Regional and subcellular distribution of [125I]endothelin binding sites in rat brain

Expression of a neuropeptide, endothelin-1 in pons and medulla of prenatal and perinatal mouse brains

Endothelin-1 (ET-1), a potent vasoconstrictor, is widely distributed in the central nervous system. This article demonstrates the spatio-temporal expression of mouse preproendothelin-1 (mPPET-1) gene in pre- and perinatal mouse brain by in situ hybridization using a probe specific for mPPET-1. mPPET-1 mRNA expression was first observed in medulla at embryonic age 11.5 (E11.5) and the level became increasingly stronger toward later stages of development. At E18.5 and postnatal day 0.5 (D0.5), mPPET-1 mRNA was found in discrete nucleus group in ventrolateral medulla. mPPET-1 mRNA was also detected in thalamic reticular nucleus at E16.5, E18.5, and D0.5. These results showed that mPPET-1 mRNA is present in neurons of central cardiorespiratory region and drastically increased during the transition from episodic fetal breathing to continuous postnatal respiration (E18.5 to D0.5), implicating the important role of ET-1 in central cardiorespiratory control regulating the onset of respiration during this critical period.

Exogenous endothelin-1 improves microvascular oxygen balance during focal cerebral ischemia in the rat

We tested the hypothesis that endothelin-1 (ET-1), a cerebrovasoconstrictive peptide, would alter microvascular oxygen balance during focal cerebral ischemia. In this study, male Wistar rats were placed in control (n=9) and ET-1-treated (n=9) groups. Cortical ischemia was induced by middle cerebral artery (MCA) occlusion in isoflurane (1.4%) anesthetized rats. Forty minutes after MCA occlusion, 10(-7) M ET-1 or saline was applied to the ischemic cortex (IC) for a period of 20 min; the fluid was changed every 5 min. After 1 h of ischemia, regional cerebral blood flow (rCBF) was determined using a 14C-iodoantipyrine autoradiographic technique. Regional arterial and venous oxygen saturation were determined microspectrophotometrically. The cerebral blood flow (45% control, 45% ET-l) and oxygen consumption (24% control, 44% ET-1) of the IC were significantly lower than the contralateral cortex. ET-1 of 10(-7) M did not cause a statistically significant alteration in regional cerebral blood flow or oxygen consumption of the IC, but did increase the average venous O(2) saturation of the IC from 50 +/- 1% to 55 +/- 2% (p<0.04). A significant (p<0.05) increase was observed in O(2) supply/consumption ratio in the ET-1-treated IC (2.79 +/- 0.26 ml O(2)/min/100 g in ET-1-treated IC vs. 2.41 +/- 0.12 ml O(2)/min/100 g in the control IC) compared to the control IC. ET-1 also significantly lowered the frequency of small veins with less than 50% O(2) saturation in the IC (39 out of 70 veins in IC vs. 17 out of 70 veins in ET-1-treated IC). Thus, the exogenous application of 10(-7) M ET-1 improved microvascular oxygen supply/consumption balance during focal cerebral ischemia.

Endothelin involvement in respiratory centre activity

To evaluate the role of endothelin (ET) in respiratory homeostasis we studied the effects of the ET(A) and ET(B) receptor blocking agent bosentan on respiratory mechanics and control in seven anaesthetised spontaneously breathing pigs, for 180 min after single bolus administration (20 mg/kg i.v.). The results show that the block of ET receptors induced a significant increase in compliance and decrease in resistance of the respiratory system, entailing a significant reduction of diaphragmatic electromyographic activity, without affecting the centroid frequency of the power spectrum. Bosentan administration induced a significant increase in tidal volume (V(T)), accompanied by a significant decrease in respiratory frequency, without any significant change in pulmonary ventilation, CO(2) arterial blood gas pressure or pH. Since the relationship between V(T) and inspiratory time remained substantially constant after bosentan administration, the changes in respiratory pattern appear to be the result of an upward shift in inspiratory off-switch threshold. Both inspiratory and expiratory times during occluded breathing were increased by block of ET receptors, suggesting also a central respiratory neuromodulator effect of ET. In conclusion the present results suggest that the block of ET receptors in spontaneously breathing pigs exerts a role on mechanical properties of the respiratory system as well as on peripheral and central mechanisms of breathing control.

Topographical distribution of neurons containing endothelin type A receptor in the rat brain

Endothelin (ET) was originally identified as a vasoactive peptide biosynthesized in vascular endothelial cells. Because ET has also been found in the brain as a neuropeptide, it has been thought to belong to the group of brain-vascular peptide hormones. To date, type A and type B receptors for ET have been found. To elucidate the topographic distribution of type A receptor (ET-AR) in the brain, we raised a specific antibody to the C-terminal (64 amino acids) peptide of rat ET-AR and immunostained rat brain sections with this antibody. Immunoreactivity for ET-AR was detected in neuronal cell bodies and also in the many proximal and some distal parts of their fibers. Nerve cell bodies containing strong ET-AR-immunoreactivity were distributed in the lateral part of the reticular formation, the nucleus of the solitary tract and its surrounding area, the dorsal midline area and medial longitudinal fasciculus, the subependymal layer of the fourth ventricular roof, the caudolateral area of the pontine tegmentum, the locus coeruleus, the rostral pontine area of the lateral reticular formation, the retrorubral area, the substantia nigra, the ventral tegmental area, the periventricular region lateral to the rostral mesencephalic aqueduct and caudal third ventricle, the arcuate hypothalamic nucleus, the caudomedial area of the zona incerta, the periventricular hypothalamic nucleus, the parvocellular portion of the paraventricular hypothalamic nucleus, and the periglomerular region of the olfactory bulb. In addition, the Purkinje cells of the cerebellar cortex, the nerve cells in the mesencephalic trigeminal nucleus, and the magnocellular neurons of the supraoptic and paraventricular hypothalamic nuclei showed weak immunoreactivity. The distribution of highly ET-AR-immunoreactive neurons is quite similar to that ofcatecholamine neurons.

