Protective effect of vinconate, a novel vinca alkaloid derivative, on glucose utilization and brain edema in a new rat model of middle cerebral artery occlusion.

1. We investigated the effect of a novel vinca alkaloid derivative, vinconate, against brain damage after focal ischemia induced by a middle cerebral artery (MCA) occlusion in rats. 2. Persistent focal ischemia was induced by 6 hr, and vinconate (50 and 100 mg/kg) was given intraperitoneally twice 10 min and 3 hr after MCA occlusion. 3. Focal ischemia produced the disturbance of glucose metabolism, the increase of water content and the impairment of protein synthesis in the surrounding occluded MCA territory. 4. Vinconate was effective in preventing marked reduction of cerebral glucose utilization in the areas surrounding the occluded MCA territory. 5. Vinconate significantly reduced an increase of water content in the surrounding the occluded MCA territory. 6. Preliminary L-[methyl-14C]methionine autoradiographic study also indicated that vinconate can partly prevent a severe impairment of protein synthesis after focal ischemia. 7. The results indicate that vinconate may ameliorate the disturbance of glucose metabolism, brain edema and the impairment of protein synthesis after persistent focal ischemia, and they also suggest that vinconate has a beneficial effect against brain damage.     

Impairment of memory and changes in neurotransmitters induced by basal forebrain lesion in rats

The effect of bilateral electrolytic lesioning of the anterior and posterior parts of the basal forebrain (BF) on learning behavior and changes in neurotransmitters in the central nervous system was investigated in rats. The posterior BF lesion caused more severe impairment than the anterior BF lesion in the acquisition of conditioned avoidance response in a two-way shuttle box. A severe deficit in acquisition of passive avoidance response was produced by the posterior BF lesion. Choline acetyltransferase (CAT) activity was decreased significantly in the parietal cortex but not in the occipital cortex in anterior BF-lesioned rats. However, it was not decreased in posterior BF-lesioned rats. The contents of monoamines in the hippocampus was decreased more significantly by the posterior BF lesion than by the anterior BF lesion. These results suggest that the impairment of memory in posterior BF-lesioned rats may be related mainly to monoaminergic function rather than to cholinergic deficit.     

The effects of THA on medial septal lesion-induced memory defects

Electrolytic lesioning of the medial septum (MS) was used to assess the effectiveness of tacrine (THA) in reversing lesion-induced spatial memory deficits in a water-maze. Lesioned animals were injected with either 3 mg/kg or 5 mg/kg of THA intraperitoneally 15 min prior to daily behavioral training. One group of the lesioned and sham-operated animals received saline. All animals underwent two training trials each day for a period of ten days, after which a spatial probe trial was performed and assessed. The accurate placement of MS lesions resulted in lowered acetylcholinesterase (AChE) and choline acetyltransferase (ChAT) activity within the hippocampus of lesioned rats. Lesioning of the MS also impaired the learning performance in locating the escape platform during training and decreased the spatial bias during the probe trial. A lower dose of THA (3 mg/kg) significantly reversed the path length increase and spatial bias decrease induced by MS lesioning, but had no effect on escape latency. However, comparison between the saline- and THA- (5 mg/kg) injected MS-lesioned rats showed no significant differences in either escape latency or spatial bias. The present results support the use of cholinesterase inhibitors in further treatment trials of geriatric memory disorders.     

Naftidrofuryl oxalate, nootropic effects on the scopolamine- and the basal forebrain lesion-induced amnesia in rats.

We studied the effects of naftidrofuryl oxalate on scopolamine- and basal forebrain (BF) lesion-induced amnesia using passive avoidance and multiple T-maze tasks, in comparison with Ca-hopantenate and physostigmine in rats. In the passive avoidance task, one-week treatment with naftidrofuryl oxalate (12.5 and 25 mg/kg, IP) ameliorated BF lesion-induced amnesia. The multiple T-maze task was done with two training sessions per day for five continuous days. We measured the number of errors made from start box to goal box. Naftidrofuryl oxalate (12.5 mg/kg, IP, b.i.d.) and physostigmine (0.1 mg/kg, IP, b.i.d.) attenuated scopolamine- and BF lesion-induced amnesia. However, treatment with naftidrofuryl oxalate for one week failed to inhibit the decrease of the choline acetyltransferase induced by the BF lesion. Ca-hopantenate did not show attenuation of amnesia induced by the scopolamine or BF lesion. These results suggest that naftidrofuryl oxalate enhances the storage of spatial information, and that the nootropic effects of naftidrofuryl oxalate may be produced by an indirect activation of the cholinergic system through serotonergic neuronal systems.     

