Roger Shannon
University of South Florida
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Featured researches published by Roger Shannon.
The Journal of Physiology | 2000
Roger Shannon; David M. Baekey; Kendall F. Morris; Zhongzeng Li; Bruce G. Lindsey
1 This study tested predictions from a network model of ventrolateral medullary respiratory neurone interactions for the generation of the cough motor pattern observed in inspiratory and expiratory pump muscles. 2 Data were from 34 mid‐collicularly decerebrated, paralysed, artificially ventilated cats. Cough‐like patterns (fictive cough) in efferent phrenic and lumbar nerve activities were elicited by mechanical stimulation of the intrathoracic trachea. Neurones in the ventral respiratory group, including the Bötzinger and pre‐Bötzinger complexes, were monitored simultaneously with microelectrode arrays. Spike trains were analysed for evidence of functional connectivity and responses during fictive cough with cycle‐triggered histograms, autocorrelograms, cross‐correlograms, and spike‐triggered averages of phrenic and recurrent laryngeal nerve activities. 3 Significant cross‐correlogram features were detected in 151 of 1988 pairs of respiratory modulated neurones. There were 59 central peaks, 5 central troughs, 11 offset peaks and 2 offset troughs among inspiratory neurone pairs. Among expiratory neurones there were 23 central peaks, 8 offset peaks and 4 offset troughs. Correlations between inspiratory and expiratory neurones included 20 central peaks, 10 central troughs and 9 offset troughs. Spike‐triggered averages of phrenic motoneurone activity had 51 offset peaks and 5 offset troughs. 4 The concurrent responses and multiple short time scale correlations support parallel and serial network interactions proposed in our model for the generation of the cough motor pattern in the respiratory pump muscles. Inferred associations included the following. (a) Excitation of augmenting inspiratory (I‐Aug) neurones and phrenic motoneurones by I‐Aug neurones. (b) Inhibition of augmenting expiratory (E‐Aug) neurones by decrementing inspiratory (I‐Dec) neurones. (c) Inhibition of I‐Aug, I‐Dec and E‐Aug neurones by E‐Dec neurones. (d) Inhibition of I‐Aug and I‐Dec neurones and phrenic motoneurones by E‐Aug neurones. The data also confirm previous results and support hypotheses in current network models for the generation of the eupnoeic pattern.
The Journal of Physiology | 2001
David M. Baekey; Kendall F. Morris; Christian Gestreau; Zhongzeng Li; Bruce G. Lindsey; Roger Shannon
1 This study addressed the hypothesis that ventrolateral medullary respiratory neurones participate in the control of laryngeal motoneurones during both eupnoea and coughing. 2 Data were obtained from 28 mid‐collicular decerebrated, artificially ventilated cats. Cough‐like motor patterns (fictive cough) in phrenic, lumbar and recurrent laryngeal nerves were elicited by mechanical stimulation of the intrathoracic trachea. Microelectrode arrays were used to monitor simultaneously several neurones in the ventral respiratory group, including the Bötzinger and pre‐Bötzinger complexes. Spike trains were evaluated for responses during fictive cough and evidence of functional connectivity with spike‐triggered averages of efferent recurrent laryngeal nerve activity. 3 Primary features were observed in averages triggered by 94 of 332 (28 %) neurones. An offset biphasic wave with a positive time lag was present in the unrectified average for 10 inspiratory and 13 expiratory neurones. These trigger neurones were respectively identified as inspiratory laryngeal motoneurones with augmenting, decrementing, plateau and ‘other’ discharge patterns, and expiratory laryngeal motoneurones with decrementing firing patterns. 4 Rectified averages triggered by inspiratory neurones included 37 offset peaks, 11 central peaks and one offset trough. Averages triggered by expiratory neurones had 12 offset peaks, six central peaks and four offset troughs. Relationships inferred from these features included premotor actions of inspiratory neurones with augmenting, decrementing, plateau and ‘other’ patterns on inspiratory laryngeal motoneurones, and premotor actions of decrementing and ‘other’ expiratory neurones on expiratory laryngeal motoneurones. Corresponding changes in neuronal firing patterns during fictive cough supported these inferences. 5 The data confirm and extend previous results on the control of laryngeal motoneurones during eupnoea and support the hypothesis that the same premotor neurones help to shape motoneurone firing patterns during both eupnoea and coughing.
