The evolution of the receptors of monoamines and the origin of motivational and emotional systems in vertebrates

The evolving vertebrate nervous system was accompanied by major gene duplic ation events generating novel organs and a sympathetic system. Vertebrate n eural pathways synthesizing catecholamine neurotransmitters (dopamine and n oradrenaline), were subsequently recruited to process increased information demands by mediating psychomotor functions such as selective attention/pre dictive reward and emotional drive via the activation of multiple G-protein linked catecholamine receptor subtypes. Here we show that the evolution of these receptor-mediated events were similarly driven by forces of gene dup lication, at the cephalochordate/vertebrate transition. In the cephalochord ate Amphioxus, a sister group to vertebrates, a single catecholamine recept or gene was found, which based on molecular phylogeny and functional analys is formed a monophyletic group with bath vertebrate? dopamine D-1 and beta adrenergic receptor classes. In addition, the presence of dopamine but not of noradrenaline was assayed in Amphioxus. In contrast, two distinct genes homologous to jawed vertebrate dopamine D-1 and beta adrenergic receptor ge nes were extant in representatives of the earliest craniates, lamprey and h agfish, paralleling high dopamine and noradrenaline content throughout the bi ain. These data suggest that a D-1/beta receptor gene duplication was re quired to elaborate novel catecholamine psychomotor adaptive responses and that a noradrenergic system specifically emerged at the origin of vertebrat e evolution.