Learned associations between rewarding stimuli and environmental cues which predict their availability play an important role in guiding behaviour. These learned associations are thought to be encoded by neuroadaptations in disperse sets of strongly activated neurons, termed neuronal ensembles, located throughout motivationally-relevant brain areas. However to date, the nature of the adaptations which occur selectively on neuronal ensembles encoding appetitive associative memories remain largely unknown. Using the Fos-GFP mouse, which expresses green fluorescent protein (GFP) in recently activated neurons, we investigated the intrinsic and synaptic excitability of neurons activated following exposure to stimuli associated with food (sucrose) or drug (cocaine) exposure. We observed that in the nucleus accumbens (NAc) shell, but not orbitofrontal cortex, neurons activated following exposure to a food-associated stimulus were more intrinsically excitable than surrounding, non-activated neurons. These neurons also demonstrated increased spontaneous excitatory transmission suggestive of potentiated synaptic strength. Following extinction of the food-cue association, NAc shell neurons activated following cue exposure were no longer more excitable than surrounding neurons. This suggests that the intrinsic excitability of striatal neurons activated by a food-associated cue is dynamically modulated by changes in associative strength. We also examined the intrinsic excitability of striatal neurons (including neurons in the NAc shell, core and dorsal striatum) activated by cocaine-associated stimuli. Interestingly, NAc shell neurons activated by cocaine-associated stimuli were not more excitable compared to the surrounding neurons regardless of extinction learning experience, possibly indicating differences between drug and food conditioning. Similar results were obtained for dorsal striatal neurons. However, NAc core neurons activated by cocaine-associated stimuli displayed an enhanced excitability which persisted following extinction, indicating that core and shell neuronal ensembles differentially encode the cocaine associative memories. Overall, by selectively recording from stimuli-activated neurons, this work reveals novel adaptations at the intrinsic and synaptic levels on neuronal ensembles following appetitive learning with both food and drug rewards.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:737656 |
| Date | January 2018 |
| Creators | Ziminski, Joseph |
| Publisher | University of Sussex |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://sro.sussex.ac.uk/id/eprint/74246/ |
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