Demonstration and nature of endothelin-3-like immunoreactivity in somatostatin and choline acetyltransferase-immunoreactive nerve cells of the neostriatum of the rat

Development and Characterization of a Macaque Model of Focal Internal Capsular Infarcts

Several studies have used macaque monkeys with lesions induced in the primary motor cortex (M1) to investigate the recovery of motor function after brain damage. However, in human stroke patients, the severity and outcome of motor impairments depend on the degree of damage to the white matter, especially that in the posterior internal capsule, which carries corticospinal tracts. To bridge the gap between results obtained in M1-lesioned macaques and the development of clinical intervention strategies, we established a method of inducing focal infarcts at the posterior internal capsule of macaque monkeys by injecting endothelin-1 (ET-1), a vasoconstrictor peptide. The infarcts expanded between 3 days and 1 week after ET-1 injection. The infarct volume in each macaque was negatively correlated with precision grip performance 3 days and 1 week after injection, suggesting that the degree of infarct expansion may have been a cause of the impairment in hand movements during the early stage. Although the infarct volume decreased and gross movement improved, impairment of dexterous hand movements remained until the end of the behavioral and imaging experiments at 3 months after ET-1 injection. A decrease in the abundance of large neurons in M1, from which the descending motor tracts originate, was associated with this later-stage impairment. The present model is useful not only for studying neurological changes underlying deficits and recovery but also for testing therapeutic interventions after white matter infarcts in primates.

Fibroblast growth factor and endothelin-1 receptors mediate the response of human striatal precursor cells to hypoxia

Fetal striatal transplantation has emerged as a new therapeutic strategy in Huntington's disease (HD). Hypoxia is one of the microenvironmental stress conditions to which fetal tissue is exposed as soon as it is isolated and transplanted into the diseased host brain. Mechanisms that support neuroblast survival and replenishment of damaged cells within the HD brain in the hypoxic condition have yet to be fully elucidated. This study is aimed at investigating the molecular pathways associated with the hypoxic condition in human fetal striatal neuroblasts (human striatal precursor (HSP) cells), using the hypoxia-mimetic agent cobalt chloride (CoCl2). We analyzed the effect of CoCl2 on HSP cell proliferation and on the expression of hypoxia-related proteins, such as hypoxia-inducible factor (HIF)-1α and vascular endothelial growth factor (VEGF). Moreover, we evaluated fibroblast growth factor 2 (FGF2; 50ng/ml) and endothelin-1 (ET-1; 100nM) proliferative/survival effects in HSP cells in normoxic and hypoxic conditions. Dose-response experiments using increasing concentrations of CoCl2 (50-750μM) showed that the HSP cell growth was unaffected after 24h, while it increased at 48h, with the maximal effect observed at 400μM. In contrast, cell survival was impaired at 72h. Hypoxic conditions determined HIF-1α protein accumulation and increased gene and protein expression of VEGF, while FGF2 and ET-1 significantly stimulated HSP cell proliferation both in normoxic and hypoxic conditions, thus counteracting the apoptotic CoCl2 effect at 72h. The incubation with selective receptor (FGFR1, endothelin receptor A (ETA) and endothelin receptor B (ETB)) inhibitors abolished the FGF2 and ET-1 neuroprotective effect. In particular, ET-1 stimulated HSP cell survival through ETA in normoxic conditions and through ETB during hypoxia. Accordingly, ETA expression was down-regulated, while ETB expression was up-regulated by CoCl2 treatment. Overall, our results support the idea that HSP cells possess the machinery for their adaptation to hypoxic conditions and that neurotrophic factors, such as FGF2 and ET-1, may sustain neurogenesis and long-term survival through complex receptor-mediated mechanisms.

Endothelin-1 is over-expressed in amyotrophic lateral sclerosis and induces motor neuron cell death

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disorder characterized by progressive loss of motor neurons (MNs) and astrogliosis. Recent evidence suggests that factors secreted by activated astrocytes might contribute to degeneration of MNs. We focused on endothelin-1 (ET-1), a peptide which is strongly up-regulated in reactive astrocytes under different pathological conditions. We show that ET-1 is abundantly expressed by reactive astrocytes in the spinal cord of the SOD1-G93A mouse model and sporadic ALS patients. To test if ET-1 might play a role in degeneration of MNs, we investigated its effect on MN survival in an in vitro model of mixed rat spinal cord cultures (MSCs) enriched of astrocytes exhibiting a reactive phenotype. ET-1 exerted a toxic effect on MNs in a time- and concentration-dependent manner, with an exposure to 100-200nM ET-1 for 48h resulting in 40-50% MN cell death. Importantly, ET-1 did not induce MN degeneration when administered on cultures treated with AraC (5μM) or grown in a serum-free medium that did not favor astrocyte proliferation and reactivity. We found that both ETA and ETB receptors are enriched in astrocytes in MSCs. The ET-1 toxic effect was mimicked by ET-3 (100nM) and sarafotoxin S6c (10nM), two selective agonists of endothelin-B receptors, and was not additive with that of ET-3 suggesting the involvement of ETB receptors. Surprisingly, however, the ET-1 effect persisted in the presence of the ETB receptor antagonist BQ-788 (200nM-2μM) and was slightly reversed by the ETA receptor antagonist BQ-123 (2μM), suggesting an atypical pharmacological profile of the astrocytic receptors responsible for ET-1 toxicity. The ET-1 effect was not undone by the ionotropic glutamate receptor AMPA antagonist GYKI 52466 (20μM), indicating that it is not caused by an increased glutamate release. Conversely, a 48-hour ET-1 treatment increased MN cell death induced by acute exposure to AMPA (50μM), which is indicative of two distinct pathways leading to neuronal death. Altogether these results indicate that ET-1 exerts a toxic effect on cultured MNs through mechanisms mediated by reactive astrocytes and suggest that ET-1 may contribute to MN degeneration in ALS. Thus, a treatment aimed at lowering ET-1 levels or antagonizing its effect might be envisaged as a potential therapeutic strategy to slow down MN degeneration in this devastating disease.

