REM sleep abnormalities in a new animal model of endogenous depression

Early life sleep disruption has long lasting, sex specific effects on later development of sleep in prairie voles

In mammals, sleep duration is highest in the early postnatal period of life and is critical for shaping neural circuits that control the development of complex behaviors. The prairie vole is a wild, highly social rodent that serves as a unique model for the study of complex, species-typical social behaviors. Previous work in our laboratory has found that early life sleep disruption (ELSD) in prairie voles during a sensitive window of postnatal development leads to long lasting changes in social and cognitive behaviors as well as structural changes in excitatory and inhibitory neural circuits in the brain. However, it is currently unknown how later sleep is impacted by ELSD, both shortly after ELSD and over the long term. Therefore, the aim of this study was to describe the effects of ELSD on later life sleep, compared to sleep in normally developing prairie voles. First, we conducted tethered electroencephalogram/electromyogram (EEG/EMG) recordings in juvenile prairie voles undergoing ELSD, compared to Control conditions. Second, we conducted 24 h of home cage tethered EEG/EMG recordings in either adolescent or adult male and female prairie voles that had previously undergone ELSD or Control conditions as juveniles. We found that, as adults, male ELSD prairie voles showed persistently lower REM sleep duration and female ELSD prairie voles showed persistently higher NREM sleep duration compared to Controls, but no other sleep parameters differed. We concluded that 1) persistent effects of ELSD on sleep into adulthood may contribute to the social and cognitive deficits observed in adult voles, and 2) sleep disruption early in life can influence later sleep patterns in adulthood.

Melatonin Reduces Alcohol Drinking in Rats with Disrupted Function of the Serotonergic System

The reason for the limited treatment success of substance-use-related problems may be a causal heterogeneity of this disorder that, at least partly, is manifested as differences in substance-use motives between individuals. The aim of the present study was to assess if rats with pharmacologically induced differences in the function of the serotonergic system would respond differently to melatonin treatment compared to control rats with respect to voluntary alcohol consumption. To achieve this goal, we treated rats neonatally with the selective serotonin transporter (SERT) inhibitor escitalopram. This procedure has been reported to cause long-lasting sleep abnormalities in rodents. The study demonstrated that during adulthood, rats that had been treated with escitalopram tended to drink higher amounts of alcohol compared to control rats. Further, administration of melatonin significantly decreased the alcohol intake in escitalopram-treated animals but caused only a slight, nonsignificant reduction in the alcohol consumption by control rats. In conclusion, our data support the therapeutic potential of melatonin as a treatment for alcohol use disorder. However, interindividual differences between alcohol users may considerably modify the outcome of the melatonin treatment, whereby patients that manifest lower sleep quality due to disruption of serotonergic activity are more likely to benefit from this treatment.

Sleep Disturbances and Depression Are Co-morbid Conditions: Insights From Animal Models, Especially Non-human Primate Model

The incidence rates of depression are increasing year by year. As one of the main clinical manifestations of depression, sleep disorder is often the first complication. This complication may increase the severity of depression and lead to poor prognosis in patients. In the past decades, there have been many methods used to evaluate sleep disorders, such as polysomnography and electroencephalogram, actigraphy, and videography. A large number of rodents and non-human primate models have reproduced the symptoms of depression, which also show sleep disorders. The purpose of this review is to examine and discuss the relationship between sleep disorders and depression. To this end, we evaluated the prevalence, clinical features, phenotypic analysis, and pathophysiological brain mechanisms of depression-related sleep disturbances. We also emphasized the current situation, significance, and insights from animal models of depression, which would provide a better understanding for the pathophysiological mechanisms between sleep disturbance and depression.

The Ontogenesis of Mammalian Sleep: Form and Function

PURPOSE OF REVIEW

To present an up-to-date review and synthesis of findings about perinatal sleep development and function. I discuss landmark events in sleep ontogenesis, evidence that sleep promotes brain development and plasticity, and experimental considerations in this topic.

RECENT FINDINGS

Mammalian sleep undergoes dramatic changes in expression and regulation during perinatal development. This includes a progressive decrease in rapid-eye-movement (REM) sleep time, corresponding increases in nonREM sleep and wake time, and the appearance of mature sleep regulatory processes (homeostatic and circadian). These developmental events coincide with periods of rapid brain maturation and heightened synaptic plasticity. The latter involve an initial experience-independent phase, when circuit development is guided by spontaneous activity, and later occurring critical periods, when these circuits are shaped by experience.

