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Development of microglia and macrophages in the postnatal rat pituitary
1Department of Human Anatomy, University of Oxford, South Parks Road, Oxford OX1 3QX, UK. jfmorris@vax.oxford.co.uk
Abstract:
Microglia and macrophages, immunolabelled with F4/80 (which binds a 160-kDa plasmalemmal glycoprotein) and OX-42 (which labels the complement type 3 receptor, CR3), were identified in the neuro- and adenohypophyses, respectively, of postnatal rats from day 1 to adulthood. In the neurohypophysis, the numerical density (cells/mm2) of microglia increased from postnatal day 1 to day 7 but was then unchanged from the adult density. In the adenohypophysis, the numerical density of macrophages increased from postnatal day 1 to day 21. The increasing size of the pituitary meant that the total number of such cells increased rapidly in the neurohypophysis up to day 14, but was then essentially unchanged; in the adenohypophysis macrophages increased in proportion to the increasing size of the gland up to day 21. Proliferation of the mononuclear cells was analysed by the immunodetection of bromodeoxyuridine incorporation into the nuclei of microglia and macrophages. F4/80-immunoreactive cells incorporating bromodeoxyuridine were found on all the postnatal days studied. The proportion of such cells in the neurohypophysis was high from postnatal day 1 to day 14 and in the adenohypophysis was maximal on day 14, decreasing in both parts of the pituitary by day 21. The estimated total number of proliferating cells was maximal in both parts of the pituitary on day 14. In both parts, OX-42-immunoreactive cells were less numerous than F4/80-immunoreactive cells up to postnatal day 14; CR3 expression may therefore be associated with maturation of these cells. Neurohypophysial microglia increased in size to postnatal day 7, consistent with the assumption of a 'compact' microglial morphology; adenohypophysial macrophages did not change in size over the postnatal period. Throughout the period studied, neurohypophysial microglia were significantly more densely distributed and larger in size than adenohypophysial macrophages. Neurohypophysial microglia phagocytose terminals of neurosecretory neurons from day 7, concurrent with the development of a distinct perivascular space. In the adenohypophysis, the perivascular space was present from birth and macrophages were not phagocytic. There are, therefore, considerable differences in the density, morphology and activity between the populations of myelomonocytic cells in the postnatal rat neuro- and adenohypophyses.
Insights
This study reveals distinct developmental patterns for microglia and macrophages in rat pituitary glands. These immune cells show different proliferation, density, and phagocytic activity in the neurohypophysis versus the adenohypophysis during postnatal development.
Area of Science:
- Neuroimmunology
- Developmental Biology
- Endocrinology
Background:
- Microglia and macrophages are key immune cells in the central nervous system and pituitary gland.
- Their roles and development in the pituitary during the critical postnatal period are not fully understood.
- Understanding these myeloid cell populations is crucial for pituitary function and development.
Purpose of the Study:
- To investigate the developmental dynamics of microglia and macrophages in the neurohypophysis and adenohypophysis of postnatal rats.
- To compare the density, proliferation, morphology, and phagocytic activity of these cells in both pituitary compartments.
- To elucidate the maturation process and functional differences of these immune cells during early life.
Main Methods:
- Immunohistochemistry using F4/80 and OX-42 antibodies to identify microglia and macrophages.
- Bromodeoxyuridine incorporation assay to assess cell proliferation.
- Quantitative analysis of cell density, size, and distribution.
- Morphological assessment and evaluation of phagocytic activity.
Main Results:
- Microglia density increased in the neurohypophysis by day 7, while macrophage density increased in the adenohypophysis by day 21.
- Cell proliferation peaked around day 14 in both pituitary regions.
- Neurohypophysial microglia were larger, denser, and phagocytosed neuronal terminals, unlike adenohypophysial macrophages.
Conclusions:
- Microglia and macrophages exhibit distinct developmental trajectories and functional specializations in the postnatal rat pituitary.
- Complement type 3 receptor (CR3) expression, labeled by OX-42, appears to correlate with cell maturation.
- These findings highlight significant differences in the myelomonocytic cell populations between the neuro- and adenohypophysis.