HIF-1 and c-Src mediate increased glucose uptake induced by endothelin-1 and connexin43 in astrocytes

In previous work we showed that endothelin-1 (ET-1) increases the rate of glucose uptake in astrocytes, an important aspect of brain function since glucose taken up by astrocytes is used to supply the neurons with metabolic substrates. In the present work we sought to identify the signalling pathway responsible for this process in primary culture of rat astrocytes. Our results show that ET-1 promoted an increase in the transcription factor hypoxia-inducible factor-1α (HIF-1α) in astrocytes, as shown in other cell types. Furthermore, HIF-1α-siRNA experiments revealed that HIF-1α participates in the effects of ET-1 on glucose uptake and on the expression of GLUT-1, GLUT-3, type I and type II hexokinase. We previously reported that these effects of ET-1 are mediated by connexin43 (Cx43), the major gap junction protein in astrocytes. Indeed, our results show that silencing Cx43 increased HIF-1α and reduced the effect of ET-1 on HIF-1α, indicating that the effect of ET-1 on HIF-1α is mediated by Cx43. The activity of oncogenes such as c-Src can up-regulate HIF-1α. Since Cx43 interacts with c-Src, we investigated the participation of c-Src in this pathway. Interestingly, both the treatment with ET-1 and with Cx43-siRNA increased c-Src activity. In addition, when c-Src activity was inhibited neither ET-1 nor silencing Cx43 were able to up-regulate HIF-1α. In conclusion, our results suggest that ET-1 by down-regulating Cx43 activates c-Src, which in turn increases HIF-1α leading to the up-regulation of the machinery required to take up glucose in astrocytes. Cx43 expression can be reduced in response not only to ET-1 but also to various physiological and pathological stimuli. This study contributes to the identification of the signalling pathway evoked after Cx43 down-regulation that results in increased glucose uptake in astrocytes. Interestingly, this is the first evidence linking Cx43 to HIF-1, which is a master regulator of glucose metabolism.

Connexin43 is involved in the effect of endothelin-1 on astrocyte proliferation and glucose uptake

In previous studies, we showed that endothelin-1 increased astrocyte proliferation and glucose uptake. These effects were similar to those observed with other gap junction inhibitors, such as carbenoxolone (CBX). Because 24-h treatment with endothelin-1 or CBX downregulates the expression of connexin43, the main protein forming astrocytic gap junctions, which can also be involved in proliferation, in this study, we addressed the possible role of connexin43 in the effects of endothelin-1. To do so, connexin43 was silenced in astrocytes by siRNA. The knock down of connexin43 increased the rate of glucose uptake, characterized by the upregulation of GLUT-1 and type I hexokinase. Neither endothelin-1 nor CBX were able to further increase the rate of glucose uptake in connexin43-silenced astrocytes. In agreement, no effects of endothelin-1 and CBX on GLUT-1 and type I hexokinase were observed in connexin-43 silenced astrocytes or in astrocytes from connexin43 knock-out (KO) mice. Our previous studies suggested a close relationship between glucose uptake and astrocyte proliferation. Consistent with this, connexin43-silenced astrocytes exhibited an increase in Ki-67, a marker of proliferation. The effects of ET-1 on retinoblastoma phosphorylation on Ser780 and on the upregulation of cyclins D1 and D3 were affected by the levels of connexin43. In conclusion, our results indicate that connexin43 participates in the effects of endothelin-1 on glucose uptake and proliferation in astrocytes. Interestingly, although the rate of growth in connexin43 KO astrocytes has been reported to be reduced, we observed that an acute reduction in connexin43 by siRNA increased proliferation and glucose uptake.

Endothelin-1 stimulates the translocation and upregulation of both glucose transporter and hexokinase in astrocytes: relationship with gap junctional communication

We have previously shown that endothelin-1 increases glucose uptake in astrocytes. In the present work we investigate the mechanism through which endothelin-1 (ET-1) increases glucose uptake. Our results show that ET-1 activates a short-term and a long-term mechanism. Thus, ET-1 induced a rapid change in the localization of both GLUT-1 and type I hexokinase. These changes are probably aimed at rapidly increasing the entry and phosphorylation of glucose. In addition, ET-1 upregulated GLUT-1 and type I hexokinase and induced the expression of isoforms not normally expressed in astrocytes, such as GLUT-3 and type II hexokinase. These changes provide astrocytes with the machinery required to sustain a high rate of glucose uptake for a longer period of time. Our previous work had suggested that the effect of ET-1 on glucose uptake was associated with the inhibition of gap junctions. In this work, we compare the effect of ET-1 with that of carbenoxolone, a classical inhibitor of gap junction communication. Carbenoxolone increased glucose uptake to the same extent as ET-1 following the same mechanisms. Thus, carbenoxolone induced a rapid change in the localization of both GLUT-1 and type I hexokinase, upregulated GLUT-1 and type I hexokinase and induced the expression of GLUT-3 and type II hexokinase. When the inhibition of gap junction was prevented by tolbutamide, neither ET-1 nor carbenoxolone were able to increase the levels of GLUT-1, GLUT-3, type I hexokinase or type II hexokinase, indicating that these events are closely related to gap junctions.

Endothelins regulate astrocyte gap junctions in rat hippocampal slices

Gap junctional communication (GJC) is a typical feature of astrocytes proposed to contribute to the role played by these glial cells in brain physiology and pathology. In acutely isolated hippocampal slices from rat (P11-P19), intercellular diffusion of biocytin through gap junction channels was shown to occur between hundreds of cells immuno-positive for astrocytic markers studied in the CA1/CA2 region. Single-cell RT-PCR demonstrated astrocytic mRNA expression of several connexin (Cx) subtypes, the molecular constituent of gap junction channels, whereas immunoblotting confirmed that Cx43 and Cx30 are the main gap junction proteins in hippocampal astrocytes. In the brain, astrocytes represent a major target for endothelins (Ets), a vasoactive family of peptides. Our results demonstrate that Ets decrease the expression of phosphorylated Cx43 forms and are potent inhibitors of GJC. The Et-induced effects were investigated using specific Et receptor agonists and antagonists, including Bosentan (Tracleer trade mark ), an EtA/B receptor antagonist, and using hippocampal slices and cultures from EtB-receptor-deficient rats. Interestingly, the pharmacological profile of Ets effects did not follow the classical profile established in cardiovascular systems. The present study therefore identifies Ets as potent endogenous inhibitory regulators of astrocyte networks. As such, the action of these peptides on astrocyte GJC might be involved in the contribution of astrocytes to neuroprotective processes and have a therapeutic potential in neuropathological situations.

