A reanalysis of the ventrolateral input in slow and fast pyramidal tract neurons of the cat motor cortex.
In deeply anesthetized cats the temporal characteristics of ventro-lateral (thalamic) excitatory postsynaptic potentials (EPSPs) induced in pyramidal tract cells were studied with an averaging technique. Stimulation of the ventrolateral thalamus induced EPSPs in all pyramidal tract neurons at latencies of 1-5 ms. It was found that there was a positive relationship between the latency and rise time of stimulation-induced EPSPs and the latency of antidromic invasions of pyramidal tract neurons. In response to two closely spaced shocks the second EPSP had the same latency and amplitude as the first one in both slow and fast pyramidal tract neurons. Moreover, the span of antidromic latencies of ventrolateral thalamic relay cells to motor cortex stimulation showed that these thalamic neurons had the necessary conduction velocities to account for the distribution EPSP latencies recorded in pyramidal tract neurons. From these electrophysiological results, it has been concluded that slow and fast pyramidal tract morphological evidence, obtained at the electron-microscopic level, supporting this conclusion. Terminal degeneration induced by a lesion in the ventrolateral thalamus was found on the apical dendrite of a slow pyramidal tract neurons that had been injected with horseradish peroxidase. It is proposed that the matching between the latencies of EPSPs evoked from the ventrolateral thalamus and the latencies of antidromic invasions of pyramidal tract neurons may reflect a matching between the conduction velocity of thalamocortical and cortico-spinal neurons and/or it may be due to the electrotonic properties of the apical dendrites.
D000818:Animals; D002415:Cats; D003712:Dendrites / Q000502:physiology; D004558:Electric Stimulation; D005071:Evoked Potentials; D008854:Microscopy, Electron; D009044:Motor Cortex / Q000502:physiology*; D009412:Nerve Fibers / Q000502:physiology; D009431:Neural Conduction; D009474:Neurons / Q000502:physiology; D011712:Pyramidal Tracts / Q000502:physiology*; D009435:Synaptic Transmission; D013787:Thalamic Nuclei / Q000502:physiology*