Characteristics of Column Organization Sharpening Frequency Tunings of Bat Auditory Cortical Neurons

98 auditory cortical (AC) neurons were obtained on the 6 big brown bats (Eptesicus fuscus) with the two-tone stimulation and multi-barrel electrode method s and the characteristics of column organization sharpening frequency tunings of AC neurons were studied.The results showed that neurons from the same orthogonal penetration had basically same inhibitory tuning curve or area at low or/and high limbs of excitatory tuning curve.The neurons isolated within an obliquely (45° with AC surface) penetrated electrode to cross multi-columns were with different excitatory and inhibitory areas.Two penetrated ways of electrode demonstrated the characteristics of column organization sharpening frequency tuning of AC neurons,in other words,AC neurons that had same function on the frequency ana lysis were with the same type of neural inhibition and they located within a same column forming a functional organization unit-"mini-frequency processor".The multi-peaked frequency tuning curves observed in the experiment were considered to be essential for complex sound information processing.We can reasonably hy pothesize that AC neurons with multipeaked frequency tuning curves could execute a function as a highly tuned preprocessor of complex spectral information.In or der to investigate further the mechanism sharpening frequency tuning,GABAergic receptor-a (GABAa) antagonist,bicuculline,was injected ionophoreticaly to the AC neuron recorded through mult-barrel electrode and inhibitory areas of the neurons could be abolished mostly or completely by bicuculline application.These results showed that GABAergic inhibition participated in forming inhibitory area of frequency tuning of AC neuron and increased the ability of frequency resolu tion under the normal physiologic condition,whereas frequency tuning curve became the wider and decreased the abilities of frequency selectivity and resolution after GABAergic disinhibition by bicuculline.