Early changes in the rat hippocampus following seizures induced by bicuculline or L-allylglycine: a light and electron microscope study.

Status epilepticus was induced in thirteen paralysed and ventilated rats by the injection of either bicuculline or L-allylglycine. After 1-2 h of seizure activity the animals were intracardially perfused with a 2% glutaraldehyde/3% paraformaldehyde solution. Hippocampal blocks from each rat were processed for light and electron microscopy. The effects of L-allylglycine were more severe than those of bicuculline. Changes include perivascular and perineuronal swelling of astrocytic processes, and neuronal alterations which were graded as follows: Grade I (least severe), neuronal cytoplasm appears slightly darker than usual; Grade II, condensed or dark neurons, usually with microvacuoles; and Grade III classical 'ischaemic cell change'--the cytoplasm and karyoplasm is dark and shrunken, with or without microvacuoles. Many of the microvacuoles originate from mitochondria. In a few cases swollen and disrupted mitochondria are also seen is distended basal dendrites of the CA3 and CA1 pyramidal neurons. Dentate granule cells appear unaffected. The hippocampal neuronal alterations induced by seizure activity include those of 'ischaemic cell change'. The pathogenetic factors common to hypoxia/ischaemia and status epilepticus remain to be identified.