SUMMARY

These ontogenetic changes suggest important interactions between sleep and brain development. More specifically, sleep may promote developmental programs of synaptogenesis and synaptic pruning and influence the opening and closing of critical periods of brain plasticity.

Depression-like behavior is associated with lower Per2 mRNA expression in the lateral habenula of rats

Circadian rhythm dysfunction is primary symptom of depression and is closely related to depression onset. The role of the lateral habenula (LHb) of the thalamus in the pathogenesis of depression has been a research topic of great interest. The neuronal activity of this structure has circadian characteristics, which are related to the regulation of circadian rhythms. However, in depression model of rats, the role of clock genes in the LHb has not been assessed. To address this gap, we used a clomipramine (CLI) injection-induced depression model in rats to assess the daily expression of rhythmic genes in the LHb and depression-like behavior in rats at multiple time points. In determining the role of the Per2 gene in the development of depression-like behavior in the LHb, we found that the expression of this clock gene differed in a circadian manner. Per2 expression was also significantly decreased in CLI-treated rats in late afternoon (17:00) and in the middle of the night (1:00). Furthermore, silencing Per2 in the LHb of normal rats induced depression-like behavior at night, suggesting that Per2 may play an important role in the pathogenesis of depression. Collectively, these results indicate that decreased Per2 expression in the LHb may be related to increased depression-like behavior at night in depression model of rats.

Chronic brain stimulation rewarding experience ameliorates depression-induced cognitive deficits and restores aberrant plasticity in the prefrontal cortex

BACKGROUND

Major depressive disorder (MDD) is a multifactorial disease which often coexists with cognitive deficits. Depression-induced cognitive deficits are known to be associated with aberrant reward processing, neurochemical and structural alterations. Recent studies have shown that chronic electrical stimulation of brain reward areas induces a robust antidepressant effect. However, the effects of repeated electrical self-stimulation of lateral hypothalamus - medial forebrain bundle (LH-MFB) on depression-induced cognitive deficits and associated neurochemical and structural alterations in the prefrontal cortex (PFC) are unknown.

OBJECTIVES

We investigated the effect of chronic rewarding self-stimulation of LH-MFB in neonatal clomipramine (CLI) model of depression. During adulthood, neonatal CLI and saline administered rats were implanted with bilateral electrodes stereotaxically in the LH-MFB and trained to receive intracranial self-stimulation (ICSS) for 14 days. The rats were tested for depressive-like behaviors, learning and memory followed by estimation of PFC volumes, levels of monoamines and its metabolites in the PFC.

RESULTS

We found that chronic ICSS of LH-MFB reverses CLI-induced behavioral despair and anhedonia. Interestingly, self-stimulation normalizes the impaired novel object and location recognition memory in CLI rats. The amelioration of learning impairments in CLI rats was associated with the reversal of volume loss and restoration of monoamine metabolism in the PFC.

CONCLUSION

We demonstrated that repeated intracranial self-stimulation of LH-MFB ameliorates CLI-induced learning deficits, reverses altered monoamine metabolism and the atrophy of PFC. Our results support the hypothesis that chronic brain stimulation rewarding experience might be evolved as a potential treatment strategy for reversal of learning deficits in depression and associated disorders.

The truncated TrkB receptor influences mammalian sleep

Brain-derived neurotrophic factor (BDNF) is a neurotrophin hypothesized to play an important role in mammalian sleep expression and regulation. In order to investigate the role of the truncated receptor for BDNF, TrkB.T1, in mammalian sleep, we examined sleep architecture and sleep regulation in adult mice constitutively lacking this receptor. We find that TrkB.T1 knockout mice have increased REM sleep time, reduced REM sleep latency, and reduced sleep continuity. These results demonstrate a novel role for the TrkB.T1 receptor in sleep expression and provide new insights into the relationship between BDNF, psychiatric illness, and sleep.

