The neuropeptide arginine vasotocin alters male call characteristics involved in social interactions in the grey treefrog, Hyla versicolor

Vasotocin but not isotocin is involved in the emergence of the dominant-subordinate status in males of the weakly electric fish, Gymnotus omarorum

The establishment of the dominant-subordinate status implies a clear behavioral asymmetry between contenders that arises immediately after the resolution of the agonistic encounter and persists during the maintenance of stable dominance hierarchies. Changes in the activity of the brain social behavior network (SBN) are postulated to be responsible for the establishment and maintenance of the dominant-subordinate status. The hypothalamic nonapeptides of the vasopressin (AVP) and oxytocin (OT) families are known to modulate the activity of the SBN in a context-dependent manner across vertebrates, including status-dependent modulations. We searched for status-dependent asymmetries in AVP-like (vasotocin, AVT) and OT-like (isotocin, IT) cell number and activation immediately after the establishment of dominance in males of the weakly electric fish, Gymnotus omarorum, which displays the best understood example of non-breeding territorial aggression among teleosts. We used immunolabeling (FOS, AVT, and IT) of preoptic area (POA) neurons after dyadic agonistic encounters. This study is among the first to show in teleosts that AVT, but not IT, is involved in the establishment of the dominant-subordinate status. We also found status-dependent subregion-specific changes of AVT cell number and activation. These results confirm the involvement of AVT in the establishment of dominance and support the speculation that AVT is released from dominants' AVT neurons.

Mate calling alters expression of neuropeptide, cocaine- and amphetamine- regulated transcript (CART) in the brain of male frog Microhyla nilphamariensis

Croaking is a unique component of reproductive behaviour in amphibians which plays a key role in intraspecies communication and mate evaluation. While gonadal hormones are known to induce croaking, central regulation of sound production is less studied. Croaking is a dramatic, transient activity that sets apart an animal from non-croaking individuals. Herein, we aim at examining the profile of the neuropeptide cocaine- and amphetamine-regulated transcript (CART) in actively croaking and non-croaking frog Microhyla nilphamariensis. In anurans, this peptide is widely expressed in the areas inclusive of acoustical nuclei as well as areas relevant to reproduction. CART immunoreactivity was far more in the preoptic area (POA), anteroventral tegmentum (AV), ventral hypothalamus (vHy), pineal (P) and pituitary gland of croaking frog compared to non-croaking animals. On similar lines, tissue fragments collected from the mid region of the brain inclusive of POA, vHy, AV, pineal and pituitary gland of croaking frog showed upregulation of CART mRNA. However, CART immunoreactivity in the neuronal perikarya of raphe (Ra) was completely abolished during croaking activity. The data suggest that CART signaling in the brain may be an important player in mediating croaking behaviour in the frog.

Social regulation of androgenic hormones and gestural display behavior in a tropical frog

Many animals use forms of gesture and dance to communicate with conspecifics in the breeding season, though the mechanisms of this behavior are rarely studied. Here, we investigate the hormone basis of such visual signal behavior in Bornean rocks frogs (Staurois parvus). Our results show that males aggregating at breeding waterfalls have higher testosterone (T) levels, and we speculate that this hormone increase is caused by social cues associated with sexual competition. To this end, we find that T levels in frogs at the waterfall positively predict the number waving gestures-or "foot flags"-that males perform while competing with rivals. By contrast, T does not predict differences in male calling behavior. In these frogs, vocal displays are used largely as an alert signal to direct a rival's attention to the foot flag; thus, our results are consistent with the view that factors related to reproductive context drive up T levels to mediate displays most closely linked to male-male combat, which in this case is the frog's elaborate gestural routine.

Arginine vasotocin affects motivation to call, but not calling plasticity, in Cope's gray treefrog Hyla chrysoscelis

The ability to respond to competition is critical for social behaviors involved in mating, territoriality and foraging. Physiological mechanisms of competitive social behaviors may determine not only baseline behavior, but possibly also the plasticity of the response to competition. We examined the effects of the neuropeptide arginine vasotocin (AVT), which is implicated in social behavior in non-mammalian vertebrates, on both spontaneous acoustic advertisement calling behavior and the plastic response to a simulated competitive challenge in Cope's gray treefrogs, Hyla chrysoscelis. We injected males either with AVT or a saline control and then analyzed recordings of spontaneous calling prior to playback, playback of average advertisement calls, playback of highly competitive advertisement calls, and spontaneous calling after playback. We found a tendency for AVT-treated males to be more likely to resume calling, and AVT males had higher call rates than control males, although they did not differ in pulse number or call effort. There were no differences between the AVT and control treatments in the plasticity of calling behavior in response to simulated competitors. Our results generally align with other studies on how AVT affects anuran vocalizations, and suggest that its primary effect is on motivation to call, with less of an effect on plasticity in response to competition. Nevertheless, these effects on call motivation are significant, because mating success is often determined more by participation in the chorus than by the values of specific call characteristics.

