Regulation of synaptic ribbons in rat pineal gland explants by norepinephrine and sympathetic neurons in a co-culture model (original) (raw)
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Pinealocyte synaptic ribbons and neuroendocrine function
Microscopy Research and Technique, 1992
A comparative study of pinealocyte synaptic ribbons (SR) revealed two predominant populations exhibiting either a rodhibbon shape (Sk) or a spherical/punctate shape (SR,,). Species-specific differences were found in the abundance of SR, the ratio of SR,JSRsp, 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 p-adrenergic agonist, isoproterenol. These data are consistent with the hypothesis that SR function is linked to receptor mechanisms regulating indoleamine production in the pineal serotonin, Ribbon fields gland. o
Functional synaptogenesis and the rat pineal gland: A pharmacological investigation
Journal of Neural Transmission, 1983
Pineal glands obtained from rats of different ages were incubated in vitro with drugs known to specifically alter pre-or postsynaptic noradrenergic neurotransmission to determine when during development nerve terminal or receptor mediated control of glandular N-acetyltransferase (NAT) activity might reach functional maturation. Basal daytime NAT activity measured in vitro was lowest in fetal rats, increased dramatically by the day of birth, peaked at 10 days postnatally, and subsequently declined to near adult levels by 25 days of age. Drugs (isoproterenol, norepinephrine, or propranolol) known to influence pineal gland NAT activity by acting directly on pinealocyte postsynaptic p-noradrenoceptors produced comparable changes in enzyme activity at all ages studied, although larger doses of the receptor agonist were required in fetal animals to elevate NAT activity. In contrast, in vitro incubation with indirect acting drugs (amphetamine or 1-dopa) which require functional presynaptic nerve terminals to exert their pharmacological effects, failed to increase pineal gland NAT activity until early in postnatal life. Hence, postsynaptic fl-noradrenoceptors may function to control pineal gland NAT activity prior to the time when the presynaptic sympathetic neurons innervating the gland attain maturational status.
Annals of Anatomy - Anatomischer Anzeiger, 2003
Synaptic ribbons (SRs) of mammalian pinealocytes exhibit day/night changes in number and size, changes that are apparently regulated by the suprachiasmatic nucleus via postganglionic sympathetic nerve fibres. Since the neural control of SR changes is far from clear and as pinealocytes produce action potentials, we undertook to investigate whether electrical stimulation affects SR changes. Isolated rat pineal glands removed during the daytime were kept in vitro for 0, 30, 60, 90 or 120 rain, with or without continuous electrical stimulation (1 mA, 1 Hz), followed by the quantification of SR profiles (SRPs) by transmission electron microscopy. SRs were categorised as to whether they lay less than 100 nm away from the pinealocyte plasmalemma (SRPsnear) or more distant from it (SRPSdist) and the lengths of the profiles were measured. Cultured pineal organs showed a significant numerical depression of SRPsnear, irrespective of whether the organs had been electrically stimulated or not. SRPsnear length revealed a significant increase at 60 min in unstimulated control tissue and at 30 min in electrically stimulated glands. SRPsdist length decreased significantly at 30 min in control glands and after 60 rain in electrically stimulated glands. Thus, action potentials inside the pineal gland appear to be minor factors regulating SR numbers. In future pineal studies, SRPs .... and SRPSdist should be considered separately as they differ in plasticity.
Pineal ribbon synapses: regulated by the gland's central innervation
Neuro endocrinology letters, 2010
The pineal gland is part of the circadian clock system and is under the predominant influence of the endogenous oscillator located in the suprachiasmatic nucleus. A polysynaptic pathway involving hypothalamus, spinal cord and sympathetic system regulates the so far best-studied aspect of its neuroendocrine output, i.e., the synthesis and secretion of melatonin. This parameter increases dramatically at night upon sympathetic activation in rats and many other mammals including man. In addition, parasympathetic, trigeminal, diencephalic and other sites or mechanisms connect the gland, mainly via its stalk, to the nervous system. However, their function for pineal metabolic or morphological features are hardly known. An interesting ultrastructural attribute of the pineal gland are ribbon synapses. These presynaptic structures in pinealocytes are composed of a ribbon and vesicles. They are thought to regulate and facilitate multivesicular release, and display a circadian rhythm with high...
