Light microscopic autoradiography of rat retinae after intravitreal injection of [3H]6-methoxy-tetrahydro-beta-carboline.

Many beta-carbolines have recently been shown to occur in the human body and animals. beta-carbolines may act as neuromodulators although their physiological role is not known. We have studied the autoradiographic retinal distribution of intravitreally injected [3H]6-methoxy-tetrahydro-beta-carboline (6-MeO-THBC) in rats. The synaptic and ganglion cell layers accumulate pronounced radioactivity, as do some intra- and extracellular locations in the inner nuclear layer and the outer segments of the photoreceptors. The pigment epithelium gradually accumulates a very dense band of radioactivity. 6-MeO-THBC (pinoline, 5-methoxytryptoline, 6-methoxy-1,2,3,4-tetrahydronorharmane) has been shown to possess many important biochemical and pharmacological properties. It has been demonstrated to occur as a normal constituent in the retina of some animals. The relationship between 6-MeO-THBC, melatonin and other 5-methoxy-indoles is discussed.