Afferent projections to the dorsal and ventral respiratory nuclei in the medulla oblongata of the cat studied by the horseradish peroxidase technique

Mechanisms of respiratory innervation during embryonic development

During embryogenesis, the development of the respiratory tract is closely associated with the formation of an extensive neuronal network. While the topic of respiratory innervation is not new, and similar articles were published previously, recent studies using animal models and genetic tools are breathing new life into the field. In this review, we focus on signaling mechanisms that underlie innervation of the embryonic respiratory tract.

Functional connectivity in the pontomedullary respiratory network

Current models propose that a neuronal network in the ventrolateral medulla generates the basic respiratory rhythm and that this ventrolateral respiratory column (VRC) is profoundly influenced by the neurons of the pontine respiratory group (PRG). However, functional connectivity among PRG and VRC neurons is poorly understood. This study addressed four model-based hypotheses: 1) the respiratory modulation of PRG neuron populations reflects paucisynaptic actions of multiple VRC populations; 2) functional connections among PRG neurons shape and coordinate their respiratory-modulated activities; 3) the PRG acts on multiple VRC populations, contributing to phase-switching; and 4) neurons with no respiratory modulation located in close proximity to the VRC and PRG have widely distributed actions on respiratory-modulated cells. Two arrays of microelectrodes with individual depth adjustment were used to record sets of spike trains from a total of 145 PRG and 282 VRC neurons in 10 decerebrate, vagotomized, neuromuscularly blocked, ventilated cats. Data were evaluated for respiratory modulation with respect to efferent phrenic motoneuron activity and short-timescale correlations indicative of paucisynaptic functional connectivity using cross-correlation analysis and the "gravity" method. Correlogram features were found for 109 (3%) of the 3,218 pairs composed of a PRG and a VRC neuron, 126 (12%) of the 1,043 PRG-PRG pairs, and 319 (7%) of the 4,340 VRC-VRC neuron pairs evaluated. Correlation linkage maps generated for the data support our four motivating hypotheses and suggest network mechanisms for proposed modulatory functions of the PRG.

Functional and structural models of pontine modulation of mechanoreceptor and chemoreceptor reflexes

The dorsolateral and ventrolateral pons (dl-pons, vl-pons) are critical brainstem structures mediating the plasticity of the Hering-Breuer mechanoreflex (HBR) and carotid chemoreflex (CCR). Review of anatomical evidence indicates that dl-pons and vl-pons are connected reciprocally with one another and with medullary nucleus tractus solitarius (NTS) and ventral respiratory group (VRG). With this structural map, functional models of HBR and CCR are proposed in which the respiratory rhythm is modulated by short-term depression (STD) or potentiation (STP) of corresponding primary NTS-VRG and auxiliary pons-VRG excitatory or inhibitory pathways. Behaviorally, STD and STP of respiratory reflexes are akin to non-associative learning such as habituation, sensitization or desensitization to afferent inputs. Computationally, the STD and STP effects amount to signal differentiation and integration in the time domain, or high-pass and low-pass filtering in the frequency domain, respectively. These functional and structural models of pontomedullary signal processing provide a novel conceptual framework that unifies a wealth of experimental observations regarding mechanoreceptor and chemoreceptor reflex control of breathing.

Depletion of substance P and glutamate by capsaicin blocks respiratory rhythm in neonatal rat in vitro

The specific role of the neuromodulator substance P (SP) and its target, the neurokinin 1 receptor (NK1R), in the generation and regulation of respiratory activity is not known. The preBötzinger complex (preBötC), an essential site for respiratory rhythm generation, contains glutamatergic NK1R-expressing neurones that are strongly modulated by exogenously applied SP or acute pharmacological blockade of NK1Rs. We investigated the effects of capsaicin, which depletes neuropeptides (including SP) and glutamate from presynaptic terminals, on respiratory motor output in medullary slice preparations of neonatal rat that generate respiratory-related activity. Bath application of capsaicin slowed respiratory motor output in a dose- and time-dependent manner. Respiratory rhythm could be restored by bath application of SP or glutamate transporter blockers. Capsaicin also evoked dose-dependent glutamate release and depleted SP in fibres within the preBötC. Our results suggest that depletion of SP (or other peptides) and/or glutamate by capsaicin causes a cessation of respiratory rhythm in neonatal rat slices.

Mucosal afferents mediate laryngeal adductor responses in the cat

Laryngeal adductor responses (LAR) close the airway in response to stimulation of peripheral afferents in the superior laryngeal nerve. Although both mucosal afferents and proprioceptive receptors are present in the larynx, their relative contribution for reflex elicitation is unknown. Our purpose was to determine which receptor types are of importance in eliciting the LAR. A servomotor with displacement feedback was used to deliver punctate displacements to the body of the arytenoid cartilage and overlying mucosa on each side of the larynx in eight anesthetized cats. The same displacements were delivered both before and after surgical excision of the overlying mucosa. With the mucosa intact, early short-latency component R1 LAR responses recorded from the thyroarytenoid muscles were frequent (ipsilateral > 92%, contralateral > 95%). After the mucosa was removed, the LAR became infrequent (<3%) and was reduced in amplitude in both the ipsilateral and contralateral thyroarytenoid muscle recording sites (P < 0.0005). These findings demonstrate that mucosal mechanoreceptors and not proprioceptive afferents contribute to the elicitation of LAR responses in the cat.

Modulation of expiratory motor output evoked by chemical activation of pre-Bötzinger complex in vivo

We have previously demonstrated that chemical stimulation of the pre-Bötzinger complex (pre-BötC) in the anesthetized cat produces either phasic or tonic excitation of phrenic nerve discharge. This region is characterized by a mixture of inspiratory-modulated, expiratory-modulated, and phase-spanning (including pre-inspiratory (pre-I)) neurons; however, its influence on expiratory motor output is unknown. We, therefore, examined the effects of chemical stimulation of the pre-BötC on expiratory motor output recorded from the caudal iliohypogastric (lumbar, L(2)) nerve. We found that unilateral microinjection of DL-homocysteic acid (DLH; 10 mM; 10-20 nl) into 16 sites in the pre-BötC enhanced lumbar nerve discharge, including changes in timing and patterning similar to those previously reported for phrenic motor output. Both increased peak amplitude and frequency of phasic lumbar bursts as well as tonic excitation of lumbar motor activity were observed. In some cases, evoked phasic lumbar nerve activity was synchronized in phase with phrenic nerve discharge. These findings demonstrate that chemical stimulation of the pre-BötC not only excites inspiratory motor activity but also excites expiratory motor output, suggesting a role for the pre-BötC in generation and modulation of inspiratory and expiratory rhythm and pattern.

Brain stem control of swallowing: neuronal network and cellular mechanisms

Swallowing movements are produced by a central pattern generator located in the medulla oblongata. It has been established on the basis of microelectrode recordings that the swallowing network includes two main groups of neurons. One group is located within the dorsal medulla and contains the generator neurons involved in triggering, shaping, and timing the sequential or rhythmic swallowing pattern. Interestingly, these generator neurons are situated within a primary sensory relay, that is, the nucleus tractus solitarii. The second group is located in the ventrolateral medulla and contains switching neurons, which distribute the swallowing drive to the various pools of motoneurons involved in swallowing. This review focuses on the brain stem mechanisms underlying the generation of sequential and rhythmic swallowing movements. It analyzes the neuronal circuitry, the cellular properties of neurons, and the neurotransmitters possibly involved, as well as the peripheral and central inputs which shape the output of the network appropriately so that the swallowing movements correspond to the bolus to be swallowed. The mechanisms possibly involved in pattern generation and the possible flexibility of the swallowing central pattern generator are discussed.

