Laser speckle contrast imaging reveals large-scale synchronization of cortical autoregulation dynamics influenced by nitric oxide

Abstract

Mitrou N, Scully CG, Braam B, Chon KH, Cupples WA. Laser speckle contrast imaging reveals large-scale synchronization of cortical autoregulation dynamics influenced by nitric oxide. Am J Physiol Renal Physiol 308: F661-F670, 2015. First published January 13, 2015; doi:10.1152/ajprenal.00022.2014.-Synchronization of tubuloglomerular feedback (TGF) dynamics in nephrons that share a cortical radial artery is well known. It is less clear whether synchronization extends beyond a single cortical radial artery or whether it extends to the myogenic response (MR). We used LSCI to examine cortical perfusion dynamics in isoflurane-anesthetized, male LongEvans rats. Inhibition of nitric oxide synthases by N -nitro-L-arginine methyl ester (L-NAME) was used to alter perfusion dynamics. Phase coherence (PC) was determined between all possible pixel pairs in either the MR or TGF band (0.09 -0.3 and 0.015-0.06 Hz, respectively). The field of view (Ϸ4 ϫ 5 mm) was segmented into synchronized clusters based on mutual PC. During the control period, the field of view was often contained within one cluster for both MR and TGF. PC was moderate for TGF and modest for MR, although significant in both. In both MR and TGF, PC exhibited little spatial variation. After L-NAME, the number of clusters increased in both MR and TGF. MR clusters became more strongly synchronized while TGF clusters showed small highly coupled, high-PC regions that were coupled with low PC to the remainder of the cluster. Graph theory analysis probed modularity of synchronization. It confirmed weak synchronization of MR during control that probably was not physiologically relevant. It confirmed extensive and long-distance synchronization of TGF during control and showed increased modularity, albeit with larger modules seen in MR than in TGF after L-NAME. The results show widespread synchronization of MR and TGF that is differentially affected by nitric oxide.

Transient impairment of dynamic renal autoregulation in early diabetes mellitus in rats

“…Previously, we, and others, reported that autoregulation dynamics are synchronized on the surface of the kidney (9,23,39,45). Simulation studies suggest that networks of arterioles would provide smoothing of blood flow in space and time (18,58), which suggests synchronization may contribute to the efficacy of autoregulation.…”

“…Previously, we, and others, reported large-scale synchronization of renal autoregulation dynamics in renal surface perfusion (9,23,39,45) and suggested that it is mediated by communication among vascular branches via gap junctions (9,39). Furthermore, previous results suggest synchronized autoregulation dynamics contribute to the effectiveness of autoregulation (18,58).…”

“…Simulation studies suggest that networks of arterioles would provide smoothing of blood flow in space and time (18,58), which suggests synchronization may contribute to the efficacy of autoregulation. It is likely that synchronization is mediated by electrotonic conduction of electrical signals via endothelial gap junctions (35,39,53). In DM, the distribution of renal arteriolar gap junctions is abnormal, with an accentuated difference in the preglomerular and postglomerular arte-rioles (71).…”

“…Laser speckle contrast imaging. During each RBF recording period, renal cortical perfusion was monitored using laser speckle contrast imaging (LSCI), as described previously (39,45,46). Briefly, the LSCI camera (FLPI, Moor Instruments, Axminster, UK) was positioned Ϸ18 cm above the surface of the kidney.…”

Detecting Interactions between the Renal Autoregulation Mechanisms in Time and Space

“…Data were used from a previously published report that probed a different question [25]. All experiments were approved by the Animal Care Committee of Simon Fraser University, in accordance with the guidelines of the Canadian Council of Animal Care.…”