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.