Study of layer 6b cortical neurons in vitro

Abstract

Cortical layer 6b (L6b), located between layer 6 and the corpus callosum, is a remnant of the subplate which, in rodents, persists into adulthood. Using mouse brain slices of the somatosensory cortex, we first confirmed previous results obtained in rats by our lab, that only L6b neurons are directly sensitive to the wake-promoting transmitter hypocretin/orexin (hcrt/orx). Then, using patch-clamp recordings, histological and morphological techniques, we identified four neuronal populations based on their intrinsic properties and responses to hcrt/orx and other major wake-promoting transmitters. Two were deemed particularly interesting as they had peculiar rhythmic firing properties. First, fast spiking GABAergic parvalbumin-positive neurons known to be implicated in gamma rhythm during wakefulness and second, slow bursting neurons possibly involved in slow wave sleep. Given the strong responses of both to hcrt/orx and the other transmitters, it is suggested that L6b could be a major relay for the cortical activation associated with wakefulness.