Medulla Of Cat Research Articles

Distribution of two types of monoamine oxidase-containing neurons in the cat medulla oblongata demonstrated by an improved histochemical method

The topographic distribution of cells containing monoamine oxidase, the enzyme which deaminates amines, was studied in the cat medulla oblongata. By means of enzyme histochemistry using a new coupled peroxidation method, monoamine oxidase activity was demonstrated in the somata, dendrites and fibers. Type A monoamine oxidase, inhibited by clorgyline but not deprenyl, were localized in the cells distributed in the ventrolateral and dorsomedial medulla where catecholaminergic neurons are present. Type B monoamine oxidase-positive cell bodies were identified in the regions containing serotonergic neurons. Furthermore, we found an intense activity of type A monoamine oxidase in many cells of the dorsal motor nucleus of the vagus of the rostrocaudal extent, and more rostrally in the nucleus parvocellularis where few or no aminergic neruons have been described.

Distribution of PNMT-immunoreactive neurons in the cat medulla oblongata

The distribution and morphology of presumptive adrenaline neurons in the cat medulla oblongata were studied in conjunction with the indirect immunoperoxidase technique utilizing antibody raised against bovine adrenal phenylethanolamine-N-methyltransferase (PNMT), an enzyme which converts noradrenaline to adrenaline. Small PNMT-immunoreactive (IR) perikarya are located in the dorsomedial part of the medulla (C2 group) extending from P17 to P12, and larger ones in the ventrolateral part (Cl group) from P11 to P9 of the caudorostral extent. In the rostral medulla (P11-10), larger cells extended more dorsally in the lateral tegmental field, where only a few catecholamine cells are localized. No midline PNMT-IR cells were identified corresponding to C3 cell group in the rat. Distinct longitudinal PNMT-IR axon bundles can be traced through the dorsal part of the lateral tegmental field. Comments are made on the relative localizations of the PNMT-IR and DBH-IR cells, as well as on species differences in comparison with the results reported in the rat.

Location of neurones with cardiovascular and respiratory function, at the ventral surface of the cat's medulla

A study has been made of the ventral surface of the medulla, to identify neurones with cardiovascular and respiratory functions. Experiments were performed on chloralose-anaesthetized. artifically ventilated cats. Ventral medullary neurones were stimulated by microinjections of excitant amino acid (which selectively activates cell bodies), and responses measured in blood pressure, heart rate. renal sympathetic and phrenic nerve activity. A small region of ventral medulla was found, corresponding to the “glycinc-sensitive area”, from which large increases in blood pressure and renal nerve activity were evoked by amino acid injections. More caudally. another cell group was localized lateral to the hypoglossal nerve roots, and these neurones depressed blood pressure and renal nerve activity. Two distinct regions were found to increase phrenic nerve activity: rostral to the pressor neurones. encroaching on the trapezoid body (roughly corresponding to area “M”). and a caudal group, close to the depressor neurones (i.e. lateral to the hypoglossal roots). No respiratory response could he evoked from medial to the hypoglossal roots (area “I.”) and stimulation of neurones in area “S” generally depressed phrenic activity. Neurones with cardiovascular and respiratory actions could the distinguished anatomically. Their locations have been mapped and compared with previous studies.

Neurohistological and histochemical characteristics of Loeschcke's zone of the cat medulla

Neuronal organization and transmitter profile of the chemosensitive area on the ventral medulla surface (zone L) were studied in the cat using neurohistological and histochemical techniques. Neurons of different shapes and sizes distributed through this area are concentrated mainly at the level of the medial hypoglossal nerve root, with their numbers gradually decreasing rostrally and caudally from this nerve. Only an insignificant proportion of zone L neurons are cholinergic and monoaminergic, while the remainder probably employ other biologically active substances as transmitters. Cholinergic and noncholinergic cholinoceptive neurons were found in zone L, as well as neurons sensitive to catecholamines and serotonin. It is postulated that the catecholaminergic, serotoninergic, and cholinergic fibers observed in zone L may be of local origin or may originate from other structures.

