ABSTRACT
Formation of neurites and their differentiation into axons and dendrites requires precisely controlled changes in the cytoskeleton. While small GTPases of the Rho family appear to be involved in this regulation, it is still unclear how Rho function affects axonal and dendritic growth during development. Using hippocampal neurones at defined states of differentiation, we have dissected the function of RhoA in axonal and dendritic growth. Expression of a dominant negative RhoA variant inhibited axonal growth, whereas dendritic growth was promoted. The opposite phenotype was observed when a constitutively active RhoA variant was expressed. Inactivation of Rho by C3-catalysed ADP-ribosylation using C3 isoforms (Clostridium limosum, C3(lim) or Staphylococcus aureus, C3(stau2)), diminished axonal branching. By contrast, extracellularly applied nanomolar concentrations of C3 from C. botulinum (C3(bot)) or enzymatically dead C3(bot) significantly increased axon growth and axon branching. Taken together, axonal development requires activation of RhoA, whereas dendritic development benefits from its inactivation. However, extracellular application of enzymatically active or dead C3(bot) exclusively promotes axonal growth and branching suggesting a novel neurotrophic function of C3 that is independent from its enzymatic activity.
Subject(s)
Axons/physiology , Dendrites/physiology , Hippocampus/physiology , Neurons/physiology , rho GTP-Binding Proteins/metabolism , ADP Ribose Transferases/genetics , ADP Ribose Transferases/metabolism , ADP Ribose Transferases/pharmacology , Adenosine Diphosphate Ribose/metabolism , Animals , Axons/drug effects , Axons/enzymology , Botulinum Toxins/genetics , Botulinum Toxins/metabolism , Botulinum Toxins/pharmacology , Cells, Cultured , Dendrites/drug effects , Dendrites/enzymology , Gene Transfer Techniques , Genes, Dominant , Hippocampus/enzymology , Hippocampus/ultrastructure , Isoenzymes/genetics , Isoenzymes/metabolism , Isoenzymes/pharmacology , Mice , Mice, Inbred Strains , Neurons/enzymology , Neurons/ultrastructure , Phenotype , Recombinant Proteins/genetics , Recombinant Proteins/metabolism , Recombinant Proteins/pharmacology , rho GTP-Binding Proteins/antagonists & inhibitors , rho GTP-Binding Proteins/geneticsABSTRACT
The effects of deltamethrin on neuronal development and survival were studied using primary mouse hippocampal neurons in culture. Repeated applications of deltamethrin (between 2 nM and 2000 nM) decreased the number of neurons by 16-40%, respectively. Neuronal death was accompanied by an overall decrease of synaptic proteins. Deltamethrin treatment increased the K(+)-stimulated release of amino acid transmitters, GABA and glutamate. The release of the latter might also contribute to neuronal damage. A considerable number of neurons survived treatment with high concentrations of deltamethrin (200-2000 nM) and still displayed characteristics of mature neurons such as synaptic contacts or the expression of members of the Kv1 channel family. When analyzing subtypes of neurons calbindin- as well as somatostatin-positive neurons decreased by 50% after repeated treatment with 2 nM deltamethrin. Under the same conditions neuropeptide Y-positive neurons were up-regulated by 250%.Taken together these data show that deltamethrin at concentrations relevant in human toxicology differentially affects survival of neuronal subtypes by exerting either deleterious or supportive effects. We conclude that deltamethrin disturbs fine-tuning of neuronal efficiency in neuronal networks and might also interfere with the correct wiring during development.
