Innervation of the pineal gland in the Arctic fox (Vulpes lagopus) by nerve fibres immunoreactive to substance P and calcitonin gene-related peptide

BACKGROUND

The study demonstrates, for the first time, the presence of substance P (SP) and calcitonin gene-related peptide (CGRP) in the nerve fibres supplying the pineal gland in the Arctic fox.

MATERIALS AND METHODS

The expression and distribution pattern of the studied substances were examined by double-labelling immunofluorescence technique.

RESULTS

The SP-positive fibres enter into the pineal gland through the capsule as the nervi conarii. The fibres formed thick bundles in the capsule and connective tissue septa, from where they penetrated into the pineal parenchyma. Inside the parenchyma, the nerve fibres created basket-like structures surrounding clusters of pinealocytes. The density of intrapineal SP positive fibres was slightly higher in the distal and middle parts of the gland than in the proximal one. Double immunostaining with antibodies against SP and CGRP revealed that the vast majority of SP positive fibres were also CGRP positive. The fibres showing a positive reaction to SP and negative to CGRP were scattered within the whole gland. The fibres immunopositive to CGRP and immunonegative to SP were not observed. In the habenular and posterior commissural areas adjoining to the pineal gland the immunoreactive nerve fibres were not found. Moreover, no immunopositive cell bodies were observed in both the pineal gland and the commissural areas.

CONCLUSIONS

These results reveal that SP and CGRP are involved in the innervation of pineal gland in carnivores. In turn we suggest that these peptides can regulate/modulate melatonin secretion.

Diurnal and circadian variations in indole contents in the goose pineal gland

The diurnal and circadian profiles of pineal indoles, except melatonin, are poorly characterized in birds. Moreover, there are no data on the effect of sudden changes in the light-dark cycle on these profiles. Therefore, we investigated the diurnal (Experiment I) and circadian variation (Experiment II) of nine pineal indoles (tryptophan, 5-hydroxytryptophan, serotonin, N-acetylserotonin, melatonin, 5-hydroxyindole acetic acid, 5-methoxytryptophol, 5-methoxyindole acetic acid, 5-methoxytryptamine) in geese, as well as the changes in the profiles of these substances in geese subjected to a reversed light-dark cycle (Experiment III). For the first 12 weeks of life, all geese were kept under a diurnal cycle of 12 h of light and 12 h of darkness (12L:12D). In Experiment I (n = 48), they were kept under these conditions for another 14 days before being sacrificed at 2-h intervals for sampling of the pineal glands. In Experiment II, the geese (n = 48) were divided into three groups (12L:12D, 24L:0D, 0L:24D) for 10 days before sampling at 6-h intervals. In Experiment III, 24 geese were exposed to a reversed light-dark cycle before sampling at 14:00 and 02:00 on the first, second and third days after light-dark cycle reversal. To determine the content of the indoles in the goose pineals, HPLC with fluorescence detection was used. We found that, with the exception of tryptophan, all the investigated indoles showed statistically significant diurnal variation. When geese were kept in constant darkness, most of the indoles continued to show this variation, but when geese were kept in constant light, the indoles did not show significant variation. When the light-dark cycle was reversed (12L:12D to 12D:12L), the profiles of NAS, melatonin, 5-MTAM and 5-MTOL reflected the new cycle within 2 days. The content of serotonin in geese in 12L:12D was higher than that observed in other birds under these conditions, which suggests that this compound may play a special role in the pineal physiology of this species. In conclusion, our results show that the daily variations in the metabolism of melatonin-synthesis-related indoles in the goose pineal gland are generated endogenously and controlled by environmental light conditions, as in other birds. However, comparison of the results obtained with the goose to those obtained with other species (chicken, duck) unambiguously shows that the profiles of pineal indoles differ markedly between species, in both the quantitative proportions of the compounds and the characteristics of the diurnal changes. These findings provide strong arguments for the need for comparative studies.

