs, sEPSCs, and mEPSCs were enhanced following CIH. However, none were enhanced in TRPV1-/- null mice. Normoxic tractus solitarii (TS)-evoked EPSC amplitude, and the decrease after CIH, were comparable in control and null mice. In rats, TRPV1 was localized in the nodose-petrosal ganglia (NPG) and their central branches. CIH did not alter TRPV1 mRNA but increased its protein in NPG consistent with an increased contribution of TRPV1. Together, our studies indicate TRPV1 contributes to the CIH increase in aEPSCs and mEPSCs, but the CIH reduction in TS-EPSC amplitude occurs via an alternative mechanism. NEW & NOTEWORTHY This study provides information on the underlying mechanisms responsible for the chronic intermittent hypoxia (CIH) increase in synaptic transmission that leads to exaggerated sympathetic nervous and respiratory activity at baseline and in response to low oxygen. We demonstrate that the CIH increase in asynchronous and spontaneous excitatory postsynaptic currents (EPSCs) and miniature EPSCs, but not decrease in afferent-driven EPSCs, is dependent on transient receptor potential vanilloid type 1 (TRPV1). Thus TRPV1 is important in controlling nucleus tractus solitarii synaptic activity during CIH.

Angiotensin II system in the nucleus tractus solitarii contributes to autonomic dysreflexia in rats with spinal cord injury

Background

Autonomic dysreflexia (AD) is a potentially life-threating complication after spinal cord injury (SCI), characterized by episodic hypertension induced by colon or bladder distension. The objective of this study was to determine the role of impaired baroreflex regulation by the nucleus tractus solitarii(NTS) in the occurrence of AD in a rat model.

Methods

T4 spinal cord transection animal model was used in this study, which included 40 Male rats Colorectal distension (CD) was performed to assess AD and compare the changes of BP, HR, and BRS, six weeks after operation. After that, SCI rats with successfully induced AD were selected. Losartan was microinjected into NTS in SCI rats, then 10, 30, 60 minutes later, CD was performed to calculate the changes of BP, HR, and BRS in order to explicit whether Ang II system was involved in the AD occurrence. Ang II was then Intra-cerebroventricular infused in sham operation rats with CD to mimic the activation of Ang II system in AD. Finally, the level of Ang II in NTS and colocalization of AT1R and NMDA receptor within the NTS neurons were also detected in SCI rats.

Results

Compared with sham operation, SCI significantly aggravated the elevation of blood pressure (BP) and impaired baroreflex sensitivity (BRS) induced by colorectal distension; both of which were significantly improved by microinjection of the angiotensin receptor type I (AT₁R) antagonist losartan into the NTS. Level of angiotensin II (Ang II) in the NTS was significantly increased in the SCI rats than sham. Intracerebroventricular infusion of Ang II also mimicked changes in BP and BRS induced by colorectal distension. Blockade of baroreflex by sinoaortic denervation prevented beneficial effect of losartan on AD.

Conclusion

We concluded that the activation of Ang II system in NTS may impair blood pressure baroreflex, and contribute to AD after SCI.

Effects of intraperitoneally administered L-histidine on food intake, taste, and visceral sensation in rats

To evaluate relative factors for anorectic effects of L-histidine, we performed behavioral experiments for measuring food and fluid intake, conditioned taste aversion (CTA), taste disturbance, and c-Fos immunoreactive (Fos-ir) cells before and after i.p. injection with L-histidine in rats. Animals were injected with saline (9 ml/kg, i.p.) for a control group, and saline (9 ml/kg, i.p.) containing L-histidine (0.75, 1.5, 2.0 g/kg) for a L-histidine group. Injection of L-histidine decreased the average value of food intake, and statistically significant anorectic effects were found in animals injected with 1.5 or 2.0 g/kg L-histidine but not with 0.75 g/kg L-histidine. Taste abnormalities were not detected in any of the groups. Animals injected with 2.0 g/kg L-histidine were revealed to present with nausea by the measurement of CTA. In this group, a significant increase in the number of Fos-ir cells was detected both in the area postrema and the nucleus tractus solitarius (NTS). In the 0.75 g/kg L-histidine group, a significant increase in the number of Fos-ir cells was detected only in the NTS. When the ventral gastric branch vagotomy was performed, recovery from anorexia became faster than the sham-operated group, however, vagotomized rats injected with 2.0 g/kg L-histidine still acquired CTA. These data indicate that acute anorectic effects induced by highly concentrated L-histidine are partly caused by induction of nausea and/or visceral discomfort accompanied by neuronal activities in the NTS and the area postrema. We suggest that acute and potent effects of L-histidine on food intake require substantial amount of L-histidine in the diet.

[THE ROLE OF TAURINE THE PROCESS OF ADAPTATION OF VISCERAL SYSTEMS UNDER PSYCHO-EMOTIONAL STRESS IN RAT]

In recent years the identification of regulatory mechanisms of the general adaptation syndrome, manifesting itself as the response of an organism to drastic changes in the environment and leading to emotional stress, acquires a special significance. The control over visceral functions plays a particular role in stress reactions because of emerging threat of violation of neurodynamic balance of sympathetic-para- sympathetic relationships with their most sensitive element - the heart. Quick adaptation to stress helps to restore not only the sympathetic-parasympathetic homeostasis but also the energy metabolism. One of the essential components, activating metabolic processes, is taurine. This paper considers the descending influence of the paraventricular nucleus (PVN) on neuronal reactions of the solitary tract nucleus (NTS), the first linking pathways of visceral sensitivity, the mechanisms of central control over visceral reactions by mathematical model analysis of heart rate variability (MMA HRV) as well as morpho-histochemical changes in brain structures integrating and regulating the visceral sphere (PVN of the hypothalamus and the amygdala) under psycho-emotional stress without and with intraperitoneal injection of taurine (50 mg/kg). Acute and semichronic experiments were conducted on white nonlinear rats under 5-hour- long immobilization psycho-emotional stress. A highly defined centralization of vegetative HRV parame- ters (HR, IVR, INRS) was revealed, these parameters being normalized on days 7 and 14 at the background of taurine injections. The interaction and interdependence of the central regulatory mechanisms of cardiovascular reactions are shown as well as a considerable protective effect of taurine on promoting early restoration of adaptive properties of the central and peripheral segments of visceral sensitivity under development of long-term psycho-emotional stress.

Geophysical Variables and Behavior: Xcix. Reductions in Numbers of Neurons within the Parasolitary Nucleus in Rats Exposed Perinatally to a Magnetic Pattern Designed to Imitate Geomagnetic Continuous Pulsations: Implications for Sudden Infant Death

Correlational analyses have shown a moderate strength association between the occurrence of continuous pulsations, a type of geomagnetic activity within the 0.2-Hz to 5-Hz range, and the occurrence of Sudden Infant Deaths. In the present study, rats were exposed continuously from two days before birth to seven days after birth to 0.5-Hz pulsed-square wave magnetic fields whose intensities were within either the nanoTesla or microTesla range. The magnetic fields were generated in either an east-west (E-W) or north-south (N-S) direction. At 21 days of age, the area of the parasolitary nucleus (but not the solitary nucleus) was significantly smaller, and the numbers of neurons were significantly less in rats that had been exposed to the nanoT fields generated in the east-west direction or to the microTesla fields generated within either E-W or N-S direction relative to those exposed to the N-S nanoTesla fields. These results suggest nanoTesla magnetic fields, when applied in a specific direction, might interact with the local geomagnetic field to affect cell migration in structures within the brain stem that modulate vestibular-related arousal and respiratory or cardiovascular stability.

