Pineal Content Research Articles

On the presence of melatonin in pineal glands and plasma of foetal sheep

Melatonin is shown to accumulate within the foetal sheep pineal gland in the last few days of gestation. The mean ± S.E.M. foetal content was 79 ± 25 pg per gland for 30 foetuses obtained from day 124–145 gestation and 836 ± 286 pg per gland for 21 foetuses judged to be within 5 days of birth. In 5 neonates, the mean pineal content on day 1 was 899 ± 280 pg per gland. This accumulation correlates to a rise in tissue hydroxyindole-O-methyltransferase activity and foetal plasma melatonin. The possible relationship between these parameters and the endocrine changes preceding parturition is discussed. Significant levels of monoamine oxidase activity were found in foetal sheep pineal and the possibility is raised of other indoles (e.g. 5-methoxy tryptophol) being of importance in foetal pineal function.

Diurnal rhythm of vasotocin in the pineal of the male rat.

The pineal content of arginine vasotocin in the male rat is subject to diurnal changes, having a high value around noon and a low value around midnight. Since in rats exposed to 24 h constant light the pineal content in arginine vasotocin decreases, and in the rats exposed to 24 h constant darkness the pineal content in arginine vasotocin increases, it appears that during the night both the synthesis and release of arginine vasotocin is enhanced.

Thyrotropin Releasing Hormone (TRH) in Pineal and Hypothalamus of the Frog: Effect of Season and Illumination11

The influence of photo-illumination and season on the pineal and hypothalamic content of TRH in the leopard frog (Rana pipiens) was studied. Animals (4-6 in each group) were exposed to constant light or darkness for 72 h and then sacrificed. The pineal and hypothalamus from each frog were extracted for TRH measurement by radioimmunoassay. The experiment was performed in spring, autumn, early winter and mid-winter. In early winter, mid-winter and spring the pineal content of TRH ranged from 0.14-0.70 ng. Significant differences between groups due to season and illumination were recorded. In autumn, mean levels of TRH were 12.95 ng (dark exposed) and 4.19 ng (light exposed)-values 10-20 times higher than at other times of the year (P less than 0.001). The hypothalamic content of TRH ranged from 11.4 ng in spring to 19.5 ng in autumn. Seasonal differences were present, but no effect of light or darkness was found. There was no definite relation between the TRH levels in hypothalamus and pineal. The alteration in pineal and hypothalamic TRH produced by season, and the effect of illumination on pineal TRH content, support the view that TRH has a neuronal function in vertebrates, possibly as a neurotransmitter.

Diurnal rhythm in rat pineal cyclic nucleotide phosphodiesterase activity

MANY substances in the rat pineal organ exhibit marked diurnal variations; some of these fluctuations are circadian, that is, cued but not driven by environmental lighting. The content of the pineal hormone melatonin1 for example, is seven- to tenfold higher during the dark phase of the diurnal cycle than during the light phase2. Similarly, the activities of the melatonin-synthesising enzymes 5-hydroxytryptarnine-N-acetyl transferase (NAT) and hydroxyindole-O-methyl transferase (HIOMT) are also higher in the dark (by factors of 15–70-fold and threefold, respectively3,4). The immediate precursor of melatonin, N-acetyl 5-HT is 10–30-fold higher in the dark than in the light5. In contrast the pineal content of the precursor of N-acetyl 5-HT, 5-HT is twofold higher in the light than in the dark phase of the diurnal cycle6, suggesting that changes in NAT activity regulate changes in melatonin biosynthesis. These changes have been shown to be controlled by environmental light acting through the retina by way of central nervous pathways to the superior cervical ganglion, and thence through postganglionic sympathetic fibres to the pineal body7. Nor-adrenaline released from these fibres acts on β adrenoceptors on the parenchymal pineal cells to stimulate adenylate cyclase, causing an increase in intracellular cyclic AMP which is followed by increased NAT activity and melatonin biosynthesis8,9. Decentralisation, superior cervical ganglionectomy, administration of β-adrenoceptor blocking drugs or protein synthesis inhibitors can all block the light–dark changes observed in NAT activity in this organ10,11.

Correlations of Melatonin Content in Pineal Gland, Blood, and Brain of Some Birds and Mammals

Diurnal, rhythmic variation of melatonin content in the pineal gland, blood serum, and brain have been found in chickens, with greater amounts present in all tissues during nighttime than during daytime. Similar daily rhythms appear to occur in the pineal gland and serum of rats and in the serum and urine of humans. It is proposed that these correlated fluctuations in melatonin levels are causally related, elevated pineal content resulting in increased melatonin content of the blood and increased accumulation by the brain. The brain of chickens, especially the hypothalamus, appears to accumulate melatonin and is probably a primary site of action of melatonin.

