Analysis of behavioral and hippocampal variation in congenic albino and pigmented BALB mice

Identification of the main active antidepressant constituents in a traditional Turkish medicinal plant, Centaurea kurdica Reichardt

ETHNOPHARMACOLOGICAL RELEVANCE

In Turkish folk medicine, infusions and decoctions prepared from the flowers, fruits and aerial parts of Centaurea kurdica Reichardt (Asteraceae) are used as sedative and antidepressant-like effects of various sedative plants have been identified in many studies. The present study was designed to evaluate the antidepressant activity of this plant.

MATERIALS AND METHODS

n-Hexane, ethyl acetate (EtOAc), and methanol (MeOH) extracts were prepared from the branches with leaves and also flowers of the plant. Antidepressant potentials of these extracts were researched by using the forced swimming test, tail suspension test, and antagonism of tetrabenazine-induced ptosis, hypothermia, and suppression of locomotor activity.

RESULTS

After determination of high antidepressant potentials of MeOH extract prepared from flowers and n-hexane extract prepared from branches with leaves, isolation studies were carried out on these two extracts and the main active components were determined as β-amyrin, mixture of β-sitosterol and stigmasterol and costunolide for the branches with leaves and quercitrin, isoquercetin and naringenin-7-O-glucopyranoside for the flowers.

CONCLUSIONS

As a result of the mechanistic and toxicity studies planned on this plant, it is thought that C. kurdica may be a glimmer of hope for depressed patients.

Quantitative Trait Loci and a Novel Genetic Candidate for Fear Learning

Trauma- and stress-related disorders are clinically heterogeneous and associated with substantial genetic risk. Understanding the biological origins of heterogeneity of key intermediate phenotypes such as cognition and emotion can provide novel mechanistic insights into disorder pathogenesis. Performing quantitative genetics in animal models is a tractable strategy for examining both the genetic basis of intermediate phenotypes and functional testing of candidate quantitative traits genes (QTGs). Here, existing and newly collected data were used for collaborative genome-wide mapping of cued fear acquisition and expression in 65 mouse strains from the BXD genetic reference panel. For fear acquisition, we identified a significant locus on chromosome (Chr) 10 and eight suggestive loci on Chr 2, 4, 5, 11, 13, and 15. For fear expression, we identified one significant and another highly suggestive locus on Chr 13, as well as four suggestive loci on Chr 10, 11, and X. Across these loci, 60 putative QTGs were identified. The quantitative trait locus on distal Chr 13 contained a single, highly promising gene at the location of the peak likelihood ratio statistic score. The gene, hyperpolarization-activated cyclic nucleotide-gated channel 1 (Hcn1), regulates neuronal excitability. Validation experiments using behavioral pharmacology revealed that functional Hcn channels in the basolateral amygdala are necessary for conditioned fear acquisition and expression. Hcn1, together with the other candidate QTGs, thus provide new targets for neurobiological and treatment studies of fear learning and trauma- and stress-related disorders.

SIGNIFICANCE STATEMENT

There is a knowledge gap in understanding the genetic contributions to behavioral heterogeneity in typical and atypical populations. Mouse genetic reference panels (GRPs) provide one approach for identifying genetic sources of variation. Here, we identified three loci for conditioned fear acquisition and expression in a mouse GRP. Each locus contained candidate quantitative trait genes (QTGs). One locus had a single QTG, Hcn1 (hyperpolarization-activated cyclic nucleotide-gated channel 1), which has been implicated in neuronal excitability and learning. This discovery was validated using behavioral pharmacology, revealing that Hcn channels in the basolateral amygdala are required for fear acquisition and expression. The study thus identifies novel candidate QTGs that may contribute to variation in emotional learning and highlight the utility of mouse GRPs for the identification of genes underlying complex traits.

Unique genetic loci identified for emotional behavior in control and chronic stress conditions

An individual's genetic background affects their emotional behavior and response to stress. Although studies have been conducted to identify genetic predictors for emotional behavior or stress response, it remains unknown how prior stress history alters the interaction between an individual's genome and their emotional behavior. Therefore, the purpose of this study is to identify chromosomal regions that affect emotional behavior and are sensitive to stress exposure. We utilized the BXD behavioral genetics mouse model to identify chromosomal regions that predict fear learning and emotional behavior following exposure to a control or chronic stress environment. 62 BXD recombinant inbred strains and C57BL/6 and DBA/2 parental strains underwent behavioral testing including a classical fear conditioning paradigm and the elevated plus maze. Distinct quantitative trait loci (QTLs) were identified for emotional learning, anxiety and locomotion in control and chronic stress populations. Candidate genes, including those with already known functions in learning and stress were found to reside within the identified QTLs. Our data suggest that chronic stress history reveals novel genetic predictors of emotional behavior.

