Time course of alterations after olfactory bulbectomy in mice

Blocking olfactory input alters aggression in male and female California mice (Peromyscus californicus)

Olfactory input into the brain can be disrupted by a variety of environmental factors, including exposure to pathogens or environmental contaminants. Olfactory cues are often eliminated in laboratory rats and mice through highly invasive procedures like olfactory bulbectomy, which may also disrupt accessory olfactory pathways and detection of non-volatile odors. In the present study, we tested whether inducing anosmia through intranasal infusion of zinc gluconate alters aggression in a monogamous, biparental rodent species, the California mouse (Peromyscus californicus). This less invasive method of manipulating olfaction selectively targets the olfactory epithelium and reduces the detection of volatile odors. Treatment with zinc gluconate extended the time required for male and female California mice to find hidden pieces of apple and reduced the amount of time spent investigating bedding that was soiled by unfamiliar males. Moreover, inhibition of olfaction with zinc gluconate reduced aggressiveness in both sexes as demonstrated by an increased attack latency in the resident-intruder test among same-sex dyads from the same treatment group. These results suggest that volatile olfactory cues are necessary for agonistic responses in both male and female California mice. Therefore, even in species with complex social systems that include territorial aggression and monogamy, volatile olfactory cues modulate agonistic behavior.

The olfactory bulbectomy disease model: A Re-evaluation

The olfactory bulbectomized rodent has long been one of the preferred animal models of depression and certain other neuropsychiatric diseases. In fact, it is considered unparalleled, by some, in the search for antidepressant medication and the literature generated about the model is prodigious. We have revisited the "syndrome" of behavioral sequela following bulbectomy choosing ecologically valid tests likely to be underpinned with evolutionarily preserved neural circuits. Our test battery included measurements of activity, intermale aggression, pleasure seeking, stress/fear and non-spatial memory. The emphasis was on the timetable of syndrome emergence, since this has been understudied and bears on the widely held belief that non-olfactory effects dominate. Our results largely agree with previous reports describing the behavioral syndrome in that we document bulbectomized mice as hyperactive, non-aggressive and fearless. However, we did not find deficits in memory as have frequently been reported in previous studies. Notably, our results revealed that some syndrome behaviors-including the hallmark of hyperactivity-appear immediately or soon after surgery. This rapid appearance casts doubt on the widely held view that compensatory reorganization of limbic and prefrontal cortical areas following bulbectomy underlies the syndrome. Rather, hyperactivity, non-aggressiveness, reduced fear and diminished sucrose preference in the olfactory bulbectomized mouse find ready explanations in the loss of smell that is the immediate and irreversible outcome of bulbectomy. Finally, after a critical consideration of the literature and our results, we conclude that the olfactory bulbectomy model lacks the validity and simplicity previously credited to it. Indeed, we deem this lesion unsuitable as a model of most neuropsychiatric diseases since its effects are at least as complex and misunderstood as the disorders it is purported to model.

Antidepressant-Like Effects of Chronic Guanosine in the Olfactory Bulbectomy Mouse Model

Major depressive disorder (MDD) leads to pervasive changes in the health of afflicted patients. Despite advances in the understanding of MDD and its treatment, profound innovation is needed to develop fast-onset antidepressants with higher effectiveness. When acutely administered, the endogenous nucleoside guanosine (GUO) shows fast-onset antidepressant-like effects in several mouse models, including the olfactory bulbectomy (OBX) rodent model. OBX is advocated to possess translational value and be suitable to assess the time course of depressive-like behavior in rodents. This study aimed at investigating the long-term behavioral and neurochemical effects of GUO in a mouse model of depression induced by bilateral bulbectomy (OBX). Mice were submitted to OBX and, after 14 days of recovery, received daily (ip) administration of 7.5 mg/kg GUO or 40 mg/kg imipramine (IMI) for 45 days. GUO and IMI reversed the OBX-induced hyperlocomotion and recognition memory impairment, hippocampal BDNF increase, and redox imbalance (ROS, NO, and GSH levels). GUO also mitigated the OBX-induced hippocampal neuroinflammation (IL-1, IL-6, TNF-α, INF-γ, and IL-10). Brain microPET imaging ([¹⁸F]FDG) shows that GUO also prevented the OBX-induced increase in hippocampal FDG metabolism. These results provide additional evidence for GUO antidepressant-like effects, associated with beneficial neurochemical outcomes relevant to counteract depression.

Long-term stability and characteristics of behavioral, biochemical, and molecular markers of three different rodent models for depression

OBJECTIVE

The present study was designed to explore the long-term differences between three mouse models for depression.

