Biomedical subjects

L Vollrath

Publications and source records attributed to L Vollrath.

At least 109 records · Page 6Linked to original sources

PubMed1986

Quantitative light microscopic observations on Paneth cells of germ-free and ex-germ-free Wistar rats.

Germ-free rats were inoculated with bacteria from feces of SPF rats, and the Paneth cells in the ileal crypts were observed at different time intervals after inoculation. 12 h after inoculation, the Paneth cells showed a striking degranulation and the occurrence of supranuclear vacuoles. The Paneth cell area was significantly reduced. Four days to 3 weeks after inoculation, the secretory granules of Paneth cells were abundant, and both number and area of Paneth cells showed a progressive increase coming close to the data in SPF rats. The present study demonstrates interrelationships between secretory activity of Paneth cells and the microbial milieu in the small intestine and that the presently used experimental model is well suited for examining the histophysiology of Paneth cells. Moreover, the results suggest that Paneth cell numbers may also be closely related to crypt length.

Animals↗

PubMed1985

Evidence for the involvement of the visual system in mediating magnetic field effects on pineal melatonin synthesis in the rat.

In order to elucidate whether magnetic field effects on mammalian pineal function are direct, or instead indirect via retinal disturbances, acutely blinded and intact male rats were subjected to a single nocturnal magnetic stimulus. Then pineal N-acetyltransferase activity and melatonin content were assayed. Only in intact animals did the magnetic stimulus significantly reduce pineal activity, i.e. no effects were detected in blinded animals. These data point to a retinal magnetosensitivity which may serve to modulate pineal gland function.

Acetyltransferases↗

PubMed1985

Mammalian pinealocytes: ultrastructural aspects and innervation.

In the mammalian pineal gland it is notoriously difficult to relate structure to function. The pineal-specific cells, the pinealocytes, contain only inconspicuous numbers of secretory granules, and the variable amounts of smooth and rough endoplasmic reticulum also do not point to a particular function. In addition to these widely known cellular components, pinealocytes contain organelles, the so-called 'synaptic' ribbons, histophysiological studies of which provide important insights into the structural and functional complexity of the organ. As synaptic ribbons may be involved in neuronal functions of pinealocytes it is notable that these organelles are structurally heterogeneous. Ribbons fall into at least two categories: rod-like (RSR) and sphere-like (SS) structures. RSR and SS usually do not lie within the same pinealocyte profile and appear to be regulated by different mechanisms. It is conceivable that they are important components of the biological clock system. These findings are related to our knowledge of the innervation of the mammalian pineal gland and to electrophysiological characteristics of pinealocytes.

Animals↗

PubMed1985

Postnatal development of "synaptic" ribbons and spherules in the guinea pig pineal gland.

Previous studies have shown that the functionally enigmatic pineal "synaptic" ribbons are structurally a heterogeneous group of organelles consisting of rodlike ribbons sensu stricto, spherules, and intermediate forms. As ribbons and spherules react differently under various experimental conditions, these organelles were studied qualitatively and quantitatively during the postnatal period in guinea pigs. It was found that the pinealocytes were highly differentiated at birth and contained all three forms of "synaptic" structures. Ribbons and intermediate forms were more abundant than spherules and exhibited a striking increase in number on postnatal days 1 and 2; this increase was followed by a distinct trough and by a second peak at days 12 and 13, after which their numbers declined to reach adult levels by day 20. The spherules were small in number at birth and did not show the large immediate postnatal increase observed for the ribbons and intermediate forms. Instead there was a steady numerical increase up to day 12 (absolute number) or day 15 (relative numbers), followed by a decrease to adult level by day 20. Whereas during the early postnatal period (days 1 to 3) the majority of pinealocytes were characterized by ribbons and intermediate forms, with increasing age spherule-bearing pinealocytes increased in number. As ribbons and spherules were usually not found in the same pinealocyte, the present findings are interpreted to mean that ribbons and spherules characterize different types of pinealocytes showing an inverse numerical development postnatally. Developmentally intermediate forms behave like ribbons.

Animals↗

PubMed1985

Number and size of rat thyroid C cells: no effect of pinealectomy.

A method for the estimation of the size and total number of calcitonin-containing cells (C cells) in the rat thyroid gland has been devised. The total area, the number of C cells per unit area, and the areal fraction of C cells were determined for the C cell region using step serial sections. From these data it was estimated that from 0.3 X 10(6) to 1.0 X 10(6) C cells were evenly divided between the two thyroid lobes. Approximately 150 micron3 of cytoplasm were associated with each of these cells. In comparison with sham-operated rats, pinealectomy had little effect on the number of C cells. In an experiment terminated in the summer, there was a statistically insignificant decrease 6 weeks postsurgery; no effect was seen at 12 weeks. On the other hand, a slight increase in the number of C cells was seen in January, 12 weeks postsurgery. The volume of cytoplasm per cell was not altered by pinealectomy.

