Postnatal fluoxetine treatment affects the development of serotonergic neurons in rats

Maternal fluoxetine impairs synaptic transmission and plasticity in the medial prefrontal cortex and alters the structure and function of dorsal raphe nucleus neurons in offspring mice

Selective serotonin (5-HT) reuptake inhibitors (SSRIs) are commonly prescribed to women during pregnancy and breastfeeding despite posing a risk of adverse cognitive outcomes and affective disorders for the child. The consequences of SSRI-induced excess of 5-HT during development for the brain neuromodulatory 5-HT system remain largely unexplored. In this study, an SSRI - fluoxetine (FLX) - was administered to C57BL/6 J mouse dams during pregnancy and lactation to assess its effects on the offspring. We found that maternal FLX decreased field potentials, impaired long-term potentiation, facilitated long-term depression and tended to increase the density of 5-HTergic fibers in the medial prefrontal cortex (mPFC) of female but not male adolescent offspring. These effects were accompanied by deteriorated performance in the temporal order memory task and reduced sucrose preference with no change in marble burying behavior in FLX-exposed female offspring. We also found that maternal FLX reduced the axodendritic tree complexity of 5-HT dorsal raphe nucleus (DRN) neurons in female but not male offspring, with no changes in the excitability of DRN neurons of either sex. While no effects of maternal FLX on inhibitory postsynaptic currents (sIPSCs) in DRN neurons were found, we observed a significant influence of FLX exposure on kinetics of spontaneous excitatory postsynaptic currents (sEPSCs) in DRN neurons. Finally, we report that no changes in field potentials and synaptic plasticity were evident in the mPFC of the offspring after maternal exposure during pregnancy and lactation to a new antidepressant, vortioxetine. These findings show that in contrast to the mPFC, long-term consequences of maternal FLX exposure on the structure and function of DRN 5-HT neurons are mild and suggest a sex-dependent, distinct sensitivity of cortical and brainstem neurons to FLX exposure in early life. Vortioxetine appears to exert fewer side effects with regards to the mPFC when compared with FLX.

Fluoxetine alters rat's milk properties causing impact on offspring's development

Fluoxetine is an antidepressant used to treat several conditions including postpartum depression. This disease causes cognitive, emotional, behavioral and physical changes, negatively affecting the mother, child and family life. However, fluoxetine is excreted in breast milk, causing short and long-term effects on children who were exposed to the drug during lactation, so studies that seek to uncover the consequences of these effects are needed. Thus, the aim of this study was to evaluate the effects of fluoxetine on the nutritional characteristics of milk and on growth and neurobehavioral development of the offspring on a rat model. Lactating rats were divided into 4 groups: control group and three experimental groups, which were treated with different doses of fluoxetine (1, 10 and 20 mg/kg) during the lactation. Dams body weight and milk properties were measured, as well as offspring's growth and physical and neurobehavioral development. Results showed that the use of fluoxetine during lactation decreased dam's body weight and alters milk's properties, leading to a decrease in offspring's growth until adulthood. Therefore, the use of fluoxetine during lactation needs to be cautiously evaluated, with the benefits to the mothers and the associated risk to the offspring carefully balance.

Prenatal exposure to fluoxetine modulates emotionality and aversive memory in male and female rat offspring

During pregnancy, women are prone to depression, for which selective serotonin reuptake inhibitors (SSRIs), such as fluoxetine, are usually the first-line treatment. However, fluoxetine can cross the placental barrier and affect fetuses, causing changes in serotonin levels early in life. Long-term effects in the brain circuits that control cognitive and emotional behavior are related to early fluoxetine exposure during development. In this study, we aimed to investigate whether fluoxetine exposure (10 mg/kg/day) from the 13th gestational day (GD13) to GD21 may lead to behavioral emotional-cognitive changes in male and female rat offspring approximately 90 days postnatally (~PN90). We have analyzed the performance of individuals in the open field and in the plus-maze discriminative avoidance task, which assesses anxiety and learning/memory processing behaviors. We have found that prenatal (GD13-GD21) exposure to fluoxetine strengthened aversive memory and induced higher anxiety levels in males, and quick extinction of aversive memory in females. Taken together, these results suggest that early exposure to fluoxetine impairs the basal state of anxiety and the cognitive functions of rats during adulthood, which may be in a sex-specific manner because males appear more susceptible than females.

