Natural Amyloid-Beta Oligomers Acutely Impair the Formation of a Contextual Fear Memory in Mice

Memory loss is one of the hallmark symptoms of Alzheimer's disease (AD). It has been proposed that soluble amyloid-beta (Abeta) oligomers acutely impair neuronal function and thereby memory. We here report that natural Abeta oligomers acutely impair contextual fear memory in mice. A natural Abeta oligomer solution containing Abeta monomers, dimers, trimers, and tetramers was derived from the conditioned medium of 7PA2 cells, a cell line that expresses human amyloid precursor protein containing the Val717Phe familial AD mutation. As a control we used 7PA2 conditioned medium from which Abeta oligomers were removed through immunodepletion. Separate groups of mice were injected with Abeta and control solutions through a cannula into the lateral brain ventricle, and subjected to fear conditioning using two tone-shock pairings. One day after fear conditioning, mice were tested for contextual fear memory and tone fear memory in separate retrieval trials. Three experiments were performed. For experiment 1, mice were injected three times: 1 hour before and 3 hours after fear conditioning, and 1 hour before context retrieval. For experiments 2 and 3, mice were injected a single time at 1 hour and 2 hours before fear conditioning respectively. In all three experiments there was no effect on tone fear memory. Injection of Abeta 1 hour before fear conditioning, but not 2 hours before fear conditioning, impaired the formation of a contextual fear memory. In future studies, the acute effect of natural Abeta oligomers on contextual fear memory can be used to identify potential mechanisms and treatments of AD associated memory loss

Natural Abeta oligomer solution and injection.

<p>A) Blot image showing the presence of Abeta monomers, dimers, trimers, and tetramers in the Abeta solution. The 6E10 antibody was used for detection of Abeta oligomers that were removed from the Abeta solution using immunoprecipitation with A/G beads and 4G8 antibody (IP1, IP2, IP3: oligomers bound to beads used for first, second, and third immunoprecipitation). No oligomers were detected after three rounds of immunoprecipitation, which confirmed the absence of Abeta oligomers in the control solution (see “<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0029940#s4" target="_blank">Materials and Methods</a>” for a detailed description of how Abeta and control solutions were generated). B) Diagram showing the location of the guide cannula (green) and the injector cannula (red) in a Nissl-stained coronal section of the mouse brain <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0029940#pone.0029940-Lein1" target="_blank">[38]</a>. The tip of the guide cannula stopped just above the corpus callosum. The tip of the injection cannula extended into the lateral ventricle.</p

Experiment 2: single Abeta injection 1 hour before fear conditioning.

<p>Top) Diagram showing the design of experiment 2. Separate groups of mice were injected one time with either control or Abeta solution 1 hour before fear conditioning. Bottom) Graphs showing average freezing scores during fear conditioning on day 1 and the two retrieval trials on day 2. Mice injected with the Abeta solution (n = 8) had significantly lower freezing scores during the context fear retrieval trial as compared with mice injected with the control solution (n = 10). Error bars are standard errors of means. * <i>P</i><0.05.</p

Experiment 1: repeated Abeta injection.

<p>Top) Diagram showing the design of experiment 1. Separate groups of mice were injected three times with either control or Abeta solution. Bottom) Graphs showing average freezing scores during fear conditioning on day 1 and the two retrieval trials on day 2 (see “<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0029940#s4" target="_blank">Materials and Methods</a>: Analysis of freezing behavior” for explanation of intervals on the X axis). Mice injected with the Abeta solution (n = 5) had significantly lower freezing scores during the context fear retrieval trial as compared with mice injected with the control solution (n = 6). Error bars are standard errors of means. * <i>P</i><0.05.</p

Experiment 3: single Abeta injection 2 hours before fear conditioning.

<p>Top) Diagram showing the design of experiment 3. Separate groups of mice were injected one time with either control or Abeta solution 2 hours before fear conditioning. Bottom) Graphs showing average freezing scores during fear conditioning on day 1 and the two retrieval trials on day 2. There was no difference during any of the intervals analyzed between mice injected with the Abeta solution (n = 10) and mice injected with the control solution (n = 8). Error bars are standard errors of means.</p

Global COVID-19 lockdown highlights humans as both threats and custodians of the environment

The global lockdown to mitigate COVID-19 pandemic health risks has altered human interactions with nature. Here, we report immediate impacts of changes in human activities on wildlife and environmental threats during the early lockdown months of 2020, based on 877 qualitative reports and 332 quantitative assessments from 89 different studies. Hundreds of reports of unusual species observations from around the world suggest that animals quickly responded to the reductions in human presence. However, negative effects of lockdown on conservation also emerged, as confinement resulted in some park officials being unable to perform conservation, restoration and enforcement tasks, resulting in local increases in illegal activities such as hunting. Overall, there is a complex mixture of positive and negative effects of the pandemic lockdown on nature, all of which have the potential to lead to cascading responses which in turn impact wildlife and nature conservation. While the net effect of the lockdown will need to be assessed over years as data becomes available and persistent effects emerge, immediate responses were detected across the world. Thus initial qualitative and quantitative data arising from this serendipitous global quasi-experimental perturbation highlights the dual role that humans play in threatening and protecting species and ecosystems. Pathways to favorably tilt this delicate balance include reducing impacts and increasing conservation effectiveness