In-vitro stability of peripheral nerve preparations: Relation to ischemic responses

Although in-vitro peripheral nerve preparations are useful tools in studying the physiology of axons, their function invariably declines gradually over time. This study investigates the effects of age and temperature on both the in-vitro stability of rat sciatic nerve and the response of the nerve to acute hypoxia. Comparison of the effects of age and temperature in these two models can clarify a possible connection between the hypoxic response and the stability of in-vitro preparations. In in-vitro preparations, the amplitude of the nerve action potential (NAP) declines more rapidly at high temperatures than low temperatures. At high temperatures, the decline in NAP amplitude is faster in nerves taken from younger animals while at low temperatures, the NAP amplitude is the same in both young and old animals. This dependence is similar to that of the time required for the NAP to reach 50% of its baseline value after recovery from hypoxia and the NAP amplitude after a 1.5-h period of hypoxia. It is different from the behavior of the time required for the NAP to drop to 50% of its initial value during hypoxia since the effects of temperature and age on this parameter are independent. This provides evidence of a relationship between the injury caused by hypoxia and the changes that occur after transection. However, since the effect of age on the changes in conduction velocity after transection and after hypoxia are different, the two processes must differ in the response of myelin to the metabolic changes in these conditions.