GM1 ganglioside counteracts cholinergic and behavioral deficits induced in the rat by intracerebral injection of vincristine

Ganglioside GM1 and the Central Nervous System

GM1 is one of the major glycosphingolipids (GSLs) on the cell surface in the central nervous system (CNS). Its expression level, distribution pattern, and lipid composition are dependent upon cell and tissue type, developmental stage, and disease state, which suggests a potentially broad spectrum of functions of GM1 in various neurological and neuropathological processes. The major focus of this review is the roles that GM1 plays in the development and activities of brains, such as cell differentiation, neuritogenesis, neuroregeneration, signal transducing, memory, and cognition, as well as the molecular basis and mechanisms for these functions. Overall, GM1 is protective for the CNS. Additionally, this review has also examined the relationships between GM1 and neurological disorders, such as Alzheimer's disease, Parkinson's disease, GM1 gangliosidosis, Huntington's disease, epilepsy and seizure, amyotrophic lateral sclerosis, depression, alcohol dependence, etc., and the functional roles and therapeutic applications of GM1 in these disorders. Finally, current obstacles that hinder more in-depth investigations and understanding of GM1 and the future directions in this field are discussed.

Astroglia in Alzheimer's Disease

Alzheimer's disease is the most common cause of dementia. Cellular changes in the brains of the patients suffering from Alzheimer's disease occur well in advance of the clinical symptoms. At the cellular level, the most dramatic is a demise of neurones. As astroglial cells carry out homeostatic functions of the brain, it is certain that these cells are at least in part a cause of Alzheimer's disease. Historically, Alois Alzheimer himself has recognised this at the dawn of the disease description. However, the role of astroglia in this disease has been understudied. In this chapter, we summarise the various aspects of glial contribution to this disease and outline the potential of using these cells in prevention (exercise and environmental enrichment) and intervention of this devastating disease.

Profound destructive effects of adolescent exposure to vincristine accompanied with some sex differences in motor and memory performance

Vincristine, an anticancer drug, is known to induce neuronal cell damage. We have elucidated the alteration in performance of the hippocampus and cerebellum following chronic vincristine treatment (0.2 mg·(kg body mass)–1·week–1) in male and female rats. Intraperitoneal injection of vincristine in adolescent rats caused impairment of motor and cognitive behavior. In the probe test, the length of path traveled and percent swimming time for vincristine-treated rats in the correct quadrant was significantly less than for the saline-treated (control) groups. The path length and time latency at the 2nd and 3rd blocks of trials for the male vincristine-treated group was significantly higher than that for the female saline- and the vincristine-treated rats. In the rod test, vincristine exposure impaired the motor coordination in both male and female rats. Exposure to vincristine caused a significant decrease in hanging time in male rats, compared with the saline- and the vincristine-treated female rats, while there were no differences between the female vincristine-treated rats and the saline-treated rats of both sexes. The rearing frequency, total distance moved, and velocity for both male and female rats were dramatically affected by exposure to vincristine. We have observed that the hippocampal and cerebellar functions of male and female rats were profoundly affected by exposure to vincristine, especially the male rats, suggesting a sexual dimorphism in the developing central nervous system that is affected by chemicals such as anticancer drugs.

Neurogenesis in Alzheimer's disease

It is widely acknowledged that neural stem cells generate new neurons through the process of neurogenesis in the adult brain. In mammals, adult neurogenesis occurs in two areas of the CNS: the subventricular zone and the subgranular zone of the dentate gyrus of the hippocampus. The newly generated cells display neuronal morphology, generate action potentials and receive functional synaptic inputs, their properties being equivalent to those of mature neurons. Alzheimer's disease (AD) is the widespread cause of dementia, and is an age-related, progressive and irreversible neurodegenerative disease that results in massive neuronal death and deterioration of cognitive functions. Here, we overview the relations between adult neurogenesis and AD, and try to analyse the controversies in the field. We also summarise recent data obtained in the triple transgenic model of AD that show time- and region-specific impairment of neurogenesis, which may account for the early changes in synaptic plasticity and cognitive impairments that develop prior to gross neurodegenerative alterations and that could underlie new rescue therapies.

