Intertrigeminal Region Research Articles

Efferent and afferent connections of supratrigeminal neurons conveying orofacial muscle proprioception in rats.

The supratrigeminal nucleus (Su5) is a key structure for controlling jaw movements; it receives proprioceptive sensation from jaw-closing muscle spindles (JCMSs) and sends projections to the trigeminal motor nucleus (Mo5). However, the central projections and regulation of JCMS proprioceptive sensation are not yet fully understood. Therefore, we aimed to reveal the efferent and afferent connections of the Su5 using neuronal tract tracings. Anterograde tracer injections into the Su5 revealed that the Su5 sends contralateral projections (or bilateral projections with a contralateral predominance) to the Su5, basilar pontine nuclei, pontine reticular nucleus, deep mesencephalic nucleus, superior colliculus, caudo-ventromedial edge of the ventral posteromedial thalamic nucleus, parafascicular thalamic nucleus, zona incerta, and lateral hypothalamus, and ipsilateral projections (or bilateral projections with an ipsilateral predominance) to the intertrigeminal region, trigeminal oral subnucleus, dorsal medullary reticular formation, and hypoglossal nucleus as well as the Mo5. Retrograde tracer injections into the Su5 demonstrated that the Su5 receives bilateral projections with a contralateral predominance (or contralateral projections) from the primary and secondary somatosensory cortices, granular insular cortex, and Su5, and ipsilateral projections (or bilateral projections with an ipsilateral predominance) from the dorsal peduncular cortex, bed nuclei of stria terminalis, central amygdaloid nucleus, lateral hypothalamus, parasubthalamic nucleus, trigeminal mesencephalic nucleus, parabrachial nucleus, juxtatrigeminal region, trigeminal oral and caudal subnuclei, and dorsal medullary reticular formation. These findings suggest that the Su5, which receives JCMS proprioception, has efferent and afferent connections with multiple brain regions that are involved in emotional and autonomic functions as well as orofacial motor functions.

IMMUNOHISTOCHEMICAL IDENTIFICATION AND DISTRIBUTION OF GLUTAMATERGIC NMDA AND mGlu1 RECEPTORS IN THE PONTINE INTERTRIGEMINAL REGION IN RATS

Local glutamate simulation of intertrigeminal region (ITR) in the lateral pons evoked immediate cardiovascular and respiratory effects proposing its role in central cardiorespiratory control. Since pharmacological studies provided only functional evidence for the existence of glutamate receptors in the ITR and thereby specifying putative neurochemical substrate involved in this control, here we employed immunohistochemistry to examine expression and distribution of NMDA and mGlu1 receptors in this structure. Thirty adult male Sprague-Dawley rats were perfuse-fixed, their brains frozen and cut into sequential series of 20 µm thick sections through the ITR. Immunohistochemistry was performed using polyclonal antibodies against NMDA-NR1, NMDA-NR2A and mGlu1 receptors. Labeled neurons in the ITR were analyzed using light microscope and computerized image analysis system for quantification of relative immunoreactivity as the mean of integrated optical density (IOD), and counting the immunopositive cells. Light microscopic analyses demonstrated NMDA-NR1-immunoreactivity mainly localized in the neuronal cell bodies with sparse distribution on primary dendrites, while NMDA-NR2A-immunoreactivity was basically somatically distributed. The mGlu1-immunoreactivity was moderate and observed both in neuronal bodies and primary dendrites or extracellular matrix suggesting somatodendritic localization. Quantitative analyses of IOD showed very strong expression of NMDA-NR1, weak of NMDA-NR2A and strong-to-moderate expression of mGluR1, with differences in immunostaining signal distribution over rostro-caudal span of the ITR. Counting of immunopositive cells followed similar expression profile. Our data directly confirm the presence of glutamatergic NMDA and mGlu1 receptors in the ITR apparently involved in signaling pathways by which this region modulates cardiorespiratory functions such as blood pressure, heart rate and breathing.

