Regressive post-hatching development of acetylcholinesterase-positive neurons in the pineal organs of Coturnix coturnix japonica and Gallus gallus

Summary Distribution and number of acetylcholinesterase-positive neurons were studied in the Japanese quail and the domestic fowl during the post-hatching period by means of the acetylcholinesterase method. For comparison, the development of the catecholamine-containing (sympathetic) pinealopetal fibers of the domestic fowl was demonstrated with the use of the glyoxylic acid method. The number of acetylcholinesterase-positive ganglion cells in the pineal organs of both avian species decreased rapidly after hatching, with a concentration of these elements in the basal portion (stalk) of the pineal organ.In 3-day-old chickens, perivascular catecholamine-containing nerve fibers penetrate the antero-lateral walls of the pineal organ and are found exclusively in the interfollicular and perivascular tissues. In 13-day-old and adult fowl, these fibers increase in number and terminate not only in the interfollicular space but also in the neuroepithelial parenchyma of the pineal body.The ontogenetic regression of the sensory structures paralleled by an expanding sympathetic innervation in the pineal organ of a galliform species resembles somewhat the process of phylogenetic transformation leading from pineal sense organs to pineal glands.This work was supported by a grant (No. 56480080) from the Ministry of Education, Science and Culture of Japan.Fellow of the Alexander von Humboldt Foundation (1982).     

Characteristic pattern of monoaminergic nerve fibers in the pineal organ of the monkey,Macaca fuscata

Summary Monoaminergic nerve fibers were studied in the pineal organ of the monkey, Macaca fuscata, by use of fluorescence and immunohistochemical procedures. Abundant formations of noradrenergic nerve fibers were observed in the pineal organ. They entered the parenchyma in the form of several coarse bundles via the capsule in the distal portion of the organ and spread throughout the organ after branching into smaller units. The density of the autonomic innervation decreased gradually toward the proximal portion of the organ. In the distal portion, numerous nerve fibers formed perivascular plexuses around the blood vessels and some fibers ran as bundles unrelated to the blood vessels in the stroma. Fine varicose fibers and bundles derived from these plexuses penetrated among the pinealocytes. However, only a few intraparenchymal fluorescent fibers were detected in the proximal third of the gland. With the use of serotonin antiserum serotonin-immunoreactive nerve fibers were clearly restricted to the ventroproximal part of the pineal organ. Although the somata of the pinealocytes showed intense immunoreactivity, their processes were not stained. In one exceptional case, clusters of pinealocytes displaying very intense immunoreactivity were found in an area extending from the distal margin of the ventral portion of the pineal stalk to the proximal portion of the pineal organ proper; these cells were bipolar or multipolar and endowed with well-stained processes.     

Pinealocytes immunoreactive with antisera against secretory glycoproteins of the subcommissural organ: A comparative study

Summary By means of light-microscopic immunocyto-chemistry two polyclonal antibodies (AFRU, ASO; see p. 470) directed against secretory glycoproteins of the subcom-missural organ were shown to cross-react with cells in the pineal organ of lamprey larvae, coho salmon, a toad, two species of lizards, domestic fowl, albino rat and bovine (taxonomic details, see below). The AFRU-immunoreactive cells were identified as pinealocytes of the receptor line (pineal photoreceptors, modified photoreceptors or classical pinealocytes, respectively) either due to their characteristic structural features or by combining AFRU-immunoreaction with S-antigen and opsin immunocytochemistry in the same or adjacent sections. Depending on the species, AFRU- or ASO-immunoreactions were found in the entire perikaryon, inner segments, perinuclear area, and in basal processes facing capillaries or the basal lamina. In most cases, only certain populations of pinealocytes were immunolabeled; these cells were arranged in a peculiar topographical pattern. In lamprey larvae, immunoreactive pinealocytes were observed only in the pineal organ, but not in the parapineal organ. In coho salmon, the immunoreaction occurred in S-antigen-positive pinealocytes of the pineal end-vesicle, but was absent from S-antigen-immunoreactive pinealocytes of the stalk region. In the rat, AFRU-immunoreaction was restricted to S-antigen-immunoreactive pinealocytes found in the deep portion of the pineal organ and the habenular region. These findings support the concept that several types of pinealocytes exist, which differ in their molecular, biochemical and functional features. They also indicate the possibility that the AFRU- and ASO-immunoreactive material found in certain pinealocytes might represent a proteinaceous or peptidic compound, which is synthesized and released from a specialized type of pinealocyte in a hormone-like fashion. This cell type may share functional characteristics with peptidergic neurons or paraneurons.Supported by Grant I 38259 from the Stiftung Volkswagenwerk, Federal Republic of Germany, to E.M.R. and A.O.; Grant S-85-39 from the Direccion de Investigaciones, Universidad Austral de Chile, to E.M.R.; Grant 187 from FONDECYT, Chile, to C.R.Y.; and Grant Ko 758/3-1 from the Deutsche Forschungsgemeinschaft, Federal Republic of Germany, to H.W.K.     