Effects of prenatal exposure to fluoxetine on circadian rhythmicity in the locomotor activity and neuropeptide Y and 5-HT expression in male and female adult Wistar rats

Serotonin (5-HT) reuptake inhibitors, such as fluoxetine, are the most prescribed antidepressant for maternal depression. In this sense, it exposes mothers and the brains of infants to increased modulatory and trophic effects of serotonergic neurotransmission. 5-HT promotes essential brain changes throughout its development, which include neuron migration, differentiation, and organization of neural circuitries related to emotional, cognitive, and circadian behavior. Early exposure to the SSRIs induces long-term effects on behavioral and neural serotonergic signalization. We have aimed to evaluate the circadian rhythm of locomotor activity and the neurochemical content, neuropeptide Y (NPY) and 5-HT in three brain areas: intergeniculate leaflet (IGL), suprachiasmatic nuclei (SCN) and raphe nuclei (RN), at two zeitgebers (ZT6 and ZT18), in male and female rat's offspring early exposed (developmental period GD13-GD21) to fluoxetine (20mg/kg). First, we have conducted daily records of the locomotor activity rhythm using activity sensors coupled to individual cages over four weeks. We have lastly evaluated the immunoreactivity of NPY in both SCN and IGL, and as well the 5-HT expression in the dorsal and medial RN. In summary, our results showed that (1) prenatal fluoxetine affects phase entrainment of the rest/activity rhythm at ZT6 and ZT18, more in male than female specimens, and (2) modulates the NPY and 5-HT expression. Here, we show male rats are more susceptible to phase entrainment and the NPY and 5-HT misexpression compared to female ones. The sex differences induced by early exposure to fluoxetine in both the circadian rhythm of locomotor activity and the neurochemical expression into SCN, IGL, and midbrain raphe are an important highlight in the present work. Thus, our results may help to improve the knowledge on neurobiological mechanisms of circadian rhythms and are relevant to understanding the "broken brains" and behavioral abnormalities of offspring early exposed to antidepressants.

Neonatal fluoxetine exposure delays reflex ontogeny, somatic development, and food intake similarly in male and female rats

Serotonin (5-HT) acts as a neuromodulator and plays a critical role in brain development. Changes in 5-HT signaling during the perinatal period can affect neural development and may result in behavioral changes in adulthood; however, further investigations are necessary including both sexes to study possible differences. Thus, the aim of this study was to investigate the impact of neonatal treatment with fluoxetine on the development of male and female offspring. The animals were divided into four groups according to sex and treatment. The experimental groups received fluoxetine at 10 mg·kg-1 (1 μL/g of body weight (bw)) and the animals of control group received saline solution 0.9% (1 μL/g of bw) from postnatal days 1-21. In the neonatal period, reflex ontogeny, somatic development, physical features, and food intake were recorded. In the postnatal period (until day 31) bw and post-weaning food intake were recorded. Chronic administration of fluoxetine in the neonatal period caused a delay in the reflex ontogeny and somatic development, as well as reduction of lactation, post-weaning bw, and post-weaning food intake in rats. No difference was found between the sexes. These changes reaffirm that serotonin plays an important role in regulating the plasticity of the brain during the early development period, but without sex differences.

The effects of perinatal SSRI exposure on anxious behavior and neurobiology in rodent and human offspring

While the postpartum period is typically associated with increased positive affect, many women will develop a depressive- or anxiety-related disorder during this time, which can degrade the mother-infant bond and lead to detrimental consequences for the infant. Given the potential for negative consequences, effective treatments have been critical, with selective serotonin reuptake inhibitors (SSRIs) being the most commonly-prescribed pharmaceutical agents to treat postpartum depression and anxiety. However, SSRIs can readily cross the placenta and are present in breast milk, so they might, therefore, unintentionally interact with the developing fetus/infant. There is already experimental evidence that perinatal SSRI exposure has a number of long-term effects on offspring, but this review focuses on the current literature examining the timing and consequences of perinatal SSRI exposure specifically on anxiety-like behaviors in rodents and humans, with an emphasis on the anxiety-related brain regions of the amygdala and hippocampus. This review also discusses discrepancies between the rodent and human literatures and how they might inform future studies. Finally, some key factors to consider when examining the role of perinatal SSRIs on offspring anxiety will be discussed, such as the duration of SSRI exposure and the potential neuroprotective effects of SSRIs. Given the extensive prescribing of SSRIs, the potential health consequences of perinatal SSRI exposure, and the discrepancies in the literature, it will be necessary to critically examine the factors underlying offspring anxiety outcomes.

Exposure of dams to fluoxetine during lactation disturbs maternal behavior but had no effect on the offspring behavior

Fluoxetine is one of the most commonly prescribed drugs for treatment of depression during pregnancy as well as postpartum. Nevertheless, fluoxetine can cross the placental barrier and/or be secreted through breastmilk and questions remain unanswered regarding safety of the unborn and/or nursing infant. Passive administration of antidepressants to infants can cause neurological developmental delay and/or dysfunction. To date, there are limited studies on neurobehavioral effects due to passive administration of fluoxetine in nursing animals. Thus, the aim of the present study was to evaluate the effects of fluoxetine exposure on the behavior of lactating dams and their offspring. Dams received either 1, 10 or 20 mg/kg fluoxetine via oral gavage (controls received water alone) from lactating day (LD) 1 to 21. Maternal behavioral studies were conducted from LD5 to LD7 and offspring studies were conducted from LD2 to LD60. Results showed dysfunction in maternal behavior, both in direct and indirect behavior, but there were no differences and/or deficiencies observed in offspring behavior. These data suggest that the impairment of dams maternal behavior combined with the amount of fluoxetine that the offspring received through breast milk during lactation did not alter their social behavior in infancy and/or adulthood, suggesting no neurodevelopmental damage associated with maternal use of fluoxetine. This study contributes to the field of human psychiatric diseases by further elucidating the effects of antidepressant medications on the health of mothers as well as children who were passively exposed to drug treatment.

