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1. The central nervous system of Nereis virens occupies a deeper position. than does that of most Polychaetes. It is separated from the hypodermis by the circular muscles, and is enveloped by an elaborate protective tissue. 2. The protective tissue consists of two parts jan inner spongy layer, the neuroglia, of ectodermic origin, and an outer sheath, the neurilemma, of mesodermic origin. 3. The" mushroom bodies" of insects and decapod Crustacea are represented in the brain of Nereis by the anterior masses of small nuclei. 4. The optic ganglion, which in some species of Nereis lies beneath the anterior eye, may in other species lie within the brain capsule. 5. There is no neuropil in the ventral nerve cord. 6. There are three longitudinal connectives between each two successive ganglia of the ventral nerve cord, one small median and two larger lateral ones. 7. The sheaths of the nerve fibres of the ventral cord have no nuclei, and hence must be a product of the fibres themselves. 8. The nerve cells of the ventral cord commonly have one or more centrosomes. 9. The giant fibres are nervous in function, and are put into relation with peripheral organs through ordinary centrifugal fibres. 10. The giant fibres give off no fibrillations, and nervous relation with other fibres is established directly between the axis cylinders. 11. Certain decussating fibres are always united in pairs by anastomoses between the axis cylinders where they cross each other. 12. Certain centripetal fibres of the same set are always united by anastomoses between the ends of the branches. 13. Contact between axis cylinders may possibly be one of the means of bringing nerve fibres into functionall'elation with each other.
The term cephalic sensory organ (CSO) is used for specialised structures in the head region of adult Opisthobranchia. These sensory organs show a high diversity in form and function, and the gross morphology of these organs differs considerably among taxa. They can be identified as cephalic shields, oral veils, Hancocks organs, lip organs, rhinophores or oral tentacles. Because of this extremely high diversity, the homology and the evolution of these organs have not been clarified yet. My intention was to use neuroanatomical data sets in order to find putative homologous CSOs. In this study, I will show data about immunohistochemical neurotransmitter content and cellular innervation patterns and their applicability as morphological characters for the homologisation of structures. I support earlier investigations that neurotransmitter content is often related to function. In contrast, axonal tracing patterns can be used to homologise nerves. Overall the aim of this study was to reconstruct the evolution of the CSOs of the Opisthobranchia, by projecting our neuroanatomical data sets onto a molecular phylogeny.
A detailed understanding of how potassium channels function is crucial e. g. for the development of drugs, which could lead to novel therapeutic concepts for diseases ranging from diabetes to cardiac abnormalities. An improved understanding of channel structure may allow researchers to design medication that can restore proper function of these channels. This is particularly important for KCNQ channels, since four out of five family members are involved in human inherited disease. In addition to structure and function relationships the determinants which govern assembly of KCNQ subunits are decisive to understand the physiological role of the KCNQ channel family members. Many details of KCNQ channel assembly remain incompletely understood. Previous work has shown that the subunit-specific heteromerisation between KCNQ subunits is determined by a ~115 amino acid-long subunit interaction domain (si) within the C-terminus (Schwake et al., 2003). Recently, Jenke et al. (2003) proposed that the C-terminal domains in eag and erg K+ channels act as sites which drive tetramerization. From their ability to form coiled coils, these domains were referred to as tetramerizing coiled-coil (TCC) sequences. Jenke et al. also pointed out that KCNQ channels contain bipartite TCC motifs within their C-termini, exactly within the si domain, which is responsible for the subunit-specific interaction pattern. The first part of this thesis was dedicated to determine the individual role of these TCC domains on homomeric and heteromeric channel formation in order to further characterize the molecular determinants of KCNQ channel assembly. In the second part of this thesis cystein-scanning mutagenesis was employed, followed by thiol-specific modification using MTS reagents to screen more than 20 residues in the S3-S4 linker region and in the S4 transmembrane domain of the KCNQ1 channel to gain information about residue accessibility, the functional effects of thiol-modifying reagents (MTSES), and effects of crosslinking selected pairs of Cys residues by Cd+ ions, which could be used for testing model predictions based upon known Kv channel structures from the literature. According to homology modelling based on the Kv1.2 structure it was attempted to determine the proximity of individual residues from different transmembrane segments using the metal bridge approach (crosslinking by Cd+ ions). This led us to derive structural constraints for interactions between the S4 voltage sensor and adjacent transmembrane segments of KCNQ1. Similar studies have previously been performed on the Shaker K+ channel, which has served as a paradigm for structure-function research of voltage-gated K+ channels for a long time, but little is known for KCNQ channels concerning their similarity to published K+ channel structures.