Effect of baclofen on sensory transmission through the ventrobasal thalamic nucleus of the rat

Previous work suggests that after administration of baclofen there is a reduction in excitatory cuneothalamic transmission, while preliminary experiments in this laboratory had shown that baclofen produces lowered level of cortical activity. Since much of the corticothalamic output is inhibitory, the consequences of possible reductions in excitatory corticopetal and inhibitory corticofugal flow into the ventrobasal thalamus required investigation. Baclofen produced increased latency and decreased probability of discharge of the short-latency discharge of single ventrobasal thalamic units to peripheral stimulation. It is suggested that these observations are compatible with a decreased excitatory cuneothalamic volley. Accompanying the decline in the early discharge was a development of later rhythmic discharges at 80-100 msec intervals, lasting up to 900 msec. This type of response is also seen in decorticate rats and has the same temporal pattern as the inhibition of the response to the second of a pair of peripheral stimuli shown in rats with an intact cerebral cortex. Since baclofen produced a decline in cortical activity (N1 wave of evoked potential, synchronisation of the ECoG), is suggested that this emergence of rhythmic activity is produced by a reduction of corticothalamic inhibition.