Biomedical subjects

B Stankov

Publications and source records attributed to B Stankov.

At least 19 recordsLinked to original sources

PubMed2001

Sexual differences and effect of photoperiod on melatonin receptor in avian brain.

Several data suggest that melatonin may influence avian reproduction by acting at the level of the hypothalamic-hypophisial-gonadal axis, and/or on neural circuits controlling reproductive behaviours. The action of melatonin is exerted through specific receptors whose distribution and pharmacological properties have been extensively investigated. This review will focus on the distribution, sexual dimorphism, and dependence upon the photoperiod of melatonin binding sites in avian species with a special emphasis on Japanese quail. Melatonin receptors are widely distributed in avian brain. They are mostly present in the visual pathways of all the investigated species and in the song controlling nuclei of oscine birds. Sexual dimorphism of melatonin binding sites (higher density in males than in females) was detected in some telencephalic nuclei of songbirds, in the visual pathways, and in the preoptic area of quail. The last region plays a key role in the activation of male quail copulatory behaviour and it hosts a large population of gonadotropin-releasing hormone-containing neurons. Sexual dimorphism of melatonin-binding sites in the above-mentioned regions suggests a differential role for this hormone in the modulation of visual perception, gonadotropin production, and seasonally activated behaviours in male and female quail. Further studies are necessary to understand interrelationships among photic cues, gonadal steroids, density, and sexually dimorphic distribution of melatonin receptors.

Animals↗

PubMed1998

Neuroendocrine, immunohistochemical, and ultrastructural study of pineal region tumors.

Thirteen patients with tumors in the pineal region were submitted to pre- and post-operative blood sampling (08:00, 14:00, 20:00, and 02:00 hr) for three or four consecutive days. A single cerebrospinal fluid (CSF) sample was collected at surgery, and melatonin levels determined. In all patients, serum and CSF beta subunit of human chorionic gonadotrophin (betaHCG), carcino embryonic antigen (CEA), and alpha-fetoprotein (AFP) levels were measured. Histology revealed four pineocytomas, one pineoblastoma, four germinomas, one immature teratoma, one pilocytic astrocytoma, one lymphoma, and one meningioma. Serum and CSF levels of serological biomarkers were normal, except for one of the germinoma cases. In most patients, alteration either in the circadian rhythm or in the melatonin concentration was observed before surgery. In benign neoplasms the circadian rhythm was conserved. In pineoblastoma, lymphoma, and three out of four germinomas, melatonin concentrations were undetectable. In one case of germinoma, melatonin levels were high, with the circadian rhythm being abolished. According to conventional histology, all germinomas were similar. Therefore, in a rare case of pineal germinoma with high melatonin levels, the tissue was subjected to an in depth investigation (immunohistochemical and ultrastructural) in order to determine the pathology and the possible differences from the other typical germinomas. Results were compared to those provided from other pineal neoplasms. Electron microscopy examination detected the presence of clusters of intermediate filaments and numerous electrondense granules only in the case of a germinoma producing melatonin.

Adult↗

PubMed1996

Expression of the melatonin receptor in Xenopus laevis: a comparative study between protein and mRNA distribution.

Reverse transcription-polymerase chain reaction (RT-PCR) analysis performed on total RNA from different tissues of Xenopus laevis showed that the melatonin receptor gene cloned from dermal melanophores is expressed in the whole brain, skin, and retina, and that apart from the ovary, there is no expression in tissues having origin outside the central nervous system. Comparative studies using in vitro autoradiography and in situ hybridization demonstrated that the melatonin receptor is expressed with discrete allocation in Xenopus brain. Though the distribution pattern of the specific messenger RNA conforms well with that of the corresponding receptor protein, it is not always coincident.

Animals↗

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

Triazolam and melatonin effects on cardiac autonomic function during sleep.

After benzodiazepine (BDZ) administration, a decrease in cardiac vagal tone has been described during wakefulness, but data on cardiac autonomic function during sleep are lacking. Melatonin (MLT), reported to have hypnotic properties, caused an increase in vagal tone in animals. The aim of this study was to evaluate heart rate (HR) variability during sleep after a single bedtime dose of triazolam (TRI, 0.125 mg) and MLT (100 mg) in six healthy young subjects. We evaluated tonic (vagal activity) HR modifications in relation to sleep as well as phasic (sympathetic activity) HR modifications in relation to spontaneous body movements during rapid-eye-movement (REM) and non-REM (NREM) sleep. No significant change in sympathetic activity was observed after TRI and MLT in comparison with placebo, whereas TRI caused a significant decrease in vagal tone during sleep. Our nocturnal study seems to confirm previous diurnal findings about a decrease in vagal tone by BDZs.

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

Melatonin and delayed sleep phase syndrome: ambulatory polygraphic evaluation.