Premotoneuronal inputs to early developing trigeminal motoneurons

ABSTRACT Objectives We previously reported that masseter motoneurons (MMNs) and digastric motoneurons (DMNs) in postnatal day (P) 1–5 rats receive convergent inputs from the lateral (l-) and medial (m-) supratrigeminal regions (SupV), intertrigeminal region (IntV), and dorsal region of the principal sensory trigeminal nucleus (PrV). The l-SupV sends burst inputs predominantly to the MMNs. We compared the synaptic inputs to P9–12 rat MMNs and DMNs with those found in the previous study involving P1–5 rats. Methods We performed whole-cell recordings and laser photolysis of caged glutamate in the MMNs and DMNs of P9–12 rats. Results Similar to P1–5 rats, the photostimulation of multiple regions within the l-SupV, m-SupV, IntV, and dorsal PrV, induced postsynaptic currents (PSCs) in both P9–12 MMNs and DMNs. Photostimulation induced predominantly low-frequency PSCs in both P9–12 motoneurons, whereas l-SupV photostimulation predominantly induced burst PSCs in P1–5 rats. However, when the caged glutamate concentration was doubled, l-SupV photostimulation evoked burst PSCs in all P9–12 MMNs. Furthermore, l-SupV and m-SupV photostimulation evoked burst or low-frequency PSCs at significantly higher rates in the MMNs compared to in the DMNs. Conclusions These results suggested that, similar to P1–5 motoneurons, both P9–12 motoneurons received convergent inputs from the SupV, IntV, and PrV; however, the input–output gains of some of the premotor neurons decreased. These synaptic input changes may contribute to the proper development of chewing.

Convergent Pre-motoneuronal Inputs to Single Trigeminal Motoneurons

Because pre-motor neurons targeting trigeminal motoneurons are located in various regions, including the supratrigeminal (SupV) and intertrigeminal (IntV) regions, the principal sensory trigeminal nucleus (PrV), and the region dorsal to the PrV (dRt), a single trigeminal motoneuron may receive differential convergent inputs from these regions. We thus examined the properties of synaptic inputs from these regions to masseter motoneurons (MMNs) and digastric motoneurons (DMNs) in brainstem slice preparations obtained from P1-5 neonatal rats, using whole-cell recordings and laser photolysis of caged glutamate. Photostimulation of multiple regions within the SupV, IntV, PrV, and dRt induced post-synaptic currents (PSCs) in 14 of 19 MMNs and 18 of 26 DMNs. Furthermore, the stimulation of the lateral SupV significantly induced burst PSCs in MMNs more often than low-frequency PSCs in MMNs or burst PSCs in DMNs. Similar results were obtained in the presence of the GABAA receptor antagonist SR95531 and the glycine receptor antagonist strychnine. These results suggest that both neonatal MMNs and DMNs receive convergent glutamatergic inputs from the SupV, IntV, PrV, and dRt, and that the lateral SupV sends burst inputs predominantly to the MMNs. Such convergent pre-motoneuronal inputs to trigeminal motoneurons may contribute to the proper execution of neonatal oro-motor functions.

Impact of the vagal feedback on cardiorespiratory coupling in anesthetized rats

Cardiorespiratory coupling can be significantly influenced by both pontine and vagal modulation of medullary motor and premotor areas. We investigated influences of the pontine intertrigeminal region (ITR) and peripheral vagal pathways on the coupling between systolic blood pressure (SBP) and respiration in 9 anesthetized rats. Glutamate injection into the ITR perturbed both respiration and SBP and decreased SBP-respiratory coherence (0.95±0.01 vs 0.89±0.02; (p=0.01). Intravenous infusion of serotonin (5-HT) produced apnea and hypertension and also decreased SBP-respiratory coherence (0.95±0.01 vs 0.72±0.06; p=0.04). Bilateral vagotomy eliminated the cardiorespiratory coherence perturbations induced by central (glutamate injection into the ITR: 0.89±0.03 vs 0.86±0.03; p=0.63) and peripheral (5-HT infusion: 0.89±0.03 vs 0.88±0.02; p=0.98) pharmacologic manipulations. Glutamate stimulation of the ITR postvagotomy increased the relative spectral power density of SBP in the respiratory frequency range (0.25±0.08 vs 0.55±0.06; p=0.01). The data suggest that SBP-respiratory coupling is largely mediated within the central nervous system, with vagal systems acting in a way that disrupts coherence during transient cardiorespiratory disturbances. Although decreased cardiorespiratory coherence may increase cardiac work during perturbations, this may be physiologically advantageous in restoring homeostatic equilibrium of respiration and blood pressure.