Evaluation of animal models of obsessive-compulsive disorder: correlation with phasic dopamine neuron activity

Obsessive compulsive disorder (OCD) is a psychiatric condition defined by intrusive thoughts (obsessions) associated with compensatory and repetitive behaviour (compulsions). However, advancement in our understanding of this disorder has been hampered by the absence of effective animal models and correspondingly analysis of the physiological changes that may be present in these models. To address this, we have evaluated two current rodent models of OCD; repeated injection of dopamine D2 agonist quinpirole and repeated adolescent injection of the tricyclic agent clomipramine in combination with a behavioural paradigm designed to produce compulsive lever pressing. These results were then compared with their relative impact on the state of activity of the mesolimbic dopaminergic system using extracellular recoding of spontaneously active dopamine neurons in the ventral tegmental area (VTA). The clomipramine model failed to exacerbate compulsive lever pressing and VTA dopamine neurons in clomipramine-treated rats had mildly diminished bursting activity. In contrast, quinpirole-treated animals showed significant increases in compulsive lever pressing, which was concurrent with a substantial diminution of bursting activity of VTA dopamine neurons. Therefore, VTA dopamine activity correlated with the behavioural response in these models. Taken together, these data support the view that compulsive behaviours likely reflect, at least in part, a disruption of the dopaminergic system, more specifically by a decrease in baseline phasic dopamine signalling mediated by burst firing of dopamine neurons.

Towards translational rodent models of depression

Rodent models of depression have been developed in an effort to identify novel antidepressant compounds and to further our understanding of the pathophysiology of depression. Various rodent models of depression and antidepressant-like behaviour are currently used but, clearly, none of these current models fully recapitulate all features of depression. Moreover, these models have not resulted in the development of novel non-monoaminergic-based antidepressants with clinical efficacy. Thus, a refinement of the current models of depression is required. The present review outlines the most commonly used models of depression and antidepressant drug-like activity and suggests several factors that should be considered when refining these models.

Sleep phenotyping in a mouse model of extreme trait anxiety

Background

There is accumulating evidence that anxiety impairs sleep. However, due to high sleep variability in anxiety disorders, it has been difficult to state particular changes in sleep parameters caused by anxiety. Sleep profiling in an animal model with extremely high vs. low levels of trait anxiety might serve to further define sleep patterns associated with this psychopathology.

Methodology/Principal Findings

Sleep-wake behavior in mouse lines with high (HAB), low (LAB) and normal (NAB) anxiety-related behaviors was monitored for 24 h during baseline and recovery after 6 h sleep deprivation (SD). The amounts of each vigilance state, sleep architecture, and EEG spectral variations were compared between the mouse lines. In comparison to NAB mice, HAB mice slept more and exhibited consistently increased delta power during non-rapid eye movement (NREM) sleep. Their sleep patterns were characterized by heavy fragmentation, reduced maintenance of wakefulness, and frequent intrusions of rapid eye movement (REM) sleep. In contrast, LAB mice showed a robust sleep-wake rhythm with remarkably prolonged sleep latency and a long, persistent period of wakefulness. In addition, the accumulation of delta power after SD was impaired in the LAB line, as compared to HAB mice.

Conclusions/Significance

Sleep-wake patterns were significantly different between HAB and LAB mice, indicating that the genetic predisposition to extremes in trait anxiety leaves a biological scar on sleep quality. The enhanced sleep demand observed in HAB mice, with a strong drive toward REM sleep, may resemble a unique phenotype reflecting not only elevated anxiety but also a depression-like attribute.

Sleep homeostasis and depression: studies with the rat clomipramine model of depression

Neonatal treatment of rat pups with clomipramine (CLI) has been shown to cause long-lasting and persistent depression-related behaviors and changes in sleep architecture and in brain-derived neurotrophic factor (BDNF) signaling in adult animals, producing an animal model of depression. However, the molecular mechanisms which mediate these effects of early-life CLI treatment on adult animals remain largely unknown. In order to characterize these further, we investigated in neonatally CLI-treated rats the sleep architecture as well as the extracellular and cellular levels of sleep regulators (nitric oxide, adenosine) and BDNF, respectively, in the basal forebrain (BF), i.e. the brain area which is implicated in sleep and depression. We found that CLI-treated rats exhibited a disturbed sleep architecture (REM sleep fragmentation was increased and NREM periods preceding REM were shorter) and reduced levels of BDNF and adenosine in the BF, whereas the levels of nitric oxide were elevated. Next, we examined sleep deprivation (SD)-induced homeostatic responses on sleep regulation and brain BDNF levels in CLI-treated rats. Compared to control rats, 3h of SD induced a smaller increase in the amount of NREM sleep during sleep recovery. At the molecular level, the normal homeostatic response was dissociated: the rise in the adenosine level was not accompanied by a rise in the nitric oxide concentration. Moreover, while BF BDNF levels decreased during SD in control rats, such a decline was not observed in CLI rats. Taken together, neonatal CLI treatment produces long-lasting functional changes in the sleep architecture and sleep regulation in adult rats, accompanied by dysregulated BDNF signaling in the BF.

