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G G Green

Publications and source records attributed to G G Green.

At least 37 records · Page 2Linked to original sources
PubMed1996

Membrane properties of complex spike firing neurons of the mouse dorsal cochlear nucleus in vitro.

Intracellular recordings were made from complex spike firing neurons of the mouse dorsal cochlear nucleus (DCN) in vitro. The whole cochlear nucleus was dissected out and maintained submerged in rapidly flowing artificial cerebrospinal fluid (CSF). Recordings were made with current clamp techniques in the presence or absence of ion channel blocking drugs tetrodotoxin (TTX, 1 microM), tetraethylammonium (TEA, 20 mM), 4-aminopyridine (4-AP, 5 mM) or verapamil (50, 100, 150, 250 microM). The cells showed both spontaneous firing and responses to injections of depolarising current consisting of a mixture of a tall single action potential and complexes of 2 to 3 smaller wider action potentials superimposed on a plateau depolarisation. The membrane properties were: resting membrane potential -68.8 +/- 8.5 mV, cell resistance 54.1 +/- 26.5 M omega, time constant 9.6 +/- 5.4 ms and capacitance 0.25 +/- 0.5 nF; the first three variables had bimodel distributions. The current/voltage (I/V) relationship at membrane below resting was non-linear. Previously published histological evidence from the mouse DCN has shown that both cartwheel cells and Purkinje-like neurons are present. Both DCN cartwheel cells and cerebellar Purkinje cells are known to fire both tall single action potentials and complexes of smaller wider action potentials. It is therefore possible that the recordings shown here were made from these neuron types. TTX (1 microM) abolished both the tall single and the complexes of smaller action potentials, suggesting that the tall single action potentials are sodium dependent and possibly that a TTX sensitive sodium channel is responsible for the plateau as is suggested for Purkinje cells in the cerebellum. Verapamil (100 microM) abolished only the complex action potentials and the plateau leaving the tall narrow action potentials intact, which is consistent with the smaller complexes being calcium dependent. Higher concentrations abolished all spiking activity. TEA and 4-AP used separately both caused marked depolarisation to around -20 mV, suggesting that there is a large potassium current active at and near resting.

4-Aminopyridine↗
PubMed1996

Membrane properties of mouse anteroventral cochlear nucleus neurons in vitro.

Intracellular recordings were made from neurons of the mouse anteroventral cochlear nucleus (AVCN) in vitro. The whole cochlear nucleus was dissected out and maintained submerged in rapidly flowing artificial CSF. This preparation has the advantages of maintaining cell-to-cell connections and dendritic trees whereas slices and enzymatically separated preparations do not. Recordings were made using current clamp technique in the presence and absence of the ion channel blockers, tetrodotoxin (TTX 1 microM), tetraethylammonium (TEA 20 mM), 4-aminopyridine (4-AP 5 mM) or verapamil (150 microM). Two distinct types of neurons were observed when tested with depolarizing current pulses: one which fired only a single action potential at the onset of stimulation followed by a relative depolarization for the remainder of the stimulus period, and the other which fired a sustained train of action potentials, each followed by a large undershoot, then a rapid recovery phase and the slower depolarization to threshold. The single spike cells (n = 24) had resting membrane potentials of -63.4 +/- 4.7 mV, resistance of 48.4 +/- 29.6 M omega, time constant of 3.47 +/- 3.1 ms, capacitance of 0.081 +/- 0.079 nF. The I/V plot was non-linear above the resting membrane potential and linear below. Spike train cells (n = 24) had resting membrane potentials of -64.2 +/- 4.54 mV, resistance of 69.8 +/- 28.9 M omega, time constant of 6.51 +/- 3.09 ms, capacitance of 0.11 +/- 0.087 nF. The I/V plot was linear both below resting membrane potential and up to threshold for spike firing. TTX abolished spike firing in both cell types. TEA significantly increased the spike duration in both cell types. 4-AP increased the spike duration in spike train cells but not in single spike cells. Verapamil had no effect on the firing properties of both cells but it significantly increased the spike duration of spike train cells. The single spike cells are known to fire rapidly and repetitively in vivo. Injection of sine wave currents caused rapid and repetitive firing suggesting that these cells require hyperpolarization to allow for removal of inactivation. There was a linear relationship between injected depolarizing current and the rate of action potential firing in spike train cells.

4-Aminopyridine↗
PubMed1992

Culture of human middle ear mucosal explants; mucin production.

