Rat Model Of Forebrain Ischemia Research Articles

Hippocampal sub-regional differences in the microRNA response to forebrain ischemia

Transient forebrain ischemia, as occurs with cardiac arrest and resuscitation, results in impaired cognitive function secondary to delayed neuronal cell death in hippocampal cornu ammonis-1 (CA1). Comparatively, hippocampal neurons in the adjacent dentate gyrus (DG) survive, suggesting that elucidating the molecular mechanisms underpinning hippocampal sub-regional differences in ischemic tolerance could be central in the development of novel interventions to improve outcome in survivors of forebrain ischemia. MicroRNAs (miRNAs) are non-coding RNAs that modulate the translation of target genes and have been established as an effective therapeutic target for other models of injury. The objective of the present study was to assess and compare post-injury miRNA profiles between CA1 and DG using a rat model of forebrain ischemia. CA1 and DG sub-regions were dissected from rat hippocampi following 10 min of forebrain ischemia at three time points (3 h, 24 h, and 72 h) and at baseline. Pronounced differences between CA1 and DG were observed for several select miRNAs, including miR-181a-5p, a known regulator of cerebral ischemic injury. We complexed fluorescent in situ hybridization with immunohistochemistry to observe cell-type specific and temporal differences in mir-181a-5p expression between CA1 and DG in response to injury. Using established miRNA-mRNA prediction algorithms, we extended our observations in CA1 miRNA dysregulation to identify key functional pathways as potential modulators of CA1 ischemic vulnerability. In summary, our observations support a central role for miRNAs in selective CA1 ischemic vulnerability and suggest that cell-specific miRNA targeting could be a viable clinical approach to preserve CA1 neurons and improve cognitive outcomes for survivors of transient forebrain ischemia.

Profiling the Post‐Injury Hippocampal MicroRNA Response to Transient Forebrain Ischemia: Sub‐regional Differences Between Cornu Ammonis‐1 and Dentate Gyrus

ObjectivesEven brief periods of ischemia can result in delayed neuronal cell death in hippocampal cornu ammonis‐1 (CA1), resulting in impaired memory and learning, whereas neurons in the adjacent dentate gyrus (DG) are relatively ischemia resistant. Understanding the pathophysiological and molecular mechanisms underpinning the selective ischemic vulnerability of the CA1 may translate to novel clinical interventions improving outcome in survivors of cerebral ischemia. MicroRNAs (miRNAs) are short (~18–25 nucleotides long) non‐coding RNAs that modulate translation of target messenger RNAs. To date, the miRNA expression profiles of hippocampal CA1 and DG sub‐regions in response to forebrain ischemia have not been examined. The objective of the present study was to assess and compare post‐injury miRNA expression patterns between CA1 and DG in a rat model of forebrain ischemia.MethodsAll experiments were conducted in conformance with the FASEB Statement of Principles for the use of Animals in Research and Education. CA1 and DG sub‐regions were dissected from rat hippocampi following a 10‐minute forebrain ischemia at 3 time points (3h, 24h, and 48h) and at baseline. Total RNA was extracted from samples using Quick‐RNA™ MiniPrep kits (Zymo Research), and the expression of 423 miRNAs were analyzed using nCounter® miRNA expression panel (NanoString). Successful sub‐regional dissection was validated using RT‐qPCR detection of the DG‐rich gene desmoplakin.ResultsPronounced differences between CA1 and DG in miRNA expression was observed for several miRNAs, greatest with mir‐329, mir‐219‐2‐3p and mir‐181a, known regulators of ischemic injury. Relative levels of CA1 and DG miRNA expression were greatest in established brain‐enriched miRNAs, including mir‐124.ConclusionsMiRNA expression profiles in response to transient forebrain ischemia were assessed and compared between hippocampal sub‐regions for the first time. Observed differences in microRNA expression patterns between CA1 and DG may explain selective CA1 ischemic vulnerability. Targeted modulation of select miRNAs identified here may serve as a therapeutic intervention to improve cognition in survivors of cerebral ischemia.Support or Funding InformationSupported by Finnish Cultural Foundation award to Dr. Arvola and American Heart Association award 14FTF19970029 to Dr. Stary.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Vinconate prevents ischemic neuronal damage in the rat hippocampus