Increased ALZ-50 immunoreactivity in sudden infant death syndrome

Neuronal expression of the ALZ-50 epitope was investigated in hippocampus and medulla from infants dying of sudden infant death syndrome or known causes (controls). Hippocampal studies include data from 31 infants dying of known causes between 32 weeks' gestation and 16 months postpartum and 46 infants who died of sudden infant death syndrome. The medulla at the level of the mid olivary protuberance was investigated in 22 infants with sudden infant death syndrome and 11 controls matched for age and postmortem interval. Medullary sections were also examined using immunohistochemical methods to demonstrate reactivity to glial fibrillary acidic protein antibody. The density of ALZ-50-immunodecorated neurons in control hippocampus rises from the level observable in utero to a maximum between 1 and 4 months of age and declines thereafter. The density of ALZ-50-immunoreactive neurons in hippocampus is significantly increased in infants with sudden infant death syndrome at all ages. Significant regionally specific increases in the number of ALZ-50-immunoreactive neurons, and glial fibrillary acidic protein-reactive cells were found in sudden infant death syndrome medulla; coincidental increases were observed in only the solitary nucleus. Neurons exhibiting the ALZ-50 epitope may reflect apoptotic neuron death of normal development, and increased numbers of immunoreactive neurons may suggest enhanced neurodegeneration in sudden infant death syndrome.

Afferent projections to the Bötzinger complex from the upper cervical cord and other respiratory related structures in the brainstem in cats: retrograde WGA-HRP tracing

Following injection of WGA-HRP (30-60 nl, 5%) into the Bötzinger complex (Böt.c), a group of expiratory neurons in the vicinity of the retrofacial nucleus, a number of labeled neurons were observed, predominantly ipsilaterally, in the intermediate zone of the upper cervical cord at the C1 and C2 segments, the retrotrapezoid nucleus (RTN) in the ventrolateral medulla and the parabrachial-Kölliker-Fuse nuclear complex in the rostral pons. In addition, clusters of labeled cells were also observed in and around the solitary tract nucleus, nuclei ambiguus and retroambiguus, and nucleus raphe magnus. Control injections into the magnocellular tegmental field adjacent to the Böt.c resulted in a diffuse distribution of labeled neurons in the reticular formation. These results demonstrate that the Böt.c receives convergent monosynaptic axonal projections from the upper cervical spinal cord, the pontine pneumotaxic area, the RTN and several other respiratory related structures in the medulla.

Medullary visceral reflex circuits: local afferents to nucleus tractus solitarii synthesize catecholamines and project to thoracic spinal cord

Visceral feedback circuits in lower brainstem were elucidated with retrograde tracers by mapping neurons that issue local projections to the general visceral afferent division of the nucleus tractus solitarii (NTS) and dorsomotor vagal nucleus (DMX) in adult male rats. In study 1, spinal and intramedullary afferents to the visceral-sensorimotor complex (NTS-X) were traced to contiguous populations of cell bodies arranged in cylindrical segmental organization. NTS-X afferents derive from curvilinear arrays of neurons that parallel the efferent radiations of the solitariotegmental tract. Newly discovered afferents arise from circumscribed cell groups in the dorsal reticular formation and periventricular zone. Another source was traced to a paraambigual cell column in the apex of the rostral ventrolateral reticular nucleus (n.RVL). In study 2, catecholaminergic afferents were initially defined with combined retrograde transport-immunocytochemical methods. Deposits of retrograde tracers into NTS-X transported to neurons containing tyrosine hydroxylase (TH) in the A1, C1, and C3 areas or phenylethanolamine N-methyltransferase (PNMT) in the C1 area of the n.RVL and C3 area. In study 3, it was revealed that NTS-X afferents arise, in part, as collaterals of thoracic reticulospinal neurons. Deposits of the retrograde fluorescent tracer Fluorogold into the upper thoracic cord and rhodamine-labeled microbeads into NTS-X transported to the same neurons within a subambigual locus in n.RVL and parts of nucleus raphe magnus. In study 4, dual retrograde tracer-immunocytochemical analysis demonstrated that catecholamines are synthesized by a subset of neurons in the n.RVL that issue collaterals to the NTS-X and thoracic cord. Double retrogradely labeled TH- or PNMT-immunoreactive cell bodies were restricted to the C1 area within a 450-microns column bordered rostrally by the facial nucleus and ventrally by the medullary subpial surface. We conclude that visceral reflex arcs are reciprocally organized. Targets of NTS projection are also sources of local NTS-X afferent innervation. Catecholaminergic and other local afferents from reticular formation, periventricular, and spinal gray may, via collaterals, simultaneously modulate visceral reflex excitability at the level of NTS and the outflow of autonomic and respiratory motoneurons.

Metabotropic glutamate receptors are involved in the control of breathing at the medulla oblongata level of anaesthetized rats

The goal of the present study was to identify sites in the medulla oblongata where metabotropic glutamate receptors are involved in regulating respiration. Unilateral microinjections (50 nl) of L-glutamate (L-glu) (10-25-50 mM) into the nucleus tractus solitarii (NTS) of anaesthetized rats elicited apnea (8.6 +/- 0.3 sec; 21.3 +/- 3.6 sec; 66.3 +/- 16.5 sec respectively; N = 6) and arterial hypotension (7.3 +/- 2.4 mmHg; 10.1 +/- 2.3 mmHg; 35.3 +/- 7.5 mmHg respectively; N = 6). Similarly, in other rats 1-aminocyclopentane-1, 3-dicarboxylic acid (ACPD) (1-5-10 mM), a selective agonist of metabotrophic glutamate receptors, also induced apnea (22.4 +/- 2.5 sec; 32.5 +/- sec; 92.5 +/- 1.4 sec respectively; N = 6) and arterial hypotension (12.7 +/- 2.2 mmHg; 19.6 +/- 4.3 mmHg; 26.5 +/- 1.5 mmHg respectively; N = 6). Paired experiments showed that unilateral microinjections of L-glu (50 mM) and ACPD (1 mM) into the nucleus retroambigualis (NRA) of anaesthetized rats elicited apnea (20.2 +/- 2.6 sec and 33.8 +/- 3.2 sec respectively; N = 6) and arterial hypotension (15.7 +/- 3.7 mmHg and 22.5 +/- 4.5 mmHg respectively; N = 6). The ACPD effects on apnea and hypotension in NTS and NRA were not prevented by a 3 min pretreatment with L-AP3 (30 mM), a putative antagonist of metabotropic glutamate receptors (19.5 +/- 1.4 sec; 12.3 +/- 3.2 mmHg and 30.6 +/- 2.9 sec; 23.4 +/- 3.8 mmHg respectively; N = 6). These data suggest that metabotropic glutamate receptors are involved in NTS and NRA regulation of cardiorespiratory functions.(ABSTRACT TRUNCATED AT 250 WORDS)

CNS innervation of airway-related parasympathetic preganglionic neurons: a transneuronal labeling study using pseudorabies virus

