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

Reduced cell proliferation and increased apoptosis in the hippocampal formation in a rat model of Hirschsprung's disease

Hirschsprung's disease (HSCR) is a congenital malformation characterized by the absence of enteric ganglia in the distal intestine and gut obstruction. Some HSCR patients also have associated neurological symptoms. We studied a rat model of HSCR, also known as spotting lethal (sl/sl) rat, which carries a spontaneous deletion in the gene of endothelin receptor B (EDNRB) and a similar phenotype as humans with HSCR. We focused on the changes in cell proliferation and apoptosis in the hippocampal formation of the sl/sl rat. Proliferating cells in wildtype (+/+), heterozygous (+/sl) and homozygous (sl/sl) rats were labelled by intraperitoneal injection of 5-bromo-2'-deoxyuridine (BrdU) at postnatal day 2. The density of proliferating cells in the CA1 and CA3 regions of the hippocampus and dentate gyrus of sl/sl rats was significantly reduced compared to +/+ rats. The effect of EDNRB mutation on cell apoptosis was examined by using terminal deoxynucleotidyl transferase-mediated dUTP nick end-labelling assay. This showed that the density of apoptotic cells in the hippocampal formation, particularly in the CA1 region of sl/sl rats, was significantly increased compared to +/+ rats. The expression of brain derived neurotrophic factor (BDNF) and glial cell line-derived neurotrophic factor (GDNF) was measured with ELISA in the hippocampal formation, but no difference was revealed between genotypes. These results suggest that EDNRB mutation reduces cell proliferation and increases apoptosis in the hippocampal formation of the sl/sl rat, but does not alter the levels of BDNF and GDNF. Our findings provide an insight into the cellular changes in the brains of HSCR patients caused by EDNRB mutation.

Activation of either the ETA or the ETB receptors is involved in the development of electrographic seizures following intrahippocampal infusion of the endothelin-1 in immature rats

The period around birth is a risky time for stroke in infants, which is associated with two major acute and subacute processes: anatomical damage and seizures. It is unclear as to what extent each of these processes independently contributes to poor outcome. Furthermore, it is unclear whether there is an interaction between the two processes - does seizure activity cause additional brain damage beyond that produced by ischemia and/or does brain damage foster seizures? The model of focal cerebral ischemia induced by the intrahippocampal infusion of endothelin-1 (ET-1) in 12-day-old rat was used to examine the role of the endothelin receptors in the development of focal ischemia, symptomatic acute seizures and neurodegeneration. ET-1 (40pmol/μl) was infused either alone or co-administered with selective antagonists of ETA (BQ123; 70nmol/μl) or ETB receptors (BQ788; 70nmol/1μl). Effects of activation of ETB receptors were studied using selective agonist 4-Ala-ET-1 (40pmol/1μl). Regional cerebral blood flow (rCBF) and tissue oxygenation (pO2) were measured in anesthetized animals with a Doppler-flowmeter and a pO2-sensor, respectively. Seizure development was assessed with video-EEG in freely moving rats. Controls received the corresponding volume of the appropriate vehicle (10mM PBS or 0.01% DMSO-PBS solution; pH7.4). The extent of hippocampal lesion was determined using FluoroJade B staining performed 24h after ET-1 infusion. Infusion of ET-1 or ET-1+ETB receptor antagonist reduced rCBF to ~25% and pO2 to ~10% for about 1.5h, whereas selective ETB agonist, ET-1+ETA antagonist and the PBS vehicle had only negligible effect on the rCBF and pO2 levels. Reduction of rCBF was associated with the development of lesion in the injected hippocampus. In all groups, except sham operated and PBS controls, epileptiform activity was observed after activation of the ETA or the ETB receptors. The data revealed a positive correlation between the severity of morphological damage and all the measured seizure parameters (seizure frequency, average and total seizure duration) in the ET-1 group. In addition, the severity of morphological damage positively correlated with the average seizure duration in animals after infusion of ET-1+ETA receptor antagonist or after infusion of ET-1+ETB receptor antagonist. Our results indicate that the activation of ETA receptors is crucial for ischemia development, however either ETA or ETB receptors mediate the development of seizures following the application of ET-1 in immature rats. The dissociation between the ischemic-producing and seizure-producing processes suggests that damage is not necessary to induce seizures, although it may exacerbate them.

