Biomedical subjects

J Vriend

Publications and source records attributed to J Vriend.

At least 19 recordsLinked to original sources

PubMed2006

Melatonin: effects on dopaminergic and serotonergic neurons of the caudate nucleus of the striatum of male Syrian hamsters.

The effects of daily late afternoon administration of the indoleamine, melatonin, on the in situ activity of tyrosine hydroxylase (TH) and tryptophan hydroxylase (TPH) were examined in the caudate nuclei of the striatum of male Syrian hamsters. TH and TPH activities were determined in tissue extracts by measuring the accumulation of L-Dopa and 5-HTP respectively, following the administration of the aromatic L-amino acid decarboxylase inhibitor, NSD-1015. Animals were sacrificed at 4 time points over the 24 light/dark cycle after 9.5 weeks of melatonin treatment. TH activity was significantly increased by melatonin during the early part of the dark phase of the light/dark cycle. While no significant effects of melatonin on TPH was observed, melatonin significantly increased 5-HT concentrations, suggesting a melatonin-induced inhibition of 5-HT release. The data suggest that the striatum may be a region in which dopaminergic neurons are subject to significant regulation by melatonin, either directly or through serotonergic neurons which synapse on dopaminergic neurons in the striatum.

5-Hydroxytryptophan↗

PubMed2005

Effects of haloperidol and melatonin on the in situ activity of nigrostriatal tyrosine hydroxylase in male Syrian hamsters.

Haloperidol, an antipsychotic drug, was tested for its effects on the in situ activity of nigrostriatal and hypothalamic tyrosine hydroxylase, in control male Syrian hamsters and in those receiving a high daily dose of melatonin. After receiving daily ip injections (1.25 mg/kg ip) of haloperidol for 21 days, the animals were sacrificed and brain tissue collected for analysis of dopamine and metabolites by HPLC with electrochemical detection. In situ activity of tyrosine hydroyxlase (TH) activity was determined by measuring the accumulation of L-Dopa after administration of the L amino acid decarboxylase inhibitor, mhydroxybenzylhydrazine. Tissue content of dopamine and its metabolites, DOPAC and HVA, was depressed in striatum of animals receiving haloperidol, and tyrosine hydroxylase (TH) activity was significantly decreased 20-24 h after the last injection (from 1823 +/- 63 to 1139 +/- 85 pg l-dopa/mg tissue). The decrease in TH activity in striatum was significantly inhibited by daily injections of a high dose of melatonin (2.5 mg/kg ip) (from 1139 +/- 85 to 1560 +/- 116 pg L-dopa/mg tissue). In the substantia nigra and in the hypothalamus, on the other hand, haloperidol significantly increased the activity of tyrosine hydroxylase. Melatonin administration did not significantly influence TH activity in the substantia nigra, but inhibited TH activity in the hypothalamus and in the pontine brainstem. One explanation for these data is that chronic haloperidol administration in Syrian hamsters increases TH activity in hypothalamus and substantia nigra, but decreases TH activity in striatum by a mechanism involving D2 presynaptic receptors and a melatonin sensitive kinase which regulates TH phosphorylation.

Animals↗

PubMed1997

Lamotrigine inhibits the in situ activity of tyrosine hydroxylase in striatum of audiogenic seizure-prone and audiogenic seizure-resistant Balb/c mice.

Lamotrigine (LTG), an anticonvulsive drug, was tested for its effects on striatal content of DA and its metabolites, DOPAC and HVA, in audiogenic seizure-resistant (ER) and audiogenic seizure-prone (EP) lines of Balb/c mice. A single dose of LTG (20 mg/kg) prevented audiogenic seizures in seizure-prone mice, while reducing substantially the striatal content of the DA metabolite, DOPAC (to less than 50% of saline-injected controls) in both seizure-resistant and seizure-prone mice. LTG administration also resulted in significant reduction of striatal content of HVA. The in situ activity of tyrosine hydroxylase (TH) in extracts of striatum was significantly reduced by LTG administration in both ER and EP mice. These data show that DA synthesis in the striatum of mice is substantially reduced by LTG administration.

3,4-Dihydroxyphenylacetic Acid↗

PubMed1996

Melatonin increases the in situ activity of tyrosine hydroxylase in the mediobasal hypothalamus of male Syrian hamsters.

