A Physiological Investigation of the Two Corticostriatal Systems in Rat Somatsensory Striatum
In Chloralose and Urethane (1% & 10%; 1.0 ml/Kg, i.p.) anaesthetised rats we have studied the responses of single striatal neurones to stimulation of the contralateral barrel cortex and of the contralateral whisker pad. The effects of cortical stimulation are likely to be transmitted along the ‘diffuse’ pathway that projects bilaterally to the striatum. Stimulation of the whisker pad would probably activate the other corticostriatal system, which arises as collaterals from corticofugal fibres. The synchronous volley arising from the electrical stimulus to the whisker pad would have travelled via brain stem and thalamus to the barrel centres in the somatosensory cortex. It is from the barrels that the ipsilateral, topographic system arises and so the peripheral stimulus would be able to activate this system first. Later phases of the response might include activation of the septa surrounding the barrels and hence of the diffuse system.
Both stimuli are able to depolarise the spiny neurones to their firing threshold. The excitatory postsynaptic potentials (EPSPs) from the two stimulus sites had similar latencies (in spite of very different path lengths and numbers of synapsesen route).However, the responses to whisker pad stimulation were rapidly rising and showed very little variation in latency to action potential generation, while the contralateral cortically derived EPSPs were slower to rise and the spike initiation latency was more variable. These characteristics might be predicted from the morphology of the two systems.
KeywordsSomatosensory Cortex Fixed Time Interval Excitatory Postsynaptic Potential Striatal Cell Contralateral Cortex
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