Biology of Reproduction, Vol 50, 301-308, Copyright © 1994 by Society for the Study of Reproduction

ARTICLES

Diurnal expression of Fos in luteinizing hormone-releasing hormone neurons of Syrian hamsters

A Doan and HF Urbanski
Division of Neuroscience, Oregon Regional Primate Research Center, Beaverton 97006.

The aim of the present study was two-fold: first, to examine the temporal relationship between increased expression of Fos in LHRH neurons of proestrous hamsters and increased plasma levels of LH, FSH, estradiol-17 beta (E2), and progesterone (P4); and second, to establish whether male hamsters, like females, also show diurnal variations in the number of LHRH neurons expressing Fos. Blood samples were collected from proestrous females at 0900 n, 1200 h, 1500 h, and 1800 h and also from males at 0300 h, 0900 h, 1500 h, and 2100 h. RIA of the plasma revealed significant peaks of LH, FSH, and E2 at 1500 h, and of P4 at 1800 h in the females; a significant but smaller peak of LH also occurred at 1500 h in the males. Double-label immunocytochemistry, using antibodies directed against amino acids 127-152 of the human Fos protein and against LHRH, showed that female hamsters expressed Fos in fewer than 10% of their LHRH neurons during the morning and at noon of proestrus but in approximately 41% of these neurons during the late afternoon (1800 h). In contrast, no expression of Fos occurred in LHRH neurons of male hamsters at any time of the day. The finding that the females showed an increase in the number of LHRH neurons expressing Fos after, and not before, the initiation of the preovulatory gonadotropin surge is significant because it does not readily support the hypothesis that this expression of immediate-early genes is in some way associated with the induction of the surge. Instead, the results are consistent with the view that expression of Fos in LHRH neurons reflects either the activation of a mechanism responsible for terminating the surge or, alternatively, the activation of a compensatory mechanism responsible for replenishing depleted neuropeptide stocks.

This article has been cited by other articles:

				M. M. Mahoney, C. Sisk, H. E. Ross, and L. Smale Circadian Regulation of Gonadotropin-Releasing Hormone Neurons and the Preovulatory Surge in Luteinizing Hormone in the Diurnal Rodent, Arvicanthis niloticus, and in a Nocturnal Rodent, Rattus norvegicus Biol Reprod, April 1, 2004; 70(4): 1049 - 1054. [Abstract] [Full Text] [PDF]

				H. O. de la Iglesia, J. Meyer, and W. J. Schwartz Lateralization of Circadian Pacemaker Output: Activation of Left- and Right-Sided Luteinizing Hormone-Releasing Hormone Neurons Involves a Neural Rather Than a Humoral Pathway J. Neurosci., August 13, 2003; 23(19): 7412 - 7414. [Abstract] [Full Text] [PDF]

				S. L. Meddle, D. L. Maney, and J. C. Wingfield Effects of N-Methyl-D-Aspartate on Luteinizing Hormone Release and Fos-Like Immunoreactivity in the Male White-Crowned Sparrow (Zonotrichia leucophrys gambelii) Endocrinology, December 1, 1999; 140(12): 5922 - 5928. [Abstract] [Full Text]

				T. L. McElhinny, C. L. Sisk, K. E. Holekamp, and L. Smale A Morning Surge in Plasma Luteinizing Hormone Coincides with Elevated Fos Expression in Gonadotropin-Releasing Hormone-Immunoreactive Neurons in the Diurnal Rodent, Arvicanthis niloticus Biol Reprod, October 1, 1999; 61(4): 1115 - 1122. [Abstract] [Full Text]

				P. D. Finn, R. A. Steiner, and D. K. Clifton Temporal Patterns of Gonadotropin-Releasing Hormone (GnRH), c-fos, and Galanin Gene Expression in GnRH Neurons Relative to the Luteinizing Hormone Surge in the Rat J. Neurosci., January 15, 1998; 18(2): 713 - 719. [Abstract] [Full Text] [PDF]

				S. L. Meddle and B. K. Follett Photoperiodically Driven Changes in Fos Expression within the Basal Tuberal Hypothalamus and Median Eminence of Japanese Quail J. Neurosci., November 15, 1997; 17(22): 8909 - 8918. [Abstract] [Full Text] [PDF]