The CNS cell groups that innervate the tracheal parasympathetic preganglionic neurons were identified by the viral retrograde transneuronal labeling method. Pseudorabies virus (PRV) was injected into the tracheal wall of C8 spinal rats and after 4 days survival, brain tissue sections from these animals were processed for immunohistochemical detection of PRV. Retrogradely labeled parasympathetic preganglionic neurons were seen in three sites in the medulla: the compact portion of the nucleus ambiguus, the area ventral to the nucleus ambiguus, and the rostralmost portion of the medial nucleus tractus solitarius (NTS); this labeling pattern correlated well with the retrograde cell body labeling seen following cholera toxin beta-subunit injections in the tracheal wall. PRV transneuronally labeled neurons were found throughout the CNS with the most abundant labeling concentrated in the ventral medulla oblongata. Labeled neurons were identified along the ventral medullary surface, and in nearby areas including the parapyramidal, retrotrapezoid, gigantocellular and lateral paragigantocellular reticular nuclei as well as the caudal raphe nuclei (raphe pallidus, obscurus, and magnus). Serotonin (5-HT) neurons of the caudal raphe complex (B1-B3 cell groups) and ventromedial medulla were labeled as well as a few C1 adrenergic neurons. The A5 cell group was the major noradrenergic area labeled although a small number of locus coeruleus neurons were also labeled. Several NTS regions contained labeled cells including the commissural, intermediate, medial, central, ventral, and ventrolateral subnuclei. PRV infected neurons were present in the Kölliker-Fuse and Barrington's nuclei. In the rostral mesencephalon, the precommissural nucleus of the dorsal periventricular gray matter was labeled. Labeling was present in the dorsal, lateral and paraventricular hypothalamic nuclei. In summary, the airway parasympathetic preganglionic neurons are innervated predominantly by a network of lower brainstem neurons that lie in the same regions known to be involved in respiratory and cardiovascular regulation. These findings are discussed in relationship to some of the potential CNS mechanisms that may be operative in airway disorders as well as potentially involved in certain fatal respiratory conditions such as Ondine's curse and sudden infant death syndrome (SIDS).

Brainstem connections of the rat ventral respiratory subgroups: afferent projections

Propriobulbar neurons having axonal projections to the Ventral Respiratory Group (VRG) were retrogradely labeled after discrete injections of Fast blue into one of the three physiologically identified subdivisions (Bötzinger Complex, rostral inspiratory and caudal expiratory regions). Neurons that project to these regions were found throughout the rostrocaudal extent of the medulla and the pons in a variety of areas known to have cardio-respiratory function. Labeled somata were located within the nuclei of the solitary tract (commissural, intermediate and ventrolateral), other subdivisions of VRG, parabrachial nuclei (medial, dorsolateral and central lateral), Kölliker-Fuse nucleus, retrotrapezoid nucleus, lateral paragigantocellular nucleus and lateral tegmental field of the pons. Within the nuclei of the solitary tract and the Kölliker-Fuse nucleus, there was a topographical organization with respect to the three subdivisions of the VRG.

The Bötzinger complex as the pattern generator for retching and vomiting in the dog

To clarify the location of the pattern generator for the emetic act, the bulb was systematically stimulated and partially cut in decerebrate, paralyzed dogs. Stimulation of the following bulbar structures elicited the activities which could be recognized as retching and vomiting in the following muscle nerves. The bulbar structures were: the intra-bulbar bundle of the vagal afferents, the solitary tract and the medial subdivision of its nucleus (NTS), the area postrema, the commissural nucleus, the raphe area at the obex level, and the longitudinal reticular column which consists of 3 areas--the area between the caudal parts of the solitary complex (SC) and the nucleus ambiguus, the area ventromedial to the rostral part of the nucleus and the area dorsomedial to the retrofacial nucleus (RFN) which may correspond to the Bötzinger complex (BOT). The muscle nerves were: the phrenic branches to the dome and hiatal parts of the diaphragm, the abdominal muscle nerve, the pharyngo-esophageal branch of the vagus nerve, the mylohyoid muscle nerve, and the recurrent nerve branches to the adductors and abductor of the glottis. Emetic responses to stimulation of the vagal ventral trunk and the rostral SC still remained after cutting of the bilateral SCs at about 1 mm rostral to the obex, but disappeared after cutting at about 3.5 mm rostral to the obex. After the rostral cuts, stimulation of the SC part caudal to the cuts and the reticular column still induced the emetic act. Emetic responses to stimulation of the caudal SC remained after transection of the bulb at the rostral end of the RFN, but disappeared after transection at its caudal end or after partial cutting of the caudal BOT. The following hypothesis was proposed from these results. Emetic vagal afferents enter the rostral bulb, then descend through the SC to the area subpostrema. Subpostrema neurons project through the reticular column to the pattern generator of the emetic act in the BOT and activate it.

Reciprocal connections between rostral ventrolateral medulla and inspiration-related medullary areas in the cat

We investigated connections between the rostral ventrolateral medulla (rVLM) and the two main inspiration-related medullary areas, i.e., the dorsal respiratory group (DRG) and the rostral ventral respiratory group (rVRG) in the cat. Non respiration-related tonically firing units encountered in the rVLM displayed either antidromic or orthodromic responses to DRG or rVRG microstimulation. Some units responded to the stimulation of both regions. We suggest that at least part of rVLM neurons are components of medullary loops operating in the control of breathing.

Efferent projections of pulmonary rapidly adapting receptor relay neurons in the cat

Axonal projections of second order neurons activated by vagal afferent fibers originating from pulmonary rapidly adapting receptors (RARs) were studied electrophysiologically in Nembutal-anesthetized, paralyzed and artificially ventilated cats. Extracellular recordings from these neurons (referred to as 'RAR-cells') were made in the commissural subnucleus (COM) of the nucleus of the solitary tract (NTS). They were identified by a combination of stimuli including stimulation of the vagus nerve(s), hyperinflation and deflation of the lungs, and a brief period of ammonia vapor inhalation. A total of 80 RAR-cells were tested for axonal projections to a respiration-related area in the brain-stem, either the dorsolateral rostral pons or the dorsal respiratory group (DRG) or the ventral respiratory group (VRG) or the Bötzinger complex (BOT) and/or the spinal cord. Twenty-two of the 47 (47%) RAR-cells tested for ipsilateral pontine projection could be antidromically activated, and in 8 cases evidence for axonal arborization was obtained. Only 1 of the 11 RAR-cells tested for DRG projection, and 1 of the 10 RAR-cells tested for VRG projection, were antidromically activated. No RAR-cells were activated from the BOT (n = 8) or from the C3-C4 segments of the spinal cord (n = 11). Bilateral lesions of the COM abolished the reflex responses induced by ammonia inhalation or hyperinflation of the lungs, but not the Hering-Breuer reflex. These results indicate that a pathway from the COM to the rostral pons forms part of the reflex arc originating from RARs.

[The nucleus tractus solitarius: neuroanatomic, neurochemical and functional aspects]

The nucleus tractus solitarii (NTS) has long been considered as the first central relay for gustatory and visceral afferent informations only. However, data obtained during the past ten years, with neuroanatomical, biochemical and electrophysiological techniques, clearly demonstrate that the NTS is a structure with a high degree of complexity, which plays, at the medullary level, a key role in several integrative processes. The NTS, located in the dorsomedial medulla, is a structure of small size containing a limited number of neurons scattered in a more or less dense fibrillar plexus. The distribution and the organization of both the cells and the fibrillar network are not homogeneous within the nucleus and the NTS has been divided cytoarchitectonically into various subnuclei, which are partly correlated with the areas of projection of peripheral afferent endings. At the ultrastructural level, the NTS shows several complex synaptic arrangements in form of glomeruli. These arrangements provide morphological substrates for complex mechanisms of intercellular communication within the NTS. The NTS is not only the site of vagal and glossopharyngeal afferent projections, it receives also endings from facial and trigeminal nerves as well as from some renal afferents. Gustatory and somatic afferents from the oropharyngeal region project with a crude somatotopy within the rostral part of the NTS and visceral afferents from cardiovascular, digestive, respiratory and renal systems terminate viscero-topically within its caudal part. Moreover the NTS is extensively connected with several central structures. It projects directly to multiple brain regions by means of short connections to bulbo-ponto-mesencephalic structures (parabrachial nucleus, motor nuclei of several cranial nerves, ventro-lateral reticular formation, raphe nuclei...) and long connections to the spinal cord and diencephalic and telencephalic structures, in particular the hypothalamus and some limbic structures. The NTS is also the recipient of several central afferent inputs. It is worth to note that most of the structures that receive a direct projection from the NTS project back to the nucleus. Direct projections from the cerebral cortex to the NTS have also been identified. These extensive connections indicate that the NTS is a key structure for autonomic and neuroendocrine functions as well as for integration of somatic and autonomic responses in certain behaviors. The NTS contains a great diversity of neuroactive substances. Indeed, most of the substances identified within the central nervous system have also been detected in the NTS and may act, at this level, as classical transmitters and/or neuromodulators.(ABSTRACT TRUNCATED AT 400 WORDS)

