Anatomy of the sleep-wake systems in four species of Equid

• Main Author: Chaumeton, Alexis Sarah
• Format: Others
• Language: en
• Published: 2018
• Online Access: https://hdl.handle.net/10539/24793

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