Strong-meter and weak-meter rhythm identification in spina bifida meningomyelocele and volumetric parcellation of rhythm-relevant cerebellar regions.

Children with spina bifida meningomyelocele (SBM) are impaired relative to controls in terms of discriminating strong-meter and weak-meter rhythms, so congenital cerebellar dysmorphologies that affect rhythmic movements also disrupt rhythm perception. Cerebellar parcellations in children with SBM showed an abnormal configuration of volume fractions in cerebellar regions important for rhythm function: a smaller inferior-posterior lobe, and larger anterior and superior-posterior lobes.

Respiratory rhythm generation: A modeling study of the respiratory central pattern generator and the phrenic motor neuron

The respiratory central pattern generator is a collection of medullary neurons that generates the rhythm of respiration. The respiratory central pattern generator feeds phrenic motor neurons, which, in turn, drive the main muscle of respiration, the diaphragm. The purpose of this thesis is to understand the neural control of respiration through mathematical models of the respiratory central pattern generator and phrenic motor neurons. ^ We first designed and validated a Hodgkin-Huxley type model that mimics the behavior of phrenic motor neurons under a wide range of electrical and pharmacological perturbations. This model was constrained physiological data from the literature. Next, we designed and validated a model of the respiratory central pattern generator by connecting four Hodgkin-Huxley type models of medullary respiratory neurons in a mutually inhibitory network. This network was in turn driven by a simple model of an endogenously bursting neuron, which acted as the pacemaker for the respiratory central pattern generator. Finally, the respiratory central pattern generator and phrenic motor neuron models were connected and their interactions studied. ^ Our study of the models has provided a number of insights into the behavior of the respiratory central pattern generator and phrenic motor neurons. These include the suggestion of a role for the T-type and N-type calcium channels during single spikes and repetitive firing in phrenic motor neurons, as well as a better understanding of network properties underlying respiratory rhythm generation. We also utilized an existing model of lung mechanics to study the interactions between the respiratory central pattern generator and ventilation. ^

CIRCADIAN RHYTHM IN THE BIOAVAILABILITY OF ORALLY ADMINISTERED THEOPHYLLINE

The effect of time (i.e., biologic time structure) of drug administration on the bioavailability of theophylline was investigated in man after both a single dosage as well as after repeated, or chronic, drug administrations. Preliminary laboratory investigations on Balb-C mice showed the toxic

Biomarker circadian rhythm profiles in critically ill mechanically ventilated patients

Objective: To explore the natural trajectory of core body temperature (CBT) and cortisol (CORT) circadian rhythms in mechanically ventilated intensive care unit (MV ICU) patients. ^ Design: Prospective, observational, time-series pilot study. ^ Setting: Medical-surgical and pulmonary ICUs in a tertiary care hospital. ^ Sample: Nine (F = 3, M = 6) adults who were mechanically ventilated within 12 hrs of ICU admission with mean ± SD age of 65.2 ± 14 years old. ^ Measurements: Core body temperature and environmental measures of light, sound, temperature, and relative humidity were logged in 1-min intervals. Hourly urine specimens and 2-hr interval blood specimens were collected for up to 7 consecutive days for CORT assay. Mechanical ventilation days, ICU length of stay, and ICU mortality were documented. Acute Physiology and Chronic Health Evaluation (APACHE) II scores were computed for each study day. The data of each biologic and environmental variable were analyzed using single cosinor analysis of 24-hr serial segments. One patient did not complete the study because mortality occurred within 8 hrs of enrollment. Nine ICU patients completed the study in 1.6 to 7.0 days. ^ Results: No normal circadian rhythm pattern was found when the cosinor-derived parameters of amplitude (one-half the peak-trough variability) and acrophase (peak time) were compared with cosinor-derived parameter reference ranges of healthy, diurnally active humans, although 83% of patient-day CBT segments showed statistically significant (p ≤ .05) and biologically meaningful (R2≥ 0.30) 24-hr rhythms with abnormal cosinor parameters. Cosinor parameters of the environmental temporal profiles showed 27% of light, 76% of ambient temperature, and 78% of relative humidity serial segments had a significant and meaningful 24-hr diurnal pattern. Average daily light intensity varied from 34 to 187 lx with a maximum light exposure of 1877 lx. No sound measurement segment had a statistically significant cosine pattern, and numerous 1-minute interval peaks ≥ 60 dB occurred around the clock. Average daily ambient temperature and relative humidity varied from 19 to 24°C and from 25% to 61%, respectively. There was no statistically significant association between CBT or clinical outcomes and cosinor-derived parameters of the environmental variables. Circadian rhythms of urine and plasma CORT were deferred for later analysis. ^ Conclusions: The natural trajectory of the CBT circadian rhythm in MV ICU patients demonstrated persistent cosinor parameter alteration, even when a significant and meaningful 24-hr rhythm was present. The ICU environmental measures showed erratic light and sound exposures. Room temperature and relative humidity data produced the highest rate of significant and meaningful diurnal 24-hr patterns. Additional research is needed to clarify relations among the CBT biomarker of the circadian clock and environmental variables of MV ICU patients. ^