METHOD

In the present study, the unpredictable chronic mild stress (UCMS) model, the glucocorticoid/corticosterone model, and the olfactory bulbectomy model were compared at two, three, and five weeks after model induction. Behavioral testing performed included forced-swimming, tail suspension, open-field and elevated plus-maze tests. In addition, 5-hydroxytryptamine (5-HT) and dopamine levels, and mRNA and protein expressions related to 5-HT synthesis, transport, and signaling were analyzed in the hippocampus of tested animals.

RESULTS

Our results revealed that each model demonstrated a specific profile of markers, whereas the stability of them differed over testing time.

CONCLUSIONS

Each model provided a unique set of advantages that can be considered depending on the context and aims of each study. Among the three models, the UCMS model was mostly stable and appeared to the best model for testing long-term depression-like state.

Animal models of major depressive disorder and the implications for drug discovery and development

INTRODUCTION

Depression is a highly debilitating psychiatric disorder that affects the global population and causes severe disabilities and suicide. Depression pathogenesis remains poorly understood, and the disorder is often treatment-resistant and recurrent, necessitating the development of novel therapies, models and concepts in this field. Areas covered: Animal models are indispensable for translational biological psychiatry, and markedly advance the study of depression. Novel approaches continuously emerge that may help untangle the disorder heterogeneity and unclear categories of disease classification systems. Some of these approaches include widening the spectrum of model species used for translational research, using a broader range of test paradigms, exploring new pathogenic pathways and biomarkers, and focusing more closely on processes beyond neural cells (e.g. glial, inflammatory and metabolic deficits). Expert opinion: Dividing the core symptoms into easily translatable, evolutionarily conserved phenotypes is an effective way to reevaluate current depression modeling. Conceptually novel approaches based on the endophenotype paradigm, cross-species trait genetics and 'domain interplay concept', as well as using a wider spectrum of model organisms and target systems will enhance experimental modeling of depression and antidepressant drug discovery.

Medium- and high-intensity rTMS reduces psychomotor agitation with distinct neurobiologic mechanisms

Definitive data are lacking on the mechanism of action and biomarkers of repetitive transcranial magnetic stimulation (rTMS) for the treatment of depression. Low-intensity rTMS (LI-rTMS) has demonstrated utility in preclinical models of rTMS treatments but the effects of LI-rTMS in murine models of depression are unknown. We examined the behavioral and neurobiologic changes in olfactory bulbectomy (OB) mice with medium-intensity rTMS (MI-rTMS) treatment and fluoxetine hydrochloride. We then compared 10-Hz rTMS sessions for 3 min at intensities (measured at the cortical surface) of 4 mT (LI-rTMS), 50 mT (medium-intensity rTMS [MI-rTMS]), or 1 T (high-intensity rTMS [HI-rTMS]) 5 days per week over 4 weeks in an OB model of agitated depression. Behavioral effects were assessed with forced swim test; neurobiologic effects were assessed with brain levels of 5-hydroxytryptamine, brain-derived neurotrophic factor (BDNF), and neurogenesis. Peripheral metabolomic changes induced by OB and rTMS were monitored through enzyme-linked immunosorbent assay and ultrapressure liquid chromatography-driven targeted metabolomics evaluated with ingenuity pathway analysis (IPA). MI-rTMS and HI-rTMS attenuated psychomotor agitation but only MI-rTMS increased BDNF and neurogenesis levels. HI-rTMS normalized the plasma concentration of α-amino-n-butyric acid and 3-methylhistidine. IPA revealed significant changes in glutamine processing and glutamate signaling in the OB model and following MI-rTMS and HI-rTMS treatment. The present findings suggest that MI-rTMS and HI-rTMS induce differential neurobiologic changes in a mouse model of agitated depression. Further, α-amino-n-butyric acid and 3-methylhistidine may have utility as biomarkers to objectively monitor the response to rTMS treatment of depression.

Behavioral changes induced through adenosine A2A receptor ligands in a rat depression model induced by olfactory bulbectomy

Background

Major depressive disorders are characterized by their severity and long-lasting symptoms, which make such disorders highly disabling illnesses. Unfortunately, 50% of major depressive patients experience relapses, perhaps partly because drug research has been performed only in animal models that screen for antidepressant drugs that appear to only ameliorate acute depression symptoms. The bilateral olfactory bulbectomy (OBX) animal model presents the advantage of mimicking the symptoms of chronic depression by means of brain surgery. Adenosine purinergic receptors A2A (A2AR) have been the target of interest in the field of psychiatric diseases. This study aimed to show which A2A receptor ligands exert antidepressive-like effects in the OBX rat model.

