The anatomical structure of central respiratory chemoreceptors in the superficial ventral medulla of rats was studied by using hypercapnia-induced c-fos labeling to identify cells directly stimulated by extracellular pH or PCO(2). The distribution of c-fos-positive cells was found to be predominantly perivascular to surface vessels. In the superficial ventral medullary midline, parapyramidal, and ventrolateral regions where c-fos-positive cells were concentrated, we found a common, characteristic, anatomical architecture. The medullary surface showed an indentation covered by a surface vessel, and the marginal glial layer was thickened. We classified c-fos-positive cells into two types. One (type I cell) was small, was located inside the marginal glial layer and close to the medullary surface, and surrounded fine vessels. The other (type II cell) was large and located dorsal to the marginal glial layer. c-fos Expression under synaptic blockade suggested that type I cells are intrinsically chemosensitive. The chemosensitivity of surface cells (possible type I cells) surrounding vessels was confirmed electrophysiologically in slice preparations. We suggest that this characteristic anatomical structure may be the central chemoreceptor.

The characteristics of GABAergic neurons involved in respiratory control have not been fully understood because identification of GABAergic neurons has so far been difficult in living tissues. In the present in vitro study, we succeeded in analysing the electrophysiological as well as morphological characteristics of GABAergic neurons in the pre-Bötzinger complex. We used 67-kDa isoform of glutamic acid decarboxylase-green fluorescence protein (GAD67-GFP) (Delta neo) knock-in (GAD67(GFP/+)) mice, which enabled us to identify GABAergic neurons in living tissues. We prepared medullary transverse slices that contained the pre-Bötzinger complex from these neonatal mice. The fluorescence intensity of the pre-Bötzinger complex region was relatively high among areas of the ventral medulla. Activities of GFP-positive neurons in the pre-Bötzinger complex were recorded in a perforated whole-cell patch-clamp mode. Six of 32 GFP-positive neurons were respiratory and the remaining 26 neurons were non-respiratory; the respiratory neurons were exclusively inspiratory, receiving excitatory post-synaptic potentials during the inspiratory phase. In addition, six inspiratory and one expiratory neuron of 30 GFP-negative neurons were recorded in the pre-Bötzinger complex. GFP-positive inspiratory neurons showed high membrane resistance and mild adaptation of spike frequency in response to depolarizing current pulses. GFP-positive inspiratory neurons had bipolar, triangular or crescent-shaped somata and GFP-negative inspiratory neurons had multipolar-shaped somata. The somata of GFP-positive inspiratory neurons were smaller than those of GFP-negative inspiratory neurons. We suggest that GABAergic inhibition not by expiratory neurons but by inspiratory neurons that have particular electrophysiological and morphological properties is involved in the respiratory neuronal network of the pre-Bötzinger complex.

Due to the currently ongoing pandemic of coronavirus disease 2019 (COVID-19), it is strongly recommended to wear facemasks to minimize transmission risk. Wearing a facemask may have the potential to increase dyspnea and worsen cardiopulmonary parameters during exercise; however, research-based evidence is lacking. We investigated the hypothesis that wearing facemasks affects the sensation of dyspnea, pulse rate, and percutaneous arterial oxygen saturation during exercise. Healthy adults (15 men, 9 women) underwent a progressive treadmill test under 3 conditions in randomized order: wearing a surgical facemask, cloth facemask, or no facemask. Experiment was carried out once daily under each condition, for a total of 3 days. Each subject first sat on a chair for 30 minutes, then walked on a treadmill according to a Bruce protocol that was modified by us. The experiment was discontinued when the subject’s pulse rate exceeded 174 beats/min. After discontinuation, the subject immediately sat on a chair and was allowed to rest for 10 minutes. Subjects were required to rate their levels of dyspnea perception on a numerical scale. Pulse rate and percutaneous arterial oxygen saturation were continuously monitored with a pulse oximeter. These parameters were recorded in each trial every 3 minutes after the start of the exercise; the point of discontinuation; and 5 and 10 minutes after discontinuation. The following findings were obtained. Wearing a facemask does not worsen dyspnea during light to moderate exercise but worsens dyspnea during vigorous exercise. Wearing a cloth facemask increases dyspnea more than wearing a surgical facemask during exercise and increases pulse rate during vigorous exercise, but it does not increase pulse rate during less vigorous exercise. Wearing a surgical facemask does not increase pulse rate at any load level. Lastly, wearing a facemask does not affect percutaneous arterial oxygen saturation during exercise at any load level regardless of facemask type.

