Rostrocaudal changes in the protein expression of NMDA receptor subunits within the rostral ventrolateral medulla of sedentary and active rats (875.12)

Abstract

Recently we found enhanced sympathoexcitatory responses to glutamate in the RVLM following sedentary conditions. We have also reported increased dendritic branching in more rostral compared to caudal regions within the RVLM of sedentary rats. The mechanisms by which physical inactivity increases glutamatergic neurotransmission and produces structural changes in more rostral regions of the RVLM is unclear. The NMDA subtype of glutamate receptor has been associated with neuroplasticity in other brain regions of sedentary versus active rats. We hypothesized that sedentary conditions would alter protein expression of NMDA receptor subunits in a rostrocaudal manner within the RVLM. To test this hypothesis, male Sprague Dawley rats were allowed to remain sedentary (n=4) or exercise voluntarily via running wheels (n=4) for 14 weeks. Animals were then sacrificed and the RVLM cryosectioned (80 μm) and micropunched bilaterally. Sections were stained using cresyl violet to identify the rostrocaudal boundary of the RVLM. Based on their location relative to the caudal pole of the facial nucleus (FN), punches were pooled into four regions: caudal ‐480 µm (FN‐480), caudal ‐240 µm (FN‐240), rostral +240 µm (FN+240) and rostral +480 µm (FN+480). Preliminary western blot results showed that within the RVLM of sedentary rats, NR1 protein expression normalized to actin was significantly higher at FN‐480 (2.6 ± 0.2) compared to FN+240 (1.6 ± 0.2, p < 0.005). Interestingly, within the caudal regions of the active rats, NR1 protein expression was significantly lower at FN‐480 (1.4 ± 0.2) compared to FN‐240 (2.3 ± 0.2, p < 0.005). Changes were not observed for NR2A protein expression within both groups. Rostrocaudal differences observed in sedentary rats were not consistent with our structural findings. However, it is important to further investigate these novel findings, including examination of other receptor subunits which could relate to the structural neuroplasticity observed in sedentary rats.Grant Funding Source: R01HL096787