L-arginine ameliorates cerebral blood flow and metabolism and decreases infarct volume in rats with cerebral ischemia

Zhilong Huoxue Tongyu Capsules' Effects on ischemic stroke: An assessment using fecal 16S rRNA gene sequencing and untargeted serum metabolomics

Zhilong Huoxue Tongyu capsule (ZHTC) is an effective traditional Chinese medicine compound for the treatment of ischemic stroke, which is widely used in clinical ischemic stroke patients. However, it is uncertain whether ZHTC affects ischemic stroke through gut microbiota and serum metabolites. In this study, a rat model of middle cerebral artery occlusion (MCAO) was prepared. By evaluating motor nerve function score, cerebral infarct size, brain tissue damage and intestinal barrier damage, it was found that ZHTC improved stroke-related symptoms in MCAO rats. Using 16S rRNA gene sequencing, fecal microbial transplantation (FMT), untargeted metabolomics, and spearman correlation analysis of gut microbiota and serum metabolites, we found that ZHTC can regulate the abundance of p_Firmicutes, p_Bacteroidota,p_Proteobacteria, g_Prevotella, and g_Lactobacillus, and regulated 23 differential metabolites. Spearman correlation analysis found that Arginine was positively correlated with p_Firmicutes, o_Clostridiales, c_Clostridia, and negatively correlated with p_Bacteroidetes, c_Bacteroidia,o_Bacteroidales; L-Lysine was negatively correlated with f_Christensenellaceae; L-methionine was positively correlated with o_Lactobacillales, f_Lactobacillaceae, and g_Lactobacillus. Altogether, this study shows for the first time that ZHTC can ameliorate ischemic stroke by modulating gut microbiota and metabolic disturbances. This lays the foundation for further revealing the causal relationship between ZHTC, gut dysbiosis, plasma metabolite levels and ischemic stroke, and provides a scientific explanation for the ameliorating effect of ZHTC on ischemic stroke.

Treatment of acute cerebral ischemia using animal models: a meta-analysis

BACKGROUND

There are numerous potential treatments assessed for acute cerebral ischemia using animal models. This study aimed to assess the effect of these treatments in terms of infarct size and neurobehavioral change. This meta-analysis was conducted to determine if any of these treatments provide a superior benefit so that they might be used on humans.

METHODS

A systematic search was conducted using several electronic databases for controlled animal studies using only nonsurgical interventions for acute cerebral ischemia. A random-effects model was used.

RESULTS

After an extensive literature search, 145 studies were included in the analysis. These studies included 1408 treated animals and 1362 control animals. Treatments that had the most significant effect on neurobehavioral scales included insulin, various antagonists, including N-methyl-D-aspartate (NMDA) receptor antagonist ACEA1021, calmodulin antagonist DY-9760e, and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor antagonist YM872, and antiviral agents. Treatments providing the greatest effect on infarct size included statins, sphingosine-1-phosphate agonist (fingolimod), alcohol, angiotensin, and leukotrienes. Treatments offering the greatest reduction in brain water content included various agonists, including sphingosine-1-phosphate agonist fingolimod, statins, and peroxisome proliferator-activated receptor gamma (PPAR-γ). Treatment groups with more than one study all had high heterogeneity (I² > 80%), however, using meta-regression we determined several sources of heterogeneity including sample size of the treatment and control groups, the occlusion time, but not the year when the study was conducted.

CONCLUSIONS

Some treatments stand out when compared to others for acute cerebral ischemia in animals. Greater replication of treatment studies is required before any treatments are selected for future human trials.

Depletion of arginine by recombinant arginine deiminase induces nNOS-activated neurotoxicity in neuroblastoma cells

The abnormal regulation of inducible nitric oxide synthase (iNOS) and neuronal nitric oxide synthase (nNOS) is associated with neurodegenerative disorders. Recombinant arginine deiminase (rADI) is a selective NO modulator of iNOS and eNOS in endothelial cells, and it also exhibits neuroprotective activity in an iNOS-induced neuron-microglia coculture system. However, the effect of rADI on nNOS remains unknown. Addressing this issue is important for evaluating the potential application of rADI in neurodegenerative diseases. SH-SY5Y cells were treated with N-methyl-D-aspartic acid (NMDA) to activate nNOS. NMDA increased NO production by 39.7 ± 3.9% via nNOS under arginine-containing conditions, but there was no significant increase in both arginine-free and rADI pretreated arginine-containing (citrulline) buffer. Subsequently, neither NMDA nor rADI alone caused cytotoxicity, whereas cotreatment with NMDA and rADI resulted in dissipation of the cell mitochondrial membrane potential and decreased cell viability. The mechanism of rADI cytotoxicity in the presence of NMDA is caused by the inhibition of NO production via nNOS mediated by the NMDA receptor, which was abolished when extracellular arginine was absent, even in the presence of citrulline. rADI not only reduced NO production but also caused cellular toxicity in nNOS-activated SH-SY5Y cells, suggesting a dual role for rADI in NOS-mediated neurotoxicity.

