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Biomedical subjects

M D Egger

Publications and source records attributed to M D Egger.

At least 37 records · Page 2Linked to original sources
PubMed1986

The facial "motor" nerve of the rat: control of vibrissal movement and examination of motor and sensory components.

Rhythmical whisking of the mystacial vibrissae at about 7 Hz during exploration is one of the most conspicuous behavioral patterns in the rat. To identify the final common pathway for vibrissal movement, individual motor branches of the facial nerve, including the posterior auricular, temporal, zygomatic, buccal, marginal mandibular, cervical, stylohyoid, and posterior digastric branches, were cut, either singly or in various combinations. We found that vibrissal movement could be abolished only by transection involving the buccal branch and the upper division of the marginal mandibular branch. To trace back the central origins of the buccal and marginal mandibular, as well as the other branches of the facial nerve, all distal to the stylomastoid foramen, horseradish peroxidase (HRP) was applied to the cut proximal ends of these individual branches. The retrograde HRP labelling in the facial motor nucleus revealed topographical representation of these branches in which the buccal and marginal mandibular branches were represented laterally. The stylohyoid and posterior digastric branches originated from cells in the suprafacial nucleus. Consistent with earlier observations with intramuscular HRP injections, the motoneuronal population devoted to vibrissal movement did not seem to be substantially larger than that for other facial movements. An additional examination was made of the labelled afferent component of the facial motor nerve. We confirmed and extended previous findings that none of the above facial motor nerve branches, except the posterior auricular branch, contained a significant number of afferent fibers originating from the geniculate ganglion, the sensory ganglion of the seventh nerve. In addition, no labelling was seen in the mesencephalic trigeminal nucleus or trigeminal ganglion. These findings, in combination, suggest that, with the exception of the posterior auricular branch, all the facial motor nerve branches, including those involved in vibrissal movement, are almost entirely efferent.

Animals↗
PubMed1985

4-Aminopyridine induces expansion of cutaneous receptive fields of dorsal horn cells.

Systemic administration of 4-aminopyridine (4-AP) increased the size of the cutaneous receptive fields of 9 of the 15 dorsal horn cells tested. These receptive fields were on the feet and toes of the hind limbs of cats. Receptive field sizes increased with increasing doses of 4-AP. However, 4-AP administration did not change the responses of dorsal horn cells to graded mechanical stimuli administered near the centers of their receptive fields.

4-Aminopyridine↗
PubMed1985

An electron microscopic study of terminals of rapidly adapting mechanoreceptive afferent fibers in the cat spinal cord.

The intra-axonal horseradish peroxidase technique was used to examine the central terminals of 7 A beta primary afferent fibers from rapidly adapting (RA) mechanoreceptors in the glabrous skin of the cat's hindpaw. At the light microscopic level, labelled collaterals were seen to bear occasional boutonlike swellings, mostly (75-82%) of the en passant type. These swellings were distributed more or less uniformly from lamina III to a dorsal part of lamina VI in the dorsal horn, over a maximum longitudinal extent of about 4 mm. At the electron microscopic level, we observed that labelled boutons of RA afferent fibers were 1.0 to 3.3 micrometers in longest sectional dimension, and contained clear, round synaptic vesicles. They frequently formed asymmetric axospinous and axodendritic synapses and commonly appeared to receive contacts from unlabelled structures containing flattened or pleomorphic vesicles plus occasional large dense-cored vesicles. The examination of synaptic connectivity over the entire surface of individual boutons indicated that RA afferent boutons each made contacts with an average of one spine and one dendrite and, in addition, appeared to be postsynaptic to an average of two unlabelled vesicle-containing structures. This synaptic organization was, in general, more complex than that we had seen previously in Pacinian corpuscle (PC) and slowly adapting (SA) type I mechanoreceptive afferent fibers. Our findings indicate that RA, SA, and PC afferent terminals, while displaying some differential synaptic organizations, have many morphological and synaptological characteristics in common. These afferent terminals, in turn, seem to be generally distinguishable from the terminals of muscle spindle Ia afferents or unmyelinated primary afferents.

