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M V Siegler

Publications and source records attributed to M V Siegler.

28 records · Page 2Linked to original sources
PubMed1979

The morphology of local non-spiking interneurones in the metathoracic ganglion of the locust.

The morphology is described of a number of non-spiking interneurones in the metathoracic ganglion of the locust that control motor neurones innervating muscles in the coxa and femur of a hind leg. The non-spiking interneurones are penetrated with microelectrodes, physiologically characterized, injected with cobalt, and the stain subsequently intensified with silver. The interneurones have diverse shapes but all are local, intraganglionic interneurones. Their cell bodies are 10-20 micrometer in diameter and lie in either the ventral or dorsal layers of cell bodies that form a cortex around the ganglion. The branches of the interneurones are profuse and overlap those of the motor neurones that they affect. On interneurone may have branches in both the most ventral and the most dorsal areas of the neuropile. Most interneurones have branches only in one half of the ganglion, but one interneurone has extensive and asymmetrical regions of branches in both halves of the ganglion (fig. 4). Similar physiological effects can be mediated by interneurones with distinct morphologies. For example, the single slow extensor motor neurone is excited by six distinct morphological types of interneurones (figs. 10-13). It is suggested that as many as 65% of the neurones within a ganglion may be local interneurones, many of which in turn may be non-spiking.

Action Potentials↗
PubMed1978

Graded synaptic transmission between local interneurones and motor neurones in the metathoracic ganglion of the locust.

1. In the metathoracic ganglion of the locust some neurones can effect changes in the membrane potential of identified post-synaptic motor neurones without themselves spiking. 2. These 'non-spiking' neurones have processes only within the metathoracic ganglion, and therefore are local intraganglionic interneurones. 3. The absence of spikes in the interneurones reflects their normal physiological state and is not due to the experimental conditions. 4. When the interneurones are depolarized by the injection of current pulses lasting several hundred milliseconds, post-synaptic motor neurones are either depolarized, or hyperpolarized, for the duration of the pulse. 5. The magnitude of the change in post-synaptic voltage is graded according to the amount of presynaptic current. 6. A number of physiological tests indicate that the graded effects upon motor neurones are mediated by chemical synaptic transmission. For example, an evoked hyperpolarization of a motor neurone can be reversed in polarity by simultaneously hyperpolarizing the motor neurone with injected current. 7. At their resting potential some interneurones tonically release sufficient transmitter to have a measurable post-synaptic effect. The injection of depolarizing and hyperpolarizing currents into these interneurones effects opposite changes in post-synaptic potential. 8. Other interneurones must be depolarized from resting potential before a post-synaptic effect is observed, and hyperpolarizing currents have no post-synaptic effect. In these interneurones it is estimated that a depolarization of only 2 mV is sufficient to effect the release of transmitter. 9. The membrane potentials of non-spiking interneurones can fluctuate by as much as 15 mV during active movements of the hind legs and individual p.s.p.s as large as 5 mV can be recorded. Therefore, summed p.s.p.s or even single ones are expected to be the electrophysiological signals effecting transmitter release from these interneurones.

Action Potentials↗