Dissociation of oxytocin, vasopressin and corticotropin secretion during different types of stress

Oxytocin (OT), vasopressin (AVP), and corticotropin (ACTH) levels were measured in peripheral plasma of male rats subjected to one of three models of stress: restraint, cold, or ether. ACTH secretion was increased in all three groups compared to unstressed controls. OT secretion was increased in rats subjected to restraint or ether but not cold. AVP secretion was increased only by ether stress. The data suggest that the hypothalamic and neurohypophysial contribution to the control of ACTH secretion may vary in response to different types of stress.     

Both oxytocin and vasopressin may influence alloparental behavior in male prairie voles

Neuropeptides, especially oxytocin (OT) and arginine vasopressin (AVP), have been implicated in several features of monogamy including alloparenting. The purpose of the present study was to examine the role of OT and AVP in alloparental behavior in reproductively na?ve male prairie voles. Males received intracerebroventricular (ICV) injections of artificial cerebrospinal fluid (aCSF), OT, an OT receptor antagonist (OTA), AVP, an AVP receptor antagonist (AVPA), or combinations of OTA and AVPA and were subsequently tested for parental behavior. Approximately 45 min after treatment, animals were tested for behavioral responses to stimulus pups. In a 10-min test, spontaneous alloparental behavior was high in control animals. OT and AVP did not significantly increase the number of males that showed parental behavior, although more subtle behavioral changes were observed. Combined treatment with AVPA and OTA (10 ng each) significantly reduced male parental behavior and increased attacks; following a lower dose (1 ng OTA/1 ng AVPA), males were less likely to display kyphosis and tended to be slower to approach pups than controls. Since treatment with only one antagonist did not interfere with the expression of alloparenting, these results suggest that access to either OT or AVP receptors may be sufficient for the expression of alloparenting.     

小型田鼠:研究单配制进化与调控的模型

哺乳动物的单配制通常被认为是社会性单配制,它不是单纯地由性行为来决定,而是由诸多因素,包括长期的pair bond、夫妻双方共同抚育后代、免近亲交配以及雌雄两性相似等来决定的。在这篇综述中,我们论述了如何以啮齿类田鼠属(Microtus)为模型,通过比较研究来帮助我们理解社会性单配制的进化以及其神经调控机制。对田鼠属的研究不仅证实了单配制起源于艰苦的生存条件的假说,而且还证实了雌性性选择可能有利于维持单配制。不仅如此,哺乳动物单配制的进化还需要雄性的prosocial行为的不断强化。例如,亲近行为可以促进pairbond的形成并强化雄性对后代的哺育行为,而这种强化则来源于神经多肽催产素(OT)和加压素(AVP)与类固醇类激素的相互作用。催产素和加压素调控pairbond和双亲哺育行为的表达,而单配制和多配制田鼠的催产素和加压素受体在脑内的分布有显的不同。比较研究揭示了小型田鼠单配制的调控机制,而种内差异和行为上的可塑性则有助于我们进一步理解这种机制。比如,在某些条件下,多配制的草原田鼠(Microtus pennsylvanicu)的雄性个体具有哺育后代的行为。尽管草原田鼠的加压素Vla受体在脑内的分布与其他多配制的田鼠相似,但是如果脑室注射加压素,仍可以诱发其哺育后代的行为。同样是单配制的橙腹田鼠(Microtus ochrogaster),生活在：Illnois的显示出高水平的prosocial行为,而生活在Kansas的则表现出较低水平的社会性行为。即使两个种群的催产素或加压素Vla受体在脑内的分布相同,它们的雌激素受体表达水平显不同,这在雄性个体表现尤其明显。与Kansas的雄性个体相比,在终纹床核(bed rucleus of the stria tenninalis)和杏仁核中区(medial amygdala)这两个调控亲近行为和攻击行为的脑区,Illinois的雄性个体的α雌激素受体的水平要低得多。这些研究表明对雌激素的低敏感程度有利于高水平地表达prosocial行为并降低特定类型的攻击行为。     

Non-invasive measurement of small peptides in the common marmoset (Callithrix jacchus): a radiolabeled clearance study and endogenous excretion under varying social conditions

