Biomedical subjects

P Langhorst

Publications and source records attributed to P Langhorst.

At least 19 recordsLinked to original sources

PubMed2000

Phase transitions in the common brainstem and related systems investigated by nonstationary time series analysis.

Neuronal activities of the reticular formation (RF) of the lower brainstem and the nucleus tractus solitarii (NTS, first relay station of baroreceptor afferents) were recorded together in the anesthized dog with related parameters of EEG, respiration and cardiovascular system. The RF neurons are part of the common brainstem system (CBS) which participates in regulation and coordination of cardiovascular, respiratory, somatomotor systems, and vigilance. Multiple time series of these physiological subsystems yield useful information about internal dynamic coordination of the organism. Essential problems are nonlinearity and instationarity of the signals, due to the dynamic complexity of the systems. Several time-resolving methods are presented to describe nonlinear dynamic couplings in the time course, particularly during phase transitions. The methods are applied to the recorded signals representing the complex couplings of the physiological subsystems. Phase transitions in these systems are detected by recurrence plots of the instationary signals. The pointwise transinformation and the pointwise conditional coupling divergence are measures of the mutual interaction of the subsystems in the state space. If the signals show marked rhythms, instantaneous frequencies and their shiftings are demonstrated by time frequency distributions, and instantaneous phase differences show couplings of oscillating subsystems. Transient signal components are reconstructed by wavelet packet time selective transient reconstruction. These methods are useful means for analyzing coupling characteristics of the complex physiological system, and detailed analyses of internal dynamic coordination of subsystems become possible. During phase transitions of the functional organization (a) the rhythms of the central neuronal activities and the peripheral systems are altered, (b) changes in the coupling between CBS neurons and cardiovascular signals, respiration and the EEG, and (c) between NTS neurons (influenced by baroreceptor afferents) and CBS neurons occur, and (d) the processing of baroreceptor input at the NTS neurons changes. The results of this complex analysis, which could not be done formerly in this manner, confirm and complete former investigations on the dynamic organization of the CBS with its changing relations to peripheral and other central nervous subsystems.

Action Potentials↗

PubMed2000

Nonstationary time-series analysis applied to investigation of brainstem system dynamics.

Previous investigations of the dynamic organization of the lower brainstem and its relation to peripheral and other central nervous systems were predominantly performed by linear methods. These are based on time-averaging algorithms, which merely can be applied to stationary signal intervals. Thus, the current concept of the common brainstem system (CBS) in the reticular formation (RF) of the lower brainstem and basic types of its functional organization have been developed. Here, we present experiments where neuronal activities of the RF and the nucleus tractus solitarii (NTS, first relay station of baroreceptor afferents) were recorded together with related parameters of electroencephalogram (EEG), respiration, and cardiovascular system. The RF neurons are part of the CBS, which participates in regulation and coordination of cardiovascular, respiratory, and motor systems, and vigilance. The physiological time series, thus acquired, yield information about the internal dynamic coordination of the participating regulation processes. The major problem in evaluating these data is the nonlinearity and nonstationarity of the signals. We used a set of especially designed time resolving methods to evaluate nonlinear dynamic couplings in the interaction between CBS neurons and cardiovascular signals, respiration and the EEG, and between NTS neurons (influenced by baroreceptor afferents) and CBS neurons.

Algorithms↗

PubMed1999

Interbeat interval variability in isolated working rat hearts at various dynamic conditions and temperatures.