Middle ear mucosal biopsies could be maintained in culture for up to 7 days, the longest time attempted in this study. Mucin biosynthesis and secretion were measured by incorporation of 14C-glucosamine. Three peaks of radioactivity were present when the dialysed medium was chromatographed. Peak I which accounted for about 10% of the total radioactivity had properties characteristic of mucin. The other two peaks were not characteristic of mucins. Labelled macromolecules excluded on Sepharose 2B were also present in the tissue. Autoradiography of the explants showed that the labelled glucosamine was concentrated in the epithelial layer. Morphometry demonstrated that 1-2% of the epithelial cell volume consisted of goblet cells. The proportionate incorporation of radioactivity into macromolecules increased with increasing epithelial cell volume. This system will allow assessment of factors implicated in the pathogenesis of otitis media with effusion and the study of the action of pharmacological agents on biosynthesis and secretion.

Autoradiography↗
PubMed1992

Otitis media with effusion: components which contribute to the viscous properties.

Middle ear effusions from children undergoing myringotomy were classified into thick (mucoid) and thin (serous) on the basis of their flow properties. Their composition was analysed and their rheological properties measured. The viscosity of the effusions was measured using a Contraves low shear viscometer and expressed as specific viscosity per mg/ml of non-dialysable solids present. In order to measure the effusion viscosity it was necessary to solubilize the effusion by mild homogenisation in a phosphate buffer pH 6.7 containing a cocktail of proteolytic inhibitors. The viscosity of mucoid effusions was significantly greater than that of the serous effusions. There was a small but measurable amount of proteolytic activity in the effusions, range 0.05-1.79 micrograms/mg of non-dialysable solids. This proteolytic activity was not significantly different between the thick and thin effusions and was therefore unlikely to explain the difference in viscosity. Analysis of the constituents of the effusions showed that glycoprotein and DNA but not protein nor lipid were significantly higher in the mucoid effusions compared to the serous effusions. The viscosity of the effusions correlated with the glycoprotein concentration but not with the protein or lipid concentration. Under certain circumstances the DNA concentration did correlate with the viscosity of the effusion. However, digestion with a proteinase free DNase did not reduce the viscosity of the effusion. These results demonstrate that classifying effusions as thick and thin based on visual inspection and flow properties is valid and that the only constituent present in the effusions that determines viscosity is mucin.

Body Water↗
PubMed1989

Neurophysiological evidence of auditory channel anomalies in developmental dysphasia.

Steady-state auditory evoked responses to frequency-modulated tones were obtained from normal children and two groups of children with developmental language disorders (developmental dysphasia). Children with predominantly expressive language impairment produced responses not different from normal children, while children with primary receptive language impairment produced responses that were markedly diminished, even absent. This occurred in recordings from either cerebral hemisphere and at mean frequency-modulation depths ranging from +/- 20 to +/- 100 Hz. Pathophysiology of auditory mechanisms concerned with frequency-modulation analysis are particularly associated with receptive developmental language impairment and may underlie associated difficulties in speech perception.

Acoustic Stimulation↗
PubMed1989

Rheologic studies on middle ear effusions and their mucus glycoproteins.

The properties of pooled thick and thin middle ear effusions, from children with otitis media with effusion, were studied by viscometry. Mucus glycoproteins were responsible for effusion viscosity. Their percentage by weight in thick and thin effusions was 25% and 8.2%, respectively. N-acetylcysteine and 0.2 mol/L of mercaptoethanol caused a 39% viscosity drop in a 5-mg/mL glycoprotein solution, whereas S-carboxymethylcysteine had no effect. Treatment of thick effusions with 0.2 mol/L of mercaptoethanol initially caused a viscosity decrease followed by a gradual increase. Higher reducing agent concentrations (0.5 mol/L) caused a more rapid decrease followed by a rapid increase, presumably by causing nonspecific aggregation of reduced protein molecules. These results suggest that the concentration of and the time that a mucolytic is in the middle ear would be of prime importance in achieving the desired decrease in viscosity.

Acetylcysteine↗
PubMed1988

Mucolytic agents and otitis media with effusion.

Middle ear effusion was obtained from children with otitis media with effusion and separated into thick (mucoid) and thin (serous) pools. Both effusion types contained similar amounts of non-dialysable solids. However, the thick effusions contained more mucus glycoprotein than the thin effusions, 25% and 8.2% respectively. Amino acid and carbohydrate analysis of the CsCl purified mucus glycoproteins demonstrated that the glycoprotein from the thick and thin effusions differed in their protein core, those from the thick effusions possessing a higher percentage of serine and threonine, the amino acids to which the sugar side-chains attach. They are also more glycosylated. N-acetyl cysteine and mercaptoethanol caused a fall in the viscosity of solutions of purified middle ear glycoprotein and effusion homogenate. However, longer term incubation caused a rise above the starting viscosity. This effect was concentration-dependent, and was mediated by low molecular weight components in the effusion and not the mucus glycoprotein. S-carboxymethyl cysteine had no effect on the viscosity of either the purified mucus glycoprotein or the effusion homogenate. Therefore, to produce a decrease in effusion viscosity in vivo, the concentration of mucolytic reaching the middle ear and the time it remains there are critical factors.

