Neuropeptide Y increases intracellular calcium in rat pinealocytes

Melatonin Synthesis Enzymes Activity: Radiometric Assays for AANAT, ASMT, and TPH

Melatonin is synthesized and secreted by the pineal gland in mammals. Its synthesis is triggered at night by norepinephrine released in the interstices of the gland. This nocturnal production is dependent on the transcription, translation, and/or activation of the enzymes arylalkylamine-N-acetyltransferase (AANAT), acetylserotonin O-methyltransferase (ASMT), and tryptophan hydroxylase (TPH). In this chapter, the methodology for the analysis of AANAT, ASMT, and TPH activities by radiometric assays will be presented. Several papers were published by our group utilizing these methodologies, evaluating the enzymes modulation by voltage-gated calcium channels, angiotensin II, insulin, anhydroecgonine methyl ester (AEME, crack-cocaine product), ethanol, monosodium glutamate (MSG), signaling pathways such as NFkB, and pathophysiological conditions such as diabetes.

Mass-spectrometry analysis of the human pineal proteome during night and day and in autism

The human pineal gland regulates day-night dynamics of multiple physiological processes, especially through the secretion of melatonin. Using mass-spectrometry-based proteomics and dedicated analysis tools, we identify proteins in the human pineal gland and analyze systematically their variation throughout the day and compare these changes in the pineal proteome between control specimens and donors diagnosed with autism. Results reveal diverse regulated clusters of proteins with, among others, catabolic carbohydrate process and cytoplasmic membrane-bounded vesicle-related proteins differing between day and night and/or control versus autism pineal glands. These data show novel and unexpected processes happening in the human pineal gland during the day/night rhythm as well as specific differences between autism donor pineal glands and those from controls.

Neuropeptide Y expression confers benzo[a]pyrene induced anxiolytic like behavioral response during early adolescence period of male Wistar rats

Environmental neurotoxicant like benzo[a]pyrene (B[a]P) is known to induce neurobehavioral changes. Our previous reports address the adverse effect of B[a]P on the neurobehavioral responses and neuromorphology of sensitive brain regions in adolescent rats. Present study was conducted on male Wistar rat neonates at postnatal day 5 (PND5) to ascertain B[a]P induced anxiolytic like behavioral response could be an outcome of neuropeptide Y (NPY) overexpression in brain. Single intracisternal administration of B[a]P was carried out at PND5 to elucidate the role of NPY on neurobehavioral responses at PND30. The behavioral studies showed anxiolytic like effect of B[a]P in both light and dark box and elevated plus maze tests. Antioxidant assay involving glutathione peroxidase activity was significantly decreased where as lipid peroxidation was significantly augmented in both hippocampus and hypothalamus of B[a]P treated group as compared to naive and control. The neurotransmitter estimation by HPLC-ECD showed significant increase in 5-HT level in both hippocampus and hypothalamus of B[a]P treated group. Significant elevation in NPY expression was observed in both hippocampus and hypothalamus of B[a]P group. Intracellular Ca²⁺ estimation using Fura-2AM by fluorometry showed that B[a]P induced increase in Ca²⁺ influx was associated with augmented NPY expression in brain. As NPY has orexigenic effect, our result revealed that there was a significant increase in body weight at PND30 following B[a]P administration to rat neonates at PND5. These findings suggested that NPY overexpression in brain regions might be associated with anxiolytic like behavioral response and orexigenic effect in rats following single intracisternal B[a]P administration. Future research directing towards understanding the signaling cascades of B[a]P induced biochemical and neuromorphological alteration might address the independent pathway which induce neurodegeneration despite NPY overexpression in brain regions of adolescent rats.

Stimulatory effect of RFRP-3 on the gonadotrophic axis in the male Syrian hamster: the exception proves the rule

In seasonal mammals, a distinct photoneuroendocrine circuit that involves the pineal hormone melatonin tightly synchronizes reproduction with seasons. In the Syrian hamster, a seasonal model in which sexual activity is inhibited by short days, we have previously shown that the potent GnRH stimulator, kisspeptin, is crucial to convey melatonin's message; however, the precise mechanisms through which melatonin affects kisspeptin remain unclear. Interestingly, rfrp gene expression in the neurons of the dorsomedial hypothalamic nucleus, a brain region in which melatonin receptors are present in the Syrian hamster, is strongly down-regulated by melatonin in short days. Because a large body of evidence now indicates that RFamide-related peptide (RFRP)-3, the product of the rfrp gene, is an inhibitor of gonadotropin secretion in various mammalian species, we sought to investigate its effect on the gonadotrophic axis in the Syrian hamster. We show that acute central injection of RFRP-3 induces c-Fos expression in GnRH neurons and increases LH, FSH, and testosterone secretion. Moreover, chronic central administration of RFRP-3 restores testicular activity and Kiss1 levels in the arcuate nucleus of hamsters despite persisting photoinhibitory conditions. By contrast RFRP-3 does not have a hypophysiotrophic effect. Overall, these findings demonstrate that, in the male Syrian hamster, RFRP-3 exerts a stimulatory effect on the reproductive axis, most likely via hypothalamic targets. This places RFRP-3 in a decisive position between the melatonergic message and Kiss1 seasonal regulation. Additionally, our data suggest for the first time that the function of this peptide depends on the species and the physiological status of the animal model.

