The Study Of Synaptic Mechanism Underlying CF-CF Combination Sensitive Neurons In Inferior Colliculus Of Pratt’s Roundleaf Bat

Combination sensitive neurons contribute to the integration of spectrally and temporally information when bat analyzing complex sounds. Previous studies mainly reported the properties of constant frequency-constant frequency (CF-CF) combination sensitive neurons, which were unique to constant frequency-frequency modulation (CF-FM) bats, by using extracellular recording. But the mechanism underlying combination sensitive interaction is still unclear. For this purpose, we studied the proportions and underlying mechanisms of different types of CF-CF combination sensitive neurons in inferior colliculus (IC) of pratt’s roundleaf bat, Hipposideros Pratti, using in vivo intracellular recording. The main results are as follows:1.104neurons were obtained from IC of pratt’s roundleaf bat, the ranges of best frequency (BF)(kHz), resting potential (RP)(mV) and recording depth (RD)(μm) of these neurons were52.0～62.6(56.6±2.9),-70--5(-19.3±10.0) and1571～4650(2974.6±589.3), respectively. The delay tuning properties of72neurons were examined by measuring the delay-tuned curves. Among72neurons,37(51.4%) were the CF-CF combination sensitive neurons including13(18.1%) facilitatory CF-CF combination sensitive neurons and24(33.3%) inhibitory ones.2. According to whether showed hyperpolarizations when neurons were stimulated by different sounds, facilitatory CF-CF combination sensitive neurons could be divided into three kinds:15.4%showed transient hyperpolarizations only to fundamental CF (CF1) sound,7.7%showed transient hyperpolarizations to both CF1and BF sounds,76.9%showed no transient hyperpolarizations to both sounds; inhibitory CF-CF combination sensitive neurons could be divided into two kinds:12.5%showed transient hyperpolarizations only to CF1sound,87.5%showed no transient hyperpolarizations to both CF1and BF sounds.3. According to the area of delay-tuned curves of facilitatory or inhibitory CF-CF combination sensitive neurons, these neurons could be divided into two kinds:exact harmonically and non-exact harmonically related neurons. Among facilitatory/inhibitory CF-CF combination sensitive neurons, non-exact harmonically related neurons were8/14, exact harmonically related neurons were5/5. These results indicated that:(1) The proportion of inhibitory CF-CF combination sensitive neurons was larger than facilitatory ones in inferior colliculus of pratt’s roundleaf bat.(2) Most facilitatory CF-CF combination sensitive neurons did not show hyperpolarization to CF1sound alone, these facilitatory interactions might be electrically segregated from the soma, isolated in dendritic regions, and other facilitatory interaction might be formed in soma because neurons showed hyperpolarization to CF1sound alone. Most inhibitory CF-CF combination sensitive neurons did not show hyperpolarization to CF1sound alone, these inhibitory interactions might be origined in auditory centers below the IC, and other inhibitory interaction might be modified in IC because neurons showed hyperpolarization to CF1sound alone.(3) The number of non-exact harmonically related neurons was larger than exact harmonically related neurons in CF-CF combination-sensitive neurons of IC in pratt’s roundleaf bat. This was consistented with bats’ behavioral characteristics, because non-exact harmonically related neurons can be used to obtain the information of velocity between bats and insects in bats doppler-shift compensation during hunting.