Thalamic burst patterns in the naturally sleeping cat: a comparison between cortically projecting and reticularis neurones.

Abstract

SUMMARY1. Unit discharges were extracellularly recorded from antidromically identified thalamocortical neurones of ventralis lateralis (v.1.) and centralis lateralis (c.l.) nuclei as well as from reticularis thalami (re.) neurones during wakefulness and electroencephalogram-synchronized sleep of the behaving cat. Various parameters of sleep-related discharge bursts were analysed.2. Statistical analyses revealed striking similarities between motor relay (v.1.) and intralaminar (c.l.) neurones. More than 60 % of bursts consist of three to five spikes at 250-400 Hz. The defining feature of bursts in all cortically projecting neurones is a progressive increase in the duration of successive interspike intervals. 3. As in thalamocortical cells, all re. neurones change their tonic discharges in waking to bursting firing in sleep, regardless of the increased or decreased firing rates from wake to sleep in individual neurones. The bursts of re. neurones are essentially different from those of thalamocortical cells. In re. neurones, burst structure consists of an initial progressive decrease in duration of interspike intervals, followed by an increase in duration of successive intervals, eventually leading to a long-lasting tonic spike train at about 100 Hz. In contrast with bursts of thalamocortical neurones, only 6 % of re. bursts are shorter than 50 ms; the total duration of the burst extends between 50 ms and 1'5 s. Population periburst histograms show the beginning of a decline in firing probability about 1-5 s prior -to burst onset and an increased firing probability persisting for 300-350 ms after burst onset.4. The different electrophysiological properties underlying the burst structure of cat's thalamocortical and re. neurones are discussed, with emphasis on dissimilar aspects of re. bursts in unanaesthetized and barbituratized preparations. Various factors that may account for the transition from tonic mode in waking to bursting mode in sleep are envisaged.

Circuits for Multisensory Integration and Attentional Modulation Through the Prefrontal Cortex and the Thalamic Reticular Nucleus in Primates

“…The TRN contains at least two types of neurons that exhibit two activity modes, burst and tonic. Importantly, the type of activity depends on the animal's behavioral state / 45,74,112,119,157,159 /. Dual discharge modes have also been observed in thalamic relay neurons but they differ in duration and interval between spikes / 47,100 /.…”

Excitatory Effects of Thyrotropin-Releasing Hormone in the Thalamus

“…In the awake attentive animal, thalamocortical neurons are relatively depolarized, discharge almost exclusively in the single-spike firing mode, and faithfully transfer inputs from the sensorium. With the transition to slowwave sleep, thalamic neurons hyperpolarize and increasingly replace single-spike discharge with rhythmic burst firing, such as spindle waves (McCarley et al, 1983;Domich et al, 1986;Steriade et al, 1986Steriade et al, , 1993. Spindle waves are observed in the electroencephalogram (EEG) as waxing and waning 6 -15 Hz oscillations (Steriade et al, 1993).…”

Dendritic organization in thalamocortical neurons and state-dependent functions of inhibitory synaptic inputs

“…The hyperpolarization is essential to the oscillatory dynamics because the deep potentials enhance de-inactivation of T-type low-voltage activated Ca 2+ channels (Coulter et al, 1989;Crunelli et al, 1989;Jahnsen and Llinás, 1984). From the de-inactivated state, T-channels are able to mediate rebound low-threshold Ca 2+ potentials (rLTCPs), which often culminate in a short burst of conventional Na + /K + action potentials (Domich et al, 1986; typically 3-4 spikes). During induction of oscillatory states, few TRNs would be participating, and the inhibitory drive on any given TCN is likely to be spatially non-uniform.…”