The effects of daily late afternoon injections of melatonin on the in situ activity of tyrosine hydroxylase (TH) were examined in the median eminence/arcuate region of the mediobasal hypothalamus (MBH) and the neurointermediate lobe (NIL) of the male Syrian hamster. TH activity was determined in tissue extracts by measuring the accumulation of L-DOPA following administration of the dopa decarboxylase inhibitor, NSD-1015. After 9 weeks of melatonin treatment, highly significant increases in the activity of MBH TH were demonstrated over a 24 hr period, compared to saline-treated controls. Melatonin-induced elevations in TH occurred concomitantly with decreases in tuberoinfundibular dopamine (TIDA) and tuberohypophyseal dopamine (THDA) concentrations. Similar findings were observed in castrated hamsters, indicating that the melatonin-induced increase in TH was not secondary to melatonin-induced changes in circulating levels of gonadal hormones. These data led to the interpretation that melatonin treatment elevated TIDA synthesis either through a direct action on the arcuate nuclei or on neurons impinging on these nuclei.

Animals↗

PubMed1996

Neurochemical effects of static magnetic field exposure.

BACKGROUND: There has been considerable interest in both the lay and scientific media concerning the putative effects of exposure to electromagnetic fields. An assessment of the effects of static magnet exposure on neurochemistry was undertaken to determine potential risks to patients and staff involved with magnetic resonance imaging and spectroscopy. METHODS: One set of rats were exposed to weak static field (800 gauss [G]) in an otherwise normal laboratory surrounding. Another set of rats were exposed to 7-Tesla fields, both with suitable controls. RESULTS: Exposure of rats (n=8) to weak static fields for periods between 12 hours and 8 days produced no significant change in nighttime pineal or serum melatonin levels, as compared to controls, nor did it significantly influence levels of pontine medullary 5-hydroxytryptamine [5-HT] and hypothalamic 5-hydroxyindoleacetic acid [5-HIAA]. Placing rats in a 7-Tesla MRI magnet for 45 minutes produced similar results. CONCLUSIONS: These experiments suggest that daily light/dark cycle has much greater influence on levels of melatonin, catecholamines, serotonin, or their metabolites than does exposure to a static magnetic field.

Animals↗

PubMed1993

Determination of amino acids and monoamine neurotransmitters in caudate nucleus of seizure-resistant and seizure-prone BALB/c mice.

Amino acid and monoamine concentrations were examined in tissue extracts of caudate nucleus of genetic substrains of BALB/c mice susceptible or resistant to audiogenic seizures. Amino acids [aspartate, glutamate, glycine, taurine, serine, gamma-aminobutyric acid (GABA)], monoamines, and related metabolites were separated by isocratic reverse-phase chromatography and detected by a coulometric electrode array system. In situ activity of tyrosine hydroxylase and tryptophan hydroxylase were determined by measuring the accumulation of L-DOPA and 5-hydroxytryptophan after administration of the decarboxylase inhibitor NSD-1015. Highly significant decreases in concentrations of both excitatory (glutamate and aspartate) and inhibitory amino acids (GABA and taurine) were observed in extracts of caudate nucleus of seizure-prone mice. Substantial decreases in concentrations of dopamine (DA) and its metabolites, 3,4-dihydroxyphenylacetic acid and homovanillic acid, were also noted. Decreased accumulation of L-DOPA after NSD-1015 administration provided evidence for decreased tyrosine hydroxylase activity and decreased DA synthesis in striatum of seizure-prone mice compared with seizure-resistant mice. Decreased concentrations of the DA metabolite 3-methoxytyramine (after NSD-1015 administration) suggested that DA release was also compromised in seizure-prone mice. No significant difference in 5-hydroxytryptophan accumulation in striatum of seizure-prone and seizure-resistant mice suggested that tryptophan hydroxylase activity and serotonin synthesis were not affected. The data suggest that seizure-prone BALB/c mice have a deficiency in intracellular content of both excitatory and inhibitory amino acids. The data also raise the issue of whether GABAergic interactions with the nigrostriatal DA system are important in the regulation of audiogenic seizure susceptibility.

3,4-Dihydroxyphenylacetic Acid↗

PubMed1992

Changes in hippocampal monoamine concentration following halothane anesthesia and concussion.

The concentration of norepinephrine in the hippocampus of rats anesthetized with halothane (Wyeth-Ayerst, Philadelphia, Pa) is found to be markedly increased, presumably due to the stress of handling and administering the anesthetic. This increased norepinephrine concentration persists for about 50 minutes but is obliterated when the anesthetized rat is concussed. This 50-minute period corresponds to the time it takes for a rat (or human), comatose for 1-2 seconds following concussion, to regain normal memory. No changes in 3,4-dihydroxybenzene-acetic acid (DOPAC), 3-(3,4-dihydroxyphenyl) alanine (L-DOPA), and 3,4-dihydroxybenzylamine (DHBA) were noted. 5-Hydroxy indole acetic acid (HIAA) showed a depression at 5 minutes and again at 30 minutes, changes that were consistent but not considered statistically significant.

