Specific Oxytocin Receptor Research Articles

Blocking oxytocin receptors inhibits vaginal marking to male odors in female Syrian hamsters

In Syrian hamsters ( Mesocricetus auratus), precopulatory behaviors such as vaginal scent marking are essential for attracting a suitable mate. Vaginal marking is dependent on forebrain areas implicated in the neural regulation of reproductive behaviors in rodents, including the medial preoptic/anterior hypothalamus (MPOA-AH). Within MPOA-AH, the neuropeptide oxytocin (OT) acts to facilitate copulation (lordosis), as well as ultrasonic vocalizations towards males. It is not known, however, if OT in this area also facilitates vaginal marking. In the present study, a specific oxytocin receptor antagonist (OTA) was injected into MPOA-AH of intact female Syrian hamsters to determine if oxytocin receptor-dependent signaling is critical for the normal expression of vaginal marking elicited by male, female, and clean odors. OTA injections significantly inhibited vaginal marking in response to male odors compared with vehicle injections. There was no effect of OTA on marking in response to either female or clean odors. When injected into the bed nucleus of the stria terminalis (BNST), a nearby region to MPOA-AH, OTA was equally effective in decreasing marking. Finally, the effects of OTA appear to be specific to vaginal marking, as OTA injections in MPOA-AH or BNST did not alter general locomotor activity, flank marking, or social odor investigation. Considered together, these results suggest that OT in MPOA-AH and/or BNST normally facilitates male odor-induced vaginal marking, providing further evidence that OT generally supports prosocial interactions among conspecifics.

Cardiac oxytocin receptor blockade stimulates adverse cardiac remodeling in ovariectomized spontaneously hypertensive rats

An increasing amount of evidence demonstrates the beneficial role of oxytocin (OT) in the cardiovascular system. Similar actions are attributed to genistein, an isoflavonic phytoestrogen. The treatment with genistein activates the OT system in the aorta of ovariectomized (OVX) Sprague-Dawley (SD) rats. The objective of this study was to determine the effects of low doses of genistein on the OT-induced effects in rat hypertension. The hypothesis tested was that treatment of OVX spontaneously hypertensive rats (SHRs) with genistein improves heart structure and heart work through a mechanism involving the specific OT receptor (OTR). OVX SHRs or SD rats were treated with genistein (in microg/g body wt sc, 10 days) in the presence or absence of an OT antagonist (OTA) [d(CH(2))(5), Tyr(Me)(2), Orn(8)]-vasotocin or a nonspecific estrogen receptor antagonist (ICI-182780). Vehicle-treated OVX rats served as controls. RT-PCR and Western blot analysis demonstrated that left ventricular (LV) OTR, downregulated by ovariectomy, increased in response to genistein. In SHRs or SD rats, this effect was blocked by OTA or ICI-182780 administration. The OTR was mainly localized in microvessels expressing the CD31 marker and colocalized with endothelial nitric oxide synthase. In SHRs, the genistein-stimulated OTR increases were associated with improved fractional shortening, decreased blood pressure (12 mmHg), decreased heart weight-to-body weight ratio, decreased fibrosis, and lowered brain natriuretic peptide in the LV. The prominent finding of the study is the detrimental effect of OTA treatment on the LV of SHRs. OTA treatment of OVX SHRs resulted in a dramatic worsening of ejection fractions and an augmented fibrosis. In conclusion, these results demonstrate that cardiac OTRs are involved in the regulation of cardiac function of OVX SHRs. The decreases of OTRs may contribute to cardiac pathology following menopause.

