海馬迴中的神經網路主要由兩種神經細胞所組成：分別是提供興奮性神經衝動的 principal neuron 及擁有抑制能力的 interneuron。雖然 interneuron 僅佔有少數的組成，但因為其多樣的形態及生理功能，在修飾及整合神經網路訊號上扮演著相當重要的角色。一般認為principal neuron 能夠發展出較長的軸突，並且延伸到遠端的目標腦區，而 interneuron 僅能長出較短的軸突，與周圍的目標連結，形成局部性抑制迴路 (local inhibitory circuit)。在本實驗中將探討軸突生長能力的差異是否受到環境中目標有無 (target-specify) 的影響，抑或是由內在能力 (intrinsic capacity) 導致的生長限制。由於在大腦皮質區及海馬迴中，大部分的 principal neuron 皆使用麩胺酸 (glutamate) 作為神經傳導物質。以及不同的 interneuron 族群則表現不同的 calcium-binding protein，因此在本實驗中我們使用 vGLUT1 抗體來標記大鼠海馬迴中的 principal neuron 及 calbidin 和 parvalbumin 抗體來標記 interneuron。為了模擬神經細胞在真實生長環境中，在此我們將細胞培養在覆蓋 poly-L-lysine (PLL) 的蓋玻片上，軸突在上面可隨意地與周圍目標連結。結果發現當有生長目標時 principal neuron 軸突生長能力顯著的大於 interneuron。接著我們利用微接觸壓印配合模版侷限技術 (Wu et al., 2010) 將目標去除後，卻觀察到 interneuron 軸突生長能力也能夠提升到與 principal neuron 相當的程度。經由本實驗結果我們推測，在胚胎時期海馬迴中的 interneuron 之軸突生長能力與 principal neuron 相當，當軸突逐漸發育接觸到目標之後，才受到目標所釋放的訊息分子的影響導致生長停止。

Hippocampal neural network is mainly composed of two neuronal populations, the majority of the network is principal neurons, which provide the excitatory synaptic output to the circuit, and the rest is the inhibitory interneuron. Even the less number of interneuron population, because of its diverse morphology and physiological function, interneurons play an important role in the modification and integration of hippocampal neural network. In general, principal neuron can develop very long axons to target distal brain region. In contrast to principal neurons, interneurons can only extend much shorter axons to surrounding target to form local inhibitory circuit, in this study, we try to determine whether the axon growth capacity is caused by target-specify or the intrinsic capacity.
Because most principal neurons in the cerebral cortex and hippocampus use glutamate as neurotransmitter, so we use vesicular glutamate transporter 1 (vGLUT1) to label hippocampal principal neurons. Calcium-binding proteins also expressed in non-overlapped hippocampal interneuronal population, so we can use calbidin and parvalbumin to label different interneuron in the hippocampus. We cultured the hippocampal neurons on the PLL-covered coverslips to mimic the real growth environment for the hippocampal neurons that axonal fibers can randomly extend to the targets, in this experiment we found that the axon growth capacity of principal neuron is significantly greater than interneurons. Then we use micro-contact printing to remove the targets in the cultured environment, results show that the axon growth capacity of interneurons can elevate a great extent to the level of principal neurons.

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