Lateral Paragigantocellular Nucleus Research Articles

Hypoxia and Hypercapnia Impairs Cardiac Vagal Control: the Role of Orexin

Patients with obstructive sleep apnea (OSA) have an increased risk of cardiovascular diseases and altered plasma levels of orexin. REM sleep further increases the incidence of adverse cardiovascular events. The mechanisms underlying REM sleep‐related reduction in parasympathetic activity include activation of inhibitory input to cardiac vagal neurons (CVNs) in the brainstem originating from the lateral paragigantocellular nucleus (LPGi), a nucleus which plays a role in REM sleep control. This study tests the hypotheses that (1) chronic intermittent hypoxia and hypercapnia (CIHH) inhibits CVNs due to exaggeration of GABAergic pathway from the LPGi to CVNs; (2) orexinergic signaling in CVNs is diminished by CIHH; and (3) identified orexin neurons (orexin‐EGFP‐2A‐Cre rat) are inhibited by acute hypoxia/hypercapnia. GABAergic neurotransmission to CVNs evoked by electrical stimulation of the LPGi was examined using whole‐cell patch‐clamp recordings in rats exposed to CIHH and control rats. GABAergic synaptic events were enhanced following 4 weeks of CIHH. Orexin‐A elicited inhibition of LPGi‐evoked GABAergic current in control animals but evoked no significant changes in CIHH rats. Acute hypoxia/hypercapnia inhibited the firing activity of orexin neurons and diminished glutamatergic neurotransmission to orexin neurons. In summary, repetitive episodes of hypoxia/hypercapnia would diminish activity of orexin neurons, including the orexinergic neurotransmission to CVNs. Diminished orexinergic signaling, along with exaggerated inhibitory neurotransmission from the LPGi to CVNs would reduce cardio‐protective parasympathetic activity and increase risk of cardiovascular diseases.Support: Christian Gillin Research Grant 004GN12 to O.D. and NIH grants HL49965, HL59895 and HL72006 to D.M.

Terminations of reticulospinal fibers originating from the gigantocellular reticular formation in the mouse spinal cord.

The present study investigated the projections of the gigantocellular reticular nucleus (Gi) and its neighbors--the dorsal paragigantocellular reticular nucleus (DPGi), the alpha/ventral part of the gigantocellular reticular nucleus (GiA/V), and the lateral paragigantocellular reticular nucleus (LPGi)--to the mouse spinal cord by injecting the anterograde tracer biotinylated dextran amine (BDA) into the Gi, DPGi, GiA/GiV, and LPGi. The Gi projected to the entire spinal cord bilaterally with an ipsilateral predominance. Its fibers traveled in both the ventral and lateral funiculi with a greater presence in the ventral funiculus. As the fibers descended in the spinal cord, their density in the lateral funiculus increased. The terminals were present mainly in laminae 7-10 with a dorsolateral expansion caudally. In the lumbar and sacral cord, a considerable number of terminals were also present in laminae 5 and 6. Contralateral fibers shared a similar pattern to their ipsilateral counterparts and some fibers were seen to cross the midline. Fibers arising from the DPGi were similarly distributed in the spinal cord except that there was no dorsolateral expansion in the lumbar and sacral segments and there were fewer fiber terminals. Fibers arising from GiA/V predominantly traveled in the ventral and lateral funiculi ipsilaterally. Ipsilaterally, the density of fibers in the ventral funiculus decreased along the rostrocaudal axis, whereas the density of fibers in the lateral funiculus increased. They terminate mainly in the medial ventral horn and lamina 10 with a smaller number of fibers in the dorsal horn. Fibers arising from the LPGi traveled in both the ventral and lateral funiculi and the density of these fibers in the ventral and lateral funiculi decreased dramatically in the lumbar and sacral segments. Their terminals were present in the ventral horn with a large portion of them terminating in the motor neuron columns. The present study is the first demonstration of the termination pattern of fibers arising from the Gi, DPGi, GiA/GiV, and LPGi in the mouse spinal cord. It provides an anatomical foundation for those who are conducting spinal cord injury and locomotion related research.

Chronic intermittent hypoxia alters neurotransmission from lateral paragigantocellular nucleus to parasympathetic cardiac neurons in the brain stem.

