[Morphological properties of fast and slow PT cells in the cat revealed by intracellular pressure injection of HRP ].

Intracellular pressure injection of horseradish peroxidase (HRP) was applied to PT cells in the motor cortex of awake cats to reveal morphological properties. All PT cels recovered (N = 23) had pyramidal shaped somata located in layer V. All had apical dendrites going toward superficial layers and had basal dendrites spreading in layers V and VI. Fast and slow PT cells had axon collaterals which extended in layers V and VI. The spine density of fast PT cells in layer III was lower than that of slow ones as an average, but some fast PT cells had spines as many as slow ones. This was not in agreement with the previous report (Labelle and Deschênes16).) Morphological features to separate fast and slow PT cells were: (1)Fast PT cells had larger somata (20-50 micrometers in long axis) than slow PT cells (20-28 micrometers). (2)Horizontal spread of the dendritic field in layer V was larger in fast PT cells (mean : 654.7 micrometers) than in slow PT cells (mean : 222.0 micrometers).