The avian pineal organ. Distribution of endogenous monoamines; a fluorescence microscopic, microspectrofluorimetric and pharmacological study in the parakeet

Abstract

SummaryThe distribution of endogenous monoamines was investigated in the pineal organ of adult parakeet (Melopsittacus undulatus, Shaw) using the Falck and Hillarp technique.Formaldehyde-treated pineal organs of birds, kept under natural photoperiodical conditions and autopsied in the morning, show:1. an intense yellow fluorescence in the parenchyma, present only in the secretory rudimentary photoreceptor (SRP) cells at the level of the proximal part of the inner segment, perinuclear cytoplasm and basal processes; 2. scarce green-fluorescent nerve fibres which run in the perivascular spaces bordering the pineal tissue.The microspectrofluorimetric analysis indicates: 3. that the yellow SRP fluorophore is identical with serotonin (5-hydroxytryptamine, 5-HT), although the presence of 5-hydroxytryptophan cannot be excluded; 4. that noradrenaline is the normal neurotransmitter in the sympathetic nerve fibres.Aiter the depleting activity of reserpine, pineal monoamines are absent. The amount of 5-HT is more or less decreased in SRP cells afLer inhibition of the hydroxylating and decarboxylating enzymes. 5-HT and noradrenaline Ievels are increased aPcer monoamine-oxidase inhibitors, It is concluded that 5-HT, a precursor of mdatonin, is stored in the regions in which dense secretory granules (500--1200 A) are present in the SRP cells. As a result of this study and other cytophysiologicat inVestigat!ons on the pineal of Lacertilians and biochemical tindings in birds, it is proposed that pathways of synthesis and metabolism of 5-HT are located in SRP cells. The distribution of endogenous arid exogenous (Collin et al., 1976) indoleamines is similar.

The proteinaceous content and possible physiological significance of dense-cored vesicles in hamster and mouse pinealocytes

“…When Romijn (1972Romijn ( , 1976) used p-CPA, an inhibitor of the biosynthesis of 5-HT and p-chloroamphetamine lowering the activity of tryptophan-5-mono-oxygenase, no apparent changes were observed in the DCV of rabbits. Similar results were obtained recently using complementary techniques in a very complete study of the parakeet Juillard et al, 1977 ;Juillard and Collin, 1978). In Amniota, variations observed after drug treatments mainly concern the number and the diameter of DCV.…”

“…Most authors consider that the DCV in Pi are the storage sites of one or more active compounds. It has been concluded previously in some reptiles and birds (Collin, 1969 ;Meiniel, 1971, 1973a, b ;Collin et al,1976Collin et al, , 1977aCollin, 1976, 1978 ;Juillard et al, 1977) that a proteinaceous compound is regularly present in the DCV and that serotonin (5-HT), probably bound to this proteinaceous compound, may be also stored in the DCV of some species and/or under certain circumstances.…”

Evolution of photosensory pineal organs in new light: the fate of neuroendocrine photoreceptors

“…Direct identification of melatonin by immunocytochemistry has been questioned on methodological grounds (Ekströ m & Meissl 1997). The presence of indoleamines has usually been demonstrated by biochemical and autoradiographic methods (Meiniel et al 1972;Collin et al 1982;Falcon & Collin 1985;Meiniel 1987), formaldehyde-induced fluorescence (Collin 1968a;Ueck 1973;Juillard et al 1977;Meiniel 1978;Falcó n et al 1980) Oksche (1983); cf. figures 6 and 7) in the vertebrate groups discussed in this paper.…”

L'organe pinéal du Brochet (Esox lucius, L.). II. Etude en microscopie électronique de la différenciation et de la rudimentation partielle des photorécepteurs ; conséquences possibles sur l'élaboration des messages photosensoriels

“…Chez certains Sauropsidés, les messages neuro-hormonaux sont élaborés dans les PR (réf. in Collin, 1977 ;Collin et al, 1977 ;Juillard et al, 1977) ; cette propriété est plus admise qu'établie au niveau des Pi, chez les Mammifères (Collin, 1977).…”