23Perinatal depression (PND) affects approximately 15% of women, and de novo postpartum 24 depression affects approximately 40% of PND cases. Selective serotonin reuptake inhibitors 25 (SSRIs) are a common class of antidepressants prescribed to treat PND. However, the safety and 26 efficacy of SSRIs have been questioned in both clinical and preclinical research. Here, using a 27 preclinical rodent model of postpartum depression, we aim to better understand 28 neuroinflammatory cytokines and tryptophan mechanisms that may be related to SSRIs efficacy. 29Rodent dams were treated with high corticosterone (CORT; 40mg/kg, s.c.) for 21 days in the 30 postpartum period to simulate depressive-like behaviors in the late postpartum period. 31Concurrently, a subset of dams was treated with the SSRI, fluoxetine (FLX; 10mg/kg, s.c.), in 32 the postpartum period. We showed, consistent with previous studies, that although maternal FLX 33 treatment prevented CORT-induced disturbances in maternal care behavior during the early 34 postpartum, it failed to prevent the expression of CORT-induced depressive-like behavior in the 35 late postpartum. Furthermore, FLX treatment, regardless of CORT treatment, increased maternal 36 hippocampal IL-1β and decreased maternal plasma tryptophan levels, plasma tryptophan, 4'-37 pyridoxic acid, and pyridoxal concentrations. Maternal CORT treatment reduced maternal 38 hippocampal TNF-α and IFN-γ levels. Our work suggests that the limited efficacy of FLX in the 39 late postpartum may be associated with elevated levels of the proinflammatory cytokine IL-1β in 40 the maternal hippocampus, decreased plasma tryptophan concentration, and changes in vitamin 41 B6 dependent tryptophan-kynurenine pathway. These findings suggest novel pathways for 42 improving SSRI efficacy in alleviating perinatal depression. 43 : postpartum, corticosterone, females, antidepressant efficacy, cytokines, 44 serotonin, frontal cortex, hippocampus 45 2009). In addition, pregnancy and the postpartum also induce changes in the immune system in 87 the hippocampus (Haim et al., 2017;Sherer et al., 2017) and in blood (Eid et al., 2019; reviewed 88 in Duarte-Guterman et al., 2019). Elevated levels of peripheral proinflammatory immune 89 markers, particularly the cytokines IL-1β, interferon-gamma (IFN-γ) and IL-6, are reported in 90 women endorsing PND (Groer and Morgan, 2007;Corwin et al., 2008) or associated with 91
KeywordsHere, we sought to characterize markers of inflammation in the maternal hippocampus 129 and frontal cortex, and plasma tryptophan metabolism markers in a CORT-induced model of 130 postpartum depression and SSRI treatment. We hypothesized that CORT treatment would induce 131 depressive-like endophenotypes, including disruptions in maternal care behavior and increased 132 passive-coping behavior. Furthermore, we expected that the SSRI, fluoxetine (FLX), will show 133 limited efficacy at reducing CORT-induce depressive-like endophenotypes. We also 134 hypothesized that FLX treatment would alter markers of neuro...