number of different factors that
regulate neurogenesis have been identified.
Physicial activity and environmental
conditions have been known to affect
proliferation and survival of neurons
in vertebrates as well as invertebrates.
It has been found that crayfish
in an "enriched" environment
had increased neurogenesis and neuronal
compared to siblings in an "impoverished" environment.
Hormones have also been found to
influence the rate of neurogenesis
in vertebrates (e.g. testosterone)
and invertebrates (e.g. ecdysone).
Serotonin is believed to play a key
role in neurogenesis in a variety
of organisms. In lobsters, depletion
of serotonin dramatically reduced
the proliferation and survival of
olfactory projection neurons and
local interneurons. Most recently,
neurogenesis was found to follow
a circadian rhythm in the juvenile
lobster. Although neurons were born
throughout the day, significantly
were born at dusk, the most active
time for lobsters.