Brain, behavior and evolution
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A tyrosine hydroxylase-immunoreactive cell mass is found in the caudal portion of the dorsal nerve ganglion of the red-eared slider, Trachemys scripta elegans. The ganglion appears as a flat oval structure in the horizontal plane, where the major axis runs latero-medially, and the minor axis rostro-caudally in the ventral view. A communicating branch to the sympathetic chain diverges from the top of each tubercle which lies on the caudo-lateral side of the ganglion. ⋯ Tyrosine hydroxylase-immunoreactive cells, that contain Nissl bodies in cytoplasm and are enveloped by the satellite cells, are multipolar and their neural processes are distributed in a distal direction into the spinal nerve. The range of distribution of the synapsin I-immunoreactive structures is limited to the tyrosine hydroxylase-immunoreactive cell mass. The chelonian dorsal spinal nerve ganglia are a conglomerate of the spinal nerve ganglion proper and the sympathetic ganglion.
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In contrast to mammals, adult teleost fish exhibit an enormous capacity to replace damaged neurons with newly generated ones after injuries in the central nervous system. In the present study, the role of microglia/macrophages, identified by tomato lectin binding, was examined in this process of neuronal regeneration in the corpus cerebelli of the teleost fish Apteronotus leptorhynchus. ⋯ The density remained elevated until it reached background levels approximately one month after the injury. By comparing the time course of the appearance of microglia/macrophages with that of other regenerative events occurring within the first few weeks of wound healing in this model system, we hypothesize that one possible function of microglia/macrophages might be to remove debris of cells that have undergone apoptotic cell death at the lesion site.
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Review Comparative Study
Modulating the modulators: parasites, neuromodulators and host behavioral change.
Neuromodulators can resculpt neural circuits, giving an animal the behavioral flexibility it needs to survive in a complex changing world. This ability, however, provides parasites with a potential mechanism for manipulating host behavior. This paper reviews three invertebrate host-parasite systems to examine whether parasites can change host behavior by secreting neuromodulators. ⋯ For example, parasites may induce the host's immune system to produce the appropriate neuromodulators. In many parasites, the ability to manipulate host behavior may have evolved from adaptations designed to circumvent the host's immune system. Immune-neural-behavioral connections may be pre-adapted for parasitic manipulation.
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In contrast to mammals, teleost fish exhibit an enormous potential to produce new neurons in the adult central nervous system and to replace damaged neurons by newly generated ones. In the gymnotiform fish Apteronotus leptorhynchus, on average, 100,000 cells, corresponding to roughly 0.2% of the total population of cells in the adult brain, are in S-phase within any 2-h period. As in all other teleosts examined thus far, many of these cells are produced in specific proliferation zones located at or near the surface of ventricular, paraventricular, and cisternal systems, or in areas that are likely derived from proliferation zones located at ventricular surfaces during embryonic development. ⋯ The potential to produce new neurons, together with the ability to guide the young cells to their target areas by radial glial fibers and to eliminate damaged cells through apoptosis, also forms the basis for the enormous regenerative capability of the central nervous system of Apteronotus, as demonstrated in the cerebellum and spinal cord. A factor involved in the cerebellar regeneration appears to be somatostatin, as the expression of this neuropeptide is up-regulated in a specific spatio-temporal fashion following mechanical lesions. Besides its involvement in neuronal regeneration adult neurogenesis in Apteronotus, and possibly teleost fish in general, appears to play a role in providing central neurons to match the growing number of sensory and motor elements in the periphery, and to establish the neural substrate to accommodate behavioral plasticity.