Methods

Forty Sprague-Dawley male rats were divided into four groups: control, OBX + vehicle, OBX + ZM 241385, and OBX + adenosine groups. Pharmacological treatment was administered for 14 days, and the rats were examined via the forced swim test (FST), open field test (OFT), and sucrose preference test (SPT).

Results

The OBX + ZM 241385 group exhibited decreased immobility time in the FST, decreased isolation time in the OFT, and reversed anhedonia behavior in the SPT compared to the vehicle group. However, no significant differences for adenosine treatment were found.

Conclusions

ZM 241385 administration (2 mg/kg i.p.) restored behavioral changes associated with OBX-induced depression.

Olfactory bulbectomy in mice triggers transient and long-lasting behavioral impairments and biochemical hippocampal disturbances

Major depressive disorder (MDD) is a neuropsychiatric disease that is associated with profound disturbances in affected individuals. Elucidating the pathophysiology of MDD has been frustratingly slow, especially concerning the neurochemical events and brain regions associated with disease progression. Thus, we evaluated the time-course (up to 8weeks) behavioral and biochemical effects in mice that underwent to a bilateral olfactory bulbectomy (OBX), which is used to modeling depressive-like behavior in rodents. Similar to the symptoms in patients with MDD, OBX induced long-lasting (e.g., impairment of habituation to novelty, hyperactivity and an anxiety-like phenotype) and transient (e.g., loss of self-care and motivational behavior) behavioral effects. Moreover, OBX temporarily impaired hippocampal synaptosomal mitochondria, in a manner that would be associated with hippocampal-related synaptotoxicity. Finally, long-lasting pro-oxidative (i.e., increased levels of reactive oxygen species and nitric oxide and decreased glutathione levels) and pro-inflammatory (i.e., increased levels of pro-inflammatory cytokines IL-1, IL-6, TNF-α and decreased anti-inflammatory cytokine IL-10 levels) effects were induced in the hippocampus by OBX. Additionally, these parameters were transiently affected in the posterior and frontal cortices. This study is the first to suggest that the transient and long-lasting behavioral effects from OBX strongly correlate with mitochondrial, oxidative and inflammatory parameters in the hippocampus; furthermore, these effects show a weak correlation with these parameters in the cortex. Our findings highlight the underlying mechanisms involved in the biochemical time course of events related to depressive behavior.

Organization of prefrontal network activity by respiration-related oscillations

The medial prefrontal cortex (mPFC) integrates information from cortical and sub-cortical areas and contributes to the planning and initiation of behaviour. A potential mechanism for signal integration in the mPFC lies in the synchronization of neuronal discharges by theta (6–12 Hz) activity patterns. Here we show, using in vivo local field potential (LFP) and single-unit recordings from awake mice, that prominent oscillations in the sub-theta frequency band (1–5 Hz) emerge during awake immobility in the mPFC. These oscillation patterns are distinct from but phase-locked to hippocampal theta activity and occur synchronized with nasal respiration (hence termed prefrontal respiration rhythm [PRR]). PRR activity modulates the amplitude of prefrontal gamma rhythms with greater efficacy than theta oscillations. Furthermore, single-unit discharges of putative pyramidal cells and GABAergic interneurons are entrained by prefrontal PRR and nasal respiration. Our data thus suggest that PRR activity contributes to information processing in the prefrontal neuronal network.

Rapamycin blocks the antidepressant effect of ketamine in task-dependent manner

OBJECTIVE

The aim of our study was to test whether ketamine produces an antidepressant effect in animal model of olfactory bulbectomy and assess the role of mammalian target of rapamycin (mTOR) pathway in ketamine's antidepressant effect.

METHODS

Bulbectomized (OBX) rats and sham controls were assigned to four subgroups according to the treatment they received (ketamine, saline, ketamine + rapamycin, and saline + rapamycin). The animals were subjected to open field (OF), elevated plus maze (EPM), passive avoidance (PA), Morris water maze (MWM), and Carousel maze (CM) tests. Blood samples were collected before and after drug administration for analysis of phosphorylated mTOR level. After behavioral testing, brains were removed for evaluation of brain-derived neurotrophic factor (BDNF) in prefrontal cortex (PFC) and hippocampus.

RESULTS

Ketamine normalized hyperactivity of OBX animals in EPM and increased the time spent in open arms. Rapamycin pretreatment resulted in elimination of ketamine effect in EPM test. In CM test, ketamine + rapamycin administration led to cognitive impairment not observed in saline-, ketamine-, or saline + rapamycin-treated OBX rats. Prefrontal BDNF content was significantly decreased, and level of mTOR was significantly elevated in OBX groups.