Animals↗

PubMed1985

Influence of melatonin and serotonin on the number of rat pineal "synaptic" ribbons and spherules in vitro.

Previous studies have shown that the "synaptic" ribbons (SR) and spherules (SS) of the mammalian pineal gland may respond differently under physiological and various experimental conditions. The aim of the present study was to gain insight into the mechanisms that may be responsible for the numerical changes of these organelles during a 24-h cycle. As the possibility exists that the structures are influenced by substances synthesized within the pinealocyte, rat pineal glands were cultured with and without added melatonin or serotonin, using an experimental protocol such that the addition of melatonin and serotonin mimicks the circadian changes of the respective substances within the pineal. The tissue was processed for electron microscopy and the numbers of SR and SS were counted in a unit area of pineal tissue. The results obtained indicate that melatonin added to the incubation medium increases the number of SR in the first half of the night; serotonin decreases SR numbers in the morning. SS numbers, by contrast, decrease following melatonin administration in the afternoon, and increase in the morning following serotonin administration. It thus appears that the numbers of SR and SS are influenced by melatonin and serotonin and that the two structures are regulated by differential, but nevertheless biochemically closely related mechanisms.

Animals↗

PubMed1985

Distribution of dopamine-beta-hydroxylase-like immunoreactivity in the rat pineal organ.

The aim of the present investigation was to study the distribution in the rat pineal gland of dopamine-beta-hydroxylase (DBH) which is essential for the formation of the melatonin synthesis-regulating substance noradrenaline (NA). In 5- and 8-month-old male Sprague-Dawley rats DBH-like immunoreactivity (DBH-LI) was studied using polyclonal antibodies against DBH and the indirect immunofluorescent technique. DBH-LI was mainly located in pineal nerve fibres coming from the superior cervical ganglia. The intensity of the staining reaction was considerably lower than in non-pineal noradrenergic nerve fibres and the impression was gained by comparison of DBH-LI specimens with glyoxylic acid-treated sections that only approximately one third of the NA-containing intrapineal nerve fibres exhibited DBH-LI. There were no detectable differences in DBH-LI with regard to time of day and age of the animals. These results suggest that NA synthesis may be relatively low in intrapineal sympathetic nerve fibers and that the NA required for the regulation of pineal melatonin synthesis may, to a large degree, stem from the circulation. In addition to nerve fibres, some rare intrapineal cell bodies exhibited DBH-LI; in 5-month-old rats their numbers did not reveal significant differences between day and night. These cells do not appear to represent pinealocytes. They may be a special population of noradrenergic nerve cells perhaps belonging to an as yet unknown intrapineal regulatory system.

Adrenal Medulla↗

PubMed1985

Melatonin formation in different parts of the guinea-pig pineal complex as assessed over 24 hours.

There is morphological evidence that the pineal gland is not a uniformly built organ but rather a complex. In the guinea-pig the gland is 6--7 mm in length and dumbbell-shaped, the proximal part coming into intimate contact with central commissural fibres. The aim of the present 24-hour study was to examine in male guinea-pigs whether the proximal, intermediate and distal areas of the gland are involved in melatonin formation and to compare their rhythmicities. Levels of melatonin in serum and the whole pineal gland as assessed by RIA show day/night ratios of 1 : 1.25 and 1 : 3.3, respectively. Serotonin N-acetyltransferase activity was found to exhibit ratios of 1 : 1.75 (Experiment I) and 1 : 4.4 (Experiment II). All three pineal regions are involved in melatonin formation, and to the same extent. Whether the rhythms in the different regions are identical could not be clarified as the curves obtained exhibited striking oscillations and the day/night differences were rather small. As the extrapineal portion of the habenular commissure was found to contain melatonin there is a possibility that melatonin may be taken up when the commissural fibres pass through the pineal parenchyma.

Acetylserotonin O-Methyltransferase↗

PubMed1985

Changes in the electrical activity of the rat pineal gland following stimulation of the cervical sympathetic ganglia.

In order to elucidate the role of sympathetic innervation for pineal function, the influence of both unilateral and bilateral electrical stimulation of the superior cervical ganglia on the electrical activity of single cells in the rat pineal gland was investigated. These experiments revealed a clear influence on spontaneous electrical activity of single pinealocytes. About half of the units tested by unilateral stimulation exhibited either a graded continuous augmentation or inhibitions of different magnitude. In addition, 'silent' cells without spontaneous activity could be activated by sympathetic stimulation. Sequential and simultaneous bilateral stimulations showed that only a few cells could be influenced by both ganglia and in these cases the influence seemed to be additive. Some pineal cells do not appear to be under the control of the sympathetic nervous system.

