Search

Aging invariably decreases sensory and motor stimuli and affects several neuronal systems and their connectivity to key brain regions, including those involved in breathing. Nevertheless, further investigation is needed to fully comprehend the link between senescence and respiratory function. Here, we investigate whether a mouse model of accelerated senescence could develop central and peripheral respiratory abnormalities. Adult male Senescence Accelerated Mouse Prone 8 (SAMP8) and the control SAMR1 mice (10 months old) were used. Ventilatory parameters were assessed by whole-body plethysmography, and measurements of respiratory input impedance were performed. SAMP8 mice exhibited a reduction in the density of neurokinin-1 receptor immunoreactivity in the entire ventral respiratory column. Physiological experiments showed that SAMP8 mice exhibited a decreased tachypneic response to hypoxia (FiO2 = 0.08; 10 min) or hypercapnia (FiCO2 = 0.07; 10 min). Additionally, the ventilatory response to hypercapnia increased further due to higher tidal volume. Measurements of respiratory mechanics in SAMP8 mice showed decreased static compliance (Cstat), inspiratory capacity (IC), resistance (Rn), and elastance (H) at different ages (3, 6, and 10 months old). SAMP8 mice also have a decrease in contractile response to methacholine compared to SAMR1. In conclusion, our findings indicate that SAMP8 mice display a loss of the NK1-expressing neurons in the respiratory brainstem centers, along with impairments in both central and peripheral respiratory mechanisms. These observations suggest a potential impact on breathing in a senescence animal model., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Mutations in the transcription factor Phox2b cause congenital central hypoventilation syndrome (CCHS). The syndrome is characterized by hypoventilation and inability to regulate breathing to maintain adequate O 2 and CO 2 levels. The mechanism by which CCHS impact respiratory control is incompletely understood, and even less is known about the impact of the non-polyalanine repeat expansion mutations (NPARM) form. Our goal was to investigate the extent by which NPARM Phox2b mutation affect (a) respiratory rhythm; (b) ventilatory responses to hypercapnia (HCVR) and hypoxia (HVR); and (c) number of chemosensitive neurons in mice. We used a transgenic mouse line carrying a conditional Phox2b Δ8 mutation (same found in humans with NPARM CCHS). We crossed them with Atoh1 cre mice to introduce mutation in regions involved with respiratory function and central chemoreflex control. Ventilation was measured by plethysmograph during neonatal and adult life. In room air, mutation in neonates and adult did not greatly impact basal ventilation. However, Phox2b Δ8 , Atoh1 cre increased breath irregularity in adults. The HVR and HCVR were impaired in neonates. The HVR, but not HCVR, was still partially compromised in adults. The mutation reduced the number of Phox2b + /TH - -expressing neurons as well as the number of fos-activated cells within the ventral parafacial region (also named retrotrapezoid nucleus [RTN] region) induced by hypercapnia. Our data indicates that Phox2b Δ8 mutation in Atoh1 -expressing cells impaired RTN neurons, as well as chemoreflex under hypoxia and hypercapnia specially early in life. This study provided new evidence for mechanisms related to NPARM form of CCHS neuropathology., Competing Interests: CF, TS, PS, CC, CC, JO, AT, TM No competing interests declared, (© 2022, Ferreira et al.)

Growth hormone (GH)-responsive neurons regulate several homeostatic behaviors including metabolism, energy balance, arousal, and stress response. Therefore, it is possible that GH-responsive neurons play a role in other responses such as CO 2 /H + -dependent breathing behaviors. Here, we investigated whether central GH receptor (GHR) modulates respiratory activity in conscious unrestrained mice. First, we detected clusters of GH-responsive neurons in the tyrosine hydroxylase-expressing cells in the rostroventrolateral medulla (C1 region) and within the locus coeruleus (LC). No significant expression was detected in phox2b-expressing cells in the retrotrapezoid nucleus. Whole body plethysmography revealed a reduction in the tachypneic response to hypoxia (FiO 2  = 0.08) without changing baseline breathing and the hypercapnic ventilatory response. Contrary to the physiological findings, we did not find significant differences in the number of fos-activated cells in the nucleus of the solitary tract (NTS), C1, LC and paraventricular nucleus of the hypothalamus (PVH). Our finding suggests a possible secondary role of central GH action in the tachypneic response to hypoxia in conscious mice., (Copyright © 2022. Published by Elsevier B.V.)

