Regional distribution of putative vasopressin receptors in rat brain and pituitary by quantitative autoradiography

A phosphoinositide-linked peptide response in astrocytes: evidence for regional heterogeneity

A phosphoinositide-linked peptide response in cultured rat astrocytes was studied by measuring the accumulation of [3H]inositol phosphates in the presence of lithium. Cultures derived from cortex, cerebellum and spinal cord each showed a unique pattern or degree of stimulation to a panel of neuropeptides. Cortical and cerebellar astrocytes were similar, responding to bradykinin, oxytocin, vasopressin, eledoisin and neurokinin beta, whereas spinal cord astrocytes were stimulated by substance P, bradykinin, eledoisin, and neurokinins alpha and beta. These observations are evidence in favour of regional specialisations of astrocytes which may respond uniquely to peptides released by particular populations of neurons.

Subcellular localization and characterization of vasopressin binding sites in the ventral septal area, lateral septum, and hippocampus of the rat brain

[Arg8]-Vasopressin (AVP) has been shown to exert characteristic central physiological actions in the ventral septal area of the rat brain. This study reports the characterization of receptors for AVP in synaptic plasma membranes prepared from the ventral septal area, the lateral septum, and the hippocampus. Binding of [3H]AVP was temperature and time dependent, linearly related to protein concentration, saturable, and specific. Scatchard plot analysis suggested the presence of a population of binding sites in the three brain areas with dissociation constants and maximal binding capacities, respectively, of 1.06 +/- 0.39 nM and 24.0 +/- 7.01 fmol/mg of protein (mean +/- SEM; n = 3 for the ventral septal area, 0.92 +/- 0.13 nM and 47.0 +/- 4.96 fmol/mg of protein (n = 3) for the lateral septum, and 0.91 +/- 0.14 nM and 25 +/- 5.02 fmol/mg of protein (n = 3) for the hippocampus. In all three brain regions, the rank order of potencies of several vasopressin analogs, unrelated peptides, and other compounds for competitive displacement of ligand indicated a receptor with properties resembling those of the V1-like receptor for AVP. These data document the presence of a high-affinity, V1-like vasopressin receptor in the rat ventral septal area for which the pharmacological properties are similar to those previously reported in physiological studies.

Solubilization and purification of the Ni-stimulated arginine-vasopressin binding site of rat brain membranes

Arginine vasopressin binding sites on rat brain membranes were solubilized and purified by affinity chromatography. Membrane protein solubilized with CHAPS bound arginine vasopressin (AVP) only in the presence of divalent cations. Specific binding to the solubilized tissue was maximally stimulated by Ni2+, and markedly stimulated by Co2+ (30% of maximal binding with Ni2+), Zn2+ (18%), and Fe2+ (11%), parallel to the effects of these ions on the binding of AVP to neural membranes. Binding to solubilized tissue was not stimulated by Mg2+, Cu2+, Mn2+, or Ca2+. In the presence of Ni2+, binding of AVP to solubilized tissue was reversible, and the dissociation constant (10.5 nM), pH optimum, and time course were virtually identical to those of the membrane-bound AVP binding site. Purification of solubilized AVP-binding proteins by affinity chromatography on AVP-sepharose followed by gel electrophoresis yielded a major band of 55 kdalton molecular weight when purified in the presence of 5 mM Mg2+, or a major band of 62 kdaltons when purified in the presence of 1-5 mM Ni2+ or 10 microM Zn2+. By means of a new binding assay involving conjugation of the 62 kdalton fraction to brain membranes, the extent of purification of AVP binding activity was 150-fold in the presence of Ni2+. We suggest that the 62 kdalton protein is a component of the Ni-stimulated AVP binding site.

Regulatory peptide receptors: visualization by autoradiography

The receptors for regulatory peptides have been extensively characterized using radioligand binding techniques. By combining these binding techniques with autoradiography it is possible to visualize at the light and electron microscopic levels the anatomical and cellular localization of these receptors. In this review we discuss the procedures used to label peptide receptors for autoradiography and the peculiarities of peptides as ligands. The utilization of autoradiography in mapping peptide receptors in brain and peripheral tissues, some of the new insights revealed by these studies particularly the problem of 'mismatch' between endogenous peptides and receptors, the existence of multiple receptors for a given peptide family and the use of peptide receptor autoradiography in human tissues are also reviewed.

Cardiovascular effects of injections of vasopressin into the nucleus tractus solitarius in conscious rats

The effects of injections of arginine vasopressin (AVP) into the nucleus tractus solitarius (NTS) on mean arterial pressure (MAP), heart rate (HR) and plasma concentrations of noradrenaline and adrenaline were investigated in conscious, unrestrained rats. Injection of 2 ng AVP into the NTS significantly increased MAP but not plasma catecholamine concentrations, while injection of 10 ng AVP significantly increased MAP and plasma noradrenaline and adrenaline levels. Neither dose of AVP produced any change in HR. The vehicle did not affect MAP, HR or plasma catecholamine levels. Injection of a specific pressor antagonist of AVP, d(CH2)5Tyr-(Me)AVP (10 ng), did not change MAP, HR or plasma noradrenaline or adrenaline levels. These results suggest that the NTS is a central site of the pressor action of AVP. However, since the injection of the AVP antagonist did not reduce MAP or plasma noradrenaline or adrenaline levels, it suggests that AVP does not act tonically at the NTS to influence sympathoadrenal outflow.

