octopamine promotes escalation and maintenance but not initiation

Biogenic amines have widespread effects on numerous behaviors, but their natural functions are often unclear. We investigated the role of octopamine (OA), the invertebrate analog of noradrenaline, on initiation and maintenance of aggression in male crickets of different social status. The key-releasing stimulus for aggression is antennal fencing between males, a behavior occurring naturally on initial contact. We show that mechanical antennal stimulation (AS) alone is sufficient to initiate an aggressive response (mandible threat display). The efficacy of AS as an aggression releasing stimulus was augmented in winners of a previous fight, but unaffected in losers. The efficacy of AS was not, however, influenced by OA receptor (OAR) agonists or antagonists, regardless of social status. Additional experiments indicate that the efficacy of AS is also not influenced by dopamine (DA) or serotonin (5HT). In addition to initiating an aggressive response, prior AS enhanced aggression exhibited in subsequent fights, whereby AS with a male antenna was now necessary, indicating a role for male contact pheromones. This priming effect of male-AS on subsequent aggression was dependent on OA since it was blocked by OAR-antagonists, and enhanced by OAR-agonists. Together our data reveal that neither OA, DA nor 5HT are required for initiating aggression in crickets, nor do these amines influence the efficacy of the natural releasing stimulus to initiate aggression. OA's natural function is restricted to promoting escalation and maintenance of aggression once initiated, and this can be invoked by numerous experiences, including prior contact with a male antenna as shown here

A Consequence of Recovery from Defeat in a Territorial Animal

Population density has profound influences on the physiology and behaviour of many animal species. Social isolation is generally reported to lead to increased aggressiveness, while grouping lowers it. We evaluated the effects of varying degrees of isolation and grouping on aggression in a territorial insect, the Mediterranean field cricket, Gryllus bimaculatus. Substantiating early observations, we show that dyadic contests between weight-matched, adult male crickets taken from groups rarely escalate beyond threat displays, whereas interactions between pairs of previously isolated crickets typically escalate to physical fights lasting several seconds. No significant differences were found between 1, 2 and 6-day isolates, or between individuals grouped for a few hours or lifelong. Unexpectedly, crickets grouped in immediate proximity within individual mesh cages that precluded fighting while permitting visual, olfactory and mechanical, antennal contact, were as aggressive as free isolates. This suggests that reduced aggression of grouped animals may be an acquired result of fighting. Supporting this notion, isolated crickets initially engage in vigorous fights when first grouped, but fighting intensity and duration rapidly decline to the level of life-long grouped crickets within only 10 min. Furthermore, grouped crickets become as aggressive as life-long isolates after only 3 hours of isolation, and on the same time course required for crickets to regain their aggressiveness after social defeat. We conclude that the reduced aggressiveness of grouped crickets is a manifestation of the loser effect resulting from social subjugation, while isolation allows recovery to a state of heightened aggressiveness, which in crickets can be considered as the default condition. Given the widespread occurrence of the loser effect in the Animal Kingdom, many effects generally attributed to social isolation are likely to be a consequence of recovery from social subjugation

Das dopaminerge System im Gehirn des Menschen: molekulare Grundlagen, Anatomie, Physiologie und Pathologie

Diese Arbeit ist Teil des Toxnetz-Projekts des Fachbereichs Toxikologie an der Universität Leipzig und behandelt Themen rund um den Botenstoff Dopamin. Es wurden hierfür Texte und Essays zu Funktionen, Mechanismen, Hirnarealen und Krankheitsbildern geschrieben, die den Studierenden der Toxikologie als Lernhilfe und Wissensspeicher dienen sollen. Ausführliche Erläuterungen finden sich zu den vier dopaminergen Projektionsbahnen und ihren Interaktionen mit den Basalganglien, dem präfrontalen Cortex, dem Hippocampus und der Amygdala. Die Rolle von Dopamin bei Motivation, Belohnung, Lernen, Gedächtnisbildung und Aufmerksamkeit wird ebenso beleuchtet, wie die bei der Parkinson Krankheit, Schizophrenie, ADHS und Drogensucht

Flight and Walking in Locusts–Cholinergic Co-Activation, Temporal Coupling and Its Modulation by Biogenic Amines

Walking and flying in locusts are exemplary rhythmical behaviors generated by central pattern generators (CPG) that are tuned in intact animals by phasic sensory inputs. Although these two behaviors are mutually exclusive and controlled by independent CPGs, leg movements during flight can be coupled to the flight rhythm. To investigate potential central coupling between the underlying CPGs, we used the muscarinic agonist pilocarpine and the amines octopamine and tyramine to initiate fictive flight and walking in deafferented locust preparations. Our data illustrate that fictive walking is readily evoked by comparatively lower concentrations of pilocarpine, whereas higher concentrations are required to elicit fictive flight. Interestingly, fictive flight did not suppress fictive walking so that the two patterns were produced simultaneously. Frequently, leg motor units were temporally coupled to the flight rhythm, so that each spike in a step cycle volley occurred synchronously with wing motor units firing at flight rhythm frequency. Similarly, tyramine also induced fictive walking and flight, but mostly without any coupling between the two rhythms. Octopamine in contrast readily evoked fictive flight but generally failed to elicit fictive walking. Despite this, numerous leg motor units were recruited, whereby each was temporarily coupled to the flight rhythm. Our results support the notion that the CPGs for walking and flight are largely independent, but that coupling can be entrained by aminergic modulation. We speculate that octopamine biases the whole motor machinery of a locust to flight whereas tyramine primarily promotes walking

