Biomedical subjects

L Vollrath

Publications and source records attributed to L Vollrath.

At least 73 records · Page 4Linked to original sources

PubMed1990

The pineal complex in Roman high avoidance and Roman low avoidance rats.

Previous studies have shown that the pineal gland of Roman high avoidance (RHA/Verh) rats is larger than that of Roman low avoidance rats (RLA/Verh). In the present study measurement of enzyme activities (serotonin-N-acetyl-transferase, hydroxyindole-O-methyltransferase) revealed that pineals of RHA/Verh rats are twice as active in melatonin production than pineals of RLA/Verh rats. Indoleamine content was also higher in RHA/Verh rats, whereas noradrenaline content was the same in both lines. When values were expressed per mg protein, these differences disappeared except for N-acetyl-serotonin and noradrenaline which were higher or lower in RHA/Verh rats, respectively. Both lines had higher serum levels of melatonin during the dark phase than during the light phase. However, RHA/Verh rats had increased serum levels as compared to RLA/Verh rats during both day and night. Morphometric analysis of the deep and superficial part of the pineal complex revealed, that the volumes of both parts are enlarged in RHA/Verh rats. Electron microscopic studies of pineals collected during day- and nighttime showed higher numbers of synaptic ribbons per unit area in pineals of RHA/Verh rats. In pineals collected during June synaptic ribbons displayed a day/night rhythm in RHA/Verh rats only, whereas in glands of both lines collected during November no daily changes were found. These results show that closely related but divergently selected rat lines may differ in pineal ultrastructure and pineal function.

Acetylserotonin O-Methyltransferase↗

PubMed1990

The aged pineal gland: reduction in pinealocyte number and adrenergic innervation in male rats.

Previous biochemical and physiological studies point to an age-related loss of pineal function. Morphological studies revealed increased connective tissue and glial cell numbers in the gland. In the present study we investigated whether the number of parenchymal cells and the incidence of sympathetic fibers in the rat pineal gland is altered with advanced age. The comparison of pineal histology of young adult (2-3 months old) and aged animals (22-26 months old) showed that pinealocyte number in old animals is decreased by 18%. In addition, sympathetic innervation of the gland as revealed by glyoxylic acid fluorescence is drastically reduced in these animals. It is concluded that the age-related decline in pineal metabolism may be due to both decreased parenchymal cell number and reduced sympathetic innervation.

Aging↗

PubMed1990

'Synaptic' bodies in the pineal glands of the cow, sheep and pig.

The present results show that 'synaptic' bodies (SB) are a heterogeneous group of organelles in the pineal glands of Artiodactyla. Basically, rod-like (ribbons) and sphere-like (spherules) SB can be distinguished. In the pig small numbers of both 'synaptic' ribbons (SR) and 'synaptic' spherules (SS) are found. In bovine and ovine pineal glands few SS but no SR were seen. The same results were obtained from animals of the same species but from different continents. This suggests that the numbers of SB are species specific rather than influenced by the different lighting conditions in Europe and in equatorial Africa.

Africa↗

PubMed1990

Developmental changes and daily rhythm in melatonin-induced inhibition of 3',5'-cyclic AMP accumulation in the rat pituitary.

Melatonin's transduction mechanisms were investigated using in vitro cultured anterior hemipituitaries. Melatonin inhibited cAMP and 3',5'-cyclic GMP accumulation in neonatal rat anterior pituitary stimulated with LHRH. Maximal inhibitory effect was reached within 25 min and persisted for at least 20 min. Inhibition of cAMP accumulation is specific for melatonin because its analogs N-acetylserotonin and 5-methoxytryptamine are 1000 times less potent. Melatonin effect is age- and time-dependent. Marked inhibition was observed in 5-, 10-, and 14-day-old rats but not in 29-day-old ones. Melatonin was significantly more potent when applied at the end of the light period as compared with the first half of the day. Melatonin's effects on cAMP correlate with its effect on reproductive functions and on LH release. Cyclic nucleotides may thus serve as second messengers transducing the effect of melatonin on cellular level.