Effects of ketamine and 1-glutamic acid diethyl ester on concept learning in rats.

The effects of ketamine, an NMDA receptor antagonist, and 1-glutamic acid diethyl ester (LGDE), a non-NMDA glutamate antagonist, were evaluated in the acquisition of concept learning in a water maze. In concept learning, the rats must locate an invisible platform whose location changes from day to day. In spatial learning (Morris task), the rats must locate an invisible (or visible) platform whose location does not change. Ketamine increased quadrant entries at 5, 10 and 20 mg/kg, and latencies at 10 and 20 mg/kg on the final two days of training on the concept task. At 5 mg/kg ketamine disrupted concept learning but not spatial learning or visuo-motor coordination as assessed by invisible and visible platform conditions of the Morris maze. Progressively higher doses of ketamine affected first the invisible condition and then the visible platform condition. On the other hand, LGDE did not affect the Morris task at any dose. However, there was no decrease in latencies over days in concept learning at the two highest doses (240 and 360 mg/kg) of LGDE. Thus LGDE appeared to slow down decision time in the concept task but not the spatial task in the absence of an effect on quadrant entries in any version. These results indicate that NMDA receptors are involved in spatial and concept learning. Non-NMDA receptors appear to be involved only in concept learning.     

Comparative embryolethal effect of bromofenofos and dephosphate bromofenofos in rats

Bromofenofos (BF) and dephosphate bromofenofos (DBF) were administered at equimolar doses to rats on day 10 of pregnancy. The dams were killed on day 21, and the fetuses were removed, weighed and examined by routine teratological methods. BF caused a significant increase in fetal resorptions at 58.2 mg/kg. Approximately 69% of the implants were resorbed at this dose level. In rats given DBF equimolar to 58.2 mg/kg BF, the resorption rate was 81.9%. Administration of BF resulted in a dose-dependent decrease in fetal body weights which was significant at 29.1 mg/kg or more. DBF caused a significant decrease in fetal body weights, beginning at 25.1 mg/ kg equimolar to 29.1 mg/kg BF, and the decreased fetal body weights were almost the same between BF and DBF. BF at 58.2 mg/kg induced significant gross and skeletal malformations, with incidences of 35.6 and 27.6%, respectively. In rats given DBF equimolar to 58.2 mg/kg BF, gross and skeletal malformations were seen in 54.5 and 61.5% of the fetuses, respectively. There were similarities in the types of malformations observed between BF and DBF. Both compounds induced no significant internal malformations. It was concluded from these results that the embryolethal and teratogenic effects of BF is due to its metabolite, DBF, which cannot respond to cholinesterase inhibition.     

Basal forebrain lesioned mice exhibit deterioration in memory acquisition process in step through passive avoidance test.

Effects of the basal forebrain (BF) lesion on memory and learning performances were investigated in mice. Eight-week-old male mice received bilateral BF lesion by delivering a radiofrequency current. From fifteen days after the surgery, the step through type passive avoidance task was performed daily for 10 days. Lesioned animals showed severe impairment in the acquisition process of this task, but not in the retention process. Ambulatory activity of the BF-lesioned mice did not differ from those of the control group, suggesting the observed learning impairment was not due to the alteration of motor activity. These results indicate that a memory impaired model mice can be successfully made by the radiofrequency lesion of bilateral BF neurons.     

Cholecystokinin protects cholinergic neurons against basal forebrain lesion.

Alzheimer's Disease (AD) patients have a severe degeneration of cholinergic neurons in their cerebral cortices. Basal forebrain (BF)-lesioned rat is used as a model animal of a cholinergic deficit in the cerebral cortex. Cholinergic markers were decreased in the cerebral cortex of BF-lesioned rats. Intracerebroventricular continuous infusion of cholecystokinin octapeptide (CCK8) following BF lesion obviously preserved these cholinergic markers. These results suggest that CCK8 prevents the degeneration of cholinergic neurons in the cerebral cortex following BF lesion.     

