Biomedical subjects

R Shannon

Publications and source records attributed to R Shannon.

At least 37 records · Page 2Linked to original sources

PubMed1997

Repeated patterns of distributed synchrony in neuronal assemblies.

Models of brain function predict that the recurrence of a process or state will be reflected in repeated patterns of correlated activity. Previous work on medullary raphe assembly dynamics revealed transient changes in impulse synchrony. This study tested the hypothesis that these variations in synchrony include distributed nonrandom patterns of association. Spike trains were recorded simultaneously in the ventrolateral medulla, n. raphe obscurus, and n. raphe magnus of four anesthetized (Dial), vagotomized, paralyzed, and artificially ventilated adult cats. The "gravitational" representation of spike trains was used to detect moments of impulse synchrony in neuronal assemblies visualized as variations in the aggregation velocities of particles corresponding to each neuron. Template matching algorithms were developed to identify excessively repeating patterns of particle condensation rates. Repeating patterns were detected in each animal. The reiterated patterns represented an emergent property not apparent in either corresponding firing rate histograms or conventional gravity representations. Overlapping subsets of neurons represented in different patterns were unmasked when the template resolution was changed. The results demonstrate repeated transient network configurations defined by the tightness and duration of synchrony in different combinations of neurons and suggest that multiple information streams are conveyed concurrently by fluctuations in the synchrony of on-going activity.

Algorithms↗

PubMed1996

Inspiratory drive and phase duration during carotid chemoreceptor stimulation in the cat: medullary neurone correlations.

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.

Animals↗

PubMed1996

Long-term facilitation of phrenic nerve activity in cats: responses and short time scale correlations of medullary neurones.

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.

Animals↗

PubMed1994

Distributed actions and dynamic associations in respiratory-related neuronal assemblies of the ventrolateral medulla and brain stem midline: evidence from spike train analysis.

1. Considerable evidence indicates that neurons in the brain stem midline and ventrolateral medulla participate in the control of breathing. This work was undertaken to detect and evaluate evidence for functional links that coordinate the parallel operations of neurons distributed in these two domains. 2. Data were from 51 Dial-urethan-anesthetized, bilaterally vagotomized, paralyzed, artificially ventilated cats. Planar arrays of tungsten microelectrodes were used to monitor simultaneously spike trains in two or three of the following regions: n. raphe obscurus-n. raphe pallidus, n. raphe magnus, rostral ventrolateral medulla, and caudal ventrolateral medulla. Efferent phrenic nerve activity was recorded to indicate the phases of the respiratory cycle. Electrodes in the ventral spinal cord (C3) were used in antidromic stimulation tests for spinal projections of neurons. 3. Spike trains of 1,243 neurons were tested for respiratory modulated firing rates with cycle-triggered histograms and an analysis of variance with the use of a subjects-by-treatments experimental design. Functional associations were detected and evaluated with cross-correlograms, snowflakes, and the gravity method. 4. Each of 2,310 pairs of neurons studied included one neuron monitored within 0.6 nm of the brain stem midline and a second cell recorded in the ventrolateral medulla; 117 of these pairs (5%) included a neuron with a spinal projection, identified with antidromic stimulation methods, that extended to at least the third cervical segment. Short-time scale correlations were detected in 110 (4.7%) pairs of neurons. Primary cross-correlogram features included 40 central peaks, 47 offset peaks, 4 central troughs, and 19 offset troughs. 5. In 14 data sets, multiple short-time scale correlations were found among three or more simultaneously recorded neurons distributed between both midline and ventrolateral domains. The results suggested that elements of up to three layers of interneurons were monitored simultaneously. Evidence for concurrent serial and parallel regulation of impulse synchrony was detected. Gravitational representations demonstrated respiratory-phase dependent synchrony among neurons distributed in both brain stem regions. 6. The results support a model of the brain stem respiratory network composed of coordinated distributed subassemblies and provide evidence for several hypotheses. 1) Copies of respiratory drive information from rostral ventrolateral medullary (RVLM) respiratory neurons are transmitted to midline neurons. 2) Midline neurons act on respiratory-related neurons in the RVLM to modulate phase timing. 3) Impulse synchrony of midline neurons is influenced by concurrent divergent actions of both midline and ventrolateral neurons.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1993

Percutaneous endoscopic gastrostomy--its application in patients with neurological disease.

