Conclusion
A fundamental feature of animal life is the need to acquire
energy through the consumption of material derived from
other organisms. This is accomplished through coordinated
movements in the service of food acquisition and
its transit to an internal chamber for digestion. It is perhaps
fitting that one of the most phylogenetically ancient signaling
molecules would be intimately involved in the regulation
of processes so fundamental to animal life. Serotonergic
regulation of behavioral responses to energy status, the
sensing of food stimuli, the release of digestive enzymes,
CPGs that mediate ingestion, gut motility, and interoceptive
feedback occur widely among both invertebrate and
vertebrate species. Throughout phylogeny, both synaptic
and paracrine serotonergic signaling mechanisms mediate
these processes. Although serotonergic influences
on each of the physiological determinants of energy balance
are not entirely consistent across vertebrate and
invertebrate species, some of these influences do appear
to generalize. This highlights the potential utility of model
invertebrate organisms to provide insights relevant to
serotonergic mechanisms of energy balance in mammals.