Intracerebroventricular administration of endothelin-1 impairs the habituation of rats to a novel environment in conjunction with brain serotonergic activation

The effects of i.c.v. administration of endothelin-1, at a low dose that does not produce abnormal behaviors such as barrel-rolling, on the emotional state of rats exposed to a novel environment were examined. Changes in the emotional state of rats with a novel environment were evaluated in terms of changes in exploratory activity in the hole-board apparatus, i.e., locomotor activity as well as the number and duration of rearing and head-dipping behaviors. Rats treated with i.c.v. saline showed marked exploratory behaviors immediately after exposure to the hole-board apparatus, but these exploratory behaviors decreased rapidly with time. On the other hand, the habituation of rats to a novel environment was prolonged by the i.c.v. administration of endothelin-1 (0.3 and 1 pmol). Furthermore, we also found that i.c.v. administration of endothelin-1 (1 pmol) significantly increased the serotonin (5-hydroxytryptamine) turnover in some brain regions, i.e., the cerebral cortex, hippocampus and midbrain, and the inhibition of brain 5-hydroxytryptamine synthesis by treatment with p-chlorophenylalanine (200 mg/kg/day, s.c.) for 2 days suppressed the behavioral effects of endothelin-1 (1 pmol, i.c.v.). In addition, i.c.v. administration of endothelin-1 (1 pmol) did not affect the spontaneous motor activity of rats. The present study demonstrated that i.c.v. administration of low doses of endothelin-1 impairs the habituation of rats to a novel environment in conjunction with brain 5-hydroxytryptaminergic activation. These results suggest that the central endothelin system may play a significant role in mediating emotionality.

Endothelin-evoked Release of Arachidonic Acid from Mouse Astrocytes in Primary Culture

In striatal astrocytes, receptors for the vasoactive peptide endothelin (ET) are associated with several intracellular signalling pathways: ET-1 increases the breakdown of phosphoinositides, induces a sustained influx of Ca2+ and inhibits the isoproterenol-induced formation of cAMP (Marin et al., J. Neurochem., 56, 1270 - 1275, 1991). In the present study, it will be shown that ET-1 and ET-3 markedly stimulate the release of arachidonic acid (AA) from cultured astrocytes from the mouse striatum (EC50=3 and 7 nM for ET-1 and ET-3, respectively), mesencephalon and cerebral cortex. The ET-1-evoked release of AA probably resulted from the activation of a phospholipase A2, since it required extracellular Ca2+ and was prevented by mepacrine but not by RHC 80267, an inhibitor of diacylglycerol lipase. The ET-1-induced release of AA was shown to be partially mediated by a guanine nucleotide-binding protein sensitive to pertussis toxin but not to cholera toxin. A cAMP-dependent process is not involved since the ET-1-evoked release of AA was not affected when cells were incubated with either isoproterenol or 8-bromo-cAMP. The ET-1-evoked release of AA could be mimicked by the co-application of a calcium ionophore and a protein kinase C activator. However, staurosporine, a potent inhibitor of protein kinase C, which blocked the release of AA induced by the combined application of ionomycin and phorbol 12-myristate 12-acetate (PMA), was without effect on the ET-1-evoked response, indicating that protein kinase C is not directly involved in the ET-1-induced release of AA. Furthermore, the responses induced by ET-1 and by PMA were found to be additive. These results suggest that (1) ET-1 receptors are coupled to the release of AA by a mechanism independent of both protein kinase C activation and the adenylate cyclase pathway, possibly via the activation of phospholipase A2, (2) different mechanisms (or different phospholipase A2 subtypes) are involved in the control of AA release in astrocytes.

Endothelins Inhibit Junctional Permeability in Cultured Mouse Astrocytes

Endothelins, a family of potent vasoconstrictor peptides initially characterized in peripheral tissues, have also been reported to be synthesized in the brain. In this structure several cell types, including astrocytes, endothelial cells and certain neurons, are potential targets for these peptides. In astrocytes, endothelins induce changes in the concentration of several second messengers (calcium, diacylglycerol, arachidonic acid, cAMP) known to be involved in the regulation of gap junction channels. Using the scrape loading/dye transfer technique we have observed that two isoforms of endothelin, endothelin-1 and endothelin-3, strongly inhibit the extent of dye-coupling between confluent astrocytes, suggesting that gap junction permeability was reduced. This inhibitory effect on dye coupling was reproduced by the snake venom sarafotoxin. When used at 10-7 M, these three compounds had inhibitory effects on gap junction channels which were comparable to those induced by the well known uncoupling agents octanol and halothane. In the absence of extracellular calcium, the effects of endothelins were largely prevented, suggesting that second messengers linked to the activation of phospholipases C and/or A2, which both are dependent on external calcium, could be involved in the uncoupling mechanism.

Sequential and opposite regulation of two outward K(+) currents by ET-1 in cultured striatal astrocytes

In the brain, astrocytes represent a major target for endothelins (ETs), a family of peptides that can be released by several cell types and that have potent and multiple effects on astrocytic functions. Four types of K(+) currents (I(K)) were detected in various proportions by patch-clamp recordings of cultured striatal astrocytes, including the A-type I(K), the inwardly rectifying I(K IR), the Ca(2+)-dependent I(K) (I(K Ca)), and the delayed-rectified I(K) (I(K DR)). Variations in the shape of current-voltage relationships were related mainly to differences in the proportion of these currents. ET-1 was found to regulate with opposite effects the two more frequently recorded outward K(+) currents in striatal astrocytes. Indeed, this peptide induced an initial activation of I(K Ca) (composed of SK and BK channels) and a delayed long-lasting inhibition of I(K DR). In current-clamp recordings, the activation of I(K Ca) correlated with a transient hyperpolarization, whereas the inhibition of I(K DR) correlated with a sustained depolarization. These ET-1-induced sequential changes in membrane potential in astrocytes may be important for the regulation of voltage gradients in astrocytic networks and the maintenance of K(+) homeostasis in the brain microenvironment.

Ca(2+) influx through nonselective cation channels plays an essential role in endothelin-1-induced mitogenesis in C6 glioma cells

Ca(2+) channels activated by endothelin-1 (ET-1) in C6 glioma cells (C6 cells) were characterized using whole-cell patch-clamps and by monitoring the intracellular free Ca(2+) concentration ([Ca(2+)](i)), when administering Ca(2+) channel blockers such as LOE 908 and SK&F 96365. Using this methodology, the Ca(2+) channels involved in ET-1-induced mitogenesis were identified. The patch-clamp study and [Ca(2+)](i) monitoring showed that 10 nM ET-1 activated two types of Ca(2+)-permeable nonselective cation channels (NSCC); one was sensitive to LOE 908 but resistant to SK&F 96365 (NSCC-1) and the other was sensitive to both LOE 908 and SK&F 96365 (NSCC-2). Conversely, 0.1 nM ET-1 activated only NSCC-1.ET-1-induced mitogenesis in a concentration-dependent manner, with the maximum effect arising at concentrations > or =10 nM. LOE 908 completely suppressed the 10 nM ET-1-induced mitogenesis, whereas SK&F 96365 only partially suppressed it. The IC(50) values of these blockers for the ET-1-induced mitogenesis were similar to those for the 10 nM ET-1-induced increase in [Ca(2+)](i). In contrast, LOE 908 completely suppressed 0.1 nM ET-1-induced mitogenesis, whereas SK&F 96365 did not affect it.Collectively, these results demonstrate that the sustained increase in [Ca(2+)](i), via NSCC-1 and NSCC-2, may be essential for ET-1-induced mitogenesis in C6 cells. Moreover, the sensitivity of NSCC-1 to ET-1 is higher than that of NSCC-2 to ET-1.

