Expression of tissue kallikrein mRNA in developing rat brains

Immunoreactive kallikrein has been demonstrated in the neurons of both prenatal and adult rat brains. However, the preferential site is quite different between the prenatal and adult brains, i.e., the former is mainly in the nuclei, and the latter is in the cell bodies and processes. In this study, the intensity of kallikrein mRNA expression was investigated in prenatal and postnatal rat brains by reverse transcription polymerase chain reaction (RT-PCR). A marked progressive increase in kallikrein mRNA expression was observed during the prenatal and early postnatal stage, with the maximum level at postnatal days 0 and 1 (P0 to P1). This helps to explain the previous immunohistochemical findings in which a strong immuno-intensity of kallikrein in the neurons of prenatal and newborn rat brains was found as compared with adult rats. The function(s) of kallikrein expressed in the neurons in the developing stages is unclear, but the role(s) must be different from that of the adult because of the unequivocal difference in its location between them. It is thus possible that kallikrein has certain unknown important role(s) in the neuronal physiology acting on nuclear protein(s) in the developing stages, although the possibility of function via kinin receptors cannot be excluded at present.