Massive cell death of cerebellar granule neurons accompanied with caspase-3-like protease activation and subsequent motor discoordination after intracerebroventricular injection of vincristine in mice

Vincristine, a microtubule-depolymerizing agent, is known to induce neuronal cell damage. Biochemical, histological and behavioral alterations were investigated after intracerebroventricular injection of vincristine in mice. Intracerebroventricular injection of vincristine caused caspase-3-like protease activation followed by nucleosomal release in the cerebellum. Histological examinations showed that vincristine-induced damage was relatively specific to granule cells in the cerebellum, and terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick-end labeling-positive cells were observed among these cells. Chromatin condensation, one of the criteria for apoptosis, was seen on electron microscopy. Behavioral changes, namely head movements, pivoting and backward walking, were observed in parallel with the increase of caspase-3-like protease activity and nucleosomal release. Furthermore, motor function tests (bulb balance test and rotating rod test) showed deficits of motor coordination ability. These observations suggest that intracerebroventricular vincristine causes massive apoptosis of cerebellar granule cells accompanied with caspase-3-like protease activation, leading to motor dysfunction, in this model. These vincristine-treated mice should be a useful in vivo model for examination of neuronal apoptosis, which might be involved in a variety of neurodegenerative diseases.

Spatial learning deficits in rats after injection of vincristine into the dorsal hippocampus

In the present study, performance in the Morris water escape task after bilateral lesioning of the dorsal hippocampus induced by the microtubule poison vincristine is discussed as a cognitive deficit model in rats. As we are especially interested in spontaneous or pharmacologically induced recovery processes after experimentally induced cognitive dysfunctions, the model should fulfil a number of criteria. Firstly, a clear dose-effect relationship between the dose of vincristine and the amount of spatial learning impairments should be present. Secondly, lesions must remain within the target area. Thirdly, there should be an observable behavioural recovery or compensation of the induced deficit. Two experiments evaluated the influence of the application volume (experiment 1) and the concentration of vincristine (experiment 2) on lesion location and size, and on spatial learning. The results of both experiments demonstrated that the effect of vincristine on the performance in the Morris water escape task seems to be characterized by an "all-or-none" relationship. Concentrations above a "threshold" value induced severe damage in the hippocampus and adjacent brain structures, whereas concentrations below the "threshold" value had marginal or no effects. The non-selective and highly toxic properties of vincristine make this neurotoxin an unsuitable tool for the establishment of a learning and memory deficit model.

Exogenous GM1 ganglioside effects on conductive and sensorineural hearing losses

Both CBA/J mice with neonatal cochlea removals and CBA/J mice with neonatal atresias of the external auditory meatus have significantly smaller ventral cochlear nucleus is greater in the mice with cochlea removals, but the soma area reduction is greater in the mice with external auditory meatus atresias. GM1 gangliosides were subcutaneously injected daily into a group of CBA/J mice with conductive hearing loss caused by neonatal removals of their left external auditory meatus, and into a group of CBA/J mice unilaterally deafened by left cochlea removals. In the mice with conductive hearing loss, the ganglioside treatment significantly ameliorated the atrophy of spiral ganglion neurons, ventral cochlear nucleus neurons, and ventral cochlear nucleus volume. In unilaterally deafened mice, the ganglioside treatment had no measurable effect on the atrophy of ventral cochlear nucleus neurons or of ventral cochlear volume. It is suggested that GM1 ganglioside treatment potentiates growth factors which sustain spiral ganglion integrity and that this sustained activity of the spiral ganglion in turn maintains the integrity of the cochlear nuclei.