Rapid eye movement sleep percentage in children with autism compared with children with developmental delay and typical development

OBJECTIVE

To compare objective polysomnographic parameters between 3 cohorts: children with autism, typical development, and developmental delay without autism.

DESIGN

Overnight polysomnographic recordings were scored for sleep architecture according to American Academy of Sleep Medicine criteria by a board-certified sleep medicine specialist blind to diagnosis for studies collected between July 2006 and September 2009.

SETTING

Subjects were evaluated in the pediatric ward in the Clinical Research Center of the National Institutes of Health.

PARTICIPANTS

First 60 consecutive children with autism, 15 with typical development, and 13 with developmental delay matched for nonverbal IQ to the autism group, ranging in age from 2 to 13 years, selected without regard to the presence or absence of sleep problem behavior.

MAIN OUTCOME MEASURES

Total sleep time, latencies to non-rapid eye movement (REM) and REM sleep, and percentages of total sleep time for stages 1 and 2 sleep, slow-wave sleep, and REM sleep.

RESULTS

There were no differences between the typical vs developmental delay groups. Comparison of children with autism vs typical children revealed shorter total sleep time (P = .004), greater slow-wave sleep percentage (P = .001), and much smaller REM sleep percentage (14.5% vs 22.6%; P < .001). Comparison of children with autism vs children with developmental delay revealed shorter total sleep time (P = .001), greater stage 1 sleep percentage (P < .001), greater slow-wave sleep percentage (P < .001), and much less REM sleep percentage (14.5% v 25%; P < .001).

CONCLUSION

A relative deficiency of REM sleep may indicate an abnormality in neural organization in young children with autism that is not directly associated with or related to inherent intellectual disability but may serve as a window into understanding core neurotransmitter abnormalities unique to this disorder.

A role for sleep in brain plasticity

The idea that sleep might be involved in brain plasticity has been investigated for many years through a large number of animal and human studies, but evidence remains fragmentary. Large amounts of sleep in early life suggest that sleep may play a role in brain maturation. In particular, the influence of sleep in developing the visual system has been highlighted. The current data suggest that both Rapid Eye Movement (REM) and non-REM sleep states would be important for brain development. Such findings stress the need for optimal paediatric sleep management. In the adult brain, the role of sleep in learning and memory is emphasized by studies at behavioural, systems, cellular and molecular levels. First, sleep amounts are reported to increase following a learning task and sleep deprivation impairs task acquisition and consolidation. At the systems level, neurophysiological studies suggest possible mechanisms for the consolidation of memory traces. These imply both thalamocortical and hippocampo-neocortical networks. Similarly, neuroimaging techniques demonstrated the experience-dependent changes in cerebral activity during sleep. Finally, recent works show the modulation during sleep of cerebral protein synthesis and expression of genes involved in neuronal plasticity.

Effects of postnatal isolation rearing and antidepressant treatment on the density of serotonergic and noradrenergic axons and depressive behavior in rats

