Development of manganese-enhanced magnetic resonance imaging of the rostral ventrolateral medulla of conscious rats: Importance of normalization and comparison with other regions of interest.

Spinally projecting neurons in the rostral ventrolateral medulla (RVLM) are believed to contribute to pathophysiological alterations in sympathetic nerve activity and the development of cardiovascular disease. The ability to identify changes in the activity of RVLM neurons in conscious animals and humans, especially longitudinally, would represent a clinically important advancement in our understanding of the contribution of the RVLM to cardiovascular disease. To this end, we describe the initial development of manganese-enhanced magnetic resonance imaging (MEMRI) for the rat RVLM. Manganese (Mn2+ ) has been used to estimate in vivo neuronal activity in other brain regions because of both its paramagnetic properties and its entry into and accumulation in active neurons. In this initial study, our three goals were as follows: (1) to validate that Mn2+ enhancement occurs in functionally and anatomically localized images of the rat RVLM; (2) to quantify the dose and time course dependence of Mn2+ enhancement in the RVLM after one systemic injection in conscious rats (66 or 33 mg/kg, intraperitoneally); and (3) to compare Mn2+ enhancement in the RVLM with other regions to determine an appropriate method of normalization of T1 -weighted images. In our proof-of-concept and proof-of-principle studies, Mn2+ was identified by MRI in the rat RVLM after direct microinjection or via retrograde transport following spinal cord injections, respectively. Systemic injections in conscious rats produced significant Mn2+ enhancement at 24 h (p < 0.05). Injections of 66 mg/kg produced greater enhancement than 33 mg/kg in the RVLM and paraventricular nucleus of the hypothalamus (p < 0.05 for both), but only when normalized to baseline scans without Mn2+ injection. Consistent with findings from our previous functional and anatomical studies demonstrating subregional neuroplasticity, Mn2+ enhancement was higher in the rostral regions of the RVLM (p < 0.05). Together with important technical considerations, our studies support the development of MEMRI as a potential method to examine RVLM activity over time in conscious animal subjects.

Safety and outcomes in stroke mimics after intravenous tissue plasminogen activator administration: a single-center experience.

BACKGROUND: Patients with symptoms that impersonate a stroke but are later found to have an alternate diagnosis are termed stroke mimics. Stroke mimics treated with intravenous (IV) tissue plasminogen activator (t-PA) are exposed to hemorrhagic complications without benefit. The objective of this study is to describe the characteristics, safety, and outcomes of stroke mimic patients treated with t-PA within 4.5 hours. METHODS: All patients hospitalized after IV t-PA treatment at a tertiary care hospital and primary stroke center from January 2008 through December 2011 were reviewed. Stroke mimics were determined by review of clinical and imaging findings. Stroke mimics are described and compared with acute ischemic stroke patients for demographics, clinical characteristics, and bleeding complications. RESULTS: We identified 38 stroke mimic (12%) and 285 ischemic stroke (88%) t-PA-treated patients. Compared with ischemic stroke patients, mimic patients were younger, more often female, and reported a history of stroke more often. There were no differences in race, baseline stroke scale, or onset to treatment time. There were no intracerebral hemorrhages or deaths in the mimic patients but there were 2 systemic hemorrhages (5.2%). CONCLUSIONS: Treatment of mimic patients with IV t-PA appears to be safe in this cohort. Concern for intracerebral hemorrhage in mimic patients need not dissuade clinicians from administering t-PA when significant concern for ischemic etiology exists.