Adrenergic control of pinealocyte chondriome – an in vitro study

Norepinephrine released from sympathetic innervation plays the main role in the regulation of melatonin secretion in mammalian pinealocytes. The present study was conducted for the following reasons: 1) to establish whether the pinealocyte chondriome is controlled by norepinephrine, 2) to determine the effect of adrenergic stimulation on mitochondria, and 3) to characterize adrenoceptors involved in the regulation of the chondriome.

The static organ culture of the pineal gland was used. The explants were incubated for 5 consecutive days in control medium and between 20:00 and 08:00 in medium with the presence of 10 μM norepinephrine – adrenergic agonist; isoproterenol – beta-adrenoceptor agonist; cirazoline, methoxamine, M-6364 – alfa1 – adrenoceptors agonists or PMA – activator of PKC. The explants were then subjected to ultrastructural examination and morphometric analysis.

The incubation of explants in the presence of norepinephrine or isoproterenol caused a decrease in the relative volume and the numerical density of mitochondria and induced an increase in the percentage of free mitochondria in pinealocytes. Significant changes in these parameters were not observed after treatment with methoxamine, cirazoline, M-6463 and PMA.

The results obtained show that the chondriome of pig pinealocytes is controlled by norepinephrine acting via beta-adrenoceptors. Adrenergic stimulation, repeated for five consecutive days of organ culture, causes a decrease in the number of mitochondria and a shift in the distribution of mitochondria from the form of networks and filaments into the form of single particles. This indicates the intensive remodeling of the mitochondria network, which is closely linked to the metabolic status of the cell.

Regulation of melatonin secretion in the pineal organ of the domestic duck--an in vitro study

The aim of study was to determine the mechanisms regulating melatonin secretion in the pineal organs of 1-day-old and 9-month-old domestic ducks. The pineals were cultured in a superfusion system under different light conditions. Additionally, some explants were treated with norepinephrine. The pineal glands of 1-day-old ducks released melatonin in a well-entrained, regular rhythm during incubation under a 12 hrs light:12 hrs dark cycle and adjusted their secretory activity to a reversed 12 hrs dark:12 hrs light cycle within 2 days. In contrast, the diurnal changes in melatonin secretion from the pineals of 9-month-old ducks were largely irregular and the adaptation to a reversed cycle lasted 3 days. The pineal organs of nestling and adult ducks incubated in a continuous light or darkness secreted melatonin in a circadian rhythm. The treatment with norepinephrine during photophases of a light-dark cycle resulted in: 1) a precise adjustment of melatonin secretion rhythm to the presence of this catecholamine in the culture medium, 2) a very high amplitude of the rhythm, 3) a rapid adaptation of the pineal secretory activity to a reversed light-dark cycle. The effects of norepinephrine were similar in the pineal organs of nestlings and adults. In conclusion, melatonin secretion in the duck pineal organ is controlled by three main mechanisms: the direct photoreception, the endogenous generator and the noradrenergic transmission. The efficiency of intra-pineal, photosensitivity-based regulatory mechanism is markedly lower in adult than in nestling individuals.

Neuropeptide Y as a presynaptic modulator of norepinephrine release from the sympathetic nerve fibers in the pig pineal gland

