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Biomedical subjects

M Devor

Publications and source records attributed to M Devor.

108 records · Page 6Linked to original sources
PubMed1979

Ephaptic transmission in chronically damaged peripheral nerves.

Several weeks after damage of the sciatic nerve in adult rats, a stable electrical (ephaptic) interaction forms between pairs of injured sensory and motor axons. Fiber-fiber interaction occurs when the nerve ends in a neuroma, after end-to-end nerve suture and after nerve crush injury. Unlike the transient "artificial synapse" created acutely on section of a nerve, this form of crosstalk is long-lasting. Its existence lends support to the hypothesis that ephaptic interaction is an important factor in neurologic pathophysiology.

Animals↗
PubMed1977

Dorsal horn cells that respond to stimulation of distant dorsal roots.

Experiments were carried out to find if there were post-synaptic effects produced by impulses in the long ranging primary afferents, which had been shown by Wall & Werman (1976) to extend from upper lumbar dorsal roots to the sacral segments. Dorsal rootlets were stimulated in decerebrate low-spinal adult cats.1. The dorsal root potential and ventral root reflex were recorded on S1 root filaments, in response to stimulation of dorsal rootlets extending from L1 to S1. With increasing distance between stimulating and recording segments, these potentials became smaller and more delayed. In two animals, there was no response at S1 to stimulation of L1 and L2 dorsal roots.2. In all animals, stimulation of L3 or L4 dorsal roots produced cell responses in dorsal horn segments L7 or S1. The density of such cells was variable, from animal to animal. Responding cells were mainly concentrated laterally in the dorsal horn.3. The latency and response variability of L7-S1, dorsal horn cells to L3-L4 stimulation was consistent with at least some of them being fired monosynaptically.4. Cells that respond to stimulation of one distant rootlet respond to many closer rootlets as well.5. The receptive fields of L7-S1 dorsal horn cells, responsive to stimulation of L3-L4 rootlets, were typical of those generally found in the L7-S1 segments, and were at some distance from the L4 dermatome. Only twenty cells had receptive fields which extended into the dermatome of the rootlets stimulated.6. It was established that some L4 cells respond to S1 dorsal root stimulation, just as the main study had shown that S1 responds to L4.7. It is concluded that substantial numbers of dorsal horn cells, including cells with many types of cutaneous receptive field, respond to two classes of synaptic in-put: one effective in firing the cell upon natural cutaneous stimulation, and one relatively ineffective, capable of driving the cell only when stimulated electrically and thus carrying a synchronous volley from a number of highly convergent axons. The contribution of this secondary afferent channel to normal and pathological cord physiology has now to be determined.

Afferent Pathways↗
PubMed1976

Fiber trajectories of olfactory bulb efferents in the hamster.

Olfactory bulb efferents sweep caudally over the surface of the piriform lobe in a broad fiber sheet. The internal organization of this axon population was analysed by topologically transforming the cortical surface from its in situ cylindrical form into an unrolled (flattened) map. The distribution of degeneration elicited by restricted bulb lesions and fiber transections was then reconstructed onto this map. Most of the projection cortex of the main olfactory bulb is innervated in a widespread, non-topographic manner by axons that collect in the compact bundle of the lateral olfactory tract (LOT). LOT collateral branches bound for the prepiriform cortex veer laterally off the main trajectory of the tract at an angle of 50 degrees or less. Thus, transection of discrete fiber populations leaves only a small wedge-shaped pocket of totally denervated cortex distal to the cut. The medial half of the olfactory tubercle and the hippocampal rudiment receive their bulbar input along medially disposed fibers that do not join the LOT proper. The lateral half of the olfactory tubercle, however, receives an input from LOT fiber collaterals as well as these medial bulb efferents. Finally, much of the corticomedial amygdaloid complex receives fibers from the accessory olfactory bulb along a specialized subdivision of the LOT, the accessory olfactory tract. These observations are expressed in a schematic summary of the trajectories of olfactory bulb efferents as they appear in the unrolled map and in the more standard ventral view of the hamster brain.

Animals↗
PubMed1976

Neuroplasticity in the rearrangement of olfactory tract fibers after neonatal transection in hamsters.

Olfactory bulb efferent axons run caudally in the lateral olfactory tract (LOT) to end in a broad cortical field in the ventral forebrain. Principles governing the plastic rearrangement of this fiber population after early lesions were probed by cutting the tract in hamster pups and studying the distribution of surviving olfactory bulb projections in adulthood using silver and autoradiographic techniques. The spatial pattern of rearrangement proved to depend on the extent of the cut and also the age at which it was made. For example, after complete LOT section at seven days of age no bulb efferents appeared distal to the cut but the proximal projection increased in laminar thickness and spread laterally and medially beyond its normal cytoarchitectonic boundaries. This spread was less pronounced in animals with earlier or later lesions. After transection of only part of the LOT fibers at seven days of age the proximal input was similarly increased. Just distal to the transection, uncut fibers sprouted collaterals to fill the terminal sites vacated as a result of the lesion. In these cases, however, the farthest distal parts of the projection field lost their normal innervation. In a tentative interpretation of these data it is proposed that developing LOT fibers tend to conserve their total amount of axonal arbor. That is, when distal branches are pruned off surgically, the axon compensates by producing extra proximal branches. When an overabundance of proximal collaterals are produced in axons that have not been surgically pruned the growth of more distal axonal branches is stunted in compensation.

Animals↗
PubMed1975

A normally laminated afferent projection to an abnormally laminated cortex: some olfactory connections in the reeler mouse.

