Adenylate cyclase and histopathological changes in the gerbil brain following prolonged unilateral ischemia and recirculation

Assessment of cerebrovascular reserve with N-isopropyl-p-[123I]-iodoamphetamine time series analysis in patients with cerebrovascular disease

Using N-isopropyl-p-[123I]-iodoamphetamine(123I-IMP) and single-photon emission computed tomography (SPECT), the relationship between cerebrovascular reserve and the 123I-IMP redistribution phenomenon was investigated.The 50 patients who matched the inclusion criteria were divided into control and ischemia groups, and the redistribution phenomenon was examined on resting images. The delayed images showed higher 123I-IMP accumulation in lesions in the middle cerebral artery(MCA) area and anterior cerebral artery(ACA) area, these watershed areas in the ischemia group than in the control group, confirming that the redistribution phenomenon exists with statistical significance (Wilcoxon test; control group vs ischemic group in the ACA area[P = .002], ACA-MCA watershed area(P = .014), MCA area(P = .025), and MCA-posterior cerebral artery(PCA) watershed area(P = .002). The patients were then divided into 4 types according to the Kuroda grading system, and the difference in the redistribution phenomenon was investigated between type III and the other 3 types.Compared with type I and type II, type III had a significantly lower rate of decrease in the radioisotope (RI) count, verifying the redistribution phenomenon (Student t test: type I vs type III in the ACA area(P = .008), ACA-MCA watershed area(P = .009), MCA area(P < .001), and MCA-PCA watershed area(P = .002); type II vs type III in the ACA area(P = .004), ACA-MCA watershed area(P = .2575), MCA area(P < .001), and MCA-PCA watershed area(P < .001). No significant difference between type III and type IV was observed in any area [(Student t test: type III vs type IV in the ACA area(P = .07), ACA-MCA watershed area(P = .38), MCA area(P = .05), and MCA-PCA watershed area(P = .24)].The redistribution phenomenon is associated with resting cerebral blood flow (CBF), but not necessarily with cerebral vascular reactivity (CVR).

Effect of D-003, a mixture of very-long-chain aliphatic acids purified from sugarcane wax, on cerebral ischemia in Mongolian gerbils

D-003 is a mixture of very-high-molecular-weight aliphatic acids purified from sugar cane wax (Saccharum officinarum), which inhibits platelet aggregation and lipid peroxidation. The objective of the present study was to evaluate the effect of D-003 on cerebral ischemia induced by ischemia-reperfusion (I-R) in Mongolian gerbils. Two experimental series were conducted. The first series investigated the effects of D-003 on cerebral edema, neurological symptoms, and mortality in Mongolian gerbils with cerebral ischemia induced by I-R, while the second series investigated the effects on histological markers of cerebral injury, such as edema intensity (vacuolization) and cerebral necrosis. Animals were randomly distributed in five experimental groups: a sham-operated group experiencing surgical handling except the clamping and orally treated with Tween/water vehicle and four groups subjected to the I-R surgical procedure. One of these groups was treated with the same vehicle, and the other three groups received D-003 at 25, 100, and 200 mg/kg, respectively. All treatments were administered for 14 days. D-003 (200 mg/kg) significantly reduced the cerebral edema and clinical symptoms provoked by I-R compared with the positive control group, whereas lower doses (25 and 100 mg/kg) were not effective. Positive control animals showed an injury profile characterized by swelling (tissue vacuolization) and necrosis of neurons in all areas of the brain studied (frontal cortex, hippocampus, and striatum). The results of the histological study were consistent with those observed by determining cerebral edema and symptoms observation. Thus, D-003 at 200 mg/kg significantly reduced histological markers of brain injury (swelling and necrosis) compared with the control group. It is concluded that D-003 administered orally at 200 mg/kg for 14 days protected against cerebral damage caused by bilateral cerebral ischemia in Mongolian gerbils.

