Behavioral and neuronal changes due to 13-Cis-retinoic acid treatment
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13-Cis-retinoic acid (13-cis-RA) is a synthetic retinoid and the active ingredient in the oral acne treatment Accutane. The medical literature has suggested that the use of 13-cis-RA for acne treatment can induce depression, but because acne itself can have a negative psychosocial impact on self esteem, whether or not 13-cis-RA can cause depression remains controversial. The purpose of this work was to examine whether chronic 13-cis-RA administration could induce depression-related behaviors in mice and to determine the impact 13-cis-RA has on regions of the brain thought to be associated with mood and depression. We found that chronic treatment of adolescent male mice with 13-cis-RA induced depression-related behaviors, as assessed by immobility in the tail suspension and forced swim tests. Although depression is a multifaceted disease in which many brain regions are involved, the regions that seem particularly vulnerable to the effects of 13-cis-RA are the serotonergic and hippocampal systems. In serotonergic cells in vitro, 13-cis-RA treatment increases protein levels of the serotonergic 5-HT[subscript 1A] autoreceptor and the serotonin reuptake transporter (SERT), two inhibitory components of serotonin (5-HT) signaling. In vivo, the median and dorsal raphe nuclei contain the main 5-HT producing cells. 13-Cis-RA uncoupled the functional connectivity of dorsal raphe nuclei from the hippocampal regions as measured by interregional correlations of cytochrome oxidase (CO) activity, a metabolic marker of neuronal activity. Decreased hippocampal neurogenesis is thought to occur in depression and is decreased by 13-cis-RA. 5-HT is also a known regulator of hippocampal neurogenesis. Uncoupling of the dorsal raphe nuclei from the regions of the hippocampus by 13-cis-RA treatment may be the cause of, or a result from, the decreased neurogenesis. Although retinoids are known regulators of apoptosis, the uncoupling of the dorsal raphe nuclei from the hippocampal regions was not due to serotonergic cell loss. Interestingly, 13-cis-RA treated animals with the lowest CO activity in the dentate gyrus have the highest immobility in the tail suspension and forced swim tests. Ultimately, the effects of 13-cis-RA on the serotonergic and hippocampal systems might be inducing depression-related behaviors.