Anatomical and functional connections between the locus coeruleus and the nucleus tractus solitarius in neonatal rats

This study was designed to investigate brain connections among chemosensitive areas in newborn rats. Rhodamine beads were injected unilaterally into the locus coeruleus (LC) or into the caudal part of the nucleus tractus solitarius (cNTS) in Sprague-Dawley rat pups (P7-P10). Rhodamine-labeled neurons were patched in brainstem slices to study their electrophysiological responses to hypercapnia and to determine if chemosensitive neurons are communicating between LC and cNTS regions. After 7-10 days, retrograde labeling was observed in numerous areas of the brainstem, including many chemosensitive regions, such as the contralateral LC, cNTS and medullary raphe. Whole-cell patch clamp was done in cNTS. In 4 of 5 retrogradely labeled cNTS neurons that projected to the LC, firing rate increased in response to hypercapnic acidosis (15% CO2), even in synaptic blockade medium (SNB) (high Mg(2+)/low Ca(2+)). In contrast, 2 of 3 retrogradely labeled LC neurons that projected to cNTS had reduced firing rate in response to hypercapnic acidosis, both in the presence and absence of SNB. Extensive anatomical connections among chemosensitive brainstem regions in newborn rats were found and at least for the LC and cNTS, the connections involve some CO2-sensitive neurons. Such anatomical and functional coupling suggests a complex central respiratory control network, such as seen in adult rats, is already largely present in neonatal rats by at least day P7-P10. Since the NTS and the LC play a major role in memory consolidation, our results may also contribute to the understanding of the development of memory consolidation.

Hypothalamic paraventricular nucleus stimulation reduces intestinal injury in rats with ulcerative colitis

AIM: To investigate the effect and mechanism of stimulation of the hypothalamic paraventricular nucleus with glutamate acid in rats with ulcerative colitis (UC).

METHODS: The rats were anesthetized with 10% chloral hydrate via abdominal injection and treated with an equal volume of TNBS + 50% ethanol enema, injected into the upper section of the anus with the tail facing up. Colonic damage scores were calculated after injecting a certain dose of glutamic acid into the paraventricular nucleus (PVN), and the effect of the nucleus tractus solitarius (NTS) and vagus nerve in alleviating UC injury through chemical stimulation of the PVN was observed in rats. Expression changes of C-myc, Apaf-1, caspase-3, interleukin (IL)-6, and IL-17 during the protection against UC injury through chemical stimulation of the PVN in rats were detected by Western blot. Malondialdehyde (MDA) content and superoxide dismutase (SOD) activity in colon tissues of rats were measured by colorimetric methods.

RESULTS: Chemical stimulation of the PVN significantly reduced UC in rats in a dose-dependent manner. The protective effects of the chemical stimulation of the PVN on rats with UC were eliminated after chemical damage to the PVN. After glutamate receptor antagonist kynurenic acid was injected into the PVN, the protective effects of the chemical stimulation of the PVN were eliminated in rats with UC. After AVP-Vl receptor antagonist ([Deamino-penl, val4, D-Arg8]-vasopressin) was injected into NTS or bilateral chemical damage to NTS, the protective effect of the chemical stimulation of PVN on UC was also eliminated. After chemical stimulation of the PVN, SOD activity increased, MDA content decreased, C-myc protein expression significantly increased, caspase-3 and Apaf-1 protein expression significantly decreased, and IL-6 and IL-17 expression decreased in colon tissues in rats with UC.

CONCLUSION: Chemical stimulation of the hypothalamic PVN provides a protective effect against UC injury in rats. Hypothalamic PVN, NTS and vagus nerve play key roles in this process.

Long-term moderate exercise accelerates the recovery of stress-evoked cardiovascular responses

Psychological stress is an important global health problem. It is well documented that stress increases the incidences of various cardiovascular disorders. Regular exercise is known to reduce resting blood pressure (BP) and heart rate (HR). This study was designed to clarify the effects of long-term exercise on stress-evoked cardiovascular responses and to emphasize post-stress recovery effects. Male Wistar rats underwent 8 weeks of moderate treadmill training, with cardiovascular responses, autonomic nervous system activities and local Fos reactivity changes in the cardiovascular regulation center were monitored before, during and after immobilization stress. A spectral analysis of cardiovascular parameters was used to examine autonomic nervous activities. We found that long-term exercise (i) lowered resting BP, HR and sympathetic activity, but increased resting parasympathetic activity and baroreflex sensitivity (BRS); (ii) accelerated post-stress recovery of stress-evoked cardiovascular and sympathetic responses along with increased BRS and (iii) accelerated post-stress recovery of stress-evoked neuron activations in the paraventricular nucleus, but delayed it in the nucleus of the tractus solitarius. We conclude that, in rats, long-term exercise accelerated recovery of stress-evoked cardiovascular responses differentially altering hypothalamic and medullar neuron activities.

Acute intermittent optogenetic stimulation of nucleus tractus solitarius neurons induces sympathetic long-term facilitation

Acute intermittent hypoxia (AIH) induces sympathetic and phrenic long-term facilitation (LTF), defined as a sustained increase in nerve discharge. We investigated the effects of AIH and acute intermittent optogenetic (AIO) stimulation of neurons labeled with AAV-CaMKIIa, hChR2(H134R), and mCherry in the nucleus of the solitary tract (NTS) of anesthetized, vagotomized, and mechanically ventilated rats. We measured renal sympathetic nerve activity (RSNA), phrenic nerve activity (PNA), power spectral density, and coherence, and we made cross-correlation measurements to determine how AIO stimulation and AIH affected synchronization between PNA and RSNA. Sixty minutes after AIH produced by ventilation with 10% oxygen in balanced nitrogen, RSNA and PNA amplitude increased by 80% and by 130%, respectively (P < 0.01). Sixty minutes after AIO stimulation, RSNA and PNA amplitude increased by 60% and 100%, respectively, (P < 0.01). These results suggest that acute intermittent stimulation of NTS neurons can induce renal sympathetic and phrenic LTF in the absence of hypoxia or chemoreceptor afferent activation. We also found that while acute intermittent optogenetic and hypoxic stimulations increased respiration-related RSNA modulation (P < 0.01), they did not increase synchronization between central respiratory drive and RSNA. We conclude that mechanisms that induce LTF originate within the caudal NTS and extend to other interconnecting neuronal elements of the central nervous cardiorespiratory network.

The effect of tracheal occlusion on respiratory load compensation: changes in neurons containing inhibitory neurotransmitter in the nucleus of the solitary tract in conscious rats

Respiratory load compensation volume-time (Vt-T) relationships have been extensively studied in anesthetized animals. There are only a few studies in conscious animals although consciousness and behavior play a critical role in modulation of breathing. The aims of the study were to determine the effect of intermittent and transient tracheal occlusions (ITTO) elicited load compensation responses and the changes in activation of inhibitory glycinergic neurons in the nucleus of solitary tract (NTS) in conscious rats. The results showed that ITTO elicited an increase in expiratory time (T(e)) but did not affect inspiratory time (T(i)) and diaphragm activity (EMG(dia)). An increase in total breathing time (Ttot) was due exclusively to the increase in T(e). In addition, glycinergic neurons were activated in the intermediate NTS (iNTS) but not in the caudal NTS (cNTS). These results suggest that the activated glycinergic neurons in the iNTS may be important for the neurogenesis of load compensation responses in conscious animals.

