8-bromocyclic-gmp and Nerve-Degeneration

Axotomised dorsal root ganglia (DRG) neurons show an increased expression of neuronal nitric oxide synthase (nNOS) compared with neurons from the intact ganglia. Increased nNOS expression resulted in synthesis of nitric oxide (NO) and the subsequent activation of cGMP in satellite glia cells surrounding the DRG neuron soma. In dissociated DRG we have demonstrated that the increase in nNOS expression is regulated by nerve growth factor and that the subsequent inhibition of NO production or cGMP synthesis precipitates apoptosis of neurons expressing nNOS and some non-nNOS neurons. Hence, NO or the NO-cGMP cascade appears to have a neuroprotective action in trophic factor-deprived DRG neurons. In the present study, using immunocytochemistry, we have investigated some of the factors associated with apoptosis that are activated when nNOS activity is blocked with NOS inhibitor in DRG neurons in vitro. Marked elevation of bax was observed within a few hours of NOS inhibition in nNOS containing neurons, whereas pretreatment of cultures with l-arginine completely abolished this effect in almost all nNOS neurons and 8-bromo-cGMP in some neurons. The apoptosis precipitated by NOS inhibition was also partially prevented by a number of caspase inhibitors; of those a caspase-9 blocker was the most effective. These observations further support the neuroprotective role of NO/NO-cGMP in stressed DRG neurons in an autocrine fashion that involves the suppression of bax, caspase-3 and -9 activation.

Topics: Animals; Animals, Newborn; Apoptosis; Arginine; Autocrine Communication; bcl-2-Associated X Protein; Caspase Inhibitors; Caspases; Cells, Cultured; Cyclic GMP; Enzyme Inhibitors; Female; Ganglia, Spinal; Immunohistochemistry; Male; Nerve Degeneration; Neurons, Afferent; Nitric Oxide; Nitric Oxide Synthase; Peripheral Nervous System Diseases; Proto-Oncogene Proteins; Proto-Oncogene Proteins c-bcl-2; Rats; Signal Transduction; Stress, Physiological

The microdialysis technique was used to study the effect of nitric oxide synthase (NOS) activity on taurine release. Taurine release was characterized in rat striatum that was excitotoxically lesioned compared to normal conditions. The basal taurine level of the dialysate decreased during quinolinate (QUIN) lesion in parallel to the cell degeneration process. The K+-stimulated taurine concentration also decreased during QUIN-lesion, but to an extent that was different from that of basal values. K+-stimulated taurine levels were further markedly lowered by coapplication of the NOS inhibitor L-NAME in control and in lesioned animals up to 30 days after QUIN-injection. Postdegenerative tissue did not show any NOS-dependency in K+-induced taurine release. We conclude that a substantial part of K+-induced taurine release depends on NOS-activity both in normal brain tissue and in excitotoxically induced neurodegeneration. The main source of K+-induced taurine release in control rats are neurons but in lesioned animals are activated astroglial cells.

Topics: Animals; Corpus Striatum; Cyclic GMP; Male; Microdialysis; Nerve Degeneration; Neurotoxins; NG-Nitroarginine Methyl Ester; Nitric Oxide Synthase; Potassium Chloride; Quinolinic Acid; Rats; Rats, Wistar; Taurine; Time Factors