Medullary Nuclei Research Articles

Synaptogenesis and Myelination in the Nucleus/Tractus Solitarius: Potential Role in Apnea of Prematurity, Congenital Central Hypoventilation, and Sudden Infant Death Syndrome.

Fetuses as early as 15 weeks' gestation exhibit rhythmical respiratory movements shown by real-time ultrasonography. The nucleus/tractus solitarius is the principal brainstem respiratory center; other medullary nuclei also participate. The purpose was to determine temporal maturation of synaptogenesis. Delayed synaptic maturation may explain neurogenic apnea or hypoventilation of prematurity and some cases of sudden infant death syndrome. Sections of medulla oblongata were studied from 30 human fetal and neonatal brains 9 to 41 weeks' gestation. Synaptophysin demonstrated the immunocytochemical sequence of synaptogenesis. Other neuronal markers and myelin stain also were applied. The nucleus/tractus solitarius was similarly studied in fetuses with chromosomopathies, metabolic encephalopathies, and brain malformations. Synapse formation in the nucleus solitarius begins at about 12 weeks' gestation and matures by 15 weeks; myelination initiated at 33 weeks. Synaptogenesis was delayed in 3 fetuses with different conditions, but was not specific for only nucleus solitarius. Delayed synaptogenesis or myelination in the nucleus solitarius may play a role in neonatal hypoventilation, especially in preterm infants and in some sudden infant death syndrome cases.

Involvement of the avian song system in reproductive behaviour.

The song system of songbirds consists of an interconnected set of forebrain nuclei that has traditionally been regarded as dedicated to the learning and production of song. Here, however, we suggest that the song system could also influence muscles used in reproductive behaviour, such as the cloacal sphincter muscle. We show that the same medullary nucleus, retroambigualis (RAm), that projects upon spinal motoneurons innervating expiratory muscles (which provide the pressure head for vocalization) and upon vocal motoneurons for respiratory-vocal coordination also projects upon cloacal motoneurons. Furthermore, RAm neurons projecting to sacral spinal levels were shown to receive direct projections from nucleus robustus arcopallialis (RA) of the forebrain song system. Thus, by indicating a possible disynaptic relationship between RA and motoneurons innervating the reproductive organ, in both males and females, these results potentially extend the role of the song system to include consummatory as well as appetitive aspects of reproductive behaviour.

Two different motor systems are needed to generate human speech

Vocalizations such as mews and cries in cats or crying and laughter in humans are examples of expression of emotions. These vocalizations are generated by the emotional motor system, in which the mesencephalic periaqueductal gray (PAG) plays a central role, as demonstrated by the fact that lesions in the PAG lead to complete mutism in cats, monkeys, as well as in humans. The PAG receives strong projections from higher limbic regions and from the anterior cingulate, insula, and orbitofrontal cortical areas. In turn, the PAG has strong access to the caudal medullary nucleus retroambiguus (NRA). The NRA is the only cell group that has direct access to the motoneurons involved in vocalization, i.e., the motoneuronal cell groups innervating soft palate, pharynx, and larynx as well as diaphragm, intercostal, abdominal, and pelvic floor muscles. Together they determine the intraabdominal, intrathoracic, and subglottic pressure, control of which is necessary for generating vocalization. Only humans can speak, because, via the lateral component of the volitional or somatic motor system, they are able to modulate vocalization into words and sentences. For this modulation they use their motor cortex, which, via its corticobulbar fibers, has direct access to the motoneurons innervating the muscles of face, mouth, tongue, larynx, and pharynx. In conclusion, humans generate speech by activating two motor systems. They generate vocalization by activating the prefrontal‐PAG‐NRA‐motoneuronal pathway, and, at the same time, they modulate this vocalization into words and sentences by activating the corticobulbar fibers to the face, mouth, tongue, larynx, and pharynx motoneurons. J. Comp. Neurol. 524:1558–1577, 2016. © 2015 Wiley Periodicals, Inc.

Galanin-Mediated Behavioural Hyperalgesia from the Dorsomedial Nucleus of the Hypothalamus Involves Two Independent Descending Pronociceptive Pathways.

