Cholinergic mechanisms are known to play a key role in the regulation of breathing, but the distribution of muscarinic receptor (mAChR) subtypes has not been localized within brain stem respiratory nuclei. This study examined the hypothesis that mAChR subtypes are heterogeneously distributed across brain stem nuclei that control breathing. With the use of in vitro receptor autoradiography, the results provide the first selective labeling and quantitative mapping of M1, M2, and M3 mAChR subtypes in cat brain stem regions known to regulate breathing. Among brain stem nuclei known to contain respiratory-related neurons, the greatest amount of mAChR binding was measured in the lateral and medial parabrachial nuclei and the lateral nucleus of the solitary tract. Fewer mAChRs were localized in nuclei comprising the ventral respiratory group (nucleus ambiguous, retrofacial nucleus) and ventral medulla (retrotrapezoid nucleus and ventrolateral medulla). The data provide an essential first step for future studies aiming to specify the regulatory role of mAChR subtypes within brain stem respiratory nuclei.

No abstract

This study examined the effect of exercise mode and intensity on physiological and perceptual responses to exercise. Twelve active adults (6 men and 6 women, age 5 21.7 6 1.6 years) initially performed incremental testing on the treadmill (TM) and cycle ergometer (CE) to assess maximal oxygen uptake (V Ȯ2 max) and ventilatory threshold (VT). During the next 4 visits in a randomized order, subjects performed 20 minutes of moderate-intensity continuous exercise (MICE) at an intensity 20% below VT on the TM (TM MICE ) and cycle ergometer (CE MICE ) as well as time-matched high-intensity interval exercise (HIIE; 10 1-minute bouts at workload equal to 20% above VT followed by 1-minute active recovery) on both modes (TM HIIE and CE HIIE ). During exercise, gas exchange data, blood lactate concentration, and perceptual responses (rating of perceived exertion, affective valence, and enjoyment) were assessed. Heart rate (p , 0.001) and V Ȯ2 (p , 0.001) were higher in response to TM HIIE vs. CE HIIE as well as TM MICE vs. CE MICE . Blood lactate concentration was higher (p 5 0.003) in response to CE HIIE vs. TM HIIE . The rating of perceived exertion was significantly higher (p , 0.001) in TM MICE compared with CE MICE which showed the most positive affective valence (p 5 0.009). Enjoyment was similar across all bouts (p 5 0.11). Treadmill-based HIIE leads to higher heart rate and V Ȯ2 vs. CE HIIE , although there was no difference in affective valence or enjoyment. Practitioners aiming to optimize the cardiorespiratory response to moderate or interval exercise in their clientele should recommend TM running rather than cycling.

Previous studies have shown the existence of an ideal respiratory rate (fR) for a given ventilation at which the respiratory work rate (J.s-1) is minimum. The purpose of the present study was to measure the effect of fR, tidal volume and breathing pattern on the respiratory work per breath and respiratory work rate during exercise on a cycle ergometer. Three work rates on the cycle ergometer were used and at each work rate the ventilation was kept constant. Two different breathing patterns were applied at each ventilation. Nine male trained cyclists [mean (SD) maximum oxygen consumption, 57 (5.47) ml.kg-1.min-1] participated in this study. The results indicated that there was a significant difference in the respiratory work per breath, with different breathing patterns at a given ventilation and for all levels of ventilation. There was no significant difference in the respiratory work rate with different breathing patterns at a given ventilation and for all levels of ventilation. In addition, the respiratory work per breath and respiratory work rate were increased with increasing ventilation. Thus, the data indicated that the manipulation of tidal volume, respiratory rate and breathing pattern had no significant effect on the energy cost of breathing for a given ventilation. The absence of this significant effect on respiratory work rate was observed across a range of ventilation from 24 to 72 l.min-1. These findings suggest that the breathing pattern is predominantly an expression of the function of the higher respiratory brain center instead of energy economy, at least within this range of ventilation.