Spiny stellate neurones in layer VI of the rat cerebral cortex.

From 109 neurones labelled intracellularly in layer VIa of rat neocortical slices, four non-pyramidal, spiny stellate neurones were identified by their common morphological characteristics. They had a small cell body and densely spiny dendrites extending radially, but no dominant apical dendrite. The main axons ran briefly to the pial surface, and then made a characteristic U-turn to descend toward the white matter. In immunofluorescence cytochemistry, all the spiny stellate neurones were immunopositive for glutaminase but not for calcium-binding proteins, suggesting that they were glutamatergic. Electrophysiologically, they belonged to the regular spiking type and showed a small fast afterhyperpolarization. Thus, the spiny stellate neurones were considered to represent a unique group of excitatory neurones in layer VI of the cerebral cortex.