Protective effect of nimodipine on behavior and white matter of rats with hydrocephalus

OBJECT: Hydrocephalus, a pathological dilation of the ventricles of the brain, causes damage to periventricular white matter, at least in part, through chronic ischemia. The authors tested the hypothesis that treatment with nimodipine, an L-type calcium channel-blocking agent with demonstrated efficacy in a range of cerebral ischemic disorders, would ameliorate the adverse effects of experimental hydrocephalus. METHODS: Hydrocephalus was induced in 3-week-old rats by injection of kaolin into the cisterna magna. The rats were treated by continuous administration of nimodipine or control vehicle for 2 weeks, beginning 2 weeks after induction of hydrocephalus. During the treatment period, the animals underwent repeated tests of motor and cognitive behavior. At the end of the treatment period, the rat brains were analyzed by histopathological and biochemical means. Nimodipine treatment prevented the declines in motor and cognitive behavior that were observed in untreated control rats. During the treatment period, ventricular enlargement, determined by magnetic resonance imaging, was equal in the two groups, although the corpus callosum was thicker in the treated rats. Myelin content in white matter and synaptophysin content in gray matter, an indicator of synapses, did not differ. CONCLUSIONS: The protective effect of nimodipine is most likely based on improved blood flow, although prevention of calcium influx-mediated proteolytic processes in axons cannot be excluded. Adjunctive pharmacological therapy may be beneficial to patients with hydrocephalus.     

Changes in periventricular vasculature of rabbit brain following induction of hydrocephalus and after shunting

Hydrocephalus was induced in rabbits by injection of silicone oil into the cisterna magna. At 1 and 8 weeks postinjection the rabbits were either sacrificed or treated by cerebrospinal fluid shunting for 1 week. Blood vessel profiles in the periventricular neuropil were examined by light microscopy. In the caudate nucleus, septal area, and corpus callosum, hydrocephalus caused a reduction in the number of capillaries but no changes were observed in the number of larger blood vessels. Shunting reduced the size of the ventricles to normal and the number of capillaries increased if hydrocephalus was present for 1 week prior to shunting. If hydrocephalus was present for 8 weeks prior to shunting, the number of capillaries did not increase. These observations support the concept that collapse of capillaries may account for the decreased cerebral blood flow that has been measured in hydrocephalic brains.     

Lipid peroxide level increase in experimental hydrocephalus

Summary The aetiology of incomplete adrenergic denervation and reduction in the number and caliber of the cerebral vessels in hydrocephalus is still obscure. Stretching of the blood vessels alone is far from explaining these major vascular changes. Previous studies have shown that increased lipid peroxidation produces toxic effects on vessels. This experimental study was designed to investigate the possible aetiology of vascular changes in hydrocephalic rats with special reference to lipid peroxidation.Hydrocephalus was induced by injecting 50 mg/Kg sterilized kaolin suspension into the cisterna magna in 10 rats (Group A). A sham operation was performed for Group B. After three weeks the rats were anaesthetized and perfused transcardially. The brains were dissected, and cut to visualize the degree of hydrocephalus. The arteries of the circle of Willis were removed for light microscopic examination and the brains were kept for the measurement of lipid peroxidation levels. Light microscopic studies of cerebral arteries in hydrocephalic rats revealed spastic vessels with folding and corrugation of the lamina elastica. The level of lipid peroxidation in group A (260±9.129 nmol TBAR/gr wet tissue) was significantly higher than that of group B (106±3.59 nmol TBAR/gr wet tissue). It is suggested that vascular changes observed in hydrocephalic rats may be due to the high level of lipid peroxidation, which in turn may be the consequence of ischaemia caused by the hydrocephalus related stretching of cerebral vessels.     

