Gangliosides in lesion-induced synaptogenesis: studies in the hippocampus of the rat brain

Imaging mass spectrometry technology and application on ganglioside study; visualization of age-dependent accumulation of C20-ganglioside molecular species in the mouse hippocampus

Gangliosides are particularly abundant in the central nervous system (CNS) and thought to play important roles in memory formation, neuritogenesis, synaptic transmission, and other neural functions. Although several molecular species of gangliosides have been characterized and their individual functions elucidated, their differential distribution in the CNS are not well understood. In particular, whether the different molecular species show different distribution patterns in the brain remains unclear. We report the distinct and characteristic distributions of ganglioside molecular species, as revealed by imaging mass spectrometry (IMS). This technique can discriminate the molecular species, raised from both oligosaccharide and ceramide structure by determining the difference of the mass-to-charge ratio, and structural analysis by tandem mass spectrometry. Gangliosides in the CNS are characterized by the structure of the long-chain base (LCB) in the ceramide moiety. The LCB of the main ganglioside species has either 18 or 20 carbons (i.e., C18- or C20-sphingosine); we found that these 2 types of gangliosides are differentially distributed in the mouse brain. While the C18-species was widely distributed throughout the frontal brain, the C20-species selectively localized along the entorhinal-hippocampus projections, especially in the molecular layer (ML) of the dentate gyrus (DG). We revealed development- and aging-related accumulation of the C-20 species in the ML-DG. Thus it is possible to consider that this brain-region specific regulation of LCB chain length is particularly important for the distinct function in cells of CNS.

Dynamics of synapsin I gene expression during the establishment and restoration of functional synapses in the rat hippocampus

Synapse development and injury-induced reorganization have been extensively characterized morphologically, yet relatively little is known about the underlying molecular and biochemical events. To examine molecular mechanisms of synaptic development and rearrangement, we looked at the developmental pattern of expression of the neuron-specific gene synapsin I in granule cell neurons of the dentate gyrus and their accompanying mossy fibers during the main period of synaptogenic differentiation in the rat hippocampus. We found a significant difference between the temporal expression of synapsin I messenger RNA in dentate granule somata and the appearance of protein in their mossy fiber terminals during the postnatal development of these neurons. Next, to investigate the regulation of neuron-specific gene expression during the restoration of synaptic contacts in the central nervous system, we examined the expression of the synapsin I gene following lesions of hippocampal circuitry. These studies show marked changes in the pattern and intensity of synapsin I immunoreactivity in the dendritic fields of dentate granule cell neurons following perforant pathway transection. In contrast, changes in synapsin I messenger RNA expression in target neurons, and in those neurons responsible for the reinnervation of this region of the hippocampus, were not found to accompany new synapse formation. On a molecular level, both developmental and lesion data suggest that the expression of the synapsin I gene is tightly regulated in the central nervous system, and that considerable changes in synapsin I protein may occur in neurons without concomitant changes in the levels of its messenger RNA. Finally, our results suggest that the appearance of detectable levels of synapsin I protein in in developing and sprouting synapses coincides with the acquisition of function by those central synapses.

Effects of GM1 ganglioside upon neuronal degeneration during withdrawal from alcohol

In previous studies we demonstrated that chronic alcohol consumption induced hippocampal cell and synapse loss in offset with an increase in the length of granule cell dendrites. In addition we observed that withdrawal after long periods of alcohol intake worsened the degenerative processes and that dendritic alterations were no longer apparent. In an attempt to reverse these structural changes we tested the action of GM1 ganglioside during the withdrawal period as there is evidence that GM1 may enhance neuronal recovery after different kinds of brain lesions. Cell and synaptic quantifications were performed and the branching pattern of the granule cell dendritic arborizations was analysed. The number of dentate granule and CA3 pyramidal cells from GM1-treated animals was found not to be significantly different from that of the alcohol-treated and withdrawal groups. No quantitative changes were found in the number of mossy fiber-CA3 pyramidal cell synapses when the aforementioned groups were compared. Whether the lack of effectiveness of GM1 can be related to the model employed or not is thoroughly discussed.

The expression of a fucosyl-ganglioside in the molecular layer of the dentate gyrus following entorhinal cortical lesions

alpha-Galactosyl (alpha-fucosyl) GM1 is a ganglioside present in the outer two-thirds of the molecular layer of the dentate gyrus of the rat. This region is the terminal zone for afferents from the entorhinal cortex. In order to evaluate changes in ganglioside expression in this region following deafferentation, a monoclonal antibody (WCC4) was used to monitor the ganglioside from 3 to 30 days following a lesion to the entorhinal cortex. From 7 to 14 days postlesion, there was a relative decrease in the width of the band of immunohistochemical staining on the ipsilateral (lesioned) as compared with the contralateral (non-lesioned) side. The results of these studies indicate that alpha-galactosyl (alpha-fucosyl) GM1 is likely to be associated with dendritic shafts in the dentate molecular layer.