Effect of treating severe nasal obstruction on the severity of obstructive sleep apnoea.

An association between mouth breathing during sleep and increased propensity for upper airway collapse is well documented, but the effect of treatment for nasal obstruction on mouth breathing during sleep and simultaneous obstructive sleep apnoea (OSA) severity has not been described previously. A randomised single blind placebo- and sham-controlled crossover study of treatment (topical decongestant and external dilator strip) for nasal obstruction was carried out in 10 patients (nine males; mean+/-SEM 46+/-5 yrs) with nasal obstruction and OSA. All patients had normal acoustic pharyngometry. The effect of treatment on nasal resistance, mouth breathing during sleep and OSA severity was quantified. Treatment of nasal obstruction was associated with a dramatic and sustained reduction in nasal resistance and the oral fraction of ventilation during sleep (mean (95% confidence interval) absolute reduction in oral fraction 30% (12-49)). Improvements in sleep architecture were observed during active treatment, and there was a modest reduction in OSA severity (change in apnoea-hypopnoea index 12 (3-22)). In conclusion, treating nasal obstruction reduced mouth breathing during sleep and obstructive sleep apnoea severity, but did not effectively alleviate obstructive sleep apnoea.

Application of Nomarski interference contrast microscopy as a thickness monitor in the preparation of transparent, SiC-based, cross-sectional TEM samples.

Reflected light optical microscopy using a Nomarski prism and a differential interference contrast filter have been employed in concert to achieve a technique that provides an accurate color reference for thickness during the dimpling and ion milling of transparent transmission electron microscopy samples of 6H-SiC(000 1) wafers. The samples had thin films of AIN, GaN, and Au deposited on the SiC substrate. A sequence of variously colored primary and secondary interference bands was observed when the SiC was thinner than 20 microm using an optical microscope. The color bands were correlated with the TEM sample thickness as measured via scanning electron microscopy. The interference contrast was used to provide an indication of the dimpling rate, the ion milling rate, and also the most probable location of perforation, which are useful to reduce sample breakage. The application of pressure during the initial cross-sectional preparation reduced the separation of the two halves of the sample sandwich and resulted in increased shielding of the film surface from ion milling damage.

Ontogenesis of presynaptic GABAB receptor-mediated inhibition in the CA3 region of the rat hippocampus.

gamma-Aminobutyric acid-B(GABAB) receptor-dependent and -independent components of paired-pulse depression (PPD) were investigated in the rat CA3 hippocampal region. Intracellular and whole cell recordings of CA3 pyramidal neurons were performed on hippocampal slices obtained from neonatal (5-7 day old) and adult (27-34 day old) rats. Electrical stimulation in the hilus evoked monosynaptic GABAA postsynaptic currents (eIPSCs) isolated in the presence of the ionotropic glutamate receptor antagonists 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 10 microM) and D(-)2-amino-5-phosphovaleric acid (-AP5, 50 microM) with 2(triethylamino)-N-(2,6-dimethylphenyl) acetamine (QX314) filled electrodes. In adult CA3 pyramidal neurons, when a pair of identical stimuli was applied at interstimulus intervals (ISIs) ranging from 50 to 1,500 ms the amplitude of the second eIPSC was depressed when compared with the first eIPSC. This paired-pulse depression (PPD) was partially blocked by P-3-aminoprophyl -P-diethoxymethylphosphoric acid (CGP35348, 0.5 mM), a selective GABAB receptor antagonist. In neonates, PPD was restricted to ISIs shorter than 200 ms and was not affected by CGP35348. The GABAB receptor agonist baclofen reduced the amplitude of eIPSCs in a dose-dependent manner with the same efficiency in both adults and neonates. Increasing the probability of transmitter release with high Ca2+ (4 mM)/low Mg2+ (0.3 mM) external solution revealed PPD in neonatal CA3 pyramidal neurons that was 1) partially prevented by CGP35348, 2) independent of the membrane holding potential of the recorded cell, and 3) not resulting from a change in the reversal potential of GABAA eIPSCs. In adults the GABA uptake blocker tiagabine (20 microM) increased the duration of eIPSCs and the magnitude of GABAB receptor-dependent PPD. In neonates, tiagabine also increased duration of eIPSCs but to a lesser extent than in adult and did not reveal a GABAB receptor-dependent PPD. These results demonstrate that although GABAB receptor-dependent and -independent mechanisms of presynaptic inhibition are present onGABAergic terminals and functional, they do not operate at the level of monosynaptic GABAergic synaptic transmission at early stages of development. Absence of presynaptic autoinhibition of GABA release seems to be due to the small amount of transmitter that can access presynaptic regulatory sites.