Modulation of Fear and Arousal Behavior by Serotonin Transporter (5-HTT) Genotypes in Newly Hatched Chickens

The serotonin transporter (5-HTT) plays a key role in regulating serotonergic transmission via removal of serotonin (5-hydroxytryptamine, 5-HT) from synaptic clefts. Alterations in 5-HTT expression and 5-HT transmission have been shown to cause changes to adult behavior including fear. The objective of the present study was to investigate the 5-HTT role in fear in birds at the very early stages of post-hatching life. Using an avoidance test with an elevated balance beam, which was based on depth perception and the respective fear of heights, we assessed fear-related avoidance behaviors of newly hatched chicks of the three functional 5-HTT genotypes W/W, W/D and D/D. Newly hatched chicks of the genotype D/D, which was linked to high 5-HTT expression, showed less intensive avoidance responses as measured by decreased latency to jump than W/W and W/D chicks. Further, significantly fewer D/D hens than W/W hens showed fear-like behavior that resembled a freezing response. Furthermore, in an arousal test the arousal reaction of the chicks in response to an acute short-term visual social deprivation in the home compartment was assessed 5 weeks after hatching, which also revealed that D/D chicks exhibited decreased arousal reaction, compared to W/W chicks. Thus, the results indicate that fear responses differ in D/D chicks in the early post-hatching periods, possibly due to the different expression of 5-HTT respectively 5-HT levels in this strain.

Serotonin transporter inhibition during neonatal period induces sex-dependent effects on mitochondrial bioenergetics in the rat brainstem

The serotonin reuptake is mainly regulated by the serotonin transporters (SERTs), which are abundantly found in the raphe nuclei, located in the brainstem. Previous studies have shown that dysfunction in the SERT has been associated with several disorders, including depression and cardiovascular diseases. In this manuscript, we aimed to investigate how gender and the treatment with a serotonin selective reuptake inhibitor (SSRI) could affect mitochondrial bioenergetics and oxidative stress in the brainstem of male and female rats. Fluoxetine, our chosen SSRI, was used during the neonatal period (i.e., from postnatal Day 1 to postnatal Day 21-PND1 to PND21) in both male and female animals. Thereafter, experiments were conducted in adult rats (60 days old). Our results demonstrate that, during lactation, fluoxetine treatment modulates the mitochondrial bioenergetics in a sex-dependent manner, such as improving male mitochondrial function and female antioxidant capacity.

Fluoxetine treatment of prepubertal male rats uniformly diminishes sex hormone levels and, in a subpopulation of animals, negatively affects sperm quality

Fluoxetine (Flx) is a selective serotonin reuptake inhibitor that alters the male reproductive system when administered at the adult stage or after maternal exposure. In the present study we evaluated the effects of Flx administration on reproductive parameters during juvenile–peripubertal development when treated male rats reached adulthood. Groups of rats were treated daily with Flx (5 mg kg−1, i.p.) or saline (0.9% NaCl), or were left untreated. Rats were treated between 30 and 53 days of age and were killed at 65 days of age. Serotonin concentrations were determined in the hypothalamus, hypophysis and testis. Gonadotrophins, sex steroids and sperm quality (membrane integrity, sperm with functional mitochondria, sperm density, sperm motility and morphological abnormalities) were also evaluated. Flx did not affect bodyweight, but significantly diminished LH, FSH, progesterone and testosterone serum concentrations. After graphical analysis, a subgroup of rats was identified whose sperm quality parameters were greatly affected by Flx. In the present study we show that Flx administered to juvenile rats disrupts the hypothalamic–hypophyseal–testicular axis and its effects on sperm quality are not homogeneous in adults. In contrast, Flx altered concentrations of gonadotrophins and sexual steroids in all treated rats. These results suggest caution should be exercised in the prescription of Flx to prepubertal males.

Perinatal serotonergic activity: A decisive factor in the control of food intake

ABSTRACT The serotoninergic system controls key events related to proper nervous system development. The neurotransmitter serotonin and the serotonin transporter are critical for this control. Availability of these components is minutely regulated during the development period, and the environment may affect their action on the nervous system. Environmental factors such as undernutrition and selective serotonin reuptake inhibitors may increase the availability of serotonin in the synaptic cleft and change its anorectic action. The physiological responses promoted by serotonin on intake control decrease when requested by acute stimuli or stress, demonstrating that animals or individuals develop adaptations in response to the environmental insults they experience during the development period. Diseases, such as anxiety and obesity, appear to be associated with the body’s response to stress or stimulus, and require greater serotonergic system action. These findings demonstrate the importance of the level of serotonin in the perinatal period to the development of molecular and morphological aspects of food intake control, and its decisive role in understanding the possible environmental factors that cause diseases in adulthood.