Low oral doses of bisphenol A increase volume of the sexually dimorphic nucleus of the preoptic area in male, but not female, rats at postnatal day 21

Perinatal treatment with relatively high doses of bisphenol A (BPA) appears to have little effect on volume of the rodent sexually dimorphic nucleus of the preoptic area (SDN-POA). However, doses more relevant to human exposures have not been examined. Here, effects of pre- and post-natal treatment with low BPA doses on SDN-POA volume of postnatal day (PND) 21 Sprague-Dawley rats were evaluated. Pregnant rats were orally gavaged with vehicle, 2.5 or 25.0 μg/kg BPA, or 5.0 or 10.0 μg/kg ethinyl estradiol (EE₂) on gestational days 6-21. Beginning on the day after birth, offspring were orally treated with the same dose their dam had received. On PND 21, offspring (n=10-15/sex/group; 1/sex/litter) were perfused and volume evaluation was conducted blind to treatment. SDN-POA outline was delineated using calbindin D28K immunoreactivity. Pairwise comparisons of the significant treatment by sex interaction indicated that neither BPA dose affected female volume. However, females treated with 5.0 or 10.0 μg/kg EE₂ exhibited volumes that were larger than same-sex controls, respectively (p<0.001). Males treated with either BPA dose or 10.0 μg/kg/day EE₂ had larger volumes than same-sex controls (p<0.006). These data indicate that BPA can have sex-specific effects on SDN-POA volume and that these effects manifest as larger volumes in males. Sensitivity of the methodology as well as the treatment paradigm was confirmed by the expected EE₂-induced increase in female volume. These treatment effects might lead to organizational changes within sexually dimorphic neuroendocrine pathways which, if persistent, could theoretically alter adult reproductive physiology and socio-sexual behavior in rats.

Endothelium-derived hyperpolarizing factor in the brain: influence of sex, vessel size and disease state

The endothelial layer of cells lining the intimal surface of blood vessels is essential for vascular function. The endothelium releases multiple vasodilator and protective factors, including nitric oxide, prostacyclin and endothelium-derived hyperpolarizing factor; an imbalance in these factors predisposes individuals to vascular diseases such as stroke. These factors are differentially regulated by vessel size, sex hormones and disease state, therefore playing differential roles in different tissues following vascular injury. In particular, the endothelium-derived hyperpolarizing factor candidate termed epoxyeicosatrienoic acid, plays a prominent role in microvessel function, especially after ischemia, thereby making this signaling pathway an attractive target for therapy in vascular disease, including stroke.

Cerebral blood flow alteration in neuroprotection following cerebral ischaemia

The best neuroprotectant for acute ischaemic stroke would always be the rapid return of oxygen and glucose to physiological levels. This is currently provided by thrombolysis which restores blood flow to the ischaemic region. The attempt to confer neuroprotection by targeting the brain parenchyma has shown promise in experimental stroke models, but has unequivocally failed to translate to the clinic. Neuroprotective therapy primarily targets the biochemical cascade that produces cell death following cerebral ischaemia. However, these agents may also alter signal transduction that controls cerebral blood flow, for example glutamate, which may affect the outcome after ischaemia. In these cases, neuroprotection may potentially be due to the improved access to oxygen and glucose rather than biochemical prevention of cell death. Improvement in cerebral blood flow is an important but often overlooked effect of neuroprotective therapy, analogous to the protective effects of drug-induced hypothermia. This short review will discuss cerebral blood flow alteration and protection of the brain in the context of ischaemic preconditioning, oxygen sensing and thrombolysis. Future neuroprotection studies in cerebral ischaemia require stringent monitoring of cerebral blood flow, plus other physiological parameters. This will increase the chances that any protection observed may be able to translate to human therapy.

Combining glial cell line-derived neurotrophic factor gene delivery (AdGDNF) with L-arginine decreases contusion size but not behavioral deficits after traumatic brain injury

Our laboratory has previously demonstrated that viral administration of glial cell line-derived neurotrophic factor (AdGDNF), one week prior to a controlled cortical impact (CCI) over the forelimb sensorimotor cortex of the rat (FL-SMC) is neuroprotective, but does not significantly enhance recovery of sensorimotor function. One possible explanation for this discrepancy is that although protected, neurons may not have been functional due to enduring metabolic deficiencies. Additionally, metabolic events following TBI may interfere with expression of therapeutic proteins administered to the injured brain via gene therapy. The current study focused on enhancing the metabolic function of the brain by increasing cerebral blood flow (CBF) with l-arginine in conjunction with administration of AdGDNF immediately following CCI. An adenoviral vector harboring human GDNF was injected unilaterally into FL-SMC of the rat immediately following a unilateral CCI over the FL-SMC. Within 30min of the CCI and AdGDNF injections, some animals were injected with l-arginine (i.v.). Tests of forelimb function and asymmetry were administered for 4weeks post-injury. Animals were sacrificed and contusion size and GDNF protein expression measured. This study demonstrated that rats treated with AdGDNF and l-arginine post-CCI had a significantly smaller contusion than injured rats who did not receive any treatment, or injured rats treated with either AdGDNF or l-arginine alone. Nevertheless, no amelioration of behavioral deficits was seen. These findings suggest that AdGDNF alone following a CCI was not therapeutic and although combining it with l-arginine decreased contusion size, it did not enhance behavioral recovery.

The contribution of L-arginine to the neurotoxicity of recombinant tissue plasminogen activator following cerebral ischemia: a review of rtPA neurotoxicity

Alteplase is the only drug licensed for acute ischemic stroke, and in this formulation, the thrombolytic agent recombinant tissue plasminogen activator (rtPA) is stabilized in a solution of L-arginine. Improved functional outcomes after alteplase administration have been shown in clinical trials, along with improved histological and behavioral measures in experimental models of embolic stroke. However, in animal models of mechanically induced ischemia, alteplase can exacerbate ischemic damage. We have systematically reviewed the literature of both rtPA and L-arginine administration in mechanical focal ischemia. The rtPA worsens ischemic damage under certain conditions, whereas L-arginine can have both beneficial and deleterious effects dependent on the time of administration. The interaction between rtPA and L-arginine may be leading to the production of nitric oxide, which can cause direct neurotoxicity, altered cerebral blood flow, and disruption of the neurovascular unit. We suggest that alternative formulations of rtPA, in the absence of L-arginine, would provide new insight into rtPA neurotoxicity, and have the potential to offer more efficacious thrombolytic therapy for ischemic stroke patients.

