Biomedical subjects

V Lucini

Publications and source records attributed to V Lucini.

At least 37 records · Page 2Linked to original sources

PubMed1996

The melatonin receptor in the human brain: cloning experiments and distribution studies.

The adult human cerebellum expresses melatonin receptors with high density in the external zone of the molecular layer. Cloning of the receptor cDNA isolated by RT-PCR from human cerebellar specimens and sequencing analysis of the full-length coding region revealed that the receptor protein is encoded by a transcript identical to that recently cloned from the human hypothalamus (Mel1a). In situ hybridization using an antisense cRNA-probe demonstrated that the melatonin receptor mRNA is localized in the cerebellar granule cells. Mapping of the messenger by RT-PCR with Mel1a specific primers in different areas of the human brain disclosed a quite widespread distribution of the transcript, although expressed at very low levels. Semi-quantitative comparison between the different brain regions allowed to establish the following relative mRNA abundance: cerebellum > or = occipital cortex > or = parietal cortex > temporal cortex > thalamus > frontal cortex > or = hippocampus. No mRNA was detected in white blood cells.

Adult↗

PubMed1995

2-[125I]iodomelatonin binding sites in the bovine hippocampus are not sensitive to guanine nucleotides.

The discrete distribution and pharmacological characteristics of melatonin binding sites in the bovine hippocampus were determined. Autoradiography revealed the presence of melatonin binding sites in the stratum lacunosum-molecularis of the hippocampus (CA1), stratum molecularis of the subiculum and in the enthorhinal cortex. Analysis of the kinetic parameters demonstrated that the binding was stable and reversible, represented by a single class high affinity binding sites (Kd 40 pM, Bmax = 3.9 fmol/mg protein). However, 2-iodomelatonin and 2-bromomelatonin inhibited 2-[125I]iodomelatonin binding in a biphasic manner. The presence of 4 mM CaCl2 did not cause changes in the affinity constant values. Finally, experiments performed with GTP gamma S revealed that binding affinity was not decreased even with high concentrations of the nucleotide. These findings show that 2-[125I]iodomelatonin binding sites in the bovine parahippocampal-hippocampal region possess some binding features not common to melatonin receptors described so far; moreover they seem not to be linked to a regulatory G-protein.

Animals↗

PubMed1995

Characterisation of melatonin binding sites in the eye of the Japanese quail (Coturnix japonica).

Melatonin binding sites were examined in the quail eye using 2-[125]iodomelatonin. Radioreceptor assays indicated similar binding sites in membrane preparations of neural retina (NR) and choroid-retinal pigment epithelium (C-RPE) eye components. In both tissues binding of the radioligand was specific, saturable, and of high affinity [Kd values NR 50.8 +/- 19.5 pM, C-RPE 98.2 +/- 35.4 pM, mean +/- SEM (n = 4)] and low capacity (Bmax values NR 12.4 +/- 2.7 fmol/mg protein, C-RPE 21.5 +/- 3.2 fmol/mg protein). Kinetic studies demonstrated that association of 2-[125I]iodomelatonin was rapid and further that this binding was reversible upon the addition of 1 microM melatonin. The order of pharmacological potencies of various indoles tested in 2-[125I]iodomelatonin displacement studies was melatonin > 6-chloromelatonin > 6-hydroxymelatonin > N-acetylserotonin >> 5-methoxytryptophol > 5-hydroxytryptamine > 5-methoxytryptamine (5-hydroxytryptamine > 5-methoxytryptophol for C-RPE). Studies with guanine nucleotides indicated that the signal transduction mechanism of the binding site may involve a G-protein linkage. This melatonin binding site displays several pharmacological similarities with those investigated in the retina of other species and with those previously characterised in the quail brain.

Animals↗

PubMed1995

Neutral amino acid availability in two major psychiatric disorders.

1. Evidence suggests catecholamines and indoleamines may play a role in the pathogenesis of several psychiatric disorders. These neurotransmitters (i.e. dopamine, norepinephrine and serotonin) are synthesized within the human brain from their precursors, the aromatic large neutral amino acids tyrosine and tryptophan. Other large neutral amino acids, namely valine, isoleucine, leucine and phenylalanine affect precursor availability by competing with tryptophan and tyrosine for the transport system across the blood brain barrier. 2. The authors evaluated the brain availability of L-tryptophan and tyrosine in a sample of psychiatric patients with a diagnosis of major depression and schizophrenia. 3. The present results suggest a possible usefulness of Tryptophan/Large Neutral Amino Acids ratio in distinguishing major depression from schizophrenia, while Tyrosine/Large Neutral Amino Acids ratio shows a very limited usefulness. The absolute need of powerful and accurate statistical analysis to evaluate the power of a biological test clearly stands out from the present study.