Gastrointestinal intervention ameliorates high blood pressure through antagonizing overdrive of the sympathetic nerve in hypertensive patients and rats

Background

We investigated the hypothesis that the favorable effects of gastrointestinal (GI) intervention on hypertension (HTN) and cardiovascular (CV) disturbances are mediated by antagonizing overdrive of the sympathetic nervous system (SNS).

Methods and Results

Hypertensive patients with metabolic disturbances underwent laparoscopic Roux‐en‐Y gastric bypass surgery, and spontaneously hypertensive rats (SHRs) underwent RYGB or sham surgery. Blood pressure (BP), heart rate (HR), endothelium‐dependent flow‐mediated dilation, and anthropometric as well as laboratory parameters were measured at baseline and during follow‐up. Changes of BP and HR in response to cold stress, renal sympathetic nervous activity (RSNA), vasoconstriction induced by electrical field stimulation, microinjection of nucleus of the solitary tract (NTS), and CV function and structure were examined in SHRs with or without surgery. Compared with baseline, BP and HR were significantly reduced in both hypertensive patients with type 2 diabetes and rats. Impaired endothelial‐dependent vasodilatation and metabolic disturbances in hypertensive patients were also ameliorated after surgery. CV disturbances were reversed by surgery in SHRs. Under acute cold exposure, the variations in BP and HR were smaller in surgically treated SHRs, compared to sham SHRs. RSNA and vasoconstriction induced by perivascular nerve stimulation as well as NTS‐mediated changes of BP were decreased in surgically treated SHRs, compared to sham SHR. Weight loss did not affect BP and RSNA in sham SHRs.

Conclusions

GI intervention ameliorates HTN in both hypertensive patients and rats by inhibiting overdrive of the SNS. Therefore, targeting gastrointestine could be a novel strategy to treat HTN with metabolic disturbances.

Neural regulation of pancreatic islet cell mass and function

Intracellular glucose signalling pathways control the secretion of glucagon and insulin by pancreatic islet α- and β-cells, respectively. However, glucose also indirectly controls the secretion of these hormones through regulation of the autonomic nervous system that richly innervates this endocrine organ. Both parasympathetic and sympathetic nervous systems also impact endocrine pancreas postnatal development and plasticity in adult animals. Defects in these autonomic regulations impair β-cell mass expansion during the weaning period and β-cell mass adaptation in adult life. Both branches of the autonomic nervous system also regulate glucagon secretion. In type 2 diabetes, impaired glucose-dependent autonomic activity causes the loss of cephalic and first phases of insulin secretion, and impaired suppression of glucagon secretion in the postabsorptive phase; in diabetic patients treated with insulin, it causes a progressive failure of hypoglycaemia to trigger the secretion of glucagon and other counterregulatory hormones. Therefore, identification of the glucose-sensing cells that control the autonomic innervation of the endocrine pancreatic and insulin and glucagon secretion is an important goal of research. This is required for a better understanding of the physiological control of glucose homeostasis and its deregulation in diabetes. This review will discuss recent advances in this field of investigation.

Proposed toxic and hypoxic impairment of a brainstem locus in autism

Electrophysiological findings implicate site-specific impairment of the nucleus tractus solitarius (NTS) in autism. This invites hypothetical consideration of a large role for this small brainstem structure as the basis for seemingly disjointed behavioral and somatic features of autism. The NTS is the brain's point of entry for visceral afference, its relay for vagal reflexes, and its integration center for autonomic control of circulatory, immunological, gastrointestinal, and laryngeal function. The NTS facilitates normal cerebrovascular perfusion, and is the seminal point for an ascending noradrenergic system that modulates many complex behaviors. Microvascular configuration predisposes the NTS to focal hypoxia. A subregion--the "pNTS"--permits exposure to all blood-borne neurotoxins, including those that do not readily transit the blood-brain barrier. Impairment of acetylcholinesterase (mercury and cadmium cations, nitrates/nitrites, organophosphates, monosodium glutamate), competition for hemoglobin (carbon monoxide, nitrates/nitrites), and higher blood viscosity (net systemic oxidative stress) are suggested to potentiate microcirculatory insufficiency of the NTS, and thus autism.

[Vagus nerve stimulation in patients with migraine]

INTRODUCTION

Vagus nerve stimulation (VNS) has been approved for the treatment of refractory epilepsy when resective surgery is not possible, and has proved to be highly effective. Series published in the literature suggest a beneficial effect of VNS in the treatment of migraine.

AIMS

To determine the degree to which headaches improve in patients with migraine after the placement of VNS to treat refractory epilepsy, and to evaluate what variables are associated with an increased chance of success with this measure.

PATIENTS AND METHODS

An observation-based retrospective study was conducted from 1st January 1999 until 31st December 2010. Patients with VNS for refractory epilepsy were contacted by telephone, after selecting those who fulfilled International Headache Society criteria for migraine. Data collected included age, gender, year of placement, age at onset of epilepsy and migraine, improvement of seizures and migraine, presence of migraine with aura and coexistence of anxious-depressive syndrome. Ninety-four patients with VNS were contacted and 13 patients with migraine were selected.

RESULTS

Following placement of the VNS, the number of episodes of migraine was seen to decrease by at least 50% in nine patients (69%) (p = 0.004) and there was a drop in the number of episodes of migraine in those patients who had also reduced their epileptic seizures (p = 0.012). No statistically significant associations were observed as regards sex, age, length of disease history, existence of migraine with aura or coexistence of anxious-depressive syndrome.

CONCLUSIONS

VNS could have beneficial effects for patients with migraine, especially in cases that are difficult to control. Due to the type of study, these conclusions must be taken with caution. Prospective clinical studies are needed before introducing the technique into daily clinical practice.

The time-course of hindbrain neuronal activity varies according to location during either intraperitoneal or subcutaneous tumor growth in rats: single Fos and dual Fos/dopamine β-hydroxylase immunohistochemistry

Neuronal activity in the nucleus of the solitary tract, ventrolateral medulla, area postrema, and parabrachial nucleus was studied in rats with intraperitoneal or subcutaneous tumors on the 7th, 14th, 21st, and 28th day after injection of fibrosarcoma tumor cells. We found that the number of Fos and dopamine β-hydroxylase immunopositive neurons differs between animals with intraperitoneal and subcutaneous tumors and also between tumor-bearing rats at different times following injection. Our data indicate that responses of the brainstem structures to peripheral tumor growth depend on the localization as well as the stage of the tumor growth.

GABAB receptor gene transfer into the nucleus tractus solitarii induces chronic blood pressure elevation in normotensive rats

BACKGROUND

Increasing evidence indicates that GABAergic neurons in the nucleus of the solitary tract (NTS) play a significant role in the arterial baroreceptor reflex and control of cardiovascular homeostasis. However, the role of these neurons in the development of hypertension is not yet fully clear.