Patients with sleep-related disorders, including obstructive sleep apnea (OSA), have an increased risk of cardiovascular diseases. OSA events are more severe in rapid eye movement (REM) sleep. REM sleep further increases the risk of adverse cardiovascular events by diminishing cardioprotective parasympathetic activity. The mechanisms underlying REM sleep-related reduction in parasympathetic activity likely include activation of inhibitory input to cardiac vagal neurons (CVNs) in the brain stem originating from the lateral paragigantocellular nucleus (LPGi), a nucleus that plays a role in REM sleep control. This study tests the hypothesis that chronic intermittent hypoxia and hypercapnia (CIHH), an animal model of OSA, inhibits CVNs because of exaggeration of the GABAergic pathway from the LPGi to CVNs. GABAergic neurotransmission to CVNs evoked by electrical stimulation of the LPGi was examined with whole cell patch-clamp recordings in an in vitro brain slice preparation in rats exposed to CIHH and control rats. GABAergic synaptic events were enhanced after 4-wk CIHH in both male and female rats, to a greater degree in males. Acute hypoxia and hypercapnia (H/H) reversibly diminished the LPGi-evoked GABAergic neurotransmission to CVNs. However, GABAergic synaptic events were enhanced after acute H/H in CIHH male animals. Orexin-A elicited a reversible inhibition of LPGi-evoked GABAergic currents in control animals but evoked no significant changes in CIHH male rats. In conclusion, exaggerated inhibitory neurotransmission from the LPGi to CVNs in CIHH animals would reduce cardioprotective parasympathetic activity and enhance the risk of adverse cardiovascular events.

Connections of the magnocellular medial preoptic nucleus (MPN mag) in male Syrian hamsters. II. The efferents

The magnocellular medial preoptic nucleus (MPN mag) plays a critical role in the regulation of male copulatory behavior in the Syrian hamster. Our study of the afferents are consistent with the hypothesis that the MPN mag receives input from areas in the chemosensory pathway and nuclear groups that contain receptors for gonadal steroids (Wang and Swann, 2006). The goal of the present study is to identify targets of the MPN mag by describing the location of labeled fibers following an injection of biotinylated dextran amine (BDA) into the MPN mag. Our results indicate that targets of the MPN mag include: (1) brainstem nuclei implicated in regulating male mating behavior in other species, such as the periaqueductal gray, deep mesencephalic nucleus, retrorubral field, ventral tegmental area and lateral paragigantocellular nucleus and (2) steroid-concentrating nuclei in the septum, preoptic area and hypothalamus. The lack of projections from the MPN mag to its chemosensory afferents indicate that the connections of the MPN mag with the posterior medial bed nucleus of the stria terminalis, medial and anterior cortical nuclei of the amygdala are unidirectional, and that chemosensory information flows from the medial amygdala and bed nucleus of the stria terminalis (BST) to the MPN mag. The bidirectional nature of the connections between the MPN mag and steroid-concentrating nuclei suggest that the MPN mag may influence the function of a steroid-concentrating network that regulates behaviors. Together these results support the hypothesis that the MPN mag regulates male mating behavior by integrating chemosensory and hormonal signals and relaying this information to brainstem areas that control motor output.

Activation of Neurons in the Rat Medulla Following a Gag Reflex Stimulus

Despite the fact that a number of individuals present with a hypersensitive gag reflex, research in this area has been limited to clinical applications. An animal model that describes the neurologic underpinnings of the gag reflex has not been reported. Thus, the objective of the current study was to localize activated neurons in the rat medulla and to investigate their neurochemistry following mechanostimulation to the posterior pharyngeal wall eliciting a gag reflex response. Activated neurons, determined using c-fos immunohistochemistry, were observed in subnuclei of the nucleus tractus solitarius (NTS) and motor regions such as dorsal motor vagus, hypoglossal, and nucleus ambiguus. The lateral and dorsal paragigantocellular nuclei and the medial rostral ventrolateral nucleus involved in bitter taste processing, also showed robust activation. Tyrosine hydroxylase and/or choline acetyltransferase immunoreactivity was localized in many activated neurons. The results of the present study provide the first documentation of activated neurons and preliminary neurochemistry in brainstem nuclei that are unique to mechanostimulation to the posterior pharyngeal wall. Our results support postulated medullary structures involved with the gag reflex and propose new regions to be added to the circuitry model. Further, our results reveal an activation pattern within the NTS unique to the gag reflex. Keywords: Brain stem, Nucleus of the solitary tract, neuroanatomy, animal model, pediatric feeding. Read more →

