[Infants stage of rat development in behavioral parameters of depression-like state and pain response]

In the 7-8- and the 10-11-day old male rat pups born to dams exposed to an immobilization stress for the last week of pregnancy and to the dams exposed to no stress (control), behavioral parameters were studied: the level of depression in the test of forced swimming (the Porsolt's test) and 24 h after a long pain response during inflammation (the formalin test--a subcutaneous injection of 2.5% formalin into the hind leg plantar pad). In control pups, significant age-related changes in the forced swimming were revealed: the immobility time was longer in animals of the older age group, whereas no age differences were found in parameters of the persistent inflammatory pain and in flexing + shaking behavior. The prenatal stress produced an increase in the immobility time and the flexing + shaking behavior in the 7-8-day old, but not in the 10-11-day old pups. This resulted in elimination of the age differences in the immobility time in the prenatally stressed animals. Thus, use if different methodic approaches has allowed peculiarities in the parameters of the degree of depression and duration of the pain response at inflammation in the 7-8- and 10-11-day old rat pups, which indicates heterogeneity of the infant development stage that, according to literature data, includes in rats the period from the 5th to the 10th postnatal days.