Changes in muscarinic cholinergic receptors and cholinergic neurons in experimental hydrocephalic rat brain

Recently, the relationship between neurological disorders and neurotransmitters has received much attention. Many studies have been reported about the changes of neurotransmitters and their metabolites in cerebrospinal fluid (CSF) in hydrocephalus, and it is presumed that neurotransmitters may play a role in the regulation of CSF dynamics. We injected kaolinum suspension into the cisterna magna of rats and created experimental hydrocephalus. Here we define the acute hydrocephalic stage to be the seventh day after injection and the chronic to be the twenty-first day after injection. We made studies about the changes of muscarinic cholinergic receptors in experimental hydrocephalic rat brains using binding assay, macroautoradiography, and microautoradiography with 3H-quinuclidinyl benzilate (QNB), which has a high and specific affinity for muscarinic receptors. We also studied the changes of cholinergic neurons in experimental hydrocephalic rat brains by immunohistochemical methods with anti-choline acetyltransferase (CAT), the antibody for the synthetic enzyme of acetylcholine which is thought to exist only in cholinergic neurons. Muscarinic cholinergic receptors were increased in acute hydrocephalus, and tended to normalize in chronic hydrocephalus but no change was observed in its distribution. There seemed to be no difference in the number of CAT positive cells between normal and hydrocephalic rat brains, but in hydrocephalic rat brain, CAT positive cells were compressed by the dilated ventricles, and they might have fallen into hypofunction. It is thought that muscarinic receptors were increased by some mechanism like denervation hypersensitivity because of the reduction of ACh production or release. Recent advancement of PET or SPECT has made it possible to investigate the changes of neurotransmitter receptors in human brain. Such biochemical examination may offer some information to assess the functional state of hydrocephalus and to find a new approach to its treatment.     

Anesthetic properties of riluzole (54274 RP), a new inhibitor of glutamate neurotransmission.

It has been suggested that some anesthetic agents could exert their hypnotic/anesthetic effects by selectively blocking receptors involved in the central excitatory neurotransmission mediated by glutamate. In the present study, we analyzed whether riluzole (54274 RP), a novel compound that inhibits both the release and some postsynaptic effects of glutamate in some brain structures, has anesthetic properties in rats. For this purpose, we investigated whether 1) riluzole administered intraperitoneally (ip) at doses ranging from 2.5 to 45 mg/kg induces loss of righting reflex (LRR); 2) riluzole (2.5 and 5 mg/kg) prolongs sleep-times induced by either ketamine (30 or 80 mg/kg ip) or thiopental (25 or 35 mg/kg ip); 3) a 5-mg/kg subanesthetic riluzole dose affects the minimum alveolar concentration of halothane (MACh). Onset of drug action was defined as the period of time from the ip injection to LRR. Sleep-time was considered the period of time from LRR to restoration of righting reflex. Riluzole at doses greater than 15 mg/kg was able to induce LRR (riluzole dose for which LRR was achieved in 50% of the rats [ED50 = 25.6 mg/kg]). A positive correlation was found between the dose of riluzole and sleep-time (r = 0.92, P less than 0.001). A 5-mg/kg (but not 2.5-mg/kg) riluzole dose significantly prolonged sleep-times induced by both ketamine (30 and 80 mg/kg) and thiopental (25 but not 35 mg/kg).(ABSTRACT TRUNCATED AT 250 WORDS)     

Experimental study on pathophysiology and treatment of congenital hydrocephalus evaluated by magnetic resonance imaging and magnetic resonance spectroscopy]

I. Experimental Study on Pathophysiology of Congenital Hydrocephalus It is well known that the major pathogenic mechanism of hydrocephalus is disturbance in cerebrospinal fluid (CSF) circulation. For this reason, many studies on hydrocephalus were intended from the viewpoint of CSF circulation both experimentally and clinically. However, few studies have yet been done on the correlation between the morphological changes and the changes in cerebral energy metabolism in hydrocephalus in vivo. So, in this study, the correlation between the morphological changes and the changes in cerebral energy metabolism in congenital hydrocephalic rats was evaluated experimentally. The morphological changes were estimated by using magnetic resonance imaging (MRI), and the longitudinal relaxation time (T1) of brain tissue at parietal area was also measured. The cerebral energy metabolism was evaluated by using 31P magnetic resonance spectroscopy (MRS) method, and cerebral phospholipid membrane metabolism was also evaluated by using 31P-MRS method. The region of interest (ROI) giving rise to the 31P spectra was placed at fore-brain and parietal area. The PCr/Pi ratio was used as the chosen indicator of cellular bioenergetic status. The PME/beta-ATP ratio and PDE/beta-ATP ratio were used as the chosen indicator of cerebral phospholipid membrane metabolism. The intracellular pH was also evaluated by using 31P-MRS method. Fifty congenital hydrocephalic rats of the HTX strain were used. The animals were divided into two groups--non-hydrocephalic group (n = 15) and hydrocephalic group (n = 35)--. The rats of hydrocephalic group were subdivided into three smaller groups according to the degree of hydrocephalus--mild (n = 15), moderate (n = 10) and severe (n = 10)--, which was estimated by using the cerebro-ventricular ratio (CVR) in coronal section of MRI. Experimental results were as follows: 1) The T1 values in rats of mild, moderate and severe hydrocephalic groups showed significant elongation in comparison with the value in non-hydrocephalic group (p less than 0.01), which indicated the expansion of interstitial edema in cerebral cortex. 2) The correlation between the T1 value and the CVR was evaluated and the correlation coefficient (r) was 0.932 which indicated high correlation. 3) The PCr/Pi ratios in rats of mild, moderate and severe hydrocephalic groups were decreased significantly in comparison with the value in non-hydrocephalic group (p less than 0.01), which demonstrated the disturbance of cerebral energy metabolism in congenital hydrocephalic rats. 4) The PCr/Pi ratio seemed to give the indicative data concerning the prognosis of congenital hydrocephalus.(ABSTRACT TRUNCATED AT 400 WORDS)     

