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W J Hendelman

Publications and source records attributed to W J Hendelman.

18 recordsLinked to original sources
PubMed1986

Reciprocal peer teaching by medical students in the gross anatomy laboratory.

The use of reciprocal peer teaching (RPT) was evaluated by 66 first-year medical students participating in gross anatomy laboratory sessions at the University of Ottawa Faculty of Health Sciences. In RPT each student in turn served as a teacher of his peers. The students compared RPT with staff teaching, and almost all reported that they acquired as much knowledge of topics taught by their peers and greater knowledge of topics that they taught personally than they acquired from staff teaching. In addition, most students reported improved study habits, better attitudes toward anatomy, and more independent study. A majority of the students felt they would be better able to communicate with patients and felt more like students of medicine than before participating in RPT. The authors concluded that the active involvement of students in teaching will help prepare students to be continual and independent self-learners throughout their professional careers.

Anatomy↗
PubMed1985

Growth and myelination of explant cultures in defined medium.

The purpose of this study was to compare the development of organotypic cultures in defined medium versus nutrient containing serum and embryo extract (EE). Explant cultures of cerebellum with or without locus ceruleus were grown in the Maximow system and monitored in the living state and with histological stains. Thinner explants, fibronectin and a more frequent feeding schedule were required to overcome the growth differences encountered using a defined medium. The final medium formulation was arrived at by evaluation of living cultures and consisted of a basal medium (Dulbecco's minimal essential medium), a number of hormones and other supplements, and a final glucose concentration of 750 mg%. Using a Golgi stain and histofluorescence, it was shown that the three major types of neurons - Purkinje, deep nuclear, and locus ceruleus - developed similarly in the defined medium and in serum-EE cultures. Myelination occurred in virtually all cerebellar cultures in defined medium and the onset was earlier than in serum-EE cultures. These results indicate that differentiation of oligodendroglia and maturation of neurons occur in a defined medium. Elimination of thyroid hormone delayed the maturation of the cultures, both neurons and myelin, by 3-4 days.

Animals↗
PubMed1985

Noradrenergic responses of spinal neurons in locus coeruleus-spinal cord co-cultures.

Locus coeruleus (LC) explants were co-cultured with dissociated spinal neurons of mice. Nerve fibers exhibiting catecholamine fluorescence radiated from the explants and frequently invested spinal cord (SC) neurons close to the explants. Electrical stimulation of the explant and iontophoretic application of norepinephrine evoked a spectrum of slow depolarizing, hyperpolarizing, and biphasic responses in the SC cells. The responses to LC stimulation and to application of norepinephrine were usually similar in a given cell. The depolarizing responses were associated with an increase in apparent input resistance and pharmacologic tests indicated that the responses were mediated by alpha-receptors. Neurons in regions innervated by catecholamine-containing fibers usually gave depolarizing responses to LC stimulation and such neurons had a very high probability of exhibiting depolarizing responses to applied norepinephrine. It would appear that either locus coeruleus explants favored the survival of cells with alpha-receptors or expression of these receptors in SC neurons was induced by innervation of the neurons by locus coeruleus axons.

Action Potentials↗
PubMed1984

Calcium-binding protein immunocytochemistry in organotypic cultures of cerebellum.

Vitamin D-dependent calcium-binding protein is known to be present in specific classes of neurons including Purkinje cells of the rat and chick. Explant cultures of newborn mouse cerebellum consisting of cerebellar cortex and deep nuclear region were fixed at maturity (20 days in vitro). Paraffin sections were reacted with the antiserum to purified chick duodenal calcium-binding protein. The Purkinje cell of these cultures reacted in its entirety--neuronal soma, dendrite, axon and terminals (in the deep nuclear region). The results verified many of the findings of our previous morphological studies. Qualitatively similar results were obtained with cultures maintained either in medium containing serum and embryo-extract or in a defined medium. There is not yet sufficient data to indicate whether this protein in the neurons in culture is dependent upon an exogenous source of vitamin D. This immocytochemical marker should prove useful to identify a specific neuron-type in culture.

Animals↗
PubMed1983

Morphologic alterations in the Purkinje neuron of the rat induced by lysergic acid diethylamide and fixation.

