Showing papers on "Pinealocyte published in 1992"

Circadian rhythms of vasopressin content in the suprachiasmatic nucleus of the rat.

Abstract: The suprachiasmatic nucleus (SCN) of the anterior hypothalamus contains a circadian pacemaker in mammals. We determined the circadian profiles of arginine-vasopressin (AVP), a major peptide in the dorsomedial SCN, in rats under light-dark (LD), constant dark (DD) and constant light (LL) conditions. Under LD conditions, AVP levels in the SCN showed circadian rhythmicity with a peak at early light phase and a broad trough during the dark phase. This rhythm in the AVP contents was maintained even after 14 days of free-running under DD conditions and 3 days under LL conditions. These circadian patterns of AVP are similar to those of somatostatin, another peptide in the dorsomedial SCN. This indicates a common mode of regulation for peptides in this subfield of the SCN.

Regulation of the Rhythmic Melatonin Secretion by Fish Pineal Photoreceptor Cells

Abstract: Many, if not most, biochemical, physiological and behavioural events are rhythmic. Rhythms with a periodicity of 24 h (daily) or one year (annual) represent major components in the adaptation of organisms to their environment. Environmental factors, such as light and temperature, play an important role in the synchronization of these rhythms. In vertebrates, synchronization is mediated through the circadian system, which is composed of sensors and circadian oscillators. These include the pineal organ, the lateral eyes and the suprachiasmatic nuclei of the hypothalamus.

Melatonin, The Pineal Gland and Circadian Rhythms.

Abstract: Amniote circadian organization derives from the interactions of circadian oscillators and photoreceptors located in the hypothalamic suprachiasmatic nuclei (SCN), the pineal gland, and the eyes. In mammals, circadian organization is dominated by the SCN, which serve as "master pacemakers" in the control of a wide array of behavioral and physiological rhythms (including locomotion, sleep-wake, thermoregulation, cardiovascular function, and many endocrine processes). Among the rhythms under SCN control in mammals are the circadian synthesis and secretion of the pineal hormone melatonin, which relies on a multisynaptic pathway via the sympathetic nervous system to maintain and entrain rhythmicity in this hormone. Several studies have indicated that pineal melatonin feeds back on SCN rhythmicity to modulate circadian patterns of activity and other processes. However, the nature and system-level significance of this feedback are unknown. Recently published work indicates that although pinealectomy does not affect rat circadian rhythms in light-dark cycles or constant darkness, wheel-running activity rhythms are severely disrupted in constant light. These data suggest that either (1) pineal feedback regulates the light sensitivity of the SCN, and/or (2) it affects coupling among circadian oscillators within the SCN or between the SCN and its output. Research in our laboratory is currently addressing each of these hypotheses.

Fine structure of the pinealopetal innervation of the mammalian pineal gland

Abstract: The mammalian pineal gland is innervated by peripheral sympathetic and parasympathetic nerve fibers as well as by nerve fibers originating in the central nervous system (central innervation). The perikarya of the sympathetic fibers are located in the superior cervical ganglia, while the fibers terminate in boutons containing small granular vesicles and a few large granular vesicles. Both noradrenaline and neuropeptide Y are contained in these neurons. The parasympathetic fibers originate from perikarya in the pterygopalatine ganglia. The neuropeptides, vasoactive intestinal peptide and peptide histidine isoleucine, are present in these fibers, the boutons of which contain small clear transmitter vesicles and larger granular vesicles. The fibers of the central innervation originate predominantly from perikarya located in hypothalamic and limbic forebrain structures as well as from perikarya in the optic system. These fibers terminate in boutons containing small clear and, in certain fibers, an abundant number of large granular vesicles. In rodents, the majority of the central fibers terminate in the deep pineal gland and the pineal stalk. From these areas impulses might be transmitted further caudally to the superficial pineal gland via neuronal structures or processes from pinealocytes. Several hypothalamic neuropeptides and monoamines might be contained in the central fibers. The intrapineal nerve fibers are located both in the perivascular spaces and intraparenchymally. The majority of the intraparenchymally located fibers terminate freely between the pinealocytes. However, some nerve terminals make synaptic contacts with the pinealocytes and in some species with intrapineal neurons. In fetal mammals, sympathetic, parasympathetic, and central fibers are also present. In addition, an unpaired nerve, connecting the caudal part of the pineal gland with the extreme rostral part of the mesencephalon, is present. This nerve is a homologue to the pineal nerve (nervus pinealis) observed in lower vertebrates. © 1992 Wiley-Liss, Inc.

