Identity of the cells recruited to a lesion in the central nervous system of a decapod crustacean

Contrasting alterations in brain chemistry in a crustacean intermediate host of two acanthocephalan parasites

The dynamic properties of neural systems throughout life can be hijacked by so-called manipulative parasites. This study investigated changes in the brain chemistry of the amphipod Gammarus fossarum in response to infection with two trophically-transmitted helminth parasites known to induce distinct behavioral alterations: the bird acanthocephalan Polymorphus minutus and the fish acanthocephalan Pomphorhynchus tereticollis. We quantified brain antioxidant capacity as a common marker of homeostasis and neuroprotection, and brain total protein, on 72 pools of six brains. We analyzed the concentration of serotonin (5HT), dopamine (DA) and tyramine in 52 pools of six brains, by using ultrafast high performance liquid chromatography with electrochemical detection (UHPLC-ECD). Brain total protein concentration scaled hypo-allometrically to dry body weight, and was increased in infected gammarids compared to uninfected ones. The brain of gammarids infected with P. minutus had significantly lower total antioxidant capacity relative to total proteins. Infection with P. tereticollis impacted DA level compared to uninfected ones, and in opposite direction between spring and summer. Brain 5HT level was higher in summer compared to spring independently of infection status, and was decreased by infection after correcting for brain total protein concentration estimated from dry whole-body weight. The potential implication of 5HT/DA balance in parasite manipulation, as a major modulator of the reward-punishment axis, is discussed. Taken together, these findings highlight the need to consider both brain homeostatic and/or structural changes (antioxidant and total protein content) together with neurotransmission balance and flexibility, in studies investigating the impact of parasites on brain and behavior.

Central nervous system regeneration in ascidians: cell migration and differentiation

Adult ascidians have the capacity to regenerate the central nervous system (CNS) and are therefore excellent models for studies on neuroregeneration. The possibility that undifferentiated blood cells are involved in adult neuroregeneration merits investigation. We analyzed the migration, circulation, and role of hemocytes of the ascidian Styela plicata in neuroregeneration. Hemocytes were removed and incubated with superparamagnetic iron oxide nanoparticles (SPION), and these SPION-labeled hemocytes were injected back into the animals (autologous transplant), followed by neurodegeneration with the neurotoxin 3-acetylpyridine (3AP). Magnetic resonance imaging showed that 1, 5, and 10 days after injury, hemocytes migrated to the intestinal region, siphons, and CNS. Immunohistochemistry revealed that the hemocytes that migrated to the CNS were putative stem cells (P-element-induced wimpy testis + or PIWI + cells). In the cortex of the neural ganglion, migrated hemocytes started to lose their PIWI labeling 5 days after injury, and 10 days later started to show β-III tubulin labeling. In the neural gland, however, the hemocytes remained undifferentiated during the entire experimental period. Transmission electron microscopy revealed regions in the neural gland with characteristics of neurogenic niches, not previously reported in ascidians. These results showed that migration of hemocytes to the hematopoietic tissue and to the 3AP-neurodegenerated region is central to the complex mechanism of neuroregeneration.

A Balancing Act: The Immune System Supports Neurodegeneration and Neurogenesis

Decapod crustaceans, like mammals, retain the ability to make new neurons throughout life. In mammals, immune cells are closely associated with stem cells that generate adult-born neurons. In crayfish, evidence suggests that immune cells (hemocytes) originating in the immune system travel to neurogenic regions and transform into neural progenitor cells. This nontraditional immune activity takes place continuously under normal physiological conditions, but little is known under pathological conditions (neurodegeneration). In this study, the immune system and its relationship with neurogenesis were investigated during neurodegeneration (unilateral antennular ablation) in adult crayfish. Our experiments show that after ablation (1) Proliferating cells decrease in neurogenic areas of the adult crayfish brain; (2) The immune response, but not neurogenesis, is ablation-side dependent; (3) Inducible nitric oxide synthase (iNOS) plays a crucial role in the neurogenic niche containing neural progenitors during the immune response; (4) Brain areas targeted by antennular projections respond acutely (15 min) to the lesion, increasing the number of local immune cells; (5) Immune cells are recruited to the area surrounding the ipsilateral neurogenic niche; and (6) The vasculature in the niche responds acutely by dilation and possibly also neovascularization. We conclude that immune cells are important in both neurodegeneration and neurogenesis by contributing in physiological conditions to the maintenance of the number of neural precursor cells in the neurogenic niche (neurogenesis), and in pathological conditions (neurodegeneration) by coordinating NO release and vascular responses associated with the neurogenic niche. Our data suggest that neural damage and recovery participate in a balance between these competing immune cell roles.

Culture of neural cells of the eyestalk of a mangrove crab is optimized on poly-L-ornithine substrate

Although there is a considerable demand for cell culture protocols from invertebrates for both basic and applied research, few attempts have been made to culture neural cells of crustaceans. We describe an in vitro method that permits the proliferation, growth and characterization of neural cells from the visual system of an adult decapod crustacean. We explain the coating of the culture plates with different adhesive substrates, and the adaptation of the medium to maintain viable neural cells for up to 7 days. Scanning electron microscopy allowed us to monitor the conditioned culture medium to assess cell morphology and cell damage. We quantified cells in the different substrates and performed statistical analyses. Of the most commonly used substrates, poly-L-ornithine was found to be the best for maintaining neural cells for 7 days. We characterized glial cells and neurons, and observed cell proliferation using immunocytochemical reactions with specific markers. This protocol was designed to aid in conducting investigations of adult crustacean neural cells in culture. We believe that an advantage of this method is the potential for adaptation to neural cells from other arthropods and even other groups of invertebrates.