Norepinephrine (NE) released from the sympathetic nerve endings is the main neurotransmitter controlling melatonin synthesis in the mammalian pineal gland. Although neuropeptide Y (NPY) co-exists with NE in the pineal sympathetic nerve fibers it also occurs in a population of non-adrenergic nerve fibers located in this gland. The role of NPY in pineal physiology is still enigmatic. The present study characterizes the effect of NPY on the depolarization-evoked 3H-NE release from the pig pineal explants. The explants of the pig pineal gland were loaded with 3H-NE in the presence of pargyline and superfused with Tyrode medium. They were exposed twice to the modified Tyrode medium containing 60 mM of K+ to evoke the 3H-NE release via depolarization. NPY, specific agonists of Y1- and Y2- receptors and pharmacologically active ligands of α2-adrenoceptors were added to the medium before and during the second depolarization. The radioactivity was measured in medium fractions collected every 2 minutes during the superfusion. NPY (0.1-10 μM) significantly decreased the depolarization-induced 3H-NE release. Similar effect was observed after the treatment with Y2-agonist: NPY13-36, but not with Y1-agonist: [Leu31,Pro34]-NPY. The tritium overflow was lower in the explants exposed to the 5 μM NPY and 1 μM rauwolscine than to rauwolscine only. The effects of 5 μM NPY and 0.05 μM UK 14,304 on the depolarization-evoked 3H-NE release were additive. The results show that NPY is involved in the regulation of NE release from the sympathetic terminals in the pig pineal gland, inhibiting this process via Y2-receptors.

The influence of methisoprinol administered in ovo on the morphological structure of the spleen in turkeys

This study analyzed the effect of a synthetic, low-toxic immunomodulator - methisoprinol - administered in ovo on the morphological structure of the spleen in turkeys. Experiments were conducted on three groups of 5-day-old BUT 9 turkeys (35 birds in each group) hatched from eggs which, on day 26 of incubation, had been administered methisoprinol (VetAgro, Lublin, Poland) in ovo in a dose of 5 mg (group I) or 20 mg per egg (group II). Poults hatched from eggs administered a physiological solution of NaCl in a dose of 0.1 ml per egg in ovo served as a control (group III). Samples of the spleen were collected from 5 birds selected at random from a group of decapitated 5-day-old poults and the prepared 7 fm-paraffin sections were stained with HE. A morphometric analysis of the germinal centres of the white pulp of the spleen was conducted by subjecting pictures taken with an optical microscope to a Digital Image Analysis using Axio Vision software (by Zeiss). The study demonstrated that in terms of the morphological structure, the spleen of the poults hatched from eggs administered 5 mg of methisoprinol (group I) did not differ considerably from the spleen of the control birds. In turn, spleens of the poults hatched from eggs administered 20 mg of methisoprinol per embryo were characterized by distinctively developed red pulp and within the area of the white pulp by distinct cortical section containing numerous lymphocytes. In spleens of the poults from this group, the morphometric examination also demonstrated a higher number of germinal centres of the white pulp as compared to their number in spleens of the birds from the other groups.

Calcium concrements in the pineal gland of the Arctic fox (Vulpes lagopus) and their relationship to pinealocytes, glial cells and type I and III collagen fibers

The aim of the present study was to analyze the presence and morphology of the pineal concretions in the Arctic fox and their relationship to pinealocytes, glial cells and collagen fibers. Pineals collected from 7-8 month-old and 3-4 year-old foxes (6 in each age-group) were investigated. Sections of the glands were stained with HE, Mallory's method and alizarin red S as well as subjected to a combined procedure involving immunofluorescent staining with antibodies against antigen S, glial fibril acid protein (GFAP), type I and III collagen and histochemical staining with alizarin red S. The pineal concretions were found in 2 of 6 investigated Arctic foxes aged 3 years and they were not observed in animals aged 7-8 months. The acervuli were present in the parenchyma and the connective tissue septa. They were more numerous in the distal part than in the proximal part of the gland. The acervuli stained with alizarin red S revealed an intensive red fluorescence, what enabled the use of this compound in a combined histochemical-immunofluorescent procedure. A majority of cells in the fox pineal showed positive staining with antibodies against antigen S, a marker of pinealocytes. GFAP-positive cells were especially numerous in the proximal part of the gland. Both antigen S- and GFAP-positive cells were frequently observed close to the concrements. Collagen fibers of type I and III were found in the capsule, connective tissue septa and vessels. Immunoreactive fibers did not form any capsules or basket-like structures surrounding the concrements.

