Perinatal choline supplementation improves cognitive functioning and emotion regulation in the Ts65Dn mouse model of Down syndrome

Abstract

In addition to mental retardation, individuals with Down syndrome (DS) also develop the neuropathological changes typical of Alzheimer's disease (AD) and the majority of these individuals exhibit dementia. The Ts65Dn mouse model of DS exhibits key features of these disorders, including early degeneration of cholinergic basal forebrain (CBF) neurons and impairments in functions dependent on the two CBF projection systems; namely, attention and explicit memory. Herein, we demonstrate that supplementing the maternal diet with excess choline during pregnancy and lactation dramatically improved attentional function of the adult trisomic offspring. Specifically, the adult offspring of choline-supplemented Ts65Dn dams performed significantly better than unsupplemented Ts65Dn mice on a series of 5 visual attention tasks, and in fact, on some tasks did not differ from the normosomic (2N) controls. A second area of dysfunction in the trisomic animals, heightened reactivity to committing an error, was partially normalized by the early choline supplementation. The 2N littermates also benefited from increased maternal choline intake on 1 attention task. These findings collectively suggest that perinatal choline supplementation might significantly lessen cognitive dysfunction in DS and reduce cognitive decline in related neurodegenerative disorders such as AD.

Figure 1. Mean (±SE) percentage of correct responses in Attention task 1 (no pre-cue delay, 2 s cue duration), collapsed across all sessions

The unsupplemented Ts65Dn mice performed significantly worse than both groups of wild-type mice (2N). The performance of the trisomic mice supplemented with choline early in life did not differ from the 2N mice but also did not differ significantly from their unsupplemented counterparts. * p < 0.05, relative to the unsupplemented Ts65Dn mice.

Figure 2. Attention task 2 (no pre-cue delay, 1s cue duration)

(A) Mean (± SE) percentage of correct responses, collapsed across all sessions. The Ts65Dn mice performed significantly more poorly than both groups of 2N mice. In contrast, the choline-supplemented Ts65Dn mice did not differ significantly from either group of 2N mice, and performed significantly better than their unsupplemented counterparts. (B) Mean (± SE) percentage of a long (> 5 s) Alcove Latency, collapsed across all sessions: There were no treatment differences for trials that followed a correct response whereas for the trials that followed an error, the incidence of long ALs was significantly greater for the unsupplemented Ts65Dn mice than for either group of 2N mice, as well as their choline-supplemented counterparts. The supplemented trisomic mice did not differ from either group of 2N mice. *, p < 0.05, relative to the unsupplemented Ts65Dn mice

Figure 3. Attention task 3 (Variable pre-cue delay: 0, 2, 4 s; constant 1 s cue duration)

(A) Mean (± SE) percentage of correct responses (averaged across the 20 sessions). The unsupplemented Ts65Dn mice performed significantly worse than both groups of 2N mice. The choline-supplemented Ts65Dn mice did not differ significantly from either group of 2N mice, and tended to perform better than their unsupplemented counterparts. (B) Mean (± SE) percentage of correct responses, as a function of the four session-blocks (5 sessions/block). Although the four groups did not differ in the first session block, differences emerged during the last three session blocks. During these latter 15 sessions, the unsupplemented Ts65Dn mice performed significantly more poorly than both groups of 2N mice. In contrast, the choline-supplemented Ts65Dn mice did not differ from the unsupplemented 2N mice for any session-block, and performed better than their unsupplemented counterparts mice for session blocks 2 and 3. The choline-supplemented 2N mice performed significantly better than their unsupplemented counterparts during session-block 2. (C) Mean (± SE) percentage of a long (> 5s) Alcove Latency: Whereas no treatment differences were seen for trials that followed a correct response, the incidence of long ALs following an error was significantly greater for the unsupplemented trisomic mice than for ether group of 2N mice as well as the supplemented trisomic mice. *, p < 0.05

Figure 4. Attention task 4 (Variable pre-cue delay: 0, 2, 4 s; variable cue duration: 0.8, 1.0, or 1.4 s)

