PARENT SESSION
MINISYMPOSIUM VI. NEUROENDOCRINOLOGY OF DOMESTIC ANIMALS

Tuesday, August 3, 2004
9:00 AM–10:30 AM
Buchanan A202
Chair: Thomas R. Hansen (University of Wyoming, Laramie, WY), Co-Chair: Debora L. Hamernik (USDA-CSREES, Washington, DC)

(MS18) NEUROENDOCRINE SYSTEMS EXHIBIT BOTH FUNCTIONAL DECLINE AND PLASTICITY DURING AGING.

Ottinger, Mary Ann¹, Panzica, GianCarlo², Micevych, Paul³, ¹ University of Maryland, College Park, MD² University of Torino, Torino, Italy³ UCLA, Los Angeles, CA

ABSTRACT- During reproductive aging, hypothalamic-pituitary-gonadal axis function decline leading to reproductive failure, due in part to altered function of hypothalamic neuroendocrine systems. Our studies in Japanese quail have shown deteriorating function at each level of the HPG axis, coincident with the loss of sexual behavior in the aging male. Further, there appears to be coincident (and possibly linked) demise in both hypothalamic and gonadal function leading to reproductive senescence. This presentation will focus on the age-related deterioration in reproductive function and sexual behavior as related to hypothalamic neuroendocrine systems. Because reproductively senescent male quail have restored sexual behavior with exogenous testosterone replacement, and restimulation of specific neuroendocrine systems, we have examined possible neuroplasticity in hypothalamic neural systems, including tyrosine hydroxylase (TH), aromatase enzyme (AROM), and vasotocin (AVT). In quail, chicken gonadotropin releasing hormone-I (GnRH-I) production and release is stimulated by catecholamines (NE; E) and inhibited by opioid peptides (ENK, END, DYN). A series of studies have investigated hypothalamic neural systems during aging and with sexual behavior, including immunoreactivity (-ir) for GnRH-I, ENK, delta opioid receptor (DOR), TH, AROM, and AVT. Results showed a widespread decline in TH-ir, including both hypothalamic areas and other brain regions. Similarly, AROM-ir in the preoptic-septal region was drastically reduced in senescent males. Sexual dimorphism of GnRH-I system was maintained, with males showing loss of GnRH-I-ir. Further, both males and females exhibited decreased responsiveness of the GnRH-I system in vitro studies. A subset of TH and GnRH-I neurons colocalized DOR. The GnRH-I/DOR neurons showed an age-related loss in these cells in both males and females with reproductive aging. Testosterone replacement in aged males stimulated behavioral recovery and coincident restoration of TH-ir, AROM-ir and AVT-ir neurons. In summary, the quail provides a model for examining reproductive aging with focus on specific neural systems critical in the aging cascade. Supported by EPA R826134, IBN-9817024 (MAO) & NS 39495.

KEY WORDS: quail model for aging, GnRH, neuroendocrine aging, opioid peptides