Evaluation of the neuroprotective action of WEB 1881 FU on hypoglycemia/hypoxia-induced neuronal damage using rat striatal slices

Decreased cholinergic receptor expression in the striatum: motor function deficit in hypoglycemic and diabetic rats

Hypoglycemic brain injury is a common and serious complication of insulin therapy associated with diabetes. This study evaluated the effect of insulin-induced hypoglycemia and STZ-induced diabetes on striatal cholinergic receptors and enzyme expression and on motor function. Cholinergic enzymes: AChE and ChAT gene expression, radioreceptor binding assay and immunohistochemistry of muscarinic M1, M3 receptors and α7nAChR were carried out. Motor performance on grid walk test was analysed. AChE and ChAT expression significantly downregulated in hypoglycemic and diabetic rats. Total muscarinic and Muscarinic M3 receptor binding decreased in hypoglycemic rats compared to diabetic rats whereas muscarinic M1 receptor binding increased in hypoglycemic rats compared to diabetic rats. Real-time PCR analysis and confocal imaging of muscarinic M1, M3 receptors confirmed the changes in muscarinic receptor binding in hypoglycemic and diabetic rats. In hypoglycemic rats, α7nAChR expression significantly up regulated compared to diabetic rats. Grid walk test demonstrated the impairment in motor function and coordination in hypoglycemic and hyperglycemic rats. Neurochemical changes along with the behavioral data implicate a role for impaired striatal cholinergic receptor function inducing motor function deficit induced by hypo and hyperglycemia. Hypoglycemia exacerbated the neurobehavioral deficit in diabetes which has clinical significance in the treatment of diabetes.

Potentiation by cadmium ion of ATP-evoked dopamine release in rat phaeochromocytoma cells

1. The effects of cadmium ion (Cd2+) on release of dopamine and on an inward current evoked by extracellular ATP were investigated in rat phaeochromocytoma PC12 cells. 2. Cd2+ (100 microM-3 mM) potentiated the dopamine release evoked by 30 microM ATP from the cells. Cd2+ (100 microM) shifted the concentration-response curve of ATP-evoked dopamine release to the left without affecting the maximal response. 3. Suramin (30 microM) completely abolished the dopamine release evoked by 30 microM ATP but only partially inhibited the release evoked by 100 microM ATP consistent with its role as a competitive antagonist. The response evoked by 30 microM ATP in the presence of Cd2+ (300 microM) was comparable to that observed with 100 microM ATP alone; however, only the former was almost completely inhibited by suramin. 4. Cd2+ (100 microM) potentiated an inward current activated by 30 microM ATP alone. A higher concentration of Cd2+ (300 microM) had a smaller effect on amplitude potentiation but significantly prolonged the duration of the current. 5. The time-course of the ATP-evoked dopamine release was investigated using a real-time monitoring system for dopamine release. Although Cd2+ (300 microM) had little effect on the time-course of activation the ATP-evoked dopamine release, it produced a long-lasting dopamine release which slowly returned to the baseline. 6. Taken together, these observations suggest that Cd2+ enhances ATP-evoked dopamine release by affecting P2-purinoceptor/channels. The enhancement may be attributed to a Cd(2+)-dependent increase in sensitivity to ATP.

Inhibitory action of nebracetam on various stimuli-evoked increases in intracellular Ca2+ concentrations in cultured rat cerebellar granule cells

Nebracetam (10-100 microM) dose-dependently inhibited increases in intracellular Ca2+ concentrations evoked by various stimuli in cultured rat cerebellar granule cells. The magnitude of the nebracetam (100 microM)-induced inhibition of L-glutamate- and N-methyl-D-aspartate-evoked Ca2+ responses was 1.5-fold and 1.7-fold greater, respectively, than the inhibition of the high K(+)-evoked response. These findings suggest that in cultured cerebellar granule cells, nebracetam attenuates the external Ca2+ influx derived from the activation of N-methyl-D-aspartate receptor-gated rather than voltage-gated Ca2+ channels.

Histological evidence for neuroprotective action of nebracetam on ischemic neuronal injury in the hippocampus of stroke-prone spontaneously hypertensive rats

The protective effect of nebracetam on ischemic neuronal damage was histologically examined in the pyramidal cell layer of the hippocampal CA1 subfield 7 days after operation using stroke-prone spontaneously hypertensive rats (SHRSP) subjected to 10-min bilateral carotid occlusion. Nebracetam (50 and 100 mg/kg), given orally 10 min after reperfusion, dose-dependently protected against ischemic delayed neuronal damage in the SHRSP with occlusion; however, the blood pressure remained unchanged following nebracetam administration. These findings further support the notion that nebracetam protects against ischemic delayed neuronal cell death in the hippocampus.

