Autoradiographic distribution of the eye monoaminergic synaptic vesicles

The ligand [3H]dihydrotetrabenazine ([3H]TBZOH), a tritiated derivative of the monoamine depleting agent tetrabenazine, 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.