Neural respiratory and circulatory interaction during chemoreceptor stimulation and cooling of ventral medulla in cats.

Neural respiratory and circulatory interaction during chemoreceptor stimulation and cooling of ventral medulla in cats.

Neural respiratory and circulatory interaction during chemoreceptor stimulation and cooling of ventral medulla in cats.

The effects on respiratory and sympathetic neural activity, measured as integrated phrenic and cervical nerve activities respectively, during changing input from the central chemoreceptors was studied in anaesthetized, paralysed cats whose carotid sinus nerves and vagus nerves had been cut. Central respiratory drive was altered either by graded cold block of the intermediate areas, located bilaterally near the ventral surface of the medulla oblongata, or by step increases in end-tidal PCO2. Cervical nerve activity showed both a tonic (or mean) level of activity and a prominent cyclic discharge that was in phase with phrenic nerve activity. Graded focal cooling of the intermediate areas to 20 degrees C when end-tidal PCO2 was kept constant caused progressive decreases in phrenic activity, the amplitude of the inspiratory related discharge and mean arterial pressure, but only a small decrease in mean cervical nerve activity. Cooling the intermediate areas in the absence of the inspiratory related discharge (i.e. when phrenic activity was below the apnoeic threshold) led to a much smaller decrease in arterial pressure. Step increases of end-tidal PCO2 caused progressive increases of both cervical and phrenic nerve activities. The increase in cervical activity was due primarily, if not wholly, to a progressive increase in the amplitude of the inspiratory related discharge. These findings show that the predominant effect on sympathetic activity during stimulation of the central chemoreceptor and graded cold block of the intermediate areas is a change in the amplitude of the inspiratory related discharge and suggest that the change in arterial pressure that accompanies central chemoreceptor stimulation and graded cold block of the intermediate areas is mediated by the inspiratory related discharge rather than by an increase in the mean level of sympathetic activity. When phrenic activity was lowered to below apnoeic threshold by cooling the intermediate areas, step increases in end-tidal PCO2 caused inhibition rather than stimulation of cervical nerve activity. This finding indicates that sympathetic neurones are not activated by central chemoreceptor input directly, but rather indirectly via intracranial connexions with neuronal networks involved in regulation of respiration.

Differentiation of two respiratory areas in the cat medulla using kainic acid

Kainic acid (KA) was used to destroy neuronal perikarya in different areas of the brainstem. Single KA microinjections were performed in 30 anaesthetized, vagotomized, artificially ventilated cats. Consequences were studied on the phrenic nerve activity (PNA) and blood pressure. We observed changes of the PNA unrelated to blood pressure alteration. Destruction of the dorsal respiratory area (DRA) including the nucleus tractus solitarius at the obex level produced a 40% decrease of the PNA frequency. Destruction restricted to the lateral part of the ventral respiratory area (VRA1) including the ambiguus nucleus induced a 60% decrease of the integrated PNA amplitude followed by a 40% increase of PNA frequency. These latter effects were also observed after destruction inside the infra solitary reticular formation (ISRF). No effect was observed after destruction in other brain structures. We concluded that ISRF and VRA1 form a single ventral bulbar respiratory area. This area controls respiration in a way different from that of the dorsal respiratory area (DRA).

A cross-correlation study of interactions among respiratory neurons of dorsal, ventral and retrofacial groups in cat medulla

