A vasopressin-sensitive mechanism within the medial preoptic area-anterior hypothalamus (MPOA-AH) appears to be essential for expression of a complex behavior involved in olfactory communication in Golden hamsters called flank marking. The present study investigated whether the induction of flank marking by arginine-vasopressin (AVP) within the MPOA-AH is mediated by a receptor that is more similar to the vasopressor (Vl) or the antidiurectic (V2) AVP receptor. Adult male hamsters were anesthetized and implanted with a 26 gauge guide cannula stereotaxically aimed at the MPOA-AH and then microinjected with analogs of vasopressin, oxytocin, and selective Vl and V2 antagonists. Hamsters were tested for flank-marking behavior during a 5 or 10 min observation period following the injection of peptlde in a vehicle of 100 nl of saline. None of the 15 analogs of AVP and oxytocin produced more flank marking than the 50.8 + 16.2 and 76.8 f 4.4 (mean f SEW, II = 4) flank marks observed following injection of AVP at the 1 or 10 ng dose, respectively. The number of flank marks produced by each analog was found to be highly related to the pressor activity of that analog at both the 1 ng (p = +0.74, p < 0.01) and 10 ng (p = +0.82, p < 0.01) doses. In contrast, no statistically reliable relationship between flank marking and the antidiuretic activity of these analogs was found at either dose (1 ng: p = +O.O7,p > 0.05; 10 ng: p = +O.lO,p > 0.05). In a second series of studies, microinjection of 2 different Vl antagonists into the MPOA-AH significantly (p < 0.005) inhibited flank marking in response to AVP. However, microinjection of a V2 antagonist or saline did not inhibit flank marking. These data indicate that the receptors mediating the induction of 'flank marking within the MPOA-AH are more similiar to Vl (pressor) receptors than to V2 (antidiuretic) receptors. Scent marking is a major form of communication in mammals.Odors deposited in the environment can serve a variety of social functions from attracting mates to repelling competitors (Yahr, 1984). In the Golden hamster (Mesocricetus auratus), one form of scent marking, termed flank gland marking, is accomplished by rubbing a dorsal flank gland against vertical objects in the environment. Flank gland marking is commonly observed in both male and female hamsters and can be elicited by the odors of other hamsters and aggression during social encounters (Johnston, 1975).Several lines of evidence now indicate that neurons within the medial preoptic area-anterior hypothalamus (MPOA-AH) Received Dec. 2, 1985; revised Jan. 20, 1986; accepted Jan. 22, 1986. We wish to thank Professor Maurice Manning for providing several vasopressin analogs and for his comments on the manuscript. This work was supported by NIH Grants (to H.E.A.) and HD-18022 (to C.F.F. are critical for the expression of scent marking behavior. Lesions that destroy the MPOA-AH severely reduce scent-marking behavior in several mammalian species (Hart, 1974;Hart and Voith, 1978;Yahr, 1984). Implants of testoster...

Previous studies have indicated that administration of the serotonin releaser p-chloroamphetamine HCl produces a dose-dependent increase in renin secretion through a blood-borne renin-releasing factor. The present studies were designed to partially characterize this renin-releasing factor using an in vitro kidney slice method for the bioassay of renin-releasing activity. Plasma from p-chloroamphetamine-treated, nephrectomized rats was used to obtain the renin-releasing factor, which was fractionated by ultrafiltration into fractions of molecular weight ranges of 1000 to 5000, 5000 to 10,000, and 10,000 to 20,000. The molecular weight ranges of the renin-releasing factor was determined to be between 5000 and 10,000. Since previous studies have shown that lesions in the hypothalamus prevent the effect of p-chloroamphetamine on renin secretion, we tested whether a hypothalamic extract can release renin from kidney slices. Addition of extracts of boiled rat hypothalamic tissue to the kidney slices caused an increase in renin release. Addition of cerebellar extracts produced a smaller increase in renin release, whereas addition of pituitary extracts had no effect. Fractionation by ultrafiltration of bovine hypothalamic extract revealed that the fraction with a molecular weight range of 5000 to 10,000 possessed the highest renin-releasing ability. The 1000 to 5000 (molecular weight) fraction possessed a sizeable renin-releasing activity, but the 10,000 to 20,000 fraction had no renin-releasing activity. Both bovine hypothalamus fractions (molecular weights between 1000-5000 and 5000-10,000) and plasma fraction lost their renin-releasing activity after digestion with pronase, suggesting that the renin-releasing factor or factors are peptides. These results suggest that a renin-releasing factor originate in the hypothalamus.