Evidence of regional specializations in regenerated zebrafish retina.

Adult zebrafish are capable of functional retinal regeneration following damage. A goal of vision science is to stimulate or permit a similar process in mammals to treat human retinal disease and trauma. Ideally such a process would reconstitute the stereotyped, two-dimensional topographic patterns and regional specializations of specific cell types, functionally important for representation of the visual field. An example in humans is the cone-rich fovea, essential for high-acuity color vision. Stereotyped, global topographic patterns of specific retinal cell types are also found in zebrafish, particularly for cone types expressing the tandemly-replicated lws (long wavelength-sensitive) and rh2 (middle wavelength-sensitive) opsins. Here we examine whether regionally specialized patterns of LWS1 and LWS2 cones are restored in regenerated retinas in zebrafish. Adult transgenic zebrafish carrying fluorescent reporters for lws1 and lws2 were subjected to retinal lesions that destroy all neurons but spare glia, via intraocular injection of the neurotoxin ouabain. Regenerated and contralateral control retinas were mounted whole or sectioned, and imaged. Overall spatial patterns of lws1 vs. lws2 opsin-expressing cones in regenerated retinas were remarkably similar to those of control retinas, with LWS1 cones in ventral/peripheral regions, and LWS2 cones in dorsal/central regions. However, LWS2 cones occupied a smaller fraction of regenerated retina, and several cones co-expressed the lws1 and lws2 reporters in regenerated retinas. Local patterns of regenerated LWS1 cones showed modest reductions in regularity. These results suggest that some of the regional patterning information, or the source of such signals, for LWS cone subtypes may be retained by undamaged cell types (Müller glia or RPE) and re-deployed during regeneration.

Acute intrathecal administration of quipazine elicits air-stepping behavior.

Serotonin plays a pivotal role in the initiation and modulation of locomotor behavior in the intact animal, as well as following spinal cord injury. Quipazine, a serotonin 2 receptor agonist, has been used successfully to initiate and restore motor behavior in rodents. Although evidence suggests that the effects of quipazine are spinally mediated, it is unclear whether intrathecal (IT) quipazine administration alone is enough to activate locomotor-like activity or whether additional stimulation is needed. Thus, the current study examined the effects of IT administration of quipazine in postnatal day 1 rats in two separate experiments. In experiment 1, quipazine (0.1, 0.3, or 1.0 mg/kg) was dissolved in saline and administered via IT injection to the thoracolumbar cord. There was no significant effect of drug on hindlimb alternating stepping. In experiment 2, quipazine (0.3 or 1.0 mg/kg) was dissolved in a polysorbate 80-saline solution (Tween 80) and administered via IT injection. Polysorbate 80 was used to disrupt the blood-brain barrier to facilitate absorption of quipazine. The injection was followed by tail pinch 5 minutes post-injection. A significant increase in the percentage of hindlimb alternating steps was found in subjects treated with 0.3 mg/kg quipazine, suggesting that IT quipazine when combined with sensory stimulation to the spinal cord, facilitates locomotor-like behavior. These findings indicate that dissolving the drug in polysorbate 80 rather than saline may heighten the effects of IT quipazine. Collectively, this study provides clarification on the role of quipazine in evoking spinally-mediated locomotor behavior.