The avian pineal gland

The pineal gland plays a key role in the control of the daily and seasonal rhythms in most vertebrate species. In mammals, rhythmic melatonin (MT) release from the pineal gland is controlled by the suprachiasmatic nucleus via the sympathetic nervous system. In most non-mammalian species, including birds, the pineal gland contains a self-sustained circadian oscillator and several input channels to synchronize the clock, including direct light sensitivity. Avian pineal glands maintain rhythmic activity for days under in vitro conditions. Several physical (light, temperature, and magnetic field) and biochemical (Vasoactive intestinal polypeptide (VIP), norepinephrine, PACAP, etc.) input channels, influencing release of melatonin are also functional in vitro, rendering the explanted avian pineal an excellent model to study the circadian biological clock. Using a perifusion system, we here report that the phase of the circadian melatonin rhythm of the explanted chicken pineal gland can be entrained easily to photoperiods whose length approximates 24 h, even if the light period is extremely short, i.e., 3L:21D. When the length of the photoperiod significantly differs from 24 h, the endogenous MT rhythm becomes distorted and does not follow the light-dark cycle. When explanted chicken pineal fragments were exposed to various drugs targeting specific components of intracellular signal transduction cascades, only those affecting the cAMP-protein kinase-A system modified the MT release temporarily without phase-shifting the rhythm in MT release. The potential role of cGMP remains to be investigated.     

Innervation of the avian pineal organ

The innervation of the pineal organ was studied in 26 avian species under particular consideration of comparative aspects. A population of nerve cells and their pinealofugal (afferent) fiber systems were stained by means of the acetylcholinesterase method, while catecholamine-containing pinealopetal (efferent) fibers were demonstrated with the use of the glyoxylic acid method. Afferent axons were mainly found in the postero-proximal portion of the organ, and the patterns of their distribution were classified into three groups according to the characteristic densities of the reaction product. The number of acetylcholinesterase-positive neurons in the avian pineal organs examined in this study varied extremely from species to species, ranging from 0 to 362. Catecholamine-containing nerve fibers penetrating the antero-lateral walls of the pineal follicles accompanied blood vessels and were arranged more densely in the distal portion of the organ, in contrast to the distribution of the acetylcholinesterase-positive nerve fibers. Three-dimensional reconstruction of the distributional patterns of both types of neural projections was performed for the pineal organ of every avian species examined. In avian species possessing a relatively conspicuous afferent projection, such as Passeriformes, Nycticorax, and Milvus, terminals of catecholamine-containing nerve fibers were observed exclusively in the interfollicular and perivascular tissues. In Galliformes, which display only few pineal afferents, catecholamine-containing fibers terminate not only in the interfollicular space, but also in the neuroepithelial parenchyma. The regional differences in the innervation in the avian pineal organ suggest that the pinealocytes ranging from more sensory-like to more secretory-like elements are arranged in a mosaic-like pattern.     

Multiple redundant circadian oscillators within the isolated avian pineal gland

Summary The avian pineal gland contains a circadian pacemaker that oscillates in vitro. Using a flow-through culture system it is possible to measure melatonin production from very small subsections of an individual gland. We have used this technique to attempt to localize the oscillators in the pineal. Progressive tissue reduction did not affect the rhythmicity of cultured pineals. Multiple pieces (up to eight) from a single pineal all were capable of circadian oscillation — establishing directly that a pineal gland contains at least eight oscillators. All pineal pieces were responsive to light, and single light pulses shifted the phase of the melatonin rhythm. Because pieces equivalent to less than one per cent of the whole gland were rhythmic and because the capacity for oscillation was distributed throughout the gland, an individual pineal appears to be composed of a population of circadian oscillators.     