The effects of maternal antidepressant use on offspring behaviour and brain development: Implications for risk of neurodevelopmental disorders

Approximately 10% of pregnant women are prescribed antidepressant drugs (ADDs), with selective serotonin reuptake inhibitors (SSRIs) the most widely prescribed. SSRIs bind to the serotonin transporter (SERT), blocking the reabsorption of serotonin by the presynaptic neuron and increasing serotonin levels in the synaptic cleft. The serotonergic system regulates a range of brain development processes including neuronal proliferation, migration, differentiation and synaptogenesis. Given the presence of SERT in early brain development, coupled with the ability of SSRIs to cross the placenta and also enter breast milk, concerns have been raised regarding the effects of SSRI exposure on the developing foetus and newborns. In this review, we evaluate preclinical and clinical studies that have examined the effects of maternal SSRI exposure and the risk for altered neurodevelopment and associated behaviours in offspring. While the current body of evidence suggests that maternal SSRI treatment may cause perturbations to the neurobiology, behaviour and ultimately risk for neurodevelopmental disorders in exposed offspring, conflicting findings do exist and the evidence is not conclusive. However, given the increasing incidence of depression and number of women prescribed ADDs during pregnancy, further investigation into this area is warranted.

Refining the Role of 5-HT in Postnatal Development of Brain Circuits

Changing serotonin (5-hydroxytryptamine, 5-HT) brain levels during critical periods in development has long-lasting effects on brain function, particularly on later anxiety/depression-related behaviors in adulthood. A large part of the known developmental effects of 5-HT occur during critical periods of postnatal life, when activity-dependent mechanisms remodel neural circuits. This was first demonstrated for the maturation of sensory brain maps in the barrel cortex and the visual system. More recently this has been extended to the 5-HT raphe circuits themselves and to limbic circuits. Recent studies overviewed here used new genetic models in mice and rats and combined physiological and structural approaches to provide new insights on the cellular and molecular mechanisms controlled by 5-HT during late stages of neural circuit maturation in the raphe projections, the somatosensory cortex and the visual system. Similar mechanisms appear to be also involved in the maturation of limbic circuits such as prefrontal circuits. The latter are of particular relevance to understand the impact of transient 5-HT dysfunction during postnatal life on psychiatric illnesses and emotional disorders in adult life.

Circadian behavior of adult mice exposed to stress and fluoxetine during development

INTRODUCTION

Women of child-bearing age are the population at greatest risk for depression. The stress experienced during pregnancy and the associated antidepressant treatments can both affect fetal development. Fluoxetine (FLX) is among the most common antidepressants used by pregnant women. We have previously demonstrated that perinatal exposure to FLX can alter expression of circadian rhythms in adulthood. Here, we examine the combined effects of maternal stress during pregnancy and perinatal exposure to the antidepressant FLX on the circadian behavior of mice as adults.

METHODS

Mouse dams were exposed to chronic unpredictable stress (embryonic (E) day 7 to E18), FLX (E15 to postnatal day 12), a combination of both stress and FLX, or were left untreated. At 2 months of age, male offspring were placed in recording chambers and circadian organization of wheel running rhythms and phase shifts to photic and non-photic stimuli were assessed.

RESULTS

Mice exposed to prenatal stress (PS) had smaller light-induced phase delays. Mice exposed to perinatal FLX required more days to re-entrainment to an 8-h phase advance of their light-dark cycle. Mice subjected to either perinatal FLX or to PS had larger light-induced phase advances and smaller phase advances to 8-OH-DPAT. FLX treatment partially reversed the effect of PS on phase shifts to late-night light exposure and to 8-OH-DPAT.

CONCLUSIONS

Our results suggest that, in mice, perinatal exposure to either FLX, or PS, or their combination, leads to discernible, persistent changes in their circadian systems as adults.

Activity of Raphé Serotonergic Neurons Controls Emotional Behaviors

Despite the well-established role of serotonin signaling in mood regulation, causal relationships between serotonergic neuronal activity and behavior remain poorly understood. Using a pharmacogenetic approach, we find that selectively increasing serotonergic neuronal activity in wild-type mice is anxiogenic and reduces floating in the forced-swim test, whereas inhibition has no effect on the same measures. In a developmental mouse model of altered emotional behavior, increased anxiety and depression-like behaviors correlate with reduced dorsal raphé and increased median raphé serotonergic activity. These mice display blunted responses to serotonergic stimulation and behavioral rescues through serotonergic inhibition. Furthermore, we identify opposing consequences of dorsal versus median raphé serotonergic neuron inhibition on floating behavior, together suggesting that median raphé hyperactivity increases anxiety, whereas a low dorsal/median raphé serotonergic activity ratio increases depression-like behavior. Thus, we find a critical role of serotonergic neuronal activity in emotional regulation and uncover opposing roles of median and dorsal raphé function.

Transient postnatal fluoxetine decreases brain concentrations of 20-HETE and 15-epi-LXA4, arachidonic acid metabolites in adult mice

BACKGROUND

Transient postnatal exposure of rodents to the selective serotonin (5-HT) reuptake inhibitor (SSRI) fluoxetine alters behavior and brain 5-HT neurotransmission during adulthood, and also reduces brain arachidonic (ARA) metabolic consumption and protein level of the ARA metabolizing enzyme, cytochrome P4504A (CYP4A).