We performed percutaneous endoscopic gastrostomy (PEG) in 30 patients with prolonged swallowing difficulty (> 4 weeks duration). The average procedure time was 25 minutes. PEG insertion was done on an outpatient basis in four patients. The complication rate was 10% and included failed insertion, peristomal infection and herniation of the gastric mucosa at the gastrostomy exist site. At follow-up, the PEG tube continued to function in 18/22 of the surviving patients with a median in-use time of 85 days. Seven patients died from their original disease. Over a 28-day period, the weight gain among the patients ranged from 3kg to 7kg (mean 4.5kg) and average serum albumin increased from 29g/dl to 35g/dl. This confirms that PEG is a safe, easy and effective method of long-term enteral feeding in patients with neurological disease.

Adult↗

PubMed1993

Cerebral cortical evoked potentials elicited by cat intercostal muscle mechanoreceptors.

Intercostal muscle afferents discharge in response to changes in intercostal muscle mechanics and have spinal and brain stem projections. It was hypothesized that intercostal muscle mechanoreceptors also project to the sensorimotor cortex. In cats, the proximal muscle branch of an intercostal nerve was used for electrical stimulation. The mechanical stimulation was stretch of an isolated intercostal space. The sensorimotor cortex was mapped with a surface ball electrode. Primary cortical evoked potentials (CEP) were found in area 3a of the sensorimotor cortex with mechanical and electrical stimulation. The CEP was elicited with the smallest stretch amplitude used, 50 microns. The CEP response showed little increase beyond 300-microns stretch. The CEP elicited by 50-microns stretch suggests an initial cortical activation by intercostal muscle spindles. The minimal increase in CEP amplitude with stretch > 300 microns suggests that the CEP response is primarily due to muscle spindle recruitment. The increase in amplitude beyond this stretch may be due to recruitment of tendon organs. These results demonstrate a short-latency projection of intercostal muscle mechanoreceptors to the sensorimotor region of the cerebral cortex. This cortical activation may be involved in respiratory sensations and/or transcortical reflex responses to changes in respiratory muscle mechanics.

Animals↗

PubMed1993

An analysis of a board game as a treatment activity.

Occupational therapists often use tabletop board games in treatment to help adult clients with physical disabilities improve the perceptual, cognitive, sensory, and fine motor skill components of occupational behavior. Detailed activity analyses of these types of activities, including performance norms, are not available in the occupational therapy literature. Such analyses would help therapists consider the multiple skill demands of tabletop games and allow more systematic grading of these treatment activities. This paper presents a model for analyzing therapeutic activities in relation to relevant motor learning and cognitive-perceptual literature. Included in this analysis are a description of the activity, examination of its component skills and of the qualitative features of activity performance, suggestions for grading and for treatment goals, and some preliminary performance standards derived from a pilot study of 18 adults without physical disabilities. The issue of transfer of skills between games and functional activities is also discussed.

Adult↗

PubMed1993

Immunohistochemical assessment of proliferative activity in adrenocortical neoplasms.

