Search

Carotid bodies and their nerves were excised from rabbits or cats, cleaned of surrounding connective tissue and placed in a chamber through which mammalian saline equilibrated with different gas mixtures was allowed to flow. Single fibers were isolated and identified as chemosensory by their response to hypoxia, hypercapnia, or NaCN. Mass receptor potentials (recorded at some distance from the sensory nerve endings) were evoked by the same stimuli and registered as close as possible to the carotid body. Both cats and rabbits exhibited receptor depolarization and an increased discharge in response to NaCN, hypoxia, hypercapnia and cyanide. However, the effects of some pharmacological agents were quite different in rabbits and cats. In the rabbit, ACh 10-100 microgram and carbachol 1-10 microgram produced receptor hyperpolarization and discharge depression followed by discharge increase. Nicotine 0.3-20 microgram induced receptor depolarization and increased chemosensory discharge frequency. Nicotinic stimulation was antagonized by D-tubocurarine 10(-6)-10(-4) g/ml. Pilocarpine 2-50 microgram hyperpolarized the receptors and depressed discharge frequency. Pilocarpine-induced depression was reduced by atropine 10(-6) g/ml. Dopamine 5-100 microgram depolarized the receptors and increased the chemosensory discharge frequency. This effect of dopamine was reduced by haloperidol (10(-11)-10(-7) M). In the cat, ACh, carbachol and nicotine (same doses as those used in rabbits) induced receptor depolarization and increased the sensory discharge frequency. Pilocarpine (up to 50 microgram) had little effect on either discharge frequency or the receptor potential. Dopamine 5-100 microgram induced receptor hyperpolarization and depression of discharge frequency, and these effects were reduced by haloperidol.

Input--output (I--O) relationships were studied in cercal "thread-hair" sensilla (THS) on Periplaneta americana L. by recording from individual axons of THS while displacing the corresponding hair with a galvanometric device. Sinusoidal analysis was attempted and pulse- and ramplike displacements were then tested. The effects of stimulus orientation were also investigated. THS were spontaneously active and purely phasic and did not respond to sustained displacements. With small sinusoidal displacements (less than 30 degrees) they behaved as a linear, second-order lead system sensitive to velocity. With larger amplitudes, however, they exhibited prominent nonlinear features with minimal consequences of displacements at the extremes. Responses to other waveforms indicated second-order response components. THS were directionally sensitive. Phasic behavior and the nonlinearities may be due to mechanical properties at the base of the hair. The spike-firing threshold may also contribute. Resting activity appears to be due to neuronal factors since it was not abolished by preventing hair movements. Transducer operations were simulated in a digital computer.

Two schedules of treatment were adopted for an experimental evaluation of drug induced alterations in mid-small intestinal flora of normal rats. Test substances were given orally twice daily for 3 days at large doses and once daily for 30 days at lower doses. Indometacin, benzydamine, phenylbutazone, pheprazone, picosulfol, magnesium sulfate, tolbutamide, phenformin, dexamethasone acetate and prednisolone acetate were tested. Drug-induced alterations in rat intestinal flora resulted more evidently following multiple short-time treatments.

Intracellular recordings were made from glomus cells in the excised, intact or sliced (150-200 microns) carotid body. Carotid nerve discharge was also recorded from intact preparations. Slices were prepared for visual (Nomarski) control of microelectrode impalement. Resting potential (Em), input resistance (Ro) and voltage noise (Erms) were measured in control conditions and in response to several stimulants (interruption of flow, hypoxic and histotoxic [NaCN]anoxia, hypercapnia, asphyxia and acidity) and depressants (alkalinity, cooling) of the carotid nerve sensory discharge. Different glomus cells responded differently to the same stimulus but significant trends were found. The more common responses to zero flow and anoxia (hypoxic and histotoxic) were depolarization (64%) and decreases in Erms (63%) and Ro (71%). When extracellular pH was varied from 8.5 to 5.0, the preponderant responses were cell depolarization, and increases in noise and input resistance as pH decreased. Consequently, cell depolarization induced by zero flow and anoxia tended to be accompanied by reduced Ro, whereas that induced by acidity generally showed increased Ro. Changes in voltage noise usually followed variations in Ro. When nerve discharge frequency was plotted against delta Em or delta Erms there were positive correlations during acid stimulation. However, these correlations were complex (parabolic) during flow interruption and anoxia: an increase in discharge occurred in response to cell depolarization and to hyperpolarization. These results suggest that hypoxia and hypercapnic or acidic stimuli act on glomus cells by different mechanisms. This finding is consistent with evidence obtained by recording carotid nerve discharges in intact animals.

The reactions of cis- and trans-2-tert-butyl-4,5-epoxytetrahydropyran with HBr and with LAH have been examined as a model for the nucleophilic step of the reaction of the corresponding olefin with NBA in aqueous dioxane. A remarkable 90:10 preference for electrophilic attack syn to the tert -butyl group in the NBA reaction is found and shows that the two epoxides, as well as the intermediate epibromonium ions, undergo nucleophilic attack with high preference for diaxial opening, even when this requires reaction at carbon 5, which is more subject than carbon 4 to the unfavourable inductive effect of the pyran ring oxygen. These results constitute a further proof in favour of a mechanism of N-haloamide promoted electrophilic additions in which the electrophilic step is rapidly reversible and product composition is determined during the nucleophilic step.

