Abstract
In vitro investigations were performed to study the proton T~2~ relaxation spectrum of rat optic nerve. Studies in which the nerve was incubated in a D~2~Oβbased solution revealed that >98% of the spectrum originated from the water protons. The spectrum was found to consist of three components having relaxation times and sizes similar to those reported in the literature for peripheral nerve. Procedures were taken to confirm the existence of a third optic nerve component and that it was not an artifact of the longβlived water protons of the in vitro incubation solution. Evidence using paramagnetic agents in the incubation solution, which removed the two longestβlived nerve components from the spectrum, revealed the existence of a small fourth component (<10% of total) having a T~2~ relaxation time similar to that of the intermediateβlived nerve component. Bathing the nerves in a 10βmM glutamate solution, glutamate known to result in cellular swelling in mammalian central nervous system (CNS), was found to increase the component size of the longestβlived nerve component, suggestive that this component may result from cellular water. Copyright Β© 2006 John Wiley & Sons, Ltd.