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J Halliwell

Publications and source records attributed to J Halliwell.

4 recordsLinked to original sources
PubMed1994

The effect of age on dendrites in the rat superior cervical ganglion.

Intracellular injection of a biotinylated probe in fixed superior cervical ganglia followed by confocal microscopy was used to investigate the effects of age on the dendritic arborisation of sympathetic neurons in rats aged 6 wk (young adult), 7 months (fully grown adult) and 24 months (aged). In accordance with other studies considerable dendritic growth was observed during postnatal development. However, in old age dendritic growth did not continue, and significant atrophy was observed. Quantitation of neuronal morphology showed significant reductions in soma size, total dendritic length, number of branch points and total area of dendritic arborisation in old age. Unexpectedly, significant reductions in the numbers of primary dendrites were observed in maturity and in old age. Concomitant with this atrophy there was an increase in age-related morphological abnormalities. The similarities between the atrophy and dendritic abnormalities shown by our aged neurons and those seen in other studies of young adult sympathetic neurons following axotomy or trophic factor deprivation are discussed.

Aging↗
PubMed1988

Some properties of the membrane currents underlying the fertilization potential in sea urchin eggs.

1. The ionic currents that underly the fertilization potential of sea urchin eggs were studied in Lytechinus pictus using a single-electrode voltage clamp technique. 2. In unfertilized eggs, a transient inward current was activated at membrane potentials more positive than -45 mV. The maximum amplitude of the current was 0.56 +/- 0.35 nA (mean +/- S.D., n = 33) at a membrane potential of -35 to -25 mV. 3. The amplitude of this transient inward current was decreased by reducing the external concentration of calcium ions and by substituting barium or strontium ions for calcium in the external medium. Cobalt (10-20 mM) and gadolinium (200-500 microM) ions reduced the amplitude of this current in the presence of calcium ions. 4. A transient outward current was activated in unfertilized eggs at membrane potentials more positive than -10 mV. This current inactivates with a time constant of 16 ms at a membrane potential of -9 mV and re-activates over a period of several seconds at a membrane potential of -72 mV. 5. When unfertilized eggs were treated with the calcium ionophore A23187 under voltage clamp conditions, an inward current developed. It reached a maximum 30 s after its onset and declined thereafter. By 90 s it had become constant at 10% of its peak value. 6. The inward current induced by A23187 was voltage dependent. It was maximal at -25 mV in the steady state. 7. When eggs were fertilized under voltage clamp conditions, the fertilization current, If, was recorded. At a holding potential of -50 or -70 mV If had the following characteristics: (a) an initial inward shoulder with a duration ranging from 12 to 30 s; (b) an inward current peak that was attained between 40 and 100 s after the onset of the shoulder current and declined over the next 60 s; (c) an outward current that appeared after the inward current had declined. 8. Current-voltage relations obtained during If showed that the late component of the inward current was voltage dependent. It was maximal at -25 mV in the steady state and resembled the late component of the inward current recorded in A23187-activated eggs. 9. These results indicate that the form of the action potential in unfertilized eggs is due to the activation of a transient inward current and an inactivating outward current. The sustained depolarization after fertilization is due to the activation of a voltage-dependent inward current by the increase in intracellular free calcium concentration that occurs at fertilization.

Action Potentials↗