Ganglioside AGF2 promotes task-specific recovery and attenuates the cholinergic hypofunction induced by AF64A

Molecular and Cellular Mechanisms of Sporadic Alzheimer's Disease: Studies on Rodent Models in vivo

In this review, recent data are presented on molecular and cellular mechanisms of pathogenesis of the most widespread (about 95%) sporadic forms of Alzheimer's disease obtained on in vivo rodent models. Although none of the available models can fully reproduce the human disease, several key molecular mechanisms (such as dysfunction of neurotransmitter systems, especially of the acetylcholinergic system, β-amyloid toxicity, oxidative stress, neuroinflammation, mitochondrial dysfunction, disturbances in neurotrophic systems) are confirmed with different models. Injection models, olfactory bulbectomy, and senescence accelerated OXYS rats are reviewed in detail. These three approaches to in vivo modeling of sporadic Alzheimer's disease have demonstrated a considerable similarity in molecular and cellular mechanisms of pathology development. Studies on these models provide complementary data, and each model possesses its specific advantages. A general analysis of the data reported for the three models provides a multifaceted and the currently most complete molecular picture of sporadic Alzheimer's disease. This is highly relevant also from the practical viewpoint because it creates a basis for elaboration and preclinical studies of means for treatment of this disease.

Antiamnesic effects of azaindolizinone derivative ZSET845 on impaired learning and decreased ChAT activity induced by amyloid-beta 25-35 in the rat

Antiamnesic effects of a newly synthesized azaindolizinone derivative ZSET845 were assessed in rats made learning ability deficient by amyloid-beta (Abeta)25-35 treatment. Intracerebroventricular injection of Abeta25-35 induced a marked decrease in step-through latency in passive avoidance task and reduction in choline acetyltransferase (ChAT) activity in the medial septum and hippocampus, but not in the basal forebrain and cortex. The number of ChAT-immunoreactive cells was decreased in the medial septum. Oral administration of ZSET845 at a dose of 1 or 10 mg/kg ameliorated learning impairment in passive avoidance task and enhanced ChAT activity in the basal forebrain, medial septum and hippocampus, and increased in the number of ChAT-immunoreactive cells in the medial septum in Abeta-treated rats to the levels of vehicle-injected control rats. These results suggest that ZSET845 is worth testing for further preclinical study aimed for the treatment of senile dementia such as Alzheimer's disease.

Analysis of gangliosides by capillary zone electrophoresis and capillary zone electrophoresis-electrospray mass spectrometry

Gangliosides, sialic acid(s)-containing glycosphingolipids, were separated by capillary zone electrophoresis and detected with either UV or electrospray mass spectrometry. Several electrolyte system were evaluated for the separation of underivatized gangliosides. The best result was obtained by using 50 mM borate and 50 mM phosphate buffer containing 20 mM alpha-cyclodextrin at pH 9.9. The four major ganglioside forms (GM1, GD1a, GD1b, GT1b) were successfully separated, and, moreover, each ganglioside yielded two peaks, splitting by the difference in chain length of the ceramide moiety. The resolution obtained in CE-UV could not be reproduced in CE-MS because of the incompatibility of the borate/phosphate buffer to ESI-MS. With the use of more volatile buffers, such as ammonium acetate or 2-[N-cyclohexylamino]-ethanesulfonic acid, baseline resolution was obtained for gangliosides having different number of sugars, but the two disialoganglioside isomers, GD1a and GD1b, were coeluted.

Effects of basic fibroblast growth factor and ganglioside GM1 on neuronal survival in primary cultures and on eight-arm radial maze task in adult rats following partial fimbria transections

