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Biomedical subjects

L Vollrath

Publications and source records attributed to L Vollrath.

At least 145 records · Page 8Linked to original sources
PubMed1981

Electrical responses of pineal cells to thyroid hormones and parathormone. A microelectrophoretic study.

The effects of microelectrophoretic application of thyroxin, thyrocalcitonin and parathormone on pineal cells of urethane anesthetized guinea pigs were evaluated. A total of 162 cells were tested with thyroxin, 122 of these units also being subjected to the microelectrophoresis of the indolamine melatonin. 68 cells were excited by the administration of thyroxin, 63 were inhibited while the remaining cells did not respond. 79% of the cells tested with both thyroxin and melatonin responded in a similar way to two substances. The responses to thyroxin varied significantly depending on whether the cells were tested during the day or at night. 104 pineal cells were tested with thyrocalcitonin, 20 U exhibiting an increased firing frequency, 58 showing an inhibitory response and the remaining 26 being unresponsive. Parathormone was applied to 64 pineal cells. Of the 43 cells responding to the hormone, 29 were excited and 14 showed decreased activity. In general, these results suggest that pineal cells may be subject to feedback control by the hormones of the thyroid and parathyroid glands.

Animals↗
PubMed1980

Effects of an earth-strength magnetic field on electrical activity of pineal cells.

Although magnetic fields can influence biological systems, including those of man and other vertebrates, no central nervous structure has been identified that might be involved in their detection. From a theoretical point of view, the pineal organ might be such a structure for the following reasons: (1) It is involved in the regulation of circadian rhythms and is thus essential for migratory restlessness ('Zugunruhe'). Orientation at that time can be altered by an artificial magnetic field (MF) with a direction differing by 90 degrees from that of the Earth. Circadian rhythms can be inhibited from phase shifting by compensation of the Earth's MF and can be influenced by an artificial MF. (2) The pineal organ is strongly dependent on its sympathetic innervation and the sympatho-adrenergic system as a whole is sensitive to magnetic stimuli. (3) The pineal organ is a light-sensitive time-keeping organ and could form part of a combined compass--solar-clock system, which has been postulated for maintaining orientation in birds. We have therefore investigated the effect of a MF on electrophysiological activity of the guinea pig pineal organ, which is a useful system for such studies on individual cells. We report here that activity was depressed by an induced MF and restored when the MF was inverted.

Action Potentials↗
PubMed1980

Electrophysiological evidence for circadian rhythmicity in a mammalian pineal organ.

Long-term electrophysiological recordings from the guinea-pig pineal organ show that three types of intrinsic cells can be distinguished: (i) Cells showing constant firing rates over periods of up to 24 hours. (ii) Cells which are highly active during the day and show a low firing rate during the night. (iii) Cells which exhibit low activity during the day and enhanced activity during the night; these cells can be strongly inhibited by 1 min of light given during the night. Both the light- and darkness-activated cells show activity patterns which closely follow season-dependent differences in day- and night-lengths. In addition, both cell types show an oscillatory pattern in maintained activity.

Animals↗
PubMed1979

Electrophysiology of the guinea-pig pineal organ: sympathetically influenced cells responding differently to light and darkness.

Single cell recordings (extracellular) from the posterior part of the guinea-pig pineal organ reveals two groups of sympathetically influenced spontaneously active cells: one group is stimulated by light and inhibited by darkness; the other type of cell whose activity was monitored over a period of 15 h shows activation by darkness and diminished activity after the onset of light. It is suggested that latter type is involved in melatonin synthesis.

Animals↗
PubMed1977

Tentative immunohistochemical demonstration of melatonin in the rat pineal gland.

In the present study an attempt was made to demonstrate melatonin in the rat pineal gland by means of immunohistochemistry. The anitbody used was raised against 5-methoxy-N-acetyltryptophan which is chemically similar to melatonin. Specific fluorescence was demonstrable only in pineals from rats killed during the night, when melatonin formation is high. It was restricted to parenchymal cells lying in a marginal zone of the organ. These results are discussed in relation to a subdivision of the pineal parenchyma into cortical and medullary areas.

Animals↗
PubMed1976

Light and drug induced changes of epiphysial synaptic ribbons.

In the present investigation experiments were carried out to determine whether the functionally obscure synaptic rebbons of mammalian pinealocytes can be affected by acute changes in environmental lighting and which chemical processes may be involved in their regulation. Experiments carried out in male guinea-pigs have shown that the amounts of synaptic ribbons are immediately affected by changes in the lighting pattern. Extension of the light period reduced the normally occurring increase, whereas extension of the dark period inhibited the normally occurring decrease in the amount of synaptic ribbons. Results following injections of a number of drugs known to influence pineal function (noradrenaline, L-DOPA, propranolol, reserpine and p-chlorophenylalanine, respectively) suggest that synaptic ribbons may be directly or indirectly regulated by beta-adrenergic mechanisms.

Animals↗