Alteration of second messengers during acute cerebral ischemia - adenylate cyclase, cyclic AMP-dependent protein kinase, and cyclic AMP response element binding protein

A variety of neurotransmitters and other chemical substances are released into the extracellular space in the brain in response to acute ischemic stress, and the biological actions of these substances are exclusively mediated by receptor-linked second messenger systems. One of the well-known second messenger systems is adenylate cyclase, which catalyzes the generation of cyclic AMP, triggering the activation of cyclic AMP-dependent protein kinase (PKA). PKA controls a number of cellular functions by phosphorylating many substrates, including an important DNA-binding transcription factor, cyclic AMP response element binding protein (CREB). CREB has recently been shown to play an important role in many physiological and pathological conditions, including synaptic plasticity and neuroprotection against various insults, and to constitute a convergence point for many signaling cascades. The autoradiographic method developed in our laboratory enables us to simultaneously quantify alterations of the second messenger system and local cerebral blood flow (lCBF). Adenylate cyclase is diffusely activated in the initial phase of acute ischemia (< or = 30 min), and its activity gradually decreases in the late phase of ischemia (2-6 h). The areas of reduced adenylate cyclase activity strictly coincide with infarct areas, which later become visible. The binding activity of PKA to cyclic AMP, which reflects the functional integrity of the enzyme, is rapidly suppressed during the initial phase of ischemia in the ischemic core, especially in vulnerable regions, such as the CA1 of the hippocampus, and it continues to decline. By contrast, PKA binding activity remains enhanced in the peri-ischemia area. These changes occur in a clearly lCBF-dependent manner. CREB phosphorylation at a serine residue, Ser(133), which suggests the activation of CREB-mediated transcription of genes containing a CRE motif in the nuclei, remains enhanced in the peri-ischemia area, which is spared of infarct damage. On the other hand, CREB phosphorylation at Ser133 rapidly diminishes in the ischemic core before the histological damage becomes manifest. The Ca2+ influx during membrane depolarization contributes to CREB phosphorylation in the initial phase of post-ischemic recirculation, while PKA activation and other signaling elements seem to be responsible in the later phase. These findings suggest that derangement of cyclic AMP-related intracellular signal transduction closely parallels ischemic neuronal damage and that persistent enhancement of this signaling pathway is important for neuronal survival in acute cerebral ischemia.

Effect of policosanol on cerebral ischemia in Mongolian gerbils

Policosanol is a mixture of higher aliphatic primary alcohols isolated from sugar cane wax, whose main component is octacosanol. An inhibitory effect of policosanol on platelet aggregation and cerebral ischemia in animal models has been reported. Thus, the objective of the present study was to evaluate the effect of policosanol on cerebral ischemia induced by unilateral carotid ligation and bilateral clamping and recirculation in Mongolian gerbils. Policosanol (200 mg/kg) administered immediately after unilateral carotid ligation and at 12- or 24-h intervals for 48 h significantly inhibited mortality and clinical symptoms when compared with controls, whereas lower doses (100 mg/kg) were not effective. Control animals showed swelling (tissue vacuolization) and necrosis of neurons in all areas of the brain studied (frontal cortex, hippocampus, striatum and olfactory tubercle), showing a similar injury profile. In the group treated with 200 mg/kg policosanol swelling and necrosis were significantly reduced when compared with the control group. In another experimental model, comparison between groups showed that the brain water content of control gerbils (N = 15) was significantly higher after 15 min of clamping and 4 h of recirculation than in sham-operated animals (N = 13), whereas policosanol (200 mg/kg) (N = 19) significantly reduced the edema compared with the control group, with a cerebral water content identical to that of the sham-operated animals. cAMP levels in the brain of control-ligated Mongolian gerbils (N = 8) were significantly lower than those of sham-operated animals (N = 10). The policosanol-treated group (N = 10) showed significantly higher cAMP levels (2.68 pmol/g of tissue) than the positive control (1.91 pmol/g of tissue) and similar to those of non-ligated gerbils (2.97 pmol/g of tissue). In conclusion, our results show an anti-ischemic effect of policosanol administered after induction of cerebral ischemia, in two different experimental models in Mongolian gerbils, suggesting a possible therapeutic effect in cerebral vascular disorders.

Alteration of second-messenger ligand binding following 2-hr hemispheric ischemia in the gerbil brain