A non-invasive assay for measurement of oxytocin (OT) and vasopressin (AVP) in primates would enable researchers to study the relationship between the endocrine system and behavior without disturbing potentially endangered animals in their natural habitats. In order to test whether or not OT specifically would be measurable in the urine of a primate, 10 microCi of tritium-labeled OT were injected into the peripheral blood supply of four adult male common marmosets (Callithrix jacchus), with continuous urinary collection over 48 h. When urine was processed by HPLC separation and beta counting for radioactive clearance, the label was present in all samples in the fraction where OT elutes. Large amounts of OT were also seen in a fraction other than that containing the OT standard, indicating that OT is measurable but that it also undergoes substantial metabolic breakdown. In a second experiment, we isolated six common marmosets for 48 h and then exposed them to social contact to evaluate the effect of changing social stimuli on endogenous urinary measurement of both OT and AVP. Both were measured after HPLC separation to isolate the intact molecule and also to control for cross-reactivity with metabolites in subsequent RIA. Cortisol was also measured to objectively evaluate the stress response. A priori assumptions were that urinary OT and AVP would be lower during a period of isolation and higher during periods of social contact. These assumptions were met, leading us to conclude that peripheral OT and AVP are measurable via urinary assay and that such an assay is a valid means of evaluating social condition in this species.     

Peripherally administered non-peptide oxytocin antagonist, L368,899, accumulates in limbic brain areas: a new pharmacological tool for the study of social motivation in non-human primates

Central administration of oxytocin (OT) antagonists inhibits maternal and sexual behavior in non-primates, providing the strongest experimental evidence that endogenous OT facilitates these behaviors. While there have been a few reports that ICV administration of OT increases social behaviors in monkeys, no studies to date have assessed the effects of OT antagonists. Therefore, we studied in rhesus monkeys whether L368,899, a non-peptide antagonist produced by Merck that selectively blocks the human uterine OT receptor, penetrates the CNS after peripheral administration and alters female maternal and sexual behavior. In two studies in four male monkeys, L368,899 was injected iv (1 mg/kg) after which (1) CSF samples were collected at intervals over 4 h and (2) brains were collected at 60 min. Assay of samples confirmed that iv-administered L368,899 entered CSF and accumulated in the hypothalamus, septum, orbitofrontal cortex, amygdala and hippocampus, but not other areas. An adult female monkey was tested for interest in either an infant or sexual behavior, receiving a different iv treatment prior to each test (1 or 3 mg/kg of L368,899 or saline). OT antagonist treatment reduced or eliminated interest in the infant and sexual behavior. These results, although preliminary, are the first to directly implicate endogenous OT in activation of primate maternal interest and sexual behavior. While it remains to be empirically demonstrated that peripherally administered L368,899 blocks central OT receptors, our behavioral findings suggest that this non-peptide antagonist may facilitate testing OT involvement in a variety of social and other behaviors in primates.     

Preferential release of oxytocin in response to vasoactive intestinal polypeptide in rats

Vasoactive intestinal polypeptide (VIP) was infused into the aorta of pentobarbitone-anesthetized rats (n = 12) in stepwise increasing doses of 0.001 to 10 micrograms/rat at rates varying from 0.3 pmol/min/kg to 3000 pmol/min/kg over 3 min. Blood was withdrawn from the vena cava inferior for the measurement of oxytocin (OT) and vasopressin (AVP) by RIA. The loss of blood was compensated for by infusion of isotonic saline (0.9% NaCl with 0.5% human serum albumin). Control rats received this solution only (n = 11). VIP infusions resulted in a dose-dependent increase in plasma OT which was significantly greater than the slight rise observed in the controls. The difference from controls was significant at infusion rates of 3 pmol/min/kg and more. Plasma AVP, on the other hand, did not rise in response to VIP infusions until the infusion rate was increased to 300 and 3000 pmol/min/kg. At these infusion rates, the increments in AVP were much smaller than those of OT, the levels during the highest infusion rates rising to 8.6 +/- 2.8 and 27.2 +/- 4.8 microU/ml, respectively (log normal means). The preferential release of OT in response to exogenous VIP in rats differs from the response in cats where intracarotid administration of VIP resulted in the release of proportionately more AVP than OT. Immunoreactive VIP is found in the hypothalamo-neurohypophyseal system of rats in close proximity of some of the magnocellular neurons as well as within the nerve terminals. This, together with our data, suggests that endogenous VIP may participate in the release mechanism for OT in rats.     