Circadian rhythm profiles in porcine ICU subjects

Purpose: To explore the natural trajectory of circadian rhythms of sedation requirement, core body temperature (CBT), pulmonary mechanics (PM), and gas exchange (GE) in mechanically ventilated swine, as these variables affect the duration of mechanical ventilation. ^ Design: A secondary analysis to describe and compare circadian rhythms of study variables in swine mechanically ventilated for ≤ 7 days. ^ Setting: Porcine Intensive Care Unit (ICU).^ Sample: Six male swine. ^ Methods: Sedation requirements were recorded hourly and the CBT, PM and GE variables were sampled every 1 s – 1 min for ≤ 7 days. The data sets for each pig with > 5 days ICU length of stay were divided into one section representing the first 3 days and one section representing subsequent days. The Lomb periodogram was used to estimate the circadian time period for each variable, and cosinor analysis with the estimated time period to obtain amplitude and mesor. Circadian to ultradian bandpower ratio to assess rhythm quality and stability over time and goodness-of-fit index to describe biological significance of a rhythm were used. Together, these two parameters were used to define rhythm robustness over time. The masking effect of sedation as a potential confounder of the circadian rhythms of CBT, PM, and GE was explored, and circadian rhythm profiles of CBT of pigs in the ICU setting were compared with those of the same pigs in the ambulatory setting. ^ Results: All pigs had significant rhythms in CBT, respiratory rate, and peripheral oxygen saturation across ICU data sets. Healthier pigs had more robust rhythms of study variables over time. Sedation did not appear to mask the circadian rhythms of CBT, PM, and GE. The circadian rhythm of CBT was less robust in the ICU setting than in the ambulatory setting. ^ Conclusions: Individual subject observations provided preliminary evidence that robustness of rhythms varies with subject acuity. Comparison of profiles of circadian rhythms among ICU subjects with similar acuity and disease processes is warranted to determine if the profiles in the present study are reproducible. Identification of consistent patterns may provide insight into subject morbidity and timing of such therapeutic interventions as weaning from mechanical ventilation. ^

Simulation of Drosophila circadian oscillations, mutations, and light responses by a model with VRI, PDP-1, and CLK.

A model of Drosophila circadian rhythm generation was developed to represent feedback loops based on transcriptional regulation of per, Clk (dclock), Pdp-1, and vri (vrille). The model postulates that histone acetylation kinetics make transcriptional activation a nonlinear function of [CLK]. Such a nonlinearity is essential to simulate robust circadian oscillations of transcription in our model and in previous models. Simulations suggest that two positive feedback loops involving Clk are not essential for oscillations, because oscillations of [PER] were preserved when Clk, vri, or Pdp-1 expression was fixed. However, eliminating positive feedback by fixing vri expression altered the oscillation period. Eliminating the negative feedback loop in which PER represses per expression abolished oscillations. Simulations of per or Clk null mutations, of per overexpression, and of vri, Clk, or Pdp-1 heterozygous null mutations altered model behavior in ways similar to experimental data. The model simulated a photic phase-response curve resembling experimental curves, and oscillations entrained to simulated light-dark cycles. Temperature compensation of oscillation period could be simulated if temperature elevation slowed PER nuclear entry or PER phosphorylation. The model makes experimental predictions, some of which could be tested in transgenic Drosophila.