Monoclonal anti-vasopressin (VP) antibodies penetrate into VP neurons, in vivo

The fate of monoclonal anti-vasopressin antibodies (VP-MAbs) injected in vivo into the paraventricular nucleus (PVN) of the rat brain was studied by immunocytochemistry. Depending on the post survival time, VP-MAbs contained in an ascites fluid were stained at different levels of the VP neurons: the cytoplasm of the PVN neurons, the fibres of the median eminence and the granular layer of the Gyrus Dentatus. The identification of endogenous peptides synthesized by PVN neurons showed that the VP-MAbs uptake was specific: it did not appear either in the oxytocinergic neurons or in the non immunoreactive neurons of the Brattleboro rat brain, this rat being genetically incapable of synthesizing central VP. Conversely, VP-MAbs only penetrated into the VP neurons: ascites fluid containing monoclonal antibodies prepared against bovine thyroglobulin (the carrier conjugated to VP in our immunizations) was neither stained in magnocellular neurons nor carried in nerve fibres. The neuronal uptake and transport of VP-MAbs occurred in vivo: they were totally inhibited by heating of the ascites fluid at 56 degrees C for 30 min; this treatment did not alter the VP-MAbs themselves but probably destroyed some thermic sensitive component essential to the macromolecule internalization. The biological effects of antibodies injected in vivo have been reported. The results described here suggest that some specific antibodies passively transferred into the brain could act directly on the peptide synthesis recognized by the antibodies.

Vasopressin promotes neurite growth in cultured embryonic neurons

Vasopressin (AVP) has been identified as a neural peptide which may influence memory function. Because of this action, we investigated the effect of AVP on neurons growing in culture. Vasopressin was found to markedly increase neurite outgrowth from cultured embryonic neurons and to also accelerate the rate of neuritic growth. Maximal stimulation of neurite production occurred after 24-hour incubation in the presence of 1 microM AVP. In AVP-treated cultures the profuse neuritic arborization was characterized by numerous microspikes along the neuritic shafts and at the perimeters of growth cones. These data provide strong evidence for a neurotrophic effect of AVP which, we suggest, may be relevant to neuronal development as well as to morphological changes which occur in the mature nervous system, possibly during memory formation.

Quantitation of vasopressin mRNA and oxytocin mRNA in hypothalamic nuclei by solution hybridization assays

Concentrations of vasopressin (VP) precursor and oxytocin (OT) precursor mRNA were measured in magnocellular cell groups of the rat hypothalamus by newly developed solution hybridization assays. The assays employed single-stranded 35S-labeled VP-specific and OT-specific DNA probes that were prepared by primer extension on recombinant M13 DNA templates. Solution hybridization assays were standardized by known amounts of cloned DNA. The detection limit was less than 1 pg DNA equivalent of the respective mRNA. In total RNA preparations of microdissected supraoptic nucleus (SON) mean (+/- SEM) basal levels of 1.37 +/- 0.18 pg VP mRNA and 1.95 +/- 0.14 pg OT mRNA were measured. RNA of the microdissected paraventricular nucleus (PVN) contained 0.35 +/- 0.02 pg VP mRNA and 1.77 +/- 0.15 pg OT mRNA. Elevation of plasma osmolality induced by drinking of 2% saline for 25 days resulted in a 1.85-fold increase in VP mRNA levels of the SON and a 1.6-fold increase in VP mRNA levels of the PVN. The solution hybridization assays are suitable tools to study the regulation of VP and OT mRNAs in magnocellular neurons of the brain.

Arginine-vasopressin stimulates inositol phospholipid metabolism in rat hippocampus

The hippocampal vasopressin receptors have been characterised by measuring the stimulated accumulation of inositol monophosphate in the presence of 10 mM LiCl after hippocampal slices were prelabelled with [3H]inositol. Arginine-vasopressin caused a dose-dependent increase in inositol monophosphate accumulation (ED50 = 7.1 nM). The response was unchanged in the absence of Ca2+ and significantly reduced in the presence of a V1-receptor antagonist. Equimolar oxytocin was ineffective as a stimulus. This suggests that the hippocampal receptors are of the V1 type.

Two classes of arginine vasopressin binding sites on rat brain membranes

Specific binding sites for arginine vasopressin (AVP) were demonstrated on rat brain membranes using [3H]AVP of high specific activity. At pH 7.4 in the presence of 5 mM MgCl2, one class of sites was measured with a KD of 0.56 nM and a Bmax of 4.3 fmol/mg protein. At pH 8.0 in the presence of MgCl2, two distinct sites were observed, having KD values of 0.42 and 13 nM and Bmax values of 5.6 and 68 fmol/mg protein, respectively, and similar results were obtained at pH 7.4 after repeatedly freezing and thawing the membranes. Binding increased with pH, apparently representing increased occupancy of the high capacity, lower affinity site. Binding to the lower affinity site was also enhanced by freezing and thawing membranes, or by adding 5 mM NiCl2 or 10 microM ZnCl2 to the incubation medium, whereas binding to the high affinity site was dependent on the addition of Mg. AVP was over 35 times more active in displacing 0.4 nM AVP than oxytocin or arginine-vasotocin, and 10,000 times more active than somatostatin. A number of other peptides had no effect on [3H]AVP binding at concentrations up to 10(-5) M. Autoradiography and regional dissection studies revealed a marked concentration of high affinity AVP-binding sites in the supraoptic and paraventricular nuclei of the hypothalamus, and Mg significantly enhanced the binding in these regions.