Effect of prenatal exposure to antidepressants on 5-HT-stimulated phosphoinositide hydrolysis and 5-HT2 receptors in rat brain

Maternal exposure to fluoxetine during gestation and lactation does not alter plasma concentrations of testosterone, oestrogen or corticosterone in peripubertal offspring

Antidepressants are widely used around the world, primarily for the treatment of mood disorders, anxiety and pain syndromes. Women who use antidepressants often continue to use them during pregnancy. Selective serotonin reuptake inhibitors, including fluoxetine, are the main class of antidepressants prescribed to pregnant women. It is known that fluoxetine crosses the placental-blood barrier and is excreted in breast milk. Consequently, indirect exposure of the infant occurs. Knowing that fluoxetine alters the balance of neurotransmitters in the central nervous system, several studies have shown that maternal exposure to this drug leads to various adverse effects on the nervous, reproductive and cardiovascular systems of the offspring. The aim of the present study was to evaluate the effects of exposure to fluoxetine during gestation and lactation on parameters related to steroid hormones in prepubertal and pubertal male and female rats. The endpoints evaluated were date of puberty onset, plasma testosterone and oestrogen concentrations before and after puberty onset and corticosterone concentration before and after adrenocorticotrophin stimulus. None of the parameters was affected by fluoxetine exposure.

Prenatal fluoxetine modifies the behavioral and hormonal responses to stress in male mice: role for glucocorticoid insensitivity

Women with major depressive disorder during pregnancy often use selective serotonin reuptake inhibitors (SSRIs) antidepressants. These drugs readily cross the placental barrier and impact the developing fetal brain. Recently, we reported that prenatal fluoxetine (FLX), an SSRI antidepressant drug, altered corticosterone and behavioral responses to stress in female mouse offspring. The present study assessed the effects of prenatal FLX on these responses in males. The results showed that prenatal FLX significantly augmented the corticosterone response to acute stress in young prepubescent mice. The corticosterone response to continuous stress was not affected by prenatal FLX irrespective of age. In addition, continuous stress reduced general activity, and anxiety-like and depressive-like behaviors in adult animals prenatally exposed to FLX, but not in controls. The dexamethasone suppression test showed that prenatal FLX induced a state of glucocorticoid insensitivity in adult males, indicating that the negative feedback control of the hypothalamic-pituitary-adrenal axis response to stress was disrupted. Together, these findings indicate that prenatal FLX altered hormonal and behavioral responses to stress and suggest a role for the development of glucocorticoid insensitivity in these effects. These findings may aid understanding of the limitations and precautions that should be taken in the use of SSRIs by pregnant women.

Prenatal SSRI alters the hormonal and behavioral responses to stress in female mice: Possible role for glucocorticoid resistance

Life time prevalence of major depression disorder (MDD) is higher in women compared to men especially during the period surrounding childbirth. Women suffering from MDD during pregnancy use antidepressant medications, particularly Selective Serotonin Reuptake Inhibitors (SSRI). These drugs readily cross the placental barrier and impact the developing fetal brain. The present study assessed the effects of prenatal exposure to fluoxetine (FLX), an SSRI antidepressant drug, on corticosterone and behavioral responses to stress in female mice. In young females, prenatal FLX significantly elevated corticosterone response to continuous stress. In adults, prenatal FLX augmented corticosterone response to acute stress and suppressed the response to continuous stress. Additionally, prenatal FLX significantly augmented stress-induced increase in locomotion and reduced anxiety- and depressive-like behaviors in adult, but not young mice. The dexamethasone suppression test revealed that prenatal FLX induced a state of glucocorticoid resistance in adult females, indicating that the negative feedback control of the hypothalamic-pituitary-adrenal axis response to stress was disrupted. These findings provide the first indication of altered hormonal and behavioral responses to continuous stress and suggest a role for the development of glucocorticoid resistance in these effects. According to these findings, prenatal environment may have implications for stress sensitivity and responsiveness to life challenges. Furthermore, this study may assist in understanding the limitations and precautions that should be taken in the use of SSRIs during pregnancy.

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..

Prenatal Cocaine Disrupts Serotonin Signaling-Dependent Behaviors: Implications for Sex Differences, Early Stress and Prenatal SSRI Exposure