The reactions of 3,4-epoxytetrahydropyran and of its cis - and trans -2-methyl derivatives with hydrogen halides and with lithium aluminum hydride have been investigated in order to assess the influence of an O atom in the β position on the regioselectivity of the epoxide ring opening. All these reactions exhibit a high preference for nucleophilic attack at position 4, which decreases moderately only when the inductive effect of the O atom and the stereoelectronic requirements of the attack act in opposite directions. Similar trends are observed in the reactions of the 5,6-dihydro-2 H -pyrans with NBA, which occur with preferential nucleophilic attack by water at position 4 of the intermediate epibromonium ions. A remarkably high preference (96%) for electrophilic attack syn to the 2-Me group is observed in the latter type of reaction, in accordance with a previous proposal of a mechanism in which the nucleophilic step is rate determining.

This investigation involved extracellular recordings of cockroach abdominal giant interneuron (GI) action potentials evoked by cercal "threadlike" hair sensilla (THS) stimulation with a galvanometric device, by controlled displacements of about seven THS. Small and large GIs, distinguished by their amplitudes, were studied simultaneously. Only the small GIs were spontaneously active. Responses to sine, pulse, and ramp stimulation of sensilla produced phasic responses in both GI types. Some GIs were directionally sensitive and had shorter response latencies in the direction of best sensitivity while others were omnidirectional. Contralateral stimulation decreased responses to homolateral stimuli. In experiments using paired pulses (less than 50-ms intervals) there is a period of hyperexcitability, in large GIs, in which the response to the second stimulus is greater. Repeated stimulation caused an exponential decline in the response which was steeper in GIs at higher stimulating frequencies and had a faster time course in large GIs. Because of this last property GIs function as low-pass filters limiting the flow of information, with large GIs having a lower frequency "cutoff" than smaller GIs.

Publisher Summary This chapter explores the effects of different stimuli on the glomus cell membrane. The study described in the chapter involved removing the carotid body and sinus nerve from anesthetized cats and placing the preparation in a chamber through which flowed physiological saline equilibrated with 50% O2. The nerve discharges were registered with wire electrodes connected to an a.c. recording system. The carotid body was impaled with microelectrodes filled with 3M KCl, and intracellular potentials were recorded with a high impedance electrometer connected to the d.c. amplifier of an oscilloscope. The intracellularly recorded elements were often stained by using microelectrodes filled with a procion dye, which was ejected from the micropipette after recordings were made. The tissues were then prepared for histology and observation with interference contrast optics. The other method consisted of cutting the carotid body into 100 to 200 μm slices, which were placed in a chamber mounted on the stage of an inverted microscope equipped with Nomarski optics. Impalements of carotid body cells yielded membrane potentials (MPs) of 10–60 mV and mean about 20 mV. These values are low, probably because of partial membrane injury produced by insertion of the electrode into these small cells.

The four legume species of concern here are unequally distributed throughout Europe in relation to climatic diversity and soil type. In general, the area sown to pea, faba bean, chickpea and lentil (the ranking following that order) has decreased sharply during the past thirty years, reflecting changes in eating habits. But, there has been renewed interest in these crops in recent years, especially in pea and faba bean, as feed for non-ruminant animals. Increases in the price of nitrogen fertilizer and the potential for legumes as break crops in cereal-dominated rotations have also stimulated interest. New breeding programmes in many countries are seeking to develop improved plant types and production technology (e.g. better weed and pest control). Significant progress has been made.

The conformational equilibrium of the title compound has been determined by correlating its n.m.r. parameters with those of its 2,2,6,6-tetradeuterio derivative and trans - and cis -2- tert -butyl-4,5-epoxytetrahydropyran. The high preference (Δ G ∼ −0.8 kcal/mol) for the half-chair conformation in which the pyranoid oxygen is furthest from the oxirane oxygen atom can be interpreted in terms of electrostatic interactions between the two oxygen atoms.

Interrupting the blood supply to the carotid body by ligating arteries of its vascular peduncle altered the chemoreceptive properties of the carotid nerve and produced structural changes in parenchymal (glomus and sustentacular) cells. The onset of ischemia was marked by an increase in the discharge of both A (myelinated) and C (unmyelinated) sensory fibers followed by depression and finally by receptor silence. The discharge of A-fibers disappeared after 30–50 min and that of C-fibers after 60–90 min. During ischemia of 15–60 min duration the threshold to pharmacological (NaCN, ACh) and ‘natural’ (hypoxic) stimuli progressively increased and was accompanied by reversible changes in the structure of parenchymal cells and nerve endings. Ischemia for 2 h or longer produced irreversible functional damage and disappearance of glomus and sustentacular cells from the carotid body. Following ischemic injury, nerve fibers regenerated and all responded to mechanical stimuli but only a few were stimulated by natural or pharmacological agents. Thus, parenchymal cells of the carotid body appear to be most important in transduction by allowing sensory fibers to respond to chemical stimuli.

Racemic oleandrose (2,6-dideoxy-3-O-methyl-arabino-hexone) has been obtained starting from the Diels-Alder adduct between 4-methoxy-3-buten-2-one and isobutyl vinyl ether, which was converted into a mixture of the isobutyl β- and α-oleandrosides through hydroboration-oxidation. The latter reaction is highly diastereoselective since attack by borane takes place exclusively anti to the OMe group: none of the diasteroisomeric cymarosides are formed. The only side-products are small amounts of the isobutyl β- and α-amicetodies formed by a demthoxylation occuring during the hydroboration step.

Nicotinic and muscarinic sites on glomus cell membranes of cats, rabbits and mice were determined in carotid body slices. Cells were impaled under Nomarski optics. Resting potentials were 11.1-73.1 mV and input resistances were 11-250 M omega. Nicotine, pilocarpine or bethanechol depolarized glomus cells and their input resistance decreased. Curare or alpha-bungarotoxin reduced nicotine effects. Atropine had similar effects on the responses to pilocarpine or bethanechol.