Serotonin and vasotocin function in territoriality

This ethopharmacological investigation comprised a long-term field study that examined the function of serotonergic and vasotonergic systems in territoriality. Adult territorial and non-territorial (silent) male coquí frogs (Eleutherodactylus coqui) were injected (IP) with either arginine vasotocin (AVT) or one of two serotonin agonists, 5-HT_2A/2C selective agonist, (±) DOI - [(±)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane], or 2) the 5-HT_1A selective agonist, 8-OH-DPAT - [(±)-2-dipropylamino-8-hydroxy-1,2,3,4-tetrahydronaphthalene]. Control groups received saline injections. Each male received two injections. Following the first injection, whether AVT or a 5HT agonist, the male was observed so that behavior could be documented prior to the second injection, which consisted of the other drug class. All frogs were marked, placed back in the exact location as captured, and observed for all behaviors and vocalizations. Territoriality in E. coqui includes several behavioral components: movement into a calling site, presentation of dominant physical displays, emitting advertisement calls, and defense a territory (including the use of physical force and/or aggressive vocalizations). This investigation found that particular territorial behaviors were significantly influenced by 5HT and AVT action. Initiation of advertisement calling is activated by AVT and suppressed by 5HT, calling rate is affected by 5HT activation, presentation of dominant physical displays are activated by AVT and repressed by 5HT activation, and movement associated with activation of territorial behavior is stimulated by AVT. These data suggested that both 5HT and AVT have a profound impact on territoriality and are two fundamental neuroendocrine systems that govern territorial behavior in social systems.

Arginine Vasotocin, the Social Neuropeptide of Amphibians and Reptiles

Arginine vasotocin (AVT) is the non-mammalian homolog of arginine vasopressin (AVP) and, like vasopressin, serves as an important modulator of social behavior in addition to its peripheral functions related to osmoregulation, reproductive physiology, and stress hormone release. In amphibians and reptiles, the neuroanatomical organization of brain AVT cells and fibers broadly resembles that seen in mammals and other taxa. Both parvocellular and magnocellular AVT-containing neurons are present in multiple populations located mainly in the basal forebrain from the accumbens-amygdala area to the preoptic area and hypothalamus, from which originate widespread fiber connections spanning the brain with a particularly heavy innervation of areas associated with social behavior and decision-making. As for mammalian AVP, AVT is present in greater amounts in males in many brain areas, and its presence varies seasonally, with hormonal state, and in males with differing social status. AVT's social influence is also conserved across herpetological taxa, with significant effects on social signaling and aggression, and, based on the very small number of studies investigating more complex social behaviors in amphibians and reptiles, AVT may also modulate parental care and social bonding when it is present in these vertebrates. Within this conserved pattern, however, both AVT anatomy and social behavior effects vary significantly across species. Accounting for this diversity represents a challenge to understanding the mechanisms by which AVT exerts its behavioral effects, as well are a potential tool for discerning the structure-function relationships underlying AVT's many effects on behavior.

Vasotocin increases dominance in the weakly electric fish Brachyhypopomus gauderio

Animals establish social hierarchies through agonistic behavior. The recognition of the own and others social ranks is crucial for animals that live in groups to avoid costly constant conflicts. Weakly electric fish are valuable model systems for the study of agonistic behavior and its neuromodulation, given that they display conspicuous electrocommunication signals that are generated by a very well-known electromotor circuit. Brachyhypopomus gauderio is a gregarious electric fish, presents a polygynous breeding system, morphological and electrophysiological sexual dimorphism during the breeding season, and displays a typical intrasexual reproduction-related aggression. Dominants signal their social status by increasing their electric organ discharge (EOD) rate after an agonistic encounter (electric dominance). Subordinates only occasionally produce transient electric signals (chirps and offs). The hypothalamic neuropeptide arginine-vasotocin (AVT) and its mammalian homologue, arginine- vasopressin (AVP) are key modulators of social behavior across vertebrates. In this study, we focus on the role of AVT on dominance establishment in Brachyhypopomus gauderio by analyzing the effects of pharmacological manipulations of the AVT system in potential dominants. AVT exerts a very specific direct effect restricted only to EOD rate, and is responsible for the electric dominance. Unexpectedly, AVT did not affect the intensity of aggression in either contender. Nor was the time structure affected by AVT administration. We also present two interesting examples of the interplay between contenders by evaluating how AVT modulations, even when directed to one individual, affect the behavior of the dyad as a unit. First, we found that V1a AVT receptor antagonist Manning Compound (MC) induces a reversion in the positive correlation between dominants' and subordinates' attack rates, observed in both control and AVT treated dyads, suggesting that an endogenous AVT tone modulates aggressive interactions. Second, we confirmed that AVT administered to dominants induces an increase in the submissive transient electric signals in subordinates.

