Cardiorespiratory Response to Moderate Hypercapnia in Female College Students Expressing Behaviorally Inhibited Temperament.

Behaviorally inhibited (BI) temperament is marked by heightened behavioral sensitivity to environmental threats. The degree to which threat sensitivity is reflected in cardiorespiratory responses has been relatively unexplored. Female college students were exposed to modest hypercapnia (7.0% CO2) or ambient air (AA) while engaging in a computerized task with cued reinforcement features. All physiological variables except for blood pressure were processed in 4 min epochs corresponding to pre-exposure, exposure, and post-exposure. Primary respiratory measures were respiratory frequency (fb), tidal volume (VT), and minute ventilation (VE). Electrocardiograms (ECGs) were processed using ARTiiFACT software with resultant heart rate variability (HRV) measures in the frequency domain and time domain. Consistent with the literature, modest hypercapnia increased VT, Fb, and VE. No differences in respiratory parameters were detected between BI and non-behaviorally inhibited individuals (NI). For HRV in the time domain, RMSSD and NN50 values increased during CO2 inhalation which then returned to pre-exposure levels after CO2 cessation. Hypercapnia increased high frequency (HF) power which then recovered. BI exhibited reduced low frequency (LF) power during the pre-exposure period. For NI, LF power reduced over the subsequent phases ameliorating differences between BI and NI. Hypercapnia improved the task performance of BI. This is the largest study of female reactivity to hypercapnia and associated HRV to date. In general, hypercapnia increased time domain HRV and HF power, suggesting a strong vagal influence. Those expressing BI exhibited similar respiratory and HRV reactivity to NI despite inherently reduced LF power. Although 7% CO2 represents a mild challenge to the respiratory and cardiovascular systems, it is nonetheless sufficient to explore inherent difference in stress reactivity in those vulnerable to develop anxiety disorders.

Genetic mutation of Kcnj16 identifies Kir5.1-containing channels as key regulators of acute and chronic pH homeostasis.

Acute and chronic homeostatic pH regulation is critical for the maintenance of optimal cellular function. Renal mechanisms dominate global pH regulation over longer time frames, and rapid adjustments in ventilation compensate for acute pH and CO2 changes. Ventilatory CO2 and pH chemoreflexes are primarily determined by brain chemoreceptors with intrinsic pH sensitivity likely driven by K+ channels. Here, we studied acute and chronic pH regulation in Kcnj16 mutant Dahl salt-sensitive (SS Kcnj16-/-) rats; Kcnj16 encodes the pH-sensitive inwardly rectifying K+ 5.1 (Kir5.1) channel. SS Kcnj16-/- rats hyperventilated at rest, likely compensating for a chronic metabolic acidosis. Despite their resting hyperventilation, SS Kcnj16-/- rats showed up to 45% reduction in the ventilatory response to graded hypercapnic acidosis vs. controls. SS Kcnj16-/- rats chronically treated with bicarbonate or the carbonic anhydrase inhibitor hydrochlorothiazide had partial restoration of arterial pH, but there was a further reduction in the ventilatory response to hypercapnic acidosis. SS Kcnj16-/- rats also had a nearly absent hypoxic ventilatory response, suggesting major contributions of Kir5.1 to O2- and CO2-dependent chemoreflexes. Although previous studies demonstrated beneficial effects of a high-K+ diet (HKD) on cardiorenal phenotypes in SS Kcnj16-/- rats, HKD failed to restore the observed ventilatory phenotypes. We conclude that Kir5.1 is a key regulator of renal H+ handling and essential for acute and chronic regulation of arterial pH as determinants of the ventilatory CO2 chemoreflex.-Puissant, M. M., Muere, C., Levchenko, V., Manis, A. D., Martino, P., Forster, H. V., Palygin, O., Staruschenko, A., Hodges, M. R. Genetic mutation of Kcnj16 identifies Kir5.1-containing channels as key regulators of acute and chronic pH homeostasis.

Strain differences in pH-sensitive K+ channel-expressing cells in chemosensory and nonchemosensory brain stem nuclei.