The parafacial respiratory group (pFRG), located in the lateral aspect of the rostroventral lateral medulla, has been described as a conditional expiratory oscillator that emerges mainly in conditions of high metabolic challenges to increase breathing. The convergence of inhibitory and excitatory inputs to pFRG and the generation of active expiration may be more complex than previously thought. We hypothesized that the medullary raphe, a region that has long been described to be involved in breathing activity, is also responsible for the expiratory activity under hypercapnic condition. To test this hypothesis, we performed anatomical and physiological experiments in urethane-anesthetized adult male Wistar rats. Our data showed anatomical projections from serotonergic (5-HT-ergic) and GABAergic neurons of raphe magnus (RMg) and obscurus (ROb) to the pFRG region. Pharmacological inhibition of RMg or ROb with muscimol (60 pmol/30 nL) did not change the frequency or amplitude of diaphragm activity and did not generate active expiration. However, under hypercapnia (9-10% CO 2 ), the inhibition of RMg or ROb increased the amplitude of abdominal activity, without changing the increased amplitude of diaphragm activity. Depletion of serotonergic neurons with saporin anti-SERT injections into ROb and RMg did not increase the amplitude of abdominal activity during hypercapnia. These results show that the presumably GABAergic neurons within the RMg and ROb may be the inhibitory source to modulate the activity of pFRG during hypercapnia condition. NEW & NOTEWORTHY Medullary raphe has been involved in the inspiratory response to central chemoreflex; however, these reports have never addressed the role of raphe neurons on active expiration induced by hypercapnia. Here, we showed that a subset of GABA cells within the medullary raphe directly project to the parafacial respiratory region, modulating active expiration under high levels of CO 2 .

Active expiration (AE) is part of the breathing phase; it is conditional and occurs when we increase our metabolic demand, such as during hypercapnia, hypoxia, or exercise. The parafacial respiratory group (pFRG) is involved in AE. Data from the literature suggest that excitatory and the absence of inhibitory inputs to the pFRG are necessary to determine AE. However, the source of the inputs to the pFRG that trigger AE remains unclear. We show in adult urethane-anesthetized Wistar rats that the pharmacological inhibition of the medial aspect of the nucleus of the solitary tract (mNTS) or the rostral aspect of the pedunculopontine tegmental nucleus (rPPTg) is able to generate AE. In addition, direct inhibitory projection from the mNTS or indirect cholinergic projection from the rPPTg is able to contact pFRG to trigger AE. The inhibition of the mNTS or the rPPTg under conditions of high metabolic demand, such as hypercapnia (9-10% CO 2 ), did not affect the AE. The present results suggest for the first time that inhibitory sources from the mNTS and a cholinergic pathway from the rPPTg, involving M2/M4 muscarinic receptors, could be important sources to modulate and sustain AE.

The brain regulates breathing in response to changes in tissue CO 2 /H + via a process called central chemoreception. Neurons and astrocytes in the retrotrapezoid nucleus (RTN) function as respiratory chemoreceptors. The role of astrocytes in this process appears to involve CO 2 /H + -dependent release of ATP to enhance activity of chemosensitive RTN neurons. Considering that in most brain regions extracellular ATP is rapidly broken down to adenosine by ectonucleotidase activity and since adenosine is a potent neuromodulator, we wondered whether adenosine signaling contributes to RTN chemoreceptor function. To explore this possibility, we pharmacologically manipulated activity of adenosine receptors in the RTN under control conditions and during inhalation of 7-10% CO 2 (hypercapnia). In urethane-anesthetized or unrestrained conscious rats, bilateral injections of adenosine into the RTN blunted the hypercapnia ventilatory response. The inhibitory effect of adenosine on breathing was blunted by prior RTN injection of a broad spectrum adenosine receptor blocker (8-PT) or a selective A1-receptor blocker (DPCPX). Although RTN injections of 8PT, DPCPX or the ectonucleotidase inhibitor ARL67156 did not affected baseline breathing in either anesthetized or awake rats. We did find that RTN application of DPCPX or ARL67156 potentiated the respiratory frequency response to CO 2 , suggesting a portion of ATP released in the RTN during high CO 2 /H + is converted to adenosine and serves to limit chemoreceptor function. These results identify adenosine as a novel purinergic regulator of RTN chemoreceptor function during hypercapnia., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

