Neuroplastic adaptations to exercise: neuronal remodeling in cardiorespiratory and locomotor areas.

Nelson AJ, Juraska JM, Musch TI, Iwamoto GA.

J Appl Physiol. 2005 Dec;99(6):2312-22. PMID: 16123206

Objective:   Voluntary exercise in animal models has been shown to cause changes in neuronal morphology and function as well as changes in the function of peripheral organs such as decreases in heart rate and blood pressure.  In this paper, Golgi-Cox staining was used to examine changes in dendritic morphology in six areas related to cardiorespiratory-locomotor activity and in one area of the cerebral cortex in active and inactive animals.

Results:

·         In active animals, running increased from week 1 to week 8 before declining until week 14, where it remained level until week 18.  No differences were found between rats of the 85 (week 12) and 120 (week 18)day groups when examined for heart rate, dendritic branching, maximum oxygen consumption, fat-free mass.  Data from the two groups were pooled.
·         Active animals had significantly lower body weight, maximum oxygen uptake, and heart rate and significantly higher heart weight, heart weight to body mass ratio, and heart weight to fat-free mass ratio when compared to inactive animals.
·         Significantly more dendritic branching was seen within the first 120um from the soma in the periaqueductal gray, posterior hypothalamus, cuneiform nucleus, and nucleus tractus solitarious, but not in the rostral ventrolateral medlla (RVLM),  nucleus cuneatus, or the hindlimb area of the cortex when comparing these areas in active animals to inactive animals. The somata of neurons in the periaqueductal gray and cuneiform nucleus were significantly smaller in active animals than those in inactive animals.

Conclusions:

·          Exercise results in morphological changes in neurons of some cardiorespiratory-locomotor centers as demonstrated by reductions in dendritic branching and soma diameter.
·          The RVLM did not show changes, possibly because of its involvement in other functions such as sympathoexcitation and because its continuous activity in blood pressure maintenance results in a stable morphology.

Methods:   Active rats were allowed access to a running wheel and monitored for activity while inactive rats were not.  After 85 or 120 days, all animals were given two familiarization trials on a treadmill with increasing speed.  During testing trials, rats were monitored for oxygen uptake and carbon dioxide production.  Two days after, rats were monitored for resting heart rate, killed, and had their hearts and brains removed for examination.  Brains were immersed in Golgi-Cox impregnating solution for 2 weeks, frozen, cut in to 200um sections, and stained for examination of cell morphology.  Neurons in regions of interest were traced/drawn using camera lucida and examined for the number of dendritic branch points and their distances from the soma.

 -DH