Dear Enemies Elicit Lower Androgen Responses to Territorial Challenges than Unfamiliar Intruders in a Cichlid Fish

In many territorial species androgen hormones are known to increase in response to territorial intrusions as a way to adjust the expression of androgen-dependent behaviour to social challenges. The dear enemy effect has also been described in territorial species and posits that resident individuals show a more aggressive response to intrusions by strangers than by other territorial neighbours. Therefore, we hypothesized that the dear enemy effect may also modulate the androgen response to a territorial intrusion. Here we tested this hypothesis in male cichlid fish (Mozambique tilapia, Oreochromis mossambicus) using a paradigm of four repeated territorial intrusions, either by the same neighbour or by four different unfamiliar intruders. Neighbour intruders elicited lower aggression and a weaker androgen response than strangers on the first intrusion of the experiment. With repeated intrusions, the agonistic behaviour of the resident males against familiar intruders was similar to that displayed towards strangers. By the fourth intrusion the androgen response was significantly reduced and there was no longer a difference between the responses to the two types of intruders. These results suggest that the dear enemy effect modulates the androgen response to territorial intrusions and that repeated intrusions lead to a habituation of the androgen response.

Behavioral responses to catecholamine depletion in unmedicated, remitted subjects with bulimia nervosa and healthy subjects

BACKGROUND: Bulimia nervosa (BN) has been associated with dysregulation of the central catecholaminergic system. An instructive way to investigate the relationship between catecholaminergic function and psychiatric disorder has involved behavioral responses to experimental catecholamine depletion (CD). The purpose of this study was to examine a possible catecholaminergic dysfunction in the pathogenesis of bulimia nervosa. METHODS: CD was achieved by oral administration of alpha-methyl-para-tyrosine (AMPT) in 18 remitted female subjects with BN (rBN) and 31 healthy female control subjects. The study design consisted of a randomized, double blind, placebo-controlled crossover, single-site experimental trial. The main outcome measures were bulimic symptoms assessed by the Eating Disorder Examination-Questionnaire. Measures were assessed before and 26, 30, 54, 78, 102 hours after the first AMPT or placebo administration. RESULTS: In the experimental environment (controlled environment with a low level of food cues) rBN subjects had a greater increase in eating disorder symptoms during CD compared with healthy control subjects (condition × diagnosis interaction, p < .05). In the experimental environment, rBN subjects experienced fewer bulimic symptoms than in the natural environment (uncontrolled environment concerning food cues) 36 hours after the first AMPT intake (environment × diagnosis interaction, p < .05). Serum prolactin levels increased significantly, and to a comparable degree across groups, after AMPT administration. CONCLUSIONS: This study suggests that rBN is associated with vulnerability for developing eating disorder symptoms in response to reduced catecholamine neurotransmission after CD. The findings support the notion of catecholaminergic dysfunction as a possible trait abnormality in BN.

Concurrent activation of dopamine D1 and D2 receptors is required to evoke neural and behavioral phenotypes of cocaine sensitization

Repeated exposure to psychomotor stimulants produces a striking behavioral syndrome involving repetitive, stereotypic behaviors that occur if an additional exposure to the stimulant is experienced. The same stimulant exposure produces specific alterations in gene expression patterns in the striatum. To identify the dopamine receptor subtypes required for the parallel expression of these acquired neural and behavioral responses, we treated rats with different D1-class and D2-class dopamine receptor agonists and compared the responses of drug-naive rats with those of rats given previous intermittent treatment with cocaine. In rats exposed to repeated cocaine treatment, the effects of a subsequent challenge treatment with either a D1-class agonist (SKF 81297) or a D2-class agonist (quinpirole) were not significantly different from those observed in drug-naive animals: the drugs administered singly did not induce robust stereotyped motor behaviors nor produce significantly striosome-predominant expression of early genes in the striatum. In contrast, challenge treatment with the D1-class and D2-class agonists in combination led to marked and correlated increases in stereotypy and striosome-predominant gene expression in the striatum. Thus, immediately after repeated psychomotor stimulant exposure, only the concurrent activation of D1 and D2 receptor subclasses evoked expression of the neural and behavioral phenotypes acquired through repeated cocaine exposure. These findings suggest that D1-D2 dopamine receptor synergisms underlie the coordinate expression of both network-level changes in basal ganglia activation patterns and the repetitive and stereotypic motor response patterns characteristic of psychomotor stimulant sensitization.

A physiological and behavioral mechanism for leaf-herbivore induced systemic root resistance

Indirect plant-mediated interactions between herbivores are important drivers of community composition in terrestrial ecosystems. Among the most striking examples are the strong indirect interactions between spatially separated leaf- and root-feeding insects sharing a host plant. Although leaf feeders generally reduce the performance of root herbivores, little is known about the underlying systemic changes in root physiology and the associated behavioral responses of the root feeders. We investigated the consequences of maize (Zea mays) leaf infestation by Spodoptera littoralis caterpillars for the root-feeding larvae of the beetle Diabrotica virgifera virgifera, a major pest of maize. D. virgifera strongly avoided leaf-infested plants by recognizing systemic changes in soluble root components. The avoidance response occurred within 12 h and was induced by real and mimicked herbivory, but not wounding alone. Roots of leaf-infested plants showed altered patterns in soluble free and soluble conjugated phenolic acids. Biochemical inhibition and genetic manipulation of phenolic acid biosynthesis led to a complete disappearance of the avoidance response of D. virgifera. Furthermore, bioactivity-guided fractionation revealed a direct link between the avoidance response of D. virgifera and changes in soluble conjugated phenolic acids in the roots of leaf-attacked plants. Our study provides a physiological mechanism for a behavioral pattern that explains the negative effect of leaf attack on a root-feeding insect. Furthermore, it opens up the possibility to control D. virgifera in the field by genetically mimicking leaf herbivore-induced changes in root phenylpropanoid patterns.

Intra- and interspecific social challenges modulate the levels of an androgen precursor in a seasonally territorial tropical damselfish.

Studies on different vertebrate groups have provided evidence that androgen levels in males increase after competitive social interactions during the breeding season, as postulated by the Challenge Hypothesis. However, social modulation of androgen levels may vary with latitude and may differ between species holding seasonal versus year-round territories. Here, we tested the Challenge Hypothesis on a seasonal tropical damselfish, Abudefduf sexfasciatus, where males temporarily defend territory and eggs against both intra- and interspecific individuals. Carrying out simulated territorial intrusions (STIs) in the laboratory, we document for the first time a consistent increase in the plasma level of the androgen precursor 11-ketoandrostenedione (11KA) in fish confronted to either intra- or interspecific challenges. Collecting samples in the field also revealed higher 11KA levels in fish facing frequent territorial interactions than in non-territorial individuals. Levels of 11-ketotestosterone (11KT) were high in territorial males in the field, but were not incremented after simulated territorial intrusions in the laboratory. Plasma levels of cortisol and testosterone were not affected by challenges but were different in wild and captive specimens. Although the endocrine responses to STIs did not differ between intra- and interspecific challenges, agonistic displays expressed by resident fish were more intense towards intraspecific intruders. Taken together, our study emphasizes the need to incorporate androgen precursor concentrations to advance our understanding on the physiology of territorial interactions.