Cerebral metabolism in experimental hydrocephalus: an in vivo 1H and 31P magnetic resonance spectroscopy study.

OBJECT: Brain damage in patients with hydrocephalus is caused by mechanical forces and cerebral ischemia. The severity and localization of impaired cerebral blood flow and metabolism are still largely unknown. Magnetic resonance (MR) spectroscopy offers the opportunity to investigate cerebral energy metabolism and neuronal damage noninvasively and longitudinally. Previous 1H MR spectroscopy studies have shown an increased lactate resonance that is suggestive of anaerobic glycolysis. The aim of this study was to assess cerebral damage and energy metabolism in kaolin-induced hydrocephalus in adult rats by using in vivo 1H and 31P MR spectroscopy. The presence of lactate was correlated with high-energy phosphate metabolism and intracellular pH. The measurement of relative concentrations of N-acetyl aspartate (NAA), choline (Cho), and total creatine (tCr) served to assess neuronal damage. METHODS: Hydrocephalus was induced in adult rats by surgical injection of kaolin into the cisterna magna. Magnetic resonance studies, using a 4.7-tesla magnet, were performed longitudinally in hydrocephalic animals at 1 (10 rats), 8 (six rats), and 16 weeks (six rats) thereafter, as well as in eight control animals. To evaluate ventricular size and white matter edema T2-weighted MR imaging was performed. The 1H MR spectra were acquired from a 240-microl voxel, positioned centrally in the brain, followed by localized 31P MR spectroscopy on a two-dimensional column that contained the entire brain but virtually no extracranial muscles. The 1H and 31P MR spectroscopy peak ratios were calculated after fitting the spectra in the time domain, intracellular pH was estimated from the inorganic phosphate (Pi) chemical shift, and T2 relaxation times of 1H metabolites were determined from the signal decay at increasing echo times. CONCLUSIONS: In hydrocephalic rats, ventricular expansion stabilized after 8 weeks. White matter edema was most pronounced during acute hydrocephalus. Lactate peaks were increased at all time points, without a decrease in phosphocreatine (PCr)/Pi and PCr/adenosine triphosphate (ATP) peak ratios, or pH. Possibly lactate production is restricted to periventricular brain tissue, followed by its accumulation in cerebrospinal fluid, which is supported by the long lactate T2 relaxation time. Alternatively, lactate production may precede impairment of ATP homeostasis. The NAA/Cho and tCr/Cho ratios significantly decreased during the acute and chronic stages of hydrocephalus. These changes were not caused by alterations in metabolite T2 relaxation time. The decreases in the NAA/Cho and tCr/Cho ratios implicate neuronal loss/dysfunction or changes in membrane phospholipid metabolism, as in myelin damage or gliosis. It is suggested that 1H MR spectroscopy can be of additional value in the assessment of energy metabolism and cerebral damage in clinical hydrocephalus.     

