MUSCARINIC cholinergic receptors (mAChRs) within the pontine brain stem play a key role in generating rapid eye movement (REM) sleep. Using an in vitro autoradio-graphic technique that permits selective labeling of mAChR subtypes by radioligand binding, this study provides the first quantitative map of mAChR subtypes in cat brain stem areas important for REM sleep generation. M1, M2 and M3 mAChR subtypes were distributed hetero-geneously throughout the brain stem. For all 3 mAChR subtypes, the greatest levels of binding were found in the dorsal raphe and locus cocruleus, and the least amount of binding was in the reticular formation. These findings are consistent with data from in vivo studies showing that multiple mAChR subtypes are involved in REM sleep generation.
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.
The aim was to investigate the potential differences in muscle (vastus lateralis) and cerebral (prefrontal cortex) oxygenation levels as well as in the number of repetitions and total work output between isokinetic eccentric and concentric exercise at a moderate relative intensity until exhaustion. Ten recreationally active young men underwent two isokinetic exercise sessions either concentric or eccentric, one on each randomly selected leg. The protocols were performed at 60°/s and an intensity corresponding to 60% of the maximal voluntary contraction (MVC) of each contraction type. Concentric torque was significantly lower compared to eccentric torque in both peak values and at values corresponding to 60% of MVC [230 ± 18 Nm vs. 276 ± 19 Nm (P = .014) and 137 ± 12 Nm vs. 168 ± 11 Nm, respectively (P = .010)]. The participants performed 40% more contractions during eccentric compared to concentric exercise [122 ± 15 vs. 78 ± 7, respectively]. No differences were found in the levels of oxyhaemoglobin, deoxyhemoglobin, total haemoglobin and tissue saturation index when eccentric and eccentric exercise regimes were compared (all P > .05). Our results demonstrate that eccentric exercise of moderate intensity leads to greater resistance to fatigue and more work output compared to concentric exercise, despite the comparable muscle and cerebral oxygenation levels.