Math1 Is Essential for the Development of Hindbrain Neurons Critical for Perinatal Breathing

Mice lacking the proneural transcription factor Math1 (Atoh1) lack multiple neurons of the proprioceptive and arousal systems and die shortly after birth from an apparent inability to initiate respiration. We sought to determine whether Math1 was necessary for the development of hindbrain nuclei involved in respiratory rhythm generation, such as the parafacial respiratory group/retrotrapezoid nucleus (pFRG/RTN), defects in which are associated with congenital central hypoventilation syndrome (CCHS). We generated a Math1-GFP fusion allele to trace the development of Math1-expressing pFRG/RTN and paratrigeminal neurons and found that loss of Math1 did indeed disrupt their migration and differentiation. We also identified Math1-dependent neurons and their projections near the pre-Bötzinger complex, a structure critical for respiratory rhythmogenesis, and found that glutamatergic modulation reestablished a rhythm in the absence of Math1. This study identifies Math1-dependent neurons that are critical for perinatal breathing that may link proprioception and arousal with respiration.

Corticofugal projections to trigeminal motoneurons innervating antagonistic jaw muscles in rats as demonstrated by anterograde and retrograde tract tracing

Little is known about the organization of corticofugal projections controlling antagonistic jaw muscles. To address this issue, we employed retrograde (Fluorogold; FG) and anterograde (biotinylated dextran amine; BDA) tracing techniques in rats. Three groups of premotoneurons were identified by injecting FG into the jaw-closing (JC) and -opening (JO) subdivisions of the trigeminal motor nucleus (Vmo). These were 1) the intertrigeminal region (Vint) and principal trigeminal sensory nucleus for JC nucleus; 2) the reticular region medial to JO nucleus (RmJO) for JO nucleus; and 3) the parabrachial (Pb) and supratrigeminal (Vsup) nuclei, reticular regions medial and ventral to JC nucleus, rostrodorsomedial oralis (Vor), and juxtatrigeminal region (Vjuxt) containing a mixture of premotoneurons to both the nuclei. Subsequently, FG was injected into the representative premotoneuron structures. The JC and JO premotoneurons received main afferents from the lateral and medial agranular fields of motor cortex (Agl and Agm), respectively, whereas afferents to the nuclei with both JC and JO premotoneurons arose from Agl also and from primary somatosensory cortex (S1). Finally, BDA was injected into each of the three cortical areas representing the premotoneuron structures to complement the FG data. The Agl and Agm projected to reticular regions around the Vmo, whereas the Pb, Vsup, Vor, and Vjuxt received input from Agl. The S1 projected to the trigeminal sensory nuclei as well as to the Pb, Vsup, and Vjuxt. These results suggest that corticofugal projections to Vmo via premotoneuron structures consist of multiple pathways, which influence distinct patterns of jaw movements.

Cardiorespiratory effects of intertrigeminal area stimulation in vagotomized rats

It has been recently shown that the pontine intertrigeminal region (ITR) plays an important role in respiratory regulation, including vagally mediated apneic reflexes. Neurons of the ITR have connections with the nucleus tractus solitarius and projections to the ventrolateral medulla. However, the functional targets of these projections are not fully defined. Stimulation of ITR neurons produced respiratory effects, but cardiovascular responses have not been explored. We investigated impact of bilateral vagotomy on respiratory and cardiovascular responses to glutamate microinjections within the ITR in ketamine/xylazine anesthetized rats. Cardiorespiratory indices, including breath duration (TT), tidal volume (VT), mean cardiac intervals (RR), systolic blood pressure (SBP), pulse pressure (PP) and their coefficients of variation (CVTT, CVVT, CVSBP, CVPP, respectively) were analyzed in 30 s segments before and after injection of glutamate (10 mM, 30 L) into the ITR. This assessment was carried out both before and after bilateral vagotomy. Glutamate injection evoked apnea and increased CVTT, but these responses were not altered by bilateral vagotomy. In contrast, removing vagal pathways significantly increased volume variability (CVVT), making tidal volume more vulnerable to perturbation from the ITR. Vagotomy prolonged the increase of mean systolic blood pressure observed after glutamate injection and unmasked a delayed but sustained elevation of PP and CVPP after ITR stimulation. The present findings indicate a broad involvement of the ITR in autonomic regulation, including at least cardiovascular and respiratory effects.

