Reticularis thalami neurons revisited: activity changes during shifts in states of vigilance

Abstract

This study tested the hypothesis that inhibitory actions are exerted by reticularis thalami (RE) neurons upon thalamocortical neurons. The RE neurons were recorded in the rostral pole and lateral districts of the nucleus, and were activated monosynaptically by cortical volleys. Thalamocortical neurons were identified antidromically in intralaminar and ventrolateral nuclei. During sleep with EEG synchronization, prolonged spike barrages of RE neurons extended over the whole spindle sequences. This result suggests that RE neurons are depolarized throughout spindle oscillations, whereas thalamocortical neurons show, simultaneously, long hyperpolarizations and short rebounds. During waking, parallelism rather than reciprocity was found between RE and thalamocortical neurons. Spontaneous discharge rates almost doubled in RE neurons on arousal from sleep, and the probability of cortically evoked short-latency discharges increased. The increase in spontaneous firing rates of RE neurons during natural arousal is consistent with their short-latency synaptic excitation by stimulating the rostral brain stem reticular formation after chronic degeneration of passing fibers. We suggest that RE cells inhibit GABAergic local-circuit cells, in addition to inhibiting thalamocortical neurons, and that different ratios of inhibitory effects are exerted by RE neurons upon these two cell classes during waking and sleep. We further suggest that, upon arousal, disinhibition of thalamocortical neurons (via the local-circuit neurons) outweighs direct inhibition of the thalamocortical neurons.

Neuronal Basis of the Slow (<1 Hz) Oscillation in Neurons of the Nucleus Reticularis ThalamiIn Vitro

“…The main findings of this study are (1) reduction of I Leak via exogenous or synaptic activation of mGluR1a in NRT neurons in vitro leads to the instatement of an intrinsic slow (Ͻ1 Hz) oscillation with similar properties to those observed in vivo during deep sleep Steriade et al, 1986) and certain types of anesthesia (Steriade et al, 1993c;Contreras and Steriade, 1995;Steriade et al, 1996;Timofeev and Steriade, 1996), (2) the slow oscillation is predominantly reliant on I Twindow and I h , and (3) the properties of the slow oscillation are also influenced by the activity of a CAN current (I CAN ), a Ca 2ϩ -activated K ϩ current (I K(Ca) ) and an Na ϩ -activated K ϩ current (I K(Na) ). This study is the first to expound the mechanisms of the slow oscillation in NRT neurons and endorses the idea that the slow (Ͻ1 Hz) sleep rhythm is actively shaped by the thalamus (Hughes et al, 2002a).…”

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).…”