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Biomedical subjects

E Horn

Publications and source records attributed to E Horn.

100 records · Page 6Linked to original sources
PubMedDate not supplied

Readaptation of the vestibuloocular reflex to 1g-condition in immature lower vertebrates (Xenopus laevis) after micro- or hypergravity exposure.

The effects of altered gravitational conditions (AGC) on the development of the static vestibulo-ocular reflex (VOR) and readaptation to 1g were investigated in the amphibian Xenopus laevis. Tadpoles were exposed to microgravity during the German Space Mission D-2 for 10 days, using the STATEX closed survival system, or to 3g for 9 days during earth-bound experiments. At the beginning of AGC, the tadpoles had not yet developed the static VOR. The main results were: (i) Tadpoles with microgravity- or 3g-experience had a lower gain of the static VOR than the 1g-controls during the 2nd and 5th post-AGC days. (ii) Readaptation to response levels of 1g-reared controls usually occurred during the following weeks, except in slowly developing tadpoles with 3g-experience. Readaptation was less pronounced if, during the acute VOR test, tadpoles were rolled from the inclined to the normal posture than in the opposite test situation. It is postulated that (i) gravity is necessarily involved in the development of the static VOR, but only during a period including the time before onset of the first behavioural response; and (ii) readaptation which is superimposed by the processes of VOR development depends on many factors including the velocity of development, the actual excitation level of the vestibular systems and the neuroplastic properties of its specific pathways.

Adaptation, Physiological↗
PubMedDate not supplied

In vitro isolation and cultivation of Cowdria ruminantium under serum-free culture conditions.

Three stocks of Cowdria ruminantium, the causative agent of heartwater in domestic ruminants, were propagated in bovine endothelial cells in a serum-free culture medium. The Vosloo, Welgevonden and Senegal stocks were propagated for a period of more than 203, 134, and 43 days, respectively. Two of the C ruminantium stocks (Vosloo and Senegal) were also successfully initiated under serum-free culture conditions. The serum-free medium consisted of a modified HL-1 medium. The Senegal stock was successfully propagated in Dulbecco's modified Eagle's medium nutrient mixture Ham F-12 containing 10 per cent fetal bovine serum.

Animals↗
PubMedDate not supplied

Crickets in space.

"Crickets in Space" (CRISP) was a Neurolab experiment by which the balance between genetic programs and the gravitational environment for the development of a gravity sensitive neuronal system was studied. The model character of crickets was justified by their external gravity receptors, identified position-sensitive interneurons (PSI) and gravity-related compensatory head response, and by the specific relation of this behavior to neuronal activation systems. These advantages allowed us to study the impact of modified gravity on cellular processes in a complex organism. Eggs, 1st, 4th and 6th stage larvae of Acheta domesticus were used. Post-flight experiments revealed a low susceptibility of the behavior to microgravity and hypergravity (hg) while the physiology of the PSI was significantly affected. Immunocytological investigations revealed a stage-dependent sensitivity of thoracic GABAergic motoneurons to 3g-conditions concerning their soma sizes but not their topographical arrangement. Peptidergic neurons from cerebral sensorimotor centers revealed no significant modifications by microgravity. The contrary physiological and behavioral results indicate a facilitation of 1g-readaptation by accessory gravity. proprioceptive and visual sense organs. Absence of anatomical modifications point to an effective time window of microgravity or hg-exposure related to the period of neuronal proliferation. Grant numbers: 50WB9553-7.

Adaptation, Physiological↗
PubMedDate not supplied

A hormonal component in central vestibular compensation.

In developing clawed toads Xenopus laevis, the compensation mechanism of behavioural defects caused by unilateral labyrinthectomy consists of two components, a vestibular one and a hormonal one. Thyroxine accelerates this compensation.

Animals↗
PubMedDate not supplied

The role of the locus coeruleus in the gain regulation of vestibulospinal reflexes.

In precollicular decerebrate cats, activation of limb extensors during side-down roll tilt of the animal depends on both an increased discharge of excitatory vestibulospinal neurons and a reduced discharge of inhibitory medullary reticulospinal (mRS) neurons. These inhibitory neurons are tonically excited by a cholinergic pontine reticular formation (pRF) system, which is in turn inhibited by norepinephrine (NE)-containing locus coeruleus (LC) neurons. Functional inactivation of LC neurons, produced by local injection of clonidine, which acts on the somatodendritic alpha 2-adrenoceptors by enhancing recurrent and/or lateral inhibition of the NE neurons, enhanced the response gain of the triceps brachii to animal tilt. We postulate that inactivation of LC neurons releases the cholinergic pRF system and the related mRS system from the suppressive influence exerted by the noradrenergic terminals. The increased discharge of these neuronal systems in the animal at rest would lead to a greater disinhibition which affects the limb extensor motoneurons during side-down tilt, thus increasing the response gain of the corresponding muscle to the same amount of labyrinth stimulation.

Animals↗