Previous investigations revealed that the growth of fish inner ear otoliths (otolith size and calcium-incorporation) depends on the amplitude and the direction of gravity, suggesting the existence of a (negative) feedback mechanism. In search for the regulating unit, the vestibular nerve was transacted unilaterally in neonate swordtail fish (Xiphophorus helleri) which were subsequently incubated in the calcium-tracer alizarin-complexone. Calcium incorporation ceased on the transacted head sides, indicating that calcium uptake is neurally regulated. Grant numbers: 50 WB 9533, 50 WB 9997.

Animals↗

PubMedDate not supplied

Neurobiological responses of fish to altered gravity conditions: a review.

In vertebrates (including man), altered gravitational environments such as weightlessness can induce malfunctions of the inner ears, based on an irregular dislocation of the inner ear otoliths from the corresponding sensory epithelia. This dislocation leads to an illusionary tilt, since the otolithic inputs are not confirmed by the other sensory organs, which results in an intersensory conflict. Vertebrates in the orbit therefore face severe orientation problems. In humans, the intersensory conflict may additionally lead to a malaise, commonly referred to as space motion sickness (SMS). During the first days at weightlessness, the orientation problems (and SMS) disappear, since the brain develops a new compensatory interpretation of the available sensory data. The present review reports on the neurobiological responses--particularly of fish--observed at altered gravitational states, concerning behaviour and neuroplastic reactivities.

Animals↗

PubMedDate not supplied

Brain gangliosides during the life span (embryogenesis to senescence) of the rat.

The concentration of gangliosides, sialoglycoproteins and proteins was studied in the whole brains and single brain structures (cortex, olfactory bulb, corpora quadrigemina region equals midbrain, cerebellum, thalamic region and oblongated medulla) of female rats from 14 developmental stages ranging from day 8 of gestation to more than 3 years of age. The content of protein- and ganglioside-bound neuraminic acid showed a peak at 3 weeks of age and then decreased with aging, whereas that of proteins increased until senescence. All over the life span the developmental profiles of 12 individual gangliosides in the different brain structures (cortex, corpora quadrigemina region approximately midbrain, cerebellum, thalamic region, medulla) and in whole brain samples were followed. There are distinct differences between the brain structures. Additionally each brain region is characterized by specific developmental ganglioside profiles. However, some ganglioside changes are common to all regions: GD3 in general is a marker for cell division and migration, whereas the polar ganglioside fractions GQ1b and GP1 are characteristic for nerve cell sprouting and arborization. Especially in the cortex GD1a seems to be the marker for synaptogenesis and GM1 and GM4 for myelination. The results were discussed in view of the main morphological patterns of differentiation.

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