ON-retinal bipolar cell survival in RCS rats.
OBJECTIVE
In retinitis pigmentosa (RP), the slow and progressive death of inner retinal neurons is thought to be inevitable after the death of photoreceptors. However, even in the advanced stage of RP, all inner retinal neurons are not completely lost. The morphological and electrophysiological modifications in ON-retinal bipolar cells (ON-RBCs) of Royal College of Surgeons (RCS) rats (RCS-ON-RBCs) were investigated to elucidate the mechanisms of survival of RCS-ON-RBCs in RP.


METHODS
Control (CTR) and RCS rats were divided into age groups according to postnatal stage: postnatal day 21 (Pn21d), postnatal day 30 (Pn30d), postnatal day 60 (Pn60d), and postnatal day 90 (Pn90d). Lucifer yellow staining of single ON-RBCs and double-immunofluorescence of the retinal frozen sections were used to detect the morphological modifications and loss of RCS-ON-RBCs in different retinal regions. The whole-cell patch clamping technique was used to record the electrophysiological properties of ON-RBCs.


RESULTS
There was a significant loss of RCS-ON-RBCs compared with CTR (p < 0.01) at Pn60d. Loss of the RCS-ON-RBCs differed by region. From Pn60d onwards, the loss was more severe in the peripheral retinal regions (p < 0.01). From Pn21d, the ectopic neurites from the RCS-ON-RBCs reached the outer and inner nuclear layers. At Pn60d, terminal branches of RCS-ON-RBCs axons vanished and ectopic neurites from the RCS-ON-RBCs became entwined. The resting membrane potential, input resistance and outward membrane current amplitude of RCS-ON-RBCs were significantly higher than those of the ON-RBCs of CTR rats at Pn60d (p < 0.05).


CONCLUSIONS
Our results indicate that more RCS-ON-RBCs survived in the central retinal area near cone clusters, potentially as a result of ectopic neuritis. Meanwhile the surviving RCS-ON-RBCs remained immature and had no normal electrophysiological characteristics.
Zhang
Chen Xing
CX
Southwest Hospital/Southwest Eye Hospital, Third Military Medical University, Chongqing, People's Republic of China.
Yin
Zheng Qin
ZQ
Chen
Li-Feng
LF
Weng
Chuang-Huang
CH
Zeng
Yu-Xiao
YX
D000818:Animals; D001369:Axons / Q000502:physiology; D002470:Cell Survival / Q000502:physiology; D004594:Electrophysiology; D019084:Fluorescent Antibody Technique, Indirect; D008564:Membrane Potentials / Q000502:physiology; D016501:Neurites / Q000502:physiology; D018408:Patch-Clamp Techniques; D051381:Rats; D011922:Rats, Mutant Strains; D051245:Retinal Bipolar Cells / Q000502:physiology*; D012174:Retinitis Pigmentosa / Q000378:metabolism* / Q000473:pathology