THE JOURNAL OF EXPERIMENTAL ZOOLOGY 264461-467 (1992) Arginine Vasotocin Concentrations in the Supraoptic Nucleus of the Lizard zyxw Anolis carolinensis Are Associated With Reproductive State but Not Oviposition zy CATHERINE R. PROPPER, RICHARD E. JONES, ROBERT M. DORES, AND KRISTIN H. LOPEZ zyxwvu Laboratory zyxwvuts of Comparative Reproduction, Department of EPU Biology, University of Colorado, Boulder, Colorado 80309 (C.R.P., R.E.J., K.H.L.) and Department of Biology, University of Denver, Denver, Colorado 80210 (R.M.D.) ABSTRACT Arginine vasotocin (AVT) is a neuropeptide involved in reproductive function in many nonmammalian vertebrates. We determinedbrain and plasma AVT concentrations during the estrous cycle and oviposition in the lizard Anolis carolinensis. There were no differences in AVT concentra- tions in the plasma or any brain region during the ovipositional sequence. However, we found that females with an egg in each oviduct and a large pre-ovulatory follicle (diameter zyx > 4.5 mm) in one- ovary had significantly higher AVT concentrations in the supraoptic nucleus (SON) of the hypothal- amus than did females with small pre-ovulatory follicles in both ovaries. In a second study, females with an egg in each oviduct and a large pre-ovulatory follicle had significantly greater AVT concen- trations in the SON than females with only one oviductal egg and a large pre-ovulatory follicle or females with an egg in each oviduct and a small pre-ovulatory follicle in each ovary. Concentrations of AVT in other brain regions and in the plasma did not differ among these groups. Changes in ste- roid profiles during estrous and/or direct neural communication between the uterus, ovary, and brain may account for the changes in AVT concentrations seen in the supraoptic nucleus during the estrous cycle of Anolis carolinensis. zyxwvut o 1992 Wiley-Liss, Inc. Arginine vasotocin (AVT), a small neuropeptide synthesized in the hypothalamus of many nonmam- malian vertebrates, is evolutionarily and function- ally related to the peptides oxytocin (OXY) and arginine vasopressin (AVP) which are produced in the hypothalamus of mammals (Sawyer, '77; Acher, '80; Acher et al., '85). In many species ofbirds, rep- tiles, and amphibians, AVT induces oviductal con- tractions and oviposition (LaPointe, '77; Guillette and Jones, '82; Jones and Guillette, '82), and OXY plays a similar role in mammalian parturition (Cross, '58; Fuchs, '64; Fuchs et al., '83). Plasma levels of AVT are elevated during oviposition in chickens (Shimada et al., '86; Koike et al., '88), sea turtles (Figler et al., '89), and the tuatara Sphen- odon punctutus (Guillette et al., '91), and in the viviparous lizard Tiliqua rugosa prior to parturi- tion (Fergusson and Bradshaw, '91). Brain concentrations of OXY also change over time. In rats, OXY levels are elevated in specific hypothalamic areas during late pregnancy (Cald- well et al., '87) and change during the estrous cycle (Crowley et al., '78; Greer et al., '86). These stud- ies demonstrate that there are dramatic changes in brain and plasma neuropeptide concentrations 0 1992 WILEY-LISS, INC. around the time of parturition or oviposition. How- ever, nothing is known about how concentrations of AVT change in the brain during oviposition of any nonmammalian vertebrate. Arginine vasotocin induces oviductal contractions (Guillette and Jones, '80) and oviposition (Summers et al., '85) in the lizard Anolis carolinensis, suggest- ing that changes in plasma AVT levels may be re- sponsible for oviposition in this species. The ovarian cycle of A. carolinensis is unusual for lizards because females ovulate a single egg from each ovary alter- nately (Noble and Greenberg, '41; Smith et al., '73). Because of this ovulatory pattern, only one egg is shelled and ready for oviposition at any one time. Thus, if endogenous AVT is responsible for ovipo- sition, the timing of release of this neuropeptide from the pars nervosa may correspond to oviductal sensitivity to AVT. Because we know that immu- noreactive AVT cells and fibers are present in sev- eral brain areas in A. carolinensis (Propper et al., Received January 7,1992; revision accepted July 26,1992. Address reprint requests to Catherine R. Propper, Department of Bio- logical Sciences, Box 5640, Northern Arizona University, Flagstaff, A2 86011.