Axonal Transport in the Rat Optic Nerve Following Short-Term Reduction in Cerebrospinal Fluid Pressure or Elevation in Intraocular Pressure

Abstract

 

Purpose

 

To examine the influence of short-term reduction in cerebrospinal fluid pressure (CSFP) as compared to short-term elevation in intraocular pressure (IOP) on axonal transport.

 

Methods

 

The study included 111 adult Sprague-Dawley rats. For six hours, IOP was elevated to 40mmHg (IOP40-study-group) (n=27,right eyes), IOP was increased to a value of 25mmHg below the mean blood pressure (“PP25-study-group”) (n=27,right eyes), or cerebrospinal fluid pressure was reduced by continuous aspiration of cerebrospinal fluid (“Low-CSFP-study-group”) (n=27). A “sham control group” (with a trocar in cisterna magna without cerebrospinal fluid release) included 24 rats. The left eyes of the IOP40-study-group and PP25-study-group served as additional “control group”. The orthograde axonal transport was examined by intravitreally injected rhodamine-ß-isothiocyanate, the retrograde axoplasmic flow was assessed by fluorogold injected into the superior colliculi.

 

Results

 

At 24hours after baseline, the intensity of RITC staining of the optic nerve was significantly (P<0.05) lower in the IOP40-study-group, PP25-study-group and Low-CSFP-study-group than in the control groups. At six hours after the fluorogold injection, fluorogold fluorescence was significantly lower in the IOP40-study-group, the PP25-study-group and the Low-CSFP-study-group than in the control groups. At 5 days after baseline, fluorogold fluorescence no longer differed significantly between the IOP40-study-group or the Low-CSFP-study-group and the control groups.

 

Conclusions

 

Both, short-term lowering of CSFP and short-term rise in IOP, were associated with a disturbance of both the orthograde and retrograde axonal transport. The finding supports the notion of an association between abnormally low CSFP and optic nerve damage.  

 

Staining of Retinal Ganglion Cells by Fluorogold on Retinal Flat Mounts after Injection of Fluorogold in Both Superior Colliculi in Rats of the Control Group (A), in Rats with a Short-Term (6 Hours) Elevation of Intraocular Pressure to 40 mmHg (B), in Rats with a Short-Term (6 Hours) Reduction of the Ocular Perfusion Pressure to 25mmHg (C), in Rats of a Sham Control Group (D), and in Rats with an Experimental Short-Term (6 Hours) Reduction in Cerebrospinal Fluid Pressure (E), Imaged at Six Hours after Baseline; F: Quantitative Analysis of the Retrograde Axonal Transport Assay.