Respiration Physiology | 1980
Roger Shannon
Studies were performed on anesthetized, paralyzed, artificially ventilated cats. Phrenic (C5) efferent activity, dorsal respiratory group (DRG) neuron activity in the vicinity of the medullary solitary tract complex, and thoracic dorsal root compound action potentials were recorded during electrical stimulation of intercostal and lumbar nerves. DRG neurons were identified by their firing pattern and response to lung inflation. Phrenic activity (PA) was inhibited by stimulating external intercostal nerves T3-T10, internal intercostal nerves T3-T12, lateral branch of the main intercostal nerves T6-T12, or lumbar nerves 1-2. Stimulation of lower (T9-T11) intercostal or lumbar nerves produced a short duration (10-20 msec) facilitation of PA prior to the inhibition. Facilitation and inhibition of PA were correlated with recruitment of afferent fibers from muscle proprioceptors. Inspiratory neurons (I alpha and I beta) in the DRG were inhibited simultaneously with PA regardless of the nerves stimulated. DRG neurons which fired in phase with lung inflation (P cells) were unaffected by nerve stimulation even though PA was inhibited. Lower intercostal nerve (T9-T11) stimulation produced a brief facilitation of medullary neuron activity simultaneous with facilitation of PA. It is concluded that intercostal and abdominal muscle proprioceptor afferents, and perhaps cutaneous afferents, reflexly alter the activity of DRG inspiratory neurons (I alpha, I beta) which drive the phrenic motoneurons. The inhibitory effect is not via P cells but may be via other interneurons in close proximity to the I cells.
The Journal of Physiology | 1996
Kendall F. Morris; A. Arata; Roger Shannon; Bruce G. Lindsey
1. Stimulation of either peripheral chemoreceptors or nucleus raphe obscurus results in long‐term facilitation of phrenic motoneurone activity. The first objective of this work was to measure the concurrent responses of neurones in the nucleus raphe obscurus, the nucleus tractus solitarii, and the regions of the retrofacial nucleus, nucleus ambiguus and nucleus retroambigualis during induction of long‐term facilitation. A second goal was to assess functional relationships of the chemoresponsive raphe neurones with neurones in the other monitored locations and with phrenic motoneurones. 2. Up to thirty single medullary neurones and phrenic nerve efferent activity were recorded simultaneously in fifteen anaesthetized, paralysed, vagotomized, artificially ventilated adult cats. Carotid chemoreceptors were stimulated by close arterial injection of 200 microliters of CO2‐saturated saline solution. Spike trains were analysed with cycle‐triggered histograms and two statistical tests for respiratory modulation. Peristimulus‐time histograms and cumulative sum histograms were used to assess responses to stimulation. Cross‐correlation was used to test for non‐random temporal relationships between spike trains. Spike‐triggered average histograms provided evidence for functional associations with phrenic motoneurones. 3. One hundred and thirteen of 348 neurones were monitored in the nucleus raphe obscurus. The firing rates of twenty‐nine raphe neurones increased during stimulation; eighteen decreased. In twenty‐one pairs of concurrently monitored raphe neurones, the firing rate of one increased its activity during stimulation then decreased, while the other showed an increase that began as the rate of the former declined. Eighteen chemoresponsive raphe neurones had short time scale features in their phrenic spike‐triggered averages. Short time scale features were found in cross‐correlograms from 184 of 1407 neurone pairs. 4. The data suggest parallel routes by which carotid chemoreceptors influence medullary raphe neurones and support the hypotheses that mid‐line respiratory‐related neuronal assemblies transform information from those receptors and regulate the gain of respiratory motor output.
The Journal of Physiology | 1998
Bruce G. Lindsey; A. Arata; Kendall F. Morris; Y. M. Hernandez; Roger Shannon
1 Perturbations of arterial blood pressure change medullary raphe neurone activity and the respiratory motor pattern. This study sought evidence for actions of baroresponsive raphe neurones on the medullary respiratory network. 2 Blood pressure was perturbed by intravenous injection of an α1‐adrenergic receptor agonist, unilateral pressure changes in the carotid sinus, or occlusion of the descending aorta in thirty‐six Dial‐urethane‐anaesthetized, vagotomized, paralysed, artificially ventilated cats. Neurones were monitored with microelectrode arrays in two or three of the following domains: nucleus raphe obscurus‐nucleus raphe pallidus, nucleus raphe magnus, and rostral and caudal ventrolateral medulla. Data were analysed with cycle‐triggered histograms, peristimulus time and cumulative sum histograms, cross‐correlograms and spike‐triggered averages of efferent phrenic nerve activity. 3 Prolongation of the expiratory phase and decreased peak integrated phrenic amplitude were most frequently observed. Of 707 neurones studied, 310 had altered firing rates during stimulation; changes in opposite directions were monitored simultaneously in fifty‐six of eighty‐seven data sets with at least two baroresponsive neurones. 4 Short time scale correlations were detected between neurones in 347 of 3388 pairs. Seventeen pairs of baroresponsive raphe neurones exhibited significant offset correlogram features indicative of paucisynaptic interactions. In correlated raphe‐ventrolateral medullary neurone pairs with at least one baroresponsive neurone, six of seven ventrolateral medullary decrementing expiratory (E‐Decr) neurones increased their firing rate during baroreceptor stimulation. Thirteen of fifteen ventrolateral medullary inspiratory neurones correlated with raphe cells decreased their firing rate during baroreceptor stimulation. 5 The results support the hypothesis that raphe neuronal assemblies transform and transmit information from baroreceptors to neurones in the ventral respiratory group. The inferred actions both limit and promote responses to sensory perturbations and match predictions from simulations of the respiratory network.