In anesthetized or decerebrated cats, extracellular activities of pairs of respiratory neurons located in the regions of the dorsal (DRN), ventral (VRN) and retrofacial (RFN) medullary respiratory nuclei were recorded using two separate microelectrodes. Neurons were classified as bulbospinal or laryngeal if stimulation of the spinal cord or vagus nerve elicited antidromic action potentials, or as propriobulbar if they were not antidromically activated. Of 163 pairs of single unit activities, either inspiratory (143 pairs) or expiratory (20 pairs), cross-correlation analyses indicated that 23% had short latency peaks, either broad (12%) or sharp (1%) in their cross-correlograms, 3% had short latency troughs and 74% had flat cross-correlograms. When the two neurons were located in the DRN (68 pairs) the probability of obtaining a positive cross-correlogram was high for inspiratory bulbospinal neurons, indicating shared inputs and excitatory relationships. When one neuron of the pair was located in the RFN and the other in either the DRN or VRN (95 pairs), cross-correlation analysis revealed shared inputs, excitatory and inhibitory relationships. Among expiratory neurons interactions were only inhibitory with a more frequent incidence ( 320) than between inspiratory neurons ( 2143. Our results indicate that: (i) short time scale synchrony due to shared inputs (broad peaks) are largely distributed in the respiratory neuronal network and operate over long distance (i.e. RFN, caudal medulla); (ii) excitatory coupling may exist between remote neurons but is more frequent between inspiratory bulbospinal neurons located in the DRN.

Types and locations of respiratory-related neurons in lateral tegmental field of cat medulla oblongata

Extracellular microelectrode recordings were made from a total of 868 neurons in the medullas of cats in regions known to contain high densities of respiratory-related neurons (solitary tract complex, nucleus ambiguus/retroambigualis, lateral tegmental field). Both the discharge patterns and the locations of units were noted and correlated with a recently described substructure of the tegmental field of the cat medulla in which neuronal cell bodies are found associated with sheets of blood vessels supplying the brainstem 28,29. The majority of cells were phasically firing (59%) with activity confined to either the inspiratory or the expiratory phase, 21% were tonically firing cells with no discernible respiratory modulation and 20% were silent neurons, responsive to electrical stimulation of the vagus nerves or the dorsolateral pons in the vicinity of nucleus parabrachialis, but not to various respiratory stimuli. Within the solitary tract complex inspiratory discharge patterns were predominant (94%), while in nucleus ambiguus/retroambigualis 26% of the neurons had expiratory patterns with the rest being inspiratory (68%) or tonic (6%). Within the lateral tegmental field, the percentages of inspiratory, expiratory and tonic patterns were 51,9 and 40%. Thus, inspiratory type patterns were found throughout the medulla, but expiratory patterns were most common in the ambiguus/retroambigualis nuclei. Found within all 3 major regions, but primarily within the lateral tegmental field of the rostral medulla were neurons that discharged with a brief burst at the inspiratory to expiratory phase transition. These cells had properties consistent with the off-switch mechanism: extreme late-inspiratory onset of discharge with the onset time being delayed by lung inflation, peak discharge at or slightly after the peak activity of the diaphragmatic EMG and a discharge rate which was insensitive to lung inflation. Within the lateral tegmental field, where longitudinal sheets of blood vessels running radially with respect to the IVth ventricle have been described 29, it was found that 85% of the tonically active units and 93% of the respiratory modulated cells were located less than 200 μm from the planes of these sheets. In addition, 87% of the neurons that could be antidromically or synaptically activated from the dorsolateral rostral pons were similarly located.

Cross-correlation of ventrolateral inspiratory neurons in the cat

Abstract The ventrolateral region in the medulla of cats was explored with pairs of microelectrodes with tip separations from 100 to 300 μm such that extracellular potentials of pairs of near-neighboring neurons were recorded simultaneously. At least one neuron of each pair was antidromically activated from the spinal cord. Cross-correlation histograms were computed and showed the existence of short-term synchronization of firing for 8 of 20 neuron pairs (40%). The primary feature of the cross-correlation histograms was, typically, asymmetrical peaks on each side of time zero. The peaks were dissimilar, one low and broad, the other high and narrow, and occurred within a millisecond of time zero. Poststimulus histograms computed for one of the pair, during antidromic activation of the other, indicated a possible interaction between the neurons in one case but not in another. The results are suggestive of neuronal interactions among the late-firing inspiratory neurons of the nucleus retroambigualis but are not conclusive.