Tryptophan hydroxylase is modulated by L-type calcium channels in the rat pineal gland

Calcium is an important second messenger in the rat pineal gland, as well as cAMP. They both contribute to melatonin synthesis mediated by the three main enzymes of the melatonin synthesis pathway: tryptophan hydroxylase, arylalkylamine N-acetyltransferase and hydroxyindole-O-methyltransferase. The cytosolic calcium is elevated in pinealocytes following alpha(1)-adrenergic stimulation, through IP(3)-and membrane calcium channels activation. Nifedipine, an L-type calcium channel blocker, reduces melatonin synthesis in rat pineal glands in vitro. With the purpose of investigating the mechanisms involved in melatonin synthesis regulation by the L-type calcium channel, we studied the effects of nifedipine on noradrenergic stimulated cultured rat pineal glands. Tryptophan hydroxylase, arylalkylamine N-acetyltransferase and hydroxyindole-O-methyltransferase activities were quantified by radiometric assays and 5-hydroxytryptophan, serotonin, N-acetylserotonin and melatonin contents were quantified by HPLC with electrochemical detection. The data showed that calcium influx blockaded by nifedipine caused a decrease in tryptophan hydroxylase activity, but did not change either arylalkylamine N-acetyltransferase or hydroxyindole-O-methyltransferase activities. Moreover, there was a reduction of 5-hydroxytryptophan, serotonin, N-acetylserotonin and melatonin intracellular content, as well as a reduction of serotonin and melatonin secretion. Thus, it seems that the calcium influx through L-type high voltage-activated calcium channels is essential for the full activation of tryptophan hydroxylase leading to melatonin synthesis in the pineal gland.

Effect of delta-sleep inducing peptide-containing preparation Deltaran on biomarkers of aging, life span and spontaneous tumor incidence in female SHR mice

From the age of 3 months until their natural deaths, female Swiss-derived SHR mice were subcutaneously injected 5 consecutive days every month with 0.1 ml of normal saline (control) or with 2.5 microg/mouse (approximately 100 microg/kg) of delta-sleep inducing peptide (DSIP, Trp-Ala-Gly-Gly-Asp-Ala-Ser-Gly-Glu) as the preparation Deltaran solved in 0.1 ml of saline. There were 54 mice in each group. The results of this study show that the treatment with Deltaran did not influence food consumption, but decreased the body weight of mice; it slowed down the age-related switching-off of estrous function; it decreased by 22.6% the frequency of chromosome aberrations in bone marrow cells; it did not influence mean life span; and it increased by 17.1% life span of the last 10% of the survivors and by 24.1% maximum life span in comparison with the control group. We also found that treatment with Deltaran significantly decreased total spontaneous tumor incidence (by 2.6-fold), mainly mammary carcinomas and leukemias in mice as compared with the control group. This is the first report on geroprotector and anticarcinogenic effect of DSIP-containing preparation Deltaran.

Neuropeptide Y inhibits spontaneous alpha-melanocyte-stimulating hormone (alpha-MSH) release via a Y(5) receptor and suppresses thyrotropin-releasing hormone-induced alpha-MSH secretion via a Y(1) receptor in frog melanotrope cells

In amphibians, the secretion of alpha-MSH by melanotrope cells is stimulated by TRH and inhibited by NPY. We have previously shown that NPY abrogates the stimulatory effect of TRH on alpha-MSH secretion. The aim of the present study was to characterize the receptor subtypes mediating the action of NPY and to investigate the intracellular mechanisms involved in the inhibitory effect of NPY on basal and TRH-induced alpha-MSH secretion. Y(1) and Y(5) receptor mRNAs were detected by RT-PCR and visualized by in situ hybridization histochemistry in the intermediate lobe of the pituitary. Various NPY analogs inhibited in a dose-dependent manner the spontaneous secretion of alpha-MSH from perifused frog neurointermediate lobes with the following order of potency porcine peptide YY (pPYY) > frog NPY (fNPY) > porcine NPY (pNPY)-2-36) > pNPY-(13-36) > [D-Trp(32)]pNPY > [Leu(31),Pro(34)]pNPY. The stimulatory effect of TRH (10(-8)6 M) on alpha-MSH release was inhibited by fNPY, pPYY, and [Leu(31),Pro(34)]pNPY, but not by pNPY-(13-36) and [D-Trp(32)]pNPY. These data indicate that the inhibitory effect of fNPY on spontaneous alpha-MSH release is preferentially mediated through Y(5) receptors, whereas the suppression of TRH-induced alpha-MSH secretion by fNPY probably involves Y(1) receptors. Pretreatment of neurointermediate lobes with pertussis toxin (PTX; 1 microg/ml; 12 h) did not abolish the inhibitory effect of fNPY on cAMP formation and spontaneous alpha-MSH release, but restored the stimulatory effect of TRH on alpha-MSH secretion, indicating that the adenylyl cyclase pathway is not involved in the action of fNPY on TRH-evoked alpha-MSH secretion. In the majority of melanotrope cells, TRH induces a sustained and biphasic increase in cytosolic Ca(2+) concentration. Preincubation of cultured cells with fNPY (10(-7) M) or omega-conotoxin GVIA (10(-7) M) suppressed the plateau phase of the Ca(2+) response induced by TRH. However, although fNPY abrogated TRH-evoked alpha-MSH secretion, omega-conotoxin did not, showing dissociation between the cytosolic Ca(2+) concentration increase and the secretory response. Collectively, these data indicate that in frog melanotrope cells NPY inhibits spontaneous alpha-MSH release and cAMP formation through activation of a Y(5) receptor coupled to PTX- insensitive G protein, whereas NPY suppresses the stimulatory effect of TRH on alpha-MSH secretion through a Y(1) receptor coupled to a PTX-sensitive G protein-coupled receptor.