Henrike Scholz

Dopamine and Octopamine Differentiate between Aversive and Appetitive Olfactory Memories in Drosophila

The catecholamines play a major role in the regulation of behavior. Here we investigate, in the fly Drosophila melanogaster, the role of dopamine and octopamine (the presumed arthropod homolog of norepinephrine) during the formation of appetitive and aversive olfactory memories. We find that for the formation of both types of memories, cAMP signaling is necessary and sufficient within the same subpopulation of mushroom-body intrinsic neurons. On the other hand, memory formation can be distinguished by the requirement for different catecholamines, dopamine for aversive and octopamine for appetitive conditioning. Our results suggest that in associative conditioning, different memories are formed of the same odor under different circumstances, and that they are linked to the respective motivational systems by their specific modulatory pathways.

The Ets transcription factors encoded by the Drosophila gene pointed direct glial cell differentiation in the embryonic CNS

The Drosophila gene pointed (pnt) encodes two putative transcription factors (P1 and P2) of the Ets family, which in the embryonic CNS are found exclusively in glial cells. Loss of pnt function leads to poorly differentiated glial cells and a marked decrease in the expression of the neuronal antigen 22C10 in the MP2 neurons, which are known to interact intimately with the pntP1-expressing longitudinal glial cells. Ectopic expression of pntP1 RNA forces additional CNS cells to enter the glial differentiation pathway. Interestingly, the additional glial-like cells are often flanked by cells that ectopically express the neuronal antigen 22C10. Therefore, both the pnt loss-of-function as well as the gain-of-function phenotype suggest that glial cells are able to induce 22C10 expression on neighboring neurons. This was further verified by cell transplantation experiments. Thus, pnt is not only required but also sufficient for several aspects of glial differentiation.

Functional Ethanol Tolerance in Drosophila

In humans, repeated alcohol consumption leads to the development of tolerance, manifested as a reduced physiological and behavioral response to a particular dose of alcohol. Here we show that adult Drosophila develop tolerance to the sedating and motor-impairing effects of ethanol with kinetics of acquisition and dissipation that mimic those seen in mammals. Importantly, this tolerance is not caused by changes in ethanol absorption or metabolism. Rather, the development of tolerance requires the functional and structural integrity of specific central brain regions. Mutants unable to synthesize the catecholamine octopamine are also impaired in their ability to develop tolerance. Taken together, these data show that Drosophila is a suitable model system in which to study the molecular and neuroanatomical bases of ethanol tolerance.

Flies lacking all synapsins are unexpectedly healthy but are impaired in complex behaviour

Vertebrate synapsins are abundant synaptic vesicle phosphoproteins that have been proposed to fine‐regulate neurotransmitter release by phosphorylation‐dependent control of synaptic vesicle motility. However, the consequences of a total lack of all synapsin isoforms due to a knock‐out of all three mouse synapsin genes have not yet been investigated. In Drosophila a single synapsin gene encodes several isoforms and is expressed in most synaptic terminals. Thus the targeted deletion of the synapsin gene of Drosophila eliminates the possibility of functional knock‐out complementation by other isoforms. Unexpectedly, synapsin null mutant flies show no obvious defects in brain morphology, and no striking qualitative changes in behaviour are observed. Ultrastructural analysis of an identified ‘model’ synapse of the larval nerve muscle preparation revealed no difference between wild‐type and mutant, and spontaneous or evoked excitatory junction potentials at this synapse were normal up to a stimulus frequency of 5 Hz. However, when several behavioural responses were analysed quantitatively, specific differences between mutant and wild‐type flies are noted. Adult locomotor activity, optomotor responses at high pattern velocities, wing beat frequency, and visual pattern preference are modified. Synapsin mutant flies show faster habituation of an olfactory jump response, enhanced ethanol tolerance, and significant defects in learning and memory as measured using three different paradigms. Larval behavioural defects are described in a separate paper. We conclude that Drosophila synapsins play a significant role in nervous system function, which is subtle at the cellular level but manifests itself in complex behaviour.

Three Dopamine Pathways Induce Aversive Odor Memories with Different Stability

Animals acquire predictive values of sensory stimuli through reinforcement. In the brain of Drosophila melanogaster, activation of two types of dopamine neurons in the PAM and PPL1 clusters has been shown to induce aversive odor memory. Here, we identified the third cell type and characterized aversive memories induced by these dopamine neurons. These three dopamine pathways all project to the mushroom body but terminate in the spatially segregated subdomains. To understand the functional difference of these dopamine pathways in electric shock reinforcement, we blocked each one of them during memory acquisition. We found that all three pathways partially contribute to electric shock memory. Notably, the memories mediated by these neurons differed in temporal stability. Furthermore, combinatorial activation of two of these pathways revealed significant interaction of individual memory components rather than their simple summation. These results cast light on a cellular mechanism by which a noxious event induces different dopamine signals to a single brain structure to synthesize an aversive memory.

Control of midline glia development in the embryonic Drosophila CNS.