The contribution of oxytocin and vasopressin to mammalian social behavior: potential role in autism spectrum disorder

Oxytocin (OT) and arginine-vasopressin (AVP) are 2 peptides that are produced in the brain and released via the pituitary gland to the peripheral blood, where they have diverse physiological functions. In the last 2 decades it has become clear that these peptides also play a central role in the modulation of mammalian social behavior by their actions within the brain. Several lines of evidence suggest their involvement in autism spectrum disorder (ASD), which is known to be associated with impaired social cognition and behavior. Recent clinical trials using OT administration to autistic patients have reported promising results. Here, we aim to describe the main data that suggest a connection between these peptides and ASD. Following a short illustration of several major topics in ASD biology we will (a) briefly describe the oxytocinergic and vasopressinergic systems in the brain, (b) discuss a few compelling cases manifesting the involvement of OT and AVP in mammalian social behavior, (c) describe data supporting the role of these peptides in human social cognition and behavior, and (d) discuss the possibility of the involvement of OT and AVP in ASD etiology, as well as the prospect of using these peptides as a treatment for ASD patients.     

田鼠婚配制度的神经内分泌基础

作为繁殖行为的一种表现形式,婚配制度是通过长期进化而形成的,具有种属特异性及可遗传性。因此,不同的婚配制度具有不同的生理基础。这种生理基础由3级结构组成：神经直接启动并维持繁殖行为;激素或通过诱导特异神经通路的发育或直接激活神经传导影响繁殖行为;基因则可能是通过调节激素的代谢和作用方式来控制与繁殖行为相关的神经系统。田鼠脑中涉及婚配制度的区域集中在视前区中部（MPOA）,腹被盖区（VTA）,膈部及纹状体端部。起作用的激素主要是催产素（OT）和后叶加压素（AVP）。导致田鼠形成不同婚配制度的最终原因可能是这两种激素受体基因上的差异。受体基因调控区的启动子序列存在变异,导致脑中受体基因在表达区域上的差异,进而使激素激活不同的神经通路,产生不同的繁殖行为及婚配制度。     

U-Shaped Relation between Plasma Oxytocin Levels and Behavior in the Trust Game

Trust underpins much of social and economic exchanges across human societies. In experimental economics, the Trust Game has served as the workhorse for the study of trust in a controlled incentivized setting. Recent evidence using intranasal drug administration, aka ‘sniffing’, suggests that oxytocin (OT) can function as a social hormone facilitating trust and other affiliative behaviors. Here we hypothesized that baseline plasma OT is a biomarker that partially predicts the degree of trust and trustworthiness observed in the trust game. Using a large sample of 1,158 participants, we observed a significant U-shaped relationship between plasma OT with the level of trust, and marginally with the level of trustworthiness, especially among males. Specifically, subjects with more extreme levels of plasma OT were more likely to be trusting as well as trustworthy than those with moderate levels of plasma OT. Our results contribute to a deeper understanding of the biological basis of human trust and underscore the usefulness of peripheral plasma OT measures in characterizing human social behavior. “You must trust and believe in people or life becomes impossible.” Anton Chekhov.     

Social environment regulates corticotropin releasing factor, corticosterone and vasopressin in juvenile prairie voles

Stressful social conditions, such as isolation, that occur during sensitive developmental periods may alter present and future social behavior. Changes in the neuroendocrine mechanisms closely associated with affiliative behaviors and stress reactivity are likely to underlie these changes in behavior. In the present study, we assessed the effects of post-weaning social housing conditions on the neuropeptides arginine vasopressin (AVP) and oxytocin (OT), and components of the hypothalamic-pituitary-adrenal axis (corticotropin releasing factor: [CRF], and corticosterone: [CORT]) in the prairie vole (Microtus ochrogaster), a socially monogamous bi-parental rodent. Following weaning at 21 days of age, prairie voles were maintained in one of three housing conditions: social isolation (isolate), paired with a same sex sibling (sibling) or paired with a stranger (stranger) of the same sex and age. Housing conditions were maintained for either 4 or 21 days. Central CRF, AVP and OT immunoreactivity (ir) were quantified and circulating plasma CORT, AVP and OT were assayed. Isolated voles had higher CRF-ir in the paraventricular nucleus of the hypothalamus (PVN) compared with sibling and stranger housed voles. Plasma CORT was significantly higher in isolates. AVP-ir was significantly lower in the PVN of isolate females compared to either sibling females or stranger females. However, AVP-ir was significantly higher in the supraoptic nucleus (SON) of isolates compared to siblings. There were no differences in central OT-ir or plasma OT. These results identify neuroendocrine mechanisms which respond to isolation and potentially modulate behavior.     