A reduced model clarifies the role of feedback loops and time delays in the Drosophila circadian oscillator.

Although several detailed models of molecular processes essential for circadian oscillations have been developed, their complexity makes intuitive understanding of the oscillation mechanism difficult. The goal of the present study was to reduce a previously developed, detailed model to a minimal representation of the transcriptional regulation essential for circadian rhythmicity in Drosophila. The reduced model contains only two differential equations, each with time delays. A negative feedback loop is included, in which PER protein represses per transcription by binding the dCLOCK transcription factor. A positive feedback loop is also included, in which dCLOCK indirectly enhances its own formation. The model simulated circadian oscillations, light entrainment, and a phase-response curve with qualitative similarities to experiment. Time delays were found to be essential for simulation of circadian oscillations with this model. To examine the robustness of the simplified model to fluctuations in molecule numbers, a stochastic variant was constructed. Robust circadian oscillations and entrainment to light pulses were simulated with fewer than 80 molecules of each gene product present on average. Circadian oscillations persisted when the positive feedback loop was removed. Moreover, elimination of positive feedback did not decrease the robustness of oscillations to stochastic fluctuations or to variations in parameter values. Such reduced models can aid understanding of the oscillation mechanisms in Drosophila and in other organisms in which feedback regulation of transcription may play an important role.

Intracranial EEG reveals a time- and frequency-specific role for the right inferior frontal gyrus and primary motor cortex in stopping initiated responses.

Inappropriate response tendencies may be stopped via a specific fronto/basal ganglia/primary motor cortical network. We sought to characterize the functional role of two regions in this putative stopping network, the right inferior frontal gyrus (IFG) and the primary motor cortex (M1), using electocorticography from subdural electrodes in four patients while they performed a stop-signal task. On each trial, a motor response was initiated, and on a minority of trials a stop signal instructed the patient to try to stop the response. For each patient, there was a greater right IFG response in the beta frequency band ( approximately 16 Hz) for successful versus unsuccessful stop trials. This finding adds to evidence for a functional network for stopping because changes in beta frequency activity have also been observed in the basal ganglia in association with behavioral stopping. In addition, the right IFG response occurred 100-250 ms after the stop signal, a time range consistent with a putative inhibitory control process rather than with stop-signal processing or feedback regarding success. A downstream target of inhibitory control is M1. In each patient, there was alpha/beta band desynchronization in M1 for stop trials. However, the degree of desynchronization in M1 was less for successfully than unsuccessfully stopped trials. This reduced desynchronization on successful stop trials could relate to increased GABA inhibition in M1. Together with other findings, the results suggest that behavioral stopping is implemented via synchronized activity in the beta frequency band in a right IFG/basal ganglia network, with downstream effects on M1.