Pineal concretions in turkey (Meleagris gallopavo) as a result of collagen-mediated calcification

The intra-pineal calcification is a well-known phenomenon in mammals, however it is almost completely unknown in birds. The aim of the present work was to analyze morphology and genesis of the pineal concretions in the turkey. The studies were performed on the pineals collected from one-year-old turkeys (Meleagris gallopavo). In addition to standard morphological methods, the alizarin red S and potassium pyroantimonate methods were employed for localization of calcium at the light and electron microscopy level. In light microscopy, calcified concretions with diameters from 300 microm to 2 mm and quantities from 3 to 6 per gland were observed in all the examined pineals. They were stained red with alizarin S and showed the presence of collagen in Mallory's staining. Two types of cells were noted inside the concretion: polygonal and elongated ones. Using electron microscopy, three parts were distinguished within the calcification area. The peripheral part contained densely packed collagen fibrils, some elongated cells and numerous pyroantimonate precipitates demonstrating the presence of calcium ions. In the intermediate part, the fibrils were covered by almost continuous sheets of pyroantimonate precipitates and fused side by side. The central part showed an appearance of calcified hard tissue and contained some polygonal (osteocyte-like) cells. The obtained data demonstrated that the formation of the pineal concretions in the turkey is associated with the mineralization of collagen. This process is completely different from the mechanisms responsible for the formation of the concretions in the mammalian pineal.

Peptidergic and Nitrergic Innervation of the Pineal Gland in the Domestic Pig: An Immunohistochemical Study

The presence and co-localization of vasoactive intestinal polypeptide (VIP), peptide N-terminal histidine C-terminal isoleucine (PHI), pituitary adenylate cyclase-activating peptide (PACAP), somatostatin (SOM), calcitonin gene-related peptide (CGRP), substance P (SP) and the neuronal isoform of nitric oxide synthase (NOS) were studied in neuronal structures of the pig pineal gland. Paraformaldehyde-fixed pineals of 3-month-old gilts were sliced into serial cryostat sections, which were subjected to a set of double immunofluorescence stainings. Based on the co-existence patterns of neuropeptides, five populations of nerve fibres supplying the pig pineal were distinguished: (1) PHI-positive, (2) PACAP-positive, (3) SOM-positive, (4) SP/CGRP-positive and (5) SP-positive/CGRP-negative. Only a subpopulation of PHI-positive fibres contained VIP at the level detectable by immunofluorescence. NOS was found in some intrapineal PHI- and VIP-positive fibres. PHI-, VIP- and NOS-positive nerve fibres were more numerous in the peripheral than in the central part of the pineal. PACAP-positive fibres were equally distributed within the gland. The density of SOM-positive fibres was higher in the ventro-proximal than in the dorso-distal part of the pineal. SOM was also detected in some neuronal-like cells or specialized pinealocytes situated in the central region of the gland. Two populations of fibres containing SP were found: CGRP-positive, present in the distal and central parts of the pineal as well as CGRP-negative, localized in the proximal compartment of the gland.

Histology and ultrastructure of the pineal organ in the domestic goose

The pineal organs of 14-week-old domestic geese were investigated with light and electron microscopy. The pineals consisted of a wide distal part and a narrow middle-proximal one. The glands were attached to the intercommissural region via the choroid plexus. The pineal parenchyma was formed by round or elongated follicles. The follicular wall was composed predominantly by cells immunoreactive with antibodies against hydroxyindolo-O-methyltransferase (HIOMT) or glial fibrillary acid protein (GFAP). They formed two or more layers. HIOMT-positive elements were represented by elongated cells bordering the follicular lumen and oval cells located in the external layer of the follicular wall. These cells were identified in ultrastructural studies as rudimentary-receptor pinealocytes and secretory pinealocytes, respectively. Among rudimentary-receptor pinealocytes two types of cells, designed as A and B, were distinguished due to structural differences. Type A cells extended through the whole follicular wall and showed regular stratified distribution of organelles in well-recognizable zones with rough endoplasmic reticulum, the Golgi apparatus and mitochondria. Type B cells, like type A pinealocytes, contacted the pineal lumen and showed polarity of their internal structure. However, they were markedly shorter than the cells of type A and lacked stratified distribution of organelles. Secretory pinealocytes contained irregularly dispersed organelles. A prominent feature of all types of goose pinealocytes was the presence of numerous dense core vesicles. The population of GFAP-positive cells consisted of ependymal-like supporting cells and astrocyte-like cells.