The pineal gland influences rat circadian activity rhythms in constant light.

Abstract: Mammalian circadian organization is believed to derive primarily from circadian oscillators within the hypothalamic suprachiasmatic nuclei (SCN). The SCN drives circadian rhythms of a wide array of...

Magnetic field effects on pineal indoleamine metabolism and possible biological consequences.

Abstract: In recent years, there has been a great deal of publicity concerning the possible health effects of electric and/or magnetic field exposure. One of the most frequently reported observations after the exposure of animals to either electric or magnetic fields relates to alterations in the metabolism of serotonin (5HT) to melatonin within the pineal gland. This review summarizes these results particularly in animals exposed to intermittently inverted, non-time varying magnetic fields, i.e., pulsed static magnetic fields. When exposure occurs at night, the conversation of 5HT to melatonin is typically depressed, not unlike that after light exposure at night. The mechanisms by which pulsed magnetic fields alter the ability of the pineal to convert 5HT to the chief pineal hormone melatonin remains unknown but may involve effects on any or all of the following: the retinas, the suprachiasmatic nuclei, the peripheral sympathetic nervous system, and the pinealocytes. Results to date suggest that induced electrical currents (eddy currents) produced by the pulsed magnetic fields are particularly detrimental to pineal indoleamine metabolism and may be an important causative factor in the metabolic changes measured. The physiological consequences of perturbations in the melatonin rhythm induced by magnetic field exposure remain unknown.

Photoreceptors of the retina and pinealocytes of the pineal gland share common components of signal transduction

Abstract: Light absorbed by retinal photoreceptors triggers a cascade of reactions that initiate cGMP hydrolysis, cation channel closure and membrane hyperpolarization. Down-regulation of the cascade involves additional proteins that interfere with amplification along the cascade. Pinealocytes are activated by norepinephrine during the dark phase of the day/night cycle. Mature pinealocytes of the mammalian pineal express the known photoreceptor proteins that are implicated in down-regulation of the visual cascade, but the cascade components that produce cGMP hydrolysis and membrane hyperpolarization are absent. Pinealocytes accumulate cyclic AMP minimally when norepinephrine activates their beta adrenergic receptors alone, but the response is potentiated by the simultaneous activation of their alpha-1 adrenergic receptors. A model is proposed whereby phosducin, a phosphoprotein that binds the beta,gamma subunit of G-proteins, could modulate the synthesis of cyclic AMP by buffering the amount of beta,gamma G-protein subunits that are available for activating adenylate cyclase.

Immunocytochemical demonstration of rod-opsin, S-antigen, and neuron-specific proteins in the human pineal gland.

Abstract: The aim of this study was to examine whether rod-opsin and S-antigen immunoreactions were present in the pineal organ of adult man and how these immunoreactions were correlated with neuronal markers, e.g., synaptophysin, and neurofilaments L, H and M. Three perfusion-fixed epithalamic regions including the pineal organ and five pineal glands obtained at routine autopsy were used. The specimens were taken from female or male patients, 25 to 85 years of age. All immunoreactions were performed using highly specific, well-characterized antibodies. Rod-opsin and S-antigen-immunoreactive pinealocytes occurred in all pineal organs investigated; however, the immunoreaction was restricted to small subpopulations of pinealocytes (rod-opsin immunoreaction: approximately 3%–5%; S-antigen immunoreaction: approximately 5%–10% of the total population). In contrast, immunoreactions for synaptophysin and neurofilaments M and H were present in numerous pinealocytes. Immunoreactivity for neurofilament L was not found. These data suggest that the cellular composition of the human pineal organ is heterogeneous. Moreover, the presence of rod-opsin and S-antigen immunoreactions in the human pineal organ indicates that it may be affected by autoimmune retinal diseases that are provoked by antibodies against these proteins, as is the case in rodents and non-human primates.

Morphofunctional aspects of the mammalian pineal gland.

Abstract: The primary aim of this review is to present the current state of knowledge of the ultrastructure of the mammalian pineal gland, with emphasis on its functional aspects. Basic ultrastructural features of the mammalian pinealocytes are presented with special attention paid to ultrastructural aspects of pineal secretion.