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     

Separation of the pineal vesicle from the wall of the third ventricle during the post-hatching development of the chicken

Summary According to light- and electron-microscopic observations the pineal organ of the 3-day-old chicken consists of a prominent end vesicle and a tapering parenchymal stalk. During this stage the pineal lumen is in open communication with the third ventricle. However, in the 40-day-old chicken, which still possesses a well-developed end vesicle, the proximal portion of the pineal stalk displays regressive changes leading to local fragmentation. At this stage the pineal stalk is reduced, and the pineal lumen is missing. In 1-year-old chickens the parenchyma of the proximal portion of the stalk is further diminished, and in 3-year-old domestic fowl is completely displaced by bundles of collagenous fibers, only some nerve fibers being present. This post-hatching pineal development may reflect the sequence of changes leading from pineal sense organs to pineal glands.This work was supported by a grant-in-aid for Scientific Research from the Ministry of Education, Science and Culture of Japan     

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     

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.     

Acetylcholinesterase-positive intrapineal neuronal system in the palm squirrel Funambulus pennanti (Wroughton)

A well-developed acetylcholinesterase (AChE)-positive neuronal system could be demonstrated in the pineal organ of the palm squirrel. There are two longitudinal nerve tracts which run all along the margin of the pineal organ from its distal to proximal regions. These nerve tracts are confluent distally. Another short, but deep tract was seen in the middle part of the pineal organ which joins one of these tracts. A large number of AChE-positive neurons whose processes actually form the tracts are present all along the pineal organ. They are distinguished into multipolar and pseudounipolar/unipolar neurons. A few neurons seen outside the nerve tract form a network of nerve fibres among the pinealocytes and also link the main tracts. The nerve tracts appear wavy, irregular and tortuous. A large number of round ring-like bodies seen in close association with neuronal perikarya and nerves may represent the axo-somatic and axo-dendritic contacts.     

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     

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.     

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     

A Golgi study of the parvocellular neurons in the paraventricular nucleus of the domestic fowl

The present study was focussed on the typology of small and medium-sized neurons in the hypothalamic paraventricular nucleus (PVN) of the domestic fowl as revealed by means of Golgi impregnation. This region is provided with different systems of neurons that can be distinguished on the basis of their location and dendritic morphology. Intraependymal neurons and CSF-contacting nerve cells are found in the periventricular layer together with bipolar elements endowed with processes extending parallel to the surface of the third ventricle. The short axons of these neurons may contact the magnocellular elements. Numerous isodendritic neurons are scattered throughout the entire PVN; these nerve cells possessing short and branched axons may be considered as local-circuit neurons. The complex intrinsic organization of the PVN of the domestic fowl might provide the structural basis for local interactions among the neuronal elements of this hypothalamic region.     

GABA-immunoreactive neurons in the photosensory pineal organ of the rainbow trout: two distinct neuronal populations

Summary The distribution of putative GABA-ergic neurons in the photosensory pineal organ of the rainbow trout was investigated by use of a specific antiserum against -aminobutyric acid (GABA). GABA-immunoreactive (GABA-IR) neurons were located in the rostral portion of the pineal end-vesicle, presumably constituting a population of interneurons. GABA-IR neurons were also found in the pineal stalk. The axons of these neurons were traced along the pineal stalk toward the brain. The terminal areas of these axons could not be established. GABA-IR glial cells were observed in the pineal end-vesicle, but not in the pineal stalk.     

Cholinergic and GABAergic neuronal elements in the pineal organ of lampreys, and tract-tracing observations of differential connections of pinealofugal neurons

