Evolution of vertebrate survival circuits

Abstract

Evolution selects those adaptive features that increase reproductive probabilities and facilitate survival. Analysing the brain circuits mediating risk-avoidance (e.g. defense) and those allowing reward-seeking (motivated) behaviours in different vertebrates leads to several main conclusions. First, circuits mediating risk-avoidance are similar in all studied vertebrates, where they include amygdala homologues located in the posterior half of the cerebral hemispheres, in close relationship with the chemosensory systems. Second, in all vertebrates, reward-seeking behaviours involve the activity of tegmento-striatal dopaminergic pathways, plus other inputs to the ventral striatum, including amygdalostriatal glutamatergic projections. Third, output structures in these forebrain circuits for both risk-avoidance and reward-seeking behaviours occupy the caudal and rostral poles of the ventral striato-pallidum, namely the central amygdala and nucleus accumbens-olfactory tubercle respectively. This brain configuration was already present in at least the ancestral amniote, likely also in anamniotes. Finally, social behaviours (sexual, agonistic-territorial, parental) are fundamental for reproduction and survival. Consequently, the so-called socio-sexual brain network that governs these conducts is closely related with brain centres mediating motivation (maybe also risk-avoidance). Central nonapeptidergic circuits are apparently required for endowing social stimuli with rewarding (attractive) properties. More studies in non-mammals are required to further test and expand these ideas.

The dorsal arcopallium of chicks displays the expression of orthologs of mammalian fear related serotonin receptor subfamily genes

“…The arcopallium is a large, heterogenous brain region, but we are beginning to understand the contribution of its individual subdivisions to the regulation of fear-related behaviours 10 . Our findings support the proposal that the dorsal arcopallium is homologous to a part of the BLA based on developmental studies 11,12,29 . The lateral nidopallium is also proposed to be partially homologous to the BLA based on a detailed analysis of the embryonic origin and gene expression profile 11,12,29 .…”

“…Our findings support the proposal that the dorsal arcopallium is homologous to a part of the BLA based on developmental studies 11,12,29 . The lateral nidopallium is also proposed to be partially homologous to the BLA based on a detailed analysis of the embryonic origin and gene expression profile 11,12,29 . Our data showed that 5-HTR4 was preferentially expressed in the dorsal arcopallium (Figs.…”

“…In summary, we found that all the 5-HTRs used in this study were expressed in the dorsal arcopallium, which was proposed to be homologous to a part of the mammalian BLA 11,12,29 . This result may support the proposed homology between the dorsal arcopallium in birds and the BLA in mammals.…”

“…In this study, we showed that all the used orthologs of 5-HTR s were expressed in the dorsal arcopallium of chicks, which was proposed to be homologous to a part of mammalian BLA based on a detailed analysis of the embryonic origin and molecular profile (pattern of expression of morphogenetic genes during development) (Fig. 9 ) 11 , 12 , 29 ; this suggests that the role of the dorsal arcopallium in fear-related behaviour is similar to that of the mammalian BLA. The arcopallium is a large, heterogenous brain region, but we are beginning to understand the contribution of its individual subdivisions to the regulation of fear-related behaviours 10 .…”

“…In this study, we selected chick orthologs of six mammalian 5-HTR genes and performed in situ hybridisation in the chick telencephalon. We found that all the used orthologs of 5-HTRs were expressed in the dorsal arcopallium of chicks, which was proposed to be homologous to a part of mammalian BLA based on a detailed analysis of the embryonic origin and molecular profile (pattern of expression of morphogenetic genes during development) 11,12,29 . This result may support the proposed homology between dorsal arcopallium in birds and BLA in mammals.…”