Maternal Voluntary Exercise during Pregnancy Enhances the Spatial Learning Acquisition but not the Retention of Memory in Rat Pups via a TrkB-mediated Mechanism: The Role of Hippocampal BDNF Expression

Abstract

Objective(s): The effect of maternal voluntary exercise on hippocampal BDNF level in rat offspring was studied. In addition, the possible role of hippocampal BDNF receptors in maternal exercise induced enhancement of learning in the rat pups was investigated.

Materials and methods: Pregnant rats have been randomly assigned to sedentary control or voluntary exercise groups. Each of the exercising pregnant rats was given access to a cage that was equipped with a running wheel until the end of their pregnancy. On post natal day (PND) 36, two groups consisted of 7 male rat pups in each group from sedentary or exercised mothers were sacrificed and the hippocampus was dissected for BDNF proteins level determination. Also, bilateral injection of K252a to the hippocampus was used to block the hippocampal BDNF action on PND59 in the rat pups.

Results: Voluntary exercise during pregnancy significantly increased the level of BDNF protein in the hippocampus of the rat pups on PND36 compared to the control group (P=0.048). Inhibiting BDNF action abolished the exercise-induced improvement of learning acquisition in offspring in training trials (P=0.0001). No difference was observed in the platform location latency and the time spent in the target in the probe test between two groups. Conclusion : This study demonstrates that voluntary exercise during pregnancy via a TrkB-mediated mechanism enhances the spatial learning acquisition, however, not the retention of memory in the rat pups.

Keywords: BDNF; Hippocampus; K252a; Memory; Offspring; TrkB; Voluntary exercise.

Figure 1

Timelines of experiments

Figure 2

Tissue section in the coronal plane of the hippocampus showing the injection site of the microbeads  into the stratum lacunosum moleculare (SLM). For convenience, the hippocampal areas have been labeled

Figure 3

The effect of maternal voluntary exercise during pregnancy on BDNF protein level in the hippocampus. The BDNF levels are displayed as the percentages of the Sed-control levels (represented by the 100% line). The data are expressed as the mean ± SEM. Maternal voluntary exercise during pregnancy significantly increased the levels of BDNF in the hippocampus of the rat pups.*represent the significant difference between two groups (P=0.048

Figure 4

The effect of blocking BDNF action on pups learning as measured by the WM task. Exercise effectively improved learning, as evidenced by the fact that Exc/Cyt C group took significantly less time to find the platform on day 5 of training. The blockade of BDNF action during exercise abolished the exercise-induced enhancement of learning because the exercising rats that were given K252a injection took longer time to find the platform compared to the exercising controls (Exc/K252a and the Exc/Cyt C). *represents the significant difference between the Exc/Cyt C and Sed/Cyt C groups, and **represents the significant difference between the Exc/K252a and Exc/Cyt C groups

Figure 5

The effect of maternal voluntary exercise during pregnancy on pup’s memory retention as measured by the WM task using the probe trial. (A) The mean latency to reach the previous location of the platform. (B) The mean time spent in within a target zone or on an equivalent location in other quadrants, was expressed as a percentage of the total time spent in both of the zones. (A) The platform location latency and (B) percentage of the time spent in each equivalent location in other quadrants did not differ significantly between groups (P> 0.05)