In 10 cats undergoing deep enflurane anesthesia, depth recordings were made from amygdala, dorsal and pes hippocampus, VPL, VL, CM, and DM of thalamus, midbrain reticular formation, red nucleus, dentate nucleus, and cerebellar cortex, as well as surface recordings from cerebral cortex. At brain equilibrated end tidal concentrations of 3.0 to 4.0% enflurane, tonic clonic seizures could be elicited by auditory, visual, or tactile stimulation and, at somewhat higher levels, spontaneous seizures were seen. Fast sinusoidal activity (16 to 24 Hz) originating in CM and amygdala occurred continuously or in spindles and spread predominantly to neocortex, although it also appeared to a lesser degree at all depth locations. This activity characteristically was seen late in the electrographic seizure and typically lasted for 5 to 15 sec but sometimes continued for up to 1 min after the seizure. The frequency of the sinusoidal activity progressively decreased and the amplitude increased, a sequence which consistently coincided with the abrupt end of the clinical and electrographic seizure and was usually associated with desynchronization of the electrocorticogram. The frequency and duration of this activity were inversely related to the duration of the electrographic seizure and to the depth of anesthesia above the miminum epileptogenic concentration of enflurane and were directly related to the P(A)CO2 at the onset of the seizure; it was unrelated to respiratory rhythm or olfactory stimulation and was unaffected by stimulation of midbrain reticular formation or neuromuscular blockade. The results of this preliminary study indicate that this phenomenon may reflect the metabolic status of the reticular formation near the end of enflurane induced seizures and could represent an 'arousal rhythm' of the diffuse projection system (including amygdala). It may also be related to similar activity reported from the amygdala following prolonged circulatory arrest (Gurvitch, 1964).
|Original language||English (US)|
|Number of pages||2|
|State||Published - 1975|
ASJC Scopus subject areas
- Clinical Neurology