Although many histologic criteria have been utilized to help distinguish benign from malignant adrenocortical tumors, it still may be difficult to assess the biologic potential of a given tumor. We evaluated 19 adenomas and 15 primary carcinomas with the avidin-biotin complex peroxidase method utilizing formalin-fixed, paraffin-embedded tissues with monoclonal antibodies for proliferating cell nuclear antigen (PC10) and Ki-67 (MIB 1) to determine if staining for these antigens could be used to help differentiate benign from malignant adrenocortical neoplasms. We also evaluated whether these markers could be used as prognostic indicators. Labeling indices for both PCNA and Ki-67 were determined by enumerating 1000 tumor cells, and expressed as a percentage of cells with nuclear staining. A PCNA and a Ki-67 score was obtained by the product of the staining intensity (0-3+) and the extent of nuclear staining, expressed as an estimate of the percentage of cells staining. Both PCNA and Ki-67 score and labeling index were correlated with mitotic counts, histologic diagnosis, and clinical outcome. Follow-up period for patients ranged from 4 months to 12 years with a mean of 25 months. Mitotic counts correlated with histologic diagnosis and clinical outcome. Both Ki-67 score and labeling index were significantly higher in malignant than in benign tumors, and correlated with mitotic counts and clinical outcome. There was a strong correlation between Ki-67 score and labeling index, indicating that Ki-67 score may be a more rapid and equally accurate method of estimating proliferative index of a tumor. PCNA score and labeling index did not correlate with histologic diagnosis or clinical outcome.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenoma↗

PubMed1992

Functional connectivity between brain stem midline neurons with respiratory-modulated firing rates.

1. Recent evidence supports the idea that neurons distributed along the midline of the brain stem contribute to the regulation of breathing. This study sought evidence for functional connections between midline neurons with respiratory-modulated firing rates. 2. Experiments were conducted on 38 anesthetized, paralyzed, bilaterally vagotomized, artificially ventilated cats. Planar arrays of tungsten microelectrodes were used to monitor spike trains of two or more midline neurons simultaneously in the regions of n. raphe obscurus, n. raphe pallidus, and n. raphe magnus. Efferent phrenic nerve activity was recorded. Data were analyzed with auto- and cross-correlograms and cycle-triggered histograms. Spike trains of neurons were also tested for respiratory modulation by an analysis of variance with the use of a subjects-by-treatments experimental design. 3. Of 584 neurons studied, 99.1% were tonic, i.e., they had firing probabilities greater than zero in all phases of the respiratory cycle. Fifty-three percent of the neurons had respiratory-modulated firing rates; 223 cells were more active during the expiratory (E) interval; 88 neurons were inspiratory (I)-related. The remaining cells were classified as having no respiratory-related modulation of firing rate (NRR). 4. The spike trains of 210 of 1,078 pairs (19.5%) of brain stem midline neurons exhibited short-time scale correlations indicative of paucisynaptic interactions. Primary cross-correlogram features included 129 central peaks, 45 offset peaks, two central troughs, and 57 offset troughs. Twenty-two of the neuronal pairs analyzed had both offset peaks and troughs. Correlograms from an additional 35 pairs of neurons had multiple peaks and troughs without a significant primary feature. 5. The frequency of correlations for neuron pairs composed of cells with respiratory-modulated firing rates was as follows: E-E, 40/185 (22%); E-I, 23/111 (21%); E-NRR, 45/297 (15%); I-I, 11/25 (44%); and I-NRR, 13/104 (13%). Twenty-two percent of the NRR pairs (79/357) exhibited short-time scale correlations. 6. Thirty pairs of neurons included a cell with an antidromically identified axonal projection extending to at least the third cervical segment. The mean estimated conduction velocity based on the single-site stimulation method was 26.5 +/- 9.9 (SD) m/s. 7. The results provide evidence for inhibitory and excitatory functional connections between midline brain stem neurons. Data support the hypothesis that the respiratory-modulated discharge patterns of midline neurons are, at least in part, a consequence of the synaptic actions of other midline cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Analysis of Variance↗

PubMed1992

Respiratory-related neural assemblies in the brain stem midline.