Role of tissue interaction between pineal primordium and neighboring tissues in avian pineal morphogenesis studied by intraocular transplantation

Tissue interactions play an essential role in organogenesis during embryonic development. However, virtually no attempts have been made to study the role of tissue interaction in pineal development. In the present study we examined the inductive role of the epidermis and mesenchyme in the morphogenesis of quail pineal glands. The pineal rudiment is first observed at embryonic day 2 (E2: 2 days of incubation) at the dorsal midline of the diencephalon as a short semi-spherical protrusion. Electron microscopic observations revealed that no mesenchymal cells are found between the epidermis and the distal end of the E2 pineal primordium but that a thin layer of mesenchymal cells separate the epidermis from the pineal primordium at E3. Small pieces containing pineal rudiment were cut off from E2 or E3 embryos. They were treated with enzymes to eliminate the epidermis and/or mesenchyme, grafted into E5 chicken eyes, and cultured there for 1 week. When E3 pineal rudiment was treated with Dispase to remove the epidermis, the pineal gland developed normally. When the rudiment was further treated with collagenase to remove the surrounding mesenchymal cells, a multi-follicular structure was still formed, but to a lesser extent than when rudiments were treated with Dispase alone. When E2 quail pineal rudiment with the epidermis was grafted without any treatment, a multi-follicular structure developed which morphologically resembled embryonic pineal organs. When the epidermis was removed from E2 rudiments by Dispase, a single large vesicular structure was formed. These results suggest that the overlying epidermis and/or mesenchymal cells play some inductive role in the initial pineal development, while the mesenchymal tissue plays an important role in pineal follicular formation later during development. Since only a few experimental studies have been done to examine pineal morphogenesis, the present study provides fundamental insights into avian pineal development.     

Chickens' Cry2: molecular analysis of an avian cryptochrome in retinal and pineal photoreceptors

We have identified and characterized an ortholog of the putative mammalian clock gene cryptochrome 2 (Cry2) in the chicken, Gallus domesticus. Northern blot analysis of gCry2 mRNA indicates widespread distribution in central nervous and peripheral tissues, with very high expression in pineal and retina. In situ hybridization of chick brain and retina reveals expression in photoreceptors and in visual and circadian system structures. Expression is rhythmic; mRNA levels predominate in late subjective night. The present data suggests that gCry2 is a candidate avian clock gene and/or photopigment and set the stage for functional studies of gCry2.     

Pneuma between body and soul

This paper explores the divergent ideas that different ancient Greek thinkers entertained on the nature of wind and air outside the body, on the role of breath and air within it (e.g. in causing disease), on their contribution to life and intelligence, and on the mind-body problem, where dualists who insisted that the soul is incorporeal were locked in controversy with monists who denied that. One of the distinctive features of Greek thought is its polemical nature, with rival views on offer both on substantive questions and on methodology. Alongside the speculative theories of the philosophers, there were those who tackled the problems empirically. But the advances that Galen (in particular) made in his understanding of the anatomy of the nervous and blood-vascular systems did nothing to resolve the problem of the physical basis of vital functions.     

A pineal ganglion associated with the pineal tract in the domestic fowl

Summary A ganglion-like aggregate consisting of acetyl-cholinesterase-positive neurons was demonstrated in the pineal organ of the domestic fowl by means of light and electron microscopy. This ganglion is located in juxtaposition with the pineal tract at the posterior (caudal) aspect of the pineal stalk. Numerous large and small neurons formed the ganglion in 40-day-old domestic fowl. Some of these nerve cells established direct neuro-neuronal contacts, others were surrounded by satellite cells. These ganglion cells displayed axo-somatic and axo-dendritic synapses. The above-mentioned cluster of nerve cells may be considered as a pineal ganglion. Its central or peripheral nature is open to discussion. Send offprint requests to: Dr. K. Wake, Department of Anatomy, Faculty of Medicine, Tokyo Medical and Dental University, Yushima, Bunkyo-ku, 113, Japan     

Inhibition of avian and mammalian hydroxy-indole-o-methyl-transferase (HIOMT) with low molecular weight fractions of mammalian pineal glands

Partially purified fractions from sheep pineal gland extracts, which show a fluorescence like pteridines, were shown to suppress the enzyme hydroxy-indole-o-methyltransferase (HIOMT) isolated from avian pineals and retinas. The results described demonstrate that the mechanism of inhibition of HIOMT activity is independent of the species and organ. A blocking effect was found in experiments whether retinal or pineal HIOMT were used and the effect was found as well with bovine HIOMT. It is shown that low molecular weight molecules show inhibitory activity and accompany the high molecular weight enzyme HIOMT.     

