Abstract
Purpose :
There is increasing indication that intracranial pressure (ICP) may play a role in glaucoma since the lamina cribrosa of the optic nerve head is exposed to intraocular pressure (IOP) on one side and ICP on the other. The purpose of this study is to monitor ICP in awake and anesthetized animals to understand its dynamics, and how IOP responds to changes in ICP.
Methods :
Experiments were done with adult Brown Norway rats housed in a 12-hr light-dark cycle with access to food and water ad libitum. Continuous recording of ICP in awake rats was done by implanting a fine cannula into the subarachnoid space through a hole in the skull. The cannula was connected to a custom wireless telemetry device attached to a jacket worn on the animal’s back. ICP and IOP were concurrently recorded in anesthetized rats. Subarachnoid and ventricular ICP were recorded via a vented screw in the skull and a 25-gauge needle in a cerebral ventricle, respectively. Ventricular pressure was altered by varying the height of a fluid reservoir connected via a three-way stopcock to the needle. IOP was recorded via a 33-gauge needle in the anterior chamber of one eye. Data was analyzed in terms of means and variances. Variance was analyzed in randomly selected 1-hr samples of the ICP record.
Results :
ICP was successfully recorded from 3 awake rats for 3 days to 4 weeks, and a diurnal ICP rhythm was observed in every animal. Mean ICP was 5.2 ± 1.8 mmHg during the light phase and 12.3 ± 4.2 mmHg during the dark phase (p < 0.03). ICP records of at least an hour in length were recorded from 6 awake rats and 6 anesthetized rats. Average variance of ICP fluctuations was 0.06 ± 0.04 mmHg for awake animals and 4.68 ± 4.49 mmHg for anesthetized animals (p < 0.03). IOP was observed to increase by 4.1 ± 4.0 mmHg after ICP elevation of 10 mmHg in 5 anesthetized rats (p = 0.08).
Conclusions :
Our results show that ICP has a diurnal rhythm in conscious rats, with ICP being significantly higher during the animal’s waking hours. We have previously shown that IOP is also higher at night, which implies that translaminar pressure is relatively stable throughout the day. ICP variance in conscious rats can be attributed in large part to animal activity as variance is greatly reduced by anesthesia. Effects of ICP elevation on IOP are reportedly due to changes in ocular blood volume and/or outflow facility and under further investigation.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.