Spatial memory and hippocampal plasticity are differentially sensitive to the availability of choline in adulthood as a function of choline supply in utero

Abstract

Altered dietary choline availability early in life leads to persistent changes in spatial memory and hippocampal plasticity in adulthood. Developmental programming by early choline nutrition may determine the range of adult choline intake that is optimal for the types of neural plasticity involved in cognitive function. To test this, male Sprague-Dawley rats were exposed to a choline chloride deficient (DEF), sufficient (CON), or supplemented (SUP) diet during embryonic days 12-17 and then returned to a control diet (1.1 g choline chloride/kg). At 70 days of age, we found that DEF and SUP rats required fewer choices to locate 8 baited arms of a 12-arm radial maze than CON rats. When switched to a choline-deficient diet (0 g/kg), SUP rats showed impaired performance while CON and DEF rats were unaffected. In contrast, when switched to a choline-supplemented diet (5.0 g/kg), DEF rats' performance was significantly impaired while CON and SUP rats were less affected. These changes in performance were reversible when the rats were switched back to a control diet. In a second experiment, DEF, CON, and SUP rats were either maintained on a control diet, or the choline-supplemented diet. After 12 weeks, DEF rats were significantly impaired by choline supplementation on a matching-to-place water-maze task, which was also accompanied by a decrease in dentate cell proliferation in DEF rats only. IGF-1 levels were elevated by both prenatal and adult choline supplementation. Taken together, these findings suggest that the in utero availability of an essential nutrient, choline, causes differential behavioral and neuroplastic sensitivity to the adult choline supply.

Figure 1

Experimental timeline of procedures. Rats that were prenatally choline deficient (DEF), supplemented (SUP), or on a control (CON) diet on ED 12-17 were used as subjects either in Experiment 1 (panel A) and Experiment 2 (panel B). In Experiment 1, PD 70 rats from each prenatal treatment group were first trained on the radial arm maze (RAM) (Before) and then divided into two groups after 24 days of training. One group received a diet depleted of choline while the other group received a choline supplemented diet (5 g/kg choline chloride). After 10 days of the adult diet manipulation, rats were retrained for 14 days on the RAM (During). Rats were then put back on the choline control diet (1.1 g/kg) for 10 days and retrained on the RAM for 14 days (After). In Experiment 2, rats approximately 12 months of age from each prenatal treatment group were divided into two groups. One group was maintained on the standard control diet, while the other group was given a choline supplemented diet. After 12 weeks of the adult diet manipulations, rats were trained for 4 days on a water maze task, given 2 weeks of rest, administered 10 days of BrdU injections, and then sacrificed 24 hours after the last injection.

Figure 2

Mean ± SEM choices to criterion as a function of the choline treatment phase (Before, During, and After) for rats in the prenatal DEF, CON, and SUP treatment groups tested under the treatment conditions of adult choline deprivation (panel A) or adult choline supplementation (panel B). Eight is the minimum number of choices required to locate the 8 baited arms of the 12-arm maze. During the Before phase, CON and SUP rats had significantly fewer choices than DEF rats (p < 0.05). Adult choline deprivation slightly impaired prenatal SUP rats (p < .05) in the During phase, whereas adult choline supplementation in prenatal CON and DEF rats lead to a robust impairment of maze performance in the During phase with prenatal DEF rats showing the greatest impairment (ps < 0.05).

Figure 3

Mean ± SEM latencies to find the hidden platform after a 1-2 min. and 60 min. delay as a function of adult choline supply for prenatal DEF (panel A), CON (panel B), and SUP (panel C) rats. There was a significant effect of Delay for CON rats where rats exhibited longer latencies at the 60 min. delay, whereas SUP rats' latencies did not increase with the 60 min. delay. After adult choline supplementation, DEF rats had significantly longer latencies at the 1-2 min. delay while CON and SUP rats were not affected. * statistically significant at p < 0.05.

Figure 4

Mean (±SEM) numbers of BrdU-labeled cells detected in the dentate gyrus (panel A) and mean (± SEM) IGF-1 protein levels (expressed as percent of control levels) in the hippocampus hippocampal IGF-1 protein (panel B) of prenatal DEF, CON, and SUP rats that were either maintained on a standard control diet (open bars) or supplemented with choline for 16 weeks (hatched bars). A significant Prenatal Diet × Adult Diet interaction (p < .05) revealed that adult choline supplementation decreased the number of BrdU-labeled cells in DEF rats, increased the number of BrdU-labeled cells in CON rats, and had no effect on SUP rats (4A). Analysis of IGF-1 protein levels indicated a significant main effect of Prenatal Diet where SUP rats had the highest levels and prenatal DEF rats had the lowest levels of IGF-1 overall, and a significant main effect of Adult Diet where choline supplementation to adult rats in all prenatal diet groups increased IGF-1 expression (4B).