The development of monoaminergic axons is affected by pharmacological and environmental manipulations during early periods of brain development. In addition, it has been proposed that changes in the density of monoaminergic axons are involved in the pathophysiology of depression. The present experiments examined the effects of neonatal treatment with antidepressants on the density of monoaminergic axons containing 5-HT or noradrenaline (NA) and depressive behavior in rats. In this study, clomipramine (CL) was used as an antidepressant, because a large amount of data has been accumulated on the effects of neonatal CL treatment on monoaminergic neurons and depressive behavior. It was also examined whether the effects of neonatal CL treatment could be further modified by environmental conditions. In the present experiments, postweaning isolation rearing (Iso) was examined as an environmental condition, because postweaning Iso is reported to change the density of 5-HT axons in the rat brain. Unexpectedly, neonatal CL treatment alone had no effect on the density of 5-HT or NA axons or depressive behavior. Postweaning social Iso rearing reduced the density of 5-HT axons in the central nucleus and basolateral nucleus of the amygdala and CA3 of the hippocampus. In the prelimbic area and infralimbic area of medial prefrontal cortex and the dentate gyrus of the hippocampus, the density of 5-HT axons was not affected by social Iso alone, but was reduced when animals were socially isolated after neonatal CL treatment. Postweaning Iso, but not neonatal CL treatment, increased immobility in the forced swim test in adolescence/early adulthood. These findings suggest that postweaning social Iso alters the density of monoaminergic axons, particularly 5-HT axons, and induces a possible model of depression, while neonatal CL treatment alone has no effect on the density of NA or 5-HT axons or depressive behavior in adolescence/early adulthood.

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.

Animal models of mood disorders: Recent developments

PURPOSE OF REVIEW

The wide spectrum of disruptions that characterizes depression and bipolar illness highlights the difficulties researchers are posed with as they try to mimic these disorders in the laboratory. Nonetheless, numerous attempts have been made to create rodent models of mood disorders, or at least models of the symptoms of depression and bipolar illness. Despite many advances, however, there are no satisfactory animal models available. The need for improved animal models for identifying new antidepressants and providing insights into the neuropathology underlying the disease is critical. This review focuses on the attempts to improve current paradigms and also illustrates examples where current paradigms are used to uncover novel molecular targets of antidepressants.

RECENT FINDINGS

Currently, there is a shift away from traditional animal models to a more focused research dealing with an endophenotype-style approach, genetic models and incorporation of new findings from human neuroimaging and genetic studies.

SUMMARY

Endophenotype-based modelling of depression and bipolar illness is opening up more tractable avenues for understanding the neurobiological and genetic bases of these disorders. Further, advances in the clinical dissection of the psychiatric illnesses using molecular genetics, coupled with functional neuroimaging techniques, promises to yield better translational animal models and hence more fruitful therapeutic targets.

Antidepressant effects of nicotine and fluoxetine in an animal model of depression induced by neonatal treatment with clomipramine

The association between smoking and depression has been widely investigated. Most of these reports suggest that nicotine (NIC) may act as an antidepressant. To examine the suggested antidepressant effect of nicotine and its possible interaction with the serotonergic system, we assessed the effect of nicotine and fluoxetine (FLX) in an animal model of depression induced by neonatal treatment with clomipramine (CLI) and submitted to the forced swim test (FST). Results corroborated that CLI-treated rats displayed higher levels of immobility. After the administration of nicotine (0.4 mg/kg sc) acutely (1 day), subchonically (7 days), and chronically (14 days), CLI-treated rats significantly reduced the immobility and increased swimming without affecting climbing. These effects were similar to the effects induced for subchronic and chronic administration of the antidepressant fluoxetine (5 mg/kg sc), a selective serotonin re-uptake inhibitor. However, fluoxetine failed to affect immobility when it was administered acutely. No synergism was observed when both drugs were administered simultaneously. The present results further corroborate the antidepressant action of nicotine and fluoxetine. The increase of swimming during the FST has been linked to an increase of serotonergic activity. Thus, it could be possible that the antidepressant action of nicotine is mediated by the serotonergic system.

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.

Chronic mild stress affects sucrose intake and sleep in rats

Depression in humans is associated with sleep abnormalities of three types: altered rapid eye movement (REM) sleep, fragmented sleep, and reduced delta sleep. In an animal model of depression, chronic exposure to mild stressors (CMS, e.g. periods of soiled cage, reversed light/dark cycle, grouped housing, food and/or water deprivation) causes behavioral and hormonal changes which, in humans, often are associated with depression. In the CMS model, a reduced sucrose intake has been defined as one of the core symptoms of depression, anhedonia, although this finding is not consistent among various laboratories. In the present study, we investigated if the CMS procedure, in our laboratory, would cause decreased sucrose intake and, also, give sleep changes similar to what is found in depressed patients. Exposure to CMS decreased sucrose intake in our rats. The largest effect was obtained after 2 weeks of the stress protocol. CMS rats spent more time in REM sleep and showed more fragmented sleep compared to their baseline recording, while there were no changes in the control rats. Increased sleep fragmentation in CMS rats was particularly evident by increased number of arousals, and increased REM sleep and slow-wave-sleep-1 (SWS-1) episodes. The duration of sleep stage episodes was decreased. The amount of slow-wave-sleep-2 (SWS-2) was not decreased, however SWS-2 in percent of total SWS was reduced. Correlation analysis showed that animals that had less consumption of sucrose spent more time in REM sleep and had increased number of REM sleep episodes. In this study, CMS appears to be a model of depression.