The A5 area at the ventrolateral pons contains noradrenergic neurons connected with other medullary areas involved in the cardiorespiratory control. Its contribution to the cardiorespiratory regulation was previously evidenced in anesthetized conditions. In the present study, we investigated the involvement of the A5 noradrenergic neurons to the basal and chemoreflex control of the sympathetic and respiratory activities in unanesthetized conditions. A5 noradrenergic neurons were lesioned using microinjections of anti-dopamine β-hydroxylase saporin (anti-DβH-SAP). After 7-8days, we evaluated the arterial pressure levels, heart rate and minute ventilation in freely moving adult rats (280-350g) as well as recorded from thoracic sympathetic (tSN) and phrenic nerves (PN) using the arterially perfused in situ preparation of juvenile rats (80-90g). Baseline cardiovascular, sympathetic and respiratory parameters were similar between control (n=7-8) and A5-lesioned rats (n=5-6) in both experimental preparations. In adult rats, lesions of A5 noradrenergic neurons did not modify the reflex cardiorespiratory adjustments to hypoxia (7% O 2 ) and hypercapnia (7% CO 2 ). In the in situ preparations, the sympatho-excitation, but not the PN reflex response, elicited by either the stimulation of peripheral chemoreceptors (ΔtSN: 110±12% vs 58±8%, P<0.01) or hypercapnia (ΔtSN: 9.5±1.4% vs 3.9±1.7%, P<0.05) was attenuated in A5-lesioned rats compared to controls. Our data demonstrated that A5 noradrenergic neurons are part of the circuitry recruited for the processing of sympathetic response to hypoxia and hypercapnia in unanesthetized conditions., (Copyright © 2017 IBRO. Published by Elsevier Ltd. All rights reserved.)

The stimuli that commonly activate the catecholaminergic C1 neurons (nociception, hypotension, and hypoxia) also increase breathing. Pharmacogenetic evidence suggests that catecholaminergic neurons regulate breathing. Therefore, we evaluated whether the loss of C1 cells affects cardiorespiratory control during resting, hypoxic (8% O 2 ) and hypercapnic (7% CO 2 ) conditions. A bilateral injection of the immunotoxin anti-dopamine β-hydroxylase-saporin (anti-DβH-SAP; 2.4ng/100nl) or saline was performed in adult male Wistar rats (270-300g, N=5-8/group). Histology revealed a 60-75% loss of C1 neurons in anti-DβH-SAP-treated rats, but no significant changes or C1 cell loss was observed in sham-treated rats or those with off-target injection sites. Bilateral depletion of C1 neurons did not alter cardiorespiratory variables during rest and hypercapnia (7% CO 2 ), but it did affect the response to hypoxia. Specifically, the increase in ventilation, the number of sighs, and the tachycardia were reduced, but unexpectedly, the mean arterial pressure increased during hypoxia (8% O 2 ). The present study indicates that C1 neurons contribute to cardiorespiratory control during hypoxia rather than at rest or during hypercapnia., (Copyright © 2017 IBRO. Published by Elsevier Ltd. All rights reserved.)

Central chemoreception is the mechanism by which the brain regulates breathing in response to changes in tissue CO(2)H+. A brainstem region called the retrotrapezoid nucleus (RTN) contains a population of CO2/H+-sensitive neurons that appears to function as an important chemoreceptor. Evidence also indicates that CO2-evoked ATP release from RTN astrocytes modulates activity of CO2/H+-sensitive neurons; however, the extent to which purinergic signalling contributes to chemoreception by RTN neurons is not clear and the mechanism(s) underlying CO2/H+-evoked ATP release is not fully elucidated. The goals of this study are to determine the extent to which ATP contributes to RTN chemoreception both in vivo and in vitro, and whether purinergic drive to chemoreceptors relies on extracellular Ca(2+) or gap junction hemichannels. We also examine the possible contribution of P2Y1 receptors expressed in the RTN to the purinergic drive to breathe.We show that purinergic signalling contributes, in part, to the CO(2)/H+ sensitivity of RTN neurons. In vivo, phrenic nerve recordings of respiratory activity in adult rats show that bilateral injections of pyridoxal-phosphate-6-azophenyl-2',4'-disulfonate (PPADS, a P2 receptor blocker) decreased the ventilatory response to CO2 by 30%. In vitro, loose-patch recordings from RTN neurons show that P2 receptor blockers decreased responsiveness to both 10% and 15% CO2 also by 30%. In the slice, the contribution of purinergic signalling to RTN chemoreception did not increase with temperature (22–35◦C) and was retained in low extracellular Ca2+ medium. Conversely, the gap junction blockers carbenoxolone and cobalt decreased neuronal CO2/H+ sensitivity by an amount similar to P2 receptor antagonists. Inhibition of the P2Y1 receptor in the RTN had no effect on CO2 responsivness in vitro or in vivo; thus, the identity of P2 receptors underlying the purinergic component of RTN chemoreception remains unknown. These results support the possibility that CO2/H+-evoked ATP release is mediated by a mechanism involving gap junction hemichannels.