Characterization of respiratory-related neurons in the isolated brainstem of the frog.

Using intra- and extracellular recording techniques we examined the spontaneous discharge and membrane properties of respiratory-related neurons in isolated brainstem preparations of the frogs Rana catesbeiana and Rana pipiens that display spontaneous respiratory related activity in vitro. We observed neurons that depolarize during the fictive lung ventilation cycle as well as neurons that depolarize during the non-lung ventilation phase. Respiratory-related neurons demonstrated significant decreases in membrane input resistance during the fictive lung ventilation cycle but showed no evidence of voltage-dependent membrane conductances activated near resting membrane potential. Furthermore, respiratory neurons showed little spike frequency adaptation, their oscillatory activity was not dissociated from the global respiratory motor output following imposed changes in membrane potential, and spontaneous fluctuations in membrane potential were not observed following reversible interruption of respiratory burst activity by application of solutions low in calcium and high in magnesium. Taken together these results suggest that bulbar respiratory neurons in the isolated frog brainstem sampled in our study do not display endogenous bursting characteristics. Rather, they are strongly influenced by synaptic input.

Bidirectional plasticity expressed by GABAergic synapses in the neonatal rat hippocampus.

1. Activity-dependent plasticity of GABAergic synaptic transmission was investigated in neonatal rat hippocampal slices obtained between postnatal day (P) 2-10 using intracellular recording techniques. In all experiments, AMPA receptors were blocked by continual application of CNQX (10 microM). 2. Between P2 and P4, tetanic stimulation (TS) evoked NMDA receptor-dependent long-term depression of monosynaptic GABAA EPSPS (LTDGABAA). In contrast, when NMDA receptors were blocked by D-AP5 (50 microM), the same TS evoke long-term potentiation of GABAA EPSPS (LTPGABAA). 3. Between P6 and P10, TS failed to produce either LTP or LTD or hyperpolarizing monosynaptic GABAA IPSPS under the same recording conditions. However, when GABAergic potentials were rendered depolarizing (KCl-filled electrode) Ts induced either LTPGABAA or LTDGABAA in the presence or absence of D-AP5, respectively. 4. Both LTPGABAA and LTDGABAA were specific to the conditioned pathway and could be sequentially expressed at the same synapses. Potentiation of GABAergic synaptic efficacy was induced more easily following previous induction of LTDGABAA than in naive slices. 5. In conclusion, early in development, bidirectional synaptic plasticity is expressed by GABAA receptors and the activation (or not) of NMDA receptors determines the induction of either LTPGABAA or LTDGABAA.

Spontaneous release of GABA activates GABAB receptors and controls network activity in the neonatal rat hippocampus.

