Descending axonal projections from the medial parabrachial and Kölliker-Fuse nuclear complex to the nucleus raphe magnus in cats

Neurochemistry of the Kölliker-Fuse nucleus from a respiratory perspective

The Kölliker-Fuse nucleus (KF) is a functionally distinct component of the parabrachial complex, located in the dorsolateral pons of mammals. The KF has a major role in respiration and upper airway control. A comprehensive understanding of the KF and its contributions to respiratory function and dysfunction requires an appreciation for its neurochemical characteristics. The goal of this review is to summarize the diverse neurochemical composition of the KF, focusing on the neurotransmitters, neuromodulators, and neuropeptides present. We also include a description of the receptors expressed on KF neurons and transporters involved in each system, as well as their putative roles in respiratory physiology. Finally, we provide a short section reviewing the literature regarding neurochemical changes in the KF in the context of respiratory dysfunction observed in SIDS and Rett syndrome. By over-viewing the current literature on the neurochemical composition of the KF, this review will serve to aid a wide range of topics in the future research into the neural control of respiration in health and disease.

Identification of neural networks that contribute to motion sickness through principal components analysis of fos labeling induced by galvanic vestibular stimulation

Motion sickness is a complex condition that includes both overt signs (e.g., vomiting) and more covert symptoms (e.g., anxiety and foreboding). The neural pathways that mediate these signs and symptoms are yet to identified. This study mapped the distribution of c-fos protein (Fos)-like immunoreactivity elicited during a galvanic vestibular stimulation paradigm that is known to induce motion sickness in felines. A principal components analysis was used to identify networks of neurons activated during this stimulus paradigm from functional correlations between Fos labeling in different nuclei. This analysis identified five principal components (neural networks) that accounted for greater than 95% of the variance in Fos labeling. Two of the components were correlated with the severity of motion sickness symptoms, and likely participated in generating the overt signs of the condition. One of these networks included neurons in locus coeruleus, medial, inferior and lateral vestibular nuclei, lateral nucleus tractus solitarius, medial parabrachial nucleus and periaqueductal gray. The second included neurons in the superior vestibular nucleus, precerebellar nuclei, periaqueductal gray, and parabrachial nuclei, with weaker associations of raphe nuclei. Three additional components (networks) were also identified that were not correlated with the severity of motion sickness symptoms. These networks likely mediated the covert aspects of motion sickness, such as affective components. The identification of five statistically independent component networks associated with the development of motion sickness provides an opportunity to consider, in network activation dimensions, the complex progression of signs and symptoms that are precipitated in provocative environments. Similar methodology can be used to parse the neural networks that mediate other complex responses to environmental stimuli.

Pontine mechanisms of respiratory control

Pontine respiratory nuclei provide synaptic input to medullary rhythmogenic circuits to shape and adapt the breathing pattern. An understanding of this statement depends on appreciating breathing as a behavior, rather than a stereotypic rhythm. In this review, we focus on the pontine-mediated inspiratory off-switch (IOS) associated with postinspiratory glottal constriction. Further, IOS is examined in the context of pontine regulation of glottal resistance in response to multimodal sensory inputs and higher commands, which in turn rules timing, duration, and patterning of respiratory airflow. In addition, network plasticity in respiratory control emerges during the development of the pons. Synaptic plasticity is required for dynamic and efficient modulation of the expiratory breathing pattern to cope with rapid changes from eupneic to adaptive breathing linked to exploratory (foraging and sniffing) and expulsive (vocalizing, coughing, sneezing, and retching) behaviors, as well as conveyance of basic emotions. The speed and complexity of changes in the breathing pattern of behaving animals implies that "learning to breathe" is necessary to adjust to changing internal and external states to maintain homeostasis and survival.

Pontine-ventral respiratory column interactions through raphe circuits detected using multi-array spike train recordings

