Physical Activity and Cardiorespiratory Fitness Are Beneficial for White Matter in Low-Fit Older Adults

Agnieszka Zofia Burzynska, Laura Chaddock-Heyman, Michelle W. Voss, Chelsea N. Wong, Neha P. Gothe, Erin A. Olson, Anya Knecht, Andrew Lewis, Jim M. Monti, Gillian E. Cooke, Thomas R. Wojcicki, Jason Fanning, Hyondo David Chung, Elisabeth Awick, Edward McAuley, and Arthur F. Kramer

PLoS One. 2014; 9(9): e107413.

Our lab studies effects of sedentary vs physical activity on the brain and have shown an active lifestyle to be overall beneficial to cardiovascular health. I found this paper exciting because it looks at not only how an active lifestyle and good cardiovascular health can have positive effects on white matter later in life but also the neural correlates for these relationships. Using 88 healthy low-fit adults they examined the relationship between cardiorespiratoy fitness (CRF) with three different levels of physical activity (PA) and how it affected the levels of white matter (WM). Adults used for this study were between the ages of 60-79 years old, had no history of stroke or neurological illness, and had similar scores thresholds many other test. Participants PA was monitored for a week with a accelerometer worn on the hip and measurements collected placed them in one of the three levels of PA: sedentary behavior, light PA, and moderate to vigorous PA (MV-PA). T2 weighted MRI images were used to examine the integrity of WM and presence of white matter hyperintensities (WMH); lesions that appear in WM during old age that damage WM integrity. Age-related degeneration of WM micro-structures can be captured as decreased fractional anisotropy (FA) measured with diffusion tensor imaging (DTI). The study concluded that higher levels of MV-PA were linked to lower WMH volume, PA and CRF are related but not equivalent in their relationships with WM health in aging, and PA is associated with WM health in aging in an intensity- and region-specific manner. 

It’s interesting to look at the additional effects an active lifestyle can have on the body past the cardiovascular level. This paper shows it’s never too late to start doing any level of PA and that its has many of its benefits are still unknown to us. 

Zachery

Sympathetic activity and blood pressure are tightly coupled at 0.4 Hz in conscious rats

David R. Brown, Laura V. Brown, Abhijit Patwardham, and David C. Randall

Am J Physiol. 1994 Nov;267(5 Pt 2):R1378-84

This study looked at the interactions of sympathetic nerve activity (SNA), blood pressure (BP), and heart rate (HR) at the 0.4Hz frequency. As where the studies in our lab are looking at the changes of signal coherence of active and sedentary conditions is study look at the coherence in rats while they rested in a cloth sock, roamed freely in there home cage, and after anesthesia. The data was obtained in a similar method that our lab uses. Electrodes were attached to the renal sympathetic nerve to measure SNA, while catheters were placed in the left jugular and aorta to administer drugs. All the data for each rat was collected over a 9.56 min period. The data showed in conscious rats that SNA frequency peaked at 0.4Hz while the BP and HR were at lower frequency's. Although they did note that the BP did display a some higher 0.4Hz frequency not seen in HR. The coherence of the SNA - BP was at its highest at the 0.4Hz and declined as the frequency got lower. Anesthesia did not change the coherence of SNA - BP. This study shows that SNA and BP are coupled at the 0.4Hz frequency and suggest that maybe BP reflects SNA. I agree with these results because SNA results from output of rostral ventral lateral medulla (RVLM) unit neurons which are influenced by BP.

-Zachery

Role of ventrolateral medulla in generating the 10-Hz rhythm in sympathetic nerve discharge

Susan M. Barman and Gerard L. Gebber
Am J Physiol Regul Integr Comp Physiol 293: R223–R233, 2007.

The main focus of this study is how inputs of selective and non-selective excitatory amino acid receptor antagonists affect the ventrolateral medulla (VLM) in generating a 10-Hz rhythm in sympathetic nerve discharge. Using urethane-anesthetized, baroreceptor-denervated cats, they would record the changes of frequency in both the right inferior cardiac and  left inferior cardiac nerves. After unilateral injections of bicuculline (GABA-A receptor antagonists) were giving 1 and 5 mm rostral to the obex in the VLM, they found it would completely remove or reduce the 10-Hz rhythm on both sides of the body. Similarly they did unilateral injections kynurenate, (nonselective excitatory amino acid receptor antagonist) but this time did the injections both caudal or rostral in the VLM. Results found that the 10-Hz frequency was reduced but not eliminated. This study shows that GABAerginc transmission is in some way necessary for this 10-Hz rhythm to occur in sympathetic nerve discharge and that both rostral and caudal GABAerginc neurons play a role. - ZAK