The Journal of Physiology | 2001
Kendall F. Morris; Roger Shannon; Bruce G. Lindsey
1 Long‐term facilitation is a respiratory memory expressed as an increase in motor output lasting more than an hour. This change is induced by repeated hypoxia, stimulation of carotid chemoreceptors, or electrical stimulation of the carotid sinus nerve or brainstem mid‐line. The present work addressed the hypothesis that persistent changes in medullary respiratory neural networks contribute to long‐term facilitation. 2 Carotid chemoreceptors were stimulated by close arterial injection of CO2‐saturated saline solution. Phrenic nerve efferent activity and up to 30 single medullary neurones were recorded simultaneously in nucleus tractus solitarii (NTS) including the dorsal respiratory group (DRG), Bötzinger‐ventral respiratory group (Böt‐VRG), and nucleus raphe obscurus of nine adult cats, anaesthetized, injected with a neuromuscular blocking agent, vagotomized and artificially ventilated. 3 The firing rates of 87 of 105 neurones (83 %) changed following induction of long‐term facilitation. Nine of eleven DRG and Böt‐VRG putative premotor inspiratory neurones had increased firing rates with long‐term facilitation. Fourteen of twenty‐one raphe obscurus neurones with control firing rates less than 4 Hz had significant long‐term increases in activity. 4 Cross‐correlogram analysis suggested that there were changes in effective connectivity of neuron pairs with long‐term facilitation. Joint peristimulus time histograms and pattern detection methods used with ‘gravity’ analysis also detected changes in short time scale correlations associated with long‐term facilitation. 5 The results suggest that changes in firing rates and synchrony of VRG and DRG premotor neurones and altered effective connectivity among other functionally antecedent elements of the medullary respiratory network contribute to the expression of long‐term facilitation.
The Journal of Physiology | 1996
Kendall F. Morris; A. Arata; Roger Shannon; Bruce G. Lindsey
1. This study addressed the hypothesis that there is a parallel processing of input from carotid chemoreceptors to brainstem neurones involved in inspiratory phase timing and control of inspiratory motor output amplitude. Data were from fifteen anaesthetized, bilaterally vagotomized, paralysed, artificially ventilated cats. Carotid chemoreceptors were stimulated by close arterial injection of 200 microliters of CO2‐saturated saline solution. 2. Planar arrays of tungsten microelectrodes were used to monitor simultaneously up to twenty‐two neurones in the nucleus tractus solitarii (NTS) and ventral respiratory group (VRG). Spike trains were analysed with two statistical tests of respiratory modulation, cycle‐triggered histograms, peristimulus‐time histograms, cumulative sum histograms and cross‐correlograms. 3. In NTS, 16 of 26 neurones with respiratory and 12 of 27 without respiratory modulation changed firing rate during carotid chemoreceptor stimulation. In the VRG 72 of 112 respiratory and 14 of 48 non‐respiratory neurones changed firing rate during stimulation. 4. The spike trains of 85 of 1276 pairs (6.7%) of cells exhibited short time scale correlations indicative of paucisynaptic interactions. Ten pairs of neurones were each composed of a rostral VRG phasic inspiratory neurone that responded to carotid chemoreceptor stimulation with a decline in firing rate and a caudal VRG phasic inspiratory neurone that increased its firing rate. Cross‐correlograms from two of the pairs had features consistent with excitation of the caudal neurones by the rostral cells. A decrease in the duration of activity of the rostral VRG neurones was paralleled by the decrease in inspiratory time of phrenic nerve activity. Caudal VRG inspiratory neurones increased their activity as phrenic amplitude increased. Spike‐triggered averages of all four neurones indicated post‐spike facilitation of phrenic motoneurones. 5. The results support the hypothesis that unilateral stimulation of carotid chemoreceptors results in parallel actions. (a) Inhibition of rostral VRG I‐Driver neurones decreases inspiratory duration. (b) Concurrent excitation of premotor VRG and dorsal respiratory group inspiratory neurones increases inspiratory drive to phrenic motoneurones. Other data suggest that responsive ipsilateral neurones act to regulate contralateral neurones.
