Spatio-Temporal Distribution of Microglia/Macrophages during Regeneration in the Cerebellum of Adult Teleost Fish, <i>Apteronotus leptorhynchus:</i> A Quantitative Analysis

Abstract

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. In the intact corpus cerebelli, or after short survival times following application of a mechanical lesion to this cerebellar subdivision, microglia/macrophages were virtually absent. Conversely, approximately 3 days after application of the lesion, the areal density of microglia/macrophages started to increase at and near the lesion site in the ipsilateral hemisphere, as well as in the contralateral hemisphere, and reached maximum levels at approximately 10 days post lesion. 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.

Monitoring of Cell Migration and Apoptosis in Cerebellum of Juvenile Masu Salmon Oncorhynchus Masou After Injury

“…Such large condensed fragments cannot be utilized by macrophages/microglia [6]. Similar observations were also identified in morphogenetic study on mammals [20,21].…”

“…However, it remains unknown how the process of reparative neurogenesis correlates with cell proliferation and apoptosis. It was shown that the nervous tissue of fish is restored within a few weeks after injury [6]. The high regenerative potential of these animals is determined by the sequence of some morphogenetic processes, one of them is apoptosis.…”

Quantitative investigation of antigen and immune response in nervous and lymphoid tissues of Atlantic halibut (Hippoglossus hippoglossus) challenged with nodavirus

“…The observed co-localisation of IgMþ cells and nodavirus infected cells in the retina is consistent with this notion. In contrast to mammals, the teleost neurons possess a large regenerative capacity, and the nervous tissues thus have a superior ability to reverse damage [15,16]. The consequences of immunopathology inflicted by local immune responses are therefore likely to be less severe, and this could allow for greater access of immune cells to teleost nervous tissues.…”

“…The relative absence of immune response in these tissues is linked to the restricted regenerative capacity of mammalian neurons and the prospect of immuno-pathological damage of these vital tissues. In contrast to mammals, the teleost neuron has a remarkable ability to regenerate damaged CNS tissues [15,16], which in turn might permit a more unrestrained immune defence in teleost nervous tissues. Consistent with this notion, relatively high numbers of lymphocytes have been demonstrated in the normal spinal cord of fish [17].…”

Adult and Reparative Neurogenesis in Fish Brain

“…Microglia/macrophages have been identified within a few days after lesions in several divisions of the CNS of teleost fish-the cerebellum [38], the dorsal telencephalon [39,40], and the retina [41]. We used multiphoton confocal microscopy for the in vivo study of early response of microglia/macrophages in the damaged midbrain of juvenile chum salmon Oncorhynchus keta [42].…”