METHODS AND RESULTS

In the present study, we first confirmed that GABAB receptor (GBR) expression is enhanced in the NTS of SHR as compared with WKY rats using real-time RT-PCR and western blots. To study the functional consequence of upregulated GBR expression, GBR was overexpressed in the NTS by bilateral microinjection of the AAV2-GBR1 viral vector into the NTS of WKY rats. Immunofluorescence staining and western blots demonstrated that microinjection of AAV2-GBR1 into the NTS of WKY rats resulted in a significant increase in GBR1 expression in the NTS neurons. Overexpression of GBR in the NTS induced a chronic elevation in blood pressure and heart rate in the normotensive WKY rats. In an acute study, the pressor response to baclofen microinjected into the NTS was enhanced in SHR as compared with WKY rats.

CONCLUSIONS

GBR1 expression is enhanced in the NTS of SHR vs. WKY rats and overexpression of this gene in the NTS results in chronic elevation of blood pressure and heart rate in normotensive rats. 

Gastric electrical stimulation decreases gastric distension-induced central nociception response through direct action on primary afferents

Background & Aims

Gastric electrical stimulation (GES) is an effective therapy to treat patients with chronic dyspepsia refractory to medical management. However, its mechanisms of action remain poorly understood.

Methods

Gastric pain was induced by performing gastric distension (GD) in anesthetized rats. Pain response was monitored by measuring the pseudo-affective reflex (e.g., blood pressure variation), while neuronal activation was determined using c-fos immunochemistry in the central nervous system. Involvement of primary afferents was assessed by measuring phosphorylation of ERK1/2 in dorsal root ganglia.

Results

GES decreased blood pressure variation induced by GD, and prevented GD-induced neuronal activation in the dorsal horn of the spinal cord (T9–T10), the nucleus of the solitary tract and in CRF neurons of the hypothalamic paraventricular nucleus. This effect remained unaltered within the spinal cord when sectioning the medulla at the T5 level. Furthermore, GES prevented GD-induced phosphorylation of ERK1/2 in dorsal root ganglia.

Conclusions

GES decreases GD-induced pain and/or discomfort likely through a direct modulation of gastric spinal afferents reducing central processing of visceral nociception.

A role for nitric oxide within the nucleus tractus solitarii in the development of muscle mechanoreflex dysfunction in hypertension

Evidence suggests that the muscle mechanoreflex, a circulatory reflex that raises blood pressure and heart rate (HR) upon activation of mechanically sensitive afferent fibres in skeletal muscle, is overactive in hypertension. However, the mechanisms underlying this abnormal reflex function have yet to be identified. Sensory input from the mechanoreflex is processed within the nucleus tractus solitarii (NTS) in the medulla oblongata. Within the NTS, the enzymatic activity of nitric oxide synthase produces nitric oxide (NO). This centrally derived NO has been shown to modulate muscle reflex activity and serves as a viable candidate for mediating the mechanoreflex dysfunction that develops in hypertension. We hypothesized that mechanoreflex dysfunction in hypertension is mediated by abnormal alterations in NO production in the NTS. Mechanically sensitive afferent fibres were stimulated by passively stretching hindlimb muscle before and after blocking the endogenous production of NO within the NTS via microdialysis of the NO synthase inhibitor L-NAME (1 and 5 mM) in normotensive Wistar-Kyoto rats and spontaneously hypertensive rats (SHRs). Changes in HR and mean arterial pressure in response to stretch were significantly larger in SHRs compared with Wistar-Kyoto rats prior to L-NAME dialysis. Attenuating NO production via L-NAME in normotensive rats recapitulated the exaggerated cardiovascular response to stretch observed in SHRs. Dialysing L-NAME in SHRs further accentuated the increases in HR and mean arterial pressure elicited by stretch. These findings support the contention that reductions in NO production within the NTS contribute to the generation of abnormal cardiovascular control by the skeletal muscle mechanoreflex in hypertension.

A2 noradrenergic lesions prevent renal sympathoinhibition induced by hypernatremia in rats

Renal vasodilation and sympathoinhibition are recognized responses induced by hypernatremia, but the central neural pathways underlying such responses are not yet entirely understood. Several findings suggest that A2 noradrenergic neurons, which are found in the nucleus of the solitary tract (NTS), play a role in the pathways that contribute to body fluid homeostasis and cardiovascular regulation. The purpose of this study was to determine the effects of selective lesions of A2 neurons on the renal vasodilation and sympathoinhibition induced by hypertonic saline (HS) infusion. Male Wistar rats (280-350 g) received an injection into the NTS of anti-dopamine-beta-hydroxylase-saporin (A2 lesion; 6.3 ng in 60 nl; n = 6) or free saporin (sham; 1.3 ng in 60 nl; n = 7). Two weeks later, the rats were anesthetized (urethane 1.2 g⋅kg(-1) b.wt., i.v.) and the blood pressure, renal blood flow (RBF), renal vascular conductance (RVC) and renal sympathetic nerve activity (RSNA) were recorded. In sham rats, the HS infusion (3 M NaCl, 1.8 ml⋅kg(-1) b.wt., i.v.) induced transient hypertension (peak at 10 min after HS; 9±2.7 mmHg) and increases in the RBF and RVC (141±7.9% and 140±7.9% of baseline at 60 min after HS, respectively). HS infusion also decreased the RSNA (-45±5.0% at 10 min after HS) throughout the experimental period. In the A2-lesioned rats, the HS infusion induced transient hypertension (6±1.4 mmHg at 10 min after HS), as well as increased RBF and RVC (133±5.2% and 134±6.9% of baseline at 60 min after HS, respectively). However, in these rats, the HS failed to reduce the RSNA (115±3.1% at 10 min after HS). The extent of the catecholaminergic lesions was confirmed by immunocytochemistry. These results suggest that A2 noradrenergic neurons are components of the neural pathways regulating the composition of the extracellular fluid compartment and are selectively involved in hypernatremia-induced sympathoinhibition.

The role of nausea in food intake and body weight suppression by peripheral GLP-1 receptor agonists, exendin-4 and liraglutide

The FDA-approved glucagon-like-peptide-1 receptor (GLP-1R) agonists exendin-4 and liraglutide reduce food intake and body weight. Nausea is the most common adverse side effect reported with these GLP-1R agonists. Whether food intake suppression by exendin-4 and liraglutide occurs independently of nausea is unknown. Further, the neurophysiological mechanisms mediating the nausea associated with peripheral GLP-1R agonist use are poorly understood. Using two established rodent models of nausea [conditioned taste avoidance (CTA) and pica (ingestion of nonnutritive substances)], results show that all peripheral doses of exendin-4 that suppress food intake also produce CTA, whereas one dose of liraglutide suppresses intake without producing CTA. Chronic (12 days) daily peripheral administration of exendin-4 produces a progressive increase in pica coupled with stable, sustained food intake and body weight suppression, whereas the pica response and food intake reduction by daily liraglutide are more transient. Results demonstrate that the nausea response accompanying peripheral exendin-4 occurs via a vagal-independent pathway involving GLP-1R activation in the brain as the exendin-4-induced pica response is attenuated with CNS co-administration of the GLP-1R antagonist exendin-(9-39), but not by vagotomy. Direct administration of exendin-4 to the medial subnucleus of the nucleus tractus solitarius (mNTS), but not to the central nucleus of the amygdala, reduced food intake and produced a pica response, establishing the mNTS as a potential GLP-1R-expressing site mediating nausea responses associated with GLP-1R agonists.