HYPOTHESIS

Brain 20-hydroxyeicosatetraenoic acid (20-HETE), converted by CYP4A from ARA, will be reduced in adult mice treated transiently and postnatally with fluoxetine.

METHODS

Male mice pups were injected i.p. daily with fluoxetine (10mg/kg) or saline during P4-P21. At P90 their brain was high-energy microwaved and analyzed for 20-HETE and six other ARA metabolites by enzyme immunoassay.

RESULTS

Postnatal fluoxetine vs. saline significantly decreased brain concentrations of 20-HETE (-70.3%) and 15-epi-lipoxin A4 (-60%) in adult mice, but did not change other eicosanoid concentrations.

CONCLUSIONS

Behavioral changes in adult mice treated postnatally with fluoxetine may be related to reduced brain ARA metabolism involving CYP4A and 20-HETE formation.

Effect of fluoxetine treatment on mitochondrial bioenergetics in central and peripheral rat tissues

Recent investigations have focused on the mitochondrion as a direct drug target in the treatment of metabolic diseases (obesity, metabolic syndrome). Relatively few studies, however, have explicitly investigated whether drug therapies aimed at changing behavior by altering central nervous system (CNS) function affect mitochondrial bioenergetics, and none has explored their effect during early neonatal development. The present study was designed to evaluate the effects of chronic treatment of newborn male rats with the selective serotonin reuptake inhibitor fluoxetine on the mitochondrial bioenergetics of the hypothalamus and skeletal muscle during the critical nursing period of development. Male Wistar rat pups received either fluoxetine (Fx group) or vehicle solution (Ct group) from the day of birth until 21 days of age. At 60 days of age, mitochondrial bioenergetics were evaluated. The Fx group showed increased oxygen consumption in several different respiratory states and reduced production of reactive oxygen species, but there was no change in mitochondrial permeability transition pore opening or oxidative stress in either the hypothalamus or skeletal muscle. We observed an increase in glutathione S-transferase activity only in the hypothalamus of the Fx group. Taken together, our results suggest that chronic exposure to fluoxetine during the nursing phase of early rat development results in a positive modulation of mitochondrial respiration in the hypothalamus and skeletal muscle that persists into adulthood. Such long-lasting alterations in mitochondrial activity in the CNS, especially in areas regulating appetite, may contribute to permanent changes in energy balance in treated animals.

Increased expression of Hes5 protein in Notch signaling pathway in the hippocampus of mice offspring of dams fed a high-fat diet during pregnancy and suckling

Maternal high-fat diet (HFD) impairs hippocampal development of offspring promoting decreased proliferation of neural progenitors, in neuronal differentiation, in dendritic spine density and synaptic plasticity reducing neurogenic capacity. Notch signaling pathway participates in molecular mechanisms of the neurogenesis. The activation of Notch signaling leads to the upregulation of Hes5, which inhibits the proliferation and differentiation of neural progenitors. This study aimed to investigate the Notch/Hes pathway activation in the hippocampus of the offspring of dams fed an HFD. Female Swiss mice were fed a control diet (CD) and an HFD from pre-mating until suckling. The bodyweight and mass of adipose tissue in the mothers and pups were also measured. The mRNA and protein expression of Notch1, Hes5, Mash1, and Delta1 in the hippocampus was assessed by RT-PCR and western blotting, respectively. Dams fed the HFD and their pups had an increased bodyweight and amount of adipose tissue. Furthermore, the offspring of mothers fed the HFD exhibited an increased Hes5 expression in the hippocampus compared with CD offspring. In addition, HFD offspring also expressed increased amounts of Notch1 and Hes5 mRNA, whereas Mash1 expression was decreased. However, the expression of Delta1 did not change significantly. We propose that the overexpression of Hes5, a Notch effector, downregulates the expression of the proneural gene Mash1 in the offspring of obese mothers, delaying cellular differentiation. These results provide further evidence that an offspring's hippocampus is molecularly susceptible to maternal HFD and suggest that Notch1 signaling in this brain region is important for neuronal differentiation.

Fluoxetine treatment of rat neonates significantly reduces oxidative stress in the hippocampus and in behavioral indicators of anxiety later in postnatal life

The brain, more than any other organ in the body, is vulnerable to oxidative stress damage, owing to its requirement for high levels of oxygenation. This is needed to fulfill its metabolic needs in the face of relatively low levels of protective antioxidants. Recent studies have suggested that oxidative stress is directly involved in the etiology of both eating and anxiety behavior. The aim of this study was to evaluate the effect of fluoxetine-inhibited serotonin reuptake in nursing rat neonates on behavior and on oxidative stress in the hypothalamus and the hippocampus; brain areas responsible for behavior related to food and anxiety, respectively. The results show that increased serotonin levels during a critical period of development do not induce significant differences in food-related behavior (intake and satiety), but do result in a in a significant decrease in anxiety. Measurements of oxidative stress showed a significant reduction of lipid peroxidation in the hippocampus (57%). In the hypothalamus, antioxidant enzymes were unchanged, but in the hippocampus, the activity of catalase and glutathione-S-transferase was increased (80% and 85% respectively). This suggests that protecting neural cells from oxidative stress during brain development contributes to the anxiolytic effects of serotonin.