Brain neuronal activation induced by flibanserin treatment in female rats

Flibanserin, a 5-HT1A agonist and 5-HT2A antagonist, is developed for the treatment of hypoactive sexual desire disorder in women, and its efficacy has been evidenced in several clinical studies. Flibanserin prosexual effects have been also evidenced in preclinical animal models. However, the mechanism of action of flibanserin remains not fully understood. The aim of the present study was to examine brain neuronal activation in female rats treated with flibanserin, using single immunocytochemical labeling of Fos protein, a marker of neuronal activation, and co-localization of Fos and catecholaminergic marker. Six groups of female rats received either acute or chronic administrations of vehicle, flibanserin 15mg/kg or flibanserin 45mg/kg. The brains were collected and processed for immunocytochemical labeling. Acute flibanserin increased levels of Fos immunoreactivity in the nucleus accumbens, arcuate hypothalamic nucleus, locus coeruleus, lateral paragigantocellular nucleus, and nucleus of the solitary tract. Chronic 22-day treatment with flibanserin increased Fos expression in the medial preoptic area and arcuate nucleus of the hypothalamus, ventral tegmental area, locus coeruleus, and lateral paragigantocellular nucleus. Both acute and chronic flibanserin increased the density of activated catecholaminergic neurons in the ventral tegmental area but not in the locus coeruleus. Altogether, our results showed that flibanserin, at the dose known to enhance female sexual motivation, preferentially activated the brain regions belonging to the mesolimbic dopaminergic pathway and hypothalamic structures involved in the integration of sexual cues related to sexual motivation.

Expression of the ghrelin receptor gene in neurons of the medulla oblongata of the rat

There is ambiguity concerning the distribution of neurons that express the ghrelin receptor (GHSR) in the medulla oblongata. In the current study we used a sensitive nonradioactive method to investigate GHSR mRNA distribution by in situ hybridization. Strong expression of the GHSR gene was confirmed in neurons of the facial nucleus (FacN, 7), the dorsal vagal complex (DVC), and the semicompact (but not compact) nucleus ambiguus (AmbSC and AmbC). In addition, expression of GHSR was found in other regions, where it had not been described before. GHSR-positive neurons were observed in the gustatory rostral nucleus tractus solitarius and in areas involved in vestibulo-ocular processing (such as the medial vestibular nucleus and the nucleus abducens). GHSR expression was also noted in ventral areas associated with cardiorespiratory control, including the gigantocellular reticular nucleus, the lateral paragigantocellular nucleus, the rostral and caudal ventrolateral medulla, the (pre)-Bötzinger complex, and the rostral and caudal ventrolateral respiratory group. However, GHSR-positive neurons in ventrolateral areas did not express markers for cardiovascular presympathetic vasomotor neurons, respiratory propriobulbar rhythmogenic neurons, or sensory interneurons. GHSR-positive cells were intermingled with catecholamine neurons in the dorsal vagal complex but these populations did not overlap. Thus, the ghrelin receptor occurs in the medulla oblongata in 1) second-order sensory neurons processing gustatory, vestibulo-ocular, and visceral sensation; 2) cholinergic somatomotor neurons of the FacN and autonomic preganglionic neurons of the DMNX and AmbSC; 3) cardiovascular neurons in the DVC, Gi, and LPGi; 4) neurons of as yet unknown function in the ventrolateral medulla.

Postnatal development of brain‐derived neurotrophic factor (BDNF) and tyrosine protein kinase B (TrkB) receptor immunoreactivity in multiple brain stem respiratory‐related nuclei of the rat

Previously, we found a transient imbalance between suppressed excitation and enhanced inhibition in the respiratory network of the rat around postnatal days (P) 12-13, a critical period when the hypoxic ventilatory response is at its weakest. The mechanism underlying the imbalance is poorly understood. Brain-derived neurotrophic factor (BDNF) and its tyrosine protein kinase B (TrkB) receptors are known to potentiate glutamatergic and attenuate gamma-aminobutyric acid (GABA)ergic neurotransmission, and BDNF is essential for respiratory development. We hypothesized that the excitation-inhibition imbalance during the critical period stemmed from a reduced expression of BDNF and TrkB at that time within respiratory-related nuclei of the brain stem. An in-depth, semiquantitative immunohistochemical study was undertaken in seven respiratory-related brain stem nuclei and one nonrespiratory nucleus in P0-21 rats. The results indicate that the expressions of BDNF and TrkB: 1) in the pre-Bötzinger complex, nucleus ambiguus, commissural and ventrolateral subnuclei of solitary tract nucleus, and retrotrapezoid nucleus/parafacial respiratory group were significantly reduced at P12, but returned to P11 levels by P14; 2) in the lateral paragigantocellular nucleus and parapyramidal region were increased from P0 to P7, but were strikingly reduced at P10 and plateaued thereafter; and 3) in the nonrespiratory cuneate nucleus showed a gentle plateau throughout the first 3 postnatal weeks, with only a slight decline of BDNF expression after P11. Thus, the significant downregulation of both BDNF and TrkB in respiratory-related nuclei during the critical period may form the basis of, or at least contribute to, the inhibitory-excitatory imbalance within the respiratory network during this time.