Aging↗

PubMed1990

Effects of adrenergic agonists and antagonists on the numbers of synaptic ribbons in the rat pineal gland.

In the pineal gland numbers of synaptic ribbons (SR) undergo day/night changes which parallel the rhythm of melatonin synthesis. Since pineal biosynthetic activity is controlled by activation of adrenoreceptors, we investigated the effects of adrenergic agonists and antagonists on pineal synaptic ribbon numbers and N-acetyltransferase (NAT) activity, the key enzyme of melatonin synthesis in rats. In vivo application of the beta-adrenergic antagonist propranolol decreased melatonin synthesis when given during the dark phase but did not affect SR numbers. Treatment during daytime with the beta-adrenergic agonist isoproterenol increased pineal NAT activity whereas SR numbers did not change. Norepinephrine stimulated NAT activity in vitro in a dose-dependent manner, but did not elevate SR numbers. Incubation with an analog of the second messenger cyclic adenosine monophosphate increased both NAT activity and SR numbers. These results suggest that the beta-adrenergic system does not play a decisive role in the regulation of the nocturnal increase in SR numbers observed in the rat pineal gland.

Animals↗

PubMed1989

Melatonin inhibits cyclic AMP and cyclic GMP accumulation in the rat pituitary.

Subnanomolar concentrations of melatonin inhibit cyclic AMP and cyclic GMP accumulation in neonatal rat anterior pituitary stimulated in vitro with luteinizing-hormone releasing-hormone. Melatonin also inhibited forskolin-stimulated cyclic AMP accumulation in pars tuberalis. Inhibition of cyclic AMP accumulation is specific for melatonin, since its analogs N-acetylserotonin and 5-methoxytryptamine are 1000 times less potent. Cyclic nucleotides may thus serve as second messengers transducing the effect of melatonin on cellular level.

Animals↗

PubMed1989

Day-night differences in the sensitivity of adrenoceptors in the Syrian hamster pineal gland: an in vivo iontophoretic study.

Investigations on the regulation of pineal melatonin synthesis in the Syrian hamster revealed distinct differences compared to this well-understood mechanism in rat. E.g., a circadian profile of pineal norepinephrine (NE) is absent, there is no beta-adrenoceptor sensitivity during daytime and adrenergic receptor supersensitivity is not easily achieved. To elucidate the action of NE on pineal receptor sites, the effects of iontophoretic application of adrenergic compounds on spontaneous electrical discharge rates of pinealocytes were investigated during day- and nighttime. Following application of either NE, isoproterenol or clonidine, cells were activated, inhibited or not affected. Whereas about one-third of the units responded to iontophoretic application of sympathomimetics at daytime, the number of affected cells was doubled during the night. These results demonstrate the involvement of adrenoceptors in the regulation of circadian rhythms in electrophysiological properties of Syrian hamster pinealocytes. Since relatively few cells responded during daytime and inhibitory adrenergic mechanisms dominated at night, the classification of receptors by means of iontophoresis may provide a basis to explain the difficulty to influence pineal melatonin synthesis by sympathomimetics in the Syrian hamster.

Action Potentials↗

PubMed1989

One millisecond of light suffices to suppress nighttime pineal melatonin synthesis in rats.

The effect of a single high-intensity light pulse with a duration of 1 ms on nighttime pineal activity of male Sprague-Dawley rats was investigated. 10 minutes after light exposure pineal N-actyltransferase activity and melatonin content were significantly reduced. These results show that the rat pineal is capable of responding to very short light flashes of high intensity.

Acetyltransferases↗

PubMed1989

Interrelationship among morphology, metabolism, and proliferation of tumor cells in monolayer and spheroid culture.

