Retarded growth and deficits in the enteric and parasympathetic nervous system in mice lacking GFR alpha2, a functional neurturin receptor

Glial cell line-derived neurotrophic factor (GDNF) and a related protein, neurturin (NTN), require a GPI-linked coreceptor, either GFR alpha1 or GFR alpha2, for signaling via the transmembrane Ret tyrosine kinase. We show that mice lacking functional GFR alpha2 coreceptor (Gfra2-/-) are viable and fertile but have dry eyes and grow poorly after weaning, presumably due to malnutrition. While the sympathetic innervation appeared normal, the parasympathetic cholinergic innervation was almost absent in the lacrimal and salivary glands and severely reduced in the small bowel. Neurite outgrowth and trophic effects of NTN at low concentrations were lacking in Gfra2-/- trigeminal neurons in vitro, whereas responses to GDNF were similar between the genotypes. Thus, GFR alpha2 is a physiological NTN receptor, essential for the development of specific postganglionic parasympathetic neurons.

Nerve growth factor and brain-derived neurotrophic factor mRNAs are regulated in distinct cell populations of rat heart after ischaemia and reperfusion

Neurotrophins play a crucial role in the development of the peripheral nervous system and their mRNAs are often regulated after several types of tissue injury. This study has investigated the regulation of nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), and neurotrophin-3 (NT-3) mRNAs 30 min after myocardial ischaemia followed by reperfusion, by northern blotting, and in situ hybridization in a rat model. Between 2 and 120 h of reperfusion, Ngf mRNA levels showed two- to four-fold up-regulation compared with sham-operated hearts. Scattered Ngf-expressing cells, probably pericytes, were detected in the viable border zone of the myocardium in close association with capillaries, venules, and arterioles. In addition, diffuse Ngf expression was seen in the infarct area after 120 h of reperfusion. Bdnf mRNA showed transient up-regulation after 2 and 5 h of reperfusion and remained at control levels thereafter. Bdnf was expressed in the myocytes of the viable border zone. Nt-3 expression showed no significant changes compared with sham-operated hearts. These results suggest a role for NGF and/or BDNF in the pathogenesis of reperfusion injury or in the alterations of cardiac sensory and sympathetic neuronal function after myocardial ischaemia and reperfusion.

Neurturin is a neurotrophic factor for penile parasympathetic neurons in adult rat

Neurturin (NRTN), a member of the GDNF family of neurotrophic factors, promotes the survival and function of several neuronal populations in the peripheral and central nervous system. Recent gene ablation studies have shown that NRTN is a neurotrophic factor for many cranial parasympathetic and enteric neurons, whereas its significance for the sacral parasympathetic neurons has not been studied. NRTN signals via a receptor complex composed of the high-affinity binding receptor component GFRalpha2 and the transmembrane tyrosine kinase Ret. The aim of this study was to determine whether NRTN could be an endogenous trophic factor for penis-projecting parasympathetic neurons. NRTN mRNA was expressed in smooth muscle of penile blood vessels and corpus cavernosum in adult rat as well as in several intrapelvic organs, whereas GFRalpha2 and Ret mRNAs were expressed in virtually all cell bodies of the penile neurons, originating in the major pelvic ganglia. (125)I-NRTN injected into the shaft of the penis was retrogradely transported into the major pelvic and dorsal root ganglia. Mice lacking the GFRalpha2 receptor component had significantly less nitric oxide synthase-containing nerve fibers in the dorsal penile and cavernous nerves. In conclusion, these data suggest that NRTN acts as a target-derived survival and/or neuritogenic factor for penile erection-inducing postganglionic neurons.

The messenger RNAs for both glial cell line-derived neurotrophic factor receptors, c- ret and GDNFRα, are induced in the rat brain in response to kainate-induced excitation

Glial cell line-derived neurotrophic factor (GDNF) has two receptors, receptor-tyrosine kinase c-ret and glycosylphosphatidylinositol-linked cell surface receptor GDNFRalpha. Kainate-induced seizures, a widely studied model of neuronal plasticity and human epilepsy, have been shown to increase gene expression of several trophic factors, including GDNF, in the rat hippocampus. Here we show that systemic kainate-induced excitation leads to a transient increase of both c-ret and GDNFRalpha messenger RNAs in the rat brain. Northern analysis demonstrated that, in the hippocampus, the maximal 2.5-fold increase of c-ret and four-fold increase of GDNFRalpha messenger RNAs was observed after 12 h of kainate injection, in contrast to GDNF messenger RNA, which reaches its maximum in 4-6 h. The blocking of de novo protein synthesis by cycloheximide inhibited the induction of GDNF receptors by kainate, whereas blocking of the N-methyl-D-aspartate-type glutamate receptors by the antagonist dizocilpine maleate did not significantly alter the response. Thus, GDNF receptor messenger RNA increase by kainate depends on protein synthesis, but is not mediated by the N-methyl-D-aspartate receptor. GDNFRalpha and c-ret show distinct, but partially overlapping, patterns of expression in the brain after kainate treatment. GDNFRalpha messenger RNA was prominently induced in the dentate gyrus of the rat hippocampus, less in the habenular and reticular thalamic nuclei and cerebral cortex as revealed by in situ hybridization. C-ret transcripts were induced in the hilus of the hippocampus, several thalamic and amygdala nuclei and in superficial layers of the piriform cortex. These data suggest that GDNF and its receptors may play a local role in neuronal plasticity and in neuronal protection following epileptic insults.