Pituitary adenylate cyclase-activating polypeptide-immunoreactive (PACAP-IR) nerve fibers in the pig pineal gland

The present study demonstrates the occurrence of PACAP-immunoreactive (PACAP-IR) nerve fibers in different compartments of the pig pineal gland, including glandular capsule (where they form a very dense network) and subependymal tissue close to the pineal recess (moderate to dense meshwork of varicose fibers). Furthermore, several varicose fibers penetrate from the capsule into the connective tissue septa and then into the parenchyma, where they form unequally distributed, fine network and, in some cases, basket-like structures around pinealocytes. Some of the PACAP-IR nerve fibers, observed both in the habenular and posterior epithalamic areas, extend to the pineal gland. PACAP-IR cells could be demonstrated neither in the pineal gland, nor in epithalamic areas.

Distribution of NADPH-diaphorase activity in the pineal gland of the Turkey

NADPH-diaphorase activity was histochemically demonstrated in the nerve fibers, neuronal-like cell bodies and in the endothelial cells of the vasculature in the pineal gland of the turkey. The nerve fibers were localized in the choroid plexus, connecting the pineal gland with the diencephalon as well as inside the pineal gland, where they formed basket-like structures around the pineal follicles. A group of neuronal-like cell bodies was observed in the proximal part of the gland. The positive staining was not observed in the pinealocytes of rudimentary-photoreceptor type and in the supporting cells.

Leu-enkephalin immunoreactivity in the pig pineal gland

Leu-enkephalin-positive structures in the pig pineal gland were demonstrated immunohistochemically using mouse monoclonal antibody. The pineal glands were obtained from the newborn, 21-day and 7-month old female pig. The immunopositive nerve fibers were observed in the pineal gland as well as in the epithalamic areas. The leu-enkephalin-immunoreactive nerve fibers (single or forming small bundles) were localized mainly in the proximal part of the pineal and they were scarce in other parts. The localization of the fibers points to a central source of this innervation. The study did not show any age-dependent differences in the distribution and density of leu-ekephalin-positive nerve fibers.

Localization of NADPH-diaphorase activity in the pineal gland of the domestic pig

The study showed the presence of NADPH-diaphorase containing structures in the pineal gland of the domestic pig. NADPH-diaphorase activity was found in the nerve fibers and in the endothelial cells of the vasculature. The nerve fibers were localized in the capsule, around the blood vessels as well as in the parenchyma. The positive staining was not observed in the pig pinealocytes.

Distribution of growth associated protein (GAP-43) immunoreactivity in nerve fibers supplying the pig pineal gland

An immunohistochemical study of the pig pineal gland was carried out using monoclonal mouse antiserum against growth-associated protein GAP-43. The pineal glands were obtained from the 3, 5, 8 weeks old piglets. The immunopositive nerve fibers were observed in the pineal gland as well as in the habenular and the posterior comissural areas. They formed a dense network in the habenular area and the proximal part of the pineal gland. In the comissural area and in the apical part of the gland. single positive fibers were observed. The obtained results may suggest a difference in the plasticity of innervation between the particular regions of the pineal gland.