Local antagonism of intertrigeminal region metabotropic glutamate receptors exacerbates apneic responses to intravenous serotonin.

Injections of a broad spectrum glutamate receptor antagonist into the pontine intertrigeminal region (ITR) exacerbate vagal reflex apnea produced by intravenous serotonin infusion. This effect is not reproduced by ITR injections with either NMDA or AMPA receptor antagonists. Here, we tested the hypothesis that ITR injection with a metabotropic glutamate antagonist would alter respiratory responses to serotonin (5-HT) intravenous infusions. In anesthetized adult male rats (N=20; Sprague-Dawley) AIDA (1-aminoindan-1,5-dicarboxylic acid), a specific antagonist of the type 1 metabotropic glutamate receptor (mGlu1R), was microinjected unilaterally into the ITR to block 5-HT evoked apnea. Respiratory pattern changes evoked by ITR-glutamate injection and by intravenous serotonin (5-HT) infusion (0.5 microl, 0.05 M; or 2.5x10(-8) mol) were characterized according to apnea expression and duration, as well as coefficients of variation for breath duration (CVTT) and amplitude (CVVT) before and after ITR AIDA injection. Unilateral AIDA blockade of the ITR significantly increased the duration of apnea evoked by 5-HT infusion (p<0.03 for each dose tested) during the 30s following infusion in a dose-dependent fashion, with the two highest doses resulting in intermittent apneas for at least 10 min following a bolus 5-HT infusion. Similar prolonged increases in CVTT and CVVT with respect to control were associated with ITR AIDA injections. These findings suggest that brief perturbations of vagal afferent pathways can produce ongoing respiratory dysrhythmia, including spontaneous apnea, and that glutamatergic neurotransmission within ITR may be important for damping such disturbances. The present observations also suggest that such respiratory damping may be mediated by mGlu1 receptors. These findings extend our understanding of the role of the intertrigeminal region in modulating respiratory reflexes.

The Motor Atonia of REM Sleep: A Critical Topics Forum

The Motor Atonia of REM Sleep: A Critical Topics Forum

Retrograde projections to a discrete apneic site in the midline medulla oblongata of the rat

We have recently described a discrete region of the medullary raphe nuclei, termed the midline apneic site (MAS) that produces profound apnea upon chemical stimulation. The aim of the present study was to identify brain regions that innervate the MAS. The MAS was functionally identified and then the retrograde tracer, cholera toxin B subunit was injected in Sprague Dawley rats ( n = 5). The MAS received projections of varying intensity from a number of brain regions previously associated with thermoregulation, fear, nociception, cardiovascular regulation and respiration. These include: the medial preoptic nucleus; median and lateral preoptic area; medial division of the bed nucleus of stria terminalis; paraventricular nucleus; central nucleus of the amygdala; dorsal hypothalamic area/dorsomedial hypothalamus; lateral hypothalamic area; lateral, ventrolateral and dorsomedial divisions of the periaqueductal grey; dorsal raphe nuclei; parabrachial nuclei; Kölliker–Fuse nucleus; intertrigeminal region; rostral ventrolateral medulla; lateral parafacial region; and the ventral respiratory group. The intermingling of functionally distinct cell groups in the raphe probably explains the large diversity of projections as found in other tracing studies of the raphe although the possibility remains that the MAS may integrate signals from multiple sites. The connection between the intertrigeminal region of the pons and the MAS indicates the possibility that this pathway participates in airway protective reflexes such as the Hering–Breuer and diving reflexes. One previously undescribed region that we have termed the lateral parafacial region was consistently labeled. The role of this region is yet to be determined.