1. We investigated the effects of the selective gamma-aminobutyric acid-B (GABAB) receptor antagonist, P-3 aminopropyl-P-diethoxymethyl phosphoric acid (CGP 35348), on spontaneous and evoked postsynaptic potentials (PSPs) and currents (PSCs) in CA3 pyramidal cells and interneurons of hippocampal slices obtained between postnatal day 3 and 7 with the use of intracellular and whole cell recording techniques. The intracellular pipette solution contained either 2 M CsCl or 50 mM 2(triethylamino)-N-(2,6-dimethylphenyl) acetamine (QX314) dissolved in 2 M KMeSO4. Cesium and QX314 block postsynaptic responses mediated by GABAB receptors. 2. Under control conditions, bath application of CGP 35348 (0.5-1 mM) progressively increased the duration of spontaneous and evoked polysynaptic giant GABAergic PSPs leading to the appearance of ictal-like discharges. The effects of CGP 35348 were dose dependent and voltage independent. 3. In CA3 pyramidal neurons, CGP 35348 (0.5 mM) had no effect on monosynaptic GABAergic inhibitory PSPs (IPSPs) that were isolated in the presence of ionotropic glutamate receptor antagonists 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 10 microM) and D(-)2-amino-5-phosphovaleric acid (D-APV, 50 microM). Similarly, CGP 35348 (0.5 mM) had no effect on monosynaptic glutamatergic excitatory PSPs (EPSPs) that were isolated in the presence of bicuculline (10 microM) and high divalent cation artificial cerebrospinal fluid (ACSF; 6 mM Mg2+/4 mM Ca2+). 4. In CA3 pyramidal neurons exposed to CNQX (20 microM) and D-APV (50 microM), application of the potassium channel blocker 4-aminopyridine (4-AP, 50 microM) generated synchronous giant GABAergic PSPS that were blocked in the presence of high divalent cation ACSF (6 mM Mg2+/4 mM Ca2+) or bicuculline (10 microM). The duration of these synchronous GABAergic PSPs was prolonged in the presence of CGP 35348 (0.5 mM) but did not lead to the appearance of ictal-like discharges. 5. In the presence of bicuculline, interictal giant glutamatergic potentials were observed in simultaneously recorded CA3 pyramidal cells and interneurons. CGP 35348 (0.5 mM) progressively increased the duration of these bicuculline-induced glutamatergic bursts leading to the simultaneous appearance of ictal discharges in both pyramidal cells and interneurons. 6. These results suggest that in the neonatal CA3 hippocampal region, when synchronous giant polysynaptic GABAergic PSPs are present (i.e., under basal, control conditions), spontaneously released GABA reaches a critical level and activates GABAB receptors on both pyramidal cells and interneurons thus regulating the level of glutamatergic and GABAergic activity in the CA3 neuronal network.

A cholecystokinin-B receptor antagonist potentiates GABAergic and glycinergic inhibition in the nucleus of the solitary tract of the rat.

In both rodent and primate in vivo models, cholecystokininB (CCKB) antagonists such as PD134,308 have anxiolytic effects that may involve the potentiation of GABAergic transmission. We have investigated this interaction using exogenous application of GABA and whole cell patch recording techniques in neurons of the nucleus of the solitary tract (NTS) in brainstem slice preparations. In the presence of PD143,308 the magnitude of the GABA-evoked decrease in membrane input resistance was enhanced by 41.2 +/- 3.1% and the duration of the response was prolonged by 34.8 +/- 2.2%. Also, PD134, 308 potentiated glycine-evoked decreases in membrane input resistance, increasing the amplitude of the response by 62.8 +/- 4. 85 and prolonging the duration of the response by 23.5 +/- 3.6%. The effect of PD134,308 persisted in the presence of tetrodotoxin, after reversal of the transmembrane gradient of chloride ions and under conditions of exaggerated GABAA receptor desensitization. Our results demonstrate that at least part of the functional link between PD134,308 and the GABAA response occurs postsynaptically.

The frog brainstem preparation as a model for studying the central control of breathing in tetrapods

Our frog brainstem preparation revealed mechanisms for the central control of breathing that are in many ways similar to those of mammals. Thus, the basic control mechanisms for air-breathing appear to have been present in the Devonian common ancestors of frogs and mammals and may be common to all lung-breathing vertebrates. Location: The in vitro frog brainstem, including motor nuclei of cranial nerves V to X, maintains frequency and ratio of fictive buccal oscillations to fictive lung inflation episodes comparable with that of the living animal. In this preparation, transaction caudal to V abolishes spontaneous discharge in X but slow, spontaneous discharge in V may remain. Independent central pattern generation is present in the left and right half-brainstems. Chemosensitivity: The frequency of fictive lung inflation increases with decrease in pH within the physiological range. Response to glutamate: Biphasic response, consisting of a pause, followed by a dramatic increase in the frequency of fictive inspirations and positive baseline deflection, followed, in turn, by slow return of the baseline to the control level with frequency remaining above control as long as glutamate is applied. Local application reveals glutamate-sensitive sites in the ventral reticular formation. Response to substance P and physalaemin: Similar to glutamate but the frequency of fictive inspirations decreases below control values. Response to strychnine: The normal temporal sequence in firing of motor neurons of cranial nerves is disrupted and all nerves are synchronously active. The firing sequence of respiratory neurons is consistent with a grouping possibly homologous to the mammalian inspiratory, post-inspiratory and expiratory phases.

The frog brainstem preparation as a model for studying the central control of breathing in tetrapods.