The commissural nucleus of the solitary tract (commNTS) is a main area that receives afferent signals involved in the cardiovascular and respiratory control like those related to chemoreceptor activation, however, the importance of the commNTS for the cardiorespiratory responses to chemoreceptor activation is still controversial. In the present study, we investigated the cardiorespiratory responses to hypoxia or hypercapnia in anesthetized and conscious rats treated with injections of the GABA-A agonist muscimol into the caudal portion of the commNTS. Male Holtzman rats (280-300 g) were used. In conscious rats that had a stainless steel cannula previously implanted into the commNTS, the injection of muscimol (2 mM) into the commNTS reduced the pressor response (16±2 mmHg, vs. saline: 36±3 mmHg) and the increase in ventilation (250±17 ml/min/kg, vs. saline: 641±28 ml/min/kg) produced by hypoxia (8-10% O(2)). In urethane anesthetized rats, the injection of muscimol into the commNTS eliminated the pressor response (5±2 mmHg, vs. saline: 26±5 mmHg) and the increase in phrenic nerve discharge (PND) (20±6%, vs. saline: 149±15%) and reduced the increase in splanchnic sympathetic nerve discharge (sSND) (93±15%, vs. saline: 283±19% of baseline) produced by hypoxia. However, muscimol injected into the commNTS did not change hypercapnia (8-10% CO(2)) induced pressor response or the increase in the sSND or PND in urethane anesthetized rats or the increase in ventilation in conscious rats. The present results suggest that the cardiorespiratory responses to hypoxia are strongly dependent on the caudal portion of the commNTS, however, this area is not involved in the responses to hypercapnia., (Crown Copyright © 2011. Published by Elsevier B.V. All rights reserved.)

Aging invariably decreases sensory and motor stimuli and affects several neuronal systems and their connectivity to key brain regions, including those involved in breathing. Nevertheless, further investigation is needed to fully comprehend the link between senescence and respiratory function. Here, we investigate whether a mouse model of accelerated senescence could develop central and peripheral respiratory abnormalities. Adult male Senescence Accelerated Mouse Prone 8 (SAMP8) and the control SAMR1 mice (10 months old) were used. Ventilatory parameters were assessed by whole-body plethysmography, and measurements of respiratory input impedance were performed. SAMP8 mice exhibited a reduction in the density of neurokinin-1 receptor immunoreactivity in the entire ventral respiratory column. Physiological experiments showed that SAMP8 mice exhibited a decreased tachypneic response to hypoxia (FiO2 = 0.08; 10 min) or hypercapnia (FiCO2 = 0.07; 10 min). Additionally, the ventilatory response to hypercapnia increased further due to higher tidal volume. Measurements of respiratory mechanics in SAMP8 mice showed decreased static compliance (Cstat), inspiratory capacity (IC), resistance (Rn), and elastance (H) at different ages (3, 6, and 10 months old). SAMP8 mice also have a decrease in contractile response to methacholine compared to SAMR1. In conclusion, our findings indicate that SAMP8 mice display a loss of the NK1-expressing neurons in the respiratory brainstem centers, along with impairments in both central and peripheral respiratory mechanisms. These observations suggest a potential impact on breathing in a senescence animal model. [ABSTRACT FROM AUTHOR]

