The reduction in the concentration of striatal ACh induced in the present study by administration of DMT could also be the result of direct stimulation by DMT of the release of ACh. The results of numerous studies indicate that the concentration of ACh in brain is reduced when its rate of release or turnover is increased s, Administration of 5-HTP, a precursor for 5-HT which stimulates both the synthesis and neuronal release of 5-HT, also causes a decrease in the level of ACh in the corpus striatum of rats la. This finding, along with the present results, suggests the possibility that cholinergic neurons of the corpus striatum contain receptors for tryptamine, and raises the possibility that these cholinergic interneurons are under the control of an excitatory serotonergic system, In support of this hypothesis, it has been shown that treatment of rats with either 5,6-dihydroxytryptaminO ° or p-chloroamphetamine 17, both of which destroy serotonergic neurons of the brain, causes an increase in the brain concentration of ACh. Treatment with DMT had no effect on the level of ACh in the cortex (Table 1), suggesting that cholinergic neurons of this region are not under serotonergic control. Further studies of the effects of lesions and electrical stimulation of raphe neurons on the rate of turnover of striatal ACh would help to further elucidate the relationship between central cholinergic and serotonergic neurons.