Animals↗
PubMed1984

Examination of geniculate ganglion cells contributing sensory fibers to the rat facial 'motor' nerve.

Using a method to visualize HRP-containing cells in the geniculate ganglion (GG) in situ after decalcifying surrounding bone, we found that about 30% of the total (about 1000) GG cells contributed sensory fibers to the posterior auricular branch of the facial motor nerve. These cells are relatively large for GG cells in general. The remaining facial motor nerve branches, including those involved in vibrissal movement, contained few sensory afferent fibers originating from GG cells.

Animals↗
PubMed1984

Trigeminal sensorimotor mechanisms and eating in the rat.

Photographic, electrophysiological and neurobehavioral analyses were used to examine the contribution of trigeminal inputs to the behavioral organization of eating in the rat. During eating, jaw opening was always preceded by a period of perioral contact with the food source. Mechanical or electrical stimulation of oral and perioral areas in anesthetized animals elicited compound action potentials in the mylohyoid nerve (jaw-opener innervation) at short latencies and low stimulus intensities. Trigeminal orosensory deafferentation (sparing jaw muscle afferents and efferents) abolished or significantly reduced mouth opening during eating. We conclude that trigeminal orosensory inputs provide an essential link in the stimulus-response chain mediating eating in the rat.

Animals↗
PubMed1984

Ultrastructure of pacinian corpuscle primary afferent terminals in the cat spinal cord.

The glabrous skin of the hindlimb of the cat contains 3 types of low-threshold mechanoreceptors: Pacinian corpuscles (PC), and slowly and rapidly adapting receptors. In the present study, 12 primary afferent fibers transmitting impulses from PC were injected intra-axonally with horseradish peroxidase (HRP) in the spinal cord to examine the morphology of their terminals in the dorsal horn. At the light microscopic level, terminal arborizations were observed in laminae II-VI of the dorsal horn, extending up to 7 mm rostrocaudally in and near the seventh lumbar segment. Bouton-like swellings, predominantly (67%) of the en passant type, were distributed in two discrete clusters, one concentrated rostrally in Rexed's laminae III-IV, and the other concentrated caudally in lamina V. At the electron microscopic level, a combination of morphometric and serial reconstructive analyses with 3 fibers revealed the following. Boutons labelled with HRP invariably contained clear round vesicles, approximately 40 nm in diameter. Labelled bouton sections had longest dimensions of 1.84 +/- 0.63 micron. Their shapes varied from rounded to elongated forms with occasional scalloped appearances. A majority (73%) of the contacts associated with HRP-filled boutons were made with dendritic spines and shafts. Thick postsynaptic densities were usually associated with these synapses, although thinner densities were also observed. 24% of the contacts made by labelled boutons were synapse-like contacts with unlabelled vesicle-containing structures. The vesicles in the unlabelled structures were usually pleomorphic, but sometimes round. These contacts were identified as 'synapse-like' because labelling obscured possible landmarks necessary for definitive identification of synapses. However, in most of these contacts, there was an accumulation of vesicles near the cleft on the unlabelled side, suggesting that the labelled boutons were postsynaptic. Only 3% of the contacts made by labelled boutons were axosomatic. The lengths of contacts with dendritic spines (0.49 +/- 0.23 micron) or with dendrites proper (0.45 +/- 0.20 micron) were significantly longer than those with vesicle-containing unlabelled structures (0.31 +/- 0.18 micron). The portions of cross-sectional bouton contours devoted to synaptic or synapse-like contacts accounted for 9-13% of the perimeters. The larger the bouton, the longer the summed lengths of contacts. Serial reconstruction of selected labelled boutons revealed both simple and quite complex synaptic organizations, including glomeruli with labelled boutons as the central component.(ABSTRACT TRUNCATED AT 400 WORDS)

Afferent Pathways↗
PubMed1983

An electron microscopic study of primary afferent terminals from slowly adapting type I receptors in the cat.

