Study On The Effect And Mechanism Of Quinolinic Acid On Primarily Cultured Cortical Neurons

【Objective】To investigate the effects of quinolinic acid (QUIN) on the primarily cultured cortical neurons and involved mechanisms in order to find the latent targets for the development of new neuroprotective agents.【Methods】The effects of QUIN and MCLM used alone or in combination on the growth, activity, and integrality of primarily cultured neurons from the cereberal cortex of newborn mice were studied by means of pathomorphology, biochemistry, immunohistochemistry, laser scanning confocal microscope, and HPLC technique, and the relationship between the effects above and excitatory amino acids and their receptors, cytokines, intracellular calcium, as well as oxidative stress were analyzed.【Results】1. There existed a significant difference at the level of the quality related to the effects of QUIN with various concentrations on the cortical neurons. 10μmol/L and 100μmol/L QUIN made the dendrite and axon of neurons more flourishing, intercellular net work thicker, MTT value higher, and amount of LDH leakage less, compared with control. No significant change of neurons was found when 500μmol/L and 1 mmol/L were used. However, high concentrations of QUIN (3 mmol/L and 5 mmol/L) induced serious damage to the neurons in concentration-depennt manner: made cell body swollen, even disrupted with the loss of cellular refractability and numbers, as well as MTT and LDH leakage decreased.2. MCLM alone showed the damage to the neurons in concentration- and time-dependant manners. The most distinct injury was observed when 1:1concentration of MCLM was used. There were significantly pathological changes about morphology,numbers,viability,and integrality of neurons even as early as 3 h after 1:1MCLM was given. On the contrary,1:30 MCLM had no effect on the cultured neurons.3. 1:30MCLM increased the toxical effects of QUIN on the neurons when they were used in combination,which could be shown that the beneficial effects of low concentration QUIN(10 and 500μmol/L)on neuron growth were abolished,even the obviously toxical effects of QUIN occurred at the levels of 500μmol/L and 1 mmol/L.4. Pretreatments of either AP-5 or DNQX did not interfere with the beneficial effects of 10μmol/L QUIN on the neuron growth,but the former markedly diminished the toxicity to the neurons from 5 mmol/L QUIN and combination of 1:30 MCLM with 1 mmol/L QUIN and the later did not have same effects as the former.5. Both of 5 mmol/L QUIN and combination of 1:30MCLM with 1 mmol/L QUIN elevated the levels of TNF-α,IL-1β,IL-10,Glu,Asp,MDA,and intracellular calcium,and decreased activity of SOD without any influences on the level of IL-6. Pretreatment of AP-5 significantly prevented the changes of the parameters above. No influences were observed in the groups of DNQX pretreatment except blunting the elevation of intracellular calcium.【Conclusion】1. There exists a dualism about the effects of QUIN on the growth of cultured neurons: beneficial effects at the concentrations lower than 100μmol/L and toxical effects at the high concentrations more than 3 mmol/L.2. MCLM containing some substances alone or in combination with QUIN strongly causes the damage to the neurons.3. Unlikely AMPA and kainite receptors, the NMDA receptor and release of excitatory amino acids (EAAs), as well as secretions of TNF-αand IL-1βare considered to be responsible for the neurotoxicity induced by 5 mmol/L QUIN or 1 mmol/L QUIN plus 1:30 MCLM.4. The interrelation between the beneficial effects of low concentration QUIN on the neuron growth and EAAs and their receptors fails to be evidenced. The mechanism needs to be illustrated.