Neuropeptide Y (NPY) and C-flanking peptide of NPY in the pineal gland of normal and ganglionectomized sheep.

Abstract: The present immunohistochemical study describes the presence and distribution of nerve fibers containing neuropeptide Y (NPY), and C-Flanking Peptide Of NPY (CPON) in the pineal gland of the sheep. Nerve fibers were detected by using a series of antisera directed against NPY or against CPON. Many positive immunoreactive nerve fibers were identified in the pial capsule of the pineal, in connective septae and in the parenchyma between pinealocytes. The intraparenchymal fibers were particularly evident and created an extensive network throughout the gland. Nerve fibers immunoreactive for all the peptides were also observed in the posterior commissure and in the stria medullaris thalami. No NPY- or CPON-positive neurons were found in the pineal gland. In order to study the site of origin of NPY- and CPON-immunoreactive nerve fibers, the superior cervical ganglia were bilaterally removed in a series of animals. Sympathetic denervation was checked by using an antiserum against tyrosine hydroxylase (TH). Nearly all TH-immunoreactive elements disappeared in the pineal glands of animals sacrificed 15 days after surgery. Also the density of NPY- and CPON-immunoreactive nerve fibers decreased in the animals after the ganglionectomy. However, a number of nerve fibers still remained in the gland. These data indicate that some NPY- and CPON-immunoreactive nerve fibers of the sheep pineal gland derive from an extrasympathetic origin. The very dense innervation of the sheep pineal gland with nerve fibers containing NPY and CPON strongly indicates a functional role for this family of peptides in the pineal gland of this species.

Pineal photoreceptor cells in culture: fine structure, and light/ dark control of cyclic nucleotide levels and melatonin secretion.

Abstract: Trout pineal photoreceptor cells were dissociated by trypsin-DNase digestion and further purified by a Percoll gradient centrifugation Total cells or purified photoreceptor cells were then embedded in a collagen gel, or layered on culture-treated polycarbonate membranes, or maintained in suspension, with RPMI 1640 medium or BGjb medium It has been shown that cells maintain a rhythmic production of melatonin for at least seven 24 h light/dark cycles under these conditions In this complementary study, the morphofunctional state of the photoreceptor cells was examined 1) by electron (transmission, scanning) microscopy, and 2) by pharmacological tests under different lighting conditions Using polycarbonate membranes together with RPMI 1640 medium appeared the most suitable The segmented organization of photoreceptor cells was well preserved when using the culture-treated membranes It tended to disappear in cells embedded in the collagen gel and was lost after passage through the Percoll gradient However, this one allowed obtention of an homogeneous population of photoreceptors, as recognized by their intracellular components Intracellular organelles were rather well preserved in the embedded photoreceptors The study also provides novel information on the nature of second messengers involved in the photoperiodic control of melatonin production in photoreceptor cells From the effects of an adenylyl cyclase activator and a phosphodiesterase inhibitor it appeared that 1) total cells and Percoll-selected cells behaved similarly, 2) the nocturnal rise in melatonin secretion was associated with an increase in cAMP content, and 3) a fall in cAMP may be a mechanism through which light reduces melatonin secretion by photoreceptor cells Cyclic GMP, the metabolism of which also appeared to be controlled by light, did not seem involved in the photoperiodic control of melatonin production The method proposed herein offers interesting perspectives for the study of the photoneuroendocrine properties of isolated photoreceptor cells

Immunocytochemistry and Calcium Cytochemistry of the Mammalian Pineal Organ: A Comparison With Retina and Submammalian Pineal Organs

