Spatial distribution of external and internal intercostal activity in dogs.
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1. The observation that the external and internal interosseous intercostal muscles in the dog show marked regional differences in mechanical advantage has prompted us to re-examine the topographic distribution of electrical activity among these muscles during spontaneous breathing. 2. Inspiratory activity was recorded only from the areas of the external intercostals with an inspiratory mechanical advantage, and expiratory activity was recorded only from the areas of the internal intercostals with an expiratory mechanical advantage. The expiratory discharges previously recorded from the caudal external intercostals and the inspiratory discharges recorded from the rostral internal intercostals were probably due to cross-contamination. 3. Activity in each muscle area was also quantified relative to the activity measured during tetanic, supramaximal nerve stimulation (maximal activity). External intercostal inspiratory activity was consistently greater in the areas with a greater inspiratory advantage (i.e. the dorsal aspect of the rostral segments) than in the areas with a smaller inspiratory advantage, and internal intercostal expiratory activity was invariably greatest in the areas with the greatest expiratory advantage (i.e. the dorsal aspect of the caudal segments). 4. This topographic distribution of neural drive confers to the external intercostal muscles an inspiratory action on the lung during breathing and to the internal interosseous intercostals an expiratory action. (+info)
Impact of ethnic origin and quinidine coadministration on codeine's disposition and pharmacodynamic effects.
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CYP2D6 is polymorphically distributed so that in poor metabolizers enzyme activity is missing. The goal of this study was to compare the pharmacokinetics and pharmacodynamics of codeine with and without quinidine between Caucasian and Chinese extensive metabolizers of debrisoquin. Nine Caucasians and eight Chinese subjects received in random, double blind fashion, on two occasions, codeine 120 mg. with placebo or with quinidine 100 mg. Pharmacodynamic effects were determined over 6 h. Codeine-apparent clearance and partial metabolic clearance by O-demethylation were significantly greater in the Caucasian than in the Chinese subjects (1939 +/- 175 ml/min versus 1301 +/- 193 ml/min, p <.03 and 162.7 +/- 36.6 ml/min versus 52.7 +/- 12.7 ml/min, p <.02, respectively). Codeine's respiratory effects (except on resting ventilation) were significantly greater in the Caucasian than in the Chinese subjects (p <.05), but no interethnic differences were noted in codeine's effect on the digit symbol substitution test and pupillary ratio. No morphine or morphine metabolites were detected in plasma when codeine was coadministered with quinidine. Codeine O-demethylation was significantly reduced after quinidine in both ethnic groups; however, the absolute decrease was greater in Caucasians (115.8 +/- 25.9 ml/min versus 46.8 +/- 10.6 ml/min, respectively, p <.03). The diminished production of morphine after quinidine was associated in the Caucasians, but not in the Chinese, with a marked reduction in codeine's effects (p <.01). In conclusion, Chinese produce less morphine from codeine, exhibit reduced sensitivity to that morphine, and therefore might experience reduced analgesic effect in response to codeine. In addition, quinidine induced inhibition of codeine O-demethylation is ethnically dependent with the reduction being greater in Caucasians. (+info)
The neuromuscular control of birdsong.
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Birdsong requires complex learned motor skills involving the coordination of respiratory, vocal organ and craniomandibular muscle groups. Recent studies have added to our understanding of how these vocal subsystems function and interact during song production. The respiratory rhythm determines the temporal pattern of song. Sound is produced during expiration and each syllable is typically followed by a small inspiration, except at the highest syllable repetition rates when a pattern of pulsatile expiration is used. Both expiration and inspiration are active processes. The oscine vocal organ, the syrinx, contains two separate sound sources at the cranial end of each bronchus, each with independent motor control. Dorsal syringeal muscles regulate the timing of phonation by adducting the sound-generating labia into the air stream. Ventral syringeal muscles have an important role in determining the fundamental frequency of the sound. Different species use the two sides of their vocal organ in different ways to achieve the particular acoustic properties of their song. Reversible paralysis of the vocal organ during song learning in young birds reveals that motor practice is particularly important in late plastic song around the time of song crystallization in order for normal adult song to develop. Even in adult crystallized song, expiratory muscles use sensory feedback to make compensatory adjustments to perturbations of respiratory pressure. The stereotyped beak movements that accompany song appear to have a role in suppressing harmonics, particularly at low frequencies. (+info)
Role of potassium channels and nitric oxide in the relaxant effects elicited by beta-adrenoceptor agonists on hypoxic vasoconstriction in the isolated perfused lung of the rat.