Endothelin-3 stimulates inositol 1,4,5-trisphosphate production and Ca2+ influx to produce biphasic dopamine release from rat striatal slices

1. Real-time monitoring of dopamine (DA) release from rat striatal slices demonstrated that endothelin (ET)-3 (0.1-10 microM) produced a biphasic DA release consisting of transient and sustained components. When extracellular Ca2+ was removed, the sustained but not transient response remarkably decreased. 2. ET-3 (1-10 microM) stimulated an increase in the intracellular Ca2+ concentration ([Ca(2+)]i), which also consisted of two components. The external Ca2+ depletion inhibited primarily the sustained component of the Ca2+ response to ET-3. 3. ET-3 increased inositol 1,4,5-trisphosphate (IP3) concentrations in striatal slices. This response peaked at 10 to 20 sec and returned to the basal level 2 min after stimulation, an event which was in good accord with a prompt and transient phase of both cytosolic Ca2+ activity and DA release evoked by ET-3. 4. Thus, ET-3 produces a transient and a sustained release of DA from striatal slices by stimulating intracellular Ca2+ mobilization via IP3 formation and extracellular Ca2+ influx, respectively.

A facilitatory role of vasopressin in hypoxia/hypoglycemia-induced impairment of dopamine release from rat striatal slices

The excitatory amino acid, glutamate plays a crucial role in the pathogenesis of brain damage caused by anoxia and/or hypoglycemia. Although vasopressin (VP) also acts as an excitatory transmitter in the CNS, little is known about its effect on hypoxic and/or ischemic brain damage. In this study, we investigated the effect of arginine vasopressin (AVP) on hypoxia/hypoglycemia-induced impairment of dopamine release from striatal slices. Striatal slices were incubated in hypoxia-/hypoglycemia-inducing medium with or without AVP (0.01-1.0 microM) for 20 min. After 1-3 h of washout in normal medium, high K(+)-evoked dopamine release from the slices were examined. Hypoxia/hypoglycemia-induced decrease of striatal dopamine release was reversed by the removal of Ca2+ in the medium, but not by VP1- or VP2-receptor antagonist. In contrast, AVP potentiated the hypoxia/hypoglycemia-induced decrease of dopamine release in the striatum. This AVP-induced deterioration of the striatal response was antagonized by VP2 receptor antagonist, but not by VP1 receptor antagonist. The present results suggest that AVP may play a facilitatory role in hypoxia/hypoglycemia-induced dopamine release deficit mediated through the activation of VP2 receptor.

Effects of idebenone on information processing in aged Long-Evans rats

Idebenone (6-(10-hydroxydecyl)-2,3-dimethoxy-5-methyl-1,4-benzoquinone) is a benzoquinone that has been shown to improve cognitive function in animals subjected to cerebral ischemia and in rats with lesions of the basal forebrain cholinergic system. Because the cognitive deficits observed in aged rats have been associated with decreased cerebral blood flow and basal forebrain cholinergic dysfunction, it was hypothesized that IDE might improve cognition in aged animals. In the present study, the effects of idebenone on cognitive function in aged Long-Evans rats were assessed using a battery of tests that evaluated attention, habituation, and spatial learning. Selective attention was assessed using an overshadowing paradigm, where IDE (30 mg/kg, IP) was injected 30 min prior to compound cue exposure. IDE enhanced the overshadowing effect in aged rats. The Morris water maze was used to assess spatial learning, where IDE (3 mg/kg, IP) was injected daily throughout the course of training. IDE did not improve the impaired performance of aged rats in the Morris task. Habituation was tested by measuring recovery from gustatory neophobia. IDE (30 mg/kg, IP) was injected 30 min prior to the first exposure to the novel taste. IDE normalized habituation rate in aged rats. It was concluded that IDE improves some forms of acquisition in aged rats, and may do so by decreasing general reactivity to novel stimuli.