Endothelin-1 protects astrocytes from hypoxic/ischemic injury

Under pathological conditions such as ischemia (I), subarachnoid hemorrhage, and Alzheimer's disease, astrocytes show a large increase in endothelin (ET) -like immunoreactivity. However, it is not clear whether ET is protective or destructive to these cells during brain injury. Using astrocytes from ET-1-deficient mice, we determined the effect of ET-1 on these cells under normal, hypoxic (H), and hypoxic/ischemic (H/I) conditions. Under normal culture conditions, astrocytes from wild-type and ET-1-deficient mice showed no difference in their morphology and cell proliferation rates. ET-3 and ETA receptor mRNAs were up-regulated whereas ETB receptor mRNA was down-regulated in ET-1-deficient astrocytes, suggesting that ET-1 and ET-3 may complement each other's functions and that the expressions of these endothelins and their receptors are regulated by a complex feedback mechanism. Under H and H/I conditions, ET-1 peptide and mRNA were up-regulated in wild-type astrocytes, and the astrocytes without ET-1 died faster than the wild-type astrocytes, as indicated by greater efflux of lactate dehydrogenase. The present study suggests that astrocytes without ET-1 are more vulnerable to H and H/I injuries and that the up-regulation of astrocytic ET-1 is essential for the survival of astrocytes.

Endothelin-converting enzymes and endothelin receptor B messenger RNAs are expressed in different neural cell species and these messenger RNAs are coordinately induced in neurons and astrocytes respectively following nerve injury

There is some evidence that endothelins may be a signal mediator between neuronal and glial cells, at least in some regions of the brain. To evaluate this possibility, the localization of messenger RNAs for endothelin-converting enzymes and endothelin receptor B in the rat brain were examined using in situ hybridization histochemistry. The messenger RNAs for endothelin-converting enzyme-1 and endothelin-converting enzyme-2 were expressed mainly in neurons located in various brain regions, whereas the messenger RNA for endothelin receptor B was mainly localized in the astrocytes located throughout the brainstem, Bergmann glia, choroid plexus and ependymal cells. The localization patterns of endothelin-converting enzyme and endothelin receptor B messenger RNAs were strikingly different. For instance, in the cerebellum, endothelin-converting enzyme-1 messenger RNA was localized in Purkinje cells, and endothelin-converting enzyme-2 mRNA was expressed in Purkinje cells and granule cells. On the other hand, endothelin receptor B messenger RNA was expressed in Bergmann glia and the astrocytes located in the granule cell layer. This suggests that final cleavages of big endothelins are performed on neuronal cells, and the major target of the processed endothelins could be astrocytes, which express endothelin receptor B most abundantly in the brain. Since evidence that endothelin is implicated in brain injury has also accumulated, we examined whether the expressions of endothelin-converting enzymes and endothelin receptor B are regulated by nerve injury. Following hypoglossal nerve injury, expression of messenger RNA for endothelin-converting enzymes-1 and -2 and endothelin receptor B was enhanced in the injured motor neurons and astrocytes respectively. The up-regulation of these messenger RNAs was also confirmed by a reverse transcription-polymerase chain reaction based strategyThese results lead us to suggest that endothelin can be an inducible intercellular mediator between injured neurons and astrocytes in response to nerve injury.

Hypoxic modulation of striatal lesions induced by administration of endothelin-1

Levels of endothelin-1 (ET-1), a potent endogenous vasoconstrictor, are elevated in plasma and cerebrospinal fluid (CSF) following cerebral ischemia and reperfusion injury. The present study sought insight into the potential differential vasoactive effects on the cerebral vasculature and resultant neural damage of ET-1 during normoxic vs. ischemic conditions and upon reperfusion. Under normoxic conditions, intrastriatal stereotaxic injection of exogenous ET-1 (40 pmol) induced a significant (P<0.05) reduction (</=29+/-12%) in the regional (striatal) cerebral blood flow measured by Laser Doppler flowmetry (CBF(LDF)) for up to 40 min in halothane-anesthetized male Long-Evans rats. Intrastriatal injection of ET-1 10 min after the onset of hypoxia (12% O(2), balance N(2)) tended to blunt, but not significantly, the striatal CBF(LDF) responses to the 35 min period of hypoxia. ET-1 given during reoxygenation significantly (P<0.05) reduced striatal CBF(LDF), which was similar to the effect of ET-1 during normoxia. ET-1-induced infarction when administered prior to hypoxia, but not during or post-hypoxia, was significantly (P<0.05) exacerbated compared to infarction of ET-1 without hypoxia. These results suggest that exogenous ET-1 administered into the brain parenchyma can induce an infarction associated with modulation of CBF(LDF) during the normoxic or reoxygenation period, but not during the hypoxic period and that the increased release of ET-1 in any pathological phase of cerebral ischemia contributes to irreversible neural damage with associated hemodynamic disturbances.

Effect of coenzyme Q(10) on biochemical and morphological changes in experimental ischemia in the rat brain

The aim of the work was to evaluate an influence of CoQ(10) on lactate acidosis, adenosine-5'-triphosphate (ATP) concentrations, oxidized to reduced glutathione ratio and on superoxide dismutase activity in endothelin model of cerebral ischemia in the rat. Light microscopic studies in the central nervous system and morphometric analysis of pyramidal cells in the hippocampus were also performed. Endothelins (ET-1 or ET-3; 20 pmoles) were injected into the right lateral cerebral ventricle (intracerebroventricularly). CoQ(10) was given intraperitoneally (i.p.) just before the operation (i.p. 10 mgkg b. wt.). More severe changes of investigated biochemical parameters were observed in the animals treated with ET-1 in comparison with ET-3. Recovery was noted earlier in the group subjected to ET-3 and CoQ(10) administration, than in the animals subjected to ET-1 and CoQ(10) treatment. Histopathological observations showed sparse foci of a neuronal loss in the cerebral cortex and in the hippocampus only in the ET-1 model of ischemia. Additionally more numerous dark neurons were present in above brain structures following ET-1 administration comparing with ET-3 one. Morphometrical studies demonstrated that CoQ(10) diminished neuronal injury in the hippocampal CA1, CA2 and CA3 zones. Above data indicate on neuroprotective effect of CoQ(10) as a potent antioxidant and oxygen derived free radicals scavenger in the cerebral ischemia.

