Diminished sexual activity in a new animal model of endogenous depression

Rapid Eye Movement Sleep during Early Life: A Comprehensive Narrative Review

The ontogenetic sleep hypothesis suggested that rapid eye movement (REM) sleep is ontogenetically primitive. Namely, REM sleep plays an imperative role in the maturation of the central nervous system. In coincidence with a rapidly developing brain during the early period of life, a remarkably large amount of REM sleep has been identified in numerous behavioral and polysomnographic studies across species. The abundant REM sleep appears to serve to optimize a cerebral state suitable for homeostasis and inherent neuronal activities favorable to brain maturation, ranging from neuronal differentiation, migration, and myelination to synaptic formation and elimination. Progressively more studies in Mammalia have provided the underlying mechanisms involved in some REM sleep-related disorders (e.g., narcolepsy, autism, attention deficit hyperactivity disorder (ADHD)). We summarize the remarkable alterations of polysomnographic, behavioral, and physiological characteristics in humans and Mammalia. Through a comprehensive review, we offer a hybrid of animal and human findings, demonstrating that early-life REM sleep disturbances constitute a common feature of many neurodevelopmental disorders. Our review may assist and promote investigations of the underlying mechanisms, functions, and neurodevelopmental diseases involved in REM sleep during early life.

Fluoxetine exposure in adolescent and adult female mice decreases cocaine and sucrose preference later in life

BACKGROUND

Preclinical evidence from male subjects indicates that exposure to psychotropic medications, during early development, results in long-lasting altered responses to reward-related stimuli. However, it is not known if exposure to the antidepressant fluoxetine, in female subjects specifically, changes sensitivity to natural and drug rewards, later in life.

AIMS

The aim of this work was to investigate if exposure to fluoxetine mediates enduring changes in sensitivity to the rewarding properties of cocaine and sucrose, using female mice as a model system.

METHODS

We exposed C57BL/6 female mice to fluoxetine (250 mg/L in their drinking water) for 15 consecutive days, either during adolescence (postnatal day 35-49) or adulthood (postnatal day 70-84). Twenty-one days later, mice were examined on their behavioral reactivity to cocaine (0, 2.5, 5, 7.5 mg/kg) using the conditioned place preference paradigm, or assessed on the two-bottle sucrose (1%) test.

RESULTS

We found that regardless of age of antidepressant exposure, female mice pre-exposed to fluoxetine displayed reliable conditioning to the cocaine-paired compartment. However, when compared to respective age-matched controls, antidepressant pre-exposure decreased the magnitude of conditioning at the 5 and 7.5 mg/kg cocaine doses. Furthermore, fluoxetine pre-exposure reduced sucrose preference without altering total liquid intake.

CONCLUSIONS

The data suggest that pre-exposure to fluoxetine, during adolescence or adulthood, results in a prolonged decrease in sensitivity to the rewarding properties of both natural and drug rewards in female C57BL/6 mice.

Early postnatal treatment with clomipramine induces female sexual behavior and estrous cycle impairment

Administration of clomipramine (CMI), a tricyclic antidepressant, in early stages of development in rats, is considered an animal model for the study of depression. This pharmacological manipulation has induced behavioral and physiological alterations, i.e., less pleasure-seeking behaviors, despair, hyperactivity, cognitive dysfunction, alterations in neurotransmitter systems and in HPA axis. These abnormalities in adult male rats are similar to the symptoms observed in major depressive disorders. One of the main pleasure-seeking behaviors affected in male rats treated with CMI is sexual behavior. However, to date, no effects of early postnatal CMI treatment have been reported on female reproductive cyclicity and sexual behavior. Therefore, we explored CMI administration in early life (8-21 PN) on the estrous cycle and sexual behavior of adult female rats. Compared to the rats in the early postnatal saline treatment (CTRL group), the CMI rats had fewer estrous cycles, fewer days in the estrous stage, and longer cycles during a 20-day period of vaginal cytology analysis. On the behavioral test, the CMI rats displayed fewer proceptive behaviors (hopping, darting) and had lower lordosis quotients. Also, they usually failed to display lordosis and only rarely manifested marginal or normal lordosis. In contrast, the CTRL rats tended to display normal lordosis. These results suggest that early postnatal CMI treatment caused long-term disruptions of the estrous cycle and female sexual behavior, perhaps by alteration in the hypothalamic-pituitary-gonadal (HPG) axes and in neuronal circuits involved in the regulation of the performance and motivational of sexual behavior as the noradrenergic and serotonergic systems.

Chronic treatment with estradiol restores depressive-like behaviors in female Wistar rats treated neonatally with clomipramine

Neonatal administration of clomipramine (CMI) induces diverse behavioral and neurochemical alterations in adult male rats that resemble major depression disorder. However, the possible behavioral alterations in adult female rats subjected to neonatal treatment with clomipramine are unknown. Therefore, the aim of this study was to explore the effect of neonatal treatment with CMI on adult female rats in relation to locomotion and behavioral despair during the estrus cycle. Also evaluated was the effect of chronic treatment with E2 on these female CMI rats. We found no effects on spontaneous locomotor activity due to neonatal treatment with CMI, or after 21days of E2 administration. In the FST, neonatal treatment with CMI increased immobility and decreased active swimming and climbing behaviors. Influence of the ovarian cycle was detected only in relation to climbing behavior, as the rats in the MD phase displayed less climbing activity. Chronic E2 administration decreased immobility but increased only swimming in CMI rats. These results suggest that neonatal treatment with CMI induces despair-like behavior in female rats, but that chronic E2 administration generates antidepressant-like behavior by decreasing immobility and increasing swimming, perhaps through interaction with the serotonergic system.

Drug induces depression-like phenotypes and alters gene expression profiles in Drosophila

BACKGROUND

Major depressive disorder (MDD) is a severe mental illness that affects more than 350 million people worldwide. However, the molecular mechanisms of depression are currently unclear. Studies suggest that Drosophila and humans have similar depression-like symptoms under pressure. In this research, we choose Drosophila melanogaster as the animal model to explore the molecular mechanisms that trigger depression.

RESULTS

We found that feeding D. melanogaster with the medium containing Levodopa or Chlorpromazine could induce depression-like phenotypes in both behavioral and biochemical biomarkers, including significantly decreased food intake, mating frequency, serotonin (5-HT) concentration, and increased malondialdehyde (MDA) concentration as well as reduced activity of superoxide dismutase (SOD). Moreover, the progeny of Chlorpromazine-treated flies also showed these depression-like features. By RNA-seq technology, we identified 467 genes that were differentially expressed between Chlorpromazine treated (CPZ) and control male flies [fold-change of ≥2 (q-value<5%)]. When comparing CPZ with control flies, 312 genes were upregulated and 155 genes downregulated. Differential expression of genes related to metabolic pathway, Parkinson's disease, Huntington's disease, Alzheimer's disease and lysozyme pathways were observed. Quantitative reverse transcriptase PCR (qRT-PCR) confirmed that 19 genes are differentially expressed in CPZ and control male flies.

