RWTH Aachen, Institut für Biologie II (Zoologie), Abteilung für Entwicklungsbiologie und Morphologie der Tiere, Helmertweg 3, Aachen, D-52074, Germany.
Front Zool. 2013 Sep 10;10(1):54. doi: 10.1186/1742-9994-10-54.
The great majority of afferent neurons of insect legs project into their segmental ganglion. Intersegmental projections are rare and are only formed by sense organs associated with the basal joints of the legs. Such intersegmental projections never ascend as far as the brain and they form extensive ramifications within thoracic ganglia. A few afferents of chordotonal organs of the subcoxal joints ascend as far as the suboesophageal ganglion.
We describe novel afferent neurons in distal segments of locust legs that project directly into the brain without forming ramifications in other ganglia. In the brain, the fibres terminate with characteristic terminals in a small neuropile previously named the superficial ventral inferior protocerebrum. The somata of these neurons are located in the tibiae and tarsi of all legs and they are located within branches of peripheral nerves, or closely associated with such branches. They are not associated with any accessory structures such as tendons or connective tissue strands as typical for insect internal mechanoreceptors such as chordotonal organs or stretch receptors. Morphologically they show great similarity to certain insect infrared receptors.We could not observe projections into the superficial ventral inferior protocerebrum after staining mandibular or labial nerves, but we confirm previous studies that showed projections into the same brain neuropile after staining maxillary and antennal nerves, indicating that most likely similar neurons are present in these appendages also.
Because of their location deep within the lumen of appendages the function of these neurons as infrared receptors is unlikely. Their projection pattern and other morphological features indicate that the neurons convey information about an internal physiological parameter directly into a special brain neuropile. We discuss their possible function as thermoreceptors.
昆虫腿部的绝大多数传入神经元都投射到它们的节段神经节中。节间投射很少见，仅由与腿部基关节相关的感觉器官形成。这些节间投射从未像大脑那样上升，而是在胸神经节中形成广泛的分支。一些亚关节的音叉感觉器官的传入神经纤维上升到食管下神经节。
我们描述了直翅目腿部远端节段的新型传入神经元，它们直接投射到大脑，而不在其他神经节中形成分支。在大脑中，纤维在一个名为浅腹下原脑的小神经球中以特征性终末终止。这些神经元的体位于所有腿部的胫骨和跗骨中，位于周围神经的分支内或与之密切相关。它们与任何附属结构（如肌腱或结缔组织束）无关，而典型的昆虫内部机械感受器（如音叉感受器或拉伸感受器）则具有这些结构。从形态上看，它们与某些昆虫红外感受器非常相似。我们在染色下颌或唇神经后无法观察到向浅腹下原脑的投射，但我们证实了先前的研究，即染色上颌和触角神经后向同一脑神经球投射，表明很可能在这些附肢中也存在类似的神经元。
由于它们位于附肢管腔深处，这些神经元作为红外感受器的功能不太可能。它们的投射模式和其他形态特征表明，神经元将关于内部生理参数的信息直接传递到特殊的脑神经球中。我们讨论了它们作为热敏感受器的可能功能。
