Glutamatergic stimulation of luteinising hormone secretion in relatively refractory male songbirds.
Seasonal breeding in two Sonoran desert passerines, the Cassin's (Aimophila cassinii) and Rufous-crowned (Aimophila ruficeps) Sparrows is thought to be terminated by the development of a decrease in responsiveness to photostimulation, a condition known as relative photorefractoriness. It was predicted that the development of relative refractoriness is a consequence of a decrease in gonadotrophin-releasing hormone (GnRH) synthesis and associated stores of releasable GnRH. This hypothesis was tested by determining the luteinising hormone (LH) responses to the excitatory amino acid glutamate agonist N-methyl-D,L-aspartate (NMA) in males of the two species subjected to photomanipulations aimed at generating five groups: Fully photosensitive with undeveloped testes on short days (8L : 16D); fully photosensitive with developed testes on 13L : 11D; relatively photorefractory with regressed testes on 13L : 11D, and groups with developed testes held on 15L : 9D or 16L : 8D. LH release was stimulated in the Cassin's Sparrow by NMA most in the 8L group; to a lesser, but similar extent in the two 13L groups; and not at all in the 15L and 16L groups. LH release was not stimulated by NMA in any of the photoperiodic regimes in the Rufous-crowned Sparrow. In both species, NMA induced Fos-like immunoreactivity in the anterior and basal hypothalamus, but not in GnRH cell bodies. It is concluded that the development of relative photorefractoriness in Cassin's Sparrows is a consequence of reduced GnRH synthesis, reflected in a reduction in releasable GnRH. The lack of LH response of the Rufous-crowned Sparrows to NMA administration may be a consequence of high responsiveness to handling stress.
Deviche
P
P
School of Life Sciences, Arizona State University, Tempe, AZ 85287-4501, USA. deviche@asu.edu
Sabo
J
J
Sharp
P J
PJ
D000818:Animals; D018690:Excitatory Amino Acid Agonists / Q000378:metabolism; D018698:Glutamic Acid / Q000378:metabolism*; D007987:Gonadotropin-Releasing Hormone / Q000378:metabolism; D008027:Light; D007986:Luteinizing Hormone / Q000097:blood / Q000378:metabolism*; D008297:Male; D016202:N-Methylaspartate / Q000378:metabolism; D009474:Neurons / Q000166:cytology / Q000378:metabolism; D017440:Photoperiod; D011301:Preoptic Area / Q000166:cytology / Q000378:metabolism; D012621:Seasons; D012726:Sexual Behavior, Animal / Q000502:physiology*; D020308:Songbirds / Q000502:physiology*; D013737:Testis / Q000033:anatomy & histology; D013997:Time Factors
D018690:Excitatory Amino Acid Agonists; D007987:Gonadotropin-Releasing Hormone; D018698:Glutamic Acid; D016202:N-Methylaspartate; D007986:Luteinizing Hormone