Behavioral analysis during the forced swimming test using a joystick device

A deep-learning-based threshold-free method for automated analysis of rodent behavior in the forced swim test and tail suspension test

BACKGROUND

The forced swim test (FST) and tail suspension test (TST) are widely used to assess depressive-like behaviors in animals. Immobility time is used as an important parameter in both FST and TST. Traditional methods for analyzing FST and TST rely on manually setting the threshold for immobility, which is time-consuming and subjective.

NEW METHOD

We proposed a threshold-free method for automated analysis of mice in these tests using a Dual-Stream Activity Analysis Network (DSAAN). Specifically, this network extracted spatial information of mice using a limited number of video frames and combined it with temporal information extracted from differential feature maps to determine the mouse's state. To do so, we developed the Mouse FSTST dataset, which consisted of annotated video recordings of FST and TST.

RESULTS

By using DSAAN methods, we identify immobility states at accuracies of 92.51 % and 88.70 % for the TST and FST, respectively. The predicted immobility time from DSAAN is nicely correlated with a manual score, which indicates the reliability of the proposed method. Importantly, the DSAAN achieved over 80 % accuracy for both FST and TST by utilizing only 94 annotated images, suggesting that even a very limited training dataset can yield good performance in our model.

COMPARISON WITH EXISTING METHOD(S)

Compared with DBscorer and EthoVision XT, our method exhibits the highest Pearson correlation coefficient with manual annotation results on the Mouse FSTST dataset.

CONCLUSIONS

We established a powerful tool for analyzing depressive-like behavior independent of threshold, which is capable of freeing users from time-consuming manual analysis.

A Tellurium-Based Small Immunomodulatory Molecule Ameliorates Depression-Like Behavior in Two Distinct Rat Models

Major depressive disorder (MDD) is a leading cause of morbidity, and the fourth leading cause of disease burden worldwide. While MDD is a treatable condition for many individuals, others suffer from treatment-resistant depression (TRD). Here, we suggest the immunomodulatory compound AS101 as novel therapeutic alternative. We previously showed in animal models that AS101 reduces anxiety-like behavior and elevates levels of the brain-derived neurotrophic factor (BDNF), a protein that has a key role in the pathophysiology of depression. To explore the potential antidepressant properties of AS101, we used the extensively characterized chronic mild stress (CMS) model, and the depressive rat line (DRL Finally, in Exp. 3 to attain insight into the mechanism we knocked down BDNF in the hippocampus, and demonstrated that the beneficial effect of AS101 was abrogated. Together with the previously established safety profile of AS101 in humans, these results may represent the first step towards the development of a novel treatment option for MDD and TRD.

Forced swimming sabotages the morphological and synaptic maturation of newborn granule neurons and triggers a unique pro-inflammatory milieu in the hippocampus

Recent experimental data suggest that mood disorders are related to inflammatory phenomena and have led to the "inflammatory hypothesis of depression". Given that the hippocampus is one of the most affected areas in these disorders, we used a model of acute stress (the Porsolt test) to evaluate the consequences of forced swimming on two crucial events related to the pathophysiology of major depression: the functional maturation of newborn granule neurons; and the hippocampal inflammatory milieu. Using PSD95:GFP-expressing retroviruses, we found that forced swimming selectively alters the dendritic morphology of newborn neurons and impairs their connectivity by reducing the number and volume of their postsynaptic densities. In addition, acute stress triggered a series of morphological changes in microglial cells, together with an increase in microglial CD68 expression, thus suggesting the functional and morphological activation of this cell population. Furthermore, we observed an intriguing change in the hippocampal inflammatory milieu in response to forced swimming. Importantly, the levels of several molecules affected by acute stress (such as Interleukin-6 and eotaxin) have been described to also be altered in patients with depression and other mood disorders.

Prelimbic Stimulation Ameliorates Depressive-Like Behaviors and Increases Regional BDNF Expression in a Novel Drug-Resistant Animal Model of Depression

BACKGROUND

Approximately one third of all major depression patients fail to respond to conventional pharmacological antidepressants, and brain stimulation methods pose a promising alternative for this population. Recently, based on repeated multifactorial selective inbreeding of rats for depressive-like behaviors, we introduced a novel animal model for MDD. Rats from this Depressive Rat Line (DRL) exhibit inherent depressive-like behaviors, which are correlated with lower levels of brain-derived neurotrophic factor (BDNF) in specific brain regions. In addition, DRL rats do not respond to antidepressant medication but respond to electroconvulsive treatment, and they can thus be utilized to test the effectiveness of brain stimulation on hereditary, medication-resistant depressive-like behaviors.

OBJECTIVE

To test the effect of sub-convulsive electrical stimulation (SCES) of the prelimbic cortex, using TMS-like temporal pattern of stimulation, on depressive-like behaviors and regional BDNF levels in DRL rats.

METHODS

SCES sessions were administered daily for 10 days through chronically implanted electrodes. Temporal stimulation parameters were similar to those used in TMS for major depression in human patients. Depressive-like behaviors were assayed after treatment, followed by brain extraction and regional BDNF measurements.