The ventilatory CO2 chemoreflex is inherently low in inbred Brown Norway (BN) rats compared with other strains, including inbred Dahl salt-sensitive (SS) rats. Since the brain stem expression of various pH-sensitive ion channels may be determinants of the CO2 chemoreflex, we tested the hypothesis that there would be fewer pH-sensitive K(+) channel-expressing cells in BN relative to SS rats within brain stem sites associated with respiratory chemoreception, such as the nucleus tractus solitarius (NTS), but not within the pre-Bötzinger complex region, nucleus ambiguus or the hypoglossal motor nucleus. Medullary sections (25 µm) from adult male and female BN and SS rats were stained with primary antibodies targeting TASK-1, Kv1.4, or Kir2.3 K(+) channels, and the total (Nissl-stained) and K(+) channel immunoreactive (-ir) cells counted. For both male and female rats, the numbers of K(+) channel-ir cells within the NTS were reduced in the BN compared with SS rats (P < 0.05), despite equal numbers of total NTS cells. In contrast, we found few differences in the numbers of K(+) channel-ir cells among the strains within the nucleus ambiguus, hypoglossal motor nucleus, or pre-Bötzinger complex regions in both male and female rats. However, there were no predicted functional mutations in each of the K(+) channels studied comparing genomic sequences among these strains. Thus we conclude that the relatively selective reductions in pH-sensitive K(+) channel-expressing cells in the NTS of male and female BN rats may contribute to their severely blunted ventilatory CO2 chemoreflex.

The carotid chemoreceptors are a major determinant of ventilatory CO2 sensitivity and of PaCO2 during eupneic breathing.

Both carotid and intracranial chemoreceptors are critical to a normal ventilatory CO2-H+ chemosensitivity. At low levels of hypercapnia, the carotid contribution is probably greater than the central contribution but, at high levels, the intracranial chemoreceptors are dominant. The carotid chemoreceptors are also critical to maintaining a stable and normal eupneic PaCO2, but lesion-induced attenuation of intracranial CO2-H+ chemosensitivity does not consistently alter eupneic PaCO2. A major unanswered question is why do intracranial chemoreceptors in carotid body denervation (CBD) animals tolerate an acidosis during eupnea which prior to CBD elicits a marked increase in breathing.

Effects of vitamin E and C supplementation either alone or in combination on exercise-induced lipid peroxidation in trained cyclists.

Seven trained male cyclists (ate 22.3 +/- 2 years) participated in 4 separate supplementation phases. They ingested 2 capsules per day containing the following treatments: placebo (placebo plus placebo); vitamin C (1 g per day vitamin C plus placebo); vitamin C and E (1 g per day vitamin C plus 200 IU per kg vitamin E); and vitamin E (400 IU per kg vitamin E plus placebo). The treatment order (placebo, vitamin C, vitamin C and E, and vitamin E) was the same for all subjects. Performance trials consisting of a 60-minute steady state ride (SSR) and a 30-minute performance ride (PR) on Cybex 100 Metabolic cycles were performed after each trial. Workloads of 70% of the VO2max were set for the SSR and PR rides, with pedal rate maintained at 90 rpm (SSR) or self determined (PR). Blood samples (5 ml) were drawn pre- and postexercise and analyzed for malonaldehyde (MDA) and lactic acid. The results indicate that vitamin E treatment was more effective than vitamin C alone or vitamin C and E. Pre-exercise plasma levels of MDA in the vitamin E trial was 39% below the pre-exercise MDA levels of the placebo: 2.94 +/- 0.54 and 4.81 +/- 0.65 micromol per ml, respectively. Plasma MDA following exercise in the vitamin E group was also lower than teh placebo: 4.32 +/- 0.37 vs 7.89 +/- 1.0 micromol per ml, respectively. Vitamin C supplementation, on the other hand, elevated both the resting and exercise plasma levels of MDA. None of th supplemental phases had any significant effect on performance. In conclusion, the results indicate that 400 IU/day of vitamin E reduces membrane damage more effectively than vitamin C but does not enhance performance. Athletes are encouraged to include antioxidants, such as vitamin E and C, in their diet to counteract these detrimental effects of exercise. The data presented here suggests that 400 IU/day of vitamin E will provide adequate protection but supplementing the diet with 1 g per day of vitamin C may promote cellular damage. However neither of these vitamins, either alone or in combination, will enhance exercise performance.

