Acetylcholinesterase-containing nerve cells in the pineal complex and subcommissural area of the frogs,Rana ridibunda and Rana esculenta

Summary In Rana esculenta and Rana ridibunda the frontal organ and the pineal organ (epiphysis cerebri) form a pineal complex. Approximately 60 nerve cells of the frontal organ and 220–320 nerve cells of the pineal organ display a positive acetylcholinesterase reaction (Karnovsky and Roots, 1964). The dorsal wall of the pineal organ is considerably richer in acetylcholinesterase-positive neurons than the ventral wall (ratio 31); a group of unusually large-sized nerve cells occurs in the rostral portion of the frog pineal. Two different types of nerve cells were observed in the pineal complex: multipolar and pseudounipolar elements. The former are embedded in the pineal parenchyma and their processes penetrate radially into the plexiform layer, whereas the latter are distributed along the roots of the pineal tract near the basal lamina. The ratio of the multipolar to pseudounipolar neurons is 14 for the frontal organ and 35 for the pineal organ. The multipolar elements may be interneurons; the pseudouni-polar cells send one of their processes into the pineal tract. At the caudal end of the pineal organ 30–50 unipolar nerve cells are clustered in juxtaposition with the pineal tract, and other 30–50 unipolar neurons are scattered along the basis of the subcommissural organ. Some of these nerve cells emit their processes toward the mesencephalon and others toward the pineal organ via the pineal tract. The results are discussed with respect to previous physiological and morphological findings on the pineal complex of Anura.Supported by a fellowship from the Alexander von Humboldt Foundation, Federal Republic of Germany, to K. Wake. Completed November 22, 1973.Supported by the Deutsche Forschungsgemeinschaft.     

Histological,histochemical and electron microscopical studies on the nervous apparatus of the pineal organ in the tiger salamander,Ambystoma tigrinum

Summary 150–190 photoreceptor cells form a basic structural component of the pineal organ of Ambystoma tigrinum. Most of the outer and inner segments of these cells project into the lumen horizontally. Only 10 percent of the total number of photoreceptor cells are located within the pineal roof which is composed of a single cell layer. The photoreceptor cells are connected with nerve cells by synapses displaying characteristic ribbons. Different types of synaptic contacts, i.e. simple, tangential, dyad, triad and invaginated, are found. They are embedded in extended neuropil zones. A particular type of synapse indicates the presence of interneurons. The basal processes of some photoreceptor cells leave the pineal organ and make synaptic contacts with nervous elements located within the area of the subcommissural organ. Employing the method of Karnovsky and Roots (1964) for histochemical demonstration of acetylcholinesterase (AChE) approximately 70 neurons (intrapineal neurons) can be discerned in the pineal organ of Ambystoma tigrinum. In analogy to the distribution of photoreceptor cells only few nerve cells are observed in the roof portion of the pineal organ. Evidently, two different types of AChE-positive intrapineal neurons are present. About 40–50 AChE-positive neurons (extrapineal neurons) are scattered in the area of the subcommissural organ. In this area two types of nerve cells can be distinguished: 1) neurons which send pinealofugal (afferent) axons toward the posterior commissure and 2) neurons which emit pinealopetal (efferent) axons into or toward the pineal organ.The nervous pathways connecting the pineal organ with the diencephalomesencephalic border area are represented by a distinct pineal pedicle and several accessory pineal tracts.Granular nerve fibers run within the posterior commissure and establish synaptic contacts in the commissural region adjacent to the pineal organ. Some of these granular elements enter the pineal organ.The morphology of the nervous apparatus of the pineal organ of Ambystoma tigrinum is discussed in context with evidence from physiological experiments.In partial fulfillment of the requirements for the degree of Dr. med., Faculty of Medicine, Justus Liebig University, GiessenThe author is indebted to Professors A. Oksche and M. Ueck for their interest in this study. Thanks are due to Professor Ch. Baumann, Giessen, and Professor H. Langer, Bochum, for stimulating discussions. The technical assistance of Miss R. Liesner is gratefully acknowledgedDedicated to Professor Berta Scharrer on the occasion of her 70th birthday. Supported by grants from the Deutsche Forschungsgemeinschaft to A.O. and M.U.     

