Spindle-like thalamocortical synchronization in a rat brain slice preparation

We obtained rat brain slices (550-650 mm) that contained part of the fronto parietal cortex along with a portion of the thalamic ventrobasal complex (V B) and of the reticular nucleus (RTN). Maintained reciprocal thalamocortica l connectivity was demonstrated by VB stimulation, which elicited orthodrom ic and antidromic responses in the cortex, along with re-entry of thalamoco rtical firing originating in VB neurons excited by cortical output activity . In addition, orthodromic responses were recorded in VB and RTN following stimuli delivered in the cortex. Spontaneous and stimulus-induced coherent rhythmic oscillations (duration = 0.4-3.5 s; frequency = 9-16 Hz) occurred in cortex, VB, and RTN during application of medium containing low concentr ations of the K+ channel blocker 4-aminopyridine (0.5-1 mu M). This activit y, which resembled electroencephalograph (EEG) spindles recorded in vivo, d isappeared in both cortex and thalamus during application of the excitatory amino acid receptor antagonist kynurenic acid in VB (n = 6). By contrast, cortical application of kynurenic acid (n = 4) abolished spindle-like oscil lations at this site, but not those recorded in VB, where their frequency w as higher than under control conditions. Our findings demonstrate the prese rvation of reciprocally interconnected cortical and thalamic neuron network s that generate thalamocortical spindle-like oscillations in an in vitro ra t brain slice. As shown in intact animals, these oscillations originate in the thalamus where they are presumably caused by interactions between RTN a nd VB neurons. We propose that this preparation may help to analyze thalamo cortical synchronization and to understand the physiopathogenesis of absenc e attacks.