Cross-correlation of ventrolateral inspiratory neurons in the cat

The ventrolateral region in the medulla of cats was explored with pairs of microelectrodes with tip separations from 100 to 300 μm such that extracellular potentials of pairs of near-neighboring neurons were recorded simultaneously. At least one neuron of each pair was antidromically activated from the spinal cord. Cross-correlation histograms were computed and showed the existence of short-term synchronization of firing for 8 of 20 neuron pairs (40%). The primary feature of the cross-correlation histograms was, typically, asymmetrical peaks on each side of time zero. The peaks were dissimilar, one low and broad, the other high and narrow, and occurred within a millisecond of time zero. Poststimulus histograms computed for one of the pair, during antidromic activation of the other, indicated a possible interaction between the neurons in one case but not in another. The results are suggestive of neuronal interactions among the late-firing inspiratory neurons of the nucleus retroambigualis but are not conclusive.

High levels of neuropeptide Y in peripheral noradrenergic neurons in various mammals including man

Using a highly specific radioimmunoassay for neuropeptide Y (NPY), levels in the peripheral nervous g −1 were found in sympathetic ganglia and in tissues which received a dense sympathetic innervation, such as vas deferens, heart atrium, blood vessels and spleen. By immunocytochemistry, NPY-immunoreactive (-IR) principal ganglion cells in sympathetic ganglia and the pelvic plexus were also found to contain dopamine-β-hydroxylase (DBH) and tyrosine hydroxylase (TH), strongly suggesting that the NPY-IR cells are noradrenergic. NPY- and DBH-IR nerves had a roughly parallel occurrence in the heart, spleen, kidney, respiratory and urogenitary tracts, around blood vessels and within visceral smooth muscle. Considerably more NPY-IR than DBH-IR nerve fibres were seen in the gastrointestinal tract from the oesophagus to the anal sphincter. In addition, NPY-IR local ganglion cells were observed in the submucous and myentric plexuses. NPY-like immunoreactivity was also observed in the adrenal medulla of guinea-pig and cat. NPY thus seems to be a major peptide in the sympathetic nervous system, supporting its proposed role in sympathetic neurotransmission.

Interactions among inspiratory neurons in dorsal and ventral respiratory groups in cat medulla.