1. The initial objective of this study was to determine whether respiratory-related neural assemblies exist in the brain stem midline. A second goal was to seek evidence for concurrent relationships among the neurons that could generate the detected synchrony. 2. Experiments were conducted on anesthetized, paralyzed, bilaterally vagotomized, artificially ventilated cats. Spike trains of four to nine simultaneously monitored neurons were recorded in the regions of n. raphe obscurus-n. raphe pallidus and n. raphe magnus. 3. Data were analyzed with cycle-triggered histograms, cross-correlograms, snowflakes, and the gravitational representation. A significance test for the gravity method was developed and tested with spike trains generated by simulated networks with defined connections. 4. Ninety-three groups of neurons from 24 cats were studied. Thirty-nine groups from 19 cats included neurons that discharged synchronously on a millisecond time scale; less than or equal to 19 pairs of synchronously discharging neurons were found in one group. Twenty-seven of these 39 groups included neurons that had respiratory-modulated firing rates and discharged synchronously with other group members. Synchronous assemblies included cells monitored at rostral or caudal locations, or both. 5. Six classes of relationships were inferred from groups of neurons with multiple correlations: divergence (n = 11); convergence (n = 7); connections with opposite actions between neurons (n = 5); projections of synchronous neurons to separate targets (n = 5); projections to one neuron in a synchronous group (n = 4); and projections between two synchronous groups with common elements (n = 6). 6. The results document the existence of assemblies of synchronously discharging respiratory-related neurons in midline regions of the brain stem and suggest that divergent excitatory and inhibitory connections within the midline participate in the generation of that synchrony. Links between assemblies may operate to stabilize their collective activity in a particular state.

Afferent Pathways↗

PubMed1992

Dynamic reconfiguration of brain stem neural assemblies: respiratory phase-dependent synchrony versus modulation of firing rates.

1. The objective of this work was to determine whether configurations of midline brain stem neural assemblies change during the respiratory cycle. 2. Spike trains of several single neurons were recorded simultaneously in anesthetized, paralyzed, bilaterally vagotomized, artificially ventilated cats. Data were analyzed with cross-correlational and gravity methods. 3. Sequential samples from each of eight groups of neurons known to contain synchronously discharging neurons exhibited temporal variations in that synchrony. 4. Gravity analysis of short (less than 200-s) samples of spike train data revealed 20 pairs of clustered particles that were not predicted from cross-correlation analysis of the parent data sets (greater than 20 min). 5. Twenty-nine groups of three to eight simultaneously monitored neurons, each with at least two synchronously discharging neurons, were analyzed for evidence of respiratory phase-dependent modulation of that coordinated activity. Spikes from successive interleaved inspiratory and expiratory intervals were analyzed separately. 6. Neurons pairs in 11 groups were more synchronous during the inspiratory interval; six groups had pairs that were more synchronous during the expiratory period. In two groups, different pairs were synchronous in different respiratory phases. In 11 of the 26 pairs that exhibited phase-dependent differences in synchrony, neither neuron had a respiratory-modulated firing rate as judged by either the cycle-triggered histogram or an analysis of variance of their firing rates. 7. Configurations of respiratory-related brain stem neural networks changed with time and the phases of breathing. Neurons with no apparent respiratory modulation of their individual firing rates collectively exhibited respiratory phase-dependent modulation of their impulse synchrony.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1991

Hepatic artery aneurysm.

OBJECTIVE: To present a successfully treated case of hepatic artery aneurysm. CLINICAL FEATURES: A 76-year-old, retired male Caucasian presented with acute abdominal pain which was diagnosed as acute cholecystitis. An aneurysm of the hepatic artery was found at operation for cholecystectomy, and an arteriogram confirmed the position of the aneurysm, distal to the origin of the gastroduodenal artery. INTERVENTION AND OUTCOME: The aneurysm was resected and replaced with an 8 mm diameter woven Dacron graft. The postoperative course was uneventful and the patient was discharged on the ninth postoperative day. CONCLUSION: Aneurysms of the hepatic artery can be resected with restoration of arterial continuity.

Aged↗

PubMed1991

Absence of both auditory evoked potentials and auditory percepts dependent on timing cues.