Immunohistochemical localization of substance P in the pineal gland of the domestic pig

An immunohistochemical study of the pig pineal gland was carried out using polyclonal rabbit antiserum raised against substance P (SP). The pineal glands were taken from the newborn, 21-day- and 7-month-old female pigs. Immunoreactive nerve fibers were observed in the pineal gland as well as in the posterior commissure and habenular areas. The bundles of SP-immunoreactive fibers were also seen in the subependymal layer of the pineal tissue. The single SP-immunoreactive nerve fibers and few small bundles of nerve fibers were located with equal density throughout the pineal gland, in the connective tissue septa and in the parenchyma. SP-immunoreactive cell bodies were observed in the medial habenular nucleus. The obtained results point to this nucleus as one of the central sources of SP innervation in the pig pineal gland. The study did not show any differences in the distribution and the density of SP-immunoreactive nerve fibers between newborn, 21-day- and 7 month-old pigs.

Somatostatin and somatostatin receptors in the pig pineal gland during postnatal development: an immunocytochemical study

An immunohistochemical study of the pineal gland of the domestic pig was carried out using rabbit antisera raised against synthetic peptide fragments corresponding to different amino acid sequences of the prosomatostatin, the somatostatin-14, and the somatostatin-28 molecule. The study was supplemented by immunohistochemical staining with rabbit antisera raised against five subtypes of somatostatin receptors. The pineal glands were taken from the newborn, 21-day-old and 7-month-old pigs. Immunoreactive nerve fibers and cells were observed in the pineal gland with all the antisera against somatostatin and prosomatostatin. The nerve fibers were located throughout the pineal gland-in the capsule, connective septa, and parenchyma-with the highest density in proximo-ventral part of the gland. The somatostatin positive fibers were also found in the habenular and posterior commissurae areas. Somatostatin-immunoreactive cell bodies were observed mostly in the central part of the gland. These results point to the existence of two somatostatin sources in the pig pineal gland: 1) nerve fibers, probably of central origin; and 2) cells that may represent intrapineal neurons or specialised pinealocytes. A clear difference in the immunoreactivity between newborn, 21-day-old, and 7-month-old pigs was found. Generally, the density of nerve fibers was lower in adult than young animals. The number of the cells also decreased with age. By using the antisera against the five somatostatin receptors, only sst3 - receptor immunoreactivity could be detected. The receptor-immunoreactivity was confined to varicose and smooth fibers and some cells. The sst(3)-receptor positive structures were localised in all parts of the gland and their number was higher in younger pigs.

An immunohistochemical study on the postnatal changes in the C-terminal flanking peptide of neuropeptide Y (CPON)--positive nerve fibers in pineal gland of the pig

Postnatal development of innervation of the porcine pineal gland by C-terminal flanking peptide of neuropeptide Y (CPON)-immunoreactive nerve fibers was examined using the immunohistochemical technique. CPON-positive nerve fibers appeared in the pineal gland of the new-born piglets and formed plexus in the capsula and connective tissue septa of the gland. The nerve terminals branched off from the plexus and penetrated into adjacent parenchyma. The number of nerve fibers immunoreactive to CPON in parenchyma is very low in new-born and 20-day-old piglets. In 7-month-old pigs they created a dense network.

Membrane bounded dense bodies (MBB) of the domestic pig pinealocytes--current state of knowledge

The results of our former investigations concerning the pig pinealocyte organelles named membrane bounded dense bodies (MBB) have been summarized. The presence of MBB is the most conspicuous morphological feature of pinealocytes of genus Suidae. The relative volume of MBB in the cell bodies of pinealocytes in adult domestic pigs ranges from 8% to 16% of whole cytoplasm. On the basis of their morphology, membrane bounded bodies were divided into two main types: MBB-1 and MBB-2. Dense bodies of MBB-1 type have various inner structure and are present both in perikaryons and processes of the pinealocytes. Dense bodies of MBB-2 type are characterised by regular, multilammellar structure and their presence is restricted to pinealocyte perikaryons. The origin and transformations of the MBB are enigmatic. The relative volume of dense bodies in the pig pinealocytes changes during postnatal development and under various physiological and experimental conditions. The system of dense bodies is controlled by sympathetic innervation and environmental light. Dense bodies are also influenced by changes in function of pituitary-gonadal axis in female pigs and by administration of melatonin. High number of the dense bodies in the pig pinealocytes, significant changes in their number and inner structure in various physiological and experimental conditions as well as their exocytosis from pinealocyte processes suggest that these structures are involved in secretory processes in the pig pinealocytes.