CONCLUSIONS

Levodopa, or Chlorpromazine can induce depression-like phenotypes in D. melanogaster regarding changes of appetite and sexual activity, and some key biochemical markers. A total of 467 genes were identified by RNA-seq analysis to have at least a 2-fold-change in expression between CPZ and control flies, including genes involved in metabolism, neurological diseases and lysozyme pathways. Our data provide additional insight into molecular mechanisms underlying depressive disorders in humans and may also contribute to clinical treatment.

Developmental emergence of an obsessive-compulsive phenotype and binge behavior in rats

RATIONALE

Obsessive-compulsive disorder (OCD) gradually emerges and reaches clinical significance during early adulthood. Whether a predisposition for OCD manifests as binge eating disorder earlier during adolescence is proposed.

OBJECTIVES

To further characterize how OCD-like behaviors increase across maturation and to determine whether an OCD-like predisposition increases the likelihood of binge eating during adolescence.

METHODS

Male and female Sprague-Dawley rats were injected with the tricyclic antidepressant clomipramine (CMI, 15 mg/kg) or saline vehicle twice daily between postnatal days 9-15. Both groups were tested for perseverative (spontaneous alternation) and anxiety-like (elevated plus maze; marble burying) behaviors during juvenility (day 28), adolescence (day 60), and adulthood (day 90). Both motivations to eat sucrose pellets and binge eating on fat were investigated.

RESULTS

Sex- and age-dependent increases in anxiety-like and perseverative behavior were observed in CMI subjects. Differences in consummatory behaviors emerged during late adolescence, while no significant differences in alternation or anxiety-like behaviors were detected between CMI and vehicle animals until adulthood. Adolescent CMI females consumed more sucrose pellets in 30 min relative to vehicle females, whereas adolescent CMI males consumed approximately half as much as vehicle males. Sucrose consumption did not differ between groups in adulthood. Adolescent CMI rats demonstrated more fat bingeing than vehicles, independent of sex.

CONCLUSIONS

OCD-like behaviors are emerging during adolescence, but sucrose consumption and fat bingeing in CMI-treated animals significantly precedes the appearance of anxiety and perseveration. This OCD-like phenotype emerges fully during adulthood, suggesting that eating may likely serve as a coping strategy in these animals.

Hormone replacement with 17β-estradiol plus dihydrotestosterone restores male sexual behavior in rats treated neonatally with clomipramine

Male sexual behavior (MSB) in rodents, in both its consummatory and motivational components, is regulated by hormones such as testosterone, 17β-estradiol and 5-α-dihydrotestosterone. In experiments, neonatal treatment with clomipramine (CMI; a serotonin reuptake inhibitor) reproduces some of the signs of depression in adult age, including reduced sexual behavior manifested in a lower percentage of subjects that mount, intromit and ejaculate, although their testosterone levels were not altered. However, the effect of this treatment on estrogen levels and the consequences of hormone substitution using 17β-estradiol and 5-α-dihydrotestosterone on the expression of male sexual behavior are still unknown. Therefore, the objective of the present study was to analyze the effect of neonatal treatment with CMI on plasma testosterone and 17β-estradiol levels, and the role of testosterone, 17β-estradiol and 5-α-dihydrotestosterone in altering the consummatory and motivational components of sexual behavior in male rats. To this end, it analyzed the copulatory parameters and sexual incentive motivation (SIM) of rats treated with CMI under two conditions: basal and post-hormone replacements. Neonatal treatment with CMI did not affect plasma testosterone or 17β-estradiol concentrations, but did decrease both the consummatory component and sexual motivation according to the results of the SIM test. These aspects were recovered after administering 17β-estradiol +5-α-dihydrotestosterone, but not testosterone.

Sexual performance and precontact 50-kHz ultrasonic vocalizations in WAG/Rij rats: effects of opioid receptor treatment

WAG/Rij rats are genetically selected animals that model absence epilepsy in rats. Ultrasonic vocalizations and sexual behavior - both ethologically relevant markers of reward system functioning - are poorly described in this strain. The aim of our experiment was to investigate reward-dependent precontact 50-kHz vocalizations (PVs) and copulatory behavior as well as the effects of opioid receptor treatment on such behaviors in sexually experienced WAG/Rij males and rats from two control strains: Sprague-Dawley and Crl: Han Wistar. We analyzed the effects of the opioid receptor antagonist naltrexone (3 mg/kg) and the agonist morphine (1 mg/kg) administration. Additionally, we analyzed the initiation of copulation in sexually naïve males before drug treatment. A significantly lower number of sexually naïve WAG/Rij rats initiated copulation. Sexually experienced WAG/Rij males differed at the control session (after physiological saline treatment) compared with Sprague-Dawley rats: WAG/Rij rats displayed more 50-kHz precontact vocalizations and had longer mount and intromission latencies, longer ejaculation latency, longer postejaculatory latency to exploration, longer 22-kHz vocalization duration after ejaculation, and longer postejaculatory intromission latency. Compared with Crl: Han Wistar rats, WAG/Rij males displayed longer mount latency and shorter 22-kHz vocalization duration. Neither naltrexone nor morphine affected PVs in all groups. On the other hand, opioid receptor treatment differently influenced the number of intromissions required to achieve ejaculation and 22-kHz postejaculatory vocalization duration in WAG/Rij rats than in both control groups. This suggests functional differences in the opioid system in this strain. As a result of the number of males that initiated copulation as well as the number of intromissions to ejaculation and 22-kHz postejaculatory vocalizations which all depend on D1 receptor activation, we suggest that the proportion of opioid receptor to D1 receptors in WAG/Rij rats is different when compared with the control strains. The reward system of Wag/Rij rats with absence epilepsy is sensitive to social rewards (high level of precontact 50-kHz ultrasounds) although this strain displays a lower level of sexual motivation (longer mount latency) compared with other control strains. A lower number of sexually naïve rats initiating copulation and longer mount latency in sexually experienced males could suggest a moderate depressive-like syndrome in this strain of rats.

Lasting neurobehavioral abnormalities in rats after neonatal activation of serotonin 1A and 1B receptors: possible mechanisms for serotonin dysfunction in autistic spectrum disorders

RATIONALE

Perinatal exposure of rats to selective serotonin reuptake inhibitors (SSRIs) produces sensory and social abnormalities paralleling those seen in autistic spectrum disorders (ASDs). However, the possible mechanism(s) by which this exposure produces behavioral abnormalities is unclear.

OBJECTIVE

We hypothesized that the lasting effects of neonatal SSRI exposure are a consequence of abnormal stimulation of 5-HT1A and/or 5-HT1B receptors during brain development. We examined whether such stimulation would result in lasting sensory and social deficits in rats in a manner similar to SSRIs using both direct agonist stimulation of receptors as well as selective antagonism of these receptors during SSRI exposure.

