Maturation of somatomotor responses to strychnine in the albino rat.

1. The maturation of the convulsogenic activity of the caudal brainstem and spinal cord in the developing albino rat was studied by intraperitoneal injections of strychnine sulphate.2. The observed responses were classed as hyperexcitability and hypertonic responses, graded 1 to 4. The complete tonic seizure (grade 4 hypertonic reaction, strychnine tetanus, maximal response) was obtained in all age groups, from birth to adulthood. The responses were grouped in sequences, and two patterns were distinguished: an infant one (from birth to 3 weeks) and an adult one (from 3 weeks on).3. All doses varied according to age. The curve obtained for the median convulsive dose falls into two parts: descending, from birth to 3 weeks, and ascending, from 3 weeks on. Each part corresponded to a sequence pattern, the descending one to the infant pattern, and the ascending one to the adult pattern.4. From these patterns and the corresponding median effective doses, three stages of the convulsogenic maturation of the spinal cord were distinguished: immaturity, pharmacological maturity and convulsogenic maturity.5. It is suggested that the mechanism responsible for the complete tonic seizure is fully functional from birth, while that responsible for clonic seizure only reaches full maturity at 3 weeks of age.