Recently, Segers et al. identified functional connectivity between the ventrolateral respiratory column (VRC) and the pontine respiratory group (PRG). The apparent sparseness of detected paucisynaptic interactions motivated consideration of other potential functional pathways between these two regions. We report here evidence for "indirect" serial functional linkages between the PRG and VRC via intermediary brain stem midline raphé neurons. Arrays of microelectrodes were used to record sets of spike trains from a total of 145 PRG, 282 VRC, and 340 midline neurons in 11 decerebrate, vagotomized, neuromuscularly blocked, ventilated cats. Spike trains of 13,843 pairs of neurons that included at least one raphé cell were screened for respiratory modulation and short-time scale correlations. Significant correlogram features were detected in 7.2% of raphé-raphé (291/4,021), 4.3% of VRC-raphé (292/6,755), and 4.0% of the PRG-raphé (124/3,067) neuron pairs. Central peaks indicative of shared influences were the most common feature in correlations between pairs of raphé neurons, whereas correlated raphé-PRG and raphé-VRC neuron pairs displayed predominantly offset peaks and troughs, features suggesting a paucisynaptic influence of one neuron on the other. Overall, offset correlogram features provided evidence for 33 VRC-to-raphé-to-PRG and 45 PRG-to-raphé-to-VRC correlational linkage chains with one or two intermediate raphé neurons. The results support a respiratory network architecture with parallel VRC-to-PRG and PRG-to-VRC links operating through intervening midline circuits, and suggest that raphé neurons contribute to the respiratory modulation of PRG neurons and shape the respiratory motor pattern through coordinated divergent actions on both the PRG and VRC.

Raphe magnus nucleus is involved in ventilatory but not hypothermic response to CO2

There is evidence that serotonin [5-hydroxytryptamine (5-HT)] is involved in the physiological responses to hypercapnia. Serotonergic neurons represent the major cell type (comprising 15-20% of the neurons) in raphe magnus nucleus (RMg), which is a medullary raphe nucleus. In the present study, we tested the hypothesis 1) that RMg plays a role in the ventilatory and thermal responses to hypercapnia, and 2) that RMg serotonergic neurons are involved in these responses. To this end, we microinjected 1) ibotenic acid to promote nonspecific lesioning of neurons in the RMg, or 2) anti-SERT-SAP (an immunotoxin that utilizes a monoclonal antibody to the third extracellular domain of the serotonin reuptake transporter) to specifically kill the serotonergic neurons in the RMg. Hypercapnia caused hyperventilation and hypothermia in all groups. RMg nonspecific lesions elicited a significant reduction of the ventilatory response to hypercapnia due to lower tidal volume (Vt) and respiratory frequency. Rats submitted to specific killing of RMg serotonergic neurons showed no consistent difference in ventilation during air breathing but had a decreased ventilatory response to CO(2) due to lower Vt. The hypercapnia-induced hypothermia was not affected by specific or nonspecific lesions of RMg serotonergic neurons. These data suggest that RMg serotonergic neurons do not participate in the tonic maintenance of ventilation during air breathing but contribute to the ventilatory response to CO(2). Ultimately, this nucleus may not be involved in the thermal responses to CO(2).

Serotonergic raphe magnus cell discharge reflects ongoing autonomic and respiratory activities

Serotonergic cells are located in a restricted number of brain stem nuclei, send projections to virtually all parts of the CNS, and are critical to normal brain function. They discharge tonically at a rate modulated by the sleep-wake cycle and, in the case of medullary serotonergic cells in raphe magnus and the adjacent reticular formation (RM), are excited by cold challenge. Yet, beyond behavioral state and cold, endogenous factors that influence serotonergic cell discharge remain largely mysterious. The present study in the anesthetized rat investigated predictors of serotonergic RM cell discharge by testing whether cell discharge correlated to three rhythms observed in blood pressure recordings that averaged >30 min in length. A very slow frequency rhythm with a period of minutes, a respiratory rhythm, and a cardiac rhythm were derived from the blood pressure recording. Cross-correlations between each of the derived rhythms and cell activity revealed that the discharge of 38 of the 40 serotonergic cells studied was significantly correlated to the very slow and/or respiratory rhythms. Very few serotonergic cells discharged in relation to the cardiac cycle and those that did, did so weakly. The correlations between serotonergic cell discharge and the slow and respiratory rhythms cannot arise from baroreceptive input. Instead we hypothesize that they are by-products of ongoing adjustments to homeostatic functions that happen to alter blood pressure. Thus serotonergic RM cells integrate information about multiple homeostatic activities and challenges and can consequently modulate spinal processes according to the most pressing need of the organism.

