Creatine transporter knockout mice (Slc6a8) show increases in serotonin-related proteins and are resilient to learned helplessness

Abstract

Approximately 20% of adults in the U.S. will experience an affective disorder during their life. While it is well established that serotonin (5-HT) is a crucial factor in mood, impaired cellular bioenergetics are also implicated. Creatine (Cr), through the Cr/Phospho-Cr (PCr) shuttle, maintains high ATP concentrations in the neuron. This system may be implicated in the etiology of affective disorders, as reduced Cr, PCr, and ATP are often seen in the brains of affected patients. To address this issue, Cr transporter (Crt) deficient male mice (Slc6a8-/y) and female mice heterozygous for Crt expression (Slc6a8+/-) were used to evaluate how a Cr deficient system would alter affective-like behaviors. Slc6a8-/y and Slc6a8+/- mice had more escapes and faster escape latencies in learned helplessness, indicating a potential resilience to behavioral despair. Elevated zero maze and tail-suspension test performance matched that of wildtype mice, however. Slc6a8-/y mice have increased 5-hydroxyindoleacetic acid content in the hippocampus and striatum and increased monoamine oxidase protein and tryptophan hydroxylase-2 protein content in the hippocampus, while serotonin levels are unchanged. This indicates an increase in 5-HT turnover. Our results indicate that Cr plays a complex role in affective disorders and 5-HT neurotransmission, warranting further investigation.