Amino Acids↗
PubMed1987

Characterization of human middle ear mucus glycoprotein in chronic secretory otitis media (CSOM).

Middle ear effusion was obtained from children with chronic secretory otitis media undergoing myringotomy. The effusions contained about 120 mg/ml non-dialysable solids, of which 18-31% was mucus glycoprotein. The purified mucus glycoprotein had a composition characteristic of other mucus glycoproteins. Amino acid analysis of the glycoprotein indicates a protein core consisting of glycosylated regions resistant to proteolysis and non-glycosylated regions susceptible to proteolysis. Analysis of the mucus glycoprotein by gel filtration on Sepharose 2B showed that reduction caused a decrease in hydrodynamic size and proteolysis caused a further decrease. The difference was confirmed by sedimentation coefficient and viscosity measurements. The reduced glycoprotein had an intrinsic viscosity of 0.113 ml/mg and an S0(20) of 15.2S compared to a value of 0.018 ml/mg and 9.6S for the proteolytically digested glycoprotein. These results suggest a model for this middle ear mucus glycoprotein, in which the native glycoprotein is a large molecular mass polymer maintained by disulphide bridges. These disulphide linked glycoprotein units are broken down into smaller units by proteolysis. The mucus glycoprotein could not be purified completely free from low molecular mass components. A glycoprotein, susceptible to proteolysis Mr 28,000-33,000 co-fractionates with the major high molecular mass mucus glycoprotein.

Child↗
PubMed1986

Steady-state evoked responses to sinusoidally amplitude-modulated sounds recorded in man.

Steady-state potentials evoked in response to binaural, sinusoidally amplitude-modulated (AM) pure tones and broadband noise signals were recorded differentially from position F4 and the ipsilateral mastoid on the human scalp. The responses elicited by the AM stimuli were approximately periodic waveforms whose energy was predominantly at the modulation frequency of the stimulus. The magnitude of responses was between 0.1 and 4 microV for modulation frequencies between 2 and 400 Hz imposed on a 1-kHz carrier signal. The magnitude of the responses increased linearly with log modulation depth for low (4 Hz) and high (80 Hz) modulation rates. The response magnitude also increased linearly with the mean intensity of the sound for intensities up to 60 dB above the subject's pure tone threshold; at higher levels the response saturated. The relationship between response magnitude and modulation frequency (the modulation transfer function) was a lowpass function for both pure tone and broadband noise carrier signals. The modulation transfer functions were similar to those obtained from human psychophysical measurements where spectral cues are either unavailable or not used by the subject. The responses also contained a significant component at the second harmonic of the modulation frequency. The magnitude of this component was greatest at modulation rates between 5 and 20 Hz. The responses elicited by ipsilateral and contralateral monaural stimulation were approximately equal in magnitude, and binaural stimulation produced a potential 30% greater than the individual monaural responses. It is suggested that the evoked response represents the entrained neural activity to temporal amplitude fluctuations, and reflects the psychophysically measured performance of the auditory system for the detection and analysis of amplitude modulation.

Adult↗
PubMed1985

Fourier analysis of ECochG templates.

Computer templates of the action potential/summating potential waveforms from electrocochleograms have been analysed in the frequency domain following the Fast Fourier Transform. Analysis in the frequency domain is compared with standard time domain analysis and some inadequacies of the latter technique are shown. A simple account of the principles of Fourier analysis is given which may be of assistance to the general reader, particularly as computer packages currently being marketed with electric response audiometry equipment make this analytical technique readily available.

Action Potentials↗
PubMed1978

Combined left ventricular aneurysm and coronary artery bypass surgery: long-term results of 100 consecutive patients.

Forty-four percent of 2,367 patients who had operations for the complications of coronary atherosclerosis between 1971 and 1977 were noted to have major left ventricular wall motion abnormalities. Of this group, 100 patients required left ventricular aneurysm resections or plications (4.2%). There were 85 men and 15 women. Their average age was 52 years (range, 30 to 68 years). Concomitant coronary artery bypass grafting was required in 95 patients. The operative mortality was 7% and the actuarial survival at six years was 78%. Patients were followed for an average of 31 months (range, 3 to 72 months). Eighty-eight percent of the survivors had excellent or good results with improvement of their functional status to the New York Heart Association classes I and II. Age, congestive heart failure, and poor residual left ventricular function had an adverse effect on the outcome of these patients. Concomitant coronary artery bypass grafting seems to have favorably influenced their outcome and functional recovery. Surgical judgment is of great importance in selecting which patients require left ventricular aneurysm resection.

Adult↗