The midline glial cells are required for correct formation of the axonal pattern in the embryonic ventral nerve cord of Drosophila. Initially, six midline cells form an equivalence group with the capacity to develop as glial cells. By the end of embryonic development three to four cells are singled out as midline glial cells. Midline glia development occurs in two steps, both of which depend on the activation of the Drosophila EGF-receptor homolog and subsequent ras1/raf-mediated signal transduction. Nuclear targets of this signalling cascade are the ETS domain transcription factors pointedP2 and yan. In the midline glia pointedP2 in turn activates the transcription of argos, which encodes a diffusible negative regulator of EGF-receptor signalling.

The hangover gene defines a stress pathway required for ethanol tolerance development

Repeated alcohol consumption leads to the development of tolerance, simply defined as an acquired resistance to the physiological and behavioural effects of the drug. This tolerance allows increased alcohol consumption, which over time leads to physical dependence and possibly addiction. Previous studies have shown that Drosophila develop ethanol tolerance, with kinetics of acquisition and dissipation that mimic those seen in mammals. This tolerance requires the catecholamine octopamine, the functional analogue of mammalian noradrenaline. Here we describe a new gene, hangover, which is required for normal development of ethanol tolerance. hangover flies are also defective in responses to environmental stressors, such as heat and the free-radical-generating agent paraquat. Using genetic epistasis tests, we show that ethanol tolerance in Drosophila relies on two distinct molecular pathways: a cellular stress pathway defined by hangover, and a parallel pathway requiring octopamine. hangover encodes a large nuclear zinc-finger protein, suggesting a role in nucleic acid binding. There is growing recognition that stress, at both the cellular and systemic levels, contributes to drug- and addiction-related behaviours in mammals. Our studies suggest that this role may be conserved across evolution.

A systems medicine research approach for studying alcohol addiction

According to the World Health Organization, about 2 billion people drink alcohol. Excessive alcohol consumption can result in alcohol addiction, which is one of the most prevalent neuropsychiatric diseases afflicting our society today. Prevention and intervention of alcohol binging in adolescents and treatment of alcoholism are major unmet challenges affecting our health‐care system and society alike. Our newly formed German SysMedAlcoholism consortium is using a new systems medicine approach and intends (1) to define individual neurobehavioral risk profiles in adolescents that are predictive of alcohol use disorders later in life and (2) to identify new pharmacological targets and molecules for the treatment of alcoholism. To achieve these goals, we will use omics‐information from epigenomics, genetics transcriptomics, neurodynamics, global neurochemical connectomes and neuroimaging (IMAGEN; Schumann et al. ) to feed mathematical prediction modules provided by two Bernstein Centers for Computational Neurosciences (Berlin and Heidelberg/Mannheim), the results of which will subsequently be functionally validated in independent clinical samples and appropriate animal models. This approach will lead to new early intervention strategies and identify innovative molecules for relapse prevention that will be tested in experimental human studies. This research program will ultimately help in consolidating addiction research clusters in Germany that can effectively conduct large clinical trials, implement early intervention strategies and impact political and healthcare decision makers.

Inter-leg coordination in the control of walking speed in Drosophila

SUMMARY Legged locomotion is the most common behavior of terrestrial animals and it is assumed to have become highly optimized during evolution. Quadrupeds, for instance, use distinct gaits that are optimal with regard to metabolic cost and have characteristic kinematic features and patterns of inter-leg coordination. In insects, the situation is not as clear. In general, insects are able to alter inter-leg coordination systematically with locomotion speed, producing a continuum of movement patterns. This notion, however, is based on the study of several insect species, which differ greatly in size and mass. Each of these species tends to walk at a rather narrow range of speeds. We have addressed these issues by examining four strains of Drosophila, which are similar in size and mass, but tend to walk at different speed ranges. Our data suggest that Drosophila controls its walking speed almost exclusively via step frequency. At high walking speeds, we invariably found tripod coordination patterns, the quality of which increased with speed as indicated by a simple measure of tripod coordination strength (TCS). At low speeds, we also observed tetrapod coordination and wave gait-like walking patterns. These findings not only suggest a systematic speed dependence of inter-leg movement patterns but also imply that inter-leg coordination is flexible. This was further supported by amputation experiments in which we examined walking behavior in animals after the removal of a hindleg. These animals show immediate adaptations in body posture, leg kinematics and inter-leg coordination, thereby maintaining their ability to walk.

Development and function of embryonic central nervous system glial cells in Drosophila.

Each abdominal neuromere of a Drosophila embryo contains about 60 glial cells [Klämbt C, Goodman CS (1991): Glia 4:205-213; Ito et al. (1995): Rouxs Arch Dev Biol, 204:284-307]. Among these, the midline and longitudinal glia are described to some detail. The midline glia are located dorsally in the nerve cord ensheathing the two segmental commissures. They are required for the proper establishment of commissures. The longitudinal glia, the A and B glia, and the segment boundary cells (SBC) are covering the longitudinal connectives. The longitudinal glia prefigure longitudinal axon paths and appear capable of regulating the expression of neuronal antigens. In the following we summarize the knowledge on the function of these glial cells.