Olfaction in Olfactory Bulbectomized Rats

鼻子中的感觉细胞对气味做出反应，并将信号发送回大脑的嗅球。这些细胞只能存活几周，当它们死亡时，它们会被嗅觉组织中生发细胞层的成熟细胞所取代。成熟的细胞将它们的轴突延伸到嗅球中，在那里它们取代了濒临死亡的神经元的轴突进行的接触。嗅觉感受器上皮以这种方式自我重建的能力是独一无二的，因为如果其他感觉系统中的神经元死亡，它们不会被取代。特别有趣的是，如果去除嗅球，成熟感觉神经元的轴突将继续生长，直到到达脑组织。然后，他们将与正常情况下不接受嗅觉感受器细胞输入的神经元进行突触接触。虽然这一神经可塑性的显著例子已经在解剖学研究中得到了证明，但目前还不清楚这些新的突触接触是否可以被大脑用来支持嗅觉。我们建议通过移除新生大鼠的嗅球来研究这个问题，并测试它们成年后检测和辨别气味的能力。手术后的大鼠将在精密嗅觉仪设备中接受训练，以确定它们的气味敏感度，以及它们是否能够辨别气味。行为结果将与对起源于嗅球的前脑连接的解剖学分析相关联。一个积极的结果将为大脑利用新信息并将其转化为有意识的感觉信号的迄今未被识别的能力提供证据。

Sensory cells in the nose respond to odors and send signals back to the olfactory bulb of the brain. These cells live for only a few weeks and, when they die, they are replaced by maturing cells from a germinal cell layer in the olfactory tissue. The maturing cells extend their axons into the olfactory bulb where they replace the contacts made by the axons of the dying neuron. The ability of the olfactory receptor epithelium to reconstitute itself in this fashion is unique because neurons in other sensory systems are not replaced if they die. Of particular interest is the fact that if the olfactory bulb is removed, the axons of maturing sensory neurons will continue to grow until they reach brain tissue. They will then make synaptic contact with neurons that do not normally receive inputs from olfactory receptor cells. While this remarkable example of neural plasticity has been demonstrated in anatomicalstudies, it remains unclear whether these new synaptic contacts can be used by the brain to support the sense of smell. We propose to examine this issue by removing the olfactory bulb in neonatal rats and testing their ability to detect and discriminate odors when they are adults. Operated rats will be trained in a precision olfactometer device to determine their odor sensitivity and whether they can discriminate among odors. Behavioral results will be correlated with an anatomical analysis of forebrain connections originating from the olfactory bulb. A positive outcome would provide evidence for a hitherto unrecognized ability of the brain to utilize novel information and translate it into conscious sensory signal