Diurnal variation in the serotonin content and turnover in the pineal gland of the Syrian hamster

Melatonin: from basic research to cancer treatment clinics

Melatonin, the chief secretory product of the pineal gland, is a direct free radical scavenger, an indirect antioxidant, as well as an important immunomodulatory agent. In both in vitro and in vivo investigations, melatonin protected healthy cells from radiation-induced and chemotherapeutic drug-induced toxicity. Furthermore, several clinical studies have demonstrated the potential of melatonin, either alone or in combination with traditional therapy, to yield a favorable efficacy to toxicity ratio in the treatment of human cancers. This study reviews the literature from laboratory investigations that document the antioxidant and oncostatic actions of melatonin and summarizes the evidence regarding the potential use of melatonin in cancer treatment. This study also provides rationale for the design of larger translational research-based clinical trials.

Indoleamine metabolism in the pineal gland of the Chinese hamster, Cricetulus griseus

Day- and nighttime contents of pineal melatonin and other indoleamines were measured in the Chinese hamster, Cricetulus griseus. The hamsters were inbred in our colony and kept in LD 14:10. Absolute levels of pineal melatonin and N-acetylserotonin contents were extremely low, but showed a significant circadian rhythm with a minor peak during the light period. Pineal hydroxytryptophan and serotonin (5HT) contents were also found to be higher in the light period. The activity of N-acetyltransferase in the pineal was higher in the light period than in the dark period, whereas there was no difference in hydroxyindole-O-methyltransferase activity between the light and dark periods. The uptake level of tryptophan into the pineal gland was higher in the light period than in the dark period. These results suggest that the 5HT synthesis pathway and/or tryptophan uptake may be involved in forming the circadian rhythm of 5HT content in the Chinese hamster pineal gland.

Diurnal changes in the content of indoleamines, catecholamines, and methoxyindoles in the pineal gland of the Djungarian hamster (Phodopus sungorus): effect of photoperiod

Previous studies in Syrian hamster have shown that the correlations between the daily fluctuations in the contents of pineal indoleamines and methoxyindoles are influenced by the photoperiod, and that dopamine may play a role in the regulation of pineal function. The present study investigated the 24 hour changes in the content of 5-hydroxytryptophan (5-HTP), serotonin (5-HT), 5-hydroxyindoleacetic acid (5-HIAA), N-acetylserotonin (NAS), melatonin, 5-methoxytryptophol (5-MT), noradrenaline (NA), dopamine (DA), and 3,4-dihydroxyphenylacetic acid (DOPAC) in the pineal gland of female Djungarian hamsters exposed to long (LP; LD 16:8) or short (SP; LD 10:14) photoperiods for 10 weeks. Pronounced nocturnal increases of N-acetylserotonin and melatonin content were observed irrespective of the photoperiod regime. The content of 5-HT was markedly decreased during the first hour of the night in LP, which contrasted with the lack of changes in NAS and melatonin content at this time. In SP, an increased 5-HTP content and a less obvious decrease in 5-HT content was observed during the night, although melatonin and NAS content were even higher than in LP. Similar daily patterns as for 5-HT were observed in the 5-HT oxidative metabolites (5-HIAA and 5-MT). When considering values throughout the day, a poor correlation for 5-HT vs.. NAS and melatonin content was observed, which was particularly evident during the nighttime. These data indicate that the daily variation of pineal indoles may not only be dependent on changes in the N-acetyltransferase activity but also in other mechanisms regulating pinealocyte 5-HT availability. As previously reported in other species of hamster, pineal NA content did not show daily variations in LP conditions, although a nocturnal increase was detected in SP. In contrast, pronounced nocturnal increases were observed in the content of DA and its acid metabolite, DOPAC, irrespective of the photoperiod. These data indicate the existence of an increased dopaminergic turnover during the night and further support a role for DA in the regulation of melatonin synthesis and in the synchronization of the pineal functions.

