The effects of NMDA on spontaneous motility and its development in chick embryos

The effects of acute and chronic systemic application of N-methyl-D-aspartate (NMDA) on the spontaneous motor activity, its development and sensitivity to some drugs connected with the function of the NMDA-receptor were studied in chick embryos aged from 4 to 19 days of incubation. 1. The acute application of NMDA in doses from 20 to 50 mg/kg e.w. evoked in 15- and 17-day-old embryos the paroxysmal activation of spontaneous motility in chick embryos both normal and chronically decapitated (i.e. in spinal preparations). After chronic pre-treatment by ketamine (7.17 mg/kg e.w./24 h, from day 4 to day 12 or 16 of incubation) the activatory effects of acute NMDA application decreased and amounted two thirds of the value in control embryos. 2. As a result of damaged development of central motor generator the chronic application of NMDA (the average dosis of 2.55 +/- 0.25 mg/kg e.w./24 h) from day 4 of incubation to day 12 or 16 resulted in 17-day-old embryos in reduction of resting spontaneous motility on one hand, and in changed reactivity to acute application of NMDA (20 mg/kg e.w.) and ketamine (12.5 mg/kg e.w.) on the other hand: the activatory effect of NMDA was augmented, whereas the inhibitory effect of ketamine was diminished. On the contrary the response of spontaneous motility to acute application of glycine (100 mg/kg e.w.) and glutamate (15 mg/kg e.w.) remained unchanged. 3. Presented results are evaluated as the proof of possible participation of the NMDA-ergic mechanism in the genesis of embryonic spontaneous motility.