The Journal of Neuroscience, September 1994, 14(9): 5381-5392 Patterns of Brain Vasopressin Receptor Distribution Associated with Social Organization in Microtine Rodents Thomas R. Insel,’ Zuo-Xin Wang,2 and Craig F. Ferris3 ‘Lab of Neurophystilogy, NIMH, Poolesville, Maryland 20837, *Department of Psychology, University of Massachusetts, Amherst, Massachusetts 01003, and 3Department of Psychiatry, University of Massachusetts, Medical Center, Worcester, Massachusetts 01655 Central vasopressin pathways have been implicated in the modulates the isolation call (Winslow and Insel, 1993), and in mediation of paternal behavior, selective aggression, and the squirrel monkey alters the behavioral responseto social affiliation in monogamous prairie voles. Here we demon- separation (Winslow and Insel, 1991a). Remarkably, many of strate markedly different patterns of brain vasopressin re- the AVP effects on social behavior have been reported exclu- ceptor binding in the monogamous prairie vole and the con- shely in males and appear androgen dependent (BluthC et al., generic nonmonogamous (promiscuous) montane vole. 1990; Winslow and Insel, 199lb; Ferris, 1992). Perhaps the Vasopressin binding was assessed with both 3H-vasopres- most ambitious claims for AVP as a peptide facilitating male sin and Y-sarc-AVP using receptor autoradiography. The social behavior come from recent studies with a monogamous specificity of binding was consistent with a V,, receptor, the rodent, Micro&s ochrogaster, the prairie vole. In the male of saturation kinetics were similar in the two species, and nei- this species,AVP hasbeen implicated in mate guarding, paternal ther species showed evidence of sexual dimorphisms. In the behavior, and the development of a preference for one specific prairie vole, highest specific binding was observed in the mate-all critical to the processof pair bonding that character- accessory olfactory bulb, diagonal band, laterodorsal thal- izes monogamous social organization (Winslow et al., 1993; amus, and superior colliculus. In the montane vole, specific Wang et al., in press). binding was observed in the accessory olfactory bulb and If AVP were essentialfor the mediation of pair bonding, one superior colliculus as well, but in several other regions with might predict that neural circuits for this peptide would differ high levels of binding in the prairie vole, binding was low or in monogamousand polygynous species,as pair bonding is ob- undetectable in the montane vole. In this nonmonogamous served in the former and not the latter. Voles of the genus species, specific binding was high in lateral septum. Func- Microtus display diverse patterns of socialorganization and may tional studies demonstrated the induction of phosphoinositol provide some useful comparisonsin which to test this predic- by AVP in the septum of the montane vole but not in the tion. For instance, prairie voles and montane voles (M. mon- prairie vole. The pattern of Y-sarc-AVP binding to lateral tanus), two speciesthat are similar in appearanceand many septum may reflect the social organization of these two spe- aspectsof nonsocial behavior, display marked differences in cies, as similar differences in AVP receptor distribution in social affiliation (Shapiro and Dewsbury, 1990). In their natural the lateral septum were also observed in two related spe- habitat, prairie voles frequently form long-term monogamous cies, pine voles and meadow voles, which are monogamous relationships and show high levels of parental care (Dewsbury, and nonmonogamous, respectively. These results, along with 1981; Getz et al., 1981; Getz and Hofman, 1986). Even in the earlier studies of AVP’s effects on pair bonding, suggest the laboratory, adult prairie voles usually sit side by side with a importance of this neuropeptide for the mediation of behav- mate, attack strange adults, and display intense maternal and iors related to social organization. paternal care (Oliveras and Novak, 1986; Carter et al., 1990; [Key words: vasopressin, AVP, vole, septum, thalamus, Shapiro and Dewsbury, 1990). In contrast, montane vole adults phosphoinositol, monogamy] live in isolated burrows and show no evidence of monogamy (Jannett, 1980). In the laboratory, montane voles appear min- Central administration of the neuropeptide arginine-vasopres- imally parental and generally spend little time in contact with sin (AVP) has been associatedwith a variety of effects from conspecifics(McGuire and Novak, 1986; Shapiro and Dews- enhanced learning to antipyresis (reviewed in de Wied et al., bury, 1990). Speciesdifferences in social behavior are evident 1993). One cluster of central effects of AVP that has received very early in life, as prairie vole young show marked increases recent attention