Indian J. Sci. Technol., 9 th ISRPF Issue           Proceedings of 9 th International Symposium on Reproductive Physiology of Fish, Cochin, India. August 9-14, 2011 33 EXPRESSION PATTERNS OF THE KISSPEPTIN SYSTEM AND GnRH1 CORRELATE IN THEIR RESPONSE TO GONADAL FEEDBACK IN FEMALE STRIPED BASS Klenke U. , Zmora N., Stubblefield J., Zohar Y. Department of Marine Biotechnology, University of Maryland Baltimore County, Baltimore, Maryland USA, euek@yahoo.com Introduction: The regulatory role of sex steroids in the neuroendocrine control of vertebrate reproduction is very complex [1]. One key steroidal target is the GnRH1 system, the main regulator of the hypothalamic-pituitary- gonadal (HPG) axis. GnRH1 is responsible for releasing gonadotropins from the pituitary, which stimulate gonadal development and steroid production [1]. However, GnRH1 neurons lack estrogen receptor alpha [1], the steroid receptor implicated in steroid feedback, and thus the link between gonadal feedback and the HPG axis had been unclear. The kisspeptin system has recently emerged as a central processor for relaying signals from the periphery (e.g. gonadal feedback) to GnRH1 neurons, as shown in many mammalian studies [2]. Also, in fish, kisspeptin has been shown to be involved in the regulation of the reproductive cycle [3]. There are two different kisspeptin systems reported in most fish species. Both have been implicated in the control of the HPG axis in different fish species [3]. The present study tests the potential mediatory role of the kisspeptin system between the gonads and the HP axis in striped bass, during two distinct stages of the reproductive cycle of females: recrudescence and mid-vitellogenesis. Methods: Bilateral gonadectomies were carried out and control fish were given a sham-operation. After surgery, the gonadectomized fish were divided into 3 groups. During early recrudescence, one group was given a vehicle Figure 1: Brain kiss1, kiss2, kiss2r and gnrh1 tranript levels in recrudescent (rec) and mid-vitellogenic (vit) female striped bass. Results are presented as copy numbers x 10 4 / 50 ng total RNA ± SEM; * p < 0.05. Fig 2: Effects on transcript levels of the kiss/gnrh1 system due to (A) gonad removal [gdx] and steroid replacement [gdx+E and gdx+K] during early recrudescence and (B) gdx and testosterone replacement [gdx+T] during mid-vitellogenesis. Results presented as % of control ± SEM, numbers within bars = number of fish/group (n); * p < 0.05.