New Findings: What is the central question of this study?How does the 6‐hydroxydopamine (6‐OHDA)‐induced Parkinson's disease model affect the respiratory response in female rats? What effect does ovariectomy have on that response?What is the main finding and its importance?The results suggest a protective effect of ovarian hormones in maintaining normal neuroanatomical integrity of the medullary respiratory nucleus in females. It was observed that ovariectomy alone reduced neurokinin‐1 density in the pre‐Bötzinger complex and Bötzinger complex, and there was an incremental effect of 6‐OHDA and ovariectomy on retrotrapezoid nucleus neurons. Emerging evidence indicates that the course of Parkinson's disease (PD) includes autonomic and respiratory deficiencies in addition to the classical motor symptoms. The prevalence of PD is lower in women, and it has been hypothesized that neuroprotection by ovarian hormones can explain this difference. While male PD animal models present changes in the central respiratory control areas, as well as ventilatory parameters under normoxia and hypercapnia, little is known about sex differences regarding respiratory deficits in this disease background. This study aimed to explore the neuroanatomical and functional respiratory changes in intact and ovariectomized (OVX) female rats subjected to chemically induced PD via a bilateral intrastriatal injection of 6‐hydroxydopamine (6‐OHDA). The respiratory parameters were evaluated by whole‐body plethysmography, and the neuroanatomy was monitored using immunohistochemistry. It was found that dopaminergic neurons in the substantia nigra and neurokinin‐1 receptor density in the rostral ventrolateral respiratory group, Bötzinger and pre‐Bötzinger complex were reduced in the chemically induced PD animals. Additionally, reduced numbers of Phox2b neurons were only observed in the retrotrapezoid nucleus of PD‐OVX rats. Concerning respiratory parameters, in OVX rats, the resting and hypercapnia‐induced tidal volume (VT) is reduced, and ventilation (V̇E${\dot V_{\rm{E}}}$) changes independently of 6‐OHDA administration. Notably, there is a reduction in the number of retrotrapezoid nucleus Phox2b neurons and hypercapnia‐induced respiratory changes in PD‐OVX animals due to a 6‐OHDA and OVX interaction. These results suggest a protective effect induced by ovarian hormones in neuroanatomical changes observed in a female experimental PD model. [ABSTRACT FROM AUTHOR]

The retrotrapezoid nucleus (RTN) contains chemosensitive cells that distribute CO2-dependent excitatory drive to the respiratory network. This drive facilitates the function of the respiratory central pattern generator (rCPG) and increases sympathetic activity. It is also evidenced that during hypercapnia, the late-expiratory (late-E) oscillator in the parafacial respiratory group (pFRG) is activated and determines the emergence of active expiration. However, it remains unclear the microcircuitry responsible for the distribution of the excitatory signals to the pFRG and the rCPG in conditions of high CO2. Herein, we hypothesized that excitatory inputs from chemosensitive neurons in the RTN are necessary for the activation of late-E neurons in the pFRG. Using the decerebrated in situ rat preparation, we found that lesions of neurokinin-1 receptor-expressing neurons in the RTN region with substance P-saporin conjugate suppressed the late-E activity in abdominal nerves (AbNs) and sympathetic nerves (SNs) and attenuated the increase in phrenic nerve (PN) activity induced by hypercapnia. On the other hand, kynurenic acid (100 mM) injections in the pFRG eliminated the late-E activity in AbN and thoracic SN but did not modify PN response during hypercapnia. Iontophoretic injections of retrograde tracer into the pFRG of adult rats revealed labeled phox2b-expressing neurons within the RTN. Our findings are supported by mathematical modeling of chemosensitive and late-E populations within the RTN and pFRG regions as two separate but interacting populations in a way that the activation of the pFRG late-E neurons during hypercapnia require glutamatergic inputs from the RTN neurons that intrinsically detect changes in CO2/pH. [ABSTRACT FROM AUTHOR]

Bulbospinal catecholaminergic neurons located in the rostral aspect of the ventrolateral medulla (C1 neurons) or within the ventrolateral pons (A5 neurons) are involved in the regulation of blood pressure and sympathetic outflow. A stimulus that commonly activates the C1 or A5 neurons is hypoxia, which is also involved in breathing activation. Although pharmacological and optogenetic evidence suggests that catecholaminergic neurons also regulate breathing, a specific contribution of the bulbospinal neurons to respiratory control has not been demonstrated. Therefore, in the present study, we evaluated whether the loss of bulbospinal catecholaminergic C1 and A5 cells affects cardiorespiratory control during resting, hypoxic (8% O), and hypercapnic (7% CO) conditions in unanesthetized rats. Thoracic spinal cord (T4-T8) injections of the immunotoxin anti-dopamine β-hydroxylase-saporin (anti-DβH-SAP-2.4 ng/100 nl) and the retrograde tracer Fluor-Gold or ventrolateral pontine injections of 6-OHDA were performed in adult male Wistar rats (250-280 g, N = 7-9/group). Anti-DβH-SAP or 6-OHDA eliminated most bulbospinal C1 and A5 neurons or A5 neurons, respectively. Serotonergic neurons and astrocytes were spared. Depletion of the bulbospinal catecholaminergic cells did not change cardiorespiratory variables under resting condition, but it did affect the response to hypoxia and hypercapnia. Specifically, the increase in the ventilation, the number of sighs, and the tachycardia were reduced, but the MAP increased during hypoxia in anti-DβH-SAP-treated rats. Our data reveal that the bulbospinal catecholaminergic neurons (A5 and C1) facilitate the ventilatory reflex to hypoxia and hypercapnia. [ABSTRACT FROM AUTHOR]

