Semaphorin 3A inhibits growth of adult sympathetic and parasympathetic neurones via distinct cyclic nucleotide signalling pathways.

BACKGROUND AND PURPOSE: Semaphorin 3A (Sema3A) is an important secreted repulsive guidance factor for many developing neurones. Sema3A continues to be expressed in adulthood, and expression of its receptor, neuropilin-1 (Nrp-1), can be altered by nerve injury. Autonomic neurones innervating the pelvic viscera are particularly susceptible to damage during pelvic surgical procedures, and failure to regenerate or aberrant growth of sympathetic and parasympathetic nerves lead to organ dysfunction. However, it is not known if adult pelvic neurones are potential targets for Sema3A. EXPERIMENTAL APPROACH: The effects of Sema3A and activation or inhibition of cyclic nucleotide signalling were assessed in adult rat pelvic ganglion neurones in culture using a growth cone collapse assay. KEY RESULTS: Sema3A caused growth cone collapse in both parasympathetic and sympathetic neurones expressing Nrp-1. However, the effect of Sema3A was mediated by distinct cyclic nucleotide signalling pathways in each neurone type. In parasympathetic neurones, cAMP and downstream activation of protein kinase A were required for growth cone collapse. In sympathetic neurones, cGMP was required for Sema3A-induced collapse; cAMP can also cause collapse but was not required. Sema3A-mediated, cGMP-dependent collapse in sympathetic neurones may require activation of cyclic nucleotide-gated ion channels (CNGCs). CONCLUSIONS AND IMPLICATIONS: We propose that Sema3A is an important guidance factor for adult pelvic autonomic neurones, and that manipulation of their distinct signalling mechanisms could potentially promote functional selective regeneration or attenuate aberrant growth. To our knowledge, this is also the first study to implicate CNGCs in regulating growth cone dynamics of adult neurones.

Effects of interleukin-6 treatment on neurovascular function, nerve perfusion and vascular endothelium in diabetic rats.

AIM: Interleukin-6 (IL-6), a member of the neuropoietic cytokine family, participates in neural development and has neurotrophic activity. Recent research has also indicated actions to improve vasa nervorum function in diabetes. Both these facets are potentially relevant for treatment of diabetic neuropathy. The aim of this study was to determine whether IL-6 treatment corrected changes in neurovascular function in streptozotocin-induced diabetic rats. METHODS: After 1 month of diabetes, rats were given IL-6 for 1 month. The rats were subjected to sensory testing and measurements of nerve conduction velocities and nerve blood flow by hydrogen clearance microelectrode polarography. Further groups were used to study responses of the isolated gastric fundus and renal artery. Results were statistically analysed using ANOVA and post hoc tests. RESULTS: Diabetic rats showed mechanical hyperalgesia, thermal hyperalgesia, and tactile allodynia. The former was unaffected by IL-6 treatment, whereas the latter two measures were corrected. Immunohistochemical staining of dorsal root ganglia for IL-6 did not reveal any changes with diabetes or treatment. The results showed that 22 and 17.4% slowing of sciatic motor and saphenous sensory nerve conduction velocities, respectively, with diabetes were improved by IL-6. Sciatic endoneurial perfusion was halved by diabetes and corrected by IL-6. A 40.6% diabetic deficit in maximal non-adrenergic, non-cholinergic relaxation of gastric fundus to nerve stimulation was unaffected by IL-6. Renal artery endothelium-dependent relaxation was halved by diabetes, the endothelium-derived hyperpolarizing factor (EDHF) component being severely attenuated. IL-6 did not affect nitric oxide-mediated vasorelaxation, but markedly improved EDHF responses. CONCLUSIONS: IL-6 improved aspects of small and large nerve fibre and vascular endothelium dysfunction in diabetic rats. The functional benefits related to increased nerve blood flow via an EDHF mechanism, and IL-6 could have therapeutic potential in diabetic neuropathy and vasculopathy, which should be further evaluated.

Correction of nitrergic neurovascular dysfunction in diabetic mouse corpus cavernosum by p38 mitogen-activated protein kinase inhibition.

Increased p38 mitogen-activated protein kinase (MAPK) in response to stress stimuli, including hyperglycemia, contributes to diabetic somatic neuropathy. However, effects on autonomic nerve and vascular function have not been determined. The aim of this study was to investigate the effects of the p38 MAPK inhibitor, LY2161793, on penile neurovascular function in streptozotocin-induced diabetic mice. Diabetes duration was 6 weeks and intervention LY2161793 treatment was given for the final 2 weeks. In vitro measurements on phenylephrine-precontracted corpus cavernosum revealed a 32% reduction in maximum nitrergic nerve-mediated relaxation with diabetes that was 74% corrected by LY2161793 treatment. Maximum nitric oxide-mediated endothelium-dependent relaxation to acetylcholine was 42% attenuated by diabetes and 88% restored by LY2161793. Moreover, treatment partially corrected a diabetic deficit in endothelium-independent relaxation to a nitric oxide donor. Thus, p38 MAPK inhibition corrects nitric oxide-dependent indices of diabetic erectile autonomic neuropathy and vasculopathy, a therapeutic approach potentially worthy of consideration for clinical trials.

An in vitro investigation of aorta and corpus cavernosum from eNOS and nNOS gene-deficient mice.

In order to ascertain the relative contribution of the endothelial and neuronal nitric oxide (NO) synthase isoforms on NO-dependent vascular and nerve function in vitro, aorta and corpus cavernosum from mice deficient in their expression (eNOS-/- and nNOS-/-) were isolated in organ baths for tension measurements. Agonist or electrical field stimulation (EFS) evoked nerve-mediated responses were compared against wild-type controls. In aortas from nNOS-/- mice, contraction responses to phenylephrine were increased. Conversely, endothelium-dependent relaxation (EDR) to acetylcholine (ACh) was decreased. In contrast, eNOS-/- aortas showed decreased sensitivity to phenylephrine and developed a flurbiprofen-sensitive contraction to ACh, and sensitivity to the NO-donor sodium nitroprusside was increased. In cavernosum from eNOS-/- and nNOS-/- mice, maximum contractions to phenylephrine and EFS, and relaxation responses to nitroprusside, were increased. As in aorta, ACh addition led to a contractile response in eNOS-/- cavernosum. Maximum EFS induced non-adrenergic, non-cholinergic (NANC) nerve-mediated relaxation was increased in eNOS-/-, whilst being decreased in nNOS-/- cavernosum. These data suggest that whilst NO-dependent vascular function is primarily eNOS mediated, and nerve function nNOS mediated, aorta function may be at least partially reliant on nNOS-related mechanisms. In addition, mechanisms of physiological compensation were observed, which require further study.