Meeting Abstract

1.2  Thursday, Jan. 3  Endocrine response to N-methyl-D-aspartate in relatively photorefractory male passerines: Effect of the photoperiodic condition DEVICHE, Pierre*; SABO, John; SHARP, Peter; Arizona State University, Tempe; Arizona State University, Tempe; Roslin Institute, Scotland, UK deviche@asu.edu

The glutamate analog N-methyl-D-aspartate (NMA) increases plasma luteinizing hormone (LH) by inducing release of gonadotropin-releasing hormone (GnRH) and is used to assess GnRH sensitivity to glutaminergic stimulation. We measured plasma LH following NMA injection (60 mg/kg i.m.) to adult male Cassin�s (Aimophila cassinii; CASP) and Rufous-crowned (A. ruficeps; RCSP) Sparrows as a function of the photoperiodic condition. Plasma LH and gonad size determination during sequential chronic exposure to short days (SD: 8L:16D) followed with long days (LD: 13L:11D and then 15L:9D, 13L:11D, and 16L:8D) showed that both species are relatively photorefractory. NMA increased plasma LH within 15 min. Within 60 min, it increased FOS (c-fos gene product) expression in brain regions controlling GnRH secretion but not in GnRH cells, suggesting indirect activation of these cells. NMA treatment elevated plasma LH less in CASP exposed to LD (13L:11D after 8L:16D, 15L:9D; elevated baseline plasma LH) than to SD (low baseline plasma LH), but was equally effective in SD- and 13L:11D after 15L:9D-exposed males. Thus, sustained secretion of GnRH in LD-exposed CASP apparently maintains elevated plasma LH and prevents accumulation of the neuropeptide in GnRH-producing neurons. In contrast, decreased GnRH release in relatively photorefractory males (13L:11D after 15L:9D; low plasma LH) causes the neuropeptide to accumulate in GnRH-producing neurons. Even though NMA treatment activated brain FOS expression similarly in CASP and RCSP, this treatment increased plasma LH less in RCSP than CASP, demonstrating species differences in sensitivity to the agonist.