An attempt to activate the spontaneous motility in chick embryos with tetanus toxin.

The effect of tetanus toxin on spontaneous motor activity was studied in chick embryos between the 11th and 19th day of incubation. The toxin--dose 20 mg/kg egg weight ( = 2.86 X 10(3) mouse MLD) in 25 microliters isotonic NaCl solution--was injected into the tibial or the wing muscles. Tetanus toxin induced demonstrable activation of embryonic motility from the 15th day of incubation onwards. Activation attained 155-200% of resting activity. The activating effect was manifested for the first time by motor paroxysms in 17-day and particularly 19-day embryos. Tetanus toxin activation was effectively depressed by glycine (100 mg/kg e.w.) and GABA (100 mg/kg e.w.), the former having a stronger effect than the latter. The effect of tetanus toxin on spinal embryos was relatively more pronounced, while the depressant effect of the inhibitory amino acids (especially glycine) was weaker. The results are evaluated as further evidence that central inhibitory mechanisms are connected up in regulation of the spontaneous motor output activity of chick embryos on about the 15th day of incubation.