Orexin/hypocretin is indicated to affect various physiological functions and behaviors
such as energy balance
feeding
wake-sleep cycle
stress response
and reproduction. This study investigated postnatal development and aging changes of the orexin neuron in the male rat hypothalamus. The brain tissue of rats from I week to 24 months old was analyzed by immunohistochemistry for two forms of orexin peptides
orexin-A and -B. The number of immunoreactive cells for each age group was counted and the immunoreactive intensity was also analyzed in order to reveal the changes in the number of expressing cells and the relative amount of the peptides. The number of orexin immunoreactive cells increased from postnatal 2 weeks to maturation
then slightly decreased and stabilized until the age of 8 months old
but it was significantly decreased by 24 months old. The intensity of the immunoreaction followed almost the same pattern. Our findings demonstrate that orexin neurons are increased during maturation and then are significantly decreased during the period from 8 to 24 months old
indicating an involvement of orexin in the physiological changes in rat aging such as energy balance
sleep
stress response
and reproduction. (C) 2009 Elsevier Ireland Ltd. All rights reserved.
