Impact of prenatal serotonergic manipulation across the lifespan: exploring sensitive periods

INTRODUCTION Serotonin (5-HT) is a key modulator of brain development [1] and the main regulator of extracellular 5-HT homeostasis is the serotonin transporter, responsible for the reuptake of 5-HT. Perturbation of 5-HT, especially when happens during perinatal stages leads to alterations of brain functioning and the onset of neuropsychiatric disorders later in life. To study the complex interplay between 5-HT and the pathophysiology of these diseases, several animal models based on the manipulation of the serotonergic system in early life have been used in research. Among these, perinatal exposure to selective serotonin reuptake inhibitors can lead to pathological-like phenotypes later in life [2]. On these bases, we exposed rats to fluoxetine (FLX) during gestation. Throughout behavioral and molecular analyses during adolescence and adulthood, we observe sex- and time-dependent behavioral effects mirrored by biological changes at central and peripheral levels [3]. AIMS In this study, we aimed to explore the potential impact of prenatal serotonergic manipulation on the dynamics of sensitive periods by evaluating the expression of their trigger and brake markers at three distinct ages (postnatal-day (PND)21, 35, 70) to identify changes that may underlie the behavioral outcome observed at adulthood. Indeed, since the modulation of the serotonergic system took place during the early developmental stages, we hypothesize that certain modifications may be established before the emergence of behavioral effects. METHODS Male and female Wistar rats were subjected to FLX exposure (15 mg/Kg/day) throughout gestation (from GD0 to PND0) and subsequently underwent a battery of behavioral tests during adolescence or adulthood. One week later, animals were decapitated, and the prefrontal cortex (Pfc), the dorsal (dHip), and ventral (vHip) hippocampus were dissected and stored at -80°C. Through qRT-PCR, we assessed changes in the expression of genes linked to triggers, including Bdnf, and to brakes, such as Ncan, a component of the perineuronal nets (PNNs), pertaining to sensitive periods. Statistical significance was ascertained by two-way ANOVA, with prenatal-FLX and age as variables, followed by the Tukey multiple comparisons test. SUMMARY OF RESULTS Our findings revealed sex- and brain-region-specific effects that may contribute to the development of pathological-like phenotypes observed in adulthood. In particular, we observed specifically in dHip an increased level of total Bdnf in the prenatal-FLX group at PND35 (p<0.05) and a decreased at PND70 (p<0.01) compared to the control group. Similarly, females exposed to prenatal manipulation showed decreased total Bdnf expression in dHip at PND70 (p<0.001) alongside higher expression in vHip at PND35 (p<0.01). Furthermore, the statistical analysis revealed significantly higher Ncan mRNA levels at PND21 in both dHip (p<0.001) and vHip (p<0.05) in comparison to the control group selectively in males and not in females. CONCLUSIONS Our findings suggest that changes in total Bdnf and Ncan influence the development of pathological conditions and in particular, the decreased levels of total Bdnf in dHip at PND70 could underpin the anhedonic-like phenotype observed in adults. These results should be further investigated to better understand the etiological mechanisms underlying neuropsychiatric conditions, aiming for earlier diagnosis and improved patient stratification.