Hippocampal ultrastructural changes and apoptotic cell death in rats following endurance training and acute exhaustive exercise

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Abstract

BACKGROUND:

Exhaustive exercise can lead to apoptosis of skeletal muscle cells and myocardial cells as a result of pathological changes in the corresponding cellular ultrastructure. It is hypothesized that such changes could also occur in neurons.

OBJECTIVE:

To observe brain cell apoptosis and ultrastructural changes in hippocampal neurons in rats following endurance training and acute exhaustive exercise.

DESIGN, TIME AND SETTING:

A randomized, controlled, morphological analysis was performed at the Medical Laboratory Center of Zhengzhou University between July and November 2007.

MATERIALS:

Forty male, 8-week-old, Sprague Dawley rats were included in this study.

METHODS:

Endurance training consisted of treadmill running once a day, 6 days a week, for 4 weeks. For acute exhaustive exercise, graded treadmill running was conducted. Rats were exposed to exercise at an increasing speed (10 m/min, increasing to 20 and 36 m/min for moderate- and high-intensity exhaustive exercise, respectively, and then was continued until exhaustion). A total of 40 rats were evenly distributed into the following 4 groups: Group A-rats were not exercised; Group B-rats were not trained but sacrificed 24 hours after acute exhaustive treadmill running exercise; Group C-rats were subjected to endurance training and sacrificed immediately after acute exhaustive treadmill running exercise; Group D-rats were subjected to endurance training and sacrificed 24 hours after acute exhaustive treadmill running exercise.

MAIN OUTCOME MEASURES:

Apoptotic cell death was detected by the TUNEL method and hippocampal neuronal ultrastructural change was observed through using transmission electron microscopy.

RESULTS:

All 40 rats were included in the final analysis. Subsequent to exhaustive exercise, rat cerebral cortex and hippocampal neurons appeared contracted and degenerated. In addition, high amount of lipofuscin was visible in the hippocampal region. Necrotic neurons encased by glial cells appeared in the cerebral cortex and hippocampus. Glial cells exhibited different degrees of swelling. Subsequent to exhaustive exercise, brain cell apoptosis rate significantly increased, and reached over 30% in some regions, compared with group A (P < 0.05). No significant difference in apoptosis rate existed between groups B, C, and D (P < 0.05).

CONCLUSION:

Endurance training and acute exhaustive exercise cause, to some degree, injuries to glial cells, resulting in apoptosis of numerous brain cells. Subsequent to exhaustive exercise, high amounts of lipofuscin appear in the hippocampus, indicating that exhaustive exercise possibly contributes to neural cell aging or dysmetabolism.

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