Neurons of self-defence: neuronal innervation of the exocrine defence glands in stick insects. Issue 1 (December 2015)

• Record Type: Journal Article
• Authors: Stolz, Konrad; von Bredow, Christoph-Rüdiger; von Bredow, Yvette; Lakes-Harlan, Reinhard; Trenczek, Tina; Strauß, Johannes
• Is Part Of: Frontiers in zoology. Volume 12:Issue 1(2015)
• Page Start: 1
• Page End: 16
• Publication Date: 2015-12
• Subjects: Insect -- Neuroanatomy -- Neuronal innervation -- Defence glands -- Stick insect -- Neuronal tracing -- Motoneuron -- Defence behaviour; Zoology -- Periodicals; 590.5
• DOI: 10.1186/s12983-015-0122-0
• Languages: English
• ISSNs: 1742-9994

Abstract

Abstract Background Stick insects (Phasmatodea) use repellent chemical substances (allomones) for defence which are released from so-called defence glands in the prothorax. These glands differ in size between species, and are under neuronal control from the CNS. The detailed neural innervation and possible differences between species are not studied so far. Using axonal tracing, the neuronal innervation is investigated comparing four species. The aim is to document the complexity of defence gland innervation in peripheral nerves and central motoneurons in stick insects. Results In the species studied here, the defence gland is innervated by the intersegmental nerve complex (ISN) which is formed by three nerves from the prothoracic (T1) and suboesophageal ganglion (SOG), as well as a distinct suboesophageal nerve (Nervus anterior of the suboesophageal ganglion). InCarausius morosus andSipyloidea sipylus, axonal tracing confirmed an innervation of the defence glands by thisN. anterior SOG as well asN. anterior T1 andN. posterior SOG from the intersegmental nerve complex. InPeruphasma schultei, which has rather large defence glands, only the innervation by theN. anterior SOG was documented by axonal tracing. In the central nervous system of all species, 3-4 neuron types are identified by axonal tracing which send axons in theN. anterior SOG likely innervating the defence gland as well as adjacent muscles. These neurons are mainly suboesophageal neurons with one intersegmental neuron located in the prothoracic ganglion. The neuron types are conserved in the species studied, but the combination of neuron types is not identical. In addition, the central nervous system inS. sipylus contains one suboesophageal and one prothoracic neuron type with axons in the intersegmental nerve complex contacting the defence gland. Conclusions Axonal tracing shows a very complex innervation pattern of the defence glands of Phasmatodea which contains different neurons in different nerves from two adjacent body segments. The gland size correlates to the size of a neuron soma in the suboesophageal ganglion, which likely controls gland contraction. InP. schultei, the innervation pattern appears simplified to the anterior suboesophageal nerve. Hence, some evolutionary changes are notable in a conserved neuronal network.