视觉和嗅觉密度信号对布氏田鼠社会应激的影响

鼠类具有密度依赖的行为—内分泌反馈调节机制:当其种群密度升高时,会产生社会应激,增加紧张焦虑、攻击等行为,同时其神经内分泌也产生相应变化.然而,密度升高引起的社会应激可能涉及到视觉、嗅觉、触觉、听觉、味觉等不同感官,而不同感官对社会应激反应产生的独特作用尚不清楚.我们以前的研究发现,高密度饲养可导致雄性布氏田鼠脑部催产...     

Adolescent oxytocin exposure causes persistent reductions in anxiety and alcohol consumption and enhances sociability in rats

Previous studies have suggested that administration of oxytocin (OT) can have modulatory effects on social and anxiety-like behavior in mammals that may endure beyond the time of acute OT administration. The current study examined whether repeated administration of OT to male Wistar rats (n = 48) during a key developmental epoch (early adolescence) altered their physiology and behavior in later-life. Group housed rats were given intraperitoneal injections of either 1 mg/kg OT or vehicle during early adolescence (post natal-days [PND] 33–42). OT treatment caused a transient inhibition of body weight gain that recovered quickly after the cessation of treatment. At PND 50, the rats pre-treated with OT displayed less anxiety-like behavior on the emergence test, while at PND 55 they showed greater levels of social interaction. A subgroup of OT pre-treated rats examined at PND 63 showed a strong trend towards increased plasma OT levels, and also displayed significantly increased OT receptor mRNA in the hypothalamus. Rats pre-treated with OT and their controls showed similar induction of beer intake in daily 70 min test sessions (PND 63 onwards) in which the alcohol concentration of beer was gradually increased across days from 0.44% to 4.44%. However, when given ad libitum access to beer in their home cages from PND 72 onwards (early adulthood), consumption of beer but not water was significantly less in the OT pre-treated rats. A “booster” shot of OT (1 mg/kg) given after 25 days of ad libitum access to beer had a strong acute inhibitory effect on beer intake without affecting water intake. Overall these results suggest that exogenous OT administered during adolescence can have subtle yet enduring effects on anxiety, sociability and the motivation to consume alcohol. Such effects may reflect the inherent neuroplasticity of brain OT systems and a feed-forward effect whereby exogenous OT upregulates endogenous OT systems.     

Evoked axonal oxytocin release in the central amygdala attenuates fear response

The hypothalamic neuropeptide oxytocin (OT), which controls childbirth and lactation, receives increasing attention for its effects on social behaviors, but how it reaches central brain regions is still unclear. Here we gained by recombinant viruses selective genetic access to hypothalamic OT neurons to study their connectivity and control their activity by optogenetic means. We found axons of hypothalamic OT neurons in the majority of forebrain regions, including the central amygdala (CeA), a structure critically involved in OT-mediated fear suppression. In vitro, exposure to blue light of channelrhodopsin-2-expressing OT axons activated a local GABAergic circuit that inhibited neurons in the output region of the CeA. Remarkably, in vivo, local blue-light-induced endogenous OT release robustly decreased freezing responses in fear-conditioned rats. Our results thus show widespread central projections of hypothalamic OT neurons and demonstrate that OT release from local axonal endings can specifically control region-associated behaviors.     

Locus Coeruleus Lesions Decrease Oxytocin and Vasopressin Release Induced by Hemorrhage

The role of the noradrenergic nucleus Locus Coeruleus (LC) on hemorrhage-induced vasopressin (AVP) and oxytocin (OT) secretion was examined. Rats with LC lesion were submitted to three 1-min hemorrhage sessions at 5-min intervals; 15% of the total blood volume was withdrawn in each session. OT and AVP were measured in plasma, paraventricular (PVN) and supraoptic (SON) nuclei and in posterior pituitary (PP). LC Lesion did not affect basal plasma AVP or OT levels, but partly blocked the increase in plasma AVP and OT induced by hemorrhage. Hemorrhage produced decreases in content of AVP and OT in the PVN and SON and increased levels in the PP. These responses were attenuated in the lesioned group, but only in the PVN and PP. Data suggest a stimulatory role of the inputs from LC to PVN neurons on hemorrhage-induced OT and AVP secretion and that, this pathway is critical in the hypo-volemic neuroendocrine reflex.Special Issue Dedicated to Miklós Palkovits.     