The effects of basic fibroblast growth factor (bFGF) and ganglioside GM1 (GM1) were evaluated alone and simultaneously in two types of experiments. First, the neuronal survival of primary culture neurons from fetal rat brain was measured. Then, performance on radial maze task in adult male rats following bilateral partial Fimbria-Fornix transections (F-F lesion) was tested. In primary culture neurons, bFGF (1-10 ng/ml) supported the neuronal survival from three regions (hippocampus, cortex and septum) of embryonic rat brain. However, GM1 (0.1-10 micrograms/ml) did not support the neuronal survival from any regions. Survival of cultured neurons was not supported by addition of 0.1 ng/ml bFGF, but when bFGF (0.1 ng/ml) and GM1 (0.1, 1 microgram/ml) were given to the cultured neurons simultaneously, the number of surviving neurons increased significantly. In the eight-arm radial maze task, where only the same four arms were baited, F-F lesion produced substantial memory impairment. In this task, administration of bFGF (10 micrograms/ml) or GM1 (1 mg/ml) alone did not produce any effects. However, when they were given simultaneously, the number of working memory errors decreased significantly, in spite of no amelioration for hippocampal choline acetyl transferase (ChAT) depletion. These findings indicate that actions of bFGF may be potentiated by the addition of GM1 in both primary neuronal cultures and radial maze task performance. These results suggest that the combination of bFGF and GM1 may synergistically improve spatial memory deficits.

The effects of intrahippocampal raphe and/or septal grafts in rats with fimbria-fornix lesions depend on the origin of the grafted tissue and the behavioural task used

Long-Evans female rats sustained electrolytic lesions of the fimbria and the dorsal fornix and, two weeks later, received intrahippocampal suspension grafts of fetal tissue. The grafts were prepared from regions including either the medial septum and the diagonal band of Broca (septal grafts), or the mesencephalic raphe (raphe grafts), or from both these regions together (co-grafts). All rats were submitted to a series of behavioural tests (home cage and open-field locomotion, spontaneous alternation, radial-arm maze and Morris water maze performance) run over two periods after grafting (one to nine weeks and 20-35 weeks). Two weeks after completion of behavioural testing, histological (acetylcholinesterase and Cresyl Violet staining) and/or neurochemical (choline acetyltransferase activity, high-affinity synaptosomal uptake of choline and serotonin, noradrenaline, serotonin and 5-hydroxyindolacetic acid concentrations) verifications were performed on the hippocampus. Compared to sham-operated rats, lesion-only rats exhibited hyperactivity which was transient in a familiar environment (home cage) and lasting in an unfamiliar one (open field), decreased rates of spontaneous T-maze alternation, and impaired memory performance in both the radial-arm maze and the Morris water maze. These rats also showed decreased cholinergic and serotonergic markers with a maximal depletion in the septal two-thirds of the hippocampus. Noradrenaline concentration tended to be increased in the dorsal third of the hippocampus, but was not modified in the other two-thirds. While septal grafts specifically increased the cholinergic markers and raphe grafts the serotonergic ones, neither of these grafts produced a lasting effect on any behavioural variable. Conversely, the co-grafts, which increased both the cholinergic and serotonergic markers in the septal two-thirds of the hippocampus, completely normalized the Morris water maze probe trial performance, but failed to affect any of the other behavioural variables. Our present results confirm that grafts of fetal neurons injected into the denervated hippocampus may induce a neurochemical recovery that depends on the anatomical origin of the grafted cells, and that co-grafting two fetal brain regions allows the combination of their individual neurochemical properties. Furthermore, our results show that these neurochemical effects of the co-grafts may be involved in the recovery of behavioural function observed in the water maze. However, somewhat paradoxically, those effects appear inefficient for inducing any recovery in other behavioural tasks, even in the radial-arm maze; which is assumed to measure similar spatial functions.(ABSTRACT TRUNCATED AT 400 WORDS)

Behavioral and neuroanatomical consequences of a unilateral intraventricular infusion of AF64A and limitations on the neuroprotective effects of nimodipine

