PARENT SESSION

(140) DISTRIBUTION OF KAPPA OPIOID RECEPTOR mRNA IN THE PREOPTIC AREA AND HYPOTHALAMUS OF THE EWE.

Amstalden, Marcel¹, Foradori, Chad¹, Coolen, Lique¹, Goodman, Robert², Lehman, Michael¹, ¹ University of Cincinnati College of Medicine, Cincinnati, OH² West Virginia University Health Sciences Center, Morgantown, WV

ABSTRACT- Endogenous opioid peptides (EOPs) play a major role in the control of GnRH secretion and evidence suggests that the EOP, dynorphin, mediates the inhibitory influence of progesterone on the pulsatile release of GnRH. Dynorphin terminals synapse upon GnRH perikarya in both the preoptic area (POA) and mediobasal hypothalamus (MBH). Dynorphin acts via the kappa opioid receptor (KOR) and the administration of KOR antagonist into the MBH or POA increases the frequency of LH pulses in luteal phase ewes. In this experiment, we determined the distribution of KOR mRNA in the POA and hypothalamus of ewes and compared KOR gene expression in intact luteal phase ewes (n=3), ovariectomized ewes (OVX; n=3) and ovariectomized ewes treated with progesterone (OVX+P; n=3). A partial sequence of the ovine KOR gene was cloned and used to synthesize ³⁵S-labeled riboprobe for in situ hybridization histochemistry in 20 m, fresh-frozen sections. Cells expressing KOR mRNA were identified on the basis of silver grain density at least five times above background levels. KOR mRNA-expressing cells were seen in a number of diencephalic regions, including the bed nucleus of the stria terminalis, POA, anterior hypothalamic area, supraoptic and paraventricular (PVN) nuclei, lateral hypothalamus, ventromedial and dorsomedial hypothalamic nuclei, arcuate nucleus (ARC) and ventral premammillary area. We have begun quantitative analyses of the number and silver grain density of KOR mRNA-expressing cells. Preliminary results thus far demonstrate similar levels of KOR expression in the POA, PVN and ARC among the 3 groups of ewes, suggesting that cellular KOR are not influenced by the presence of progesterone. In summary, KOR mRNA-expressing neurons are found in a number of regions of the ovine hypothalamus implicated in the control of reproductive neuroendocrine function, including the MBH where GnRH neurons are found in the ewe; whether KOR mRNA is present in ovine GnRH neurons remains to be determined. (Supported by NIH HD39916 to MNL and RLG)

KEY WORDS: kappa opioid receptor, mRNA, hypothalamus, ovine