Perturbations in three medullary nuclei enhance fractionated breathing in awake goats.

Our aim was to determine the frequency and characteristics of a fractionated pattern of diaphragm and upper airway muscle activity and airflow during wakefulness and sleep in adult goats. A fractionated breath (FBr) was defined as three or more brief (40-150 ms) interruptions in the diaphragm activity not associated with multiple swallows, eructation, mastication, or movement. During a FBr, the discharge pattern in the diaphragm and upper airway muscles showed complete cycles of inspiration and expiration. Whereas the interval between peak diaphragm activity of the breath preceding the FBr to the first diaphragm peak of the FBr was 15-20% less than the average interval of the preceding five control breaths, the breath-to-breath interval of the five breaths after a FBr did not differ from the control breaths before the FBr event. In normal goats, FBr was evident in only 4 of 18 (22%) awake goats and in only one of these goats during non-rapid eye movement sleep. In 35 goats with implanted microtubules in the medulla, FBr were present in 14 (40%) goats. In these goats with FBr, 78% (11 of 14) had one or more implantations into or near the facial, vestibular, or raphe nuclei. The effect of perturbations in these nuclei is probably nonspecific, because injections into these nuclei with mock cerebrospinal fluid or excitatory amino acid-receptor agonist or antagonist produced both increases and decreases in the frequency of the FBr while not altering their characteristics. Finally, a swallow occurred at the termination or during the first breath after 60% of the FBr. We speculate that the FBr manifest 1) the disruption of a neuronal network, which coordinates breathing and other functions (such as swallowing), utilizing the same anatomic structures, and/or 2) transient changes in synaptic inputs that increase the rate of the normal respiratory rhythm generator or allow an ectopic, anomalous generator to become dominant.

Contributions from rostral medullary nuclei to coordination of swallowing and breathing in awake goats.

The purpose of this study was to determine whether neurons in the facial (FN), gigantocellularis reticularis (RGN), and vestibular (VN) nuclei contribute to the regulation of breathing, swallowing, and the coordination of these two functions. Microtubules were chronically implanted bilaterally in goats. Two weeks later during wakefulness, 100-nl unilateral injections were made of mock cerebral spinal fluid or an excitatory amino acid receptor agonist or antagonists. When the agonist, N-methyl-D-aspartic acid, was injected into any nuclei, breathing and swallowing increased transiently (15-30%; P < 0.05), whereas only injections of the antagonist 2,3-dihydroxy-6-nitro-7-sulfamoylbenzo-(f)quinoxaline into VN increased swallowing (20%; P < 0.05). The phase of breathing in which the swallows occurred was not altered by any injections. However, more importantly, injections of the agonist and the antagonists significantly altered (P < 0.05) by 5-50% the respiratory phase-dependent timing and tidal volume effect of swallows on breathing relative to mock cerebral spinal fluid injections. In addition, these effects were not uniform for all three nuclei. We conclude that the FN, RGN, and VN are part of a neural circuit in the rostral medulla that regulates and/or modulates breathing, swallowing, and their coordination in the awake state.

Effects of spontaneous swallows on breathing in awake goats.

The effects of spontaneous swallows on breathing before, during, and after solitary swallows were investigated in 13 awake goats. Inspiratory (TI) and expiratory (TE) time and respiratory output were determined from inspiratory airflow [tidal volume (VT)] and peak diaphragmatic activity (Dia(peak)). The onset time for 1,128 swallows was determined from pharyngeal muscle electrical activity. During inspiration, the later the swallowing onset, the greater increase in TI and VT, whereas there was no significant effect on TE and Dia(peak). Swallows in early expiration increased the preceding TI and reduced TE, whereas later in expiration swallows increased TE. After expiratory swallows, TI and VT were reduced whereas minimal changes in Dia(peak) were observed. Phase response analysis revealed a within-breath, phase-dependent effect of swallowing on breathing, resulting in a resetting of the respiratory oscillator. However, the shift in timing in the breaths after a swallow was not parallel, further demonstrating a respiratory phase-dependent effect on breathing. We conclude that, in the awake state, within- and multiple-breath effects on respiratory timing and output are induced and/or required in the coordination of breathing and swallowing.