Adolescent↗

PubMed1995

Twenty-four-hour melatonin and cortisol plasma levels in relation to timing of cluster headache.

The cyclic recurrence of cluster periods and the regular timing of headache occurrence in cluster headache (CH) induced us to study the circadian secretion of melatonin and cortisol in 12 patients with episodic CH, during a cluster period, and compare them with 7 age- and sex-matched healthy controls. Blood was sampled every 2 h for 24 h. All subjects were confined to a dark room from 22.00 to 08.00. Plasma melatonin levels were significantly reduced in CH patients (repeated measures ANOVA p < 0.03; mesor p < 0.02), and the cortisol mesor was significantly increased (p < 0.03). Amplitudes and acrophases did not differ between the groups. Individual cosinor analysis showed that 4/12 (33.3%) CH patients had no significant melatonin rhythm, and that 5/11 (45.5%) had no cortisol rhythm. Group analysis of cosinor revealed significantly rhythmicity of melatonin and cortisol secretion in both groups. In controls, the timing of melatonin and cortisol acrophase significantly correlated with each other, indicating that the biorhythm controllers for the secretion of these hormones were synchronized. Such correlation was not found in the CH patients; mesor, amplitude and acrophase of melatonin and cortisol did not correlate with duration of illness, duration of headache in course, or time since last headache attack.

Adult↗

PubMed1995

Distribution and characterization of the melatonin receptors in the hypothalamus and pituitary gland of three domestic ungulates.

With some exceptions, in most of the mammals the pituitary pars tuberalis and the hypothalamic suprachiasmatic nuclei are reportedly the main targets for the pineal hormone melatonin. However, it is not known if the conspicuous diversity in the distribution pattern of melatonin binding sites in these areas depicts differences in reproductive behavior observed in the seasonally breeding species in the temperate zones. We explored the distribution and the characteristics of melatonin binding sites in the hypothalamus and pituitary of three species (bovine, horse, and donkey) different in terms of seasonal reproductive competence. The topographical localization, investigated by in vitro autoradiography, revealed 2-[125I]iodomelatonin binding sites only in the pituitary gland in all three species, primarily in the pars tuberalis (PT), but also in the pars distalis (PD) and pars intermedia (PI). Kinetic, inhibition, and saturation studies, performed by means of in vitro binding, revealed presence of a single class high affinity binding sites. The Kd values, melatonin, and 2-iodomelatonin Ki values were in the low picomolar range. Coincubation with GTP gamma S inhibited 2-[125I]iodomelatonin binding, demonstrating that these putative receptors are linked to a G protein in their signal-transduction pathway. The hypothalamus was devoid of specific binding. In conclusion, the results suggest that in these species, the hypophysis may be a principal target for the melatonin action on the reproductive system.

Animals↗

PubMed1994

The density of melatonin receptors is dependent upon the prevailing photoperiod in the Japanese quail (Coturnix japonica).

Two groups of Japanese quail (Coturnix japonica) were exposed to two different photoperiods (short and long days: LD 8:16 and LD 16:8, respectively), and their brains examined for the presence and distribution of melatonin receptors by means of quantitative in vitro autoradiography. Animals belonging to the LD 8:16 group expressed a significantly higher melatonin receptor density in the optic tectum and nucleus triangularis, while the LD 16:8 animals had a higher density of receptors in the hyperstriatum and nucleus preopticus dorsalis. These data demonstrate an apparent influence of the photoperiod on the density of melatonin receptors, especially in nuclei of the tectofugal pathway, related to the control of visual pattern and intensity discrimination, localization and orientation.

Animals↗

PubMed1994

Modulation of melatonin secretion by acetyl-L-carnitine in adult and old rats.

Modification of melatonin synthesis and release by acetyl-L-carnitine (ALC) was studied in adult (2 month old) and old (24-month-old) male Sprague Dawley rats. When ALC was injected at 1500 into adult rats at doses of 10, 30, or 90 mg/kg, there was a remarkable increase in their pineal and serum melatonin 1 hr later. However, using the same experimental protocol acute ALC administration in old rats did not modify pineal and serum melatonin levels. ALC administered in the same dose range induced a significant increase in pineal and serum melatonin in adult rats treated at 0100 h following exposure of 30 min to bright, white light to suppress endogenous melatonin. In the same conditions, in old rats, only the higher dose (90 mg/kg) caused any noteworthy increase in melatonin pineal content while lower doses were uneffective both on serum and pineal melatonin levels. It is known that ALC affects fatty acid transport in the cells, modulates CoA, modifies neuronal transmission and reduces lipofuscin accumulation which is related to lipid peroxidation. The action of ALC on melatonin synthesis could be the result of a modulation of the neuronal transmission related to circadian pineal endocrine activity. Moreover, since both ALC and melatonin exert remarkable scavenger activity, it is possible to suppose that ALC effects in reversing certain aging processing may be due to its ability to promote melatonin production.

