In vivo binding of [3H]ketanserin on serotonin S2-receptors in rat brain.

In vivo binding of [3H]ketanserin was studied in various brain regions in rats. After i.v. injection of [3H]ketanserin (5 micrograms . kg-1), the highest labelling was found in the frontal cortex. Brain disposition of labelled drug correlated with the distribution of serotonin S2-receptors detected in vitro. The binding was saturable in the serotonergic areas but not in the cerebellum. Various drugs were tested for their ability to displace or to prevent [3H]ketanserin binding: these results were then compared to those obtained with [3H]spiperone in the frontal cortex. Although [3H]spiperone can be used to differentiate the affinity of a drug for serotonin (frontal cortex) and dopamine (striatum) receptors, the great advantage of [3H]ketanserin is that it labels serotonin S2-receptors exclusively.