Impaired hippocampal synaptic plasticity in C6 glioma-bearing rats

For many glioblastoma multiforme patients, cognitive deficits are part of the disease process. In this study we attempted to determine the role of synaptic plasticity and glutamate (Glu) in C6 glioma-bearing rats. Male Sprague-Dawley (SD) rats were subjected to tumor implantation in the right caudate putamen nucleus. At 17 days after tumor implantation, animals were exposed to an open field test. The numbers of crossings and rearings were used as measures of exploration processes. An input/output (I/O) curve was first determined using the measurements of field excitatory postsynaptic potential (fEPSP) slope in response to a series of stimulation intensities. The short-term potentiation (STP) and long-term potentiation (LTP) induced by high-frequency stimulation (HFS) in the CA1 region of the contralateral hippocampus to the tumor were recorded. The glutamate and γ-aminobutyric acid (GABA) content of contralateral hippocampus were quantified by high-performance liquid chromatography (HPLC). C6 glioma-bearing rats showed a trend for a rightward shift of input/output relationship and significant deficits in maintenance of STP and LTP. Quantitative analysis by HPLC of glutamate and γ-aminobutyric acid revealed that Glu concentration and Glu/GABA ratio were increased significantly in contralateral hippocampus, suggesting impairment of excitatory and inhibitory synaptic transmission. The results suggest that the neurocognitive deficits in C6 glioma-bearing rats may be mediated via profound changes in neuroplasticity and elevated Glu concentration and Glu/GABA ratio in hippocampus area of the brain.