Role of the Lateral Paragigantocellular Nucleus in the Network of Paradoxical (REM) Sleep: An Electrophysiological and Anatomical Study in the Rat

The lateral paragigantocellular nucleus (LPGi) is located in the ventrolateral medulla and is known as a sympathoexcitatory area involved in the control of blood pressure. In recent experiments, we showed that the LPGi contains a large number of neurons activated during PS hypersomnia following a selective deprivation. Among these neurons, more than two-thirds are GABAergic and more than one fourth send efferent fibers to the wake-active locus coeruleus nucleus. To get more insight into the role of the LPGi in PS regulation, we combined an electrophysiological and anatomical approach in the rat, using extracellular recordings in the head-restrained model and injections of tracers followed by the immunohistochemical detection of Fos in control, PS-deprived and PS-recovery animals. With the head-restrained preparation, we showed that the LPGi contains neurons specifically active during PS (PS-On neurons), neurons inactive during PS (PS-Off neurons) and neurons indifferent to the sleep-waking cycle. After injection of CTb in the facial nucleus, the neurons of which are hyperpolarized during PS, the largest population of Fos/CTb neurons visualized in the medulla in the PS-recovery condition was observed in the LPGi. After injection of CTb in the LPGi itself and PS-recovery, the nucleus containing the highest number of Fos/CTb neurons, moreover bilaterally, was the sublaterodorsal nucleus (SLD). The SLD is known as the pontine executive PS area and triggers PS through glutamatergic neurons. We propose that, during PS, the LPGi is strongly excited by the SLD and hyperpolarizes the motoneurons of the facial nucleus in addition to local and locus coeruleus PS-Off neurons, and by this means contributes to PS genesis.

Hypocretin-1 (orexin A) prevents the effects of hypoxia/hypercapnia and enhances the GABAergic pathway from the lateral paragigantocellular nucleus to cardiac vagal neurons in the nucleus ambiguus

Hypocretins (orexins) are hypothalamic neuropeptides that play a crucial role in regulating sleep/wake states and autonomic functions including parasympathetic cardiac activity. We have recently demonstrated stimulation of the lateral paragigantocellular nucleus (LPGi), the nucleus which is thought to play a role in rapid eye movement (REM) sleep control, activates an inhibitory pathway to preganglionic cardiac vagal neurons in the nucleus ambiguus (NA). In this study we test the hypothesis that hypocretin-1 modulates the inhibitory neurotransmission to cardiac vagal neurons evoked by stimulation of the LPGi using whole-cell patch-clamp recordings in an in vitro brain slice preparation from rats. Activation of hypocretin-1 receptors produced a dose-dependent and long-term facilitation of GABAergic postsynaptic currents evoked by electrical stimulation of the LPGi. Hypoxia/hypercapnia diminished LPGi-evoked GABAergic current in cardiac vagal neurons and this inhibition by hypoxia/hypercapnia was prevented by pre-application of hypocretin-1. The action of hypocretin-1 was blocked by the hypocretin-1 receptor antagonist SB-334867. Facilitation of LPGi-evoked GABAergic current in cardiac vagal neurons under both normal condition and during hypoxia/hypercapnia could be the mechanism by which hypocretin-1 affects parasympathetic cardiac function and heart rate during REM sleep. Furthermore, our findings indicate a new potential mechanism that might be involved in the cardiac arrhythmias, bradycardia, and sudden cardiac death that can occur during sleep.

The Lateral Paragigantocellular Nucleus Modulates Parasympathetic Cardiac Neurons: A Mechanism for Rapid Eye Movement Sleep-Dependent Changes in Heart Rate

Rapid eye movement (REM) sleep is generally associated with a withdrawal of parasympathetic activity and heart rate increases; however, episodic vagally mediated heart rate decelerations also occur during REM sleep. This alternating pattern of autonomic activation provides a physiological basis for REM sleep-induced cardiac arrhythmias. Medullary neurons within the lateral paragigantocellular nucleus (LPGi) are thought to be active after REM sleep recovery and play a role in REM sleep control. In proximity to the LPGi are parasympathetic cardiac vagal neurons (CVNs) within the nucleus ambiguus (NA), which are critical for controlling heart rate. This study examined brain stem pathways that may mediate REM sleep-related reductions in parasympathetic cardiac activity. Electrical stimulation of the LPGi evoked inhibitory GABAergic postsynaptic currents in CVNs in an in vitro brain stem slice preparation in rats. Because brain stem cholinergic mechanisms are involved in REM sleep regulation, we also studied the role of nicotinic neurotransmission in modulation of GABAergic pathway from the LGPi to CVNs. Application of nicotine diminished the GABAergic responses evoked by electrical stimulation. This inhibitory effect of nicotine was prevented by the alpha7 nicotinic receptor antagonist alpha-bungarotoxin. Moreover, hypoxia/hypercapnia (H/H) diminished LPGi-evoked GABAergic current in CVNs, and this inhibitory effect was also prevented by alpha-bungarotoxin. In conclusion, stimulation of the LPGi evokes an inhibitory pathway to CVNs, which may constitute a mechanism for the reduced parasympathetic cardiac activity and increase in heart rate during REM sleep. Inhibition of this pathway by nicotinic receptor activation and H/H may play a role in REM sleep-related and apnea-associated bradyarrhythmias.

