Effects of soluble laminin on organelle transport and neurite growth in cultured mouse dorsal root ganglion neurons: Difference between primary neurites and branches

Antisense oligonucleotides targeting alternative splicing of Nrcam exon 10 suppress neurite outgrowth of ganglion sensory neurons in vitro

Neuron-glial-related cell adhesion molecule (NrCAM) is a neuronal cell adhesion molecule that has been shown to be involved in several cellular processes in the peripheral nervous system, including neurite outgrowth. We recently reported that alternative splicing of Nrcam mRNA at exon 10 in the dorsal root ganglion (DRG) contributes to the peripheral mechanism of neuropathic pain. Specially, Nrcam antisense oligonucleotides (ASO) targeting Nrcam exon 10, attenuated neuropathic pain hypersensitivities in mice. Here, we investigated the effect of Nrcam ASO on neurite outgrowth of DRG neurons in vitro. By immunostaining DRG neurons with different DRG markers, Nrcam ASO significantly reduced neurite lengths in neurofilament 200-, calcitonin gene-related peptide and isolectin B4-positive neurons in primary DRG neuronal culture. Moreover, Nrcam ASO activates epidermal growth factor receptor, which may mediate the effect of Nrcam ASO on neurite outgrowth of cultured DRG neurons. These results provide evidence that Nrcam ASO suppresses neurite outgrowth in DRG neurons by regulating alternative splicing of Nrcam gene at exon 10 and activation of epidermal growth factor receptor signaling, indicating the differential roles of NrCAM variants/isoforms in neurite outgrowth.

Progress in cell based assays for botulinum neurotoxin detection

Botulinum neurotoxins (BoNTs) are the most potent human toxins known and the causative agent of botulism, and are widely used as valuable pharmaceuticals. The BoNTs are modular proteins consisting of a heavy chain and a light chain linked by a disulfide bond. Intoxication of neuronal cells by BoNTs is a multi-step process including specific cell binding, endocytosis, conformational change in the endosome, translocation of the enzymatic light chain into the cells cytosol, and SNARE target cleavage. The quantitative and reliable potency determination of fully functional BoNTs produced as active pharmaceutical ingredient (API) requires an assay that considers all steps in the intoxication pathway. The in vivo mouse bioassay has for years been the 'gold standard' assay used for this purpose, but it requires the use of large numbers of mice and thus causes associated costs and ethical concerns. Cell-based assays are currently the only in vitro alternative that detect fully functional BoNTs in a single assay and have been utilized for years for research purposes. Within the last 5 years, several cell-based BoNT detection assays have been developed that are able to quantitatively determine BoNT potency with similar or greater sensitivity than the mouse bioassay. These assays now offer an alternative method for BoNT potency determination. Such quantitative and reliable BoNT potency determination is a crucial step in basic research, in the development of pharmaceutical BoNTs, and in the quantitative detection of neutralizing antibodies.

Differentiation state-dependent effects of in vitro exposure to atrazine or its metabolite diaminochlorotriazine in a dopaminergic cell line

AIMS

This study sought to determine the impact of in vitro exposure to the herbicide atrazine (ATR) or its major mammalian metabolite diaminochlorotriazine (DACT) on dopaminergic cell differentiation.

MAIN METHODS

N27 dopaminergic cells were exposed for 24 or 48 h to ATR or DACT (12-300 μM) and their effects on cell viability, ATP levels, ADP:ATP ratio and differentiation markers, such as soma size and neurite outgrowth, were assessed.

KEY FINDINGS

Overall, intracellular ATP levels and soma size (decreased by ATR at ≥12 μM; 48 h) were the two parameters most sensitive to ATR exposure in undifferentiated and differentiating dopaminergic cells, respectively. At the morphological level, ATR, but not DACT, increased the percentage of morphologically abnormal undifferentiated N27 cells. On the other hand, exposure to DACT (300 μM; 48 h), but not ATR, increased the ADP:ATP ratio regardless of the differentiation state and it moderately disrupted thin neurite outgrowth. Only the highest concentration of ATR or DACT (300 μM) was cytotoxic after a longer exposure (48 h) and undifferentiated N27 cells were the least sensitive to the cytotoxic effects of ATR or DACT.

SIGNIFICANCE

Our results suggest that the energy perturbation and morphological disruption of dopaminergic neuronal differentiation induced by ATR and, to a lesser extent, DACT, may be associated with reported neurological deficits caused by developmental ATR exposure in rodents.

