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Abstract
The ability to recognize the novelty component of taste modality has an important survival value for animals. Consumption of a new taste, without hazardous consequence, leads to the formation of an incidental taste memory measured by increase in the preference for the given taste. The anterior portion of the insular cortex contains the main gustatory cortex (GC). It is strongly involved in saliency detection and deviation embedded in a stream of continuous stimuli. Biochemical, electmphysiological, and imaging studies suggest that the anterior part of the insular cortes serves as primary taste cortes.
Novel taste learning is associated with many biochemical changes in the GC which subserve taste memory consolidation in rodents, including changes in cholinergic activity, tyrosine phosphorylation of the NR2B subunit of the N-methyl D-aspartate receptors, activation of extracellular regulated kinase I/II (ERKI/II), and activation of the mTOR pathway.
Immediate eurly genes (IEG) are the first genes to be expressed following internal and external stimulation and are well known molecular markers for neuronal activation anil synaptic plasticity. IEG are used frequently to delineate active neummal populations, and may therefore be the link between changes in neuronal circuit activity and intra-cellular and molecular mechanisms.
For many brain systems the actual involvement of a particular structure in cognition is left right asymmetric, with a strong bias or greater involvement of one hemisphere: Lateralization and its behavioral expression are associated with motor, perceptual, and functional phenotypes found to be both correlated and necessary for normal brain function. Lateralization of nervous system observed throughout the animal kingdom, from netnaindes to humans. The degree lateralization can be measured by comparing the physiological responses in left and right hemisphere to the total response.
Specifically, while lateralization or brum asymmetry is a well-known phenomenon important for many cognitive functions, its involvement in memory formation at the molecular and circuit levels is almost unknown. In parallel, the temporal changes in cortical molecular machinery during memory consolidation require better quantitative and qualitative characterization In my thesis, I locused on the immediate early gene, activity regulated cytoskeleton associated protein (Arc/Arg3.1), which is frequently used as a marker of neuronal activation and synaptic plasticity and on general tramcriptional response to novel taste learning. We hypothesized that:
1. Differential transcription and translation of Arc/Arg). Iwill take place in the insalar cottes following novel taste learning
2. Differential regulation will occur for the temporal distribution of general gene response profile in the GC at the first hours following learning of a novel tusde, when compared to hydration related consequences.
First, we explored An Arg7. Iprotein expression in the different sub-regions of the GC focusing on its lell-right hemispherical distribution after novel tade leaming. In addition, we studied Arc Arg31 mRNA and the general gene transcription programs following drinking, focusing on changes that involve hydration and its consequence (changes in blood osmolarity, reward, arousal), novel taste learning, and the interaction between the two at the transcriptional level.
When we focused on the distribution of Arc/Arg3.1 protein expression in both hemispheres, we found that when left and right insular cortes were examined sepurately, Arc/Arg7.1 protein expression was lateralized following nuvel taste learning, but not following familiar taste consumption. Moreover, Ar/Arg3.1 lateralization was inversely correlated with taste familiarny, ie, the high lateralization of Arc/Arg.3.1 expression observed following novel taste learning was reduced in propustion to the increment in taste familiarity.