Synaptic events in ventral respiratory neurones during apnoea induced by laryngeal nerve stimulation in neonatal pig

1. Postsynaptic potentials evoked by electrical stimulation of superior laryngeal nerve (SLN) were recorded during SLN-induced apnoea from the respiratory neurones of the ventral respiratory group (VRG) in pentobarbitone-anaesthetized, vagotomized and artificially ventilated newborn piglets (n = 14, 4-7 days old). All recorded inspiratory (n = 10), post-inspiratory (n = 10) and expiratory (n = 20) neurones had a triphasic pattern of membrane potential and were identified for their projections to the spinal cord or cervical vagus nerve. 2. During long-lasting apnoea, induced by SLN stimulation, the membrane potential trajectory of each type of recorded neurone was held at the level corresponding approximately to the membrane potential reached during stage I of expiration. Compound postsynaptic potentials evoked in most respiratory-related neurones had an early short-lasting and a late long-lasting component. 3. Postsynaptic potentials in four out of seven inspiratory neurones, in which postsynaptic potentials were well demonstrated, were characterized by an early depolarization followed by long-lasting hyperpolarization. In three other inspiratory neurones only late hyperpolarization was present. The reversal of the late hyperpolarization by intracellular chloride injection was achieved to a different degree in the early and late portions of late hyperpolarization. 4. Postsynaptic potentials evoked in expiratory neurones were studied in sixteen neurones and displayed two patterns: early hyperpolarization followed by long-lasting hyperpolarization (n = 7, six were not antidromically activated after spinal cord stimulation) or early hyperpolarization followed by late depolarization (n = 9, eight projected to the spinal cord). The early hyperpolarization was readily reversed by chloride injection. The late hyperpolarization was more difficult to reverse and usually the reversal was not completed. 5. Postsynaptic potentials evoked in post-inspiratory neurones showed a pattern of two consecutive phases of depolarization. 6. The present study revealed that during long-lasting apnoea evoked by SLN stimulation each category of VRG respiratory neurones received a temporally synchronized combination of an initial fast input derived reflexly from laryngeal afferents, and of late inputs representing involvement of the whole respiratory network in the response.

Patterns of membrane potentials and distributions of the medullary respiratory neurons in the decerebrate rat

We analyzed the membrane potential of 161 respiratory neurons in the medulla of decerebrate rats which were paralyzed and ventilated. Three types of inspiratory (I) neurons were observed: those displaying progressive depolarization in inspiration (augmenting I neurons), those which gradually repolarized after maximal depolarization at the onset of inspiration (decrementing I neurons) and those exhibiting a plateau or bell-shaped membrane potential trajectory throughout inspiration (I-all neurons). Three types of expiratory (E) neurons were also encountered: those in which the membrane potential progressively depolarized (augmenting E neurons), those in which the membrane potential repolarized during the interval between phrenic bursts (decrementing E or post-I neurons) and those exhibiting a plateau or bell-shaped membrane potential trajectory throughout expiration (E-all neurons). Axonal projections of these medullary neurons were identified in the cranial nerves (n = 34), or in the spinal cord (n = 19) as revealed by antidromic stimulation and/or by reconstruction following horseradish peroxidase (HRP) labeling. The other 108 neurons were not antidromically activated (NAA) by the stimulations tested, or had their axons terminating inside the medulla as revealed by HRP labeling. All these respiratory neurons, except for 3 which were hypoglossal motoneurons, had their somata within the ventrolateral medulla, in the region of the nucleus ambiguus, homologous to the ventral respiratory group (VRG) of the cat. No dorsal respiratory group (DRG) was detected within the medulla of the rats. Due to this absence of a DRG, it is concluded that the neural organization of respiratory centers is quite different in cats and rats.

Expiration-related neurons in the caudal ventral respiratory group of the cat: influences of the activation of Bötzinger complex neurons

The functional role of Bötzinger complex (Böt. c.) projections to the expiration-related (ER) area of the caudal ventral respiratory group (cVRG) was investigated in anesthetized, vagotomized, paralyzed and artificially ventilated cats. ER neurons in both the ipsi- and the contralateral cVRG displayed excitatory responses to Böt. c. electrical microstimulation. They were also activated by microinjections of D,L-homocysteic acid into the Böt. c. region. We propose that at least part of the Böt. c. projections to the cVRG have an excitatory function.

Extensive monosynaptic inhibition of ventral respiratory group neurons by augmenting neurons in the Bötzinger complex in the cat

Axonal projections and synaptic connectivity of expiratory Bötzinger neurons with an augmenting firing pattern (Bot-Aug neurons) to neurons in the ipsilateral ventral respiratory group (VRG) were studied in anaesthetized cats. Antidromic mapping revealed extensive axonal arborizations of Bot-Aug neurons (24 of 45) to the rostral or caudal VRG, with some having arbors in both regions. Of 234 pairs of neurons studied with intracellular recording and spike-triggered averaging, monosynaptic inhibitory postsynaptic potentials (IPSPs) were evoked in 49/221 VRG neurons by 38/98 Bot-Aug neurons. The highest incidence of monosynaptic inhibition was found in inspiratory bulbospinal neurons (10 of 23 tested). Evidence was also found for monosynaptic inhibition, by a separate group of Bot-Aug neurons, of expiratory bulbospinal neurons (12/58), while excitatory postsynaptic potentials (EPSPs) were identified in another two of these neurons. In addition, monosynaptic IPSPs were recorded from 13 of 53 identified laryngeal motoneurons, and from 14 of 100 respiratory propriobulbar neurons. Presumptive disynaptic IPSPs were recorded from 11 of the 221 VRG neurons. We conclude that Bot-Aug neurons exert widespread inhibition on all major neuron categories in the ipsilateral VRG, and should be regarded as an important element in shaping the spatiotemporal output pattern of both respiratory motoneurons and premotor neurons.