ArticlesInteractions among inspiratory neurons in dorsal and ventral respiratory groups in cat medullaJ. L. Feldman, and D. F. SpeckJ. L. Feldman, and D. F. SpeckPublished Online:01 Feb 1983https://doi.org/10.1152/jn.1983.49.2.472MoreSectionsPDF (3 MB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInWeChat Previous Back to Top Next Download PDF FiguresReferencesRelatedInformation Cited ByFree-running circadian breathing rhythms are eliminated by suprachiasmatic nucleus lesionBenton S. Purnell and Gordon F. Buchanan29 June 2020 | Journal of Applied Physiology, Vol. 129, No. 1Identification of the pre-Bötzinger complex inspiratory center in calibrated “sandwich” slices from newborn mice with fluorescent Dbx1 interneurons19 August 2014 | Physiological Reports, Vol. 2, No. 8Functional Connectivity in the Pontomedullary Respiratory NetworkLauren S. Segers, Sarah C. Nuding, Thomas E. Dick, Roger Shannon, David M. Baekey, Irene C. Solomon, Kendall F. Morris, and Bruce G. Lindsey1 October 2008 | Journal of Neurophysiology, Vol. 100, No. 4Reconfiguration of the Pontomedullary Respiratory Network: A Computational Modeling Study With Coordinated In Vivo ExperimentsI. A. Rybak, R. O'Connor, A. Ross, N. A. Shevtsova, S. C. Nuding, L. S. Segers, R. Shannon, T. E. Dick, W. L. Dunin-Barkowski, J. M. Orem, I. C. Solomon, K. F. Morris, and B. G. Lindsey1 October 2008 | Journal of Neurophysiology, Vol. 100, No. 4Medullary lateral tegmental field: control of respiratory rate and vagal lung inflation afferent influences on sympathetic nerve dischargeShaun W. Phillips, Gerard L. Gebber, and Susan M. Barman1 May 2005 | American Journal of Physiology-Regulatory, Integrative and Comparative Physiology, Vol. 288, No. 5Glutamatergic pathways from the Kölliker–Fuse nucleus to the phrenic nucleus in the ratBrain Research, Vol. 995, No. 1Physiological Properties of Late Inspiratory Neurons and Their Possible Involvement in Inspiratory Off-Switching in CatsAkira Haji, Mari Okazaki, Hiromi Yamazaki, and Ryuji Takeda1 February 2002 | Journal of Neurophysiology, Vol. 87, No. 2Analysis of Firing Correlations Between Sympathetic Premotor Neuron Pairs in Anesthetized CatsR. M. McAllen, D. Trevaks, and A. M. Allen1 April 2001 | Journal of Neurophysiology, Vol. 85, No. 4Functional connectivity among ventrolateral medullary respiratory neurones and responses during fictive cough in the cat1 May 2000 | The Journal of Physiology, Vol. 525, No. 1Differential Roles of Ionotropic Glutamate Receptors in Canine Medullary Inspiratory Neurons of the Ventral Respiratory GroupM. Krolo, E. A. Stuth, M. Tonkovic-Capin, Z. Dogas, F. A. Hopp, D. R. McCrimmon, and E. J. Zuperku1 July 1999 | Journal of Neurophysiology, Vol. 82, No. 1Possible mutual excitatory couplings between inspiratory neurons in caudal ventrolateral medulla of brainstem-spinal cord preparation isolated from newborn ratNeuroscience Letters, Vol. 150, No. 2Bulbospinal respiratory neurons are a source of double synapses onto phrenic motoneurons following cervical spinal cord hemisection in adult ratsBrain Research, Vol. 600, No. 1Decussation of bulbospinal respiratory axons at the level of the phrenic nuclei in adult rats: A possible substrate for the crossed phrenic phenomenonExperimental Neurology, Vol. 111, No. 1Spinal respiratory motoneuronsProgress in Neurobiology, Vol. 37, No. 2Synaptic connections between medullary respiratory neurons and considerations on the genesis of respiratory rhythmProgress in Neurobiology, Vol. 35, No. 6Effects of contralateral superior laryngeal nerve stimulation on dorsal medullary inspiratory neuronsBrain Research, Vol. 505, No. 1Dorsal medullary inspiratory neurons: effects of superior laryngeal afferent stimulationBrain Research, Vol. 491, No. 2The activity of late inspiratory cells during the behavioral inhibition of inspirationBrain Research, Vol. 458, No. 2Discharge properties of dorsal medullary inspiratory neurons in newborn pigsBrain Research, Vol. 408, No. 1-2Electrophysiological evidence for the modular organization of the reticular formation: sympathetic controlling circuitsBrain Research, Vol. 410, No. 1Discharge patterns of bulbar respiratory neurons in response to the morphinomimetic agent, fentanyl, in chloralosed dogsEuropean Journal of Pharmacology, Vol. 122, No. 3The neuronal determinants of respiratory rhythmProgress in Neurobiology, Vol. 27, No. 2Neural elements subserving pulmonary stretch receptor-mediated facilitation of phrenic motoneuronsBrain Research, Vol. 346, No. 2Responses or recurrent laryngeal motoneurons to changes of pulmonary afferent inputsRespiration Physiology, Vol. 62, No. 2Short-latency interactions among dorsomedial medullary inspiratory neurons in the catExperimental Neurology, Vol. 88, No. 3A cross-correlation study of interactions among respiratory neurons of dorsal, ventral and retrofacial groups in cat medullaBrain Research, Vol. 302, No. 1Two descending medullary inspiratory pathways to phrenic motoneuronesNeuroscience Letters, Vol. 43, No. 2-3 More from this issue > Volume 49Issue 2February 1983Pages 472-490 Copyright & PermissionsCopyright © 1983 the American Physiological Societyhttps://doi.org/10.1152/jn.1983.49.2.472PubMed6300345History Published online 1 February 1983 Published in print 1 February 1983 Metrics

Immunoreactive vasoactive intestinal polypeptide is concentrated in the sacral spinal cord: a possible marker for pelvic visceral afferent fibers.

