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L Tauc

Publications and source records attributed to L Tauc.

At least 109 records · Page 6Linked to original sources
PubMed1968

A direct synaptic connexion between the left and right giant cells in Aplysia.

1. In Aplysia fasciata, intrasomatic stimulation of the giant cell (RGC) of the right upper quadrant of the abdominal ganglia is followed after a constant delay by the appearance of a synaptic potential recorded in the giant cell (LGC) of the left pleural ganglion.2. The synaptic potential recorded in the LGC soma has a biphasic form (hence biphasic post-synaptic potential or BPSP) consisting of a fast depolarizing phase of about 200-800 muV amplitude and 0.15-0.25 sec duration, followed by a slow hyperpolarizing phase of about 200-800 muV amplitude and 1-3 sec duration.3. During repetitive stimulation summation results in an over-all hyperpolarization at low frequencies (less than 5/sec) and an over-all depolarization for higher frequencies. Very high frequencies (25/sec) of stimulation of the RGC may elicit a spike in the LGC.4. Stimulation with two shocks showed increasing effects with shorter intervals on both the depolarizing and hyperpolarizing phase. These effects were progressive and there was no falling out of one of the two phases as might be expected if the BPSP was a composite of an inhibitory post-synaptic potential (IPSP) and an excitatory post-synaptic potential (EPSP).5. The effects of artificially imposed polarization of the LGC through a second micro-electrode suggest that the BPSP results from a chemical transmission mechanism for both its depolarizing and hyperpolarizing phases but electrical transmission cannot be excluded.6. Curare has no effect on the BPSP and thus excludes a cholinergic transmission mechanism. Chloride ions injected into the LGC soma do not appear to modify the BPSP and hence it is concluded that the hyperpolarizing phase is different from IPSPs of the same cell.7. No synaptic potential is recorded in the RGC following stimulation of the LGC, except in a single preparation in which the RGC soma was situated in the right pleural ganglion. In this case the synaptic potential recorded in both giant cells following stimulation of the other, was biphasic in form.8. It is concluded that the BPSP is a unitary monosynaptic potential which is a characteristic feature of the organization of these two giant cells.

Abdomen↗
PubMed1966

Input organization of two symmetrical giant cells in the snail brain.

1. The ventral surface of the snail brain contains two symmetrical giant cells which are readily identifiable in each preparation. These cells lie in the left and right metacerebrum, a cerebral integrative structure which makes afferent and efferent connexions with the periphery and with the infraoesophageal ganglia on each side by means of four ipsi- and four contralateral peripheral nerves and three ipsi- and three contralateral connectives.2. In order to examine the functional consequences of this anatomical symmetry single or double micro-electrodes, for intracellular recording and for direct stimulation, were placed in one or both of the ventral metacerebral giant cells.3. Responses from 6 ipsi- and 6 contralateral inputs were examined for orthodromic and antidromic components. The results of these experiments revealed that the output organization (the pathways of the three axonal branches of the giant cells) as well as the input organization were completely symmetrical in the two cells. The anatomical symmetry therefore seems to have been functionally preserved. Simultaneous recordings from both cells failed to reveal direct interconnexions, but did show that the cells do share in common the output of at least two interneurones.4. By recording from both cells it was also possible to demonstrate, for each of the symmetrical nerves and connectives, that laterality of an input was signalled by latency and by synaptic efficacy; the ipsilateral input produced EPSPs that were consistently more effective and of shorter latency than the contralateral ones.5. Pharmacological studies revealed that both cells fall into the category called D cells by Tauc & Gerschenfeld (1961); they responded with depolarization to iontophoretic injection of ACh and all excitatory synaptic inputs were blocked by d-tubocurarine.6. With none of the twelve afferent inputs was synaptic inhibition observed. The results support the notion that D cells do not receive inhibitory input.

Acetylcholine↗
PubMed1966

Anomalous rectification in the metacerebral giant cells and its consequences for synaptic transmission.

1. In the central neurones that have so far been examined the passive electrical properties of the extrasynaptic membrane has been shown to be relatively constant in the subthreshold range. Consequently, excitatory synaptic potentials produced by chemical transmission tend to vary in amplitude with changes in membrane potential, decreasing with depolarization and increasing with hyperpolarization.2. In the two symmetrical giant cells of the ventral metacerebrum of the snail, the EPSPs failed to show the expected alterations in amplitude with changes in membrane potential. Near the resting level the EPSP increased slightly with membrane depolarization and decreased slightly with hyperpolarization.3. These paradoxical results were not attributable to a change in transmitter release since similar results were obtained when ACh, the putative transmitter, was released iontophoretically on to the cell membrane by means of an extracellular pipette.4. Measurement of the current-voltage relation of the extrasynaptic membrane revealed two types of rectifying conductance changes. The first, an increase in conductance with depolarization, was turned on at a depolarization of about 15 mV. Its conductance change was similar to the delayed rectification familiar from studies of peripheral nerve and muscle. The second occurred on either side of the resting level, from about 15 mV hyperpolarization to about 10 mV depolarization, and manifested itself as a decrease in conductance with depolarization and an increase with hyperpolarization. By analogy to a similar phenomenon known to occur in skeletal muscle this second rectification has been termed anomalous rectification.5. The average resistance at 25 mV hyperpolarization was 2.3 x 10(6) Omega, while at 10 mV depolarization it was 2.1 x 10(7) Omega, yielding an average rectification ratio of 10 for the anomalous conductance change.6. The anomalous rectifying conductance seems to account for the paradoxical behaviour of the EPSP and ACh response to changes in membrane potential. Moreover, the finding that the sharpest change in the anomalous rectification curve occurred on either side of the resting level suggests that this rectification is functionally important as a postsynaptic determinant of synaptic efficacy. Several additional lines of evidence in support of this suggestion have been obtained.

Acetylcholine↗