Biphasic protective effect of oxytocin on cardiac ischemia/reperfusion injury in anaesthetized rats

Oxytocin (OT) is well known for its role in reproduction. However, evidence has emerged suggesting a role in cardiovascular system. The aim of this study was to investigate the cardioprotective effect of oxytocin on ischemia/reperfusion (I/R) injury in an in vivo rat. Myocardial ischemia, was surgically induced by means of left anterior descending coronary artery occlusion for 25 min followed by reperfusion for 120 min. Infarct size was evaluated using the staining agent 2,3,5-triphenyltetrazolium chloride. Creatine kinase-MB isoenzyme (CK-MB) and lactate dehydrogenase (LDH) levels in plasma were analyzed to assess the degree of cardiac injury. Intraperitoneal administration of OT 0.001, 0.01 and 0.1 μg significantly reduced infarct size, LDH and CK-MB levels as compared to control (I/R) group and it had a biphasic effect on the reduction of ischemia/reperfusion injury. This biphasic effect was revealed as a U-shaped curve in which efficacy was optimal between very low and very high doses. Furthermore there were no significant differences in mean arterial pressure or heart rate between the OT treatment groups and control group during I/R. Blockade of specific OT receptors by atosiban (10 −6 M) abolished or attenuated the effect of OT preconditioning. The result of this study shows that OT possess a dose-dependent cardioprotective effect against ischemia/reperfusion injury and so study of OT preconditioning may provide a new target site for therapeutic exploitation.

Oxytocin enhances the inhibitory effects of diazepam in the rat central medial amygdala

Oxytocin is a neuropeptide that can reduce neophobia and improve social affiliation. In vitro, oxytocin induces a massive release of GABA from neurons in the lateral division of the central amygdala which results in inhibition of a subpopulation of peripherally projecting neurons in the medial division of the central amygdala (CeM). Common anxiolytics, such as diazepam, act as allosteric modulators of GABA(A) receptors. Because oxytocin and diazepam act on GABAergic transmission, it is possible that oxytocin can potentiate the inhibitory effects of diazepam if both exert their pre, – respectively postsynaptic effects on the same inhibitory circuit in the central amygdala. We found that in CeM neurons in which diazepam increased the inhibitory postsynaptic current (IPSC) decay time, TGOT (a specific oxytocin receptor agonist) increased IPSC frequency. Combined application of diazepam and TGOT resulted in generation of IPSCs with increased frequency, decay times as well as amplitudes. While individual saturating concentrations of TGOT and diazepam each decreased spontaneous spiking frequency of CeM neurons to similar extent, co-application of the two was still able to cause a significantly larger decrease. These findings show that oxytocin and diazepam act on different components of the same GABAergic circuit in the central amygdala and that oxytocin can facilitate diazepam effects when used in combination. This raises the possibility that neuropeptides could be clinically used in combination with currently used anxiolytic treatments to improve their therapeutic efficacy.

Estradiol upregulates the expression of oxytocin receptor in colon in rats

The study was designed to investigate the effect of estradiol on the excitatory effect of oxytocin (OT) on colon motility. Female Wistar rats were used, and some of them were ovariectomized (OVX) and treated with vehicle or estradiol (E(2)). A plastic balloon made of condom was inserted into colon to monitor the change of colonic pressure in vivo. Longitudinal muscle strips of distal colon were prepared to monitor the spontaneous contraction of colon in vitro. Expression of OT receptor (OTR) was investigated by Western blot analysis. Expression of OTR mRNA was detected by RT-PCR. Immunohistochemistry was used to locate OTR. In OVX rats, pretreatment of E(2) (4-100 microg/kg sc) dose-dependently increased the excitatory effect of OT on colon motility both in vivo and in vitro and increased the expression of OTR and OTR mRNA in colon. Systemic administration of OT excited the colon motility in vivo in rats at perioda of proestrus and estrus but did not influence it at diestrus period, when the concentration of plasma E(2) was lowest in the estrous cycle. Pretreatment of atosiban, the specific OTR antagonist, and TTX, the blocker of voltage-dependent sodium channel on nerve fiber, attenuated the excitatory effect of OT on colon motility. OTR was located in myenteric plexus of colon. These results suggested that E(2) increased the excitatory effect of OT on colon motility by upregulating the expression of OTR in myenteric plexus.

Oxytocin receptor activity in the ventrocaudal periaqueductal gray modulates anxiety-related behavior in postpartum rats.