Foregut smooth muscle reactivity changes in the hydrocephalus-induced infantile rats

BACKGROUND: An association between hydrocephalus and gastroesophageal motor abnormalities that cause gastroesophageal reflux (GER) is well known. Our aim was to investigate hydrocephalus-induced alterations in esophageal and gastric smooth muscle reactivity and their modulation by pharmacological interventions in the rat model. MATERIALS AND METHODS: Hydrocephalus was induced in infantile rats by injection of kaolin into the cisterna magna. Hydrocephalic and sham-operated rats were exsanguinated 2 weeks after surgery. Esophageal and gastric fundus smooth muscle strips were studied in vitro for their contractile and relaxant response to receptor activation in the organ chambers set up. Additionally, esophageal and gastric tissue specimens were examined histologically for GER-induced changes. RESULTS: No histological evidence of esophageal and gastric changes reflecting GER was observed in the specimens of the control and hydrocephalus-induced rats. Maximum contractile responses of esophageal and gastric fundus smooth muscle to KCl and muscarinic receptor agonist carbachol were increased in the hydrocephalic groups compared with the control groups. These changes were statistically significant. Relaxant responses to beta adrenoceptor agonist isoprenaline were similar in the esophageal muscle strips of both hydrocephalic groups and the control groups. However, isoprenaline-induced relaxant responses of the gastric fundus muscle strips in the hydrocephalus-induced groups were significantly decreased as compared with the control groups. The relaxant responses to papaverine in the esophageal and gastric fundus smooth muscle strips were similar in the two groups. CONCLUSIONS: Our study revealed alterations of receptor-dependent and receptor-independent foregut smooth muscle reactivity in the hydrocephalus-induced rat pups. Therefore, we suggest that impaired smooth muscle reactivity at least in part may contribute to abnormalities of foregut motor function seen in patients with hydrocephalus.     

Alteration of Ischemic Reperfusion Injury in the Rat Neocortex by a Potent Antioxidant Mexiletine

Summary.  The mechanisms by which mexiletine exerts its effects in increasing myocardial circulation, and smooth muscle perfusion and alleviating diabetic neuropathic pain have been widely discussed. The purpose of this study was to examine the protective effect of this compound in ischemia/reperfusion-induced cerebral injury following middle cerebral artery occlusion in Spraque-Dawley rats. Blood flow to the left cerebral hemisphere of the animals was interrupted by occluding the left cerebral artery and both carotid arteries simultaneously for 3 hrs. These animals were assigned to one of ten groups and devided into treatment group and pretreatment group; 1) control treatment group (n=8); 2) vehicle treatment group (n=8); 3) lower dose mexiletine (400 μg/kg) treatment group (n=8); 4) medium dose mexiletine (800 μg/kg) treatment group (n=8); 5) high dose mexiletine (2 mg/kg) treatment group (n=8); 6) control pretreatment group (n=8); 7) vehicle pretreatment group (n=8); 8) lower dose mexiletine (400 μg/kg) pretreatment group (n=8); 9) medium dose mexiletine (800 μg/kg) pretreatment group (n=8); and 10) high dose mexiletine (2 mg/kg) pretreatment group (n=8). The volume of cerebral infarction was measured in serial brain sections stained with triphenyltetrazolium chloride (TTC). Tissue infarction volume and tissue edema were estimated for each animal. The volume of cerebral infarction was significantly decreased in rats pretreated with mexiletine, and the ratio of tissue edema was also decreased as the dose of mexiletine increased.  These results demonstrate that mexiletine, an anti-arrhythmic and use-dependent Na⁺ channel blocker, has protective effects in stroke at concentrations sufficient to confer significant protection, as measured by the volume of infarction and brain edema index in a model of focal, neocortical ischemia in Spraque-Dawley rats.     

Angiotensin II Receptor Content Within the Circumventricular Organs Increases After Experimental Hydrocephalus in Rats

Summary  Hydrocephalus is known to cause various endocrinological abnormalities. These abnormalities are either though a direct effect on anterior hypothalamus or pituitary gland. However almost nothing is known about the effects of hydrocephalus on the intrinsic angiotensin system of the brain. The aim of this study is to investigate the effect of hydrocephalus on neurotransmitter-rich circumventricular organ systems. Such an effect was investigated by means of angiotensin receptor content in subfornical organ (SFO), organum vasculosum lamina terminalis (OVLT), area postrema (AP) and the median eminence (ME). Experimental hydrocephalus was created in rats by the intracisternal kaolin injection method as descibed by Shapiro et al.. The receptor content was measured at 4–6 weeks by in-vitro autoradiography method as descibed by Israel et al.. Angiotensin II receptor content in hydrocephalic animals was found to be statistically increased in SFO, OVLT and ME but not in AP when compared with the normal animals. Receptor content was found to have increased by 182.4% at SFO, 76.7% at ME, 7.7% at AP and 22.1% at OVLT after kaolin injection. These findings may indicate the possible role of CVO's on pathological conditions such as hydrocephalus.     

