Activation of mGlu3 Receptors Stimulates the Production of GDNF in Striatal Neurons

Metabotropic glutamate (mGlu) receptors have been considered potential targets for the therapy of experimental parkinsonism. One hypothetical advantage associated with the use of mGlu receptor ligands is the lack of the adverse effects typically induced by ionotropic glutamate receptor antagonists, such as sedation, ataxia, and severe learning impairment. Low doses of the mGlu2/3 metabotropic glutamate receptor agonist, LY379268 (0.25–3 mg/kg, i.p.) increased glial cell line-derived neurotrophic factor (GDNF) mRNA and protein levels in the mouse brain, as assessed by in situ hybridization, real-time PCR, immunoblotting, and immunohistochemistry. This increase was prominent in the striatum, but was also observed in the cerebral cortex. GDNF mRNA levels peaked at 3 h and declined afterwards, whereas GDNF protein levels progressively increased from 24 to 72 h following LY379268 injection. The action of LY379268 was abrogated by the mGlu2/3 receptor antagonist, LY341495 (1 mg/kg, i.p.), and was lost in mGlu3 receptor knockout mice, but not in mGlu2 receptor knockout mice. In pure cultures of striatal neurons, the increase in GDNF induced by LY379268 required the activation of the mitogen-activated protein kinase and phosphatidylinositol-3-kinase pathways, as shown by the use of specific inhibitors of the two pathways. Both in vivo and in vitro studies led to the conclusion that neurons were the only source of GDNF in response to mGlu3 receptor activation. Remarkably, acute or repeated injections of LY379268 at doses that enhanced striatal GDNF levels (0.25 or 3 mg/kg, i.p.) were highly protective against nigro-striatal damage induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine in mice, as assessed by stereological counting of tyrosine hydroxylase-positive neurons in the pars compacta of the substantia nigra. We speculate that selective mGlu3 receptor agonists or enhancers are potential candidates as neuroprotective agents in Parkinson's disease, and their use might circumvent the limitations associated with the administration of exogenous GDNF

Perinatal asphyxia: current status and approaches towards neuroprotective strategies, with focus on sentinel proteins

Delivery is a stressful and risky event menacing the newborn. The mother-dependent respiration has to be replaced by autonomous pulmonary breathing immediately after delivery. If delayed, it may lead to deficient oxygen supply compromising survival and development of the central nervous system. Lack of oxygen availability gives rise to depletion of NAD+ tissue stores, decrease of ATP formation, weakening of the electron transport pump and anaerobic metabolism and acidosis, leading necessarily to death if oxygenation is not promptly re-established. Re-oxygenation triggers a cascade of compensatory biochemical events to restore function, which may be accompanied by improper homeostasis and oxidative stress. Consequences may be incomplete recovery, or excess reactions that worsen the biological outcome by disturbed metabolism and/or imbalance produced by over-expression of alternative metabolic pathways. Perinatal asphyxia has been associated with severe neurological and psychiatric sequelae with delayed clinical onset. No specific treatments have yet been established. In the clinical setting, after resuscitation of an infant with birth asphyxia, the emphasis is on supportive therapy. Several interventions have been proposed to attenuate secondary neuronal injuries elicited by asphyxia, including hypothermia. Although promising, the clinical efficacy of hypothermia has not been fully demonstrated. It is evident that new approaches are warranted. The purpose of this review is to discuss the concept of sentinel proteins as targets for neuroprotection. Several sentinel proteins have been described to protect the integrity of the genome (e.g. PARP-1; XRCC1; DNA ligase IIIα; DNA polymerase β, ERCC2, DNA-dependent protein kinases). They act by eliciting metabolic cascades leading to (i) activation of cell survival and neurotrophic pathways; (ii) early and delayed programmed cell death, and (iii) promotion of cell proliferation, differentiation, neuritogenesis and synaptogenesis. It is proposed that sentinel proteins can be used as markers for characterising long-term effects of perinatal asphyxia, and as targets for novel therapeutic development and innovative strategies for neonatal care

Increased tumor cell multiplication after radiofrequency lesions in median hypothalamus in the mouse and rat

