Physical Activity Correlates with Glutamate Receptor Gene Expression in Spinally-Projecting RVLM Neurons: A Laser Capture Microdissection Study

Madhan Subramanian, Avril G. Holt, Patrick J. Mueller

The economic cost of cardiovascular disease in the United States is enormous. Treatment for cardiovascular disease accounts for one sixth of all health care dollars spent in the United States, and in 2010 the economic cost of cardiovascular disease was almost $450 billion. Studies have shown that the rostral ventrolateral medulla is the main control of sympathetic outflow and that increased sympathetic outflow is correlated with cardiovascular diseases such as hypertension. The exact mechanisms of this process are yet to be elucidated.

The current study aimed to assess glutamate and GABA receptor gene expression in RVLM neurons in sedentary and active rats. Male Sprague-Dawley rats were used during this study. The active group was put in a cage with a running wheel and running parameters were tracked using a bike computer; the sedentary group was put in a cage with no running wheel. At the end of the running time rats were sacrificed to allow evaluation of gene expression in RVLM neurons. Prior to sacrificing the rats, neurons in the RVLM were retrogradely labeled using Flourogold so specific RVLM neurons could be identified. Laser capture microdissection was used to separate specific populations of spinally projecting RVLM neurons that have previously been shown to be involved in control of the cardiovascular system.

After laser capture microdissection was used Glutamate and GABA subunit gene expression was compared in the active and sedentary rats. The NR1 subunit of the NMDA receptor showed a trend towards upregulation in the active group of rats, while the other subunits of the NMDA receptor showed no change. None of the AMPA receptor subunits showed a change in gene expression in the active vs. sedentary groups. In evaluation of the GABA-A receptor subunits it was found that GABA-A2 subunit had a trend towards upregulation in the active group compared to the sedentary group. In further analysis it was found that two subunit’s gene expression, NR2C of the NMDA receptor, and GLUR3 of the AMPA receptor, both showed a positive correlation with the total running distance of the rats in the active group.

This study was successful in showing that laser capture microdissection is a good tool to use in identifying specific populations of cells and using them to assess gene expression using their RNA. The study did not find any significant changes in gene expression between Glutamate/GABA receptors in the sedentary vs. active rat groups. Further studies need to be conducted to evaluate the effect that physical activity has on receptor subunit gene expression.

- Ben R.