Peripheral sensory axon growth: from receptor binding to cellular signaling

Regeneration following axonal injury of the adult peripheral sensory nervous system is heavily influenced by factors located in a neuron's extracellular environment. These factors include neurotrophins, such as Nerve Growth Factor (NGF) and the extracellular matrix, such as laminin. The presence of these molecules in the peripheral nervous system (PNS) is a major contributing factor for the dichotomy between regenerative capacities of central vs. peripheral neurons. Although PNS neurons are capable of spontaneous regeneration, this response is critically dependent on many different factors including the type, location and severity of the injury. In this article, we will focus on the plasticity of adult dorsal root ganglion (DRG) sensory neurons and how trophic factors and the extracellular environment stimulate the activation of intracellular signaling cascades that promote axonal growth in adult dorsal root ganglion neurons.

Effects of clonidine on lidocaine-induced inhibition of axonal transport in cultured mouse dorsal root ganglion neurones

BACKGROUND

The alpha(2)-adrenoceptor agonist clonidine is used in combination with lidocaine for anaesthesia. Lidocaine inhibits axonal transport and neurite growth, whereas alpha(2)-adrenoceptor agonists have neurotrophic effects. Here we have investigated whether clonidine reduces lidocaine-induced inhibition of axonal transport in cultured mouse dorsal root ganglion neurones.

METHODS

Axonal transport of organelles and neurite growth were assessed by video microscopy in cells treated with clonidine and lidocaine for 1 h. Stable responses were achieved within this period.

RESULTS

Clonidine (10 and 100 microM) increased and lidocaine (10, 100 microM, and 1 mM) decreased axonal transport. The inhibitory effects of lidocaine were reduced by simultaneous treatment with clonidine. The actions of clonidine were antagonized by the alpha(2)-adrenoceptor antagonist yohimbine. Since clonidine was reported to block N-type channels, we further investigated the role of ion channels in the antagonistic action of clonidine on the lidocaine response. The action of lidocaine on axonal transport was not mimicked by the Na+ channel blocker tetrodotoxin and not blocked by the Na+ channel activator veratridine. The action of lidocaine was not blocked by the L-type Ca2+ channel blocker nifedipine, but was blocked by the N-type channel blocker omega-conotoxin MVIIA. These effects on axonal transport correlated with the effects on neurite growth.

CONCLUSIONS

Inhibition of axonal transport induced by lidocaine, which may be mediated by N-type channel activation, can be blocked by clonidine. Clonidine may alleviate the effects of lidocaine on neuronal dysfunction.

Cross-midline interactions between mouse commissural hindbrain axons contribute to their efficient decussation

Information from both sides of the brain is integrated by axons that project across the midline of the central nervous system via numerous commissures present at all axial levels. Despite the accumulated experimental evidence, questions remain regarding the formation of commissures in the presence of strong repulsive signals in the ventral midline. Studies from invertebrates suggest that interaction at the midline between homologous axons of specific decussating neurons contributes to efficient midline crossing, but such evidence is lacking in vertebrate systems. We performed experiments to determine whether commissural axons of the caudal region of the hindbrain interact with their contralateral counterparts at the ventral midline and to evaluate the relevance of this reciprocal interaction. Double anterograde axon labeling with lipophilic tracers revealed close apposition between growth cones of contralateral pioneer decussating axons at the midline. Later, we detected fasciculation between contralateral axons that is maintained even after they have crossed the midline. Blocking axon projections unilaterally with a solid mechanical barrier decreased dramatically the midline crossing of the equivalent population from the contralateral side. Decussation was also blocked by a unilateral barrier permeable to diffusible molecules but not by an axon-permeable barrier. These results suggest that in the caudal region of the hindbrain, midline crossing is facilitated by interactions between decussating contralateral axon partners.

Optimal Micropattern Dimensions Enhance Neurite Outgrowth Rates, Lengths, and Orientations

Micropattern dimensions can significantly influence neurite outgrowth orientation, rate, and length. Laminin micropatterns of various widths from 10 to 50 microm at 10 microm intervals separated by 40 microm spaces were generated on poly(methyl methacrylate) surfaces using microscale plasma-initiated patterning (microPIP). Dissociated dorsal root ganglion (DRG) neurons were seeded on the micropatterned surfaces and cultured for 24 h in serum-free media. Neurite outgrowth numbers, lengths, rates, and orientations were measured on all micropatterned substrates. The results indicated that the dimension of the laminin pattern influenced the neurite outgrowth length, rate, and orientation, but not the numbers of neurite outgrowth. Neurons on more than 30 microm wide laminin pattern showed faster neurite outgrowth compared to other dimensions, and relatively low orientation at 50 microm pattern dimensions. Neurites at 40 microm laminin pattern widths demonstrated the fastest outgrowth rates and were highly oriented. The 40 microm laminin dimension is wide enough to provide sufficient laminin amounts for neuron growth and narrow enough to efficiently guide neurites. Based on these results, adhesive protein micropatterns of 40 microm dimensions are recommended when investigating DRG neurons.