Activation of the dorsomedial nucleus of the hypothalamus (DMH) by galanin (GAL) induces behavioural hyperalgesia. Since DMH neurones do not project directly to the spinal cord, we hypothesized that the medullary dorsal reticular nucleus (DRt), a pronociceptive region projecting to the spinal dorsal horn (SDH) and/or the serotoninergic raphe-spinal pathway acting on the spinal 5-HT3 receptor (5HT3R) could relay descending nociceptive facilitation induced by GAL in the DMH. Heat-evoked paw-withdrawal latency (PWL) and activity of SDH neurones were assessed in monoarthritic (ARTH) and control (SHAM) animals after pharmacological manipulations of the DMH, DRt and spinal cord. The results showed that GAL in the DMH and glutamate in the DRt lead to behavioural hyperalgesia in both SHAM and ARTH animals, which is accompanied particularly by an increase in heat-evoked responses of wide-dynamic range neurons, a group of nociceptive SDH neurones. Facilitation of pain behaviour induced by GAL in the DMH was reversed by lidocaine in the DRt and by ondansetron, a 5HT3R antagonist, in the spinal cord. However, the hyperalgesia induced by glutamate in the DRt was not blocked by spinal ondansetron. In addition, in ARTH but not SHAM animals PWL was increased after lidocaine in the DRt and ondansetron in the spinal cord. Our data demonstrate that GAL in the DMH activates two independent descending facilitatory pathways: (i) one relays in the DRt and (ii) the other one involves 5-HT neurones acting on spinal 5HT3Rs. In experimental ARTH, the tonic pain-facilitatory action is increased in both of these descending pathways.

Nuclear organization of some immunohistochemically identifiable neural systems in two species of the Euarchontoglires: A Lagomorph, Lepus capensis, and a Scandentia, Tupaia belangeri

The present study describes the organization of the nuclei of the cholinergic, catecholaminergic, serotonergic and orexinergic systems in the brains of two members of Euarchontoglires, Lepus capensis and Tupaia belangeri. The aim of the present study was to investigate the nuclear complement of these neural systems in comparison to previous studies on Euarchontoglires and generally with other mammalian species. Brains were coronally sectioned and immunohistochemically stained with antibodies against choline acetyltransferase, tyrosine hydroxylase, serotonin and orexin-A. The majority of nuclei revealed in the current study were similar between the species investigated and to mammals generally, but certain differences in the nuclear complement highlight potential phylogenetic interrelationships within the Euarchontoglires and across mammals. In the northern tree shrew the nucleus of the trapezoid body contained neurons immunoreactive to the choline acetyltransferase antibody with some of these neurons extending into the lamellae within the superior olivary nuclear complex (SON). The cholinergic nature of the neurons of this nucleus, and the extension of cholinergic neurons into the SON, has not been noted in any mammal studied to date. In addition, cholinergic neurons forming the medullary tegmental field were also present in the northern tree shrew. Regarding the catecholaminergic system, the cape hare presented with the rodent specific rostral dorsal midline medullary nucleus (C3), and the northern tree shrew lacked both the ventral and dorsal divisions of the anterior hypothalamic group (A15v and A15d). Both species were lacking the primate/megachiropteran specific compact portion of the locus coeruleus complex (A6c). The nuclei of the serotonergic and orexinergic systems of both species were similar to those seen across most Eutherian mammals. Our results lend support to the monophyly of the Glires, and more broadly suggest that the megachiropterans are more closely related to the primates than are any other members of Euarchontoglires studied to date.

Impaired neural structure and function contributing to autonomic symptoms in congenital central hypoventilation syndrome.