Exposure to chronic isolation modulates receptors mRNAs for oxytocin and vasopressin in the hypothalamus and heart

The goal of our study was to explore the effect of social isolation stress of varying durations on the plasma oxytocin (OT), messenger ribonucleic acid (mRNA) for oxytocin receptor (OTR), plasma arginine vasopressin (AVP) and mRNA for V_1a receptor of AVP (V_1aR) expression in the hypothalamus and heart of socially monogamous female and male prairie voles (Microtus ochrogaster). Continuous isolation for 4 weeks (chronic isolation) increased plasma OT level in females, but not in males. One hour of isolation every day for 4 weeks (repeated isolation) was followed by a significant increase in plasma AVP level. Chronic isolation, but not repeated isolation, significantly decreased OTR mRNA in the hypothalamus and heart in both sexes. Chronic isolation significantly decreased cardiac V_1aR mRNA, but no effect on hypothalamic V_1aR mRNA expression. We did not find a gender difference within repeated social isolation groups. The results of the present study reveal that although chronic social isolation can down-regulate gene expression for the OTR in both sexes, the release of the OT peptide was increased after chronic isolation only in females, possibly somewhat protecting females from the negative consequences of isolation. In both sexes repeated, but not chronic, isolation increased plasma AVP, which could be permissive for mobilization and thus adaptive in response to a repeated stressor. The differential effects of isolation on OT and AVP systems may help in understanding mechanisms through social interactions can be protective against emotional and cardiovascular disorders.     

Salivary vasopressin increases following intranasal oxytocin administration

Extant research has documented the effects of intranasal administration of oxytocin (OT), and to a lesser degree Arginine Vasopressin (AVP) – two structurally-related neuropeptides – on brain and behaviour, yet the effects of exogenous manipulation of one on circulating levels of the other remain unknown. Studies have shown that OT administration impacts the peripheral levels of numerous hormones; however, whether OT administration also increases AVP concentrations has not been explored. Utilizing a double-blind placebo-controlled within-subject design, ten male and female subjects provided ten saliva samples over four consecutive hours: at baseline and nine times following OT administration. Results indicate that salivary AVP increased in the first hour following OT manipulation (OT condition: mean AVP = 2.17 pg/ml, SE = 28, placebo condition: mean AVP = 1.42 pg/ml, SE = .18) but returned to baseline levels at the next assessment (80 min) and remained low for the remaining period. Similar to OT, AVP showed high degree of individual stability and baseline levels of AVP correlated with AVP concentrations at the first and second post-administration hours regardless of drug condition (Pearson r = .85–.93). Validity of salivary AVP ELISA measurement was verified by demonstrating individual stability of salivary AVP over a six-month period (r = .70, p < .000) as well correlation with plasma levels over the same period (r = .32, p = .037) in a sample of 45 young adults who did not participate in the current study. Overall, findings suggest a potential crosstalk between OT and AVP and indicate that baseline levels of the two neuropeptides may shape the degree to which these systems respond to exogenous manipulation.     

Focus: Rare Disease: Oxytocin and Oxytocin Receptor Gene Regulation in Williams Syndrome: A Systematic Review

Williams Syndrome (WS) is a rare genetic multisystem disorder that occurs because of a deletion of approximately 25 genes in the 7q11.23 chromosome region. This causes dysmorphic facial appearances, multiple congenital cardiovascular defects, delayed motor skills, and abnormalities in connective tissues and the endocrine system. The patients are mostly diagnosed with mild to moderate mental retardation, however, they have a hyper sociable, socially dis-inhibited, and outgoing personality, empathetic behavior, and are highly talkative. Oxytocin (OT), a neuropeptide synthesized at the hypothalamus, plays an important role in cognition and behavior, and is thought to be affecting WS patients’ attitudes at its different amounts. Oxytocin receptor gene (OXTR), on chromosome 3p25.3, is considered regulating oxytocin receptors, via which OT exerts its effect. WS is a crucial disorder to understand gene, hormone, brain, and behavior associations in terms of sociality and neuropsychiatric conditions. Alterations to the WS gene region offer an opportunity to deepen our understandings of autism spectrum disorder, schizophrenia, anxiety, or depression. We aim to systematically present the data available of OT/OXTR regulation and expression, and the evidence for whether these mechanisms are dysregulated in WS. These results are important, as they predict strong epigenetic control over social behavior by methylation, single nucleotide polymorphisms, and other alterations. The comparison and collaboration of these studies may help to establish a better treatment or management approach for patients with WS if backed up with future research.     

