Transient anhedonia phenotype and altered circadian timing of behaviour during night-time dim light exposure in Per3(-/-) mice, but not wildtype mice.

Industrialisation greatly increased human night-time exposure to artificial light, which in animal models is a known cause of depressive phenotypes. Whilst many of these phenotypes are 'direct' effects of light on affect, an 'indirect' pathway via altered sleep-wake timing has been suggested. We have previously shown that the Period3 gene, which forms part of the biological clock, is associated with altered sleep-wake patterns in response to light. Here, we show that both wild-type and Per3(-/-) mice showed elevated levels of circulating corticosterone and increased hippocampal Bdnf expression after 3 weeks of exposure to dim light at night, but only mice deficient for the PERIOD3 protein (Per3(-/-)) exhibited a transient anhedonia-like phenotype, observed as reduced sucrose preference, in weeks 2-3 of dim light at night, whereas WT mice did not. Per3(-/-) mice also exhibited a significantly smaller delay in behavioural timing than WT mice during weeks 1, 2 and 4 of dim light at night exposure. When treated with imipramine, neither Per3(-/-) nor WT mice exhibited an anhedonia-like phenotype, and neither genotypes exhibited a delay in behavioural timing in responses to dLAN. While the association between both Per3(-/-) phenotypes remains unclear, both are alleviated by imipramine treatment during dim night-time light

Forced Alternation (Y-Maze).

<p><b>A)</b> Scopolamine-HBr (10 mg/kg) or saline was administered by i.p. injection 30 min before the sample trial. A retrieval trial was conducted 30 min after the sample trial. The time spent in the novel arm during the first minute of the retrieval trial was analyzed. For both treatment groups (saline control: Ctrl; scopolamine: SCP), time spent in the novel arm was about 33%, with no statistically significant difference between groups (n = 9/group). <b>B)</b> In the second arm entry of the retrieval trial, saline-injected control mice entered the novel arm less often than scopolamine-treated mice (SCP). <b>C)</b> 129S6/Tg2576 mice (11–13 months) spent significantly less time in the novel arm during the retrieval trial and <b>D)</b> entered significantly less often into the novel arm (n = 19-20/group). The control has no error bar because all mice (100%) first went into the novel arm. Mice with less than 3 arm entries in the first minute were excluded from the analysis. Data are mean ± SEM; **<i>p <</i> 0.01; ***<i>p <</i> 0.001 (Student’s <i>t</i>-test for Fig 2A and 2C; Chi-squared test for Fig 2B and 2D).</p

Behavioral Test Battery.

<p>Mice were tested in a behavioral test battery consisting of (top panel, from left to right): forced alternation (Y-maze), novel object recognition, Morris water maze, radial arm water maze, and spontaneous alternation (Y-maze) over a period of 8 weeks. Top panel: Behavioral tests conducted in the study. Middle panel: Timeline of tests. Bottom panel: Trials conducted per behavioral test. Tests were conducted in the order of increasing invasiveness. The spontaneous alternation test was performed last to maximize the interval to the forced alternation test, which utilized the same maze.</p

A Comprehensive Behavioral Test Battery to Assess Learning and Memory in 129S6/Tg2576 Mice

<div><p>Transgenic Tg2576 mice overexpressing human amyloid precursor protein (hAPP) are a widely used Alzheimer’s disease (AD) mouse model to evaluate treatment effects on amyloid beta (Aβ) pathology and cognition. Tg2576 mice on a B6;SJL background strain carry a recessive <i>rd1</i> mutation that leads to early retinal degeneration and visual impairment in homozygous carriers. This can impair performance in behavioral tests that rely on visual cues, and thus, affect study results. Therefore, B6;SJL/Tg2576 mice were systematically backcrossed with 129S6/SvEvTac mice resulting in 129S6/Tg2576 mice that lack the <i>rd1</i> mutation. 129S6/Tg2576 mice do not develop retinal degeneration but still show Aβ accumulation in the brain that is comparable to the original B6;SJL/Tg2576 mouse. However, comprehensive studies on cognitive decline in 129S6/Tg2576 mice are limited. In this study, we used two dementia mouse models on a 129S6 background—scopolamine-treated 129S6/SvEvTac mice (3–5 month-old) and transgenic 129S6/Tg2576 mice (11–13 month-old)–to establish a behavioral test battery for assessing learning and memory. The test battery consisted of five tests to evaluate different aspects of cognitive impairment: a Y-Maze forced alternation task, a novel object recognition test, the Morris water maze, the radial arm water maze, and a Y-maze spontaneous alternation task. We first established this behavioral test battery with the scopolamine-induced dementia model using 129S6/SvEvTac mice and then evaluated 129S6/Tg2576 mice using the same testing protocol. Both models showed distinctive patterns of cognitive impairment. Together, the non-invasive behavioral test battery presented here allows detecting cognitive impairment in scopolamine-treated 129S6/SvEvTac mice and in transgenic 129S6/Tg2576 mice. Due to the modular nature of this test battery, more behavioral tests, e.g. invasive assays to gain additional cognitive information, can easily be added.</p></div