Targeting endothelin receptors A and B attenuates the inflammatory response and improves locomotor function following spinal cord injury in mice

After spinal cord injury (SCI), the disruption of blood-spinal cord barrier by activation of the endothelin (ET) system is a critical event leading to leukocyte infiltration, inflammatory response and oxidative stress, contributing to neurological disability. In the present study, we showed that blockade of ET receptor A (ETAR) and/or ET receptor B (ETBR) prevented early inflammatory responses directly via the inhibition of neutrophil and monocyte diapedesis and inflammatory mediator production following traumatic SCI in mice. Long-term neurological improvement, based on a series of tests of locomotor performance, occurred only in the spinal cord‑injured mice following blockade of ETAR and ETBR. We also examined the post‑traumatic changes of the micro-environment within the injured spinal cord of mice following blockade of ET receptors. Oxidative stress reflects an imbalance between malondialdehyde and superoxide dismutase in spinal cord‑injured mice treated with vehicle, whereas blockade of ETAR and ETBR reversed the oxidation state imbalance. In addition, hemeoxygenase-1, a protective protease involved in early SCI, was increased in spinal cord‑injured mice following the blockade of ETAR and ETBR, or only ETBR. Matrix metalloproteinase-9, a tissue-destructive protease involved in early damage, was decreased in the injured spinal cord of mice following blockade of ETAR, ETBR or a combination thereof. The findings of the present study therefore suggested an association between ETAR and ETBR in regulating early pathogenesis of SCI and determining the outcomes of long‑term neurological recovery.

The protective effects of endothelin-A receptor antagonist BQ-123 in pentylenetetrazole-induced seizure in rats

Endothelin-1 has been shown to increase neuronal activity and glutaminergic synaptic transmission by endothelin-A receptors (ETAR) in the nucleus tractus solitarius neurons that play an important role in epileptic seizures. Therefore, BQ-123 as an ETAR antagonist might attenuate neuronal excitability and glutaminergic synaptic transmission. The main purpose of the present study is to investigate the protective effect of acute BQ-123 treatment against pentylenetetrazole (PTZ)-induced tonic–clonic seizures. Wistar albino rats were divided into three groups: control, PTZ, and PTZ + BQ-123 groups. BQ-123 (3 mg/kg, intravenously) was administered for 15 min before injecting with PTZ (50 mg/kg, intraperitoneally). We determined a delay resulting from BQ-123 in “duration of the seizure onset.” “Number of rats with major seizure” also decreased according to scoring with video camera in PTZ + BQ-123 group. In BQ-123-treated group, there were eight rats without a major seizure, but only one rat had a delayed major seizure. The brain tissue glutathione peroxidase activity was significantly decreased in the PTZ and PTZ + BQ-123 groups. According to the results of the control group, there was a significant increase in the protein carbonyl levels of the PTZ group and a significant increase in the nitric oxide levels of the PTZ + BQ-123 group. Histological examination showed an increase in the number of neuronal hyperchromatic nucleus especially in hippocampal gyrus dentatus region of BQ-123-treated group. We concluded that BQ-123 impeded the formation and spread of seizure to a great degree. The beneficial effects of BQ-123 were comparatively supported with biochemical parameters and histological examinations.

Intrahippocampal injection of endothelin-1 in immature rats results in neuronal death, development of epilepsy and behavioral abnormalities later in life

The direct injection of endothelin-1 (ET-1) into brain parenchyma was recently suggested as a suitable model of stroke. The present study was designed to assess whether intrahippocampal injection of ET-1 in immature rats causes neurodegeneration and immediate seizures, and results in impairment of motor development, cognitive decline, epilepsy and chronic hippocampal lesion. ET-1 was injected unilaterally into the dorsal hippocampus in doses of 20 or 40 pmol at the age of 12 (P12) or 25 (P25) days. Video-electroencephalographic monitoring performed during 100 min after the injection of ET-1 demonstrated the development of convulsive epileptic seizures in 75-100% of animals of individual age-and-dose groups. Long-term behavioral follow-up did not reveal impairment of motor development in any dose-and-age group. At 2 months after ET-1 injection, impairment of spatial memory occurred only in rats with 40 pmol of ET-1 at P12. At 3 months after ET-1 injection spontaneous electrographic seizures occurred in 62.5-100% animals of both ages with no relation to the dose used. Seizures were always non-convulsive. The total seizure duration per 24 h was higher in the P12 than the P25 group, suggesting more severe epilepsy. The extent of the hippocampal lesion increased with the dose of ET-1 and was significantly higher in the P12 than the P25 group. The severity of the ET-1-induced lesion correlated positively with total seizure duration per 24 h at both ages. Our results document that early intrahippocampal injection of ET-1 results in lesion development and both immediate seizures and chronic epilepsy in either age group. Cognitive impairment occurred only in rats with ET-1 injection at P12.