An 11-yr-old girl had an absence of sensory components of auditory evoked potentials (brainstem, middle and long-latency) to click and tone burst stimuli that she could clearly hear. Psychoacoustic tests revealed a marked impairment of those auditory perceptions dependent on temporal cues, that is, lateralization of binaural clicks, change of binaural masked threshold with changes in signal phase, binaural beats, detection of paired monaural clicks, monaural detection of a silent gap in a sound, and monaural threshold elevation for short duration tones. In contrast, auditory functions reflecting intensity or frequency discriminations (difference limens) were only minimally impaired. Pure tone audiometry showed a moderate (50 dB) bilateral hearing loss with a disproportionate severe loss of word intelligibility. Those auditory evoked potentials that were preserved included (1) cochlear microphonics reflecting hair cell activity; (2) cortical sustained potentials reflecting processing of slowly changing signals; and (3) long-latency cognitive components (P300, processing negativity) reflecting endogenous auditory cognitive processes. Both the evoked potential and perceptual deficits are attributed to changes in temporal encoding of acoustic signals perhaps occurring at the synapse between hair cell and eighth nerve dendrites. The results from this patient are discussed in relation to previously published cases with absent auditory evoked potentials and preserved hearing.

Acoustic Stimulation↗

PubMed1990

Hypoxemia alone does not explain blood pressure elevations after obstructive apneas.

In patients with obstructive sleep apnea (OSA), substantial elevations of systemic blood pressure (BP) and depressions of oxyhemoglobin saturation (SaO2) accompany apnea termination. The causes of the BP elevations, which contribute significantly to nocturnal hypertension in OSA, have not been defined precisely. To assess the relative contribution of arterial hypoxemia, we observed mean arterial pressure (MAP) changes following obstructive apneas in 11 OSA patients during non-rapid-eye-movement (NREM) sleep and then under three experimental conditions: 1) apnea with O2 supplementation; 2) hypoxemia (SaO2 80%) without apnea; and 3) arousal from sleep with neither hypoxemia nor apnea. We found that apneas recorded during O2 supplementation (SaO2 nadir 93.6% +/- 2.4; mean +/- SD) in six subjects were associated with equivalent postapneic MAP elevations compared with unsupplemented apneas (SaO2 nadir 79-82%): 18.8 +/- 7.1 vs. 21.3 +/- 9.2 mmHg (mean change MAP +/- SD); in the absence of respiratory and sleep disruption in eight subjects, hypoxemia was not associated with the BP elevations observed following apneas: -5.4 +/- 19 vs. 19.1 +/- 7.8 mmHg (P less than 0.01); and in five subjects, auditory arousal alone was associated with MAP elevation similar to that observed following apneas: 24.0 +/- 8.1 vs. 22.0 +/- 6.9 mmHg. We conclude that in NREM sleep postapneic BP elevations are not primarily attributable to arterial hypoxemia. Other factors associated with apnea termination, including arousal from sleep, reinflation of the lungs, and changes of intrathoracic pressure, may be responsible for these elevations.

Adult↗

PubMed1990

Reduced subendocardial coronary reserve. A potential mechanism for impaired diastolic function in the hypertrophied and failing heart.

The association between pressure overload, left ventricular (LV) hypertrophy and failure, and abnormalities in diastolic function has been described both clinically and experimentally. The mechanisms underlying this association, however, are complex and controversial. Factors that have been implicated include mechanical alterations due to hypertrophy alone, changes in collagen type and content, alterations in beta-adrenergic responsiveness, and chronic myocardial ischemia. Studies in our laboratory have identified limitations in subendocardial flow reserve in compensated LV hypertrophy and near exhaustion in subendocardial reserve in animals with decompensated LV hypertrophy and failure. These abnormalities in coronary reserve are associated with impaired diastolic function, particularly during periods of physiological stress. For example, with pacing-induced stress, impairment in diastolic function was observed in conscious dogs with compensated LV hypertrophy. In conscious dogs with LV hypertrophy and failure, isoproterenol also resulted in altered diastolic function. Thus, in the model of severe pressure-overload hypertrophy, which is characterized by limitations in coronary reserve, the mechanism of subendocardial ischemia might be responsible in part for the impairment in diastolic function observed in response to superimposed stress.