Acute reductions in blood flow restricted to the dorsomedial medulla induce a pressor response in rats

OBJECTIVES

The brainstem nucleus of the solitary tract (nucleus tractus solitarii, NTS) is a pivotal region for regulating the set-point of arterial pressure, the mechanisms of which are not fully understood. Based on evidence that the NTS exhibits O2-sensing mechanisms, we examined whether a localized disturbance of blood supply, resulting in hypoxia in the NTS, would lead to an acute increase in arterial pressure.

METHODS

Male Wistar rats were used. Cardiovascular parameters were measured before and after specific branches of superficial dorsal medullary veins were occluded; we assumed these were drainage vessels from the NTS and would produce stagnant hypoxia. Hypoxyprobe-1, a marker for detecting cellular hypoxia in the post-mortem tissue, was used to reveal whether vessel occlusion induced hypoxia within the NTS.

RESULTS

Following vessel occlusion, blood flow in the dorsal surface of the medulla oblongata including the NTS region showed an approximately 60% decrease and was associated with hypoxia in neurons located predominantly in the caudal part of the NTS as revealed using hypoxyprobe-1. Arterial pressure increased and this response was pronounced significantly in both magnitude and duration when baroreceptor reflex afferents were sectioned.

CONCLUSION

These results suggest that localized hypoxia in the NTS increases arterial pressure. We suggest this represents a protective mechanism whereby the elevated systemic pressure is a compensatory mechanism to enhance cerebral perfusion. Whether this physiological mechanism has any relevance to neurogenic hypertension is discussed.

Neurostimulatory and ablative treatment options in major depressive disorder: a systematic review

INTRODUCTION

Major depressive disorder is one of the most disabling and common diagnoses amongst psychiatric disorders, with a current worldwide prevalence of 5-10% of the general population and up to 20-25% for the lifetime period.

HISTORICAL PERSPECTIVE

Nowadays, conventional treatment includes psychotherapy and pharmacotherapy; however, more than 60% of the treated patients respond unsatisfactorily, and almost one fifth becomes refractory to these therapies at long-term follow-up.

NONPHARMACOLOGICAL TECHNIQUES

Growing social incapacity and economic burdens make the medical community strive for better therapies, with fewer complications. Various nonpharmacological techniques like electroconvulsive therapy, vagus nerve stimulation, transcranial magnetic stimulation, lesion surgery, and deep brain stimulation have been developed for this purpose.

DISCUSSION

We reviewed the literature from the beginning of the twentieth century until July 2009 and described the early clinical effects and main reported complications of these methods.

Obesity alters circadian expressions of molecular clock genes in the brainstem

Major components of energy homeostasis, including feeding behavior and glucose and lipid metabolism, are subject to circadian rhythms. Recent studies have suggested that dysfunctions of molecular clock genes are involved in the development of obesity and diabetes. To examine whether metabolic states per se alter the circadian clock in the central nervous system (CNS), we analyzed the daily mRNA expression profiles of core clock genes in the caudal brainstem nucleus of the solitary tract (NTS). In lean C57BL/6 mice, transcript levels of the core clock genes (Npas2, Bmal1, Per1, Per2 and Rev-erbalpha) clearly showed 24-h rhythmicity. On the other hand, the expression profiles of Bmal1 and Rev-erbalpha were attenuated in mice with high fat diet-induced obesity as well as genetically obese KK-A(y) and ob/ob mice. Clock expression levels were increased in mice with high fat diet-induced obesity and Cry1 expression levels were decreased in KK-A(y) and ob/ob mice. In addition, peroxisome proliferator-activated receptor alpha (PPARalpha), which reportedly increases the BMAL1 transcriptional level, was up-regulated in the NTS of these murine models of obesity and insulin resistance, suggesting involvement of PPARalpha in the attenuation of circadian rhythms in the NTS in obese states. Furthermore, a circadian expression profile of a downstream target of clock genes, the large conductance Ca(2+)-activated K(+)channel, was disturbed in the NTS of these murine obesity models. These perturbations might contribute to neuronal dysfunction in obese states. This is the first report showing that obesity perturbs the circadian expressions of core clock genes in the CNS.

Gene expression profiles of major cytokines in the nucleus tractus solitarii of the spontaneously hypertensive rat

Since the nucleus of the solitary tract (NTS) is a pivotal region for regulating the set-point of arterial pressure, we proposed a role for it in the development of neurogenic hypertension. Recent studies have suggested that pro-inflammatory molecules are highly expressed in the NTS of an animal model of human essential hypertension--the spontaneously hypertensive rat (SHR), compared to normotensive Wistar-Kyoto rat (WKY). Based on this evidence, we hypothesized that inflammatory mediators such as cytokines are up-regulated in the hypertensive NTS. In the present study, we have assessed the level of gene expression of some cytokines in the NTS of SHR compared to WKY. In addition, for further confirmation of abnormal inflammatory condition within the NTS of SHR, we identified gene expression levels of an inflammatory marker, glycoprotein-39 (gp39) precursor, which is homologous to chitinase 3-like protein 1, human cartilage-gp39 or YKL40. The NTS was micro-dissected from 15-week-old male SHR and WKY rats. Total RNA was extracted and quantitative RT-PCR was performed. Gene expression of gp39 precursor and monocyte chemoattractant protein-1 were higher in the NTS of SHR while inter-leukin-6 was lower in the NTS of SHR compared to the WKY. In contrast, there were no significant differences in the expression of other cytokines including: inter-leukin-1 beta, tumor necrosis factor-alpha and transforming growth factor beta 1. These data together with our previous published finding of an over expression of junctional adhesion molecule-1 suggest that the NTS of the SHR exhibits a specific inflammatory state.

The NTS and integration of cardiovascular control during exercise in normotensive and hypertensive individuals

Due to upward resetting of baroreceptors, tachycardia coexists with increased pressure during dynamic exercise. This review critically evaluates current knowledge of proposed mechanisms to explain the continuous resetting of baroreflex control of heart rate and sympathetic nerve activity during and after exercise and exercise training. Of interest is the exercise-induced upward resetting that occurs in hypertensive and normotensive individuals. Accumulated evidence indicates that not only somatosensory afferents, but also inputs from central command projecting to the nucleus tractus solitarius (NTS) in the dorsal brainstem may mediate inhibition of excitatory neurotransmission on barosensitive neurons. Specific coordinated activation of vasopressinergic and oxytocinergic projections to the NTS is essential to tonically maintain baroreflex sensitivity and to adjust heart rate and cardiac output to circulatory demand at rest and during exercise in both sedentary and trained individuals. These findings reinforce the paramount importance of the NTS in integration of cardiovascular control during exercise.

