Nitric oxide down-regulates brain-derived neurotrophic factor secretion in cultured hippocampal neurons

Abstract

The regulation of neurotrophin (NT) secretion is critical for many aspects of NT-mediated neuronal plasticity. Neurons release NTs by activity-regulated secretion pathways, initiated either by neurotransmitters and͞or by existing NTs by a positive-feedback mechanism. This process depends on calcium release from intracellular stores. Little is known, however, about potential pathways that down-regulate NT secretion. Here we demonstrate that nitric oxide (NO) induces a rapid down-regulation of brain-derived neurotrophic factor (BDNF) secretion in cultured hippocampal neurons. Similar effects occur by activating a downstream target of intracellular NO, the soluble guanylyl cyclase, or by increasing the levels of its product, cGMP. Furthermore, down-regulation of BDNF secretion is mediated by cGMP-activated protein kinase G, which prevents calcium release from inositol 1,4,5-trisphosphate-sensitive stores. Our data indicate that the NO͞cGMP͞protein kinase G pathway represents a signaling mechanism by which neurons can rapidly down-regulate BDNF secretion and suggest that, in hippocampal neurons, NT secretion is finely tuned by both stimulatory and inhibitory signals.N eurotrophins (NTs), such as nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), neurotrophin-4͞5 (NT-4͞5), and neurotrophin-3 (NT-3), regulate neuronal survival and differentiation during embryonic development (1, 2). In addition to their trophic role, NTs are thought to participate in certain brain functions such as modulation of synaptic transmission and memory formation (3-6). NTs have been shown to modulate synaptic transmission across a broad temporal spectrum ranging from short-term modulation, which occurs in the order of seconds to minutes (7-17), to a prolonged effect that persists for many hours, such as the long-term potentiation (LTP) (18-23) or long-term depression (24-27) response. In fact, NTs are required for the maintenance of LTP in hippocampal slices, because inhibition of BDNF signaling by using receptor bodies applied early after LTP induction restored potentiated synaptic transmission to baseline levels (22). In addition, pretreatment of hippocampal neuron slices with anti-NT receptor antiserum prevented the late phase of the LTP (22). It has been suggested that BDNF concentrations in CA3͞ CA1 hippocampal slices must reach a critical threshold level to initiate and maintain the LTP response (18). This phenomenon has been demonstrated in heterozygous BDNF-defective mice (18,20) that, having impaired endogenous NT production, require either the exogenous administration (20) or local reexpression (19) of BDNF to initiate the LTP response. These observations emphasize the important role played by NTs in modulating synaptic activity and the need to understand better the mechanisms that regulate NT secretion.Recent studies have investigated how neuronal activity can modulate NT secretion. NGF and BDNF secretion is induced in hippocampal slices and cultured hippocampal neurons in response to excitatory neurotransmitters ...

Induction of long-term potentiation and depression is reflected by corresponding changes in secretion of endogenous brain-derived neurotrophic factor

“…This interpretation is supported by previous experiments in our laboratory, showing that BDNF secretion in hippocampal cultures is rapidly induced by BDNF by means of a mechanism involving TrkB-mediated IP3 formation (23) and subsequent calcium release from intracellular stores (21,23). This positive feedback might persist until counterregulatory mechanisms come into play, such as internalization of TrkB receptors and͞or a reduction of BDNF secretion induced by nitric oxide3protein kinase G signaling (30).…”

“…A comparable rate of decrease in BDNF concentrations was observed in the absence of electrical stimulation (to 94 Ϯ 3% after 20 min and to 82 Ϯ 2% after 100 min; data not shown), indicating that endogenous BDNF secretion occurs spontaneously from the slice preparation. Basal release of endogenous BDNF, analyzed previously in hippocampal neurons (19,21,22,30), results from combined ''constitutive'' and ''regulated'' secretion. The regulated component of this pathway is an activity-dependent process that includes both stimulatory and inhibitory signals (30).…”

“…Basal release of endogenous BDNF, analyzed previously in hippocampal neurons (19,21,22,30), results from combined ''constitutive'' and ''regulated'' secretion. The regulated component of this pathway is an activity-dependent process that includes both stimulatory and inhibitory signals (30). To evaluate whether and to what extent the regulated pathway plays an essential role in our slice preparations, the sodium channel blocker tetrodotoxin (TTX; 1 M) was added to the perfusion medium.…”

Endothelial Nitric Oxide Synthase Regulates Brain-Derived Neurotrophic Factor Expression and Neurogenesis after Stroke in Mice

“…However, Canossa et al (2002) reported in studies with cultured embryonic hippocampal neurons that L-N--nitro-L-arginine methyl ester, a nonspecific NOS inhibitor, increased BDNF secretion, and an NO donor decreased BDNF secretion. In contrast to our in vivo studies in adult cerebral tissue, their studies were performed in vitro with embryonic cells.…”

“…Recent studies show that NO regulates BDNF expression, which affects neural progenitor cell proliferation and differentiation in the mammalian brain (Canossa et al, 2002;Cheng et al, 2003). NO mediates BDNFinduced growth-associated protein 43 (GAP-43) mRNA expression (Klocker et al, 2001).…”