GABAERGIC INHIBITION CAN SHARPEN FREQUENCY TUNING OF AUDITORY CORTICAL NEURONS IN BIG BROWN BAT (EPTESICUS FUSCUS)

摘要

Nine adult big brown bats were used in this experiment.The GABAergic inhibition sharpening the frequency tuning of primary auditory cortical (AC) neurons was studied with the multi barrel electrode for iontophoresis and two tone stimulation method.We observed that excitatory frequency tuning curves appeared three types: the single peak opening, multi peak opening, and single peak closed.The inhibitory inputs to AC neurons could be activated by inhibitory tone and they had their best frequencies.The inhibitory frequency tuning curve or inhibitory frequency intensity response area at the low limb or/and high limb of an excitatory frequency tuning curve could be tested and obtained according to effective degree of GABAergic inhibition on the excitatory response induced by the tone of 10 dB above minimum threshold and by systematic change of inhibitory tone intensity.The result showed that GABAergic inhibition could decrease the firing rate of excitatory response to 10 dB stimulation above minimum threshold and increase the inhibitory effectiveness with the elevation of inhibitory tone intensity.GABAergic inhibition disinhibited during iontophoresis of bicuculline could make the excitatory frequency tuning curve to become the wider, the multi peak tuning curve to become the single peak, and single peak closed tuning curve to become the single peak opening tuning curve.Therefore, the results described above demonstrated that GABAergic inhibition participate in the formation of inhibitory input to AC neuron, it could help to sharpen the frequency tuning of the central auditory neurons, and this is the reason that frequency tuning curves become the “pencil shaped” and “spindle shaped”, and that central frequency tuning is more sensitive than peripheral.