Postpartum rats are less anxious than diestrous virgin females, a phenomenon requiring that mothers have recent contact with their infants. Oxytocin (OT) is one of many neurochemicals released intracerebrally while mothers interact with infants, and we investigated whether OT receptor activity in the ventrocaudal periaqueductal gray (cPAGv) contributes to mothers' reduced anxiety. Infusion of the highly specific OT receptor antagonist, desGly-NH2,d(CH2)5[D-Tyr2,Thr-sup-4]OVT, into the cPAGv reduced the percentage of time dams spent in the open arms of an elevated plus-maze, but had no effect on the open-arm behavior of diestrous virgins. Conversely, after separating dams from their litters for 4 hr to increase anxiety, a lower (2 ng) but not higher (5 ng) dose of OT infused into each hemisphere of the cPAGv doubled the percentage of time dams spent in open arms, but did not do so in virgins. OTergic manipulations inconsistently affected risk-assessment behaviors (stretch-attend postures, head dips) in both virgins and dams. Therefore, OT receptor activation in the cPAGv is an important consequence of contact with infants that reduces some anxiety-related behaviors in mother rats.

Systemic oxytocin and vasopressin excite gastrointestinal motility through oxytocin receptor in rabbits

The aim of the present study was to investigate the effect of systemic oxytocin (OT) and vasopressin (VP) on the motility of stomach and duodenum. Two plastic balloons made of condom were inserted into stomach and duodenum to monitor the change of mean pressure. Intravenous injection of OT (0.1-0.8 microg kg(-1)) or VP (0.02-0.08 IU kg(-1)) dose-dependently increased the stomach and duodenum pressure. Pretreatment of atosiban (1 microg kg(-1)), the specific OT receptor (OTR) antagonist, attenuated the excitatory effect of OT or VP on the pressure of stomach and duodenum. Pretreatment of V1880 (1 microg kg(-1)), the specific V1 receptor blocker, did not influence this effect. So we conclude that both of OT and VP injected systemically increased the gastric and duodenum motility via OTR.

Mutual regulation of vasopressin- and oxytocin-induced glucagon secretion in V1b vasopressin receptor knockout mice

[Arg8]-vasopressin (AVP) and oxytocin (OT) are neurohypophysial hormones which exert various actions, including the control of blood glucose, in some peripheral tissues. To investigate the type of receptors involved in AVP- and OT-induced glucagon secretion, we investigated the effect of these peptides on glucagon secretion in islets of wild-type (V1bR+/+) and vasopressin V1b receptor knockout (V1bR-/-) mice. AVP-induced glucagon secretion was significantly inhibited by the selective V1b receptor antagonist, SSR149415 (30%), and OT-induced glucagon secretion by the specific OT receptor antagonist, d(CH2)5[Tyr(Me)2, Thr4, Tyr-NH(2)(9)]OVT (CL-14-26) (45%), in islets of V1bR+/+mice. AVP- and OT-induced glucagon secretions were not by the antagonist of each, but co-incubation with both 10(-6) M SSR149415 and 10(-6) M CL-14-26 further inhibited AVP- and OT-induced glucagon secretions in islets of V1bR+/+ mice (57 and 69% of the stimulation values respectively). In addition, both AVP and OT stimulated glucagon secretion with the same efficacy in V1bR-/- mice as in V1bR+/+ mice. AVP- and OT-induced glucagon secretion in V1bR-/- mice was significantly inhibited by CL-14-26. These results demonstrate that V1b receptors can mediate OT-induced glucagon secretion and OT receptors can mediate AVP-induced glucagon secretion in islets from V1bR+/+mice in the presence of a heterologous antagonist, while AVP and OT can stimulate glucagon secretion through the OT receptors in V1bR-/-mice, suggesting that the other receptor can compensate when one receptor is absent.