Intracellular chemical messengers and neuronal function: Two examples

Two distinct classes of neurons have been examined in the nervous system of Aplysia. The membrane properties of these neurons are regulated by intracellular signalling molecules in both a short-term and a long-term fashion.^ The role of the phosphatidylinositol cycle in the control of neuronal properties was studied in a class of bursting pacemaker cells, the left upper-quadrant bursting neurons (cells L2, L3, L4, and L6) of the abdominal ganglion of Aplysia. These cells display a regular burst-firing pattern that is controlled by cyclic changes of intracellular Ca$\sp{2+}$ that occur during the bursting rhythm. The characteristic bursting pattern of these neurons occurs within a range of membrane potentials ($-35$ to $-50$ mV) called the pacemaker range. Intracellular pressure injection of inositol 1,4,5-trisphosphate (IP$\sb3$) altered the bursting rhythm of the bursting cells. Injection of IP$\sb3$ induced a brief depolarization that was followed by a long-lasting (2-15 min) hyperpolarization. When cells were voltage-clamped at potentials within the pacemaker range, injection of IP$\sb3$ generally induced a biphasic response that had a total duration of 2-15 min. An initial inward shift in holding current (I$\sb{\rm in}$), which lasted 5-120 sec, was followed by a slow outward shift in holding current (I$\sb{\rm out}$). At membrane potentials more negative than $-40$ mV, I$\sb{\rm in}$ was associated with a small and relatively voltage-independent increase in membrane conductance. I$\sb{\rm in}$ was not blocked by bath application of TTX or Co$\sp{2+}$. Although I$\sb{\rm in}$ was activated by injection of IP$\sb3$, it was not blocked by iontophoretic injection of ethyleneglycol-bis-(beta-aminoethyl ether), N, N$\sp\prime$-tetraacetic acid (EGTA) sufficient to block the Ca$\sp{2+}$-activated inward tail current (I$\sb{\rm B}$).^ Long-term (lasting at least 24 hours) effects of adenylate cyclase activation were examined in a well characterized class of mechanosensory neurons in Aplysia. The injected cells were analyzed 24 hours later by two-electrode voltage-clamp techniques. We found that K$\sp+$ currents of these cells were reduced 24 hours after injection of cAMP. The currents that were reduced by cAMP were very similar to those found to be reduced 24 hours after behavioral sensitization. These results suggest that cAMP is part of the intracellular signal that induces long-term sensitization in Aplysia. (Abstract shortened with permission of author.) ^

Temporal variations of dyspnea, fatigue, and lung function in chronic lung disease

Background. Research investigating symptom management in patients with chronic obstructive pulmonary disease (COPD) largely has been undertaken assuming the homeostatic construct, without regard to potential roles of circadian rhythms. Temporal relations among dyspnea, fatigue, peak expiratory flow rate (PEFR) and objective measures of activity/rest have not been reported in COPD. ^ Objectives. The specific aims of this study were to (1) explore the 24-hour patterns of dyspnea, fatigue, and PEFR in subjects with COPD; (2) examine the relations among dyspnea, fatigue, and PEFR in COPD; and (3) examine the relations among objective measures of activity/rest and dyspnea, fatigue, and PEFR in COPD. ^ Methods. The repeated-measures design involved 10 subjects with COPD who self-assessed dyspnea and fatigue by 100 mm visual analog scales, and PEFR by peak flow meter in their home 5 times a day for 8 days. Activity/rest was measured by wrist actigraphy. Single and population mean cosinor analyses and correlations were computed for dyspnea, fatigue, and PEFR; correlations were done among these variables and activity/rest. ^ Results. Circadian rhythms were documented by single cosinor analysis in 40% of the subjects for dyspnea, 60% for fatigue, and 60% for PEFR. The population cosinor analysis of PEFR yielded a significant rhythm (p < .05). The 8-day 24-hour means of dyspnea and fatigue was moderately correlated (r = .48, p < .01). Dyspnea and PEFR, and fatigue and PEFR, were weakly correlated in a negative way (r = −.11, p < .05 and r = −.15, p < .01 respectively). Weak to moderate correlations (r = .12–.34, p < .05) were demonstrated between PEFR and mean activity level measured up to 4 hours before PEFR measurement. ^ Conclusions. The findings suggest that (1) the dyspnea and fatigue experienced by COPD patients are moderately related, (2) there is a weak to modest positive relation between PEFR and activity levels, and (3) temporal variation in lung function may not affect the dyspnea and fatigue experienced by patients with COPD. Further research, examining the relations among dyspnea, fatigue, PEFR, and activity/rest is needed. Replication of this study is suggested with a larger sample size. ^