Previous descriptions of immunoreactive vasoactive intestinal polypeptide (VIP) in small-diameter dorsal root ganglion cells in the superficial dorsal horn implicated this 28 amino acid peptide in nociceptive transmission. In this study, we examined the distribution of immunoreactive VIP in the spinal cord and caudal medulla of cats and rats. The PAP method was used on paraffin and frozen sections of 4% paraformaldehyde-fixed tissue, using antibodies to VIP that were raised in rabbits. The distribution of immunoreactive VIP, while similar to that of substance P (SP), a putative primary afferent peptide neurotransmitter, is more restricted. VIP staining is found in sacral dorsal roots and densely in the Lissauer tract. Dorsal horn staining is concentrated in lamina I. In contrast to SP, lamina II is almost devoid of staining. Labeled VIP axons course along the lateral curvature of the dorsal horn and arborize across lamina V and around the central canal. A collateral branch of these fibers distributes to the sacral autonomic nucleus. A few fibers could be traced from the root entry zone to the contralateral central gray. VIP axons also terminate between ependymal cells of the central canal. Unlike SP, immunoreactive VIP was restricted, almost exclusively, to the sacral cord. The few fibers in the lumbar enlargement and in the coccygeal cord apparently derive from ascending and descending sacral primary afferents. In fact, the VIP pattern is almost identical to that reported for afferents from the pelvic viscera, including a discontinuous rostrocaudal distribution. Since the staining pattern is also very similar to that of A-delta high-threshold mechanoreceptors, the possibility is discussed that whereas VIP is not a general "somatic" primary afferent transmitter, it may transmit nociceptive input from the pelvic viscera.

Phrenic motoneurone activity in split-brainstem cats and monkeys

A mid-line incision of the lower brainstem (from 2 mm caudal to 14 mm rostral to the obex) was performed in 14 cats and (from 2 mm caudal to 7 mm rostal to the obex) in three green monkeys and its effects on the respiratory activity of both phrenic nerves were studied under similar experimental conditions (halothane anaesthesia, artificial ventilation). Splitting the medulla in cats abolished the phrenic nerve activity under eupnoeic conditions, but hypercapnia or (with more rostral cuts) hypercapnia with hypoxia restored synchronous, rhythmic firing in both phrenic nerves. The response to splitting in eupnoeic monkeys was qualitatively different and consisted in a ‘desynchronisation’, i.e. independent firing of both phrenic nerves at different rhythm and patterns. It is concluded that cats and monkeys have basically different functional organisation of the respiratory controller.

Classification of raphe neurons with cardiac-related activity.

The cardiac-related component of sympathetic nerve discharge (SND) results from entrainment of a rhythm of brain stem origin by the baroreceptor reflexes [Gebber, Am. J. Physiol. 239 (Heart Circ. Physiol. 8): H143-H155, 1980]. As a consequence, changes in heart rate are accompanied by shifts in the phase relations between SND and the arterial pulse wave. This observation presented us with the opportunity of distinguishing brain stem neurons whose discharges are locked to SND from other neuronal types that exhibit cardiac-related activity. Raphe neurons in the cat medulla with cardiac-related activity were identified using post-R wave interval analysis. The discharges of one group of these neurons remained locked to inferior cardiac SND during changes in ventricular rate which shifted the phase relations between SND and the arterial pulse wave. Most importantly, the lag between unit spike occurrence and the peak of the cardiac-related component of SND was unchanged during ventricular pacing (as demonstrated with cross-correlation analysis). It is suggested that these neurons were contained in brain stem networks which control SND. The discharges of two additional types of raphe neurons remained locked to the arterial pulse wave during ventricular pacing. Neurons of the first type exhibited an increase in discharge probability in late diastole and early systole. Neurons of the second type exhibited a period of reduced activity time-locked to systole.

