Tracing of Noradrenergic Neuronal Circuitry and Functional Recovery after Permanent Focal Cerebral Ischemia in Mice

Abstract

Background: Cardiovascular autonomic imbalances after stroke may be responsible for dysfunction of noradrenergic (NA) system in brain. However, exact locations or extent of NA-circuitry damage after stroke and its functional implications are remaining to be elucidated. Methods: Adult male C57BL/6J mice were subjected to permanent focal cerebral ischemia (pFCI) by intraluminal suture occlusion of middle cerebral artery. Recombinant adenoviral vector introducing wheat germ agglutinin (WGA)-cDNA was injected into locus coelureus (LC) using stereotaxic method. Behavioral and physiological tests were executed and immunohistochemistry for BrdU, tyrosine hydroxylase (TH), and WGA were performed at the same time. Results: Colocalization of GFP, TH, and WGA and restrictive expression of WGAmRNA in LC showed that WGA protein was endogenously synthesized in NA-cells of LC. Within 6 months after pFCI onset, the extensively damaged NA-circuitry was observed in thalamic nuclei, lateral hypothalamic area, hippocampus, and amygdaloid nuclei in ipsilateral side. The damaged NA-circuits were partly reorganized over time in the area of previous lesion with the gradual recovery of autonomic dysfunction and neurobehavioral deficits. Many migrated BrdU-immunopositive cells were detected in the lesioned thalamus and hypothalamus. Conclusion: In this study, we successfully visualized NA-circuitries in mice by using transsynaptic tracing with PRSWGA adenovirus. It was also confirmed the close relationships between the functional recovery and the reorganization of damaged NA-circuits. Moreover, this study demonstrated that the process of reorganization may involve axonal sprouting of intact NA-projections on newly proliferated and migrated neurons to the infarct area.