The alterations of second-messenger ligand binding and cerebral blood flow (CBF) were evaluated in the gerbil brain after 2-h unilateral common carotid artery occlusion. [3H]Forskolin (FK) and [3H]phorbol-12,13-dibutyrate (PDBu) were used as specific ligands for adenylate cyclase (AC) and protein kinase C (PKC) activity estimation, respectively. CBF was determined at the end of the experiment by the [14C]iodoantipyrine method. A quantitative autoradiographic method permitted simultaneous measurement of the three parameters in the same brain. The levels in the caudate-putamen, globus pallidus, and hippocampus were analyzed. The animals were divided into three groups: Group 1 with severe ischemia (CBF in the lateral nuclei of the thalamus (CBFt) less than 50 ml/100 g/min), Group 2 with mild ischemia (CBFt greater than or equal to 50 ml/100 g/min), and the Sham Group. The PDBu binding revealed a statistically significant increase in the caudate-putamen, lateral nuclei of the thalamus and hippocampus (CA1 and CA3 regions and dentate gyrus) on the ischemic side in Group 1 as compared to that in Group 2 and the Sham Group. In contrast, the FK binding did not show any significant changes in any of the regions. These data and our previous findings for 6-h ischemia suggest that (1) PKC translocation to the cell membrane may occur at the early ischemic phase in particular regions including the caudate-putamen, lateral nuclei of the thalamus and hippocampus, with the translocated PKC gradually diminishing during the subsequent ischemic period; and (2) the suppression of the AC system observed in 6-h ischemia may not appear in the early ischemic phase.

Autoradiographic analysis on second-messenger systems and local cerebral blood flow in ischemic gerbil brain

Alterations of the second-messenger systems, adenylate cyclase (AC) and protein kinase C (PKC), and local cerebral blood flow (lCBF) were evaluated during experimental cerebral ischemia in gerbils employing a quantitative autoradiographic method, which permitted these three parameters to be measured in the same brain. Ischemia was induced by occlusion of the right common carotid artery for 6 h. Animals attaining more than 5 in their ischemic scores were utilized for further experiments. At the end of ischemia, lCBF was measured by the [14C]iodoantipyrine method. The AC and PKC activities were estimated by the autoradiographic technique developed in our laboratory using [3H]forskolin (FK) and [3H]phorbol-12,13-dibutyrate (PDBu), respectively. The lCBF fell below 10 ml/100 g/min in most cerebral regions on the ligated side. The greatest reduction in FK binding was noted in the olfactory tubercle, caudate-putamen, and globus pallidus, followed by the hippocampus and cerebral cortices. The FK binding tended to be low at lCBF less than 20 ml/100 g/min in the cerebral cortices. However, the PDBu binding was relatively well preserved in each cerebral structure, and no significant correlation between lCBF and PDBu binding was noted in the cerebral cortices. The AC system may thus be vulnerable to ischemic insult over extensive brain regions, while the PKC system may be relatively resistant to ischemia.

The auditory evoked potentials of gerbils after temporary occlusion of the left carotid artery

This study examined brain-stem auditory evoked potentials response (BAEP) changes in the gerbil after temporary occlusion of the left carotid artery. Fourteen adult gerbils were subjected to unilateral left carotid ligation for 30 min. BAEPs were registered before and 5 min after occlusion, then 5 min, 60 min, 120 min, 24 h, 7 days and 28 days after release of the clip. Waves I (cochlear nerve), III (superior olivary complex) and V (inferior colliculus) were examined. Results were analysed using paired Student's t-test. Transient ischaemia increased latencies of waves I, III and V and the changes were more severe 5 min after release of the clip. In the gerbil, BAEPs might be a suitable method to study cerebral ischaemia.

Posthoc phosphorylation of proteins derived from ischemic rat hippocampus, striatum and neocortex

Disruption of the brain's protein phosphorylation system by ischemia may cause irreversible metabolic and structural alterations leading eventually to cell death. To examine the effect of ischemia on the phosphorylation state of brain proteins, tissue homogenates derived from the hippocampus, striatum and neocortex of normal rats and rats subjected to severe forebrain ischemia were phosphorylated with [gamma-32P]ATP. The phosphorylated proteins were separated by two-dimensional polyacrylamide gel electrophoresis and changes were assessed by autoradiography. Cerebral ischemia caused marked alterations of the phosphorylation state of many brain proteins; phosphorylation of some proteins was increased while phosphorylation of others was decreased. Despite differences in the sensitivity of the hippocampus, striatum and neocortex to ischemic injury the direction and approximate magnitude of protein phosphorylation changes caused by ischemia were similar in all three regions. Since the pattern of protein phosphorylation in the ischemia-vulnerable hippocampus was identical to that in the ischemia-resistant paramedian neocortex we conclude that abnormalities of protein phosphorylation may be necessary for ischemic injury to neurons but none are sufficient to explain the selective vulnerability of certain brain regions to ischemic damage.