The chronobiology of the menstrual life sequence of American women

Seasonal variation in menarche, menstrual cycle length and menopause was investigated using Tremin Trust data. Too, self-reported hot flash data for women with natural and surgically-induced menopause were analyzed for rhythms.^ Menarche data from approximately 600 U.S. women born between 1940 and 1970 revealed a 6-month rhythm (first acrophase in January, double amplitude of 58%M). A notable shift from a December-January peak in menarche for those born in the 1940s and 1950s to an August-September peak for those born in the 1960s was observed. Groups of girls 8-14 and 15-17 yr old at menarche exhibited a seasonal difference in the pattern of menarche occurrence of about 6 months in relation to each other. Girls experiencing menarche during August-October were statistically significantly younger than those experiencing it at other times. Season of birth was not associated with season of menarche.^ The lengths of approximately 150,000 menstrual intervals of U.S. women were analyzed for seasonality. Menstrual intervals possibly disturbed by natural (e.g., childbirth) or other events (e.g., surgery, medication) were excluded. No 6- or 12-month rhythmicities were found for specific interval lengths (14-24, 25-31 and 32-56 days) or ages in relation to menstrual interval (9-11, 12-13, 15-19, 20-24, 25-39, 40-44 and 44 yr old and older).^ Hot flash data of 14 women experiencing natural menopause (NM) and 11 experiencing surgically-induced menopause (SIM) did not differ in frequency of hot flashes. Hot flashes in NM women exhibited 12- and 8-hr, but not 24-hr rhythmicities. Hot flashes in SIM women exhibited 24- and 12-hr, but not 8-hr, rhythmicities. Regardless of type of menopause, women with a peak frequency in hot flashes during the morning (0400 through 0950) were distinguishable from those with such in the evening (1600 through 2159).^ Data from approximately 200 U.S. women revealed a 6-month rhythm in menopause with first peak in May. No significant 12-month variation in menopause was detected by Cosinor analysis. Season of birth and age at menopause were not associated with season of menopause. Age at menopause declined significantly over the years for women born between 1907 and 1926, inclusive. ^

TEMPORAL VARIATION OF ACUTE AND LUNG TUMORIGENIC EFFECTS OF URETHAN ON STRAIN A MICE (CHRONOBIOLOGY, CARCINOGENICITY, ANESTHETIC, DNA SYNTHESIS)

The effect of circadian variation on susceptibility to the chemical induction of cancer was assessed utilizing the mouse pulmonary adenoma bioassay. Different groups of male A/Jax mice (standardized for rhythm analysis with light from 0600-1800 and darkness from 1800-0600) each received a single timed i.p. injection of urethan (Bioassay I: 0.25, 0.5 or 1.0 mg/g body weight; Bioassay II: 0.75, 1.0, 1.25 mg/g body weight; Bioassay III: 1.0 mg/g body weight) at the following times, 0100, 0500, 0900, 1300, 1700 or 2100. Mice were sacrificed 16 weeks after treatment. The tumorigenic effect of urethan on the lungs (lung surface pulmonary adenomas) was assessed. In addition, mortality, body weight changes and the anesthetic effect of urethan were determined. The rhythmic pattern of DNA synthesis in the lung and the comparative rhythmic pattern in the liver were assessed using a tritiated thymidine incorporation assay.^ In the first adenoma bioassay, the lung tumorigenic response in mice given the highest dose of urethan exhibited a 12-hour rhythm with a major peak in tumor yield at 0100 and a secondary peak at 1300; reduced yields occurred at 0500-0900 and 2100. The second adenoma bioassay, studied at a 6-month seasonal divergence in time from the first study showed a peak at 1300 but not at 0100. The mice from the third adenoma bioassay, studied at an 11-month seasonal divergence in time from the 2nd study showed an increase in tumor yield during the rest cycle (0900-1700).^ This study found a definite suggestion of a low amplitude rhythm in susceptibility to urethan induced effects. The acute toxic and pharmacological effects correlated to exhibit a maximal effect during dark hours (activity span). This rhythmicity might be explained by an alteration in the amplitude of hepatic metabolism. The chronic carcinogenic response exhibited an opposite pattern. Urethan induced tumor response was greater during daylight hours (rest cycle). This correlated with the slight elevation in DNA synthetic activity found in the lung and liver which might be responsible for the increase in carcinogenic response. (Abstract shortened with permission of author.) ^