AJP - Regulatory, Integrative and Comparative Physiology, Vol 273, Issue 6 2032-R2039, Copyright © 1997 by American Physiological Society
Rapid photoperiod-induced increase in detectable GnRH mRNA-containing cells in Siberian hamster
T. Porkka-Heiskanen, N. Khoshaba, K. Scarbrough, J. H. Urban, M. H. Vitaterna, J. E. Levine, F. W. Turek and T. H. Horton
Department of Neurobiology and Physiology, Northwestern University, Evanston, Illinois 60208, USA.
To determine whether changes in gonadotropin-releasing hormone (GnRH)
neurons are early indicators of photostimulation, Siberian hamsters were
placed in short days (6:18-h light-dark) at 3 (experiment 1) or 6
(experiment 2) wk of age where they were held for 3 (experiment 1) or 4
(experiment 2) wk. Hamsters were then moved to long photoperiod (16:8-h
light-dark). In experiment 1, brains were collected 1-21 days after
transfer from short to long days. In experiment 2, brains were collected
only on the second morning of long day exposure. Long and short day
controls were included in both experiments. Cells containing GnRH mRNA, as
visualized by in situ hybridization, were counted. As expected, there were
no differences in the number of detectable GnRH mRNA-containing cells among
animals chronically exposed to long or short photoperiods. However, on the
second morning after transfer from short to long photoperiod, a positive
shift in the distribution of GnRH mRNA-containing cells occurred relative
to the respective controls in the two experiments. Increases in
follicle-stimulating hormone secretion and gonadal growth occurred days
later. In conclusion, a rapid but transient increase in the distribution of
detectable GnRH mRNA-containing cells is an early step in the
photostimulation of the hypothalamic-pituitary-gonadal axis.