GDNF family receptors in the embryonic and postnatal rat heart and reduced cholinergic innervation in mice hearts lacking ret or GFRalpha2

Members of the GDNF family, which are important during peripheral nervous system development and kidney organogenesis, signal via Ret and GFRalpha receptors. Here we have studied their possible role in heart development. Gfra1 was expressed in the endocardial cushion mesenchyme at E12 and later, in the developing and mature valves, and in the walls of the aorta and the pulmonary trunk. Gfra2 was expressed in the outer layers of the aorta and pulmonary trunk and in the valves at E18-P60. Endocardial cells showed moderate Gfra2 mRNA and protein expression between E12 and E15. Gfra3 mRNA was detected, mainly postnatally, in scattered cells of the atria and the great vessels. In embryonic and postnatal rat cardiac ganglia, Ret and Gfra2 transcripts were seen in the neurons, whereas Gfra1 and Gfra3 mRNA were preferentially found in non-neuronal cells within the ganglia. GFRalpha2 immunoreactivity was seen in both cardiac ganglion neurons and their nerve fibers. There were no obvious non-neuronal defects in hearts of Ret-, GFRalpha1-, or GFRalpha2-deficient mice, suggesting that these receptors are not essential for gross cardiac development. However, E18 Ret-deficient mice exhibited a reduced volume of cardiac ganglia and cholinergic innervation of the ventricular conduction system. Moreover, adult Gfra2(-/-) mice showed reduced cholinergic innervation by 40% in their ventricles and by 60% in the ventricular conduction system. These findings indicate that GFRalpha2/Ret signaling is required for normal cholinergic innervation of heart.

Glial cell line-derived neurotrophic factor is expressed in penis of adult rat and retrogradely transported in penile parasympathetic and sensory nerves

Glial cell line-derived neurotrophic factor (GDNF), a member of the GDNF family of neurotrophic factors, promotes the survival and function of several neuronal populations in the peripheral and central nervous system. In the present study, expression of GDNF mRNA in the shaft of adult rat penis is demonstrated. In situ hybridization revealed GDNF mRNA expression in cells lying in the narrow zone between the tunica albuginea and the cavernous tissue. Most subtunical cells exhibited immunoreactivity for vimentin and S100 beta, but they did not stain for smooth muscle alpha actin or PGP9.5. This suggests that the GDNF mRNA-expressing cells may have a mesenchymal origin. Also retrograde axonal transport of intracavernously injected 125I-labeled GDNF in penile parasympathetic and sensory neurons is shown. The transport was inhibited by excess unlabeled GDNF, whereas excess cytochrome c had no effect. This is in agreement with the view that the transport was mediated by binding to specific receptors located on axon terminals. In addition, this study demonstrates expression of GDNF family receptor-alpha 3 (GFR alpha 3) mRNA in most adrenergic, but only in a minor part (5.3%) of the penis-projecting adult rat major pelvic ganglion neurons, as well as in almost half (45.6%) of the penile S1 dorsal root ganglion neurons. In conclusion, the present data suggest that GDNF may act as a neurotrophic factor for subpopulations of adult rat penile parasympathetic and sensory neurons.

Neurotrophin-3 is a target-derived neurotrophic factor for penile erection-inducing neurons

The aim of this study was to determine whether the neurotrophins nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), and neurotrophin (NT)-3 could act as endogenous target-derived trophic factors for erection-inducing, i.e. penis-projecting major pelvic ganglion (MPG) neurons, and/or penile sensory neurons in adult rat. This was accomplished by studying the expression of NT mRNAs in the penis and their cognate receptors in the MPG and dorsal root ganglia (DRGs), and the retrograde axonal transport of radioiodinated NTs injected into the corpora cavernosa. Northern hybridization showed that NGF, BDNF, and NT-3 mRNAs are expressed in the shaft of the penis. In situ hybridization combined with usage of the retrograde tracer Fluoro-Gold showed that TrkC and p75 receptors are expressed in penis-projecting neurons of the MPG whereas the mRNAs for TrkA and TrkB receptors were undetectable. However, all the NT receptor mRNAs were expressed in penile sensory neurons of sacral level 1 (S1) DRG. (125)I-NT-3 injected into the shaft of the penis was retrogradely transported into the MPG and S1 DRG, whereas radioiodinated NGF and BDNF were transported specifically into the S1 DRG, thus confirming the existence of functional NT receptors in these penile neurons. In conclusion, these data suggest that NT-3 may act as a target-derived neurotrophic factor for both erection-inducing and penile sensory neurons, whereas NGF and BDNF may be more important for the sensory innervation of the penis.