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Functional magnetic resonance imaging during hypotension in the developing animal

¹Department of Neurobiology and ⁴Brain Research Institute, University of California at Los Angeles, Los Angeles, California 90095-1763; ²Department of Anatomy and Histology, University of Sydney, Sydney, New South Wales 2006, Australia; and ³Department of Radiology, University of Arizona, Tucson, Arizona 85724

Submitted 18 March 2004 ; accepted in final form 20 June 2004

Hypotension in adult animals recruits brain sites extending from cerebellar cortex to the midbrain and forebrain, suggesting a range of motor and endocrine reactions to maintain perfusion. We hypothesized that comparable neural actions during development rely more extensively on localized medullary processes. We used functional MRI to assess neural responses during sodium nitroprusside challenges in 14 isoflurane-anesthetized kittens, aged 14–25 days, and seven adult cats. Baseline arterial pressure increased with age in kittens, and basal heart rates were higher. The magnitude of depressor responses increased with age, while baroreceptor reflex sensitivity initially increased over those of adults. In contrast to a decline in adult cats, functional MRI signal intensity increased significantly in dorsal and ventrolateral medullary regions and the midline raphe in the kittens during the hypotensive challenges. In addition, significant signal intensity differences emerged in cerebellar cortex and deep nuclei, dorsolateral pons, midbrain tectum, hippocampus, thalamus, and insular cortex. The altered neural responses in medullary baroreceptor reflex sites may have resulted from disinhibitory or facilitatory influences from cerebellar and more rostral structures as a result of inadequately developed myelination or other neural processes. A comparable immaturity of blood pressure control mechanisms in humans would have significant clinical implications.

cat; heart rate; respiration; blood pressure; baroreceptor reflex

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