Acetylcarnitine↗

PubMed1994

Plasma tryptophan to large neutral amino acids ratio and therapeutic response to a selective serotonin uptake inhibitor.

The molar ratio of total plasma tryptophan (Trp) to the sum of the other large neutral amino acids (LNAAs), thought to reflect brain serotonin (5-HT) formation, was estimated in 47 patients with major depression (unipolar and bipolar) before and after 6 weeks of treatment with a serotonin uptake inhibitor, fluvoxamine. We found a significant difference between responders (n = 39) and nonresponders (n = 8) for the pre- and in-treatment plasma Trp to LNAAs ratios. In contrast, there were no differences between the two groups for the mean plasma steady-state fluvoxamine levels. These findings suggest that a specific plasma amino acid profile may be a useful indicator of good clinical response to a selective 5-HT uptake inhibitor.

Adult↗

PubMed1994

A carnivore species (Canis familiaris) expresses circadian melatonin rhythm in the peripheral blood and melatonin receptors in the brain.

Dogs kept under controlled photoperiodic conditions of 12 h light and 12 h dark expressed a clear diurnal melatonin rhythm in the peripheral blood, with a swift peak restricted to the late part of the scotophase. The highest density of high-affinity, G-protein-linked 2-[125I]iodomelatonin binding sites was found in the pars tuberalis of the pituitary gland. Binding sites were found also in the pars distalis, and light microscopy/high-resolution autoradiography showed that binding was located exclusively over the chromophobe and basophilic cells forming the adenopituitary zona tuberalis, well developed in this species, and extending into the gland as a continuation of pars tuberalis. Cords of basophilic cells located in the pars distalis proper also expressed high receptor density. The eosinophils in the adenohypophysis and the neural lobe were devoid of binding. Heavily labeled were the external laminar and the mitral cell layers of the olfactory bulbs, but no binding was detected in the filae nervi olfactorii or tractus olfactorius. The hypothalamic suprachiasmatic nuclei were discernible clearly. Quantitative autoradiography inhibition experiments revealed that the apparent melatonin inhibitory constant (IC50) in all those areas was around 0.1 nmol/l, which is a physiologically appropriate value considering the peripheral blood melatonin levels. Co-incubation with guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S) led to a consequential decrease in the binding density. The specific binding observed in other areas (hippocampus, frontal, parietal, occipital cortex and cerebellum) was rather weak, diffuse and could not be attributed to a particular layer; the apparent IC50 for melatonin was about 1 mumol/l, and co-incubation with GTP gamma S did not modify the binding density. Collectively, these data show that the dog possess all the prerequisites for an efficient network adapted to photoperiodic time measurements. A circadian melatonin signal in the peripheral blood and an apparently functional readout receptor system located in key positions within the brain are both present in this species.

Animals↗

PubMed1993

2-Substituted 5-methoxy-N-acyltryptamines: synthesis, binding affinity for the melatonin receptor, and evaluation of the biological activity.

A series of 2-substituted 5-methoxy-N-acyltryptamines was synthesized and their affinity for the melatonin receptor, isolated from whole quail brains, was tested in a succession of in vitro ligand-receptor binding experiments, using 2-[125I]iodomelatonin as a labeled ligand. Optimization of the C2 substituent and the N-acyl group resulted in compounds having picomolar affinity for the receptor (vs nanomolar affinity for melatonin). In two tests for evaluation of the biological activity (effects on the spontaneous firing activity of single neurons in the rabbit parietal cortex in situ, and the Syrian hamster gonadal regression model in vivo) most of the analogs behaved as agonists. Isopropyl substitution at C2 alone, or concomitantly with cyclopropyl substitution at the N-acyl position, resulted in much lower affinity and weaker biological effect, or lack of activity in the latter case. Of interest are the compounds 4d (R = phenyl, R1 = CH3) and 4g (R = phenyl, R1 = cyclopropyl), which expressed high affinity for the receptor and apparent antagonistic activity under the conditions of the experimental models employed, though the analog 4g (R = phenyl, (R1 = cyclopropyl) seemingly was a weak antagonist and in situ expressed mixed activity in the higher concentration range. Cyclopropyl substitution at the N-acyl position inevitably resulted in lower affinity for the receptor and weaker biological activity. These data demonstrate that the N-acetyl group is important for both affinity and agonist biological activity. The substituents at C2 are crucial for the affinity of the compound for the receptor and can be utilized to create putative high-affinity agonists or antagonists.

