Gesangskontrolle durch Neurone des Zentralkomplexes: Physiologische und immunzytochemische Untersuchungen an primären Zellkulturen aus dem Feldheuschreckengehirn

Abstract

Acridid grasshoppers communicate with specific song patterns in the context of attracting partners for reproduction, courting and agonistic behavior. When to sing and which song pattern to perform is determined by the brain, particularly by the central body complex and a distinct neuropil that contains the dendrites of command neurons, each of which controls the performance of a particular stridulatory pattern. Sensory information related to acoustic communication behavior is first analyzed by specific neural circuits and then relayed to the central body to generate arousal that promotes the production of specific sound patterns.Various sensory systems relay information to the central nervous system, about whether it appears appropriate to stridulate with a particular pattern or not. Accordingly, multiple signaling pathways (excitatory transmitters/second messengers: ACh, proctolin/cAMP, IP3/DAG; inhibitory transmitters/second messengers: GABA, glycine, NO/cGMP) have been demonstrated to converge in the central body and to contribute to the control of stridulation by mediating both fast ionotropic and prolonged metabotropic excitatory and inhibitory effects respectively.In order to identify central body neurons that integrate signals associated with sensory stimuli relevant for stridulation and mediate the decision about when to produce which sound pattern, we followed an in vitro approach. Initially, intact grasshoppers were placed in an experimental setup suitable for pressure injections of small volumes of dissolved drugs into the brain. At particular locations within the protocerebrum, where either specific singing behavior could be pharmacologically stimulated or pharmacologically stimulated stridulation could be suppressed by interfering with a particular signaling pathway, small fluorescent dextrans were co-injected as vital tracers. The dextrans were incorporated by intact neurons via their postsynaptic sites, thereby labeling those neurons that potentially were directly affected by the stimulating or inhibiting drug. After taking whole grasshopper brains into dissociated cell culture, these neurons could be recognized by their dextran-related fluorescence and their responses to the particular neuroactive drug used in the preceding physiological experiment.Additional the primary cultured neurons were prepared for optical imaging. During calcium imaging, the cultured neurons were subjected to drugs, known to interfere with the generation of excitation during song control in the central body neuropil. The physiological data were complemented by subsequent immunocytochemical detection of transmitters and other cellular components indicative for the functional presence of specific signal transduction mechanisms. According to their characteristics, the cultured neurons were classified and their potential contribution to the control of stridulation by the central body was estimated on the basis of the existing knowledge from previous behavioral and pharmacological studies.