Repeated agonistic encounters in hamsters modulate AVP V1a receptor binding

Arginine vasopressin (AVP) regulates aggression in male Syrian hamsters. In this study, we used radioligand receptor autoradiography to examine whether changes in agonistic behavior following acute and repeated social defeat are accompanied by changes in AVP V1a receptor binding. Social defeat produced high levels of submissive behavior and a loss of territorial aggression when hamsters were subsequently tested with a novel intruder, and repeated agonistic encounters produced similar behavioral changes in subordinates. AVP V1a receptor binding was not reduced by acute social defeat but was affected by repeated agonistic encounters. Dominants had significantly more AVP V1a receptor binding in lateral portions of the ventromedial hypothalamus (VMHL) than did their subordinate opponents, but subordinates were no different from controls. In contrast, receptor binding did not differ in most other brain regions examined. The changes in receptor binding appear to be independent of testosterone levels, as testosterone levels did not differ among dominants, subordinates, and controls. Our results suggest that changes in AVP V1a receptors do not account for the changes in agonistic behavior produced by acute social defeat but AVP V1a binding in the VMHL correlates with, and may modulate, the behavioral changes that occur following repeated experiences of victory.     

Corticosterone manipulations alter morph-specific nestling provisioning behavior in male white-throated sparrows, Zonotrichia albicollis

In the polymorphic white-throated sparrow (Zonotrichia albicollis), tan-striped males provision nestlings at higher rates than do white-striped males. In a previous study, we found that tan-striped males had lower baseline corticosterone levels than white-striped males during the nestling stage. To determine if this variation in corticosterone influences morph-specific differences in nestling provisioning behavior, we used intraperitoneal osmotic pumps to increase baseline corticosterone levels in tan-striped males (TS CORT) and administer RU486, a glucocorticoid receptor antagonist, in white-striped males (WS RU486). These manipulations essentially reversed morph-specific nestling provisioning behavior in males. TS CORT males fed nestlings at lower rates than TS controls (vehicle-only implant), and at similar rates to WS controls (vehicle-only implant), while WS RU486 males fed nestlings at higher rates than WS controls, and at similar rates to TS controls. These results demonstrate that (1) increases in baseline corticosterone (i.e., below concentrations associated with the adrenocortical response to stress) can directly or indirectly inhibit nestling provisioning behavior, and (2) corticosterone influences morph-specific variation in parental behavior in male white-throated sparrows. This study contributes to the growing evidence that modulating baseline CORT mediates parental care and self-maintenance activities in birds, and thus may serve as a mechanism for balancing current reproductive success with survival.     

Corticosterone manipulations alter morph-specific nestling provisioning behavior in male white-throated sparrows,Zonotrichia albicollis

In the polymorphic white-throated sparrow (Zonotrichia albicollis), tan-striped males provision nestlings at higher rates than do white-striped males. In a previous study, we found that tan-striped males had lower baseline corticosterone levels than white-striped males during the nestling stage. To determine if this variation in corticosterone influences morph-specific differences in nestling provisioning behavior, we used intraperitoneal osmotic pumps to increase baseline corticosterone levels in tan-striped males (TS CORT) and administer RU486, a glucocorticoid receptor antagonist, in white-striped males (WS RU486). These manipulations essentially reversed morph-specific nestling provisioning behavior in males. TS CORT males fed nestlings at lower rates than TS controls (vehicle-only implant), and at similar rates to WS controls (vehicle-only implant), while WS RU486 males fed nestlings at higher rates than WS controls, and at similar rates to TS controls. These results demonstrate that (1) increases in baseline corticosterone (i.e., below concentrations associated with the adrenocortical response to stress) can directly or indirectly inhibit nestling provisioning behavior, and (2) corticosterone influences morph-specific variation in parental behavior in male white-throated sparrows. This study contributes to the growing evidence that modulating baseline CORT mediates parental care and self-maintenance activities in birds, and thus may serve as a mechanism for balancing current reproductive success with survival.