Conditioned drug reward enhances subsequent spatial learning and memory in rats

Rationale Chronic exposure to drugs of abuse alters neural processes that normally promote learning and memory. A context that is repeatedly paired with reinforcing drugs will acquire secondary reinforcing properties (conditioned reward). However, the effects of conditioned reward on spatial learning are unknown. Objective Using the conditioned place preference procedure and Morris water maze task, we examined the role of conditioned reward or aversion in spatial learning. Materials and methods Groups of rats acquired morphine (10 mg/kg), cocaine (10 mg/kg), or oral sucrose (15%) conditioned place preference (CPP). Another group of morphine-dependent rats acquired conditioned place aversion (CPA) to a context paired with precipitated opiate withdrawal induced by naloxone injections (1 mg/kg). To examine the role of conditioned reward or aversion in spatial learning, rats were then exposed to the previously morphine-, cocaine-, sucrose- or naloxone-paired context for 10 min before training of spatial learning in the Morris water maze. Results Exposure to the morphine- or cocaine-paired but not the sucrose- or the naloxone-paired context decreased the latency to find the platform in the Morris water maze test. Conclusions Our results provide the first evidence that conditioned drug reward promotes spatial learning. We speculate that this enhancement of spatial learning by the drug-paired context may promote contextual-cue-induced relapse to drug taking by facilitating exploratory drug-seeking behaviors.     

Protective effect of a novel vinca alkaloid derivative, vinconate, against alterations in binding sites of second messengers after transient cerebral ischemia in gerbils.

1. We investigated the alterations in binding sites of three major second messengers, phorbol 12,13-dibutyrate, inositol 1,4,5-trisphosphate and forskolin following transient cerebral ischemia in gerbils, and examined the effects of a novel vinca alkaloid derivative, vinconate against the alterations in the binding of the second messengers following ischemia. 2. Transient cerebral ischemia produced by bilateral occlusion of the common carotid arteries was induced for 10 min, and intraperitoneal administration of vinconate (100 mg/kg and 300 mg/kg) was given 10 min before ischemia. 3. Morphological study indicated that transient ischemia can produce severe neuronal damage in striatum, hippocampal CA1 sector and hippocampal CA3 sector. 4. Transient cerebral ischemia caused the postischemic alterations in the binding of three second messengers. 5. The postischemic alterations in the binding of second messengers were ameliorated by pretreatment with vinconate. This effect was especially observed in the striatum which was most vulnerable to ischemia. 6. These findings are discussed in relation to the mechanism of ischemic neuronal damage.     

Effects of concurrent manipulations of nicotinic and muscarinic receptors on spatial and passive avoidance learning

The present study investigates the effects of concurrent manipulations of nicotinic and muscarinic cholinergic receptors on spatial and passive avoidance learning/retention in rats. Daily pretraining test injections of combinations of the subthreshold doses of muscarinic (scopolamine 0.3 mg/kg) and nicotinic (mecamylamine 2.5 mg/kg or 10 mg/kg) antagonists impaired acquisition of the water-maze task (WM). Drug-induced deficits were also observed during the retention trial: the groups injected with scopolamine 0.3 mg/kg, mecamylamine 10 mg/kg and scopolamine 0.3 mg/kg in combination with mecamylamine 2.5 mg/kg showed reduced spatial bias compared with controls. Single preretention test injections of the combination of subthreshold doses of mecamylamine (10 mg/kg) and scopolamine (0.8 mg/kg) impaired memory retrieval in WM. Combined pretraining injections of subthreshold doses of scopolamine (1.0 mg/kg) and mecamylamine (10 mg/kg) induced a severe passive avoidance impairment comparable to 2.0 mg/kg of scopolamine. However, preretention test injections did not impair passive avoidance retention. Either single or combined injections of hexamethonium (5.0 mg/kg, SC) and methylscopolamine (1.0 mg/kg) did not impair either passive avoidance or water-maze performance. The present results suggest that 1) nicotinic and muscarinic systems jointly modulate performance in spatial and avoidance learning tasks and 2) cholinergic antagonists affect acquisition functions more effectively than retention ability. These findings may be relevant to the clinical disorders, like Alzheimer's disease, which are associated with a loss of both cholinergic neurons and nicotinic receptors.     