Long-term outcomes of developmental exposure to fluoxetine: a review of the animal literature

During and following pregnancy, women are at high risk of experiencing depression, for which fluoxetine (FLX; brand names Prozac, Sarafem, Rapiflux) is the most commonly prescribed treatment. An estimated 1.4-2.1% of pregnant women use this medication, which inhibits the reuptake of serotonin and thereby increases serotonergic activity at the synapse. Serotonin acts as a cue guiding numerous neurodevelopmental processes, and changes in the concentration of serotonin can disrupt normal in utero brain development and organization in humans and other animals, thus providing a mechanism by which maternal intake of FLX might alter neural development and ultimately behaviour. Despite this possibility, long-term alterations of behaviour and the brain have not been well studied in individuals exposed to FLX during pregnancy or soon after birth, perhaps because conducting such studies beyond infancy presents significant challenges. To remedy this problem, many researchers have turned to modelling the effects of developmental FLX exposure in non-human animals, primarily rodents. The body of literature on this topic has expanded considerably over the past several years, yet a comprehensive review is lacking. In order to fill this gap, we have summarized the findings of those studies describing the long-term behavioural and neurophysiological effects of FLX exposure in non-human animals in early development. We also discuss methodological considerations and common shortcomings of research in this area. The precise nature of the long-term effects of developmental FLX exposure remains difficult to specify, as these effects appear to be highly variable and dependent on numerous factors. Overall, however, it is clear that early FLX exposure in non-human animals can alter the development of the brain in ways that are relevant to behaviour in adulthood, decreasing exploration and social interaction, and in some cases altering anxiety- and depression-like behaviours..

Hippocampal HDAC4 contributes to postnatal fluoxetine-evoked depression-like behavior

Fluoxetine treatment in adulthood evokes antidepressant and anxiolytic responses. Paradoxically, postnatal fluoxetine (PNFlx) induces persistent depression- and anxiety-like behaviors. The mechanistic underpinnings of this paradox remain poorly understood. Here, we examined specific molecular changes in the rat hippocampus that accompany perturbed emotionality observed across life following PNFlx. PNFlx-induced hippocampal gene regulation observed in microarray and quantitative PCR studies indicate functional enrichment of genes involved in response to organic substances, protein kinase pathways, DNA binding, and transcriptional repression. We noted specific transcripts (Hdac4, mammalian target of rapamycin (mTOR), Gnai1, protein kinase C gamma (Prkcc), and hyperpolarization-activated cyclic nucleotide-gated channel 1 (Hcn1)) that were consistently dysregulated across life, and selectively influenced by postnatal, but not adult, fluoxetine. Increased histone deacetylase-4 (HDAC4) recruitment, accompanied by decreased activating histone acetylation marks at the mTOR and Gnai1 promoters, indicate a role for HDAC4 in PNFlx-mediated gene dysregulation. Strikingly, coadministration of the HDAC inhibitor sodium butyrate with PNFlx prevented the dysregulation of Hdac4 and mTOR, and the emergence of depression- and anxiety-like behavior. Importantly, we also find that retreatment of PNFlx animals with fluoxetine in adulthood reversed the increased Hdac4 expression, prevented HDAC4 recruitment to the mTOR and Gnai1 promoters, and attenuated the decline in mTOR and Gnai1 expression, coincident with normalization of PNFlx-evoked depression- and anxiety-like behavior. Further, we show that viral-mediated hippocampal overexpression of Hdac4 was sufficient to induce depression-, but not anxiety-, like behavior in adulthood. Our results highlight the unique nature of molecular signatures evoked by PNFlx, and implicate HDAC4 in the dysregulated gene expression and emergence of perturbed emotionality following fluoxetine exposure in early life.

Long-term consequences of neonatal fluoxetine exposure in adult rats

Serotonin (5-HT) plays important roles during neural development. Administration of selective serotonin reuptake inhibitor (SSRI)-type medication during gestation may influence the maturation of the fetal brain and subsequent brain functions. To mimic the condition of late-gestation SSRI exposure, we administered fluoxetine (FLX) in neonatal rats during the first postnatal week, which roughly corresponds to the third trimester period of human gestation. FLX-exposed adult male rats exhibited reduced locomotor activity and depression-like behaviors. Furthermore, sensorimotor gating capacity was also impaired. Interestingly, increased social interaction was noticed in FLX-exposed rats. When the levels of 5-HT and tryptophan hydroxylase were examined, no significant changes were found in FLX rats compared to control (CON) rats. The behavioral phenotypes of FLX rats suggested malfunction of the limbic system. Dendritic architectures of neurons in the medial prefrontal cortex (mPFC) and basolateral amygdala (BLA) were examined. Layer II/III mPFC pyramidal neurons in FLX rats had exuberant dendritic branches with elongated terminal segments compared to those in CON rats. In BLA pyramidal neurons, the dendritic profiles were comparable between the two groups. However, in FLX rats, the density of dendritic spines was reduced in both mPFC and BLA. Together, our results demonstrated the long-lasting effects of early FLX treatment on emotional and social behaviors in adult rats in which impaired neuronal structure in the limbic system was also noticed. The risk of taking SSRI-type antidepressants during pregnancy should be considered.