RESULTS

SCES normalized both the depressive-like behaviors and the reduced BDNF levels observed in DRL rats. Correlation analyses suggest that changes in specific behaviors are mediated, at least in part, by BDNF expression in reward-related brain regions.

CONCLUSIONS

Brain stimulation is effective in a drug-resistant, inherited animal model for depression. BDNF alterations in specific regions may mediate different antidepressant effects.

Altered brain-derived neurotrophic factor expression in the ventral tegmental area, but not in the hippocampus, is essential for antidepressant-like effects of electroconvulsive therapy

BACKGROUND

Impaired neuronal plasticity and, specifically, altered expression of brain-derived neurotrophic factor (BDNF) were shown to play a critical role in depressive behavior and the mechanism of various antidepressant treatments including electroconvulsive therapy (ECT). Interestingly, opposing roles were suggested for BDNF in the hippocampus and the ventral tegmental area (VTA), while interactions between these regions were shown on various levels. Here, we evaluated whether BDNF plays an essential role in the antidepressant-like effects of ECT and performed a direct comparison between BDNF manipulations in the VTA and the hippocampus.

METHODS

Knockdown or overexpression of BDNF was induced in hippocampus or VTA of rats by microinjection of specific lentiviral vectors. The effects of these manipulations on antidepressant outcomes of ECT were evaluated by the forced swim test and by sucrose preference measurements, and BDNF expression levels were assessed in other reward-related brain regions.

RESULTS

Here, we show that whereas ECT increased hippocampal BDNF expression, induction of hippocampal BDNF knockdown did not block its antidepressant-like effect. Importantly, we found that ECT caused a robust reduction in VTA BDNF levels. Moreover, VTA BDNF knockdown alone was sufficient to induce an antidepressant-like effect, and VTA BDNF overexpression blocked the antidepressant-like effect of ECT.

CONCLUSIONS

While neuroplastic alterations, as expressed by changes in BDNF expression within different brain regions, are induced by ECT, the antidepressant-like effect of ECT in an animal model depends on reduction of VTA BDNF expression but not on the elevation of hippocampal BDNF expression.

Resilience to chronic stress is mediated by hippocampal brain-derived neurotrophic factor

Chronic stress is a trigger for several psychiatric disorders, including depression; however, critical individual differences in resilience to both the behavioral and the neurochemical effects of stress have been reported. A prominent mechanism by which the brain reacts to acute and chronic stress is activation of the hypothalamic-pituitary-adrenal (HPA) axis, which is inhibited by the hippocampus via a polysynaptic circuit. Alterations in secretion of stress hormones and levels of brain-derived neurotrophic factor (BDNF) in the hippocampus were implicated in depression and the effects of antidepressant medications. However, the potential role of hippocampal BDNF in behavioral resilience to chronic stress and in the regulation of the HPA axis has not been evaluated. In the present study, Sprague Dawley rats were subjected to 4 weeks of chronic mild stress (CMS) to induce depressive-like behaviors after lentiviral vectors were used to induce localized BDNF overexpression or knockdown in the hippocampus. The behavioral outcome was measured during 3 weeks after the CMS procedure, then plasma samples were taken for measurements of corticosterone levels, and finally hippocampal tissue was taken for BDNF measurements. We found that hippocampal BDNF expression plays a critical role in resilience to chronic stress and that reduction of hippocampal BDNF expression in young, but not adult, rats induces prolonged elevations in corticosterone secretion. The present study describes a mechanism for individual differences in responses to chronic stress and implicates hippocampal BDNF in the development of neural circuits that control adequate stress adaptations.

Knockdown of brain-derived neurotrophic factor in specific brain sites precipitates behaviors associated with depression and reduces neurogenesis

Depression has been associated with reduced expression of brain-derived neurotrophic factor (BDNF) in the hippocampus. In addition, animal studies suggest an association between reduced hippocampal neurogenesis and depressive-like behavior. These associations were predominantly established based on responses to antidepressant drugs and alterations in BDNF levels and neurogenesis in depressive patients or animal models for depressive behavior. Nevertheless, there is no direct evidence that the actual reduction of the BDNF protein in specific brain sites can induce depressive-like behaviors or affect neurogenesis in vivo. Using BDNF knockdown by RNA interference and lentiviral vectors injected into specific subregions of the hippocampus we show that a reduction in BDNF expression in the dentate gyrus, but not the CA3, reduces neurogenesis and affects behaviors associated with depression. Moreover, we show that BDNF has a critical function in neuronal differentiation, but not proliferation in vivo. Finally, we found that a specific BDNF knockdown in the ventral subiculum induces anhedonic-like behavior. These findings provide substantial support for the neurotrophic hypothesis of depression and specify anatomical and neurochemical targets for potential antidepressant interventions. Moreover, the specific effect of BDNF reduction on neuronal differentiation has broader implications for the study of neurodevelopment and neurodegenerative diseases.