Inhibition of cardiac baroreflex by noxious thermal stimuli: A key role for lateral paragigantocellular serotonergic cells

The present study was designed to identify the neuronal mechanisms causing cardiac baroreflex inhibition associated with thermal nociception in rats. Under urethane-anesthesia, noxious thermal stimuli ⩾48 °C were found to inhibit the cardiac baroreflex, whereas noxious stimuli ⩽46 °C had no effect. Using double immunohistochemical labeling, noxious stimuli ⩾48 °C were found to evoke primarily a strong expression of Fos protein (Fos) encoded by c-fos gene in serotonergic neurons of lateral paragigantocellular reticular nucleus (LPGi). Noxious stimuli ⩽46 °C did not evoke Fos expression in any serotonergic neurons of the brainstem. Local blockade of neuronal activity by bilateral microinjections of fluorescent muscimol (a GABA A receptor agonist tagged with a fluorophore that allowed visualization of the injections) into both the LPGi and the raphe magnus nucleus prevented the inhibitory effect of noxious stimuli ⩾48 °C on the cardiac baroreflex. Bilateral microinjections of granisetron (a 5-HT 3 antagonist) within the nucleus tractus solitarius also prevented the inhibition of cardiac baroreflex elicited by noxious stimuli ⩾48 °C. These results show that activation of serotonergic cells in the LPGi is critical to trigger nucleus tractus solitarius-mediated cardiac baroreflex inhibition elicited by intense thermal noxious stimuli.

Extracellular-signal regulated kinases expression is altered in brainstem nuclei during neuropathic pain and antidepressants treatment

Event Abstract Back to Event Extracellular-signal regulated kinases expression is altered in brainstem nuclei during neuropathic pain and antidepressants treatment Gisela Borges1, Esther Berrocoso2, Antonio Ortega-Alvaro2, Juan Antonio-Mico2 and Fani L. Neto1* 1 Universidade do Porto, Instituto de Histologia e Embriologia, Faculdade de Medicina do Porto e Instituto de Biologia Molecular e Celular (IBMC), Portugal 2 Universitad de Cadiz, Departamento de Neurociencias,Facultad de Medicina, Spain Antidepressants are prescribed for neuropathic pain relief but the underlying mechanisms are not understood. Extracellular-signal regulated kinases (ERKs) have been implicated both in antidepressants effects and in pain processing. Here, we evaluated the effect of noxious stimulation or antidepressants administration on ERKs’ activation in the chronic constriction injury (CCI) model of neuropathic pain in rats.CCI was surgically induced by loose ligation of the sciatic nerve. Control rats were sham-operated. To evaluate the effect of noxious stimulation on ERKs activation, SHAM and CCI anaesthetised rats received mechanical stimulation in the ipsilateral hindpaw (SHAM or CCI stimulated, SS and CCI-S, respectively). Other rats did not receive stimulation (SHAM or CCI not stimulated, SNS and CCI-NS, respectively). To study the influence of two antidepressants, separate groups of CCI or SHAM rats were treated for 21 days with saline (SA), amitrityline (AMI, a tricyclic antidepressant) or duloxetine (DLX, a serotonin and norepinephrine reuptake inhibitor). The amount of antidepressant diluted in water/day was evaluated for each rat. Hyperalgesia was analysed by the plantar and the paw pinch nociceptive tests. Immunoreactive cells against pERKs1/2 were counted in monoaminergic brainstem nuclei.Baseline ERKs1/2 activation was observed in monoaminergic brainstem areas of SNS and SHAM-SA animals, like the A5, Locus Coeruleus (LC), Lateral Paragigantocellular (LPGi) and Lateral Reticular (LRt) nuclei. CCI-S or CCI-NS rats showed increased pERKs expression in the A5, LPGi and LRt, but in LC labelling intensity decreased. No changes were detected between stimulated and non-stimulated either in SHAM or CCI groups of rats. AMI and either AMI or DLX induced increases in pERKs expression in A5 and LPGI, respectively, of SHAM rats. Contrarily, among CCI rats antidepressants had no effect on ERKs activation in any region studied, but significant decreases were detected in CCI-AMI when compared to SHAM-AMI rats, in A5 and in Dorsal Raphe. No differences were detected for DLX.Neuropathic pain changed ERKs1/2 activation pattern on some brainstem regions while noxious stimulation had no effects. Additionally antidepressants seem to act on ERKs pathway in serotonergic and/or noradrenergic regions under normal conditions. However, under chronic painful input these mechanisms seem altered.Grant: PI070687, HP2006-0062, Spain; E-42/07, CRUP, Portugal. Conference: 11th Meeting of the Portuguese Society for Neuroscience, Braga, Portugal, 4 Jun - 6 Jun, 2009. Presentation Type: Oral Presentation Topic: Symposium 5 – Pain Citation: Borges G, Berrocoso E, Ortega-Alvaro A, Antonio-Mico J and Neto FL (2009). Extracellular-signal regulated kinases expression is altered in brainstem nuclei during neuropathic pain and antidepressants treatment. Front. Neurosci. Conference Abstract: 11th Meeting of the Portuguese Society for Neuroscience. doi: 10.3389/conf.neuro.01.2009.11.024 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 05 Aug 2009; Published Online: 05 Aug 2009. * Correspondence: Fani L Neto, Universidade do Porto, Instituto de Histologia e Embriologia, Faculdade de Medicina do Porto e Instituto de Biologia Molecular e Celular (IBMC), Porto, Portugal, fanineto@med.up.pt Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Gisela Borges Esther Berrocoso Antonio Ortega-Alvaro Juan Antonio-Mico Fani L Neto Google Gisela Borges Esther Berrocoso Antonio Ortega-Alvaro Juan Antonio-Mico Fani L Neto Google Scholar Gisela Borges Esther Berrocoso Antonio Ortega-Alvaro Juan Antonio-Mico Fani L Neto PubMed Gisela Borges Esther Berrocoso Antonio Ortega-Alvaro Juan Antonio-Mico Fani L Neto Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Development of the Vestibular Apparatus and Central Vestibular Connections in a Wallaby (Macropus eugenii)

