Autoradiographic Distribution of the Eye Monoaminergic Synaptic Vesicles

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 (Kd = 4.1 nM, Bmax = 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.