A significant increase of cell multiplication in inoculated ascitic and solid tumors was demonstrated in both DBA/2 and C57BL/6 mice as well as in Wistar rats after radiofrequency lesions in the median hypothalamus (ventromedial and dorsomedial nuclei; part of arcuate nucleus). The following tests were performed: Mitotic and metaphasic index, doubling time of tumor, incorporation of tritiated thymidine into DNA, cell cycle parameters and growth fraction. The increased rate of cell proliferation measured was predominantly due to the higher speed of DNA biosynthesis with a minor contribution by an increase of the growth fraction. In the animals with hypothalamic lesions we demonstrated a slight decrease in the secretory activity of the adenohypophysis. Because it is generally stated that failure of hypophysis function hinders cell multiplication in normal and neoplastic tissues, we think that heightened cell proliferation after hypothalamic lesions is due to suppression of an inhibitory mechanism located in the hypothalamus and which is independent of the hypophysis

Recovery of damaged skeletal muscle in mdx mice through low-intensity endurance exercise

The lack of dystrophin in mdx mice leads to cycles of muscle degeneration and regeneration processes. Various strategies have been proposed in order to reduce the muscle-wasting component of muscular dystrophy, including implementation of an exercise programme. The aim of this study was to examine how low-intensity endurance exercise affects the degeneration-regeneration process in dystrophic muscle of male mdx mice. Mice were subjected to low-intensity endurance exercise by running on a motorized Rota-Rod for 5 days/week for 6 weeks. Histomorphological analysis showed a significant reduction of measured inflammatory-necrotic areas in both gastrocnemius and quadriceps muscle of exercised mdx mice as compared to matched sedentary mdx mice. The degenerative-regenerative process was also evaluated by examining the protein levels of connexin 39 (Cx39), a specific gene expressed in injured muscles. Cx39 was not detected in sedentary wild type mice, whereas it was found markedly increased in sedentary mdx mice, revealing active muscle degeneration-regeneration process. These Cx39 protein levels were significantly reduced in muscles of mdx mice exercised for 30 and 40 days, revealing together with histomorphological analysis a strong reduction of degeneration process in mice subjected to low-intensity endurance exercise. Muscles of exercised mdx mice did not show significant changes in force and fatigue resistance as compared to sedentary mdx mice. Overall in this study we found that specific low-intensity endurance exercise induces a beneficial effect probably by reducing the degeneration of dystrophic muscle

Identification and functional expression of HCx31.9, a novel gap junction gene

By combining in silico and bench molecular biology methods we have identified a novel human gap junction gene that encodes a protein designated HCx31.9. We have determined its human chromosomal location and gene structure, and we have identified a putative mouse ortholog, mCx30.2. We have observed the presence of HCx31.9 in human cerebral cortex, liver, heart, spleen, lung, and kidney and the presence of mCx30.2 in mouse cerebral cortex, liver and lung. Moreover, preliminary data on the electrophysiological properties of HCx31.9 have been obtained by functional expression in paired Xenopus oocytes and in transfected N2A cells.link_to_subscribed_fulltex

Altered gastrointestinal motility in an animal model of Lesch-Nyhan disease

Mutations in the HGPRT1 gene, which encodes hypoxanthine-guanine phosphoribosyltransferase (HGprt), housekeeping enzyme responsible for recycling purines, lead to Lesch-Nyhan disease (LND). Clinical expression of LND indicates that HGprt deficiency has adverse effects on gastrointestinal motility. Therefore, we aimed to evaluate intestinal motility in HGprt knockout mice (HGprt). Spontaneous and neurally evoked mechanical activity was recorded in vitro as changes in isometric tension in circular muscle strips of distal colon. HGprt tissues showed a lower in amplitude spontaneous activity and atropine-sensitivity neural contraction compared to control mice. The responses to carbachol and to high KCl were reduced, demonstrating a widespread impairment of contractility. L-NAME was not able in the HGprt tissues to restore the large amplitude contractile activity typical of control. In HGprt colon, a reduced expression of dopaminergic D1 receptor was observed together with the loss of its tonic inhibitory activity present in control-mice. The analysis of inflammatory and oxidative stress in colonic tissue of HGprt mice revealed a significant increase of lipid peroxidation associated with over production of oxygen free radicals. In conclusion, HGprt deficiency in mice is associated with a decrease in colon contractility, not dependent upon reduction of acetylcholine release from the myenteric plexus or hyperactivity of inhibitory signalling. By contrast the increased levels of oxidative stress could partially explain the reduced colon motility in HGprt mice. Colonic dysmotility observed in HGprt mice may mimic the gastrointestinal dysfunctions symptoms of human syndrome, providing a useful animal model to elucidate the pathophysiology of this problem in the LND