Transient postnatal fluoxetine leads to decreased brain arachidonic acid metabolism and cytochrome P450 4A in adult mice

Fetal and perinatal exposure to selective serotonin (5-HT) reuptake inhibitors (SSRIs) has been reported to alter childhood behavior, while transient early exposure in rodents is reported to alter their behavior and decrease brain extracellular 5-HT in adulthood. Since 5-HT2A/2C receptor-mediated neurotransmission can involve G-protein coupled activation of cytosolic phospholipase A2 (cPLA2), releasing arachidonic acid (ARA) from synaptic membrane phospholipid, we hypothesized that transient postnatal exposure to fluoxetine would alter brain ARA metabolism in adult mice. Brain ARA incorporation coefficients k* and rates Jin were quantitatively imaged following intravenous [1-(14)C]ARA infusion of unanesthetized adult mice that had been injected daily with fluoxetine (10mg/kg i.p.) or saline during postnatal days P4-P21. Expression of brain ARA metabolic enzymes and other relevant markers also was measured. On neuroimaging, k* and Jin was decreased widely in early fluoxetine- compared to saline-treated adult mice. Of the enzymes measured, cPLA2 activity was unchanged, while Ca(2+)-independent iPLA2 activity was increased. There was a significant 74% reduced protein level of cytochrome P450 (CYP) 4A, which can convert ARA to 20-HETE. Reduced brain ARA metabolism in adult mice transiently exposed to postnatal fluoxetine, and a 74% reduction in CYP4A protein, suggest long-term effects independent of drug presence in brain ARA metabolism, and in CYP4A metabolites. These changes might contribute to reported altered behavior following early SSRI in rodents.

Effect of fluoxetine on disease progression in a mouse model of ALS

Selective serotonin reuptake inhibitors (SSRIs) and other antidepressants are often prescribed to amyotrophic lateral sclerosis (ALS) patients; however, the impact of these prescriptions on ALS disease progression has not been systematically tested. To determine whether SSRIs impact disease progression, fluoxetine (Prozac, 5 or 10 mg/kg) was administered to mutant superoxide dismutase 1 (SOD1) mice during one of three age ranges: neonatal [postnatal day (P)5-11], adult presymptomatic (P30 to end stage), and adult symptomatic (P70 to end stage). Long-term adult fluoxetine treatment (started at either P30 or P70 and continuing until end stage) had no significant effect on disease progression. In contrast, neonatal fluoxetine treatment (P5-11) had two effects. First, all animals (mutant SOD1(G93A) and control: nontransgenic and SOD1(WT)) receiving the highest dose (10 mg/kg) had a sustained decrease in weight from P30 onward. Second, the high-dose SOD1(G93A) mice reached end stage ∼8 days (∼6% decrease in life span) sooner than vehicle and low-dose animals because of an increased rate of motor impairment. Fluoxetine increases synaptic serotonin (5-HT) levels, which is known to increase spinal motoneuron excitability. We confirmed that 5-HT increases spinal motoneuron excitability during this neonatal time period and therefore hypothesized that antagonizing 5-HT receptors during the same time period would improve disease outcome. However, cyproheptadine (1 or 5 mg/kg), a 5-HT receptor antagonist, had no effect on disease progression. These results show that a brief period of antidepressant treatment during a critical time window (the transition from neonatal to juvenile states) can be detrimental in ALS mouse models.

Delayed physical and neurobehavioral development and increased aggressive and depression-like behaviors in the rat offspring of dams fed a high-fat diet

Early maternal exposure to a high-fat diet (HFD) may influence the brain development of rat offspring and consequently affect physiology and behavior. Thus, in the present study, we investigated the somatic, physical, sensory-motor and neurobehavioral development of the offspring of dams fed an HFD (52% calories from fat, mainly saturated) and the offspring of dams fed a control diet (CD - 14.7% fat) during lactation from the 1st to the 21st postnatal day (P). Maternal body weights were evaluated during lactation. In the progeny, somatic (body weight, head and lengths axes) and physical (ear unfolding, auditory conduit opening, eruption of the incisors and eye opening) development and the consolidation of reflex responses (palm grasp, righting, vibrissa placing, cliff avoidance, negative geotaxis, auditory startle response and free-fall righting) were determined during suckling. Depressive and aggressive behaviors were tested with the forced swimming test (FST) and the "foot-shock" test on days 60 and 110, respectively. The open field test was used to assess motor function. Compared to controls, the HFD-pups exhibited decreases in body weight (P7-P21) and body length (P4-P18), but by days P71 and P95, these pups were overweight. All indicators of physical maturation and the consolidation of the following reflexes, vibrissa placing, auditory startle responses, free-fall righting and negative geotaxis, were delayed in HFD-progeny. In addition, the pups from HFD dam rats also exhibited reduced swimming and climbing times in the FST and increased aggressive behavior. No changes in locomotion were observed. These findings show developmental and neurobehavioral changes in the rat offspring of dams fed the HFD during lactation and suggest possible disruption of physical and sensory-motor maturation and increased susceptibility to depressive and aggressive-like behavior.