Opsin-immunoreactive outer segments and acetylcholinesterase-positive neurons in the pineal complex of Phoxinus phoxinus (Teleostei,Cyprinidae)

Summary The pineal complex of the teleost, Phoxinus phoxinus L., was studied light-microscopically by the use of the indirect immunocytochemical antiopsin reaction and the histochemical acetylcholinersterase (AChE) method.Opsin-immunoreactive outer segments of photoreceptor cells were demonstrated in large numbers in all divisions of the pineal end-vesicle and in the pineal stalk. Moreover, they were found in the roof of the third ventricle, adjacent to the orifice of the pineal recess as well as scattered in the parapineal organ. These immunocytochemical observations provide direct evidence of the presence of an opsin associated with a photopigment in the photosensory cells of the pineal and parapineal organs of Phoxinus. By means of the AChE reaction (Karnovsky and Roots 1964) inner segments of pineal photoreceptors, intrinsic nerve cells, several intrapineal bundles of nerve fibers, and a prominent pineal tract were specifically marked. The pineal neurons can be divided into two types: one is located near the pineal lumen, the other near the basal lamina. The latter perikarya bear stained processes directed toward the photoreceptor layer. A rostral aggregation of two types of AChE-positive nerve cells occurs in the ventral wall of the pineal end-vesicle. The main portion of the AChE-positive pineal tract, which lies within the dorsal wall of the pineal stalk, can be followed to the posterior commissure where some of the nerve fibers course laterally. A few AChE-positive pineal nerve fibers run toward the lateral habenular nucleus via the habenular commissure. In the region of the subcommissural organ single AChE-positive neurons accompany the pineal tract. The nerve cells of the parapineal organ exhibit a moderate AChE activity.These findings extend the structural basis for the remarkable light-dependent activity of the pineal organ of Phoxinus phoxinus. To the memory of Professor Karl von Frisch, pioneer and master in the field of photoneuroendocrine systemsThis investigation was supported by grants from the Deutsche Forschungsgemeinschaft to A.O. (Ok 1/24; 1/25: Mechanismen biologischer Uhren) and to H.-W. K. (Ko 758/1; 758–2)On leave from the 2nd Department of Anatomy, SOTE, Budapest, Hungary     

The parapineal and pineal organs of the elver (glass eel), Anguilla anguilla L.

Summary The parapineal organ of the glass eel (elver) consists of approximately 400 cells and is situated to the left of the connection of the pineal stalk to the third ventricle. A conspicuous nerve tract containing approximately 350 fibers arises from the parapineal organ and runs in spatial relationship to the habenular commissure toward the left habenular nucleus. The dominating cell type of the parapineal organ of the elver is a neuron (sensory neuron) of small diameter provided with atypical cilia (9×2+0, or rarely 8×2+0 types). Well-developed photoreceptor outer segments are lacking, and no interstitial cells of ependymal type have been observed with certainty in the parapineal organ. The axonal processes from the nerve cells form the tract leaving the parapineal organ.The pineal organ proper of the elver consists of photoreceptor cells with well-developed outer segments, interstitial cells of ependymal type, and ganglion cells. Axons from the latter form the pineal tract, which leaves the pineal organ and runs in close contact with the subcommissural organ toward the posterior commissure. The proximal part of the pineal stalk contains only a few photoreceptor cells the outer segments of which are less developed than those of the pineal body and the distal part of the pineal stalk.     

The Parapineal Organ of Teleosts

A parapineal organ was found to be present in 21 teleost fishes belonging to 20 different families, but was absent in poecilids and cyprinodontids. The parapineal organ was situated on the left side of the brain and sent a nerve tract to the left habenular nucleus, except in Gadus, where a “parapineal organ” appeared to send a nerve tract into the pineal stalk. The parapineal organ of adult Gasterosteus consisted of glial elements and parapinealocytes. The latter were small neurons which sent off the unmyelinated axons that formed the parapineal tract. A single photoreceptor cell was found in a stickleback parapineal organ.     

The pineal complex of the three-spined stickleback,Gasterosteus aculeatus L.