Projections of the parabrachial nucleus in the pigeon (Columba livia)

The ascending and descending projections of the parabrachial nuclear complex in the pigeon have been charted with autoradiographic and histochemical (WGA-HRP) techniques. The ascending projections originate from a group of subnuclei surrounding various components of the brachium conjunctivum, namely, the superficial lateral, dorsolateral, dorsomedial, and ventromedial subnuclei. The projections are predominantly ipsilateral and travel in the quintofrontal tract. They are primarily to the medial and lateral hypothalamus (including the periventricular nucleus and the strata cellulare internum and externum), certain dorsal thalamic nuclei, the nucleus of the pallial commissure, the bed nucleus of the stria terminalis, the ventral paleostriatum, the olfactory tubercle, the nucleus accumbens, and a dorsolateral nucleus of the posterior archistriatum. There are weaker or more diffuse projections to the rostral locus coeruleus (cell group A8), the compact portion of the pedunculopontine tegmental nucleus, the central grey and intercollicular region, the ventral area of Tsai, the medial spiriform nucleus, the nucleus subrotundus, the anterior preoptic area, and the diagonal band of Broca. The parabrachial subnuclei have partially differential projections to these targets, some of which also receive projections from the nucleus of the solitary tract (Arends, Wild, and Zeigler: J. Comp. Neurol. 278:405-429, '88). Most of the targets, particularly those in the basal forebrain (viz., the periventricular nucleus and the strata cellulare internum and externum of the hypothalamus, the bed nucleus of the stria terminalis, and its lateral extension into the ventral paleostriatum, which may be comparable with the substantia innominata), have reciprocal connections with the parabrachial and solitary tract subnuclei and therefore may be said to compose parts of a "visceral forebrain system" analogous to that described in the rat (Van der Kooy et al: J. Comp. Neurol. 224:1-24, '84). The descending projections to the lower brainstem arise in large part from a ventrolateral subnucleus that may be comparable with the Kölliker-Fuse nucleus of mammals. They are mainly to the ventrolateral medulla, nucleus ambiguus, and massively to the hypoglossal nucleus, particularly its tracheosyringeal portion. These projections are therefore likely to be importantly involved in the control of vocalization and respiration (Wild and Arends: Brain Res. 407:191-194, '87). Some of these results have been presented in abstract form (Wild, Arends, and Zeigler: Soc. Neurosci. Abst. 13:308, '87).

Brainstem projections to the phrenic nucleus: an anterograde and retrograde HRP study in the rabbit

Brainstem projections to the phrenic nucleus were studied in rabbits using horseradish peroxidase conjugated with wheat germ agglutinin (WGA-HRP) as a retrograde and anterograde neuronal tracer. Injections of 1% WGA-HRP were centered in the phrenic nucleus in the C4-C5 ventral horn in 4 rabbits to identify pontomedullary nuclear groups that contain neurons projecting to the midcervical spinal cord. Regions of the rabbit brainstem that are homologous to the ventral respiratory group (VRG), dorsal respiratory group (DRG), Bötzinger Complex (BötC) and Kölliker-Fuse nucleus in the cat and rat were shown to provide the major pontomedullary projections to the phrenic nucleus. Injections of WGA-HRP into physiologically identified locations within DRG, VRG and BötC anterogradely labelled bulbospinal axons of these groups. These injections produced presumptive terminal labelling in the C4-C5 ventral horn in the region containing the phrenic cell column and the transverse phrenic motoneuron dendrite bundles as defined by WGA-HRP labelling of phrenic motoneurons. These results indicate: 1) The presumptive excitatory (DRG, VRG) and inhibitory (BötC) bulbospinal control of phrenic motoneurons arise from the same medullary respiratory groups in the rabbit as in the cat and rat. 2) The bulbospinal control of phrenic motoneurons is primarily via direct projections to the phrenic motor nucleus, and not through segmental propriospinal interneurons. 3) As in the rat, the bulbospinal contribution of the DRG is less pronounced in the rabbit than in the cat. 4) The rabbit and rat have a slight ipsilateral predominance in their bulbospinal projections to phrenic nucleus; whereas these projections have a contralateral predominance in the cat.

Anatomical substrates of cholinergic-autonomic regulation in the rat

Acetylcholine (ACh) plays a major role in central autonomic regulation, including the control of arterial blood pressure (AP). Previously unknown neuroanatomic substrates of cholinergic-autonomic control were mapped in this study. Cholinergic perikarya and bouton-like varicosities were localized by an immunocytochemical method employing a monoclonal antiserum against choline acetyltransferase (ChAT), the enzyme synthesizing ACh. In the forebrain, bouton-like varicosities and/or perikarya were detected in the septum, bed nucleus of the stria terminalis, amygdala (in particular, autonomic projection areas AP1 and AP2 bordering the central subnucleus), hypothalamus (rostrolateral/innominata transitional area, perifornical, dorsal, incertal, caudolateral, posterior [PHN], subparafascicular, supramammillary and mammillary nuclei). Few or no punctate varicosities were labeled in the paraventricular (PVN) or supraoptic (SON) hypothalamic nuclei. In the mid- and hindbrain, immunoreactive cells and processes were present in the nucleus of Edinger-Westphal, periaqueductal gray, parabrachial complex (PBC), a periceruleal zone avoiding the locus ceruleus (LC), pontine micturition field, pontomedullary raphe, paramedian reticular formation and periventricular gray, A5 area, lateral tegmental field, nucleus tractus solitarii (NTS), nucleus commissuralis, nucleus reticularis rostroventrolateralis (RVL), and the ventral medullary surface (VMS). In the PBC, immunoreactive varicosities identified areas previously unexplored for cholinergic autonomic responsivity (superior, internal, dorsal, and central divisions of the lateral subnucleus, nucleus of Koelliker-Fuse and the medial subnucleus). In the NTS, previously undescribed ChAT-immunolabeled cells and processes were concentrated at intermediate and subpostremal levels and distributed viscerotopically in areas receiving primary cardiopulmonary afferents. In the nucleus RVL, cholinergic perikarya were in proximity to the VMS and medial to adrenergic cell bodies of the C1 area. Punctate varicosities of unknown origin and dendrites extending ventrally from the nucleus ambiguus overlapped the C1 area and immediate surround of RVL.

IN CONCLUSION

1) Cholinergic perikarya and putative terminal fields, overlap structures that are rich in cholinoreceptors and express autonomic, neuroendocrine, or behavioral responsivity to central cholinergic stimulation (PHN, NTS, RVL). The role of ACh in most immunolabeled areas, however, has yet to be determined. Overall, these data support the concept that cholinergic agents act at multiple sites in the CNS and with topographic specificity.(ABSTRACT TRUNCATED AT 400 WORDS)

A pontine call site in the domestic cat: behavior and neural pathways

Electrical stimulation of the brain of the domestic cat elicited vocalizations from a site in the ventrolateral pons in the region of the medial lemniscus. The evoked vocalizations were analysed by means of sound spectrographs and classified as meows, growls, hisses and meow-growls. The neural pathways associated with these call sites were traced by following the pattern of fiber degeneration resulting from lesions placed at these sites. A descending fiber pathway was traced to the magnocellular tegmental field, the facial nucleus and the retrofacial nucleus, while an ascending system terminated in the zona incerta, the red nucleus, contralateral oculomotor nucleus, the ventroposterior lateral nucleus of the thalamus and inferior colliculus. It is concluded from these findings and the nature of the behavior evoked that the ventrolateral pontine call site lies on common pathway for a majority of vocalizations in the cat.

Origin of serotonin-containing projections to the ventral respiratory group in the rat

The major purpose of the present study was to determine the origin of the serotonin-containing neurons which project to the rostral ventral respiratory group in the rat. This was accomplished by using the technique of retrograde tracing with rhodamine-labeled latex microspheres (beads) combined with immunochemistry. The rhodamine-labeled beads were microinjected into electrophysiologically identified groups of inspiratory neurons in the rostral ventral respiratory group to retrogradely label neurons projecting to this site. Immunohistochemical processing of the tissue was then done to determine if serotonin was present in the retrogradely-labeled neurons. Serotonin-containing neurons projecting to the rostral ventral respiratory group were found in the raphe magnus, raphe obscurus, raphe pallidus and in the paraolivary region extending to the ventral medullary surface. No serotonin-containing neurons in more rostrally located raphe nuclei were found to project to the rostral ventral respiratory group. The findings suggest that caudal raphe serotonergic projections may affect the activity of respiratory neurons in the rostral ventral respiratory group. Projections to the rostral ventral respiratory group from other pontomedullary nuclei were also identified. Rhodamine-labeled neurons were found in the area of the Kölliker-Fuse nucleus, lateral and medial parabrachial nuclei, retrofacial nucleus, nucleus ambiguus/retroambigualis, nucleus tractus solitarius, A5 region, nucleus paragigantocellularis lateralis, retrotrapezoid nucleus, area postrema and spinal trigeminal nucleus. The projections to the rostral ventral respiratory group in the rat are similar to those previously described in the cat and suggest a common circuitry for the CNS control of breathing.