This study quantifies the effect of afterload and preload changes and of temperature on interbeat interval variability of the intact isolated heart. Ventricular pressure pulse records were obtained from isolated working rat hearts. The variability of interbeat intervals (BIs) was quantified by C90, the central 90% range of the BIs during 10 min periods; predominant frequencies were searched for by power spectral analysis. At 37 degrees C the BI lengths oscillated pseudo-randomly with BI variability C90< or =4 ms. Alternating signs of consecutive BI differences were predominant, and no peaks. were seen in the power spectra. Changes in end-diastolic and aortic pressure had little effect. From 37 degrees C down to 27 degrees C the variability increased about sevenfold, run phase length became randomly distributed, and individual, time-variant peaks occurred in the power spectra. BI variability vanished during atrial pacing. We conclude that: (1) effective mutual synchronization with minimal fluctuation happens within the sino-atrial node of intact rat hearts at body temperature, and synchronization is not affected even by extreme changes in pre- and afterload, (2) the sino-atrial node is the sole source of BI variability in the intact isolated rat heart, (3) low temperature hampers this functional organization which can be reestablished by sinus node accelerating agents (isoprenaline, theophylline), (4) decreasing frequency by N6-Cyclopentyladenosine at normothermia also increases BI variability but less pronouncedly than hypothermia does.

Adenosine↗

PubMed1998

Simultaneous changes of rhythmic organization in brainstem neurons, respiration, cardiovascular system and EEG between 0.05 Hz and 0.5 Hz.

Several neurons from different regions of the brainstem of anesthetized dogs were simultaneously recorded, together with various parameters of the cardiovascular system, respiration, efferent sympathetic neural activities and cortical activity. Often rhythmic changes of activity in the range 0.05-0.5 Hz could be observed in the simultaneously recorded signals. The rhythms were analysed in time domain and by power spectra and their changes depicted over the time. The most striking rhythms between 0.05 Hz and 0.5 Hz are the respiratory rhythm and those rhythms that originate in reticular neurons of the common brainstem system as well as their respective harmonics, i.e. the ranges around the integer multiple frequencies of these basic rhythms. The observed oscillations can vanish and reappear at times. Frequencies of basic oscillations and harmonics and their amplitudes are subject to distinct slow modulations. These modulations can have irregular as well as regular courses. The different rhythms can appear separately or simultaneously in the single signals. The most important phenomenon to be observed is that the rhythms mutually influence their frequencies, which follows the rules of 'relative coordination' as described by E. v. Holst. Such changes of rhythmic activities generally also concern the ranges of harmonics of the basic rhythms. Rhythmic influences on peripheral functional systems, e.g. the cardiovascular system, are most distinct at times when the different rhythms overlap in their frequency ranges. This holds not only for the ranges of basic frequencies, but also for the ranges of their harmonics. Further it was found that rhythms with the same basic frequencies may not only appear simultaneously, but also at various times in the different functional systems. The temporal course of changes of these rhythms, their interactions and their influence on the processing of cardiac rhythmic neuronal discharge patterns is demonstrated. The meaning of the mutually influencing rhythms for the functional organization of central nervous structures is discussed.

Animals↗

PubMed1997

Influences of mandatory breathing on rhythmical components of electrodermal activity.

We investigated whether rhythmical components of electrodermal activity (EDA) can be influenced by voluntary modification of the respiratory frequency. Fifty-five volunteers participated in an experiment with nine mandatory sections of cycle times between 3.1 s and 12.2 s. The cycle time of the rhythmical EDA components often differed considerably from respiratory cycle time. ANOVA yielded that both cycle time and position within the section had an effect on the EDA power of the mandatory cycles (P < 0.05). No significant interaction between effects of section and of position was discovered (P > 0.1). A separate analysis of the cycle times of the rhythmical EDA components revealed integer relationship with the respiratory cycle times. Thus, voluntary changes in the respiratory frequency can influence occurrence and cycle time of rhythmical EDA components in a way similar to sliding coordination in the sense of E. von Holst.

Adult↗

PubMed1996

Relationship between rhythmic discharge patterns of neurons in the central nucleus of the amygdala, blood pressure fluctuations and cortical activity.

In the discharge sequences recorded from single neurons in the central nucleus of the amygdala of chronically instrumented awake cats, rhythmical patterns with period durations of 5-12 s were observed. At the same time blood pressure and the degree of synchronisation of the EEG showed similar period fluctuations with positive correlation to neuronal activity. It is proposed that the central amygdaloid nucleus uses rhythmic patterns to coordinate somatomotor and vegetative systems.