CONCLUSIONS

OBX animals significantly differed from sham controls in most of the tests used. Treatment had more profound effect on OBX phenotype than controls. Pretreatment with rapamycin eliminated the anxiolytic and antidepressant effects of ketamine in task-dependent manner. The results indicate that ketamine + rapamycin application resulted in impaired stress responses manifested by cognitive deficits in active place avoidance (CM) test. Intensity of stressor (mild vs. severe) used in the behavioral tests had opposite effect on controls and on OBX animals.

Alterations in behavioral responses to dopamine agonists in olfactory bulbectomized mice: relationship to changes in the striatal dopaminergic system

BACKGROUND

Olfactory bulbectomy (OBX) in rodents is considered a putative animal model of depression. It has been reported that some abnormal behaviors observed in this animal model of depression involve dopaminergic neurons of the mesolimbic pathway. Therefore, we examined changes in the dopaminergic system in the caudate putamen (CPu), nucleus accumbens core (NAcC), and shell (NAcSh) of OBX mice and whether or not these alterations were reversed by chronic administration of imipramine.

METHODS

We observed climbing behavior, which is a dopamine (DA) receptor-associated behavior, to demonstrate changes in the dopaminergic system of the mesolimbic pathway, when mice were administrated either the nonselective DA agonist apomorphine only or were pre-treated with the selective D1 antagonist SCH23390, with the selective D2 antagonist sulpiride, or with the D2/D3 partial agonist aripiprazole (ARI). Moreover, we examined tyrosine hydroxylase (TH) and D1- and D2-like receptor levels in the CPu, NAcC, and NAcSh using immunohistochemistry and autoradiography.

RESULTS

The OBX group exhibited significantly enhanced apomorphine-induced climbing behavior, and this enhanced behavior was reversed by administration of sulpiride, ARI, and imipramine but not SCH23390. Moreover, we found a reduction in TH levels in the CPu, NAcC, and NAcSh of OBX mice and an increase in D2 receptor densities in the NAcC of OBX mice. The increased D2 receptor density observed in OBX mice was reversed by imipramine administration.

CONCLUSIONS

These findings reveal that OBX mice display enhanced DA receptor responsiveness, which may relate to some of the behavioral abnormalities reported in this animal model.

Effects of 4-hydroxyisoleucine from Fenugreek Seeds on Depression-like Behavior in Socially Isolated Olfactory Bulbectomized Rats

Context:

Antidepressant-like effects of (2S, 3R, 4S)-4-hydroxyisoleucine (4-HI), a major amino acid from fenugreek seeds, has been reported in the animal model of acute depression.

Aims:

To evaluate effects of subacute administration of 4-HI in animal model of stress-induced depression namely socially isolated olfactory bulbectomized rats.

Materials and Methods:

Bilateral olfactory bulbectomy (OBX) were induced in 30 Sprague-Dawley rats. After recovery period of 14 days, rats were randomized into five groups of 6 rats each and stressed with social isolation (individual housing). The rats were orally treated with either vehicle (OBX-Iso), positive control, fluoxetine (30 mg/kg) or 4-HI (10, 30, 100 mg/kg) once a day from day 14 onward. Separate group of rats with social isolation but without OBX (Sham-Iso) was also maintained. The behavioral depression and anxiety related parameters using open field test (OFT), sucrose intake test, novelty suppressed feeding (NSF) and forced swim test (FST), and neurochemical estimation (brain monoamines viz., serotonin and nor-adrenaline, serotonin turnover, and serum cortisol) were performed.

Statistical Analysis Used:

Data was analyzed by either two-way ANOVA (OFT and FST) or one-way ANOVA (sucrose intake test, NSF, and neurochemical estimation) followed by Dunnett's multiple comparisons test. Differences were considered significant at P < 0.05.

Results:

The significant and dose-dependent protection from behavioral and neurochemical changes were observed in 4-HI co-administrated OBX-Iso rats.

Conclusion:

4-HI demonstrated the antidepressant and antianxiety effects in socially isolated stress-induced OBX rats with possible involvement of multiple stress relieving mechanisms.

HIGHLIGHTS OF PAPER

In this study, the subacute pretreatment of 4-HI showed strong and dose-dependent prevention of isolation stress related behavioral and neurochemical responses in olfactory bulbectomized rats. The prevention of hyperactive HPA axis in OBX-Iso stress-induced rats can be envisaged as probable mechanism of antidepressant and antianxiety effects of 4-HI.