Effects of cholesterol manipulation on the signaling of the human oxytocin receptor

We have recently shown that oxytocin inhibits cell growth when the vast majority of oxytocin receptors (OTRs) are excluded from detergent-resistant membranes (DRMs; the biochemical counterpart of lipid rafts), but has a strong mitogenic effect when the receptors are targeted to these plasma membrane domains upon fusion with caveolin-2, a resident raft protein. The aim of this study was to investigate whether the manipulation of total cell cholesterol can influence OTR localization and signaling. Our data indicate that cholesterol depletion in HEK-293 cells does not affect the signaling events mediated by the OTRs located outside DRMs. When treated with 2 mM methyl-beta-cyclodextrin (MbetaCD), the receptors remained outside and continued to inhibit cell growth. On the contrary, the MbetaCD treatment of cells expressing receptors fused to caveolin-2 led to their redistribution outside DRMs, and converted the receptor-mediated proliferative effect into cell growth inhibition. These data indicate that 1) once released from DRMs, the receptors fused to caveolin-2 signal exactly as wild-type OTRs and 2) their DRM location is responsible for the specific OTR signaling leading to cell proliferation. Finally, we evaluated whether cholesterol loading could force the OTRs into lipid rafts and change their signaling, but, after cell treatment with an MbetaCD/cholesterol complex, receptor stimulation continued to lead to cell growth inhibition, thus indicating that increasing cell cholesterol levels is not sufficient per se to affect OTR signaling.

Oxytocin microinjected into dorsal motor nucleus of the vagus excites gallbladder motility via NMDA receptor–NO-cGMP pathway

Our recent study indicated that, in the dorsal motor nucleus of the vagus (DMV), the N-methyl- d-aspartic acid (NMDA) receptor–nitric oxide (NO)–cGMP pathway participated in the regulation of gallbladder motility in rabbits. Oxytocin (OT) is involved as a neurotransmitter in autonomic regulation. The aim of the present experiments is to investigate the effect of OT microinjected into DMV on the gallbladder motility and the involvement of NMDA receptor–NO–cGMP pathway. A frog bladder connected with transducer was inserted into the gallbladder to record the gallbladder pressure. Microinjection of OT (10–50 nmol/L, 100 nl) dose dependently increased the strength of gallbladder phasic contraction. The excitatory effect of OT (10 nmol/L, 100 nl) was completely abolished by atosiban (10 mmol/L, 100 nl), the specific OT receptor antagonist, but was not influenced by [deamino-Pen 1, O-Me-Tyr 2,Arg 8]-vasopressin (10 mmol/L, 100 nl), the V 1 receptor antagonist. Pretreatment of ketamine (10 mmol/L, 100 nl), the NMDA receptor antagonist, suppressed the gallbladder motor response to OT; but pretreatment of 6-Cyaon-7-Nitroquinoxaline-2,3-(1H,4H)-Dione (CNQX; 10 mmol/L, 100 nl), the non-NMDA receptor antagonist, did not affect it. Pretreatment of l-NAME (10 mmol/L, 100 nl), the nitric oxide synthase (NOS) inhibitor, or methyl blue (10 mmol/L, 100 nl), the guanylyl cyclase inhibitor, inhibited the excitatory effect of OT on gallbladder motility. Hence, we deduced that the microinjection of OT into the DMV enhanced the gallbladder motility through binding specific OT receptors and activating the NMDA receptor–NO–cGMP pathway.

Effect of an oxytocin receptor antagonist and rho kinase inhibitor on the [Ca ++] i sensitivity of human myometrium

Objective The purpose of this study was to assess the possible mechanism and effect of oxytocin receptor on the sensitization of the contractile proteins to [Ca ++] i. Study design Myometrial strips were prepared from biopsy specimens that had been taken at term (37–40 weeks of gestation) cesarean delivery from 22 women, before the onset of labor. Simultaneous measurements of [Ca ++] i and tension were performed on spontaneously contracting strips. The effects of a specific oxytocin receptor antagonist, L371,257, and a rho kinase inhibitor, Y-27632, on the [Ca ++] i and tension transients were determined. Results Application of L371,257 (90 nmol/L) to spontaneously contracting muscle strips reduced peak tension to 43%±12% of its original value without affecting peak [Ca ++] i (105%±15%). More tension is developed at each [Ca ++] i during the falling phase, relative to the rising phase of each spontaneous contraction; this asymmetric [Ca ++] i-tension relationship was abolished by L371,257. The subsequent application of oxytocin (3 μmol/L) reversed the effects of the antagonist on tension. An inhibitor of rho kinase (Y-27632) caused a concentration-dependent inhibition of spontaneous contractions without affecting the underlying Ca ++ signals. The addition of oxytocin (1 nmol/L) to spontaneously active myometrium increased both the duration of the Ca ++ signal and the sensitivity of the contractile machinery to [Ca ++] i; only the latter effect was prevented by Y-27632. Conclusion Oxytocin independently regulates the duration of the periodic Ca ++ signals and the sensitivity of the contractile machinery to Ca ++. The latter is likely to be mediated by rho kinase, which is essential for the effective coupling of increases in [Ca ++] i to tension.