3-acetylpyridine-induced degeneration in the adult ascidian neural complex: Reactive and regenerative changes in glia and blood cells

Ascidians are interesting neurobiological models because of their evolutionary position as a sister-group of vertebrates and the high regenerative capacity of their central nervous system (CNS). We investigated the degeneration and regeneration of the cerebral ganglion complex of the ascidian Styela plicata following injection of the niacinamide antagonist 3-acetylpyridine (3AP), described as targeting the CNS of several vertebrates. For the analysis and establishment of a new model in ascidians, the ganglion complex was dissected and prepared for transmission electron microscopy (TEM), routine light microscopy (LM), immunohistochemistry and Western blotting, 1 or 10 days after injection of 3AP. The siphon stimulation test (SST) was used to quantify the functional response. One day after the injection of 3AP, CNS degeneration and recruitment of a non-neural cell type to the site of injury was observed by both TEM and LM. Furthermore, weaker immunohistochemical reactions for astrocytic glial fibrillary acidic protein (GFAP) and neuronal βIII-tubulin were observed. In contrast, the expression of caspase-3, a protein involved in the apoptotic pathway, and the glycoprotein CD34, a marker for hematopoietic stem cells, increased. Ten days after the injection of 3AP, the expression of markers tended toward the original condition. The SST revealed attenuation and subsequent recovery of the reflexes from 1 to 10 days after 3AP. Therefore, we have developed a new method to study ascidian neural degeneration and regeneration, and identified the decreased expression of GFAP and recruitment of blood stem cells to the damaged ganglion as reasons for the success of neuroregeneration in ascidians.

The crustacean central nervous system in focus: subacute neurodegeneration induces a specific innate immune response

To date nothing is known about the subacute phase of neurodegeneration following injury in invertebrates. Among few clues available are the results published by our group reporting hemocytes and activated glial cells at chronic and acute phases of the lesion. In vertebrates, glial activation and recruitment of immunological cells are crucial events during neurodegeneration. Here, we aimed to study the subacute stage of neurodegeneration in the crab Ucides cordatus, investigating the cellular/molecular strategy employed 48 hours following ablation of the protocerebral tract (PCT). We also explored the expression of nitric oxide (NO) and histamine in the PCT during this phase of neurodegeneration. Three immune cellular features which seem to characterize the subacute phase of neurodegeneration were revealed by: 1) the recruitment of granulocytes and secondarily of hyalinocytes to the lesion site (inducible NO synthase- and histamine-positive cells); 2) the attraction of a larger number of cells than observed in the acute phase; 3) the presence of activated glial cells as shown by the round shaped nuclei and increased expression of glial fibrillary acidic protein. We suggest that molecules released from granulocytes in the acute phase attract the hyalinocytes thus moving the degeneration process to the subacute phase. The importance of our study resides in the characterization of cellular and biochemical strategies peculiar to the subacute stage of the neurodegeneration in invertebrates. Such events are worth studying in crustaceans because in invertebrates this issue may be addressed with less interference from complex strategies resulting from the acquired immune system.

Adult neurogenesis: ultrastructure of a neurogenic niche and neurovascular relationships

The first-generation precursors producing adult-born neurons in the crayfish (Procambarus clarkii) brain reside in a specialized niche located on the ventral surface of the brain. In the present work, we have explored the organization and ultrastructure of this neurogenic niche, using light-level, confocal and electron microscopic approaches. Our goals were to define characteristics of the niche microenvironment, examine the morphological relationships between the niche and the vasculature and observe specializations at the boundary between the vascular cavity located centrally in the niche. Our results show that the niche is almost fully encapsulated by blood vessels, and that cells in the vasculature come into contact with the niche. This analysis also characterizes the ultrastructure of the cell types in the niche. The Type I niche cells are by far the most numerous, and are the only cell type present superficially in the most ventral cell layers of the niche. More dorsally, Type I cells are intermingled with Types II, III and IV cells, which are observed far less frequently. Type I cells have microvilli on their apical cell surfaces facing the vascular cavity, as well as junctional complexes between adjacent cells, suggesting a role in regulating transport from the blood into the niche cells. These studies demonstrate a close relationship between the neurogenic niche and vascular system in P. clarkii. Furthermore, the specializations of niche cells contacting the vascular cavity are also typical of the interface between the blood/cerebrospinal fluid (CSF)-brain barriers of vertebrates, including cells of the subventricular zone (SVZ) producing new olfactory interneurons in mammals. These data indicate that tissues involved in producing adult-born neurons in the crayfish brain use strategies that may reflect fundamental mechanisms preserved in an evolutionarily broad range of species, as proposed previously. The studies described here extend our understanding of neurovascular relationships in the brain of P. clarkii by characterizing the organization and ultrastructure of the neurogenic niche and associated vascular tissues.