Wachowiak Matt, McGann John P, Heyward Philip M, Shao Zuoyi, Puche Adam C, Shipley Michael T
Department of Biology, Boston University, MA 02215, USA.
J Neurophysiol. 2005 Oct;94(4):2700-12. doi: 10.1152/jn.00286.2005. Epub 2005 May 25.
We investigated the cellular mechanism underlying presynaptic regulation of olfactory receptor neuron (ORN) input to the mouse olfactory bulb using optical-imaging techniques that selectively report activity in the ORN presynaptic terminal. First, we loaded ORNs with calcium-sensitive dye and imaged stimulus-evoked calcium influx in a slice preparation. Single olfactory nerve shocks evoked rapid fluorescence increases that were largely blocked by the N-type calcium channel blocker omega-conotoxin GVIA. Paired shocks revealed a long-lasting suppression of calcium influx with approximately 40% suppression at 400-ms interstimulus intervals and a recovery time constant of approximately 450 ms. Blocking activation of postsynaptic olfactory bulb neurons with APV/CNQX reduced this suppression. The GABA(B) receptor agonist baclofen inhibited calcium influx, whereas GABA(B) antagonists reduced paired-pulse suppression without affecting the response to the conditioning pulse. We also imaged transmitter release directly using a mouse line that expresses synaptopHluorin selectively in ORNs. We found that the relationship between calcium influx and transmitter release was superlinear and that paired-pulse suppression of transmitter release was reduced, but not eliminated, by APV/CNQX and GABA(B) antagonists. These results demonstrate that primary olfactory input to the CNS can be presynaptically regulated by GABAergic interneurons and show that one major intracellular pathway for this regulation is via the suppression of calcium influx through N-type calcium channels in the presynaptic terminal. This mechanism is unique among primary sensory afferents.
我们使用光学成像技术研究了小鼠嗅球中嗅觉受体神经元（ORN）输入的突触前调节的细胞机制，该技术可选择性地报告ORN突触前终末的活动。首先，我们用钙敏染料加载ORN，并在脑片标本中对刺激诱发的钙内流进行成像。单个嗅神经电刺激引起快速的荧光增加，这在很大程度上被N型钙通道阻滞剂ω-芋螺毒素GVIA所阻断。成对电刺激显示钙内流受到长期抑制，在400毫秒的刺激间隔下约有40%的抑制率，恢复时间常数约为450毫秒。用APV/CNQX阻断突触后嗅球神经元的激活可减少这种抑制。GABA(B)受体激动剂巴氯芬抑制钙内流，而GABA(B)拮抗剂可减少成对脉冲抑制，且不影响对条件刺激脉冲的反应。我们还使用在ORN中选择性表达突触pHluorin的小鼠品系直接对神经递质释放进行成像。我们发现钙内流与神经递质释放之间的关系是超线性的，并且APV/CNQX和GABA(B)拮抗剂可减少但不能消除神经递质释放的成对脉冲抑制。这些结果表明，中枢神经系统的初级嗅觉输入可由GABA能中间神经元进行突触前调节，并表明这种调节的一个主要细胞内途径是通过抑制突触前终末中N型钙通道的钙内流。这种机制在初级感觉传入神经中是独特的。