Abstract: Morphologically the mammalian pineal organ is a part of the diencephalon. It represents a neural tissue histologically (“pineal nervous tissue”) and is dissimilar to endocrine glands. Submammalian pinealocytes resemble the photoreceptor cells of the retina, and some of their cytologic characteristics are preserved in the mammalian pinealocytes together with compounds demonstrable by cyto- and immunocyto-chemistry and participating in photochemical transduction. In our opinion, the main trend of today's literature on pineal functions—only considering the organ as a common endocrine gland—deviates from this structural and histochemical basis. In mammals, similar to the lower vertebrates, the pinealocytes have a sensory cilium developed to a different extent. The axonic processes of pinealocytes form ribbon-containing synapses on secondary pineal neurons, and/or neurohormonal terminals on the basal lamina of the surface of the pineal nervous tissue facing the perivascular spaces. Ribbon-containing axo-dendritic synapses were found in the rat, cat, guinea pig, ferret, and hedgehog. In the cat, we found GABA-immunoreactive interneurons, while the secondary nerve cells, whose axons enter the habenular commissure, were GABA-immunonegative. GABA-immunogoldylabeled axons run between pinealocytes and form axo-dendritic synapses on intrapineal neurons. There is a similarity between the light and electron microscopic localization of Ca ions in the mammalian and submammalian pineal organs and retina of various vertebrates. Calcium pyroantimonate deposits—showing the presence of Ca ions—were found in the outer segments of the pineal and retinal photoreceptors of the frog. In the rat and human pineal organ, calcium accumulated on the plasmalemma of pinealocytes and intercellularly among pinealocytes. The formation of pineal concrements in mammals may be connected to the high need for Ca exchange of the pinealocytes for their supposed receptor and effector functions. © 1992 Wiley-Liss, Inc.

The ultrastructure of mammalian pinealocytes: a systematic investigation.

Abstract: Pinealocytes are not only the principal cellular components of the pineal gland, but they are also the principal synthetic machinery of this enigmatical gland with highly diverse and often questionable empyreal roles assigned to it. Ultrastructural descriptions of pinealocytes belonging to some 70 species of mammals (a mere 2% or less of the over 4,200 mammalian species) have been summarized from the available literature with new observations on 12 species of chiropterans. Space limitation precluded any treatment of the supporting glia, neural elements, and the perivascular spaces. A detailed table lists nearly all mammalian species whose pineal ultrastructure has been investigated. Blanks in this table point to the necessity of studies on those particular groups. A tabular listing of unusual structures reported within the pinealocyte cytoplasm points out the impending experimental work on these species. Such studies using the latest techniques might provide clearer insights into the functional role of the pineal gland as an important and integral component of the neuroendocrine axis. Whereas sufficient structural information now exists on cytoplasmic organelles such as synaptic ribbons and spherules, annulate lamellae, subsurface cisterns, and the several types of synaptic arrangements seen in relation to the pinealocyte soma and its processes, the functional role of these structures in pineal synthetic processes remains to be elucidated.

Pinealocyte synaptic ribbons and neuroendocrine function

Abstract: A comparative study of pinealocyte synaptic ribbons (SR) revealed two predominant populations exhibiting either a rod/ribbon shape (SRr) or a spherical/punctate shape (SRsp). Species-specific differences were found in the abundance of SR, the ratio of SRr/SRsp, and the occurrence of SR in ribbon fields. The close topographical relationship of SR to the plasma membrane and the numerical changes that occurred with changes in metabolism of the pinealocytes suggest that SR have important vesicle-mediated interactions with the cell membrane. Experiments designed to clarify the relationship between SR and pineal neuroendocrine function revealed a positive correlation between SR numbers and indole intermediates during pineal development in the rat, and increased SR frequency after denervation of the rat pineal gland or administration of the β-adrenergic agonist, isoproterenol. These data are consistent with the hypothesis that SR function is linked to receptor mechanisms regulating indoleamine production in the pineal gland. © 1992 Wiley-Liss, Inc.

Physical stress in the middle of the dark phase does not affect light-depressed plasma melatonin levels in humans.

Abstract: The human pineal gland has been shown to be unresponsive to stress-induced sympathetic activation during the day However, the effects of stress on human melatonin production have received little investigation at night, when the pinealocytes should be physiologically responsive to noradrenergic stimulation For this purpose, plasma melatonin and cortisol levels were measured in 7 healthy men (aged 25-34 years), both in resting condition and before and after a physical exercise performed between 2340 and 2400 h, 30 min after exposure to bright light (2,500 lx) The exercise consisted in bicycling on a bicycle ergometer at 50% of the personal maximum work capacity (MWC) for 10 min, followed by another 10 min of bicycling at 80% of the MWC The results clearly showed that physical exercise does not affect light-depressed plasma melatonin levels, whereas it clearly increased plasma cortisol concentrations (p less than 0002, two-way ANOVA with repeated measures), systolic blood pressure, pulse pressure and heart rate These findings suggest that the human pineal gland is not responsive to systemic sympathetic activation induced by physical stress even in the middle of the dark phase

Pineal photoreceptor cells: photoperiodic control of melatonin production after cell dissociation and culture.

