Hydroxyindole-O-methyltransferase (HIOMT) activity and the uptake of 3H-melatonin in the lamprey, Geotria australis Gray

Afferent and efferent connections of the parapineal organ in lampreys: a tract tracing and immunocytochemical study

The neural connections of the parapineal organ of two species of lampreys were studied with the fluorescent dye 1,1'-dioctadecyl-3,3,3'3'-tetramethylindocarbocyanine perchlorate (DiI) and with immunocytochemistry. The lamprey parapineal organ consists of a vesicle and a ganglion that are connected to the left habenula. Labeling experiments included the application of DiI to the parapineal organ, left and right fasciculus retroflexus, left habenula, and the left pretectal region. Afferent parapineal fibers run in the left fasciculus retroflexus to the interpeduncular nucleus. The parapineal fibers of this fascicle arose from parapineal ganglion cells, whereas DiI application to the left habenula labeled both neurons of this ganglion and bipolar cells in the parapineal vesicle. Efferent neurons were observed in the left habenula, and bilaterally in the subhippocampal nucleus and the dorsal pretectum. Labeling with DiI also revealed a hippocampal projection. Immunocytochemical study of the parapineal vesicle revealed serotonin-immunoreactive cells in both species of lamprey, as well as substance P-immunoreactive (SP-ir) cells in sea lamprey and choline acetyltransferase-immunoreactive (ChAT-ir) cells in the river lamprey. The SP-ir cells and ChAT-ir cells formed a rich neuropil in the parapineal ganglion. Calretinin-ir cells were numerous in the ganglion. Neuropeptide Y-immunoreactive and gamma-aminobutyric acid-immunoreactive efferent fibers were observed in the parapineal organ. Neuropeptide Y-immunoreactive fibers originate in the subhippocampal nucleus, whereas gamma-aminobutyric acid-immunoreactive fibers might also arise in the pretectal nucleus. A few galanin-ir fibers were observed. These results indicate that the parapineal connections are completely different from those of the pineal organ. The possible homology between parapineal organs of vertebrates is discussed.

Localization and partial characterization of melatonin receptors in amphioxus, hagfish, lamprey, and skate

Through its secretion of melatonin, the pineal complex of vertebrates exerts a range of physiological effects including regulation of circadian rhythms, seasonal reproduction, metamorphosis, and body color change. Little is known about phylogenetic differences in the distribution and characteristics of melatonin binding sites in fishes. We used in vitro autoradiography to examine binding of [2-125I]iodomelatonin (IMEL) in 20-micron frozen sections of amphioxus (Branchiostoma lanceolatum), Atlantic hagfish (Myxine glutinosa), larval and adult lamprey (Petromyzon marinus), little skate (Raja erinacea), and rainbow trout (Oncorhynchus mykiss). Tissue was incubated with IMEL in the presence or absence of unlabeled melatonin (1 muM, in order to assess nonspecific binding). A concentration of 32 pM IMEL was used for single point assays and competition studies. No specific binding was found in hagfish or amphioxus, which lack a pineal complex. In the optic tecta of lamprey, skate, and trout, IMEL binding is highly specific (melatonin >> N-acetylserotonin > 5- methoxytryptophol >> serotonin). Scatchard analysis revealed that the tectal binding sites are of high affinity (Kd = 36, 38, and 50 pM) and low capacity (Bmax = 8.1, 19.8, and 21.8 fmol/mg protein) in lamprey, skate, and trout, respectively. In adult lampreys, intense specific IMEL binding is found in the optic tectum (layer I > II > III) and preoptic nucleus (pars parvocellularis > magnocellularis). Binding was less intense and consistent in the same areas of ammocoete brain. In skates and trout, intense specific binding is found in optic tectum, lateral geniculate body, diencephalic preoptic and suprachiasmatic nuclei, basal hypothalamus, and the medial pallium. These results indicate that specific melatonin binding sites are present in all craniate taxa examined except in hagfish. Although we cannot rule out the possibility that melatonin receptors are secondarily lost in hagfish, their absence in amphioxus makes this unlikely. We speculate that melatonin actions in early vertebrates may have included regulation of visual and endocrine responses to light.

Secretion of methoxyindoles from trout pineal organs in vitro: indication for a paracrine melatonin feedback

Synthesis and release of the pineal hormone melatonin is in all vertebrates primarily regulated by the light/dark cycle. In pineal organs of teleost fish, like in other non-mammalian vertebrates, melatonin formation is regulated by a direct photoreception of the pineal organ. We performed measurements in explanted, perifused pineal organs of the rainbow trout, Oncorhynchus mykiss, to examine whether melatonin can influence its own production. For this purpose we have continuously perifused isolated pineal organs under light- and dark-adapted conditions and measured the release of melatonin and other methoxy-indoles by HPLC with electrochemical detection. Addition of 2-iodomelatonin to the perifusate in a concentration of 2 ng/ml significantly inhibited melatonin release in light-, as well as in dark-adapted organs. The release of 5-methoxytryptamine and 5-methoxytryptophol was also significantly reduced in light-adapted organs. These results indicate that extracellular melatonin may act as a paracrine or autocrine feedback signal and may be important for the illumination-dependent melatonin production.

