Interactions between serotonergic and enkephalinergic neurons in rat striatum and hypothalamus.

We report evidence for an interaction between serotonergic and enkephalinergic neurons in rat striatum and hypothalamus. The administration of drugs such as p-chlorophenylalanine (PCPA), 5,6-dihydroxytryptamine (5,6-DHT) and fenfluramine that lower the striatal and hypothalamic serotonin (5-HT) content caused an increase in Met-enkephalin-like immunoreactive material (ME-IR) in these brain areas. Moreover, chronic treatment with PCPA induced an increase in the number of striatal [3H][D-Ala2, Met5]enkephalinamide binding sites. These observations suggest that serotonergic neurons modulate the functional activity of enkephalinergic neurons in the rat striatum and hypothalamus. The significance of this interaction is discussed.