Nishino Hiroshi, Watanabe Hidehiro, Kamimura Itsuro, Yokohari Fumio, Mizunami Makoto
Research Institute for Electronic Science, Hokkaido University, Sapporo 060-0812, Japan.
Faculty of Science, Fukuoka University, Fukuoka 814-0180, Japan.
Neurosci Lett. 2015 May 19;595:35-40. doi: 10.1016/j.neulet.2015.04.006. Epub 2015 Apr 4.
In contrast to visual, auditory, taste, and mechanosensory neuropils, in which sensory afferents are topographically organized on the basis of their peripheral soma locations, axons of cognate sensory neurons from different locations of the olfactory sense organ converge onto a small spherical neuropil (glomerulus) in the first-order olfactory center. In the cockroach Periplaneta americana, sex pheromone-sensitive afferents with somata in the antero-dorsal and postero-ventral surfaces of a long whip-like antenna are biased toward the anterior and posterior regions of a macroglomerulus, respectively. In each region, afferents with somata in the more proximal antenna project to more proximal region, relative to the axonal entry points. However, precise topography of afferents in the macroglomerulus has remained unknown. Using single and multiple neuronal stainings, we showed that afferents arising from anterior, dorsal, ventral and posterior surfaces of the proximal regions of an antenna were biased progressively from the anterior to posterior region of the macroglomerulus, reflecting chiasmatic axonal re-arrangements that occur immediately before entering the antennal lobe. Morphologies of individual afferents originating from the proximal antenna matched results of mass neuronal stainings, but their three-dimensional origins in the antenna were hardly predictable on the basis of the projection patterns. Such projection biases made by neuronal populations differ from strict somatotopic projections of antennal mechanosensory neurons in the same species, suggesting a unique sensory mechanism to process information about odor location and direction on a single antenna.
与视觉、听觉、味觉和机械感觉神经纤维网不同，在这些神经纤维网中，感觉传入神经根据其外周躯体位置进行拓扑组织，来自嗅觉感觉器官不同位置的同源感觉神经元的轴突汇聚到一级嗅觉中枢的一个小球形神经纤维网（glomerulus）中。在美洲大蠊中，躯体位于长鞭状触角前背和后腹表面的性信息素敏感传入神经分别偏向一个大glomerulus的前部和后部区域。在每个区域，躯体位于触角更近端的传入神经相对于轴突进入点投射到更近端的区域。然而，大glomerulus中传入神经的精确拓扑结构仍然未知。通过单神经元和多神经元染色，我们发现来自触角近端区域前、背、腹和后表面的传入神经从大glomerulus的前部到后部区域逐渐偏向，这反映了在进入触角叶之前立即发生的交叉轴突重排。来自近端触角的单个传入神经的形态与大量神经元染色的结果相符，但根据投射模式很难预测它们在触角中的三维起源。神经元群体产生的这种投射偏向不同于同一物种中触角机械感觉神经元的严格躯体定位投射，这表明存在一种独特的感觉机制来处理关于单个触角上气味位置和方向的信息。
