Effect of calcium on melatonin secretion in chick pineal gland I

Bipedal ambulation induces experimental scoliosis in C57BL/6J mice with reduced plasma and pineal melatonin levels

In addition to the induction of scoliosis in chickens by pinealectomy (PINX), we previously demonstrated that removal of the pineal gland also produces scoliosis in bipedal rats, which can be inhibited by melatonin treatment. Using C57BL/6J mice with genetically low circulating melatonin levels, the main objective of the present study was to investigate whether bipedal ambulation in C57BL/6J mice has the same effects on spinal deformity as those seen in pinealectomized bipedal rats. The present study consisted of two phases. The aim of the first experiment was to determine whether the C57BL/6J mouse strain actually exhibits depressed plasma concentrations and/or pineal contents of melatonin during both the light and the dark phase of the light:dark cycle. The aims of the second experiment were to evaluate; (i) whether bipedal ambulation alone in the C57BL/6J mouse induces scoliosis, and (ii) whether PINX with bipedal ambulation in another mouse strain, i.e. C3H/HeJ, which normally exhibits diurnal fluctuations in melatonin synthesis and secretion, has effects similar to those of bipedal ambulation alone in C57BL/6J mice. C3H/HeJ mice, serving as controls, showed significant increases in both plasma concentrations and pineal contents of melatonin during the dark phase when compared with the light phase. In contrast, there were no differences in either circulating levels or pineal contents of melatonin between the light and dark phases in C57BL/6J mice. Moreover, plasma melatonin levels were below the detection limit of the assay in both phases and pineal melatonin was < 10% of that in C3H/HeJ mice. Bipedal ambulation for 40 wk in C57BL/6J mice induced scoliosis at a rate of 64.3%, and two of nine scoliotic mice showed two sites of spinal deformity. This type of ambulation in C3H/HeJ mice resulted in scoliosis at a lower rate (25%), and affected animals had only a single scoliotic site. However, PINX combined with bipedal ambulation in C3H/HeJ mice produced scoliosis at a rate (70%) similar to that seen in C57BL/6J mice, and some double deformations were induced. These results confirm our previous observations in rats, and also support our hypothesis that melatonin as well as the bipedal ambulation appear to play a critical pathogenic role in scoliosis in experimental mammals.

Comparative ultrastructure and cytochemistry of the avian pineal organ

The breeding of birds is expected to solve problems of nourishment for the growing human population. The function of the pineal organ synchronizing sexual activity and environmental light periods is important for successful reproduction. Comparative morphology of the avian pineal completes data furnished by experiments on some frequently used laboratory animals about the functional organization of the organ. According to comparative histological data, the pineal of vertebrates is originally a double organ (the "third" and the "fourth eye"). One of them often lies extracranially, perceiving direct solar radiation, and the other, located intracranially, is supposed to measure diffuse brightness of the environment. Birds have only a single pineal, presumably originating from the intracranial pineal of lower vertebrates. Developing from the epithalamus, the avian pineal organ histologically seems not to be a simple gland ("pineal gland") but a complex part of the brain composed of various pinealocytes and neurons that are embedded in an ependymal/glial network. In contrast to organs of "directional view" that develop large photoreceptor outer segments (retina, parietal pineal eye of reptiles) in order to decode two-dimensional images of the environment, the "densitometer"-like pineal organ seems to increase their photoreceptor membrane content by multiplying the number of photoreceptor perikarya and developing follicle-like foldings of its wall during evolution ("folded retina"). Photoreceptor membranes of avian pinealocytes can be stained by antibodies against various photoreceptor-specific compounds, among others, opsins, including pineal opsins. Photoreceptors immunoreacting with antibodies to chicken pinopsin were also found in the reptilian pineal organ. Similar to cones and rods representing the first neurons of the retina in the lateral eye, pinealocytes of birds possess an axonal effector process which terminates on the vascular surface of the organ as a neurohormonal ending, or forms ribbon-containing synapses on pineal neurons. Serotonin is detectable immunocytochemically on the granular vesicles accumulated in neurohormonal terminals. Pinealocytic perikarya and axon terminals also bind immunocytochemically recognizable excitatory amino acids. Peripheral autonomic fibers entering the pineal organ through its meningeal cover terminate near blood vessels. Being vasomotor fibers, they presumably regulate the blood supply of the pineal tissue according to the different levels of light-dependent pineal cell activity.

Effects of ethylene glycol tetraacetic acid, A23187 and calmodulin, calcium activated neutral proteinase antagonists on melatonin secretion in perifused chick pineal gland

We have recently described, using perifused pineal glands, that calcium influx participates in the activation of chick pineal gland. This study shows that the loss of perifused chick pineal gland activity is a complex process which seems to involve the release of calcium from intracellular stores, calmodulin and calcium-activated neutral protease (CANP). Pineal glands were perifused with Krebs medium (controls) or with Krebs medium plus the drugs ethylene glycol tetraacetic acid (EGTA; calcium chelator), A23187 (calcium ionophore), EGTA plus A23187 (extra-intra cellular calcium chelation), trifluoperazine and CGS9343B (calmodulin inhibitors), and E-64 (CANP inhibitor) at the time of the natural peak of melatonin release. When EGTA or A23187 were added to the perifusion medium, no effects were observed. On the other hand, when the calcium chelator EGTA plus A23187 (free extra and intracellular calcium levels were dramatically decreased), trifluoperazine, CGS 9343B or E-64 were added to the perifusion medium melatonin synthesis increased significantly and was sustained for 8 h. We propose a prominent role for calcium output from intracellular stores in regulating melatonin production primarily by acting on Ca-calmodulin and calcium-activated neutral protease.

Melatonin and serotonin interactions with calmodulin: NMR, spectroscopic and biochemical studies

It has been reported that the hormone melatonin binds tightly to the ubiquitous calcium-regulatory protein, calmodulin (CaM) with a Kd value around 0.1 nM [Benítez-King et al., Biochim. Biophys. Acta, 1290 (1993) 191-196]. Normally CaM only binds to target proteins and various 20-residue synthetic peptides encompassing the CaM-binding domain of these target proteins with K(d) values ranging between 1.0 microM and 0.1 nM. Here we have studied the interaction of melatonin and several structurally related compounds--serotonin, 5-hydroxytryptophan, and tryptophan--to CaM through gel band shift assays, enzymatic competition assays with calcineurin, fluorescence spectroscopy, far and near UV circular dichroism spectropolarimetry and NMR spectroscopy. Fluorescence spectra show that the binding is calcium dependent. NMR studies with biosynthetically labelled methyl-13C-Met CaM show that melatonin and the other compounds interact with the hydrophobic cleft regions of the protein. Our NMR data show that melatonin binds to both domains of the dumbbell-shaped CaM, while serotonin appears to bind only to the C-terminal domain. This binding mode is further substantiated by fluorescence and gel band shift competition experiments with synthetic peptides from myosin light chain kinase and constitutive nitric oxide synthase. Circular dichroism spectra indicate that the secondary structure of CaM is not altered by addition of melatonin. Our data are internally consistent and reveal Kd values in the mM range for melatonin. Thus the binding of these compounds to CaM is substantially weaker than was previously reported and is unlikely to be of physiological significance.