Modulation by oxytocin of ATP-activated currents in rat dorsal root ganglion neurons

The modulatory effect of oxytocin (OT) on ATP-activated currents (I ATP) was studied in freshly isolated dorsal root ganglion (DRG) neurons of rats using whole cell clamp technique. In most of the neurons examined (50/70, 71.4%) extracellular application of OT (10 −9–10 −5 mol/L) suppressed I ATP while in the rest (20/70, 28.6%) no modulatory effect was observed. OT shifted the ATP concentration-response curve downwards with a decrease of 39.8±4.2% in the maximal current response and with no significant change of Kd value. This OT-induced inhibition of I ATP showed no voltage dependence, and could be blocked by [d(CH 2) 5,Tyr(Me) 2,Thr 4,Tyr-NH 2 9]-OVT (d(CH 2) 5-OVT) (10 −8 mol/L), a specific OT receptor antagonist. Intracellular application of H-9 (4×10 −5 mol/L, an inhibitor of protein kinase A) ( n=12), BAPTA (10 −2 mol/L, a chelator of calcium ions) ( n=4) could reverse the inhibitory effect of extracellular OT (10 −7 mol), while inclusion of H-7 (2×10 −5 mol/L, a protein kinase C inhibitior) ( n=8) and KN-93 (10 −5 mol/L, an inhibitor of CaMKII) ( n=9) in the recording pipette did not affect this effect. The results suggested that OT inhibition on ATP-activated currents was mediated by OT receptors in the membrane of DRG neurons; and this inhibitory effect involved the transduction of intracellular cAMP-PKA and Ca 2+.

Oxytocin modulates estrogen receptor α expression and function in MCF7 human breast cancer cells

Oxytocin (OT) inhibits the proliferation of MCF7 estrogen-dependent human breast cancer cells, via specific OT receptors (OTR). Besides this effect, we report that OT modulates the expression of estrogen receptor alpha (ERalpha) in MCF7 cells, both at mRNA and protein level. Since the first 24 h of OT treatment the ERalpha mRNA levels are down-regulated; in contrast, ERalpha protein expression decreases at a later time. The reduced number of ERalpha goes in parallel to a temporary increase in the binding affinity of these receptors as well as to a significant increase in their estradiol (E2)-induced transcription activity. The increase in both binding affinity and transcriptional activity of ERalpha likely balances the reduction in the number of ERalpha binding sites, ruling out the hypothesis that part of the OT contrasting effect on E2-induced cell proliferation could depend on the reduced E2 binding to MCF7 cells and supporting the hypothesis of an exclusively direct OT-antimitogenic effect. This is the first evidence that OT modulates the expression of ERalpha receptors in human neoplastic cells.

Function and localization of oxytocin receptors in the reproductive tissue of rams

Oxytocin is present in the male reproductive tract and has been shown to increase contractility in the epididymis and to modulate steroidogenesis. This study investigated the effects of oxytocin in the testis in vivo, and the presence and cellular localization of oxytocin receptors in the reproductive tract of rams. During the breeding season, mature rams underwent efferent duct ligation before injection of either oxytocin (20 microg) or oxytocin plus an oxytocin antagonist (20 microg) into the testicular artery; the contralateral testicular artery received saline. Injection of oxytocin caused a significant increase (P < 0.05) in the concentration of spermatozoa collected from the rete testis. This effect was not observed after treatment with the oxytocin antagonist plus oxytocin. Western blot analysis performed using a specific oxytocin receptor antibody (020) identified a single immunoreactive band of 66 kDa in testicular and epididymal tissue. This band was present in uterine tissue but not in liver or muscle. Immunocytochemistry identified oxytocin receptors on Leydig and Sertoli cells of the testis, on epithelial cells throughout the epididymis, on peritubular smooth muscle cells in the cauda epididymidis, and on the epithelial cells and circular smooth muscle layer of the ductus deferens. These findings indicate that oxytocin can modulate sperm transport in the ram testis. A role for oxytocin in promoting sperm transit is supported by the localization of oxytocin receptors in the cauda epididymis and ductus deferens, and the presence of receptors on Leydig, Sertoli and epididymal epithelial cells provides further evidence that oxytocin may be involved in the local regulation of steroidogenesis.