The neuroprotective effect of vinconate, a novel vinca alkaloid derivative, was examined in a rat model of forebrain ischemia induced by 4-vessel occlusion. Hippocampal cell loss was quantified histologically 3 days after 10 or 15 min of ischemia. Intraperitoneal application of vinconate (25 and 50 mg/kg) 10 min before and immediately after 10 min of ischemia significantly reduced the neuronal cell loss in the CA1 sector of the hippocampus. Protective effect of vinconate against 15 min of ischemia was reduced, but there was still significant protection at the higher dose. Autoradiography using 14C-vinconate showed that the drug easily penetrates the blood-brain barrier and distributes in the hippocampus. The result suggests that vinconate prevents ischemic neuronal damage by direct action on the hippocampal CA1 neurons.

The effect of chronic dexamethasone-induced hyperglycemia and its acute treatment with insulin on brain glucose and glycogen concentrations in rats.

In the rat model of forebrain ischemia, long-term dexamethasone treatment is reported to cause hyperglycemia and worsen postischemic functional and histologic injury. This effect was assumed to result from glucose enhancement of intraischemic lactic acidosis within the brain. Short-term insulin therapy restored normoglycemia but did not return histologic injury completely to baseline values. Using a nonischemic rat model, the current study attempted to identify a metabolic basis for such outcome data. Fifty-eight halothane-anesthetized (1.3% inspired) Sprague-Dawley rats were assigned randomly to be administered either no treatment (N = 18) or 2 mg/kg intraperitoneal dexamethasone (N = 40). The latter were administered dexamethasone 3 h before the study only (N = 8) or for 3 h before the study plus daily for 1 day (N = 8), 2 days (N = 8), or 4 days (N = 16). Of the rats treated with dexamethasone for 4 days, one half (N = 8) were administered an insulin-containing saline infusion subsequently to restore normoglycemia short-term. All other rats (N = 50) were administered an infusion of saline without insulin. Plasma glucose was quantified, and brains were excised after in situ freezing. Brain glucose and glycogen concentrations were measured using enzymatic fluorometric analyses. After 4 days of dexamethasone treatment, plasma glucose was 159% greater than in rats administered placebo (i.e., 22.01 +/- 4.66 vs. 8.51 +/- 1.65 micromol/ml; mean +/- SD; P < 0.0001). Brain glucose concentrations increased parallel to plasma glucose. An insulin infusion for 27 +/- 5 min restored normoglycemia but resulted in a brain-to-plasma glucose ratio that was 32% greater than baseline values (P < 0.01). Neither dexamethasone nor the combination of dexamethasone plus insulin affected brain glycogen concentrations. In a nonischemic rat model, dexamethasone alone had no independent effect on the brain-to-plasma glucose ratio. However, short-term insulin therapy caused a dysequilibrium between plasma and brain glucose, resulting in an underestimation of brain glucose concentrations when normoglycemia was restored. The dysequilibrium likely was caused by the rapid rate of glucose reduction. The magnitude of the effect may account for the failure of insulin to reverse dexamethasone enhancement of neurologic injury completely in a previous report that used the rat model of forebrain ischemia.

Effect of temperature on the kinetics of lactate production and clearance in a rat model of forebrain ischemia

To investigate the effect of brain temperature on metabolic perturbations during and following forebrain ischemia, localized 1H magnetic resonance spectroscopy was used to measure the kinetics of lactate production and clearance in a rat model of 12- or 20-min forebrain ischemia (two-vessel occlusion with hypotension) at a brain temperature of either 34.5 ± 0.5°C or 37.5 ± 0.5°C. During ischemia, lactate production was modeled with apparent first order kinetics. Hypothermia did not affect the rate or the extent of lactate production during ischemia. Upon reperfusion, a delay in the decrease of the cerebral lactate level was found in the normothermia groups. Such a delay was absent in hypothermia groups, which may reflect faster resumption of cerebral oxidative metabolism upon reperfusion in the hypothermic animals. The rate constant for lactate clearance postischemia was larger for normothermic animals and for the 20-min ischemia groups, perhaps because of increased blood-brain barrier permeability following more severe ischemia.Key words: forebrain ischemia, temperature, hypothermia, lactate, magnetic resonance spectroscopy.

Effect of temperature on the kinetics of lactate production and clearance in a rat model of forebrain ischemia.