METHODS

Male and female rat pups were treated from postnatal days 8 to 21. In Experiment 1, pups received citalopram (20 mg/kg/day), saline, (±)-8-hydroxy-dipropylaminotetralin hydrobromide (8-OH-DPAT; 0.5 mg/kg/day) or 7-trifluoromethyl-4(4-methyl-1-piperazinyl)-pyrrolo[1,2-a]-quinoxaline dimaleate (CGS-12066B; 10 mg/kg/day). In Experiment 2, a separate cohort of pups received citalopram (20 mg/kg/day), or saline which was combined with either N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-2-pyridinylcyclo-hexanecarboxamide maleate (WAY-100635; 0.6 mg/kg/day) or N-[4-methoxy-3-(4-methyl-1-piperazinyl)phenyl]-2'-methyl-4'-(5-methyl-1,2,4-oxadiazol-3-yl)-1-1'-biphenyl-4-carboxamide (GR-127935; 6 mg/kg/day) or vehicle. Rats were then tested in paradigms designed to assess sensory and social response behaviors at different time points during development.

RESULTS

Direct and indirect neonatal stimulation of 5-HT1A or 5-HT1B receptors disrupts sensory processing, produces neophobia, increases stereotypic activity, and impairs social interactions in manner analogous to that observed in ASD.

CONCLUSION

Increased stimulation of 5-HT1A and 5-HT1B receptors plays a significant role in the production of lasting social and sensory deficits in adult animals exposed as neonates to SSRIs.

Administration of clomipramine to neonatal mice alters stress response behavior and serotonergic gene expressions in adult mice

Early life exposure to antidepressants frequently occurs when pregnant mothers take the medication during late pregnancy. Previous studies in animal models have shown that early exposure to certain antidepressants can alter some behaviors in adulthood. We examined whether the administration of clomipramine, a serotonin reuptake inhibitor, to neonatal mice could result in depression-related behavioral alterations in adult mice. In addition, in an attempt to uncover the mechanism underlying these behavioral changes, we examined the expression of candidate genes in different areas of the brain. Here we show that mice chronically injected with clomipramine specifically during early postnatal development demonstrated depression-like behavior as well as altered stress responses in adulthood. An analysis of the expression of serotonergic genes after exposure to social defeat stress revealed small but significant changes in the expression of 5-HT1A receptor gene (Htr1a) and 5-HTT gene (Slc6a4) in the mice treated with clomipramine compared with the mice injected with saline. We concluded that antidepressant exposure in early days of life could alter stress-related behavior in adulthood and that the behavioral alterations are accompanied by altered serotonergic gene expressions.

Sleep-related epilepsy in a Long-Evans hooded rat model of depression

INTRODUCTION

Neonatal treatment with clomipramine (CLI) has been shown to have reliable behavioral and biological changes that mimic major symptomatic and biochemical changes found in depression. This paper further explores a common feature of depression, the comorbidity of seizure activity and depressive behaviors in this mode.

METHODS

Rat pups were neonatally treated with 40 mg/kg/day of CLI from postnatal day 8 through 21. In adulthood, they were instrumented with electroencephalographic (EEG) and electromyographic (EMG) electrodes for 24 h of polysomnogram (PSG) recordings. PSG data were analyzed for: (1) sleep-wake cycle; (2) spectral power; and (3) epileptiform activity, including NREM-to-REM transition (NRT) bursts.

RESULTS

Neonatal treatment with CLI reliably produces enhanced levels of REM (p < 0.01) and reduced sexual activity (p < 0.05). Theta power was enhanced during NREM sleep in the CLI group (p = 0.02). CLI-treated animals experienced increased frequency at the NRT (p < 0.01), as well as additional epileptiform activity of continuous (CTS; p < 0.05) and petite-continuous (P-CTS; p < 0.01) types, across the sleep-wake cycle. There is a strong temporal correlation with increased REM sleep duration, increased frequency of NRT bursts, and increased theta power during NREM sleep in CLI-treated animals.

DISCUSSION

Neonatal CLI-treated animals experienced significantly more epileptiform activity as a whole, in addition to comorbid features of depression in adulthood. Neonatal exposure to CLI will not only produce depressive phenotype but may also enhance risk for epilepsy in some individuals. This warrants further investigation into currently acceptable medicinal use in humans.

Dose-dependent effects of neonatal SSRI exposure on adult behavior in the rat

Neonatal exposure to antidepressants produces lasting impairments in male sexual behavior. Although perturbation of the serotonin system during neonatal life has been implicated in the long-term behavioral effects of neonatal antidepressant exposure, dose-response studies were necessary to confirm that inhibition of the serotonin transporter during the neonatal period is sufficient to produce impairments in sexual behavior. Therefore, the present study examined the dose-response effects of neonatal citalopram exposure on sexual behavior. In addition, the effects of exposure on anxiety-related behavior were examined since alterations in this behavioral measure could affect sexual behavior. Male Long-Evans rats were injected subcutaneously with citalopram (CTM) in one of three doses (5, 10 or 20mg/kg/d), or saline (SAL) in a volume of 0.1 ml twice daily (07:00 and 14:00 h) from PD8 to PD21. The rats were tested as adults (>PD90) for anxiety-like behavior and exploration in the elevated plus maze test and sexual behavior. Neonatal citalopram exposure produced persistent reductions in male sexual behavior characterized by significant dose-dependent reductions in the percentage of male rats displaying mounting as well as dose-dependent reductions in the number of mounts and mount latency. Neonatal citalopram exposure also produced significant dose-dependent linear trends for reductions in intromission and ejaculation behavior. However, neonatal SSRI exposure was not found to produce any effects on exploration or anxiety-like behavior in the elevated plus maze test. The present findings support the hypothesis that inhibition of the serotonin transporter during neonatal life by an SSRI is directly responsible for the long-term effects on male sexual behavior.

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.

Programming of offspring sex ratios by maternal stress in humans: assessment of physiological mechanisms using a comparative approach

Sex ratio adjustment has become a hot topic in ecology and evolutionary biology, as documentations of sex ratio skews are numerous, and include examples in diverse animal species. Over the past several decades, scientists have repeatedly debated whether human sex ratios also significantly deviate toward one sex or the other based on environmental or social conditions. An increasing number of studies supports the idea that exposure to stressful conditions can influence the sexes of offspring produced by humans, a majority of which document significantly fewer males after exposure to adverse conditions such as severe life events, economic disruption, or natural disasters. From a comparative standpoint, these findings are similar to studies in non-human mammals and other vertebrate species showing a bias toward females during times of stress. However, the mechanisms by which stress-related biases in the offspring sex ratio may occur remain elusive, and the involvement of glucocorticoids indicating a true influence of stress itself remains unstudied. Here, I review the evidence that stressful events induce sex ratio adjustment in humans. Additionally, I discuss the possibility for glucocorticoid mediation of sex ratio adjustment and the potential reproductive stages during which stress-induced sex ratio adjustment may occur in humans and other mammals.

Effect of neonatal clomipramine in the pathogenesis of ligature-induced periodontitis in Lewis rats

OBJECTIVE

The aim of this study was to verify the association between an endogenous depression model and the development of ligature-induced periodontitis in rats.

MATERIAL AND METHODS

Nine male Lewis rats received 30 mg/kg clomipramine from neonatal day 8 to day 21 (depressed group), while 13 control Lewis rats were left untouched (control group). On day 150, ligatures were placed around the 2nd upper molars in both groups, i.e. the contralateral molar of the intra-group control. On day 190, the rats were killed and the maxillae were defleshed. The distance between the cemento-enamel junction and the alveolar bone crest was measured by a blinded examiner using standardized digital photographs.