We have studied the early development of the vestibular apparatus and its central connections in the tammar wallaby (Macropus eugenii) in order to determine whether the vestibular system anatomy is sufficiently mature at birth to assist in climbing to the pouch. Structural development was studied with the aid of hematoxylin and eosin stained sections and immunoreactivity for GAP-43, whereas the development of vestibular system connections was examined by carbocyanine dye tracing. At the time of birth, the otocyst has distinct utricle, saccule and semicircular canals with immature sensory regions receiving innervation by GAP-43 immunoreactive fibers. Vestibular nerve fibers can be traced into the brainstem to the developing vestibular nuclei, which are not yet cytoarchitectonically distinct. The vestibular nuclei do not contribute direct projections to the lower cervical spinal cord at birth; most bulbospinal projections in the newborn appear to be derived bilaterally from the gigantocellular, lateral paragigantocellular reticular and ventral medullary nuclei. A substantial bilateral projection to the vestibular ganglion and apparatus from the region of the gigantocellular and lateral paragigantocellular nuclei was seen at birth, but not in subsequent ages. This is similar to a projection seen in newborn Ameridelphians. By postnatal day (P) 5, the vestibular apparatus had extensive projections to all vestibular nuclei and neurons projecting in the lateral vestibulospinal tract could be identified in the lateral vestibular nucleus. Cytoarchitectonic differentiation of the vestibular nuclei proceeded over the next 3 to 4 weeks with the emergence of discrete parvicellular and magnocellular components of the medial vestibular nucleus by P19. GAP-43 immunoreactivity stayed high in the lateral vestibulospinal tract for several months after birth, suggesting that the development of this tract followed a prolonged timecourse. Our findings indicate that central and peripheral connections of the vestibular ganglion are present at birth, but that there is no direct projection from the vestibular nuclei to the cervical spinal cord until P5. Nevertheless, the possibility remains that an indirect projection between the vestibular nuclei and the medial reticular formation is present at birth and mediates control of the climb.