The proliferative activity of tumor cells is positively correlated with the cellular respiration rate. Thus, a decrease in the proliferative fraction during monolayer growth of EMT6 cells is associated with a decrease in the oxygen consumption rate both per cell and per cellular volume. These changes are paralleled by variations in the morphology of the tumor cells. The cellular volume, the cytoplasmic volume, the number and volume of mitochondria is decreased, whereas the volume of the nucleus remains relatively constant during the transition of cells from the exponential to the plateau growth phase. Similar observations have been made in outer, highly proliferative and inner non-proliferating cells in EMT6 spheroids. However, the local oxygen consumption in this three dimensional, tissue-like assemblage of cells is obviously modified by the cellular packing density leading to a rather uniform oxygen uptake in the proliferating and non-proliferating cell areas.

Animals↗

PubMed1989

Effects of electrical stimulation of the superior cervical ganglia on the number of "synaptic" ribbons and the activity of melatonin-forming enzymes in the rat pineal gland.

Melatonin metabolism in the mammalian pineal gland is under the clear influence of sympathetic fibers originating in the superior cervical ganglia (SCG). Previous studies suggested that pineal "synaptic" ribbons (SR) as well are regulated by the gland's sympathetic innervation. To gain more insight into the mechanisms involved, we examined the effects of sympathetic stimulation on SR number and on the activity of melatonin forming enzymes, serotonin N-acetyltransferase (NAT) and hydroxyindole-O-methyltransferase (HIOMT). The SCG in adult male rats were stimulated electrically during daytime for either 15 or 120 min. Immediately following stimulation, the glands were removed and processed for electron microscopy and for the determination of NAT and HIOMT activities. No differences in pineal SR number, size or location were found in rats stimulated with either parameters when compared with sham-stimulated or control animals. While the activity of HIOMT remained unchanged, the activity of NAT was also unaltered following 15 min of stimulation, but was augmented approximately three-fold in animals stimulated for 120 min. It is concluded that if SR in the rat pineal gland are under sympathetic control, the regulation is different from that involved in melatonin formation.

Acetylserotonin O-Methyltransferase↗

PubMed1989

Ribbon synapses of the mammalian retina contain two types of synaptic bodies--ribbons and spheres.

The present paper reports that the synaptic bodies of the retinal ribbon synapses in rat, guinea pig, golden hamster and mouse are a heterogeneous population of organelles. In addition to the well-known synaptic ribbons sensu stricto which consist of a platelike electron-dense central structure surrounded by electron-lucent synaptic vesicles, there are what is termed synaptic spheres, in which the core is not platelike, but round to oval. In rat retinae procured at day, ribbons outnumbered spheres by a factor of 4. At night spheres were not seen in photoreceptor cells. Spheres, like ribbons, may lie some distance from the synaptic site, perhaps indicating transit from their site of origin to the synapse. At night ribbons are longer than at daytime. In addition to the previously described connecting stalks between synaptic vesicles and the electron-dense ribbons, the presence of filamentous stalks between adjacent synaptic vesicles is described. The latter stalks, depending on their presence or absence, may influence the position of the synaptic vesicles in relation to the synaptic body and/or the presynaptic membrane. It is concluded that the plasticity of retinal synapses cannot be fully appreciated unless the temporal changes of ribbons, spheres and the connecting stalks are taken into consideration.

Animals↗

PubMed1989

Effects of melatonin on spontaneous electrical activity of neurons in rat suprachiasmatic nuclei: an in vitro iontophoretic study.

Circadian rhythms, endogenously generated in suprachiasmatic nuclei (SCN), seem to be under the direct influence of melatonin. Therefore, the effect of iontophoretically applied melatonin on electrical activity of SCN neurons was investigated in vitro. Usually, melatonin had an inhibitory effect. In the 3-h periods before (2.00-5.00 p.m.) or after (5.00-8.00 p.m.) the light-dark transition the percentage of SCN neurons sensitive to melatonin was very high (80% and 100%, respectively). However, efficacy of melatonin was low in the periods preceeding (20%) and following (33%) this 6-h time interval.