Spontaneous Alternation (Y-Maze).

<p><b>A)</b> Scopolamine-injected mice (SCP) and control (Ctrl) mice showed the same level of spontaneous alternation (n = 9-10/group). <b>B)</b> Scopolamine-treated mice had significantly more arm entries than control mice. <b>C)</b> 129S6/Tg2576 mice and WT mice performed showed the same level of spontaneous alternation (n = 16-19/group). <b>D)</b> The number of total arm entries between WT and 129S6/Tg2576 mice was not statistically different. Mice with less than 8 arm entries were excluded from the alternation analysis. Data are mean ± SEM; **<i>p</i> < 0.01 (Student’s <i>t</i>-test).</p

Novel Object Recognition.

<p><b>A)</b> Both control (Ctrl) and scopolamine-treated (SCP) mice showed no preference for the novel object over the familiar object (n = 8-9/group), but control mice showed a trend to interact more with the novel object (<i>p</i> = 0.466). <b>B)</b> Tg2576 mice showed a trend to interact less with the novel object (<i>p</i> = 0.257; n = 18-19/group). Mice with less than 7 sec of object interaction in either trial were excluded from the analysis. Data are mean ± SEM; Student’s <i>t</i>-test was used to calculate <i>p</i> values.</p

Radial Arm Water Maze.

<p><b>A)</b> Scopolamine-treated mice (SCP) made more errors at learning (trials 1–4) and remembering (trial 5) the hidden platform location than control mice (Ctrl) did (n = 9-10/group). <b>B)</b> Long-term (24 h) memory of mice was evaluated by averaging the entries into the previous target arm during the first trial of days 2–12. SCP mice entered into the last target arm significantly less than control mice. <b>C)</b> 129S6/Tg2576 mice made significantly more errors during the learning phase (trials 1–4) of the radial arm water maze test compared to WT control mice. <b>D)</b> The number of entries into the last target arm were not different between 129S6/Tg2576 mice and WT control mice (n = 19-20/group). Data are mean ± SEM; 6A and 6C: *<i>p</i> < 0.05; **<i>p</i> < 0.01; ***<i>p</i> < 0.001 (repeated measures ANOVA); 6B and 6D: ***<i>p</i> < 0.001 (repeated measures ANOVA was used for Fig 6A and 6C; Student’s t-test was used to calculated p values for Fig 6B and 6D).</p

Morris Water Maze: Retention of Spatial Reference Memory.

<p><b>A)</b> Compared to control mice (Ctrl), scopolamine-treated mice (SCP) spent less time in the target quadrant during the retention trial on days 14 and 17 and <b>B)</b> in the 40 cm annulus around the platform center on day 14 (n = 10/group). <b>C)</b> The group occupancy plot from the last retention trial (day 17) shows a similar search pattern for both groups. Red and yellow regions represent areas of high occupancy; green and blue represent areas of low occupancy. <b>D)</b> On days 14 and 17 of the retention trials, 129S6/Tg2576 mice spent less time in the target quadrant compared to WT control mice (statistically not significant). <b>E)</b> 129S6/Tg2576 mice spent significantly less time in the 40 cm platform annulus compared to age-matched WT control mice (n = 18-19/group) on days 14 and 17 of the retention trials. <b>F)</b> Occupancy plots obtained from WT and transgenic mice in the last retention trial (day 17) exhibited a similar search pattern for both groups. Mice that showed repeated episodes of extensive floating (> 10 s/trial; >25% of trials) were excluded from analysis for the entire experiment. Data are mean ± SEM; *<i>p</i> < 0.05; **<i>p</i> < 0.01 (Student’s <i>t</i>-test).</p