SUMMARY

Effect of 4-hydroxyisoleucine (4-HI) in olfactory bulbectomized and socially isolated (Iso) rats was evaluated

4-HI showed significant and dose-dependent antidepressant effects during novelty suppressed feeding (NSF) and forced swim test (FST)

4-HI showed significant and dose-dependent antianxiety effects during OFT (open field test) and sucrose intake test

4-HI showed protection from OBX-Iso stress-induced brain monoamines, serotonin turnover, and serum cortisol level elevation.

Abbreviations used: SSRI: Selective Serotonin Reuptake Inhibitor; 4-HI: (2S, 3R, 4S)-4-hydroxyisoleucine; OBX: Olfactory bulbectomy; CPCSEA: Committee for the Purpose of Control and Supervision of Experiments on Animals; OFT: Open Field Test; NSF: Novelty Suppressed Feeding; FST: Forced Swimming Test; 5HT: 5-Hydroxytryptamine; 5-HIAA: 5-Hydroxyindoleacetic Acid; NA: Nor-adrenaline; and HPA: Hypothalamic-Pituitary Adrenal.

Connectivity of Pathology: The Olfactory System as a Model for Network-Driven Mechanisms of Alzheimer's Disease Pathogenesis

The pathogenesis of Alzheimer’s disease (AD) has been postulated to preferentially impact specific neural networks in the brain. The olfactory system is a well-defined network that has been implicated in early stages of the disease, marked by impairment in olfaction and the presence of pathological hallmarks of the disease, even before clinical presentation. Discovering the cellular mechanisms involved in the connectivity of pathology will provide insight into potential targets for treatment. We review evidence from animal studies on sensory alteration through denervation or enrichment, which supports the notion of using the olfactory system to investigate the implications of connectivity and activity in the spread of pathology in AD.

Social isolation differentially affects anxiety and depressive-like responses of bulbectomized mice

Social isolation in rodents may interfere in their behavioural responses on paradigms used to test anxiety- and depressive-like states. Herein we study the influence of social isolation upon the behavioural responses of olfactory bulbectomized mice (OBX). In the open-field test (OFT), social isolation enhanced OBX-induced hyperactivity and exploratory behaviour. However, OBX-induced anxiety in the OFT (central activity) was less apparent after isolation, due to the increased level of anxiety showed by the sham-isolated counterparts. In the novelty-suppressed feeding (NSF), isolation derived in an increased latency to feeding of both OBX and sham mice. The isolation did not affect the response of OBX mice and sham mice in the forced-swimming test (FST). Interestingly, OBX animals exhibited an increased immobility time during the FST, though a dramatic decrease in the climbing scores. Finally, OBX-induced anhedonia in the sucrose intake test was not affected by housing conditions. Our findings demonstrate that social isolation influences the performance of OBX mice in some behavioural paradigms, thus facilitating the characterization of depressive-like states, and by contrast, hindering anxiety-related behaviours. This fact should be taken into account in order to minimize economical and time-consuming efforts when assessing potential antidepressant and anxiolytic drugs.

Rosmarinus officinalis L. hydroalcoholic extract, similar to fluoxetine, reverses depressive-like behavior without altering learning deficit in olfactory bulbectomized mice

ETHNOPHARMACOLOGICAL RELEVANCE

Rosemary, Rosmarinus officinalis L., has several therapeutic applications in folk medicine for the treatment of a wide range of diseases, including depression.

AIM OF THE STUDY

To evaluate the ability of Rosmarinus officinalis hydroalcoholic extract (ROHE), as compared to the positive control fluoxetine, to reverse behavioral (hyperactivity, anhedonic behavior and learning deficit in water maze) and biochemical alterations (serum glucose level and acetylcholinesterase, AChE, activity) induced by an animal model of depression, the olfactory bulbectomy (OB) in mice.

MATERIALS AND METHODS

Locomotor and exploratory behavior was assessed in the open-field, novel object and novel cage tests, anhedonic behavior was assessed in the splash test; cognitive deficits were evaluated in the water maze task. For the first set of experiments, ROHE (10-300 mg/kg) or fluoxetine (10mg/kg) was administered once daily (p.o.) for 14 days after OB and the behavioral tests were performed. For the second set of experiments, serum glucose and hippocampal and cerebrocortical AChE activity were determined in OB and SHAM-operated mice treated orally with ROHE (10mg/kg), fluoxetine (10mg/kg) or vehicle.

