A novel approach to induction and rehabilitation of deficits in forelimb function in a rat model of ischemic stroke

Abstract

Aim: Constraint-induced movement therapy (CIMt), which forces use of the impaired arm following unilateral stroke, promotes functional recovery in the clinic but animal models of CIMT have yielded mixed results. The aim of this study is to develop a refined endothelin-1 (ET-1) model of focal ischemic injury in rats that resulted in reproducible, well-defined lesions and reliable upper extremity impairments, and to determine if an appetitively motivated form of rehabilitation (voluntary forced use movement therapy; FuMt) would accelerate post-ischemic motor recovery. Methods: Male Sprague Dawley rats (3 months old) were given multiple intracerebral microinjections of et-1 into the sensorimotor cortex and dorsolateral striatum. Sham-operated rats received the same surgical procedure up to but not including the drill holes on the skull. Functional deficits were assessed using two tests of forelimb placing, a forelimb postural reflex test, a forelimb asymmetry test, and a horizontal ladder test. In a separate experiment et-1 stroke rats were subjected to daily rehabilitation with FuMt or with a control therapy beginning on post-surgery d 5. Performance and post-mortem analysis of lesion volume and regional BDnF expression were measured. Results: Following microinjections of ET-1 animals exhibited significant deficits in contralateral forelimb function on a variety of tests compared with the sham group. These deficits persisted for up to 20 d with no mortality and were associated with consistent lesion volumes. FUMT therapy resulted in a modest but significantly accelerated recovery in the forelimb function as compared with the control therapy, but did not affect lesion size or BDnF expression in the ipsilesional hemisphere. Conclusion: We conclude that refined ET-1 microinjection protocols and forcing use of the impaired forelimb in an appetitively motivated paradigm may prove useful in developing strategies to study post-ischemic rehabilitation and neuroplasticity.

Ischemic lesions localized to the medial prefrontal cortex produce selective deficits in measures of executive function in rats

“…The surgical protocols for producing an ET-1 stroke lesion were as reported previously , with the exception of injection coordinates and volumes [18,19]. Rats (ET-1 n = 19, sham n = 18) were anaesthetised by being placed into an induction box prefilled with 3.5% isoflurane (PPC, Richmond Hill, Canada) in oxygen for 8 min, and anaesthesia was maintained throughout the surgery with a 2-3% isoflurane mixture.…”

“…Other commonly used models such as 2-and 4-vessel occlusion and hypoxia-ischemia are similarly compromised in that the lesions are typically localized to specific regions, notably the CA1 region of the hippocampus, and photothrombotic models are largely restricted to surface vasculature [16,17]. Recently, we have described how small well-localized ischemic lesions produced by surgical microinjection of endothelin-1 (ET-1) have been used successfully to produce discreet functional deficits in rats [18][19][20]. Endothelin-1 is a potent vasoconstrictor capable of temporarily occluding blood vessels via an action on endothelin receptors [21].…”

Which Aspects of Stroke Do Animal Models Capture? A Multitracer Micro-PET Study of Focal Ischemia with Endothelin-1

“…In a comparative study of various ET-1 applications, the intracerebral injection into the forelimb motor region of the cortex and especially the combination of intracortical and intrastriatal injections produced more consistent injuries resulting in more consistent behavioral deficits than applications near the MCA or on the cortex. In these cases, gradual reperfusion occurs over several hours [15] , making this model especially suited for studies of recovery and rehabilitation after focal ischemia [16] .…”

Animal models of post-ischemic forced use rehabilitation: methods, considerations, and limitations

“…Endothelin-1 (ET-1) is a potent vasoconstrictor that can be used to induce ischemia directly when applied topically [54,55] or injected intracerebrally [56,57] or indirectly if injected proximal to the MCA [58]. ET-1 affects arteries in the immediate area of injection, and causes a rapid and temporary reduction in blood flow followed by reperfusion over several hours [33], making it more representative of the clinical condition compared to the immediate reduction and reperfusion associated with MCAo [59].…”