Huang Zhenbo, Thiebaud Nicolas, Fadool Debra Ann
Program in Neuroscience, The Florida State University, Tallahassee, FL, USA.
Department of Biological Science, The Florida State University, Tallahassee, FL, USA.
J Physiol. 2017 Jun 1;595(11):3515-3533. doi: 10.1113/JP273945. Epub 2017 Mar 31.
There are serotonergic projections to both the main (MOB) and the accessory olfactory bulb (AOB). Current-clamp experiments demonstrate that serotonergic afferents are largely excitatory for mitral cells (MCs) in the MOB where 5-HT receptors mediate a direct excitatory action. Serotonergic afferents are predominately inhibitory for MCs in the AOB. There are two types of inhibition: indirect inhibition mediated through the 5-HT receptors on GABAergic interneurons and direct inhibition via the 5-HT receptors on MCs. Differential 5-HT neuromodulation of MCs across the MOB and AOB could contribute to select behaviours such as olfactory learning or aggression.
Mitral cells (MCs) contained in the main (MOB) and accessory (AOB) olfactory bulb have distinct intrinsic membrane properties but the extent of neuromodulation across the two systems has not been widely explored. Herein, we investigated a widely distributed CNS modulator, serotonin (5-HT), for its ability to modulate the biophysical properties of MCs across the MOB and AOB, using an in vitro, brain slice approach in postnatal 15-30 day mice. In the MOB, 5-HT elicited three types of responses in 93% of 180 cells tested. Cells were either directly excited (70%), inhibited (10%) or showed a mixed response (13%)- first inhibition followed by excitation. In the AOB, 82% of 148 cells were inhibited with 18% of cells showing no response. Albeit located in parallel partitions of the olfactory system, 5-HT largely elicited MC excitation in the MOB while it evoked two different kinetic rates of MC inhibition in the AOB. Using a combination of pharmacological agents, we found that the MC excitatory responses in the MOB were mediated by 5-HT receptors through a direct activation. In comparison, 5-HT-evoked inhibitory responses in the AOB arose due to a polysynaptic, slow-onset inhibition attributed to 5-HT receptor activation exciting GABAergic interneurons. The second type of inhibition had a rapid onset as a result of direct inhibition mediated by the 5-HT class of receptors. The distinct serotonergic modulation of MCs between the MOB and AOB could provide a molecular basis for differential chemosensory behaviours driven by the brainstem raphe nuclei into these parallel systems.
存在向主嗅球（MOB）和副嗅球（AOB）的5-羟色胺能投射。电流钳实验表明，5-羟色胺能传入纤维对MOB中的二尖瓣细胞（MCs）大多具有兴奋性，其中5-羟色胺受体介导直接的兴奋作用。5-羟色胺能传入纤维对AOB中的MCs主要起抑制作用。有两种类型的抑制：通过GABA能中间神经元上的5-羟色胺受体介导的间接抑制和通过MCs上的5-羟色胺受体的直接抑制。MOB和AOB中MCs的5-羟色胺差异神经调节可能有助于选择诸如嗅觉学习或攻击等行为。
主嗅球（MOB）和副嗅球（AOB）中的二尖瓣细胞（MCs）具有不同的内在膜特性，但尚未广泛探索这两个系统间神经调节的程度。在此，我们使用出生后15至30天小鼠的体外脑片方法，研究了一种广泛分布的中枢神经系统调节剂5-羟色胺（5-HT）调节MOB和AOB中MCs生物物理特性的能力。在MOB中，5-HT在测试的180个细胞中的93%中引发了三种类型的反应。细胞要么被直接兴奋（70%）、抑制（10%），要么表现出混合反应（13%）——先是抑制，随后是兴奋。在AOB中，148个细胞中的82%被抑制，18%的细胞无反应。尽管位于嗅觉系统的平行分区中，但5-HT在MOB中大多引发MC兴奋，而在AOB中则诱发了两种不同动力学速率的MC抑制。使用多种药剂组合，我们发现MOB中MC的兴奋反应是由5-羟色胺受体通过直接激活介导的。相比之下，AOB中5-HT诱发的抑制反应是由于5-羟色胺受体激活兴奋GABA能中间神经元导致的多突触、起效缓慢的抑制。第二种抑制类型是由5-羟色胺类受体介导的直接抑制，起效迅速。MOB和AOB中MCs的5-羟色胺能调节差异可为脑干中缝核驱动至这些平行系统的不同化学感受行为提供分子基础。
