摘要
Abstract
The electrosensory system in mormyrid fish serves three functions: ac tive electrolocation, in which external object are sensed by the distortions of the electric field of the fish's electric organ discharge (EOD);electrocommuni cation, in which EODs convey information between fish;and passive electrolocati on, in which the low frequency electric fields from other animals in the water a re sensed. These functions are served by three classes of electroreceptors in th e fish skin. The primary afferents from these electroreceptors terminate in diff erent regions of the electrosensory lobe (ELL). ELL is a cerebellum like structu re which is also strongly affected by descending electric organ corollary discha rge signal (EOCD) associated with the motor command signals that drives EOD. Thu s, the descending EOCD signal and the EOD electrosensory input converge onto the ELL.In vivo studies have indicated that the EOCD signal generates negative images of predictable features in the sensory inflow in mormyrid ELL. Addition of such negative images to the actual or concurrent sensory input minim izes the predictable features and allows novel or unexpected inputs to stand out more clearly. The generation of negative images is largely due to plasticity at the parallel fiber synapses onto Purkinje-like cell in ELL.The present study extended these in vivo findings to in vitro slice pr eparation. The basic features and mechanisms of such plasticity were studied in ELL slices with the intracellular recording method. The plasticity was rapidly e stablished by pairing the electric-activated parallel fiber epsp with a post-s ynaptic broad spike evoked by depolarizing current pulse in a Purkinje-like cel l, at 1 Hz for 5 min at 0 to 50 ms delays. After such pairing, the parallel fibe r epsp was depressed by 25%～30% for over 30 min. This depression was blocked by adding NMDA receptor antagonist AP5 to the bath or injecting calcium chelator B APTA into the recorded cell. The depression could be reversed by stimulating the parallel fiber at 1 Hz without pairing with post-synaptic broad spike, this hap pens under natural physiological conditions. It is hypothesized that the broad s pike leads to calcium influx through NMDA receptors during pairing. The elevatio n in post-synaptic calcium in turn leads to the depression of synaptic transmis sion in the post-synaptic cell by activating different protein kinases. Such re versibility and a narrow timing window are the most important features of this p lasticity and has not been demonstrated in any system of its kind, including the mammalian cerebellum. The reversibility allows the neuron to "forget" the pas t event and get ready for a new task. The narrow timing window renders the cell able to selectively "remember" some information, not every single input signal .关键词
神经元可塑性/突触/浦肯野氏细胞/电感受叶/电鱼Key words
neuronal plasticity/synapses/Pur kinje cells/electrosensory lobe/electric fish分类
医药卫生