Summary The pineal complex of the three-spined stickleback (Gasterosteus aculeatus L.) was investigated by light and electron microscopy, as well as fluorescence histochemistry for demonstration of catecholamines and indolamines. The pineal complex of the stickleback consists of a pineal organ and a small parapineal organ situated on the left side of the pineal stalk. The pineal organ, including the entire stalk, is comprised mainly of ependymal-type interstitial cells and photoreceptor cells with well-developed outer segments. Both unmyelinated and myelinated nerve fibres are present in the pineal organ. Nerve tracts from the stalk enter the habenular and posterior commissures. A small bundle of nerve fibres connects the parapineal organ and the left habenular body. The presence of indolamines (5-HTP, 5-HT) was demonstrated in cell bodies of both the pineal body and the pineal stalk, and catecholaminergic nerve fibres surround the pineal complex.     

The expression of α-internexin and peripherin in the developing mouse pineal gland

Summary The mammalian pineal gland contains pinealocytes, interstitial glial cells, perivascular macrophages, neurons and neuron-like cells. The neuronal identity of neurons and neuron-like cells was an enigma. α-Internexin and peripherin are specific neuronal intermediate filament proteins and are expressed differentially in the CNS and PNS. We investigated the development of immunoreactivity and expression patterns of mRNAs for α-internexin and peripherin in the mouse pineal gland to determine the neuronal identity of these cells. Both α-internexin- and peripherin-immunoreactive cells were readily visualized only after birth. Both proteins were at the highest level on the postnatal day 7 (P7), rapidly declined at P14, and obtained their adult level at P21. Both protein and mRNA of α-internexin are expressed in some cells and nerve processes, but not all, of adult mouse pineal gland. Less number of peripherin immunoreactive or RNA-expressing cells and nerve processes were identified. Accumulations of α-internexin and peripherin proteins were also found in the cells from the aged pineal gland (P360). We concluded that some cells in the developing mouse pineal gland may differentiated into neurons and neuron-like cells expressing both α-internexin and/or peripherin only postnatally, and these cells possess dual properties of CNS and PNS neurons in nature. We suggested that they may act as interneurons between the pinealocyte and the distal neurons innervating the pinealocytes, or form a local circuitry with pinealocytes to play a role of paracrine regulatory function on the pinealocytes.     

Pattern of synaptic connections in the pineal organ of the ayu,Plecoglossus altivelis (Teleostei)

Summary Synaptic connections were studied by means of electron microscopy in the sensory pineal organ of the ayu, Plecoglossus altivelis, a highly photosensitive teleost species. Three types of specific contacts were observed in the pineal end-vesicle: 1) symmetrically organized gap junctions between the basal processes of adjacent photoreceptor cells; 2) sensory synapses endowed with synaptic ribbons, formed by basal processes of photoreceptor cells and dendrites of pineal neurons; 3) conventional synapses between pineal neurons, containing both clear and dense-core vesicles at the presynaptic site. Based on these findings, the following interpretations are given: (i) The gap junctions may be involved in an enhancement of electric communication and signal encoding between pineal photoreceptor cells. (ii) The sensory synapses transmit photic signals from the photoreceptor cells to pineal nerve cells. (iii) The conventional synapses are assumed to be involved in a lateral interaction and/or summation of information in the sensory pineal organ. A concept of synaptic relationships among the sensory and neuronal elements in the pineal organ of the ayu is presented.Fellow of the Alexander von Humboldt Foundation, Federal Republic of Germany     

The pineal organ of Raja clavata: Opsin immunoreactivity and ultrastructure

Summary The pineal organ of Raja clavata was studied by light and electron microscopy, including the immunocytochemical antiopsin reaction. The pineal organ of the ray consists of three portions: (i) a large proximal pineal, (ii) a long tube-like connecting stalk, and (iii) a short distal terminal enlargement. This latter end-vesicle lies in the deep connective tissue layers of the braincase. All portions of the pineal are composed of pinealocytes, intrinsic neurons, ependymal/glial cells, and bundles of nerve fibers embedded in thin neuropil formations. The inner segments of the pinealocytes protrude into the lumen in all parts of the organ and usually contain basal bodies and numerous mitochondria. Often, two outer segments were found to arise from the basal bodies of a single inner segment. By means of light-microscopic immunocytochemistry the outer segments showed a strong antiopsin reaction.The axons of the pinealocytes form ribbon-containing synapses on dendritelike profiles, which appear to belong to the intrinsic pineal neurons. There are other axo-dendritic synapses established by presynaptic terminals lacking ribbons and containing granular and synaptic vesicles. Pineal neurons may contain granular vesicles approximately 60–100 nm in diameter; their processes contribute to the bundles of unmyelinated axons.The fine structural organization of the pineal organ and the opsin immunoreactivity of the outer segments of the pinealocytes indicate a photoreceptive capacity of the organ. The double outer segments represent a peculiar multiplication of the photoreceptor structures.This investigation was supported by grants from the Deutsche Forschungsgemeinschaft to A. Oksche (Ok 1/24; 1/25: Mechanismen biologischer Uhren)On leave from the 2nd Department of Anatomy, Semmelweis OTE, Budapest, Hungary     

