Caudate evoked synaptic activities in nigral neurons

Abstract

Intracellular recordings from neurons in the substantia nigra have revealed three varieties of monosynaptic PSPs in response to stimulation of the ipsilateral head of the caudate nucleus: short (3–5 msec) latency EPSPs; short (3–5 msec) latency IPSPs; and long (15–20 msec) latency IPSPs. The data indicate that at least three efferent fiber systems link the caudate to the nigra: two fast conducting axonal systems of comparable diameters mediate the short-latency PSPs whereas a slow conducting axonal system mediates the long-latency PSPs. The caudate evoked long-latency IPSPs in nigral neurons were preceded by antidromic and orthodromic potentials in the motor cortex; these cortical potentials are regarded as epiphenomena. The dual, facilitatory-inhibitory control of caudate on nigral neurons is consonant with the proposal that the caudate self-regulates its input from the nigra. The caudate-evoked EPSPs in nigral neurons are sine qua non for the operation of the caudato-nigrothalamic projection system.