Anesthesia, Inhalation↗

PubMed1991

Effects of daily afternoon melatonin administration on monoamine accumulation in median eminence and striatum of ovariectomized hamsters receiving pargyline.

The effects of daily afternoon melatonin injections on the accumulation of monoamines were studied in extracts of median eminence, and of caudate nucleus, of intact and ovariectomized Syrian hamsters which were administered pargyline 2 h prior to sacrifice. Although no significant effect of melatonin administration on the serotonin (5HT) accumulation after pargyline could be detected, significantly increased amounts of 5HT and of the 5HT metabolite, 5-hydroxyindole acetic acid, were detected in median eminence and in caudate nucleus of melatonin-injected hamsters not treated with pargyline. In both median eminence and in posterior pituitary, dopamine (DA) concentrations were significantly reduced by melatonin administration. In the median eminence of intact hamsters, the accumulation of DA after pargyline was reduced to 22% of controls by melatonin injections; in ovariectomized hamsters, the accumulation of DA was reduced to 9% of controls by melatonin injections. The accumulation of norepinephrine after pargyline was significantly reduced by melatonin administration only in ovariectomized hamsters. No significant inhibitory effects of melatonin injections could be detected on DA accumulation in caudate nucleus. These data suggest that melatonin injections result in substantial inhibition of daytime DA synthesis in median eminence independently of its effects on gonadal steroids. Paradoxically, melatonin-induced inhibition of median eminence DA activity occurred concomitantly with suppression of pituitary and plasma prolactin (PRL). We conclude that daily afternoon melatonin injections inhibit PRL secretion and interfere with cycles of LH in spite of decreased DA activity in the median eminence.

Animals↗

PubMed1990

Melatonin increases serum growth hormone and insulin-like growth factor I (IGF-I) levels in male Syrian hamsters via hypothalamic neurotransmitters.

In male Syrian hamsters daily evening melatonin injections resulted in increased circulating levels of growth hormone (GH), as well as a modest increase in body weight. A substantial increase in serum levels of insulin-like growth factor I (IGF-I) was observed in all hamsters receiving evening injections of melatonin for 10 weeks. The melatonin-induced increase in serum IGF-I levels was interpreted as a result of increased release of GH during the 10 week period of melatonin administration. The increase in serum GH and IGF-I was associated with significantly decreased hypothalamic turnover of norepinephrine (NE). Since blocking NE synthesis with alpha methyl-p-tyrosine reduced serum GH, the melatonin-induced increase in GH could not readily be attributed to decreased NE turnover. Highly significant increases in 5-hydroxyindole acetic acid (5HIAA) concentrations and in ratios of 5HIAA to serotonin (5HT) were noted in extracts of hypothalamus and in extracts of brain stem, suggesting a serotonergic component to melatonin-induced increase in GH-induced IGF secretion and subsequent growth.

Animals↗

PubMed1989

Modification of the indolamine content in neuroblastoma x glioma hybrid NG108-15 cells upon induced differentiation.

1. The neuroblastoma x glioma hybrid NG108-15 cell line has been widely studied as a neuronal model for its serotonergic, cholinergic, and peptidergic properties. 2. The catecholamine and serotonin content and that of their major metabolites have been determined by high-performance liquid chromatography with electrochemical detection (HPLC-EC) in NG108-15 cells under differentiated and undifferentiated conditions. 3. Cellular contents of L-DOPA, norepinephrine, (NE), L-epinephrine (EPI), and dopamine (DA) in differentiated cells, induced by 1 mM dibutyryl cyclic AMP (dBcAMP), are 149, 40, 129, and 124%, respectively, higher than those in undifferentiated cells. 4. 3,4-Dihydroxyphenethylacetic acid (DOPAC), the major metabolite of DA, is detectable only in differentiated cells. Similarly, DOPAC is present only in culture medium from differentiated cells, and not that of undifferentiated cells. 5. Serotonin (5-HT) is detectable only in undifferentiated cells; and the level of 5-hydroxyindoleacetic acid (5-HIAA), the major metabolite of 5-HT, is also 12.7% higher is undifferentiated cells. 6. Comparative analyses of differentiated and undifferentiated cells in monolayer cultures and undifferentiated cells cultured in the presence of 1 mM dBcAMP under suspension conditions suggest that change in the indolamine content is due to cellular changes upon morphological differentiation. 7. The clonal NG108-15 cell line is also catecholaminergic, in addition to cholinergic and serotonergic; and a shift of neurotransmitter pattern from serotonin to dopamine production occurs during morphological differentiation.