EFFECTS OF HYPERTONIC ARGININE ON CEREBRAL BLOOD FLOW AND INTRACRANIAL PRESSURE AFTER TRAUMATIC BRAIN INJURY COMBINED WITH HEMORRHAGIC HYPOTENSION

Hypertonic saline solutions improve cerebral blood flow (CBF) when used for acute resuscitation from hemorrhagic hypotension accompanying some models of traumatic brain injury (TBI); however, the duration of increased CBF is brief. Because the nitric oxide synthase substrate l-arginine provides prolonged improvement in CBF after TBI, we investigated whether a hypertonic resuscitation fluid containing l-arginine would improve CBF in comparison to hypertonic saline without l-arginine in a model of moderate, paramedian, fluid-percussion TBI followed immediately by hemorrhagic hypotension (mean arterial pressure [MAP] = 60 mm Hg for 45 min). Sprague-Dawley rats were anesthetized with 4.0% isoflurane, intubated and ventilated with 1.5%-2.0% isoflurane in oxygen/air (50:50). After preparation for TBI and measurement of CBF using laser Doppler flowmetry and measurement of intracranial pressure (ICP) using an implanted transducer, rats were subjected to moderate (2.0 atm) TBI, hemorrhaged for 45 min, and randomly assigned to receive an infusion of hypertonic saline (7.5%, 2,400 mOsm total; 6 mL/kg; n = 6) or hypertonic saline with 50, 100, or 300 mg/kg L-arginine (2,400 mOsm; 6 mL/kg; n = 6 in each of the three dose groups) and then monitored for 120 min after the end of infusion. CBF was measured continuously and calculated as a percent of the pre-TBI baseline during the hemorrhage period, after reinfusion of one of the hypertonic arginine solutions, and 30, 60, and 120 min after reinfusion. All four hypertonic solutions initially improved MAP, which, by 120 min after infusion, had decreased nearly to the levels observed during hemorrhage. ICP remained below baseline levels during resuscitation in all groups, although ICP was slightly greater (P = NS) than baseline in the hypertonic saline group. CBF increased similarly in all groups during infusion and then decreased similarly in all groups. At 120 min after infusion, CBF was highest in the group infused with hypertonic saline, but the difference was not significant. We conclude that the improvement of MAP, ICP, and CBF produced by hypertonic saline alone after TBI and hemorrhagic hypotension is not significantly enhanced by the addition of L-arginine at these doses.

Neuroprotective effect of L-arginine in a newborn rat model of acute severe asphyxia

The left common carotid artery was ligated in anaesthetized 7-day-old Wistar rats (P7), prior to asphyxia by inhaling 100% nitrogen for 9 min. Pups recovered from asphyxia received i.p. saline (n = 16), or L-Arg 300 mg/kg (n = 14). Pups undergoing sham operation remained as controls (n = 12). At day 14, the amount of surviving or degenerating neurons was quantified under optical microscopy by Nissl technique or by Fluoro-Jade B (FJB) in CA1 area of hippocampus and in parietal cortex. In these areas, asphyxia reduced the neuronal density by 23.6 and 30%, and increased the proportion of degenerating neurons two and four times, respectively. L-Arg administration to asphyxiated pups reduced the neuronal loss and the proportion of degenerating neurons by 50% (p < 0.05). We conclude that L-Arg administration after acute severe asphyxia in newborn rats is neuroprotective, reducing early and delayed neuronal loss.

A systematic review of nitric oxide donors and L-arginine in experimental stroke; effects on infarct size and cerebral blood flow

BACKGROUND

Nitric oxide (NO) is a candidate treatment for acute ischaemic stroke, however published studies in experimental stroke have given conflicting results.

METHODS

We performed a systematic review of published controlled studies of L-arginine (the precursor for NO) and NO donors in experimental stroke. Data were analysed using the Cochrane Collaboration Review Manager software. Standardised mean difference (SMD) and 95% confidence intervals (95% CI) were calculated.

RESULTS

Altogether, 25 studies(s) were identified. L-Arginine and NO donors reduced total cerebral infarct volume in permanent (SMD -1.21, 95% CI -1.69 to -0.73, p < 0.01, s = 10) and transient models of ischaemia (SMD -0.78, 95% CI -1.21 to -0.35, p < 0.01, s = 7). Drug administration increased cortical CBF in permanent (SMD +0.86, 95% CI 0.52-1.21, p < 0.01, s = 8) but not transient models (SMD +0.34, 95% CI -0.02 to 0.70, p = 0.07, s = 4).

CONCLUSIONS

Administration of NO in experimental stroke reduces stroke lesion volume in permanent and transient models. This may be mediated, in part, by increased cerebral perfusion in permanent models. These data support clinical trials in stroke patients, although the presence of a narrow therapeutic time window may be a limiting factor.

