Statins Promote Long-Term Recovery after Ischemic Stroke by Reconnecting Noradrenergic Neuronal Circuitry

Abstract

Inhibitors of HMG-CoA reductase (statins), widely used to lower cholesterol in coronary heart and vascular disease, are effective drugs in reducing the risk of stroke and improving its outcome in the long term. After ischemic stroke, cardiac autonomic dysfunction and psychological problems are common complications related to deficits in the noradrenergic (NA) system. This study investigated the effects of statins on the recovery of NA neuron circuitry and its function after transient focal cerebral ischemia (tFCI). Using the wheat germ agglutinin (WGA) transgene technique combined with the recombinant adenoviral vector system, NA-specific neuronal pathways were labeled, and were identified in the locus coeruleus (LC), where NA neurons originate. NA circuitry in the atorvastatin-treated group recovered faster than in the vehicle-treated group. The damaged NA circuitry was partly reorganized with the gradual recovery of autonomic dysfunction and neurobehavioral deficit. Newly proliferated cells might contribute to reorganizing NA neurons and lead anatomic and functional recovery of NA neurons. Statins may be implicated to play facilitating roles in the recovery of the NA neuron and its function.

Figure 1

Expression of WGA and GFP in LC, detecting PRS-WGA adenovirus. (a) Schematic diagram representing the structure of the transgene. (b) WGA immunoreactivity in the noninjured mouse brain. After 2 days of PRS-WGA adenovirus injection in the LC, LC-originated WGA protein was detected in NA neurons and other areas. Scale bars = 500 μm.

Figure 2

Immunoreactivity of WGA in the tFCI mouse brain. WGA immunoreactivity at 30, 180, and 240 days after tFCI in the vehicle- and atorvastatin-treated groups showed that NA circuitry in the atorvastatin-treated group recovered faster than in the vehicle-treated group at 180 days. aci: anterior commissure, intrabulbar part; hf DG: hippocampal fissure and dentate gyrus; LHb: lateral habenular nucleus; Op: optic nerve layer of the superior colliculus; InWh: intermediate gray layer of the superior colliculus. Scale bar = 500 μm.

Figure 3

Ischemic brain damage and convalescent processes shown by magnetic resonance imaging (MRI) after MCAO.

Figure 4

Neurogenesis after ischemic injury in normal and vehicle- or atorvastatin-treated group. (a) Cell proliferation in SVZ of the ischemic hemisphere is identified by BrdU (green) and NeuN (red) immunoreactivity. Many BrdU-positive cells are shown in the SVZ of both groups, with increased BrdU-positive cells in the striatum of the atorvastatin-treated group. (b) A quantitative graph representing the number of BrdU-positive cells, which is increased in the atorvastatin-treated group compared with the vehicle-treated group in the SVZ. (c) The migration of the proliferated cells is identified in the cortex and striatum each stained with BrdU (green) and NeuN (red). Scale bars = 20 μm.

Figure 5

Physiological recovery and behavioral tests relating to the NA circuitry. (a) Profiles of blood pressure in vehicle-treated or atorvastatin-treated mice after tFCI. (b) Effects of atorvastatin on behavioral parameters in the light/dark test. The light/dark test was performed at 30, 180, and 240 days after tFCI in mice. The effect on mouse behavior in the light/dark test was determined by p-test. Data presented are the mean value ± S.E.M, ^∗ p < 0.05 relative to the vehicle group. (c) Effects of atorvastatin on behavioral parameters in the aggression-intruder test in mice. Aggression-intruder test was performed at 30, 180, and 240 days after tFCI in mice. The effect on mouse behavior in the aggression-intruder test was determined by p-test. Data presented are mean value ± S.E.M, ^∗ p < 0.05 relative to the vehicle group.