RESULTS

The depressed rats showed hyperactivity in open field on day 142 and greater attempts to escape on day 143 compared to controls. The other behavioral data did not show statistically significant differences between the groups (Mann-Whitney, p>0.05). In teeth with ligature, mean alveolar bone loss varied from 0.51 to 0.60 and from 0.63 to 0.64 mm for tests and controls, respectively (t-test, p>0.05). In teeth without ligature, these values varied from 0.38 to 0.43 and 0.42 to 0.45 mm in the test and control groups, respectively (t-test, p>0.05).

CONCLUSION

Induced depression did not alter ligature-induced bone loss in Lewis rats.

Changes in brain orexin levels in a rat model of depression induced by neonatal administration of clomipramine

Depression is associated with a deficiency of serotonergic neurons that have been found to suppress orexinergic neurons, which in turn activate these neurons in a feedback loop. This evidence suggests that orexins may be involved in the pathology of depression. Long Evans rats were treated with clomipramine (CLI) and saline (SAL) from postnatal days 8 through 21. One set of rats from both groups was sacrificed at 35 days of age for quantification of orexins in multiple brain regions. At 3-4 months of age a second set of rats was tested for immobility in a forced swim procedure, a common test for depressive signs in rats, and a third set was sacrificed for the quantification of orexins. Compared with the control rats, adult rats with neonatal CLI treatment had (1) increased forced swim immobility and (2) increased orexins A and B in the hypothalamus. However, both orexins A and B levels were decreased in multiple brain regions in the juvenile CLI rats compared with same-age controls. We concluded that although orexin levels were decreased in juvenile CLI rats, adult CLI rats with features of depression had significantly higher levels of hypothalamic orexins compared with adult controls. These results imply that orexins are likely to be involved in the pathological regulation of depression.

Evidence that the deficit in sexual behavior in adult rats neonatally exposed to citalopram is a consequence of 5-HT1 receptor stimulation during development

Neonatal (postnatal days 8-21) exposure of rats to the selective serotonin reuptake inhibitor (SSRI), citalopram, results in persistent changes in behavior including decreased sexual activity in adult animals. We hypothesized that this effect was a consequence of abnormal stimulation of 5-HT(1A) and/or 5-HT(1B) receptors as a result of increased synaptic availability of serotonin during a critical period of development. We examined whether neonatal exposure to a 5-HT(1A) (8OH-DPAT) or a 5-HT(1B) (CGS 12066B) receptor agonist can mimic the effect of neonatal exposure to citalopram on adult sexual behavior. Results showed that neonatal treatment with 5-HT(1B) receptor agonist robustly impaired sexual behavior similar to the effect of citalopram, whereas exposure to 5-HT(1A) receptor agonist only moderately influenced male sexual activity in adult animals. These data support the hypothesis that stimulation of serotonin autoreceptors during development contributes to the adult sexual deficit in rats neonatally exposed to citalopram.

Hippocampal upregulation of the cyclooxygenase-2 gene following neonatal clomipramine treatment (a model of depression)

Although a putative role has been attributed to inflammation in the pathogenesis of depressive disorders, the relationship of prostaglandins, known mediators of inflammation, and depression has not been elucidated. Clomipramine is an antidepressive drug with a pro-depressive paradoxical effect in adult rats when administrated neonatally. Using this effect as a model of depression, we investigated the differential expression of the cyclooxygenase (COX-2) gene in rat brains. Rats injected neonatally with clomipramine showed depressive-like symptoms in adulthood, as well as decreased levels of the brain-derived neurotrophic factor (BDNF) and a quantitative differential expression of the COX-2 gene (Real Time PCR) and protein (immunohistochemistry) in the hippocampus. As evidenced, the relationship between a key enzyme in the prostaglandin synthesis and biological and behavioral depression-like changes opens an interesting line of investigation regarding the molecular bases of depression and its potential treatment through immunomodulatory drugs.

Neonatal citalopram exposure produces lasting changes in behavior which are reversed by adult imipramine treatment

Neonatal exposure to antidepressants, including selective serotonin reuptake inhibitors such as citalopram, induces behavioral disturbances which persist in mature rats. These disturbances have been proposed to model the symptoms of endogenous depression. However, to date there is scant evidence for the predictive validity of any of these behaviors in response to adult antidepressant treatments. In order to directly assess the predictive validity of the early antidepressant exposure paradigm, the present study examined whether the behavioral abnormalities observed in adult animals exposed as neonates to citalopram can be reversed by adult antidepressant treatment with the prototypic antidepressant, imipramine. As noted earlier, neonatal citalopram exposure robustly increased locomotor activity and impaired male sexual behavior in adult rats. These behavioral changes were reversed following chronic adult imipramine treatment. No such reversal was observed in handled, saline treated rats. The present data support the hypothesis that some of the lasting behavioral abnormalities induced by early antidepressant exposure are sensitive to clinically relevant antidepressant treatments thus adding a measure of predictive validity to this paradigm as a model of these depressive symptoms.

Altering the course of neurodevelopment: a framework for understanding the enduring effects of psychotropic drugs

Childhood is a time filled with wondrous changes, as brain plasticity permits experiences to shape the immature brain to meet the demands of the environment. Change occurs at various levels--from neuroanatomy, including within a given region and its connectivity to other regions, to the function of neurotransmitter systems and their reactivity to pharmacological agents in the short- and long-term. The nature and degree to which drug exposure influences the final adult topography is influenced greatly by the maturational phase of these critical factors. Moreover, evidence is slowly emerging that suggests that the long-term effects of drug exposure are delayed and expressed once the vulnerable system reaches maturation (i.e., typically during adulthood). This phenomenon is known as neuronal imprinting and occurs when the effects of drug exposure outlast the drug itself. Thus, understanding the persistent effects critically depends on the window of observation. Embracing this concept should influence how we conduct preclinical assessments of developmental drug exposure, and ultimately how we conduct clinical assessments of drug efficacy, effectiveness, and safety for the treatment of childhood psychiatric disorders. In this article, we present a model to provide a heuristic framework for making predictions about imprinted effects of childhood drug exposure. We then review epidemiological data on attention deficit hyperactivity disorder (ADHD) and childhood depression, prescription practices, and what is known regarding the long-term consequences of drug exposure in these populations. We conclude with a discussion of the current status of preclinical studies on juvenile stimulant exposure.

Impairments of ERK signal transduction in the brain in a rat model of depression induced by neonatal exposure of clomipramine

Depression is associated with deficiencies in monoaminergic transmitters and possibly neurotrophins. A common cellular response to these molecules is the activation of extracellular signal-regulated kinase (ERK). A deficiency of ERK signal transduction in depression was therefore hypothesized and was tested in a rat model of depression, produced by neonatal treatment with clomipramine (CLI). We measured sexual behaviors and brain levels of ERK, phosphorylated ERK (pERK), protein phosphatase 1 (PP1), and MAPK phosphatase-2 (MKP-2) during adulthood in control and neonatally CLI-treated rats (CLI rats). As expected, the CLI rats exhibited significantly lower sexual activities and also exhibited (1). significant decreases of pERK1/2 in the frontal cortex and pERK1 in the hippocampus, (2). slight but significant reduction of ERK2 in the frontal cortex and hippocampus, (3). no change of pERK1/2 levels in the temporal cortex, occipital cortex, parietal cortex, midbrain, and medulla, (4). significantly higher levels of PP1 in both the frontal cortex and hippocampus, (5). no change in MKP-2 in any examined region, and (6). all five measures of sexual function were significantly correlated with ERK2 and pERK2 in the frontal cortex. These findings suggest that a deficiency in the ERK signaling pathway is involved in the display of depressive behaviors.