Involvement of adenosinergic A1 systems in the occurrence of respiratory perturbations encountered in newborns following an in utero caffeine exposure. a study on brainstem–spinal cord preparations isolated from newborn rats

Involvement of adenosinergic A1 systems in the occurrence of respiratory perturbations encountered in newborns following an in utero caffeine exposure has been investigated on pontomedullary-spinal cord, caudal pons-medullary-spinal cord and medullary-spinal cord preparations isolated from newborn rats. According to the drinking fluid of dams (tap water or 0.02% caffeine), two groups of preparations were distinguished, no-caffeine and caffeine. In the no-caffeine group, adenosine A1 receptor activation induces a decrease in respiratory frequency (Rf) in caudal pons-medullary-spinal cord and medullary-spinal cord preparations whereas, in presence of the rostral pons, an increase is observed. A parallel Fos detection indicates that this discrepancy may be due to the excitatory action of the medial parabrachial nucleus at the rostral pontine level that surpasses inhibitory influence of the adenosine A1 receptor activation at the medullary level particularly in the ventrolateral reticular nucleus of the medulla. In caffeine group, an increase in the baseline Rf in presence of the pons and no change in medullary-spinal cord preparations have been observed. Depending on Fos detection, we assume that the medial parabrachial nucleus is the main region involved in the exaggeration of Rf. Moreover, adenosine A1 receptor activation was modified by in utero caffeine exposure with an overcharge of the Rf increase in pontomedullary-spinal cord preparations and an exaggeration of the Rf decrease in medullary-spinal cord preparations. Based on Fos detection, we link the overcharge in Rf of pontomedullary spinal cord preparations to an increase in the medial parabrachial nucleus neuronal activity. Similarly, exaggeration of Rf decrease observed without the pons is linked with a decrease in activity of the ventrolateral reticular neurons. This study brings evidence for the involvement of adenosinergic A1 systems in the occurrence of respiratory perturbations in newborns following in utero caffeine exposure and the importance of rostral pons in the adenosinergic A1 modulation of the respiratory control.

Projections from the nucleus reticularis magnocellularis to the rat cervical cord using electrical stimulation and iontophoretic injection methods

The aim of this study is to clarify the fiber distribution of the nucleus reticularis magnocellularis (NRMC) and adjacent areas in the rat spinal cord. Biotinylated dextran amine was injected iontophoretically through a glass capillary into the areas, in which a single cell responded to noxious electrical stimulation of the sciatic nerve and to a pinch of the thigh skin with multiple spikes. Labeled fibers descended bilaterally through the ventral funiculi of the medulla oblongata and then through the ventral and lateral funiculi of the cervical cord with an ipsilateral predominance, and terminated in the spinal gray (laminae I-X). A single fiber sometimes ran through several laminae while bifurcating many short branches with axon varicosities and terminal buttons in one transverse section, that is, through laminae V, VII and X, through laminae V, IIl-IV and I-II, and through laminae VII to I-II. The present study showed that the wide distribution of a single fiber and a mass of fibers descending from the NRMC and adjacent areas might modulate not only somatic sensory and motor functions but also autonomic functions in the spinal cord.

Contributions of the medullary raphe and ventromedial reticular region to pain modulation and other homeostatic functions

The raphe magnus is part of an interrelated region of medullary raphe and ventromedial reticular nuclei that project to all areas of the spinal gray. Activation of raphe and reticular neurons evokes modulatory effects in sensory, autonomic, and motor spinal processes. Two physiological types of nonserotonergic cells are observed in the medullary raphe and are thought to modulate spinal pain processing in opposing directions. Recent evidence suggests that these cells may modulate stimulus-evoked arousal or alerting rather than pain-evoked withdrawals. Nonserotonergic cells are also likely to modulate spinal autonomic and motor circuits involved in thermoregulation and sexual function. Medullary serotonergic cells have state-dependent discharge and are likely to contribute to the modulation of pain processing, thermoregulation, and sexual function in the spinal cord. The medullary raphe and ventromedial reticular region may set sensory, autonomic, and motor spinal circuits into configurations that are appropriate to the current behavioral state.

The discharge of a subset of serotonergic raphe magnus cells is influenced by baroreceptor input

In order to determine whether serotonergic cells in the medullary raphe magnus (RM) receive baroreceptor input, cells were tested for their responses to descending aortic occlusion, aortic nerve stimulation, or systemic phenylephrine administration in the lightly anesthetized rat. Serotonergic cells were identified physiologically by a quantitative analysis of their slow and steady discharge. Greater than 40% of the serotonergic RM cells tested responded to brief occlusion of the descending aorta at the level of the coeliac arteries, a stimulus that elevated blood pressure by about 30 mmHg. Similarly, about 40% of the serotonergic RM cells responded to stimulation of the aortic nerve, a nerve that contains primarily baroreceptor afferents from the aortic arch. Greater than 70% of RM serotonergic cells responded to phenylephrine administration which elevated blood pressure by an average of 50 mmHg. Serotonergic cell responses to all methods of baroreceptor activation were small in magnitude and were largely restricted in time to the stimulus duration. The results indicate that a subset of serotonergic cells in RM are influenced by baroreceptor activity.

