Age and species-dependent differences in the neurokinin B system in rat and human brain

Neurokinin B and its cognate neurokinin-3 receptor are expressed more in th e forebrain than in brain stem structures but little is known about the pri mary function of this peptide system in the central professing of informati on. In general, few studies have specifically addressed age-related changes of tachykinins, notably the changes in number and/or distribution of the n eurokinin B-expressing and neurokinin-3 receptor-bearing neurons. Data on f unctions and changes of neurokinins in physiological aging are limited and apply mainly to the substance P/neurokinin-1 receptor system. In the presen t study, we analyzed neurokinin B/neurokinin-3 receptor system in young (5 months) versus middle aged (15 months) and old rats (23-25 months) and also in aging human brains. For the majority of the immunohistochemically exami ned regions of the rat brain, there was no statistically significant change in neuronal number and size of the neurokinin B and neurokinin-3 receptor staining. In the adult human brain, there was no age-associated change of t he number or size of neurokinin-B-positive neurons. However, we found a maj or decline in number of neurokinin-3 receptor-expressing neurons between yo ung/middle aged (30 years to 69 years) versus old (70 years and older) adul ts. Interestingly, numbers of neurokinin-3 receptor-positive microglia incr eased whereas the neurokinin-3 receptor-positive astrocytes remained unchan ged in both aging rat and human brains. Finally, in addition to assessing t he morphological and quantitative changes of the neurokinin B/neurokinin-3 receptor system in the rat and human brain, we discuss functional implicati ons of the observed interspecies differences. (C) 1999 Elsevier Science Inc . All rights reserved.