Figure 1.

Two projection types of pyramidal cells in layer V of the frontal cortex. A, Schematic of method for identification of two projection neuron types by retrograde tracers. Alexa Fluor 555-conjugated CTB was injected in the contralateral striatum while Fast Blue (FB) or Fluorogold (FG) was injected into the pontine nuclei. For simultaneous recording from CCS and CPn cells, RLMs were injected in the contralateral striatum, and CTB was injected in the ipsilateral pons. Ag, Agranular; ant., anterior. A1, Injection site of RLMs in the striatum. Top, Epifluorescence view. Bottom, As in above, but using bright-field microscopy. The tracer was applied obliquely through the lateral ventricle after suctioning the overlying cortex to prevent injection into the cortex. A2, Injection site of Fluorogold in the pons including the ipsilateral pontine nuclei. B, Fluorescence imaging revealed two nonoverlapping populations of CCS and CPn cells. CPn cells were distributed in patchy regions (asterisks) where CCS cells were absent. Right, As in the left but in thionin staining.