In the presence of carnosine, anserine, histidine, imidazole and 7-nitro indazole, the early postdenervation depolarization of muscle of about 8 mV was significantly increased by 2.15-4.8 mV. The presence of the imidazole ring in the molecule is apparently necessary for this effect. These compounds also eliminated an NO-mediated protective effect of L-glutamate and carbachol on the depolarization of membrane potential. The presence of imidazole, 7-nitro indazole, carnosine and anserine did not significantly change the effect of an external NO donor, sodium nitroprusside. The structural and fuhctional similarity between imidazole derivatives and the known NO synthase inhibitor, 7-nitro indazole suggests that imidazole, carnosine and anserine might act by inhibiting NO production which is stimulated by glutamate and carbachol.
In this study we investigated whether also glycine fullfils the function as co-activator in glutamatergic activation of NMDA receptors in the neuronal apparatus of spontaneous motility in chick embryos.The successive application of glycine (5 or 10 mg/kg egg weight (e.w.) and glutamate (15 mg/kg e.w.) in a 10 min interval significantly increased the activation of spontaneous motility of 17-day-old chick embryos in comparison with the effect of glutamate alone. This effect did not depend on the order of application of the drugs. In 13-day-old embryos, glycine was ineffective in both doses. It is concluded from these results that the modulatory effect of glycine is evidently a later developmental acquisition (after day 15 of incubation) in the embryogenesis of NMDA-ergic activation of spontaneous motility in chick embryos similarly as glycinergic inhibition.
Epileptic afterdischarges (ADs) elicited by electrical stimulation of sensorimotor cortical area were used as a model to study the role of neurotransmitter systems in cortical seizures in three age groups of developing rats. Drugs augmenting inhibition mediated by GABAA receptors were found to suppress ADs in all age groups, their activity was usually more marked in younger than in 25-day-old rat pups. Drugs potentiating GABAB receptors exhibit lower efficacy and more complicated developmental profile than GABAA-ergic drugs. Effects of an antagonist of GABAB receptor – marked prolongation of ADs in all three age groups – suggest an important role of GABAB receptors in arrest of cortical seizures. Drugs affecting glutamate receptors exhibit variable effects, usually better expressed in older animals than in 12-day-old ones. No specific role for ionotropic as well as metabotropic glutamate receptors could be predicted. Activation of adenosinergic inhibitory modulatory system also exhibited anticonvulsant action in the present model. All three neurotransmitter systems probably participate in mechanisms of generation, maintenance and arrest of cortical seizures., P. Mareš, H. Kubová., and Obsahuje bibliografii a bibliografické odkazy