Spindle-like oscillation in the thalamus is synchronized with the brainstem input

Abstract

In the present study, we investigated the neuronal oscillation properties in the medial geniculate body (MGB) through in-vivo intracellular recordings from the intact brain of anesthetized guinea pigs. Repeated noise bursts and pure tones with intervals of 400 ms or longer and 5-ms rise/fall time, were used to examine neuronal responses. Various oscillation rhythms: 0.05-0.2 Hz, 2 Hz, 6-14 Hz, and 26 Hz, were observed in the present study. With a confirmation of the labeling and their locations of the neurons, we demonstrated that the spindle-like oscillation started with either an inhibitory or an excitatory postsynaptic potential (EPSP). Auditory stimulus triggered membrane oscillation of similar frequency to spindles from those neurons showing spontaneous spindle-like oscillation. The spindle-like oscillation was not diminished in the MGB of the guinea pigs whose auditory cortex was ablated. Simultaneous recordings from the laterodorsal tegmental nuclei (LDT) of the brainsten reticular formation extracellularly and from the MGB intracellularly revealed that oscillatory EPSPs in the MGB was synchronized with the firing of the LDT neurons, but lagged by tens of milliseconds. An electrical stimulation of the LDT triggered a spindle-like, EPSP membrane oscillation of the MGB neurons, which preceded the membrane oscillation of TRN neurons. The present results presented a potential alternative mechanism of the genesis of spindle oscillation.