Lokalisierung absteigender Atmungsbahnen im Rückenmark der Katze mittels antidromer Reizung

Role of respiratory and non-respiratory neurones in the region of the NTS in the elaboration of the sneeze reflex in cat

Extracellular recordings were made in the dorsal respiratory group (DRG) and adjacent reticular formation following single-shock stimulation of the anterior ethmoidal nerve (AEN) and during sneeze evoked by repetitive stimulation of the AEN in nembutal-anaesthetized, curarized and ventilated cats. These neurones were characterised according to (i) their activity during the respiratory cycle (as inspiratory augmenting or decrementing (I Aug or I Dec), expiratory augmenting or decrementing (E Aug or E Dec), silent or tonic), and (ii) their axonal projection (bulbospinal or non-bulbospinal-non-vagal (BS or NBS-NV)). Following single-shock stimulation of the AEN, most of the inspiratory neurones were transiently inhibited, whereas E Aug neurones were activated and E Dec neurones were activated and then inhibited. Silent neurones responded with a multispike or a paucispike pattern. Following repetitive stimulation of the AEN and during the resulting sneeze reflex, I Aug neurones increased their activity in parallel with the phrenic activity, I Dec neurones fired at the onset and at the end of the inspiration, E Dec and some silent neurones fired either during the compressive phase or after the expulsive phase, whereas E Aug and some silent neurones fired during the expulsive phase. We conclude that sneeze involves a reconfiguration of the central respiratory drive which uses, at least partly, the respiratory network to trigger a non-ventilatory defensive motor act.

Projections from the nucleus tractus solitarii to the spinal cord

Projections from the nucleus tractus solitarii (NTS) to the spinal cord were demonstrated in the male Sprague-Dawley rat. In retrograde transport studies, a horseradish peroxidase conjugate or a fluorescent dye, FluoroGold, were injected into midcervical or upper thoracic spinal segments. Most solitariospinal neurons were multipolar or bipolar and located between the obex and spinomedullary junction. Solitariospinal neurons were concentrated in proximity to the ventral border of the solitary tract and extended dorsally into the intermediate division and ventrolaterally into the intermediate reticular zone (IRt) of the lateral tegmental field. This subgroup predominantly projects to midcervical spinal segments. A subset of small neurons was retrogradely labeled from cervical or thoracic spinal segments in the medial commissural nucleus and contiguous with a periventricular group surrounding the central canal. In anterograde transport studies, iontophoretic deposits of Phaseolus vulgaris leucoagglutinin were centered stereotaxically on sites in NTS identified by retrograde transport data. The lectin was incorporated by neurons of the solitary complex and transported bilaterally by axons that emerged from the nucleus and entered the reticular formation. The solitario-reticular (transtegmental) pathway irradiated diagonally across the IRt and extended caudally into the cervical lateral funiculus and spinal gray. A small periventricular-spinal pathway also descended longitudinally to the neuraxis. Solitariospinal neurons project to superficial lamina of the dorsal horn, laminae VII and X and ventral horn. The projections are predominantly contralateral to phrenic and intercostal motor nuclei and ipsilateral to the intermediolateral cell column. The solitariospinal projection represents the shortest route in the central nervous system, other than the local intraspinal reflex, through which first order visceral afferents signal cardiorespiratory and alimentary motor nuclei.

Neuropeptide Y-like immunoreactivity in the brain stem respiratory nuclei of the cat

The distribution of fibres and cell bodies containing neuropeptide Y-like immunoreactivity in respiratory nuclei of the brain stem was studied using an indirect immunoperoxidase technique. In order to visualize immunoreactive perikarya, intraventricular or intratissue injections of colchicine were carried out. The richest cluster of immunoreactive perikarya was localized in the Bötzinger complex, whereas in the nuclei ambiguus, retroambiguus, parabrachialis medialis and Kölliker-Fuse area, a moderate density of cell bodies was observed. The ventrolateral subnucleus of the nucleus tractus solitarii had the lowest number of immunoreactive neurons. Neuropeptide Y-like immunoreactive fibres were abundant in the Kölliker-Fuse area, and scarce in the nuclei ambiguus, parabrachialis medialis and Kölliker-Fuse area. A moderate network of immunoreactive fibres was observed in the nuclei retroambiguus and the ventrolateral subnucleus of the nucleus tractus solitarii. The presence of neuropeptide Y-like immunoreactive areas suggests a role for this peptide in the control of respiratory mechanisms. Alternatively such a cluster of cell bodies and fibre networks might be also related with neighbouring cardiovascular control areas.