Quantitative Genetic Analysis of Ventral Midbrain and Liver Iron in BXD Recombinant Inbred Mice

Male and female mice from 15 of the BXD/Ty recombinant inbred strain panel were examined for regional brain and liver iron content. Brain regions included medial prefrontal cortex, nucleus accumbens, caudate-putamen and ventral midbrain. Our focal tissue was the ventral midbrain, containing the ventral tegmentum and substantia nigra. This area contains the perikarya of the dopamine neurons that project to nucleus accumbens and caudate-putamen. Genetic correlations between ventral midbrain and liver iron content were not statistically significant, suggesting that peripheral and central iron regulatory systems are largely independent. Correlations between ventral midbrain iron and iron in the caudate-putamen and nucleus accumbens, but not the prefrontal cortex were moderately high and significant. Ventral midbrain and liver iron contents were subjected to quantitative trait loci analysis to identify associated chromosomal locations. This analysis revealed several suggestive loci for iron content in ventral midbrain but fewer loci for liver. Genetic correlations between ventral midbrain iron and published dopamine functional indices were significant, suggesting a link between ventral midbrain iron status and central dopamine neurobiology. This work shows the value of quantitative genetic analysis in the neurobiology of iron and in showing the close association between ventral midbrain iron and nigrostriatal/mesolimbic dopamine function.

Bright lighting conditions during testing increase thigmotaxis and impair water maze performance in BALB/c mice

In this study, we investigated the performance of BALB/c mice in Morris water maze task under two different illumination (bright and dim light) conditions. The results show that BALB/c mice could not complete the Morris water maze task under bright light (BLC), but performed very well under dim light (DLC). Animals that swam under BLC had a higher serum corticosterone level than those under DLC. Animals pretrained under DLC had a lower serum corticosterone level than those directly exposed to BLC. Our results also show that animals under BLC had a higher level of thigmotaxis (a behavioral anxiety measure during testing) than under DLC. Correlation analysis shows that corticosterone and thigmotaxis levels have a positive correlation with escape latency, indicating that corticosterone and thigmotaxis levels have a negative correlation with learning/memory performance. These results suggest that BALB/c mice have the ability to learn a spatial task; under BLC, they performed poorly owing to a high level of thigmotaxis.

Genetic dissection of the mouse CNS using magnetic resonance microscopy

PURPOSE OF REVIEW

Advances in magnetic resonance microscopy (MRM) make it practical to map gene variants responsible for structural variation in brains of many species, including mice and humans. We review results of a systematic genetic analysis of MRM data using as a case study a family of well characterized lines of mice.

RECENT ADVANCES

MRM has matured to the point that we can generate high contrast, high-resolution images even for species as small as a mouse, with a brain merely 1/3000th the size of humans. We generated 21.5-micron data sets for a diverse panel of BXD mouse strains to gauge the extent of genetic variation, and as a prelude to comprehensive genetic and genomic analyses. Here we review MRM capabilities and image segmentation methods; heritability of brain variation; covariation of the sizes of brain regions; and correlations between MRM and classical histological data sets.

SUMMARY

The combination of high throughput MRM and genomics will improve our understanding of the genetic basis of structure-function correlations. Sophisticated mouse models will be critical in converting correlations into mechanisms and in determining genetic and epigenetic causes of differences in disease susceptibility.

Visual detection, pattern discrimination and visual acuity in 14 strains of mice

Based on the procedure of Prusky et al. (2000, Vision Research, 40, 2201-2209), we used a computer-based, two-alternative swim task to evaluate visual detection, pattern discrimination and visual acuity in 14 strains of mice from priority groups A and B of the JAX phenome project (129S1/SvImJ, A/J, AKR/J, BALB/cByJ, BALB/cJ, C3H/HeJ, C57BL/6J, CAST/Ei, DBA/2J, FVB/NJ, MOLF/Ei, SJL/J, SM/J and SPRET/Ei). Each mouse was tested for eight trials/day for 8 days on each of the three tests. There was a significant strain difference in visual ability in all three tests. Mice with reported normal vision (129S1/SvImJ, C57BL/6J and DBA/2J) and one albino strain (AKR/J) performed very well in these tasks. The other albino strains (A/J, BALB/cByJ and BALB/cJ) took longer to learn the tasks than mice with normal vision and did not reach the criterion of 70% correct. Mice with retinal degeneration (C3H/HeJ, FVB/NJ, MOLF/Ei and SJL/J) performed only at chance levels as did the three strains with unknown visual abilities (CAST/Ei, SM/J and SPRET/Ei). Because many behavioral tasks for rodents rely on visual cues, we suggest that the visual abilities of mice should be evaluated before they are tested in commonly used visuo-spatial learning and memory tasks.