Key points Several brain regions are thought to sense changes in tissue CO2/H+ to regulate breathing (i.e. central chemoreceptors) including the nucleus of the solitary tract (NTS), medullary raphe and retrotrapezoid nucleus (RTN)., Mechanism(s) underlying RTN chemoreception involve direct activation of RTN neurons by H+-mediated inhibition of a resting K+ conductance and indirect activation of RTN neurons by purinergic signalling, most likely from CO2/H+-sensitive astrocytes., Here, we confirm that activation of P2 receptors in the RTN stimulates cardiorespiratory activity, and we show at the cellular and systems level that purinergic signalling is not essential for CO2/H+ sensing in the NTS or medullary raphe., These results support the possibility that purinergic signalling is a unique feature of RTN chemoreception., Abstract Several brain regions are thought to function as important sites of chemoreception including the nucleus of the solitary tract (NTS), medullary raphe and retrotrapezoid nucleus (RTN). In the RTN, mechanisms of chemoreception involve direct H+-mediated activation of chemosensitive neurons and indirect modulation of chemosensitive neurons by purinergic signalling. Evidence suggests that RTN astrocytes are the source of CO2-evoked ATP release. However, it is not clear whether purinergic signalling also influences CO2/H+ responsiveness of other putative chemoreceptors. The goals of this study are to determine if CO2/H+-sensitive neurons in the NTS and medullary raphe respond to ATP, and whether purinergic signalling in these regions influences CO2 responsiveness in vitro and in vivo. In brain slices, cell-attached recordings of membrane potential show that CO2/H+-sensitive NTS neurons are activated by focal ATP application; however, purinergic P2-receptor blockade did not affect their CO2/H+ responsiveness. CO2/H+-sensitive raphe neurons were unaffected by ATP or P2-receptor blockade. In vivo, ATP injection into the NTS increased cardiorespiratory activity; however, injection of a P2-receptor blocker into this region had no effect on baseline breathing or CO2/H+ responsiveness. Injections of ATP or a P2-receptor blocker into the medullary raphe had no effect on cardiorespiratory activity or the chemoreflex. As a positive control we confirmed that ATP injection into the RTN increased breathing and blood pressure by a P2-receptor-dependent mechanism. These results suggest that purinergic signalling is a unique feature of RTN chemoreception. [ABSTRACT FROM AUTHOR]

In the present study, we evaluated the role of glutamatergic mechanisms in the retrotrapezoid nucleus (RTN) in changes of splanchnic sympathetic nerve discharge (sSND) and phrenic nerve discharge (PND) elicited by central and peripheral chemoreceptor activation. Mean arterial pressure (MAP), sSND and PND were recorded in urethane-anaesthetized, vagotomized, sino-aortic denervated and artificially ventilated male Wistar rats. Hypercapnia (10% CO2) increased MAP by 32 ± 4 mmHg, sSND by 104 ± 4% and PND amplitude by 101 ± 5%. Responses to hypercapnia were reduced after bilateral injection of the NMDA receptor antagonist d,l-2-amino-5-phosphonovalerate (AP-5; 100 m m in 50 nl) in the RTN (MAP increased by 16 ± 3 mmHg, sSND by 82 ± 3% and PND amplitude by 63 ± 7%). Bilateral injection of the non-NMDA receptor antagonist 6,7-dinitro-quinoxaline-2,3-dione (DNQX; 100 mm in 50 nl) and the metabotropic receptor antagonist (+/−)-α-methyl-4-carboxyphenylglycine (MCPG; 100 m m in 50 nl) in the RTN did not affect sympathoexcitatory responses induced by hypercapnia. Injection of DNQX reduced hypercapnia-induced phrenic activation, whereas MCPG did not. In animals with intact carotid chemoreceptors, bilateral injections of AP-5 and DNQX in the RTN reduced increases in MAP, sSND and PND amplitude produced by intravenous injection of NaCN (50 μg kg−1). Injection of MCPG in the RTN did not change responses produced by NaCN. These data indicate that RTN ionotropic glutamatergic receptors are involved in the sympathetic and respiratory responses produced by central and peripheral chemoreceptor activation. [ABSTRACT FROM AUTHOR]

