From Physiology to Pathology of Cortico-Thalamo-Cortical Oscillations: Astroglia as a Target for Further Research

Abstract

The electrographic hallmark of childhood absence epilepsy (CAE) and other idiopathic forms of epilepsy are 2.5–4 Hz spike and wave discharges (SWDs) originating from abnormal electrical oscillations of the cortico-thalamo-cortical network. SWDs are generally associated with sudden and brief non-convulsive epileptic events mostly generating impairment of consciousness and correlating with attention and learning as well as cognitive deficits. To date, SWDs are known to arise from locally restricted imbalances of excitation and inhibition in the deep layers of the primary somatosensory cortex. SWDs propagate to the mostly GABAergic nucleus reticularis thalami (NRT) and the somatosensory thalamic nuclei that project back to the cortex, leading to the typical generalized spike and wave oscillations. Given their shared anatomical basis, SWDs have been originally considered the pathological transition of 11–16 Hz bursts of neural oscillatory activity (the so-called sleep spindles) occurring during Non-Rapid Eye Movement (NREM) sleep, but more recent research revealed fundamental functional differences between sleep spindles and SWDs, suggesting the latter could be more closely related to the slow (<1 Hz) oscillations alternating active (Up) and silent (Down) cortical activity and concomitantly occurring during NREM. Indeed, several lines of evidence support the fact that SWDs impair sleep architecture as well as sleep/wake cycles and sleep pressure, which, in turn, affect seizure circadian frequency and distribution. Given the accumulating evidence on the role of astroglia in the field of epilepsy in the modulation of excitation and inhibition in the brain as well as on the development of aberrant synchronous network activity, we aim at pointing at putative contributions of astrocytes to the physiology of slow-wave sleep and to the pathology of SWDs. Particularly, we will address the astroglial functions known to be involved in the control of network excitability and synchronicity and so far mainly addressed in the context of convulsive seizures, namely (i) interstitial fluid homeostasis, (ii) K+ clearance and neurotransmitter uptake from the extracellular space and the synaptic cleft, (iii) gap junction mechanical and functional coupling as well as hemichannel function, (iv) gliotransmission, (v) astroglial Ca2+ signaling and downstream effectors, (vi) reactive astrogliosis and cytokine release.

Investigation of CACNA1I Cav3.3 Dysfunction in Hemiplegic Migraine

“…Changes in Cav3 I w can contribute to pathophysiological conditions ( Tsakiridou et al, 1995 ) directly, or as co-occurring with other abnormalities, such as extracellular pH changes ( Shah et al, 2001 ), hyperpolarization-activated current and HVA Ca 2+ channel variation, or sustained hyperexcitability disorders ( Crunelli et al, 2005 ). Abnormal electrical oscillations of the cortico-thalamo-cortical network have been shown to underlay childhood absence epilepsy (CAE) and other idiopathic forms of epilepsy ( Gobbo et al, 2021 ), while dysfunction to the thalamocortical network caused by altered Cav3.3 activation that increases tonic firing has been linked to absence epilepsy ( Lee et al, 2014 ).…”

Alpha2-Adrenergic Receptors as a Pharmacological Target for Spike-Wave Epilepsy

“…It produces sustained rhythmic activity controlled by the “driving” and the “modulatory” inputs from the thalamic and cortical parts. It is known that genetically predetermined molecular impairments in cortical and thalamic neurons (and glia) cause epileptic spike-wave discharges [ 16 , 18 , 22 , 23 , 24 ].…”

Sleep Disturbances in Rats With Genetic Pre-disposition to Spike-Wave Epilepsy (WAG/Rij)

“…In the same way, SWDs in WAG/Rij rats were preceded by delta precursor (with the mean frequency of 4.1 Hz in the frontal cortex) coexisting with theta (39). In addition to the abovementioned delta, cortical slow (<1 Hz) oscillations might play an important role in SWDs in WAG/Rij rats as far as it controls alternating active (Up) and silent (Down) cortical activity excitation (23,40).…”