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Biomedical subjects

M D Egger

Publications and source records attributed to M D Egger.

45 records · Page 3Linked to original sources
PubMed1971

The plantar cushion reflex circuit: an oligosynaptic cutaneous reflex.

1. Reflex toe extension elicited by pressure on the plantar cushion (PC) was studied in cats anaesthetized with Dial. Receptive fields and adequate stimuli for the reflex were evaluated. It was concluded that the receptors for the reflex were chiefly cutaneous pressure receptors in PC.2. The fastest impulses from the PC receptors for this reflex are conducted to the spinal cord at about 64 m/sec via fibres about 10-11 mum in diameter, i.e. the largest afferent fibres from PC. The motoneurones active in the reflex mainly supplied the intrinsic plantar muscles. Most active axons ran in the S1 ventral root.3. Extracellular recordings of interneurones in the dorsal horn of L7 spinal segment revealed that many units at the medial edge of the dorsal horn, chiefly in Rexed's laminae IV and V, were activated by stimuli similar to those eliciting the PC-toe extension reflex. These were termed intermediate threshold PC units. Some of these medially located units were activated monosynaptically by PC stimulation. Intermediate threshold PC units activated disynaptically or polysynaptically were also found in this medial region of the dorsal horn, as well as ventrolaterally and caudally in lamina V.4. No intermediate threshold PC units sent axons into dorsolateral ipsilateral thoracic white matter, in contrast to lower threshold PC units, 42% of which were driven by lateral column stimulation.5. Extracellular and intracellular recordings were made from motoneurones activated by adequate stimuli for the reflex. Minimum latencies of EPSPs revealed that, for the fastest component of the reflex, at most two interneurones could be interposed between a primary sensory neurone and a motoneurone.6. Although convergence of low threshold PC units on to intermediate threshold PC units or on to motoneurones may play a part in the PC-toe extension reflex, it appears probable that the two populations of intermediate threshold PC interneurones described above, that is, the monosynaptic and the disynaptic (with higher order interneurones), mediate the reflex.

Action Potentials↗
PubMed1969

A reappraisal of reflex stepping in the cat.

1. In re-evaluating Sherrington's experiment in which deafferented muscles in decerebrated cats ;stepped', we recorded from L5 ventral roots, a chief supplier of the major extensors of the hind legs, during stimulation of the common peroneal nerves. The extensor muscles had been denervated by appropriate dorsal root sections; the cats had been paralysed with a neuromuscular blocking agent.2. Response versus interval curves were constructed using 1 Hz stimulation. When stimulation of one peroneal preceded another, the responses ipsilateral to the second stimulation were facilitated at testing intervals of -2 to 10 msec, and inhibited at intervals of 30-400 msec.3. Responses from the L5 ventral roots mimicked ;stepping', waxing and waning at 1 Hz, only when 1 Hz was the best frequency for stimuli delivered to the two common peroneals (e.g. 24 and 25 Hz). When both sides were stimulated at the same frequency, no periodic changes in response amplitudes were seen.4. It was concluded that the apparent ;stepping' in deafferented muscles seen by Sherrington may have been due to differences in frequency of the two inductoria he used to stimulate the peroneals. We found no evidence of central timing of a pattern corresponding to walking.

Animals↗
PubMed1967

New reflected-light microscope for viewing unstained brain and ganglion cells.

We have designed and constructed a new type of reflected-light microscope to form images including only light reflected near the plane of the object. This selectivity of image formation is based on a mechanical flying-spot technique. Objects difficult or impossible to see with earlier microscopes, such as unstained cells and cell processes in brains of living salamanders and in excised dorsal root ganglia of frogs, have been observed routinely with this microscope.

Animals↗