Unilateral microdialysis of gabazine in the dorsal medulla reverses thermal prolongation of the laryngeal chemoreflex in decerebrate piglets

The laryngeal chemoreflex (LCR) is elicited by water in the larynx and leads to apnea and respiratory disruption in immature animals. The LCR is exaggerated by the elevation of brain temperature within or near the nucleus of the solitary tract (NTS) in decerebrate piglets. Thermal prolongation of reflex apnea elicited by superior laryngeal nerve stimulation is reduced by systemic administration of GABA(A) receptor antagonists. Therefore, we tested the hypothesis that microdialysis within or near the NTS of gabazine, a GABA(A) receptor antagonist, would reverse thermal prolongation of the LCR. We examined this hypothesis in 21 decerebrate piglets (age 3-13 days). We elicited the LCR by injecting 0.1 ml of water into the larynx before and after each piglet's body temperature was elevated by approximately 2.5 degrees C and before and after 2-5 mM gabazine was dialyzed unilaterally and focally in the medulla. Elevated body temperature failed to prolong the LCR in one piglet, which was excluded from analysis. Elevated body temperature prolonged the LCR in all the remaining animals, and dialysis of gabazine into the region near the NTS (n = 10) reversed the thermal prolongation of the LCR even though body temperature remained elevated. Dialysis of gabazine in other medullary sites (n = 10) did not reverse thermal prolongation of the LCR. Gabazine had no consistent effect on baseline respiratory activity during hyperthermia. These findings are consistent with the hypothesis that hyperthermia activates GABAergic mechanisms in or near the NTS that are necessary for the thermal prolongation of the LCR.

Air pollutants and cough

Epidemiological studies have shown that exposure to air pollution is associated with respiratory symptoms and decreases in lung function. This paper reviews recent literature showing that exposure to particulate matter, irritant gases, environmental tobacco smoke (ETS), mixed pollutants, and molds is associated with an increase in cough and wheeze. Some pollutants, like particulate matter and mixed pollutants, appear to increase cough at least as much as wheeze. Others, like irritant gases, appear to increase wheeze more than cough. For ETS, exposure during childhood is associated with cough and wheeze in adulthood, suggesting that the pollutant permanently alters some important aspect of the lungs, immune system or nervous system. We have shown in animal studies that pollutants change the neural control of airways and cough. Second hand smoke (SHS) exposure lengthened stimulated apnoea, increased the number of stimulated coughs, and augmented the degree of stimulated bronchoconstriction. The mechanisms included enhanced reactivity of the peripheral sensory neurones and second-order neurones in the nucleus tractus solitarius (NTS). NTS effects were due to a substance P mechanism at least in part. Ozone and allergen increased the intrinsic excitability of second-order neurones in the NTS. The animal studies suggest that the cough and wheeze experienced by humans exposed to pollutants may involve plasticity in the nervous system.

Upregulation of GAD65 mRNA in the medulla of the rat model of metabolic syndrome

Metabolic syndrome is characterized by obesity, elevated blood pressure (BP), insulin resistance, and hypercholesterolemia. Recently an animal model of this disorder has been proposed in rats selectively bred based on their performance on a treadmill-running task. Accordingly, low capacity runner (LCR) rats exhibited all of the diagnostic criteria for metabolic syndrome, including elevated BP, as compared to their high capacity runner (HCR) counterparts [U. Wisløff, S.M. Najjar, O. Ellingsen, P.M. Haram, S. Swoap, Q. Al-Share, M. Fernstrom, K. Rezaei, S.J. Lee, L.G. Koch, S.L. Britton, Cardiovascular risk factors emerge after artificial selection for low aerobic capacity, Science 307 (2005) 418-420]. Previous studies have highlighted the importance of GABAergic neurotransmission in the medullary cardiovascular-regulatory areas in the central control of BP. Thus, we hypothesized a dysregulation in GABAergic transmission in the medullary cardiovascular-regulatory nuclei of LCR rats. To begin testing this hypothesis we carried out experiments examining expression of the GABA synthetic enzymes, GAD65 and GAD67, mRNAs in the two rat strains via radioactive in situ hybridization. Our results showed GAD65 and GAD67 mRNAs were widely expressed throughout the brainstem; quantification revealed increased GAD65 mRNA expression in LCR animals in the caudal nucleus tractus solitarius (NTS) and rostral ventrolateral medulla (VLM) as compared to HCR rats. Conversely, no differences in the expression of GAD67 were detected in these regions. These data are consistent with the notion of altered GABAergic neurotransmission in the NTS and VLM in metabolic syndrome, and point to the importance of these regions in cardiovascular regulation.

Voltage-dependent calcium currents are enhanced in nucleus of the solitary tract neurons isolated from renal wrap hypertensive rats

The nucleus of the solitary tract (NTS) is the central site of termination of baroreceptor afferents. We hypothesize that changes occur in voltage-gated calcium channels (VGCCs) within NTS neurons as a consequence of hypertension. Whole-cell patch-clamp recordings were obtained from adult normotensive (109+/-2 mm Hg; n=6 from 6 sham-operated and 31 nonsurgically treated) and hypertensive (158+/-6 mm Hg; n=24) rats. In some experiments, 4-(4-[dihexadecylamino]styryl)-N-methylpyridinium iodide was applied to the aortic nerve to visualize NTS neurons receiving baroreceptor synaptic contacts. Ba(2+) currents (500 ms; -80 mV prepotential; 500 ms voltage steps in 5-mV increments to +15mV) peaked between -20 and -10 mV and were blocked by 100 mum of Cd(2+). Peak VGCCs were not different comparing non-4-(4-[dihexadecylamino]styryl)-N-methylpyridinium iodide-labeled and 4-(4- [dihexadecylamino]styryl)-N-methylpyridinium iodide-labeled NTS neurons in hypertensive and normotensive rats. The peak VGCC was significantly greater in cells from hypertensive compared with normotensive rats for both non-DiA-labeled (P=0.02) and DiA-labeled (P=0.04) neurons. To separate high-voltage activated (HVA) and low-voltage activated (LVA) components of VGCCs, voltage ramps (-110 mV to +30 mV over 50 ms) were applied from a holding potential of -60 mV (LVA channels inactivated) and a holding potential of -100 mV (both LVA and HVA currents activated). HVA currents were subtracted from HVA+LVA currents to yield the LVA current. Peak LVA currents were not different between hypertensive (8.9+/-0.8 pA/pF) and normotensive (7.8+/-0.6 pA/pF) groups of NTS neurons (P=0.27). These results demonstrate that 4 weeks of renal wrap hypertension induce an increase in Ca(2+) influx through HVA VGCCs in NTS neurons receiving arterial baroreceptor inputs.

Chronic intermittent hypoxia alters NMDA and AMPA-evoked currents in NTS neurons receiving carotid body chemoreceptor inputs

Chronic exposure to intermittent hypoxia (CIH) has been used in animals to mimic the arterial hypoxemia that accompanies sleep apnea. Humans with sleep apnea and animals exposed to CIH have elevated blood pressures and augmented sympathetic nervous system responses to acute exposures to hypoxia. To test the hypothesis that exposure to CIH alters neurons within the nucleus of the solitary tract (NTS) that integrate arterial chemoreceptor afferent inputs, we measured whole cell currents induced by activation of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) and N-methyl-D-aspartate (NMDA) receptors in enzymatically dispersed NTS neurons from normoxic (NORM) and CIH-exposed rats (alternating cycles of 3 min at 10% O2 followed by 3 min at 21% O2 between 8 AM and 4 PM for 7 days). To identify NTS neurons receiving carotid body afferent inputs the anterograde tracer 4- (4-(dihexadecylamino)styryl-N-methylpyridinum iodide (DiA) was placed onto the carotid body 1 wk before exposure to CIH. AMPA dose-response curves had similar EC50 but maximal responses increased in neurons isolated from DiA-labeled CIH (20.1 +/- 0.8 microM, n = 9) compared with NORM (6.0 +/- 0.3 microM, n = 8) rats. NMDA dose-response curves also had similar EC50 but maximal responses decreased in CIH (8.4 +/- 0.4 microM, n = 8) compared with NORM (19.4 +/- 0.6 microM, n = 9) rats. These results suggest reciprocal changes in the number and/or conductance characteristics of AMPA and NMDA receptors. Enhanced responses to AMPA receptor activation could contribute to enhanced chemoreflex responses observed in animals exposed to CIH and humans with sleep apnea.