Astrocytes in sensory circumventricular organs of the rat brain express functional binding sites for endothelin

Sensory circumventricular organs bordering the anterior third cerebral ventricle, the subfornical organ and the organum vasculosum laminae terminalis, lack blood-brain barrier characteristics and are therefore accessible to circulating peptides like endothelins. Astrocytes of the rat subfornical organ and organum vasculosum laminae terminalis additionally showed immunocytochemical localization of endothelin-1/endothelin-3-like peptides, possibly acting as circumventricular organ-intrinsic modulators. Employing [125I]endothelin-1 as radioligand, quantitative autoradiography demonstrated specific binding sites throughout the rat organum vasculosum laminae terminalis and subfornical organ, and competitive displacement studies revealed expression of both ET(A) and ET(B) receptor subtypes for either circumventricular organ. ET(B) receptor binding prevailed for the whole brain and ET(A) receptors could be labelled in the peripheral vascular system. To characterize endothelin-specific receptors in astrocytes of both circumventricular organs, alterations in the intracellular calcium concentration due to endothelin-1/endothelin-3 stimulation were studied in primary culture of subfornical organ and organum vasculosum laminae terminalis cells obtained from early postnatal rat pups. Endothelin-1 and endothelin-3 induced Ca(2+) transients in 9-13% of either subfornical organ or organum vasculosum laminae terminalis astrocytes, respectively, and some glial cells (subfornical organ: 2%, organum vasculosum laminae terminalis: 5%) responded to both endothelin analogues. The antagonistic action of BQ123 specific for ET(A) receptors (74% of all astrocytes tested), and the pronounced responsiveness to the ET(B) receptor agonist [4Ala]ET-1 (subfornical organ: 27%, organum vasculosum laminae terminalis: 35%) demonstrated glial expression of both endothelin receptor subtypes. Agonist-induced elevations in the intracellular calcium concentration proved to be independent of extracellular Ca(2+). In summary, the results indicate that endothelin(s) interact(s) with circumventricular organ astrocytes. Competitive receptor binding techniques using brain tissue sections as well as a fura-2 loaded primary cell culture system of the subfornical organ and organum vasculosum laminae terminalis demonstrate glial expression of functional ET(A) and ET(B) receptors, with calcium as intracellular messenger emerging primarily from intracellular stores. Endothelin(s) of both circulating and circumventricular organ-intrinsic origin may afferently transfer information important for cardiovascular homeostasis to circumventricular organs serving as "windows to the brain".

Endothelin and dopamine release

Endothelins and endothelin receptors are widespread in the brain. There is increasing evidence that endothelins play a role in brain mechanisms associated with behaviour and neuroendocrine regulation as well as cardiovascular control. We review the evidence for an interaction of endothelin with brain dopaminergic mechanisms. Our work has shown that particularly endothelin-1 and ET(B) receptors are present at significant levels in typical brain dopaminergic regions such as the striatum. Moreover, lesion studies showed that ET(B) receptors are present on dopaminergic neuronal terminals in striatum and studies with local administration of endothelins into the ventral striatum showed that activation of these receptors causes dopamine release, as measured both with in vivo voltammetry and behavioural methods. While several previous studies have focussed on the possible role of very high levels of endothelins in ischemic and pathological mechanisms in the brain, possibly mediated by ET(A) receptors, we propose that physiological levels of these peptides play an important role in normal brain function, at least partly by interacting with dopamine release through ET(B) receptors.

Distinct pharmacological properties of ET-1 and ET-3 on astroglial gap junctions and Ca(2+) signaling

Astrocytes represent a major target for endothelins (ETs), a family of peptides that have potent and multiple effects on signal transduction pathways and can be released by several cell types in the brain. In the present study we have investigated the involvement of different ET receptor subtypes on intercellular dye diffusion, intracellular Ca(2+) homeostasis, and intercellular Ca(2+) signaling in cultured rat astrocytes from hippocampus and striatum. Depending on the ET concentration and the receptor involved, ET-1- and ET-3-induced intracellular Ca(2+) increases with different response patterns. Both ET-1 and ET-3 are powerful inhibitors of gap junctional permeability and intercellular Ca(2+) signaling. The nonselective ET receptor agonist sarafotoxin S6b and the ET(B) receptor-selective agonist IRL 1620 mimicked these inhibitions. The ET-3 effects were only marginally affected by an ET(A) receptor antagonist but completely blocked by an ET(B) receptor antagonist. However, the ET-1-induced inhibition of gap junctional dye transfer and intercellular Ca(2+) signaling was only marginally blocked by ET(A) or ET(B) receptor-selective antagonists but fully prevented when these antagonists were applied together. The ET-induced inhibition of gap junction permeability and intercellular Ca(2+) signaling indicates that important changes in the function of astroglial communication might occur when the level of ETs in the brain is increased.

Role of endothelin receptor subtypes in the behavioral effects of the intracerebroventricular administration of endothelin-1 in conscious rats

The role of endothelin receptor subtypes, i.e., ET(A) and ET(B) receptors, in the behavioral effects of the intracerebroventricular (ICV) administration of endothelin-1 were examined in conscious rats. ICV administration of endothelin-1 (1-9 pmol/rat) dose dependently produced barrel rolling and other convulsive behaviors including bodily twitching, rigidity, back crawling, fore/hindlimb dystonia, fore/hindlimb clonus, tail extension, and facial clonus. Moreover, a marked increase in spontaneous locomotor activity was observed in animals that were treated with a low dose of endothelin-1 (1 pmol/rat, ICV). Endothelin-1 (9 pmol/rat, ICV)-induced barrel rolling and other convulsive behaviors were completely suppressed by the coadministration of BQ-123 (15 nmol, ICV), a specific endothelin ET(A) receptor antagonist, but not of BQ-788 (15 nmol/rat, ICV), a specific endothelin ET(B) receptor antagonist. In contrast, increased locomotor activity produced by treatment with a low dose of endothelin-1 (1 pmol/rat, ICV) was antagonized by coadministration of BQ-788, but not of BQ123. These results indicate that endothelin-1, which has affinity for both endothelin ET(A) and ET(B) receptors, most likely acts on central ET(A) receptors to evoke barrel rolling and other convulsive behaviors. In addition, activation of central ET(B) receptors may be involved in the increase in spontaneous locomotor activity. These results suggest that brain endothelin receptor subtypes may be involved in the regulation of various physiological functions.

