Structural and functional MRI following 4-aminopyridine-induced seizures: a comparative imaging and anatomical study.

Structural and functional MRI was used in conjunction with computerized electron microscopy morphometry to study changes 2 h, 24 h and 3 days after 4-aminopyridine-induced seizures lasting 2 h in rats. T2 (relaxation time) values showed changes throughout the cerebral cortex, hippocampus, amygdala and medial thalamus, with a different temporal progression, showing a complete recovery only after 3 days. Two hours after seizures, the apparent diffusion coefficient was decreased throughout the brain compared to control animals, and a further decrease was evident 24 h after seizures. This was followed by a complete recovery at 3 days post-seizures. Functional MRI was performed using regional cerebral blood volume (rCBV) maps. The rCBV was increased shortly after convulsions (2 h) in all structures investigated, with a significant return to baseline values in the parietal cortex and hippocampus, but not in the medial thalamic nuclei, 24 h after seizure onset. No rCBV alterations were detected 3 days after seizures. Electron microscopy of tissue samples of parietal neocortex and hippocampus revealed prominent astrocytic swelling 2 h post-convulsions which decreased thereafter gradually. In conclusion, this experiment reports for the first time structural and functional brain alterations, lasting several hours, in 4-aminopyridine-treated rats after seizure onset. MRI approach combined with histological and ultrastructural analysis provided a clarification of the mechanisms involved in the brain acute response to ictal activity.

A combined electrophysiological and behavioural study for the assessment of activity-dependent changes in mice.

Activity-dependent adaptive changes in the nervous system involve structural and functional changes in the cortical circuitry. In this work the cortical function was studied by repeated recording of the somatosensory and motor potentials evoked by whisker deflections after altered sensory-motor experience in adult mice. The latencies of motor and somatosensory evoked potentials were found to shorten, while their amplitudes decreased, after a behavioural challenge involving the vibrissal apparatus. Sensory deprivation achieved by whisker trimming resulted in a partial reversal of the changes observed after increased activity. The derived parameters imply that cortical information processing speeds up as a result of experience, while decreased activity has the opposite effect. The methods used throughout the experiment were minimally invasive, and thus proved to be sufficient for the long-term follow-up of cortical functions.