Proestrus levels of estradiol during transient global cerebral ischemia improves the histological outcome of the hippocampal CA1 region: perfusion-dependent and-independent mechanisms

We conducted this study to determine whether high physiological levels of estradiol (proestrus) could protect the hippocampal CA1 neurons following transient global ischemia. Ovariectomized or ovary-intact female rats were subjected to 20 min of ischemia and allowed to survive for 96 h. Estradiol was administered subcutaneously in a group of ovariectomized rats 24 h before ischemia induction. Ending serum estrogen levels were correlated to cerebral blood flow (CBF), histologic assessment and immunofluorescent caspase-3 active peptide (C-3AP) positive cell count. Estradiol administration significantly improved CBF in the hippocampus (compared with intact or ovariectomized rats) but not in the parietal cortex. No significant differences in CBF between intact or ovariectomized rats were noted. Estradiol administration maintained serum levels of the steroid in estradiol-treated rats-about 10 times that of intact animals and more than 20 times that of ovariectomized animals. Morphologically, live cell counts in estradiol-treated rats were significantly higher than in intact or ovariectomized rats. Live cell counts were also significantly higher in intact than ovariectomized rats. C-3AP positive cell counts were much higher in ovariectomized rats than in intact and estradiol-treated rats. In conclusion, proestrus levels of 17beta-estradiol protect hippocampal CA1 neurons against transient global ischemia, through mechanisms that appear to involve improvement of perfusion and inhibition of caspase-3 activity.

Arginine metabolism and the synthesis of nitric oxide in the nervous system

The biochemistry and physiology of L-arginine have to be reconsidered in the light of the recent discovery that the amino acid is the only substrate of all isoforms of nitric oxide synthase (NOS). Generation of nitric oxide, NO, a versatile molecule in signaling processes and unspecific immune defense, is intertwined with synthesis, catabolism and transport of arginine which thus ultimately participates in the regulation of a fine-tuned balance between normal and pathophysiological consequences of NO production. The complex composition of the brain at the cellular level is reflected in a complex differential distribution of the enzymes of arginine metabolism. Argininosuccinate synthetase (ASS) and argininosuccinate lyase which together can recycle the NOS coproduct L-citrulline to L-arginine are expressed constitutively in neurons, but hardly colocalize with each other or with NOS in the same neuron. Therefore, trafficking of citrulline and arginine between neurons necessitates transport capacities in these cells which are fulfilled by well-described carriers for cationic and neutral amino acids. The mechanism of intercellular exchange of argininosuccinate, a prerequisite also for its proposed function as a neuromodulator, remains to be elucidated. In cultured astrocytes transcription and protein expression of arginine transport system y(+) and of ASS are upregulated concomittantly with immunostimulant-mediated induction of NOS-2. In vivo ASS-immunoreactivity was found in microglial cells in a rat model of brain inflammation and in neurons and glial cells in the brains of Alzheimer patients. Any attempt to estimate the contributions of arginine transport and synthesis to substrate supply for NOS has to consider competition for arginine between NOS and arginase, the latter enzyme being expressed as mitochondrial isoform II in nervous tissue. Generation of NOS inhibitors agmatine and methylarginines is documented for the nervous system. Suboptimal supply of NOS with arginine leads to production of detrimental peroxynitrite which may result in neuronal cell death. Data have been gathered recently which point to a particular role of astrocytes in neural arginine metabolism. Arginine appears to be accumulated in astroglial cells and can be released after stimulation with a variety of signals. It is proposed that an intercellular citrulline-NO cycle is operating in brain with astrocytes storing arginine for the benefit of neighbouring cells in need of the amino acid for a proper synthesis of NO.

17-beta estradiol can reduce secondary ischemic damage and mortality of subarachnoid hemorrhage

Subarachnoid hemorrhage (SAH) is a unique disorder commonly occurring when an aneurysm ruptures, leading to bleeding and clot formation, with a higher incidence in females. To evaluate the influence of 17-beta estradiol (E2) in the outcome of subarachnoid hemorrhage, SAH was induced by endovascular puncture of the intracranial segment of internal carotid artery in 15 intact females (INT), 19 ovariectomized females (OVX), and 13 ovariectomized female rats with E2 replacement (OVX + E2). Cerebral blood flow was recorded before and after SAH. All animals were decapitated immediately after death or 24 hours after SAH for clot area analysis. Brains were sliced and stained with 2,3,5-triphenyltetrazolium chloride (TTC) for secondary ischemic lesion analysis. The cortical cerebral blood flow (CBF), which was measured by a laser-Doppler flowmeter, decreased to 29.6%+/-17.7%, 22.8%+/-8.3%, and 43.5%+/-22.9% on the ipsilateral side (P = 0.01), and decreased to 63.4%+/-14.1%, 57.4%+/-11.0%, and 66.6%+/-17.9% on the contralateral side (P = 0.26) in INT, OVX, and OVX + E2, respectively. The subcortical CBF, which were measured by the H2 clearance method, were 7.77+/-12.03, 7.80+/-8.65, and 20.58+/-8.96 mL 100 g(-1) min(-1) on the ipsilateral side (P < 0.01), and 21.53+/-2.94, 25.13+/-3.01, and 25.30+/-3.23 mL 100 g(-1) min(-1) on the contralateral side in INT, OVX, and OVX + E2, respectively. The mortality was 53.3%, 68.4%, and 15.4% in INT, OVX, and OVX + E2, respectively (P = 0.01), whereas no significant difference in clot area was noted among the groups. The secondary ischemic lesion volume was 9.3%+/-8.4%, 24.3%+/-16.3%. and 7.0%+/-6.4% in INT, OVX, and OVX + E2, respectively (P < 0.01). This study demonstrated that E2 can reduce the mortality and secondary ischemic damage in a SAH model without affecting the clot volume.

