Modulation Of Medial Prefrontal Cortex On Azimuth Plasticity Of Auditory Space In Rat Primary Auditory Cortex Neurons

In experiments, we studied the modulation of medial prefrontal cortex on azimuth plasticity of auditory space in rat primary auditory cortex neurons by electrophysiological technique and histology method. It consists of two parts: 1. Induction of azimuth plasticity of auditory space in rat primary auditory cortex neuronsIn these experiments, we found that the best response azimuth of adult primary auditory cortex neurons would shift to he azimuth of acoustic conditioned stimuli when given a non-best azimuthal repeated acoustic stimuli in horizontal plane (azimuth plasticity of auditory space).We recorded 218 neurons in primary auditory cortex of 63 rats, which could be evoked by repeated acoustic stimuli. Under the stress of time, we studied 143 neurons of their azimuth plasticity of auditory space when we gave them conditioned stimulus with 5 ,10 or 15 deviation from their best azimuth.The results are as follows:i When we gave neurons the conditioned stimulus with 5 deviation from the best azimuth, there were 91.1 percent of neurons whose best azimuth can shift toward the conditioned stimulating azimuth. There were 83.9 percent of neurons shift when we gave conditioned stumuli with 10 deviation from the best azimuth. Only 25 percent of neurons shift toward the conditioned stimulating azimuth when we gave conditioned stimulus with 15 deviatior. from the best azimuth. Consequently, when we gave a non-best azimuthal repeated acoustic stimuli in horizontal plane, The best azimuth of more than 80 percent neurons could shift toward the conditioned stimulating azimuth.ii The bigger the deviation degrees between the conditioned stimulating azimuth and the best azimuth were, the longer the time of aural spatial azimuth shifting needed.iii The best azimuth usually recovered from twenty to sixty minutes after the repeated acoustic stimuli stopped.iv The best azimuth of some neurons can shift to two sides. But with the increase of the deviation degrees between the conditioned stimulating azimuth and the best azimuth, the neurons of two-side-shift in azimuth of auditory space were reduced evidently.2. The modulation of medial prefromal cortex on azimuth plasticity of auditory space in rat primary auditory cortex neuronsUsing electrophysiological techrique and histology method, we studied modulation of medial prefrontal cortex on azimuth plasticity of auditory space in rat primary auditory cortex neurons.i We found that focal electric stimuli of medial prefrontal cortex could dramatically affect the evoked potential and facilitate the azimuth plasticity of auditory space of neurons in primary auditory cortex. Compared with neurons given the repeated acoustic stimuli only, the time of conditioned stimuli shortened from 32.7 minutes to 11.5 minutes with focal electric stimuli to medial prefrontal cortex and repeated acoustic stimuli to neurons simultaneously(p<0.001). But the recovery time of such neurons was no difference to that of neurons given repeated acoustic stimulionly (p>0.05).ii In these experiments, we applie I Procaine hydrochloride to medial prefrontal cortex where we gave focal electric stimuli. We found that inactivity of medial prefrontal cortex could eliminate the facilitative effect of the azimuth plasticity of auditory space in primary auditory co tex. Furthermore, The time of conditioned stimulus prolonged from 26 minutes to 3 8 minutes (p<0.001) . The recovery time of such neurons shortened from 28.4 minutes to 23.6 minutes, which was dramatically different from neurons given repeated at oustic stimulus only. The results suggest that medial prefrontal cortex can facilitate the azimuth plasticity of auditory space in primary auditory cortex when animals are in normal state.iii When injecting Horseradish Peroxidase ( HRP) into medial prefrontal cortex, we observed some labeled ne ons in primary auditory cortex. This result suggests that the primary auditory cortex projects to the medial prefrontal cortex in rat.