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Assessment of Neuronal Activity in the Rostral Ventrolateral Medulla (RVLM) of Conscious Rats
Author(s) -
Huereca D,
Wong C,
Ingles J,
Ghoddoussi F,
Berkowitz B,
Holt A,
Mueller P
Publication year - 2015
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.29.1_supplement.652.8
Subject(s) - rostral ventrolateral medulla , magnetic resonance imaging , medicine , chemistry , medulla oblongata , premovement neuronal activity , endocrinology , anatomy , neuroscience , central nervous system , biology , radiology
Hyperactive bulbospinal neurons in the RVLM and elevated sympathetic activity likely contribute to cardiovascular disease (CVD). Measuring RVLM neuronal activity in conscious rats would represent a major advance in understanding brain‐related CVD. The present study addressed this by developing manganese (Mn 2+ ) enhanced magnetic resonance imaging (MEMRI). Mn 2+ , a paramagnetic ion, enters active neurons via Ca 2+ channels and with MRI, allows visualization and quantification of neuronal activity. The purposes of this study were to use MEMRI to: 1) identify regions in RVLM with tonically active neurons, 2) characterize a time course of Mn 2+ in RVLM after systemic injection, 3) evaluate the sensitivity of MEMRI by varying dose, and 4) compare Mn 2+ in rostral vs caudal RVLM. We hypothesized that Mn 2+ increases in RVLM 1 d after i.p. injection; is dose‐dependent; and exhibits rostrocaudal variation. Tract‐tracing and direct RVLM injection anatomically and functionally confirmed RVLM on MRI images. Ten male SD rats were administered MnCl 2 (33 or 66 mg/kg i.p., n=5 ea). MRI scans on a 7T ClinScan demonstrated increased Mn 2+ in RVLM at 1 d (p=0.002) and was higher after 66 mg/kg vs 33mg/kg (p=0.019). Mn 2+ returned to baseline by 15 and 22 days (33 and 66 mg/kg, respectively). After 66 mg/kg, increased Mn 2+ occurred in more rostral vs caudal regions of RVLM (p=0.004), consistent with our previous dendritic branching study. Results highlight MEMRI as a viable and powerful new method for examining neuronal activity in the RVLM of conscious rats and understanding mechanisms related to brain‐related CVD.