Modulation Of Frequency Receptive Field Plasticity Of Auditory Cortex Neurons By Stimulation Of Medial Prefrontal Cortex In Rats

Using conventional electrophysiological technique and horseradish peroxidase (HRP) neuron tracing method, we investigated the modulation of frequency receptive field (RF) plasticity of auditory cortex (AC) neurons by stimulation of medialPrefrontal Cortex in rats. It mainly consisted of two parts:1. Receptive field plasticity of neurons in rats auditory cortexUsing conventional electrophysiological technique, we investigated the plasticityof the frequency receptive fields (RF) of auditory cortex (AC) neurons in rats. In the AC, when the frequency difference between conditioning stimulus frequency (CSF) and the best frequency (BF) was in the range of l-4kHz, the frequency RF of AC neurons shifted. The smaller the differences between CSF and BF, the higher the probability of the RF shift and the greater the degree of the RF shift. To some extent, the plasticity of RF was dependent on the duration of the session of conditioning stimulus (CS). When the frequency difference between CSF and BF was bigger, the duration of the CS session that needed to induce the plasticity was longer. The recovery time course of the frequency RF showed opposite changes after CS cessation. The RF shift could be induced by the frequency that was either higher or lower than the control BF, demonstrating no clear directional preference. The frequency RF of some neurons showed bidirectional shift, and the RF of other neurons showed singledirectional shift. The results suggest that the frequency RF plasticity of AC neurons could be considered as an ideal model for studying plasticity mechanism. The present study also provides an important evidence for further study of learning and memory in auditory system.2. Modulation of frequency RF plasticity of AC neurons by stimulation of medial Prefrontal Cortex in ratsUsing conventional electrophysiological technique and horseradish peroxidase (HRP) neuron tracing method, we investigated the modulation of frequency RF plasticity of AC neurons by stimulation of medial Prefrontal Cortex in rats.(1) The evoked potentials of AC neurons can be modulated by electrical stimulation in mPFC (ES-mPFC). The modulation on the evoked potentials has two types: enhancement type (61.7%) and inhibition type (38.3%). Furthermore, the RF plasticity of AC neurons also can be modulated by ES-mPFC. The modulation on RF plasticity has four types: enhancement type (53.8%), inhibition type (12.5%), uncertain type (7.5%) and no effect type (18.8%). Among these four modulation types, the enhancement type is the main modulation type. The change of RF plasticity is that the time of RF shift shortened (p<0.01) and the time of RF recovery lengthened (p<0.01). The RF plasticity of inhibition type showed opposite changes. According to the difference between the CSF and the BF, the time of RF shift in difference-2kHz-group was slightly longer than that in difference-1kHz-group, while the time of RF recovery in difference-2kHz-group was slightly shorter than that in difference-IkHz-group. These differences are not significant (p>0.05). The types of RF plasticity and the proportions of different RF plasticity types in difference-IkHz-group and in difference-2kHz-group showed no significant difference.(2) The evoked potentials and the spontaneous responses of AC neurons can be modulated by deactivating mPFC with procaine (DS-mPFC). The modulation on these responses was as folio wings: the spontaneous responses increased; the evokedpotentials increased (enhancement type,60%),or decreased (inhibition type,20%),or no change (no effect,20%). Furthermore,the RF plasticity of AC neurons also can be modulated by DS-mPFC. The modulation on RF plasticity has four types: enhancement type (22.5%),inhibition type (52.5%),uncertain type (10%) and no effect type (15%). Among these four modulation types,the inhibition type is the main modulation type and the change of RF plasticity is that the time of RF shift lengthened (p<0.01) and the time of RF rec...