Photochemically induced ischemic stroke in rats
- Antje Schmidt1Email author,
- Maike Hoppen1,
- Jan-Kolja Strecker1,
- Kai Diederich1,
- Wolf-Rüdiger Schäbitz2,
- Matthias Schilling†1 and
- Jens Minnerup†1
© Schmidt et al.; licensee BioMed Central Ltd. 2012
Received: 11 July 2012
Accepted: 17 July 2012
Published: 9 August 2012
Photothrombosis was introduced as a model of ischemic stroke by Watson et al. in 1985. In the present paper, we describe a protocol to induce photothrombotic infarcts in rats.
The photosensitive dye Bengal Rose is intravenously administered and a laser beam is stereotactically positioned onto the skull. Illumination through the intact skull leads to local activation of Bengal Rose, which results in free radical formation, disturbance of endothelial function and thrombus formation in illuminated small cortical vessels.
Photochemically induced infarcts cause long-term sensorimotor deficits, allow long-term survival and are particularly suitable to assess the effectiveness of neuroregenerative therapies in chronic stroke studies.
KeywordsPhotothrombosis Experimental stroke Animal model
Stroke is the second most frequent cause of death and a leading cause of disability and cognitive impairment in developed countries [1, 2]. Ischemic stroke, which accounts for approximately 80% of strokes, constitutes a huge socioeconomic burden. Experimental models of cerebral ischemia have been developed to mimic human stroke, gain a better understanding of underlying pathophysiological mechanisms and foster the development of new therapies. Common models of focal and multifocal cerebral ischemia include the intraluminal thread middle cerebral artery occlusion (MCAo) model, surgical MCAo models using ligation, clipping, electrocauterization etc., endothelin-1-induced MCAo, and embolization models using blood clots or other embolus material for vessel occlusion (for review see ).
In 1985, Watson et al. introduced photothrombosis as a technique to induce focal cerebral infarction in the cortical vasculature of rats . The key mechanism is a photochemical reaction triggered by systemic administration of Bengal Rose and focal illumination of the skull. Illumination leads to local activation of Bengal Rose, which results in free radical formation, disturbance of endothelial function and local thrombosis in small cortical vessels [3, 5]. As compared to other animal models of stroke, animal preparation is simple because it does not require mechanical manipulation of cerebral blood vessels or parenchyma. Lesion size and location can be modulated by altering the irradiating intensity, duration of light exposure, beam position, and dye concentration. Apart from that, photothrombotic infarcts do not impede long-term survival and are thus suitable for chronic stroke studies [4, 6].
Materials and methods
Adult male Wistar rats (250 g)
S-ketamine hydrochloride 25 mg/ml (CEVA, Düsseldorf, D)
2% Xylazine (CEVA, Düsseldorf, D)
Bengal Rose (Sigma Aldrich, Steinheim, D)
4% paraformaldehyde (Merck KGaA, Darmstadt, D)
Stereotactic device (TSE Systems, Bad Homburg, D)
Laser EAGLE 60 series (G Laser Technologies, Kleinostheim, D)
Polyethylene catheter 30 m, 0,58 mm inner diameter (Smith Medical, Grasbrunn, D)
Heating device TKM-0902 (FMI, Backnang, D)
Surgical instruments: Scissors, Forceps, Razor, Stitching Set (Bayha, Tuttlingen, D)
The rats are anesthetized with an intraperitoneal injection of ketamine hydrochloride (100 mg/kg body weight; Ketanest) and xylazine hydrochloride (8 mg/kg body weight). The depth of anesthesia is verified by foot pinches. If the rats are adequately anesthetized, there is no response of extremity (flexion or withdrawal).
The body temperature is monitored and maintained at 37°C by a thermostatically controlled heating pad.
The left femoral vein is exposed and cannulated with a polyethylene catheter for Bengal Rose infusion. The catheter is fixed with threads (Figure 1).
The rats are placed in a stereotactic frame (Figure 2).
The scalp is longitudinally incised (2.0-2.5 cm) and retracted to expose the skull. To avoid wound complications the skull exposure should be achieved with a single cut.
The periost is gently removed and coronal and sagittal sutures are identified (Figure 3).
A laser beam of 8 mm diameter (G Laser Technologies) and 560 nm wavelength is stereotactically positioned onto the skull 0.5 mm anterior to the bregma and 3.5 mm lateral from the midline (Figure 4).
The skull is illuminated for 20 minutes. During the first 2 minutes of illumination, Bengal Rose (0.133 mL/kg body weight, 10 mg/mL saline) is slowly injected through the previously inserted catheter.
Afterwards, the catheter is withdrawn and the skin is sutured.
After the surgical procedures, the rats are returned to their cages in a temperature-controlled room with 12-h light and dark cycles and food and water ad libitum.
Sham-operated animals receive the same treatment including Bengal Rose injection, but without illumination of the skull.
Step 1: 8 - 12 min.
Step 2: 1 min.
Step 3: 8 - 12 min.
Step 4: 2 - 4 min.
Step 5: 1 - 2 min.
Step 6: 1 - 2 min.
Step 7: 1 min.
Step 8: 20 min.
Animal preparation is simple and requires neither craniotomy nor mechanical manipulation of cerebral blood vessels or parenchyma .
Lesion size and location can be modulated by altering the irradiating intensity, duration of light exposure, beam position, and dye concentration .
Lesion size and location are highly reproducible [5, 6].
The procedure-associated mortality rate is low (< 10%).
Animals exhibit long-term sensorimotor deficits [9, 10].
Photothrombotic infarcts allow long-term survival .
Photothrombotic infarcts severely affect vessel walls and cause an early vasogenic edema atypical of human stroke .
The penumbra is missing in this model .
Due to the cortical location and the relatively small lesion size, sensorimotor deficits are minor in comparison to other stroke models .
Photothrombotic infarcts cause long-term sensorimotor deficits and allow long-term survival in chronic stroke studies. The infarct size is hardly responsive to neuroprotective therapies. However, the lack of responsiveness to neuroprotection in the acute phase allows a differentiation between neuroprotective and neuroregenerative effects, and, as a consequence, neuroregenerative therapies can be evaluated more precisely. Altogether, photochemically induced infarcts are particularly suitable to analyse the effectiveness of neuroregenerative therapies.
JM and MS shared senior authorship.
This study was supported from grants by the German Research Foundation (Deutsche Forschungsgesellschaft [DFG]; MI 1547/2-1).
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