Definition of the anterior choroidal artery territory in rats using intraluminal occluding technique

This manuscript delineates the territory of the anterior choroidal artery (AChA) in rats, as defined by the induction of an AChA infarction. By advancing a 0.24-mm surgical suture up the internal carotid artery (ICA) to a point 0.5-2 mm proximal to the middle cerebral artery (MCA) origin, the AChA could be occluded and a reliable AChA distribution infarction was produced in 62% (23/37) of animals. The infarct volume, as defined by TTC staining, was 55+/-7 mm(3). Maps of the infarction, generated by measuring the entire area of overlapping coronal slices, demonstrated that the internal capsule was always damaged. Other areas that might be affected included the hippocampus, thalamus, amygdaloid complex, piriform cortex, dorsal caudatoputamen, and lateral ventricular wall. Positioning the coated suture proximal to the AChA produced a much smaller infarct involving the medial and lateral hypothalamus, preoptic region, optic chiasm, and marginal region of the internal capsule near to the lateral hypothalamus exempt from AChA territory damage. A causative relationship between AChA occlusion and a deep cerebral infarct centered on the internal capsule was further established by: (1) identifying the AChA on the non-ischemic side with colored silicone perfusion, and subsequent similar delineation on the ischemic side, and (2) delineating infarction in the silicone perfused AChA region using hematoxylin and eosin staining and the TUNEL method. The AChA usually originated from the ICA (91% of cases), 1.75+/-0.12 mm proximal to the MCA bifurcation. Approximately 27% of the AChAs had periamygdaloid branch(es) on its initial segment.

Treatment with an endothelin type A receptor-antagonist after cardiac arrest and resuscitation improves cerebral hemodynamic and functional recovery in rats

OBJECTIVE

Successful resuscitation of the brain after cardiac arrest requires unimpaired microcirculatory reperfusion. Postischemic cerebral hypoperfusion presumably is mediated through activation of endothelin type A receptors (ET(A)). The effect of the selective ET(A) antagonist BQ123 on cerebral blood flow and function was studied in a rat model of cardiac arrest.

DESIGN

Prospective, randomized trial.

SETTING

Experimental animal laboratory.

SUBJECTS

Twelve male Sprague-Dawley rats (290-350 g).

INTERVENTIONS

Cardiac arrest for 12 mins was induced by electrical fibrillation of the heart, followed by standardized cardiopulmonary resuscitation. BQ123 (0.8 mg/kg; n = 6) or its vehicle (saline; n = 6) was injected intravenously at 15 mins after the return of spontaneous circulation.

MEASUREMENTS

Cortical blood flow was measured by laser-Doppler flowmetry, electrophysiological function by recording the amplitude of somatosensory evoked potentials, vascular reactivity by ventilation with 6% CO2, and the functional coupling of blood flow by recording the laser-Doppler flow (LDF) changes during somatosensory stimulation. Hemodynamic and functional cerebral recovery was monitored for 3 hrs after the return of spontaneous circulation.

MAIN RESULTS

Forty-five minutes after the return of spontaneous circulation, postischemic hypoperfusion developed in both groups, as reflected by a decrease of the LDF signal to about 60% of the preischemic level. In untreated animals, hypoperfusion persisted throughout the observation time, but in animals receiving BQ123, LDF gradually returned to normal. CO2 reactivity in untreated animals was severely reduced for 2-3 hrs after the onset of recirculation, whereas after BQ123 treatment it returned to normal and after 2 hrs even above normal. The ET(A) antagonist also induced a more rapid recovery of the somatosensory evoked potentials amplitude and of the functional blood flow response to somatosensory stimulation, but these parameters did not recover completely within the observation period.

CONCLUSIONS

Application of the ET(A) antagonist BQ123 during the early reperfusion period after cardiac arrest shortens postischemic cerebral hypoperfusion and accelerates the restoration of the cerebrovascular CO2 reactivity and the recovery of electrophysiologic function.

Role of nitric oxide in the ethylcholine aziridinium model of delayed apoptotic neurodegeneration in vivo and in vitro

The involvement of nitric oxide in neurodegenerative processes still remains incompletely characterized. Although nitric oxide has been reported to be an important mediator in neuronal degeneration in different models of cell death involving NMDA-receptor activation, increasing evidence for protective mechanisms has been obtained. In this study the role of nitric oxide was investigated in a model of NMDA-independent, delayed apoptotic cell death, induced by the neurotoxin ethylcholine aziridinium ethylcholine aziridinium both in vivo and in vitro. For the in vivo evaluation rats received bilateral intracerebroventricular injections of ethylcholine aziridinium (2nmol/ventricle) or vehicle. In the hippocampus a transient decrease in nitric oxide synthase activity occurred, reaching its lowest levels three days after ethylcholine aziridinium treatment (51.7+/-9.8% of controls). The decrease coincided with the maximal reduction in choline acetyltransferase activity as marker for the extent of cholinergic lesion. The effect of pharmacological inhibition of nitric oxide synthase was tested by application of various nitric oxide synthase inhibitors with different selectivity for the nitric oxide synthase-isoforms. Unspecific nitric oxide synthase inhibition resulted in a significant potentiation of the loss of choline acetyltransferase activity in the hippocampus measured seven days after ethylcholine aziridinium application, whereas the specific inhibition of neuronal or inducible nitric oxide synthase was ineffective. These pharmacological data are suggestive for a neuroprotective role of nitric oxide generated by endothelial nitric oxide synthase. In vitro experiments were performed using serum-free primary neuronal cell cultures from hippocampus, cortex and septum of E15-17 Wistar rat embryos. Ethylcholine aziridinium-application in a range of 5-80microM resulted in delayed apoptotic neurodegeneration with a maximum after three days as confirmed by morphological criteria, life-death assays and DNA laddering. Nitric oxide synthase activity in harvested cells decreased in a dose- and time-dependent manner. Nitric oxide production as determined by measurement of the accumulated metabolite nitrite in the medium was equally low in controls and in ethylcholine aziridinium treated cells (range 0.77-1.86microM nitrite). An expression of inducible nitric oxide synthase messenger RNA could not be detected by semiquantitative RT-PCR 13h after ethylcholine aziridinium application. The present data indicate that in a model of delayed apoptotic neurodegeneration as induced by ethylcholine aziridinium neuronal cell death in vitro and in vivo is independent of the cytotoxic potential of nitric oxide. This is confirmed by a decrease in nitric oxide synthase activity, absence of nitric oxide production and absence of inducible nitric oxide synthase expression. In contrast, evidence for a neuroprotective role of nitric oxide was obtained in vivo as indicated by the exaggeration of the cholinergic lesion after unspecific nitric oxide synthase inhibition by N-nitro-L-arginine methylester.

