Reversibility of exercise-induced dendritic attenuation in brain cardiorespiratory and locomotor areas following exercise detraining.

Nelson AJ, Iwamoto GA.

J Appl Physiol. 2006 Oct;101(4):1243-51.PMID: 16794024

Objective:   The cardioprotective effects of voluntary exercise in animal models are known to decline in as little as two weeks after cessation of activity.  Having previously shown that training, or being physically active, results in morphological changes in the dendrites and somata of neurons found in cardiorespiratory-locomotor centers, the authors of this paper used Golgi-Cox staining to examine changes in dendritic morphology in areas related to cardiorespiratory-locomotor activity after “detraining,” or cessation of physical activity.

Results:

·         The 56-day trained rats ran significantly more per week than the 120-day trained rats, possibly due to differences in humidity between test groups.
·         Untrained and detrained animals at 120 days did not have significant differences in mass, body fat percentage, oxygen consumption, heart rate, heart weight, or heart weight to body ratio. 56-day trained animals had significantly higher oxygen consumption as well as significantly lower weight and heart weight to body weight ratio when compared to untrained animals.
·         Untrained and detrained rats at 120 days had no observable differences in dendritic fields or neuron size in the periaqueductal gray, posterior hypothalamic area, nucleus tractus solitarioius, or cuneiform nucleus.  Untrained animals had significantly more dendritic branching in the cuneiform nucleus and nucleus tractus solitarious than trained animals when measured at day 56.
·         The cuneiform nucleus of trained rats showed significantly smaller somata than trained rats at day 56 (consistent with previous findings) but the nucleus tractus solitarious did not.

Conclusions:

·         The morphological changes in neurons of the cardiorespiratory-locomotor centers effected by 56 days of voluntary activity are not present in rats that experience 70 days of activity followed by 50 days of inactivity.
·         The systemic cardioprotective effects of activity that decline following periods of inactivity are reflected in changes to neuronal morphology in cardiorespiratory-locomotor centers of the brain.

Methods:   Rats were divided in to three groups.  “Trained” animals were allowed free access to run on a wheel until they were killed after 56 days.  “Detrained” animals were allowed to run from days 1 to 70, but not after, and then killed at day 120. “Untrained” rats were denied access to a wheel entirely and killed at either day 56 or 120.  Animals were given two familiarization trials on a treadmill with increasing speed 4-6 days before a testing trial, rats were placed on a treadmill and monitored for maximum oxygen uptake and carbon dioxide production.  One week after the oxygen consumption test, 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