Congenital central hypoventilation syndrome (CCHS) patients show major autonomic alterations in addition to their better-known breathing deficiencies. The processes underlying CCHS, mutations in the PHOX2B gene, target autonomic neuronal development, with frame shift extent contributing to symptom severity. Many autonomic characteristics, such as impaired pupillary constriction and poor temperature regulation, reflect parasympathetic alterations, and can include disturbed alimentary processes, with malabsorption and intestinal motility dyscontrol. The sympathetic nervous system changes can exert life-threatening outcomes, with dysregulation of sympathetic outflow leading to high blood pressure, time-altered and dampened heart rate and breathing responses to challenges, cardiac arrhythmia, profuse sweating, and poor fluid regulation. The central mechanisms contributing to failed autonomic processes are readily apparent from structural and functional magnetic resonance imaging studies, which reveal substantial cortical thinning, tissue injury, and disrupted functional responses in hypothalamic, hippocampal, posterior thalamic, and basal ganglia sites and their descending projections, as well as insular, cingulate, and medial frontal cortices, which influence subcortical autonomic structures. Midbrain structures are also compromised, including the raphe system and its projections to cerebellar and medullary sites, the locus coeruleus, and medullary reflex integrating sites, including the dorsal and ventrolateral medullary nuclei. The damage to rostral autonomic sites overlaps metabolic, affective and cognitive regulatory regions, leading to hormonal disruption, anxiety, depression, behavioral control, and sudden death concerns. The injuries suggest that interventions for mitigating hypoxic exposure and nutrient loss may provide cellular protection, in the same fashion as interventions in other conditions with similar malabsorption, fluid turnover, or hypoxic exposure.

Patterns of Brain Activation and Meal Reduction Induced by Abdominal Surgery in Mice and Modulation by Rikkunshito.

Abdominal surgery inhibits food intake and induces c-Fos expression in the hypothalamic and medullary nuclei in rats. Rikkunshito (RKT), a Kampo medicine improves anorexia. We assessed the alterations in meal microstructure and c-Fos expression in brain nuclei induced by abdominal surgery and the modulation by RKT in mice. RKT or vehicle was gavaged daily for 1 week. On day 8 mice had no access to food for 6–7 h and were treated twice with RKT or vehicle. Abdominal surgery (laparotomy-cecum palpation) was performed 1–2 h before the dark phase. The food intake and meal structures were monitored using an automated monitoring system for mice. Brain sections were processed for c-Fos immunoreactivity (ir) 2-h after abdominal surgery. Abdominal surgery significantly reduced bouts, meal frequency, size and duration, and time spent on meals, and increased inter-meal interval and satiety ratio resulting in 92–86% suppression of food intake at 2–24 h post-surgery compared with control group (no surgery). RKT significantly increased bouts, meal duration and the cumulative 12-h food intake by 11%. Abdominal surgery increased c-Fos in the prelimbic, cingulate and insular cortexes, and autonomic nuclei, such as the bed nucleus of the stria terminalis, central amygdala, hypothalamic supraoptic (SON), paraventricular and arcuate nuclei, Edinger-Westphal nucleus (E-W), lateral periaqueduct gray (PAG), lateral parabrachial nucleus, locus coeruleus, ventrolateral medulla and nucleus tractus solitarius (NTS). RKT induced a small increase in c-Fos-ir neurons in the SON and E-W of control mice, and in mice with surgery there was an increase in the lateral PAG and a decrease in the NTS. These findings indicate that abdominal surgery inhibits food intake by increasing both satiation (meal duration) and satiety (meal interval) and activates brain circuits involved in pain, feeding behavior and stress that may underlie the alterations of meal pattern and food intake inhibition. RKT improves food consumption post-surgically that may involve modulation of pain pathway.

Intracortical and Thalamocortical Connections of the Hand and Face Representations in Somatosensory Area 3b of Macaque Monkeys and Effects of Chronic Spinal Cord Injuries.