Journal of Pineal Research, 1995
Neurotrophic effects of the pineal gland: Role of non-neuronal cells in co-cultures of the pineal gland and superior cervical ganglia McNulty JA, Tsai S-Y, Fox LM, Madsen TM, Silberman S, Tonder N. Neurotrophic effects of the pineal gland: Role of non-neuronal cells in cocultures of the pineal gland and superior cervical ganglia. J. Pineal Res. 1995; 19:40-50. 0 Munksgaard, Copenhagen Abstract: The pineal gland (PG) is a source of several trophic factors. In this study, PG and superior cervical ganglia (SCG) from Sprague-Dawley neonates (1-day-old) were co-cultured to test the hypothesis that endogenous release of PG NGF (or an NGF-like cytokine) is sufficient to promote survival of SCG neurons. Neuronal density of SCG neurons was significantly enhanced when co-cultured with PG for 7 days compared to SCG cultured alone. SCG survival and neurite formation in PG co-cultures was less than in SCG treated with exogenous NGF (100 ng/ml). The neurotrophic effect of PG co-cultures was abolished when 1% anti-NGF was added to the medium. Co-cultures of SCG neurons with established 7day PG cultures induced extensive SCG neurite formation within 24 hr compared to SCG co-cultured with 1-day PG cultures. This suggests that PG neurotrophic effects are due to PG non-neuronal cells (nnc) that proliferate to confluency by 7 days in culture. S-antigen-positive pinealocytes did not proliferate in culture. There was decreased SCG survival when neurons were seeded onto PG cultures that had been previously killed by drying, which suggests that the neurotrophic effects of nnc are not substrate-dependent. Immunocytochemical characterization of PG nnc revealed a heterogenous mixture of astrocytes, macrophagel microglia, and fibroblasts. These findings support the hypothesis that NGF is actively secreted by PG and that nnc are the principal source of this neurotophin.
Anatomy and Embryology, 1989
Melatonin metabolism in the mammalian pineal gland is under the clear influence of sympathetic fibers originating in the superior cervical ganglia (SCG). Previous studies suggested that pineal "synaptic" ribbons (SR) as well are regulated by the gland's sympathetic innervation. To gain more insight into the mechanisms involved, we examined the effects of sympathetic stimulation on SR number and on the activity of melatonin forming enzymes, serotonin N-acetyltransferase (NAT) and hydoxyindole-Omethyltransferase (HIOMT). The SCG in adult male rats were stimulated electrically during daytime for either 15 or 120 rain. Immediately following stimulation, the glands were removed and processed for electron microscopy and for the determination of NAT and HIOMT activities. No differences in pineal SR number, size or location were found in rats stimulated with either parameters when compared with sham-stimulated or control animals. While the activity of HIOMT remained unchanged, the activity of NAT was also unaltered following 15 min of stimulation, but was augmented approximately three-fold in animals stimulated for 120 min. It is concluded that if SR in the rat pineal gland are under sympathetic control, the regulation is different from that involved in melatonin formation.
“Synaptic” ribbons and spherules of the rat pineal gland: Day/night changes in vitro?
Experimental Brain Research, 1982
In the present study pineal glands of rats aged 69-71 days were studied in vivo and in vitro with respect to day/night changes of "synaptic" ribbons and spherules. It was found that ribbons outnumber spherules by a factor of 3. In vivo, both ribbons and spherules show a roughly 3-fold increase in number at 1 a.m. when compared to 1 p.m. Up to 39 h in vitro, the two structures in question did not reveal day/night differences in amount, suggesting that diurnal rhythmicity of the gland did apparently not persist in organ culture. After 3 h in organ culture, the spherules, but not the ribbons, showed a striking increase in number, showing that ribbons and spherules may be governed by different mechanisms.
