Abstract
The main aim of this thesis has been to evaluate the role of acetylcholine, specifically its muscarinic receptors, on learning and memory processes of different olfactory memory tasks. For this reason, we have investigated the effects of intracerebral infusions of scopolamine, which is a competitive muscarinic receptor antagonist, in three different brain regions, prelimbic cortex (PLC), ventral hippocampus (vHPC) and basolateral amygdala (BLA), on acquisition and/or consolidation processes of two different olfactory paradigms, the Odor Discrimination Task (ODT), a simple associative task which is rapidly acquired, and the Social Transmission of Food Preference (STFP), a relational-type associative task.In our first experiment, we observed that muscarinic receptors blockade in PLC immediately before DSO training, although it did not impair task acquisition, impaired its retention 24 hours after scopolamine infusion. We thought this could be due to the effects of scopolamine on memory formation processes instead of on olfactory stimuli initial codification. To test this hypothesis we carried out a second experiment in which muscarinic receptor blockade was made immediately or one hour post-training. The results of this study showed that such a blockade generated an important ODT retention deficit when it was made immediately after the training session, but not if it was made one hour after training. These data demonstrated that muscarinic transmission in PLC was critical for ODT early consolidation, and not for its late consolidation phases.
In order to clarify if this muscarinic regulation of CPL was exclusive only for one olfactory task or not, we assessed these receptors involvement on memory consolidation processes of another olfactory and naturalistic task, the STFP. In this context, our results showed a relevant impairment of food preference test made 24 hours after social interaction, due to immediately post-training scopolamine infusion. Therefore, PLC muscarinic transmission would have a more widespread role on olfactory memory consolidation processes.
To investigate if muscarinic receptors are involved in STFP memory consolidation in another brain region, we assessed the same post-training muscarinic receptor blockade with scopolamine of the vHPC, on STFP consolidation, because it is well known STFP is an hippocampal-dependent task. The results of this third experiment indicated a moderate impairment of STFP consolidation but not a totally interruption, as it was seen with PLC muscarinic receptors blockade.
Finally, we decided to study a third cholinergic region that has been extensively involved on olfactory memory and which has been controversially implicated in STFP, the BLA. In this last experiment, scopolamine infusion was made immediately before social interaction, and its results showed an important impairment of food preference test, possibly acting on codification or association of olfactory stimuli present in social interaction session or in initial consolidation processes.
In conclusion, data obtained from these experiments confirm and extend the role of cholinergic system on acquisition and consolidation of two olfactory memory tasks, through its muscarinic receptors activation. Currend findings, also indicate a possible neuronal pathway for olfactory memory, where PLC, vHPC and BLA could be interacting with some other brain regions, for codification, consolidation and retrieval of olfactory memory.
| Date of Award | 2 Feb 2009 |
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| Original language | Catalan |
| Awarding Institution |
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| Supervisor | Margarita Marti Nicolovius (Director) & Ana Maria Vale Martinez (Director) |