Abstract
Our general understanding of neuronal function is that dendrites receive information that is transmitted to the axon, where action potentials (APs) are initiated and propagated to eventually trigger neurotransmitter release at synaptic terminals. Even though this canonical division of labor is true for a number of neuronal types in the mammalian brain (including neocortical and hippocampal pyramidal neurons or cerebellar Purkinje neurons), many neuronal types do not comply with this classical polarity scheme. In fact, dendrites can be the site of AP initiation and propagation, and even neurotransmitter release. In several interneuron types, all functions are carried out by dendrites as these neurons are devoid of a canonical axon. In this article, we present a few examples of “misbehaving” neurons (with a non-canonical polarity scheme) to highlight the diversity of solutions that are used by mammalian neurons to transmit information. Moreover, we discuss how the contribution of dendrites and axons to neuronal excitability may impose constraints on the morphology of these compartments in specific functional contexts.
Highlights
More than a century ago, Santiago Ramon y Cajal provided us with a tremendously extensive description of the various morphologies of the neuronal types constituting the mammalian brain and other species’ nervous systems (Cajal, 1952)
Cajal noticed that these dendrite-emanating axons were present in many neuronal types in mammals, and that other neuronal types, such as the dorsal root ganglion (DRG) neurons, presented a unipolar morphology incompatible with the first version of the dynamic
We showed that the division of labor between axons and dendrites can take multiple forms associated with strong morphological variations, some neuronal types carrying out all functions (AP initiation and propagation, neurotransmitter release) in the absence of a clearly defined axon
Summary
UMR_S 1072, Aix Marseille Université, INSERM, Faculté de Médecine Secteur Nord, Marseille, France. Our general understanding of neuronal function is that dendrites receive information that is transmitted to the axon, where action potentials (APs) are initiated and propagated to eventually trigger neurotransmitter release at synaptic terminals. Even though this canonical division of labor is true for a number of neuronal types in the mammalian brain (including neocortical and hippocampal pyramidal neurons or cerebellar Purkinje neurons), many neuronal types do not comply with this classical polarity scheme. Dendrites can be the site of AP initiation and propagation, and even neurotransmitter release. We discuss how the contribution of dendrites and axons to neuronal excitability may impose constraints on the morphology of these compartments in specific functional contexts
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