Hypothetical anatomical model to describe the aberrant gag reflex observed in a clinical population of orally deprived children

In this 'clinical conundrum', we propose a hypothetical anatomical model to explain the abnormal gag reflex that is consistently observed in a clinical population of children experiencing feeding delays. This model is based on the presence of 'transient' connections formed during the normal development of autonomic brainstem circuitry involving the nucleus tractus solitarius (NTS). We propose that, as a result of normal feeding and swallowing, the activity of these transient fibers typically diminishes shortly after birth. In children who are orally deprived during infancy, these transient connections persist and the aberrant gag reflex is maintained into childhood. The most critical feature of the proposed model is the idea that swallowing during feeding initiates the retraction of the tactile 'transient' input to NTS. In the NICU feeding clinics, it has been suggested that triggering the gag reflex in neonates by tactile stimulation of non-oral body areas and anterior portions of the mouth directly or indirectly may contribute to oral feeding delays. To the contrary, we propose an anatomical model to suggest that oral feeding delays and lack of swallowing food, when experienced by neonates, actually contribute to the development of the aberrant gag reflex observed in later developmental stages.

Pharmacological MRI in awake rats reveals neural activity in area postrema and nucleus tractus solitarius: relevance as a potential biomarker for detecting drug-induced emesis

Drug-induced vomiting (emesis) is a major concern in patient care and a significant hurdle in the development of novel therapeutics. With respect to the latter, rodents, such as the rat and mouse, are typically used in efficacy and safety studies; however, drug-induced emesis cannot be readily observed in these species due to the lack of an emetic reflex. It is known that emesis can be triggered by neural activity in brain regions including area postrema (AP) and nucleus tractus solitarius (NTS). In this study, using pharmacological magnetic resonance imaging (phMRI) and a blood-pool contrast agent, we imaged the hemodynamic consequences of brain activity in awake rats initiated by the administration of compounds (apomorphine 0.1, 0.3 micromol/kg i.v. and ABT-594 0.03, 0.1, 0.3 micromol/kg i.v.) that elicit emesis in other species. Regional drug-induced relative cerebral blood volume (rCBV) changes and percent activated area within the AP and NTS were calculated, in which a dose-dependent relationship was evident for both apomorphine and ABT-594. Additionally, to correlate with behavioral readouts, it was found that the activation of AP and NTS was observed at plasma concentrations consistent with those that induced emesis in ferrets for both drugs. Our data thus suggest that phMRI in awake rats may be a useful tool for predicting emetic liability of CNS-acting drugs and may provide insights into depicting the underlying emetic neural pathways in vivo.

Modulation of emetic response by carotid baro- and chemoreceptor activations

We hypothesized that baroreceptor or chemoreceptor activation might be involved in the emetic, and prodromal cardiovascular and respiratory responses. To test this hypothesis, we induced the emetic responses by gastric distension in anesthetized Suncus murinus (house musk shrew), that had intact and absent baroreceptor and chemoreceptor afferents. Secondly, we stimulated the aortic depressor nerve (ADN) and the carotid sinus nerve (CSN) with or without gastric distension. Internal carotid artery ligation in the bifurcation area, which abolished reflex bradycardia by baroreceptor activation, and abolition of chemoreceptor reflex bradycardia and hyperventilation, by carotid body denervation, suppressed the emetic response but did not abolish it. ADN denervation, which produced no significant effects on the baroreceptor or chemoreceptor reflex bradycardia, had no effect on the emetic response, including the prodromal phase. CSN stimulation with gastric distension elicited retching accompanied by reflex bradycardia and hypotension during or just after stimulation, whereas ADN stimulation with gastric distension did not induce the cardiovascular reflex, and had no effects on the emetic response. These results indicate that carotid, rather than aortic, baroreceptor or chemoreceptor activation plays an important role in the augmentation of cardiac parasympathetic activity and the development of emetic response. In conclusion, carotid baroreceptor or chemoreceptor activation, which is non-emetic stimulation, acts as a modulator in the central mechanisms of emesis.

Effect of jejunal nutrition on pancreatic exocrine secretion in pancreatitis rats and the involvement of the nucleus tractus solitarius

Jejunal nutrition is currently used as a fundamental therapeutic measure for acute pancreatitis. Its impact on pancreatic exocrine secretion (PES) is still on dispute. The aim of this study was to determine the effect of jejunal nutrition on PES and illuminate whether NTS is involved in the regulation of PES. Firstly, we established experimental acute cutaneous pancreatitis (ACP) and acute necrotic pancreatitis (ANP) rat models, and measured the volume and protein levels of pancreatic fluid in normal and pancreatitis rats, and found that pancreatitis rats had a significantly lower pancreatic fluid volume and protein level than the normal rats. Then, we gave 0.3 mol/l maltose and 3% saline as jejunal nutrition were given to the two groups, respectively, and found that the jejunal nutrition did not increase the PES levels in both groups. In addition, we analyzed c-Fos expression in the nucleus tractus solitarius (NTS), and found c-Fos expression in NTS was stronger in rats who were given the jejunal nutrition than in those who were not. These findings suggest that jejunal nutrition excites vagal afferent nerve fibers at pancreatitis rats, and the excitation can be transmitted to medulla oblongata, but do not induce changes in PES. It is likely that the central integration mechanism, pathway of vagal efferent nerve or status of effector in acute pancreatitis may be different from normal physiological conditions.

Chronic alcohol exposure alters transcription broadly in a key integrative brain nucleus for homeostasis: the nucleus tractus solitarius

Chronic exposure to alcohol modifies physiological processes in the brain, and the severe symptoms resulting from sudden removal of alcohol from the diet indicate that these modifications are functionally important. We investigated the gene expression patterns in response to chronic alcohol exposure (21–28 wk) in the rat nucleus tractus solitarius (NTS), a brain nucleus with a key integrative role in homeostasis and cardiorespiratory function. Using methods and an experimental design optimized for detecting transcriptional changes less than twofold, we found 575 differentially expressed genes. We tested these genes for significant associations with physiological functions and signaling pathways using Gene Ontology terms and the Kyoto Encyclopedia of Genes and Genomes (KEGG) database, respectively. Chronic alcohol exposure resulted in significant NTS gene regulation related to the general processes of synaptic transmission, intracellular signaling, and cation transport as well as specific neuronal functions including plasticity and seizure behavior that could be related to alcohol withdrawal symptoms. The differentially expressed genes were also significantly enriched for enzymes of lipid metabolism, glucose metabolism, oxidative phosphorylation, MAP kinase signaling, and calcium signaling pathways from KEGG. Intriguingly, many of the genes we found to be differentially expressed in the NTS are known to be involved in alcohol-induced oxidative stress and/or cell death. The study provides evidence of very extensive alterations of physiological gene expression in the NTS in the adapted state to chronic alcohol exposure.