RESULTS

ROHE (10-300 mg/kg), similar to fluoxetine, reversed OB-induced hyperactivity, increased exploratory and anhedonic behavior. OB needed significantly more trials in the training session to acquire the spatial information, but they displayed a similar profile to that of SHAM mice in the test session (24h later), demonstrating a selective deficit in spatial learning, which was not reversed by ROHE or fluoxetine. A reduced serum glucose level and an increased hippocampal AChE activity were observed in bulbectomized mice; only the latter effect was reversed by fluoxetine, while both effects were reversed by ROHE.

CONCLUSIONS

ROHE exerted an antidepressant-like effect in bulbectomized mice and was able to abolish AchE alterations and hypoglycemia, but not spatial learning deficit induced by OB. Overall, results suggest the potential of Rosmarinus officinalis for the treatment of depression, validating the traditional use of this plant.

Diet-induced obesity resistance of Kv1.3-/- mice is olfactory bulb dependent

Gene-targeted deletion of the voltage-gated potassium channel, Kv1.3 (Kv1.3-/-), increases olfactory sensitivity and discriminatory ability, and causes resistance to diet-induced obesity (DIO) in mice. The present study aimed to determine whether the enhanced olfactory ability of the Kv1.3-/- mouse contributes to the resistance to DIO. Kv1.3+/+ and Kv1.3-/- mice were subject to bilateral olfactory bulbectomy (OBX) or sham surgery at 9 weeks of age and placed on either a control chow diet or a 32% moderately high-fat diet (MHF). Caloric and water intake, locomotor activity and oxygen consumption were monitored after 5 weeks of diet treatment. At the end of 26 weeks of diet treatment, fat pad weight and blood chemistry were evaluated. Kv1.3+/+ mice exhibited a significant increase in weight, adiposity, fasting glucose and fasting leptin in response to the MHF-diet, with or without OBX. When treated with a MHF-diet, Kv1.3-/- mice gained significantly less weight than Kv1.3+/+ mice and exhibited a significant increase in light phase metabolism. OBX of Kv1.3-/- mice prevented the resistance to DIO and concomitant up-regulation of light phase metabolism at the same time as decreasing dark phase metabolism and total energy expenditure. These findings suggest that pathways activated in Kv1.3-/- that increased energy expenditure and led to resistance to DIO are olfactory bulb dependent. Thus, these findings add to a growing body of evidence suggesting that the olfactory system can modulate the pathways involved in the regulation of energy balance.

Environmental enrichment has antidepressant-like action without improving learning and memory deficits in olfactory bulbectomized rats

Depression, especially in the elderly, is associated with poor cognitive functioning. Exercise has received much attention in the treatment for depression and also dementia. Here we studied the effect of an enriched environment combined with voluntary exercise (EE/VE) on the olfactory bulbectomized (OBX) rat. The OBX rat is hyperactive in an open field, which is normalized by chronic antidepressant treatment, and suffers from learning and memory impairments. Neurotrophic factors are thought to be involved in the antidepressant action of EE/VE. Hyperactivity and cognitive functioning (both hippocampal dependent and independent tasks) were investigated before and after EE/VE. We quantified hippocampal mRNA levels of the neurotrophic factors BDNF, VGF and VEGF. VEGF receptor (FLK-1) inhibition was achieved by i.c.v administration of the antagonist SU5416 during the period of EE/VE. OBX almost completely blocked fear memory acquired either 48 h or 28 days before surgery. EE/EV normalized OBX-induced hyperactivity in open field, while having no effect on the decrease in hippocampal dependent learning and memory. VEGF mRNA levels in hippocampus were significantly increased both in OBX and control rats following EE/VE. OBX reduced BDNF mRNA levels, but EE did not reverse this. Inhibition of the FLK-1 receptor did not suppress EE/VE induced normalization of the hyperactivity of the OBX rat. The lack of effect of EE/VE on cognitive parameters, while normalizing hyperactivity, suggests different neuronal mechanisms underlying OBX-induced behavioral changes. Since EE/VE still normalizes the OBX-induced hyperactivity while the FLK-1 receptor was blocked, we assume that VEGF is not obligatory for the antidepressant effect of EE/VE. This article is part of a Special Issue entitled 'Anxiety and Depression'.

Chronic treatment with fluoxetine for more than 6 weeks decreases neurogenesis in the subventricular zone of adult mice

Background

Recent studies indicate that chronic treatment with serotonergic antidepressants upregulates adult neurogenesis of the dentate gyrus (DG). In contrast, some studies claimed that there was very little alteration of neurogenesis in the subventricular zone (SVZ) by the antidepressants. Since almost all of those studies treated animals with drugs for 2 to 4 weeks as chronic treatment models of antidepressants, it is possible that antidepressant treatments for longer periods would affect adult neurogenesis in the SVZ.