A rise in arterial Pco2 stimulates breathing and sympathetic activity to the heart and blood vessels. In the present study, we investigated the involvement of the retrotrapezoid nucleus (RTN) and glutamatergic mechanisms in the Bötzinger/C1 region (Bötz/C1) in these responses. Splanchnic sympathetic nerve discharge (sSND) and phrenic nerve discharge (PND) were recorded in urethane-anesthetized, sino-aortic-denervated, vagotomized, and artificially ventilated rats subjected to hypercapnia (end-expiratory CO2 from 5% to 10%). Phrenic activity was absent at end-expiratory CO2 of 4%, and strongly increased when end-expiratory CO2 reached 10%. Hypercapnia also increased sSND by 103 ± 7%. Bilateral injections of the GABA-A agonist muscimol (2 mM) into the RTN eliminated the PND and blunted the sSND activation (Δ = +56 ± 8%) elicited by hypercapnia. Injections of NMDA receptor antagonist AP-5 (100 mM), non-NMDA receptor antagonist 6,7-dinitro-quinoxaline-2,3-dione (DNQX; 100 mM) or metabotropic glutamate receptor antagonist (+/-)-alpha-methyl-4-carboxyphenylglycine (MCPG; 100 mM) bilaterally into the Bötz/C1 reduced PND (Δ = +43 ± 7%, +52 ± 6% or +56 ± 11%, respectively). MCPG also reduced sSND (Δ = +41 ± 7%), whereas AP-5 and DNQX had no effect. In conclusion, the increase in sSND caused by hypercapnia depends on increased activity of the RTN and on metabotropic receptors in the Bötz/C1, whereas PND depends on increased RTN activity and both ionotropic and metabotropic receptors in the Bötz/C1. [ABSTRACT FROM AUTHOR]

A previous study has demonstrated that in the 6-hydroxydopamine (6-OHDA)-model of Parkinson's disease (PD) there is a reduction in the number of Phox2b neurons in the retrotrapezoid nucleus (RTN) and a decrease in the respiratory response to hypercapnia 40 days after PD-induction. The functional deficiency is restored 60 days after 6-OHDA injection and here we tested the hypothesis that the locus coeruleus (LC) could be a candidate to restore the breathing deficiency. Minute Ventilation (V E ) in response to hypercapnia (7% CO 2 ) was assessed one day before, and then 40 and 60 days after bilateral 6-OHDA (24 μg/μL) or vehicle injections into the LC in control or PD-induced male Wistar rats. Bilateral injections of 6-OHDA decreased catecholaminergic neurons by 86% and 83% in the substantia nigra pars compacta (SNpc) and LC, respectively. As already described, in animals with lesions to the SNpc (N = 6/group), the reduction in the ventilatory response to hypercapnia was restored 60 days after PD (1257 ± 81 vs. vehicle: 1185 ± 49 mL/kg/min). However, in animals with PD and lesion in the LC, the ventilation was blunted (674 ± 39 mL/kg/min). In another group of PD rats, we observed a reduction in the number of hypercapnia-induced-fos + cells in the RTN region (40 days: 38 ± 3 and 60 days: 8.5 ± 0.9 vs. vehicle 78 ± 3 cells) and an increase in the LC (40 days: 46 ± 4 and 60 days: 94 ± 22 vs. vehicle 1 ± 1 cells). Our data suggest that LC catecholaminergic neurons can be a candidate structure mediating chemoreceptor function in a model of PD. [ABSTRACT FROM AUTHOR]

[Display omitted] • In the PPTg, most cholinergic neurons are also glutamatergic. • There is no PPTg neuron degeneration in this experimental PD model. • The neurons of PPTg may contribute to ventilatory modulation during hypercapnia. • Hypoxia does not activate PPTg neurons. • PPTg region receives direct projections from SNpc but does not input the RTN or preBotC. Parkinson's disease (PD) is a motor disorder resulting from degeneration of dopaminergic neurons of substantia nigra pars compacta (SNpc), with classical and non-classical symptoms such as respiratory instability. An important region for breathing control, the Pedunculopontine Tegmental Nucleus (PPTg), is composed of cholinergic, glutamatergic, and GABAergic neurons. We hypothesize that degenerated PPTg neurons in a PD model contribute to the blunted respiratory activity. Adult mice (40 males and 29 females) that express the fluorescent green protein in cholinergic, glutamatergic or GABAergic cells were used (Chat-cre Ai6, Vglut 2 -cre Ai6 and Vgat-cre Ai6) and received bilateral intrastriatal injections of vehicle or 6-hydroxydopamine (6-OHDA). Ten days later, the animals were exposed to hypercapnia or hypoxia to activate PPTg neurons. Vglut 2 -cre Ai6 animals also received retrograde tracer injections (cholera toxin b) into the retrotrapezoid nucleus (RTN) or preBötzinger Complex (preBötC) and anterograde tracer injections (AAV-mCherry) into the SNpc. In 6-OHDA-injected mice, there is a 77% reduction in the number of dopaminergic neurons in SNpc without changing the number of neurons in the PPTg. Hypercapnia activated fewer Vglut 2 neurons in PD, and hypoxia did not activate PPTg neurons. PPTg neurons do not input RTN or preBötC regions but receive projections from SNpc. Although our results did not show a reduction in the number of glutamatergic neurons in PPTg, we observed a reduction in the number of neurons activated by hypercapnia in the PD animal model, suggesting that PPTg may participate in the hypercapnia ventilatory response. [ABSTRACT FROM AUTHOR]