Daily variation in the content of indoleamines, catecholamines and related compounds in the pineal gland of Syrian hamsters kept under long and short photoperiods

This study examined the diurnal changes in the content of 5-hydroxytryptophan (5-HTP), serotonin (5-HT), 5-hydroxyindoleacetic acid (5-HIAA), N-acetylserotonin (NAS), melatonin, 5-methoxytryptophol (5-ML), noradrenaline (NA), dopamine (DA), and 3, 4-dihydroxyphenylacetic acid (DOPAC) in the pineal gland of Syrian hamsters kept under long (14L:10D) and short (10L:14D) photoperiods. The nocturnal increase in NAS and melatonin levels was dependent upon the prevailing photoperiod, with a prolonged duration when the night lengthened. In both photoperiods, NAS and melatonin contents increased several hours after the onset of darkness, and, in animals kept in short photoperiod, the levels of both compounds began to decrease before light onset. On the contrary, decreases were noted in 5-HT, 5-HIAA, and 5-ML contents during the night, which was directly proportional to the dark phase. 5-HTP levels did not show a rhythmic variation. Correlations between the mean values of 5-HT-related compounds showing daily rhythms were very high when group means were compared, but they decreased when values from individual animals were considered. In addition, when correlations were calculated on per-animal basis during the night phase, a weak negative correlation was found for 5-HT vs NAS and 5-HT vs melatonin, although the correlation of 5-HT with positively 5-HT-correlated compounds (5-HIAA and 5-ML) continued to be high. These results indicate that the nocturnal increase in the N-acetyl transferase activity is the major factor generating the rhythm of pineal 5-HT content, but that other photoperiod-dependent mechanisms (i.e., 5-HT synthesis or release) seem to be also implicated. On the other hand, this study shows that NA content in the Syrian hamster pineal gland does not exhibit daily variations, although marked nocturnal increases in the levels of DA and DOPAC were evident. These results suggest the existence of parallel daily alterations in pineal catecholamine synthesis and release, and suggest a role for DA in the pineal activation at night.

Pineal stimulation produces both hypertension and tachycardia in rats

In anesthetized rats, electrical stimulation of pineal gland elicited proportional hypertension and tachycardia, which could be mimicked by microinjection of an excitatory amino acid, kainic acid (0.3 micrograms), into the pineal gland. The hypertension induced by pineal stimulation was antagonized by either spinal transection or postsynaptic blockade of serotonin receptors, while the tachycardia induced by pineal stimulation was antagonized by either serotonin receptor antagonism, bilateral vagotomy or spinal transection. In addition, postsynaptic blockade of serotonin receptors with cyproheptadine (2-5 mg/Kg, IV) produced both hypotension and bradycardia, while stimulation of 5-HT receptors with DOI (10-250 micrograms/Kg, IV) produced both hypertension and tachycardia in rats. The results indicate that pineal stimulation activates brain 5-HT receptors and results in sympathetic stimulation or parasympathetic inhibition which leads to hypertension and tachycardia in rats.

Serotonin content and melatonin production in the pineal gland of the male Djungarian hamster (Phodopus sungorus)

Diurnal variations in serum melatonin levels and pineal concentrations of serotonin (5-HT), N-acetylserotonin (NAS), 5-hydroxyindole acetic acid (5-HIAA), and melatonin were estimated in adult male Djungarian hamsters kept under long-day (LD 16:8) or short-day (LD 8:16) photoperiods. The nocturnal increase in melatonin production was accompanied by a marked drop in pineal serotonin concentrations. Serotonin levels, however, decreased approximately 4 hr before pineal melatonin increased. Correlations of the mean values for pineal serotonin and pineal melatonin indicated significant correlations at both LD 16:8 (r = -0.92, P less than 0.001) and LD 8:16 (r = -0.85, P less than 0.001). The mean levels of pineal serotonin and serum melatonin were correlated as well (LD 16:8, r = -0.91, P less than 0.001; LD 8:16, r = -0.81, P less than 0.01). The levels of pineal serotonin declined at approximately the same time as serum melatonin levels increased. These data suggest that the drop in pineal serotonin is primarily a consequence of melatonin production (as reflected by increasing serum concentrations). Consequently, pineal concentrations of melatonin may not be the best estimate of actual melatonin production, but a measure of how much melatonin is accumulated within the pineal due to high synthesis rates while the release of the hormone from the gland is limited.

