The effect of unilateral basilar papilla removal upon nuclei laminaris and magnocellularis of the chick examined with [3H]2-deoxy-D-glucose autoradiography.

The effect of unilateral basilar papilla removal on glucose uptake in the 2nd and 3rd order auditory nuclei in the chick's brain stem, nucleus magnocellularis and nucleus laminaris, respectively, was examined with [3H]2-deoxy-D-glucose (2-DG) autoradiography. The tissue was processed according to a thaw-mount technique, and the number of grains in the resulting autoradiographs was counted to assess changes in glucose uptake. It was observed that there is a greater density of grains over the neuropil regions of nucleus laminaris which receive input from the normal ear than over the corresponding regions which receive input from the operated ear. Similarly, differences in grain density are found between the normally innervated and deafferented magnocellular nuclei although these differences are not as great as those in nucleus laminaris. Differences in grain density were also apparent between the glial/fiber regions which bound the neuropil areas of nucleus laminaris; there is a greater density of grains overlying those glial/fiber regions through which fibers receiving input from the normal ear course than over those regions through which fibers which normally carry input from the operated ear travel. It is likely that this difference mainly reflects glucose uptake in the fibers although a possible contribution of glial tissue cannot be excluded. All these effects of basilar papilla removal are seen with survival times as short as 70 min and thus likely reflect the reduction of neural activity rather than the degeneration of pre- or postsynaptic elements. Finally, the same pattern of results as described above was found when using the more common [14C]2-DG procedure or when using [3H]2-DG but processing the tissue using the freeze-dried technique. The present results thus show the neuropil regions of nucleus laminaris and the adjacent glial/fiber areas to be areas of high glucose utilization. Unilateral basilar papilla removal results in the removal of an excitatory input to these regions, and this results in a reduction of glucose utilization that is specific to those neuropil regions and glial/fiber areas that receive input from the operated ear. These findings are contrasted with another study in which removal of a major excitatory input to the dentate gyrus of the rat results in a reduced glucose utilization which is not specific to the deafferented region and which largely reflects post- rather than presynatic events.