The sensory innervation of the pineal organ in the lizard,Lacerta viridis,with remarks on its position in the trend of pineal phylogenetic structural and functional evolution

Summary The sensory innervation of the pineal organ of adult Lacerta viridis has been investigated. Some specimens of Lacerta muralis lillfordi were also used. In the pineal epithelium, a small number of nerve cell pericarya of a sensory type are present. They lie either solitary or in small clusters close to the basement membrane. The axons originating from the nerve cell bodies, i. e. the pineal sensory nerve fibers, first course in the intraepithelial nerve fiber layer which is only locally present and contains a restricted number of unmyelinated fibers. In Lacerta viridis, the pineal fibers generally leave the epithelium at the proximal part of the organ proper. They then form small bundles which run along the outer surface of the basement membrane in the leptomeningeal connective tissue covering. At the proximal end of the pineal stalk the single bundles assemble constituting the pineal nerve. In Lacerta muralis the fibers leave the pineal epithelium at the proximal end of the stalk running farther down within the epithelium. Many fibers become myelinated after leaving the pineal epithelium. The pineal nerve runs ventralward in the midplane just caudal to the habenular commissure to which no fibers are given off. Continuing their ventralward course between the habenular commissure and the rostral end of the posterior commissure which is traversed by some of them, the pineal fibers reach the dorsal border of the subcommissural organ. Small separate aberrant pineal bundles traverse the posterior commissure at various more caudal levels. Having reached the dorsal border of the subcommissural organ, part of the pineal fibers continue their ventralward course directly running along the lateral sides of this organ to reach the periventricular nerve fiber layer lateral and ventral to it. A restricted number of fibers first turns in a caudal direction running between the base of the posterior commissure and the base of the subcommissural organ before turning ventralward to reach the periventricular layer. Most probably, pineal fibers do neither join the posterior commissural system nor innervate the subcommissural organ. Once having reached the periventricular layer, some pineal fibers curve in a rostral direction while others, before doing so, send a collateral in a caudal direction. Both, the main fibers and the collaterals, contribute to the formation of the periventricular layer. The sites of termination of the pineal fibers could not be ascertained.From the presence of intraepithelial sensory nerve cell bodies and from literature data on the ultrastructure of pineal neurosensory cells it is concluded that the adult pineal organ of Lacerta has a, although rudimentary, (photo)sensory function. The demonstration by our guest-worker Dr. W. B. Quay, of the intraepithelial presence of a tryptamine compound, probably serotonin, points, moreover, to a secretory function of this organ.In adult Lacerta a well-developed parietal nerve connects the parietal eye with the left lateral habenular nucleus. It traverses the habenular commissure.In gratitude and with admiration this paper is dedicated to Prof. Berta Scharrer and to the memory of Prof. Ernst Scharrer.     

Neuronal degeneration in the pineal ganglion during the post-hatching development of the domestic fowl

