Effect of Day Length on Luteinizing Hormone β-Subunit mRNA and Subsequent Gonadal Growth in the White-Crowned Sparrow, Zonotrichia leucophrys gambelii

Abstract

We have applied a cDNA probe for chicken luteinizing hormone β-subunit to adenohypophysial preparations collected from Gambell's white-crowned sparrows. In situ hybridization showed luteinizing hormone (LH) β-subunit mRNA distributed throughout the adenohypophysis in a manner identical to that of LH visualized by immunocytochemistry. Northern blot analysis showed a single band (0.8 kbp) identical to that from Japanese quail. Dot blot analysis was used to quantify changes in LH β-subunit mRNA during a photoperiodically induced gonadal cycle in white-crowned sparrows. Transfer of adult males from short days (8L 16D) to long days (20L 4D) resulted in rapid testicular growth accompanied by increases in plasma levels of LH and body and liver mass. By Day 30 of photostimulation, mRNA levels in the adenohypophysis were significantly higher than those in birds on short days. In photorefractory birds, i.e., when gonads were regressed (60 days of long days), mRNA levels were significantly lower than on Day 30 of photostimulation. The increase in mRNA during photostimulatlon was accompanied by a highly significant increase in plasma concentrations of LH. The binding of iodinated LH to testes peaked at Day 15 of photostimulation and declined by Day 30. Curiously, peak production of testosterone and cAMP (induced by incubation with gonadotropins in vitro) were highest at Day 30. By 60 days of photostimulation, when birds were photorefractory, plasma levels of LH, binding of LH to the testes, and testosterone and cAMP production were greatly reduced. These data suggest that photoperiodically induced gonadal development and regression is mediated in part by regulation of mRNA levels for LH β-subunit in the adenohypophysis.