The guinea pig optic nerve stretch was developed as an in vivo model for central nervous system (CNS) trauma. This model allows a controlled dynamic stretch to be applied to a single nerve tract with a specific set of physiological functions. The mechanical stimulus can be related directly to the resulting tissue dysfunction. However, because of the system's configuration, there are some simple, but not trivial, mechanical considerations that will strongly influence the interpretation of results from the model, especially with regard to the establishment of injury tolerance criteria. The authors performed a detailed study of the structural mechanics of the system: the globe, optic nerve, muscle and connective tissues, and their attachments to the skull and other structures. Results from these studies allowed to determine an appropriate pre-load for subsequent dynamic injury experiments. Stretches of 25% applied over 10 milliseconds reliably produced acute swelling of axons of sufficient magnitude to be observed by light microscopy with toludine blue staining. The degree of swelling reaches a peak at 4 hours post injury. These results set the stage for subsequent tests of treatments designed to intervene in the cascade of events initiated by the primary mechanical trauma. (A)
Abstract