Characterization of an Inhibitory Pathway to Feeding Command Neurons in the Brain of Pleurobranchaea Californica and an Analysis of the Changes in This Pathway That Occur as a Result of Food-Avoidance Conditioning

126 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1983.This thesis consists of a study of neural plasticity as it occurs in the brain of an invertebrate. An inhibitory pathway in the brain of the marine mollusc, Pleurobranchaea californica which influences the activity of the feeding command neurons, the paracerebral neurons (PCNs) is described and the pathway's role in feeding is analyzed. A study of the location of the oscillators which initiate and control feeding in this animal is described. The changes that occur in neurons of the inhibitory pathway as a result of food avoidance conditioning are described. The inhibitory pathway consists of 3 serially connected interneurons. The first population, the Interneuron 1s (Int-1s), mono-synaptically inhibits the PCNs. A second population, the Interneuron 2s (Int-2s) excite the Int-1s. A third population, the Interneuron 3s (Int-3s), mono-synaptically excites the Int-2s. The Int-1s and Int-2s are part of the feeding oscillator. The Int-1s and Int-2s are phasically active during the retraction phase of feeding. The Int-2s are a site of convergent information, receiving input from other Int-2s, Int-1s, mono-synaptic sensory input from the periphery, and ascending input from the buccal ganglion. The Int-2s are a gate for the feeding behavior. Stimulated activity in a single Int-2 can entirely suppress the rhythmic motor activity of the feeding network. Evidence is described for the presence of an oscillator which governs the initiation of feeding. Using a brain-oral veil preparation, rhythmic motor activity was induced in quiescent preparations by application of food to the sensory apparatus (oral veil, rhinophores). This activity continued when all peripheral nerves were severed. Cyclic activity was recorded from both sides of the brain and was phase-locked. The Int-1s and Int-2s were found to generate the tonic inhibition of the PCNs observed in food avoidance conditioned animals. The Int-1s become tonically active as a result of conditioning, but no membrane properties appeared altered. The Int-2s also become tonically active in conditioned animals and exhibit altered membrane responses. The Int-2s exhibit an enhanced depolarizing after potential (DAP) which may underlie this tonic activity. The DAP is thought to be intrinsic to the Int-2, and not caused by changes in sensory input. Possible mechanisms which underlie the DAP are discussed. This is the first report of changes that occur as a result of conditioning at an interneuron site.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD