Okutani Fumino, Zhang Jing-Ji, Otsuka Tomoko, Yagi Fumio, Kaba Hideto
Department of Physiology, Kochi Medical School, Nankoku, Kochi 783-8505, Japan.
Eur J Neurosci. 2003 Oct;18(7):2031-6. doi: 10.1046/j.1460-9568.2003.02894.x.
After training with an odour paired with foot shock on postnatal day 11, rat pups show an aversion to the odour in testing on postnatal day 12. The mechanisms underlying this aversive olfactory learning involve disinhibition of mitral/tufted cells in the olfactory bulb by the somatosensory stimulation-induced activation of centrifugal noradrenergic fibres originating in the locus coeruleus. The activity of mitral/tufted cells is regulated through gamma-aminobutyric acidA (GABA(A)) receptors in the external plexiform layer and GABA(B) receptors in the glomerular layer. We have previously presented that aversive olfactory learning in young rats is modulated through GABA(A) receptors in the olfactory bulb. In the present study we examined the consequence of manipulating GABA(B) receptors in the olfactory bulb during training. Baclofen, a GABA(B) receptor agonist when infused into the olfactory bulb during the pairing of an odour with foot shock, prevented aversive olfactory learning in a dose-dependent manner. Infusion of saclofen, a GABA(B) receptor antagonist, during training with a citral odour in the absence of foot shock produced aversive responses not only to the odour, but also to strange odours (benzaldehyde and vanillin) not previously presented. Such olfactory aversions were observed even if saclofen was infused without odour exposure. These results suggest that olfactory learning in young rats is modulated through GABA(B) receptors in the olfactory bulb.
在出生后第11天将气味与足部电击配对进行训练后，幼鼠在出生后第12天的测试中表现出对该气味的厌恶。这种厌恶嗅觉学习的潜在机制包括，源自蓝斑的离心去甲肾上腺素能纤维通过体感刺激诱导激活，从而对嗅球中的二尖瓣/簇状细胞进行去抑制。二尖瓣/簇状细胞的活动通过外丛状层中的γ-氨基丁酸A（GABA(A)）受体和肾小球层中的GABA(B)受体进行调节。我们之前提出，幼鼠的厌恶嗅觉学习是通过嗅球中的GABA(A)受体进行调节的。在本研究中，我们研究了在训练期间操纵嗅球中GABA(B)受体的后果。巴氯芬是一种GABA(B)受体激动剂，在将气味与足部电击配对时注入嗅球，会以剂量依赖的方式阻止厌恶嗅觉学习。在没有足部电击的情况下，用柠檬醛气味进行训练时注入GABA(B)受体拮抗剂沙氯芬，不仅会使幼鼠对该气味产生厌恶反应，还会对之前未出现过的陌生气味（苯甲醛和香草醛）产生厌恶反应。即使在没有气味暴露的情况下注入沙氯芬，也会观察到这种嗅觉厌恶。这些结果表明，幼鼠的嗅觉学习是通过嗅球中的GABA(B)受体进行调节的。