Low ambient temperature does not affect the pineal concentrations of either 5-methoxytryptamine or melatonin in golden hamsters kept under short photoperiod

This work investigates the rhythmic synthesis of pineal 5-methoxytryptamine and related indoles in golden hamsters as a function of ambient temperature. 5-methoxytryptamine, 5-methoxytryptophol, 5-methoxyindole acetic acid, and melatonin were measured by high pressure liquid chromatography (HPLC) in the pineal gland of golden hamsters after inhibition of monoamine oxidase. In our experimental conditions, the pineal 5-methoxyindole concentrations of hamsters kept at 5 degrees C were similar to those observed at 20 degrees C. These results suggest that low temperature, which is known to accelerate the short photoperiod-induced gonadal regression, acts at a level different to that of the pineal gland or affects another compound in the pineal gland.

Serotonin release mechanisms in bovine pineal gland: stimulation by norepinephrine and dopamine

An assessment of serotonin (5HT) release was made in bovine pineal gland. Bovine pineal fragments took up [3H]5HT by a Na+-dependent process exhibiting two apparent Km, i.e. a high affinity uptake system (Km = 220 nM) and a low affinity uptake system (Km = 197 microM). A significant release of [3H]5HT was elicited by increasing K+ concentrations in the medium (20-80 mM). Exposure of bovine pineal fragments to varying doses of catecholaminergic agonists indicated that a significant [3H]5HT release was elicited at the following threshold concentrations: 10(-6) M norepinephrine (NE), 10(-7) M dopamine (DA), 10(-6) phenylephrine and 10(-6) M isoproterenol. By employing specific receptor agonists and antagonists, the 5HT release activity of adrenergic agonists was found to be mediated by alpha 1-adrenoceptors, while that of DA by D2-dopaminergic receptors. 5HT release elicited by NE or DA, as well as that by 30 mM K+, was Ca2+-dependent. Both NE and DA increase 45Ca2+ uptake in a dispersed cell preparation of bovine pineal glands. As in the case of 5HT release, the effect of NE and DA on calcium uptake was mediated by alpha 1-adrenoceptors and D2-dopaminergic receptors, respectively. These results indicate that both NE and DA control 5HT release in bovine pineal gland.

Histochemical detection of monoamine oxidase and alcohol dehydrogenase activities in the Syrian hamster Harderian glands: existence of a sexual dimorphism

Monoamine oxidase (MAO) and alcohol dehydrogenase (AD) activities were studied histochemically in the Syrian hamster Harderian gland using tryptamine as substrate and Nitroblue Tetrazolium as the final electron acceptor. No dark: light-related changes were observed. Male type I secretory cells showed an intense MAO reaction. Female type I cells exhibited a moderate MAO activity. Both male and female glands showed a moderate/intense AD-positive reaction. Male type II cells were lacking MAO and AD activities. MAO activity found in the hamster Harderian glands corresponded mainly to MAO type A since treatment with chlorgyline (0.01, 0.1 and 0.5 mM) totally inhibited it. The possible role of these two enzymes in Harderian gland indolalkylamine metabolism is discussed.

Melatonin, serotonin, 5-hydroxyindole-3-acetic acid and N-acetyltransferase in the pineal of the European hamster (Cricetus cricetus) kept under natural environmental conditions: lack of a day/night rhythm in melatonin formation in spring and early summer

In female European hamsters killed in spring and early summer, pineal melatonin content exhibited no day/night rhythm. Absolute levels measured were relatively low, being on the order of daytime levels detected in other hamster species. An absence of day/night changes in the activity of N-acetyltransferase was also observed. However, a marked rhythm in pineal serotonin (5-HT) was found, an abrupt large increase being observed at the beginning of the light period. The day/night rhythm of pineal 5-HIAA content is similar to that of 5-HT. This absence of rhythm in pineal melatonin formation might mean that in the European hamster it is not melatonin but another substance that is of importance in photoperiodism. An absence of melatonin rhythm, however, could also be simply a peculiar pattern of melatonin production observed at a given period of the year. In this case, melatonin would be able to transduce photoperiodic information in the European hamster, as in other photoperiodic species.

