Neuronal organization of the feeding behavior of the black blowfly, Phormia regina Meigen
Abstract
Behavioral pharmacological studies in the black blowfly, Phormia regina Meigen, using the biogenic amine depleters D-amphetamine or reserpine indicated that unlike the tarsal taste threshold or meal size regulation, labellar taste thresholds are unaffected by drug treatment. The nine motoneurons involved in the extension, ingestion and retraction phases of feeding motor program were mapped using cobalt backfill techniques. The processes fall into three major morphological classes. First, the ingestion motoneurons (cibarial dilator and the gracilis), are found in the anterior portion of the tritocerebrum and the dorsal subesophageal ganglion (SEG). Secondly, the labellar lobe spreading motoneuron, the retractor furca, is found in the ventral SEG, with ipsilateral processes approaching midline. Lastly, the extension (protractor fulcrum, extensor haustellum and the adductor of the apodemes) and retraction motoneurons (retractor rostrum, accessory retractor rostrum, flexor haustellum) are found posteriorly and laterally in the ventral SEG, typically with processes in the contralateral neuropil. The findings in P. regina Meigen were repeated and subsequently confirmed in Calliphora vicina Robineau-Desvoidy. Selected motoneurons were backfilled using Lucifer yellow CH or cobaltous chloride and processed for 5-HT immunocytochemistry. The motoneurons were all found to have their processes in regions of the neuropil containing few 5-HT immunoreactive (5-HTir) processes. However, backfills of the recurrent nerve with Lucifer yellow CH did identify some processes that overlapped spatially with the 5-HTir termini in the anterior tritocerebrum, lateral to the esophageal foramen. Behavioral pharmacological studies on meal size regulation indicated that injection of 5-HT 30 min following injection of D-amphetamine returned meal sizes to normal. Electrophysiological studies with D-amphetamine-treated flies demonstrated that post-injection of 5-HT prevented the D-amphetamine related prolongation of firing of the protractor fulcrum and the cibarial dilators and avoided the delay in the firing of the retractor rostrum. Based upon these findings the effects of 5-HT on feeding could be associated with that portion of the tritocerebral neuropil in which the stretch receptors of the recurrent nerve terminate. A model accounting for the effects of 5-HTir neurons on feeding was presented.
Degree
Ph.D.
Advisors
Murdock, Purdue University.
Subject Area
Entomology|Neurology|Anatomy & physiology|Animals
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