The interleukin-1-induced increase of substance P in sympathetic ganglia is not mediated by ciliary neurotrophic factor

Factors limiting motor recovery after facial nerve transection in the rat: combined structural and functional analyses

It is believed that a major reason for the poor functional recovery after peripheral nerve lesion is collateral branching and regrowth of axons to incorrect muscles. Using a facial nerve injury protocol in rats, we previously identified a novel and clinically feasible approach to combat axonal misguidance--the application of neutralizing antibodies against neurotrophic factors to the injured nerve. Here, we investigated whether reduced collateral branching at the lesion site leads to better functional recovery. Treatment of rats with antibodies against nerve growth factor, brain-derived neurotrophic factor, fibroblast growth factor, insulin-like neurotrophic factor I, ciliary neurotrophic factor or glial cell line-derived neurotrophic factor increased the precision of reinnervation, as evaluated by multiple retrograde labelling of motoneurons, more than two-fold as compared with control animals. However, biometric analysis of vibrissae movements did not show positive effects on functional recovery, suggesting that polyneuronal reinnervation--rather than collateral branching --may be the critical limiting factor. In support of this hypothesis, we found that motor end-plates with morphological signs of multiple innervation were much more frequent in reinnervated muscles of rats that did not recover after injury (51% of all end-plates) than in animals with good functional performance (10%). Because polyneuronal innervation of muscle fibres is activity-dependent and can be manipulated, the present findings raise hopes that clinically feasible and effective therapies could be soon designed and tested.

c-Src kinase activation regulates preprotachykinin gene expression and substance P secretion in rat sensory ganglia

Increased synthesis of substance P (SP) in the dorsal root ganglia (DRG) and enhanced axonal transport to and secretion from the primary afferent sensory neurons might enhance pain signalling in the spinal dorsal horn by modifying pronociceptive pathways. IL-1beta increases SP synthesis by enhancing the expression of preprotachykinin (PPT) mRNA encoding for SP and other tachykinins in the DRG. Stimulation of IL-1 receptor by IL-1beta may induce the phosphorylation of tyrosine residues in many effector proteins through the activation of p60c-src kinase. The hypothesis that the synthesis of SP in and secretion from the primary sensory ganglia are regulated by the activation of p60c-src kinase induced by IL-1beta was tested. Pretreatment of DRG neurons in culture with herbimycin A, genistein or PP2, three structurally different nonreceptor tyrosine kinase inhibitors that act by different mechanisms, decreased the kinase activity of p60c-src induced by the activation of IL-1 receptor. PP3, a negative control for the Src family of tyrosine kinase inhibitor PP2 had no effect. Herbimycin A and genistein also decreased IL-1beta-induced expression of PPT mRNA-encoding transcripts and the levels of SP-li synthesized in the cells and secreted into the culture medium in a concentration-dependent manner. SB 203580 [a p38 mitogen-activated protein kinase (p38 MAPK) inhibitor] and PD 98059 (a p44/42 MAPK kinase inhibitor) were ineffective in modulating IL-1beta-induced SP synthesis and secretion, and p60c-src kinase activity in DRG neurons. Whereas, IL-1 receptor antagonist and cycloheximide inhibited IL-1beta-evoked secretion of SP-like immunoreactivity (SP-li), actinomycin D decreased it significantly but did not entirely abolish it. These findings show that phosphorylation of specific protein tyrosine residue(s) following IL-1 receptor activation might play a key role in IL-1beta signalling to modulate PPT gene expression and SP secretion in sensory neurons. In view of the role of SP as an immunomodulator, these studies provide a new insight into neural-immune intercommunication in pain regulation in the sensory ganglia through the IL-1beta-induced p60c-src activation.

Focal application of neutralizing antibodies to soluble neurotrophic factors reduces collateral axonal branching after peripheral nerve lesion

A major reason for the insufficient recovery of function after motor nerve injury are the numerous axonal branches which often re-innervate muscles with completely different functions. We hypothesized that a neutralization of diffusable neurotrophic factors at the lesion site in rats could reduce the branching of transected axons. Following analysis of local protein expression by immunocytochemistry and by in situ hybridization, we transected the facial nerve trunk of adult rats and inserted both ends into a silicon tube containing (i) collagen gel with neutralizing concentrations of antibodies to NGF, BDNF, bFGF, IGF-I, CNTF and GDNF; (ii) five-fold higher concentrations of the antibodies and (iii) combination of antibodies. Two months later, retrograde labelling was used to estimate the portion of motoneurons the axons of which had branched and projected into three major branches of the facial trunk. After control entubulation in collagen gel containing non-immune mouse IgG 85% of all motoneurons projecting along the zygomatic branch sprouted and sent at least one twin axon to the buccal and/or marginal-mandibular branches of the facial nerve. Neutralizing concentrations of anti-NGF, anti-BDNF and anti-IGF-I significantly reduced sprouting. The most pronounced effect was achieved after application of anti-BDNF, which reduced the portion of branched neurons to 18%. All effects after a single application of antibodies were concentration-dependent and superior to those observed after combined treatment. This first report on improved quality of reinnervation by antibody-therapy implies that, in rats, the post-transectional collateral axonal branching can be reduced without obvious harmful effects on neuronal survival and axonal elongation.

Tumor necrosis factor-alpha induces substance P in sympathetic ganglia through sequential induction of interleukin-1 and leukemia inhibitory factor

The present study establishes that tumor necrosis factor-alpha (TNF-alpha) induction of sympathetic substance P (SP) requires sequential induction of both interleukin (IL-1) and leukemia inhibitory factor (LIF). TNF-alpha dose-dependently induces SP, an induction that is secondary to an increase in the SP precursor, preprotachykinin (PPT), mRNA. Since TNF-alpha conditioned medium (CM) mimics the effect of TNF-alpha by raising SP, actions that are not antagonized by a neutralizing TNF-alpha antibody, TNF-alpha induction of SP is mediated by a soluble intermediate or intermediates. The blockade of TNF-alpha action by a specific IL-1 receptor antagonist and the induction of IL-1 mRNA by TNF-alpha suggest that IL-1 is one of the intermediates. Moreover, because immunoprecipitation with LIF antibodies decreases SP-inducing activity of TNF-alpha CM, and because LIF mRNA is also induced by TNF-alpha, LIF is a second intermediate. Furthermore, TNF-alpha-induced LIF mRNA is blocked by the IL-1 receptor antagonist, whereas IL-1-induced LIF mRNA is not affected by TNF-alpha antibodies, suggesting that TNF-alpha first induces IL-1, and IL-1 subsequently induces LIF. These data suggest that TNF-alpha induces SP in sympathetic ganglia through the sequential inductions of IL-1 and LIF.