Results

In the present study, we examined the effects of long-term (up to 9 weeks) administration of fluoxetine (FLX), a selective serotonin reuptake inhibitor, on cell proliferation and survival in the DG and the SVZ of adult mice. As reported previously, in the DG of mice treated with FLX for 3, 6, or 9 weeks that were also injected with 5-bromodeoxyuridine (BrdU) in the last 3 days before perfusion, the numbers of Ki67- and BrdU-positive cells, which are cell proliferation markers, were significantly upregulated even at 3 weeks after the onset of the FLX treatments, and these increases were sustained in mice treated with FLX for 9 weeks. On the other hand, in the SVZ, we found a small, insignificant decrease in the numbers of Ki67- and BrdU-positive cells at 3 weeks, followed by highly significant decreases in the numbers of Ki67- and BrdU-positive cells at both 6 and 9 weeks. Furthermore, among olfactory newly generated cells that survived for 3 weeks after BrdU injection, the number of new cells was decreased at 9 weeks of FLX treatment.

Conclusions

These results demonstrate that long-term (more than 6 weeks) treatment with FLX has the opposite effect on neurogenesis in the SVZ than it does in the DG. The results also suggest that the decrease in neurogenesis in the SVZ might be involved in some aspects of the drugs' therapeutic effects on depression. In addition, our findings raise the possibility that some of the side effects of antidepressants might be mediated by decreased adult neurogenesis in the SVZ.

Simvastatin improves learning and memory in control but not in olfactory bulbectomized rats

RATIONALE

Olfactory bulbectomy (OBX) in a laboratory rodent leads to numerous behavioral deficits and involves cognitive and motor changes that are used to model major depression, but may also be a valuable tool in the study of neurodegenerative disorders like Alzheimer's disease.

OBJECTIVES

This experiment evaluated the effects of simvastatin, a cholesterol-lowering drug with putative neuroprotective properties, on OBX-induced behavioral changes.

RESULTS

Chronic administration of simvastatin, starting 48 h after surgery, did not have any behavioral effect in OBX rats, as tested in open field, passive avoidance and object-recognition paradigms. In control rats, simvastatin treatment resulted in an improved performance in both the passive avoidance and the object-in-place task.

CONCLUSION

In the present study, simvastatin treatment enhanced cognition in intact rats, but had no effect in OBX rats. These results are in line with the idea that statins may attenuate (early) age-associated cognitive decline in humans.

Olfactory mechanisms of stereotyped behavior: on the scent of specialized circuits

Investigation of how specialized olfactory cues, such as pheromones, are detected has primarily focused on the function of receptor neurons within a subsystem of the nasal cavity, the vomeronasal organ (VNO). Behavioral analyses have long indicated that additional, non-VNO olfactory neurons are similarly necessary for pheromone detection; however, the identity of these neurons has been a mystery. Recent molecular, behavioral, and genomic approaches have led to the identification of multiple atypical sensory circuits that display characteristics suggestive of a specialized function. This review focuses on these non-VNO receptors and neurons, and evaluates their potential for mediating stereotyped olfactory behavior in mammals.

Improvement of depressive behaviors by nefiracetam is associated with activation of CaM kinases in olfactory bulbectomized mice

Olfactory bulbectomized (OBX) mice exhibit depressive-like behaviors as assessed by the tail suspension test (TST) and the forced swim test (FST). Interestingly, chronic intraperitoneal administration (1 mg/kg/day) of nefiracetam (DM-9384), a prototype cognitive enhancer, significantly improved depressive-like behaviors as well as spatial reference memory assessed by Y-maze task. As previously reported (Moriguchi, S., Han, F., Nakagawasai, O., Tadano, T., Fukunaga, K., 2006. Decreased calcium/calmoculin-dependent protein kinase II and protein kinase C activities mediate impairment of hippocampal long-term potentiation in the olfactory bulbectomized mice. J. Neurochem. 97, 22-29), decreased activities of Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) and extracellular signal-regulated kinase (ERK) in the hippocampal CA1 region and amygdala were observed in OBX mice. Nefiracetam treatment (1 mg/kg/day) significantly elevated CaMKII but not ERK activities in the amygdala, prefrontal cortex and hippocampal CA1 regions. In addition, we found an elevation of cAMP response element-binding protein (CREB) phosphorylation in the amygdala and prefrontal cortex but not in the hippocampal CA1 region. Increased CREB phosphorylation was associated with activation of CaMKI and CaMKIV as well as CaMKII in these regions. Taken together, in addition to CaMKII, CaMKI and CaMKIV activation mediated by nefiracetam treatment might mediate CREB phosphorylation following chronic nefiracetam treatment, thereby eliciting an anti-depressive and cognition-enhancing effect on OBX mice.

