Neuroeeienee Letters, 16 (1980) 251--255 © Elsevier/North-Holland Scientific Publishers Ltd. 251 ORTHOGRADE AND RETROGRADE AXONAL MOVEMENT OF LABEL AND TRANSNEURONAL TRANSPORT PHENOMENA AFTER INTRAOCULAR INJECTION OF [3H]ADENOSINE IN A POITCOLOTHERM VERTEBRATE (VIPERA ASPIS) J. REPlY.RANT, J.P. RIO, J. PEYRICHOUX and C. WEIDNER Labomtoirerde Neuromorphologie, INSERM U. 106, H6pital Foch, 92150 Suresnes Labomtoire de Psyehophysiologie Sensorielle, Universit~ Paris 111, 75005 Paris and Laboratoire d'An~tomie Comparde, M.N.H.N. 55 rue Buffon, 7500b Paris (France) (Received October 22rid, ~979) (Revised vemion reeeive¢~ December 13th, 1979) (Accepted December 13th, 1979) SUMMARY The axoplasmic transport of [~H]adenosine (or its related compounds) has been examined radioautographieally in the visual system of a po'ikilotherm species (Yipera aspis) folio~ ~gan intraocular injection of the nucleoside. It has been found that the axonal transport of the label occurs both in the anterograde directions. Furthermore, a considerable labelling of neuronal bodies as a result of transneuronal transport of tritiated material from the optic endings has been observed, particularly in the primary optic centers. Transneuronal labelling, however, appears less intense than retrograde cell labetling. The mode of axoplasmic transport of adenosine (or of its related com- pounds) in the central nervous system of vertebrates, particularly in po'ikilo- therms has lately been debated [1,2,7-9,11,12]. The present study was undertaken to contribute to the clarification of some aspects of this problem. The approach was to test the transport potent~ai of this nucleoside on a well knoWn model, the visual pathways of a cold-blooded species, Vipera aspis [3--e]. Five retakes received an uniocular injection of [2,8-3H]adenosine (30-,60F~ in*lotd physioi~ saline, spec. act. 30--40 Ci/mmol, NEN). The vipers we~e Idlowed to survive 3Oh to 5 days at 22--24°C and were then transcaa/ially perfused with a 10% formalin in saline. The brains were embedded in ~ m and serially sectioned at 12 ,m in a ~ontal plane. The sections were coated with ]]ford K5 Emulsion, dried and stored at 4°C in light-tight boxes for exposures of 4--6 weeks. They were then developed in