Lack of effect of increased pineal serotonin content on H3-tryptophan uptake

Major increases in the serotonin concentrations of rat pineal organs were produced by administering Catron, a monoamine oxidase inhibitor, prior to autopsy, or by preincubating the glands with serotonin (3X10-4M). These increases had no effect on pineal uptake of H3-tryptophan, the amino acid precursor for serotonin. These observations provide further evidence that the control of serotonin synthesis involves an important "open-loop" component.

Pineal canaliculi: demonstration, twenty-four-hour rhythmicity and experimental modification.

AbstractParenchymal perfusions of rat pineal glands with India ink solutions reveal an extravascular and intercellular system of continuous microscopic channels containing ink perfusate. This system has two, apparently interconnecting, components: pericapillary sleeves or networks, and intralobular canaliculi 0.2–0.4 μ in diameter and enmeshing the pinealocytes individually.Perfusion of the canaliculi was reduced or inhibited by either partial dehydration or exposure to hypertonic solutions, and was blocked when the perfusate contained either CaCl2 or trypsin. Hyaluronidase was without effect. The extent to which the canaliculi could be perfused followed a 24‐hour‐rhythm with a peak (mean maximal canalicular perfusion distance = 95 μ) near the end of the daily environmental light phase, and a trough (mean maximal canalicular perfusion distance = 13 μ) during the dark phase. This rhythm resembles that in rat pineal content of 5‐hydroxytryptamine. Dark‐phase perfusion distances equivalent to those of the light‐phase were obtained when 5‐hydroxytryptamine (5 × 10−3 M) was present in the perfusate. In similar circumstances norepinephrine, heparin and melatonin were without effect.It is suggested that this system of canaliculi may be significant for transport activities between pinealocytes and capillaries and that its circadian and local patency may be regulated in part by release of 5‐hydroxytryptamine by the pinealocytes, and in part by calcium ions.

Twenty-four-hour rhythmicity in carbonic anhydrase activities of choroid plexuses and pineal gland.

AbstractCarbonic anhydrase (CA, carbonate hydro‐lyase, EC 4.2.1.1) activity of choroid plexuses (ventricles I + II and IV) and pineal glands of adult male rats was determined by microtitration. Autopsies at precise times in relation to a daily photoperiod 14 hours long allowed in replicate series evaluation of 24‐hour rhythmicity. A slightly lower choroid CA activity during the light phase was variable and marginal in significance. A highly significant and reproducible daily fall in pineal CA activity near the onset of light was paralleled by, and probably originated from, a fall in pineal content of erythrocytes. Low pineal CA activity is consistent with its endocrine nature. Its morning changes in hemodynamics are likely to be due to local changes in content and release of norepinephrine and other vasoactive agents.

Effects of cutting nervi conarii and tentorium cerebelli on pineal composition and activity shifting following reversal of photoperiod

Two series of S 1 strain, littermate, female rats (final number = 35) were studied in individual cages in which running activity was recorded continuously. When 12 1 2 –14 1 2 (series A) or 5 1 2 –6 1 2 weeks old (series B), the transverse sinus was cut bilaterally (= S 1 sham-operation) or the tentorium and the contained nervi conarii and transverse sinus were cut surgically bilaterally about 2 mm from the pineal gland (= NC, nerve-cut operation). Normal levels of time spent in running activity per day were restored in about 10 days in the younger animals (series B) and more gradually in the older ones (series A). Reversals in the timing of the daily artificial photoperiod (LD 12 : 12) 1–5 days after surgery and again 16 days later failed to reveal any significant difference in activity phase-shifting between NC and S animals and between these and normals after postoperative recovery. Autopsy examination was used to exclude from the analyses all animals with brain injury, to confirm by means of histochemistry the reduction in pineal content of sympathetic nerves, and to demonstrate normal pineal volume, histology and cytology in all animals. It is concluded that intact nervi conarii and tentoria are unnecessary for either pineal-based delay in activity phase-shifting or maintenance of normal pineal structure.

Comparative Biochemistry of the Pineal Gland

The pineal gland is biochemically very active. In mammals, it has the unique capacity to synthesize the hormone melatonin (N-acetyl-5-methoxy-tryptamine). Although the synthesis of melatonin is confined mainly to the pineal gland of all vertebrates, the eyes and brains of amphibians and fish also can form melatonin. Melatonin is synthesized in the pineal as follows: tryptophan → 5-hydroxy-tryptophan → serotonin → N-acetylserotonin → melatonin. The final step is catalyzed by the enzyme, hydroxyindole-O-methyl transferase (HIOMT), which is highly localized in the pineal of all vertebrate species examined. The activity of HIOMT is changed when animals are kept in constant darkness or light. In rats, highest HIOMT activity is present in constant darkness, while the reverse occurs in avian species. In mammals, information about lighting reaches the pineal via the retina → inferior accessory optic tract → preganglionic sympathetic fibers → superior cervical ganglia → postganglionic fibers → pineal parenchymal cells. Lighting messages reach the hen's pineal via a nonretinal pathway. Studies with tissue culture indicate that noradrenaline liberated from sympathetic nerves stimulates synthesis of melatonin. There are circadian rhythms in pineal serotonin content which are endogenous and abolished by removal of superior cervical ganglia or by decentralization. There is also a 24-hour rhythm in pineal noradrenaline. This rhythm is exogenous and is abolished by blinding or cutting the inferior accessory optic tract.