Quantitative genetic analysis of brain copper and zinc in BXD recombinant inbred mice

Copper and zinc are trace nutrients essential for normal brain function, yet an excess of these elements can be toxic. It is important therefore that these metals be closely regulated. We recently conducted a quantitative trait loci (QTL) analysis to identify chromosomal regions in the mouse containing possible regulatory genes. The animals came from 15 strains of the BXD/Ty recombinant inbred (RI) strain panel and the brain regions analyzed were frontal cortex, caudate-putamen, nucleus accumbens and ventral midbrain. Several QTL were identified for copper and/or zinc, most notably on chromosomes 1, 8, 16 and 17. Genetic correlational analysis also revealed associations between these metals and dopamine, cocaine responses, saccharine preference, immune response and seizure susceptibility. Notably, the QTL on chromosome 17 is also associated with seizure susceptibility and contains the histocompatibility H2 complex. This work shows that regulation of zinc and copper is under polygenic influence and is intimately related to CNS function. Future work will reveal genes underlying the QTL and how they interact with other genes and the environment. More importantly, revelation of the genetic underpinnings of copper and zinc brain homeostasis will aid our understanding of neurological diseases that are related to copper and zinc imbalance.

Spatial learning induces presynaptic structural remodeling in the hippocampal mossy fiber system of two rat strains

Hebb (1949) proposed that after learning both presynaptic and postsynaptic structural changes form the neural substrate of long-lasting memory. Despite this, there are few instances linking presynaptic remodeling with learning. Here the authors demonstrate in two different rat strains that learning the location of a hidden platform induces expansion of the presynaptic hippocampal mossy fiber terminal field (MFTF) from the stratum lucidum to the distal stratum oriens (dSO). Prior to any training, Long Evans rats (LER) showed an extensive endogenous MFTF innervation of DSO, in contrast to Wistar rats (WR) that showed minimal innervation. LER showed better recall than WR on the hidden platform water maze task and a visible reversal water maze task. In both strains, significant MFTF expansion to dSO, spanning approximately 200 mum, was detected 7 days after training on the hidden platform task, but only LER showed significant MFTF expansion 24 h after training. It is attractive to think that the MFTF expansion to dSO contributes both to long-lasting memory formation and to facilitating spatial navigation strategies. The present results establish learning-induced axonal remodeling of the hippocampal MF system in adult rats as an especially useful system for exploring presynaptic morphological adjustments consequent to learning.

Comparative analysis of the anxiety-related behaviors in four inbred mice

An anxiety-related behavior is an emotional response of an organism, which is quantitatively measured by several behavioral paradigms. We employed two most frequently used behavioral tests, the open field and light-dark exploration, to comparatively analyze the anxiety-like behaviors in four inbred mice. For an accurate recording of movement, motion analysis software was developed that acquires a real-time video input to generate a behavioral path. Effects of the strains on the test results were evaluated by ANOVA with the Newman-Keuls post hoc comparison. Eight different behavioral indices, four from each tests, were grouped into two classes; the results of duration, center crossing, transition, rearing, and ambulation indicate strain differences of FVB/N>C57BL/6J>/=BALB/cA>/=CBA/N (I), while stretched-attend posture, peeping, and defecation show the tendency of FVB/N=C57BL/6J<CBA/N</=BALB/cA (II). The peeping is a novel type of behavior observed in this work. Although there is a variation among behavioral indices in their discrimination between inbred lines, the behaviors are highly correlated one another such that each class I or class II behaviors are clustered on two orthogonal factor planes as a result of the principal component analysis. The polarization of each inbred line toward these two behavioral biases may reflect genetic backgrounds of these strains.

Blind mice are not impaired in T-maze footshock avoidance acquisition and retention

The processing of visual information during learning and memory is considered to be a vital function of the hippocampus. Some researchers believe that the sole purpose of the hippocampus is to process visuo-spatial information, whereas other investigators believe that the hippocampus integrates cues from multiple sources. In the current studies, we tested the effects of vision loss on a hippocampal task, acquisition and retention with T-maze footshock avoidance conditioning. Acquisition and retention, in adult-blinded mice, were not significantly impaired in T-maze footshock avoidance. Blindness did not affect activity, footshock startle or motivation to avoid shock. The same doses of memory enhancing drugs that improve memory in sighted mice improved memory in blind mice. Electrolytic lesions in blind mice, which destroyed 31+/-4% of the hippocampus, significantly impaired acquisition and retention for T-maze footshock avoidance and so demonstrated that the hippocampus retained its integrative role in blind mice. The current findings show that blind mice are as capable of learning T-maze footshock avoidance as sighted mice and that the hippocampus retains its important role in blind mice in learning and memory processing. It is concluded that the T-maze footshock avoidance conditioning task is a spatially but not visually dependent task that is hippocampally dependent.