RFamide-related peptides signal through the neuropeptide FF receptor and regulate pain-related responses in the rat

The mammalian RFamide-related peptide RFRP1 was found to signal through the neuropeptide FF 2 receptor expressed in Xenopus oocytes. The peptide induced a dose-dependent outward current, which was dependent on the simultaneous expression of GIRK1 and GIRK4 potassium channels. In neuropathic rats, RFRP1 administered intrathecally induced tactile antiallodynia and thermal antinociception, whereas in the solitary tract nucleus it produced only mechanical antihyperalgesia. Expression of the RFamide-related peptide mRNA in the rat CNS was distinctly different from that of neuropeptide FF. Most notably, the gene was not expressed in the hindbrain or spinal cord at detectable levels. However, there was a prominent group of RFamide-related peptide mRNA-expressing neurons in the central hypothalamus, in the area in and between the dorsomedial and ventromedial nuclei. The results suggest that RFamide-related peptides are potentially involved in pain regulation through a hypothalamo-medullary projection system, and possibly via action on neuropeptide FF 2 receptors. In neuropathic animals, the pain suppressive effect of RFamide-related peptide varies depending on the submodality of noxious test stimulation and the site of RFamide-related peptide administration.

Intractable hiccup and nausea with periaqueductal lesions in neuromyelitis optica

Intractable hiccup and nausea (IHN) was found in eight of 47 cases of relapsing neuromyelitis optica (NMO) (17%) but in none of 130 cases of multiple sclerosis (MS). IHN resolved with methylprednisolone. In six cases, MRI detected linear medullary lesions involving the pericanal region, the area postrema, and the nucleus tractus solitarius. Like long and centrally located myelitis, a linear medullary lesion causing IHN may distinguish NMO from MS.

Calcium/calmodulin-dependent kinase II mediates critical components of the hypoxic ventilatory response within the nucleus of the solitary tract in adult rats

Calcium/calmodulin-dependent kinase II (CaMKII) is an ubiquitous second messenger that is highly expressed in neurons, where it has been implicated in some of the pathways regulating neuronal discharge as well as N-methyl-d-aspartate receptor-mediated synaptic plasticity. The full expression of the mammalian hypoxic ventilatory response (HVR) requires intact central relays within the nucleus of the solitary tract (NTS), and neural transmission of hypoxic afferent input is mediated by glutamatergic receptor activity, primarily through N-methyl-d-aspartate receptors. To examine the functional role of CaMKII in HVR, KN-93, a highly selective antagonist of CaMKII, was microinjected in the NTS via bilaterally placed osmotic pumps in freely behaving adult male Sprague-Dawley rats for 3 days. Vehicle-loaded osmotic pumps were surgically placed in control animals, and adequate placement of cannulas was ascertained for all animals. HVR was measured using whole body plethysmography during exposure to 10% O2-balance N2 for 20 min. Compared with control rats, KN-93 administration elicited marked attenuations of peak HVR (pHVR) but did not modify normoxic minute ventilation. Differences in pHVR were primarily attributable to diminished respiratory frequency recruitments during pHVR without significant differences in tidal volume. These findings indicate that CaMKII activation in the NTS mediates respiratory frequency components of the ventilatory response to acute hypoxia; however, CaMKII activity does not appear to underlie components of normoxic ventilation.

Morphometric evaluation of the human tractus solitarius

We measured the cross-sectional area (CSA) of the human tractus solitarius (HTS) with the help of an image-analyzer system on a cross section of the upper part of the medulla oblongata in 44 Japanese cadavers (22 males and 22 females) and examined the relationship between age, sex and whether the subjects were dentulous or edentulous. The results showed no significant differences between the left and right sides of the HTS in either male or female subjects. However, the size of HTS decreased slightly with age in males but not at all in females, whereas tooth loss had a definite incidence on the size of HTS in females but not in male, as the CSA was smaller in edentulous females but not in edentulous males. This would tend to indicate that a decreases in taste function is connected with the aging process in male, and with tooth loss in females.

Syncope: facts and fiction

According to the current state-of-art on the brainstem functional anatomy and reticular formation, authors believe that nucleus tractus solitarii (NTS) is the neural structure, which meets all the conditions of the hypothetical syncope generating, reflex centre. The afferent branch of this reflex arc represents information from different visceral sources including the brain itself. The efferent branch of this reflex arc is reticular activating system (RAS). The executive mechanism of syncope is deactivation of RAS done with the active engagement of NTS through solitarioreticular pathway (SRT) and parabrachial nuclear complex (PBC). The biological purpose of syncope would be resetting of the NTS in case of an unbearable vegetative input, which is code for triggering the mechanism described.

Effect of losartan microinjections into the NTS on the cardiovascular components of chemically evoked reflexes in a rabbit model of acute heart ischemia

In the acute phase of myocardial infarction (MI) there are modifications of the autonomic outflow with an increase in the sympathetic tone and changes in cardiovascular reflexes. Activation of angiotensin AT1 receptors in the nucleus tractus solitarii (NTS) inhibits the baroreceptor and enhances the carotid chemoreflex. In this study, we investigated the role of NTS-AT1 receptors on the cardiovascular reflex responses evoked on stimulation of carotid chemoreflex and cardiac chemosensitive fibres in the acute phase of MI. We also test the hypothesis that changes in cardiovascular responses to activation of carotid chemo and cardiac chemosensitive reflexes are secondary to changes in haemodynamic conditions due to infarction or to the activation of nociceptors of the heart. Rabbits were anaesthetised, paralysed and artificially ventilated. Carotid chemoreceptors and cardiac chemosensitive fibres were stimulated with lobeline and ATP, respectively. Arterial blood pressure, electrocardiogram and heart rate were monitored. A craniotomy was made to expose the caudal portions of the medulla and a multibarreled glass microelectrode was inserted in order to allow the identification of NTS and the microinjection of losartan (an angiotensin AT1 receptor antagonist). The heart was exposed by a midline thoracotomy and cardiac ischemia was produced by ligating the left descending coronary artery. The carotid chemoreflex and cardiac chemosensitive reflexes were evoked before and following the coronary ligation. The effect of losartan injection into the NTS on these reflexes was also assessed. In control experiments reflexes were assessed before and after the administration of capsaicin and procainamide. Results show that the activation of carotid chemoreflex elicited a greater increase of blood pressure and bradycardia after MI and that this was partially reversed by losartan microinjection after MI. Also the stimulation of cardiac chemosensitive fibres evoked a larger decrease on blood pressure and heart rate after MI and these were also partially reversed by losartan. The same enhancement of cardiovascular carotid chemo and cardiac chemosensitive receptors was observed after administration of capsaicin on the ventricular surface but not after procainamide. In conclusion, this study strongly suggests that, at NTS level, angiotensin AT1 receptors are involved in the modifications of autonomic outflow observed in the acute phase of MI.