The effect of light and darkness on lactic acid content of the pineal gland.

SummaryThe pineal lactic acid content was measured in maturing female rats kept under conditions of continuous light, continuous darkness, and alternating light and darkness (controls) from the day of weaning (at 21 days of age) for 10, 20, and 30 days.A significant increase in the pineal lactate levels of the animals kept in continuous light was observed after 20 and 30 days when compared with those of the controls. When calculated per microgram of pineal protein, the increase in pineal lactate was already significant after 10 days' exposure to continuous light.The high lactic acid level indicates suppression of oxidative cell processes, which appears to be a consequence of the depressed protein metabolism found to occur earlier in animals exposed to continuous light.No change took place throughout the duration of the experiment in the pineal lactate levels of the animals exposed to continuous darkness, this finding paralleling that obtained on the metabolism of pineal RNA and protein.

Pineal hydroxyindole-O-methyltransferase (HIOMT) activity in female Japanese quail. (Coturnix coturnix japonica).

Pineal hydroxyindole-O-mefhyltransferase (HIOMT) activity was measured in female <i>Coturnix</i> throughout maturation and under different photoperiodic conditions. Since HIOMT has been found to O-methylate both serotonin and N-acetyl-serotonin to form 5-methoxytryptamine (5-MT) and melatonin, respectively, both substrates were used in assaying HIOMT in individual pineal glands. Pineal concentrations of melatonin synthesizing activity increaseed between 25 and 30 days and decreased between 30 days of age and the onset of lay, in female <i>Coturnix</i> on l6L:8D. The pineal concentration of 5-MT synthesizing activity did not change significantly during sexual maturation. Melatonin but not 5-MT synthesizing activity was found to be greater in females maturing on 16L:8D than on 8L:16D. Melatonin but not 5-MT synthesizing activity was decreased in mature females exposed to continuous darkness for 5 days. Because changes in melatonin and 5-MT synthesizing activities differed during sexual maturation and in response to long and short photoperiods, it appears that these two activities are regulated independently.

Rhythmic and light-induced changes in levels of pineal 5-hydroxyindoles in the pigeon ( Columba livia)

Pineal 5-hydroxy- and 5-methoxyindoles of domestic pigeons were measured by differential extractions and spectrofluorometry. The daily rhythms in pineal 5-hydroxytryptamine (serotonin or 5-HT) and related indoles and in pineal 5-hydroxyindole-3-acetic acid (5-HIAA) were described in birds artificially lighted from 04:00 to 18:00. The 5-HT level was lowest at midnight (46.5 ng/pineal) and rose to a maximum of 283.9 ng/pineal at 04:30. This was immediately followed by a 50% decrease; and following the start of darkness an additional drop of 35% occurred. A different rhythm and much lower pineal content of 5-HIAA was found. 5-Hydroxytryptophan and 5-methoxyindole-3-acetic acid were too low in amount for measurement, and a melatonin fraction was too low and variable to provide evidence of a daily rhythm. Experimental changes in the timing of light and darkness showed that: (1) precocious morning rise in 5-HT could be caused by early onset of light, and possibly as well by early start of darkness during the previous evening; (2) delayed start of light did not inhibit the early morning rise; (3) continuation of light through the evening inhibited the usual nocturnal decline in 5-HT. Thus, primary phases in the daily rhythm in pineal 5-HT can be triggered in part by light and darkness. It was shown also that the morning peak in 5-HT could be increased and retained by prior injection of 5-hydroxytryptophan and a monoamine oxidase inhibitor (beta-phenylisopropylhydrazine).

NEURAL AND PHOTIC REGULATION OF 5-HYDROXYTRYPTOPHAN DECARBOXYLASE IN THE RAT PINEAL GLAND.

THE mammalian pineal gland has high concentrations of serotonin1–3 and of 5-hydroxytryptophan decarboxylase (5-HTPD) (ref. 4), the enzyme which synthesizes serotonin. Innervation of the rat pineal gland is derived largely or solely from sympathetic nerve fibres the cell bodies of which are located in the superior cervical ganglia5. Fluorescent microscopic findings indicate that a large part of pineal serotonin content is localized in sympathetic nerve endings2. Following superior cervical ganglionectomy, the specific indole fluorescence in these nerves disappears2 and there is a 50 per cent decrease in pineal serotonin2,3.