Locust thoracic dorsal unpaired median (DUM) neurons
Year: 2011
Type: dissertation
Abstract: The unique group of insect specific dorsal/ventral unpaired median (DUM/VUM) neurons is the principal source of peripherally released octopamine (OA), which as a neuromodulator/-hormone acts on essentially all system levels by modifying e.g. muscle properties, metabolism and complex behaviours. In the locust Schistocerca gregaria, pterothoracic DUM neurons form functional subpopulations which are differentially recruited during specific motor tasks. This study investigates subgroup specific DUM neuron activation and elucidates the peripheral distribution of OA and its precursor tyramine (TA) with respect to its role as independent neuroactive substance. Following nerve stimulation of the tegula, a sensory organ at the wing base, intracellularly recorded "wing group" neurons, i.e. DUMDL, DUM 3 and DUM 3,4 neurons, in general were inhibited, whereas DUM 3,4,5 neurons were activated via a segmental polysynaptic pathway. Stimulation of the tritocerebral giant interneuron elicited likewise inhibitory responses in DUM 3 and DUM 3,4 neurons via polysynaptic connections, while DUM 1b neurons received excitatory input. These findings provide evidence of so far undescribed pathways and imply their functional relevance at the onset of and/or during flight. Since electrophysiological data imply pronounced inhibitory synaptic input to "wing group", but hardly to "leg group" neurons, the amount of putative inhibitory input sites to selected branches of DUM 3,4 and DUM 3,4,5 neurons was determined using immunocytochemistry and available neuron reconstruction tools. A greater surface area of DUM 3,4 neurons was covered by putative synaptic input sites, however, the inhibitory share of these contacts did not markedly differ from that of DUM 3,4,5 neurons. These data thus do not indicate a simple quantitative correlation. The flight steering muscle M85/114 was examined to elucidate the distribution pattern of OA and TA in the periphery. With the help of reliable antibodies, TA was shown to be exclusively co-localised with OA in all neuromodulatory varicosities examined. The comparison of individual boutons from control and differentially treated animals, which had experienced flight or were exposed to stress immediately before examination, indicated dynamic activity-dependent changes of OA and TA contents. In muscle mechanograms, TA increased twitch amplitude as well as contraction and relaxation rate of individual muscle twitches, but less effectively than OA. Since the TA effect was suppressed by the OA-receptor antagonist epinastine, specific TA release and the existence of specific TA- receptors at this peripheral location seems unlikely.
Author: Stocker, Bettina
Language: English
Subfield: Cellular and Molecular Neuroscience
Field: Neuroscience
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W1566074029