Differential projections from gustatory responsive regions of the parabrachial nucleus to the medulla and forebrain

The present study combined extracellular electrophysiology with anterograde and retrograde tracing techniques to determine efferent projections from taste responsive sites within the parabrachial nucleus (PBN). Taste activity was recorded from two distinct regions of the PBN, the waist region consisting of the ventrolateral (VL) and central medial (CM) subnuclei, and the external region, consisting of the external medial (EM) and external lateral (EL) subnuclei. Ascending and descending projections from these two regions differed. Small biotinylated dextran injections placed in taste responsive sites in the waist area produced a prominent descending projection to the medullary parvocellular reticular formation, a projection nearly non-existent from the external region. Differences in ascending projections were more subtle. Projections to the thalamus were bilateral in all cases, however, the waist region had a larger ipsilateral thalamic projection than the external region and the external region had a larger contralateral projection compared to the waist. Central nucleus of amygdala (CNA) projections from the waist area were primarily from posterior tongue responsive sites in VL and terminated in the central medial and lateral CNA subnuclei; external region projections were distributed to the capsular region of CNA. Both the external and waist region projected to substantia innominata (SI). Different efferent projections from the two gustatory responsive regions of the PBN may reflect functional specialization of PBN subnuclei. Descending projections from orally responsive sites in the waist area project to the lateral parvocellular reticular formation, a region implicated in brainstem circuitry underlying consummatory components of ingestive function. The external region, contains cells responsive to pain and oral aversive stimuli, but does not apparently contribute directly to local brainstem functions. Rather, forebrain pathways appear critical to the expression of external region functions.

Cardiorespiratory responses to glutamate microinjected into the medullary raphé

The involvement of the medullary raphé in modulating cardiorespiratory activity was examined by microinjecting L-glutamate (L-Glu) into the raphé of rats. Animals were vagotomized, paralyzed, artificially ventilated, maintained at 37 degrees C, and instrumented to record arterial blood pressure (BP) and phrenic nerve activity (PNA). Mock cerebrospinal fluid (mCSF, 10 nl, pH 7.4; control) and L-Glu dissolved in mCSF (10, 100, 1000 mM; 10 nl; pH 7.4; experimental) were microinjected into the raphé. L-Glu affected both BP and PNA in a dose dependent manner. Blood pressure was reduced by 6.30 +/- 0.97 and 12.98 +/- 1.29% by 100 and 1000 mM L-Glu, respectively, without affecting heart rate. PNA increased by 23 and 38% with 100 and 1000 mM L-Glu, respectively. Mock CSF and 10 mM L-Glu had no effect. It is concluded that there are sites in the medullary raphé that affect blood pressure only and other sites which can affect both blood pressure and respiration.

Afferent projections to the rat nuclei raphe magnus, raphe pallidus and reticularis gigantocellularis pars alpha demonstrated by iontophoretic application of choleratoxin (subunit b)

The aim of the present study was to identify the specific afferent projections to the rostral and caudal nucleus raphe magnus, the gigantocellular reticular nucleus pars alpha and the rostral nucleus raphe pallidus. For this purpose, small iontophoretic injections of the sensitive retrograde tracer choleratoxin (subunit b) were made in each of these structures. In agreement with previous retrograde studies, after all injection sites, a substantial to large number of labeled neurons were observed in the dorsal hypothalamic area and dorsolateral and ventrolateral parts of the periaqueductal gray, and a small to moderate number were found in the lateral preoptic area, bed nucleus of the stria terminalis, paraventricular hypothalamic nucleus, central nucleus of the amygdala, lateral hypothalamic area, parafascicular area, parabrachial nuclei, subcoeruleus area and parvocellular reticular nucleus. In addition, depending on the nucleus injected, we observed a variable number of retrogradely labeled cells in other regions. After injections in the rostral nucleus raphe magnus, a large number of labeled cells were seen in the prelimbic, infralimbic, medial and lateral precentral cortices and the dorsal part of the periaqueductal gray. In contrast, after injections in the other nuclei, fewer cells were localized in these structures. Following raphe pallidus injections, a substantial to large number of labeled cells were observed in the medial preoptic area, median preoptic nucleus, ventromedial part of the periaqueductal gray, Kölliker-Fuse and lateral paragigantocellular reticular nuclei. Following injections in the other areas, a small to moderate number of cells appeared. After gigantocellular reticular pars alpha injections, a very large and substantial number of labeled neurons were found in the deep mesencephalic reticular formation and oral pontine reticular nucleus, respectively. After the other injections, fewer cells were seen. Following rostral raphe magnus or raphe pallidus injections, a substantial number of labeled cells were observed in the insular and perirhinal cortices. Following caudal raphe magnus or gigantocellular reticular pars alpha injections, fewer cells were found. After raphe magnus or gigantocellular reticular pars alpha injections, a moderate to substantial number of cells were localized in the fields of Forel, lateral habenular nucleus and ventral caudal pontine reticular nucleus. Following raphe pallidus injections, only a small number of cells were seen. Our data indicate that the rostral and caudal parts of the nucleus raphe magnus, the gigantocellular reticular nucleus pars alpha and the nucleus raphe pallidus receive afferents of comparable strength from a large number of structures. In addition, a number of other afferents give rise to stronger inputs to one or two of the four nuclei studied. Such differential inputs might be directed to populations of neurons with different physiological roles previously recorded specifically in these nuclei.

