The effects of inferior olive lesion on strychnine seizure

Synchronicity and Rhythmicity of Purkinje Cell Firing during Generalized Spike-and-Wave Discharges in a Natural Mouse Model of Absence Epilepsy

Absence epilepsy is characterized by the occurrence of generalized spike and wave discharges (GSWDs) in electrocorticographical (ECoG) recordings representing oscillatory activity in thalamocortical networks. The oscillatory nature of GSWDs has been shown to be reflected in the simple spike activity of cerebellar Purkinje cells and in the activity of their target neurons in the cerebellar nuclei, but it is unclear to what extent complex spike activity is implicated in generalized epilepsy. Purkinje cell complex spike firing is elicited by climbing fiber activation and reflects action potential firing in the inferior olive. Here, we investigated to what extent modulation of complex spike firing is reflected in the temporal patterns of seizures. Extracellular single-unit recordings in awake, head-restrained homozygous tottering mice, which suffer from a mutation in the voltage-gated Ca_V2.1 calcium channel, revealed that a substantial proportion of Purkinje cells (26%) showed increased complex spike activity and rhythmicity during GSWDs. Moreover, Purkinje cells, recorded either electrophysiologically or by using Ca²⁺-imaging, showed a significant increase in complex spike synchronicity for both adjacent and remote Purkinje cells during ictal events. These seizure-related changes in firing frequency, rhythmicity and synchronicity were most prominent in the lateral cerebellum, a region known to receive cerebral input via the inferior olive. These data indicate profound and widespread changes in olivary firing that are most likely induced by seizure-related activity changes in the thalamocortical network, thereby highlighting the possibility that olivary neurons can compensate for pathological brain-state changes by dampening oscillations.

Infantile spasms versus myoclonus: is there a connection?

Infantile spasms (IS) is usually classified as a form of "myoclonic epilepsy," but the nosology of this whole group of disorders is unclear. Evidence suggests that the spasms are subcortically mediated, but can be modified by input from the cortex, which is believed to be abnormally excitable and disorganized. The latter features may give rise to hypsarrhythmia. The whole issue of myoclonus rests on the phenotype of IS and precise measurements of the length of electromyographic (EMG) bursts. Based on scant EMG data, it would appear that the bursts during flexor spasms are too long for epileptic myoclonus. The nature of tonic spasms of even longer duration is not myoclonic. However, the infrequent spontaneous myoclonic jerks, which can occur without spasms, and head nodding could represent positive and negative myoclonus, respectively. Data can be collected easily through techniques such as back-averaging to resolve the issue of classification and localization of motor phenomena.