Autoradiographic Distribution of the Eye Monoaminergic Synaptic Vesicles

Abstract

The ligand [³H]dihydrotetrabenazine ([³H]TBZOH), a tri-tiated derivative of the monoamine depleting agent tetrabena-zine, has been reported to bind specifically to the transporter present on the membrane of monoaminergic synaptic vesicles. We have studied the pharmacological characteristics of [³H]TBZOH binding to rabbit eye sections and the anatomical distribution of [³H]TBZOH binding sites in rabbit, rat and human eyes by in vitro autoradiography. In rabbit eye sections, [³H]TBZOH binding bound to a single class of binding sites (K_d = 4.1 nM, B_max = 30.6 fmol/mg protein). When animals were kept for various times after death before removal of the eyes, the mean density of [³H]TBZOH binding sites decreased to 94 and 93% of control values after 24 and 48 h, respectively. In both species, the topographical distribution of [³H]TBZOH sites shows a pattern of distribution similar to that of monoaminergic innervation of the eye. The present data demonstrate that [³H]TBZOH can be used for the identification and the quantitation of monoamine-containing neurons in the mammalian eye.