Oxytocin in the NTS

The role of brain stem oxytocinergic projections in the modulation of heart rate control during exercise is discussed on the basis of both changes in endogenous peptide content and heart rate changes observed during exercise. Running on a treadmill caused an increase in oxytocin content in dorsal/ventral brain stem areas and spinal cord, specifically in trained rats. Trained rats pretreated with a specific oxytocin receptor antagonist into the dorsal brain stem area (corresponding to the nucleus tractus solitarii and dorsal motor nucleus of the vagus, or NTS/DMV) showed a significant potentiation of exercise tachycardia with no change in the blood pressure response. The same treatment in sedentary rats was without effect. On the other hand, administration of exogenous oxytocin into this area caused significant blunting of exercise tachycardia in both groups, with no change in the pressure response. It is proposed that long-descending oxytocinergic pathways from the hypothalamus to the NTS/DMV area serve as a link between the two main neural controllers of the circulation--that is, the central command and feedback control mechanisms driven by the peripheral receptor signals. Our results strongly suggest that oxytocinergic input to NTS/DMV, by restraining the tachycardic response of trained individuals, contributes to the smaller response observed after training, without compromising cardiac output adjustment and the circulatory demand during exercise.

Antagonistic oxytocin/alpha2-adrenoreceptor interactions in the nucleus tractus solitarii: relevance for central cardiovascular control.

The modulation of the central cardiovascular effects of alpha2-adrenoceptor activation by oxytocin in the nucleus tractus solitarii has been evaluated by cardiovascular analysis and by quantitative receptor autoradiography. Microinjections in the nucleus tractus solitarii of a threshold dose of oxytocin effectively and significantly counteracted the vasodepressor and bradycardic actions of an ED50 dose of the alpha2-adrenoceptor agonist clonidine. The coinjection of a threshold dose of oxytocin with a threshold dose of clonidine did not produce any changes in the mean arterial pressure but a tachycardic response was observed. Receptor autoradiographical experiments showed that oxytocin (3 nM) significantly increased the Kd and Bmax values of [3H]p-aminoclonidine binding sites in the nucleus tractus solitarii compatible with a possible antagonistic interaction with the alpha2-adrenoceptors, and this effect was blocked by the presence of the specific oxytocin receptor antagonist 1-deamino-2-D-Tyr-(OEt)-4-Thr-8-Orn-oxytocin. These findings suggest the existence of an antagonistic oxytocin/alpha2-adrenoceptor interaction in nucleus tractus solitarii that may be of relevance for the demonstrated modulation of alpha2-adrenoceptor induced cardiovascular responses by oxytocin.

