Local perfusion of the thalamus with GABA increases sleep and induces long-lasting inhibition of somatosensory event-related potentials in cats.

The extracellular concentration of gamma-aminobutyric acid (GABA) was increased in the ventroposterolateral nucleus of the thalamus in cats using in vivo microdialysis probes. In freely moving cats, the permanent injection of 8 x 10(-9) M/mm2 x min GABA induced a significant increase in sleep proportion. The duration of paradoxical sleep was particularly increased resembling the effects of benzodiazepines. In chloralose anesthesia, a similar increase in GABA concentration in the thalamus induced a tonic decrease in the peak-to-peak amplitude of cortical event-related potentials evoked by stimulation of the radial nerve. Following 10-15 min of inhibition during which the responses were as small as 20% of the original ones, the potentials started to recover. Finally, the responses were stabilized at a reduced amplitude. The present data suggests the important role of the thalamic GABAergic neurons in the regulation of sleep.