Research Report
Reproductive aging in Japanese quail,
Coturnix japonica
is
associated with changes in central opioid receptors
M.A. Ottinger
a,
⁎
, C. Corbitt
b
, R. Hoffman
c
, N. Thompson
a
,
E. Russek-Cohen
a
, P. Deviche
d
a
Dept. of Animal and Avian Sciences, University of Maryland, College Park, MD 20742, USA
b
Biology Department, University of Louisville, Louisville, KY 40292, USA
c
Inst. Arctic Biology, Univ. Alaska Fairbanks, Fairbanks, AK 99775, USA
d
School of Life Sciences, Arizona State University, Tempe, AZ 85287-4501, USA
ARTICLE INFO ABSTRACT
Article history:
Accepted 29 August 2006
Available online 12 October 2006
Quantitative in vitro autoradiography was used to measure specific μ and δ opioid receptor
densities in regions of the Japanese quail, Coturnix japonica, brain that regulates reproductive
endocrine and behavioral responses to determine the possible involvement of the opioid
system in reproductive decline seen during aging. Densities were measured in selected
brain regions of young sexually active (YAM), young photoregressed (YPM), old
reproductively senescent (OIM) male, young active (YF), and old senescent female (OF)
Japanese quail. Medial and lateral septum (SM, SL), medial preoptic area (POM), and n.
intercollicularis (ICo) were of particular interest for reproductive responses. Similar to
previous observations, μ and δ opioid receptors showed differential distributions in the
areas measured. Some age-related changes were observed, with lower SM μ receptor
densities in aged males (OIM) than females or young males (YAM). Densities of μ receptors in
the POM and in other areas examined did not vary with sex or age. Similarly, OIM males had
lower densities of δ receptors in the SM than young males (YAM and YPM); POM δ receptor
densities were also low in OIM males compared to the YPM males, and YAM males were
intermediate. Interestingly, photoregressed males (YPM) had higher SL δ receptor densities
than any other group. Thus there were age-related differences detected in μ receptor
densities among groups in the SM of OIM relative to other groups; and the μ and δ receptor
densities did not differ in females with brain region. Additionally for δ receptors specifically,
YF and OF did not differ from OIM for any brain region and similarly had lower densities of δ
receptors compared to YAM males. These data provide support for regional differences in
opioid receptor distribution and for age- and sex-related differences in δ opioid receptor
densities. The direction of change presents an interesting dichotomy in that, compared to
young active males, δ opioid receptor densities increased with loss of reproductive function
in the YPM, whereas receptor densities decreased in the OIM. Plasma androgen levels were
relatively low in both these groups compared to the young active males. This observation
suggests that there is an age-related loss in the ability of this receptor system to respond to
circulating and centrally produced steroid hormones in the POM and in some septal regions,
compared to young animals that are responding to environmental cues. Furthermore, these
Keywords:
Quail
Opioid peptide
Opioid receptor
Aging
BRAIN RESEARCH 1126 (2006) 167– 175
⁎ Corresponding author.
E-mail address: maotting@umd.edu (M.A. Ottinger).
0006-8993/$ – see front matter © 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.brainres.2006.08.110
available at www.sciencedirect.com
www.elsevier.com/locate/brainres