Comparative survey of adult neurogenic sites in adult avian species: an immunohistochemical study
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Date
2018
Authors
Mazengenya, Pedzisai
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Abstract
Adult neurogenesis is a widely accepted and preserved phenomenon throughout the
animal kingdom occurring in both invertebrates and vertebrates, including humans. The process
has been extensively studied in mammalian vertebrates and comparably less in the class aves. In
birds, the process has been studied more so in the song bird brain. The current thesis, investigated
putative adult neurogenesis in the brains of seven species of birds from different taxonomic
orders exhibiting different behavioural repertoires, particularly determining and localizing the
active neurogenic regions, migratory routes of migrating neuroblasts and regions of integration of
new neurons. The birds examined in the current thesis belonged to the following taxonomic
orders: Columbifomes (domestic pigeons; racing homer and utility carneau pigeons);
Psittaciformes (Congo African grey and Timneh grey parrots); Passeriformes (pied crow);
Struthioniformes (common ostrich) and Casuariiformes (emu). Free floating
immunohistochemical methods against proliferating cell nuclear antigen (PCNA) which labels
proliferating cells and doublecortin (DCX) which stains immature neurons were used to
determine the regions of cells proliferation, migratory routes of immature neurons and
recruitment sites as final destination in the brains of the birds to see if these processes are
associated with variations in behavioural repertoires and/or show phylogenetic relations. Results
from the current thesis showed that cell proliferation is widespread throughout the brains of all
the birds examined, with high levels of cell proliferation in the olfactory bulbs and the
subventricular zones (SVZ) of the lateral ventricles in the telencephalon; the SVZ of the lateral
ventricle is the primary neurogenic zone contributing new neurons in the adult telencephalon;
immature neurons are localised in high density in the olfactory bulb and the subdivisions of the
telencephalon, but in low densities in the subtelencephalic regions except in the ratite birds
(common ostrich and emu) where moderate densities were observed in the cortex of the
cerebellum; the distribution of the immature neurons showed region specificity within the
subdivisions of the telencephalon across all species with high densities in the medial and lateral
regions of the pallial and subpallial regions, but devoid in the core areas; species-specific
distribution of immature neurons was also observed in the hippocampal formations and song
control systems of the pied crow and cerebellum of the ratite birds indicating behavioural
specialisations and migratory routes of immature neurons were not clearly defined across species
except in the ratites birds where three distinct bundles of migrating neuroblasts were observed in
the telencephalon. In the majority of the studied birds neuroblasts migrated from the dorsal and
ventral poles of the SVZ of the lateral ventricle into the hyperpallium and medial striatum
respectively. The wide spread distribution of the proliferating cells and immature neurones in the
brains of adult from various taxonomic orders, although in varied extents indicates that adult
neurogenesis is a conserved trait in all species of birds and might be important for environmental
and behavioural adaptations. In addition, the process might also help to explain phylogenetic
relationships of birds along the evolutionary scale. Thus this thesis provides clues to the presence
and extent of adult neurogenesis in various species of birds highlighting on possible behavioural
repertoires impacted by adult neuronal plasticity.
Description
A thesis submitted to the Faculty of Health Sciences, University of the Witwatersrand, in
fulfillment of the requirements for the degree of Doctor of Philosophy.
Johannesburg, 2018.