The effects of microstimulation and microlesions in the ventral and dorsal respiratory groups in medulla of cat

The responses in respiratory outflow resulting from microstimulation and successive microlesions of the dorsal (DRG) and ventral (VRG) respiratory groups of neurons in the brainstem were studied in anesthetized, paralyzed, artificially ventilated cats. Microstimulation (2 to 120 Hz; 5 to 50 microA; 100 musec pulse duration) at almost every point within the DRG or VRG produced a bilateral short latency inhibition of phrenic nerve activity which had an onset latency of 4 to 9 msec and a duration of 4 to 24 msec. This global stereotyped phrenic inhibition was elicited by single pulses and often was accompanied by a postinhibitory excitation. In 48% (92/193) of the stimulation trials, trains of stimulus pulses during inspiration decreased the duration of inspiration. In 25% of the expiratory microstimulation trials, expiratory duration was increased and in 11%, expiration was shortened markedly by trains of pulses. Single shocks delivered to the right VRG or DRG produced a short latency excitation in the ipsilateral recurrent laryngeal nerve (RRL). This RRL excitation had an onset latency of 2 to 5 msec and a duration of 3 to 15 msec. Evidence suggests that the RRL excitation is due to a paucisynaptic activation of expiratory motoneurons in the caudal VRG. This activation is synchronous with the inhibition of inspiratory neurons in DRG and VRG. Despite the powerful short latency effects of microstimulation in VRG and DRG, extensive bilateral destruction of these neuronal populations had only modest effects on respiratory rhythm, while it decreased (or abolished) respiratory outflow in phrenic and recurrent laryngeal nerves. The combined results of the microstimulation and microlesion portions of this study suggest that a region (or regions) outside of the DRG and VRG might be important in the control of the respiratory pattern and that the DRG and VRG are important in determining the depth of inspiration; their role in generating respiratory rhythm needs to be critically re-examined.

Cross-correlation of medullary dorsomedial inspiratory neurons in the cat

The dorsomedial inspiratory nucleus in the medulla of cats was explored with pairs of microelectrodes with tip separations from 100 to 350 μm such that extracellular potentials of pairs of near neighbors were recorded simultaneously. Each neuron was identified as an Rα or Rβ type using lung volume manipulations, and cross-correlation histograms were computed. The cross-correlation histograms showed significant central peaks in four of seven Rα-Rα pairs, nine of nine Rβ-Rβ pairs, and four of six Rα-Rβ pairs. The cross-correlation histograms showed significant central peaks after bilateral vagotomy in two of two Rα-Rα pairs and three of three Rβ-Rβ pairs. These results demonstrate the existence of short-term synchronization in the firing patterns of these neurons. Such synchronization may be due to a common excitation of the neurons or to interactions between them.

Brain stem neuronal types with activity patterns related to sympathetic nerve discharge.

The relationships among the spontaneous activity of single neurons in the cat medulla and inferior cardiac sympathetic nerve discharge (SND), electroencephalogram (EEG) activity, phrenic nerve activity, and the R wave of the electrocardiogram were studied with the methods of spike-triggered averaging and postevent interval analysis. Three categories of neurons (SR, SE, and S) with activity patterns related to SND wee identified. The activity of SR units was related in time to SND and the R wave but not to EEG activity. SE unit discharges were related to SND and EEG activity but not to the R wave. S unit activity was related only to SND. Each of the three categories of neurons could be subdivided into two groups depending on whether their discharges were followed by an increase or a decrease in SND. All unit types exhibited respiratory-related discharge patterns. These data are discussed with regard to the problems associated with the identification of neurons in brain stem networks that govern the discharges of sympathetic nerves.

Spinal projections of physiologically identified axons from the rostral medulla of cats

Spinal projections of physiologically identified axons from the rostral medulla of cats