PHYSIOLOGICAL SUBGROUPS OF NONPYRAMIDAL CELLS WITH SPECIFIC MORPHOLOGICAL-CHARACTERISTICS IN LAYER II III OF RAT FRONTAL-CORTEX/

Physiological and morphological properties of nonpyramidal cells in la yer II/III of frontal cortex of young rats were studied in vitro by wh ole-cell recording and intracellular staining with biocytin, Layer II/ III nonpyramidal cells could be divided into four subgroups by their f iring patterns in response to depolarizing current pulses and their pa tterns of dendritic and axonal arborizations, (1) Fast-spiking (FS) ce lls (35% of the total sample) showed an abrupt episode of nonadapting repetitive discharges of shorter-duration action potentials, FS cells had local and horizontal axonal arbors which did not enter layer I, Th is type of FS cell was immunoreactive for parvalbumin and included som e basket cells, Three chandelier cells were identified as FS cells, al though one chandelier cell was not identified as an FS cell, (2) Late- spiking (LS) cells (11%) exhibited slowly developing ramp depolarizati ons near threshold, LS cells were neurogliaform cells, (3) Low-thresho ld spike (LTS) cells (5%) had prominent low-threshold spikes when stim ulated from hyperpolarizations, The main axons of LTS cells ascended, and the collaterals entered into layer I. (4) The remaining cells [reg ular-spiking nonpyramidal (RSNP) cells] (49%) could not be categorized into the above three subgroups, In some RSNP cells depolarizing pulse s from hyperpolarizations induced fast depolarizing notches with small amplitude, RSNP cells had vertically elongated axonal fields, extendi ng from layer I to V, sometimes to layer VI, This subgroup included do uble bouquet cells and bipolar cells, Each subgroup with a different f iring mode may differentially contribute to neocortical laminar and co lumnar circuitry.