Differential projections to the raphe nuclei from the medial parabrachial-Kölliker-Fuse (NPBM-KF) nuclear complex and the retrofacial nucleus in cats: retrograde WGA-HRP tracing

After injection of wheat germ agglutinin-conjugated horseradish peroxidase (WGA-HRP, 2 x 30 nl) [corrected] into the nucleus raphe magnus (NRM) of 6 cats, a number of retrogradely labelled neurons were observed in the rostral pons, mainly in the pontine pneumotaxic area, i.e., the medial parabrachial and Kölliker-Fuse (NPBM-KF) nuclear complex, and the tegmental field. In addition, a cluster of labelled cells was observed in the retrofacial nucleus (RFN) and its adjacent areas in the medulla. Control injections of the same volume of WGA-HRP into the medullary magnocellular tegmental field (2 mm lateral to the NRM) resulted in a much lower number of labelled neurons in the areas described above, and the labelled cells in the tegmental fields were predominant ipsilateral to the injected side. Injections into the nucleus raphe pallidus caudal to the NRM resulted in a diffuse distribution of labelled neurons, mainly in the tegmental fields of the pons and medulla. This study demonstrates that the NRM receives specific convergent projections from the NPBM-KF complex and the RFN in the medulla. It is suggested that these pathways are involved in the control of respiration.

Chronic stimulation of the Kölliker-Fuse nucleus region for relief of intractable pain in humans

Chronic electrical stimulation in the periventricular or periaqueductal gray matter regions and the thalamic somatosensory relay nuclei (ventralis posteromedialis and ventralis posterolateralis) provides long-term pain relief in about 50% of patients with intractable pain refractory to other conservative and/or surgical measures. To enhance the success of electrical stimulation in relief of pain, alternative brain and brain-stem targets have been sought. A series of laboratory studies indicated that the Kölliker-Fuse nucleus and the parabrachial region may provide appropriate alternatives to the "classic" targets. This report describes six patients with intractable chronic pain of nociceptive or central origin, in whom an electrode was stereotactically implanted in the region of the Kölliker-Fuse nucleus. Kölliker-Fuse nucleus stimulation alone or in combination with stimulation in the periaqueductal/periventricular gray matter region or the somatosensory thalamic nuclei provided excellent pain relief in three of the six patients.

Axonal projections from the pontine pneumotaxic region to the nucleus raphe magnus in cats

In 15 pentobarbital anesthetized and vagotomized cats, 60 non-respiratory units recorded from the medial parabrachial and Kölliker-Fuse nuclear complex (NPBM-KF), were found to be antidromically activated by electrical stimulation of the nucleus raphe magnus (NRM). Seven respiratory units (6 inspiratory, 1 expiratory), comprising 8.0% of the 87 respiratory units examined, were also antidromically activated by stimulation of the NRM. The antidromic latencies ranged from 0.4 to 2.5 ms (mean 1.2 ms). In 6 cats, following injection of WGA-HRP (wheat germ agglutinin-conjugated horseradish peroxidase) into the NRM, a number of retrogradely labelled neurons were observed mainly in the NPBM-KF complex, and some in subcoeruleus nucleus and adjacent tegmental field. These results demonstrate that predominantly non-respiratory and a portion of respiratory neurons in the rostral pons, especially in the NPBM-KF complex, send a monosynaptic axonal projection to the NRM. It is suggested that the NPBM-KF to NRM pathway could be, in part, involved in the control of respiration as well as nociception control.