Collateral axonal projections from rostral ventromedial medullary nitric oxide synthase containing neurons to brainstem autonomic sites

The magnocellular reticular nucleus and adjacent lateral paragigantocellular nucleus have been shown to contain a large population of nitric oxide synthase (NOS) immunoreactive neurons. However, little is known about the projections of these neurons within the central nervous system. Retrograde tract-tracing techniques combined with immunohistochemistry were used in this study to investigate whether NOS neurons in this rostral ventromedial medullary (RVMM) region send collateral axonal projections to autonomic sites in the nucleus of the solitary tract (NTS) and in the nucleus ambiguus (Amb). Fluorogold and/or rhodamine labeled latex microspheres were microinjected into the NTS and Amb at sites that elicited bardycardia and/or depressor responses ( l-glutamate; 0.25 M; 10 nl). After a survival period of 10–14 days, the rats were sacrificed and tissue sections of the brainstem were processed immunohistochemically for the identification of NOS containing neuronal perikarya. After unilateral injection of the tract-tracers into the NTS and Amb, retrogradely labeled neurons were observed bilaterally throughout the RVMM region. Of the number of RVMM neurons retrogradely labeled from the NTS (684 ± 143), 9% were found to be immunoreactive to NOS. Similarly, of those RVMM neurons retrogradely labeled from the Amb (963 ± 207), 7% also contained NOS immunoreactivity. Neurons with collateral axonal projections to NTS and Amb (14% and 10%, respectively) were observed predominantly within a region of RVMM that extended co-extensively with approximately the rostrocaudal extent of the facial nucleus. Of these double labeled neurons, 36.4 ± 20 (39%) were also found to be immunoreactive to NOS. These data indicate that the RVMM contains at least three population of NOS neurons that send axons to innervate functionally similar cardiovascular responsive sites in the NTS and Amb. Although the function of these NOS containing medullary pathways in cardiovascular control is not known, it is likely that those with collateral axonal projections represent the anatomical substrate by which the RVMM may simultaneously coordinate cardiovascular responses during physiological changes associated with respiration and/or motor movements.

Critical role of B3 serotonergic cells in baroreflex inhibition during the defense reaction triggered by dorsal periaqueductal gray stimulation

The present study was designed to identify the serotonergic pathway causing baroreflex inhibition associated with the defense reaction in rats. Under conditions that produce physiological responses typical of the defense reaction, electrical stimulation of the dorsal periaqueductal gray (dPAG) was found to double c-Fos immunoreactive serotonergic neurons within the mid-rostrocaudal extent of the B3 group (which comprises the raphe magnus and the lateral paragigantocellular reticular nuclei) in anesthetized rats. Local blockade of neuronal activity by microinjection of muscimol (a GABA(A) receptor agonist) directly into the B3 region prevented the inhibitory effect of dPAG activation on the cardiac baroreflex. Conversely, neuron activation by local application of D,L-homocysteic acid into B3 region caused baroreflex inhibition that was suppressed by microinjection of granisetron (a 5-HT(3) antagonist) into the nucleus tractus solitarius. These results show that activation of serotonergic cells in the mid-portion of B3 group is critical to trigger baroreflex inhibition occurring during the defense reaction evoked by dPAG stimulation.

Supraspinal Site of Action for the Inhibition of Ejaculatory Reflex by Dapoxetine

ObjectivesThe aim of the study was to determine whether dapoxetine, a short-acting selective serotonin reuptake inhibitor, acts at the spinal or supraspinal level to inhibit the ejaculatory reflex. MethodsThe pudendal motoneuron reflex discharges (PMRDs) model was used as an experimental paradigm of the ejaculatory expulsion reflex in anaesthetised male rats. A spinal site of action was evaluated by testing the effect of intrathecal delivery of dapoxetine on PMRDs elicited by electric stimulation of the dorsal nerves of the penis (DNP). A supraspinal site of action was evaluated by testing the effect of intravenous administration of dapoxetine on DNP-induced PMRDs in rats with chemical bilateral lesion of the lateral paragigantocellular nucleus (LPGi). ResultsCompared with control (NaCl 0.9%, intrathecally), intrathecal injection of dapoxetine (1 and 80μg) significantly increased amplitude of DNP-elicited PMRDs in a similar fashion than serotonin (5-HT; 10 and 100μg, intrathecally). In rats having received bilaterally NaCl 0.9% into LPGi, intravenous treatment with dapoxetine (3mg/kg) induced significant delay in PMRD latency and decrease in PMRD amplitude compared with pretreatment values. These effects were abolished in rats having received bilaterally kainic acid into LPGi 1 d before testing. ConclusionsThe present study showed that dapoxetine inhibits ejaculatory expulsion reflex by acting at a supraspinal level with LPGi as a necessary brain structure for this effect.