Genetic and pharmacological manipulations of the serotonergic system in early life: neurodevelopmental underpinnings of autism-related behavior

Serotonin, in its function as neurotransmitter, is well-known for its role in depression, autism and other neuropsychiatric disorders, however, less known as a neurodevelopmental factor. The serotonergic system is one of the earliest to develop during embryogenesis and early changes in serotonin levels can have large consequences for the correct development of specific brain areas. The regulation and functioning of serotonin is influenced by genetic risk factors, such as the serotonin transporter polymorphism in humans. This polymorphism is associated with anxiety-related symptoms, changes in social behavior, and cortical gray and white matter changes also seen in patients suffering from autism spectrum disorders (ASD). The human polymorphism can be mimicked by the knockout of the serotonin transporter in rodents, which are as a model system therefore vital to explore the precise neurobiological mechanisms. Moreover, there are pharmacological challenges influencing serotonin in early life, like prenatal/neonatal exposure to selective serotonin reuptake inhibitors (SSRI) in depressed pregnant women. There is accumulating evidence that this dysregulation of serotonin during critical phases of brain development can lead to ASD-related symptoms in children, and reduced social behavior and increased anxiety in rodents. Furthermore, prenatal valproic acid (VPA) exposure, a mood stabilizing drug which is also thought to interfere with serotonin levels, has the potency to induce ASD-like symptoms and to affect the development of the serotonergic system. Here, we review and compare the neurodevelopmental and behavioral consequences of serotonin transporter gene variation, and prenatal SSRI and VPA exposure in the context of ASD.

The effects of perinatal fluoxetine treatment on the circadian system of the adult mouse

RATIONAL

Depression is prevalent among women of childbearing age and is frequently treated with selective serotonin reuptake inhibitors (SSRIs). As some SSRIs, such as fluoxetine (Flx), can cross the placenta, it is possible that the neurodevelopment of the fetus may be affected, leading to altered behavior in adulthood.

OBJECTIVES

In this study, we examined the effects of perinatal Flx exposure on the subsequent expression of circadian rhythms in adult mice.

METHODS

Dams were treated with 25 mg/kg/day Flx in their drinking water from embryonic day 15 to postnatal day 12. Circadian organization of wheel running rhythms and phase shifts to photic and non-photic stimuli were assessed in the offspring starting at 6 weeks of age.

RESULTS

We found that perinatal Flx exposure led to larger light-induced phase advances (1.19 ± 0.51 vs. 0.55 ± 0.25 h), smaller phase advances to the serotonin agonist 8-OH-DPAT during the mid-subjective day (0.44 ± 0.15 vs. 0.70 ± 0.17 h), and a shorter free-running period in constant darkness (23.47 ± 0.13 vs. 23.64 ± 0.13 h).

CONCLUSIONS

These results suggest that perinatal exposure to SSRIs may have consequences for the functioning of the circadian system later in life.

Fluoxetine administration to pregnant rats increases anxiety-related behavior in the offspring

RATIONALE

Fluoxetine (Prozac®) is the most frequently prescribed drug to battle depression in pregnant women, but its safety in the unborn child has not yet been established. Fluoxetine, a selective serotonin reuptake inhibitor, crosses the placenta, leading to increased extracellular serotonin levels and potentially neurodevelopmental changes in the fetus.

OBJECTIVES

The purpose of this study was to elucidate the long-term consequences of prenatal fluoxetine in rats.

METHODS

Pregnant rats were injected daily with 12 mg/kg fluoxetine or vehicle from gestational day 11 until birth, and the behavior of the offspring was monitored.

RESULTS

Plasma fluoxetine transfer from mother to pup was 83%, and high levels of fluoxetine (13.0 μg/g) were detected in the pup brain 5 h after the last injection. Fluoxetine-treated dams gave birth to litters 15% smaller than usual and to pups of reduced weight (until postnatal day 7). Furthermore, prenatal fluoxetine exposure significantly increased anxiety in the novelty-suppressed feeding test, the footshock-induced conditioned place aversion test, and the elevated plus maze test (following footshock pre-exposure) during adulthood, and also significantly decreased components of social play behavior at 4 weeks of age, and a strong tendency for increased self-grooming and making less contact in adults. Behavioral despair, anhedonia, and sexual behavior were not different between treatment groups. Finally, the hypothermic response to the 5-HT(1A) agonist flesinoxan was observed at a lower dose in prenatally fluoxetine-exposed rats than in controls.

CONCLUSIONS

Prenatal fluoxetine exposure in rats leads to detrimental behavioral outcomes in later life, which may partly be due to altered 5-HT(1A) receptor signaling.