MUSCIMOL SUPPRESSION OF THE DORSAL COCHLEAR NUCLEUS MODIFIES FREQUENCY TUNING IN RATS

The cochlear nucleus is composed of three sub-nuclei: the dorsal (DCN) , anteroventral (AVCN) and posteroventral cochlear nucleus (PVCN). Int rinsic connections from the DCN to the AVCN are inhibitory and organis ed tonotopically. In this investigation, this pathway and its possible role in frequency tuning was examined using in vivo extracellular rec ordings. Extracellular recordings were made from 191 units in the AVCN , 69 of which were recorded after suppression of DCN by application of the GABA agonist Muscimol (15 ng, 0.26 mM). Tuning curves were plotte d and characteristic frequency (CF) and response threshold (measured i n dB SPL) were determined for each unit. Units recorded post-Muscimol showed significantly broader tuning characteristics and lower threshol ds. Primary-Like and transient chopper neurons contributed to this dec rease in threshold suggesting that they receive 'on' CF inhibitory dri ve from the DCN. Sustained chopper units did not show a significant de crease in response threshold after Muscimol; however, there was a tend ency for broader tuning and a significant increase in CF tone evoked m aximum discharge rate and chopping frequency suggesting that the DCN m ay play a role in regulating the temporal firing of these units in add ition to providing lateral inhibition. These results suggest that the DCN to AVCN pathway may aid in fine tuning frequency information. (C) 1998 Elsevier Science B.V.