Development of fetal and neonatal sleep and circadian rhythms

The origin of sleep and circadian rhythms development is found during the fetal period. Both quiet (NREM) and active (REM) sleep are distinguishable during the last 10 weeks of gestation. Comparable to fetuses, low risk preterm infants recorded at 30-40 weeks postconceptional age, had a similar development of sleep i.e. an increase in quiet sleep and a decrease in indeterminate sleep. A further development in sleep organization characterized by increased slow wave and spindle activity during quiet sleep and coupling with circadian rhythm takes place during the first 6 months of life in both term and preterm infants.Circadian rhythm of fetal heart rate synchronized with maternal rest-activity, heart rate, cortisol, melatonin, and body temperature rhythms is present during the last 10 weeks of gestation. Although maternally influenced, circadian rhythm antenatally becomes ultradian at birth. Both preterm and term infants show a significant increase in circadian body temperature rhythm amplitude during the first 3 months of life.

Sleep-wake effects of meta-chlorophenyl piperazine and mianserin in the behaviorally depressed rat

The present study examined the effects of meta-chlorophenyl piperazine (mCPP) and mianserin on the sleep-wake cycle of the clomipramine-induced behaviorally screened depressed rats. Six-hour polygraphic recordings were made between 06:00 and 12:00 h, after a single injection of either saline or mianserin or mCPP into the lateral cerebral ventricle (i.c.v.) of both the depressed (n=12) and control rats (n=12). The injection of mCPP in the depressed rats caused a significant reduction in the total duration and number of rapid eye movement (REM) sleep episodes while it increased the REM sleep onset latency compared to the control saline injections. The injection of mianserin in the depressed rats also caused a significant reduction in the total duration and number of REM sleep episodes without changing the REM sleep latency. These results demonstrate for the first time that the central administration of mCPP and mianserin could act as an antidepressant in the clomipramine-induced rat model of depression.

Differences in behavior and monoamine laterality following neonatal clomipramine treatment

Postnatal treatment between 8 to 21 days of age with clomipramine (15 mg/kg, twice daily) produces an animal model that has many of the behavioral hallmarks of depression. In this study, we investigated the enduring behavioral and neurochemical effects of this early treatment in adult animals. Locomotor activity was increased in clomipramine-treated males, but not females, relative to vehicle-treated subjects. Increases in anxiety-like behavior in the elevated plus maze also were observed in clomipramine-exposed adults, but no sex differences were detected. Clomipramine-treated animals had shifts in the laterality of monoamines in limbic regions with lower serotonin levels on the right side while vehicle-treated animals had lower serotonin on the left side. The lateralization of dopamine content demonstrated the same pattern. This decline in monoaminergic content is consistent with clinical studies demonstrating decrements in serotonin as well as alterations in the lateralization of function in individuals with major depressive order.

Effects of nicotine on alcohol intake in a rat model of depression

Clinical studies suggest that depression facilitates alcohol abuse. Depressed individuals also have increased rates of smoking, and it has been suggested that nicotine may improve depression. It is therefore possible that nicotine may reduce alcohol use in depression. To investigate this potential relationship, we evaluated alcohol intake in an animal model of depression, which consists of administering clomipramine (CLI), a preferential serotonin reuptake inhibitor, to neonatal rats. This pharmacological manipulation produces adult depression-like behaviors, such as reduced aggressiveness, decreased pleasure seeking, diminished sexual activity, increased locomotor activity and increased REM sleep. In this study, we found that CLI rats exhibited significantly higher locomotor activity, lower aggressiveness and higher alcohol intake than control rats. Chronic administration of a low dose of nicotine (0.25 mg/kg/day) or a sham operation did not modify these behaviors. However, chronic administration of nicotine at a higher dose (1.5 mg/kg/day) significantly increased aggressive behavior and reduced alcohol intake in CLI rats. The effect of nicotine on alcohol intake lasted at least 1 month after cessation of nicotine administration. These results indicate that nicotine reverted some depression signs and reduced alcohol self-administration in the CLI model of depression.

The critical window of brain development from susceptive to insusceptive. Effects of clomipramine neonatal treatment on sexual behavior

The immature brain is much more sensitive to abnormal experience, particularly sleep deprivation, drug exposure, and maternal separation. The critical time period during which features in the brain's susceptibility to such experience change, however, has not yet been determined. In previous studies on rats, we found that neonatal treatment with clomipramine (CLI) during postnatal days 8--21 (P8-21) produced behavioral and physiological abnormalities in adult rats that resembled the abnormalities found in human endogenous depression. The objective of the present study is to determine (1) the critical (more specifically, the latest) time frame in which CLI treatment will produce adult depression and (2) the shortest treatment window during which CLI can induce adult depression. Male rats were neonatally treated with CLI (20 mg/kg, sc) twice daily or with an equivolume of saline. The treatment windows were P12--17, P14--20, P16--22, and P12--15. Six variables, including number of mounts, intromission, ejaculation, mount latency, ejaculation latency, and post-ejaculation interval, were measured visually between the ages of 4 and 5 months. Rats treated with CLI showed significant sexual impairment in treatment windows P12--17 and P14--20 and slight sexual deficiency in the short window P12--15. No significant sexual impairment was found in window P16--22. We concluded that P14--20 was the latest window during which CLI treatment produces adult sexual deficiency and that 6 days might be the shortest treatment window to produce significant behavior abnormalities.

Effects of genitofemoral nerve transection on copulatory behavior and fertility in male rats

Selective transection of peripheral nerves that innervate the pelvic region results in the alteration of some aspects of copulatory behavior, including seminal plug weight. Both branches of the genitofemoral nerve primarily innervate the cremaster muscle although the genital branch has a wide distribution in the cremasteric sac. Thermoregulation of spermatogenesis and the mechanical event of ejaculation largely depend on cremaster contractility. In this study, we analyzed the effects of bilateral transection of the genitofemoral nerve on male copulatory behavior and on fertility. Sexually experienced adult male rats were submitted to sexual behavior tests before and after surgical transection of the genitofemoral nerve. Tests were made four times before and on Days 9, 12, 15, 18 and 21 after surgery, and seminal plug weight was also analyzed. In addition, fertility was tested using two different approaches: by allowing the male to ejaculate once in an estrous female or keeping the male with three females during 15 days. Results showed that there were no differences in any of the copulatory parameters, including seminal plug weight. Regarding fertility, both procedures showed that the ability to induce pregnancy was significantly diminished in the neurectomized males tested at different times after surgery. These results support the notion that genitofemoral nerve regulation of fertility via contraction of the male cremaster muscle is an important factor in reproduction in rats.

