Functional properties of putative pyramidal neurons and inhibitory interneurons in the rat gustatory cortex

In order to address how taste information is modulated by inhibitory neuronal interactions in the rat gustatory cortex, we examined putative pyramidal neurons (PY units) and putative inhibitory interneurons (fast spiking [FS] units) that were distinguished by their spike waveforms and discharge rates. FS units were strikingly different from PY units in that the majority of FS units were N- or NH-best neurons and narrowly tuned to 1 or 2 tastant(s), whereas PY units were broadly tuned to plural tastants. Compared with PY units, FS units were characterized by a shorter response latency and/or a longer response duration. These results suggest that inhibitory modulations in the gustatory cortex are carried out in a taste specific and tonic manner. Sensitivity to tastant concentrations in PY units was similar to that in FS units for NaCl but higher for HCl. FS units may act to enhance concentration sensitivity in PY units by reducing PY units' response activity. High density of FS and PY units was observed in the superficial and middle layers (mainly layers III and IV). Responses in N-best FS units in these layers were significantly larger than those in the deep layers, suggesting the existence of layer-specific inhibitory interactions.