Primary afferent fibers transmitting impulses from slowly adapting (SA) Type I receptors in the glabrous skin of the hind paw of the cat were injected intraaxonally in the spinal cord with horseradish peroxidase (HRP). At the light microscopic level, terminal arborizations were observed in the medial dorsal horn extending up to 6 mm rostrocaudally in and near the seventh lumbar segment. Boutonlike swellings labelled with HRP were distributed in clusters in Rexed's laminae III-VI. There was a tendency for the most dorsal clusters from an individual fiber to be located rostrally and for the most ventral clusters to be located caudally. At the electron microscopic level, a combination of morphometric analysis and serial reconstruction revealed the following: (1) All the boutons labelled with HRP contained predominantly clear, round synaptic vesicles, 40-50 nm in diameter. (2) Labelled boutons (n = 75) had cross-sectional longest dimensions of 1.72 +/- 0.53 micron (Mean +/- S.D.), perimeters of 4.95 +/- 1.52 micron, and areas of 1.18 +/- 0.59 micron 2. Their shapes in section varied from rounded to elongated forms. (3) The sizes of labelled boutons decreased significantly and linearly with depth from lamina IV to VI. The shapes of the bouton cross sections also became rounder with depth in the dorsal horn. (4) About 72% of synaptic contacts associated with HRP-filled boutons were with dendritic spines and shafts; most of these synapses were of the asymmetric type. (5) The remainder (28%) of the appositions were synapselike contacts between labelled boutons and unlabelled structures containing flattened or pleomorphic vesicles, and occasional dense-cored vesicles. (6) We observed no unequivocal axosomatic contacts made by labelled boutons. (7) The lengths of synaptic appositions with dendritic spines (0.46 +/- 0.20 micron) or with dendritic shafts (0.51 +/- 0.18 micron) were significantly greater than the synapselike contacts with vesicle-containing unlabelled structures (0.29 +/- 0.09 micron). (8) Complex neuropilar organization was occasionally seen with labelled boutons as central elements, although simpler organizations were much more common. In summary, HRP-labelled fibers ended predominantly in boutons containing clear, round vesicles forming axospinous and axodendritic synapses.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1982

Quantitative morphological analysis of spinal motoneurons.

Horseradish peroxidase was injected intracellularly into motoneurons responding to cutaneous stimulation of the central foot pad of the hind limb in cats. Three motoneurons were selected for detailed analysis: two excited by foot pad stimulation, and one postsynaptically inhibited by such stimulation. The overall lengths of the dendritic trees of the 3 cells ranged from 15.2 to 20.4 mm; the total surface areas ranged from 0.161 to 0.185 mm2. One cell had 9 primary dendrites, 39 terminal dendrites, and 69 dendritic branches in all. The second cell had 8 primary dendrites, 44 terminal dendrites, and 80 dendritic branches in all. For the third cell, these numbers were 14, 76 and 136. 75.2% of the total dendritic length of one of the cells was accounted for by branches of 3 of its 9 primary dendrites; for the second, 69.1% by 3 of 8; and for the third cell, 47.9% by 3 of 14. In contrast to the marked disparity in overall length of branches of the various primary dendrites, when the lengths of dendrites were analyzed by order of branching, dendritic branches of orders II-V each included greater than 15% of overall dendritic length. All 3 motoneurons displayed an exponential overall loss of total dendritic width with distance from the cell body, as well as an exponential decrease in Rall's dendritic trunk parameter. Four different patterns of branching were observed. Mean estimated electronic dendritic lengths were 1.3 for two cells, and 1.2 for the third. However, 13% to 28% of the dendrites of the 3 cells terminated more than two space constants from the cell body. In spite of striking differences among these cells in first-order morphology, on many of the detailed measures characterizing the dendritic trees of these motoneurons, they proved to be strikingly similar.

Animals↗
PubMed1981

Electron microscopic observations of terminals of functionally identified afferent fibers in cat spinal cord.

Using the method of intra-axonal injection of horseradish peroxidase, functionally identified afferent fibers from three slowly adapting (Type I) receptors and one Pacinian corpuscle in the glabrous skin of the hind paw of the cat were stained. Electron microscopic observation of the terminals of these fibers revealed predominantly axodendritic asymmetric synapses containing round, clear vesicles. Multiple synapses on a single dendrite were observed, separated by as little as 900 mm from one another.