Riluzole reduces brain swelling and contusion volume in rats following controlled cortical impact injury

Modulation of the glutamatergic and excitotoxic pathway may attenuate secondary damage following traumatic brain injury by reducing presynaptic glutamate release and blocking sodium channels in their inactivated state. The aim of the present study was to investigate the neuroprotective potential of riluzole in traumatic brain-injured rats. A left temporoparietal contusion was induced in 70 male Sprague-Dawley rats (controlled cortical impact injury). Riluzole (8 mg/kg body weight) was given 30 min, and 6, 24, and 30 h after trauma, while control rats received physiological saline. Experiments were performed at two different degrees of trauma severity as defined by penetration depth of the impactor rod (1 vs. 1.5 mm) with the aim of investigating impact of severity of tissue damage on the neuroprotective potential of riluzole. At 48 h after trauma, brains were removed to determine hemispheric swelling and water content and to assess cortical contusion volume. Before brain removal cisternal cerebrospinal fluid (CSF) was collected in all rats to determine the effects of riluzole on substances associated with edema formation. For this, the excitatory transmitter glutamate, the volume-regulatory amino acid taurine, and the ATP-degradation product hypoxanthine were analyzed by high-performance liquid chromatography. Overall, the degree of tissue damage seems to influence the neuroprotective potential of riluzole. In rats with a less severe trauma (1-mm penetration depth), hemispheric swelling, cerebral water content of the traumatized hemisphere and cortical contusion volume were significantly reduced under riluzole compared to controls (p < 0.05). In rats with a more severe trauma (1.5-mm penetration depth), the neuroprotective effect of riluzole failed to reach statistical significance. Following trauma, CSF glutamate, taurine, and hypoxanthine levels were significantly increased compared to nontraumatized rats (p < 0.001). However, these neurochemical parameters as measured in cisternal CSF failed to reflect trauma-dependent increases in severity of tissue damage and did not reveal riluzole-mediated neuroprotection. Under the present study design, riluzole significantly reduced brain edema formation and contusion volume in rats subjected to a mild focal cortical contusion.     

Factors affecting prognosis of intrauterine hydrocephalus diagnosed in the third trimester--computerized data analysis on controversies in fetal surgery.

Twenty hydrocephalic patients diagnosed in the third trimester of fetal life were evaluated and followed during a 7-year period. The factors affecting the prognosis, including the type of hydrocephalus, underlying conditions, associated anomalies, time of diagnosis and delivery, fetal period after diagnosis, head circumference and degree of ventriculomegaly at birth, and age at treatment, were comprehensively analyzed. The difference between final outcomes as assessed by developmental quotient (DQ) or intelligence quotient (IQ) were statistically tested with computation by means of STAX packages in an NEC 9801 VX. Hydrocephalus as an isolated defect occurred in six cases (30%), was associated with other central nervous system anomalies in nine (45%), and was secondary to intrauterine intraventricular hemorrhage or brain tumor in five (25%). The average age at the time of diagnosis was 33.9 weeks of gestation (range, 27-40 weeks). One fetus was treated by transabdominal cephalocentesis, but the majority of patients underwent ventriculoperitoneal shunt postnatally. The final IQ or DQ scores ranged from 20 to 120 (mean score, 50.6). The data analyses revealed that the only significant factor affecting outcome was the fetal period after diagnosis of hydrocephalus (r = -0.5076, p less than 0.01). Our data supports the fact that the results of an on-going hydrocephalic state may become irreversible during fetal life. It is emphasized that establishment of a more precise pathophysiological evaluation, and a less invasive but more reliable decompressive technique for fetal hydrocephalus, is urgent.     

