Nickell W T, Behbehani M M, Shipley M T
Department of Anatomy, University of Cincinnati, College of Medicine, OH 45267-0521.
Brain Res Bull. 1994;35(2):119-23. doi: 10.1016/0361-9230(94)90091-4.
The GABAB agonist baclofen blocks transmission from the olfactory nerve to second order neurons in the frog olfactory bulb, and GABAB receptors in the rat olfactory bulb are selectively located in the glomerular layer. A reasonable hypothesis, therefore, is that inhibition in the glomerular layer is mediated, at least in part, by GABAB receptors. Here, we investigated the role of GABAB receptors in regulating the responses of mitral cells to activation of the olfactory nerve in the rat. Topical application of baclofen to the surface of the rat olfactory bulb reduced the amplitude of field potentials evoked by olfactory nerve stimulation (orthodromic response). Baclofen reduced the orthodromic response in a dose-dependent manner but the drug had no effect on the field potential evoked by antidromic activation of mitral cell axons (antidromic response). Baclofen also reduced olfactory nerve-evoked responses of mitral cells in an olfactory bulb slice preparation. The pharmacological specificity of the inhibition was confirmed by showing that the GABAB antagonist, CGP 55845A, blocked the inhibitory action of baclofen. These results suggest that transmission from olfactory nerve terminals to second order neurons is negatively regulated by periglomerular GABAergic interneurons; this inhibition is mediated, at least partially, by GABAB receptors.
GABAB激动剂巴氯芬可阻断青蛙嗅球中从嗅神经到二级神经元的信号传递，且大鼠嗅球中的GABAB受体选择性地位于肾小球层。因此，一个合理的假设是，肾小球层中的抑制作用至少部分是由GABAB受体介导的。在此，我们研究了GABAB受体在调节大鼠嗅球中二尖瓣细胞对嗅神经激活反应中的作用。将巴氯芬局部应用于大鼠嗅球表面可降低嗅神经刺激诱发的场电位幅度（顺向反应）。巴氯芬以剂量依赖性方式降低顺向反应，但该药物对二尖瓣细胞轴突逆向激活诱发的场电位（逆向反应）没有影响。巴氯芬还可降低嗅球切片制备中二尖瓣细胞的嗅神经诱发反应。通过显示GABAB拮抗剂CGP 55845A可阻断巴氯芬的抑制作用，证实了抑制作用的药理学特异性。这些结果表明，从嗅神经末梢到二级神经元的信号传递受到肾小球周围GABA能中间神经元的负向调节；这种抑制作用至少部分是由GABAB受体介导的。