Wheel running behavior is impaired by both surgical section and genetic absence of the mouse corpus callosum

Mice lacking a corpus callosum (CC) often show little or no deficit on tests of behavior. This paper reports that on highly complex bimanual motor tasks, deficits can be found. The speed of running on a wheel with irregularly spaced rungs is reduced by both hereditary absence of the CC in 129 x BALB/c recombinant mice and surgical section of the CC in genetically normal B6D2F(2) mice. The effect of CC absence appears on measures most closely related to speed, no influence exists on the amount of running over a period of 5 days. Motor behavior on a notched balance beam, on the other hand, shows clear superiority of the hybrid mice but no relation with reduced size of the CC, whether it was produced by genotype or surgery. The effect of absent CC is task dependent, but it is not obscured by developmental compensation in the recombinant mice.

BALB/c mice are not so bad in the Morris water maze

We compared the learning performances of BALB/c mice subjected to the Morris water spatial task under two different lighting conditions. In the first one, the experimental room was lit by neon tubes (direct and bright illumination) and in the second one by a halogen lamp directed to the roof (diffuse illumination). The scores of BALB/c mice in the diffuse illumination condition clearly demonstrated that these mice could learn to escape to a hidden platform while they could not under direct illumination condition. Moreover, they were able to acquire the task by means of spatial cues. These results are interpreted in terms of a decrease of anxiety levels.

Using knockout and transgenic mice to study neurophysiology and behavior

Reverse genetics, in which detailed knowledge of a gene of interest permits in vivo modification of its expression or function, provides a powerful method for examining the physiological relevance of any protein. Transgenic and knockout mouse models are particularly useful for studies of complex neurobiological problems. The primary aims of this review are to familiarize the nonspecialist with the techniques and limitations of mouse mutagenesis, to describe new technologies that may overcome these limitations, and to illustrate, using representative examples from the literature, some of the ways in which genetically altered mice have been used to analyze central nervous system function. The goal is to provide the information necessary to evaluate critically studies in which mutant mice have been used to study neurobiological problems.

Of mice and mazes: similarities between mice and rats on dry land but not water mazes

Mice are impaired relative to rats in place and matching-to-place learning when tests are given in a swimming pool. The rat advantage may stem from a superior spatial ability or from adaptation to a niche that has prepared them for competency in the water. In the present study, mice (C57BL/6) were compared with rats (Long-Evans) in a number of dry-land spatial tasks given on a radial arm maze and in a place task given in a swimming pool. The performance of the mice matched that of the rats in all dry-land tasks, but was inferior to that of the rats in the swimming pool. The results provide further evidence for a species difference in swimming-pool performance but do not support the idea that there are necessary differences in spatial abilities between mice and rats. It is suggested that, if optimal place learning is required for neurobehavioral studies of mice, such performance is more likely to be obtained in dry-land tasks than in swimming-pool tasks. Nevertheless, the species differences warrant further study because they could provide important insights into species differences is spatial learning more generally.

Selective breeding for extremes in open-field activity of mice entails a differentiation of hippocampal mossy fibers

The brains of mice selectively bred for differential locomotor activity in an open field (DeFries et al., Behav. Genet. 8:3-13, 1978) were analyzed for selection-dependent changes in the size of synaptic fields at the midseptotemporal level for the hippocampus. Timm-stained areas of all hippocampal fields from both left and right hippocampi were measured on five horizontal sections from the midseptotemporal level. The sample included 25 mice from two replicate lines, each one consisting of a high (HI); a low (LO), and a control line (CTL). The main selection effect was an enlargement of the intra-infrapyramidal mossy fiber (IIP-MF) projection in both HI lines by about 70% compared to LO and CTL mice (p < .0001), while other mossy fiber fields did not show differences. These findings confirm that genetic variations of the IIP-MF projection influence hippocampal processes mediating exploratory activities.

Comparison of different behavioral test situations used in psychopharmacology for measurement of anxiety

In order to estimate the consistency of variables measured in different test situations classically used in psychopharmacology, a set of hybrid mice was confronted with five testing situations: responses to a novel object introduced in a familiar environment, responses to novel places, behavior in a light/dark choice situation, on the holeboard, and in an elevated plus maze. A principal component analysis was performed using two variables per device as active variables and 26 others as supplementary variables. The first factor was clearly due to opposition between high and low levels of neophobia. Only variables from the first two tests were strongly correlated to this factor. Variables from the holeboard and from the plus maze were highly correlated one another and with the second factor, which grouped locomotion and exploration criteria. The light/dark choice test was intermediate and seemed to be moderately related to both locomotion and neophobia. These results point out the difficulty in comparing different test devices from a psychological point of view.