Journal of Comparative Physiology A: Sensory, Neural, and Behavioral Physiology, 1998
There is evidence that sympathetically innervated mammalian pineal glands contain cells that exhibit action potentials. It is unknown whether ex vivo pineal glands deprived of their nervous input are still capable of ®ring. In the present study, multiple-unit recordings from rat pineals revealed spontaneously active cell clusters with a mean ®ring frequency of 1.5 0.3 Hz which could be abolished by tedrodotoxin. Regularly ®ring clusters showed no inherent periodicity in the minute range, whereas rhythmical clusters with periodically repeated bursts had period lengths of 12.6 min (day) and 9.5 min (night). Superfusion of norepinephrine reduced the ®ring frequency of both cluster types, or had no eect, and the rhythmical clusters became regular. The eects of norepinephrine appear to be mediated via b-adrenoceptors because isoproterenol, a b-agonist, had the same eect as norepinephrine and as the a-agonist phenylephrine was without eect. Evidence was obtained that the inhibitory eect of norepinephrine may be mediated by nitric oxide, which appears to aect the electrical discharge of the cells directly or indirectly through cGMP. It is discussed whether the spontaneously active pineal cells represent an intrapineal oscillator or are driven by an intrinsic oscillator which has yet to be de®ned.
Cell and Tissue Research, 1991
Postnatal development of the innervation of the pineal gland in situ as well as the reinnervation of pineal grafts by tyrosine hydroxylase (TH)-and neuropeptide Y (NPY)-immunoreactive nerve fibers were examined using the avidin-biotin-peroxidase immunohistochemical technique. TH-immunoreactive nerve fibers appeared in the pineal gland on the second postnatal day (P2) in both hamsters and gerbils. NPY-immunoreactive nerve fibers first appeared in the pineal gland of gerbils on P2 and in the hamsters on P3. By the seventh postnatal day (P7), the pineal glands of both hamsters and gerbils were richly innervated by TH-and NPY-fibers that appeared as smooth fibers or fibers with sporadic varicosities. By the age of 4 weeks, the innervation of the pineal glands of hamsters and gerbils by THand NPY-fibers was fully developed. Abundant TH-and NPY-fibers formed a dense meshwork in the parenchyma of the superficial and deep pineals. The great majority of the fibers bore a large number of varicosities. More NPY-fibers were found in the pineal glands of gerbils than hamsters. NPY fibers were distributed evenly throughout the pineal glands of the gerbil, but they were more often located in the central region of the superficial pineal of the hamster. For the pineal grafts, superficial pineals from neonatal and 4-week-old hamsters were transplanted to different sites in the third cerebral ventricle (infundibular recess, posterior third ventricle) or beneath the renal capsule. The pineal grafts from 4-weekold donors appeared to undergo severe degeneration and eventually disappeared. The pineal grafts from neonatal hamsters, however, successfully survived and became well integrated into their new locations. Abundant THand NPY-fibers in the host brain were found surrounding the pineal grafts placed in the third cerebral ventricle, but were only rarely seen entering the parenchyma of the grafts. A few TH-fibers were demonstrated in the
Reproduction, nutrition, development
The innervation of the rat pineal gland from the sphenopalatine, otic, superior cervical and trigeminal ganglia was investigated in animals by use of in vivo retrograde tracings. A solution of 2% Fluorogold was iontophoretically injected into the superficial pineal gland in a series of Wistar rats. After a survival time of 4-10 days, the animals were fixed by perfusion and the brains, sphenopalatine, otic, superior cervical and trigeminal ganglia were investigated with a fluorescence microscope. Many retrogradely labelled perikarya were found in the superior cervical ganglia, but a smaller number of neurones were also labelled in the sphenopalatine, otic and trigeminal ganglia. Injections of the tracer into the subarachnoidal space were used as the control for unspecific uptake and transport of the tracer. The input to the pineal gland from the parasympathetic sphenopalatine and otic ganglia might be involved in the regulation of the annual rhythms of the pineal gland. The projectio...