Sodium thiosulfate prevents cisplatin-induced hypomagnesemia

Clearance studies were performed in four groups of male Wistar rats to assess the protective effect of sodium thiosulfate on cisplatin-induced hypomagnesemia. In group I, sodium thiosulfate (400 mg/kg) was injected intraperitoneally once weekly for 3 consecutive weeks. In group II, only cisplatin (2.5 mg/kg) was administered. In group III, both cisplatin (2.5 mg/kg) and sodium thiosulfate (400 mg/kg) were injected via the intraperitoneal route. When both drugs were administered together, they were injected into different parts of the peritoneal cavity. In group IV cisplatin was administered intraperitoneally and sodium thiosulfate intravenously. Sodium thiosulfate prevented a rise in plasma creatinine. The overall glomerular filtration rates of groups III and IV were the same as in group I. Hypomagnesemia was noted in group II, whereas in groups I, III, and IV the plasma magnesium level remained unchanged. The fractional excretion of magnesium was also higher in group II than in groups I, III, and IV. These differences persisted for the duration of the study. These results suggest that concurrent injections of sodium thiosulfate intraperitoneally or intravenously prevented the hypomagnesemic and the nephrotoxic effects of cisplatin and can be of clinical significance.     

Effects of mexiletine,ginkgo biloba extract (EGb 761), and their combination on experimental head injury

Lipid peroxidation (LP) and brain edema are important factors that produce tissue damage in head injury. The purpose of this study was to investigate the effect of mexiletine, gingko biloba extract (EGb 761), and their combination on LP and edema after moderate head trauma. Forty rats were randomly and blindly divided into four groups of ten animals each: control group (bolus injection of physiological saline), mexiletine group (50 mg/kg per injection), EGb 761 group (30 mg/kg per injection), and mexiletine plus EGb 761 group (50 mg/kg and 30 mg/kg per injection, respectively). The injections were given intraperitoneally at 1 h, 9 h, and 17 h after trauma. Twenty-four hours after injury, the rats were killed, and malondialdehyde (MDA) levels and brain water content were determined. Rats treated with mexiletine, EGb 761, and mexiletine plus EGb 761 had significantly lower MDA levels than the control group (P<0.01). The lowest MDA levels were measured in the mexiletine plus EGb 761 group. However, there was no significant difference in brain water content between treated groups and the control group (P>0.05). These findings show the usefulness of mexiletine and its combination with EGb 761 as a cerebroprotective agent in this model of experimental head injury.     

Effects of CS-866, an angiotensin II receptor antagonist, in 5/6 nephrectomized spontaneously hypertensive rats]

To assess the chronic antihypertensive and renal protective effects of the specific angiotensin II receptor antagonist, CS-866, in the remnant kidney model of chronic renal failure, we administered it alone or in combination with temocapril, an angiotensin converting enzyme inhibitor, to 5/6 nephrectomized spontaneously hypertensive rats (SHR) for 8 weeks. At the age of 10 weeks, 5/6 nephrectomized SHR were allocated to receive two doses of CS-866 (CS-3; 3 mg/kg/day, or CS-10; 10 mg/kg/day), temocapril (TEM; 10 mg/kg/day), a combination of CS-866 (3 mg/kg/day) and temocapril (10 mg/kg/day) or the vehicle alone via oral gavage for 8 weeks. Systolic blood pressure (SBP) and urinary protein excretion (UprotV) were measured every two weeks. At the age of 18 weeks, the rats were decapitated and the blood, remnant kidney, aorta and heart were collected and used for biochemical measurements and histopathological studies. There was no significant difference in body weight among the groups during the study. All drug treatments significantly reduced SBP, UprotV, glomerular sclerosis index (GSI), relative interstitial volume (RIV) and the heart weight to body weight ratio. The hypotensive effects were in the order of combination therapy > CS-10 = TEM > CS-3. For correlational analysis, we used values for SBP and UprotV derived from the average of values in rats over the age of 12 weeks through 18 weeks. UprotV, GSI and RIV were found to be highly correlated with SBP among the individual rats pooled from all groups (r = 0.511, r = 0.754, r = 0.817, respectively) and the correlation was maintained among the group means (r = 0.945, r = 0.989, r = 0.918, respectively). Furthermore, the heart weight to body weight ratio was found to be highly correlated with SBP among the individual rats pooled from all groups (r = 0.923) and the correlation was maintained among the group means (r = 0.996). We conclude that organ protective effects of CS-866, TEM, or combination therapy are closely related to the magnitude of their antihypertensive effects.     