Serotonin Mediates Depression of Aggression After Acute and Chronic Social Defeat Stress in a Model Insect

In all animals, losers of a conflict against a conspecific exhibit reduced aggressiveness, often coupled with depression-like symptoms, particularly after multiple defeats. While serotonin (5HT) is involved, discovering its natural role in aggression and depression has proven elusive. We show how 5HT influences aggression in male crickets, before, and after single and multiple defeats using serotonergic drugs, at dosages that had no obvious deleterious effect on general motility: the 5HT synthesis inhibitor alpha-methyltryptophan (AMTP), the 5HT2 receptor blocker ketanserin, methiothepin which blocks 5HT receptor subtypes other than 5HT2, 5HT's precursor 5-hydroxytryptophan (5HTP) and re-uptake inhibitor fluoxetine. Contrasting reports for other invertebrates, none of the drugs influenced aggression at the first encounter. However, the recovery of aggression after single defeat, which normally requires 3 h in crickets, was severely affected. Losers that received ketanserin or AMTP regained their aggressiveness sooner, whereas those that received fluoxetine, 5HTP, or methiothepin failed to recover within 3 h. Furthermore, compared to controls, which show long term aggressive depression 24 h after 6 defeats at 1 h intervals, crickets that received AMTP or ketanserin regained their full aggressiveness and were thus more resilient to chronic defeat stress. In contrast, 5HTP and fluoxetine treated crickets showed long term aggressive depression 24 h after only 2 defeats, and were thus more susceptible to defeat stress. We conclude that 5HT acts after social defeat via a 5HT2 like receptor to maintain depressed aggressiveness after defeat, and to promote the susceptibility to and establishment of long-term depression after chronic social defeat. It is known that the decision to flee and establishment of loser depression in crickets is controlled by nitric oxide (NO), whereas dopamine (DA), but not octopamine (OA) is necessary for recovery after defeat. Here we show that blocking NO synthesis, just like ketanserin, affords resilience to multiple defeat stress, whereas blocking DA receptors, but not OA receptors, increases susceptibility, just like fluoxetine. We discuss the possible interplay between 5HT, NO, DA, and OA in controlling aggression after defeat, as well as similarities and differences to findings in mammals and other invertebrate model systems

Winning Fights Induces Hyperaggression via the Action of the Biogenic Amine Octopamine in Crickets

Winning an agonistic interaction against a conspecific is known to heighten aggressiveness, but the underlying events and mechanism are poorly understood. We quantified the effect of experiencing successive wins on aggression in adult male crickets (Gryllus bimaculatus) by staging knockout tournaments and investigated its dependence on biogenic amines by treatment with amine receptor antagonists. For an inter-fight interval of 5 min, fights between winners escalated to higher levels of aggression and lasted significantly longer than the preceding round. This winner effect is transient, and no longer evident for an inter-fight interval of 20 min, indicating that it does not result from selecting individuals that were hyper-aggressive from the outset. A winner effect was also evident in crickets that experienced wins without physical exertion, or that engaged in fights that were interrupted before a win was experienced. Finally, the winner effect was abolished by prior treatment with epinastine, a highly selective octopamine receptor blocker, but not by propranolol, a ß-adrenergic receptor antagonist, nor by yohimbine, an insect tyramine receptor blocker nor by fluphenazine an insect dopamine-receptor blocker. Taken together our study in the cricket indicates that the physical exertion of fighting, together with some rewarding aspect of the actual winning experience, leads to a transient increase in aggressive motivation via activation of the octopaminergic system, the invertebrate equivalent to the adrenergic system of vertebrates

Das dopaminerge System im Gehirn des Menschen: molekulare Grundlagen, Anatomie, Physiologie und Pathologie

Diese Arbeit ist Teil des Toxnetz-Projekts des Fachbereichs Toxikologie an der Universität Leipzig und behandelt Themen rund um den Botenstoff Dopamin. Es wurden hierfür Texte und Essays zu Funktionen, Mechanismen, Hirnarealen und Krankheitsbildern geschrieben, die den Studierenden der Toxikologie als Lernhilfe und Wissensspeicher dienen sollen. Ausführliche Erläuterungen finden sich zu den vier dopaminergen Projektionsbahnen und ihren Interaktionen mit den Basalganglien, dem präfrontalen Cortex, dem Hippocampus und der Amygdala. Die Rolle von Dopamin bei Motivation, Belohnung, Lernen, Gedächtnisbildung und Aufmerksamkeit wird ebenso beleuchtet, wie die bei der Parkinson Krankheit, Schizophrenie, ADHS und Drogensucht

Liberty in Byron's Childe Harold's Pilgrimage

The aim of this bachelor thesis is to analyze the concept of freedom and its manifestations in George Gordon Byron's Childe Harold's Pilgrimage. Passages in the poem, where the topic appears are discussed and analyzed in the philosophical, social and literary context of the period (including the work of Byron himself). The conclusion sums up the main points of the bachelor thesis

Politické tendence ve vybrané romantické poezii

This thesis analyses selected poetry of English Romantic poets in terms of their political opinions. The works of various poets are scrutinised and put into the context of important political events of the period. The main topics discussed are the left-right political spectrum, the conflict between monarchism and republicanism, and the critique of institutionalised religion in how the Romantic poets perceive them. In cases where more poets show interest in the same question, their ideas are compared