Impact of intertrigeminal region AMPA receptor blockade on respiratory responses in rats

We hypothesized that functional glutamatergic AMPA receptors are expressed in the intertrigeminal region (ITR) of the lateral pons, and that blockade of these receptors by a specific AMPA receptor antagonist (NBQX) would alter respiratory responses both to ITR glutamate injections as well as to vagally mediated reflex apnea induced by intravenous infusion of serotonin. Non-selective blockade of ITR glutamate receptors using kynurenic acid previously was shown to alter both of these respiratory responses. Unilateral ITR injections in 19 anaesthetized spontaneously breathing adult Sprague-Dawley rats with the vagi intact demonstrated that NBQX (10mM): (1) shortened glutamate-induced apnea duration (p=0.006), (2) reduced glutamate-induced apnea frequency (p=0.034) and (3) decreased glutamate-induced apnea density (p=0.006). The same dose of NBQX did not affect vagally mediated reflex apnea induced by intravenous infusion of serotonin. These results show that functional glutamate AMPA receptors are expressed in the ITR but fail to directly demonstrate any specific physiologic role for these receptors in respiratory control. In contrast to antagonism of NMDA receptors which completely blocked the central apnea evoked by glutamate, antagonism of AMPA receptors only partially blocked the effects of glutamate. In contrast to kynurenic acid, antagonists to NMDA and AMPA receptors given separately did not potentiate the duration of reflex apnea.

Effects of intertrigeminal region NMDA and non-NMDA receptors on respiratory responses in rats

Respiratory disturbance, including apnea, can be induced by microinjection of glutamate into the intertrigeminal region (ITR) of the lateral pons, a region that is anatomically coupled to both the dorsal and ventral respiratory groups of the medulla. We showed that the ITR plays a functional role in regulating both vagal reflex apnea and spontaneous sleep-related apnea in rats, but the mechanisms have not been determined. This study shows that functional NMDA receptors are expressed in the ITR since the blockade of these receptors by AP5, a specific NMDA receptor antagonist, was fully effective in blocking apnea induced by glutamate injection within this region. Selective blockade of ITR NMDA receptors had no effect on the immediate apnea evoked by an intravenous 5-HT bolus, whereas the nonspecific glutamate receptor antagonist kynurenic acid significantly increased the duration of this vagal reflex apnea. These findings are of interest because pontine NMDA receptors participate in inspiratory off-switch mechanisms and have been implicated in various short- and long-term potentiation and depression phenomena. These data support the involvement of ITR non-NMDA receptors in modulation of reflex apnea per se, whereas NMDA receptors play a role in damping respiratory responses to transient disturbances.

Efferent and afferent connections of GABAergic neurons in the supratrigeminal and the intertrigeminal regions

It has been reported in the cat and rat that inhibitory premotor neurons, which send their axons to motoneurons of the trigeminal motor nucleus (Vm) are distributed in the reticular regions around the Vm, especially in the supratrigeminal region (Vsup) and the intertrigeminal region (Vint). In the present study, we examined neuronal connections of GABAergic neurons in the Vsup and Vint in the mouse by utilizing the adult heterozygous GAD67-GFP knock-in mouse, in which green fluorescence protein (GFP) is expressed in GABAergic neurons under the control of the endogenous GAD (GAD67) gene promoter [Yanagawa, Y., Kaneko, K., Kanbara, N., Totsuka, M., Yagi, T., Obata, K., 2001. Development of mouse expressing GFP in GABAergic neurons. Neurosci. Res. Suppl. 25, S77; Tamamaki, N., Yanagawa, Y., Tomioka, R., Miyazaki, J.-I., Obata, K., Kaneko, T., 2003. Green fluorescent protein expression and colocalization with calretinin, parvalbumin and somatostatin in the GAD67-GFP knock-in mouse. J. Comp. Neurol. 467, 60-79]. The connections were examined light- and electron-microscopically by combining the anterograde or the retrograde tract-tracing method with the immunohistochemical method for GFP. The data indicated that the Vsup and Vint of the mouse contained GABAergic neurons, which received projection fibers from the marginal layer of the nucleus of the spinal tract of the trigeminal nerve (Vc) on the ipsilateral side and sent their axons to the Vm on the contralateral side. Some of these GABAergic neurons may represent Vm-premotor neurons that receive nociceptive input from the Vc to elicit jaw-opening reflex by inhibiting jaw-closing Vm-motoneurons.