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1. The aims of this study were to compare, in the rat isolated perfused lung preparation, the antagonist effects of a nonselective beta-adrenoceptor agonist (isoprenaline), a selective beta2-adrenoceptor agonist (salbutamol) and a selective beta3-adrenoceptor agonist (SR 59104A) on the hypoxic pulmonary pressure response, and to investigate the role of K+ channels, endothelium derived relaxing factor and prostaglandins in these effects. K+ channels were inhibited by glibenclamide, charybdotoxin or apamin, NO synthase and cyclo-oxygenase were inhibited by N(G)-nitro-L-arginine methyl ester (L-NAME) and indomethacin, respectively. 2. Hypoxic ventilation produced a significant increase in perfusion pressure (+65%, P<0.001) and L-NAME significantly increased this response further (+123%, P<0.01). After apamin, L-NAME, indomethacin, post-hypoxic basal pressure did not return to baseline values (P<0.001). 3. Glibenclamide partially inhibited the relaxant effects of isoprenaline (P<0.05) and salbutamol (P<0.001) but not that of SR 59104A. In contrast, charybdotoxin and apamin partially inhibited the relaxant effects of SR 59104A (P=0.053 and <0.01, respectively) but did not modify the effects of isoprenaline and salbutamol. L-NAME partially inhibited the dilator response of salbutamol (P<0.01) and SR 59104A (P<0.05) but not that of isoprenaline. 4. We conclude that (a) EDRF exerts a significant inhibition of the hypoxic pulmonary response, (b) SK(Ca) channel activation, EDRF and prostaglandins contribute to the reversal of the hypoxic pressure response, (c) the vasodilation induced by isoprenaline is mediated in part by activation of K(ATP) channels, that of salbutamol by activation of K(ATP) channels and EDRF. In contrast, SR 59104A partly operates through BK(Ca), SK(Ca), channels and EDRF activation, differing in this from the beta1 and beta2-adrenoceptor agonists. (+info)
Respiratory action of capsaicin microinjected into the nucleus of the solitary tract: involvement of vanilloid and tachykinin receptors.
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1. The respiratory response to microinjection of capsaicin into the commissural nucleus of the solitary tract (cNTS) of urethane-anaesthetized rats was investigated in the absence and presence of the competitive vanilloid (capsaicin) antagonist, capsazepine, and selective tachykinin NK1, NK2 and NK3 antagonists (RP 67580, SR 48968 and SR 142801, respectively). 2. Microinjection of capsaicin reduced respiratory frequency but not tidal volume (VT), leading to an overall reduction in minute ventilation (VE). The effect was dose-dependent between 0.5 and 2 nmol capsaicin. Doses greater than 2 nmol produced apnoea. Tachyphylaxis was observed following repeated injection of capsaicin (1 nmol, 30 min apart). 3. Capsazepine (1 nmol) had no effect on frequency or VT when injected alone but completely blocked the respiratory response to capsaicin (1 nmol). 4. RP 67580 (1 but not 5 nmol) alone depressed frequency and VT slightly. Moreover, RP 67580 appeared to potentiate the bradypnoeic effect of capsaicin. In contrast, SR 48968 and SR 142801 (1 and 5 nmol) alone had no significant effect on respiration. However, both agents significantly attenuated the reduction in frequency produced by capsaicin. 5. In conclusion, microinjection of capsaicin into the cNTS decreases overall ventilation, primarily by reducing frequency. The action of capsaicin appears from the data to be mediated by vanilloid receptors since it is blocked by the competitive vanilloid antagonist capsazepine and is subject to tachyphylaxis. However, since NK2 (SR 48968) and NK3 (SR 142801) receptor antagonists block the actions of capsaicin, we propose that capsaicin acts also by releasing tachykinins from central afferent terminals in the cNTS. (+info)
Intracellular sigma1 receptor modulates phospholipase C and protein kinase C activities in the brainstem.
