Dopaminergic inhibition of excitatory inputs onto pyramidal tract neurons in cat motor cortex.

The role of dopamine (DA) on motor cortical pyramidal tract neurons (PTNs) was studied in anesthetized cats with in vivo extracellular recordings in response to transcallosal (TC) and ventrolateral (VL) thalamic stimulations. An antidromic PT potential was evoked to recognize PTNs. In most PTNs, iontophoretic application of DA significantly reduced the spike activity exerted by 20 single-pulse stimulations. Both D(1)-like and D(2)-like receptor antagonists blocked (disinhibited) the effect in a similar way regardless of TC and VL stimulations, suggesting colocalization of two receptors. Except for the presence of jittering, the mean latency was usually fixed and short. These findings indicate that ventral midbrain DA imposes an intense suppression in modulating PTNs response to both callosal and thalamocortical excitatory inputs in motor cortex. Such DAergic suppression could play pivotal role to improve motor and sensorimotor signal integration.