Amygdala↗

PubMed1996

Convergence of visceral and somatic afferents on single neurones in the reticular formation of the lower brain stem in dogs.

The reticular formation of the lower brain stem contains neuronal circuits for the generation of sympathetic tone, respiratory rhythm, muscle tone and the control of vigilance. In anesthetized dogs single neurone activities were recorded in the medial two-thirds of the reticular formation to investigate the organizing principles of this multifunctional system. The results from 110 recordings demonstrate that single neurones receive information from somatosensory afferents of skin, joints and muscles together with afferents from baro-, chemo- and lung inflation and deflation receptors. Whereas the composition of afferent spectra from somatosensory sources was different from neurone to neurone, baroreceptors had a more generalized activity-decreasing effect and chemoreceptors had a generalized activity-increasing influence, the former directing physiological systems to a trophotropic and the latter towards an ergotropic state. The functional significance of the results for the co-ordination of different physiological systems is discussed.

Afferent Pathways↗

PubMed1996

Electrodermal activity reveals respiratory and slower rhythms of the autonomic nervous system.

Electrodermal Activity (EDA) was measured in 55 subjects during (1) an alarm reaction, (2) mental load, and (3) physical load. In 34 subjects, not only was a transient response observed, but also, oscillatory patterns characterizing short term variations of EDA. The durations of these oscillations varied between 3-16 s. Most commonly, they were approximately within the frequency range of respiration, or lower, at about 0.1 Hz. The EDA-rhythms were also related to the arterial blood pressure. They were, however, not strictly synchronized with respiration or with the blood pressure waves. We conclude that assessment of EDA in combination with fluctuations of the heart rate, and also, if possible, arterial blood pressure, may turn out to be a useful tool in the evaluation of the interaction between different regulatory processes that are realized by the common brainstem system.

Acoustic Stimulation↗

PubMed1995

Cardiac rhythmic patterns in neuronal activity are related to the firing rate of the neurons: I. Brainstem reticular neurons of dogs.

Cardiac rhythmic discharge patterns (CRDP) of brainstem reticular neurons in anesthetized dogs were estimated by ECG-triggered post-event-time histograms (PETH). Modulations of the CRDP occur, whenever the firing levels of the neurons slowly change with periods longer than the cardiac cycle. Therefore, in the activity of one and the same neuron different types of CRDP can occur interlaced in time. 'Partial' PETHs calculated according to the discharge level of the neurons make these various CRDP obvious. On the other hand, the CRDP are not always so clear in the 'total' PETHs, taken from the continuous periods of activity. The meaning of these different CRDP for regulatory processes of the organism is discussed. We study the processing of the easily identifiable signal in neuron activity, i.e., cardiac rhythm, to illustrate how signal processing depends on the momentary activity level of the neurons which is influenced by other afferent signals and by inflows from central structures reaching the neurons.

Animals↗

PubMed1995

Cardiac rhythmic patterns in neuronal activity related to the firing rate of the neurons: II. Amygdala neurons of cats.

Neurons of the central and basal part of the amygdala complex were recorded in conscious, freely moving cats. These neurons have various cardiac rhythmic discharge patterns (CRDPs) which are estimated by post-event-time histograms (PETH). When the firing level of the neurons changed, the CRDPs were modulated. These modulations became obvious, when 'partial' PETHs of the neuronal activity were constructed according to the discharge level of the neurons. With changes of the neuronal discharge level different types of CRDPs were observed, interlaced in time during recordings of the same neuron. In 'total' PETHs, taken from the continuous periods of neuronal activity, cardiac rhythm was hidden or often was not so clearly visible as in 'partial' PETHs, taken at different discharge levels. As in case of neurons of the nucleus tractus solitarii (NTS) and for brainstem reticular neurons, amygdala neurons exhibited modulations of CRDPs as their activity level changed. The results indicate that the processing of activity patterns in these neurons depends on their activity level and functional organization, which is essentially dependent on afferent signals and influences from central structures reaching these neurons.