No abstract

The neural mechanisms of propofol-induced central respiratory depression remain poorly understood. In the present study, we studied these mechanisms and the involvement of gamma-aminobutyric acid (GABA)A receptors in propofol-induced central respiratory depression. The brainstem and the cervical spinal cord of 1- to 4-day-old rats were isolated, and preparations were maintained in vitro with oxygenated artificial cerebrospinal fluid. Rhythmic inspiratory burst activity was recorded from the C4 spinal ventral root. The activity of respiratory neurons in the ventrolateral medulla was recorded using a perforated patch-clamp technique. We found that bath-applied propofol decreased C4 inspiratory burst rate, which could be reversed by the administration of a GABAA antagonist, bicuculline. Propofol caused resting membrane potentials to hyperpolarize and suppressed the firing of action potentials in preinspiratory and expiratory neurons. In contrast, propofol had little effect on resting membrane potentials and action potential firing in inspiratory neurons. Our findings suggest that the depressive effects of propofol are, at least in part, mediated by the agonistic action of propofol on GABAA receptors. It is likely that the GABAA receptor-mediated hyperpolarization of preinspiratory neurons serves as the neuronal basis of propofol-induced respiratory depression in the newborn rat.

Under the influence of sevoflurane, the region containing inspiratory neurons, i.e., the pre-Bötzinger complex, may determine the inspiratory rhythm, because reduced C4 bursts were still synchronized with the bursts of inspiratory neurons within the pre-Bötzinger complex. In contrast, the sevoflurane-induced decrease in C4 burst amplitude is mediated through the inhibition of phrenic motor neurons. gamma-Aminobutyric acid type A receptors may be involved in the sevoflurane-induced respiratory depression within the medulla, but not within the spinal cord.

No abstract

Nicotine exposure is a risk factor in several breathing disorders Nicotinic acetylcholine receptors (nAChRs) exist in the ventrolateral medulla, an important site for respiratory control. We examined the effects of nicotinic acetylcholine neurotransmission on central respiratory control by addition of a nAChR agonist or one of various antagonists into superfusion medium in the isolated brainstem-spinal cord from neonatal rats. Ventral C4 neuronal activity was monitored as central respiratory output, and activities of respiratory neurons in the ventrolateral medulla were recorded in whole-cell configuration. RJR-2403 (0.1-10µM), α4β2 nAChR agonist induced dose-dependent increases in respiratory frequency. Non-selective nAChR antagonist mecamylamine (0.1-100µM), α4β2 antagonist dihydro-β-erythroidine (0.1-100µM), α7 antagonist methyllycaconitine (0.1-100µM), and α-bungarotoxin (0.01-10µM) all induced dose-dependent reductions in C4 respiratory rate. We next examined effects of 20µM dihydro-β-erythroidine and 20µM methyllycaconitine on respiratory neurons. Dihydro-β-erythroidine induces hyperpolarization and decreases intraburst firing frequency of inspiratory and preinspiratory neurons. In contrast, methyllycaconitine has no effect on the membrane potential of inspiratory neurons, but does decrease their intraburst firing frequency while inducing hyperpolarization and decreasing intraburst firing frequency in preinspiratory neurons. These findings indicate that α4β2 nAChR is involved in both inspiratory and preinspiratory neurons, whereas α7 nAChR functions only in preinspiratory neurons to modulate C4 respiratory rate.