Veterinary session

People are exposed to various, positive or negative, social or non-social effects on a daily basis. These stimuli cause emotions leading to appropriate behavioural responses. Such emotions are, for example, joy or fear. There are many mental disorders which are caused by the lack or exaggeration of correct emotional responses. These affect people's lives, their social connections, jobs or even their physical health. To find an effective treatment, the first step is to understand the brain mechanisms leading to these abnormal conditions.

According to the literature and our previous results, the amygdala complex plays a pivotal role in the development of emotion-related behaviours. Especially four of the amygdaloid subregions are accepted to be crucial in behavioural responses such as the lateral, the basolateral, the central amygdala and the so-called intercalated cells mass. The question arises whether all of these amygdalar regions are equally involved in the responses to each effect.

To answer this, we used animal models. Male mice were exposed to various positive/negative/social and non-social stimuli. Then, the activation of the four amygdalar nuclei was examined via mapping the expression of an early immediate gene, the c-Fos. The natural predator’s (cat or fox) smell was used as a negative social stimulus and a fear conditioning as a negative non-social stimulus; both causing fear responses (freezing). A hormone-treated female was placed next to the male as a positive social stimulus, while sugared milk was used as a non-social stimulus; both are widely accepted to be causing pleasure for a male mouse. Sixty minutes after a stimulus presentation, mice were perfused, and the prepared brain slices went through various histochemical procedures.

Stimulus-activated c-Fos expressing neurons were visualised with either peroxidase or multiple fluorescent immunostaining approaches meanwhile each amygdala nucleus was identified with different neurochemical markers. Based on our preliminary results, stimulus-specific activation patterns were found. E.g. sugared milk caused c-Fos activation primarily in the central amygdala labelled with delta isoform of protein kinase C (PKCδ) while fear conditioning in the lateral amygdala (marked with dense calretinin immunostating). Thus, these amygdaloid subregions may contribute to the development of corresponding emotional responses.

Completing our investigations, our results will provide a more accurate picture about the functional organization of the amygdala complex by identifying emotion-specific activation patterns in distinct amygdalar microcircuits. These can contribute to our better understanding of brain mechanisms leading to the development of mental disorders, such as binge eating or panic disorder.