Periodicity of GABA-containing cells in primate prefrontal cortex

The tangential distribution of GABA-containing cells was examined in the principal sulcus of the frontal lobe in 12 macaque monkeys. Following immunostaining with GABA antisera all immunoreactive cells were charted and their distribution analyzed with both statistical and spectral density methods. In addition, a gapless series of sections was used to generate a 2-dimensional reconstruction of cell disposition in the tangential plane parallel to the pia. Our findings indicate that the GABA cells are not distributed uniformly across the cortex, as is commonly believed, but that their density is characterized by 2 independent sinusoidal fluctuations: a high-frequency component with a period ranging from 150 to 250 micron superimposed upon a lower-frequency component with a period of 1000-1275 micron. The half-cycle of the low-frequency component (roughly 625 micron) is very similar to the dimensions of afferent and efferent columns in the principal sulcus, while the half-cycle of the higher-frequency component (approximately 125 micron) is closer in size to that of the functionally defined columns of neurons found in regions of sensory cortex that share common physiological properties. To our knowledge, these findings are the first indication that inhibitory local circuit neurons are not uniformly or randomly distributed, but exhibit periodicities that may be related to the columnar, functional and architectural organization of the cortex.