Prenatal cocaine (PC) exposure negatively impacts the developing nervous system, including numerous changes in serotonergic signaling. Cocaine, a competitive antagonist of the serotonin transporter, similar to selective serotonin reuptake inhibitors (SSRIs), also blocks dopamine and norepinephrine transporters, leaving the direct mechanism through which cocaine disrupts the developing serotonin system unclear. In order to understand the role of the serotonin transporter in cocaine's effect on the serotonergic system, we compare reports concerning PC and prenatal antidepressant exposure and conclude that PC exposure affects many facets of serotonergic signaling (serotonin levels, receptors, transporters) and that these effects differ significantly from what is observed following prenatal SSRI exposure. Alterations in serotonergic signaling are dependent on timing of exposure, test regimens, and sex. Following PC exposure, behavioral disturbances are observed in attention, emotional behavior and stress response, aggression, social behavior, communication, and like changes in serotonergic signaling, these effects depend on sex, age and developmental exposure. Vulnerability to the effects of PC exposure can be mediated by several factors, including allelic variance in serotonergic signaling genes, being male (although fewer studies have investigated female offspring), and experiencing the adverse early environments that are commonly coincident with maternal drug use. Early environmental stress results in disruptions in serotonergic signaling analogous to those observed with PC exposure and these may interact to produce greater behavioral effects observed in children of drug-abusing mothers. We conclude that based on past evidence, future studies should put a greater emphasis on including females and monitoring environmental factors when studying the impact of PC exposure.

Maternal exposure to the antidepressant fluoxetine impairs sexual motivation in adult male mice

Depressive disorders have a worldwide high prevalence. Fluoxetine (FLX), a selective serotonin reuptake inhibitor (SSRI) antidepressant, has been widely prescribed for depression during pregnancy and/or lactation. Since serotonin is a neurotrophic factor, the use of FLX by mothers could disrupt brain development resulting in behavioral alterations in their progeny. The aim of the present study was to evaluate the effects of developmental FLX exposure on sexual behavior, as well as on endocrine parameters, of male mice. Swiss dams were treated daily, by gavage, with 7.5 mg/kg of FLX during pregnancy and lactation. Male pups were tested for copulatory behavior and sexual incentive motivation. Male pups also had their anogenital distance, plasmatic testosterone concentration and testis, epididymis, seminal vesicle and pituitary wet weights assessed. Copulatory behavior, anogenital distance, plasmatic testosterone concentration and organs wet weights were not affected by FLX exposure. However, this exposure eliminated preference for a sexual incentive on the sexual incentive motivation test, which indicates reduced sexual motivation, a classic side effect of SSRIs in humans who take these antidepressants.

Long-term effects of fluoxetine or vehicle administration during pregnancy on behavioral outcomes in guinea pig offspring

RATIONALE

Assessment of the benefits versus risks associated with antidepressant use during pregnancy must include an analysis of possible drug effects on fetal development. Human studies indicate that prenatal fluoxetine exposure is associated with adverse neonatal outcomes. Animal modeling may provide useful information concerning possible long-term effects of prenatal fluoxetine exposure. Limitations in previous such studies using rat models may be overcome using a guinea pig model in which fluoxetine is delivered by osmotic pump throughout pregnancy.

METHODS

Initial experiments measured the half-life of fluoxetine and dosing required to achieve human therapeutic blood levels in the guinea pig. In subsequent experiments, guinea pigs received fluoxetine or vehicle via osmotic pump or no treatment throughout pregnancy. Outcome measures included: pregnancy characteristics, weight gain, and, in offspring as adults, pain threshold, acoustic startle responses and prepulse inhibition.

RESULTS

There was no effect of treatment group on gestation length, number of live-births or still-births, maternal or offspring weight gain, and acoustic startle responses. In adult offspring, pain threshold was decreased by vehicle treatment during gestation. Prenatal fluoxetine increased pain threshold, relative to vehicle controls. Prepulse inhibition of startle was increased in adult offspring treated prenatally with either vehicle or fluoxetine compared to no treatment.

CONCLUSIONS

The guinea pig provides a practicable and clinically relevant model of prenatal fluoxetine exposure. Adult guinea pigs exposed to fluoxetine prenatally showed increased thermal pain thresholds but no change in prepulse inhibition, indicating selective long-term effects of prenatal fluoxetine on serotonin-modulated behaviors. Further studies on long-term effects of prenatal fluoxetine on nociception are warranted.

Structural Effects and Neurofunctional Sequelae of Developmental Exposure to Psychotherapeutic Drugs: Experimental and Clinical Aspects

The advent of psychotherapeutic drugs has enabled management of mental illness and other neurological problems such as epilepsy in the general population, without requiring hospitalization. The success of these drugs in controlling symptoms has led to their widespread use in the vulnerable population of pregnant women as well, where the potential embryotoxicity of the drugs has to be weighed against the potential problems of the maternal neurological state. This review focuses on the developmental toxicity and neurotoxicity of five broad categories of widely available psychotherapeutic drugs: the neuroleptics, the antiepileptics, the antidepressants, the anxiolytics and mood stabilizers, and a newly emerging class of nonprescription drugs, the herbal remedies. A brief review of nervous system development during gestation and following parturition in mammals is provided, with a description of the development of neurochemical pathways that may be involved in the action of the psychotherapeutic agents. A thorough discussion of animal research and human clinical studies is used to determine the risk associated with the use of each drug category. The potential risks to the fetus, as demonstrated in well described neurotoxicity studies in animals, are contrasted with the often negative findings in the still limited human studies. The potential risk fo the human fetus in the continued use of these chemicals without more adequate research is also addressed. The direction of future research using psychotherapeutic drugs should more closely parallel the methodology developed in the animal laboratories, especially since these models have already been used extremely successfully in specific instances in the investigation of neurotoxic agents.