Immunocytochemical study of angiotensin-II fibres and cell bodies in the brainstem respiratory areas of the cat

The distribution of fibres and cell bodies containing angiotensin-II in brainstem respiratory nuclei was studied using an indirect immunoperoxidase technique. In order to visualize immunoreactive perikarya, intracerebral injections of colchicine were carried out. The richest cluster of immunoreactive perikarya was localized in the Bötzinger complex and Kölliker-Fuse areas, whereas in the nucleus ambiguus and nucleus retroambiguus a moderate density of cell bodies was observed. The nucleus tractus solitarius (ventrolateral portion) and the nucleus parabrachialis medialis had the lowest number of immunoreactive neurons. Angiotensin-II containing fibres were abundant in the nucleus parabrachialis medialis, Bötzinger complex and Kölliker-Fuse area, and scarce in the nuclei tractus solitarius (ventrolateral part), ambiguus and retroambiguus. Moreover, in the dorsal motor nucleus of the vagus a dense network of immunoreactive fibres and a large number of cell bodies were observed. The presence of angiotensin-II in respiratory areas suggests a role for this octapeptide in controlling respiration.

Electrophysiological determination of the axonal projections of single dorsal respiratory group neurons to the cervical spinal cord of cat

Antidromic microstimulation and orthodromic extracellular spike-triggered averaging were used to determine the axonal positions, divergence and terminations of 16 axons arising from bulbospinal, inspiratory (I) neurons. Activity from these neurons was recorded in the dorsal respiratory groups (DRG) of 12 cats. Systematic tracking was done both transversely and longitudinally in the contralateral fifth and sixth cervical segments of the spinal cord. Axonal position was determined by antidromically activating axons and by recording axonal field potentials. Thirteen axons were located in the lateral funiculus, two in the ventrolateral funiculus and one in the ventral funiculus. Axonal conduction velocity (CV) was calculated from conduction distance and conduction time, the latter defined as the interval of time from the recorded action potential in the medulla to the recorded averaged axonal potential in the spinal cord. Average (+/- S.D.) axonal CV was 52 +/- 15 m/s. Terminal potentials were recorded for 13 of these axons and were coincident with the location of evoked field potentials resulting from antidromic stimulation of phrenic motoneurons. In addition, terminal potentials from single I cells were recorded at multiple sites along the longitudinal axis of the phrenic motor column. These data indicate that axons of spontaneously active, DRG bulbospinal I cells descend predominantly in the lateral columns and diverge and terminate extensively within the phrenic motor column.

Projections and terminations of single respiratory axons in the cervical spinal cord of cat

Position, divergence, branching, and termination patterns of single, respiratory axons were studied in cat cervical spinal cord by injecting horseradish peroxidase (HRP) intra-axonally. We stained 12 axons which were characterized by their firing patterns and by electrical stimulation. Five axons discharged during inspiration (I); the remaining 7 discharged during expiration (E). No injected axon was evoked by stimulating ipsilateral phrenic nerve roots while 7 (4 I, 3 E) of 12 were excited at a short latency from stimulating at a medullary site (on the midline, 1-2 mm rostral to the obex, approximately 3 mm below the dorsal medullary surface) where many bulbospinal respiratory axons decussate. All injected stem axons were located in the ventral and ventrolateral funiculi, traversed in a rostrocaudal direction, and were stained for lengths ranging from 3.6 to 12.4 mm. Mean axonal diameter was 2.9 microns. In 6 axons (4 I, 2 E), 14 collaterals were stained: 1 on each E axon, 2 on one I axon, 3 each on 2 others and 4 on another I axon. Collaterals emerged perpendicularly from the descending stem axon and projected directly to the ventral horn. The average distance between neighboring collaterals was 1.0 mm (n = 7). Collaterals did not arborize until they were near or within the ventral horn. Both en passant and terminaux types of presynaptic boutons were found primarily within the rostrocaudal cylinder that defined the phrenic motor column. In addition, some boutons were located dorsomedial to the phrenic motor column. We conclude that I axons, presumably of medullary origin, have multiple collaterals which terminate primarily in the phrenic motor column. However, the same axon can have terminals in different regions of the ventral horn, which are known to contain dendrites of phrenic motoneurons.