Effects of acute ethanol administration on nocturnal pineal serotonin N-acetyltransferase activity

The effect of acute ethanol administration on pineal serotonin N-acetyltransferase (NAT) activity, norepinephrine and indoleamine content was examined in male rats. When ethanol was administered in two equal doses (2 g/kg body weight) over a 4 hour period during the light phase, the nocturnal rise in NAT activity was delayed by seven hours. The nocturnal pineal norepinephrine content was not altered by ethanol except for a delay in the reduction of NE with the onset of the following light phase. Although ethanol treatment led to a significant reduction in nocturnal levels of pineal serotonin content, there was no significant effect upon pineal content of 5-hydroxyindoleacetic acid (5-HIAA). The data indicate that ethanol delays the onset of the rise of nocturnal pineal NAT activity.

Neonatal exposure to DES in BALB/c male mice: effects on pituitary-gonadal function

Neonatal male BALB/c mice were injected with diethylstilbestrol (DES), estradiol benzoate (E2B), testosterone propionate (TP), progesterone or DES, in combination with E2B, TP or progesterone and examined in adulthood. Body weight was reduced in males exposed to DES, TP or DES + TP, while testicular weight was reduced in animals injected with DES, E2B, TP, DES + TP or DES + progesterone. Exposure to DES and/or E2B also produced reproductive tract abnormalities and concomitant progesterone exposure did not further affect this parameter. Concomitant DES did not further alter the reduced plasma luteinizing hormone (LH) levels attributable to neonatal TP or E2B treatment. Plasma follicle-stimulating hormone (FSH) levels in intact males were increased by DES, DES + progesterone or progesterone alone. Assessment of the feedback effects of exogenous gonadal steroids on pituitary gonadotropin release in castrated adults indicated that injection of 125 micrograms TP further increased the already elevated post-castration levels of LH and FSH in mice neonatally exposed to progesterone. The increase in testosterone (T) concentration after intratesticular human chorionic gonadotropin (hCG) administration was significantly attenuated in mice neonatally exposed to DES plus E2B or to progesterone. Basal testicular T levels were significantly elevated in males exposed to DES, alone, or in combination with progesterone. Exposure to DES and TP increased hypothalamic serotonin (5-HT) levels in intact mice, while levels of 5-HT were lower after castration compared to controls. DES + E2B-treated mice had higher norepinephrine (NE) levels, and E2B-treated mice also had higher 5-HT levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Morphometric analysis of the pineal complex of the golden hamster over a 24-hour light:dark cycle: I. The superficial pineal in untreated and optically enucleated animals

Morphometric analysis of the superficial pineal gland of intact and blinded golden hamsters was conducted at both the light and electron microscopic level. The volume of the superficial gland was estimated to be 151 X 10(6) micron 3, comprising 90-94% of the total pineal parenchymal tissue. Analysis of structural rhythms in animals maintained under a 14:10 L:D cycle showed significant 24-hr variations in values for pinealocyte nuclei, nucleoli, rough and smooth endoplasmic reticulum, Golgi bodies, dense bodies, and dense-cored vesicles. Peak values for these structures generally occurred at the light:dark interface. These results provide morphological correlates for known rhythmic variations in the synthesis of pineal-gland products. Superficial pineals examined 8 weeks following optic enucleation exhibited a decrease in the volume of pinealocyte nuclei and cytoplasm, while nucleolar size and the amounts of smooth and rough endoplasmic reticulum, Golgi bodies, dense bodies and dense-cored vesicles were enhanced. The latter changes are interpreted as indications of increased synthetic activity by the superficial pineal gland in response to light deprivation.

Derivatives of [3H]serotonin in organ cultures of hamster pineal gland

The purpose of this study was to determine the viability of the hamster pineal gland in organ culture and to test the effect of norepinephrine (NE) on [3H]serotonin derivatives. In this study, elevated levels of melatonin (7-fold, p less than .05), 5- hydroxytrytophol (5-fold, p less than .001), 5-methoxytryptophol (1.78-fold, p less than .05), and depressed levels of 5-hydroxyindoleacetic acid (3.8-fold, p less than .02) and methoxyindoleacetic acid (1.78-fold, p less than .05) were detected in the glands following the addition of NE to the medium. In a separate experiment, melatonin concentration in the media was also periodically measured by radioimmunoassay to determine the viability of the organ culture over a four-day period. The melatonin level on day 2 (2321 +/- 106 pg/gland) was significantly higher (p less than 0.01) than on day 3 (1542 +/- 86 pg/gland) or day 4 (805 +/- 39 pg/gland). The results of these experiments verify the viability of the hamster pineal organ culture and show that the gland responds to NE in vitro.