Brains of adult monkeys with chronic lesions of dorsal columns of spinal cord at cervical levels undergo large-scale reorganization. Reorganization results in expansion of intact chin inputs, which reactivate neurons in the deafferented hand representation in the primary somatosensory cortex (area 3b), ventroposterior nucleus of the thalamus and cuneate nucleus of the brainstem. A likely contributing mechanism for this large-scale plasticity is sprouting of axons across the hand-face border. Here we determined whether such sprouting takes place in area 3b. We first determined the extent of intrinsic corticocortical connectivity between the hand and the face representations in normal area 3b. Small amounts of neuroanatomical tracers were injected in these representations close to the electrophysiologically determined hand-face border. Locations of the labeled neurons were mapped with respect to the detailed electrophysiological somatotopic maps and histologically determined hand-face border revealed in sections of the flattened cortex stained for myelin. Results show that intracortical projections across the hand-face border are few. In monkeys with chronic unilateral lesions of the dorsal columns and expanded chin representation, connections across the hand-face border were not different compared with normal monkeys. Thalamocortical connections from the hand and face representations in the ventroposterior nucleus to area 3b also remained unaltered after injury. The results show that sprouting of intrinsic connections in area 3b or the thalamocortical inputs does not contribute to large-scale cortical plasticity. Significance statement: Long-term injuries to dorsal spinal cord in adult primates result in large-scale somatotopic reorganization due to which chin inputs expand into the deafferented hand region. Reorganization takes place in multiple cortical areas, and thalamic and medullary nuclei. To what extent this brain reorganization due to dorsal column injuries is related to axonal sprouting is not known. Here we show that reorganization of primary somatosensory area 3b is not accompanied with either an increase in intrinsic cortical connections between the hand and face representations, or any change in thalamocortical inputs to these areas. Axonal sprouting that causes reorganization likely takes place at subthalamic levels.

Hydrogen sulfide attenuates hypoxia-induced respiratory suppression in anesthetized adult rats

Our previous study in vitro showed that hydrogen sulfide (H2S) could protect the medullary respiratory centers from injury induced by acute hypoxia in brainstem slices of neonatal rats. The present study was carried out to determine if H2S could exhibit similar protective effects in adult rats and to explore the underlying mechanisms of its protection. It was observed that hypoxia induced a diphasic respiratory response, an excitatory phase followed by an inhibitory one, as indicated by an increase followed by a decrease in frequency of rhythmic discharge of the diaphragm. Nissl staining revealed that some of the neurons in the medullary respiratory related nuclei were impaired in hypoxia rats. Hypoxia led to increases in the content of malondialdehyde (MDA) and the activities of superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px), as well as a decrease in the level of Bcl-2 mRNA of the medulla oblongata. Intracerebroventricular injection of 2.5mM NaHS (a donor of H2S) or L-cysteine (L-Cys, a substrate for H2S) could prevent inhibitory respiratory effect occurred in the rats with hypoxia. Exogenous application of NaHS and L-Cys could also reduce the content of MDA and the activities of SOD and GSH-Px, and increase the level of Bcl-2 mRNA expression of medulla oblongata caused by hypoxia. These results indicate that H2S could protect the medullary respiratory centers against injury induced by acute hypoxia in adult rats partly due to its anti-oxidant and anti-apoptotic effects.

PPG neurons of the lower brain stem and their role in brain GLP-1 receptor activation.

Within the brain, glucagon-like peptide-1 (GLP-1) affects central autonomic neurons, including those controlling the cardiovascular system, thermogenesis, and energy balance. Additionally, GLP-1 influences the mesolimbic reward system to modulate the rewarding properties of palatable food. GLP-1 is produced in the gut and by hindbrain preproglucagon (PPG) neurons, located mainly in the nucleus tractus solitarii (NTS) and medullary intermediate reticular nucleus. Transgenic mice expressing glucagon promoter-driven yellow fluorescent protein revealed that PPG neurons not only project to central autonomic control regions and mesolimbic reward centers, but also strongly innervate spinal autonomic neurons. Therefore, these brain stem PPG neurons could directly modulate sympathetic outflow through their spinal inputs to sympathetic preganglionic neurons. Electrical recordings from PPG neurons in vitro have revealed that they receive synaptic inputs from vagal afferents entering via the solitary tract. Vagal afferents convey satiation to the brain from signals like postprandial gastric distention or activation of peripheral GLP-1 receptors. CCK and leptin, short- and long-term satiety peptides, respectively, increased the electrical activity of PPG neurons, while ghrelin, an orexigenic peptide, had no effect. These findings indicate that satiation is a main driver of PPG neuronal activation. They also show that PPG neurons are in a prime position to respond to both immediate and long-term indicators of energy and feeding status, enabling regulation of both energy balance and general autonomic homeostasis. This review discusses the question of whether PPG neurons, rather than gut-derived GLP-1, are providing the physiological substrate for the effects elicited by central nervous system GLP-1 receptor activation.

