Ultrasound super-resolution imaging provides a noninvasive assessment of renal microvasculature changes during mouse acute kidney injury.

Acute kidney injury (AKI) is a risk factor for the development of chronic kidney disease (CKD). One mechanism for this phenomenon is renal microvascular rarefaction and subsequent chronic impairment in perfusion. However, diagnostic tools to monitor the renal microvasculature in a noninvasive and quantitative manner are still lacking. Ultrasound super-resolution imaging is an emerging technology that can identify microvessels with unprecedented resolution. Here, we applied this imaging technique to identify microvessels in the unilateral ischemia-reperfusion injury mouse model of AKI-to-CKD progression in vivo. Kidneys from 21 and 42 day post- ischemia-reperfusion injury, the contralateral uninjured kidneys, and kidneys from sham-operated mice were examined by ultrasound super-resolution and histology. Renal microvessels were successfully identified by this imaging modality with a resolution down to 32 µm. Renal fibrosis was observed in all kidneys with ischemia-reperfusion injury and was associated with a significant reduction in kidney size, cortical thickness, relative blood volume, and microvascular density as assessed by this imaging. Tortuosity of the cortical microvasculature was also significantly increased at 42 days compared to sham. These vessel density measurements correlated significantly with CD31 immunohistochemistry (R2=0.77). Thus, ultrasound super-resolution imaging provides unprecedented resolution and is capable of noninvasive quantification of renal vasculature changes associated with AKI-to-CKD progression in mice. Hence, this technique could be a promising diagnostic tool for monitoring progressive kidney disease.

Recording sympathetic nerve activity chronically in rats: surgery techniques, assessment of nerve activity, and quantification.

The sympathetic nervous system plays a pivotal role in homeostasis through its direct innervation and functional impact on a variety of end organs. In rats, a number of methods are available to assess sympathetic nervous system function. Traditionally, direct recording of sympathetic nerve activity (SNA) has been restricted to acute, anesthetized preparations or conscious animals within a few days after electrode implantation. However, these approaches provide short-term data in studies designed to investigate changes in SNA during chronic disease states. Over the last several years, chronic SNA recording has been pioneered in rabbits and more recently in rats. The purpose of this article is to provide insights and a "how to" guide for chronic SNA recordings in rats based on experiences from two independent laboratories. We will present common methodologies used to chronically record SNA, characteristics and methods to distinguish sympathetic bursts versus electrical artifacts (and provide corresponding audio clips when available), and provide suggestions for analysis and presentation of data. In many instances, these same guidelines are applicable to acute SNA recordings. Using the surgical approaches described herein, both laboratories have been able to chronically record SNA in >50% of rats for a duration >3 wk. The ability to record SNA over the time course of several weeks will, undoubtedly, greatly impact the field of autonomic and cardiovascular physiology.