The present study objectively evaluated the efficacy of oral 5 mg day-1 melatonin in advancing the sleep-wake rhythm in patients with delayed sleep phase syndrome (DSPS). Six patients underwent ambulatory sleep monitoring for 72 h before and 48 h after 1 month of melatonin treatment. In each patient melatonin was administered on the basis of his own estimated dim light melatonin onset (DLMO) delay. Mean advances in sleep onset time of 115 min and in final awakening hour of 106 min were found after treatment, with no significant changes in sleep architecture parameters. Our study objectively confirms previous data obtained by a sleep-wake subjective diary on the efficacy of melatonin DSPS.

Adolescent↗

PubMed1994

The adult human cerebellum is a target of the neuroendocrine system involved in the circadian timing.

In an investigation aimed at comprehensive mapping of the adult human brain with respect to receptor sites for the pineal hormone melatonin, we consistently observed specific binding in the cerebellum. Autoradiography and in vitro binding analysis with 125I-labeled melatonin were used to examine the location and the properties of these binding sites. In all cerebellar lobes, highest-density specific binding was localized to the external zone of the molecular layer. The binding was rapid, saturable, displaceable, specific and of high affinity. Physiological concentrations of NaCl decreased the affinity, while presence of calcium ions promoted it. The non-hydrolyzable GTP analog, GTP gamma S, inhibited binding in a dose-dependent manner and provoked a shift towards low affinity. The results strongly suggest that these binding sites may be functional melatonin receptors, and indicate that the adult human cerebellum is a target of melatonin, the pineal hormone involved in the control of the circadian timing.

Adult↗

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

Jackson-Weiss syndrome registered in four successive generations. The facies of Crouzon's syndrome with foot abnormalities.

A family with 15 individuals in four successive generations affected by Jackson-Weiss syndrome, craniosynostosis with Crouzon-variant-like phenotype and feet's abnormalities, is presented. An autosomal dominant inheritance pattern with complete penetrance, variable expressivity, and wide intrafamilial variation, more among, less within the same generation, was observed. Concerning the frequency and severity of complications, the evolution of craniofacial deformities seems to parallel those described with Crouzon syndrome, suggesting the similar evaluation and management.

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

Primary pharmaco-toxicological evaluation of 2-iodomelatonin, a potent melatonin agonist.

Series of experiments aimed at a primary pharmaco-toxicological evaluation of 2-iodomelatonin, a high-affinity melatonin analogue, were performed. In the rat ovulation-inhibition model, 2-iodomelatonin was much more potent than either melatonin or 6-chloromelatonin. The acute toxicity was extremely low and close to, though slightly higher than that reported previously for melatonin. In the rat, 2-iodomelatonin was slowly metabolized in vivo; its apparent elimination half-life was about 60 minutes, much longer than that reported for melatonin. The in vitro mutagenesis tests demonstrated clearly that 2-iodomelatonin in concentrations, exceeding the dose range employed in the in vivo studies, was actually devoid of mutagenic effects. The obtained results suggest that 2-iodomelatonin deserves a detailed pharmaco-toxicological evaluation and could be eventually used in pharmacokinetic and pharmacodynamic studies in humans.

Animals↗

PubMed1993

Infection and antibiotic therapy in 4000 burned patients treated in Milan, Italy, between 1976 and 1988.

The pathogenic flora, isolated from burn wounds of patients admitted to a burn care unit during the years between 1976 and 1988 were typed and the in vitro susceptibility to antibacterial agents was recorded. Between 1976 and 1988 the general therapeutic approach was changed three times, in congruence with the prevalent nosocomial bacterial resistance. The most frequent isolates were: Pseud. aeruginosa, Staphylococcus aureus, Enterococcus spp., Proteus mirabilis, Escherichia coli, Enterobacter cloacae, Klebsiella spp. and other Enterobacteriaceae, such as Acinetobacter, Citrobacter. The most striking finding was the increase in antibiotic-resistant Enterococcus isolates. Staph. aureus, Klebsiella and E. cloacae showed susceptibility to cephalosporins, imipenem, pefloxacin, vancomycin; Enterococcus susceptibility to pefloxacin and vancomycin, and Pseud. aeruginosa sensitivity to piperacillin, amikacin, tobramycin was generally good. E. coli showed a satisfactory susceptibility on average, and P. mirabilis showed a good sensitivity to piperacillin, cephalosporins, amikacin, tobramycin, aztreonam and imipenem. Thus, the general bacterial flora and susceptibility have remained mostly unchanged over the years, with the conspicuous exception of Enterococcus spp. and E. cloacae, which demonstrated a marked increase in incidence, with a concomitant dramatic decrease in the sensitivity of Enterococcus spp. to antibiotics.

Bacteria↗

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↗