Christensen T A, Waldrop B R, Hildebrand J G
Arizona Research Laboratories, University of Arizona, Tucson 85721, USA.
Ann N Y Acad Sci. 1998 Nov 30;855:475-81. doi: 10.1111/j.1749-6632.1998.tb10608.x.
Mitral/tufted cells in the olfactory bulb and projection neurons (PNs) in the insect antennal lobe are involved in complex synaptic interactions with inhibitory interneurons to help shape their odor-evoked responses. In the moth Manduca sexta, both gamma-aminobutyric acid (GABA) and the GABAA receptor agonist muscimol hyperpolarize and lower input resistance in many PNs, often blocking ongoing spike traffic. The GABA response mimics a short-latency, chloride-mediated inhibitory postsynaptic potential (IPSP) evoked in PNs by electrical or odor stimulation of afferent inputs, and the classical GABAA receptor antagonist bicuculline methiodide (BMI) quickly and reversibly blocks this IPSP. Focal injection of BMI (100 microM) immediately preceding a GABA pulse blocks the hyperpolarization evoked by GABA, but a similar injection of BMI preceding an acetylcholine (ACh) pulse fails to block the depolarization evoked by ACh. Moreover, the temporal pattern of odor-evoked activity in moth PNs is also strongly and reversibly altered by BMI. Importantly, the temporal pattern of the response depends on the temporal characteristics of the stimulus: continuous stimulation evokes more complex, rhythmic responses, whereas a pulsatile stimulus can be copied with a discrete burst of spikes for each pulse. Collectively our results indicate that PNs in the moth antennal lobe possess GABA receptors that share certain characteristics in common with vertebrate GABAA receptors. These receptors are largely responsible for helping PNs integrate information about both the molecular features and the timing of olfactory input to the brain.
嗅球中的二尖瓣/簇状细胞以及昆虫触角叶中的投射神经元（PNs），参与了与抑制性中间神经元的复杂突触相互作用，以帮助塑造它们的气味诱发反应。在烟草天蛾中，γ-氨基丁酸（GABA）和GABAA受体激动剂蝇蕈醇都会使许多PNs发生超极化并降低输入电阻，常常阻断正在进行的峰电位传导。GABA反应模拟了通过传入输入的电刺激或气味刺激在PNs中诱发的短潜伏期、氯离子介导的抑制性突触后电位（IPSP），经典的GABAA受体拮抗剂甲基荷包牡丹碱（BMI）能快速且可逆地阻断这种IPSP。在GABA脉冲之前立即局部注射BMI（100微摩尔）可阻断GABA诱发的超极化，但在乙酰胆碱（ACh）脉冲之前进行类似的BMI注射则无法阻断ACh诱发的去极化。此外，BMI也会强烈且可逆地改变蛾类PNs中气味诱发活动的时间模式。重要的是，反应的时间模式取决于刺激的时间特征：持续刺激会诱发更复杂的节律性反应，而脉冲式刺激可以通过每个脉冲的离散峰电位爆发来复制。我们的研究结果共同表明，蛾类触角叶中的PNs拥有与脊椎动物GABAA受体具有某些共同特征的GABA受体。这些受体在很大程度上负责帮助PNs整合有关嗅觉输入到大脑的分子特征和时间的信息。