Early cannabinoid exposure influences neuroendocrine and reproductive functions in mice: II. Postnatal effects

Maternal exposure to delta 9-tetrahydrocannabinol (THC), the major psychoactive component in marihuana, or to the non-psychoactive cannabinol (CBN) or cannabidiol (CBD) alters male reproductive functions and brain biogenic amines in male and female offspring. Postnatal exposure to THC or CBN reduced body weights, while testicular weights were lower in CBD-exposed mice. Testicular testosterone (T) levels were also lower in CBN- and CBD-exposed animals. Postnatal cannabinoid exposure reduced plasma luteinizing hormone (LH) levels in intact and castrated adults. Although basal T production in vitro was not affected by postnatal cannabinoid exposure, testes from CBD-exposed males were more responsive to gonadotropin stimulation. In contrast, in vivo responsiveness to intratesticular human chorionic gonadotropin (hCG) administration was significantly reduced in THC- and CBD-exposed males. Pituitary weights and their basal LH production in vitro was higher in THC- or CBN-exposed mice. Pituitaries from cannabinoid-exposed males were less responsive to LH releasing hormone (RH) stimulation, however, hypothalamic LHRH content was significantly higher in the THC-exposed males. Hypothalamic dopamine (DA) levels were significantly lower in CBN-exposed castrated mice, compared to castrated controls. The reduction in hypothalmic norepinephrine (NE) in THC- and CBN-exposed castrates after alpha-methylparatyrosine (alpha-MPT) was significantly less than that observed in control castrates. Hypothalamic DA levels were depleted to a greater extent in CBD-exposed males. Brain levels of serotonin (5-HT) and 5-HIAA were significantly higher in castrated, than in intact THC-exposed males. In ovariectomized CBN-exposed females, hypothalamic NE levels were lower, while the alpha-MPT-induced depletion of NE was less in CBD-exposed, compared to control females. Levels of 5-HT were lower only in THC-exposed females. Plasma levels of LH were significantly higher in CBN-exposed, while plasma levels of FSH were reduced in THC- and CBD females. Maternal exposure to psychoactive or non-psychoactive cannabinoids on the day of parturition results in long term alterations in neuroendocrine function in male and female offspring. It is possible that the observed alterations in biogenic amines may mediate the effects of cannabinoids on pituitary and gonadal function.

Early cannabinoid exposure influences neuroendocrine and reproductive functions in male mice: I. Prenatal exposure

Maternal exposure to delta 9-tetrahydrocannabinol (THC), the major psychoactive constituent in marihuana, or to the non-psychoactive cannabinol (CBN) or cannabidiol (CBD) alters endocrine functions and concentrations of brain biogenic amines in their male offspring. Prenatal CBN exposure on day 18 of gestation resulted in decreased plasma FSH levels, testicular testosterone (T) concentrations, and seminal vesicles weights, but increased plasma levels of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) post-castration in adulthood. Prenatal exposure to THC significantly enhanced the responsiveness of the testes to intratesticular LH injection in vivo and tended to increase human chorionic gonadotropin (hCG)-stimulated T production by decapsulated testes in vitro. In the CBN-exposed mice, hCG-stimulated T production was enhanced, while CBD exposure had no effect. Prenatal THC exposure altered the negative feedback effects of exogenous gonadal steroids in castrated adults, with lower plasma T and FSH levels after 20 micrograms T than in castrated controls. In contrast, CBD-exposed mice had higher levels of LH in plasma post-castration. In CBN-exposed adults, two weeks post-castration the concentration of norepinephrine (NE) and dopamine (DA) in hypothalamus and remaining brain were reduced, while levels of serotonin (5-HT) and its metabolite, 5-HIAA, were elevated compared to that in castrated OIL-controls. Prenatal CBD-exposure also reduced NE and elevated 5-HT and 5-HIAA, but did not affect DA levels post-castration. Concentrations of brain biogenic amines were not influenced by prenatal THC exposure in the present study. A single prenatal exposure to psychoactive or non-psychoactive components of marihuana results in long term alterations in the function of the hypothalamo-pituitary-gonadal axis. Changes in the concentrations of brain biogenic amines may be related to these effects of prenatal cannabinoids on endocrine function in adult male mice.