Antidromic mapping of descending axons of respiratory bulbospinal neurons in the nucleus tractus solitarius of the rabbit

Antidromic mapping of the descending axons of the respiratory bulbospinal neurons in the region of the nucleus tractus solitarius (NTS) was performed on rabbits anesthetized with urethane. Among 177 units tested, 29 out of 87 inspiratory (I), 27 out of 84 expiratory (E) and 2 out of 6 phase-spanning units were identified as bulbospinal. A prominent feature of the bulbospinal pathway from the NTS in the rabbit is the abundance of ipsilateral descending axons. The axons rising from one side are situated in the ventrolateral and ventral funiculi of both sides. The axonal conduction velocities are about 25-35 m/s. Both I and E bulbospinal neurons can be divided into R alpha and R beta types according to 'no I inflation' and 'maintained E inflation' tests.

Effects of carotid chemoreceptor excitation on medullary expiratory neurons in cats

A previous report (Lipski et al., 1977, J. Physiol. (London) 269, 797-810) demonstrated an inhibition of the medullary dorsal inspiratory neurons when a phasic chemoreceptor stimulus was applied during expiration. The present study tested the response of expiratory neurons which might mediate this inhibition. Recordings were made in cats anaesthetized with chloralose-urethane from the C5 phrenic rootlet and mainly from the rostral (Bötzinger) and caudal (nucleus retroambigualis, NRA) groups of medullary expiratory neurons. Carotid chemoreceptors were excited by close arterial injections of CO2-equilibrated saline. The stimuli were applied automatically with a preset delay within the respiratory cycle. The stimuli applied in inspiration excited both the phrenic activity and ventral inspiratory neurons within less than 0.5 sec. The stimuli applied in expiration excited 17 out of 25 NRA units, none of which projected to the contralateral dorsal (NTS) respiratory group. Four out of 9 units within be responsible for the expiratory inhibition of NTS inspiratory cells produced by chemoreceptor stimulation, while the caudal expiratory neurons are involved in the mediation of the chemoreceptor-induced effects upon the spinal neurons.

Synaptic action of R beta neurons on phrenic motoneurons studied with spike-triggered averaging

The functional role of dorsal medullary inspiratory neurons with excitatory input from lung stretch receptors (R beta neurons) is a matter of controversy. The present study, performed on chloralose-anesthetized and paralyzed cats, ventilated mainly with a phrenic-controlled servorespirator, deals with the spinal projection of these neurons, a property which suggests their involvement in the efferent part of the medullary respiratory complex. Out of 37 inspiratory neurons which could be excited antidromically following microstimulation within the contralateral C6 phrenic nucleus (latency 2.0 ms +/- 0.4, S.D.), 17 were classified by the 'no-inflation' test as R beta. Intracellular recording of synaptic potentials from phrenic motoneurons using the 'spike-triggered averaging' technique were made. In 10 phrenic motoneurons, the averaging revealed individual EPSPs (peak amplitude 150 +/- 110 microV, rise time 0.5 +/- 0.2 ms) time-locked to action potentials of 5 out of 7 R beta neurons tested. Cross-correlation of the R beta neurons firing with the activity of C5 and C6 phrenic rootlets indicated a divergence of excitatory action within the phrenic nucleus. For comparison, in 3 phrenic motoneurons individual EPSPs were recorded when the activity of 3 R alpha cells was used to trigger the averaging. It is concluded that at least some R beta neurons, similarly to R alpha neurons, project to the contralateral phrenic nucleus and can make monosynaptic excitatory connections with phrenic motoneurons. The finding that individual EPSPs were similar when averaging was triggered by the activity of either R beta or R alpha neurons provides new evidence for our earlier hypothesis that bulbospinal inspiratory neurons of the solitary tract nucleus may be subdivided into two categories only on a quantitative basis.