Afferent Pathways↗
PubMed1980

2-Deoxyglucose uptake in the cat spinal cord during sustained and habituated activity in the plantar cushion reflex pathway.

[14C]2-deoxy-D-glucose (2-DG) was administered intravenously to anesthetized cats during electrical stimulation of the plantar cushion (central foot pad). Afferent volleys and the efferent reflex were monitored by recording from the tibial nerve at the ankle. Plantar cushion stimulation at 3 HZ, 5 x threshold for 45 minutes led to a discrete region of increased 2-DG uptake dorsomedially in the dorsal horn, predominantly in Rexed's laminae III and IV, ipsilateral to the stimulation. A less marked increase in labeling was also sometimes observed in the medial portion of lamina V. No labeling specific to stimulation was observed in the ventral horns. A control preparation, to determine the effects of surgical manipulations alone, confirmed that the labeling was indeed specific to the plantar cushion stimulation. A pattern of labeling identical to that seen during 3 Hz, 5 x threshold stimulation occurred when 2-DG was administered during 10 Hz, 5 x threshold stimulation, after the reflex elicited by plantar cushion stimulation had completely habituated. The most straightforward interpretation of our results suggests that the increases in 2-DG labeling produced by stimulation of the plantar cushion probably occurred in regions with heavy concentrations of axon collaterals of the primary afferent A alpha beta fibers from the plantar cushion, at or near their sites of termination in the dorsal horn.

Afferent Pathways↗
PubMed1980

Morphology of spinal motoneurones mediating a cutaneous spinal reflex in the cat.

1. Intracellular injections of horseradish peroxidase were made in a functionally identified population of motoneurones in spinal cords of cats. These motoneurones were activated by tactile stimulation of the hind-limb central foot pad. 2. Cell bodies of twenty-two such motoneurones were located in the dorsolateral portion of the ventral horn in the first sacral segment. The mean diameter of the major axis of transverse sections through twelve of these cell bodies was 68 . 2 micrometer, the mean diameter of the minor axis was 48 . 7 micrometer. The major axis tended to be oriented dorsomedially-ventrolaterally. 3. In the transverse plane, the dendrites had a characteristic configuration, with a prominent group of dendrites travelling from the cell body dorsomedially into the dorsal horn, entering Rexed's lamina VI. For seventeen motoneurones with well stained dendrites, the mean medial spread of the dendrites was 960 micrometer. Though the mean lateral spread was only 508 micrometer, all of these motoneurones sent dendritic projections into the lateral white matter. The mean dorsal spread of the dendrites was 693 micrometer, the mean ventral spread, 748 micrometer. In the rostrocaudal direction, the mean spread rostrally was 911 micrometer, the mean spread caudally was 998 micrometer. The maximum dendritic spread for a single motoneurone was 2,940 micrometer, in the rostro caudal direction. The sum of dendritic lengths over an entire dendritic tree for the best-stained motoneurones exceeded 13,000 micrometer. 4. The mean diameter of the initial segment of axons of nineteen motoneurones was 4 . 3 micrometer. These axons were notable for the lack or paucity of axon collaterals. Only five of twenty-one axons possessed collaterals; of these, only one possessed more than a single collateral system. This sparseness of the collateral system was reflected in a low level of recurrent inhibition. 5. A possible relationship is discussed between the prominent dorsomedially oriented dendritic bundles of the motoneurones and the axon collaterals of dorsal horn cells mediating cutaneous stimulation which can activate these motoneurones.

Animals↗
PubMed1978

Sensitization and habituation of dorsal horn cells in cats.