Neuroprotective effects of riluzole and ketamine during transient spinal cord ischemia in the rabbit

BACKGROUND: Massive release of central excitatory neurotransmitters is an important initial step in ischemic neuronal injury, and modification of this process may provide neuroprotection. We studied the protective effects of the voltage-dependent sodium channel antagonist riluzole and the N-methyl-d-aspartate receptor antagonist ketamine on hind limb motor function and histopathologic outcome in an experimental model of spinal cord ischemia. METHODS: Temporary spinal cord ischemia was induced by 29 min of infrarenal balloon occlusion of the aorta in 60 anesthetized New Zealand white rabbits. Animals were randomly assigned to one of four treatment groups (n = 15 each): group C, saline (control); group R, riluzole, 8 mg/kg intravenously; group K, ketamine, 55 mg/kg intravenously; group RK, riluzole and ketamine. After reperfusion, riluzole treatment was continued with intraperitoneal infusions. Normothermia (38 degrees C) was maintained during ischemia, and rectal temperature was assessed before and after intraperitoneal infusions. Neurologic function, according to Tarlov's criteria, was evaluated every 24 h, and infarction volume and the number of eosinophilic neurons and viable motoneurons in the lumbosacral spinal cord was evaluated after 72 h. RESULTS: Neurologic outcome was better in groups R and RK than in groups C and K. All animals in group C (100%) and all animals but one in group K (93%) were paraplegic 72 h after the ischemic insult versus 53% in group R and 67% in group RK (P < 0.01 each). More viable motoneurons were present in groups R and RK than in controls (P < 0.05). CONCLUSIONS: The data indicate that treatment with riluzole can increase the tolerance of spinal cord motoneurons to a period of normothermic ischemia. Intraischemic ketamine did not provide neuroprotection in this model.     

Systemic Administration of Mexiletine for Attenuation of Cerebral Vasospasm Following Experimental Subarachnoid Haemorrhage

Mexiletine is a class Ib drug that is widely used to treat ventricular arrhythmias. This compound is mainly known as a sodium channel blocker, but studies have demonstrated that it can also activate ATP-sensitive K+ channels and block Ca2+ channels. Recent in vitro data from experiments on liposomes indicate that mexiletine is also a potent antioxidant. The unique activity profile of this drug raised the possibility that it might be of benefit in limiting cerebral vasospasm. Our first series of experiments assessed the effects of mexiletine on transclivally exposed rabbit basilar arteries. The arteries were treated with 50-mM KCl, 20-nM endothelin-1 (ET-1), or 100-microM lysophosphatidic acid (LPA) in the presence or absence of 400-mM mexiletine. Vasoconstriction caused by KCl, ET-1, and LPA was inhibited by mexiletine. In a second series of experiments, subarachnoid haemorrhage (SAH) was induced in rabbits by injecting 3-ml of autologous arterial blood into the cisterna magna. Forty-eight hours after SAH induction, transclivally exposed basilar arteries exhibited a spastic constriction that was partially reversed by topical application of 400-microM mexiletine. In a third set of experiments, mexiletine was administered orally at dosages of 80-, 20, and 5-mg/kg/day t.i.d., beginning 3 hours before SAH to study the prevention of vasospasm. In a separate group of animals, 80- and 20-mg/kg/day t.i.d. of mexiletine was administered 21 hours post-SAH induction, to study the reversal of vasoconstriction. Microscopic analysis of vessels from controls (no SAH), SAH-only, and SAH + mexiletine groups indicated there was 71.43% vascular constriction in the SAH-only group compared with controls. Considerable vasorelaxation was seen in the prevention study, in which average arterial cross-sectional areas were reduced by only 17.86% and 39.29% in the mexiletine 80- and 20-mg/kg/day groups, respectively, compared with controls (p < 0.001). Compared with controls, average arterial cross-sectional areas were reduced by 53.58% and 64.29% in the mexiletine 80- and 20-mg/kg/day reversal groups, respectively. Our findings indicate that mexiletine induces potent relaxation in cerebrovascular arteries contracted with various agents, and that it prevents and partially reverses SAH-induced vasoconstriction.     

Neuroprotective Effects of Riluzole and Ketamine during Transient Spinal Cord Ischemia in the Rabbit

Background: Massive release of central excitatory neurotransmitters is an important initial step in ischemic neuronal injury, and modification of this process may provide neuroprotection. We studied the protective effects of the voltage-dependent sodium channel antagonist riluzole and the N-methyl-d-aspartate receptor antagonist ketamine on hind limb motor function and histopathologic outcome in an experimental model of spinal cord ischemia.

