Tryptamine transport in rat brain slices: a comparison with 5-hydroxytryptamine.

The uptake of [14C]tryptamine (14C-T) and [3H]serotonin (3H-5HT) into slices of rat hypothalamus (HT), fronto-parietal cortex (CX), and caudate nucleus (Cau) has been investigated. In all three brain areas, the uptake of 3H-5HT at 37 degrees C was much greater than that in an ice-bath at 1.0-1.5 degrees C. In contrast, the uptake of 14C-T at 37 degrees C was not much greater than uptake at 1.0-1.5 degrees C. While markedly different amounts of 3H-5HT were accumulated by each of the brain areas studied, the regional uptake of 14C-T was quantitatively similar. In general the uptake of 14C-T was inhibited less than 3H-5HT by cocaine, DNP, ouabain, and decreased Na+ concentrations. Similarly, 14C-T was less susceptible to serotonin uptake inhibitors except in the caudate. It was concluded that though a common indoleamine uptake system accumulates both T and 5HT, a non-specific low affinity or diffusional process also transports both amines and is predominantly responsible for T, but not 5HT, uptake. The spontaneous release, or wash-out, of 14C-T from the caudate was much faster than that of 3H-5HT. In addition, while depolarizing stimuli caused little or no release of 14C-T, large releases of 3H-5HT were observed. T, therefore, does not behave like a conventional neurotransmitter.