1. Extracellular recordings were obtained from spinal dorsal horn cells in acutely spinalized cats anaesthetized with sodium pentobarbitone. The dorsal horn cells studied responded to ipsilateral tactile stimulation of the central pad of the hind foot. Eleven short latency dorsal horn cells driven by electrical stimulation of the foot pad were studied intensively; these short latency dorsal horn cells all discharged within 1.5 msec of the arrival of an afferent volley at the dorsal root entry zone. Electrode tip sites were histologically verified to lie near the medial border of the dorsal horn in the seventh lumbar segment, in Rexed's laminae III and IV. 2. Electrical stimulation of the foot pad not only activated the dorsal horn cells studied, but also produced a reflex discharge which was monitored by recording from the ipsilateral first sacral ventral root, which had been sectioned intradurally and mounted on bipolar recording electrodes. Repeated stimulation of the foot pad at moderate intensities and frequencies (e.g. three times threshold for the ventral root response at 5 Hz) typically produced a transitory increase in the magnitude of the reflex discharge (sensitization) followed by a marked waning of the reflex magnitude (habituation). Within a few minutes following cessation of stimulation, the reflex magnitude returned to its prestimulation value. During repeated bouts of five hundred stimuli each, at frequencies from 1.0 to 10.0 Hz, and intensities 1.5-10.0 times reflex threshold, the firing pattern of a short latency dorsal horn cell was monitored along with the magnitude of the ventral root response. Changes in response patterns of the dorsal horn cells were compared to those of the reflex discharges. 3. The short latency dorsal horn cells fell into two distinct patterns of response. The firing pattern of six dorsal horn cells paralleled the response pattern of the reflex discharge; when the reflex increased in magnitude, each of these dorsal horn cells increased in number of responses per stimulus; when the reflex discharge decreased in magnitude, each of these dorsal horn cells decreased the number of responses per stimulus. These dorsal horn cells were characterized by the following: intermediate thresholds to tactile stimulation, comparable to that of the reflex discharge itself; relatively low numbers of responses per stimulus (mean: 1.3/stimulus); low spontaneous activity rates (once per 10 sec or less). 4. The firing patterns of the other class of short latency dorsal horn cells did not parallel the response pattern of the reflex discharge; these showed only a rather rapid, though moderate, decrease in responses per stimulus over the entire range of intensities and frequencies tested. These five dorsal horn cells were characterized by the following: thresholds of tactile stimulation considerably below that of the reflex discharge itself; bursts of responses following each stimulation (mean: 7...

Action Potentials↗
PubMed1977

Dendritic spread of dorsal horn neurons in cats.

Observations of neurons in dorsal horn laminae IV-VI of the lumbosacral segments of Golgi-stained spinal cords in kittens and adult cats revealed laminar differences in dendritic architecture. Many neurons in lamina IV had dense, bushy dendritic fields. Lamina V contained, in addition to bushy cells similar in appearance to those of lamina IV, increasing numbers of neurons with radiating dendritic fields. Lamina VI was composed almost exclusively of neurons with radiating dendritic fields. These qualitative differences among laminae were accompanied by systematic variations in mean dendritic spread, which increased more than two-fold in adult cats between laminae IV and VI. A second gradient of dendritic spread was found within individual laminae: dendritic spread, particularly medial to lateral spread, increased for successively more lateral cells within a lamina. These differences in the spread of dendrites for neurons in different regions of the dorsal horn may be related to variations in the areas of peripheral receptive fields of dorsal horn neurons.

Age Factors↗
PubMed1976

Sensitization and habituation of the plantar cushion reflex in cats.

The plantar cushion reflex in cats was examined as a model system in a mammal for the study of the effects of repeated stimulation on neural transmission. Effects of various frequencies and intensities of stimulation were similar to those seen in other reflex systems. For instance, for a fixed number of stimuli, habituation of the plantar cushion reflex was more marked at 10 Hz than at 2.0 Hz, and with 1.0 X threshold stimulation than with 5.0 X threshold stimulation. Sensitization occurred at intermediate intensities and frequencies of stimulation. Dorsal root potentials were studied; changes in dorsal root potentials during iterated stimulation did not correlate with the changes in the plantar cushion reflex. These changes in the plantar cushion reflex were also unrelated to variations in afferent transmission peripheral to the spinal cord. Sensitization and habituation in the plantar cushion reflex occurred during iterated stimulation, were produced centrally, and were unrelated to mechanisms of presynaptic inhibition.

Animals↗