Effects of withdrawal from an escalating dose schedule of d-amphetamine on sexual behavior in the male rat

The present study sought to determine the effect of withdrawal from an escalating dose schedule of d-amphetamine on sexual behavior in male rats. Tests were conducted every 5 days until stable levels of sexual behavior were obtained. With repeated testing, male rats displayed an increase in their exploration of the testing chambers prior to the introduction of an estrous female. Half of the male rats were then subjected to a 4-day escalating dose schedule of d-amphetamine administration (1-12 mg/kg), while half received vehicle. Twelve hours after the final drug injection, subjects were tested for sexual behavior. Withdrawal from the drug was associated with decrements in several motivational components of sexual behavior, including decreased anticipatory locomotor and increased postejaculatory intervals, while consummatory measures remained largely unaffected. This pattern of sexual deficits resembles those seen in human depressive disorders, and therefore, provides additional support for the use of psychostimulant withdrawal as a rodent model of depression.

Early stress and genetic influences on hypothalamic-pituitary-adrenal axis functioning in adulthood

During early development, environmental challenges set the stage for permanent changes in the functioning of the pituitary-adrenal stress response. Since these data have been reported almost exclusively in single rat strains the role of phenotypic and genotypic factors in shaping the stress response is relatively unknown. This study examined whether the phenotypic/genetic profile of the rat influences the long-term response to challenge after early exposure to stress. Two strains of Sprague-Dawley rats were used in this study: one is a stress-induced animal model of "learned helpless" (LH) behavior and the other a resistant strain developed through selective breeding. Stress-induced adrenocorticotropic hormone (ACTH) and corticosterone release was monitored in adult congenital learned helpless (cLH) rats and congenital non-learned helpless (cNLH) rats. The rats were exposed to cold stress or maternal deprivation (on either postnatal day 7 or day 21). After the early acute stress exposure, animals remained undisturbed until challenged in adulthood (day 90) with footshock stress. In cLH animals (adults) early cold stress (particularly after acute stress on postnatal day 21) and maternal deprivation stress resulted in an enhancement of stress-induced ACTH release compared to nonstressed cLH and cNLH controls. In contrast, adrenal responsiveness was generally suppressed in cLH animals that were acutely stressed with cold stress or maternal deprivation stress early in life. The above results suggest that the genetic/phenotypic profile of the animal is a determinant in the changes observed in the adult stress response after early exposure to stressors.

Alterations in the levels of monoamines in discrete brain regions of clomipramine-induced animal model of endogenous depression

It has been hypothesized that the dysfunction of the serotonergic and catecholaminergic neurotransmission is involved in the pathogenesis of depression. These hypotheses are being tested in a novel rat model of depression developed by the treatment of antidepressant-clomipramine neonatally from postnatal day 8 to 21. After the attainment of adulthood, these rats mimicked the features of the human endogenous depression showing significant decrease in the aggressive behavior and food intake. Biogenic amine estimations in these rats revealed that the levels of serotonin and noradrenaline were decreased significantly (P < 0.001) in frontal cortex, hippocampus, brain stem, septum and hypothalamus, while the levels of dopamine were decreased significantly (P < 0.001) only in the hippocampus compared to normal control and vehicle treated groups of rats. Our results demonstrate the dysfunction of serotonergic and noradrenergic neurotransmission, with lesser involvement of dopaminergic neurotransmission in the clomipramine induced experimental model of depression.

Benzodiazepine withdrawal facilitates the subsequent onset of escape failures and anhedonia: influence of different antidepressant drugs

The effect of benzodiazepine (BDZ) withdrawal on escape acquisition and on the behavioral response to two different reinforcing stimuli was investigated. In addition, the influence of antidepressant drugs (AD) differing in their mechanism of action on these behavioral outputs was also evaluated. Rats subjected to withdrawal from a chronic treatment with diazepam (DZM; 2 mg/kg per day, i.p.) during 21 days were subsequently exposed to a brief inescapable shock session (IS) and 48 h later to an active avoidance test. Only withdrawn animals exposed to the IS exhibited enhanced escape failures. In an additional experiment, withdrawn rats were repeatedly administered with vehicle (VEH), desipramine (DMI; 5 mg/kg, i.p.), fluoxetine (FLU; 5 mg/kg, i.p.) or phenelzine (PHEN; 5 mg/kg, i.p.) and subsequently exposed to IS and to active avoidance task. A significant reversal of escape deficit was only observed following DMI and PHEN but not after FLU. Furthermore, withdrawn rats showed a reduced preference for a sexually relevant olfactory cue, this reduced sensitivity was only normalized following DMI but not after the administration of FLU or PHEN. Finally, rats exposed to abrupt cessation of chronic BDZ administration did not exhibit preference for a context previously associated with amphetamine (AMP) under the conditioned place preference (CPP) procedure. All these findings are indicative that BDZ withdrawal facilitates the subsequent occurrence of behavioral changes-escape failures and reduced behavioral response to rewarding stimuli-suggested to parallel important symptoms of human depression. In addition, DMI seems to be much more effective in restoring such behavioral abnormalities as compared to a MAO inhibitor and to a inhibitor of 5-HT uptake.

Pharmacological features of masculine sexual behavior in an animal model of depression

Neonatal treatment with clomipramine induces behavioral alterations during adulthood that resemble symptoms observed in human depression. Therefore, it has been proposed as an animal model of depression. Impairment of male sexual performance is one of the main effects of this treatment. Using this model of depression, we evaluated the effects of drugs that stimulate sexual performance by acting selectively on the adrenergic, serotonergic, or cholinergic system. Yohimbine, a selective antagonist of the alpha-2 receptors; 8-OH-DPAT, a selective agonist of the 5-HT1A receptors; and oxotremorine, a muscarinic agonist, were administered to male rats neonatally treated with clomipramine that showed sexual behavior impairments. Yohimbine and oxotremorine induced only a slight improvement of sexual deficiencies. 8-OH-DPAT not only restored sexual behavior to normal levels, but induced facilitation in most of the copulatory parameters. These results suggest that neonatal treatment with clomipramine induces sexual deficits acting mainly on the adrenergic and cholinergic systems, while the serotoninergic system seems to be preserved.

