Sigma 1 Receptor (Sig1R), a pluripotent modulator of cell survival, is a promising target for treatment of retinal degenerative diseases. Previously, we reported that administration of the high-affinity, high-specificity Sig1R ligand (+)-pentazocine, ((+)-PTZ) beginning at post-natal day 14 (P14) and continuing every other day improves visual acuity and delays loss of photoreceptor cells (PRCs) in the Pde6βrd10/J (rd10) mouse model of retinitis pigmentosa. Whether administration of (+)-PTZ, at time points concomitant with (P18) or following (P21, P24) onset of PRC death, would prove neuroprotective was investigated in this study. Rd10 mice were administered (+)-PTZ intraperitoneally [0.5 mg/kg], starting at either P14, P18, P21 or P24. Injections continued every other day through P42. Visual acuity was assessed using the optokinetic tracking response (OKR). Rd10 mice treated with (+)-PTZ beginning at P14 retained visual acuity for the duration of the study (∼0.33 c/d at P21, ∼0.38 c/d at P28, ∼0.32 c/d at P35, ∼0.32 c/d at P42), whereas mice injected beginning at P18, P21, P24 showed a decline in acuity when tested at P35 and P42. Their acuity was only slightly better than rd10-non-treated mice. Electrophysiologic function was assessed using scotopic and photopic electroretinography (ERG) to assess rod and cone function, respectively. Photopic a- and b-wave amplitudes were significantly greater in rd10 mice treated with (+)-PTZ beginning at P14 compared with non-treated mice and those in the later-onset (+)-PTZ injection groups. Retinal architecture was visualized in living mice using spectral domain-optical coherence tomography (SD-OCT) allowing measurement of the total retinal thickness, the inner retina and the outer retina (the area most affected in rd10 mice). The outer retina measured ∼35 μm in rd10 mice treated with (+)-PTZ beginning at P14, which was significantly greater than mice in the later-onset (+)-PTZ injection groups (∼25 μm) and non-treated rd10 mice (∼25 μm). Following the visual function studies performed in the living mice, eyes were harvested at P42 for histologic analysis. While the inner retina was largely intact in all (+)-PTZ-injection groups, there was a marked reduction in the outer retina of non-treated rd10 mice (e.g. in the outer nuclear layer there were ∼10 PRCs/100 μm retinal length). The rd10 mice treated with (+)-PTZ beginning at P14 had ∼20 PRCs/100 μm retinal length, whereas the mice in groups beginning P18, P21 and P24 had ∼16 PRCs/100 μm retinal length. In conclusion, the data indicate that delaying (+)-PTZ injection past the onset of PRC death in rd10 mice – even by a few days – can negatively impact the long-term preservation of retinal function. Our findings suggest that optimizing the administration of Sig1R ligands is critical for retinal neuroprotection.

Sigma 1 受体 (Sig1R) 是一种细胞存活的多能调节剂，是治疗视网膜退行性疾病的一个有前景的靶点。此前，我们报道了从出生后第 14 天 (P14) 开始并每隔一天持续施用高亲和力、高特异性 Sig1R 配体 (+)-喷他佐辛 ((+)-PTZ) 可改善视力并延迟视力Pde6βrd10/J (rd10)色素性视网膜炎小鼠模型中感光细胞 (PRC) 的损失。本研究调查了在 PRC 死亡发生的同时 (P18) 或之后 (P21、P24) 的时间点施用 (+)-PTZ 是否具有神经保护作用。从 P14、P18、P21 或 P24 开始，对Rd10小鼠腹膜内施用 (+)-PTZ [0.5 mg/kg]。注射持续每隔一天进行直至 P42。使用视动跟踪反应（OKR）评估视力。从 P14 开始用 (+)-PTZ 治疗的Rd10小鼠在研究期间保留了视力（P21 时约 0.33 c/d，P28 时约 0.38 c/d，P35 时约 0.32 c/d，P35 时约 0.32 c/d） d 在 P42），而在 P18、P21、P24 开始注射的小鼠在 P35 和 P42 测试时显示出敏锐度下降。它们的敏锐度仅比未经rd10治疗的小鼠稍好一些。使用暗视和明视视网膜电图（ERG）分别评估视杆细胞和视锥细胞功能来评估电生理功能。与未治疗的小鼠和晚发 (+)-PTZ 注射组的小鼠相比，从 P14 开始接受 (+)-PTZ 治疗的rd10小鼠的明视 a 波振幅和 b 波振幅显着更大。 使用谱域光学相干断层扫描 (SD-OCT) 对活体小鼠的视网膜结构进行可视化，从而可以测量视网膜总厚度、内视网膜和外视网膜（ rd10小鼠中受影响最严重的区域）。从 P14 开始接受 (+)-PTZ 治疗的rd10小鼠的外层视网膜测量值约为 35 μm，显着大于晚发 (+)-PTZ 注射组的小鼠 (~25 μm) 和未治疗的rd10小鼠（〜25微米）。在对活体小鼠进行视觉功能研究后，在 P42 处摘取眼睛进行组织学分析。虽然所有 (+)-PTZ 注射组的内层视网膜基本完好，但未治疗的rd10小鼠的外层视网膜明显减少（例如，在外核层中，每 100 μm 视网膜长度有约 10 个 PRC） ）。从 P14 开始用 (+)-PTZ 治疗的rd10小鼠具有约 20 PRCs/100 μm 视网膜长度，而从 P18、P21 和 P24 开始的组中的小鼠具有约 16 PRCs/100 μm 视网膜长度。总之，数据表明，在rd10小鼠 PRC 死亡之后延迟注射 (+)-PTZ，即使是几天，也会对视网膜功能的长期保存产生负面影响。我们的研究结果表明，优化 Sig1R 配体的给药对于视网膜神经保护至关重要。