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K J Muller

Publications and source records attributed to K J Muller.

53 records · Page 3Linked to original sources
PubMed1981

Long-term survival of glial segments during nerve regeneration in the leech.

Nerve injury that severs axons also disrupts ensheathing glial cells. Specifically, crushing or cutting the leech nerve cord separates the glial cell's nucleated portion from an anucleate recording, by intracellular injection of Lucifer Yellow dye and horseradish peroxidase (HRP) as tracers, and by electron microscopy. The nucleated portion of the glial cell did not divide, degenerate, or grow appreciably. The severed glial stump remained isolated from the nucleated portion but maintained its resting potential and normal morphology for months. Stumps typically began to deteriorate after 3 months. Small macrophage-like cells, or 'microglia' increased in number after injury and ensheathed axons, thus partially replacing the atrophying glial stump. Some axons in the nerve cord degenerated; the remainder appeared morphologically and physiologically normal. Thus, both nucleated and anucleate glial segments persisted throughout the one to two months required for axons to regenerate functional connections. Glial cells in the leech are therefore available to guide physically the growing axons or to contribute in other ways to nerve regeneration.

Animals↗
PubMed1981

Transmission at a 'direct' electrical connexion mediated by an interneurone in the leech.

1. Touch sensory neurones in the leech excite a rapidly conducting interneurone called the S-cell. Although the electrical synaptic connexion between the two cells is monosynaptic by physiological criteria, intracellular staining reveals that the touch cells and the S-cell do not make contact, but instead are linked by a pair of small interneurones. 2. The electrical coupling between touch cells and S-cells rectifies, in that depolarizing current but not hyperpolarizing current passes from the touch cell into the S-cell. The rectifying junction is between the touch cells and coupling interneurones, while the connexion between coupling interneurones and the S-cell passes current in both directions. 3. Selective destruction of the coupling interneurones by intracellular injection of a protease interrupts the disynaptic electrical connexion between touch and S-cells. 4. The touch cell's geometry and membrane properties account for the failure of impulses that are generated in certain portions of the receptive field in the skin to propagate beyond the first branch-points of the touch cell axon within the ganglion. Conduction block at branch-points is used to examine physiologically the spatial distribution of contacts between the touch cell and the coupling interneurones. In addition, it is shown that under natural conditions branch-point failure presynaptically reduces the effectiveness of the electrical synaptic connexions.

Horseradish Peroxidase↗
PubMed1980

Removal of the synaptic target permits terminal sprouting of a mature intact axon.

When the central nervous system (CNS) develops, neurones send out axons to make contact with appropriate synaptic target cells and then stop growing. If its usual target is missing, an axon may continue to grow until it synapses with a suitable but inappropriate target. This suggests that contact with a synaptic target is important in stopping axonal growth during development. Many classes of neurone in the adult CNS retain a capacity to grow towards denervated targets, but it is not known whether the synaptic contacts established during development continue to regulate the growth of individual mature, intact axons. This has been a difficult problem to investigate; in vertebrates most studies necessarily involve large populations of neurones, and the most direct approach, removal of a synaptic target, usually damages many neurones, including the axons that are to be studied. We report here a demonstration of target cell influences on the growth of a single mature, intact axon in the CNS of the leech by selectively destroying the axon's synaptic target without injuring the axon itself. Target removal, which itself does not trigger sprouting of intact axons, permits the intact axon to grow at its tip in response to injury of other axonal branches of the same cell.

Age Factors↗
PubMed1979

The morphological and physiological properties of a regenerating synapse in the C.N.S. of the leech.

Regeneration of an electrical synapse between particular interneurons in the medicinal leech was traced physiologically and morphologically using intracellular recording the horseradish peroxidase (HRP) injection. The synapse between S-cell interneurons lies in the connective midway between segmental ganglia, so crushing near one ganglion severs only one S-cell's axon. The severed distal stump remains connected to the adjacent uninjured S-cell and continues for weeks to conduct impulses. The injured cell regenerates, while its uninjured "target" neuron in the next ganglion does not grow. After the sprouts of the regenerating neuron cross the crush, one or a few branches grow along the surviving distal stump toward the original synapse. After about one month when the region of original synapse has been reached, regenerating neurons form electrical junctions and stop growing. Thereafter electrical coupling improves in stages. Within two months the regenerated neuron attains full caliber, the stump degenerates and function is normal. In some instances within days or weeks of crushing, the regenerating neuron forms a basket of synapses upon its severed distal stump and then continues growing to synapse with the target. When this occurs, electrical coupling and subsequent impulse transmission between S-cells rapidly resumes. These experiments indicated that the regenerating neuron is guided to its proper synaptic target by recognizing and following its severed distal stump. Sometimes the distal stump itself becomes an intermediate synaptic target.