Experimental model of small deep infarcts involving the hypothalamus in rats: changes in body temperature and postural reflex

BACKGROUND AND PURPOSE

Intraluminal middle cerebral artery (MCA) occlusion in rats has been reported to cause hyperthermia assumed to be caused by hypothalamic damage. To clarify the effects of hypothalamic ischemia on body temperature and to obtain a model simulating lacunar infarction, we attempted to produce small infarcts in deep structures (including the hypothalamus).

METHODS

A surgical suture was advanced to occlude the origin of the hypothalamic (HTA) and/or anterior choroidal arteries (AChA) without compromise of the anterior or middle cerebral artery origins. After treatment, rectal temperature and postural reflex were examined repeatedly for 3 days under nonanesthetic conditions. The AChA and HTA and their link with small deep infarction were then confirmed by TTC, hematoxylin and eosin, and TUNEL stains and by microsurgical dissection after colored silicone perfusion into the cerebral arteries.

RESULTS

Advancement of the suture near to but not occluding the MCA origin (0.5 to 1.9 mm proximal) produced small, deep, nonneocortical strokes in 25 of 36 animals without producing MCA ischemic changes. These infarctions mainly affected the hypothalamus in 13 animals (HTA area: infarct volume 6+/-1 mm(3)) and involved both the internal capsule and hypothalamus in 12 animals (HTA+AChA area infarct volume 48+/-10 mm(3)). Rats with HTA infarction alone exhibited persistent hyperthermia for 72 hours; some also had transient mild postural abnormality. The AChA+HTA infarct group showed a transient elevation of body temperature for 24 hours and definitive postural abnormality. In the remaining 11 animals, the suture was inadvertently advanced across the MCA origin, producing a large infarct that affected both the neocortex (MCA territory) and nonneocortical structures (volume 381+/-30 mm(3), n=11). The MCA infarct group displayed a transient hyperthermia and severe postural abnormality.

CONCLUSIONS

When properly positioned, the intraluminal suture method permits selective AChA and/or HTA obstruction without inducing MCA territory ischemia. This model confirms that selective hypothalamic infarction produces significant and sustained temperature regulation abnormalities. The model also may be useful in investigating the pathophysiology of small, deep, end-vessel infarction.

Effects of L-NAME and 7-NI on NOS catalytic activity and behavioral outcome after traumatic brain injury in the rat

Traumatic brain injury (TBI) produces transient increases in constitutive nitric oxide synthase (cNOS) activity and prolonged behavioral abnormalities. This study investigated the effects of nitro-L-arginine-methyl ester (L-NAME) and 3-bromo-7-nitroindazole (7-NI) treatment on cNOS catalytic activity and sensorimotor behavioral outcome after TBI. Rats underwent moderate (1.8-2.2 atm) parasagittal fluid percussion brain injury (FPI). At 5 min after FPI, cNOS activity was significantly increased within the damaged cerebral cortex of vehicle-treated rats compared to the noninjured contralateral cortex (206.7 +/- 150.5 % of contralateral, p < 0.01). Pretreatment with L-NAME and 7-NI significantly reduced injury-induced cNOS activation (47.7 +/- 42.6 %, p < 0.05, and 96.16 +/- 12.76, p < 0.05, respectively). Pretreatment with L-NAME and 7-NI also inhibited cNOS activity within the contralateral noninjured cerebral cortex compared to vehicle-treated rats (L-NAME 43.7 +/- 12.47%, p < 0.05; 7-NI 36.8 +/- 7.47%, p < 0.05). Furthermore, pretreatment with 7-NI, but not L-NAME, significantly reduced forelimb placing sensorimotor deficits (3.14 +/- 1.07, p < 0.05) at 1 day after TBI compared to vehicle-treated rats (5.38 +/- 0.42). These data indicate that inhibition of injury-induced elevations in neuronal NOS activity has a beneficial effect on neurological outcome after parasagittal FPI brain injury.

Role of nitric oxide in traumatic brain injury in the rat

OBJECT

Although nitric oxide (NO) has been shown to play an important role in the pathophysiological process of cerebral ischemia, its contribution to the pathogenesis of traumatic brain injury (TBI) remains to be clarified. The authors investigated alterations in constitutive nitric oxide synthase (NOS) activity after TBI and the histopathological response to pharmacological manipulations of NO.