Cytoplasmic dense bodies in pig pinealocyte during postnatal development. Quantitative, ultrastructural study

Cytoplasmic dense bodies, conspicuous structures of pinealocytes in the pig pineal gland were ultrastructurally examined during postnatal development from the first day after birth to puberty. The morphometric analysis was employed to estimate the quantitative changes. Process of progressive increase in the relative volume with simulatenous differentiation of structure of the bodies was observed.

Effects of sympathicolytic and sympathicomimetic drugs on pineal ultrastructure in the domestic pig

The effects of a 4-day administration of two sympathicolytic (alpha-methyl-p-tyrosine, propranolol) and three sympathicomimetic (clorgyline, isoproterenol, dobutamine) drugs on the ultrastructure of the pineal gland in the domestic pig were examined. The morphological changes in the pinealocytes of the experimental groups mainly concerned cytoplasmic dense bodies, primary lysosomes, multivesicular bodies, dense core vesicles, and smooth endoplasmic reticulum. These structures seemed to be under direct or indirect control by the adrenergic nervous system. The relative volume of dense bodies in pinealocyte perikarya increased after administration of alpha-methyl-p-tyrosine as well as propranolol and decreased on treatment with clorgyline. The decrease in the relative volume of primary lysosomes in pinealocyte perikarya was noted in pigs treated with clorgyline and isoproterenol. The number of multivesicular bodies in pinealocyte perikarya decreased after administration of alpha-methyl-p-tyrosine. The numerical density of dense core vesicles in pinealocyte perikarya increased after treatment with clorgyline. Administration of isoproterenol and clorgyline resulted in the presence of wide cisterns of smooth endoplasmic reticulum. Narrow cisterns of this form of endoplasmic reticulum and lamellar whorls were observed after treatment with alpha-methyl-p-tyrosine in pinealocytes with large dense bodies. The presence of multilamellar structures was a characteristic feature of the pinealocytes of pigs treated with isoproterenol and dobutamine. Administration of alpha-methyl-p-tyrosine and clorgyline resulted in the appearance of pinealocytes which differed in number, size, and structure of dense bodies.

Effects of sympathicolytic and sympathicomimetic drugs on plasma immunoreactive melatonin in the domestic pig

Plasma immunoreactive melatonin was monitored for 110 hr in sexually immature female domestic pigs kept under 12L:12D light conditions and treated with two sympathicolytic (alpha-methyl-p-tyrosine, propranolol) and three sympathicomimetic (clorgyline, isoproterenol, dobutamine) drugs. Mean levels of plasma melatonin in the control pigs showed significant diurnal changes with the highest values during the scotophase. In the individual gilts the diurnal changes of plasma melatonin were markedly irregular; melatonin increases were not consistently noted at night, and melatonin levels during light and darkness varied considerably between days. The lack of consistency in the diurnal patterns of plasma melatonin in individual pigs during consecutive days explains the large inter-individual differences observed in previous short-term studies. Administration of alpha-methyl-p-tyrosine resulted in the decrease in both daytime and nighttime melatonin levels, compared with the control group, but it did not eliminate the increases in melatonin during the night. Treatment with other drugs did not significantly change the level of plasma melatonin compared with the control group, however they had modulatory effects on melatonin rhythm. The results suggest that the plasma melatonin in the domestic pig is controlled by the adrenergic nervous system, but the pharmacology of the secretion and/or metabolism of this pineal hormone is different than described in other species.