Sexually dimorphic effects of melatonin on brain arginine vasotocin immunoreactivity in green treefrogs (Hyla cinerea)

Arginine vasotocin (AVT) and its mammalian homologue, arginine vasopressin (AVP), regulate a variety of social and reproductive behaviors, often with complex species-, sex- and context-dependent effects. Despite extensive evidence documenting seasonal variation in brain AVT/AVP, relatively few studies have investigated the environmental and/or hormonal factors mediating these seasonal changes. In the present study, we investigated whether the pineal hormone melatonin alters brain AVT immunoreactivity in green treefrogs (Hyla cinerea). Reproductively active male and female frogs were collected during the summer breeding season and a melatonin-filled or blank silastic capsule was surgically implanted subcutaneously. The duration of hormone treatment was 4 weeks, at which time frogs were eutha-nized and the brains and blood collected and processed for AVT immunohistochemistry and steroid hormone assay. We quantified AVT-immunoreactive (AVT-ir) cell bodies in the nucleus accumbens (NAcc), caudal striatum and amygda- la (AMG), anterior preoptic area, suprachiasmatic nucleus (SCN) and infundibular region of the ventral hypothalamus. Sex differences in AVT-ir cell number were observed in all brain regions except in the anterior preoptic area and ventral hypothalamus, with males having more AVT-ir cells than females in the NAcc, amygdala and SCN. Brain AVT was sensitive to melatonin signaling during the breeding season, and the effects of melatonin varied significantly with both region and sex. Treatment with melatonin decreased AVT immunoreactivity in both the NAcc and SCN in male H. cinerea. In contrast, brain AVT was relatively insensitive to melatonin signaling in females, indicating that the regulation of the AVT/AVP neuropeptide system by melatonin may be sexually dimorphic. Finally, melatonin did not significantly influence testosterone or estradiol concentrations of male or female frogs, respectively, suggesting that the effects of melatonin on AVT immunoreactivity are independent of changes in gonadal sex steroid hormones. Collectively, our results indicate that the AVT/AVP neuronal system may be an important target for melatonin in facilitating seasonal changes in reproductive physiology and social behavior.

The synthetic progestogen, Levonorgestrel, but not natural progesterone, affects male mate calling behavior of Xenopus laevis

Worldwide, more than 100 million women use hormonal contraceptives, which act through progestogenic modes of action. These man-made hormones can enter the aquatic environment as they are excreted via feces and urine. Xeno-progestins are able to interfere with the endocrine system of female aquatic vertebrates impairing oogenesis and reproduction. However, data on progestogenic effects on reproductive behavior of male aquatic vertebrates are lacking. To evaluate whether progestins affect the mating behavior of male Xenopus laevis, we exposed male frogs to three environmentally relevant concentrations (10(-7) M, 10(-8) M and 10(-10) M) of the synthetic progestin Levonorgestrel (LNG) and the corresponding natural steroid progesterone (PRG), respectively. LNG at all exposure concentrations increased the proportions of advertisement calling, indicating a sexually aroused state of the males. Furthermore LNG at 10(-7) M decreased the relative proportions of rasping, a call type indicating a sexually unaroused state of the male. PRG, on the other hand, did not affect any of those parameters. Temporal and spectral features of the advertisement call itself were not affected by any of the two exposure treatments. Since LNG exhibits slight androgenic activity, the results suggest that LNG effects on male mate calling behavior of X. laevis are due to its moderate androgenic but not to its progestogenic activities. However, although males' sexual arousal seems to be enhanced by LNG, the adverse effects of LNG on female reproduction presumably outweigh these enhancing effects and LNG exposure nonetheless might result in reduced reproductive success of these animals.