Respiration Physiology | 2000
Kendall F. Morris; David M. Baekey; Roger Shannon; Bruce G. Lindsey
Intermittent hypoxia results in a long-term facilitation (LTF) of respiratory efferent activity. The studies reviewed here presented data from both anesthetized and decerebrate, paralyzed, vagotomized, artificially ventilated adult cats. Multiple arrays of tungsten microelectrodes were used to record the concurrent responses of brain stem neurons that contribute to respiratory motor pattern generation. Spike trains were analyzed with firing rate histograms, peristimulus time histograms, cycle triggered histograms, spike triggered averages with multiunit phrenic efferent activity, cross correlation histograms, joint peristimulus time histograms and the gravity method. These studies addressed several hypotheses. (1) There is parallel processing of input from carotid chemoreceptors to the brain stem. (2) Respiratory related midline neurons are involved in the induction and maintenance of LTF. (3) There is a change in effective connectivity of brain stem neurons with LTF. (4) Neural networks involved in the induction and maintenance of LTF have patterns of synchrony that recur with a frequency greater than expected by chance.
The Journal of Physiology | 2008
Thomas E. Dick; Roger Shannon; Bruce G. Lindsey; Sarah C. Nuding; Lauren S. Segers; David M. Baekey; Kendall F. Morris
The dorsolateral (DL) pons modulates the respiratory pattern. With the prevention of lung inflation during central inspiratory phase (no‐inflation (no‐I or delayed‐I) tests), DL pontine neuronal activity increased the strength and consistency of its respiratory modulation, properties measured statistically by the η2 value. This increase could result from enhanced respiratory‐modulated drive arising from the medulla normally gated by vagal activity. We hypothesized that DL pontine activity during delayed‐I tests would be comparable to that following vagotomy. Ensemble recordings of neuronal activity were obtained before and after vagotomy and during delayed‐I tests in decerebrate, paralysed and ventilated cats. In general, changes in activity pattern during the delayed‐I tests were similar to those after vagotomy, with the exception of firing‐rate differences at the inspiratory–expiratory phase transition. Even activity that was respiratory‐modulated with the vagi intact became more modulated while withholding lung inflation and following vagotomy. Furthermore, we recorded activity that was excited by lung inflation as well as changes that persisted past the stimulus cycle. Computer simulations of a recurrent inhibitory neural network model account not only for enhanced respiratory modulation with vagotomy but also the varied activities observed with the vagi intact. We conclude that (a) DL pontine neurones receive both vagal‐dependent excitatory inputs and central respiratory drive; (b) even though changes in pontine activity are transient, they can persist after no‐I tests whether or not changes in the respiratory pattern occur in the subsequent cycles; and (c) models of respiratory control should depict a recurrent inhibitory circuitry, which can act to maintain the stability and provide plasticity to the respiratory pattern.
Philosophical Transactions of the Royal Society B | 2009
Sarah C. Nuding; Lauren S. Segers; Roger Shannon; Russell O'Connor; Kendall F. Morris; Bruce G. Lindsey
The brainstem network for generating and modulating the respiratory motor pattern includes neurons of the medullary ventrolateral respiratory column (VRC), dorsolateral pons (PRG) and raphé nuclei. Midline raphé neurons are proposed to be elements of a distributed brainstem system of central chemoreceptors, as well as modulators of central chemoreceptors at other sites, including the retrotrapezoid nucleus. Stimulation of the raphé system or peripheral chemoreceptors can induce a long-term facilitation of phrenic nerve activity; central chemoreceptor stimulation does not. The network mechanisms through which each class of chemoreceptor differentially influences breathing are poorly understood. Microelectrode arrays were used to monitor sets of spike trains from 114 PRG, 198 VRC and 166 midline neurons in six decerebrate vagotomized cats; 356 were recorded during sequential stimulation of both receptor classes via brief CO2-saturated saline injections in vertebral (central) and carotid arteries (peripheral). Seventy neurons responded to both stimuli. More neurons were responsive only to peripheral challenges than those responsive only to central chemoreceptor stimulation (PRG, 20 : 4; VRC, 41 : 10; midline, 25 : 13). Of 16 474 pairs of neurons evaluated for short-time scale correlations, similar percentages of reference neurons in each brain region had correlation features indicative of a specific interaction with at least one target neuron: PRG (59.6%), VRC (51.0%) and raphé nuclei (45.8%). The results suggest a brainstem network architecture with connectivity that shapes the respiratory motor pattern via overlapping circuits that modulate central and peripheral chemoreceptor-mediated influences on breathing.