might be best described as the facilitation of in ultrasonic calls and glucocorticoid secretion in responseto species-specificsocial behaviors. AVP in the golden hamster social isolation, whereasmontane vole pups show little, if any, induces flank marking (Ferris et al., 1984) in the adult rat fa- behavioral or physiologic responseto separation from the nest cilitates social memory (Dantzer et al., 1987), in the infant rat (Shapiro and Insel, 1990). It appearsthat an inherent difference in the propensity for social contact or affiliation underlies the -differencesin social organization. Received Dec. 10, 1993; revised Feb. 25, 1994; accepted March 9, 1994. We have previously described speciesdifferences in the dis- Correspondence should be addressed to Thomas R. Insel, M.D., National In- stitute of Mental Health, P.O. Box 608, Poolesville, MD 20837. tribution of oxytocin receptors in prairie and montane voles Copyright 0 1994 Society for Neuroscience 0270-6474/94/145381-12so5.00/0 (Insel and Shapiro, 1992). These differences were of interest 5382 lnsel et al. * Vasopressin Receptors and Social Organization because (1) related species selected for similar contrasts of social Based on previous experience comparing optical density quantification organization showed analogous differences in binding, (2) no to binding values obtained in homogenate assays with other iodinated species differences were detected for opiate or benzodiazepine ligands, we recommend that the absolute values obtained as dpm/tissue equivalent be treated as relative numbers for comparison within an receptors, and (3) in the montane vole female, the pattern of experiment. binding changed postpartum to resemble the pattern in the prai- Saturation and competition studies. In previous studies with rat and rie vole, with the emergence of maternal behavior. In addition, hamster, 1251-sarc-AVP appeared to bind specifically to a vasopressin oxytocin was found to facilitate selective affiliation in the female rather than an oxytocin receptor, as AVP was roughly 1000 times more potent than oxytocin for displacing 1251-sarc-AVPbihding in brain sec- prairie vole (Williams et al., in press). The present study in- tions (Phillips et al., 1988: Ferris et al.. 1993). To comnare the suecificitv vestigated the distribution of vasopressin receptors in both prai- of 12SI-sarc-kVP binding’in prairie and montane voles, 20 adjacent 16 rie and montane voles. To examine the coupling of prairie and pm sections through the laterodorsal thalamus (prairie vole) and the montane vole receptors to a second-messenger system, regional lateral septum (montane vole) were exposed to 1251-sarc-AVP using the binding protocol described above. In each region, the first and last induction of phosphoinositol by vasopressin was measured in sections were compared to ensure consistent binding along the 200 pm both species. Finally, to examine if species differences in recep- in the rostralxaudal plane. Specificity of 1251-sarc-AVP binding (70 PM) tor distribution were related to patterns of social organization, was determined in competition studies using nine concentrations of the the comparison of receptor binding was extended to two other selective V,, ligand d(CH,),[Tyr(Me)]AVP ranging from lo-l2 to 1O-6 congeneric species, pine and meadow voles, which are believed or five concentrations of Thl-LGly70T (oxytocin) and [d(CH,)S,D- Phe2,11e4,Ala9-NH,]-AVP (V,) ranging from 1O-9 to 10m6. Each of these to be monogamous and nonmonogamous, respectively. studies compared adjacent sections from a single animal with three to four animals used for each displacer. Displacer peptides were obtained Materials and Methods from Peninsula (Burlingame, CA). Animals. Both male and female prairie and montane voles from the A similar strategy was used to investigate the saturation kinetics of NIH breeding colonies in Poolesville, MD, were studied. Male pine and i251-sarc-AVP binding in 20 adjacent 10 pm sections through the later- meadow voles were obtained from the breeding colonies of the Uni- odorsal thalamus (prairie vole) and the lateral septum (montane vole). versity of Massachusetts Department of Zoology. All animals were For each species, sections from three or four animals were exposed to weaned at 21 d of age and housed with same-sex littermates until 60- 1 of 10 concentrations of ‘2sI-sarc-AVP, ranging from 2 to 1000 PM. 90 d of age, when they were used for autoradiographic experiments. All Both species were represented in every study. At each concentration, animals were sexually inexperienced. Housing was on a 12: 12 lightdark blanks were generated by adding 1 PM d(CH,),[Tyr(Me)]AVP. To fa- schedule with food and water available ad libitum. cilitate image analysis, slides exposed to the highest