To investigate the effect of brain temperature on metabolic perturbations during and following forebrain ischemia, localized 1H magnetic resonance spectroscopy was used to measure the kinetics of lactate production and clearance in a rat model of 12- or 20-min forebrain ischemia (two-vessel occlusion with hypotension) at a brain temperature of either 34.5 +/- 0.5 degrees C or 37.5 +/- 0.5 degrees C. During ischemia, lactate production was modeled with apparent first order kinetics. Hypothermia did not affect the rate or the extent of lactate production during ischemia. Upon reperfusion, a delay in the decrease of the cerebral lactate level was found in the normothermia groups. Such a delay was absent in hypothermia groups, which may reflect faster resumption of cerebral oxidative metabolism upon reperfusion in the hypothermic animals. The rate constant for lactate clearance postischemia was larger for normothermic animals and for the 20-min ischemia groups, perhaps because of increased blood-brain barrier permeability following more severe ischemia.

Metabolism of glucose, glycogen, and high-energy phosphates during transient forebrain ischemia in diabetic rats: effect of insulin treatment.

Hyperglycemia associated with diabetes mellitus will exacerbate neurologic injury after global brain ischemia. Studies in a rat model of forebrain ischemia (bilateral carotid occlusion plus hypotension for 10 min) discovered that acute restoration of normoglycemia in diabetics, using an insulin infusion, resulted in a neurologic outcome that was similar to normoglycemic rats without diabetes. The current study evaluated cerebral glucose, glycogen, lactate, and high-energy phosphate concentrations to identify metabolic correlates that might account for an alteration in postischemic outcome. Fifty-four pentobarbital-anesthetized Sprague-Dawley rats were assigned to three groups: chronically hyperglycemic diabetic rats (D; N = 18); insulin-treated, acutely normoglycemic diabetic rats (ID; N = 18); and nondiabetic rats (ND; N = 18). These groups were further divided into groups of six rats each that received either no ischemia, forebrain ischemia of 10 min duration without reperfusion, or ischemia plus 15 min of reperfusion. Brains were excised after in situ freezing, and metabolites were measured using enzymatic fluorometric techniques. Before ischemia, D rats had greater concentrations of brain glucose (12.18 +/- 2.67 micromol/g) than did either ID (5.10 +/- 1.33) or ND (3.20 +/- 0.27) rats (P < 0.05). Preischemic brain glycogen was similar in all groups. At the completion of ischemia, brain lactate concentrations in D were 86% greater than in ID and 61% greater than in ND (P < 0.05), reflecting a higher intraischemic consumption of glucose plus glycogen in D (P < 0.05). High-energy phosphate concentrations, as assessed by the energy charge of the adenylate pool, were better preserved in D (energy charge = 0.60 +/- 0.28) than in either ID (0.29 +/- 0.09) or ND (0.36 +/- 0.07; P < 0.05) rats. After 15 min of reperfusion, the energy charge returned to preischemic values (i.e., 0.91-0.92) in all groups. These studies demonstrated greater intraischemic carbohydrate consumption and lactate production in D than in ID or ND rats. Under these conditions, intraischemic-but not postischemic-energy status was better in D rats. Acute insulin therapy in ID rats resulted in a metabolic profile that was similar to that of ND rats. These results suggest that, in this model, primary energy failure during ischemia is not the origin of greater injury in hyperglycemic diabetics, nor is energy enhancement the origin of improved outcome after acute insulin treatment.

Protective effect of dichloroacetate in a rat model of forebrain ischemia

Dichloroacetate (DCA) activates the pyruvate dehydrogenase complex (PDHC), and improves the recovery of cerebral pH, lactate, ATP, and PCr following reperfusion in animal models of forebrain ischemia. In order to determine whether this results in neuroprotection, rats were administered NaDCA (100 mg/kg or 10 mg/kg i.v.) 10 min before 12 min of normothermic forebrain ischemia (bilateral carotid artery occlusion plus systemic hypotension, 45 mmHg). Neuronal injury assessed histopathologically 7 days post-ischemia was significantly reduced in the CAI region of the hippocampus, the dorsal lateral striatum, and the neocortex, in rats treated with 100 mg/kg NaDCA, but not in rats treated with 10 mg/kg NaDCA.