Tyrosine hydroxylase and neuropeptide-Y immunoreactivity in pineal glands developing in situ and in pineal grafts

Summary Postnatal development of the innervation of the pineal gland in situ as well as the reinnervation of pineal grafts by tyrosine hydroxylase (TH)- and neuropeptide Y (NPY)-immunoreactive nerve fibers were examined using the avidin-biotin-peroxidase immunohistochemical technique. TH-immunoreactive nerve fibers appeared in the pineal gland on the second postnatal day (P2) in both hamsters and gerbils. NPY-immunoreactive nerve fibers first appeared in the pineal gland of gerbils on P2 and in the hamsters on P3. By the seventh postnatal day (P7), the pineal glands of both hamsters and gerbils were richly innervated by TH- and NPY-fibers that appeared as smooth fibers or fibers with sporadic varicosities. By the age of 4 weeks, the innervation of the pineal glands of hamsters and gerbils by TH-and NPY-fibers was fully developed. Abundant TH- and NPY-fibers formed a dense meshwork in the parenchyma of the superficial and deep pineals. The great majority of the fibers bore a large number of varicosities. More NPY-fibers were found in the pineal glands of gerbils than hamsters. NPY fibers were distributed evenly throughout the pineal glands of the gerbil, but they were more often located in the central region of the superficial pineal of the hamster. For the pineal grafts, superficial pineals from neonatal and 4-week-old hamsters were transplanted to different sites in the third cerebral ventricle (infundibular recess, posterior third ventricle) or beneath the renal capsule. The pineal grafts from 4-week-old donors appeared to undergo severe degeneration and eventually disappeared. The pineal grafts from neonatal hamsters, however, successfully survived and became well integrated into their new locations. Abundant TH-and NPY-fibers in the host brain were found surrounding the pineal grafts placed in the third cerebral ventricle, but were only rarely seen entering the parenchyma of the grafts. A few TH-fibers were demonstrated in the renal grafts 4 weeks after transplantation. These studies describe the postnatal development of the innervation of the pineal glands in situ by TH-and NPY-nerve fibers, and demonstrate a lack of reinnervation of cerebroventricular pineal grafts by TH and NPY fibers from adjacent host brain.Portions of the results of this paper were previously reported in abstract form at the 1990 Meeting of The American Association of Anatomists (Anat Rec 226:57A)     

Nocturnal feeding in the mouse--opiate and pineal influences

Mice displayed daily rhythms in their basal and morphine-induced food intake, consuming significantly greater amounts of food at night. Non-invasive inhibition of the activity of the pineal gland by either exposure to a bright pulse of light or treatment with the L-amino-acid decarboxylase inhibitor, benserazide, reduced the elevated night-time food intakes. These effects on feeding were most evident on the first night the activity of the pineal was reduced. On subsequent nights light pulses had a diminished effect on basal and morphine-induced food intake. These results suggest that although the enhanced nocturnal food intake of mice may be modulated by pineal and opioid sensitive mechanisms, pineal activity is not essential for the expression of opioid-mediated feeding.     

Observations on the pineal system in the hamster. II. Fine structure of the deep pineal

Desert-dwelling male Uma notata, U. inornata and U. scoparia were autopsied monthly from 1959 through 1962. Seasonal changes in the histological morphology of the testes were observed. A series of eight stages, indicating these changes in spermatogenic activity, was established. These categories arbitrarily divide a continuous process into several recognizable stages. Present evidence indicates that male breeding cycles can be determined rather precisely by examining any of several reproductive features. Data from several sources reveal that the male breeding season of U. scoparia is shorter than that of U. notata or U. inornata. Nevertheless, the testes of all three species appear to function reproductively during the hottest month of the year. Possible explanations for this ability are suggested. Little difference was observed in the time the seminiferous tubules of U. notata testes reached full breeding condition (stage 6) following dry winters. This is in contrast to the time motile sperm appeared at the cloacal end of the vas deferens in these animals. Thus is appears that the major cause of postponement in male U. notata reproductive activity following dry winters is due to a delay in sperm reaching the vas deferens rather than a retardation in sperm production.