Relation between long-lasting amounts of excitatory amino acid and its neuronal uptake system in cultured cerebellar granule cells under hypoglycemia

1. Basal release of amino acids (Glu, Gln, Gly and Tau) in cultures of rat cerebellar granule cells was detected at 3 days in vitro (DIV). The amounts of Gln and Gly released increased according to days of culture. Moreover, the amounts of Glu in a glia poor culture of granule cells tended to be higher than those in glia rich cultured cells, while Gln, Gly and Tau concentrations were lower in glia poor cells than in glia rich cells. 2. After depolarization induced by high KCl, amounts of all measured amino acids significantly rose to more than 1.5 times their basal values. The increased values obtained in a glia rich culture of granule cells were higher than those in a glia poor culture of cells throughout all cultured days. 3. Under deprivation of glucose, most concentrations of amino acids in the medium, especially Gln concentration, increased by 50 mM KCl were lower than those seen under normal conditions. Such lesser efflux examined under hypoglycemia was much more clearly recognized in glia rich cultures than in glia poor cultures. However, the amounts of Glu at 10 and 14 DIV, and also Gly and Tau amounts at 10 DIV were significantly higher than those seen in the cultures of glia poor cells under normal conditions. 4. The dosage of 10 microM Glu-induced [Ca2+]i accumulation was inhibited by several different types of Ca antagonists and scopolamine. Meanwhile, the dosages of the tested drugs, except for scopolamine, required for blocking Glu-induced [Ca2+]i accumulation under hypoglycemia were less than those required under normal conditions. These results suggest that neuronal death induced hypoglycemia might be caused by the dysfunction of the neuronal, but not glial, Glu uptake system, and that some Ca antagonists might be useful in preventing the neuronal death caused by hypoglycemia.

Nebracetam (WEB 1881FU) prevents N-methyl-D-aspartate receptor-mediated neurotoxicity in rat striatal slices

The effects of nebracetam were investigated on N-methyl-D-aspartate (NMDA) receptor- and voltage-operated Ca2+ channels (VOCC)-mediated neural dysfunction by directly monitoring the real-time dynamics of dopamine released from rat striatal slices. Nebracetam (10(-5) and 10(-4) M) completely protected against striatal dopaminergic impairment induced by L-glutamate and NMDA, respectively. BAY K-8644-evoked striatal dysfunction was not blocked by nebracetam (10(-4) M). Therefore, nebracetam seems to produce a neuroprotective action by interacting, at least in part, with NMDA receptor-operated Ca2+ channels.

Endothelin-3 stimulates the release of catecholamine from cortical and striatal slices of the rat

Endothelin-3 (ET-3) evoked the release of dopamine/noradrenaline from cortical slices and dopamine from striatal slices in a concentration-dependent manner. This action peaked slowly and was long-lasting in real-time monitoring, being different from the high K(+)-evoked response. The striatal response to 10 microM of ET-3 was reduced by extracellular Ca2+ depletion to 40% of control and by Ca2+ antagonists, especially nifedipine and flunarizine, to 40% of control. Our findings suggest that ET has a physiological significance in the brain as a neuromodulator for catecholaminergic transmission.

Protective effect of WEB 1881 FU on AF64A (ethylcholine aziridinium ion)-induced impairment of hippocampal cholinergic neurons and learning acquisition

The effect of continuous administration of 4-aminomethyl-1-benzylpyrrolidin-2-one-hemifumarate (WEB 1881 FU) on cerebral cholinergic neurons was studied using rats treated with ethylcholine aziridinium ion (AF64A), a neurotoxic choline analog. AF64A (2.0 nmol, administered i.c.v.) caused a significant decrease in the hippocampal acetylcholine (ACh) content. This decrease in hippocampal ACh content was accompanied by a reduction of choline acetyltransferase (CAT) activity. Under these experimental conditions, the latency of the passive avoidance response of rats, determined with a step-through method, was strongly decreased as compared with that of sham-operated rats. Although treatment with WEB 1881 FU (50 mg/kg per day, administered orally for 7 days) from immediately after the administration of AF64A did not affect the AF64A-induced decrease of ACh in the hippocampus, 100 mg/kg per day of WEB 1881 FU (orally for 7 days) significantly suppressed the AF64A-induced declines in hippocampal ACh content and CAT activity. The AF64A-induced reduction in latency of the passive avoidance response was also significantly antagonized by the treatment with 100 mg/kg per day of WEB 1881 FU (administered orally for 7 days) from immediately after the administration of AF64A. Continuous administration of WEB 1881 FU (100 mg/kg per day, orally for 7 days) from 7 days after the treatment with AF64A also had a significant inhibitory effect on the AF64A-induced decrease in ACh content in the hippocampus. These results suggest that WEB 1881 FU may have protective actions on the destruction of hippocampal cholingergic neurons as well as memory impairment induced by AF64A administration.