Olfactory cues are sufficient to elicit social approach behaviors but not social transmission of food preference in C57BL/6J mice

Mouse models for the study of autistic-like behaviors are increasingly needed to test hypotheses about the causes of autism, and to evaluate potential treatments. Both the automated three-chambered social approach test and social transmission of food preference have been proposed as mouse behavioral assays with face validity to diagnostic symptoms of autism, including aberrant reciprocal social interactions and impaired communication. Both assays measure aspects of normal social behavior in the mouse. However, little is known regarding the salient cues present in each assay that elicit normal social approach and communication. To deconstruct the critical components, we focused on delivering discrete social and non-social olfactory and visual cues within the context of each assay. Results indicate that social olfactory cues were sufficient to elicit normal sociability in the three-chambered social approach test. On social transmission of food preference, isolated social olfactory cues were sufficient to induce social investigation, but not sufficient to induce food preference. These findings indicate that olfactory cues are important in mouse social interaction, but that additional sensory cues are necessary in certain situations. The present evidence that both the three-chambered social approach assay and the social transmission of food preference assay require socially relevant cues to elicit normal behavior supports the use of these two assays to investigate autism-related behavioral phenotypes in mice.

In vivo acute treatment with trimethyltin chloride causes neuronal degeneration in the murine olfactory bulb and anterior olfactory nucleus by different cascades in each region

Our earlier study demonstrated that in vivo acute treatment with trimethyltin chloride (TMT) produces severe neuronal damage in the dentate gyrus and cognition impairment in mice. In the present study, we assessed whether TMT was capable of causing neuronal degeneration in the olfactory bulb (OB) and anterior olfactory nucleus (AON) of the mouse brain. An intraperitoneal injection of TMT at the dose of 2.8 mg/kg led to a dramatic increase in the number of degenerating cells, which were reactive with antibody against single-stranded DNA, in the granule cell layer (GCL) of the OB and AON 1 day and 2 days later, respectively. TMT treatment produced a marked translocation of phospho-c-Jun-N-terminal kinase from the cytoplasm to the nucleus in the AON. Expectedly, a marked increase in phospho-c-Jun-positive cells was seen in the AON after the treatment. In addition to the AON, the mitral cell layer of the olfactory bulb showed the presence of phospho-c-Jun-positive cells after the treatment. However, the GCL had no cells positive for either phospho-c-Jun-N-terminal kinase or phospho-c-Jun at any time after the treatment with TMT. Similarly, TMT-induced nuclear translocation of the lysosomal enzyme deoxyribonuclease II was seen in the AON, but not in the GCL. On the other hand, TMT elicited the expression of activated caspase 3 in the GCL but not in the AON. Taken together, our results suggest that TMT is capable of causing neuronal degeneration in the murine OB and AON through different cascades in the two structures.

A final common pathway for depression? Progress toward a general conceptual framework

Functional neuroimaging studies of depressed patients have converged with functional brain mapping studies of depressed animals in showing that depression is accompanied by a hypoactivity of brain regions involved in positively motivated behavior together with a hyperactivity in regions involved in stress responses. Both sets of changes are reversed by diverse antidepressant treatments. It has been proposed that this neural pattern underlies the symptoms common to most forms of the depression, which are the loss of positively motivated behavior and increased stress. The paper discusses how this framework can organize diverse findings ranging from effects of monoamine neurotransmitters, cytokines, corticosteroids and neurotrophins on depression. The hypothesis leads to new insights concerning the relationship between the prolonged inactivity of the positive motivational network during a depressive episode and the loss of neurotrophic support, the potential antidepressant action of corticosteroid treatment, and to the key question of whether antidepressants act by inhibiting the activity of the stress network or by enhancing the activity of the positive motivational system.

What's wrong with my mouse model?

Stress plays a key role in pathogenesis of anxiety and depression. Animal models of these disorders are widely used in behavioral neuroscience to explore stress-evoked brain abnormalities, screen anxiolytic/antidepressant drugs and establish behavioral phenotypes of gene-targeted or transgenic animals. Here we discuss the current situation with these experimental models, and critically evaluate the state of the art in this field. Noting a deficit of fresh ideas and especially new paradigms for animal anxiety and depression models, we review existing challenges and outline important directions for further research in this field.