Oxytocin receptors on cultured astroglial cells. Kinetic and pharmacological characterization of oxytocin-binding sites on intact hypothalamic and hippocampic cells from foetal rat brain

Abstract

The ability of astroglial cells to exhibit oxytocin (OT)-binding sites has been investigated in embryonic hypothalamic and hippocampic astroglial cell cultures. The differential characteristics of binding of OT and [Arg8]vasopressin (AVP) agonists and antagonists to the OT-binding sites using the highly selective iodinated OT antagonist d(CH2)5-[Tyr(Me)2,Thr4,Tyr-NH2(9)]OVT ([125I]OTA) have been evaluated using intact cells maintained for 12 days in culture. The specific binding displayed features of reversibility. Computer analysis of the saturation studies using the LIGAND program indicated that, at 4 degrees C, the antagonist binds to a homogeneous population of sites with a Kd value of 0.02 nM and a low binding-site density of around 2 fmol/dish for hypothalamic cells and 6 fmol/dish for hippocampic cells. For hypothalamic cells, competition curves using unlabelled OT, AVP or V2 AVP agonist were characterized by a pseudo-Hill coefficient below unity (0.7), indicating possible heterogeneity among the binding sites. On the other hand, the dose-inhibition curves resulting from competition studies with hippocampic cells had a pseudo-Hill coefficient close to unity, except for OT. Computer analysis (LIGAND) indicated that the OT dose-inhibition curve was significantly better fitted to a two-site model, and this can be explained by two apparent forms of the receptor having high and low affinities for the displacing drug. The relative potencies of the peptides tested for binding to the high-affinity site were: AVP greater than OT greater than V1 AVP antagonist ([d(CH2)5-Tyr(Me)2]AVP) = V2 AVP agonist greater than AVP-Sar ([d(CH2)5-Sar7,Arg8]VP) in hypothalamic cultures, and OT = AVP greater than V1 AVP antagonist greater than V2 AVP agonist in hippocampic cultures. In addition, autoradiography allowed visualization of OT-binding sites, which are located on both soma and processes of astrocyte-like type of cells. In conclusion, these data provide evidence that glial cell cultures contain specific OT-binding sites which display pharmacological characteristics different from those already reported in neuronal cultures and in the adult rat brain.

Antagonism of mGlu2/3 receptors in the nucleus accumbens prevents oxytocin from reducing cued methamphetamine seeking in male and female rats

“…Recently, Scofield and colleagues (2015) demonstrated that specific activation of astrocytes (via Gq coupled DREADDs) in NAcore decreased cued reinstatement of cocaine seeking through an mGluR2/3-dependent mechanism. Here, we speculate that the localization of astroglial oxytocin receptors reduces relapse via Gq signaling that can activate transduction pathways including IP3 receptors and the release of intracellular calcium stores resulting in glial transmitter release, including glutamate (Di Scala-Guenot et al, 1994; Di Scala-Guenot and Strosser, 1992; Hamilton and Attwell, 2010). Extrasynaptic glutamate can thereby activate mGluR2/3 receptors located presynaptically on cortical glutamatergic axons, inhibiting synaptic release of glutamate, thus restoring glutamatergic tone (Moussawi and Kalivas, 2010).…”

Increase of intracellular calcium induced by oxytocin in hypothalamic cultured astrocytes

“…However, resolution obtained with the autoradiography does not allow precise localization of receptors on a specified cell type. By contrast, using embryonic hypothalamic cultures, it has been possible to detect and characterize OT receptors both on neurones (Di Scala-Guenot et al, 1990) and astrocytes (Di Scala-Guenot and Strosser, 1992). Their pharmacological characteristics were similar to those already described for the OT receptors in central (Elands et al, 1987) and peripheral (Elands et al, 1990;Soloff et al, 1989) membrane preparations.…”

“…

ABSTRACTA recent study demonstrated oxytocin (OT) receptors on hypothalamic cultured astrocytes (Di Scala-Guenot and Strosser, 1992). The attempt in the present paper was to determine a possible intracellular calcium mobilization induced by OT receptor activation in these cells.

…”

Chronic Hyperosmotic Stress Converts GABAergic Inhibition into Excitation in Vasopressin and Oxytocin Neurons in the Rat

“…In this study, we have not determined the source of oxytocin and the location of its receptors responsible for the E GABA shifts. Whether the activation of oxytocin receptors in MNCs (Freund-Mercier et al, 1994) or nearby glial cells (Di Scala-Guenot and Strosser, 1992;Di Scala-Guenot et al, 1994) by oxytocin from the dendrites of MNCs (Ludwig, 1998) leads to the shifts is open for additional investigation.…”