Decreased dorsal raphe nucleus neuronal activity in adult chloral hydrate anesthetized rats following neonatal clomipramine treatment: implications for endogenous depression

Although the biological cause of endogenous depression is unknown, one commonly held hypothesis proposes that depression results, in part, from decreased central serotonin (5-HT) neurotransmission. Previous research found that clomipramine (CLI) treatment of neonatal rats produced, in adult rats, a variety of behavioral and physiological dysfunctions resembling those found in human endogenous depression. It was later reported that adult CLI-treated rats exhibited a decreased discharge of 5-HT neurons in the dorsal raphe nucleus (DRN) compared with control rats. This finding, however, was not replicated in subsequent studies that detected differences in DRN receptor function. Several factors were identified that may have contributed to the inability of the latter studies to detect CLI vs. control differences in DRN firing rates and interspike interval histograms (ISIH). Among these were the anesthetic used, the age at which the adult rats were tested, and the location of the recording electrode. The present study controlled these variables by using chloral hydrate anesthesia, testing 'depressed' rats at both 2 and 3 months of age, and verifying electrode location using standard histological techniques. We found that DRN unit firing in 'depressed' rats (0.417 +/- 0.071 spikes/s) was less than half that of 'non-depressed' control rats (i.e. neonatal saline treatment 0.968 +/- 0.12 spikes/s). Additionally, ISIH's indicated that, in addition to the lower firing rate of 5-HT DRN neurons, adult CLI rats had an altered temporal discharge pattern of these neurons. Thus, the ISIH of 5-HT DRN neurons recorded from CLI rats was characterized by a flat distribution suggesting random temporal firing patterns. These results confirm previous findings of decreased DRN firing rates and flat ISIH's in 'depressed' rats and extend previous findings to younger rats of a different strain. The results thereby lend support to the hypothesis of a role for decreased central 5-HT as a substrate for the behavioral deficiencies observed in endogenous depression and suggest that these deficiencies may also result, in part, from a random, rather than orderly, temporal pattern of discharge in these neurons.

Effects of neonatally administered iprindole on adult behaviors of rats

In past studies, administration of the antidepressant drugs clorimipramine, zimeldine, or desipramine to neonatal rats produced abnormalities in adult rats that modeled some behavioral and/or REM sleep features of human endogenous depression. Although these three drugs affected different neurotransmitter systems, all caused REM sleep deprivation (RSD). This suggested the hypothesis that RSD of neonatal rats caused their adult depression. One prediction of this hypothesis is that neonatally administered iprindole, an antidepressant drug that does not produce RSD, will not produce adult rats that model depression. The present study tested this hypothesis. Iprindole was administered to neonatal experimental rats and saline was administered to neonatal control rats. When the rats matured, compared with control rats, experimental rats were not significantly different in aggressive behavior (shock induced fighting), sexual behaviors, open field locomotion, and REM sleep. In our previous studies on rats, all these adult behaviors were affected in a depressive-like way by neonatally administered clorimipramine. Because iprindole does not decrease REM sleep, the present results support the hypothesis that in rats neonatal RSD causes adult depression.

Effects of chronic treatment with zimelidine and REM sleep deprivation on the regulation of raphe neuronal activity in a rat model of depression

Electrophysiological investigations on the mechanism of action of antidepressants have shown that both deprivation of rapid eye movement (REM) sleep and chronic treatment with antidepressants render serotoninergic (5-HT) neurons less sensitive to the inhibitory effect of 5-HT reuptake blockers in the rat. It was of interest to test whether the same mechanisms could be evidenced in a possible experimental model of depression. The latter consisted of rats which had been treated neonatally with clomipramine and exhibited at adult age behavioural and sleep alterations which resemble the human disorder. Recording the electrophysiological activity of 5-HT neurons in the nucleus raphe dorsalis (NRD) revealed that both chronic treatment with zimelidine and REM sleep deprivation induced a hyporeactivity of these neurons to the inhibitory effect of citalopram in "normal" rats. However, in rats which had been treated neonatally with clomipramine, 5-HT neurons were hyporeactive to the effect of this 5-HT reuptake blocker already under baseline conditions, and no further modification could be induced by chronic zimelidine administration or REM sleep deprivation. It can be hypothesized that adaptive phenomena at the serotoninergic NRD level are not a relevant element to explain the mechanism of action of anti-depressants in the present model of depression, while they have been considered as a crucial event in "normal" rats.

An early lesion of the lateral septal nuclei produces changes in the forced swim test depending on gender

1. Several pharmacological maneuvers in very young rats produce later changes resembling human depression. 2. Rats were submitted to a wide lesion in lateral septal region at 8th day after birth and forced to swim at maturity. 3. Male lesioned group showed the highest amount of immobility; whereas, female sham lesion group showed a greater response to treatments. 4. A gender-dependent sensitivity to early lateral septal nucleus lesions and to antidepressants are concluded.

The function of fetal/neonatal rapid eye movement sleep

The hypothesis is put forward that rapid eye movement (REM) sleep in early life serves as (1) an indicator for the degree of brain maturation and (2) the promoter of further brain development. This hypothesis, although not exclusive, differs (a) from the theory of Roffwarg et al. that REM sleep substitutes for 'wakefulness' during the period (early life) in which wakefulness is limited, (b) from the theory of Crick and Mitchson, i.e., the 'unlearning' hypothesis of REM sleep, (c) from the theory of Jouvet, i.e., that REM sleep is a time for genetic read-out and (d) from the theory of Freud, i.e., that dreams fulfil our wishes (in other words, activation of neuronal systems that were disproportionally activated during wakefulness).

Effects of neonatal clomipramine on cholinergic receptor sensitivity and passive avoidance behavior in adult rats

The effects of neonatal treatment with clomipramine on the sensitivity of cholinergic receptor and passive avoidance behavior were studied to examine the activity of the central cholinergic system. Rat pups were treated twice daily from postnatal day 5 to 21 with clomipramine (15 mg/kg, s.c.) and at 3 months of age the thermic responses to three different doses of oxotremorine were measured. One day following oxotremorine challenge study, the animals were subjected to passive avoidance training and retention was measured 24-hr later. Clomipramine treated animals showed an enhanced cholinomimetic-induced hypothermia and an increased latency in passive avoidance test. These findings may reflect an altered sensitivity of central cholinergic system in rats given clomipramine as neonates. The results were compared to other animal models of depression.

Symposium: Normal and abnormal REM sleep regulation: The importance of REM sleep for brain maturation

A number of studies, some done by us, are reviewed concerning the function of foetal/neonatal REM sleep. The hypothesis is put forward that REM sleep in early life serves as an indicator for: (1) the degree of brain maturation, and (2) the promotion of further brain development. This hypothesis, although not exclusive, differs from: the original theory of Roffwarg et al. (1966) that REM sleep serves as "wakefulness" during the period in which wakefulness is limited; and also from the theory of Crick and Mitchson (1983-the "unlearning" hypothesis of REM sleep). As the functions of sleep in general, and REM sleep in particular, are still unclear, we hope this review will suggest new possibilities for future research.

Behavioral effects of neonatal treatment with clomipramine, scopolamine, and idazoxan in male rats

It has been suggested that REM sleep deprivation due to the administration of clomipramine, during early developmental stages, results in dramatic behavioral changes during adulthood. One of the main alterations is the impairment of masculine sexual behavior (MSB). Clomipramine increase monoaminergic availability at the synaptic level and also suppresses REM sleep. This study was performed to compare the effect on masculine sexual behavior of three different neonatal treatments: clomipramine, which increases monoaminergic availability at the synaptic level and suppresses REM sleep; scopolamine, a cholinergic antagonist that suppresses REM sleep; and idaxozan, a selective adrenergic agonist. Subjects (Ss) were treated neonatally and tested for masculine sexual behavior during adulthood with standard techniques. Results obtained with clomipramine administration showed a marked impairment of MSB, mainly reflected by the decrease in the percentage of active Ss and the decrease in the percentage of Ss reaching ejaculation. In contrast, idaxozan and scopolamine produce a facilitation of MSB. The effect of idaxozan was not significantly different when compared to saline control rats. The effect of scopolamine was greater, and the percentage of Ss reaching ejaculation was significantly larger than saline control. These results suggest that the alterations of sexual behavior induced with neonatally administered clomipramine are not due to early REM sleep deprivation. As idaxozan did not replicate clomipramine results, it is also possible that noradrenergic transmission is not involved in the generation of these effects. It remains possible that the serotonin system could be responsible for the impairment of sexual behavior due to neonatal clomipramine treatment.