Amygdala↗

PubMed1992

Different modes of dampening influence from baroreceptors are determined by the functional organization of the NTS neuronal network.

Simultaneous recordings of several neurones of the first relay station of baroreceptor afferents show that its general activity-dampening influence is realized via the common brainstem system (CBS) which itself controls the processing on the neurones of the nucleus of the solitary tract (NTS). This feedback system maintains the degree of activity which is necessary for the ongoing behaviour as long as it fits to the environmental situation. The output of the NTS is determined partly by the CBS, partly by the properties of the peripheral afferent input, partly by the dynamic functional organization of the local circuits and partly by influences from other brain areas.

Action Potentials↗

PubMed1987

Amygdala neurons influence cardiovascular reactions preceding psychomotor behavior.

In unanesthetized chronically instrumented cats single neuron discharges were recorded in the amygdaloid complex together with blood pressure, heart rate (HR), EEG, and motor activity. In response to complex sensory stimuli neuronal activity changed followed by blood pressure changes preceding the arousal reaction. Besides the impact of neuronal discharges on the cardiovascular system, the neurons in turn received an input from the cardiovascular system. It is hypothesized that an exaggerated reactivity of amygdala neurons to complex sensory stimuli can lead to high blood pressure.

Amygdala↗

PubMed1985

Reticular formation of the lower brainstem. A common system for cardio-respiratory and somatomotor functions. Cross-correlation analysis of discharge patterns of neighbouring neurones.

Temporal relations of discharges of 73 pairs of neurones located in the medial parts of the reticular formation of the lower brainstem were studied by cross correlation analyses in chloralose-urethane anaesthetized dogs. The action potentials of 2 or 3 neighbouring neurones were recorded with one electrode simultaneously. Uncorrelated discharges of neurones and 4 different types of correlated discharges were observed in cross correlation histograms: they were: (1) rhythmic couplings with frequencies between 2 and 5 Hz related to the same rhythm in the EEG; (2) strong, non-rhythmic couplings with short latencies up to 5 ms; (3) a combination of strong and rhythmic couplings, and (4) high-frequency oscillation couplings. Most pairs of neurones showed different types of correlation during the recordings. The different forms of correlated discharge behaviour could be related to different types of functional organization of the neuronal network in the reticular formation.

Afferent Pathways↗

PubMed1985

Reticular formation of the lower brainstem. A common system for cardio-respiratory and somatomotor functions. Considerations aided by computer simulations.

Parallel investigations were done using the reticular formation of the lower brainstem of dogs and computer simulated neuronal networks with properties of reticular neurones. By the aid of the simulations, understanding of the functional organisation of the common brainstem system, reticular formation and the experiments performed were optimized. The fact that discharge sequences of model neurones are very similar to those of reticular neurones was proved by interval histograms and covariance histograms. Discharges of neighbouring reticular neurones tend to be strongly coupled. In the model the discharges of the neurones could be coupled by common afferent inflows. Physiologically, neighbouring reticular neurones receive common afferents from peripheral somato-sensory systems. Neighbouring neurones with strongly coupled discharging are organized in subpopulations. The configurations of the subpopulations are determined by number and type of afferents actively influencing neurones and by the level of intrinsic activity of the network. Signal processing and transfer by neuronal subpopulations depend on the level of activity and on the degree of coupled discharging, i.e. the local organisation of the neurones.

Afferent Pathways↗

PubMed1983

Reticular formation of the lower brainstem. A common system for cardiorespiratory and somatomotor functions: discharge patterns of neighboring neurons influenced by cardiovascular and respiratory afferents.