Evidence for intracellular endothelin-converting enzyme-2 expression in cultured human vascular endothelial cells

We have previously reported the intracellular localization of the endothelin-converting enzyme-1 (ECE-1) in human umbilical vein endothelial cells. In the present study, we provide the first immunocytochemical and biochemical evidence for the presence of ECE-2 in human cells. ECE activity was determined by conversion of exogenously added big endothelin-1 (big ET-1) to ET-1 in subcellular fractions obtained by sucrose density gradient centrifugation of human umbilical vein endothelial cell homogenates. ECE-1 and ECE-2 can be differentiated by pH dependence for optimal activity and by sensitivity to phosphoramidon, which shows selectivity for ECE-2 over ECE-1 and PD159790, a novel ECE-1 selective inhibitor. Optimal ECE activity was measured at pH 6.0, a value intermediate between that reported for ECE-1 (pH 6.8) and ECE-2 (pH 5.5), indicating expression of both enzymes. At pH 6.9, conversion of big ET-1 was inhibited markedly by 30 micromol/L PD159790 and by 100 micromol/L phosphoramidon but not by 0.1 micromol/L phosphoramidon. In contrast, ECE activity was unaffected by 30 micromol/L PD159790 but was inhibited markedly by 0.1 and 100 micromol/L phosphoramidon at pH 5. 4 (IC50 1.5 nmol/L), consistent with ECE-2 activity. Confocal microscopy revealed a punctate pattern of ECE-2-like immunoreactive staining in the cell cytosol, suggesting localization to secretory vesicles with a possible role in processing big ET-1 while in transit to the cell surface via the constitutive secretory pathway.

Endothelin induces dopamine release from rat striatum via endothelin-B receptors

The aim of the present study was to determine whether local administration of endothelin induces the release of dopamine in the rat striatum and to characterize and localize endothelin receptors in this brain region. Local injection of endothelin-1 (10 pmol) into the ventral striatum of urethane-anaesthetized rats caused an increase of 8 microM in the extracellular concentration of dopamine as measured by in vivo chronoamperometry. The peak increase in dopamine concentration occurred within 5 min of endothelin injection. Injection of the selective endothelin-B receptor agonist [Ala1.3,11.15]endothelin-1 (10 pmol) also caused an increase in extracellular dopamine concentration, suggesting that endothelin is acting at the endothelin-B receptor to elicit its effect. In rats with unilateral 6-hydroxydopamine lesions of the nigrostriatal pathway, the response to local injection of endothelin-1 (10 pmol) was significantly inhibited on the lesioned side as compared to the non-lesioned side. In contrast, pretreatment of the rats with the N-methyl-D-aspartate receptor antagonist dizocilpine maleate (5 mg/kg, i.p.) or the nitric oxide synthase inhibitor NG-nitro-L-arginine (3 mg/kg, i.p.) did not alter the endothelin-induced release of dopamine. In binding studies, addition of endothelin-1 displaced [125I]endothelin-1 with a Ki of 220 pM. The endothelin-B receptor antagonist BQ788 displaced [125I]endothelin-1 with a Ki of 120 nM, whereas the endothelin-A receptor antagonist BQ123 produced only a 25% displacement at 10 microM, suggesting that endothelin receptors in the striatum are of the endothelin-B subtype. In rats with unilateral 6-hydroxydopamine lesions of the nigrostriatal dopamine system, [125I]endothelin-1 binding was reduced by 53% in lesioned striatum compared to non-lesioned striatum, with no difference in the Kd. These data provide evidence that endothelin acts on a homogeneous population of endothelin-B receptors within the striatum to cause the release of dopamine and that a significant proportion of these receptors is located on dopaminergic neurons.

The endothelin system and endothelin-converting enzyme in the brain: molecular and cellular studies

The biologically active vasoactive peptides, the endothelins (ETs), are generated from inactive intermediates, the big endothelins, by a unique processing event catalysed by the zinc metalloprotease, endothelin converting enzyme (ECE). In this overview we examine the actions of endothelins in the brain, and focus on the structure and cellular locations of ECE. The heterogeneous distribution in the brain of ET-1, ET-2, and ET-3 is discussed in relation to their hemodynamic, mitogenic and proliferative properties as well as their possible roles as neurotransmitters. The cellular and subcellular localization of ECE in neuronal and in glial cells is compared with that of other brain membrane metalloproteases, neutral endopeptidase-24.11 (neprilysin), angiotensin converting enzyme and aminopeptidase N, which all function in neuropeptide processing and metabolism Unlike these ectoenzymes, ECE exhibits a dual localisation in the cell, being present on the plasma membrane and also, in some instances, being concentrated in a perinuclear region. This differential localization may reflect distinct targeting of different ECE isoforms, ECE-1 alpha, ECE-1 beta, and ECE-2.

Physiological role of brain endothelin in the central autonomic control: from neuron to knockout mouse

Although endothelin (ET) was discovered as a potent vascular endothelium-derived constricting peptide, its presumed physiological and pathophysiological roles are now considered much more diverse than originally though. Endothelin in the brain is thought to be deeply involved in the central autonomic control and consequent cardiorespiratory homeostasis, possibly as a neuromodulator or a hormone that functions locally in an autocrine/paracrine manner or widely through delivery by the cerebrospinal fluid (CSF). This notion is based on the following lines of evidence. (1) Mature ET, its precursors, converting enzymes, and receptors all are detected at strategic sites in the central nervous system (CNS), especially those controlling the autonomic functions. (2) The ET is present in the CSF at concentrations higher than in the plasma. (3) There is a topographical correspondence of ET and its receptors in the CNS. (4) The ET is released by primary cultures of hypothalamic neurons. (5) When ET binds to its receptors, intracellular calcium channels. (6) An intracerebroventricular or topical application of ET to CNS sites elicits a pattern of cardiorespiratory changes accompanied by responses of vasomotor and respiratory neurons. (7) Recently generated knockout mice with disrupted genes encoding ET-1 exhibited, along with malformations in a subset of the tissues of neural crest cell lineage, cardiorespiratory abnormalities including elevation of arterial pressure, sympathetic overactivity, and impairment of the respiratory reflex. Definitive evidence is expected from thorough analyses of knockout mice by applying conventional experimental methods.

