Department of Pharmacology, Nihon University School of Dentistry, 1-8-13 Kanda-Surugadai, Chiyoda-ku, Tokyo 101-8310, Japan.
Neurobiol Learn Mem. 2011 Oct;96(3):468-78. doi: 10.1016/j.nlm.2011.07.003. Epub 2011 Aug 9.
Long-term potentiation (LTP) of the gustatory cortex (GC), a part of the insular cortex (IC) around the middle cerebral artery, is a key process of gustatory learning and memory, including conditioned taste aversion learning. The rostral (rGC) and caudal GC (cGC) process different tastes; the rGC responds to hedonic and the cGC responds to aversive tastes. However, plastic changes of spatial interaction of excitatory propagation between the rGC and cGC remain unknown. The present study aimed to elucidate spatiotemporal profiles of excitatory propagation, induced by electrical stimulation (five train pulses) of the rGC/cGC before and after LTP induction, using in vivo optical imaging with a voltage-sensitive dye. We demonstrated that tetanic stimulation of the cGC induced long-lasting expansion of the excitation responding to five train stimulation of the cGC, and an increase in amplitude of optical signals in the IC. Excitatory propagation after LTP induction spread preferentially toward the rostral IC: the length constant (λ) of excitation, obtained by fitting optical signals with a monoexponential curve, was increased to 121.9% in the rostral direction, whereas λ for the caudal, dorsal, and ventral directions were 48.9%, 44.2%, and 62.5%, respectively. LTP induction was prevented by pre-application of D-APV, an NMDA receptor antagonist, or atropine, a muscarinic receptor antagonist, to the cortical surface. In contrast, rGC stimulation induced only slight LTP without direction preference. Considering the different roles of the rGC and cGC in gustatory processing, these characteristic patterns of LTP in the GC may be involved in a mechanism underlying conversion of palatability.
味觉皮层（GC）的长时程增强（LTP）是味觉学习和记忆的关键过程，包括条件性味觉厌恶学习。大脑中动脉周围的岛叶皮层（IC）的一部分GC 分为前部（rGC）和后部 GC（cGC），两者处理不同的味道；rGC 对愉悦味道有反应，cGC 对厌恶味道有反应。然而，rGC 和 cGC 之间兴奋性传播的空间相互作用的可塑性变化仍不清楚。本研究旨在使用带电压敏感染料的活体光学成像来阐明 rGC/cGC 电刺激（五次脉冲串）前后兴奋性传播的时空特征。我们证明了 cGC 的强直刺激诱导了对 cGC 的五次脉冲串刺激的长时程扩展的兴奋，并且 IC 中的光学信号幅度增加。LTP 诱导后的兴奋性传播优先向 rGC 扩展：用单指数曲线拟合光学信号得到的兴奋长度常数（λ）在 rGC 方向增加到 121.9%，而 rGC 的 λ 对于后、背和腹方向分别为 48.9%、44.2%和 62.5%。NMDA 受体拮抗剂 D-APV 或毒蕈碱受体拮抗剂阿托品在皮层表面的预应用可防止 LTP 诱导。相比之下，rGC 刺激仅引起轻微的 LTP，没有方向偏好。考虑到 rGC 和 cGC 在味觉处理中的不同作用，GC 中的这种 LTP 特征模式可能涉及味觉可接受性转换的机制。