Summary The frequency of pineal ganglia associated with the pineal tract, and the numbers of acetylcholinesterasepositive neurons in these ganglia were studied in the domestic fowl during the post-hatching period by means of the acetylcholinesterase method. Furthermore, the degeneration of nerve cells in pineal ganglia of 40-day-old domestic fowl was investigated in detail at the electron-microscopic level. The rate of pineal organs containing one or more ganglia was 50% in 2- to 13-day-old, 38% in 40-day-old, and only 10% in 1-year-old domestic fowl. In parallel, the number of acetylcholinesterase-reactive nerve cells that constitute individual pineal ganglia decreased after hatching. Various degrees of neuronal degeneration were found in the pineal ganglia: swelling of the endoplasmic reticulum, electron-dense degeneration of the cytoplasm, and pyknosis of the nerve cell nucleus. Clusters of macrophages containing numerous lysosomes filled with debris-like material were scattered in the ganglion. In addition, plasma cells were observed in association with degenerating nerve cells. These results confirm the suggestion that the loss of acetylcholinesterase-positive nerve cells in the pineal ganglia of the domestic fowl is due to naturally occurring, programmed neuronal cell death. This process is discussed with reference to phenomena of cell death observed in other components of central nervous system.Fellow of the Alexander von Humboldt Foundation, Bonn, Federal Republic of GermanyThe authors are indebted to Professor A. Oksche and Dr. H.-W. Korf (Giessen) for stimulating discussions     

Pineal neurons projecting to the brain of the rainbow trout,Salmo gairdneri Richardson (Teleostei)

Summary The morphology of intrapineal neurons that give rise to the pineal tract and project to the brain in the rainbow trout was visualized by the use of neuronal backfilling with horseradish peroxidase (HRP). The tracing was performed on excised pineal organs under in-vitro conditions at 4° C, with filling times ranging from 6 to 24 h. Large multipolar, bipolar and unipolar neurons were visualized in the rostral tip of the pineal organ (pineal ganglion). These neurons possessed extended dendritic trees participating in the formation of a circumscribed neuropil-like area. Throughout the pineal organ small bipolar elements were the most ubiquitous type of neuron, however, with markedly smaller numbers in the proximal portion of the pineal end-vesicle. In the pineal stalk, some bipolar neurons were observed to contact the pineal lumen, which is continuous with the third ventricle, via dendritic processes of various types. It could not be established whether any of these CSF-contacting processes were identical with photoreceptor outer segments. The basal processes of the bipolar neurons sometimes possessed distally projecting collaterals. In conclusion, it has been shown that (i) different types of neurons displaying varied patterns of regional distribution contribute to the pineal tract, and (ii) certain CSF-contacting neurons in the pineal organ send axonal processes directly toward the brain.Supported by Research grant Ko 758/2-4 from the Deutsche ForschungsgemeinschaftFellow of the Alexander von Humboldt Foundation, Bonn, Federal Republic of Germany     

Light and electron microscopic studies on the pineal tract of rainbow trout, Salmo gairdneri.

The pineal tract of rainbow trout from the pineal end vesicle to the posterior commissure was studied by light and electron microscopy. Five types of nerve fibres (photoreceptor basal process, ganglion cell dendrite, electron-lucent fibre and synaptic vesicles, myelinated and unmyelinated axons) and two modes of synapses (photoreceptor basal process ganglion cell dendrite and axon terminal with synaptic vesicles-photoreceptor basal process synapses) are distinguishable in the proximal region of end vesicle. The two distinct synaptic associations with the photoreceptor basal process suggest two different (excitatory and inhibitory) control of pineal sensory activity. At the distal portion of stalk about two thousand nerve fibres converge into dorsal and ventral bundles. Posterior to the habenular commissure several small branches run out laterally from the ventral bundles to the basal margin of the ependyma, but not into the habenular commissure. The dorsal bundle passes through the dorsal side of the subcommissural organ and runs ventral to the posterior commissure. The pineal tract is composed of unmyelinated axons, electron-lucent nerve fibres and myelinated axons. The number of fibres increases throughout the stalk and reaches the maximum number at the opening of pineal lumen to IIIrd ventricle, however, the number of fibres then decreases through the subcommissural organ and posterior commissure. This increase and decrease of nerve fibres suggest the continuous participation of axonal fibres of pineal nerve cells and the ramification or branching of pineal tract, respectively.     