Regional profiles of steady-state levels of cyclic nucleotides, cyclic AMP phosphodiesterase, and guanylate cyclase activities during late stages of unilateral ischemia in gerbil forebrain

The present study was an extension of earlier work regarding the role of cyclic nucleotides and related enzymes during cerebral ischemia in the gerbil. Following unilateral carotid occlusion, levels of cyclic AMP and cyclic GMP were measured in four rapidly inactivated brain regions at 3, 6, and 24 hr after permanent occlusion and at 2 hr of occlusion plus 1 hr of reflow. An analysis of variance indicated significant minor fluctuations in the steady-state levels of the two cyclic nucleotides within the frontal cortex, the hippocampus, the striatum, and especially the olfactory tubercle with respect to occlusion time (3 and 24 hr) but not when comparing control vs ischemic hemispheres (except at 3 hr). Changes occurred only in animals developing neurological symptoms of ischemia. At 24 hr postocclusion the specific activity of the low-Km form of cyclic AMP phosphodiesterase was elevated especially on the ischemic side when determined in homogenates of the four brain regions. Alternatively, the high-Km form of the enzyme in the presence or absence of Ca2+-calmodulin was unchanged. Guanylate cyclase activity in tissue homogenates was not influenced by the conditions of ischemia until 24 hr had elapsed, an event likewise unique to symptomatic gerbils. The sensitivity of the enzyme to hematin-catalase was decreased in the ischemic hemispheres of the hippocampus, striatum, and olfactory tubercle. In addition, further activation of the hematin-catalase response by NaN3 was depressed in the ischemic side of the hippocampus and striatum. Taken together these and previous studies indicate that fluctuations in the steady-state levels of cyclic nucleotides that occur rather prominently during acute and to a lesser degree during prolonged ischemia are not correlated with associated changes in enzymes responsible for their synthesis and/or degradation.

Xanthine oxidase-derived hydrogen peroxide contributes to ischemia reperfusion-induced edema in gerbil brains

The contribution of toxic O2 metabolites to cerebral ischemia reperfusion injury has not been determined. We found that gerbils subjected to temporary unilateral carotid artery occlusion (ischemia) consistently developed neurologic deficits during ischemia with severities that correlated with increasing degrees of brain edema and brain H2O2 levels after reperfusion. In contrast, gerbils treated just before reperfusion (after ischemia) with dimethylthiourea (DMTU), but not urea, had decreased brain edema and brain H2O2 levels. In addition, gerbils fed a tungsten-rich diet for 4, 5, or 6 wk developed progressive decreases in brain xanthine oxidase (XO) and brain XO + xanthine dehydrogenase (XD) activities, brain edema, and brain H2O2 levels after temporary unilateral carotid artery occlusion and reperfusion. In contrast to tungsten-treated gerbils, allopurinol-treated gerbils did not have statistically significant decreases in brain XO or XO + XD levels, and reduced brain edema and brain H2O2 levels occurred only in gerbils developing mild but not severe neurologic deficits during ischemia. Finally, gerbils treated with DMTU or tungsten all survived, while greater than 60% of gerbils treated with urea, allopurinol, or saline died by 48 h after temporary unilateral carotid artery occlusion and reperfusion. Our findings indicate that H2O2 from XO contributes to reperfusion-induced edema in brains subjected to temporary ischemia.

A quantitative histochemical study of 5'-nucleotidase activity in rat liver after ischaemia

The lead salt method of Wachstein and Meisel15 has been applied using incubation media containing polyvinyl alcohol for the localization and quantification of 5'-nucleotidase (E.C.3.1.3.5) activity in cryostat sections from rat liver after ischaemia in vitro and ischaemia in vivo followed by different periods of re-perfusion. 5'-Nucleotidase activity at the bile canaliculi, especially in the pericentral areas, had already decreased after 60 min of ischaemia in vitro, although the total activity as measured densitometrically was not changed. After 120-240 min of ischaemia, a significant decrease of the total 5'-nucleotidase activity was found. At that stage, signs of irreversible cell damage were recognized. Short periods of re-perfusion (1 h) after ischaemia in vivo induced a decreased bile canalicular 5'-nucleotidase activity throughout the entire liver, but a restoration after longer periods of re-perfusion was observed (5, 24, and 48 h). Necrotic areas recognized by a decreased lactate dehydrogenase activity after all periods of re-perfusion showed decreased total 5'-nucleotidase activities. A correlation was observed between the decrease in bile canalicular 5'-nucleotidase activity and the disappearance of microvilli of the bile canaliculi. It is concluded that a decrease in the bile canalicular 5'-nucleotidase activity can be used as a very sensitive marker for ischaemic liver cell damage. Assessment of the irreversibility of the cell injury has to be determined using additional parameters such as a decreased lactate dehydrogenase activity.

