Developmental changes of neuromedin U and galanin-like peptide gene expressions in the rat pituitary : an analysis by in situ hybridization histochemistry

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Development of GALP in the PPThe present study first demonstrated that the GALP mRNA in the PP exhibited from the day of birth and rose to adult level during neonatal period, while that in the ARC was expressed from late neonatal period and markedly increased between weaning and pubertal period. The regulatory mechanism of the GALP in the PP might be different from that in the ARC during postnatal development. The GALP system in the PP develops in a relatively mature, although that in the ARC is still immature in the neonatal period.The GALP in the PP is important in the regulation of plasma osmolality and neurohypophysial hormones in the adult animals. Development of GALP in the PP may be associated with development of the osmoregulatory mechanism of the body fluid, which develops in a relatively mature even in the early neonates.Development of NMU in the APWe also first demonstrated that the NMU mRNA in the AP was detected at relatively high level at the day of birth. Birth is accompanied with the infant's HPA axis activation in response to stresses with the transition from intra-uterine to extra-uterine environment. This high level of NMU expression at the time of birth may have a role in the HPA axis activation to adapt the environmental changes.During development, the HPA axis is normally suppressed between postnatal day 4 and 14, which is so-called “ stress-hyporesponsive" period (SHRP). The decrease in the NMU mRNA expression at postnatal day 8 might be responsible to the inhibition of the HPA axis activity during SHRP. After postnatal day 14, the NMU mRNA in the AP gradually increased throughout postnatal development. It might be related with the maturation of HPA axis during postnatal development.In conclusion, development of the NMU and GALP, which showed different patterns in each lobe in pituitary, may be associated with the specific functional significance in each peptide during postnatal development.