METHODS

Male Sprague-Dawley rats underwent moderate (1.7-2.2 atm) parasagittal fluid-percussion brain injury. Constitutive NOS activity significantly increased within the ipsilateral parietal cerebral cortex, which is the site of histopathological vulnerability, 5 minutes after TBI occurred (234.5+/-60.2% of contralateral value [mean+/-standard error of the mean ¿SEM¿], p < 0.05), returned to control values by 30 minutes (114.1+/-17.4%), and was reduced at 1 day after TBI (50.5+/-13.1%, p < 0.01). The reduction in constitutive NOS activity remained for up to 7 days after TBI (31.8+/-6.0% at 3 days, p < 0.05; 20.1+/-12.7% at 7 days, p < 0.01). Pretreatment with 3-bromo-7-nitroindazole (7-NI) (25 mg/kg), a relatively specific inhibitor of neuronal NOS, significantly decreased contusion volume (1.27+/-0.17 mm3 [mean+/-SEM], p < 0.05) compared with that of control (2.52+/-0.35 mm3). However, posttreatment with 7-NI or pre- or posttreatment with nitro-L-arginine-methyl ester (L-NAME) (15 mg/kg), a nonspecific inhibitor of NOS, did not affect the contusion volume compared with that of control animals (1.87+/-0.46 mm3, 2.13+/-0.43 mm3, and 2.18+/-0.53 mm3, respectively). Posttreatment with L-arginine (1.1+/-0.3 mm3, p < 0.05), but not 3-morpholino-sydnonimine (SIN-1) (2.48+/-0.37 mm3), significantly reduced the contusion volume compared with that of control animals.

CONCLUSIONS

These data indicate that constitutive NOS activity is affected after moderate parasagittal fluid percussion brain injury in a time-dependent manner. Inhibition of activated neuronal NOS and/or enhanced endothelial NOS activation may represent a potential therapeutic strategy for the treatment of TBI.

Regulation of the cerebral circulation: role of endothelium and potassium channels

Several new concepts have emerged in relation to mechanisms that contribute to regulation of the cerebral circulation. This review focuses on some physiological mechanisms of cerebral vasodilatation and alteration of these mechanisms by disease states. One mechanism involves release of vasoactive factors by the endothelium that affect underlying vascular muscle. These factors include endothelium-derived relaxing factor (nitric oxide), prostacyclin, and endothelium-derived hyperpolarizing factor(s). The normal vasodilator influence of endothelium is impaired by some disease states. Under pathophysiological conditions, endothelium may produce potent contracting factors such as endothelin. Another major mechanism of regulation of cerebral vascular tone relates to potassium channels. Activation of potassium channels appears to mediate relaxation of cerebral vessels to diverse stimuli including receptor-mediated agonists, intracellular second messenger, and hypoxia. Endothelial- and potassium channel-based mechanisms are related because several endothelium-derived factors produce relaxation by activation of potassium channels. The influence of potassium channels may be altered by disease states including chronic hypertension, subarachnoid hemorrhage, and diabetes.

Transient changes in the presence of nitric oxide synthases and nitrotyrosine immunoreactivity after focal cortical lesions

Since ischemic insults lead to a deregulation of nitric oxide production which contributes to delayed neuronal death, we investigated changes in the distribution and amount of nitric oxide synthases I and II and in the appearance of nitrotyrosine caused by small, well-defined photothrombic lesions (2 mm in diameter) in the somatosensory cortex of rats. Four hours after lesioning, cell loss was evident in the core of the lesion and no nitric oxide synthase was present within this area, indicating that neurons expressing nitric oxide synthase I were lost or that nitric oxide synthase I was degraded. No increase in the number of neurons expressing nitric oxide synthase I was visible in the area surrounding the lesion, nor in other parts of the brain. One day after lesioning, NADPH-diaphorase- and nitric oxide synthase II-positive leucocytes had invaded the perilesional cortex and were accumulated in injured blood vessels. By two to three days post-lesion, layer V and VI pyramidal neurons, microglia, astrocytes and invading leucocytes had become strongly immunoreactive for nitric oxide synthase II within a perilesional rim. The number of cells expressing nitric oxide synthase I remained stable. Nitric oxide synthase II immunoreactivity and related NADPH-diaphorase had decreased by seven days post-lesion in most animals. However, the number of activated microglia or macrophages and astrocytes, as revealed by other markers, remained elevated. In addition, nitrotyrosine immunoreactivity was evident in the blood vessels close to the lesion, as well as in the ipsilateral hippocampus and thalamus. These findings indicate that no perilesional changes in the number of neurons expressing nitric oxide synthase I occur, but that a transient increase in nitric oxide synthase II does take place in the aftermath of small cortical lesions. The results suggest that increased nitric oxide production is limited to certain post-lesional intervals in this experimental model. It is also obvious that the vast majority of nitric oxide synthase-positive cells are nitric oxide synthase II-containing astrocytes three days after lesioning, suggesting that astrocyte-derived nitric oxide plays a significant role in delayed neuronal death. Such a condition points to an important aspect of post-lesional astrocytosis.

Neither L-arginine nor L-NAME affects neurological outcome after global ischemia in cats

BACKGROUND AND PURPOSE

We attempted to determine whether N-nitro-L-arginine methyl ester (L-NAME) would improve neurological outcome and whether L-arginine (L-ARG) would worsen neurological outcome after transient global ischemia.

