Dual excitatory inputs to caudate spiny neurons from substantia nigra stimulation

In the present set of experiments of two component excitatory postsynaptic potential (EPSP) (fast and slow) was recorded from caudate (Cd) neurons after substantia nigra (SN) stimulation in the alpha-chloralose anesthetized cat. Several unique properties of the fast response are demonstrated and used to determine certain functional properties of Cd neurons. The following conclusions have been drawn from these experiments. (1) A dual excitatory innervation pattern (fast and slow) exists to the Cd from SN stimulation. (2) The fast system is independent of the Cd efferent system. (3) Neurons receiving this dual input are spine laden neurons. (4) Dendritic inhibition is operating on these neurons and often has little or no direct influence on the observed soma membrane potential. The dendritic inhibition reduced test EPSP amplitude for several hundred milliseconds for all Cd afferents except for the fast SN input. Such a decoupling of the fast input from the inhibition may play an important role in Cd signal processing.