Experiments were done in dogs with chloralose-urethane anesthesia. Long-lasting extracellular recordings were made from the medial parts of the reticular formation of the lower brainstem for up to 250 min. The study is based on reactions of 103 neurons. The activities of 2 or 3 neighbouring neurons recorded under identical conditions with one electrode or of neurons recorded with two electrodes at the same time could be changed regularly and synchronously by experimental changes of hemodynamic or ventilatory parameters. Action potentials were separated by amplitude discrimination. Rhythmic pulsatile modulations were proved to be present in 78% of all neurons by post-event-time histograms triggered by the R-wave of the ECG. In the 96 neurons tested 86% changed their activity when arterial pressure was raised by inflating a balloon in the abdominal aorta (79% decreased and 7% increased their activity). In post-event-time histograms triggered by the start of inspiration, 83% of the neurons showed modulations of their activity with respiratory rhythm. Experimental lung inflation decreased the activity in 75% of the tested neurons, while experimental lung deflation activated 47% of the tested neurons. Stimulation of arterial chemoreceptors activated 77% of the tested neurons. It was thus demonstrated that receptors in the cardiovascular and respiratory systems exert an influence on nearly all neurons from which recordings were made in that part of the reticular formation. Arterial baroreceptors and lung stretch receptors revealed a generalized depressing effect on the neuronal activity while chemoreceptors exert a generalized augmenting effect. At different times of recording these neurons did not always react to the same extent to comparable stimulations of afferents.

Action Potentials↗

PubMed1983

Reticular formation of the lower brainstem. A common system for cardiorespiratory and somatomotor functions: discharge patterns of neighboring neurons influenced by somatosensory afferents.

Extracellular recordings were made from 103 neurons located in the medial parts of the reticular formation of the lower brainstem of chloralose-urethane anesthetized dogs. Activities of 2 or 3 neighbouring neurons under identical conditions could be recorded with one electrode. In 9 recordings it was possible to register simultaneously up to 5 neurons with two electrodes placed in both halves of the medulla. Action potentials of individual neighbouring neurons were identified by amplitude discrimination. The influences of somatosensory afferents from skin, joints and muscles on neuronal discharge patterns were tested. Responses of single neurons were characterized by multisensory afferent spectra including afferents from various parts of the body. The combinations of afferents converging onto neighbouring neurons were similar, whereas neurons in more distant parts of the medulla revealed different combinations of converging afferents. In long-lasting recordings the influence of somatosensory afferents on the discharge behaviour changed from time to time. When the discharge behaviour was mainly determined by somatosensory afferents, neighbouring neurons were shown to be organized in sub-populations. The results led to the conclusion that in this part of the reticular formation different types of functional organization of the neuronal network are possible. The type of functional organization depends on the actual preponderances of different inputs to the neurons.

Animals↗

PubMed1981

Central control and interactions affecting sympathetic and parasympathetic activity.

Current thinking concerning the central control of the autonomic nervous system and the central interactions affecting sympathetic and parasympathetic activity is presented. Among the questions discussed are the following: are there neurons within the common brain stem system which exert an influence on preganglionic parasympathetic neurons and can they be differentiated from neurons which affect sympathetic preganglionic neuron functions? What interactions occur between sympathetic and parasympathetic tone-mediating neurons? In discussing these problems information is presented as obtained by recording from reticular formation (RF) neurons with discharge patterns similar to efferent parasympathetic activity. The general conclusion reached is that there is a common central control; interactions occur in the brain stem as well as peripherally; depending on the functional situation, these two systems can be organized to act either reciprocally or non-reciprocally.

Afferent Pathways↗

PubMed1977

Postganglionic sympathetic activity with correlation to heart rhythm and central cortical rhythms.

1. Renal sympathetic nerve activity, ECG and parieto-occipital EEG were recorded in dogs anaesthetized with chloralose. The carotid sinus nerves were cut. Autocovariance functions and power spectra for these variables were computed. 2. During cooling of the vagus nerves, the integrated renal sympathetic activity exhibited rhythms which were correlated to the delta-theta rhythm of the EEG. This rhythm was also present with the vagus nerves functionally intact, but a cardiac rhythm was dominant. 3. Blood pressure-dependent neurones in the lower brain stem reticular formation have both cardiac and central cortical rhythms. This provides a hint that these neurones might be involved in the sympathetic tone generating network.

Animals↗