Modulation of reflex and sleep related apnea by pedunculopontine tegmental and intertrigeminal neurons

We describe and summarize here our recent findings about the role in respiration of two pontine structures that are not classically included in the pontine respiratory group: the pedunculopontine tegmental nucleus (PPT) and the intertrigeminal region (ITR). We also discuss significant contributions of other workers in the field, especially, S. Datta [Cell. Mol. Neurobiol. 17: 341-365, 1997], R. Lydic and H. Baghdoyan [Sleep, 25: 617-622, 2002], and N. Chamberlin and C. Saper [J. Neurosci. 18: 6048-6056, 1998], who postulated a role for the ITR in modulating reflex apnea. In anesthetized and freely moving rats we have consistently documented that PPT and ITR have a role in respiration. Neurochemical manipulations of each area affected the brainstem respiratory pattern generator and respiratory pattern variability,observed as spontaneous disturbances during sleep or as induced reflex apnea. Although the exact central mechanisms of apnea cannot be determined from our studies to date, we postulate that reflex and sleep-related apneas in rats share some common brainstem pathways, which may include PPT and ITR.

Functional organization of the parabrachial complex and intertrigeminal region in the control of breathing

Although the medulla oblongata contains the epicenter for respiratory rhythm generation, many other parts of the neuraxis play significant substratal roles in breathing. Accumulating evidence suggests that the pons contains several groups of neurons that may belong to the central respiratory system. This article will review data from microstimulation mapping and tract-tracing studies of the parabrachial complex (PB) and intertrigeminal region (ITR). Chemical activation of neurons in these areas has distinct effects on ventilatory and airway muscle activity. Tract-tracing experiments from functionally identified sites reveal specific respiratory-related sensory inputs and outputs that are likely anatomical substrates for these effects. The data suggest that an important physiological role for the rostral pons may be reflexive respiratory responses to airway stimuli.

Pontine intertrigeminal region attenuates sleep apneas in rats.

To determine whether the pontine intertrigeminal region (ITR), with recently described anatomic connections and an effect on vagally induced reflex apnea, has an impact on spontaneous sleep apneas in rats. Respiration, electroencephalogram (EEG), and electromyogram (EMG) were recorded in rats with lesions of the pontine ITR and in control animals. 9 adult male Sprague-Dawley rats. Rats were implanted with EEG and EMG electrodes and were polygraphically recorded for 6 hours, and their respiration was monitored by placing each animal inside a single-chamber plethysmograph. Subsequently, a respiratory-related intertrigeminal site was identified by probing on dorsoventral tracks with 2 to 5 nL glutamate (10 nL, 10 mmol) injections from a multibarrel glass pipette. This site was then lesioned by injecting ibotenic acid (10 nL, 50 mmol) from a second pipette barrel. Animals were again recorded for 6 hours on days 2, 7, and 14 after the lesion. ITR lesions exerted no impact on mean respiratory pattern during any sleep-wake state, compared to baseline recordings. In contrast, apnea frequency during non-rapid eye movement sleep increased following ITR lesion, more than doubling by day 14. This study demonstrates that a small and well-localized unilateral lesion of the ITR region in the lateral pons can increase sleep apnea expression in freely moving rats over a 2-week period. The present findings are in agreement with the general modulatory role of pontine structures in activities including respiration, heart rate, and regulation of blood pressure.

Effects of anesthetics on hypoglossal nerve discharge and c-Fos expression in brainstem hypoglossal premotor neurons.

This study examined the effects of anesthesia on the hypoglossal nerve and diaphragm activities and on c-Fos expression in brainstem hypoglossal premotor neurons (pmXII). Experiments were performed in 71 rats by using halothane inhalation, pentobarbital sodium, or mixtures of alpha-chloralose and urethane or ketamine and xylazine. First, various cardiorespiratory parameters were measured in the rats (n = 31) during both awake and anesthetized conditions. The volatile anesthetic halothane, but not the other anesthetics, was always associated with a strong phasic inspiratory activity in the hypoglossal nerve. Second, a double-immunohistochemical study was performed in awake and anesthetized rats (n = 40) to gauge the level of activity of pmXII neurons. Brainstem pmXII neurons were identified after microiontophoresis of the retrograde tracer Fluoro-Gold in the right hypoglossal motor nucleus. Patterns of c-Fos expression at different brainstem levels were compared in five groups of rats (i.e., awake or anesthetized with halothane, pentobarbital, chloralose-urethane, and ketamine-xylazine). Sections were processed for double detection of c-Fos protein and Fluoro-Gold by using the standard ABC method and a two-color peroxidase technique. Anesthesia with halothane induced the strongest c-Fos expression in a restricted pool of pmXII located in the pons at the level of the Kölliker-Fuse nucleus and the intertrigeminal region. The results demonstrated a major effect of halothane in inducing changes in hypoglossal activity and revealed a differential expression of c-Fos protein in pmXII neurons among groups of anesthetized rats. We suggest that halothane mediates changes in respiratory hypoglossal nerve discharge by altering activity of premotor neurons in the Kölliker-Fuse and intertrigeminal region.