Brain stem localization of vagal preganglionic neurons

The central distribution of vagal preganglionic neurons has been examined using the retrograde transport of horseradish peroxidase (HRP). In 27 adult cats, the entire vagus nerve was exposed to HRP. In 13 other cats we examined the brain stem following microinjections of HRP (10 microliter) into individual visceral organs - lung, heart and stomach. Comparison of individual cases led to the conclusion that different patterns exist for each visceral organ. The preganglionic (parasympathetic) innervation of the entire vagus nerve arises from the dorsal motor nucleus of the vagus (dmnX), nucleus ambiguus (nA), nucleus retroambigualis (nRA), nucleus dorso-medialis (ndm), spinal nucleus of the accessory (nspA) and from the reticular formation between the dmnX and nA. Axons arising from the nA do not traverse the medulla laterally; rather they are initially directed dorso-medially toward the dmnX where they bend at right angles and accompany axons of neurons in the dmnX. The motor nuclei innervating the lungs, heart and stomach are dmnX, the nA and nRA: the dmnX contributes fibers to the heart, lungs and stomach from a region of 10 mm of medulla rostrocaudally; the nA contributes efferents to the 3 viscera studied from the entire 6 mm contributing vagal efferents; the nRA contributes efferents to the stomach in addition to providing innervation to the larynx and trachea (see 19). The area postrema (ap) receives afferent input from the lungs, heart and stomach, as indicated by extraperikaryal grains of HRP reaction product resulting from transganglionically transported HRP (through the ganglion nodosum). Sensory terminal labeling in the various subnuclei of the nucleus of the tractus solitarius (nTS) was also examined and it was found that no specific region of the medulla is devoted to receiving input from any one visceral organ; rather the rostro-caudal extent of vagal afferent terminals in the medulla spans the entire length of the medulla. Differences between the central representation of different viscera seemed to lie within the organization of the nuclear subgroups of the nTS.

Behavior of expiratory neurons in response to mechanical and chemical loading

The response of medullary expiratory neurons to added mechanical and chemical loads was studied in anesthetized cats. Alterations in burst characteristics and central timing were compared in the intact and bilaterally vagotomized cat. The following results were obtained: (1) Graded expiratory airflow resistances caused progressive increases in burst duration, spikes per burst and firing rate; similar effects were noted for end-inspiratory tracheal occlusions and continuous positive breathing; all facilitation was eliminated by vagotomy. (2) Graded inspiratory airflow resistances delayed the onset of an expiratory burst but did not change the overall burst characteristics. (3) Acute hypercapnia increased ventilation without noticeable changes in expiratory burst characteristics; acute hypoxia produced a reduction in burst duration concomitant with changes in ventilation. It is concluded that (1) expiratory neurons are responsive to vagally mediated volume information and (2) transient hypoxia and hypercapnia sufficient to increase ventilation does not increase the firing rate of expiratory neurons but exerts differential effects with respect to timing. It is suggested that expiratory duration is related to the time integral of expired volume and that the increase in FRC imposed by expiratory loads does not alter the central timing of the next inspiration.

Excitability changes of dorsal inspiratory neurons during lung inflations as studied by measurement of antidromic invasion latencies

(1) Glass microelectrodes were used to record extracellularly the activity of single dorsal (in the region of nucleus tractus solitarius (NTS)) inspiratory neurons in either chloralose- or pentobarbitone-anaesthetized, paralyzed cats. (2) In the lateral and ventral part of NTS, 89 cells were localized which responded antidromically to stimulation applied to the contralateral spinal cord (C3). Seventy were not excited by lung inflation and were classified as Ralpha, while 19 excited by that stimulus were classified as Rbeta. Usually Rbeta neurons fired both during each pump-induced lung inflation and during the central inspiratory excitation (CIE). (3) A technique similar to Merrill's recording small variations in the antidromic latency measured to the SD spike was used to ascertain excitability of Ralpha and Rbeta cells during the CIE time and during lung inflation in expiration. The technique was extended by averaging antidromic latency patterns within many respiratory cycles. (4) In the majority of Ralpha cells the averaging revealed a shortening of the antidromic latency during lung inflation in expiration, which indicated a subthreshold depolarization. Lengthening of the antidromic latency by this stimulus was never observed. These results are in disagreement with the concept of a direct inhibitory input from Rbeta to Ralpha neurons. (5) It is concluded that the dorsal Ralpha and Rbeta neurons differ less in their properties than was previously assumed on the basis of classical extracellular techniques. The inhibitory influence of pulmonary stretch receptor input on inspiratory discharge of Ralpha cells seems to be exerted through an indirect action on the source of the CIE.

