Abstracts

Astroglial cells play a key role in energy metabolism and cycling between the inhibitory and excitatory neurotransmitters. Impaired glial metabolism due to intracortical microinjection of fluorocitrate, which reversibly inhibits glial tricarboxylic acid can induce seizures at higher doses. Further studies are required to determine the epileptogenic properties of fluorocitrate at various doses. Male SD rats (250-400gm,n=18) were anesthetized with pentobarbital to implant 8 EEG electrodes and a cannula. The electrodes were secured with dental cement and animals were allowed to recover for a week. Fluorocitrate solutions (1mM, 2mM, 3mM, 4mM, 6mM, 8mM) were prepared according to a published method. On the experiment day, 0.2[mu]L of saline (control) or fluorocitrate was injected in the right occipital cortex through the cannula 1.2 mm below the skull surface. EEG and behaviour were monitored for 6 hours and again one hour daily before they were sacrificed and perfused with 4% paraformaldehyde to perform immunohistochemistry with glial fibrilary acidic protein (GFAP) and neuronal counting 48 hours after the injection. Three rats were studied with each dose. All the rats injected with 4mM and higher doses of fluorocitrate developed seizures for up to 6 hours but none experienced seizures with lower doses of fluorocitrate or saline. Four rats that received 6 mM and 8 mM of fluorocitrate developed status epilepticus and required diazepam i.p. to terminate seizures. These rats developed seizures within 1 minute of injection of fluorocitrate. Other rats showed a delayed affect with seizures 2 hours after the injection. Only one rat that received 4mM of flourocitrate experienced one seizure 24 hours later. Other rats did not have seizures in subsequent recordings. All rats exhibited hyperactivity within the first 6 hours but abnormally low activity on subsequent days compared to control animals. There was a significant increase in GFAP staining with enlarged astrocytes that had swollen processes in doses greater and equal to 4mM of fluorocitrate. Only minimal GFAP staining at the injection site was seen with 2mM of fluorocitrate but none with 1 mM or saline injection. There was no neuronal loss. Fluorocitrate exhibits a dose-dependent epileptogenic property in SD rats resulting in focal seizures with secondary generalization. This gliotoxin can be used as a suitable animal model to study glial involvement in the development of seizures. Lower doses of fluorocitrate that do not case seizure can be used to study early metabolic changes leading to seizures. (Supported by Canadian Institutes of Health Research)