Behavioral effects of 7-nitroindazole on hyperbaric oxygen toxicity.

The aim of this study was to evaluate the role of nitric oxide (NO) upon hyperbaric oxygen (HBO) toxicity in male Sprague-Dawley rats during exposure to 0.5 MPa >99% O(2). In the first experiment, the selective neuronal NO synthase inhibitor 7-nitroindazole (7-NI) was injected intraperitoneally (ip) in 15 rats. Another 15 rats received vehicle injections of peanut oil intraperitoneally. Latency to observable tonic-clonic convulsions and motor activity during the HBO exposure were scored and compared between the control group and the 7-NI group. The results showed that injection of 7-NI (30 mg/kg) significantly prolonged the latency to observable tonic-clonic convulsions. The 7-NI group also showed a significant decrease in motor activity compared with the control group. A second experiment was performed to measure the effect of 7-NI injections upon open-field activity during normobaric conditions. Twenty-four male Sprague-Dawley rats were randomly divided into three groups, each consisting of eight rats receiving 30 mg/kg 7-NI injections, 10 mg/kg 7-NI injections or vehicle injections of peanut oil intraperitoneally, respectively. The results showed that injection of 7-NI led to a significant dose-dependent reduction in horizontal and vertical activities. This study shows that 7-NI prolongs the latency to hyperoxia-induced seizures. However, it also demonstrates that 7-NI in doses ranging from 30 to 10 mg/kg has a secondary effect upon motor behavior in general. It can therefore not be ruled out that the protective effect of 7-NI upon HBO intoxication is partly due to reduced motor activity.