Evolutionarily, olfaction is one of the oldest senses and pivotal for an individual's health and survival. The olfactory bulb (OB), as the first olfactory relay station in the brain, is known to heavily process sensory information. To adapt to an animal's needs, OB activity can be influenced by many factors either from within (intrinsic neuromodulation) or outside (extrinsic neuromodulation) the OB which include neurotransmitters, neuromodulators, hormones, and neuropeptides. Extrinsic sources seem to be of special importance as the OB receives massive efferent input from numerous brain centers even outweighing the sensory input from the nose. Here, we review neuromodulatory processes in the rodent OB from such extrinsic sources. We will discuss extrinsic neuromodulation according to points of origin, receptors involved, affected circuits, and changes in behavior. In the end, we give a brief outlook on potential future directions in research on neuromodulation in the OB.

中文翻译：

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啮齿动物嗅球的外在神经调节

从进化的角度来看，嗅觉是最古老的感官之一，对于个体的健康和生存至关重要。嗅球 (OB) 作为大脑中的第一个嗅觉中继站，众所周知，它会大量处理感官信息。为了适应动物的需求，OB 活性可能受到 OB 内部（内在神经调节）或外部（外在神经调节）的许多因素的影响，其中包括神经递质、神经调节剂、激素和神经肽。外源似乎特别重要，因为 OB 接收来自众多大脑中心的大量传出输入，甚至超过来自鼻子的感觉输入。在这里，我们回顾了啮齿动物 OB 中来自此类外源的神经调节过程。我们将根据起源点、涉及的受体、受影响的回路和行为变化来讨论外在神经调节。最后，我们对 OB 神经调节研究的未来潜在方向进行了简要展望。