Distribution of Fos-Like Immunoreactivity, Catecholaminergic and Serotoninergic Neurons Activated by the Laryngeal Chemoreflex in the Medulla Oblongata of Rats.

The laryngeal chemoreflex (LCR) induces apnea, glottis closure, bradycardia and hypertension in young and maturing mammals. We examined the distribution of medullary nuclei that are activated by the LCR and used immunofluorescent detection of Fos protein as a cellular marker for neuronal activation to establish that the medullary catecholaminergic and serotoninergic neurons participate in the modulation of the LCR. The LCR was elicited by the infusion of KCl-HCl solution into the laryngeal lumen of adult rats in the experimental group, whereas the control group received the same surgery but no infusion. In comparison, the number of regions of Fos-like immunoreactivity (FLI) that were activated by the LCR significantly increased in the nucleus of the solitary tract (NTS), the vestibular nuclear complex (VNC), the loose formation of the nucleus ambiguus (AmbL), the rostral ventral respiratory group (RVRG), the ventrolateral reticular complex (VLR), the pre-Bötzinger complex (PrBöt), the Bötzinger complex (Böt), the spinal trigeminal nucleus (SP5), and the raphe obscurus nucleus (ROb) bilaterally from the medulla oblongata. Furthermore, 12.71% of neurons with FLI in the dorsolateral part of the nucleus of the solitary tract (SolDL) showed tyrosine hydroxylase-immunoreactivity (TH-ir, catecholaminergic), and 70.87% of neurons with FLI in the ROb were serotoninergic. Our data demonstrated the distribution of medullary nuclei that were activated by the LCR, and further demonstrated that catecholaminergic neurons of the SolDL and serotoninergic neurons of the ROb were activated by the LCR, indicating the potential central pathway of the LCR.

Facilitation of the respiratory rhythm in mice by acute exposure to a progestin, the etonogestrel. Involvement of medullary areas

Background Works have underlined the facilitatory influence of progestins on central respiratory drive (CRD). The congenital central hypoventilation syndrome (CCHS) is a neuro-respiratory disease characterized by an alteration of the CO 2 /H + chemosensitivity due to dysfunction of CO 2 /H + chemosensitive/PHOX2b-positive neurons of the retrotrapezoid nucleus/parafacial respiratory group (RTN/pFRG). In our laboratory, a recovery of the CO 2 /H + chemosensitivity was fortuitously observed in two CCHS women who took a potent synthetic progestin, the desogestrel (Respir Physiol Neurobiol 2010;171:171–4). Objective Our aim was to appreciate the effects of an acute exposure to etonogestrel (ETO), the main active metabolite of the desogestrel, on the CRD and to determine its medullary action mechanisms. Methods We used: – an analysis of the effect of ETO (0.05–2 μM) on the CRD of ex vivo medullary-spinal cord preparations from newborn mice in both normopH and metabolic acidosis; – pharmacological co-application of ETO and muscimol or NMDA, agonists of GABA A or NMDA receptors known to be a target of some steroids; – an analysis of the c-fos expression in medullary respiratory structures. Results First, the respiratory frequency was: – dose-dependently increased in normopH by ETO (≈ +23–47%; P – increase by metabolic acidosis similarly under ETO (≈ +28–37% at 0.05–1 μM, P P P Second, changes in respiratory frequency induced by muscimol or NMDA at their EC 50 were more potent under ETO (≈ −60–63%, P P P P c-fos revealed ETO activated cells in respiratory medullary areas i.e. the ventrolateral medulla, nucleus of the solitary tract, RTN/pFRG and medullary raphe nuclei. Conclusions As a whole, data suggest that, by medullary mechanisms, the progestin ETO exerts a facilitatory influence on the CRD by acting at the level of respiratory structures. Involved mechanisms would implicate an interaction with GABA A and NMDA receptors. Besides, at least in newborn mice, ETO do not potentiate the respiratory response to metabolic acidosis by intrinsic medullary mechanisms.

Sporadic Creutzfeldt-Jakob Disease: Prion Pathology in Medulla Oblongata-Possible Routes of Infection and Host Susceptibility.

