Deoxyglucose uptake in the ferret auditory cortex.

Histological methods and 2-deoxyglucose autoradiography were used in an attempt at finding distinguishing characteristics that would permit the clear definition of different auditory areas on the ectosylvian gyrus. This region was studied in both coronal and flattened tangential sections. In tangential sections a crescent-shaped region of high deoxyglucose uptake was identified. The centre of this crescent was in the position of the primary auditory area on the middle ectosylvian gyrus. The ventro-anterior arm of the crescent was on the surface of the anterior ectosylvian gyrus and the ventro-posterior arm on the posterior ectosylvian gyrus. All three parts of the crescent appear to have an auditory function, because ablating the inferior colliculus or inserting a contralateral earplug reduced their deoxyglucose uptake. This was shown by using two separately distinguishable forms of 2-deoxyglucose, incorporating the 18F and 14C isotopes. In addition, another area of high deoxyglucose activity was identified in the ventral wall of the suprasylvian sulcus, which seems to correspond to the anterior auditory field. These four areas with high deoxyglucose uptake also have high levels of succinate dehydrogenase activity and moderately high densities of myelinated fibres. Succinate dehydrogenase histochemistry provides a simple method for identifying auditory cortical areas and should be of use in future physiological studies. These results provide evidence that the ferret has four separate auditory areas with relatively high metabolic and functional activity.