The effect of lysergic acid diethylamide (LSD) on the morphology of the cerebellar cortex of the rat was studied with electron microscopy. Hippocampal electrical activity was used as an objective measure of drug efficacy. At a dose of 1700 micrograms/kg, the amplitude from the hippocampus was diminished (in 2 to 5 min) and this effect lasted for about 65 to 165 min. A morphologic alteration consisting of cisternal stacks occurred in the dendrites of Purkinje neurons of rats treated with this dose of LSD, with the perfusion carried out correctly. These stacks of smooth endoplasmic reticulum were seen 2 h after injection and persisted for at least 8 h. A reduction in the volume of perfused fluid to less than 500 ml caused similar changes in the dendrites of the Purkinje neuron of untreated rats; this was one way to experimentally induce a faulty perfusion. With LSD and faulty perfusion (reduced volume) more severe changes occurred in the dendrites and small stacks of smooth endoplasmic reticulum were seen in the Purkinje soma; similar changes were also seen when the perfusion of a control animal was mismanaged during the initial 3 min. The Purkinje neuron seems to manifest morphologic alterations, generally of two types, with exposure to a variety of noxious agents. The LSD caused some perturbation of this neuron, and this was found under properly controlled conditions of fixation. The results are interpreted as indicating that LSD is causing a metabolic alteration which could disrupt the synaptic activity over several hours.

Animals↗
PubMed1982

Catecholamine neurons of the central nervous system in organotypic culture.

A standardized dissection has been designed to produce explants from the locus coeruleus of the newborn mouse brain. This area, termed the peduncular region, may be explanted with or without cerebellar neurons. Organotypic cultures with peduncular cells contain a cluster of 20-50 (or more) closely-packed large neurons, characterized by intracellular refractile granules in the living state. When treated with the glyoxylic acid method, somata of the granule-containing neurons exhibited catecholamine fluorescence, and a profuse plexus of varicose fluorescent fibers permeated the explant and its outgrowth. Intracellular staining of these cells with horseradish peroxidase demonstrated bipolar and multipolar neurons (25-30 micrometers), with stout dendrites and varicose axons. Granule-containing neurons stained for acetylcholinesterase. Electron microscopically, large dense granules were seen, which appear to correspond to the granules seen in living neurons. Cultures with these cells also have a high concentration of catecholamines in the medium. It is concluded that the granule-bearing neurons of the living culture are in fact neurons of the locus coeruleus.

Acetylcholinesterase↗
PubMed1981

A coeruleo-spinal system in culture.

In combined cultures of dissociated spinal neurons and explants from the region of locus coeruleus, rich catecholamine-containing fiber projections from the explant to the surrounding regions of spinal neurons were demonstrated by fluorescence histochemistry. Electrical stimulation of the explant resulted in slow depolarizing responses in many of the spinal neurons. Cells exhibiting this type of response were also usually depolarized by local application of noradrenaline, whereas other, unresponsive neurons usually were not. The depolarizing responses to electrical stimulation and to noradrenaline were both increased by depolarizing current injection and decreased by hyperpolarizing current. These and other data suggest that the depolarizing responses of the spinal neurons to explant stimulation are mediated by noradrenaline released from axons of locus coeruleus neurons.

Animals↗
PubMed1980

The Purkinje neuron: I. A Golgi study of its development in the mouse and in culture.

The development of the Purkinje neuron was studied in organotypic culture and compared to that occurring in the intact animal, using a modified Golgi-Cox method. The post-natal sequence of development in the intact animal occurred in five distinct stages beginning with (1) an immature state (0-3 days), (2) a stage of perisomatic dendritic processes (4-6 days), and then (3) a stage characterized by the presence of spines on the soma region (7-10 days). This stage of somatic spines has not been delineated previously in Golgi studies of the Purkinje cell during its development. There was no evidence that the lateral somatic processes resorb; rather they continue to grow and develop into dendritic branches. It is proposed that by a process of perikaryal translocation, the soma region becomes transferred "downward," resulting in an elongation of the primary, apical dendrite (stage 4, 11-14 days). Beyond 15 days (stage 5) the dendritic branches grow to the pial surface and the neuron has its full complement of secondary, tertiary, and spiny branches. In culture, the development parallels that occurring in the intact animal during the first 10 days (stages 1, 2, 3) despite the absence of extracerebellar afferents and the special conditions of the culture. However, there is an overall absence of lamination of the cortex, the Purkinje neurons do not align, and the developmental process is modified because of the failure of the process of perikaryal translocation in culture. The resultant mature neuron has an altered morphology characterized by the presence of several dendrites and spines attached to the soma, and also lacks the complete development of the smaller dendritic branches.

Animals↗
PubMed1980

The Purkinje neuron: II. Electron microscopic analysis of the mature Purkinje neuron in organotypic culture.