Effects of in utero exposure to Tityus bahiensis scorpion venom in adult rats

The toxicity of Tityus bahiensis scorpion venom is well known, but there are little data about the damage in offspring of dams that were exposed to the venom during pregnancy. The objective of this work was to determine the toxic effects of venom in adult offspring of Wistar rats exposed to venom in utero. Dams were divided into a control group, subcutaneously injected with saline solution on the 10th (GD10) and 16th (GD16) days, and two experimental groups, subcutaneously injected with venom (2.5mg/kg) on GD10 or GD16, respectively. Adult offspring were evaluated according to behavioral development and neuronal integrity in the hippocampus. Tests performed in the activity box and in the enriched environment demonstrated that males from GD10 had motor decrease. Females from GD10 showed a depressive-like state and were more anxious, as demonstrated by the forced swimming test and social interaction. The plus-maze discriminative avoidance task demonstrated that GD16 males had lower levels of anxiety. The number of neuronal cells was decreased in CA1, CA3 and CA4 hippocampal areas of males and females from GD10 group and in CA1 of females and CA4 of males from GD16 group. Thus, we conclude that venom exposure in pregnant dams causes subtle alteration in the behavioral and neuronal development of offspring in adult life in a gender-dependent manner.

Vaccination as a novel approach for treating depressive behavior

BACKGROUND

Depressive behavior in animals is often associated with reduced levels of brain-derived neurotrophic factor (BDNF) and impaired neurogenesis in the hippocampus. Recent studies showed that T cells recognizing central nervous system (CNS)-specific antigens can regulate adult hippocampal neurogenesis and expression of BDNF. On the basis of these findings, we hypothesized that controlling CNS specific immune activity by immunization with a myelin-related peptide may have an antidepressant effect.

METHODS

We investigated the impact of immunization with a CNS related peptide, on the behavioral and cellular outcomes of chronic mild stress (CMS; an animal model for depression) in rats.

RESULTS

Immunization with a weak agonist of a myelin-derived peptide ameliorated depressive behavior such as anhedonia (measured by sucrose preference), induced by CMS in rats. The behavioral outcome was accompanied by restoration of hippocampal BDNF levels and neurogenesis.

CONCLUSIONS

The results of this study introduce a novel approach of immunization with CNS-related antigens as a therapeutic means for fighting depression. Vaccination, as an antidepressant therapy, may invoke several molecular and cellular pathways that are known to be regulated by antidepressant drugs. Therefore, we suggest that immune-based therapies should be considered for treatment of depression.

Age-dependent effects of chronic stress on brain plasticity and depressive behavior

Exposure to chronic mild stress (CMS) is known to induce anhedonia in adult animals, and is associated with induction of depression in humans. However, the behavioral effects of CMS in young animals have not yet been characterized, and little is known about the long-term neurochemical effects of CMS in either young or adult animals. Here, we found that CMS induces anhedonia in adult but not in young animals, as measured by a set of behavioral paradigms. Furthermore, while CMS decreased neurogenesis and levels of brain-derived neurotrophic factor (BDNF) in the hippocampus of adult animals, it increased these parameters in young animals. We also found that CMS altered alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA) receptor GluR1 subunit levels in the hippocampus and the nucleus accumbens of adult, but not young animals. Finally, no significant differences were observed between the effects of CMS on circadian corticosterone levels in the different age groups. The substantially different neurochemical effects chronic stress exerts in young and adult animals may explain the behavioral resilience to such stress young animals possess.

The effects of exercise on spatial learning and anxiety-like behavior are mediated by an IGF-I-dependent mechanism related to hippocampal neurogenesis

Knowledge about the effects of physical exercise on brain is accumulating although the mechanisms through which exercise exerts these actions remain largely unknown. A possible involvement of adult hippocampal neurogenesis (AHN) in the effects of exercise is debated while the physiological and pathological significance of AHN is under intense scrutiny. Recently, both neurogenesis-dependent and independent mechanisms have been shown to mediate the effects of physical exercise on spatial learning and anxiety-like behaviors. Taking advantage that the stimulating effects of exercise on AHN depend among others, on serum insulin-like growth factor I (IGF-I), we now examined whether the behavioral effects of running exercise are related to variations in hippocampal neurogenesis, by either increasing or decreasing it according to serum IGF-I levels. Mutant mice with low levels of serum IGF-I (LID mice) had reduced AHN together with impaired spatial learning. These deficits were not improved by running. However, administration of exogenous IGF-I ameliorated the cognitive deficit and restored AHN in LID mice. We also examined the effect of exercise in LID mice in the novelty-suppressed feeding test, a measure of anxiety-like behavior in laboratory animals. Normal mice, but not LID mice, showed reduced anxiety after exercise in this test. However, after exercise, LID mice did show improvement in the forced swim test, a measure of behavioral despair. Thus, many, but not all of the beneficial effects of exercise on brain function depend on circulating levels of IGF-I and are associated to increased hippocampal neurogenesis, including improved cognition and reduced anxiety.