Deletion of AhR attenuates fear memory leaving other types of memory intact.

The aryl hydrocarbon receptor (AhR), a classic "environmental sensor", has been found to play an important role in cognitive and emotional function. Recent studies showed AhR deletion led to an attenuated fear memory, providing a potential target against fear memory, whether it is the consequence of attenuated sense of fear or memory ability deficit or both is unclear. Here this study aims to work this out. The freezing time in contextual fear conditioning (CFC) reduced significantly in AhR knockout mice, indicating an attenuated fear memory. Hot plate test and acoustic startle reflex showed that AhR knockout did not change the pain threshold and hearing, excluded the possibility of sensory impairments. Results from NORT, MWM and SBT showed that deletion of AhR had little effects on other types of memory. But the anxiety-like behaviors reduced both in naïve or suffered (tested after CFC) AhR knockout mice, showing that AhR-deficient mice have a reduced basal and stressful emotional response. The basal low-frequency to high-frequency (LF/HF) ratio of the AhR knockout mice was significantly lower than that of the control group, indicating lower sympathetic excitability in the basal state, suggesting a low level of basal stress in the knockout mice. Before and after CFC, the LF/HF ratio of AhR-KO mice tended to be significantly lower than that of WT mice, and their heart rate was significantly lower; and the AhR-KO mice also has a decreased serum corticosterone level after CFC, suggesting a reduced stress response in AhR knockout mice. Altogether, the basal stress level and stress response were significant reduced in AhR knockout mice, which might contribute to the attenuated fear memory with little impairment on other types of memory, suggesting AhR as a "psychologic sensor" additional to "environmental sensor".

An improved brine shrimp larvae lethality microwell test method.

This article described an improved brine shrimp larvae lethality microwell test method. A simply designed connecting vessel with alternative photoperiod was used to culture and collect high yield of active Artemia parthenogenetica nauplii for brine shrimp larvae lethality microwell test. Using this method, pure A. parthenogenetica nauplii suspension was easily cultured and harvested with high density about 100-150 larvae per milliliter and the natural mortality was reduced to near zero by elimination of unnecessary artificial disturbance. And its sensitivity was validated by determination of LC(50)-24 h of different reference toxicants including five antitumor agents, two pesticides, three organic pollutants, and four heavy metals salts, most of which exhibited LC(50)-24 h between 0.07 and 58.43 mg/L except for bleomycin and mitomycin C with LC(50)-24 h over 300 mg/L.

A touchscreen-based paradigm to measure visual pattern separation and pattern completion in mice.

Memory accuracy involves two major processes: pattern separation and pattern completion. Pattern separation refers to the ability to reduce overlap among similar inputs to avoid interference, and pattern completion refers to the ability to retrieve the whole information from partial or degraded cues. Impairments in pattern separation/pattern completion contribute to cognitive deficits in several diseases of the nervous system. Therefore, it is better to evaluate both pattern separation and pattern completion in one apparatus. However, few tools are available to assess pattern separation and pattern completion within the same apparatus for rodents. In this study, we designed a series of images with varying degrees of similarity to the correct image to evaluate pattern separation and pattern completion. First, mice were trained to discriminate between two totally different images, and once the correct percentage reached above 77% for two consecutive days, the images with different degrees of similarity were used to measure pattern separation and pattern completion. The results showed the mice performed progressively worse from S0 to S4 (increasing similarity) when discriminating similar images in pattern separation, and the mice performed progressively worse from C0 to C4 (decreasing cues information) when recalling the correct image according to partial cues in pattern completion, implying a good image similarity-dependent manner for memory accuracy evaluation. In sum, we designed a convenient, effective paradigm to evaluate pattern separation and pattern completion based on a touchscreen pairwise discrimination task, which may provide a new method for the studies of the effects and mechanisms of memory accuracy enhancing drugs.

Four chlorinated depsidones from a seaweed-derived strain of Aspergillus unguis and their new biological activities.

Four chlorinated depsidones (two reported for the second time (1 and 2) and two known (3 and 4)) were isolated from a seaweed-derived Aspergillus unguis strain. Their structures were spectroscopically elucidated. Compounds 1, 3 and 4 strongly inhibited methicillin-resistant Staphylococcus aureus (MRSA) with minimum inhibitory concentrations (MICs) of 2, 2 and 4 µg/mL and killed Artemia larva with LC50 of 4.1, 1.7 and 2.8 µg/mL, respectively. Besides, in DNA-damaging test, they also selectively inhibited a DNA repair capacity-defective Escherichia coli strain AB3027(-) (MICs: 2, 32 and 4 µg/mL, respectively) compared with the wild-type strain AB1157(+) (MICs: over 512, over 512 and 256 µg/mL, respectively). Furthermore, compound 1 also strongly inhibited cancer cell line A-549 (IC50: 0.5 µg/mL). The above-mentioned bioactivities were newly reported for compound 1. In contrast, compound 2 did not exhibit significant activity. The structure-activity relationship indicated that a complete lactone ring may be important.