Immunocytochemical localization of serotonin and photoreceptor-specific proteins (rod-opsin, S-antigen) in the pineal complex of the river lamprey, Lampetra japonica, with special reference to photoneuroendocrine cells

The pineal complex of the river lamprey, Lampetra japonica, was examined by means of immunocytochemistry with antisera against serotonin, the precursor of melatonin, and two photoreceptor proteins, rod-opsin (the apoprotein of the photopigment rhodopsin) and S-antigen. Serotonin-immunoreactive cells were observed in both the pineal and the parapineal organ. The proximal portion of the pineal organ (atrium) comprised numerous serotonin-immunoreactive cells displaying spherical somata. In the distal end-vesicle of the pineal organ, the serotonin-immunoreactive elements resembled photoreceptors in their size and shape. These cells projecting into the pineal lumen and toward the basal lamina were especially conspicuous in the ventral portion of the end-vesicle. In addition, single serotonin-immunoreactive nerve cells were found in this location. Retinal photoreceptors were never seen to contain immunoreactive serotonin; amacrine cells were the only retinal elements exhibiting serotonin immunoreaction. Strong S-antigen immunoreactivity was found in numerous photoreceptors located in the pineal end-vesicle. In contrast, the S-antigen immunoreactivity was weak in the spherical cells of the atrium. Thus, the pattern of S-antigen immunoreactivity was roughly opposite to that of serotonin. Similar findings were obtained in the parapineal organ. The rod-opsin immunoreaction was restricted to the outer segments of photoreceptors in the pineal end-vesicle and parapineal organ. No rod-opsin++ immunoreactive outer segments occurred in the proximal portion of the atrium. Double immunostaining was employed to investigate whether immunoreactive opsin and serotonin are colocalized in one and the same cell. This approach revealed that (i) most of the rod-opsin-immunoreactive outer segments in the end-vesicle belonged to serotonin-immunonegative photoreceptors; (ii) nearly all serotonin-immunoreactive cells in the end-vesicle bore short rod-opsin-immunoreactive outer segments protruding into the pineal lumen; and (iii) the spherical serotonin-immunoreactive cells in the pineal stalk lacked rod-opsin immunoreaction and an outer segment. These results support the concept that multiple cell lines of the photoreceptor type exist in the pineal complex at an early evolutionary stage.

The effects of constant light and constant darkness on daily changes in the morphology of the pineal organ in the goldfish, Carassius auratus

The fine structure of photoreceptor cells in the pineal organ of the goldfish was found to vary quantitatively over a 24-hour period. Stereological analysis revealed significant daily changes in the volume of the cell and inner segment, nuclear volume and nucleolar diameter, volume of endoplasmic reticulum and Golgi bodies, area of both rough and smooth endoplasmic reticulum, and number of vesicles associated with each Golgi body. Peak values of these variables occurred either during the dark phase or latter part of the light phase. These findings agree closely with those reported in higher vertebrates, and suggest that metabolic activities, and possible secretory functions, of the pineal organ of fishes are synchronized to the light:dark cycle. Daily changes in these variables generally persisted in fish exposed to constant darkness for seven days, with the peak in these rhythms coinciding closely with those observed in fish exposed to a light:dark cycle. In contrast, the rhythms in all variables were abolished in fish kept in continual light for seven days. Photoreceptor cells from fish exposed to continuous light had larger nucleoli and greater amounts of rough endoplasmic reticulum indicating a further effect of light on pineal metabolism in lower vertebrates.

Morphology of the pineal complex of the anadromous sea lamprey, Petromyzon marinus L

The pineal complex of the anadromous sea lamprey, Petromyzon marinus L., has been examined by light and electron microscopy. It consists of two subunits: a dorsomedial pineal organ, and a ventral, left-lateral parapineal organ, with both remaining cytologically unaltered throughout the life cycle. However, during metamorphosis there is an increase in the size and a rostral migration of the parapineal organ and a dorsolateral displacement of the pineal nerve tract. The pineal organ is composed of an end bulb, an atrium, and a nerve tract. Two varieties of photoreceptors, termed type I and type II cells, as well as supporting and ganglion cells are present. Supporting cells are ubiquitous, but there are regional variations in the distribution and abundance of the other cell types. Type I cells are a well-differentiated photoreceptor. Conversely, type II cells exhibit a poorly developed photosensory apparatus but possess some features commensurate with an endocrine activity. The parapineal organ is composed of an end bulb, a ganglion region, and a nerve tract. The end bulb is dominated by type II photoreceptor and supporting cells, whereas type I and ganglion cells are sparse. The parapineal ganglion and nerve tract include neuropil, polymorphic neurons, and ependymal cells. It is concluded that the pineal organ of P. marinus is a structurally well-developed photosensory and photoneuroendocrine organ that is probably capable of transducing photic stimuli into nervous and endocrine messages to the brain and other organs. In contrast, the parapineal of this lamprey species is a poorly developed organ of regressed or rudimentary structure.

