| Summary: | A thesis submitted to the Faculty of Health Sciences,
University of the Witwatersrand, Johannesburg,
in fulfilment of the requirements
for the degree of
Master of Science in Medicine. Johannesburg, 2017 === Within the order Perissodactyla the physiological measurable parameters of sleep
have been investigated in a number of species, however no studies exist that describe
the neuronal organisation and morphology of the sleep-wake systems in any of its
members. The central aim of this dissertation is to address this gap by providing the
first complete description of the somnogenic systems in the basal forebrain,
diencephalon, midbrain and pons of four equid species; the donkey, horse, plains and
mountain zebra. By means of standard immunohistochemical techniques the
cholinergic, catecholaminergic, serotonergic, orexinergic and GABAergic systems
were identified and qualitatively described in each of the four species. The results
revealed that, for the most part, the nuclear organisation and morphology of the sleepwake
systems did not differ between the species examined, and displayed the typical
mammalian organisational plan. However, two novel findings were noted: 1) the
presence of tyrosine hydroxylase neurons in the predominantly GABAergic thalamic
reticular nucleus; 2) the presence of a medial cluster of parvocellular orexinergic
neurons within the hypothalamus. It is proposed that the population of tyrosine
hydroxylase neurons in the thalamic reticular nucleus likely play a role in postural
maintenance during standing rapid eye movement sleep and potentially contribute to
memory consolidation in mammals with short sleep times. Additionally, the
parvocellular cluster of orexin neurons is hypothesised to balance short sleep time and
appetite drive in larger animals with high-energy demands and a low trophic status.
The data produced from this dissertation extends the pre-existing phylogenetic
database and offers further opportunity for reliable comparisons across mammals
towards a more complete definition of the phenomenon of sleep. === LG2018
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