FUNCTIONAL CONSEQUENCES OF RETROGRADE AXONAL-TRANSPORT OF RECEPTOR-BOUND NEUROTENSIN

Transport mechanisms or trafficking systems in axons allow neuronal co nstituents to reach nerve terminals. Accordingly, presynaptic receptor s undergo axonal transport through a process that is fast and bidirect ional. However, axonal transport of receptors also appears to be invol ved in the 'flow' of information from membrane receptors to genome. Th e most compelling evidence that retrograde axonal transport of recepto r-hound neuropeptide represents a long-distance signalling system in g ene expression, discussed here by Pierre Laduron, comes from the recen t observation that neurotensin injected in the striatum undergoes retr ograde transport in dopaminergic neurones to the substantia nigra, whe re it induces in the cell bodies an increase of tyrosine hydroxylase m RNA. Although the molecular mechanisms of this remain to be elucidated , the present data suggest the existence of retrograde signal molecule s, or 'third messengers', which have to be associated with synaptic or endocytotic vesicles in order to gain entry into the cell bodies, whe re they may modulate gene expression.