1. Lymnaea was the subject of an established behavioural conditioning paradigm where pairings of a neutral lip tactile stimulus (CS) and a sucrose food stimulus (US) results in a conditioned feeding response to the CS alone. The current objective was to dissect trained animals and examine electrophysiological changes in the feeding circuitry which may underlie this learning. 2. Naive subjects were used to confirm that US and CS responses in vivo persisted in vitro since this is a pre-requisite for survival of a learned memory trace. This required the development of a novel semi-intact preparation facilitating CS presentation and simultaneous access to the CNS. 3. The nature and function of the CS response was investigated using naive animals. Intracellular recordings revealed that the tactile CS evokes specific, consistent synaptic responses in identified feeding neurons. Extracellular recording techniques and anatomical investigations showed that these responses occurred through a direct pathway linking the lips to the feeding circuitry. A buccal neuron was characterized which showed lip tactile responses and supplied synaptic inputs to feeding neurons indicating that it was a second-order mechanosensory neuron involved in the CS pathway. 4. Animals trained using the behavioural conditioning paradigm were tested for conditioned responses and subsequently dissected~ Intracellular recording from specific identified feeding motoneurons revealed that CS presentation resulted in significant activation of the feeding network compared to control subjects. This activation was combined both with an increase in the amplitude of a specific synaptic input and an elevation in the extracellular spike activity recorded from a feeding-related connective. A neuronal mechanism to account for these findings is presented. 5. The role of motoneurons in the feeding circuit was reassessed. It is demonstrated, contrary to the current model, that muscular motoneurons have an important contribution during feeding rhythms through previously unreported electrotonic CPG connections.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:360541 |
| Date | January 1997 |
| Creators | Staras, Kevin |
| Publisher | University of Sussex |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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