Synaptic Inhibition in an Isolated Nerve Cell

Abstract

Following the preceding studies on the mechanisms of excitation in stretch receptor cells of crayfish, this investigation analyzes inhibitory activity in the synapses formed by two neurons. The cell body of the receptor neuron is located in the periphery and sends dendrites into a fine muscle strand. The dendrites receive innervation through an accessory nerve fiber which has now been established to be inhibitory. There exists a direct peripheral inhibitory control mechanism which can modulate the activity of the stretch receptor. The receptor cell which can be studied in isolation was stimulated by stretch deformation of its dendrites or by antidromic excitation and the effect of inhibitory impulses on its activity was analyzed. Recording was done mainly with intracellular leads inserted into the cell body. 1. Stimulation of the relatively slowly conducting inhibitory nerve fiber either decreases the afferent discharge rate or stops impulses altogether in stretched receptor cells. The inhibitory action is confined to the dendrites and acts on the generator mechanism which is set up by stretch deformation. By restricting depolarization of the dendrites above a certain level, inhibition prevents the generator potential from attaining the "firing level" of the cell. 2. The same inhibitory impulse may set up a postsynaptic polarization or a depolarization, depending on the resting potential level of the cell. The membrane potential at which the inhibitory synaptic potential reverses its polarity, the equilibrium level, may vary in different preparations. The inhibitory potentials increase as the resting potential is displaced in any direction from the inhibitory equilibrium. 3. The inhibitory potentials usually rise to a peak in about 2 msec. and decay in about 30 msec. After repetitive inhibitory stimulation a delayed secondary polarization phase has frequently been seen, prolonging the inhibitory action. Repetitive inhibitory excitation may also be followed by a period of facilitation. Some examples of "direct" excitation by the depolarizing action of inhibitory impulses are described. 4. The interaction between antidromic and inhibitory impulses was studied. The results support previous conclusions (a) that during stretch the dendrites provide a persisting "drive" for the more central portions of the receptor cell, and (b) that antidromic all-or-none impulses do not penetrate into the distal portions of stretch-depolarized dendrites. The "after-potentials" of antidromic impulses are modified by inhibition. 5. Evidence is presented that inhibitory synaptic activity increases the conductance of the dendrites. This effect may occur in the absence of inhibitory potential changes.

Control of Retinal Sensitivity

“…This suggests that the two antagonistic components of the response may not simply add algebraically. The hyperpolarization might be an IPSP that "shunts" the membrane thereby reducing the effectiveness of subsequent excitatory inputs (Kuffler and Eyzaguirre, 1955) or only part of the lateral effect from the surround might be fed forward to the ganglion cell in the form of a hyperpolarizing transient; another signal might be fed back to bipolars to limit the response. It was shown previously (Werblin, 1972) that an illuminated windmill pattern, when spinning in the far surround of the ganglion cell receptive field, was effective in antagonizing the central response.…”

Mechanism of the Paralysing Action of Piperazine on Ascaris Muscle

“…We feel inclined to construe the prolonged inhibitory effects observed in the presence of piperazine as a form of postinhibitory polarization or depression, a term introduced by Kuffler & Eyzaguirre (1955) to describe the delayed hyperpolarization and suppression of spike activity which follow the stimulation of the inhibitory axon in isolated neurone preparations from the stretch receptor of the crayfish. Although DRUG INHIBITION OF ASCARIS MUSCLE Fig.…”

“…In some of the experiments described by Kuffler & Eyzaguirre (1955) the intervals separating the first few spikes after the postinhibitory polarization are lengthened, that is the rate of rise of the prepotentials is slowed down. This is what is shown in the lower record of Fig.…”

Proceedings of the Physiological Society

“…d 3 57 P PROCEEDINGS OF THE PHYSIOLOGICAL between the present findings and the condition of precocious puberty knowil to occur in young children in association with certain hypothalamic tumours (see Bauer, 1954 (Brock, Coombs & Eccles, 1952), crayfish sensory neurones (Kuffler & Eyzaguirre, 1955) and Betz cells (Phillips, 1956). We have found that the discharge of cerebellar Purkinje cells in decerebrate cats may also be inhibited in this way.…”