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Biomedical subjects

A Hess

Publications and source records attributed to A Hess.

At least 127 records · Page 7Linked to original sources
PubMed1965

Developmental changes in the structure of the synapse on the myelinated cell bodies of the chicken ciliary ganglion.

Electron micrographs, stained Epon-embedded sections, and silver stains of the ciliary ganglion of chickens 19 days prehatched, 4 days, 5 weeks, 6 months, and 1 to 2 years of age were studied. The majority of ganglion cells are large neurons; smaller cells are restricted to a dorsal, distal part of the ganglion. The following description applies to the large neurons. Three to twenty lamellae of loose, semicompact, and compact myelin ensheathe virtually every neuron. All these types of myelin form the sheath of a single neuron. The lamellae greatly increase in number and in compactness during the period between the 19-day embryo and the 4-day-old chick. During the period between the 4-day chick and the adult chicken, the myelin becomes only slightly thicker and denser. The calyx is a large synaptic terminal encircling virtually every neuron in the ganglion up to 5 weeks of age. At 6 months of age, the calyx appears to break up; only about half the number of neurons in the ganglion have this large terminal, while the remaining neurons have numerous relatively small, boutonlike synapses. This rather remarkable transformation in the structure of the calyx is virtually complete in the 1- to 2-year-old chickens. In these older chickens all the cells have boutons, and calyces are no longer present. The entering preterminal fiber, the calyx, the neuron, and the axon hillock can all have myelin lamellae on them. It is possible that this entire complex is effectively insulated by the myelin sheath. No synaptic discs or fusion of the membranes of the preterminal fiber and the postganglionic neuron are seen. The chick ciliary ganglion cells are the only myelinated neurons so far described which receive synapses. The neurons in the small-cell part of the ganglion do not have calyces and are not ensheathed by myelin lamellae at any age.

Animals↗
PubMed1965

The sarcoplasmic reticulum, the T system, and the motor terminals of slow and twitch muscle fibers in the garter snake.

Twitch and slow muscle fibers, identified morphologically in the garter snake, have been examined in the electron microscope. The transverse tubular system and the sarcoplasmic reticulum are separate entities distinct from each other. In twitch fibers, the tubular system and the dilated sacs of the sarcoplasmic reticulum form triads at the level of junction of A and I bands. In the slow fibers, the sarcoplasmic reticulum is severely depleted in amount and the transverse tubular system is completely absent. The junctional folds of the postsynaptic membrane of the muscle fiber under an "en grappe" ending of a slow fiber are not so frequent or regular in occurrence or so wide or so long as under the "en plaque" ending of a twitch fiber. Some physiological implications of these differences in fine structure of twitch and slow fibers are discussed. The absence of the transverse tubular system and reduction in amount of sarcoplasmic reticulum, along with the consequent disposition of the fibrils, the occurrence of multiple nerve terminals, and the degree of complexity of the post junctional folds of the sarcolemma appear to be the morphological basis for the physiological reaction of slow muscle fibers.

Animals↗
PubMedDate not supplied

Calcium inhibits catecholamine depletion by reserpine from carotid body glomus cells.

Histofluorescent and quantitative microfluorimetric studies have been performed on glomus cells of the rat carotid body, which fluoresce intently after treatment by paraformaldehyde vapor. Reserpine causes a reduction in intensity of fluorescence of about 90%. Subcutaneous injections of calcium chloride (100-300 mg/kg) were given before reserpine. Calcium prevents the depletion of catecholamies from the glomus cells by reserpine. This effect is dose related in that the depletion of catecholamines by heavy reserpine doses (15 mg/kg) cannot be overcome by calcium, medium doses (5 mg/kg) can be overcome but variably, and light doses (1 mg/kg) are always overcome substantially and can result in virtually complete inhibition of the depletion by reserpine. If calcium might counteract the effects of reserpine by occupying attachment sites of the vesicular membrane, thereby preventing reserpine from reaching its site of action, resulting in the usual uptake of catecholamines by the vesicles and suppression of the depleting action of reserpine.

Animals↗
PubMedDate not supplied

Component evaluation of event size spectra for a clinical 14-MeV neutron beam.

Microdosimetric investigations were performed in a solid TE phantom at the DT-neutron generator at Hamburg-Eppendorf. Event size spectra were measured at different depths on the axis of a 10 X 10 cm2 field and at different lateral positions at a constant depth. Additionally, the microdosimetric spectrum of a 60Co source was determined. From radiobiological measurements the relative biological effectiveness (RBE) of crypt stem cells of mice was estimated as a function of lineal energy. The measured microdosimetric spectra are folded with this RBE function so that RBE values at different positions in the phantom were obtained. The predicted change of the RBE inside and outside the useful beam of a 10 X 10 cm2 field is shown. Contributions to the RBE dose from the various charged particle components are analyzed separately.

Humans↗
PubMedDate not supplied

Dosimetric investigations in the dose buildup using bolus techniques for fast neutron therapy.

A moulded bolus is commonly used to compensate for contour irregularities of patients treated with fast neutrons. The bolus material should have the same attenuation characteristics as tissue, should be easily mouldable and sufficiently solid for multiple applications. For fast neutron beams, the mixture of equal parts of beeswax and paraffin is a suitable bolus material. As in photon beams the bolus, when placed directly on the patient skin, removes completely the skin sparing effect. However, in neutron beams the dose buildup can mostly be recovered by lining the bolus surface in contact with the patient with a thin layer of lead. This paper presents dosimetric investigations in the dose buildup of a collimated 14-MeV DT-neutron beam underneath the surface of a solid phantom behind a 1.0-cm layer of bolus material lined with 0.03 cm of lead. It is shown that most of the dose buildup of the bolus-free neutron beam can be recovered.

Cobalt Radioisotopes↗
PubMedDate not supplied

The pharmacologic treatment of depression.

BACKGROUND: Family physicians often provide the first line of treatment for patients with depression. Many effective drugs are now available for the pharmacologic treatment of depression. METHODS: We searched Medline from 1991-96 under the topics of depressive disorders/treatment and antidepressant medications. Other sources were found by back-referencing from these references and from pharmacology texts. RESULTS: Although antidepressants appear to be equally effective, selective serotonin reuptake inhibitors are frequently the drugs of choice because of their safety profile the less troublesome side effects. CONCLUSIONS: When prescribing antidepressant medications, the clinician must educate patients about potential side effects and about the amount of time that must be allowed for therapeutic efficacy. Drug interactions and concurrent medical conditions are important factors in the choice of an antidepressant.

Adolescent↗