Action Potentials↗

PubMed1989

In vitro synthesis of dopamine and noradrenaline in the isolated rat pineal gland: day-night variations and effects of electrical stimulation.

Isolated rat pineal glands were incubated in vitro in a medium containing [14C]dopamine or [14C]tyrosine, and the tissue contents of 14C-labelled and total dopamine and noradrenaline were determined by HPLC followed by electrochemical detection and scintillation spectrometry. During incubation with [14C]dopamine, the labelled amine accumulated in pineal glands and was partially converted into [14C]noradrenaline. Nomifensine, a neuronal amine uptake blocker, largely inhibited the accumulation of [14C]dopamine and the formation of [14C]noradrenaline. These experiments demonstrated dopamine beta-hydroxylase activity in the sympathetic nerves of the pineal gland. During incubation with [14C]tyrosine, formation of [14C]dopamine and [14C]noradrenaline was observed in the pineal tissue, indicating that noradrenaline can also be synthesized from dopamine, endogenously formed in the gland. Electrical stimulation of the stalk region of the pineal gland during incubation with [14C]dopamine enhanced the accumulation of [14C]dopamine and synthesis of [14C]noradrenaline. Electrical stimulation also enhanced the formation of [14C]dopamine during incubation with [14C]tyrosine. Compared to that at midday, the tissue content of endogenous noradrenaline at midnight was enhanced by 50% and that of dopamine by 450%. The in vitro accumulation of [14C]dopamine, as well as the synthesis of [14C]dopamine and [14C]noradrenaline, was also increased at midnight. In conclusion, sympathetic nerves in the rat pineal gland contain tyrosine hydroxylase and dopamine beta-hydroxylase, the two enzymes required for the synthesis of noradrenaline.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1989

Development and validation of a radioimmunoassay for serum melatonin.

A radioimmunoassay using N-[3-(4-hydroxy-3-[4-hydroxy-3- [125I]iodophenylpropionyl)]-5-methoxytryptamine as tracer for determination of melatonin in the serum of different species is described. Melatonin antisera were raised in rabbits by immunization with a bovine serum albumin conjugate of N-[3-(2-aminoethyl)-5-methoxy indole] hemisuccinamide. A single high affinity, specific antiserum was obtained. In contrast to previous studies, the tracer was synthesised in one step in the absence of water, giving an excellent yield of highly pure product. No chromatographic purification step was needed. Polyethylene glycol in combination with goat antirabbit immunoglobulins was used to separate bound and unbound tracer. Sera were delipidized with Lipoclean prior the extraction of melatonin with diethyl ether. This sample preparation allows the determination of melatonin in the presence of widely varying amounts of lipids in human, rat and hamster serum. Using this extraction procedure, the sensitivity of the radioimmunoassay was approximately 1 ng/l of serum. Dilutions of sera and of synthetic melatonin gave the same parallel response in the radioimmunoassay. High performance liquid chromatography analysis of a serum extract showed only one immunoreactive peak co-eluting with synthetic melatonin. Characteristic diurnal rhythms of melatonin were observed in all species. All assay components including standards and serum controls are stable for at least 1 year at 4 degrees C, thus facilitating the determination of melatonin in a routine laboratory.

5-Methoxytryptamine↗

PubMed1989

Serotonin and melatonin contents in the pineal glands from different stocks and strains of laboratory rats.

