[Anxiety-like behavior in rats neonatally and adultly treated with 5,7-dihydroxytryptamine]

A large body of evidence has shown the involvement of serotonin (5-HT) in anxiety. The administration of serotonergic neurotoxin 5,7-dihydroxytryptamine (5,7-DHT) into adult rats has been shown to produce a prolonged reduction in the content of brain 5-HT along with anxiolytic effects. In this experiment, 5,7-DHT was administrated intraventricularly to neonatal and adult rats. All rats were tested in an elevated plus maze at 30, 50, 70, and 90 days old to evaluate the anxiety level. Adult treatment increased the time spent in open-arm, and decreased the brain 5-HT content in all the regions measured. In contrast, neonatal treatment decreased the time spent in open-arm, and 5-HT contents in these animals did not decrease in the hypothalamus and medulla oblongata. A 5-HT syndrome test was conducted once when the rats were 91 to 97 days old to evaluate the sensitivity of 5-HT recepotors. It was found that 5-HTP (25 mg/kg) produces a severe serotonin syndrome in the adult 5,7-DHT-treated rats, but only a moderate syndrome in the neonatal-treated animals. Significant negative correlation coefficients were obtained between the score of serotonin syndrome and 5-HT content in the hypothalamus, midbrain, medulla oblongata, and cerebellum of the neonatal 5,7-DHT-treated rats. The results suggest that neonatal 5,7-DHT treatment produces an anxiogenic effect in contrast with the anxiolytic effect with adult treatment.