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Most physiological effects of sigma1 receptor ligands are sensitive to pertussis toxin, suggesting a coupling with cell membrane-bound G proteins. However, the cloning of the sigma1 receptor has allowed the identification of an intracellular protein anchored on the endoplasmic reticulum. Here, we show, using the isolated adult guinea pig brainstem preparation, that activation of the sigma1 receptor results in its translocation from the cytosol to the vicinity of the cell membrane and induces a robust and rapid decrease in hypoglossal activity, which is mediated by phospholipase C. The subsequent activation of protein kinase C beta1 and beta2 isoforms and the phosphorylation of a protein of the same molecular weight as the cloned sigma1 receptor lead to a desensitization of the sigma1 motor response. Our results indicate that the intracellular sigma1 receptor regulates several components implicated in plasma membrane-bound signal transduction. This might be an example of a mechanism by which an intracellular receptor modulates metabotropic responses. (+info)
Responses of simultaneously recorded respiratory-related medullary neurons to stimulation of multiple sensory modalities.
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This study addresses the hypothesis that multiple afferent systems share elements of a distributed brain stem network that modulates the respiratory motor pattern. Data were collected from 18 decerebrate, bilaterally vagotomized, paralyzed, artificially ventilated cats. Up to 28 neurons distributed in the rostral and caudal ventral respiratory group, nucleus tractus solitarius, and raphe obscurus were recorded simultaneously with microelectrode arrays. Phases of the respiratory cycle and inspiratory drive were assessed from integrated efferent phrenic nerve activity. Carotid chemoreceptors were stimulated by injection of CO2-saturated saline solution via the external carotid artery. Baroreceptors were stimulated by increased blood pressure secondary to inflation of an embolectomy catheter in the descending aorta. Cutaneous nociceptors were stimulated by pinching a footpad. Four hundred seventy-four neurons were tested for respiratory modulated firing rates and responses; 403 neurons were tested with stimulation of all 3 modalities. Chemoreceptor stimulation and pinch, perturbations that tend to increase respiratory drive, caused similar responses in 52 neurons; 28 responded oppositely. Chemoreceptor and baroreceptor stimulation resulted in similar primary responses in 45 neurons; 48 responded oppositely. Similar responses to baroreceptor stimulation and pinch were recorded for 38 neurons; opposite effects were measured in 26 neurons. Among simultaneously recorded neurons, distinct combinations of firing rate changes were evoked in response to stimulation of the different modalities. The results show a functional convergence of information from carotid chemoreceptors, baroreceptors, and cutaneous nociceptors on respiratory-modulated neurons distributed in the medulla. The data are consistent with the hypothesis that brain stem neurons have overlapping memberships in multifunctional groups that influence the respiratory motor pattern. (+info)
Multimodal medullary neurons and correlational linkages of the respiratory network.
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This study addresses the hypothesis that multiple sensory systems, each capable of reflexly altering breathing, jointly influence neurons of the brain stem respiratory network. Carotid chemoreceptors, baroreceptors, and foot pad nociceptors were stimulated sequentially in 33 Dial-urethan-anesthetized or decerebrate vagotomized adult cats. Neuronal impulses were monitored with microelectrode arrays in the rostral and caudal ventral respiratory group (VRG), nucleus tractus solitarius (NTS), and n. raphe obscurus. Efferent phrenic nerve activity was recorded. Spike trains of 889 neurons were analyzed with cycle-triggered histograms and tested for respiratory-modulated firing rates. Responses to stimulus protocols were assessed with peristimulus time and cumulative sum histograms. Cross-correlation analysis was used to test for nonrandom temporal relationships between spike trains. Spike-triggered averages of efferent phrenic activity and antidromic stimulation methods provided evidence for functional associations of bulbar neurons with phrenic motoneurons. Spike train cross-correlograms were calculated for 6,471 pairs of neurons. Significant correlogram features were detected for 425 pairs, including 189 primary central peaks or troughs, 156 offset peaks or troughs, and 80 pairs with multiple peaks and troughs. The results provide evidence that correlational medullary assemblies include neurons with overlapping memberships in groups responsive to different sets of sensory modalities. The data suggest and support several hypotheses concerning cooperative relationships that modulate the respiratory motor pattern. 1) Neurons responsive to a single tested modality promote or limit changes in firing rate of multimodal target neurons. 2) Multimodal neurons contribute to changes in firing rate of neurons responsive to a single tested modality. 3) Multimodal neurons may promote responses during stimulation of one modality and "limit" changes in firing rates during stimulation of another sensory modality. 4) Caudal VRG inspiratory neurons have inhibitory connections that provide negative feedback regulation of inspiratory drive and phase duration. (+info)