Our frog brainstem preparation revealed mechanisms for the central control of breathing that are in many ways similar to those of mammals. Thus, the basic control mechanisms for air-breathing appear to have been present in the Devonian common ancestors of frogs and mammals and may be common to all lung-breathing vertebrates. LOCATION: The in vitro frog brainstem, including motor nuclei of cranial nerves V to X, maintains frequency and ratio of fictive buccal oscillations to fictive lung inflation episodes comparable with that of the living animal. In this preparation, transection caudal to V abolishes spontaneous discharge in X but slow, spontaneous discharge in V may remain. Independent central pattern generation is present in the left and right half-brainstems. CHEMOSENSITIVITY: The frequency of fictive lung inflations increases with decrease in pH within the physiological range. RESPONSE TO GLUTAMATE: Biphasic response, consisting of a pause, followed by a dramatic increase in the frequency of fictive inspirations and positive baseline deflection, followed, in turn, by slow return of the baseline to the control level with frequency remaining above control as long as glutamate is applied. Local application reveals glutamate-sensitive sites in the ventral reticular formation. RESPONSE TO SUBSTANCE P AND PHYSALAEMIN: Similar to glutamate but the frequency of fictive inspirations decreases below control values. RESPONSE TO STRYCHNINE: The normal temporal sequence in firing of motor neurons of cranial nerves is disrupted and all nerves are synchronously active. The firing sequence of respiratory neurons is consistent with a grouping possibly homologous to the mammalian inspiratory, post-inspiratory and expiratory phases.

NMDA-dependent GABAA-mediated polysynaptic potentials in the neonatal rat hippocampal CA3 region.

Evoked inhibitory postsynaptic potentials (IPSPs) were studied in CA3 hippocampal neurons from brain slice preparations of rats ranging from 5 to 18 days of age (P5-18) using intracellular recording techniques. With KMeSO4-filled electrodes the evoked inhibitory response consisted of fast and slow IPSPs mediated by GABAA and GABAB receptors respectively. In recordings obtained with electrodes filled with 2-(triethylamino)-N-(2,6-dimethylphenyl) acetamide and KMeSO4, electrical stimulation evoked monophasic IPSPs in mature slices (P10-18) and biphasic IPSPs with an early and a late phase in neonatal slices (P4-7). In neonates both the early and late phases of the IPSP were mediated by GABAA receptors. Pharmacological investigation revealed that the early phase arose from both direct and feedforward activation of GABAergic interneurons involving non-NMDA receptors, while the late phase resulted from polysynaptic activation of GABAergic interneurons mediated by NMDA receptors.

Fictive respiratory rhythm in the isolated brainstem of frogs.

Spontaneous rhythmically bursting activity was recorded from the trigeminal, vagal and hypoglossal nerve roots of the isolated brainstem from the frogs Rana catesbeiana and Rana pipiens superfused with a bicarbonate-free HEPES-buffer solution. Burst frequency, burst duration and the activity profile of the spontaneous neural discharges in vitro resembled those of a less radical preparation, the decerebrate, fictively breathing frog. After complete midsagittal section, each half of the isolated brainstem generated its own rhythmic neural activity which resembled that of the intact isolated brainstem. The spontaneous activity generated within each half of the brainstem is probably coordinated by decussating axons or by groups of neurons located along the midline of the brainstem Our results suggest that these coordinating entities extend the length of the brainstem (in a rostro-caudal dimension) and the degree of contact rather than the location of the contact between the two halves of the brainstem determines the synchronization of the right and left halves. Burst frequency of both the intact and hemisected brainstem preparation was decreased by alkaline challenge and increased by acid challenge. We conclude that this endogenous rhythmic activity represents the efferent motor output underlying lung ventilation in these animals.

Two regions in the isolated brainstem of the frog that modulate respiratory-related activity.