Protective effect of vinconate on ischemia-induced neuronal damage in the rat hippocampus.

The protective effect of vinconate, a vinca alkaloid derivative, on ischemia-induced neuronal damage was investigated using a model of rat forebrain ischemia caused by occlusion of four vessels. Hippocampal cell loss was observed histologically and neurochemically 5 days after 10 min of ischemia. Treatment with vinconate (50 and 200 mg/kg i.p.) before cerebral ischemia significantly suppressed neuronal cell loss in the hippocampal CA1 region and the decrease in the content of neuroactive amino acids in the hippocampus. The release of neuroactive amino acids in the hippocampus was significantly increased by cerebral ischemia. Pretreatment with vinconate (50 and 200 mg/kg i.p.) significantly attenuated the increased release of glutamic acid and aspartic acid, but not the release of gamma-aminobutyric acid (GABA), taurine and glycine. This suppressive effect of vinconate was antagonized by scopolamine (10(-5) M). The addition of vinconate (10(-11)-10(-4) M) had no effect on the binding of [3H]MK-801. These results indicate that pretreatment with vinconate attenuates the ischemia-induced release of excitatory amino acids into the extracellular space of the hippocampus via the stimulation of presynaptic muscarinic acetylcholine receptors. The present results also suggest that this suppressive effect of vinconate on the release of excitatory amino acids (glutamic acid and aspartic acid) may play a crucial role in the protective action of this agent against ischemia-induced neuronal damage in the hippocampus.     

Effects of methanol extract of Uncariae Ramulus et Uncus on ibotenic acid-induced amnesia in the rat

In the present study, we investigated the effects of Uncariae Ramulus et Uncus (UR) on learning and memory in the Morris water maze task and the central cholinergic system of rats with excitotoxic medial septum (MS) lesion. In the water maze test, the animals were trained to find a platform in a fixed position during 6 days and then received a 60-s probe trial in which the platform was removed from the pool on the 7th day. Ibotenic lesion of the MS showed impaired performance of the maze test and severe cell losses in the septohippocampal cholinergic system (SHC), as indicated by decreased choline acetyltransferase-immunoreactivity and acetylcholinesterase-reactivity in the hippocampus. Daily administrations of UR (100 mg/kg, i.p.) for 21 consecutive days produced significant reversals of ibotenic acid-induced deficit in learning and memory. These treatments also reduced the loss of cholinergic immunoreactivity in the hippocampus induced by ibotenic acid. These results demonstrated that impairments of spatial learning and memory may be attributable to degeneration of SHC neurons and that UR ameliorated learning and memory deficits partly through neuroprotective effects on the central acetylcholine system. Our studies suggest that UR may be useful in the treatment of Alzheimer's disease.     

Neurochemical studies on bifemelane, a new cerebral function improver. I. Effects of bifemelane on the function of neurotransmission-related enzymes and receptors in rat brain

We examined neurochemically the effects of bifemelane (BF) on muscarinic ACh (mACh-R) and beta-adrenergic receptors (beta-AdR) and imipramine binding sites and the activities of acetylcholinesterase (AChE), choline acetyltransferase (CAT) and monoamine oxidase (MAO) in the P2 fractions of rat brain, ex vivo and in vitro. Male rats were given daily injections of 10, 30 mg/kg BF, p.o., for a period of 4 weeks. The Kd and Bmax values for mACh-R in the rat forebrain by administration of 10, 30 mg/kg BF decreased significantly compared with that of the control, although the Kd and Bmax values for beta-AdR and imipramine binding sites were almost identical. The Km and Vmax values of A- and B-form MAO decreased in rats that had been administered 30 mg/kg BF for 4 weeks. The binding of 3H-QNB (quinuclidinyl benzilate) on mACh-R, 125I-CYP (iodocyanopindolol) on beta-AdR and 3H-imipramine on imipramine binding sites decreased by 60, 20 and 70% in the presence of 1 microM BF, respectively, while the addition of 1 microM BF inhibited MAO activity by about 50%. However, CAT and AChE activities were not inhibited by BF.     