Treatment with arginine vasotocin alters mating calls and decreases call attractiveness in male túngara frogs

The peptide hormone arginine vasotocin (AVT) and its mammalian homolog arginine vasopressin modulate a variety of social behaviors in vertebrates. In anurans, AVT influences the production of advertisement calls, the acoustic signals that males use to attract females and repel rival males. In this study, we investigate the effects of AVT on call characteristics in the túngara frog (Physalaemus pustulosus). Túngara frogs produce a "whine" that is important for species recognition; they may also produce a second, attractive call component, the "chuck". We used a field playback experiment to determine changes in male calling behavior following treatment with AVT. A previous study showed that AVT alters call rate and the production of chucks; in the current analysis, we focus on changes in the whine. Males produce shorter whines with higher initial frequencies following treatment with AVT. Call changes do not vary with a social stimulus. We also used female phonotaxis experiments to investigate the effects of call changes on female mate choice. Females disfavor the calls produced by males treated with exogenous AVT. We suggest that AVT influences motivation to call and the motor control of call production, but that over-stimulation of the vocal system limited the production of attractive calls in this experimental context.

Neurosteroid biosynthesis: enzymatic pathways and neuroendocrine regulation by neurotransmitters and neuropeptides

Neuroactive steroids synthesized in neuronal tissue, referred to as neurosteroids, are implicated in proliferation, differentiation, activity and survival of nerve cells. Neurosteroids are also involved in the control of a number of behavioral, neuroendocrine and metabolic processes such as regulation of food intake, locomotor activity, sexual activity, aggressiveness, anxiety, depression, body temperature and blood pressure. In this article, we summarize the current knowledge regarding the existence, neuroanatomical distribution and biological activity of the enzymes responsible for the biosynthesis of neurosteroids in the brain of vertebrates, and we review the neuronal mechanisms that control the activity of these enzymes. The observation that the activity of key steroidogenic enzymes is finely tuned by various neurotransmitters and neuropeptides strongly suggests that some of the central effects of these neuromodulators may be mediated via the regulation of neurosteroid production.

Sexual hearing: the influence of sex hormones on acoustic communication in frogs

The majority of anuran amphibians (frogs and toads) use acoustic communication to mediate sexual behavior and reproduction. Generally, females find and select their mates using acoustic cues provided by males in the form of conspicuous advertisement calls. In these species, vocal signal production and reception are intimately tied to successful reproduction. Research with anurans has demonstrated that acoustic communication is modulated by reproductive hormones, including gonadal steroids and peptide neuromodulators. Most of these studies have focused on the ways in which hormonal systems influence vocal signal production; however, here we will concentrate on a growing body of literature that examines hormonal modulation of call reception. This literature suggests that reproductive hormones contribute to the coordination of reproductive behaviors between signaler and receiver by modulating sensitivity and spectral filtering of the anuran auditory system. It has become evident that the hormonal systems that influence reproductive behaviors are highly conserved among vertebrate taxa. Thus, studying the endocrine and neuromodulatory bases of acoustic communication in frogs and toads can lead to insights of broader applicability to hormonal modulation of vertebrate sensory physiology and behavior.

Arginine Vasotocin Promotes Calling Behavior and Call Changes in Male Túngara Frogs

In the túngara frog, Physalaemus pustulosus, males alter calling behavior with changes in their social environment, adding 'chucks' to their advertisement calls in response to the calls of conspecific males. Other studies demonstrate that adding chucks increases the attractiveness of calls to females but also increases the risk of bat predation. In the current study, subcutaneous injections of the neuropeptide hormone arginine vasotocin (AVT) significantly increased chuck production in male túngara frogs. The effects of AVT on chuck production did not depend on the presence of playback stimuli, suggesting that AVT increased either the males' general motivation to produce chucks or their responsiveness to the calls of distant males. Injections of AVT also increased the probability that males would call and decreased the latency to call after injection, supporting the hypothesis that AVT influences motivation to call. Finally, AVT inhibited a drop in call rate after the termination of a playback stimulus and increased call rate at a lower dose of AVT. The effects of AVT on chucks and call rate appear to be independent of each other, as there was no correlation between change in chuck production and change in call rate in individual males. We conclude that AVT may play an important role in socially-mediated call changes that result from competition for mates. The behavioral changes induced by AVT might increase a male's attractiveness to females, and also may be consistent with an aggressive response to another túngara frog male.