Intertrigeminal region attenuates reflex apnea and stabilizes respiratory pattern in rats

The goal of the present study was to determine whether the newly described anatomical pathway involving the pontine intertrigeminal region (ITR), (Chamberlin and Saper, 1998), has a physiological role in mediating or modulating vagally-induced reflex apnea. We explored the ITR impact on vagal reflex apnea elicited by intravenuously injected 5-HT in ten anesthetized rats. The animals had a catheter inserted into the femoral vein for administration of 5-HT (0.00375 mg) and respiration was recorded by piezo-electric crystal. Multibarrel pipettes were used to pressure inject glutamate (5–10 nl, 10 mM), kynurenic acid (10 nl, 50 mM, a glutamate receptor antagonist), and red dye into the ITR, unilaterally and bilaterally. Intravenous administration of 5-HT produced an immediate 3-s apnea. Microinjections of glutamate into the ITR produced apneas, while microinjections of kynurenic acid blocked the glutamate effect. Following glutamate antagonism, subsequent administration of 5-HT produced apneas of much longer duration (8 s). Acute ponto-medullary transection in two animals yielded even greater prolongation of 5-HT-induced apnea. We conclude that a physiological role for the ITR in respiration is to attenuate vagally-induced reflex apneas. This finding is in agreement with the general modulatory role of pontine structures in autonomic activities including respiration, heart rate and regulation of blood pressure. In addition, our data indicate that medullary circuits, independent of pontine structures, are sufficient to produce 5-HT induced reflex apnea.

Expression of N‐methyl‐D‐aspartate receptor subunits in the rat parabrachial and Kölliker‐Fuse nuclei and in selected pontomedullary brainstem nuclei

In the present study, we investigated the expression of N-methyl-D-aspartate (NMDA) receptor subunits in the parabrachial/Kölliker-Fuse complex (PB/KF), the intertrigeminal region, the ventrolateral pons, the nucleus of the solitary tract, the ventrolateral medulla with the ambiguus nucleus, and the caudal spinal trigeminal nucleus, which are presumably involved in mediating the autonomic responses to nasotrigeminal stimulation (diving response). Our immunocytochemical data demonstrate that the majority of neurons in the respective nuclei stain for the NR1 subunit, which is a mandatory component of all NMDA receptors. NR1 immunoreactivity was found mainly on neuronal cell bodies and primary dendrites. The ubiquitous expression of the NR1 subunit was confirmed by in situ hybridization, revealing a strong NR1 mRNA signal over neurons in all nuclei investigated. Among the NR2A–D subunits, the strongest expression was observed for the NR2D transcript, both in the PB/KF and in the brainstem. For the PB/KF, we found in addition a moderate expression of NR2A mRNA in the internal lateral PB and of NR2B mRNA in the external lateral PB. The remaining PB nuclei and the KF were essentially devoid of NR2A–C transcripts. For the nucleus of the solitary tract and in the spinal trigeminal nucleus, we found, in addition to the strong NR2D mRNA signal, moderate expression of the NR2A–C transcripts. In the ventrolateral medulla, a moderate signal was seen for NR2C transcript, whereas signals for the NR2A and -B subunits were negligible. Our data suggest that, in PB/KF and pontomedullary brainstem nuclei involved in mediating the diving response, glutamatergic neurotransmission is apparently mediated through a specific type of NMDA receptor channels, consisting essentially of NR1 and NR2D subunits. J. Comp. Neurol. 415:501–517, 1999. © 1999 Wiley-Liss, Inc.