Oxytocin/Alpha2-Adrenoceptor Interactions in Feeding Responses

The modulation of α₂-adrenoceptor-induced food intake by oxytocin has been evaluated in studies on food intake and by quantitative receptor autoradiography in the hypothalamus and the amygdala of the rat. The effects of lateral intracerebroventricular administration of clonidine and oxytocin were evaluated on food intake in satiated animals. Food consumption was measured at 30, 90, 240 min and 22 h (1,320 min) after injection. The coinjection of oxytocin and clonidine was found to counteract the increase in food intake produced by clonidine (p < 0.001) in satiated rats. Receptor autoradiographic experiments showed that oxytocin significantly increased the K_d values of [³H]p-aminoclonidine α₂-agonist-binding sites in the hypothalamus. Effective oxytocin concentrations ranged between 0.3 and 1 nM (p < 0.05) with a maximal action of 250% at 1 nM. The B_max value was significantly increased (p < 0.05) for all concentrations of oxytocin. In the amygdala, oxytocin also increased both the K_d of [³H]p-aminoclonidine-binding sites by about 190% at 1 nM and the B_max values at 1 and 3 nM (p < 0.05). Oxytocin (1 nM) also significantly and substantially (p < 0.01) increased the K_d and B_max values of the [³H]UK 14.304 α₂-agonist-binding sites in the hypothalamus and amygdala in agreement with the results obtained with the other agonist of the α₂-adrenoceptor [³H]p-aminoclonidine. This effect was partially blocked by the presence of the specific oxytocin receptor antagonist, CAP. These findings suggest the existence of an antagonistic oxytocin/α₂-receptor interaction in the hypothalamus and amygdala that may be of relevance for the demonstrated modulation of α₂-adrenoceptor-induced feeding responses by oxytocin.

Presence and significance of oxytocin receptors in human neuroblastomas and glial tumors.

To determine whether oxytocin (OT) could be added to the list of growth factors acting on neoplastic cells of nervous origin, we investigated the presence of oxytocin receptors (OTR) in human primary neuroblastomas and glioblastomas and related cell lines. OTR were demonstrated both at mRNA level (using a RT-PCR procedure) and at protein level (using immunocytochemical and immunofluorescence procedures). In order to clarify whether OT exerts any biological effect on these tumors through OTR, we also studied cell proliferation in 3 human neuroblastoma cell lines (SK-N-SH, SH-SY5Y, IMR-32) and one human anaplastic astrocytoma cell line (MOG-G-UVW) treated with OT 1 nM to 100 nM for 48 and 96 hr. At these doses, a dose-dependent inhibitory effect on cell proliferation was demonstrated. This inhibition was accompanied by a significant increase in the intracellular concentration of cAMP, which we have reported to be the intracellular mediator of the OT anti-proliferative effect in breast-carcinoma cell lines. Our data indicate that specific OTR are present in human neuroblastomas and glioblastomas. Through these receptors, OT could inhibit cell proliferation and modulate tumor growth.

Oxytocin Modulates Glutamatergic Synaptic Transmission between Cultured Neonatal Spinal Cord Dorsal Horn Neurons

The functional characteristics of binding sites for the neuropeptide oxytocin (OT) detected by radioautography in laminae I and II of the dorsal horn (DH) and on cultured neonatal DH neurons were studied on the latter using perforated patch-clamp recordings. The neurons were identified by their spike discharge properties and on the basis of the presence of met-enkephalin-like and glutamate decarboxylase-like immunoreactivities. OT (100 nM) never induced any membrane current at a holding potential of -60 mV but increased the frequency of spontaneously occurring AMPA receptor-mediated EPSCs or the mean amplitude of electrically evoked EPSCs in a subset (35%) of neurons. The frequency of miniature EPSCs (m-EPSCs) recorded in the presence of 0.5 microM tetrodotoxin was also increased by OT (100 nM) without any change in their mean amplitude, indicating an action at a site close to the presynaptic terminal. The decay kinetics of any type of EPSC were never modified by OT. The effect of OT was reproduced by [Thr4, Gly7]-OT (100 nM), a selective OT receptor agonist, and blocked by d(CH2)5-[Tyr(Me)2,Thr4,Tyr-NH29]-ornithine vasotocin (100 nM), a specific OT receptor antagonist. Reducing the extracellular Ca2+ concentration from 2.5 to 0.3 mM in the presence of Cd2+ (100 microM) reversibly blocked the effect of OT on m-EPSCs. The OT receptors described here may represent the substrate for modulatory actions of descending hypothalamo-spinal OT-containing pathways on the nociceptive system.

Antiproliferative effect of oxytocin through specific oxytocin receptors in human neuroblastoma and astrocytoma cell lines.

Oxytocin receptors (OTR) have been characterized and localized in different areas of the central nervous system where they probably regulate different OT-dependent behavioural, reproductive and ingestive effects. Moreover, OTR have been described in normal glial cells (astrocytes) from rat hypothalami in culture1.