3,4-Dihydroxyphenylacetic Acid↗

PubMed1989

Melatonin reduction by lithium and albinism in quail and hamsters.

Melatonin was measured by radioimmunoassay in several genetic strains of Japanese quail. Plasma melatonin (PM), measured at the nighttime peak, was highest in wild type quail reared on a diurnal lighting schedule; this PM peak was suppressed in continuous light. Albino quail had low melatonin levels, whether reared under diurnal conditions or in continuous light. Ocular melatonin was also suppressed in albinos and in dilute mutants. At midday sampling, melatonin was only half as high in albinos as in wild types. Intraocular pressure (IOP, daytime readings) was uniformly low in diurnal birds and was elevated in all quail reared under continuous light. Thus in pigmented birds, a high melatonin level was associated with high IOP, but in albinos displaying high IOP, ocular melatonin was not elevated. Lithium chloride, mixed in the feed, brought about a pronounced reduction in plasma, pineal, and ocular melatonin, in wild-type quail reared on a diurnal schedule. This confirms earlier findings in lithium-fed rats. Golden hamsters displayed a characteristic diurnal cycle of pineal melatonin, with a sharp middark peak; in albino hamsters, also kept on a diurnal schedule, this peak occurred at the same time, but albinos had melatonin levels only about one-third as high as those of pigmented animals.

Albinism↗

PubMed1989

Effects of melatonin and hypothyroidism on somatomedin levels of female Syrian hamsters.

Female Syrian hamsters maintained on a 14 h light, 10 h dark photoperiod were injected once daily (1-2 h before lights out) with melatonin (25 micrograms), alone or in combination with thiourea, or with thiourea plus thyroxine. Serum levels of the somatomedin, Insulin-like growth factor-I (IGF-I), were significantly reduced by thiourea as well as by melatonin administration. These data suggest that in the female hamster melatonin-induced reduction of circulating IGF-I depends largely on a reduction in circulating levels of thyroid hormones. However, melatonin-induced changes in secretion of thyroid hormones, gonadal hormones, and hypothalamic hormones could contribute to decreased growth hormone (GH)-stimulated somatomedin secretion.

Animals↗

PubMed1989

Endocrine effects of blinding in male Syrian hamsters are associated with increased hypothalamic 5-hydroxyindoleacetic acid/serotonin ratios.

The antigonadal, antithyroid, and antiadrenal effects of blinding were studied in male Syrian hamsters receiving propylthiouracil (PTU) or PTU plus thyroxine (T4) replacement. Ten weeks after blinding, the expected gonadal involution and reduction of circulating levels of T4, as well as a reduction of circulating levels of corticosterone, were observed. T4 treatment significantly increased testicular weights, but it did not prevent gonadal involution. Neither PTU nor T4 administration significantly influenced the inhibition of serum corticosterone levels observed in blinded hamsters. The increase in serum thyroid-stimulating hormone (TSH) observed in hypothyroid (PTU-treated) hamsters was significantly greater in intact hamsters than in blind hamsters. Blinding was associated with a small but highly significant increase in ratios of 5-hydroxyindoleacetic acid (5HIAA) to serotonin (5HT) in extracts of the medial basal hypothalamus. Based on the assumption that 5HIAA represents primarily intraneuronal metabolism of excess 5HT, the present results are consistent with reduced 5HT release in blinded hamsters. Daily evening melatonin administration also increased the 5HIAA/5HT ratios of the mediobasal hypothalamus concurrently with gonadal involution, reduction of circulating levels of T4, and reduction of circulating levels of corticosterone. These results are consistent with the view that serotonergic neurons entering the hypothalamus are components of the photoneuroendocrine system of the hamster.

Animals↗

PubMed1988

Melatonin increases serum insulin-like growth factor-I in male Syrian hamsters.

Male Syrian hamsters maintained on a 14-h light, 10-h dark photoperiod were injected once daily (1-2 h before lights out) with melatonin (25 micrograms), once every other day with T4 (5 micrograms every other day), or melatonin every day plus T4 every other day. Hamsters which received melatonin injections, with or without T4, had serum levels of insulin-like growth factor that were increased 2-fold. The results suggest that melatonin-induced changes in body weight are a result of long-term changes in insulin-like growth factor-I secretion.

Animals↗

PubMed1987

Plasma corticosterone in chicks reared under several lighting schedules.