Cerebral ischemia-reperfusion injury in the gerbil

Gerbils subjected to cerebral ischemia (unilateral carotid occlusion for 6 hr) were either asymptomatic or developed increasingly severe neurologic deficits which correlated with degrees of brain swelling (weights of ischemic hemisphere versus the contralateral control hemispheres) following 3 hr of reperfusion. Asymptomatic gerbils or gerbils suffering only mild deficits survived for 1 week following reperfusion while gerbils suffering moderate to severe deficits had a poor survival rate with only 22% remaining alive after 1 week.

Further probes into the molecular sites of damage to cerebral adenylate cyclase following postischemic reperfusion

A variety of pharmacological agents were used as experimental probes to determine with greater precision the site(s) of damage to cerebral adenylate cyclase as a consequence of postischemic reperfusion in the gerbil. A paradigm of 60-min bilateral ischemia followed by 40-min reperfusion results in a decreased sensitivity of the catalytic site of adenylate cyclase to Mn2+. Likewise, the GTP-transducer site (guanine nucleotide regulatory or G protein) revealed depressed responses to GTP in the absence or presence of norepinephrine, dopamine agonists, substance P, yohimbine, and cholera and pertussis toxins. Moreover, a crude preparation of GTPase disclosed that damage elicited by postischemic reperfusion was directed to the higher-affinity form of this enzyme, which is associated with the overall function of the guanine nucleotide regulatory protein. Injury to adenylate cyclase was unrelated either to the ability of adrenergic ligands to bind to associated receptor sites or to the capacity of the brain to generate visual evoked potentials in response to visual stimuli.

Effects of naloxone and morphine on cerebral ischemia in gerbils

A therapeutic role for naloxone during stroke has been suggested, but a neurochemical site of action remains to be determined. Previous work with the gerbil cerebral cortex has shown that either bilateral secondary ischemia (60-min occlusion of the carotid arteries followed by 40-min reflow) or unilateral primary ischemia (permanent ligation of one carotid artery for 6 hr in symptomatic animals) produced deficits in both Na+, K+-ATPase (EC 3.6.1.3) activity and various parameters of activation of adenylate cyclase (EC 4.6.1.1). Pretreatment of gerbils with either naloxone or morphine failed to ameliorate or exacerbate, respectively, the neurological signs of ischemia; however, morphine did reduce mortality. Infusion of naloxone prior to ischemia afforded varying degrees of protection to forskolin, GTP analogs, and NE (norepinephrine) activation of adenylate cyclase, as well as to Na+, K+-ATPase (bilateral ischemia only). Similarly, morphine inhibited damage to basal activity of adenylate cyclase and to stimulation by NE, forskolin, and Gpp (NH)p (5'-guanylyl imidodiphosphate). Under in vitro conditions morphine increased the basal activity of adenylate cyclase but reduced responses to NE and forskolin. Furthermore, morphine injected into control gerbils elevated basal- and forskolin-elicited activities but reduced the activation of adenylate cyclase by NE.

Classification of ischemic-induced damage to Na+, K+-ATPase in gerbil forebrain. Modification by therapeutic agents

The activity of three forms of ATPase were examined in fractions of the brain of the gerbil treated with ethylene glycol-N-N-tetra-acetic acid (EGTA) under a variety of conditions of primary and secondary (reflow) ischemia. In animals which were unilateral ischemic (ligation of the right common carotid), damage to Na+, K+-ATPase alone was observed only after at least 6 hr of ischemia had elapsed. The phenomenon occurred in only symptomatic gerbils and was absent in animals which were either asymptomatic or only displayed partial neurological symptoms. Under conditions of bilateral cerebral ischemia, in which both carotid arteries were clamped, only irreversible ischemia (60 min) followed by reflow, was associated with highly significant damage to cerebral Na+, K+-ATPase. In regional studies of the forebrain involving ischemia for 60 min plus 30 min reflow, damage to Na+, K+-ATPase was evident in the cerebrum, hippocampus, striatum and thalamus, while the hypothalamus and olfactory bulb were spared. Pretreatment of gerbils with allopurinol, clonazepam or combinations of thiopental plus either indomethacin or methylprednisolone offered protection to cerebral Na+, K+-ATPase subsequent to secondary ischemia. With only minor exceptions (striatum) neither Ca2+, Mg2+- nor Mn2+-ATPase were altered by stroke or treatment with drugs.