Therapeutic effect of THA on hemicholinium-3-induced learning impairment is independent of serotonergic and noradrenergic systems

Tetrahydroaminoacridine (THA: Tacrine) has previously been shown to reverse deficits in spatial discrimination learning induced by hemicholinium-3 (HC-3). In the present experiments the effects of prior depletion of serotonin (5-HT) or noradrenaline (NA) on this reversal were examined. In the first experiment 5-HT lesions were made by injecting 5,7-DHT (2×50 µg/5 µl) into the lateral ventricles of rats pretreated with desmethylimipramine (DMI 25 mg/kg IP). A permanently indwelling guide tube was then implanted over the right lateral ventricle. Subsequent testing, under drug-free conditions, revealed no effect of the lesion on the number of trials needed to attain criterion (nine consecutive correct choices) in two-platform spatial discrimination learning in a watermaze. Using a latin square design rats were then tested for the effects of HC-3 and THA. HC-3 (5 µg/5 µl ICV) or placebo (CSF) were injected 60 min before the start of a 30-trial training session. THA (4.6, 10 mg/kg SC) or placebo were then injected 15 min before training. Choice accuracy but not choice latency was significantly impaired by HC-3 and the effect was reversed by THA in both sham operated and 5-HT lesioned rats. In the second experiment two injections of DSP-4 (50 mg/kg IP) were given, following cannulation, to deplete forebrain NA. The lesion had no effect on spatial learning under drug-free conditions and failed to block the THA-induced reversal of spatial discrimination learning deficits following HC-3. These results confirm that forebrain Ach depletion by HC-3 impairs spatial discrimination learning and that the deficit is reversed by THA. However, concommitant depletion of forebrain 5-HT or NA does not block the ameliorative effect of THA.     

Impaired spatial learning in the Morris water maze induced by serotonin reuptake inhibitors in rats

The effects of selective serotonin reuptake inhibitors citalopram and fluoxetine on spatial learning were assessed in rats. Adult male rats were subjected to 4 days of training in the Morris water maze with the invisible platform. Animals received different doses of citalopram (1-8 mg/kg; i.p.) or fluoxetine (1-16 mg/kg; i.p.) or their vehicles (saline or distilled water respectively) 30 minutes before training each day. The results showed that citalopram at doses of 4 and 8 mg/kg and fluoxetine at doses of 8 and 16 mg/kg significantly increased latencies to find the platform and traveled distances compared to the control group. Therefore, it appears that selective serotonin reuptake inhibitors can cause learning deficits in complex spatial tasks such as Morris water maze.     

Effects of metrifonate on escape and avoidance learning in young and aged rats

The present study assessed the effects of the indirect acetylcholinesterase inhibitor metrifonate on learning and memory functions in young (3-month-old) and aged (25-month-old) rats. In the shuttle box, metrifonate at a dose of 12.5mg/kg, p.o., 30min before each of the daily acquisition sessions, improved the acquisition of the active avoidance response, whereas a dose of 25mg/kg did not. Metrifonate, 12.5mg/kg, p.o., administered before each of the daily acquisition sessions, also facilitated the acquisition of the Morris water escape task in both young and aged rats: metrifonate-treated rats swam a shorter distance to reach the escape platform than did the vehicle-treated rats. The 3-month-old rats treated with metrifonate did not show the increase in swimming speed over training observed in vehicle-treated animals; no effects of metrifonate were found on the swimming speed of aged rats. In a probe trial carried out immediately after the fifth daily acquisition session, metrifonate treatment did not affect the bias of the aged rats for the quadrant in which the platform had been positioned during acquisition. It is concluded that metrifonate improves performance during the acquisition phase of two aversively motivated learning and memory tasks at the dose of 12.5mg/kg, p.o.     