Animals↗
PubMed1978

Nonequivalence of alpha-bungarotoxin receptors and acetylcholine receptors in chick sympathetic neurons.

alpha-Bungarotoxin binds selectively to chick sympathetic neurons that are responsive iontophoretically applied acetylcholine. alpha-Bungarotoxin (125 nM) does not affect the response of cultured neurons to acetylcholine, nor does it affect a cholinergic synaptic potential recorded from sympathetic ganglia. d-Tubocurarine (100 muM) inhibits alpha-bungarotoxin binding and blocks acetylcholine receptor function in both preparations, but alpha-bungarotoxin does not protect acetylcholine receptors against d-tubocurarine blockade of acetylcholine responses. The receptor for alpha-bungarotoxin can be extracted from neuronal membranes with nonionic detergents and, when assayed by velocity sedimentation in sucrose gradients, sediments at a rate faster than that of skeletal muscle acetylcholine receptors. Treatment of alpha-bungarotoxin-receptor complexes with glutaraldehyde (0.1%, wt/vol) increases their stability from a half-time for dissociation of 3.5 hr to greater than 6 days at 23 degrees. This permits a quantitative assay of alpha-bungarotoxin-receptor complexes after relatively long periods of velocity sedimentation. It is concluded that alpha-bungarotoxin does not bind to the acetylcholine-binding site of neuronal acetylcholine receptors. These results compel a reevaluation of studies that assume that alpha-bungarotoxin is a specific ligand for neuronal acetylcholine receptors.

Acetylcholine↗
PubMed1974

Different properties of synapses between a single sensory neurone and two different motor cells in the leech C.N.S.

In leech ganglia, an individual sensory cell that responds specifically to noxious mechanical stimulation of the skin (N cell) excites two different motoneurones. One raises the annuli of the skin into ridges (the AE cell), while the other innervates logitudinal muscles and thereby shortens the body segment (L cell). A comparison has been made of the way in which these two synapses behave when their common presynaptic cell is stimulated in various conditions.1. Using previously described criteria, N sensory cells have been shown to make monosynaptic chemical connexions with both the AE and L motoneurones (Nicholls & Purves, 1972). Following a single stimulus, the excitatory synaptic potential recorded in the AE motoneurone was only about one tenth the size of that in the L cell (approximately 0.5 mV compared to 5 mV). Trains of impulses in the same N sensory cell gave rise to synaptic potentials in the AE and the L motoneurones that underwent phases of facilitation and depression; the facilitation, however, was characteristically greater and longer lasting at synapses upon the AE motoneurone.2. The differences between the two synapses were accentuated in Ringer fluid containing increased concentrations of Ca and also in the cold. Under both of these conditions repetitive firing by the N sensory cell could give rise to synaptic potentials in the AE motoneurone which progressively increased in amplitude, while those in the L motoneurone became smaller.3. The results suggest that the differences in synaptic transmission can be accounted for by variations in the amount of transmitter released at the presynaptic N cell terminals, rather than by differences in the post-synaptic cells. The animal's behaviour corresponds to expectations from the physiology of the synapses.

Action Potentials↗
PubMed1974

Persistent modification of synaptic interactions between sensory and motor nerve cells following discrete lesions in the central nervous system of the leech.

We have examined changes that develop in the synaptic interactions of sensory and motor nerve cells following surgical lesions to the central nervous system of the leech. In one type of operation an individual ganglion was isolated from the rest of the nervous system by severing all the incoming and outgoing fibres. During the next few weeks, marked changes appeared in synaptic interactions.1. In chronically isolated ganglia inhibitory potentials were recorded in the motoneurone which raises the skin into ridges (the AE cell) following impulses in sensory neurones that respond to pressure (P) or noxious (N) stimuli. In contrast the same AE cell in ganglia taken from normal animals shows excitatory synaptic potentials when the P or N sensory cells are stimulated.2. Another altered synaptic interaction in ganglia isolated by lesions was that between sensory cells responding to touch and a motoneurone that supplies longitudinal muscles (L cell). Instead of the pure, electrical coupling potential seen normally, a large, additional chemically mediated excitatory potential was also apparent.3. Some of the changes in synaptic interactions were not restricted to synapses within the isolated ganglion, but appeared gradually over the following year in successive ganglia along the length of the ventral nerve cord.4. Indirect evidence suggests that the altered synaptic potentials that became conspicuous after operations are also present but smaller and obscured in normal animals.5. It is concluded that some synapses in the leech nervous system are more readily changed than others by cutting the connectives. Furthermore, these changes influence in a predictable manner the way in which the animal behaves in response to mechanical stimuli.

Action Potentials↗
PubMed1973

Photoreceptors in the crayfish compound eye: electrical interactions between cells as related to polarized-light sensitivity.

1. The sensitivity to plane-polarized light and the electrical interactions of photoreceptors were examined with intracellular and extracellular micro-electrodes in excised compound eyes of the crayfish.2. There are two types of photoreceptor: each photoreceptor cell responds best to polarized light when the electric-vector of the light is oriented in one of two orthogonal directions. Seven cells, representing each type, are grouped together to form ommatidia.3. In each ommatidium, cells that are sensitive to the same orientation of the electric-vector of polarized light are coupled electrically. Cells having orthogonal polarized-light sensitivities are not coupled.4. Nearly all cells studied were sensitive to orange light. A few cells of both types were found that were sensitive to blue light. Blue-sensitive cells were not coupled to orange-sensitive cells.5. The photocurrents of both cell types produce negative extracellular potentials which can be greater than 10 mV when measured near the photoreceptive membranes within ommatidia. Evidence suggests that the extracellular potentials produced by one type of cell can effectively reduce the receptor potentials recorded in the other cell type. It is proposed that such a mutual non-synaptic interaction can make a cell more sensitive to the orientation of polarized-light than would be predicted from the cell's differential absorption of polarized light (i.e. its dichroic ratio).

Animals↗