METHODS

Halothane-anesthetized cats (n = 6 for each group) were treated with intravenous saline, L-NAME (5 mg/kg or 10 mg/kg), or L-arginine (300 mg/kg) 30 minutes before 10 minutes of ischemia (temporary ligation of the left subclavian and brachiocephalic arteries with hemorrhagic hypotension to 50 mm Hg). At 30 minutes of reperfusion, cats in the L-ARG group were administered an additional 300 mg/kg dose of intravenous L-arginine.

RESULTS

Time (mean +/- SE) to isoelectric electroencephalography was similar among groups (saline, 26 +/- 11 seconds; L-NAME-5, 15 +/- 4 seconds; L-NAME-10, 36 +/- 27 seconds; and L-ARG, 22 +/- 7 seconds). At 72 hours, reperfusion pathological injury was severe and neurological deficit score (mean, range) was similar among groups (saline, 38[11 to 70]; L-NAME-5, 52 [40 to 73]; L-NAME-10, 47 [23 to 70]; and L-ARG, 40 [0 to 79]).

CONCLUSIONS

Nitric oxide is not important in the mechanism of brain injury after global ischemia in cats.

L-arginine infusion increases basal but not activated cerebral blood flow in humans

Nitric oxide is a potent vasodilator. Infusion of its precursor, L-arginine, results in increased cerebral blood flow (CBF) in experimental animals. We examined the effects of L-arginine infusion on CBF in humans using positron emission tomography and the quantitative H2(15)O method. Six subjects received 500 ml of 0.9% NaCl solution, and six subjects received an infusion of L-arginine (16.7 mg/kg/min; 500 mg/kg). Before and after the i.v. infusion, paired CBF measurements were performed at baseline and with vibrotactile stimulation of the right hand. In scans performed without vibrotactile stimulation, mean whole-brain CBF increased from 34.9 +/- 3.7 ml 100 g-1 min-1 to 38.2 +/- 4.4 ml 100 g-1 min-1. (9.5%; p < 0.005) after L-arginine infusion. The temporal pattern of CBF changes differed from that of plasma growth hormone and insulin levels and of arterial pH. In contrast, in the saline group, mean whole-brain CBF did not change significantly (35.8 +/- 5.9 ml 100 g-1 min-1 to 35.9 +/- 6.4 ml 100 g-1 min-1; 0.3%). Vibrotactile stimulation produced significant focal increases in CBF, which were unaffected by L-arginine infusion. L-arginine infusion was associated with an increase in plasma L-citrulline, a byproduct of nitric oxide synthesis.

L-arginine ameliorates recirculation and metabolic derangement in brain ischemia in hypertensive rats

The effects of L-arginine (a precursor of nitric oxide, NO) on cerebral blood flow (CBF), cerebrovascular resistance (CVR) and metabolites in the ischemic brain were examined in spontaneously hypertensive rats with bilateral carotid artery occlusion for 30 min followed by 60 min-recirculation. The administration of L-arginine (300 mg/kg, i.v.) increased the CBF by an average of 11 ml x 100 g-1 x min-1 (P < 0.05 vs. at rest), and N(omega)-nitro-L-arginine (L-NNA, an inhibitor of NO synthase, 5 mg/kg, i.v.) reduced the CBF by 5-6 ml x 100 g-1.min-1 with increase in the mean arterial pressure by 26 mmHg. During ischemia the CBF significantly decreased to below 8% of the resting values in all rats. The largest blood flow in postischemic hyperemia was 171 +/- 9% of the resting CBF in the rats with L-arginine (P < 0.05 vs. L-NNA and saline), followed by 126 +/- 5 with saline and 109 +/- 3 with L-NNA. The CVR at 60 min of recirculation was 3.291 +/- 0.144 mmHg . ml-1. 100 g-1 .min-1 in the rats with saline, remained low level of 2.711 +/- 0.124 with L-arginine (P < 0.01 vs. L-NNA and P < 0.05 vs. saline) and in contrast, significantly increased to 5.732 +/- 0.184 with L-NNA (P < 0.01 vs. L-arginine and saline, respectively). Tissue lactate with saline increased 2.3-fold at 60 min of recirculation, whereas the increase was inhibited to 1.4-fold after L-arginine treatment (P < 0.01 vs. L-NNA) and in contrast, significantly increased 5.7-fold with L-NNA. The ATP and glucose levels were better preserved in the rats with L-arginine than in those with L-NNA or saline. These findings support that the enhanced postischemic hyperemia is beneficial to the ischemic brain and the administration of L-arginine may be potentially useful for the treatment of acute stroke.

Age-related ischemia in the brain following bilateral carotid artery occlusion--collateral blood flow and brain metabolism

Cerebral blood flow (CBF) and cerebellar blood flow (CeBF) were measured and correlated with brain lactate, pyruvate and adenosine triphosphate concentrations from groups representing 3-week old suckling (n = 10), 18-22-week old adult (n = 9) and 70-week old aged (n = 7) Sprague-Dawley rats before and during bilateral carotid occlusion (BCO). The steal ratio, calculated as the ratio of %control CBF to %control CeBF, was 1.02 +/- 0.06 (mean +/- SEM) at 60 minutes of BCO in adult rats that exhibited normal levels of brain metabolites. By contrast, the ratios significantly decreased to 0.74 +/- 0.06 in suckling rats and 0.69 +/- 0.06 in aged rats with simultaneous increases by 2.4 to 2.9-fold of tissue lactate. Pyruvate and lactate/pyruvate ratio also increased by 1.4 to 1.8 times control in both suckling and aged rats. We conclude that there is age-related steal phenomenon occurring with blood flow during BCO. Ischemic derangement of the brain metabolism is in part related to poor blood supply from the posterior circulation in suckling and aged rats.