Search

Systemic administration of kainic acid induces repeated convulsive seizures (KA convulsions) that result in neuropathological changes similar to temporal lobe epilepsy and the appearance of spontaneous recurrent seizures (SRS). The appearance of SRS is considered a result of the remodeling of neuronal networks following neuronal degeneration. We investigated the changes in chondroitin sulfate proteoglycans (CSPGs) in the limbic structures after KA convulsions in the rat using monoclonal antibodies 1G2, which recognizes full-length neurocan and the C-terminal half of neurocan, neurocan C, and 6B4, which recognize phosphacan and protein tyrosine phosphatase zeta. After KA convulsions, full-length neurocan appeared by 24 h and reached a peak by 48 to 72 h, whereas phosphacan decreased within 24 h in the hippocampus. In immunohistochemistry, neurocan increased in the limbic structures coincident with the appearance of reactive astrocytes. Phosphacan decreased coincident with pyramidal cell loss in the hippocampus, and the number of phosphacan-positive perineuronal nets around parvalbumin neurons decreased, whereas parvalbumin neurons were relatively conserved. In contrast, phosphacan increased in the entorhinal and piriform cortices in correlation with the severity of neuronal loss. Both neurocan and phosphacan recovered to the control level by 8 weeks after KA convulsions in some rats, but the changes in neurocan and phosphacan described above still persisted in more than half the rats. The results indicate that KA convulsions induce prolonged changes in neurocan and phosphacan similar to those in the developing rat brain and suggest a role of these CSPGs in the remodeling of neuronal networks related to the establishment or enhancement of epileptogenesis.

Developmental changes in the distribution of brain-specific chondroitin sulfate proteoglycans, neurocan and phosphacan/RPTPzeta/beta, in the hippocampus of the Sprague-Dawley rat were examined using monoclonal antibodies 1G2 and 6B4. The 1G2 immunoreactivity was predominant in the neonatal hippocampus while the 6B4 immunoreactivity was predominant in the mature hippocampus. Moderate 1G2 immunoreactivity was detected in the dentate gyrus and subiculum immediately after birth. Immunoreactivity reached a peak on postnatal days 7-10 (P7-P10) when intense 1G2 labeling was present throughout the neuropil layers of the hippocampus except the mossy fiber tract. 6B4 immunoreactivity was limited in the stratum lacunosum moleculare of CA1 in the neonatal hippocampus. It gradually increased by P21 when diffuse 6B4 immunoreactivity was detected in the stratum oriens and radiatum of Ammon's horn, and in the hilus and inner one-third molecular layer of the dentate gyrus, while 1G2 immunoreactivity decreased after P21. In the adult hippocampus, moderate 6B4 immunoreactivity was present in the stratum oriens and radiatum of Ammon's horn, and in the hilus and inner one-third molecular layer of the dentate gyrus, but not in the mossy fiber tract. In addition, strong 6B4 labeling appeared around a subset of neurons after P21. The results suggest that neurocan may have a role in the development of neuronal organization, while phosphacan/RPTPzeta/beta may contribute to the maintenance and plasticity of synaptic structure and function. Furthermore, the absence of 1G2 and 6B4 immunoreactivities in the stratum lucidum suggests that neurocan and phosphacan/RPTPzeta/beta may function as a barrier for the extension of mossy fibers and provide an environment permissive for fasciculation of the mossy fibers.

We investigated the role of phosphacan, a chondroitin sulfate proteoglycan that is constitutively expressed in the adult hippocampus, and recombinant core proteins of phosphacan in excitotoxic cell death of primary cultured rat hippocampal neurons. Phosphacan had no significant effect on excitotoxic neuronal death. Surprisingly, one of three recombinant proteins corresponding to N-terminal portions of phosphacan core protein dramatically promoted excitotoxic neuronal death. Moreover, the recombinant protein induced cell death of rat hippocampal neurons, even when neurons were not exposed to glutamate. These results suggest that proteolytic degradation of phosphacan and resultant core protein fragments may contribute to neuronal degeneration of hippocampal neurons in various neuropathological conditions.

Ihara's epileptic rats (IER) is an animal model of temporal lobe epilepsy with mycrodysgenesis, that exhibit abnormal migration of hippocampal neurons and recurrent spontaneous seizures. As an attempt to elucidate the roles of extracellular matrix molecules in the epileptogenecity and mossy fiber sprouting, immunohistochemical localization of brain specific chondroitin sulfate proteoglycans (CSPGs), neurocan and phosphacan, was examined in the hippocampus of postnatal IER and Sprague-Dawley (SD) rats using monoclonal antibodies 1G2 against neurocan and 6B4 against phosphacan. There was no difference in the expression of these two CSPGs between IER and SD rats in the 1st postnatal week. However, the expression of neurocan was poor in the hippocampus of IER in the 2nd and 3rd weeks whereas intense labeling of neurocan was present throughout the hippocampus of SD rats. Labeling of neurocan was almost absent in the hippocampus, while phosphacan was diffusely expressed in the stratum oriens and radiatum of Ammon's horn, and in the hilus and inner one-third molecular layer of the dentate gyrus at the 2nd month after birth. There was no difference in the expression of neurocan and phosphacan between IER and SD rats at the 2nd month after birth. By contrast, phosphacan was reduced in the inner molecular layer of the dentate gyrus in 8-month-old IER, while neurocan was reexpressed in the outer molecular layer and hilus in 3- and 8-month-old IER. It was suggested that the insufficient expression of neurocan may affect the development of neuronal organization in the hippocampus, and that the remodeling of extracellular matrix in the dentate gyrus may contribute to the mossy fiber sprouting into the inner molecular layer.