Brainstem projections to the major respiratory neuron populations in the medulla of the cat

Efferent and afferent connections of the dorsal and ventral respiratory groups in the medulla of the cat were mapped by axonal transport of wheat germ agglutinin conjugated to horseradish peroxidase. Injections of wheat germ agglutinin-horseradish peroxidase into the dorsal respiratory group and the three principal subdivisions of the ventral respiratory group (caudal, rostral, and Bötzinger Complex) revealed extensive interconnections between these regions and with a limited number of other brainstem neuron populations. Major neuron populations with efferent projections to the regions of the dorsal and ventral respiratory groups include the parabrachial nuclear complex (medial parabrachial, lateral parabrachial, and Kölliker-Fuse nuclei), subregions of the lateral paragigantocellular reticular nucleus, subregions of the lateral and magnocellular tegmental fields, inferior central and postpyramidal nuclei of the raphe, and sensory trigeminal nuclei. A previously unidentified neuron population with extensive efferent projections to the dorsal and ventral respiratory groups was found near the ventral surface of the rostral medulla; we refer to this group as the retrotrapezoid nucleus. The results suggest that the dorsal and ventral respiratory groups form an extensively interconnected neuronal system receiving convergent inputs from the same brainstem nuclear groups, consistent with the hypothesis that the dorsal and ventral groups are primarily sites for integration of sensory and premotor respiratory drive inputs. Neuron populations in the rostral ventrolateral medulla with projections to both the dorsal and ventral respiratory groups, particularly the retrotrapezoid nucleus and neighboring subregions of the lateral paragigantocellular reticular nucleus, are candidate sites for participation in respiratory rhythmogenesis or other critical functions of the brainstem respiratory control system such as intracranial chemoreception.

Electrophysiological properties of rostral medullary respiratory neurones in the cat: an intracellular study

1. We recorded the membrane potentials of sixty-three respiratory neurones in the rostral, ventral medulla of decerebrate vagotomized cats. Stable recordings were obtained in thirty-eight expiratory and twenty-five inspiratory neurones. Axonal projections were identified by antidromic invasion after electrical stimulation of the region of the dorsal respiratory group (DRG), spinal cord, and the cervical vagus, superior laryngeal and pharyngeal nerves. 2. Two types of expiratory neurones were encountered: those in which the membrane potential progressively depolarized (augmenting neurons, n = 22) and those in which the membrane potential repolarized (decrementing or post-inspiratory neurones, n = 16) during the interval between phrenic bursts. Both types were hyperpolarized during inspiration by chloride-dependent, inhibitory postsynaptic potentials (IPSPs) which decreased membrane resistance. In augmenting neurones two waves of IPSPs appeared, one early and one late in inspiration. 3. Five out of seventeen augmenting expiratory neurones tested were antidromically activated by contralateral stimulation of the spinal cord (n = 3) or the DRG (n = 2). Spinal axons were not detected in any of the sixteen decrementing expiratory neurones tested. Of thirteen expiratory neurones tested with pharyngeal nerve stimulation, one (an augmenting type) was antidromically activated. Superior laryngeal or vagal axons could not be demonstrated for any expiratory neurones. 4. Two types of inspiratory neurones were also encountered: those displaying progressive depolarization throughout inspiration (n = 5) and those which gradually repolarized after maximal depolarization at the onset of inspiration (n = 10). None of the former had identifiable spinal or medullary axons, but superior laryngeal axons were demonstrated in three and pharyngeal axons were found in three. None of the latter was antidromically activated from any of the sites stimulated. 5. Stimulation of the superior laryngeal or pharyngeal nerves evoked excitatory postsynaptic potentials (EPSPs) in all neurones except in post-inspiratory neurones. In these, stimulation of the superior laryngeal or pharyngeal nerves evoked IPSPs in five of twelve neurones tested. 6. We conclude that a spectrum of respiratory neurones lie within or ventral to the retrofacial nucleus. These neurones may control upper-airway muscles or may play a role in chemoreception.

Immunohistochemical localization of serotonin- and substance P-containing fibers around respiratory muscle motoneurons in the nucleus ambiguus of the cat

Retrograde tracing with a fluorescent dye (Fast Blue) combined with immunohistochemistry was used to determine if the putative neurotransmitters, serotonin and substance P, are present around posterior cricoarytenoid muscle motoneurons. Fast Blue was injected into the posterior cricoarytenoid muscle of the larynx. Following a 14-21 day survival time to allow for transport of the dye, the animals were perfusion fixed and the brainstem was removed for analysis under the fluorescence microscope. Retrogradely labeled cell bodies containing Fast Blue were found within the nucleus ambiguus from 0.5 to 3.0 mm rostral to obex. These motoneurons ranged in size from 23 to 38 micron. The same tissue sections containing labeled posterior cricoarytenoid muscle motoneurons were then used to determine the distribution of serotonin and substance P around these motoneurons using the indirect immunofluorescence technique. A dense network of serotonin-containing immunoreactive fibers was found around posterior cricoarytenoid muscle motoneurons. The fibers contained varicosities which were in close proximity, actually appearing to surround these motoneurons. Substance P immunoreactive fibers and varicosities were also found around posterior cricoarytenoid muscle motoneurons. The density and pattern of distribution of the substance P immunoreactivity was similar to that of the serotonin immunoreactivity. These results suggest that these putative neurotransmitters may be involved in influencing the activity of posterior cricoarytenoid muscle motoneurons. Serotonin and substance P are also present around other respiratory motoneurons such as phrenic motoneurons. Therefore, these two neurotransmitters may have a more general role in influencing respiratory motor outflow.

The nature of posterior hypothalamic projections to cardiorespiratory centers in the brainstem

Focal electrical stimulation of the midlateral posterior hypothalamus in the rat produces rapid shallow respiration accompanied by a rise in arterial blood pressure. Stimulation of presumably intrinsic neurons only by glutamate induces slower deeper respiration associated with a fall in blood pressure.

Discharges of bulbar respiratory neurons during rhythmic straining evoked by activation of pelvic afferent fibers in dogs

Each cycle of rhythmic straining evoked through the reflex center in the Kölliker-Fuse nucleus by stimulation of pelvic afferents in decerebrate dogs usually began in early expiration. During the rhythmic straining cycle, postinspiratory discharges of the phrenic nerve increased simultaneously with a burst of discharges of the nerves innervating the rectus abdominis and adductors of the glottis. While about half of the bulbar expiratory units discharged concurrently with the rhythmic straining, almost none of the inspiratory units examined did so. Nearly all expiratory bulbospinal units discharged concurrently, but none of the inspiratory bulbospinal units did so. These results show that expiratory neurons in the caudal bulb relay commands for rhythmic straining from the pontine reflex center to motor neurons of expiratory muscles, but that bulbar inspiratory neurons do not relay the commands to inspiratory motor neurons. Discharges concurrent with rhythmic straining were also evoked in all 4 postinspiratory units of the ventral group, 3 very early onset expiratory units and all 9 inspiratory-expiratory units of the dorsal group. Possible roles played by these respiratory neurons in the organization of rhythmic straining were discussed.