The effect of paragigantocellularis lateralis lesion on conditioned place preference (CPP) in presence or absence of a 2 adrenergic agonist (clonidine) in male rats

The nucleus paragigantocellularis lateralis (LPGi) is located in the rostral ventrolateral medulla (RVLM), a brain stem region that regulates homeostatic functions such as blood pressure and cardiovascular reflexes, respiration, pain and opiate withdrawal syndrome. LPGi has many anatomical relationships with important nuclei such as arcute nucleus, caudal raphe nucleus, periaqueductal gray (PAG), locus coeruleus (LC), and dentate. In this study we have examined the role of LPGi in the conditioned place preference (CPP) induced by morphine in the presence and absence of clonidine in the rat. We used 49 male N-MRI rats which were divided into 7 groups randomly: 1: Control, 2: Control+saline, 3: sham control, 4: lesion, 5: lesion +0.02 mg/kg clonidine, 6: lesion +0.2 mg/kg clonidine, 7: lesion +2 mg/kg clonidine. Animals were anaesthetized with ketamine (110 mg/kg) and rampune (Xylazine) (3 mg/kg) mixture. In the process of surgery LPGi nucleus has been destroyed bilaterally by DC electrical current (1 mA, 6 second), with stainless steel electrode placed in stereotaxic coordinates of (AP = 11.8, Lat +/- 1.86 and Depth = 10.5). After the recovery period, they were treated with clonidine one hour before the application of Hand's method to induce CPP. We have not found any significant differences between the results of control, control+saline and sham groups in the CPP test but there is a significant increase in the CPP time between sham and LPGi lesion+saline groups (P < 0.019). Clonidine at different doses (0.02, 0.2 and 2 mg/kg) have decreased CPP time in LPGi lesioned group in comparison with lesioned+saline group as well (p < 0.002). In this study we have also demonstrated that clonidine has not any effects on the CPP time in the intact animals. Our results indicate that LPGi lesion induces CPP. It seems that LPGi is involved in drug reinforcements and also LPGi lesion induces sensitivity to alpha2 adrenergic agonist.

THE EFFECT OF GENDER ON THE DISTRIBUTION OF UROCORTIN NEURONS IN THE BRAINSTEM

Intraventricular (icv) administration of urocortin (ucn), a neuropeptide closely related to the hypothalamic hormone corticotropin-releasing factor, has been shown to elicit transient sympathoexcitatory responses in the male rat. However, the central sites at which ucn exerts these effects and whether gender differences exist in the location and distribution of ucn neurons are not known. In this study, experiments were done in male, and in female ovariectomized (OVX) only and OVX 17β-estradiol (30 pg/ml plasma; OVX+E) treated Wistar rats to investigate the distribution of neurons in the brainstem containing ucn-like immunoreactivity. Six to 9 weeks after OVX or OVX+E, animals were given an icv injection of colchicine 48 hours prior to sacrifice. In all three experimental cases, ucn neurons were identified in the Edinger Westphal nucleus, superior olivary nucleus, and a few scattered neurons were found in the compact formation of the nucleus ambiguus (Ambc). However, in both female groups, ucn neurons were observed within the nucleus tractus solitarius (NTS) and the number of ucn neurons in the Ambc was increased compared to the male. Finally, in the OVX group distinct groups of ucn neurons were also identified in the rostral nucleus paragigantocellularis lateralis, the magnocellular reticular nucleus, and throughout the external formation of Amb. Taken together, these data suggest that the wide distribution of ucn neurons within autonomic brainstem structures in the OVX female may be associated with the greater effects observed on cardiovascular variables during stress. Heart and Stroke Foundation of Ontario

Localization of the neurons active during paradoxical (REM) sleep and projecting to the locus coeruleus noradrenergic neurons in the rat

Locus coeruleus (LC) noradrenergic neurons are active during wakefulness, slow their discharge rate during slow wave sleep, and stop firing during paradoxical sleep (PS). A large body of data indicates that their inactivation during PS is due to a tonic GABAergic inhibition. To localize the neurons responsible for such inhibition, we first examined the distribution of retrogradely and Fos double-immunostained neurons following cholera toxin b subunit (CTb) injection in the LC of control rats, rats selectively deprived of PS for 3 days, and rats allowed to recover for 3 hours from such deprivation. We found a significant number of CTb/Fos double-labeled cells only in the recovery group. The largest number of CTb/Fos double-labeled cells was found in the dorsal paragigantocellular reticular nucleus (DPGi). It indeed contained 19% of the CTb/Fos double-labeled neurons, whereas the ventrolateral periaqueductal gray (vlPAG) contained 18.3% of these neurons, the lateral paragigantocellular reticular nucleus (LPGi) 15%, the lateral hypothalamic area 9%, the lateral PAG 6.7%, and the rostral PAG 6%. In addition, CTb/Fos double-labeled cells constituted 43% of all the singly CTb-labeled cells counted in the DPGi compared with 29% for the LPGi, 18% for the rostral PAG, and 10% or less for the other structures. Although all these populations of CTb/Fos double-labeled neurons could be GABAergic and tonically inhibit LC neurons during PS, our results indicate that neurons from the DPGi constitute the best candidate for this role.