Animals↗

PubMed1993

Identification and functional significance of nicotinic cholinergic receptors in the rat pineal gland.

The existence and subunit identification of the nicotinic cholinergic receptors in the rat pineal gland were examined by autoradiography, using [3H]cytisine and [125I]alpha-bungarotoxin as labelled ligands. The experiments performed with radioactive cytisine did not reveal specific binding, while iodinated alpha-bungarotoxin disclosed moderate specific binding density, suggesting that the nicotinic cholinergic receptor in the rat pineal is structurally organized with the alpha 7 or alpha 8 subunits present, the only ones that bind alpha-bungarotoxin with high affinity. In vitro functional experiments using pineal explants demonstrated that the binding site may represent a readily accessible nicotinic cholinergic receptor. Nicotine, though having no effect per se on the synthesis and release of melatonin, significantly diminished, in a dose-dependent manner, the norepinephrine-stimulated melatonin accumulation. This effect could be blocked by coincubation with the cholinergic antagonist d-tubocurarine, suggesting that the nicotinic cholinergic receptor in the rat pineal could be involved in the functional regulation of the gland.

Alkaloids↗

PubMed1993

Distribution and characterization of melatonin receptors in the brain of the Japanese quail, Coturnix japonica.

2-[125I]iodomelatonin was used to study the distribution and properties of the melatonin receptor in the Japanese quail brain. High receptor density was detected in the major targets of direct retinal input (optic tectum, nucleus of the optic basal rout, ventrolateral geniculate nucleus), as well as areas representing terminals in the visual pathways (nucleus rotundus, ectostriatum, thalamo-hyperstriatal pathway). Binding was also found in the piriform cortex, the hypophyseal pars tuberalis, the oculomotorius nucleus and the associated Edinger-Westphal nucleus, and in the nuclei of the third, fourth and sixth cranial nerves. A comparison of the receptor pharmacological profile to that of the mammalian brain demonstrated pharmacological identity of the two binding sites. In the saturation experiments, GPT gamma S decreased the binding affinity, numerical Kd values increasing from approximately 35 pM to approximately 150 pM.

Animals↗

PubMed1993

Serine and glycine metabolism in schizophrenic patients.

1. The brain glycine is almost exclusively derived from serine via serine-hydroxymethyltransferase. 17 males schizophrenic inpatients and 10 males healthy volunteers were submitted to the serine tolerance test. 2. Plasma serine and glycine concentration were evaluated before and after 1, 2, 3, 4 hours of an oral load with L-serine to test the interconversion between the two amino acids. 3. The authors did not find any significant difference between schizophrenic patients and control group and concluded that the enzyme serine-hydroxymethyltransferase is not deficient in the conversion of serine to glycine in schizophrenic patients as suggested by other authors.

Adult↗

PubMed1993

Autoradiographic localization of putative melatonin receptors in the brains of two Old World primates: Cercopithecus aethiops and Papio ursinus.

The distribution of putative melatonin receptors in the brains of two Old World primates of the superfamily Catarrhina, Cercopithecus aethiops and Papio ursinus, was characterized using 2-[125I]iodomelatonin autoradiography. The specific binding demonstrated a discrete distribution pattern. The median eminence was intensely labelled, and examination at the light microscopic level demonstrated that the binding was confined to the small layer of cells comprising the pars tuberalis of the pituitary gland. The collar of pars distalis, present in the baboon (Papio ursinus), was diffusely labelled. No binding was detected in the pars distalis proper or the neural lobe of the pituitary gland. The binding in the suprachiasmatic nuclei was weaker, but well discernible. Diffuse faint specific binding was found in the frontal cortex and the dentate gyrus of the hippocampus. Two non-neural sites expressed strong, well-delineated binding: the walls of some brain blood vessels (the vertebral and spinal arteries, the inferior cerebellar and acoustic arteries, the basilar, pericallosal, internal carotid arteries, the arteries forming the circle of Willis) and the choroid plexuses. Binding in the arteries of the circle of Willis, the pars tuberalis and the suprachiasmatic nuclei was readily displaceable. Addition of 1 microM unlabelled 2-iodomelatonin following 45 min of preincubation with the radioactive ligand completely abrogated the binding. Co-incubation with guanosine 5'-O-(3-thiotriphosphate) led to a significant decrease in the apparent binding density in the pars tuberalis and abolished binding in the suprachiasmatic nuclei, but was without effect on the binding in the walls of the adjacent arteries, forming the circle of Willis, in the cortex and in the hippocampus. This qualitative distribution pattern demonstrates that in the two primate species studied, melatonin high-affinity, G-protein-linked binding sites are present in the pars tuberalis and the hypothalamic suprachiasmatic nuclei, and that melatonin may be acting as a synchronizer of the endogenous pacemakers' circadian activity, apart from its possible reproductive effects at the level of pars tuberalis, where the highest receptor density was observed. The strongly labelled arterial walls, and the flimsy labelled cortex and hippocampus, expressed different characteristics: though the binding was readily reversible, it was apparently not regulated by a guanine nucleotide-binding protein.