In the present study the pineal gland was examined in 2 outbred stocks and 6 inbred strains of rats some of which were pigmented to varying degrees, to see whether inbreeding affects the variability and whether differences exist between albino and pigmented rats. The animals were kept under 12 h light: 12 h darkness (12 L:12 D) and killed 7 h after the onset of light and darkness, respectively. The parameters examined were pineal protein content, serotonin and melatonin levels and hydroxyindole-O-methyltransferase (HIOMT) activity. All the parameters examined revealed interstrain differences, independently of whether the data were expressed per pineal or per mg protein. The variation coefficients for the various parameters were relatively high. They were mostly smaller when the data were expressed per pineal rather than per mg protein. No striking differences existed between the variation coefficients in inbred and outbred rats. When pineal size and the melatonin-related parameters expressed per pineal were used to assess the melatonin-synthesizing capacity of the pineal glands, it was found that the outbred Wistar and Sprague-Dawley rats and the inbred LEWIS-derived (LEW/Han) rats, all of which were albinos, had the most active pineals. Intermediate activity was noted in the hooded E3/Han and BDE/Han and the albino BDII/Han rats. The smallest and least active pineals were found in the totally pigmented BN/Han and DA/Han rats. The results taken together show that different stocks and strains exhibit significant differences in pineal size and melatonin-forming capacity. Albino rats appear to have larger and more active pineals than pigmented rats.

Acetylserotonin O-Methyltransferase↗

PubMed1988

Melatonin and other serotonin derivatives in the guinea pig membranous cochlea.

In mammals, the indolealkylamine melatonin is synthesized mainly in the pineal gland and to a lesser degree in a number of extrapineal sites. To obtain more information on its distribution, melatonin was measured in the membranous cochlea of the guinea pig. Moreover, melatonin and other serotonin derivatives were determined in organ cultures after incubation with 14C-labelled serotonin. The results show that melatonin is detectable in the organ of Corti and the basilar membrane, and to a lesser degree also in the cochlear nerve and stria vascularis, including the spiral ligament. In vitro studies reveal the occurrence of a number of radiolabelled serotonin derivatives indicating that two of the melatonin-forming enzymes, serotonin N-acetyltransferase (NAT) and hydroxyindole-O-methyltransferase (HIOMT) are present in membranous cochlea. It is concluded that melatonin is synthesized in the guinea pig cochlea. Its role as modulator of hair cell function is dissolved.

Acetylserotonin O-Methyltransferase↗

PubMed1988

Responses of the mammalian retina to experimental alteration of the ambient magnetic field.

The detection of earth strength magnetic fields by rodents has been demonstrated previously by numerous physiological and behavioral techniques. This phenomenon appears to require input from the eyes. In an effort to better understand this phenomenon retinal melatonin synthesis and catecholamine contents were assayed in rats exposed at night to an alteration of the ambient magnetic field. In normal animals both dopamine and norepinephrine levels in the retina were reduced by this stimulus, while retinal melatonin synthesis was unaffected. Animals that had lost their intact photoreceptors as a result of 8 weeks of previous constant light exposure did not show a catecholamine response to the magnetic stimulus. These results support the view that the mammalian retina participates in the relaying of magnetic information into the central nervous system.

Animals↗

PubMed1988

Immunohistochemical evidence for the presence of peptides derived from proenkephalin, prodynorphin and proopiomelanocortin in the guinea pig pineal gland.

By using a plethora of region-specific antisera, this light microscopic immunohistochemical study revealed that derivatives from the three opioid precursors, i.e. proenkephalin, prodynorphin and proopiomelanocortin are differentially distributed in the pineal gland of guinea pig. Various molecular forms of immunoreactive opioid peptides derived from proenkephalin or prodynorphin were present in a minority of pinealocytes as well as in nerves. In contrast to this dual distribution pattern of opioid-active peptides, the opioid-inactive derivative from proopiomelanocortin, alpha-melanocyte stimulating hormone, was exclusively present in a large proportion of pinealocytes. A multiple and differential origin and function of opioidergic pineal innervation involving sympathetic, parasympathetic and sensory components is suggested. alpha-MSH is proposed as a pineal hormone which may act in concert with melatonin to regulate pineal rhythms or may function like MSH of pituitary origin.

Animals↗