(A) Mean (± SE) percentage of correct responses (averaged across all other conditions): The unsupplemented Ts65Dn mice performed significantly worse than the two groups of 2N mice. The Ts65Dn mice supplemented with choline early in life performed significantly better than the unsupplemented Ts65Dn mice and did not differ from the 2N mice. (B) Mean (± SE) percentage of correct responses as a function of the pre-cue delay: The unsupplemented Ts65Dn mice performed significantly worse than the unsupplemented 2N controls at all delays. In contrast, the choline-supplemented Ts65Dn mice did not differ significantly from either group of 2N mice for trials with either a 0s or 4s pre-cue delay, while still not differing from the supplemented 2N mice. In addition, the supplemented trisomic mice performed significantly better than their unsupplemented counterparts for trials with a 0 s or 4s pre-cue delay. (C) Mean (± SE) percentage of trials with a long Alcove Latency (> 5s), as a function of the outcome of the previous trial (correct or incorrect): No group differences were seen for trials that followed a correct response. However, for trials that followed an error, the incidence of trials with a long AL was significantly greater for the unsupplemented trisomic mice than for the two groups of 2N mice and the supplemented trisomic mice. *, p < 0.05, compared with the unsupplemented Ts65Dn mice

Figure 5. Reward Omission Task (Variable pre-cue delay: 0, 2, 4 s; constant 1 s cue duration; no reward on 20% of the correct responses)

(A) Mean (± SE) percentage of correct responses, as a function of the outcome of the previous trial: The unsupplemented trisomic mice performed more poorly than both groups of 2N mice regardless of prior trial outcome. The perinatal choline supplementation was effective: the supplemented trisomic mice performed significantly better than their unsupplemented counterparts, regardless of prior trial outcome. The Ts65Dn mice supplemented with choline did not differ from the 2N mice for trials following an error or RO, whereas they performed significantly less well than the unsupplemented 2N mice for trials following a correct response. They did not differ, however, from the supplemented 2N group regardless of prior trial outcome. (B) Mean (± SE) percentage of correct responses as a function of the pre-cue delay: The impairment of the unsupplemented trisomic mice relative to the 2N controls was most pronounced on trials with a 0 s delay prior to cue presentation. The perinatal choline supplementation was very effective in alleviating this attentional dysfunction of the trisomic mice, as they did not differ from either group of 2N at any pre-cue delay, and they were superior to the unsupplemented trisomic mice at the 0 s and 2 s delays. (C) Mean (± SE) percentage of a long Alcove Latency (> 5s)as a function of the outcome of the previous trial [correct, incorrect, or reward omission (RO)): The percentage of trials with an AL was significantly greater for the unsupplemented trisomic mice than for either group of 2N mice for trials following an error or a RO. For trials following an error or RO, the incidence of long ALs of the supplemented trisomic mice did not differ from that of controls, and was significantly lower than that of their unsupplemented counterparts. *, p < 0.05

Figure 6. Videotape results

(A) Difference between the average number of jumps/trial following an error and following a correct response (in Attention Task 3). Each dot represents one mouse. The unsupplemented trisomic mice exhibited pronounced jumping specifically after an error, contrary to the 2N mice who jumped relatively little after either an error or a correct response. The perinatal choline supplementation was not effective in normalizing this heightened reactivity to committing an error (p = 0.60; unsupplemented vs. supplemented trisomic). The perinatal choline supplementation did not affect this measure for the 2N mice (p =0 .50). (B) Activity level (square crossings/trial) in Attention Task 3, as a function of the outcome of the previous trial: The four groups did not differ significantly in square crossings per trial following a correct response (treatment group, p = 0.72). In contrast, the increase in activity level following an error (relative to after a correct response) was significantly greater for the trisomic mice than for the 2N controls (p = 0.003); this effect was not modified by perinatal choline supplementation (p = 0.21; unsupplemented vs supplemented trisomic mice). Perinatal choline supplementation did not affect activity level of the 2N mice for any condition. (C) Activity level (square crossings/trial) on RO Task, as a function of previous trial outcome: The increase in activity level seen following an error or a RO, relative to a correct response was significantly greater for the unsupplemented trisomic mice than for the 2N controls (respectively, p = 0.02 and 0.007). In contrast, the trisomic mice supplemented with choline early in life did not differ from the 2N controls for the difference score relating post-error activity to that seen after a correct response (p < 0.36), or post-RO activity relative to after a correct response (p > 0.33). Correspondingly, the post-error increase in activity (relative to after a correct response) was significantly greater for the unsupplemented trisomic mice than for their supplemented counterparts (p < 0.03).