Control of 5-HT release in the caudate nucleus and the substantia nigra of the cat.

The release of 3H-5-HT newly synthesized from 3H-tryptophan was measured in the caudate nucleus (CN), the substantia nigra (SN) and the dorsal raphe nucleus (DR) of cats slightly anaesthetized with halothane. It was observed that: 1. 3H-5-HT release was 2.5 and 3.2 times higher in the DR than in the SN and the CN respectively; 2. Cooling (0 degrees C) of the DR by the use of a cryoelectrode resulted in a decrease in 3H-5-HT release in both the CN and SN; 3. Application of 5-HT (10(-7) M) into the DR induced a local increase in 3H-5-HT release, while decreasing 3H-5-HT release in the CN and SN; 4. Conversely, the blockade of 5-HT receptors in the DR by metergoline (10(-6) M) decreased the local release of 3H-5-HT and increased 3H-5-HT release in the CN. No effect was observed in the SN. These results suggest that 5-HT releases into the DR may control the activity of serotoninergic neurons.