The effect of pinealectomy, continuous light, and continuous darkness on metamorphosis of anadromous sea lampreys, Petromyzon marinus L

The role of the pineal complex in lamprey metamorphosis was investigated by examining the influence of pinealectomy and continuous light and darkness on the initiation of this event in anadromous sea lampreys, Petromyzon marinus L. Larval lampreys, which on the basis of a condition factor were considered likely to enter metamorphosis in July, were separated in May of 1979 and 1980 into the following groups: (1) intact controls, (2) sham-operated controls, (3) pinealectomized individuals, (4) those exposed to continuous light, and (5) those exposed to continuous light or dark. The importance of the pineal complex to metamorphosis was supported by morphological evidence that, in all presumably pinealectomized individuals that entered metamorphosis, the complex had apparently not been removed during the surgical procedure. The ways in which the pineal complex may be involved in lamprey metamorphosis are discussed.

Structural changes in the pars intermedia of the cichlid teleost Sarotherodon mossambicus as a result of background and adaptation and illumination. III. The role of the pineal organ

The MSH producing cells in the pars intermedia of Sarotherodon mossambicus have been shown to be involved in background adaptation processes. Reflected light received by the eyes affects the activity of these cells. In the present study the hypothesis has been tested that also the pineal organ, as a second photoreceptor, is involved in regulation of the metabolic activity of the MSH cells. The pineal organ appears to contain photoreceptor cells and is considered to be capable of transferring information about light conditions to the animal. Removal of the pineal organ of fish kept on a black background has no effect on activity of MSH cells, whereas the activity of these cells in fish kept in darkness is increased. Thus it seems that the pineal organ exercises its influence on MSH cells only in darkness and that this influence results in a reduced activity of these cells. It is therefore concluded that the metabolic activity of MSH cells is inhibited not only by reflected light received by the eyes, but also by the action of the pineal organ as a result of the absence of illumination. No structural signs of secretory activity can be observed in the pineal, which might indicate synthesis or release of substances like melatonin. However, administration of melatonin reduces the activity of MSH cells. Neither pinealectomy nor treatment with melatonin has any influence on the second cell type of the pars intermedia, the PAS positive cells.

Indoleamines in the pineal complex of Lampetra planeri (Petromyzontidae). A fluorescence microscopic and microspectrofluorimetric study

Using the technique of Falck and Hillarp, the pineal and parapineal organs of Lampetra planeri were found to exhibit a labile yellow fluorescence characteristic of indoleamines. Microspectrofluorimetric analysis of the yellow fluorophores yielded emission and excitation spectra very similar to those of the melatonin precursors serotonin (5-HT) or 5-hydroxytryptophan (5-HTP). 5-HT/5-HTP fluorophores are concentrated essentially in the region of the atrium, along the pineal tract and in the rostral part of the parapineal organ. The fluorescence is strong in early autumn, decreases in winter and is weak or absent in spring, implying a seasonal variation in indoleamine metabolism. Fluorescence intensity increases after injections of nialamide or nialamide and 5-HTP and is lowered by injection of reserpine. Indoleamine fluorescence is localized in the recently identified sensory-type cells: the photoneuroendocrine cells (Meiniel, 1980). The ependymal-like cells, the sensory neurons and the classical photoreceptor cells (Collin, 1969 a) do not appear to be involved in indole metabolism. The absence of catecholamine fibres in the perivascular spaces suggests that indole biosynthesis is regulated via the direct photosensitivity of the pineal complex.

A comparative light and electron microscopic study of the pineal complex in the deep-sea fishes, Cyclothone signata and C. acclinidens

The pineal complexes of the two closely related deep-sea fished Cyclothone signata and C. acclinidens were compared both qualitatively and quantitatively. Photoreceptor and supportive cells were identified in both species. The deeper-dwelling species, C. acclinidens, had a significantly greater number of photoreceptor-cell outer segment saccules and a higher ratio of receptor cells to nerve fibers in the pineal stalk. It was suggested that these indicate increased photosensitivity of the pineal. Supportive cells were sometimes seen to contain arrays of undulating tubules. The functional significance of these tubules is not understood. A prominent dorsal sac is closely associated with the pineal end-vesicle. Both structures appear to have a common vascular supply suggesting that they are functionally related. Dorsal sac cells contained abundant mitochondria, glycogen, and large filament-like inclusions.