Edward A. Kravitz

Neuronal Geometry: Determination with a Technique of Intracellular Dye Injecion

In a study of the specificity of neuronal connections in lobster abdominal ganglia, the dye Procion Yellow M4RS was electrophoretically injected into identified cell bodies. This dye spreads into fine branches of cells, survives fixation and routine histological procedures, and permits the reconstruction of cell shapes through examination of serial sections of ganglia. Certain cells were found to have an internal bilateral symmetry. Repeated injection of the same cells in ganglia from different animals showed that cells have characteristic shapes and that the neuropil is highly structured. This method of dye injection should have general applicability in studies where a knowledge of the geometry of specific cells is important.

Serotonin and octopamine produce opposite postures in lobsters.

Serotonin and octopamine, injected into the circulation of freely moving lobsters and crayfish, produce opposite behavioral effects. Octopamine injection produces sustained extension of the limbs and abdomen; serotonin injection produces sustained flexion. Neurophysiological analyses show that these postures can be accounted for by opposing, coordinated effects of these amines on patterns of motoneuron activity recorded from the ventral nerve cord.

Fighting fruit flies: A model system for the study of aggression

Despite the importance of aggression in the behavioral repertoire of most animals, relatively little is known of its proximate causation and control. To take advantage of modern methods of genetic analysis for studying this complex behavior, we have developed a quantitative framework for studying aggression in common laboratory strains of the fruit fly, Drosophila melanogaster. In the present study we analyze 73 experiments in which socially naive male fruit flies interacted in more than 2,000 individual agonistic interactions. This allows us to (i) generate an ethogram of the behaviors that occur during agonistic interactions; (ii) calculate descriptive statistics for these behaviors; and (iii) identify their temporal patterns by using sequence analysis. Thirty-minute paired trials between flies contained an average of 27 individual agonistic interactions, lasting a mean of 11 seconds and featuring a variety of intensity levels. Only few fights progressed to the highest intensity levels (boxing and tussling). A sequential analysis demonstrated the existence of recurrent patterns in behaviors with some similarity to those seen during courtship. Based on the patterns characterized in the present report, a detailed examination of aggressive behavior by using mutant strains and other techniques of genetic analysis becomes possible.

Serotonin, social status and aggression

Serotonin, social status and aggression appear to be linked in many animal species, including humans. The linkages are complex, and, for the most part, details relating the amine to the behavior remain obscure. During the past year, important advances have been made in a crustacean model system relating serotonin and aggression. The findings include the demonstration that serotonin injections will cause transient reversals in the unwillingness of subordinate animals to engage in agonistic encounters, and that at specific synaptic sites involved in activation of escape behavior, the direction of the modulation by serotonin depends on the social status of the animal.

Serotonin and aggression: insights gained from a lobster model system and speculations on the role of amine neurons in a complex behavior

Abstract The amine serotonin has been suggested to play a key role in aggression in many species of animals, including man. Precisely how the amine functions, however, has remained a mystery. As with other important physiological questions, with their large uniquely identifiable neurons, invertebrate systems offer special advantages for the study of behavior. In this article we illustrate that principal with a description of our studies of the role of serotonin in aggression in a lobster model system. Aggression is a quantifiable behavior in crustaceans, the amine neuron systems believed to be important in that behavior have been completely mapped, and key physiological properties of an important subset of these neurons have been defined. These results are summarized here, including descriptions of the “gain-setter” role and “autoinhibition” shown by these neurons. Results of other investigations showing socially modulated changes in amine responsiveness at particular synaptic sites also are described. In addition, speculations are offered about how important developmental roles served by amines like serotonin, which have been well described by other investigators, may be related to the behaviors we are examining. These speculations draw heavily from the organizational/activational roles proposed for steroid hormones by Phoenix et al. (1959).

Aggression in invertebrates.

Invertebrates are outstanding model systems for the study of aggression. Recent advances and promising new research approaches are bringing investigators closer to the goal of integrating behavioral findings with those from other disciplines of the neurosciences. The presence of highly structured, easily evoked behavioral systems offer unique opportunities to quantify the aggressive state of individuals, to explore the mechanisms underlying the formation and maintenance of dominance relationships, to investigate the dynamic properties of hierarchy formation, and to explore the significance of neural, neurochemical and genetic mechanisms in these behavioral phenomena.

Neurobiology of escalated aggression and violence.

