Chemoreceptors

The benefits of pranayama for positive health are well known. Even though there are many studies published on the effectiveness of pranayama, there are very few papers, which actually have systematically studied the physiological mechanisms involved, causing the benefits of pranayama, especially with respect to the cardiac function. This article attempts to have a detailed look at the physiology behind deep breathing. The article also conjectures that voluntary, deep breathing with attention may have a role to play in faster recovery from surgeries, and prevent or delay the onset of Alzheimer's disease, Parkinson's disease and may be, even cancer. Detailed, controlled studies are needed to prove or disprove these conjectures.

Abstract : Our studies on the functional characterization of odorant receptors have developed in two directions. One direction is concerned with the characterization of the ligand specificity of a single defined odorant binding domain. The fourth and fifth transmembrane domains and their extracellular linker of the human beta (2)-adrenergic receptor have been replaced by the equivalent regions of odorant receptor I-15 (Buck and Axel, 1991), thus forming a chimaeric seven transmembrane domain containing G-protein linked receptor that couples a novel odorant binding domain consisting of the 1-15 moiety (and perhaps part of the adrenaline binding site of the adrenergic receptor) to the intracellular regions of the Beta (2)-adrenergic receptor that couples ligand binding to the production of cyclic AMP. Expression of this chimaera in eukaryotic cells and screening the expressed construct with an array of odorants is expected to identify a set of odorants that interacts with the ligand binding domain of the synthetic receptor. The binding site can then be characterized pharmacologically and the interactions of odorants with specific amino acid residues in the hybrid receptor can be studied. This information can then be used to characterize the odorant specificity of the parental 1-15 receptor, that may not be identical, but is likely to be closely related to that of the chimaera. The second direction of our research program is concerned with the question of how an ensemble of odorant receptors with overlapping ligand specificities interacts to recognize a given odorant.

Feeding behavior and chemoreception by the living fossil Priapulus caudatus is described and characterized by behavioral methods. Worms respond to chemical stimulation of the anterior circumoral field with a stereotypic feeding reflex. This response is not elicited by tactile stimuli alone. Chemoreceptors appear to be restricted to the circumoral field since the feeding response is not evoked when other regions of the body are chemically stimulated. Priapulus caudatus fed only on tissues of macrobenthic species common to its habitat. Ingestion of both live and dead tissues, in addition to algae, indicates that P. caudatus is omnivorous in the Bay of Fundy region. This feeding strategy is adaptive for survival in the extreme environmental conditions characteristic of the niche occupied by P. caudatus.

Conscious, anaesthetized and decerebrate young mammals respond to acute hypoxia with an initial increase in breathing followed by a fall to, or to below, pre-hypoxic levels--the biphasic ventilatory response. The ventilatory rise is due to sustained hypoxic stimulation of the peripheral chemoreceptors. We present evidence from brain stem and peripheral chemoreflex studies supporting the concept that, in addition to the peripheral chemoreceptors, hypoxia also activates brain stem pathways that inhibit ventilation. A key part of the inhibitory pathway is an area within the red nucleus. Destruction of this area in young decerebrate rabbits abolishes the ventilatory fall during hypoxia, yet has no effect on respiratory control during normoxia and does not affect arterial blood pressure changes in hypoxia. In support of this hypothesis, we report that there are neurones within the red nucleus that increase their discharge in hypoxia. The role of higher brain stem/hypothalamic function in...