A. V. Holden

The induction of periodic and chaotic activity in a molluscan neurone

During prolonged exposure to extracellular 4-aminopyridine (4 AP) the periodic activity of the somatic membrane of an identified molluscan neurone passes from a repetitive regular discharge of >90 mV amplitude action potentials, through double discharges to <50 mV amplitude oscillations. Return to standard saline causes the growth of parabolic amplitude-modulated oscillations that develop, through chaotic amplitude-modulated oscillations, into regular oscillations. These effects are interpreted in terms of the actions of 4 AP on the dynamics of the membrane excitation equations.

The response of excitable membrane models to a cyclic input

The response of a space-clamped patch of Hodgkin-Huxley membrane to an applied current density ofA cos(2πft)+BμA/cm2 is computed for frequencies from 5 to 250 Hz. The train of action potentials generated is phase-locked to the driving cycle,N action potentials occurring at fixed phases inM cycles. For frequencies whereN/M is a simple ratio a describing function for the membrane is computed. The phase-locked behaviour and describing functions are similar to those obtained for a simple leaky integrator neurone model.

Ionic channel density of excitable membranes can act as a bifurcation parameter

As the maximal K+-conductance (or K+-channel density) of the Hodgkin-Huxley equations is reduced, the stable resting membrane potential bifurcates at a subcritical Hopf bifurcation into small amplitude unstable oscillations. These small amplitude solutions jump to large amplitude periodic solutions that correspond to a repetitive discharge of action potentials. Thus the specific channel density can act as a bifurcation parameter, and can control the excitability and autorhythmicity of excitable membranes.

Identification of endogenous and exogenous activity in a molluscan neurone by spike train analysis

The statistical properties of background spike train activity recorded from a molluscan neurone are used to identify lengths of discharge which are produced by endogeneous pacemaker mechanisms. Such pacemaker discharge has an infinitely divisible interspike interval probability density function.

Effects of tetraethylammonium and 4-aminopyridine on the somatic potentials of an identified molluscan neuron

Abstract 1. 1. The effects of tetraethylammonium (TEA) and 4-aminopyridine (4AP) on the pattern and action potential trajectories of repetitive activity of a molluscan soma were examined using V-t and V-V (phase-plane) displays. 2. 2. 10 millimolar extracellular TEA or 4AP produced characteristic changes in both the periodicity and the action potential trajectories. 3. 3. Prolonged exposure to extracellular 4AP or intracellular TEA in the presence of depolarizing current often produced patterned, double discharges. 4. 4. Phase-plane displays provide a convenient method for quantitatively analysing the qualitative effects of drugs on identified neurons.

The response of a molluscan neurone to a cyclic input: Entrainment and phase-locking

Sinusoidally modulated current, I=A cos(2πft)+C, for A/C>1/3, was injected into the soma of an identified molluscan neurone, for frequencies that gave about one action potential/cycle. Phase locked responses were characterised by the 1:1 phase-locking-phase angle; some entrained response were not phase-locked, and some responses were not periodic. These oscillatory free runs and non-periodic responses are the result of the internal noise that is also responsible for the variability of the endogenous discharge of the neurone.

Bifurcation of periodic activity from periodic activity in a molluscan neurone

AbstractThe response of a molluscan neurone to intra-somatic micro-iontophoresis of TEA+ is a periodic discharge of action potentials that bifurcates into doublet, triplet and bursting discharges, and then through regular, small amplitude oscillations to a depolarized steady state. This response pattern is explained by the presence of two TEA+-sensitive, K+-selective conductances: we conjecture that the maximal fast, transient K+-conductance

The effects of menthol on central neurons of the pond-snail, Lymnaea stagnalis (L.)

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