Animals↗

PubMed1989

Gravitational representation of simultaneously recorded brainstem respiratory neuron spike trains.

Experiments designed to study concurrent processes in neural networks have been hampered by limitations of available analytical methods. A recently described gravitational representation of spike train data was used to evaluate groups of simultaneously monitored medullary respiratory related neurons in anesthetized, vagotomized cats. The results establish that the method can detect and define functional associations among elements of such groups after as few as 20 respiratory cycles.

Action Potentials↗

PubMed1989

Intercostal and abdominal muscle afferent influence on caudal medullary expiratory neurons that drive abdominal muscles.

Our objective was to determine if caudal ventral respiratory group (VRG) expiratory (E) neurons that drive abdominal expiratory motoneurons in the lumbar cord respond to intercostal and lumbar nerve afferent stimulation. Results showed that 92% of medullary E-neurons that were antidromically activated from the upper lumbar cord reduced their activity in response to stimulation of external and internal intercostal and lumbar nerve afferents. We conclude that afferent information from intercostal and abdominal muscle tendon organs has an inhibitory effect on caudal VRG E-neurons that drive abdominal expiratory motoneurons.

Abdominal Muscles↗

PubMed1989

Discharge patterns of rostrolateral medullary expiratory neurons in the cat: regulation by concurrent network processes.

1. The identification of numerous functional connections among medullary respiratory related neurons led us to postulate specific short time scale correlations among neuronal spike trains consistent with 1) inhibition of rostrolateral medullary augmenting expiratory (E-AUG) neurons by other E-AUG cells, and 2) inhibitory control of the postulated E-AUG neural network by decrementing expiratory (E-DEC) neurons. Recent observations of reduced rostrolateral E-AUG cell activity following stimulation of sensory afferents raised the additional question of whether reflex control mechanisms use the identified functional connections to mediate their effects. 2. Experiments were conducted on 42 anesthetized, paralyzed, bilaterally vagotomized, artificially ventilated cats. Impulse trains of two or more respiratory related neurons of the lateral medulla, including at least one rostrolateral medullary E-AUG neuron, were simultaneously recorded together with phrenic nerve efferent activity. Most neurons were tested for spinal axonal projections with antidromic stimulation methods. In some experiments, the central cut end of the right vagus nerve was electrically stimulated during the expiratory interval. Data were analyzed using cycle-triggered histograms, auto- and cross-correlograms, logical cross-correlograms, snowflake scatter diagrams, and peristimulus time histograms. 3. Seven of 73 pairs (9.6%) of ipsilateral E-AUG neurons exhibited short time scale correlations in firing probability. Two rostral pairs had coincident increases in activity. Five pairs were characterized by a reduction in activity in a rostral neuron following spikes in the other cell; concurrent serial inhibition among one set of three E-AUG neurons was indicated. These five pairs, together with three other similarly correlated pairs described previously, were studied further: spikes recorded during the first and second halves of the expiratory (E) phase were analyzed separately. This phase segmentation unmasked multiple correlations implying reciprocal inhibition between one pair of E-AUG neurons. Short time scale troughs in correlograms generated from late E-phase spike trains had significantly (P less than 0.05) greater detectability indices than troughs in early E-phase correlograms. Multineuron correlations revealed two cases in which the firing probability of the target E-AUG neuron was reduced less when only reference E-AUG cell spikes coincident with spikes in a third, E-DEC, neuron were used as trigger events. 4. Enhanced rostral E-AUG neuron firing probabilities coincident with or following impulses in ipsilateral E-DEC neurons were detected in 6 of 94 (6.4%) rostral pairs.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