The putative cholinergic and GABAergic elements of the pineal organ of lampreys were investigated with immunocytochemistry to choline acetyltransferase (ChAT) and γ-aminobutyric acid (GABA), and by acetylcholinesterase (AChE) histochemistry. For comparison we also carried out immunocytochemistry to serotonin (5-HT) and a tract-tracing investigation of the two types of projecting cells, i.e., ganglion cells and long-axon photoreceptors. Most photoreceptors were ChAT-immunoreactive (ChAT-ir) and AChE-positive, while ganglion cells and the pineal tract were ChAT-negative and AChE-negative or only faintly positive. These results strongly suggest the presence of a cholinergic system of photoreceptors in the lamprey pineal organ. GABA-ir fibers that appear to originate from faintly to moderately stained ganglion cells were observed in the pineal stalk. Immunocytochemistry to 5-HT indicated the presence of two types of 5-HT-ir cells, bipolar cells and ganglion-like cells. The connections of the ganglion cells and long-axon photoreceptors were also studied by application of DiI to the pineal stalk in fixed brains or of biotinylated dextran amine (BDA) to one of the main targets of pinealofugal fibers (optic tectum or mesencephalic tegmentum) in isolated brains in vitro. Some long-axon photoreceptors and ganglion cells were labeled from the optic tectum. However, BDA application to the tegmentum exclusively labeled ganglion cells in the pineal organ. These results indicate that the two morphological types of afferent pineal neuron have different projections. No labeled cells were observed in the parapineal organ in BDA experiments, indicating that this organ and the pineal organ are involved in different neural circuits.     

Demonstration of differential immunohistochemical localization of the neuron-specific enolase antigen in rat pinealocytes

A refined method for the immunohistological demonstration of neuron-specific enolase (NSE) on 1- to 2-micron Epon-812 section gave characteristic staining of cerebral and cerebellar neurons. This method has made it possible to obtain a more detailed characterization of the heterogeneity of rat pinealocytes in the superficial portion of the rat pineal complex. Thirty adult male rats have been studied, five of which were used in a photometric analysis of the distribution of NSE. Pinealocytes stained either intensely or weakly for the NSE antigen and exhibited an uneven distribution within a given region. Further analysis of the gland revealed a distal to proximal decrease in stain intensity. It is suggested that the more strongly stained cells, being concentrated distally, are under sympathetic control.     

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.     

Evidence for a nervous connection between the brain and the pineal organ in the guinea pig

Summary Following the injection of horseradish peroxidase into the pineal organ of the guinea pig, approximately 30 nerve fibers were demonstrated in the pineal stalk due to the retrograde transport of the tracer enzyme in these elements. Finely branched extensions of these nerve fibers are directed toward the distal portion of the pineal organ. This projection of central nervous elements enters the pineal organ via the habenular or posterior commissures. Neuronal perikarya projecting into the pineal organ are found in the region of the paraventricular nucleus near the border of the third ventricle.In partial fulfillment of the requirements for the degree of Dr. med., Faculty of Medicine, Justus Liebig University of Giessen     

Pineal organ-like organization of the retina in megachiroptean bats

Phylogenetically originated from photoreceptive structures, the pineal organ adapts the organism to circadian and circannual light periodicity of the environment, while the retina develops to a light-based locator. Bats have a nocturnal life and an echolocator orientation presumably modifying the task of photoreception. Looking for morphological basis of the special functions, in the present work we compared the fine structure and immunocytochemistry of the retina and pineal organ in micro- and megacrochiroptean bats. We found that there is a high similarity between the retina and pineal organ in megachiropterans when compared to other species investigated so far. Besides of photoreceptor derived pinealocytes, the pineal organ of both micro- and megachiropterans contain intrapineal neurons and/or ganglionic cells as well as glial cells. Like spherules and pedicles of retinal photoreceptors, axon-type processes of pinealocytes form synaptic ribbon containig terminals. Similar to retinal photoreceptors and neurons, pinealocytes and pineal neurons contain immunoreactive glutamate and aspartate. In addition, excitatory amino acids accumulate in the pineal neurohormonal endings and might have a role in the hormonal (serotonin?) release of the organ. Concerning the structure of the retina the highest similarity to the organization of the pineal organ was found in the megachiroptean fruit eating bats Cynopterus sphinx and Rusettus niloticus. The retina of these species forms folds and crypts in its photoreceptor layer. This organization is similar to the folds of the pineal wall successively developed during evolution. Since a folded photoreceptor layer is not viable for a photolocator screen in decoding two-dimensional images, we suppose that this peculiar organization of the megachiropteran retina is connected to a "pineal-like" photometer task of the eye needed by these species active at night.     

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.     

The presence of acetylcholinesterase-positive nerve fibres in the deep pineal gland and the pineal stalk but not in the superficial part of adult albino rats

Application of the histochemical method for testing acetylcholinesterase (AChE, EC 3.1.1.7) showed the presence of AChE-positive nerve fibers in the deep pineal gland and the pineal stalk but not in the superficial part of adult albino rats. These findings may indirectly support the existence of the potentially cholinergic innervation of at least some of the rat pinealocytes present in these parts of the gland and augment the evidence of the heterogeneity of the rat pinealocytes. It is possible that cholinergic neurons in the medial habenular nuclei or in the parasympathetic sphenopalatine ganglion may be a source of these AChE-positive fibres. The examination was performed at the light microscope level.