The subcommissural organ of the frog Rana perezi is innervated by nerve fibres containing GABA

The innervation of the frog subcommissural organ was studied by light-microscopic and ultrastructural immunocytochemistry using antisera against serotonin, noradrenaline, dopamine, gamma-aminobutyric acid (GABA), glutamic acid decarboxylase, different GABA receptor subunits and bovine Reissner's fibre material (AFRU). In the proximity of the organ, serotonin- and noradrenaline-containing fibres were rare whereas dopamine-immunoreactive fibres were more numerous. Many GABA- and glutamic acid decarboxylase-containing nerve fibres were found at the basal portion of the ependymal cells of the subcommissural organ. Under the electron microscope, these GABA-immunolabelled nerve endings appeared to establish axoglandular synapses with secretory ependymal cells of the subcommissural organ. In addition, the secretory ependymal cells expressed high amounts of the beta2-subunit of the GABA(A) receptor. Since GABA-immunoreactive neurons were present in the frog pineal organ proper and apparently contributed axons to the pineal tract, we suggest that at least part of the GABAergic fibres innervating the frog subcommissural organ could originate from the pineal organ.     

Putative cholinergic elements in the photosensory pineal organ and retina of a teleost,Phoxinus phoxinus L. (Cyprinidae)

Summary Putative cholinergic neurons in the photosensory pineal organ of a cyprinid teleost, the European minnow, were studied by use of choline acetyltransferase (ChAT) immunocytochemistry and acetylcholinesterase (AChE) histochemistry. Pinealofugally projecting neurons were visualized using retrograde HRP-filling through their cut axons. For comparison, the distribution of choline acetyltransferase immunoreactivity (ChAT-IR) and AChE-positive elements in the retina was investigated.While the distributional patterns of ChAT-IR and strongly AChE-positive perikarya in the retina are similar and may represent the same neuronal population, ChAT-IR and AChE-positive elements in the pineal organ appear to belong to separate populations. In the retina, small- to medium-sized perikarya in the inner nuclear layer, and small perikarya in the ganglion cell layer are ChAT-IR and AChE positive. The entire inner plexiform layer is AChE positive, while only sublaminae 1, 2 and 4 are ChAT-IR. No indication of cholinergic activity was observed in the optic axon layer.In the pineal organ, ChAT-IR is restricted to small perikarya situated rostrally and dorsally in the pineal end-vesicle. AChE-positive neurons are present throughout the pineal end-vesicle and the pineal stalk. The pineal tract (the pinealofugally projecting axons of intrapineal neurons) is strongly AChE positive, but displays no ChAT-IR. The distribution of pinealofugally projecting neurons, labeled with retrogradely transported HRP, is markedly dissimilar to that of the ChAT-IR elements. It is proposed that the photosensory pineal organ transmits photic information to the brain via a non-cholinergic pathway. The possibility that the ChAT-IR neurons represent small local interneurons is discussed in the light of comparative physiological and anatomical findings.     

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     

Glial cells phagocytose neuronal debris during the metamorphosis of the central nervous system in Drosophila melanogaster

 Using electron microscopy we demonstrate that degenerating neurons and cellular debris resulting from neuronal reorganization are phagocytosed by glial cells in the brain and nerve cord of the fruitfly Drosophila melanogaster during the first few hours following pupariation. At this stage several classes of glial cells appear to be engaged in intense phagocytosis. In the cell body rind, neuronal cell bodies are engulfed and phagocytosed by the same glial cells that enwrap healthy neurons in this region. In the neuropil, cellular debris in tracts and synaptic centres resulting from metamorphic re-differentiation of larval neurons is phagocytosed by neuropil-associated glial cells. Phagocytic glial cells are hypertrophied, produce large amounts of lysosome-like bodies and contain a large number of mitochondria, condensed chromatin bodies, membranes and other remains from neuronal degeneration in phagosomes. Received: 23 January 1996 / Accepted in revised form: 21 May 1996     

Acetylcholinesterase-containing nerve cells and their distribution in the pineal organ of the goldfish,Carassius auratus