Abstract: Trout pineal cells were dissociated using a trypsin-DNase digestion technique. An enriched population of photoreceptor cells was selected from a Percoll gradient centrifugation. The ability of cultured photoreceptor cells (selected or not on a Percoll gradient) to produce melatonin rhythmically was investigated during seven 24 h light/dark cycles. During each cycle, trout pineal photoreceptor cells released low amounts of melatonin during daytime and high amounts during night-time. Under continuous darkness, melatonin release was continually high. The profile of its rhythm and that of the activity of the hydroxyindole-O-methyltransferase-the last enzyme of the melatonin biosynthetic pathway-depended on the substrates and on the culture media used. Some of them appear suitable for short- or long-term culture of photoreceptor cells permitting the study of their neuroendocrine properties.

Immunocytochemical and circadian biochemical analysis of neuroactive amino acids in the pineal gland of the rat: effect of superior cervical ganglionectomy.

Abstract: Semiquantitative immunocytochemistry by immuno-gold techniques revealed differences in the spatial distribution of glutamate, glutamine, and taurine within the pineal gland, with greatest labeling over pinealocytes, glia, and endothelia, respectively. At the subcellular level, glutamate labeling tended to be highest over pinealocyte synaptic ribbons and mitochondria, and lowest over lipid inclusions. Pineal levels of glutamate, glutamine and taurine, as measured by high performance liquid chromatography, did not vary over a light: dark cycle. Superior cervical sympathetic denervation, which abolishes pineal melatonin synthesis, resulted in a nearly 50% reduction in pineal glutamate levels, but had no effect on levels of glutamine and taurine. Other amino acids (alanine, arginine, aspartate, serine) were reduced by 23%–33% following sympathectomy. These data suggest an important role for glutamate in pinealocyte function(s) possibly related to the noradrenergic innervation of the gland.

Immunocytochemical demonstration of interphotoreceptor retinoid-binding protein in cerebellar medulloblastoma

Abstract: Previously, immunoreactive rod-opsin and S-antigen (arrestin), two highly characteristic markers of retinal photoreceptors and pinealocytes, were shown to be present in certain medulloblastoma cells. It, thus, has been suggested that such cells differentiate along the photoreceptor lineage. This is corroborated in the present immunocytochemical investigation using antibodies against another photoreceptor-cell marker, the interphotoreceptor retinoid-binding protein (IRBP). As shown in preparations of human retina and pineal organ, IRBP can be successfully demonstrated in formalin-fixed and paraffin-embedded tissue: the IRBP immunoreaction is located to the outer and inner segments of retinal photoreceptor cells and to perikarya of certain pinealocytes. Examination of formalin-fixed, paraffin-embedded biopsy specimens of 66 cerebellar medullo-blastomas revealed varying numbers of IRBP-immuno-reactive tumor cells in 19 cases that were formerly shown to contain rod-opsin and S-antigen immunoreaction. IRBP-immunoreactive tumor cells were also found in a retinoblastoma and a pineocytoma, but not in neuroblastoma, ganglioneuroblastoma, glioblastoma, oligodendroglioma and astrocytoma. The results indicate: (1) cerebellar medulloblastomas are heterogeneous in their differentiation potential; (2) one type of medulloblastoma displays photoreceptor characteristics; (3) this type appears to be closely related to retinoblastoma and pineal cell tumors; and (4) all three types of tumors may display additional common features to be explored in future studies.

Characterization of alpha 2-adrenergic receptors on rat pinealocytes.

Abstract: alpha 2-Adrenergic receptors in rat pineal membranes were characterized using p-[125I]iodoclonidine, a highly selective, high specific activity ligand. Binding was rapid (association constant rate = 0.0462 nM/min-1) and reversible after the addition of phentolamine (apparent dissociation rate constant = 0.04 min-1). Saturation experiments indicate the presence of a single class of noncooperative binding sites, with an equilibrium binding constant (Kd) of 1.1 +/- 0.3 nM and a binding capacity (Bmax) of 69 +/- 9 fmol/mg protein. Analysis of the relative potency of selected adrenoreceptor agonists and antagonists in competition studies with p-[125I]iodoclonidine indicates that the ligand is binding to a member of the family of alpha 2-adrenergic receptors that has a high affinity for oxymetazoline, phentolamine, and (-)norepinephrine and a low affinity for prazosin, similar to the recently described alpha 2-adrenergic receptor present in the bovine pineal gland, classified as belonging to the newly described...