The monoethylcholine aziridinium ion, AF64A, (3 nmol in 1 microliter) or artificial CSF (1 microliter) was infused unilaterally into the right dorsal lateral ventricle of male adult rats. Treatment with the L-type calcium channel antagonist, nimodipine (70 micrograms/kg b.wt.) or its vehicle was administered beginning before and for seven days following surgery. The infusion of AF64A reduced spontaneous alternation rates in the T-maze when compared to CSF and sham infused animals. AF64A-treated animals also took longer to reach the goal area in a complex maze task on specific trials relative to CSF and sham-infused animals. Locomotion and habituation to the open field did not differ between surgery groups. Unilateral AF64A significantly depleted acetylcholinesterase (AChE) positive terminals in the ipsilateral hippocampus and cell bodies in the ipsilateral medial septal area (MSA). Receptors for nerve growth factor (NGF-R), often colocalized with cholinergic cell bodies and terminals, also were depleted in the ipsilateral MSA of AF64A infused animals. Treatment with nimodipine did not have a neuroprotective effect on AF64A animals in either behavioral or histological results. However, some degree of protection was found in the vehicle-treated rats. This effect was likely a consequence of the stress of the injection procedure rather than the content of the vehicle, largely polyethylene glycol 400. Nimodipine-treated animals, regardless of surgery group, exhibited fewer emotional responses and had lower spontaneous alternation rates than untreated animals. The behavioral alterations found in the nimodipine groups are most easily explained in terms of altered emotionality. Overall our findings indicate that AF64A is a potent cholinotoxin that can selectively eliminate the ipsilateral septohippocampal cholinergic system when unilaterally infused into the lateral ventricle. It is possible that the mechanism of action of AF64A, like other nitrogen mustard analogues, involves disruption of basic processes involved in protein synthesis and DNA activities. Because of this, the toxic effects of the aziridinium mustard are independent of extracellular calcium and thus may not be susceptible to protection by calcium channel antagonists.

Separation of gangliosides using cyclodextrin in capillary zone electrophoresis

Gangliosides are glycosphingolipids containing sialic acid. These glycolipids have been suggested to play important roles in biological processes such as cell growth, differentiation and malignant transformation. Based on these proposed biological functions, gangliosides can be used as diagnostic tools and therapeutics for various human diseases. In this study, capillary zone electrophoresis (CZE) was used to determine the major gangliosides GM1, GD1a, GD1b and GT1b in mammalian brains, in addition to GM3 and Lac. Enhancement of selectivity and efficiency of separation was obtained by using 50 mM borate-phosphate buffer containing 16.5 mM alpha-cyclodextrin (alpha-CD). Under this condition, several forms of gangliosides were successfully separated from extracts of deer antler, apricot seed and rat brain. The results demonstrate that the CD-modified CZE is a useful method for detecting glycolipids from various biological matrices.

Morphological assessment of ethyl choline mustard aziridinium-induced neurotoxicity in rat brain reaggregate cultures

Foetal rat brain reaggregate cultures have been employed to investigate the morphological changes associated with the neurotoxic action of ethylcholine mustard aziridinium (ECMA). In a companion study we provided evidence for apparent selective cholinergic neurotoxicity. Exposure of 9-day-old cultures to 12.5 microM ECMA for 3 days produced dilatation of selected axon preterminals and terminals in the outer core tissue layer. Axoplasm in these dilated terminals was electron lucent and contained a flocculent, plasma-like material with remnants of the smooth endoplasmic reticulum. Their synaptic vesicle content was much reduced or, absent. Microglial cells were engaged in phagocytosis of these effete structures and a few necrotic neurons were enveloped by glial processes. Exposure to 50 microM ECMA produced widespread necrosis with some surviving neurons, surrounded by the still-persisting capsular layer. Treatment with 100 microM ECMA generated a greater extent of tissue necrosis, with only a few surviving neurons and glial cells being contained within the necrotic tissue mass. Reaggregates frequently disintegrated following capsule loss. Our results indicate that the initial morphological manifestation of ECMA-induced toxicity is dilatation of axon terminals, that are probably of cholinergic origin and are targeted due to their possession of the high-affinity choline transport system which is unique to these neurons.

Comparison of GM1 ganglioside, AGF2, and D-amphetamine as treatments for spatial reversal and place learning deficits following lesions of the neostriatum

These experiments tested the effectiveness of parenterally administered gangliosides and amphetamine as treatments for spatial learning deficits caused by bilateral lesions of the neostriatum. In Expt. 1, rats were tested postsurgically for 30 days on a shock-avoidance, spatial reversal task. Treatments of gangliosides (GM1 at 30 mg/kg, and AGF2 at 20 mg/kg and 30 mg/kg) and D-amphetamine (2 mg/kg) significantly decreased lesion-induced learning deficits on this task, while treatments of 10 mg/kg AGF2 and the combination of GM1 (30 mg/kg) and D-amphetamine (2 mg/kg) were ineffective. In Expt. 2, rats were given bilateral neostriatal lesions and treated with GM1 (30 mg/kg), AGF2 (20 mg/kg) or D-amphetamine (2 mg/kg) and tested postsurgically for 5 days on a place learning task in the Morris water maze. Only the GM1-treated rats showed a reduction in lesion-induced place learning deficits on this task. Since in both experiments, cell counts near the area of the lesion revealed no differences among any of the brain-damaged groups, it was suggested that the treatments exert their behavioral effects by biochemically activating spared neurons, independent of any ultimate effects they may have on neuronal survival.

