Relations between cortical and thalamic cellular events during transition from sleep patterns to paroxysmal activity

Area of Science:

• Neuroscience
• Epileptology
• Sleep Research

Background:

• The transition from normal sleep patterns to paroxysmal activities, including epileptic seizures, is not fully understood.
• Spike-wave (SW) complexes are characteristic of certain seizure types and are associated with altered brain states.

Purpose of the Study:

• To investigate the progressive development of EEG-synchronized sleep patterns into low-frequency paroxysmal activities resembling epileptic seizures in anesthetized cats.
• To elucidate the role of neocortical, reticular thalamic (RE), and thalamocortical (TC) neurons in the generation and progression of these seizure-like events.

Main Methods:

• Multisite extra- and intracellular recordings were performed in anesthetized cats.
• Dual impalements of cortical and TC cells were utilized to examine cellular interactions.
• Simultaneous recordings of RE and TC neurons were conducted during seizure activity.

Main Results:

• A subset of TC cells (40%) exhibited spike bursts synchronized with SW seizures, while the majority (60%) showed inhibition.
• TC cell hyperpolarization duration and amplitude correlated with the EEG paroxysm extent.
• Cortical SW seizures involved tonic depolarization in cortical cells and tonic hyperpolarization with inhibitory postsynaptic potentials (IPSPs) in TC cells, mediated by RE neurons.

Conclusions:

• The study demonstrates a progression from sleep patterns to epileptic-like activities in cats.
• Inhibitory processes in TC cells during SW seizures may lead to loss of consciousness by disrupting thalamic synaptic transmission.