Immortalized schwann cells express endothelin receptors coupled to adenylyl cyclase and phospholipase C

Endothelins (ETs) are potent regulators of renal, cardiovascular and endocrine functions and act as neurotransmitters in the CNS. Here we report that immortalized Schwann cells express receptors for ETs and characterize some of the cellular events triggered by their activation. Specific binding of [125I]-ET-1 to Schwann cell membranes was inhibited by ET-1 and ETB-selective agonists ET-3, sarafotoxin 6c and [Ala1,3,11,15]-ET-1 with IC50cor values ranging between 2 and 20 nM. No competition was observed with the ETA receptor-selective antagonist BQ123. Incubation of [3H]-inositol pre-labeled Schwann cells with ET-1, ET-3 or sarafotoxin 6c elicited a concentration-dependent increase in the release of [P1 that reached a plateau at approximately 100 nM. The efficacy of [Ala1,3,11,15]-ET-1 (a linear peptide analog of ET-1) was half of that corresponding to ET-1. These stimulatory effects were partially blocked by pre-incubation with pertussis toxin. When Schwann cells were incubated in the presence of 100 nM ET-1 or ET-3 there was a significant inhibition of basal and isoproterenol-stimulated cAMP levels. The inhibitory effects of sarafotoxin 6c and [Ala1,3,11,15]-ET-1 on isoproterenol-stimulated cAMP levels were similar to that observed with ET-1. Pre-incubation with pertussis toxin completely prevented this effect. These observations indicate that immortalized Schwann cells express receptors for ET peptides (predominantly ETB) coupled to modulation of phospholipase C and adenylyl cyclase activities. The actions of ETs on Schwann cells provide a novel example of the influence of vascular factors on nerve function.

Intrastriatal injection of endothelin evokes dopaminergic turning behaviour in rats through activation of the ETB receptor

Contralateral intrastriatal injection of 0.1 pmol or 1 pmol of endothelin-1 produced ipsilateral turning behaviour in rats with unilateral 6-hydroxydopamine (6-OHDA) lesions of the nigrostriatal pathway. This effect could be abolished by pretreatment with either the endothelin ETA/B receptor antagonist bosentan (1 nmol, intrastriatally) or the dopamine D2 receptor antagonist raclopride (0.1 mg/kg, s.c.) suggesting that endothelin is acting at endothelin receptors to evoke ipsilateral turning behaviour and that this response is mediated by dopamine. Similar ipsilateral turning behaviour was observed upon intrastriatal injection of 1 pmol of endothelin-3 or the specific ETB receptor agonist, [Ala1,3,11,15]endothelin-1 when compared to endothelin-1. Pretreatment with the specific ETB receptor antagonist BQ788 blocked the ipsilateral turning response to intrastriatal injection of endothelin-1 while pretreatment with the specific ETA receptor antagonist BQ123 did not significantly change the response to injection of endothelin-1. This indicates that endothelin-1, which has affinity for both ETA and ETB receptors, is most likely acting at the ETB receptor to elicit its effect. These results suggest that low doses of endothelin may act at ETB receptors to evoke the release of dopamine from the striatum in vivo.

Endothelin-1 regulates glucose utilization in cultured astrocytes by controlling intercellular communication through gap junctions

The role played by endothelin-1 and intercellular communication mediated by gap junctions in the regulation of glucose disposal by astrocytes has been studied in primary culture. Endothelin-1 increased glucose uptake by astrocytes as did one of its putative messenger arachidonic acid and the non-physiological gap junction uncoupler alpha-glycyrrhetinic acid (AGA). None of these agents increased glucose uptake by C6 glioma cells, a cell line in which gap junction proteins are poorly expressed. In confluent astrocytes, the inhibition of gap junction permeability caused by AGA doubled the activity of the pentose phosphate shunt with minimal changes in the activity of the pyruvate dehydrogenase-catalyzed reaction and that of the tricarboxylic acid cycle. By contrast, these effects were not observed in dissociated astrocytes in which intercellular communication is lacking. The scraped loading dye transfer technique was modified to follow the passage of glucose and its metabolites through astrocyte gap junctions. The diffusion of glucose, the phosphorylated derivative glucose-6-phosphate, the phosphorylisable but not metabolisable derivative ortho-methyl-glucose, and the anaerobic glycolytic product L-lactate was much higher in astrocytes than in C6 glioma cells and was inhibited by the inhibition of gap junction permeability caused by endothelin-1, arachidonic acid, octanol, or AGA. It is concluded that gap junction permeability may regulate brain metabolism by controlling the uptake, utilization, and intercellular distribution of glucose and its metabolites in astrocytes.

The role of intracellular calcium and protein kinase C in endothelin-stimulated proliferation of rat type I astrocytes

The increased expression of immunoreactive endothelin-1 (ET-1) in reactive astrocytes and its mitogenic effects on astrocytes and glioma cell lines, have implicated endothelins in the development of reactive gliosis. In this study, an increase in DNA synthesis in rat type I astrocytes was observed after cultures were transiently exposed to ET-1 for 15 min, suggesting that early signal transduction events are essential and sufficient for the propagation of the ET-1-induced mitogenic signal. Prompt increases in inositol triphosphate (IP3) formation and [Ca2+]i were observed upon the addition of ET-1 to these cells. The ET-1-evoked increase in [Ca2+]i consisted of an initial peak which was preserved in Ca(2+)-free medium, and a sustained phase which was abolished in Ca(2+)-free medium and partly attenuated by nifedipine. ET-1 also increased the activity of membrane-associated protein kinase C (PKC) and induced the in vivo phosphorylation of the 85 kD MARCKS protein, an endogenous PKC-specific substrate. The ET-1-evoked increases in DNA synthesis, IP3, [Ca2+]i, membrane PKC, and 85 kD MARCKS protein phosphorylation in rat cortical astrocytes were prevented by either the selective endothelin ETA receptor antagonist, BQ-123, or the phospholipase C (PLC)-specific inhibitor, U-73122. However, the inhibition of PKC activity did not affect ET-1-induced DNA synthesis in rat cortical astrocytes. These results suggest that ET-1-induced IP3 and/or [CA2+]i responses, but not the activation of PKC, are essential for the growth-factor like actions of ET-1 in rat cortical astrocytes.

Two distinct pathways are involved in the endothelin-3-evoked dopamine release from rat striatal slices

We investigated mechanisms mediating endothelin-3-evoked dopamine release from rat striatal slices. Endothelin-3 stimulated dopamine release from the slices in a concentration-dependent manner over a range from 1 to 10 microM. Tetrodotoxin suppressed dopamine release, but left 40% of the release unaffected. Nifedipine, a voltage-gated Ca2+ channel (VGCC) antagonist, significantly inhibited dopamine release in the presence and absence of tetrodotoxin. Endothelin-3-evoked dopamine release was attenuated by D-2-amino-5-phosphnovaleric acid or Mg2+, N-methyl-D-aspartate receptor inhibitors, and this attenuation was not observed in the presence of tetrodotoxin, thereby indicating that the tetrodotoxin-sensitive component of dopamine release was partially mediated by glutamatergic pathways. This view was also supported by findings that endothelin-3 evoked glutamate release and the exogenously applied glutamate stimulated dopamine release. Based on these results, we hypothesize that endothelin-3 produces dopamine release through two distinct mechanisms; one is a direct stimulation of dopaminergic nerve terminals and the other was activation of interneurons which promoted the release of glutamate, resulting in dopamine release.