Sporadic Creutzfeldt-Jakob disease (sCJD), the most frequent human prion disorder, is characterized by remarkable phenotypic variability, which is influenced by the conformation of the pathologic prion protein and the methionine/valine polymorphic codon 129 of the prion protein gene. While the etiology of sCJD remains unknown, it has been hypothesized that environmental exposure to prions might occur through conjunctival/mucosal contact, oral ingestion, inhalation, or simultaneous involvement of the olfactory and enteric systems. We studied 21 subjects with definite sCJD to assess neuropathological involvement of the dorsal motor nucleus of the vagus and other medullary nuclei and to evaluate possible associations with codon 129 genotype and prion protein conformation. The present data show that prion protein deposition was detected in medullary nuclei of distinct sCJD subtypes, either valine homozygous or heterozygous at codon 129. These findings suggest that an “environmental exposure” might occur, supporting the hypothesis that external sources of contamination could contribute to sCJD in susceptible hosts. Furthermore, these novel data could shed the light on possible causes of sCJD through a “triple match” hypothesis that identify environmental exposure, host genotype, and direct exposure of specific anatomical regions as possible pathogenetic factors.

Animal models of REM dysfunctions: what they tell us about the cause of narcolepsy and RBD?

Rapid eye movement sleep behavior disorder (RBD) is a parasomnia characterized by the loss of muscle atonia during paradoxical (REM) sleep (PS). Conversely, cataplexy, one of the key symptoms of narcolepsy, is a striking sudden episode of muscle weakness triggered by emotions during wakefulness, and comparable to REM sleep atonia. The neuronal dysfunctions responsible for RBD and cataplexy are not known. In the present review, we present the most recent results on the neuronal network responsible for PS. Based on these results, we propose an updated integrated model of the mechanisms responsible for PS and explore different hypotheses explaining RBD and cataplexy. We propose that RBD is due to a specific degeneration of a subpopulation of PS-on glutamatergic neurons specifically responsible of muscle atonia, localized in the caudal pontine sublaterodorsal tegmental nucleus (SLD). Another possibility is the occurrence in RBD patients of a specific lesion of the glycinergic/GABAergic premotor-neurons localized in the medullary ventral gigantocellular reticular nucleus. Conversely, cataplexy in narcoleptics would be due to the activation during waking of the caudal PS-on SLD neurons responsible for muscle atonia. A direct or indirect pathway activated during positive emotion from the central amygdala to the SLD PS-on neurons would induce such activation. In normal conditions, the activation of SLD neurons would be blocked by the simultaneous excitation by the hypocretins of the PS-off GABAergic neurons localized in the ventrolateral periaqueductal gray and the adjacent deep mesencephalic reticular nucleus gating the activation of the PS-on SLD neurons.

Animal models of REM dysfunctions: what they tell us about the cause of narcolepsy and RBD?

Rapid eye movement sleep behavior disorder (RBD) is a parasomnia characterized by the loss of muscle atonia during paradoxical (REM) sleep (PS). Conversely, cataplexy, one of the key symptoms of narcolepsy, is a striking sudden episode of muscle weakness triggered by emotions during wakefulness, and comparable to REM sleep ato- nia. The neuronal dysfunctions responsible for RBD and cataplexy are not known. In the present review, we present the most recent results on the neuronal network responsible for PS. Based on these results, we propose an updated integrated model of the mechanisms responsible for PS and explore different hypotheses explaining RBD and cata- plexy. We propose that RBD is due to a specific degeneration of a subpopulation of PS-on glutamatergic neurons specifically responsible of muscle atonia, localized in the caudal pontine sublaterodorsal tegmental nucleus (SLD). Another possibility is the occurrence in RBD patients of a specific lesion of the glycinergic/GABAergic premoto- neurons localized in the medullary ventral gigantocellular reticular nucleus. Conversely, cataplexy in narcoleptics would be due to the activation during waking of the caudal PS-on SLD neurons responsible for muscle atonia. A direct or indirect pathway activated during positive emotion from the central amygdala to the SLD PS-on neurons would induce such activation. In normal conditions, the activation of SLD neurons would be blocked by the simulta- neous excitation by the hypocretins of the PS-off GABAergic neurons localized in the ventrolateral periaqueductal gray and the adjacent deep mesencephalic reticular nucleus gating the activation of the PS-on SLD neurons.

