BACKGROUND: It is discovered by administrating different emetics to vomiting animals, like cats, that there are a large amount of Fos positive neuronal expressions in the arc region from nucleus of solitary tract, lateral tegmentum to ventrolateral area. And it has been viewed that the arc region from area postrema, nucleus of solitary tract to ventrolateral reticular structure is the main emetic region. Whether do the non-vomiting animals reflect in response or not after emetic injection?OBJECTIVE: To observe the distribution of Fos positive neurons in relevant emetic regions of brain and spinal cord in rats after abdominal injection of emetic, cisplatin.DESIGN: Randomized controlled experiment based on animals.SETTING: Neural Physiological Research Room of Life Science College in Hebei Normal University and Physiological Room of Basic Medicine Institute in Hebei Medical University.MATERIALS: The experiment was performed in Neural Physiological Research Room of Life Science College in Hebei Normal University and Physiological Room of Basic Medicine Institute in Hebei Medical University from March to August 2003. Twelve SD male rats were employed, body weighted varied from 220 to 250 g, of clean-grade. They were randomized into experimental group of 6 rats and the control of 6 rats.INTERVENTIONS: In experimental group, the emetic, cisplatin, was injected abdominally 10 mg/kg. In the control, the physiological saline of same dose was injected. Afterwards, the activity changes in rats were observed at room temperature, quiet and light-avoided environment. Six hours later, the brain tissue was collected for frozen continuous sectioning. Immunohistochemical staining method was used to observe the distribution of Fos positive neurons in brainstem and forebrain nuclei and to count positive cell.MAIN OUTCOME MEASURES: ① Behavior observation in rats after emetic injection. ② Counts of Fos positive cell in relevant regions of brain in rats.RESULTS: Twelve rats all entered result analysis. ① In 20 minutes after injection, the rats in both groups were in tranquilizing state, lying prone with body curled, almost without any movement. In 60 minutes after injection, the rats in the control were recovered to normal, free of eating or drinking. The rats in experimental group were in prone-lying state with body curled. They rose up or shook the heads occasionally, and they breathed fast and uneven.In 2 hours after injection, in experimental group, the rats were still in abdominal prone tightly in the cage, with heads lowed and irregular shaking of noses. In 5 hours, the rats in experimental group began standing up and moving, with normal breathing, but they still did not eat or drink. ② Fos positive neurons in solitary tract, area postrema and lateral parabrachial nucleus and paraventricular nucleus, supraoptic nucleus and arc nucleus in hypothalamus (64.3 ±9.6, 83.4 ±15.0, 148.8 ±19.9, 80. 2 ± 11.8, 20.7 ±3.8, 86. 6 ± 10.8) were remarkably higher than those in the control(56. 2 ±6.3,73.5±9.9,136.9±17.8,66. 1±10.3,17.3±3.4,78.8±10.5).CONCLUSION: Emetics induce discomforts in internal organs of rats, due to which, there probably exist emetic regions similar to vomiting animals in central neural system. But it is probably lack of vomiting-related adjusting mechanism. Emetics irritate the increase of Fos positive neurons in relevant regions in the brain of rat, which suggests that there exist relevant neural chemical pathways similar to nausea in the brain of non-vomiting rats.