Effects of electrical and chemical stimulation of the Bötzinger complex on respiratory activity in the cat

The effects of electrical and chemical stimulation of the expiratory neuronal population in the region of the retrofacial nucleus, the so called 'Bötzinger complex' (Böt. c.), on respiratory activity were investigated in vagotomized cats under pentobarbitone anaesthesia. Some of the experiments were performed on paralyzed or bilaterally thoracotomized, artificially ventilated animals. Sustained tetanic electrical stimulation (20 to 100-Hz, 0.5-ms current pulses at intensities of 5-60 microA) induced strong depressant effects on the inspiratory motor output which could lead to complete apnoea. The apnoeic response was accompanied by tonic activation of expiratory muscles; the appearance and the strength of tonic expiratory activity were dependent upon the frequency of stimulation. Brief tetani (40 to 100 ms trains of 0.5-ms rectangular pulses at 100-300 Hz) timed either during the inspiratory or the expiratory phase caused depression of inspiratory activity and prolongation of expiratory time, respectively. These effects increased gradually as the onset of stimulation was progressively delayed during each respiratory phase. The effects of sustained tetanic stimulation were mimicked by microinjections (25-100 nl) of 0.5 M L-glutamate or 0.16 M DL-homocysteic acid in the same region, thus indicating that they were the result of the stimulation of cell bodies and not of axons of passage. The present results support the hypothesis that Böt. c. neurons play an important role in the control of the breathing pattern by exerting inhibitory influences on inspiratory activity and, possibly, by contributing to the off-switch mechanisms. Furthermore, they suggest that these neurons are involved in the central control of expiratory activity.

Axonal projections to the ventrolateral nucleus of the solitary tract revealed by double labelling of retrograde fluorescent markers in the cat

The retrofacial nucleus project bilaterally to the ventrolateral nucleus of the tractus solitarius (vlNTS) as revealed by means of retrograde transport of the fluorescent markers, Fast blue (FB) and Diamidino yellow (DY), in the cat. Some of the neurons of the retrofacial nucleus send axonal ramifications to both vlNTS. Extensive projections from other brainstem respiratory related nuclei to the vlNTS were also observed: bilaterally from the nucleus ambiguus, nucleus retroambiguus and nucleus parabrachialis medialis, and ipsilaterally from the Kölliker-Fuse nucleus. Axonal projections from the contralateral vlNTS were also observed.

Morphology of expiratory neurons of the Bötzinger complex: an HRP study in the cat

In anesthetized and artificially ventilated cats, the physiological and morphological properties of expiratory neurons or their axons of the Bötzinger complex (BOT) were studied using intracellular recording and intracellular HRP labeling techniques. Thirteen expiratory neurons (nine cell somata and four axons) were successfully stained. Four of them were motoneurons, having relatively large cell somata in the retrofacial nucleus (RFN) and axons without any collaterals inside the brainstem. All the motoneurons showed a plateau shape of depolarization potentials during the expiratory phase. Any of the other nine expiratory neurons exhibited augmenting type firing or membrane potential changes during the expiratory phase. In five out of nine augmenting neurons, cell somata were stained and located ventral to the RFN. In four, only axons were stained. The majority of the augmenting neurons had two major axonal branches: one traveling toward the contralateral side and the other descending ipsilaterally in the brainstem. The most striking feature of the axonal trajectory was that all of the stained augmenting expiratory neurons, including the axons, had collateral branches with synaptic boutons in the BOT area, thus indicating that BOT expiratory neurons interact with some respiratory neurons in the BOT area and its vicinity.

Projections to areas of the nucleus tractus solitarii related to circulatory and respiratory responses in cats

Using chloralose-anesthetized cats, afferent projections to the nucleus tractus solitarii (NTS) were studied in relation to circulatory and respiratory responses. Horseradish peroxidase (HRP) was injected into 3 distinct regions of the NTS: the rostral regions from which electrical stimulation elicited pressor and apneustic responses: the intermediate regions from which stimulation elicited depressor and apneic responses; the commissure regions from which stimulation elicited depressor and hypopneic responses. HRP-labeled cells were sought throughout the medulla oblongata upward including the telencephalon. The results indicate that: many neurons of the frontal cortex (sigmoid gyrus, anterior ectosylvian gyrus, anterior sylvian gyrus, and anterior suprasylvian gyrus) project bilaterally to the 3 regions, predominantly to the rostral regions; a few neurons of the bed nucleus of the stria terminalis project almost ipsilaterally to the 3 regions; a few neurons of the nucleus amygdalae centralis project almost ipsilaterally to the 3 regions; many neurons of the paraventricular nucleus project bilaterally to the 3 regions, predominantly to the ipsilateral commissure regions; a moderate number of neurons of the fastigial nucleus project contralaterally to the rostral regions. These findings suggest that there are some specific projections to each region of the NTS from various supramedullary nuclei, which may be involved in modulation of the cardiovascular and respiratory systems.

Common input of the cranial motor nuclei involved in phonation in squirrel monkey

Our aim was to locate brain regions projecting to all cranial motor nuclei involved in phonation simultaneously, that is, the ambiguus, trigeminal motor, facial, and hypoglossal nuclei. For this purpose, four squirrel monkeys (Saimiri sciureus) were injected with horseradish peroxidase, each of the four nuclei in a different animal. Those regions retrogradely labeled in all four cases then were injected in another 29 animals with [3H]leucine for anterograde tracing. We found that the only region connected directly with all phonatory motor nuclei is a restricted portion of the pontine and medullary reticular formation, including the nucl. subceruleus ventralis, nucl. parvocellularis and nucl. centralis myelencephali. It is assumed that these nuclei are involved in the integration of vocal fold adduction, articulation, and respiration during vocal utterances.

The activity of retrofacial expiratory cells during behavioral respiratory responses and active expiration

The activity of retrofacial expiratory cells was recorded from cats trained to inhibit inspiration in response to a tone. Because retrofacial expiratory cells inhibit inspiratory cells, we thought they might mediate this response. We found, however, that these cells were inactive during the response and thus could not be the mediators thereof. Moreover, retrofacial expiratory cells were inactive also during sneezing and thus were not acting as expiratory upper motoneurons during these active expirations. We propose that they act to promote and synchronize inspiratory activity.

The effects of brainstem lesions on vocalization in the squirrel monkey

The present study is an attempt to find out the brain areas involved in the motor coordination of species-specific vocalization. For this purpose, high-frequency coagulations were placed in a systematic manner throughout the brainstem and posterior diencephalon in altogether 43 squirrel monkeys (Saimiri sciureus). The effect of these lesions on different call types elicited by electrical brain stimulation was studied spectrographically. It was found that bilateral destruction of the ventrolateral, ventroposterior and intralaminar thalamus, periventricular and rostral periaqueductal gray, ventral tegmental area of Tsai, nucl. interpeduncularis, nucl. ruber, anterodorsolateral midbrain tegmentum, superior and inferior colliculi, pontine gray, cerebral peduncles, medial pontine reticular formation, raphe and vestibular nuclei did not affect the acoustic structure of the calls tested. On the other hand, lesions in the ventrolateral midbrain involving the substantia nigra and overlying reticular formation, in the midbrain tegmentum just below the inferior colliculus, in the lateral pons and almost the whole medulla (minimal lesion size: 2.5 mm3) changed vocalization significantly. It is suggested that the latter areas are more or less directly involved in the motor coordination of vocalization, while the first are not.

