Sandeman R E, Watson A H, Sandeman D C
School of Biological Science, University of New South Wales, Kensington, Australia.
J Comp Neurol. 1995 Oct 30;361(4):617-32. doi: 10.1002/cne.903610406.
The olfactory and accessory lobes in the crayfish are large spherical neuropils found on each side of its brain. The olfactory lobes receive the afferent axons of chemoreceptors that are located along the outer branches of the biramous first antennae. The accessory lobes receive a large input from interneurons whose axons lie in the deutocerebral commissure. A pair of large serotonergic neurons (the dorsal giant neurons) branch unilaterally in the accessory and olfactory lobes of each side. From physiological recordings, it has been proposed that the deutocerebral commissure interneurons synapse with elements in the accessory lobes that in turn connect to the dorsal giant neuron. It has also been proposed that the dorsal giant neuron is activated by inputs in the accessory lobe and that its output is in the olfactory lobe. This ultrastructural study tests this hypotheses by examining the polarity of synaptic terminals on dorsal giant neurons and deutocerebral interneurons that have been filled with neurobiotin. In double-labelled preparations, we found the deutocerebral interneurons to be presynaptic to elements in the accessory lobes, but none of these postsynaptic elements was identifiable as the dorsal giant neuron. The dorsal giant neurons receive many more synaptic inputs in the accessory lobes than in the olfactory lobe. Very few giant serotonin neuron output synapses were found in either lobe.
小龙虾的嗅觉叶和副叶是位于其脑两侧的大的球形神经纤维网。嗅觉叶接收位于双分支第一触角外分支上的化学感受器的传入轴突。副叶接收来自轴突位于中脑连合处的中间神经元的大量输入。一对大的5-羟色胺能神经元（背侧巨神经元）在每一侧的副叶和嗅觉叶单侧分支。根据生理学记录，有人提出中脑连合中间神经元与副叶中的元件形成突触，这些元件进而连接到背侧巨神经元。也有人提出背侧巨神经元由副叶中的输入激活，并且其输出在嗅觉叶。这项超微结构研究通过检查用神经生物素填充的背侧巨神经元和中脑中间神经元上突触终末的极性来检验这一假设。在双标记制剂中，我们发现中脑中间神经元是副叶中元件的突触前神经元，但这些突触后元件中没有一个可被识别为背侧巨神经元。背侧巨神经元在副叶中比在嗅觉叶中接收更多的突触输入。在这两个叶中都很少发现巨5-羟色胺能神经元输出突触。