Functional Connections of the Vestibulo-spino-adrenal Axis in the Control of Blood Pressure Via the Vestibulosympathetic Reflex in Conscious Rats.

Significant evidence supports the role of the vestibular system in the regulation of blood pressure during postural movements. In the present study, the role of the vestibulo-spino-adrenal (VSA) axis in the modulation of blood pressure via the vestibulosympathetic reflex was clarified by immunohistochemical and enzyme immunoassay methods in conscious rats with sinoaortic denervation. Expression of c-Fos protein in the intermediolateral cell column of the middle thoracic spinal regions and blood epinephrine levels were investigated, following microinjection of glutamate receptor agonists or antagonists into the medial vestibular nucleus (MVN) and/or sodium nitroprusside (SNP)-induced hypotension. Both microinjection of glutamate receptor agonists (NMDA and AMPA) into the MVN or rostral ventrolateral medullary nucleus (RVLM) and SNP-induced hypotension led to increased number of c-Fos positive neurons in the intermediolateral cell column of the middle thoracic spinal regions and increased blood epinephrine levels. Pretreatment with microinjection of glutamate receptor antagonists (MK-801 and CNQX) into the MVN or RVLM prevented the increased number of c-Fos positive neurons resulting from SNP-induced hypotension, and reversed the increased blood epinephrine levels. These results indicate that the VSA axis may be a key component of the pathway used by the vestibulosympathetic reflex to maintain blood pressure during postural movements.

Cardiac wall motion abnormality after bleeding from vertebral artery aneurysms.

Lesions in the medulla oblongata may be causally associated with cardiac wall motion abnormality (WMA). Although subarachnoid hemorrhage (SAH) patients occasionally develop WMA, the relationship between aneurysmal locations and the frequency of WMA has rarely been investigated. The objective of this study was to evaluate whether the frequency of WMA was higher after the rupture of vertebral artery (VA) aneurysms than that of non-VA aneurysms. We performed a retrospective chart analysis of 244 SAH patients who underwent transthoracic echocardiography and plasma catecholamine measurements. The frequencies of WMA and electrocardiographic (ECG) abnormalities were compared among patients classified by the location of aneurysms. Multivariate regression analysis was conducted to identify variables correlated with WMA. Furthermore, the relationship between plasma catecholamine levels and aneurysmal locations was evaluated. The frequency of WMA was significantly higher in patients with VA aneurysms than in those with non-VA aneurysms (45 vs. 22%, p=0.01). However, there was no significant difference in the frequency of ECG abnormalities. Multivariate regression analysis showed that VA aneurysms (OR, 3.317; 95% CI, 1.129-9.745), poor-grade SAH (OR, 2.733; 95% CI, 1.320-5.658) and concomitant hydrocephalus (OR, 3.658; 95% CI, 1.690-7.917) correlated with WMA. There were no significant intergroup differences in plasma catecholamine levels. VA aneurysms are close to several medullary nuclei that integrate autonomic inputs. A transient deformation and ischemia of the medulla oblongata caused by the mechanical stress related to the rupture of a VA aneurysm and/or a concomitant hydrocephalus may be responsible for the disproportionately high frequency of WMA.

Distribution of orexin-1 receptor-green fluorescent protein- (OX1-GFP) expressing neurons in the mouse brain stem and pons: Co-localization with tyrosine hydroxylase and neuronal nitric oxide synthase

