Distribution of tachykinin-related neuropeptide in the developing central nervous system of the moth Spodoptera litura

Neuropeptides with similarities to vertebrate tachykinins, designated tachykinin-related peptides (TRPs), have been identified in several insect species. In this investigation we have utilized an antiserum raised to one of the locust TRPs, locustatachykinin-I (LomTK-I), to determine the distribution pattern of LomTK-like immunoreactive (LTKLI) neurons in the developing nervous system of the moth Spodoptera litura. A number of LTKLI neurons could be followed from the larval to the adult nervous system: a set of median neurosecretory cells (MNCs) in the brain, a pair of brain descending neurons and a few sets on neurons in the ventral nerve cord. The distribution of LTKLI neurons in the adult brain is very similar to that seen in other insect species with prominent arborizations in the central body, antennal lobes, mushroom body calyces, optic lobe neuropils and other distinct neuropil areas in the protocerebrum and tritocerebrum. A new finding is the presence of LTKLI neurosecretory cells with axon terminals in the anterior aorta and corpora cardiaca, suggesting for the first time a neurohormonal role of tachykinin-related peptide(s) in insects. During postembryonic development the number of LTKLI neurons in the ventral nerve cord decreases somewhat, whereas the number increases in the brain. Thus the functional roles of TRPs may change to some extent during development.     

Terminal Schwann cells guide the reinnervation of muscle after nerve injury

Schwann cells and axons labeled by transgene-encoded, fluorescent proteins can be repeatedly imaged in living mice to observe the reinnervation of neuromuscular junctions. Axons typically return to denervated junctions by growing along Schwann cells contained in the old nerve sheaths or “Schwann cell tubes”. These axons then commonly “escape” the synaptic sites by growing along the Schwann cell processes extended during the period of denervation. These “escaped fibers” grow to innervate adjacent synaptic sites along Schwann cells bridging these sites. Within the synaptic site, Schwann cells, originally positioned above the synaptic site continue to cover the acetylcholine receptors (AChRs) immediately following denervation, but gradually vacate portions of this site. When regenerating axons return, they first deploy along the Schwann cells and ignore sites of AChRs vacated by Schwann cells. In many cases these vacated sites are never reinnervated and are ultimately lost. Following partial denervation, Schwann cells grow in an apparently tropic fashion from denervated to nearby innervated synaptic sites and serve as the substrates for nerve sprouting. These experiments show that Schwann cells provide pathways that stimulate axon growth and insure the rapid reinnervation of denervated or partially denervated muscles.