Immunohistochemical localization of glial fibrillary acidic protein (GFAP) in rat pineal stalk astrocytes.

Abstract: In the present work, the presence and distribution of astrocytes in the rat pineal stalk is investigated applying an immunohistochemical technique for the demonstration of glial fibrillary acidic protein (GFAP) on Epon-embedded semithin sections (05 micron thick) GFAP-immunoreactive cells are evenly and regularly distributed along the entire pineal stalk The GFAP-immunoreactive cells display a stellate shape showing variable numbers of cell processes that are mainly oriented parallel to the longitudinal stalk axis Astrocytic processes show a clear tendency to encircle the remaining elements of the pineal stalk; ie, pinealocytes, nerve fibres and blood vessels Furthermore, glial processes form a cover layer separating the stalk from surrounding anatomical structures

Pineal ‘Synaptic Ribbons’ and Serum Melatonin Levels in the Rat following the Pulse Action of 52-Gs (50-Hz) Magnetic Fields: An Evolutive Analysis over 21 Days

Abstract: In continuation of earlier studies, we have investigated the influence of 52-Gs (50-Hz) magnetic fields on the evolution of pinealocyte ‘synaptic ribbons’ and serum melatonin levels in rats, following

Inhibitory action of ethanol on L-type Ca2+ channels and Ca(2+)-dependent guanosine 3',5'-monophosphate accumulation in rat pinealocytes.

Abstract: It has previously been shown that the K+ potentiation of vasoactive intestinal peptide-stimulated cAMP and cGMP responses was inhibited by ethanol in rat pinealocytes, suggesting an inhibitory action of ethanol on the voltage-dependent Ca2+ channels (VDCC). In this study, using the whole cell version of the patch clamp technique, we found that ethanol reduced the amplitude, but did not change the voltage dependence or the time course of activation or inactivation of the L-type VDCC. The inhibitory effect of ethanol on this current was concentration dependent, and ethanol (100 mM) resulted in a 40% inhibition of this current. However, in fura-2-loaded cells, total increases in intracellular Ca2+ ([Ca2+]i) caused by ethanol and BayK 8644 did not differ from the [Ca2+]i signal caused by BayK 8644 alone, suggesting that the inhibitory action of ethanol on VDCC may not be related to a reduction in [Ca2+]i. Although there was no change in the total [Ca2+]i signal, ethanol (25-200 mM) dose-dependently inhibited ...

Delta-sleep-inducing peptide stimulates melatonin, 5-methoxytryptophol and serotonin secretion from perifused rat pineal glands.

Abstract: The pineal gland is known to synthesize numerous indolamines. Since delta-sleep-inducing peptide (DSIP, a tryptophan nonapeptide) is found in the pineal gland, its effect on the secretion of indolamines was investigated. DSIP stimulated melatonin (MEL), 5-methoxytryptophol (5-ML) and serotonin (5-HT) synthesis and release, whereas it did not affect pineal cyclic AMP levels. The stimulatory effect of DSIP on MEL secretion was dose dependent between 5 x 10(-6) and 10(-4) M, whereas the minimal effective concentration of DSIP on 5-ML secretion was higher than 10(-5) M. The effect of DSIP (10(-4) M) was compared to the effect of isoproterenol (ISO, 10(-6) M) on MEL and 5-HT release. ISO stimulated MEL secretion and concomitantly decreased 5-HT release. With regard to kinetic characteristics, the effect of DSIP (10(-4) M) on MEL release was faster and of shorter duration than the effect of ISO (10(-6) M; 2 and 4 h, respectively). At 10(-4) M, DSIP potentiated the ISO-induced increase of MEL secretion. The DSIP-stimulated release of MEL was not significantly altered when the pineal glands were treated with 10(-5) M propranolol (a beta-adrenergic antagonist), 10(-5) M prazosin (an alpha 1-adrenergic antagonist) or 10(-5) M naloxone (an opioidergic antagonist). This study demonstrates that the DSIP-induced secretion of indolamines from rat pineal glands may not be elicited through the well-known noradrenergic or opioid systems.