Blood pressure responses of endothelin-1 1-31 within the rostral ventrolateral medulla through conversion to endothelin-1 1-21

Endothelin-1 1-31 (ET-1 1-31), a novel member of the endothelin family comprising 31 amino acids and derived from the selective hydrolysis of big ET-1 by chymase, directly activates endothelin receptors or converts to ET-1 1-21 by ET converting enzyme (ECE). The cardiovascular effects of central ET-1 1-31 are not identified. The present study was designed to investigate the cardiovascular actions of ET-1 1-31 within the rostral ventrolateral medulla (RVLM) in anesthetized rats. Bilateral injection of ET-1 1-31 (0.5, 1, and 2 pmol for each side) into the rostral ventrolateral medulla produced an initial pressor and/or a long-lasting hypotensive action but did not affect HR. Unilateral microinjection of 2 and 4 pmol of ET-1 1-31 into the rostral ventrolateral medulla only produced a significant (P < 0.05) transient increase in blood pressure by an average of 13 and 12 mm Hg, respectively, whereas unilateral microinjection of 8 pmol of ET-1 1-31 produced a sustained fall in blood pressure (from 92 +/- 6 to 69 +/- 8 mm Hg, P < 0.05). The transient pressor effect of unilaterally injecting ET-1 1-31 (4 pmol) into the rostral ventrolateral medulla was completely abolished by pretreatment with either ETA receptor antagonist BQ123 (83 +/- 2 versus 84 +/- 5 mm Hg, P > 0.05) or ET converting enzyme inhibitor phosphoramidon (99 +/- 5 versus 99 +/- 7 mm Hg, P > 0.05) but not ETB receptor antagonist IRL1038 (89 +/- 6 versus 96 +/- 7 mm Hg, P < 0.05). In addition, prior injection of phosphoramidon also completely abolished the long-lasting hypotension of intra-RVLM ET-1 1-31 (8 pmol) but did not modify the depressor action of intra-RVLM ET-1 1-21 (from 100 +/- 6 to 76 +/- 8 mm Hg, P < 0.05). In conclusion, the current results suggest that the cardiovascular effects of intra-RVLM ET-1 1-31 might be the result of conversion of ET-1 1-31 to ET-1 1-21 through activation of ETA receptors.

Genome-wide linkage scan for physical activity levels in the Quebec Family study

PURPOSE AND METHODS

It is commonly recognized that there is familial aggregation for physical activity level. However, the genes and sequence variants responsible for the familial clustering have not been investigated. We performed a genome-wide linkage scan based on 432 markers typed in 767 subjects from 207 families of the Quebec Family study with the aim of identifying loci affecting physical activity levels. Four physical activity level phenotypes were used.

RESULTS

Promising evidence of linkage (P < 0.0023) was found for physical inactivity on chromosome 2p22-p16. Suggestive linkages (0.0023<P < 0.01) were found for inactivity (7p11.2, 20q13.1), total physical activity (13q22-q31), moderate to strenuous physical activity (4q28.2, 7p11.2, 9q31.1, 13q22-q31), and time spent in physical activity (11p15 and 15q13.3).

CONCLUSION

This study identified several chromosomal regions harboring genes that may contribute to the propensity to be physically active or sedentary.

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.

Intracerebroventricular injection of neuropeptide FF, an opioid modulating neuropeptide, acutely reduces food intake and stimulates water intake in the rat

Neuropeptide FF (NPFF) is a mammalian peptide that is found in high concentrations in the central nervous system (CNS) and has also been detected in plasma. Various functions have been attributed to this peptide although its main action in the CNS remains unclear. In this study we observed that intracerebroventricular (ICV) injection of human NPFF, at early light phase in fasted rats, acutely reduced food intake and caused a large increase in water intake compared with saline injected controls. This effect was independently observed in two separate studies yielding similar results. Thus the central effects of NPFF to decrease food intake may be largely attributable to increased water intake.