Endothelin-3 stimulates inositol 1,4,5-trisphosphate production and Ca2+ influx to produce biphasic dopamine release from rat striatal slices

1. Real-time monitoring of dopamine (DA) release from rat striatal slices demonstrated that endothelin (ET)-3 (0.1-10 microM) produced a biphasic DA release consisting of transient and sustained components. When extracellular Ca2+ was removed, the sustained but not transient response remarkably decreased. 2. ET-3 (1-10 microM) stimulated an increase in the intracellular Ca2+ concentration ([Ca(2+)]i), which also consisted of two components. The external Ca2+ depletion inhibited primarily the sustained component of the Ca2+ response to ET-3. 3. ET-3 increased inositol 1,4,5-trisphosphate (IP3) concentrations in striatal slices. This response peaked at 10 to 20 sec and returned to the basal level 2 min after stimulation, an event which was in good accord with a prompt and transient phase of both cytosolic Ca2+ activity and DA release evoked by ET-3. 4. Thus, ET-3 produces a transient and a sustained release of DA from striatal slices by stimulating intracellular Ca2+ mobilization via IP3 formation and extracellular Ca2+ influx, respectively.

Receptor-mediated regulation of neuropeptide gene expression in astrocytes

One of the functions of glial receptors is to regulate synthesis and release of a variety of neuropeptides and growth factor peptides, which in turn act on neurons or other glia. Because of the potential importance of these interactions in injured brain, we have examined the role of two different receptors in the regulation of astrocyte neuropeptide synthesis. Stimulation of beta-adrenergic receptors on type 1 astrocytes resulted in increased mRNA and protein for the proenkephalin (PE) and somatostatin genes. This receptor also increased expression of nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF). The potential role of opiate receptors was examined in several ways. Treatment of newborn rats for 7 days with the opiate antagonist naltrexone, prior to preparation of astrocytes, had no effect on PE mRNA or met-enkephalin content but resulted in a significant increase in NGF content. However, treatment of astrocytes in culture with met-enkephalin, morphine, or naltrexone had no effect on any of these parameters. No opiate binding could be detected, using either etorphine or bremazocine, to membranes of astrocytes prepared from cortex, cerebellum, striatum, or hippocampus of 1-day, 7-day, or 14-day postnatal rats. Thus we conclude that type 1 astrocytes do not express opiate receptors and that the in vivo effects of naltrexone are mediated indirectly via some other cell type/receptor.

Sarafotoxin expression in the bronchopulmonary tract: immunohistochemical occurrence and colocalization with endothelins

The immunohistochemical occurrence of sarafotoxin (SRTX), a snake venom peptide under strong evolutionary control, was investigated in the pulmonary diffuse neuroendocrine system (PDNES) of newborn cats and rats. By applying the avidin-biotin-peroxidase complex method on serial lung sections, we have demonstrated its distribution and colocalization with different endothelin (ET) isoforms. A light microscopic study revealed apparent immunostaining for SRTX in neuronal components and smooth muscle tissue and in neuroepithelial bodies (NEB), while isolated neuroendocrine cells (NEC) remain unlabelled. Comparison of the SRTX reactivity pattern with that of different ET peptides on adjacent lung sections showed colocalization of SRTX-b with ET-3 in NEB, intrapulmonary ganglion cells and nerve fibres, on the one hand, and with ET-1 in airway and vascular smooth muscle cells, on the other. These findings, in addition to the remarkable functional and structural similarities between SRTX and ET peptides, suggest a common evolutionary origin and biological significance of sarafotoxin and endothelins. Moreover, this is the first time that a toxic peptide has been demonstrated in the PDNES.

The structure and specificity of endothelin receptors: their importance in physiology and medicine

In addition to involvement in vascular endothelium-smooth muscle communication, the secretion of and receptors for, endothelins are widely distributed. Two cloned receptor subtypes are G-protein-coupled to several intracellular messengers, predominantly inositol phosphates. From a knowledge of structure-activity relationships and peptide conformations, details of receptor architecture and selective agents, including nonpeptides and antagonists, have been discovered. From the nature of the actions of endothelins, receptor distributions (including CNS) and plasma levels, it is concluded that they are paracrine factors normally involved in long-term cellular regulation, but which may be important in several pathologies, many of which are stress-related.

Neuroendocrine actions of endothelins

Endothelins are produced in neuronal, pituitary and peripheral endocrine cells, and act through specific endothelin receptors (predominantly the ETA subtype) that are widely distributed in the neuroendocrine system. Endothelin receptors share a common signal transduction pathway with other Ca(2+)-mobilizing receptors, and endothelins induce IP3 and diacylglycerol production, and elevation of [Ca2+]i in many cell types, with kinetics similar to the cognate agonists. As reviewed here by Stanko Stojilković and Kevin Catt, the physiological consequences of endothelin-mediated cell signalling are relevant to the control of several neuroendocrine and endocrine activities including neuropeptide release, pituitary hormone secretion, gonadal and placental function, fluid and electrolyte homeostasis and glycogenolysis.

Involvement of local ischemia in endothelin-1 induced lesions of the neostriatum of the anaesthetized rat

The present study examines the possibility that lesions induced by intrastriatal injections of endothelin-1 (ET-1, 0.43 nmol/0.5 microliter) are ischemic in nature due to a vasoconstriction of the cerebral microvessels. In time course and dose-response experiments with ET-1 and in comparisons with ET-3, the volume of the lesions has been determined based mainly on the disappearance of striatal nerve cells, using a computer assisted morphometrical analysis. The blood flow in the neostriatum close to the site of injection of ET-1 was determined acutely by Laser-Doppler flowmetry. The acute metabolic effects of ET-1 were also studied on striatal superfusate levels of lactate, pyruvate, dopamine and its metabolites DOPAC (3,4-dihydroxyphenylacetic acid) and homovanillic acid (HVA) using an intrastriatal microdialysis probe. Dose related striatal lesions were observed with ET-1 (0.043-0.43 nmol) with a peak lesion volume after 24-48 h and the possible existence of a penumbra area. ET-3 showed a reduced potency to produce striatal lesions compared to ET-1. The lesions induced by ET-1 were prevented by coinjection with dihydralazine, a vasodilator drug. Acutely ET-1 (0.43 nmol/0.5 microliter) produced a prolonged reduction of the cerebral blood flow down to 40% of control values and temporary increases of striatal lactate and DA efflux, the latter change being very marked. Also a significant reduction of DOPAC and HVA was observed. These neurochemical changes were all prevented by treatment with dihydralazine.(ABSTRACT TRUNCATED AT 250 WORDS)