Comparison of intracranial infusions of colchicine and ibotenic acid as models of neurodegeneration in the basal forebrain

Colchicine and ibotenic acid were compared for their ability to produce neurodegeneration and cognitive deficit after bilateral infusions into the nucleus basalis magnocellularis of male Long-Evans rats. Four weeks post-lesion, there was no difference in locomotor activity following infusion of either neurotoxicant or vehicle. In a passive avoidance task, both treated groups had significantly shorter step-through latencies compared with vehicle. Five weeks post-lesion, rats were killed for neurochemistry or histochemistry. Choline acetyltransferase (ChAT) activity in both the frontal and parietal cortex was significantly decreased (25-35%) in the colchicine- and ibotenic acid-infused rats when compared to control. There was no effect of either neurotoxicant on ChAT activity in the hippocampus or striatum. Both neurotoxicants produced damage in the general area of the ventromedial pallidum, although ibotenic acid infusion consistently produced a larger area of damage as assessed in Nissl-stained sections. Analysis of the number of ChAT-immunoreactive cells in the nucleus basalis magnocellularis (NBM) showed an average 60% cell loss following colchicine infusion and a 75% cell loss after ibotenic acid infusion. Area of glutamic acid decarboxylase (GAD) staining was significantly decreased in several regions surrounding the NBM for ibotenic acid (51% average decrease), and showed non-significant decreases (28%) following colchicine infusion. Colchicine infusion decreased dopamine and 3,4-dihydroxyphenylacetic acid (DOPAC) in the striatum; ibotenic acid had no effect on brain catechol of indoleamine levels. The results indicate that although similar cholinergic hypofunction and behavioral deficits were achieved, several non-cholinergic differences between the neurotoxicants were detected.

GM1 ganglioside treatment reduces visual deficits after graded crush of the rat optic nerve

Despite numerous reports of beneficial effects of GM1 ganglioside treatment following brain lesions in animals, the underlying neurobiological mechanism of ganglioside-induced functional restoration is still unclear. In order to obtain a better insight into this question, we have made use of a newly developed animal model of brain injury that would potentially permit us to determine the causal relationship(s) among behavioral and neuroanatomical/neurochemical parameters of restoration of function. Following graded crush of the adult rat optic nerve, we have treated the rats with intraperitoneally injected gangliosides and studied the functional outcome with electrophysiological and behavioral parameters. The electrophysiological recording of the compound action potential (CAP) from excised rat optic nerve revealed a significant loss of CAP throughout the first 2 weeks after the injury. However, when rats were treated daily for 7 days with GM1-gangliosides, the CAP measured 10 days after the crush was significantly larger compared to operated controls without treatment. Thus, GM1 appeared to be capable of delaying or partially preventing retinal ganglion cells or their axons from secondary degeneration. Loss of visual function was also evident on the behavioral level of analysis: when rats with unilateral optic nerve crush were evaluated in a visual orienting paradigm, the rats revealed deficits in their ability to orient towards small, moving visual stimuli. However, within about 2 weeks, the animals recovered spontaneously to near normal performance. Daily treatment with GM1-gangliosides was found to significantly improve outcome, largely due to a reduction of the immediate post-lesion deficit. In a second behavioral experiment we also created graded crush in rats bilaterally and evaluated the animals visual capacities in a two-choice brightness discrimination task. In this task, an initial loss of function was followed by recovery within about 2 weeks, but GM1 treatment was without beneficial effects in this paradigm. It is concluded that GM1 improves outcome after graded crush of the adult rat optic nerve, although it appears that improved function needs to be documented with sufficiently sensitive behavioral assays.

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.

Intrafimbrial colchicine produces transient impairment of radial-arm maze performance correlated with morphologic abnormalities of septohippocampal neurons expressing cholinergic markers and nerve growth factor receptor

The microtubule disrupting agent, colchicine, was infused both bilaterally and unilaterally into the fimbria of the rat brain. Such infusions produced a transient impairment in radial-arm maze performance during the first week following surgery but only in bilaterally injected animals. This behavioral finding was correlated with a reduction in the number of neurons expressing choline acetyltransferase and nerve growth factor receptor in the septum and vertical limb of the diagonal band but not in other regions of the basal nuclear complex. The altered expression of the two neurochemical markers was not due to cellular degeneration because numbers of neurons demonstrated by Nissl staining were unchanged. Putative cholinergic fibers in the fimbria demonstrating acetylcholinesterase and nerve growth factor receptor also showed aberrations in caliber, shape, and course.