Papel de la neocorteza en la Habituación de la Neofobia Gustativa

Abstract

The present doctoral thesis combines the nervous system and behavioral analysis with a developmental approach. The main aim is to investigate the taste recognition memory changes during adolescence and aging as well as the medial Prefrontal Cortex involvement. The first chapter includes a review of the previous knowledge in the field and in the second chapter the specific objectives are justified. In the experimental series presented in chapter 3, the changes in the neuronal activity of the different subregions that conform the medial Prefrontal Cortex were evaluated during the process of Attenuation of Taste Neophobia to a vinegar solution (3%) by applying c- Fos immunohistochemical technique in adult (5 months) and aged (24 months) rats. The behavioral analysis showed a slowed attenuation of neophobia in the aged group compared to the adult group of rats. The Immunohistochemical analyses showed that Prelimbic and Infralimbic subregions exhibit higher activity during the second taste presentation compared to the first and sixth exposure. A similar activity pattern was found in the Peduncular Cortex. However, no changes in neuronal activity were shown in the Anterior Cingulate Cortex. In the Prelimbic and Infralimbic cortex of aged rats a similar activity pattern was observed compared with adults. However, the level of activity was reduced. On the contrary, the Peduncular Cortex showed a higher activity during the first exposure of the taste, being reduced during the second exposure and drastically reduced during the sixth exposure in the aged rats group compared to the adult one. The experimental series presented in Chapter 4 consist of 4 experiments aimed to explore the behavioral changes that occur during adolescence in the safe taste recognition memory formation. Adolescent (PND28 to PND42) and adult (3 months) rats were used. In the experiment 1, attenuation of taste neophobia to a vinegar solution (3%) was studied. The results showed the same neophobic response in adolescent and adults groups. However, adolescent rats required more exposure to accept the acid vinegar solution as safe. In the second experiment of this series, the same procedures were used but this time with a non-caloric sweet saccharin (0.1%) solution. The results showed no differences between adolescent and adult rats neither in the neophobic response nor in the attenuation of taste neophobia. Taken together, the results of experiments 1 and 2 suggest that during adolescence there is a greater sensitivity to the potential stressful properties of less palatable taste stimuli such as vinegar. Additionally, in order to verify that the results are not attributable to non-specific deficits in the recognition memory formation, in the experiments 3 and 4 a Latent Inhibition and Novel Object Recognition tasks were applied. Both adolescent and adult rats showed similar performance on these tasks. In all, the results of this doctoral thesis suggest the involvement of the medial Prefrontal Cortex in the formation of safe taste memory and that the neuronal activity pattern of the different subregions is altered during aging. In addition, during adolescence there are no deficits in the formation of the taste recognition memory formation, although there seems to be a greater sensitivity to the aversive properties of less palatable stimuli such as vinegar. A general discussion of the results obtained in the previous chapters is included in Chapter 5. Finally, Chapter 6 summarizes the general conclusions drawn from this doctoral thesis.