Innervation patterns of metathoracic leg muscles in the grasshopper, Barytettix psolus, and their significance in posture, locomotion, and muscle maintenance
AdvisorArbas, Edmund A.
Strausfeld, Nicholas J.
MetadataShow full item record
PublisherThe University of Arizona.
RightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
AbstractGrasshoppers are able to spontaneously drop, or autotomize, their large metathoracic legs, at the joint between the second and third leg segments. Previous work demonstrated that in the grasshopper, Barytettix psolus, autotomy transneuronally induces atrophy in a group of six metathoracic muscles on the ipsilateral side. These muscles are neither damaged nor denervated by the loss of the leg. The experiments presented in this dissertation support and extend the earlier work by including twelve additional metathoracic muscles, one of which was discovered as a result of these studies. These experiments demonstrated that atrophy varied both between muscles, as well as between fibers within individual muscles. Some muscles degenerated uniformly, whereas others contained persisting fibers long after neighboring fibers degenerated. Extent of atrophy in each muscle was quantified by measurement of total protein content. Histochemical staining of myofibrillar ATPase activity in a subset of muscles indicated that slow type fibers comprised the majority of those persisting following autotomy. Immunohistochemical experiments suggested that persistance of muscle fibers was correlated with innervation both by motor neurons (MNs) containing proctolin-like immunoreactivity (PLI), and by an inhibitory MN containing gamma-aminobutyric acid (GABA)-like immunoreactivity (GLI). The distributions of PLI and GLI indicated that these two types of MNs innervate muscles in parallel. In an attempt to identify the proctolin-like substance, muscle extracts of fourteen muscles were purified by HPLC and subjected to bioassay for proctolin-like bioactivity (PLB). Nine muscles with PLI also contained PLB. These experiments support the presence of proctolin in muscles with PLI. Four out of the five muscles lacking PLI also contained PLB. It is likely that these muscles contain at least one bioactive peptide that is biochemically similar to proctolin. These experiments are the first to suggest the association of proctolin-like substances with the majority of leg muscles in any insect. My immunohistochemical data combined with the results of previous experiments on the functions of proctolinergic and GABAergic innervation suggest that proctolin or proctolin-like substances are commonly used to maintain postural tonus in metathoracic leg muscles during standing and locomotory activities.
Degree ProgramGraduate College