Animals↗

PubMed1992

2-Bromomelatonin: synthesis and characterization of a potent melatonin agonist.

A practical synthesis of N-[2-(2-bromo-5-methoxy-1H-indol-3-yl)ethyl]- acetamide (2-bromomelatonin) was achieved by direct bromination of melatonin with N-bromosuccinimide (NBS) in anhydrous acetic acid at room temperature under nitrogen, followed by flash-chromatography. 1H-NMR and mass spectra showed the bromine to be incorporated at the C-2 position of the indole moiety. Tests performed in vitro with isolated melatonin receptors from rabbit parietal cortex demonstrated that the relative binding affinity of 2-bromomelatonin was about ten times higher than that of melatonin and close to that of 2-iodomelatonin. 2-Bromomelatonin behaved as a potent agonist in the physiological studies. It showed enhanced activity in inhibiting the spontaneous firing activity of cortical neurons and similarly to melatonin and 2-iodomelatonin potentiated significantly the inhibitory effect of GABA. 2-Bromomelatonin was also an extremely effective agonist in the tests performed in vivo in the Syrian hamster gonadal regression model.

Animals↗

PubMed1992

Plasma tryptophan levels and plasma tryptophan/neutral amino acids ratio in patients with mood disorder, patients with obsessive-compulsive disorder, and normal subjects.

Fasting plasma tryptophan (TRP) levels and ratios of total plasma tryptophan to the sum of five large neutral amino acids (LNAAs)--tyrosine, phenylalanine, leucine, isoleucine, and valine--that compete with tryptophan for passage across the blood-brain barrier were found to be significantly lower in a group of 28 patients with major depression compared with 29 normal subjects and 21 patients with obsessive-compulsive disorder (OCD). The OCD group was divided in two subgroups: patients with OCD alone and patients with a co-diagnosis of major depression. Since it has been considered that these biological parameters reflect brain tryptophan and serotonin levels, our results suggest their importance in relation to the presence or absence of depressive symptoms. The values of the other LNAAs and their sum did not differ significantly among the groups.

Adolescent↗

PubMed1992

Regulation of the androgen receptors in the harderian gland of the male Syrian hamster: influence of photoperiod, castration, and chronic melatonin treatment.

Male Syrian hamsters that were exposed for 8 weeks to short photoperiod (LD 10:14) or treated with melatonin in the late afternoon under long photoperiod conditions (LD 14:10) had a significantly higher content of androgen receptors in the Lipidex-purified soluble fractions isolated from the Harderian glands as compared to the long photoperiod (LD 14:10) exposed controls. Simultaneous computer-assisted analyses of all series of saturation and competition experiments revealed that the numerical value of the apparent Kd, as determined by using the synthetic androgen R-1881 (methyltrienolone), was not different between the experimental groups, and ranged from 0.050 to 0.067 nM. Of the principal natural androgens, testosterone (T) was most potent in inhibiting methyltrienolone binding to the receptor (Ki values from 0.33 to 0.55 nM), and 5 alpha-dihydrotestosterone (DHT) and delta 4-androstenedione (AD) were less effective (Ki values between 1 and 1.9 nM). In the hypothalami and pituitaries of the same animals, used in parallel control assays, DHT was twice as potent as T. Short-term castration (24 hr post-orchidectomy) did not result in significant changes in the receptor binding characteristics. Following 8 weeks exposure to a long photoperiod (LD 14:10) the Bmax values demonstrated a four-fold increase in castrated animals (179 fmoles/mg protein vs. 47 fmoles/mg protein) over intact controls. The relative binding affinity of the major androgens under these conditions remained unchanged, with the exception of AD, where a five-fold increase in the numerical Ki values (decrease in the binding affinity) was recorded (Ki = 9.6 nM).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