Nuclei of the solitary tract: efferent projections to the lower brain stem and spinal cord of the cat

The efferent projections from the solitary complex to the lower brain stem and spinal cord were studied in the cat with the autoradiographic anterograde axonal transport and retrograde horseradish peroxidase (HRP) techniques. A revised cytoarchitectonic description of the caudal two-thirds of the complex is presented in which the complex was subdivided into six nuclei: lateral, ventrolateral, intermediate, medial, parvocellular, and commissural solitary tract nuclei. Following injections of 3H amino acids into electrophysiologically defined regions of the complex in which cardiac or respiratory units were recorded, labeled fibers could be traced to a number of sites in the caudal brain stem including the medial and lateral parabrachial nuclei, Kölliker-Fuse nucleus and the area ventral to this nucleus, lateral periaqueductal gray matter, ambiguus complex, which consists of the retrofacial, ambiguus and retroambiguus nuclei, ventrolateral reticular nucleus (in an area equivalent to the A1 cell group of Dahlström and Fuxe, '64), medial accessory olive, paramedian reticular formation, and lateral cuneate nucleus. Descending solitario-spinal projections have been traced bilaterally, but predominantly to the contralateral side, to the region of the phrenic motor neurons in the C4-C6 ventral horn, to the thoracic ventral horn, and intermediolateral cell column. Confirmatory evidence of some of these projections was obtained from a series of HRP experiments. Mainly small neurons of the parvocellular, medial and commissural solitary tract nuclei project to the region of the parabrachial and Kölliker-Fuse nuclei. The lateral solitary nucleus projects almost exclusively to the ipsilateral medial accessory olive. It was not possible to interpret conclusively the labeling seen in the medium and large neurons of the ventrolateral solitary nucleus after HRP injections made in the region of the ambiguus-retroambiguus complex due to the problem of fibers of passage. Following injections of HRP into the cervical, thoracic, lumbar, or sacral spinal cord, retrograde cell labeling was seen in the solitary complex. Cells in the intermediate and commissural nuclei were labeled after all four types of experiments. In the ventrolateral nucleus, medium sized neurons were predominantly labeled after the cervical spinal cord experiments, while large sized neurons were labeled mainly after the thoracic spinal cord injections. The potential physiological significance of these connections is discussed in terms of central control of cardiovascular and respiratory functions.

The recruitment times and firing patterns of the medullary respiratory neurones of the cat

The brainstem of anaesthetized cats was explored for respiratory neurones with microelectrodes in the regions of the nucleus retroambigualis (ventrolateral region) and the nucleus tractus solitarius (dorsomedial region). These neurones were analysed with respect to their firing patterns and recruitment times, as referenced to the respiratory cycle. All of the respiratory neurones showed a stable and ordered pattern of firing. Four groups of neurones with similar characteristics within each group, but differing from each other, were statistically examined; the inspiratory neurones of the dorsomedial region, the 'late' inspiratory neurones of the ventrolateral region, the 'early' inspiratory neurones of the ventrolateral region and the expiratory neurones of the ventrolateral region.

The carotid chemoreceptor input to the respiratory neurones of the nucleus of tractus solitarus

1. An investigation has been made into the connexions between the carotid body chemoreceptors and the dorsal respiratory neurones of the cat's medulla.2. In confirmation of previous work these neurones were found to be all inspiratory in firing pattern and to fall into two categories, Ralpha (forty-four units) which fire only with the central inspiratory rhythm and Rbeta (thirty-two neurones) that are also excited by lung inflation. Both categories were shown to be excited by stimuli delivered to the carotid bodies during inspiration but, with a single exception, not during expiration.3. When Rbeta neurones were made to fire tonically in expiration by maintained lung inflation, chemoreceptor activation inhibited this discharge in 7/11 cases, the remainder being unaffected.4. Iontophoretically applied DL-homocysteic acid or glutamate made both Ralpha and Rbeta neurones fire tonically in expiration. Chemoreceptor stimulation during expiration inhibited this activity in all neurones tested (nine Ralpha and three Rbeta cells).5. Using the measurement of the antidromic latency to spinal stimulation as an index of membrane potential, evidence was obtained that any subthreshold influence of the chemoreceptors on dorsal respiratory neurones during expiration was inhibitory (9/18 cases).6. It is concluded that chemoreceptors do not even subliminally excite dorsal inspiratory neurones during expiration; such influence as they have then is inhibitory. Possible reasons for this difference in chemoreceptor influence during inspiration and expiration are discussed. It is suggested that chemoreceptor excitation reaches them only as part of an enhanced central inspiratory drive from an as yet unknown source.