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.

The neurobiology of depression: perspectives from animal and human sleep studies

This article reviews human and animal studies in the neurobiology of depression. The etiology of the illness, associated neurotransmitter dysregulation, sex steroids, the role of stress, and sleep regulation are discussed. It is suggested that the genesis of depression is related to homeostatic maladaptation that is sexually dimorphic. The authors propose that depressed females are hyperresponsive to stress, whereas depressed males are hyporesponsive to stress. This divergence reflects the exaggeration of naturally occurring differences between males and females, which are most obvious under challenge conditions. The authors conclude that future work in this area should fully evaluate sexual dimorphism, neural plasticity, critical periods, and individual differences in vulnerability.

Trajectories of brain development: point of vulnerability or window of opportunity?

Brain development is a remarkable process. Progenitor cells are born, differentiate, and migrate to their final locations. Axons and dendrites branch and form important synaptic connections that set the stage for encoding information potentially for the rest of life. In the mammalian brain, synapses and receptors within most regions are overproduced and eliminated by as much as 50% during two phases of life: immediately before birth and during the transitions from childhood, adolescence, to adulthood. This process results in different critical and sensitive periods of brain development. Since Hebb (1949) first postulated that the strengthening of synaptic elements occurs through functional validation, researchers have applied this approach to understanding the sculpting of the immature brain. In this manner, the brain becomes wired to match the needs of the environment. Extensions of this hypothesis posit that exposure to both positive and negative elements before adolescence can imprint on the final adult topography in a manner that differs from exposure to the same elements after adolescence. This review endeavors to provide an overview of key components of mammalian brain development while simultaneously providing a framework for how perturbations during these changes uniquely impinge on the final outcome.

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.

Alterations in respiratory behavior, brain neurochemistry and receptor density induced by pharmacologic suppression of sleep in the neonatal period

The present study examined if drug suppression of active sleep (AS) in the neonate affected the development and expression of respiratory behavior. Secondly, we assessed brain neurochemistry and receptor density in specific supra-medullary brain regions to identify coincident biochemical alterations. Sprague-Dawley newborn rat pups were randomized and divided among six rat mothers (n=10/mother/group), each mother housed separately. Two untreated control (UC) groups received either no interventions or were fed milk vehicle twice daily and were handled similarly to the drug intervention animals. Pharmacological disruption of sleep was achieved by administration (2 groups of each) of either clonidine (CLO) 100 microm/kg, or scopolamine (SCO) 800 microm/kg, given orally twice daily for the first 7 days of life. On postnatal (P) days P10 and P19 of life, pups were assessed for metabolism, minute ventilation (VE), tidal volume (Vt) and frequency (f). On P21 (14 days after the end of drug exposure), pups from each condition were sacrificed and punch biopsies of the frontal cortex, hypothalamus, and hippocampus were examined for hydroxytryptophan (5-HT), and norepinepherine (NE) by HPLC. An equal number of pups were sacrificed and brains examined for muscarinic acetylcholine (mAch), alpha2-adrenergic and I1-imidazoline receptor density.

RESULTS

Both CLO and SCO exposed animals had a lower V(t) and respiratory quotient than UC animals (p<0.01). CLO animals exhibited a higher f (p<0.01) and both CLO and SCO exhibited a lower V(t) (p<0.05) than the UC groups; VE was reduced in the SCO groups, compared with CLO and UC groups (p<0.01). Pattern of breathing in response to brief hypoxia exposure was altered for CLO and SCO. The normal decline in VE during sleep was not observed in CLO rats. Both drug exposures resulted in a comparable reduction in hypothalamic NE and 5-HT levels (p<0.05), while in the frontal cortex, and the hippocampus variable changes in NE and 5-HT, occurred. In CLO and SCO rats mAch receptors were increased in cortex, and reduced in hypothalamus; I1-imidazoline receptors were increased in hypothalamus and decreased in hippocampus (p<0.05 for each). In contrast, alpha2-adrenergic receptors were increased in cortex for both CLO and SCO, decreased in hypothalamus for CLO, and decreased in hippocampus for SCO (p<0.05 for each).

