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

To examine the influence of short-term reduction in cerebrospinal fluid pressure (CSFP) as compared with short-term elevation in IOP on axonal transport. The study included 111 adult Sprague-Dawley rats. For 6 hours, IOP was unilaterally elevated to 40 mm Hg (IOP40-group; n = 27), IOP was unilaterally increased to a value of 25 mm Hg below the mean blood pressure (PP25-group; n = 27), or CSFP was reduced by continuous aspiration of cerebrospinal fluid (Low-CSFP-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 contralateral control group. Orthograde axonal transport was examined by intravitreally injected rhodamine-β-isothiocyanate; retrograde axoplasmic flow was assessed by fluorogold injected into the superior colliculi. At 24 hours after baseline, rhodamine-β-isothiocyanate (RITC) staining intensity of the optic nerve was lower (P < 0.05) in the IOP40-group, PP25-group, and Low-CSFP-group than in the control groups. At 6 hours after the fluorogold injection, fluorogold fluorescence was significantly lower in the IOP40-group, the PP25-group, and the Low-CSFP-group than in the control groups. At 5 days after baseline, the fluorogold fluorescence no longer differed significantly between the IOP40-group or the Low-CSFP-group and the control groups. At 1 week after baseline, retinal ganglion cell density was markedly reduced only in the PP25-group. 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 findings support the notion of an association between abnormally low CSFP and optic nerve damage.