Ultrastructural studies of the nucleus ambiguus in cat and monkey following injection of HRP into the vagus nerve

The fine structure of retrogradely labelled neurons in the nucleus ambiguus (NA) has been examined in cat and monkey (Macaca fascicularis) following injections of horseradish peroxidase (HRP) into the vagus nerve. Many retrogradely labelled neurons were observed in the NA although unlabelled neurons were also present within the boundaries of the NA as identified by the distribution of retrogradely labelled cells. In both species a wide range of sizes of labelled neurons (20-60 microns in long axis) was observed from rostral to caudal levels of the NA. Large labelled neurons were generally oval or spindle-shaped while smaller neurons were oval in cross-section. Unlabelled neurons observed among labelled NA neurons tended to be smaller on average than the labelled neurons and ranged in size from 15 to 30 microns in long axis. The unlabelled neurons typically had nuclei which were more invaginated than those of the labelled neurons. Quantitative analyses of the synaptic organization in the NA revealed high proportions of terminals containing round vesicles and making asymmetrical or symmetrical contact with the somata in both monkey and cat. Terminals containing pleomorphic vesicles and making symmetrical contact with somata were slightly less numerous. Retrogradely labelled neurons exhibited a positive correlation between the size of neuron and density of synapses on the surface. There tended to be a greater synaptic density on monkey NA neurons than on cat NA neurons of comparable size.

The laryngeal sensory pathway and its role in phonation. A brain lesioning study in the squirrel monkey

In 10 squirrel monkeys (Saimiri sciureus) uni- or bilateral lesions were placed in the nucl. solitarius, parabrachial nuclei, nucl. ventralis posterior medialis thalami or face area of primary sensory cortex. The effects of these lesions on vocalization were compared with those after transection of the internal branch of the superior laryngeal nerve. It was found that neither the cortical nor thalamic or parabrachial lesions changed the acoustic structure of vocalization. In contrast, destruction of the nucl. solitarius, like transection of the internal branch of the superior laryngeal nerve, affected vocalization severely. It is concluded that the production of species-specific vocalization depends upon a di- or, possibly, tri-synaptic laryngeal reflex control from tactile and proprioceptive laryngeal mechanoreceptors via nucl. solitarius and, possibly, lateral medullary reticular formation to nucl. ambiguus.

Medullary respiratory-related neurons with axonal connections to rostral pons and their function in termination of inspiration

In urethane-anaesthetized, paralyzed and artificially ventilated rabbits, medullary respiration-related neurons (RRU) were classified according to the phase relation of their burst discharge to phrenic nerve activity. Phase-bound inspiratory (I) or expiratory (E) neurons were discriminated from phase-spanning expiratory-inspiratory (EI) or inspiratory-expiratory (IE) units. Mechanisms of termination of inspiration by electrical stimulation of rostral pontine nuclei (Nc. parabrachialis medialis; Lc. coeruleus) were examined firstly to demonstrate whether RRU receive descending excitatory and inhibitory afferents as well as ascending efferents and secondly to analyse the time course of the neuronal pathways involved. Of 120 RRU, 38 neurons were demonstrated to receive pontine afferents. About 33% of all E neurons became orthodromically excited during rostral pons stimulation whereas 18.2% of all I cells became orthodromically inhibited. Some RRU were shown to project up to the rostral pons. 50% of these were of the phase-spanning IE type. The onset of inspiratory inhibition induced by rostral pons stimulation occurred 3.4 ms after the onset of single electrical pulse stimulation. Based on these results a neuronal model for a pontine mechanism terminating inspiration is proposed.

Immunoreactive pro-enkephalin and prodynorphin products are differentially distributed within the nucleus of the solitary tract of the rat

In this study we examined the distribution of two different endogenous opioid peptides in the nucleus of the solitary tract of the rat medulla. As a marker for immunoreactive enkephalin, we used an antiserum directed against one of the proenkephalin products, methionine enkephalin-arg-gly-leu (m-Enk). To identify immunoreactive dynorphin we used an antiserum directed against the prodynorphin product, dynorphin B (Dyn B). The PAP method was used on both colchicine and normal animals. Caudal to the obex, within the commissural nucleus, there is extensive overlap of both immunoreactive m-Enk and Dyn B terminals and cells. While the cells are morphologically similar, the immunoreactive dynorphin cells are somewhat larger. Rostral to the obex, there is a marked difference in the distribution of the two compounds. Immunoreactive m-Enk terminals are concentrated medial to the solitary tract; there is minimal staining laterally. In contrast, immunoreactive Dyn B terminals are concentrated lateral to the solitary tract. The rostral cellular distribution of the two opioid peptides follows a similar pattern. The morphology of the medially located m-Enk and laterally located Dyn B cells is also readily distinguished. The former are small, round cells with minimal dendritic labelling; the latter are larger, pyramidal neurons with prominent apical and basal dendrites. Since the medial and lateral nuclei of the solitary tract have been associated with cardiovascular and respiratory control, respectively, these data suggest that different endorphin families have different functional actions within the nucleus of the solitary tract.

Distribution of six neuropeptides in the nucleus tractus solitarii of the rat: an immunohistochemical analysis

Distribution of substance P-, [Leu]enkephalin-, cholecystokinin-8-, neurotensin-, avian pancreatic polypeptide- and gamma-melanocyte stimulating hormone-like immunoreactive structures were investigated in the nucleus tractus solitarii of the rat by means of the indirect immunofluorescence method. The density of the immunoreactive structures varied markedly according to neuropeptides or subnuclei, with the medial and commissural nuclei containing the highest density. This suggests that the peptides examined play a role in cardiovascular function. However, as seen in the substance P- and [Leu]enkephalin-like immunoreactive structures, these peptides were widely distributed in the nucleus tractus solitarii in addition to the commissural and medial nuclei; a high density of immunoreactive fibers in the ventral, dorsolateral and intermediate subnuclei. In addition to the immunoreactive fiber plexus, a group of immunoreactive cells was also identified in the subnuclei mentioned above. These findings strongly suggest that substance P- and [Leu]enkephalin-like immunoreactive structures are involved not only in cardiovascular function but also in other functions such as respiration, at least in the rat. Finally, the present study demonstrated that the area postrema, particularly its lateral portion, contains various neuropeptide-like structures, both neurons and fibers, substance P-, [Leu]enkephalin-, cholecystokinin-8- and neurotensin-like immunoreactive neurons and fibers, and avian pancreatic polypeptide- and gamma-melanocyte stimulating hormone-like immunoreactive fibers.

Muscarinic activation of rhombencephalic neurones controlling oesophageal peristalsis in the rat

The role of muscarinic cholinergic mechanisms in the brainstem in the control of oesophageal peristalsis was investigated in rats anaesthetized with urethane. Primary deglutitive peristalsis, evoked by electrical stimulation of the brainstem or intravenous administration of the serotonin agonist quipazine, was abolished for periods of 1.5 to 2 h by scopolamine and atropine (0.1-0.2 microM/kg) as well as by methscopolamine (1.25-5 microM/kg). In contrast, the buccopharyngeal stage of evoked swallowing was facilitated. A deglutitive effector area was mapped in the intermediolateral portion of the solitary complex by the use of micropneumophoretic application of S-glutamate (35-350 pM) and the cholinoceptor agonists D,L-muscarine and acetylcholine (50-100 pM). Scopolamine partially antagonized single propulsive contractions of the oesophagus evoked by S-glutamate, but completely inhibited rhythmic propulsive or synchronous oesophageal contractions evoked by muscarinic agonists or acetylcholine. Injection of S-glutamate or acetylcholine into the ambiguus complex produced propulsive or non-propulsive oesophageal responses depending on location. Responses evoked by acetylcholine were potentiated by systemic administration of physostigmine, but were resistant to scopolamine; propulsive responses evoked by S-glutamate were partially inhibited by scopolamine. Injection of the retrogradely-transported fluorescent tracer bisbenzimide into the rostral ambiguus complex resulted in labelling of a discrete cell group located within the deglutitive region of the solitary complex. It is concluded that this region contains premotor elements forming part of the internuncial network organizing oesophageal peristalsis. The source of postulated cholinergic afferents to these neurones remains to be identified.