Prenatal cocaine exposure potentiates 5-HT(2a) receptor function in male and female rat offspring

We have reported previously prenatal cocaine-induced functional deficits in serotonergic terminals, and gender-specific supersensitivity of postsynaptic 5-HT(1A) receptor-mediated hormone responses in offspring. This study investigates the effects of prenatal exposure to cocaine on postsynaptic 5-HT(2A) receptor-mediated responses in prepubescent male and female offspring. Pregnant rats were administered saline or (-)cocaine (15 mg/kg, s.c., b.i.d) from gestational day 13 through 20. Changes in 5-HT(2A) receptor function in offspring were assessed by differences in the ability of DOI [4-iodo, 2,5-dimethoxyphenyl-isopropylamine; 2. 0 mg/kg, s.c.] to elevate plasma levels of the hormones ACTH, corticosterone and renin. Basal hormone levels in male and female progeny were unaffected by prenatal cocaine exposure. However, prenatal exposure to cocaine significantly potentiated the magnitude of the ACTH response to DOI in both male (+19%) and female (+43%) progeny. Similarly, the DOI-induced elevation of plasma renin was markedly potentiated in male (+51%) and female (+83%) cocaine-exposed offspring. Although DOI significantly elevated corticosterone levels in both male and female offspring, the magnitude of corticosterone responses was not altered by prenatal exposure to cocaine. Densities of agonist ((125)I-DOI)-labeled receptors in hypothalamus and cortex were unaltered by prenatal exposure to cocaine. These data indicate prenatal cocaine-induced supersensitivity of postsynaptic 5-HT(2A) receptor function in male and female offspring without changes in receptor density. Synapse: 35:163-172, 2000.

Pharmacological characteristics and regulation of 5-HT receptor-stimulated phosphoinositide hydrolysis in the rat spinal cord

In slices from immature rat spinal cord, both 5-hydroxytryptamine (5-HT) and the 5-HT2A/C receptor agonists (+/-)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) and alpha-methyl-5-HT (alpha-Me-5-HT) stimulate phosphoinositide (PI) hydrolysis. PI breakdown is also increased by the 5-HT3 receptor agonist 2-Me-5-HT but not by phenylbiguanide. The effect of either 5-HT or DOI is blocked by selective 5-HT2A receptor antagonists such as spiperone and ketanserin and more markedly by mixed 5-HT2 receptor antagonists, such as ritanserin, methysergide and mesulergine, with higher affinity at the 2C subtype. The effect of 2-Me-5-HT is blocked by 5-HT2 and not by 5-HT3 receptor antagonists, indicating that 5-HT3 receptors do not directly or indirectly take part in PI hydrolysis in the spinal cord. Moreover, lesion with neonatal capsaicin of thin primary afferents to the dorsal spinal cord enhances inositol phosphate formation stimulated by 5-HT or DOI but not by 2-Me-5-HT. This lesion also increases 5-HT2A and 5-HT2C receptor density. After neonatal injection of 5,7-dihydroxytryptamine, which results in a marked loss of 5-HT content in the cord, 5-HT and 5-HT2 receptor agonists also enhance PI breakdown without a concomitant change in receptor number. The results suggest that the 5-HT-stimulated PI response in the rat spinal cord is associated only with the 5-HT2 receptor class, in particular with the 5-HT2C subtype.

Neonatal treatments with the serotonin uptake inhibitors clomipramine and zimelidine, but not the noradrenaline uptake inhibitor desipramine, disrupt sleep patterns in adult rats

Chronic postnatal exposure to clomipramine (CMI), a monoamine uptake inhibitor, results in persistent alterations in adult rat REM sleep. These effects have been ascribed to CMI's ability to block neonatal active sleep (AS). However, these effects have not been obtained with other anti-depressants which also block neonatal AS. We compared the long-term effects on adult rat sleep after postnatal treatments (P8-P21) with either CMI or zimelidine (ZMI, a selective serotonin uptake inhibitor) or desipramine (DMI, a selective noradrenaline uptake inhibitor). ZMI and CMI increased the frequency and decreased the duration of REM sleep bouts, increased the number of nonREM-REM transitions, and increased sigma power in REM and nonREM sleep EEGs in adulthood. In contrast, DMI had no effect on any adult sleep parameters. Since ZMI, DMI and CMI all reduce AS to similar levels, these results suggest that neonatal AS suppression is not responsible for the sleep deficits following CMI or ZMI treatment. However, since ZMI and CMI, but not DMI, increase synaptic concentrations of serotonin, elevated serotonin levels during development may instead be responsible for the long-lasting sleep deficits.