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ABSTRACT: The binding characteristics and central distribution of 125I-Linear AVP antagonist, a new ligand for vasopressin binding sites, are described in the following studies. Saturation studies performed on rat brain septal membranes demonstrated that 125I-Linear AVP antagonist binds to a single class of sites with high affinity (55 pM) and limited capacity (88 fmol/mg protein). In autoradiographic studies, 125I-Linear AVP antagonist labeled brain areas known to contain vasopressin receptors without binding to neurophysins. 125I-Linear AVP antagonist also labeled sites in cortex, hypothalamus, ventral tegmental area and substantia nigra. In competition studies, 125I-Linear AVP antagonist binding was most readily blocked by AVP and a selective V1a agonist. Oxytocin and a selective V2 ligand were effective only in micromolar concentrations. A selective oxytocin agonist was virtually ineffective in blocking 125I-Linear AVP antagonist binding. In regions that contain a high density of oxytocin binding sites, however, oxytocin-displaceable binding was observed. In agreement with studies on peripheral tissues, the binding profile generated from these studies indicates that 125I-Linear AVP antagonist binds to vasopressin receptors of the V1a subtype. These results suggest that 125I-Linear AVP antagonist is a valuable ligand for the study of central AVP receptors.
Brain Research 10/1993; 622(1-2):9-16. · 2.73 Impact Factor
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Annals of the New York Academy of Sciences 08/1993; 689:475-6. · 3.15 Impact Factor
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ABSTRACT: The strict photoperiodic dependence of gonadotropic function observed in mink provides an excellent physiological model for studying the activity of GnRH hypothalamic neurons. In mink, exposure to more than 10 h light inhibits the activity of this neurohormonal system. Melatonin plays an essential role in this type of regulation of gonadotropic function. In mink, contrary to results in many other photosensitive species, melatonin was observed to mediate the gonadostimulating effect of short days. However, the binding sites and action of this substance have not yet been defined. We thus attempted to identify melatonin binding sites in the mink brain. The study was carried out at three times during the seasonal testicular cycle in male minks maintained under natural environmental conditions. Coronal sections were taken from the whole brain and pituitary gland. Using 2-[125I]iodomelatonin, we observed a strong concentration of binding sites in the pars tuberalis and not in the part of the median eminence surrounded by the pars tuberalis. This concentrated localization of melatonin binding sites brings up the problem of defining the action of this substance in photoregulating the activity of the GnRH neurohormonal system.
Neuroscience Letters 10/1992; 144(1-2):147-51. · 2.11 Impact Factor
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Annals of the New York Academy of Sciences 07/1992; 652:39-45. · 3.15 Impact Factor
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ABSTRACT: A linear vasopressin antagonist, Phaa-D-Tyr(Me)-Phe-Gln-Asn-Arg-Pro-Arg-Tyr-NH2 (Linear AVP Antag) (Phaa = Phenylacetyl), was monoiodinated at the phenyl moiety of the tyrosylamide residue at position 9. This antagonist appeared to be a highly potent anti-vasopressor peptide with a pA2 value in vivo of 8.94. It was demonstrated to bind to rat liver membrane preparations with a very high affinity (Kd = 0.06 nM). The affinity for the rat uterus oxytocin receptor was lower (Ki = 2.1 nM), and affinities for the rat kidney- and adenohypophysis-vasopressin receptors were much lower (Ki = 47 nM and 92 nM, respectively), resulting in a highly specific vasopressin V1a receptor ligand. Autoradiographical studies using rat brain slices showed that this ligand is a good tool for studies on vasopressin receptor localization and characterization.
FEBS Letters 05/1991; 282(1):77-81. · 3.54 Impact Factor
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ABSTRACT: The distribution and the amount of [3H]oxytocin binding were studied in the brain of adult rats of either sex, as well as in male and female castrates, some of which received injections of estradiol or testosterone. Intact males were treated with an aromatase inhibitor. Castration and inhibition of aromatase activity reduced, whereas estradiol and testosterone increased oxytocin binding, particularly in regions of the brain assumed to be involved in reproductive functions, such as the ventrolateral part of the hypothalamic ventromedial nucleus and the islands of Calleja and neighbouring cell groups. Binding of oxytocin to the uterus was also estrogen-dependent. In the same animals, we also studied the distribution of [3H]vasopressin binding sites present in the brain. It was similar in males and females, and was not affected by experimentally manipulating gonadal hormone levels. In immunocytochemical studies we noticed, as others had previously, that the vasopressin content of certain areas of the rat brain was affected by castration, whereas the oxytocin innervation was not. These results are discussed in relation to the possible functions of oxytocin in the brain and of the lack of correspondence between the immunocytochemical and the autoradiographic data.
