The importance of serotonin in exercise-induced adult neurogenesis: new evidence from tph2-/- mice.

Beckman D, Santos LE.
J Neurosci. 2013 Sep 4;33(36):14283-4. PMID: 24005280

Objective:   Serotonin signaling is known to be involved in the process of adult neurogenesis.  Decreases in neurogenesis are known to occur in people with depression while treatment with monoaminergic therapy can help offset the loss.  Since exercise is also linked to mood and neurogenesis, this review paper examines some of the recent literature in order to show links between exercise and serotonin in the generation and maintenance of neurons.

·         Knockout mice deficient in the rate-limiting enzyme involved in serotonin synthesis, tryptophan hydroxylase (Tph2), develop different from control littermates and show decreases in growth and increased behavioral disorders.  When allowed free access to a running wheel for 6 days, knockout mice showed less hippocampal neurogenesis than controls, despite starting with the same total number of cells.  Since lesions in the main ascending serotonergic nucleus do result in decreased neurogenesis, this suggests a compensatory mechanism in knockout mice

·         Knockout mice also show reductions in levels of dopamine and noradrenaline, both of which have been implicated in controlling proliferation of hippocampal cells.

·         Using markers for cell proliferation and apoptosis, it has been seen that knockout mice show less hippocampal proliferation and more apoptosis than controls.

·         Knockout mice show greater microgliosis after exercising, suggesting that serotonin may be involved in suppressing inflammation.  This hypothesis is supported by other work showing that serotonin reuptake inhibitors can suppress inflammation.

-DH