Summary Histochemically, an intense acetylcholinesterase (AChE) reaction has been observed in the perikarya of the nerve cells and in the neuropil formations of the pineal organ in the goldfish, Carassius auratus. A group of AChE-rich nerve cells has also been observed between the caudal end of the pineal stalk and the habenular ganglion. No component of the complex revealed butyrylcholinesterase (BuChE) activity.Two different types of nerve cells were recognized on the basis of their size, AChE activity and distribution. Type I cells are characterized by large perikarya possessing a moderate AChE activity and by the presence of an extensive AChE-rich neuropil formation in their vicinity; they are restricted to the rostro-lateral regions of the pineal vesicle. Type II cells are situated in the medio-rostral area of the pineal vesicle and along the entire length of the stalk, and are smaller than Type I cells; they show an intense AChE activity in their perikarya.The neuropil formations in the medio-rostral area of the pineal vesicle are almost as large as those in the vicinity of the Type I cells; they exhibit a strong AChE activity. In the rostral half of the vesicle several sensory cells are associated with each nerve cell, while in the caudal portion only a few cells are apposed to each nerve cell. Thus, the ratio of the number of sensory cells to that of AChE-containing nerve cells in the anterior half of the pineal vesicle is high when compared with the remaining area. In the anterior half of the vesicle the outer segments of the sensory cells are more distinct and their inner segments possess a higher AChE activity than those in the posterior region and the stalk. A gradation in the degree of development of neuropil formations along the pineal axis is remarkable; their size and AChE activity gradually diminish in a caudal direction. In view of the structural specialization of the rostral region of the pineal organ, it has been argued that its terminal portion is more photosensitive.This work was supported by a fellowship from the Alexander von Humboldt Foundation, Federal Republic of Germany.     

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.     

Vergleichende Untersuchungen über acetylcholinesterase-haltige Neurone im Pinealorgan der Vögel

Zusammenfassung Im Pinealorgan der Vögel zeigen die acetylcholinesterase-positiven Strukturen speziesabhängige Unterschiede. Die passeriformen Arten Passer domesticus, Serinus canaria und Amadina faciata alexander besitzen acetylcholinesterase-positive Nervenzellen, deren Axone im Epiphysenstiel hirnwärts ziehen; außerdem kommen an den Blutgefäßen spezifisch tingierbare Nervenfasern vor, die offenbar zur Epiphyse verlaufen. Bei Columba livia sind diese Nervenstrukturen sehr stark reduziert. Dagegen zeigt das Parenchym der Taubenepiphyse lichtmikroskopisch eine schwache Anfärbung; diese Stellen manifestieren sich im elektronenmikroskopischen Bild als punktförmige interzelluläre Reaktionsorte zwischen einzelnen Pinealzellen. Ferner finden sich bei Passer domesticus elektronenmikroskopisch nachweisbare Reaktionsprodukte im endoplasmatischen Reticulum und im perinukleären Raum der Pinealocyten (=Pinealzellen) sowie am Plasmalemmüberzug (Außenmembran) der Perikaryen und der Axone der Nervenzellen. Die Befunde bei 3 Tage alten Küken (Gallus domesticus) und bei Excalfactoria chinensis ähneln denen bei Columba livia, während bei Coturnix coturnix japonica das Reaktionsprodukt vermehrt im basalen Abschnitt der Follikel liegt. Melopsittacus undulatus zeigt im Epiphysenstiel eine begrenzte Zahl von hirnwärts ziehenden Nervenfasern und nimmt zwischen den Passeriformes und der Taube etwa eine Mittelstellung ein. Die sensorische und sekretorische Kapazität des Pinealorgans von Passeriformes wird diskutiert.

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Comparative studies of neurons in the pineal organ of birds using the acetylcholinesterase method

Summary The acetylcholinesterase reaction of the pineal organ (epiphysis cerebri) varies among avian species. Acetylcholinesterase-positive neurons with axons running along the pineal stalk to unidentified brain centers are seen in the pineal organ of passeriform birds such as Passer domesticus, Serinus canaria, and Amadina faciata alexander. A different kind of acetylcholinesterase-positive fibers are observed running along the blood vessels to the pineal organ. The acetylcholinesterase-positive structures are much reduced in Columba livia. The pineal parenchyma in Columba livia shows a slightly brown color in the light microscope; spot-like deposits of the reaction product are seen between the pinealocytes in the electron microscope. In Passer domesticus, the reaction products are seen in the pinealocyte endoplasmic reticulum as well as at the outer membrane of the perikaryon and axon of the nerve cells. The results in three-day old chicken and in Excalfactoria chinensis are similar to those obtained in Columba livia. In Coturnix coturnix japonica, a heavy reaction is evident in the basal part of the follicles. A small number of nerve cells and fibers are seen in the pineal stalk of Melopsittacus undulatus. The results are discussed in respect of sensory and secretory functions of the pineal organs in passeriform birds.

Gastprofessor des Landes Hessen am Anatomischen Institut der Universität Gießen.