Demonstration of nerve fibers containing the C-terminal flanking peptide of neuropeptide Y (CPON) in the pig pineal gland (Sus domesticus): an immunocytochemical study by light and electron microscopy

BACKGROUND

The pineal gland is richly innervated by the neuropeptide Y (NPY)-positive nerves that mostly exibit immunoreactivity for the enzyme tyrosine hydroxylase, a marker of sympathetic nerve fibers. NPY is synthesized as a part of larger prepromolecule. The present study was undertaken to demonstrate that the posttranslational processing of preproNPY resulted in the presence of C-terminal flanking peptide of NPY (CPON) in nerve fibers of the pig pineal gland.

METHODS

An immunohistochemical anti-CPON technique was done over mounted sections of perfusion-paraformaldehyde-fixed material. An immunocytochemical preembedding technique was done to study the CPON-positive nerve terminals under electron microscopy.

RESULTS

The pig pineal gland is densely innervated by CPON-immunoreactive nerve fibers. These nerve fibers follow from the pineal capsule into the connective tissue septa and farther into the pineal parenchyma, where the varicose branches terminate between the pinealocytes. The fiber density was the highest in the peripheral and ventral parts of the gland. At the ultrastructural level, the CPON-immunoreactive nerve terminals were found in the perivascular spaces and in the parenchyma. The terminals contained small vesicles (30-40 nm in diameter), some of which showed an eccentrically located dense core. In addition, large clear vesicles (80-100 nm in diameter) were present. Some of the CPON-immunoreactive nerve terminals were found in close apposition to the pinealocyte cell membrane, making a synapticlike contact with the pinealocytes.

CONCLUSIONS

Our results show the presence of dense CPON-IR innervation in the pig pineal gland. The ultrastructural localization of CPON-IR nerve terminals shows that the peptide can be released to both perivascular and intercellular spaces. The functional role for this peptide in pig pineal gland is still an open question.

Immunohistochemical studies on the coexistence of catecholamine-synthesizing enzymes and neuropeptide Y in nerve fibers of the porcine pineal gland

The distribution of nerve fibers immunoreactive (IR) to catecholamine-synthesizing enzymes, tyrosine hydroxylase (TH), dopamine-beta-hydroxylase (D beta H), and phenylethanolamine-N-methyltransferase (PNMT) as well as neuropeptide Y (NPY), in the pineal gland of adult sows was investigated by the use of double-labeling immunohistochemistry. The porcine pineal gland was found to be supplied by TH-IR nerve fibers, the vast majority of which were also D beta H-positive. TH- and TH/D beta H-IR nerves were located mostly in the capsula and connective septa of the pineal gland, and their fine varicose branches terminated in the adherent parenchyma. NPY-IR fibers formed a loose network overlapping that was observed in the case of TH- and D beta H-IR fibers. Most of NPY-IR fibers were also positive for TH. The density of the fiber networks depended on the region of the gland. No PNMT-IR structures were observed.

Effects of p-chlorophenylalanine, amiflamine and melatonin treatment on the ultrastructure of pinealocytes in Sus scrofa

The effects of p-chlorophenylalanine (pCPA), amiflamine [Fla 336(+)] as well as melatonin (MEL) treatments on the ultrastructure of pinealocytes in immature female pigs were investigated. Treatment of pCPA-tryptophan hydroxylase inhibitor resulted in the presence of numerous membrane-bound bodies type 2, with long, narrow cisterns of endoplasmic reticulum and a large Golgi apparatus. Fla 336(+) selective MAO-A inhibitor influenced the system of dense bodies, mitochondria and lysosomes (increasing their relative volume). Injections of melatonin resulted in the appearance of numerous homogeneous, round, regular shaped structures surrounded by membrane cytoplasmic structures ('granules'). The results indicate that a peculiar system of cytoplasmic dense bodies may be involved in indoleamine secretion in the pig pinealocyte.