Purkinje neurons of organotypic cultures were investigated electron microscopically following their analysis with the Golgi technique. The purpose of this study was to critically examine the issue of synaptic specificity in CNS cultures. The unique finding was the synaptic cluster, a terminal which engulfs many Purkinje spines. In the neuropil and on the major dendrites, this synaptic arrangement was interpreted to be a hypertrophic parallel fiber, representing a type of synaptic modulation. The terminals on the somatic spines are also in the form of clusters; some or all of these spines were thought to have developed to form synapses with the climbing fiber. In the absence of this afferent, the parallel fiber--a competing system--takes over the site. This represents a form of synaptic plasticity in these cultures. The inhibitory synaptic relationships were maintained on the soma and dendrites, but it was found that the basket synapses did not quantitatively encase the soma as is seen in the intact animal. Mossy-type terminals were found occasionally synapsing with Purkinje dendritic spines, as has been seen in agranular cerebellum in animals. These mossy terminals are presently thought to originate from the deep cerebellar nuclei within these cultures. Synaptic errors were rarely encountered. It is concluded that this preparation develops in accordance with established neurobiological principles, that the Purkinje neuron reaches a mature state in culture, and that this model has a sound anatomical basis for further experimental work.

Animals↗
PubMed1977

Depression by magnesium ion of neuronal excitability in tissue cultures of central nervous system.

Magnesium ion (Mg2+) in concentrations of 5-10 micron has been used to block synaptic transmission in in vitro preparations of central nervous system tissue. We have used explants of mouse cerebellum grown in culture to test whether significant levels of direct depression of neuronal membrane excitability could occur in such experiments. Using thresholds for antidromic activation and iontophoretically applied glutamate as tests of excitability, potent depressions of membrane excitability were found using 5-10 micron Mg2+. The additive depressant effects of increased Ca2+ concentrations provided further evidence that the effects were largely on membrane excitability and not on transmitter release mechanisms.

Animals↗
PubMed1970

Observations on a transient phase of focal swelling in degenerating unmyelinated nerve fibers.

This study describes the nature and time-course of a swelling phase during the degeneration of unmyelinated nerve fibers, as observed in highly organized cultures of rodent sensory ganglia. Observations were made on nerve fascicles after they were cut and during nutritional deprivation. About 12 hr after nerve transection, large, clear vacuoles appear throughout fascicles distal to the cut. These vacuoles are most numerous at 24 hr and then gradually subside; after 48 hr, only small granules mark the severed fascicles. Electron microscopy shows that the vacuoles are, in fact, massive focal dilations of unmyelinated axons. Similar focal dilations in unmyelinated axons are observed if cultures are not refed for 5-7 days; under these conditions glucose concentrations fall below 20 mg/100 ml and degenerative changes begin to appear in neuronal somas. If the gas-tight assembly is opened and the culture refed, there is rapid disappearance of axonal dilations (usually within 1 hr) and recovery of many of the damaged neurons. Cooling (4 degrees C) prevents this reversal, suggesting that an active process is involved. It is postulated that the swellings result from the failure of active axolemmal ion-pumping mechanisms prior to loss of selective permeability in the axon membrane. The reasons for the focal nature of the swellings is unknown. A literature review indicates that a phase of focal swelling has frequently been observed during the degeneration of unmyelinated nerve fibers in vivo.

Animals↗
PubMed1969

Radioautographic studies of choline incorporation into peripheral nerve myelin.

This radioautographic study was designed to localize the cytological sites involved in the incorporation of a lipid precursor into the myelin and the myelin-related cell of the peripheral nervous system. Both myelinating and fully myelinated cultures of rat dorsal root ganglia were exposed to a 30-min pulse of tritiated choline and either fixed immediately or allowed 6 or 48 hr of chase incubation before fixation. After Epon embedding, light and electron microscopic radioautograms were prepared with Ilford L-4 emulsion. Analysis of the pattern of choline incorporation into myelinating cultures indicated that radioactivity appeared all along the length of the internode, without there being a preferential site of initial incorporation. Light microscopic radioautograms of cultures at varying states of maturity were compared in order to determine the relative degree of myelin labeling. This analysis indicated that the myelin-Schwann cell unit in the fully myelinated cultures incorporated choline as actively as did this unit in the myelinating cultures. Because of technical difficulties, it was not possible to determine the precise localization of the incorporated radioactivity within the compact myelin. These data are related to recent biochemical studies indicating that the mature myelin of the central nervous system does incorporate a significant amount of lipid precursor under the appropriate experimental conditions. These observations support the concept that a significant amount of myelin-related metabolic activity occurs in mature tissue; this activity is considered part of an essential and continuous process of myelin maintenance and repair.

Animals↗