Psychopathological violence in criminals and intense aggression in fruit flies and rodents are studied with novel behavioral, neurobiological, and genetic approaches that characterize the escalation from adaptive aggression to violence. One goal is to delineate the type of aggressive behavior and its escalation with greater precision; second, the prefrontal cortex (PFC) and brainstem structures emerge as pivotal nodes in the limbic circuitry mediating escalated aggressive behavior. The neurochemical and molecular work focuses on the genes that enable invertebrate aggression in males and females and genes that are expressed or suppressed as a result of aggressive experiences in mammals. The fruitless gene, immediate early genes in discrete serotonin neurons, or sex chromosome genes identify sexually differentiated mechanisms for escalated aggression. Male, but not female, fruit flies establish hierarchical relationships in fights and learn from previous fighting experiences. By manipulating either the fruitless or transformer genes in the brains of male or female flies, patterns of aggression can be switched with males using female patterns and vice versa. Work with Sts or Sry genes suggests so far that other genes on the X chromosomes may have a more critical role in female mouse aggression. New data from feral rats point to the regulatory influences on mesocortical serotonin circuits in highly aggressive animals via feedback to autoreceptors and via GABAergic and glutamatergic inputs. Imaging data lead to the hypothesis that antisocial, violent, and psychopathic behavior may in part be attributable to impairments in some of the brain structures (dorsal and ventral PFC, amygdala, and angular gyrus) subserving moral cognition and emotion.

Targeted Manipulation of Serotonergic Neurotransmission Affects the Escalation of Aggression in Adult Male Drosophila Melanogaster

Dopamine (DA) and serotonin (5HT) are reported to serve important roles in aggression in a wide variety of animals. Previous investigations of 5HT function in adult Drosophila behavior have relied on pharmacological manipulations, or on combinations of genetic tools that simultaneously target both DA and 5HT neurons. Here, we generated a transgenic line that allows selective, direct manipulation of serotonergic neurons and asked whether DA and 5HT have separable effects on aggression. Quantitative morphological examination demonstrated that our newly generated tryptophan hydroxylase (TRH)-Gal4 driver line was highly selective for 5HT-containing neurons. This line was used in conjunction with already available Gal4 driver lines that target DA or both DA and 5HT neurons to acutely alter the function of aminergic systems. First, we showed that acute impairment of DA and 5HT neurotransmission using expression of a temperature sensitive form of dynamin completely abolished mid- and high-level aggression. These flies did not escalate fights beyond brief low-intensity interactions and therefore did not yield dominance relationships. We showed next that manipulation of either 5HT or DA neurotransmission failed to duplicate this phenotype. Selective disruption of 5HT neurotransmission yielded flies that fought, but with reduced ability to escalate fights, leading to fewer dominance relationships. Acute activation of 5HT neurons using temperature sensitive dTrpA1 channel expression, in contrast, resulted in flies that escalated fights faster and that fought at higher intensities. Finally, acute disruption of DA neurotransmission produced hyperactive flies that moved faster than controls, and rarely engaged in any social interactions. By separately manipulating 5HT- and DA- neuron systems, we collected evidence demonstrating a direct role for 5HT in the escalation of aggression in Drosophila.

The action of serotonin on excitatory nerve terminals in lobster nerve‐muscle preparations.

1. The action of serotonin on excitatory transmission in the opener muscle of the dactyl of the lobster walking leg was examined by intracellular recording techniques. 2. Serotonin, at concentrations as low as 5 x 10(‐9) M, caused a sustained increase in the size of the excitatory junctional (synaptic) potential (e.j.p.). When serotonin was washed out of the bath the e.j.p. declined in two steps (T 1/2 approximately equal to 1‐2 min; T 1/2 approximately equal to 30 min) to the control size. The increased e.j.p. size was predominantly due to a serotonin‐induced increase in the release of quanta of excitatory transmitter with nerve stimulation. 3. The increase in transmitter release did not require nerve stimulation or the presence of Na+ or Ca2+ ions in the bathing medium during the period of serotonin treatment. 4. Three types of experiments suggested that a part of the action of serotonin on excitatory nerve terminals might involve a long‐term metabolic change within terminals, possibly involving the buffering or storage of Ca2+ ions. First, serotonin increased the frequency of spontaneous release of transmitter in both normal saline (26 mM‐Ca2+) and saline with very low levels of Ca2+ (less than 10(‐8) M). Secondly, serotonin greatly potentiated increases in miniature excitatory junctional potential frequency induced by the loading of the nerve terminal with Na+ either by veratridine or by inhibition of the Na+ pump or by the addition of the Na‐ionophore monensin in low‐Ca2+ salines. Thirdly, in some experiments, serotonin treatment produced a partial restoration of the nerve‐evoked release of transmitter in the low‐Ca2+ medium (less than 10(‐8) M).

Acetylcholine and lobster sensory neurones

Experiments are presented in support of the hypothesis that acetylcholine functions as a sensory transmitter in the lobster nervous system.