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.

Behavioural, autonomic and endocrine responses associated with C-fos expression in the forebrain and brainstem after intracerebroventricular infusions of endothelins

Endothelins are a range of peptides (endothelin-1, endothelin-2, and endothelin-3) well known to act peripherally as powerful cardiovascular-regulating agents. Recently, they have been shown to be localized in CSN, where they may act as central neurotransmitters. A variety of putative roles has been ascribed to them in the CNS. To identify those regions of the brain capable of responding to these peptides, the expression of c-fos (an immediate-early gene), has been used to map patterns of activation following intracerebroventricular (i.c.v.) infusions of endothelins in Lister-hooded rats. This has been correlated with changes in heart rate, core temperature and plasma corticosterone levels. Endothelin-3 i.c.v. (50 pmol) decreased both heart rate and core temperature (both recorded by telemetry). This effect lasted for about 30-45 min. Endothelin-1 (10 pmol) or endothelin-3 (50 pmol) i.c.v. induced c-fos expression in the specific regions in the forebrain and brainstem. Strong expression was found in the septum, bed nucleus of the stria terminalis, parvicellular paraventricular nucleus, the central nucleus of the amygdala, dorsal motor nucleus of the vagus and solitary nucleus. There was less marked c-fos expression in other areas of the basal forebrain, such as the organum vasculosum of the lamina terminals, median preoptic nucleus, supraoptic nucleus and the magnocellular. There are two classes of endothelin receptor (A and B). An endothelin-A receptor antagonist, BQ-123, abolished c-fos expression in all structures in the forebrain and brainstem following endothelin-1 infusions. However, an endothelin-B agonist (TetraAla endothelin-1) did not induce discernible c-fos expression in the forebrain or brainstem. These results suggest that the endothelin-A receptor is responsible for endothelin-dependent c-fos induction in the brain. Interactions between endothelins and angiotensin II were also studied. The pattern of c-fos induced by endothelin-3 and angiotensin II was different (particularly in the anteroventral region of the third ventricle). Furthermore, prior infusions of endothelin-3 interfered with the expression of c-fos induced by subsequent angiotensin II, and also suppressed the latter's dipsogenic effect. These results show that endothelin-3 and angiotensin II interact at both behavioural and cellular levels, and that endothelins may play significant roles in the central control of fluid balance and autonomic activity.

FR139317, a specific ETA-receptor antagonist, inhibits cerebral activation by intraventricular endothelin-1 in conscious rats

A comprehensive series of time-related behavioral, physiological and cerebral metabolic studies was conducted using conscious Sprague-Dawley rats to discern the anti-endothelin (ET) properties of the specific ETA receptor antagonist, FR139317. Endothelin-1 (9 pmol given by injection into one lateral ventricle, i.c.v.) produced convulsions, acute arterial hypertension, arterial hyperglycemia, and hyperventilation. Brain structures close to the i.c.v. site of injection, such as the caudate nucleus, lateral septal nucleus, corpus callosum and hippocampal CA3 medial lamellae, as well as 14 other individual structures, displayed moderate-to-intense levels of metabolic activation after endothelin. Data were assessed quantitatively by means of the autoradiographic [14C]deoxyglucose technique combined with image analysis. Neural circuits in the efferent projection paths of the stimulated forebrain structures, such as the midbrain oculomotor complex, amygdaloid nuclei, substantia nigra pars reticulata and caudal subicular subregions of the hippocampal formation, were stimulated focally by endothelin. Specific medullary nuclei and cerebellar cortical subregions displayed high rates of glucose metabolism following endothelin injection at the time of maximum behavioral and physiological stimulation. I.c.v. treatment with > or = 14 nmol FR139317 before endothelin significantly inhibited the effects produced by the peptide. At the highest dose of FR139317 (28 nmol), there was only mild behavioral stimulation following endothelin injection, and hypermetabolic responses in the brain were abolished except in two specific areas of the cerebellar cortex (approx 40% increases in metabolic activity in the copula pyramis and paramedian lobule). The results indicate that the cerebral stimulatory effects of i.c.v. endothelin are mediated by the A type of endothelin receptor. By itself, i.c.v. FR139317 had no effects on the parameters assessed. Further evaluation of FR139317 is warranted as a possible therapeutic agent for neuropathologies suspected of deriving from central neural or vascular stimulation by endothelin, such as aneurysmal vasospasm, ischemia, excitotoxicity, and peptide-mediated epilepsies.

Effects of total fasting or chronic food restriction on plasma endothelin levels in rats

We tested the effects of 24- and 48-h fasting and 40% calorie restriction stresses on plasma endothelin (ET)-1,2 levels in male Sprague-Dawley rats. Plasma ET-1,2 levels in pg/ml were lower in 24-h fasted rats (15.48 +/- 3.49), 48-h fasted rats (5.28 +/- 4.32), and in chronically food-deprived rats (R) (10.49 +/- 6.28) compared to ad lib-fed (AL) rats (21.23 +/- 9.38). The R rats were pair-fed 40% fewer calories than AL rats. We conclude that calorie restriction or total food deprivation stress decreases plasma ET-1,2 levels, unlike many other forms of physiological stress that have been shown to increase plasma ET-1,2 levels.