Medullary relay neurons in the carotid-body chemoreceptor pathway of cats

Central terminations of the carotid body chemoreceptor afferents were localized by recording field potentials and unit activity evoked by electrical stimulation of the carotid sinus nerve, and unit activity during chemical stimulation of the chemoreceptors. Areas where evoked responses with short latency could be recorded and which contained neurons that responded to carotid body excitation were located in two regions of the medulla, about the level of the obex: a dorsal region which included the nucleus tractus solitarius and the reticular formation just below this nucleus; and a ventrolateral region which included the nucleus ambiguus and the ventrolateral reticular formation around that nucleus. The evoked field responses in the two regions were similar. In these two regions, the only neurons which increased their firing both to NaCN and a decreased PIO2 had a respiratory, bursting activity which was phase locked with phrenic nerve firing. The authors' findings suggest that there is a direct synaptic input from carotid body chemoreceptor afferents onto medullary respiratory neurons.

Effects of various lesions on crossed and uncrossed descending inspiratory pathways in the cervical spinal cord of the cat

✓ Various cervical spinal cord lesions interrupting portions of the descending respiratory pathways were made in 12 cats. Results suggest: 1) that the descending inspiratory pathways lie in the ventrolateral portion of the high cervical spinal cord; 2) that a decussation of these pathways exists between the low medullary and high cervical level; 3) that fibers descend via both crossed and uncrossed pathways along the length of the cervical cord to innervate phrenic nuclei bilaterally; 4) that activity in the crossed pathway running along the length of the cervical cord is related to the level of PaCO2.

Extra-segmental reflexes derived from intercostal afferents: phrenic and laryngeal responses

1. Phrenic and recurrent laryngeal efferent responses were evoked by brief tetani or single shocks to the cut external intercostal nerves of anaesthetized cats. The reflexes derived from middle thoracic segments (T5 and 6) were compared with those emanating from caudal thoracic segments (T9 and 10).2. During inspiration, middle intercostal nerve stimulation transiently inhibited the spontaneous discharge in both efferent neurograms, whereas stimulation of caudal intercostal nerves facilitated phrenic discharge and usually inhibited recurrent laryngeal activity.3. During expiration, stimulation at either thoracic level enhanced recurrent laryngeal discharge while provoking little or no phrenic response.4. Superficial lesions of the lateral cervical cord, ipsilateral to the stimulus sites, above or below the phrenic outflow, eliminated all reflex responses except the phrenic response to caudal thoracic stimuli. Similarly, in the spinal animal, middle intercostal afferents could not be shown to decrease phrenic excitability. Caudal intercostal afferents cause phrenic excitation by a spinal reflex.5. Group I afferents of the mid-thoracic segments and group II afferents of the caudal thoracic segments initiate these extra-segmental reflexes.6. The recurrent laryngeal responses manifest, for the most part, changes in the discharge of fibres innervating the posterior cricoarytenoid muscle. The responses fit the overall pattern of response to middle intercostal nerve stimulation, namely, inhibition of inspiratory muscles and excitation of expiratory muscles. Intercostal afferent stimulation also activated the laryngeal adductor muscles.7. The results support the view that intercostal mechanoreceptors initiate an array of extra-segmental respiratory reflexes, including spinal and supraspinal arcs. The simplest way to account for the various responses to stimulation of middle intercostal afferents is to postulate a reflex involving supraspinal respiratory neurones.8. The observed reflexogenic differences correlate with anatomical differences between the middle and caudal ribs. Possible functional implications of this relationship are discussed.