Effects of systemic and intracerebroventricular administration of mecamylamine,a nicotinic cholinergic antagonist,on spatial memory in rats

The effects of both systemic and intracerebroventricular administration of mecamylamine, a nicotinic antagonist, were tested on the Morris water maze performance of rats. In experiment 1, mecamylamine (0, 3, and 10 mg/kg, IP) was administered before daily training sessions on the Morris water maze, a task in which rats use environmental cues to learn the location of an invisible escape platform in a large pool of water. The escape latencies of rats given the higher dose of mecamylamine were significantly longer than the latencies of rats given either saline or the peripherally-acting nicotinic antagonist hexamethonium (10 mg/kg). Analysis of search patterns during a free swim trial conducted in the absence of an escape platform confirmed the disruptive effects of the higher dose of mecamylamine. Similar drug effects were not observed when these rats were trained to a visible platform, and mecamylamine did not affect the retrieval of spatial information in well-trained rats. In experiment 2, similar effects were observed with ICV administration of mecamylamine (0, 10, 30, and 100 µg). The two higher doses increased escape latencies during the last day of place training and all three doses significantly impaired performance on a free swim. No significant effects were noted on subsequent training to a visible platform, and only the highest dose marginally impaired the retrieval of spatial information in well-trained animals. Thus, mecamylamine appears to impair the acquisition of spatial information in the Morris water maze but does not affect retrieval of previously acquired spatial information at comparable doses.     

The mGluR5 antagonist 2-methyl-6-(phenylethynyl)-pyridine (MPEP) potentiates PCP-induced cognitive deficits in rats

Rationale Recent studies have shown that metabotropic glutamate receptor 5 (mGluR5) can modulate N-methyl-d-aspartate (NMDA) receptor function in vivo. For example, the mGluR5 antagonist, 2-methyl-6-(phenylethynyl)-pyridine (MPEP) can potentiate PCP (phencyclidine)-evoked hyperactivity and PCP-induced disruptions in pre-pulse inhibition (PPI) in rats.Objective To extend these previous behavioral findings and determine whether the mGluR5 antagonist MPEP can modulate the disruptions in learning and memory induced by PCP in rats.Methods The effects of MPEP, alone and in combination with PCP, were evaluated in rats trained to perform a repeated acquisition procedure (learning) or a delayed non-matching to position (DNMTP) radial maze task (spatial memory).Results In the repeated acquisition task, MPEP (0–10 mg/kg, IP) dose-dependently decreased response rates but had no effect on response accuracy. In contrast, PCP (0.625–1.25 mg/kg, SC) reduced response rate and response accuracy in a dose-dependent manner. Although MPEP (10 mg/kg, IP) had no effect when administered alone, the mGluR5 antagonist potentiated the disruptions in learning induced by a low dose of PCP (0.625 mg/kg, SC). In the DNMTP maze task, MPEP (0–10 mg/kg, IP) had no effect on spatial memory, whereas PCP (1.25–2.5 mg/kg, SC) produced a dose-dependent disruption. MPEP (10 mg/kg, IP) potentiated the impairments in memory induced by PCP (1.25 mg/kg, SC).Conclusion The mGluR5 antagonist, MPEP, potentiated the disruptions in learning and memory induced by PCP. These behavioral data extend previous behavioral findings and further suggest that mGluR5 can modulate NMDA receptor function in vivo.     

Pharmacological studies on Y-8894. (V) Effect on learning and memory in intact and experimentally amnesic rats

The effects of Y-8894 on learning and memory were studied using the pole climbing avoidance (PCA) response in intact and experimentally induced amnesic rats. The following results were obtained: A single administration of Y-8894 (2.5 mg/kg, i.p.) to experimentally induced amnesic rats significantly antagonized the decrease in the mean number of PCA responses induced by an electroconvulsive shock (ECS). At a higher dose (10 mg/kg, i.p.), however, this effect was reduced. Repeated administration of Y-8894 (5 mg/kg, i.p.) significantly antagonized the facilitation of the extinction of the PCA response induced by exposure to CO2. Repeated administration of Y-8894 (2.5 mg/kg, i.p.) significantly facilitated the learning of the PCA response in intact rats. At a higher dose (5 mg/kg, i.p.), however, this effect was reduced. A single administration of Y-8894 (5 mg/kg, i.p. and 25 mg/kg, p.o.) significantly delayed the extinction of the PCA response in intact rats. These results suggest that Y-8894 has an ameliorative and facilitative effect on learning and memory in experimentally induced amnesic and intact rats.