Effect of strychnine on brain serotonin and catecholamine contents in the rabbit
Since the finding of relatively large amount of serotonin in the brain, extensive studies have been reported concerning the physiological significance of this of this substance in the brain function. Although there is no conclusive evidence, serotonin has been suggested to act as a chemical transmitter in the normal functioning of the central nervous system (Brodie et al., 1958).
Bonnycastle et al. (1957) found that a variety of central depressant drugs, including sedatives, hypnotics, analgesics fixed and volatile anesthetics, during the course of their pharmacological action resulted in a significant elevation of
brain serotonin. From these observations, they suggested that the increases in brain serotonin following the CNS depressants are not responsible for the altered physiological state of the animals but rather should be considered a consequence of the central depression. However, Garatinini et al. (1957) reported that both electric shock and cardiazole injection into rate also accompanied by marked elevation in brain serotonin.
In view of the above controversy, the effects of various central nervous stimulants on the brain serotonin seemed worthy of careful examination. The present experiment, therefore, was undertaken to examine the influence of strychnine on the whole brain level of serotonin. Since available information indicates that epinephrine or norepinephrine may be considered as a chemical transmitter in brain function, the concentration of brain catecholmines was also examined.
The rabbits of both sexes weighing 1.8-2.3 kg were used in this experiment. Strychnine nitrate saline was injected intravenously into the ear vein. At a particular time, the animals were killed by the air embolism and their brains were determined spectrophptofluorometrically by the methods described by Bogdanski et al. (1956) and Shore and Olin (1958), respectively.
1. The serotonin and catecholamine content in brain of normal rabbits 0.46 and 0.45 ug/gm, respectively.
2. The intravenous administration of strychnine in a dose of 0.15 mg/kg resulted in a tonic convulsion and opisthotonus within few minutes. Brain serotonin was significantly elevated soon after the convulsion but the greatest increase in brain serotonin was observed at 30 minutes after the convulsion. At 180 minutes after the convulsion, the brain serotonin level was significantly different from normal value.
3. When a dose of 0.05 mg/kg of strychnine was administered, rabbits were not appearently different from normal rabbits but the brain serotonin was markedly elevated. As the dose of strychnine increased, the serotonin content in brain increased.
4. The catecholamine concentration in brain was not significantly changed following the administration of strychnine.