CONCLUSIONS

these data show that drug-induced neonatal sleep suppression will alter ventilatory pattern, metabolism, and site-specific concentrations of adrenergic neurotransmitters and in receptor density, perhaps as a result of suppression of neonatal AS.

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.

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.

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.

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.

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).

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.

[Sleep and biological rhythms in depression. Changes caused by antidepressants]

Sleep in depression is characterized by an increase in the number and duration of awakenings, sleep instability, and SWS decrease. REM sleep occurs earlier. REMs density during the 1st REM period is higher than in normal controls matched in age. Accordingly, sleep in depression is similar to sleep in normal aging. Endogenous depression cannot be distinguished from other types of depression by means of polygraphic criteria. Sleep recordings at the beginning of tricyclic compound treatment could be predictive of clinical response to treatment. Sleep modifications induced by antidepressive drugs are reviewed. Sleep recordings enabled us to formulate several physiopathological hypotheses of depression mechanisms: cholinergic-aminergic hypothesis, phase advance, deficiency of process S. Other hypotheses are reviewed: flattening of a hypothetical circadian rhythm of arousal, depressogenic property of sleep in itself (or only of SWS) or timing delay for the start of sleep. A significant phase advance of biological rhythms (temperature, cortisol) is rarely found. A reduction in the amplitude of rhythms (temperature, TSH, melatonine) is more frequent.

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.

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.

Diminished sexual activity in a new animal model of endogenous depression

Our laboratory has proposed a new animal model of endogenous depression. The proposal is that in rats neonatal clomipramine (CLI) produces adult animals that model endogenous depression. Diminished sexual activity is a salient behavioral abnormality found in endogenous depression. This suggests that an animal model of endogenous depression should show diminished sexual activity. We report here a test of the prediction that after neonatal treatment with CLI, adult male rats show decreased sexual activity. We found that after neonatal CLI, adult male Long-Evans rats had a pervasive diminution of sexual activities including decreased mounts, intromissions, ejaculations, and increased mount latencies and postejaculatory pause. Sprague-Dawley and Wistar strains also tended to show decreased intromissions and ejaculations, but their baseline sexual activity was too low to give interpretable data. The results with the sexually active Long-Evans strain are consistent with the hypothesis that neonatal CLI produces adult rats that model human endogenous depression.

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.

Decreased intracranial self-stimulation in a new animal model of endogenous depression

Neonatal treatment of rats with clomipramine may produce adult animals which model endogenous depression. We report here that a major factor of depression in humans, the diminished capacity for pleasure, appears present in these rats. At age 7 months, bar-press responding for rewarding hypothalamic stimulation is reduced across a range of intensities. At age 4 or 5 months this effect is not seen, although other behavioral abnormalities are present at the younger age. The delayed onset of diminished intracranial self-stimulation may relate to the gradual insidious onset of endogenous depression in humans.

A new animal model of endogenous depression: a summary of present findings

In 1982 our laboratory proposed a new animal model of endogenous depression. The proposal was that in rats, neonatally administered clomipramine (CLI) will produce adult animals that model endogenous depression. We summarize here several tests of the validity of the model. Results were that after neonatal CLI, adult male rats showed behavioral abnormalities of the human disorder: decreased sexual, aggressive, and intracranial self-stimulation activities, as well as motor hyperactivity in a stressful situation. Preliminary evidence suggested that behavioral abnormalities in rats (sexual, aggressive, and motor) briefly treated with antidepressant treatments (imipramine, REM sleep deprivation) begin to normalize. Lastly, after neonatal CLI, the adult rats showed REM sleep abnormalities of endogenous depression, viz, low REM latency, frequent sleep onset REM periods, and abnormal temporal course of REM rebound after REM sleep deprivation. These results supported the hypothesis that in rats neonatal CLI produced adult animals that modelled endogenous depression.