Functional consequences of retrograde axonal transport of receptor-bound neurotensin.

Transport mechanisms or trafficking systems in axons allow neuronal constituents to reach nerve terminals. Accordingly, presynaptic receptors undergo axonal transport through a process that is fast and bidirectional. However, axonal transport of receptors also appears to be involved in the 'flow' of information from membrane receptors to genome. The most compelling evidence that retrograde axonal transport of receptor-bound neuropeptide represents a long-distance signalling system in gene expression, discussed here by Pierre Laduron, comes from the recent observation that neurotensin injected in the striatum undergoes retrograde transport in dopaminergic neurones to the substantia nigra, where it induces in the cell bodies an increase of tyrosine hydroxylase mRNA. Although the molecular mechanisms of this remain to be elucidated, the present data suggest the existence of retrograde signal molecules, or 'third messengers', which have to be associated with synaptic or endocytotic vesicles in order to gain entry into the cell bodies, where they may modulate gene expression.