Plasma corticosterone was determined by radioimmunoassay in 6-7-week-old male broiler type chicks, reared under several carefully controlled lighting regimes. When subjects were grouped by photoperiod of rearing, chicks reared in darkness had significantly lower hormone levels than diurnal controls, or than subjects reared in continuous light. Around-the-clock sampling revealed a diurnal corticosterone rhythm, with high daytime levels and lower night-time levels. This rhythm appeared to be retained in constant light, although phase shifted or free running. Neither analysis by light intensity level nor by lights on/lights off status at the time of blood sampling revealed differences in plasma corticosterone between the experimental groups which could be attributed to these factors.

Animals↗

PubMed1987

The effects of melatonin and hypothyroidism on estradiol and gonadotropin levels in female Syrian hamsters.

Since melatonin injections administered near the end of the daily photoperiod influence both gonadal and thyroid hormones in the female hamster, the present study was designed to compare the effects of melatonin and hypothyroidism on the reproductive system and to determine whether thyroid status influenced the action of melatonin on the regulation of the hormones of reproduction. The effects of daily melatonin injections were determined in control hamsters, in hamsters rendered hypothyroid with thiourea, and in hypothyroid hamsters receiving thyroxin (T4) hormone replacement. As previously reported, melatonin injections disrupted estrous cyclicity, disrupted the normal pattern of gonadotropin secretion, and resulted in atrophy of the uterus and vagina. These changes coincided with depressed serum and pituitary prolactin (PRL), and depressed levels of estradiol. The effects of melatonin on uterus, vagina, ovary, and on gonadotropin levels were not prevented by T4 replacement, with the exception of a melatonin-induced increase in serum follicle-stimulating hormone (FSH). This suggested that the cessation of estrous cyclicity was not primarily a result of thyroid deficiency. Hypothyroidism, however, like melatonin, resulted in a reduced number of developing and mature follicles and corpora lutea in the ovaries, and in reduced uterine weight. It also produced follicular atresia, reduced the circulating levels of estradiol, and resulted in reduced incidence of estrus smears. T4 replacement, for 2 weeks, prevented the decline in mature follicles and corpora lutea, reduced the extent of follicular atresia, increased circulating levels of estradiol, and increased uterine weight. PRL and luteinizing hormone (LH) data also provided evidence for antagonistic effects of melatonin and T4 in female hamsters. These data raise the question whether melatonin-induced changes in circulating levels of T4 play a role in the seasonal cycles of reproductive competence in the female hamster.

Animals↗

PubMed1987

Melatonin: its antagonism of thyroxine's antisomatotrophic activity in male Syrian hamsters.

The effects of daily evening melatonin injections on serum and pituitary levels of growth hormone (GH) and follicle stimulating hormone (FSH) were investigated in male Syrian hamsters receiving thiourea in the drinking water. Melatonin injections, by themselves, had no significant effect on serum or pituitary GH. Thiourea induced hypothyroidism reduced pituitary GH content but increased serum GH several fold. Daily thyroxin (T4) injections for 3 weeks partially restored pituitary GH content and reduced circulating GH to control values. Melatonin injections prevented T4 from reducing circulating GH levels to normal in hamsters receiving thiourea. As previously reported, FSH levels in serum and pituitary were reduced by melatonin. Thiourea-induced hypothyroidism prevented this effect. Daily T4 injections increased circulating FSH levels above control levels; melatonin injections prevented this increase in serum FSH. These observations show that melatonin and T4 have antagonistic actions on GH and FSH release from the pituitary. We conclude that melatonin influences the release of hypothalamic hormones regulating GH and FSH release from the pituitary. The effects of T4 on the sensitivity to melatonin injections could be accounted for by thyroid hormone regulation of pituitary receptors for hypothalamic hormones. An alternative explanation is that T4 regulates the concentration of melatonin receptors in the central nervous system.

Animals↗

PubMed1986

Plasma melatonin rhythm lost in preglaucomatous chicks.

Domestic chicks (Gallus domesticus) reared under continuous light, and thus developing light-induced avian glaucoma (LIAG), were tested at 4-hourly intervals around the clock, for evidence of hormonal or other rhythms which might be related to the eye effects of LIAG. Plasma melatonin, corticosterone and thyroxine (T4) all displayed daily rhythms in the young chick reared under control (diurnal) lighting conditions. These daily hormone cycles were somewhat damped under either continuous light or constant darkness, though there were hints of a surviving rhythm, albeit phase-shifted or free-running, in plasma corticosterone and T4. In the eye, mitotic rate in the corneal epithelium displayed a prominent rhythm, high in the dark and low in the light. This rhythm was suppressed by constant darkness, and also in continuous light, the latter apparently related to the impaired corneal growth of LIAG. The daily pattern of corneal mitotic activity and the diurnal curve for plasma melatonin showed remarkable similarities, suggesting the possibility of a causal relationship between the two phenomena.

Animals↗