Response of the Adrenal Cortex of the Neonatal Rat after Subjection to Stress

IT has been generally accepted that the infantile rat is incapable of an adreno-cortical response to stress in the first few days of life. Among the criteria used to support this contention are: adrenal ascorbic acid depletion 1–9 , adrenal corticosterone levels 6–8 , and plasma corticosterone levels 9 . Schapiro 7 has referred to this as an absolute “stress-non-responsive period” (SNR period) and to the period which follows as the relative SNR period. The latter is characterized by the differential onset of the adreno-cortical response to various stimuli. The absolute period is reported as lasting for at least the first 4 days of life, and the relative period which follows may last until the sixteenth day. Levine 10 has reported a significant increase in plasma corticosterone in the 3 day old rat following treatment with adrenocorticotrophic hormone or electric shock if the animal has previously received infantile stimulation. Furthermore, several other investigations have indicated that the SNR period is affected by experimental manipulation such as adrenalectomy of the mother before parturition 2 and unilateral ligature of the Fallopian tube of the mother before mating 3 .