Methods: Temporary spinal cord ischemia was induced by 29 min of infrarenal balloon occlusion of the aorta in 60 anesthetized New Zealand white rabbits. Animals were randomly assigned to one of four treatment groups (n = 15 each): group C, saline (control); group R, riluzole, 8 mg/kg intravenously; group K, ketamine, 55 mg/kg intravenously; group RK, riluzole and ketamine. After reperfusion, riluzole treatment was continued with intraperitoneal infusions. Normothermia (38[degrees]C) was maintained during ischemia, and rectal temperature was assessed before and after intraperitoneal infusions. Neurologic function, according to Tarlov's criteria, was evaluated every 24 h, and infarction volume and the number of eosinophilic neurons and viable motoneurons in the lumbosacral spinal cord was evaluated after 72 h.

Results: Neurologic outcome was better in groups R and RK than in groups C and K. All animals in group C (100%) and all animals but one in group K (93%) were paraplegic 72 h after the ischemic insult versus 53% in group R and 67% in group RK (P < 0.01 each). More viable motoneurons were present in groups R and RK than in controls (P < 0.05).     

Possible role of nitric oxide in the protective effect of resveratrol in 5/6th nephrectomized rats

BACKGROUND: Nitric oxide (NO) plays an important role in the modulation of glomerular disease. The renal protective effect of resveratrol (RVT), a polyphenolic phytoalexin, was investigated in the 5/6th nephrectomized rats. MATERIALS AND METHODS: Resveratrol (5 mg/kg, PO) was administered for 12 weeks to 5/6th nephrectomized (NX) rats together with and without nitro L-arginine methyl ester (L-NAME) (10 mg/kg, IP). We evaluated the effect of these agents on proteinuria, hypertension, renal function, glomerulosclerosis, and urinary excretion of nitric oxide metabolites. RESULTS: 5/6th NX resulted in elevation in systolic blood pressure (SBP), reduced the urinary excretion of NO metabolites, increased urinary protein excretion, and deranged renal function and glomerulosclerosis. Treatment of animals with resveratrol significantly attenuated the increase in SBP, preserved the normal renal function, reduced the urinary protein excretion, increased the urinary excretion of NO metabolites, and prevented the glomerulosclerosis. Co-administration of animals with L-NAME along with resveratrol prevented the protection observed with resveratrol. CONCLUSION: These findings indicate that resveratrol exerts its protective effect in 5/6 NX rats through a nitric oxide pathway.     

Pharmacologic evaluation of pressor and visceromotor reflex responses to bladder distension

AIMS: Several mechanisms that are involved in acute rat bladder nociception were examined. The nociceptive response was measured by analyzing both cardiovascular and visceromotor reflex responses to urinary bladder distension. The contributions of micro-opioid receptor, kappa-opioid receptor, sodium channels, muscarinic receptors, and cyclooxygenase, were explored with morphine, U50,488, mexiletine, oxybutynin, and naproxen, respectively. METHODS: Female Sprague-Dawley rats were acutely instrumented with jugular venous, carotid arterial, and bladder cannulas. Needle electrodes were placed directly into the abdominal musculature to measure myoelectrical activity subsequent to repeated phasic urinary bladder distension (60 mmHg for 20 sec in 3 min intervals) under 1% isoflurane. Drugs were administered by i.v. bolus injection 2 min prior to distension. RESULTS: The analgesics morphine (ID50 0.69 mg/kg), U50,488 (1.34 mg/kg), and mexiletine (2.60 mg/kg) significantly inhibited the visceromotor reflex response to noxious urinary bladder distension. Oxybutynin also attenuated reflex responses to noxious urinary bladder distension to 41% of the maximal pressor response and 32% of the control visceromotor reflex response (3.01 and 5.05 mg/kg), respectively, indicating a role of muscarinic receptors in bladder nociception. Naproxen did not attenuate the pressor response, but moderately inhibited visceromotor reflex to 45% of control at 30 mg/kg (P < 0.05). CONCLUSIONS: Current results using the rat urinary bladder distension model are consistent with previous research demonstrating a role of the analgesics (morphine, U50,488, and mexiletine) in the inhibition of visceral nociceptive transmission. The utility of the reflex responses to urinary bladder distension may provide a method useful to examine mechanisms which target the bladder sensory pathway.