Brain Research 04/1990; 511(1):129-40. · 2.73 Impact Factor
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Progress in brain research 02/1987; 72:173-87. · 3.04 Impact Factor
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ABSTRACT: Binding of radioactive vasopressin--but not of oxytocin--was detected by autoradiography and by labeling of membranes obtained from the rat superior cervical ganglion. In both instances binding could be displaced by V1 (smooth muscle-type) but not by V2 (kidney-type) agonists, indicating that the ganglionic vasopressin receptors are similar to those present on hepatocytes and vascular smooth muscle. In accordance with the V1 character of the receptors, vasopressin activated the turnover of membrane inositol lipids, and this effect was abolished by a structural analogue known to act as a vasopressor antagonist. A possible physiological role of vasopressin was suggested by intracellular recordings obtained from ganglion cells in vitro. Vasopressin induced a reduction in the amplitude of the fast excitatory postsynaptic potential evoked by electrical stimulation of the preganglionic nerve. This reduction in ganglionic transmission was antagonized by the same synthetic structural analogue that blocked the effect of vasopressin on inositol lipids. This study provides evidence for the presence of functional vasopressin receptors in a rat sympathetic ganglion and thus suggests that vasopressin may play a role in peripheral autonomic function.
Proceedings of the National Academy of Sciences 08/1986; 83(14):5335-9. · 9.68 Impact Factor
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ABSTRACT: The effects of VIP and of peptides of the VIP family: secretin, glucagon, the porcine histidine isoleucine containing peptide (PHI) and the rat hypothalamic growth hormone-releasing hormone (rhGRF) on the cyclic AMP and inositol phosphate contents of isolated rat superior cervical ganglia were investigated. We demonstrate that VIP is able to provoke a large inositol lipid breakdown by acting directly on ganglionic cells. This observation suggests the presence in rat superior cervical ganglia of a new type of receptors for VIP or for an unidentified peptide structurally related to VIP.
Brain Research 07/1986; 376(2):363-7. · 2.73 Impact Factor
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ABSTRACT: Synaptic plasma membranes containing binding sites for tritiated oxytocin and arginine vasopressin were isolated from rat hippocampus. The binding parameters for oxytocin and vasopressin sites were determined and statistically analysed. The fitted curve for oxytocin binding was compatible with a model where the ligand interacts with two classes of receptors with different capacities and affinities. The sites with low binding capacity had an apparent dissociation constant at equilibrium of 1.8 nM and a maximal binding capacity of 17 fmol/mg protein. By contrast, the Scatchard plot failed to reveal a marked heterogeneity in the population of sites labelled with [3H]vasopressin with an affinity of 1.5 nM and a maximal binding capacity of 39 fmol/mg protein. The specificity of these binding sites, tested in competition experiments, revealed that these neurohypophyseal hormones labelled two distinct populations of sites. One population with a high affinity for vasopressin, oxytocin and vasotocin, the other population with a high affinity for vasopressin and vasotocin and a low affinity for oxytocin. Adenylate cyclase activity was not affected by arginine-vasopressin or oxytocin. These receptors are compared with previously characterized peripheral receptors.
The EMBO Journal 07/1985; 4(6):1407-12. · 9.20 Impact Factor
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ABSTRACT: Synaptic plasma membranes containing binding sites for (3H) oxytocin and (3H) arginine vasopressin were isolated from rat amygdala, olfactory bulb and hippocampus. In the hippocampus, two specific binding sites have been characterized: an "oxytocic" binding site, which has a high affinity for oxytocin, arginine vasopressin and arginine vasotocin, and a "vasopressic" binding site, which has a high affinity for arginine vasopressin, arginine vasotocin and a low affinity for oxytocin. The specificity of these binding sites were tested in competition experiments. The affinity of different antidiuretic and vasopressic analogues for the vasopressic site was similar to that observed for the V1 type of vasopressin receptors present in the hepatocytes and vascular smooth muscle cells. The affinity of several analogues for the oxytocic site shows some similarities with their corresponding relative activities in increasing the firing rate of non pyramidal neurones in hippocampal slices. Arginine vasopressin and oxytocin did not change the activity of adenylate cyclase present in the hippocampal synaptic plasma membranes. The properties of these specific binding sites for the neurohypophyseal hormones are compared with the receptors present on the peripheral targets.
Annales d Endocrinologie 02/1985; 46(1):35-9. · 0.74 Impact Factor