We used a reporter mouse line in which green fluorescent protein (GFP) was inserted into the orexin-1 receptor (OX1) locus to systematically map the neuroanatomical distribution of the OX1 receptor in the mouse brainstem and pons. Here, we show that the OX1 receptor is expressed in a select subset of medullary and pontine nuclei. In the medulla, we observed OX1-GFP expression in the cuneate, gracile, dorsal motor nucleus of the vagus (10N), nucleus of the solitary tract and medullary raphe areas. In the pons, the greatest expression was found in the locus coeruleus (LC) and dorsal raphe nucleus (DRN). High to moderate expression was found in the pedunculopontine tegmental nucleus (PPTg), laterodorsal tegmental nucleus, A5 noradrenergic cell group (A5) and the periaqueductal gray. Double-labeling with neuronal nitric oxide synthase (NOS1) revealed extensive co-localization in cell bodies and fibers of the 10N, A5 cell group and the PPTg. Double-staining with tyrosine hydroxylase revealed extensive co-expression in the LC, DRN and the lateral paragigantocellularis cell group in the ventral medulla. Our findings faithfully recapitulate the findings of OX1 mRNA expression previously reported. This is the first study to systematically map the neuroanatomical distribution of OX1 receptors within the mouse hindbrain and suggest that this OX1-GFP transgenic reporter mouse line might be a useful tool with which to study the neuroanatomy and physiology of OX1 receptor-expressing cells.

The role of serotonin in the control of locomotor movements and strategies for restoring locomotion after spinal cord injury.

In this review we will discuss different ways for re-establishing serotonergic activity that can enhance recovery of coordinated plantar stepping after spinal cord injury in adult rats. It is well known that serotoninergic neurons located in the medulla are able to initiate locomotor activity. This effect is exerted by actions on motoneurons and on neurons of the locomotor CPG (Central Pattern Generator). Motoneuron and interneuron excitability is increased, and putative CPG interneurons display oscillatory behaviour in response to serotonin receptor activation. The medullary serotonergic nuclei play multiple roles in the control of locomotion, and they terminate on specific target neurons with different types of serotonergic receptors in the spinal cord. Activation of these serotonergic receptors can restore locomotor movements after spinal cord injury. Specifically, using defined serotonergic agonists the 5-HT2 receptors can be stimulated to control CPG activation as well as motoneuron output, while 5-HT7 receptors to control activity of the locomotor CPG. These results are consistent with the roles for these receptors during locomotion in intact rodents and in rodent brainstem-spinal cord in vitro preparations. The other possibility to encourage the remaining spinal cord circuitry below the total transection to control recovery of plantar hindlimb stepping is restoration of serotonergic innervation by intraspinal grafting of embryonic 5-HT neurons. Our data show that grafting of different populations of 5-HT neurons dissected from embryonic brainstem provides differential control over multiple components of the spinal locomotor circuitry through specific serotonin receptors. Moreover, we demonstrated that the best effect of motor recovery is obtained after grafting of neurons destined to form the B1, B2 and B3 descending 5-HT systems. Using only one of the subpopulations for intraspinal grafting, for example, B3 or the lateral group of 5-HT neurons, induces only partial recovery of plantar stepping with a clear lack of proper interlimb coordination. This confirms the hypothesis that transplantation of 5-HT neurons from specific embryonic sources is necessary to obtain optimal recovery of locomotor hindlimb movement.

Changes in the Structural Organization of the Nucleus Raphe Pallidus in Conditions of Decreased Endogenous Serotonin During Prenatal Development in Rats

The role of serotonin in the development of the nucleus raphe pallidus (NRP) and the dynamics of changes in serotonin-synthesizing neurons in this nucleus were studied at different points in the postnatal period in Wistar rats in normal conditions and in animals whose intrauterine development proceeded on the background of serotonin deficiency. The NRP was found to include two populations of serotoninergic neurons, differing in terms of their morphological characteristics. At the initial stages of postnatal development (day 5), only large neurons synthesized serotonin, while the synthetic activity of small neurons appeared later, by day 10. In normal animals, increasing age was associated with increases in the size and number of large neurons, which may be evidence for a continuing process of differentiation and/or an increase in the functional loading. The size and number of small neurons showed virtually no change with age. Serotonin deficit during prenatal development led to abnormalities in the structural organization of the NRP. As compared with controls, there were reductions in the sizes and numbers of serotonin-synthesizing neurons of both populations, with no change in size with age. Some neurons developed degenerative changes, reducing the number of cells. The damage seen would alter the serotoninergic innervation of the medullary nuclei responsible for cardiorespiratory regulation, and would thus impair the activity of the cardiovascular and respiratory systems.