Using microinjection techniques, we have explored the isolated, complete midline sectioned brainstem of the frog (Rana catesbeiana) to identify regions that influence the endogenous respiratory-related motor activity. Ten-nanoliter injections of lidocaine (1%), GABA (100mM) and glutamate (10 and 100 mM) into discrete regions of the rostral and the caudal brainstem produced different effects on the phasic neural discharge. In the rostral site lidocaine, GABA and glutamate injections altered neural burst frequency with little or no effect on burst amplitude. In the caudal site, responses to lidocaine and GABA injections consisted primarily of decreases in neural burst amplitude, often, but not always associated with minor decreases in burst frequency. In the same region, the response to glutamate was characterized by a temporary interruption of the rhythmic neural burst activity. The largest responses to substance injection in both regions were obtained at sites ranging between 200 and 500 microns from the ventral surface, in the ventral medullary reticular formation. The results reveal the existence of two areas in the frog brainstem that influence respiratory motor output, one related to the respiratory burst frequency and the other related to the amplitude of the motor output.

Respiratory motor output of the sectioned medulla of the neonatal rat.

The respiratory motor output of the isolated medulla-spinal cord of the neonatal rat was recorded after three types of sections: (1) Complete midsagittal section of the medulla abolished all rhythmic neural activity recorded from the hypoglossal C4 ventral rootlets. (2) Complete transection at the level of the root of cranial nerve X decreased the burst frequency of the respiratory related motor output; transection of the medulla caudal to the obex had no effect on burst frequency recorded from the hypoglossal roots. Combining these rostral and caudal transections resulted in a transverse slice preparation 1.6-2.0 mm thick, which displayed spontaneous burst activity in the hypoglossal roots. (3) After rostral unilateral transection, a mid-coronal section produced a ventral medullary slice connected to the intact spinal cord. This 1.5 mm thick ventral medulla preparation displayed a spontaneous bursting rhythm. Both the transverse and coronal slices exhibited changes in burst frequency with changes in superfusate PCO2. These results demonstrate that respiratory rhythmogenesis and chemoreception are preserved in transverse and coronal medullary slices of the neonatal rat having substantially reduced diffusion distances.

Effects of prolonged inflation on pulmonary stretch receptor discharge in turtles.

The tonic and phasic discharge characteristics of single, slowly adapting pulmonary stretch receptors (SAR) were examined before and after 1 h periods of constant pressure inflation to normal resting (VLr, pressure = 0 cm H2O) and elevated (VLe, pressure = 10 cm H2O) lung volumes in turtles (Chrysemys sp.). Based on their discharge at VLr, SAR were classified as either low (n = 13) or high threshold (n = 4) receptors. Inflations were performed with both air and 5% CO2 in air. Lung gas composition and arterial PCO2 and pH were measured during the maintained inflations. In animals ventilated with air, low and high threshold receptors adapted by 57 and 30% respectively over the first 3 min at VLe. During the remainder of the 1 h period, the discharge of low threshold SAR fell an additional 20% while that of the high threshold SAR remained relatively constant. There were significant increases in both alveolar and arterial PCO2 during the maintained inflations. Ventilation with 5% CO2 reduced the static discharge levels of low and high threshold SAR by 10 and 25% respectively, suggesting that a part of the apparent adaptation of these receptors to maintained inflation for 1 h with air was due to the accumulation of metabolic CO2. Following 1 h of maintained inflation, the phasic responses to pump ventilation were decreased in low threshold SAR but remained unchanged in high threshold SAR. The static discharge associated with step inflation was unchanged in both receptor groups. The data suggest that increased SAR discharge is sustained indefinitely during increased lung volume and may account for persistent changes in breathing pattern previously observed during chronic changes in lung volume.

Absence of hCG-like activity in the blood of women fitted with intra-uterine contraceptive devices.

Blood was obtained at various stages of the menstrual cycle from 201 women fitted with intra-uterine contraceptive devices (IUDs), and plasma levels of hCG were determined by radioimmunoassay. Urine samples were obtained from 117 of these women and tested, before and after sephadex gel filtration, in a haemagglutination inhibition test for pregnancy (Pregnosticon). Plasma hCG was undetectable (less than 25 MLU/ml) in all but one of the 201 women and, in this instance, the hCG-assay appeared to be measuring a midcycle peak of LH, as evidenced by high plasma FSH levels. All unextracted urines gave negative results in the Pregnosticon test but, after extraction, 18 of the 117 urines gave positive reactions, most of these being from women at midcycle or in the luteal phase. We conclude that the IUD does not permit the development of the embryo to a point where it is capable of secreting measurable amounts of hCG. Recent claims to the contrary are probably due to cross-reaction of LH or non-specific interference in the assays used for measuring hCG.