Propagation of seizure activity arising from the hippocampus: A local cerebral blood flow study

In this report the effects of phencyclidine (PCP) on physiologic variables, local cerebral blood flow (LCBF), and on hippocampal cell damage were measured in a rat model of forebrain ischemia (2-vessel occlusion and hypotension). Ischemia was induced for 10 min. LCBF was determined after 2 min of recirculation, using the [14C]iodoantipyrine technique. Hippocampal cell loss was quantified histologically 7 days postischemia as the percentage of acidic stainable neurons. Intravenous application of PCP (2 mg/kg) at 15 min prior to ischemia left postischemic LCBF unchanged, but neuronal damage was significantly reduced in hippocampal CA1 sector from 46 to 15.7%. PCP is concluded to reduce ischemic damage of neurons mainly via a direct effect on brain tissue.

Treatable hypertrophic neuropathy in childhood: Changes in nerve conduction before and after treatment

In this report the effects of phencyclidine (PCP) on physiologic variables, local cerebral blood flow (LCBF), and on hippocampal cell damage were measured in a rat model of forebrain ischemia (2-vessel occlusion and hypotension). Ischemia was induced for 10 min. LCBF was determined after 2 min of recirculation, using the [14C]iodoantipyrine technique. Hippocampal cell loss was quantified histologically 7 days postischemia as the percentage of acidic stainable neurons. Intravenous application of PCP (2 mg/kg) at 15 min prior to ischemia left postischemic LCBF unchanged, but neuronal damage was significantly reduced in hippocampal CA1 sector from 46 to 15.7%. PCP is concluded to reduce ischemic damage of neurons mainly via a direct effect on brain tissue.

The N-methyl-D-aspartate antagonist, MK-801, fails to protect against neuronal damage caused by transient, severe forebrain ischemia in adult rats

The neuroprotective effects of dizocilipine maleate (MK-801), a noncompetitive antagonist of the N-methyl-D-aspartate (NMDA) receptor/channel, were tested in the 4-vessel occlusion rat model of forebrain ischemia. Adult Wistar rats, treated intraperitoneally with MK-801 or saline using several different treatment paradigms were subjected to 5 (n = 208) or 15 (n = 62) min of severe, transient forebrain ischemia. In saline-treated animals, 15 min of ischemia (n = 13) produced extensive and consistent loss of pyramidal neurons in the CA1 zone of hippocampus. The degree and distribution of cell loss were not reduced by single dose preischemic administration of MK-801 at 1 (n = 7), 2.5 (n = 4), or 5 mg/kg (n = 8). In other animals subjected to 15 min of forebrain ischemia, multiple doses of MK-801 (5, 2.5, and 2.5 mg/kg) given immediately and at approximately 8 and 20 hr after cerebral reperfusion (n = 5) did not alter CA1 injury compared to saline-treated controls (n = 5). Five minutes of forebrain ischemia in saline-treated animals, (n = 82) resulted in significantly fewer (p less than 0.001) dead CA1 pyramidal cells and a greater variance compared to animals subjected to 15 min of ischemia. Power analysis of the preliminary saline-treated animals subjected to 5 min of ischemia (n = 22) indicated that 60 animals per group were necessary to detect a 15% difference between MK-801 and vehicle-treated groups. Multidose treatment with MK-801 (1 mg/kg) given 1 hr prior to 5 min of ischemia (n = 60) and again at approximately 8 and 16 hr after recirculation failed to attenuate hippocampal injury.(ABSTRACT TRUNCATED AT 250 WORDS)

Protective Effect of Vinpocetine against Brain Damage Caused by Ischemia

The effects of vinpocetine against hippocampal neuronal damage and on local cerebral blood flow (LCBF) were examined in a rat model of forebrain ischemia (10-min occlusion of the carotid arteries and hypotension). Histological evaluation of neuronal loss in the hippocampus was performed 7 days after ischemia. LCBF was measured before ischemia as well as after 2 min and 1 hr of recirculation. Vinpocetine (10mg/kg) administered pre- or post-ischcmically reduced the hippocampal neuronal necrosis, while pre-ischemic administration of 2 or 20 mg/kg vinpocetine was ineffective. Since vinpocetine increased the LCBF after 1 hr of recirculation, it cannot be excluded that blood flow improvements contribute to its neuroprotective activity. On the other hand, there is no clear evidence that an elevation of post-ischemic hypoperfusion could protect neurons against ischemic damage. It is, therefore, suggested that vinpocetine acts directly on brain cells.

