Incremental treatments with laser therapy augments good behavioral outcome in the rabbit small clot embolic stroke model

Transcranial near-infrared laser therapy (TLT) improves behavioral outcome in animal stroke models when applied as single treatment within the 24 h of the stroke onset. It is unknown if the multiple TLT treatments have an added beneficial effect. We aim to determine whether multiple irradiations with TLT would have further improvement in behavioral outcomes in the rabbit small clot embolic stroke model (RSCEM). Using the RSCEM, two and three TLT treatments (7.5-20 mW/cm(2)) were compared against single laser treatment alone (7.5-10.8 mW/cm(2)). Two sham irradiation groups were added for the control curves. The double treatment group received TLT at 3 and 5 h and the triple treatment group at 2, 3, and 4 h after embolization. Behavioral analysis was conducted 24 h after embolization using a dichotomized behavioral score. The determination of the effective clot amount (milligrams) that produces neurological deficits in 50 % of the rabbits (P (50)) was used to compare TLT treatments with the sham. The P (50) for double treatment was 5.47 +/- 0.90, with n = 39; the corresponding P (50) value for a single treatment was 3.87 +/- 0.73, with n = 38; and the corresponding control curve was 3.25 +/- 0.4, n = 32. The P (50) for triple treatment was 5.91 +/- 0.49, with n = 23; the corresponding P (50) value for a single treatment was 3.09 +/- 0.59, with n = 15, and the corresponding control curve was 1.71 +/- 0.26, with n = 17. The triple treatment had 91 % improvement when compared with the single treatment and 245 % improvement when compared with the sham. The present study suggests that the additional TLT treatments provide further behavioral improvement when given during the acute ischemic stroke phase.