Transplantation of fetal cholinergic neurons into the hippocampus attenuates the cognitive and neurochemical deficits induced by AF64A

The present experiments examined whether transplanted fetal cholinergic neurons would attenuate the behavioral and neurochemical deficits induced by the cholinotoxin AF64A (ethylcholine aziridinium ion). Bilateral injections of AF64A (3 nmol) into the lateral ventricles produced significant learning and memory impairments together with decreases in hippocampal high-affinity choline uptake (HAChU). AF64A-treated rats were impaired on both a standard radial arm maze (RAM) task and a working memory version in which a one-hour delay was imposed between the fourth and fifth arm choices. Transplantation of embryonic day E-17 septal/diagonal band tissue into the hippocampus (HPC) promoted recovery of performance on the standard version of the RAM task. However, this recovery was not observed when the animals were tested on the more difficult delay version of the task. Neurochemical analysis indicated that AF64A produced a significant (31%) decrease in hippocampal HAChU that was attenuated (14%) by transplantation of fetal cholinergic neurons. Histological analysis revealed that the transplants survived and innervated the HPC. There was no apparent relationship between fiber ingrowth into the HPC and behavioral recovery. These data indicate that transplant-induced behavioral recovery may be related to and limited by the cognitive demands of the testing situation. Generalized increases in cholinergic activity, transplant-mediated release of trophic factors, or a combination of both may underlie the behavioral recovery observed in the present studies.

Dose- and delay-dependent working/episodic memory impairments following intraventricular administration of ethylcholine aziridinium ion (AF64A)

The present study examined the effects of intraventricular administration of the cholinergic neurotoxin ethylcholine aziridinium ion (AF64A) on performance of a radial arm maze task. Male Sprague-Dawley rats were trained to perform a delayed-nonmatch to sample radial arm maze task in which a 1-h delay was imposed between the fourth and fifth arm selections. Following acquisition, animals were injected bilaterally with AF64A (1.5 or 0.75 nmol/side) or artificial cerebrospinal fluid into the lateral cerebral ventricles and allowed 7 days to recover before behavioral testing resumed. Significant dose- and delay-dependent impairments in the radial maze performance were observed in AF64A-treated rats as evidenced by fewer correct choices following the delay and by more errors to complete the task. Long-term testing in this task revealed significant recovery of memory performance. These findings indicate dose-dependent impairments in memory following intraventricular administration of AF64A and spontaneous behavioral recovery following such insult.

Ganglioside AGF2 prevents the cognitive impairments and cholinergic cell loss following intraventricular colchicine

Ganglioside AGF2 prevented the cognitive and locomotor alterations induced by intraventricular colchicine. Adult male rats were initially trained to perform a standard radial arm maze (RAM) task. Following training, they were injected intraperitoneally with 10 mg/kg AGF2 (COL/AGF2), cerebrospinal fluid (CSF/AGF2) or the saline vehicle (COL/SAL, CSF/SAL) for 3 days prior to and for 14 days following the bilateral injection of colchicine (7 micrograms/0.5 microliters) or artificial CSF into the lateral ventricles. Colchicine (COL/SAL) impaired performance of the standard RAM task as well as a working memory version of the task in which various delays were imposed between the fourth and fifth arm choices. Colchicine also produced a transient hyperactivity which subsided within 10 weeks following surgery. In contrast, AGF2 (COL/AGF2) prevented the impairments in RAM performance and the alterations in locomotor behavior. Colchicine also produced significant decreases in hippocampal ChAT activity and high affinity choline uptake that were prevented by prior treatment with AGF2. Finally, colchicine produced a 35% decrease in the number of acetylcholinesterase-positive (cholinergic) neurons in the medial septum and vertical limb of the diagonal band (MS/VLDB) which was also prevented by AGF2. Thus, the behavioral and neurochemical protection afforded by AGF2 was paralleled by a prevention of the loss of hippocampal cholinergic parameters and cholinergic neurons in the MS/VLDB.