The relative positions of pyramidal and polymorphic cell classes are inverted in the central olfactory cortical structures of the reeler mutant mouse. Each cell class is generated at the normal embryonic time. The polymorphic cells of the mutant, like those of the normal, are generated between E11-E13. The pyramidal cells are formed between E11-E16 in both. Despite the anomalous positions of their somata deep in the cortex the apical dendrites of many pyramidal cells reach and ramify at a superficial cortical level subjacent to the lateral olfactory tract. The main and accessory olfactory bulbs are cytoarchitectonically normal in the mutant and project normally upon the anterior olfactory nucleus, the olfactory tubercle, the hippocampal rudiment, the piriform cortex, the amygdaloid region and the entorhinal cortex. As in the normal animal the axons transverse layer Ialpha, and their terminals are concentrated in the immediately subjacent laminar zone. The rostrally directed cortic-cortical association system of the piriform cortex projects upon the anterior olfactory nucleus in the mutant just as in the normal with a relative concentration of terminals in a lamina subjacent and complementary to the zone of termination afferent systems in the abnormally laminated olfactory cortex of the mutant syggests that, in this system at least, the developmental mechanisms which determine relative position of neuron somata and those which govern axon trajectories and the distribution of axon terminals are largely independent.

Animals↗
PubMed1975

Neuroplasticity in the sparing or deterioration of function after early olfactory tract lesions.

Mating behavior in male hamsters depends on the sense of smell. Thus, complete transection of the lateral olfactory tract in adults eliminates mating. If the cut is made early in life, however, mating is spared. Partial section of the tract in adults does not affect mating, but similar cuts in the neonate lead to impaired mating performance later in life. Observed postsurgical rearrangements in the connections of axons in the lateral olfactory tract may explain both the sparing and the deterioration of function.

Age Factors↗
PubMedDate not supplied

Nerve pathophysiology and mechanisms of pain in causalgia.

In contrast to sensory endings in skin, muscle, etc., afferents in the mid-course of intact nerves are normally incapable of generating impulses upon slow or prolonged depolarization. However, after various types of nerve injury, including complete nerve section and local demyelination, an ectopic pacemaker capability develops. One peculiarity of such abnormal differentiated sites is chemosensitivity to alpha-adrenergic agonists and to sympathetic efferents discharge. Such ectopic chemosensitivity may well be involved in the etiology of paraesthesias and pain in reflex sympathetic dystrophies including causalgia. Specifically, it is proposed that the fundamental cause of these conditions is the development of abnormal electrogenic membrane properties in the region of demyelination and sprout outgrowth. These abnormal properties presumably include the appearance of excess inward current conductances and ectopic alpha-adrenergic receptors. Catecholamines released from sympathetic efferents in the area of injury locally depolarize damaged sensory fibers, and because of the abnormal electrogenic properties of these fibers, an abnormal afferent discharge is generated.

Adrenergic Fibers↗
PubMedDate not supplied

Comparison of the recurrence rate of gastric dilatation with or without volvulus in dogs after circumcostal gastropexy versus gastrocolopexy.

OBJECTIVE: To compare the recurrence rate of acute gastric dilatation with or without volvulus (GDV) after circumcostal gastropexy (CCGP) or gastrocolopexy (GCP) in dogs. STUDY DESIGN: A prospective, double-blind, multicenter, randomized, controlled, clinical trial with two groups (A and B). ANIMALS: Fifty-four client-owned dogs presented for treatment of GDV. METHODS: Dogs with acute GDV that had not previously had a gastropexy performed were included. The preoperative treatment before gastropexy was standardized. A CCGP was performed on dogs in group A, and a GCP was performed on dogs in group B. Postoperative treatment was standardized, but deviation did occur according to the special needs of particular patients. A minimal follow-up time of 180 days was required for dogs not excluded from the study. The median follow-up time in group A was 700 days; in group B, it was 400 days. The occurrence of abdominal pain and gastrointestinal problems after surgery were recorded by the owners. RESULTS: There was no significant difference in the recurrence rate of GDV between the two groups. At the end of the study, the recurrence rate was 9% and 20% in group A and in group B, respectively. CONCLUSIONS: Both surgical techniques are effective in preventing recurrence of GDV.

Acute Disease↗
PubMedDate not supplied

Chronic pain in the aged: possible relation between neurogenesis, involution and pathophysiology in adult sensory ganglia.

Certain neuropathic pain states, including postherpetic neuralgia and trigeminal neuralgia, show a dramatically increased incidence in the aged. Two recent experimental observations, unrelated a priori, might provide insight into why this is so. The first observation appeared unexpectedly during the course of a quantitative morphometric study aimed at determining the kinetics of retrograde cell death in dorsal root ganglia (DRGs) of adult male rats after nerve injury. Although the expected falloff in the ratio of neurons on the operated side versus the contralateral intact side was confirmed, much of the change resulted from an increase in the number of cells on the intact side. DRG cell counts were then carried out in intact, unoperated rats of various ages, and an increase in neuronal populations with age and size was confirmed. However, as the rats entered "old age" (greater than 400 days of age), proliferation ceased and there was an indication of secondary cell loss (involution). This is consistent with other data on DRG involution in the aged. The second observation is that regressive changes in DRGs following nerve injury are associated with enhanced generation of ectopic impulse discharge in the DRG, and potentiated cross-excitation among neighboring DRG neurons. It is likely that these post-injury changes in DRG electrogenesis contribute to the neuropathic sensory abnormalities, including chronic pain, that are associated with traumatic nerve injury. Considering both observations together, it is possible that DRG involution in the aged triggers electrical changes in the DRG resembling those associated with DRG involution following nerve injury. If so, this process could account for the special susceptibility of elderly patients to certain neuropathic pain states.

Aging↗