• Pilocarpine into the hippocampus has been used to induce status epilepticus (SE). • SE was able to impair breathing function under chemoreceptor activation. • Breathing dysfunction was due to a reduction in the chemical control of breathing. • Respiratory changes may be useful to study risk factors in epilepsy. One of the possible causes of death in epilepsy is breathing disorders, especially apneas, which lead to an increase in CO 2 levels (hypercapnia) and/or a decrease in O 2 levels in arterial blood (hypoxemia). The respiratory neurons located in the ventral brainstem respiratory column are the main groups responsible for controlling breathing. Recent data from our group demonstrated respiratory changes in two experimental models of epilepsy, i.e. audiogenic epilepsy, and amygdala rapid kindling. Here, we aimed to evaluate respiratory changes in the classic model of temporal lobe epilepsy induced by intra-hippocampal injection of pilocarpine. Adult Wistar rats with stainless-steel cannulas implanted in the hippocampus region were used. The animals were submitted to pilocarpine injection (2.4 mg/μL, N = 12–15) or saline (N = 9) into the hippocampus. The respiratory parameters analyzed by whole-body plethysmography were respiratory rate (f R), tidal volume (V T) and ventilation (V E). Respiratory mechanics such as Newtonian airway resistance (R n), viscance of the pulmonary parenchyma (G) and the elastance of the pulmonary parenchyma (H) were also investigated. No changes in baseline breathing were detected 15 or 30 days after pilocarpine-induced status epilepticus (SE). However, 30 days after pilocarpine-induced SE, a significant reduction in V E was observed during hypercapnic (7% CO 2) stimulation, without affecting the hypoxia (8% O 2) ventilatory response. We also did not observe changes in respiratory mechanics. The present results suggest that the impairment of the hypercapnia ventilatory response in pilocarpine-induced SE could be related to a presumable degeneration of brainstem respiratory neurons but not to peripheral mechanisms. [ABSTRACT FROM AUTHOR]

• Amygdala rapid kindling (ARK) has been used as an experimental model to temporal lobe epilepsy. • ARK was able to impair breathing function under hypercapnia challenge. • Breathing dysfunction was due to a reduction in the activation of RTN, RMG and NTS neurons. • Breathing impairment may be useful to validate ARK model to study the increase in risk factors in epilepsies. Temporal lobe epilepsy is often accompanied by behavioral, electroencephalographic and autonomic abnormalities. Amygdala kindling has been used as an experimental model to study epileptogenesis. Although amygdala kindling has been extensively investigated in the context of its clinical relevance to the epilepsies, potential associated respiratory alterations are not well known. Here, our main objective was to better investigate the mechanisms involved in respiratory physiology impairment in the amygdala rapid kindling (ARK) model of epileptogenesis. Male Wistar rats with electrodes implanted into the amygdaloid complex were used. After recovery from surgery, the rats were subjected to electrical stimulation of basolateral amygdala for 2 consecutive days (10 stimuli/day). The ventilatory parameters were evaluated by whole body plethysmography. Thereafter, animals were also exposed to hypercapnia (7% CO 2) for 3 h to evaluate fos protein expression in several nuclei involved in respiratory control. We observed a significant reduction in ventilation during the ictal phase elicited by ARK. We also found that 10 days after ARK, baseline ventilation as well as the hypercapnia ventilatory response (7% CO 2) were reduced compared to control rats. The number of fos-immunoreactive neurons in the retrotrapezoid nucleus, raphe magnus and nucleus of the solitary tract were also reduced after ARK. Our results showed that ARK was able to impair breathing function, demonstrating a strong coupling between amygdala and the respiratory neurons in the brainstem, with potential impact in respiratory failures, frequently fatal, during or after epileptic seizures in chronic animal models and in patients. [ABSTRACT FROM AUTHOR]