Protective Effect of Vinpocetine against Brain Damage Caused by Ischemia.

The effects of vinpocetine against hippocampal neuronal damage and on local cerebral blood flow (LCBF) were examined in a rat model of forebrain ischemia (10-min occlusion of the carotid arteries and hypotension). Histological evaluation of neuronal loss in the hippocampus was performed 7 days after ischemia. LCBF was measured before ischemia as well as after 2 min and 1 hr of recirculation. Vinpocetine (10 mg/kg) administered pre- or post-ischemically reduced the hippocampal neuronal necrosis, while pre-ischemic administration of 2 or 20 mg/kg vinpocetine was ineffective. Since vinpocetine increased the LCBF after 1 hr of recirculation, it cannot be excluded that blood flow improvements contribute to its neuroprotective activity. On the other hand, there is no clear evidence that an elevation of post-ischemic hypoperfusion could protect neurons against ischemic damage. It is, therefore, suggested that vinpocetine acts directly on brain cells.

Naftidrofuryl protects neurons against ischemic damage.

The effects of naftidrofuryl on postischemic neuronal damage and on local cerebral blood flow (LCBF) were examined in a rat model of forebrain ischemia (occlusion of carotid arteries and hypotension). Ischemia was induced for 10 min. LCBF was measured after 2 and 10 min of recirculation. A histological evaluation of cell loss in the hippocampal areas was performed 7 days after ischemia. Naftidrofuryl (10 mg/kg) was administered intraperitoneally 15 min before ischemia. The drug reduced the percentage of necrotic neurons in the CA1 and CA4 sector of the hippocampus, while the LCBF of these hippocampal sections was not significantly altered. Thus, naftidrofuryl is suggested to protect hippocampal neurons against ischemic damage mainly by a direct effect on brain parenchyma.

Effects of flunarizine on postischemic blood flow, energy metabolism and neuronal damage in the rat brain

The effects of flunarizine on local cerebral blood flow, cortical energy metabolism and neuronal necrosis were evaluated in a rat model of forebrain ischemia. The application of flunarizine (2 × 40 mg/kg p.o.) at 24 and 4 h before ischemia accelerated the restoration of cortical high-energy phosphates during early post-ischemic recirculation and also increased the flow in cortical but not in hipoocampal areas. Neuronal necrois was reduced in the hippocampal CA 1 sector but unchanged in the cortex. It is concluded that flunarizine reduces ischemic damage mainly via a direct effect on brain tissue.

Phencyclidine reduces postischemic neuronal necrosis in rat hippocampus without changing blood flow

In this report the effects of phencyclidine (PCP) on physiologic variables, local cerebral blood flow (LCBF), and on hippocampal cell damage were measured in a rat model of forebrain ischemia (2-vessel occlusion and hypotension). Ischemia was induced for 10 min. LCBF was determined after 2 min of recirculation, using the [ 14C]iodoantipyrine technique. Hippocampal cell loss was quantified histologically 7 days postischemia as the percentage of acidic stainable neurons. Intravenous application of PCP (2 mg/kg) at 15 min prior to ischemia left postischemic LCBF unchanged, but neuronal damage was significantly reduced in hippocampal CA1 sector from 46 to 15.7%. PCP is concluded to reduce ischemic damage of neurons mainly via a direct effect on brain tissue.

Vinpocetine prevents ischemic cell damage in rat hippocampus

The effects of vinpocetine on hippocampal cell damage and local cerebral blood flow (LCBF) were measured in a rat model of forebrain ischemia (2-vessel occlusion and hypotension). Duration of ischemia was 10 min. LCBF was determined after 2 min of recirculation using the 14C-iodoantipyrine technique. Hippocampal cell loss was quantified histologically 7 days postischemia. Intraperitoneal application of vinpocetine (10 mg/kg) 15 min prior to ischemia significantly reduced neuronal cell loss in hippocampal CA 1 sector from 60 % to 28 %. The drug led to a marked increase in blood flow in cortical areas, whereas LCBF remained unchanged in hippocampus and all other structures measured. It is suggested that the protective effect of vinpocetine does not depend on increased postischemic blood flow.