Animals↗

PubMed1985

Electrical stimulation of the hypothalamic paraventricular nuclei inhibits pineal melatonin synthesis in male rats.

Recent findings have shown that lesions of the hypothalamic paraventricular nuclei (PVN) disrupt the synthesis of melatonin in the rat pineal gland. In order to further clarify the role of the PVN in the control of pineal function, the effects of electrical stimulation of these nuclei were investigated in acutely blinded adult male Sprague-Dawley rats. Following electrical stimulation, pineal serotonin-N-acetyltransferase (NAT) activity and pineal melatonin content were measured by means of radioenzymatic and radioimmunoassay methods, respectively. Stimulation had no significant effect on pineal melatonin synthesis throughout the early part of the dark phase, but caused a significant reduction in NAT activity during the light phase and the latter part of the dark phase. The pineal melatonin content appeared reduced, but due to large individual variations this reduction was not statistically significant. Stimulation duration experiments reveal that reduction of NAT activity is time dependent, with significant inhibition occurring after 30 min of stimulation. These observations further support the involvement of the PVN in the melatonin rhythm generating pathway and suggest that electrical activation of fibers in the PVN is similar to the effects of light on pineal melatonin synthesis.

Animals↗

PubMed1984

Pineal gland size and serum melatonin levels in male rats are not correlated.

As both the size of the pineal gland and the serum levels of melatonin are known to be variable it was decided to assess whether the two parameters are interrelated. For this purpose male Sprague-Dawley rats were killed at 12.00 and 24.00 h, respectively. Trunk blood was collected for melatonin radioimmunoassay. The pineal glands were prepared for histological examination, serially sectioned, and from planimetric tracings the volume of the gland was computed. Neither at day nor at nighttime was there a correlation between the volume of the pineal gland and the levels of serum melatonin. There was also no correlation between body weight and the volume of the pineal gland or the levels of serum melatonin.

Animals↗

PubMed1984

Ultrastructural characterization of glial cells in the rat pineal gland with special reference to the pineal stalk.

In the present study the "interstitial" cells of the superficial pineal gland and the nonparenchymal cells of the pineal stalk in Sprague-Dawley rats were examined ultrastructurally with the aim of defining the cells more closely. The "interstitial" cells of the superficial pineal gland do not represent a homogeneous cell population. The most abundant cell type is the mononuclear phagocyte, most easily recognized by its dark appearance and its content of primary and conspicuous secondary lysosomes. Astrocytes can be distinguished by the typical appearance of their nuclei (i.e., a thin continuous rim of heterochromatin adjacent to the nuclear membrane), identical to that of astrocytes in the CNS. Depending on the absence or presence of glial filaments and their amount, a spectrum of astrocytic cells is present. Mature astrocytes with filaments throughout their cytoplasm are rare. Immature glial cells with few or no filaments predominate. In the vicinity of blood vessels pericytes are present. In view of the fact that the "interstitial" cells could generally be identified it is suggested to abandon the term interstitial for the cells in question. In the pineal stalk mature astrocytes predominate; they have some features in common with pinealocytes, i.e., the presence of intergrade endoplasmic reticulum and grumose bodies (lysosomes). Other unusual features are a relative abundance of coated pits and vesicles. Oligodendrocytes are restricted to the proximal part of the stalk, near the deep pineal, where myelinated axons are abundant. More distally a few Schwann cells were seen.

Animals↗

PubMed1984

Correlation of the number of pineal "synaptic" ribbons and spherules with the level of serum melatonin over a 24-hour period in male rabbits.

Previous studies have shown that pineal "synaptic" ribbons and spherules may respond differently under normal and experimental conditions. It has been suggested that the increase in the number of ribbons may be a prerequisite for enhanced melatonin formation. In the present study, the number of ribbons and spherules as well as the level of serum melatonin were monitored over a 24-h period in the male rabbit, the pineal gland of which is known to contain many spherules. It was found that both the number of ribbons and the levels of serum melatonin show the typical nocturnal increase, exhibiting peaks at 02:00 and 06:00 h, respectively. There is a good correlation (R = 0.8) of the two parameters. The spherules, in contrast, show no statistically significant circadian changes in number and cannot be correlated with the levels of serum melatonin. It is concluded that ribbons and spherules may differ in function and that the ribbons may be somehow involved in the regulation of melatonin formation.