Vasotocin and mesotocin stimulate the biosynthesis of neurosteroids in the frog brain

The neurohypophysial nonapeptides vasopressin (VP) and oxytocin (OT) modulate a broad range of cognitive and social activities. Notably, in amphibians, vasotocin (VT), the ortholog of mammalian VP, plays a crucial role in the control of sexual behaviors. Because several neurosteroids also regulate reproduction-related behaviors, we investigated the possible effect of VT and the OT ortholog mesotocin (MT) in the control of neurosteroid production. Double immunohistochemical labeling of frog brain sections revealed the presence of VT/MT-positive fibers in close proximity of neurons expressing the steroidogenic enzymes 3beta-hydroxysteroid dehydrogenase/delta5-delta4 isomerase (3beta-HSD) and cytochrome P450 17alpha-hydroxylase/c17, 20-lyase (P450(C17)). High concentrations of VT and MT receptor mRNAs were observed in diencephalic nuclei containing the 3beta-HSD and P450(C17) neuronal populations. Exposure of frog hypothalamic explants to graded concentrations of VT or MT produced a dose-dependent increase in the formation of progesterone, 17-hydroxypregnenolone, 17-hydroxyprogesterone, and dehydroepiandrosterone. The stimulatory effect of VT and MT on neurosteroid biosynthesis was mimicked by VP and OT, as well as by a selective V1b receptor agonist, whereas V2 and OT receptor agonists had no effect. VT-induced neurosteroid production was completely suppressed by selective V1a receptor antagonists and was not affected by V2 and OT receptor antagonists. Concurrently, the effect of MT on neurosteroidogenesis was markedly attenuated by selective OT and V1a receptor antagonists but not by a V2 antagonist. The present study provides the first evidence for a regulatory effect of VT and MT on neurosteroid biosynthesis. These data suggest that neurosteroids may mediate some of the behavioral actions of VT and MT.

Elevated corticosterone levels elicit non-calling mating tactics in male toads independently of changes in circulating androgens

Competition among males for a limited number of females may result in the expression of condition-dependent alternative mating tactics. In such cases, decision rules mediating mating tactic expression are likely to be influenced by a male's external as well as internal environment. For example, experimental studies with anuran amphibians (frogs and toads) indicate that changes in the social-acoustic environment alter the probability that an individual adopts a calling versus non-calling "satellite" mating tactic. However, there is considerable variation in the behavioral responses of individuals in such studies, suggesting that physiological differences among individuals play an important role in tactic expression. For instance, recent models predict that natural elevation in adrenal glucocorticoids during vocal production alters androgen production and/or neural activity to mediate transitions between reproductive tactic expression in anuran amphibians. Using corticosteroid injections, we show that elevation in circulating corticosterone levels significantly increase the probability that free-ranging male Great Plains toads (Bufo cognatus) and Woodhouse's toads (B. woodhousii) adopt a non-calling satellite tactic. Corticosterone-induced behavioral transitions occurred rapidly (<1 h) and independently of fluctuations in circulating androgen levels, suggesting a direct effect of glucocorticoids on brain centers controlling vocal production. We discuss our findings in the context of behavioral studies that alter the social-acoustic environment to examine its influence on tactic expression.

Current research in amphibians: studies integrating endocrinology, behavior, and neurobiology

Amphibian behavioral endocrinology has focused on reproductive social behavior and communication in frogs and newts. Androgens and estrogens are critical for the expression of male and female behavior, respectively, and their effects are relatively clear. Corticosteroids have significant modulatory effects on the behavior of both sexes, as does the peptide neuromodulator arginine vasotocin in males, but their effects and interactions with gonadal steroids are often complex and difficult to understand. Recent work has shown that the gonadal hormones and social behavior are mutually reinforcing: engaging in social interactions increases hormone levels just as increasing hormone levels change behavior. The reciprocal interactions of hormones and behavior, as well as the complex interactions among gonadal steroids, adrenal steroids, and peptide hormones have implications for the maintenance and evolution of natural social behavior, and suggest that a deeper understanding of both endocrine mechanisms and social behavior would arise from field studies or other approaches that combine behavioral endocrinology with behavioral ecology.