Differential development of the stress response in congenital learned helplessness

Early in the development of the hypothalamic-pituitary-adrenal (HPA) axis, the rat undergoes a stress hyporesponsive period of blunted responses to several stressors including cold exposure (CE) and maternal deprivation (MD). We examined the development of the axis by monitoring adrenocorticotropin hormone (ACTH) plasma levels in an animal model of depression and/or anxiety characterized by learned helpless (LH) behavior and a dysfunctional HPA axis in adult life. On postnatal day 7 there was no significant difference in basal plasma ACTH levels between congenital (cLH) and controls, but cLH animals showed a blunted response to CE (P < 0.001). By postnatal day 14 there was a dramatic increase in ACTH response to CE (P < 0.005). On postnatal day 21 baseline ACTH and response to CE were again significantly suppressed in cLH rats. Stress responsiveness to MD was present in all groups and was insignificantly different for all ages of development between groups. These findings suggest that rats with congenital learned helplessness undergo a differential response in the development of the HPA axis in that the axis was hypersensitive at postnatal day 14 and became hyporesponsive beyond day 14, and this may, in part, account for the dysfunctional stress response observed during adulthood.

DMBA-induced mammary tumor growth in rats exhibiting increased or decreased ability to cope with stress due to early postnatal handling or antidepressant treatment

Depression and an ability to cope with stress are suggested to play a role in the vulnerability to breast cancer. In rats, neonatal clomipramine administration induces subsequent behavioral abnormalities that closely resemble those seen in human endogenous depression. Early postnatal handling, on the other hand, improves subsequent ability to cope with stress in rodents. The present study examined whether early clomipramine treatment or handling influences the growth of 7,12-dimethylbenz(a)anthracene (DMBA)-induced mammary tumors in female Sprague-Dawley rats. Between postnatal days 5 and 20, rat pups were injected daily with 25 mg/kg clomipramine, handled either by holding them in a hand (H-handling) or by giving them a saline injection (I-handling), or left nonhandled. During these manipulations, but not later, body weight gain was lower in the I-handled and clomipramine-treated pups than in the H-handled rats. As adults, the time spent immobile in the swim test, a model of depressive behavior and an ability to cope with stress, was significantly lengthened in the clomipramine-treated female rats, and shortened in the handled females. Measurement of plasma 17-beta-estradiol (E2) did not reveal any significant differences between the groups. The percentage of animals developing mammary tumors was significantly higher, and the length of survival shorter among the clomipramine-treated rats than among the I-handled rats. However, both groups exhibited less tumors and longer survival than the nonhandled controls. There were no differences in mammary tumor incidence or survival between the nonhandled and H-handled rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Decreased raphe unit activity in a rat model of endogenous depression

One theory about the pathogenesis of endogenous depression is that decreased serotonergic (5-HT) neurotransmission is involved in producing the disorder. A key component of brain 5-HT neurotransmission is the discharge rate of 5-HT neurons in the dorsal raphe nucleus (DRN), a major aggregation of 5-HT neurons. We tested the hypothesis that the discharge rate of 5-HT neurons in the DRN was decreased in a new animal (rat) model of human endogenous depression. In this model, rats are treated neonatally with the antidepressant chlorimipramine. When adult, these animals exhibit several behavioral, REM sleep, and treatment response features of the human disorder. We found in a single unit measurements in adult, pentobarbital-anesthetized rats that, compared with 'non-depressed' control rats, the 'depressed' rats had a lower discharge rate of 5-HT neurons in the DRN. This correlation is consistent with the theory that 5-HT neurotransmission is diminished in endogenous depression.

Juvenile desipramine reduces adult sensitivity to imipramine in two behavioral tests

The behavioral effects of adult imipramine administration were examined in female rats treated with desipramine as juveniles (JDES), treated with saline as juveniles (JSAL), and untreated as juveniles (JUNT). In the forced swimming test, the juvenile groups displayed similar behavioral effects of imipramine when administered short term following a pretest forced swimming exposure. Similar effects of imipramine were observed when administered long term prior to the only test exposure. When rats were not given a pretest forced swimming test exposure, short-term imipramine had no effect on JDES rats but did influence JSAL and JUNT rats. In the open-field test, short- and long-term imipramine treatment affected the behavior of JUNT and JSAL rats. Short-term imipramine treatment influenced open-field behavior of JDES animals, but long-term imipramine treatment had no effect. These results suggest that JDES treatment may permanently alter the neural mechanism underlying the behavioral effects of antidepressant treatment.

Neonatal treatment with clomipramine increased immobility in the forced swim test: an attribute of animal models of depression

The forced swimming test in rats has been identified as a suitable model for detecting antidepressant activity of several drugs regardless of their mode of action. On the other hand, a number of animal models of human endogenous depression have been proposed. Recently, it has been reported that perinatal administration of clomipramine in rats elicits behavioral changes in adulthood that resemble human endogenous depression. In the present study, we showed that in this new animal model of depression immobility was increased when animals were submitted to the forced swimming test. This finding supports the notion that the amount of immobility during the forced swimming test is directly proportional to a depressive state in the rat.

In vitro neurotransmitter release in an animal model of depression

Sprague-Dawley rats exposed to uncontrollable shock can be separated by a subsequent shock escape test into two groups: a "helpless" (LH) group which demonstrates a deficit in escape behavior, and a "nonlearned helpless" (NLH) group which shows no escape deficit and acquires the escape response as readily as naive control rats (NC) do. The present studies were designed to examine the correlations between the behavioral differences and the changes of in vitro neurotransmitter release seen in these three groups of rats. The major finding concerned a significant increase in endogenous and K(+)-stimulated serotonin (5-HT) release in the hippocampal slices of LH rats. There were no apparent differences in acetylcholine, dopamine and noradrenaline release in the hippocampus of LH rats as compared to NLH and NC rats. These results add further support to previous studies in our laboratory which implicate presynaptic 5-HT mechanisms in the behavioral deficit caused by uncontrollable shock.

Procedure- and age-dependent hyperactivity in a new animal model of endogenous depression

We have replicated the findings of Mirmiran and colleagues that neonatal administration of the antidepressant clomipramine (CLI) to male rats results in hyperactivity in open-field tests in adulthood. We report that this effect does not reliably occur in a "Digiscan" activity device. The difference in effect between the two activity measuring devices may be due to more stress being present in the open-field test, and we propose that the CLI-treated rats may be more reactive to stress. This hypothesized enhanced reactivity to stress may be similar to the proposed vulnerability of depressed humans to stress. In addition, we have found that the open-field effect does not occur until the rats are at least 4 months old; this delayed effect may be analogous to the progressive onset of endogenous depression in humans.