Animals↗

PubMed1984

Electrophysiological properties of rat pinealocytes: evidence for circadian and ultradian rhythms.

Extracellular single-unit recordings were made during day- and night-time in the pineal gland of urethane-anesthetized adult male Sprague-Dawley rats. All cells exhibiting spontaneous electrical activity had firing frequencies from less than 1 Hz to about 100 Hz, and their discharge patterns were characterized as regular, irregular or bursting. While most of the spontaneously active cells (n = 163) showed a uniform activity level throughout the recording period (30-120 min), a group of 9 cells exhibited oscillatory rhythms with periods of 4-8 min. In addition, long-term recordings across day- and night-time from five cells revealed increasing activity during night-time in three cells, while the remaining two units showed constant activity throughout the recording time (8-20 h). Comparison of day- and night-data in general indicated an overall higher level of activity at night.

Action Potentials↗

PubMed1984

The effects of a number of short-term exogenous stimuli on pineal serotonin-N-acetyltransferase activity in rats.

The present study deals with the question as to what extent the sympathetically innervated rat pineal gland is affected by a number of short-term exogenous stimuli given during day-time, as assessed by measuring pineal serotonin-N-acetyltransferase activity (NAT) which is directly proportional to melatonin formation. In male Sprague-Dawley rats kept under LD 12:12 pineal NAT was statistically significantly depressed by physical immobilization for 2 hours, swimming for 15 min in water of 10 and 30 degrees C, exposure for 2 hours to cold (5 degrees C) or heat (40 degrees C), noise (90 db) for 2 hours and hunger for 17 hours. An increase in NAT was noted after swimming for 15 min in water of 20 degrees C. No effect was detectable after 17 hours of thirst or hunger combined with thirst and in one of 2 experiments involving exposure to heat (40 degrees C, 2 hours) and insulin-induced hypoglycemia. In animals kept under continuous illumination for 48 hours, immobilization resulted in a slightly smaller decrease than under LD 12:12 and insulin-induced hypoglycemia led to a striking increase of NAT. As the changes in pineal NAT are brought about by rather strong exogenous stimuli it is suspected that the rat pineal gland during day-time is not very susceptible to ambient factors of normal range.

Acetyltransferases↗

PubMed1984

Day/night changes of pineal gland volume and pinealocyte nuclear size assessed over 10 consecutive days.

Previous studies aimed at elucidating day/night changes of pineal gland size and pinealocyte nuclear volume have yielded contradictory results. The aim of the present investigation was to examine the above parameters over a period of 10 successive days, at 6-hour intervals under a lighting regimen of LD 12:12 (7 a.m. to 7 p.m.). It was found that changes in pineal gland volume could not be correlated with the light/dark phases; instead, a rhythm with a two-day period was encountered. Pinealocyte nuclear volume, by contrast, showed clear circadian changes, exhibiting troughs during photophase and peaks during scotophase. In this experimental series, the karyometric results conformed to the melatonin forming rhythm in the rat pineal gland as reported in the literature.

Animals↗

PubMed1984

Electrophysiological investigations on the central innervation of the rat and guinea-pig pineal gland.

The possible influence of central nervous structures on the electrical activity of single pineal cells was investigated in rat and guinea-pig. In the rat electrical stimulation of the hippocampal formation elicited both single cell responses with different latencies and mostly long-term excitations in single pineal cells, while stimulation of the habenular nuclei caused clear orthodromical responses with different latencies, alterations in the rate of spontaneous electrical activity and evoked discharges of "silent" units. In the guinea-pig electrical stimulation of the paraventricular nucleus influenced predominantly cells in the deeper layers of the posterior part of the pineal gland. Electrical stimulation of both the superior and inferior colliculi elicited field potentials with a constant latency, indicating a functional relationship between the corpora quadrigemina and the pineal organ.

Animals↗

PubMed1984

No correlation of pineal "synaptic" ribbon numbers and melatonin formation in individual rat pineal glands.

As previous circadian studies of pineal "synaptic" ribbon numbers and melatonin formation suggested that a positive correlation of the two variables exists, in the present investigation this problem was examined in individual pineal glands of rats killed at 1200 h and 2400 h, respectively. For this purpose, one half of the gland was processed for electron microscopy and the ribbons were counted in an area of 20,000 micron2 tissue; in the other half serotonin N-acetyltransferase (NAT) activity and melatonin content were determined. No correlation was found to exist between ribbon numbers and pineal NAT activity, pineal melatonin levels and serum melatonin levels, either at day- or at nighttime. It is concluded that the ribbons may perhaps be more closely related to the innervation of the pineal gland than to melatonin formation.

Animals↗