Historical perspective: Hormonal regulation of behaviors in amphibians

This review focuses on research into the hormonal control of behaviors in amphibians that was conducted prior to the 21st century. Most advances in this field come from studies of a limited number of species and investigations into the hormonal mechanisms that regulate reproductive behaviors in male frogs and salamanders. From this earlier research, we highlight five main generalizations or conclusions. (1) Based on studies of vocalization behaviors in anurans, testicular androgens induce developmental changes in cartilage and muscles fibers in the larynx and thereby masculinize peripheral structures that influence the properties of advertisement calls by males. (2) Gonadal steroid hormones act to enhance reproductive behaviors in adult amphibians, but causal relationships are not as well established in amphibians as in birds and mammals. Research into the relationships between testicular androgens and male behaviors, mainly using castration/steroid treatment studies, generally supports the conclusion that androgens are necessary but not sufficient to enhance male behaviors. (3) Prolactin acts synergistically with androgens and induces reproductive development, sexual behaviors, and pheromone production. This interaction between prolactin and gonadal steroids helps to explain why androgens alone sometimes fail to stimulate amphibian behaviors. (4) Vasotocin also plays an important role and enhances specific types of behaviors in amphibians (frog calling, receptivity in female frogs, amplectic clasping in newts, and non-clasping courtship behaviors). Gonadal steroids typically act to maintain behavioral responses to vasotocin. Vasotocin modulates behavioral responses, at least in part, by acting within the brain on sensory pathways that detect sexual stimuli and on motor pathways that control behavioral responses. (5) Corticosterone acts as a potent and rapid suppressor of reproductive behaviors during periods of acute stress. These rapid stress-induced changes in behaviors use non-genomic mechanisms and membrane-associated corticosterone receptors.

Arginine vasotocin activates advertisement calling and movement in the territorial Puerto Rican frog, Eleutherodactylus coqui

Arginine vasotocin (AVT) is a neuropeptide that modulates social behavior in amphibians and activates calling in frogs. The Puerto Rican coqui frog, Eleutherodactylus coqui, is a terrestrial anuran that exhibits complex social behaviors, including territoriality and paternal care. Males have a distinctive social hierarchy and can be any of the following: satellite (non-calling), territorial (calling), or paternal (guards and broods embryos). Field experiments were conducted to determine the effects of AVT on satellite behavior and the male social hierarchy of E. coqui. Satellite males were captured within the territory held by a resident male, given injections (i.p.) of AVT or saline (control) and placed back in their original location. To determine if AVT affects all males, not merely satellite males, territorial (calling) males were injected with AVT. Significantly more satellite males commenced advertisement calling following AVT injections than did control males injected with saline. AVT-activated satellites did not challenge the resident territorial male for possession of the territory but instead moved into a new area before commencing to call. In fact, AVT-activated satellite males were significantly more likely to move into a new territory following AVT injections than AVT-injected territorial males. The effect of AVT was short lived, lasting only one night in all but two cases. It is concluded that AVT stimulates advertisement calling and AVT-activated males displayed territorial characteristics of E. coqui.

Behavioral and hormonal effects of exogenous vasotocin and corticosterone in the green treefrog

Vasotocin (AVT) promotes courtship in a wide range of vertebrates. However, this effect is not independent of steroid hormones. For example, androgens may work in concert with AVT and corticosterone (CORT) may work to oppose AVT action. In frogs, AVT promotes calling, and in some species, CORT inhibits calling. In addition, androgens are known to modulate AVT in the brain, and CORT may depress androgen secretion. Previous work in amphibians has suggested that AVT promotes courtship by overcoming a CORT-mediated stress response. Possible behavioral and hormonal interactions among AVT, CORT, and androgens were investigated in wild, free-living green treefrogs (Hyla cinerea). Saline, AVT, CORT, or a combination of AVT and CORT were administered to calling males, and several measures of spontaneous calling were evaluated for 1.5 h following injection. Plasma testosterone, dihydrotestosterone, and CORT were also measured. Saline-injected males had low CORT levels, and AVT and CORT injection elevated plasma CORT levels. AVT increased the likelihood of calling, but, in males who did call, AVT did not influence latency to call or how often they were observed calling. Very few saline-injected males resumed calling after injection, and therefore a CORT effect was only detectable in AVT-injected males. CORT inhibited calling in AVT-injected males only at the highest dose of CORT (40 microg); lower levels of CORT were unsuccessful at inhibiting AVT-induced calling. AVT appeared to have a specific effect on calling motivation. Further, the data suggest that disinhibition of a CORT response is not the primary mechanism by which AVT increases calling. In addition, CORT injection reduced endogenous androgen levels. Finally, endogenous androgens were negatively correlated with latency to begin calling, suggesting that they may have a positive effect on calling. These data indicate that AVT has positive effects on calling but provide only weak evidence that CORT inhibits courtship in this species.