A qualitative and quantitative study of the somnogenic neural systems in the brains of cetaceans and closely related species

[摘要] Cetaceans show an unusual form of mammalian sleep, with unihemispheric slow waves(USWS), suppressed REM sleep and continuous bodily movement, however the mechanism bywhich USWS occurs is unclear. This thesis describes the detailed anatomy of the neural systemssystems involved in the control and regulation of sleep in the basal forebrain, diencephalon,midbrain and pons in three Cetartiodactyla species namely the Harbour porpoise, Northernminke whale and the Hippopotamus, as well as a broader study of the orexinergic system inCetartiodactyls by means of immunohistochemistry and stereological analysis. All the neuralelements involved in sleep regulation and control found in bihemispheric sleeping mammalswere present in the harbour porpoise, minke whale and hippopotamus with no specific nucleibeing absent, and the only novel nuclei being identified was the parvocellular orexinergic clusterin the hypothalamus- a feature seen in cetartiodactyla and the Africa elephant. This qualitativesimilarity of nuclear organization relates to the cholinergic, noradrenergic, serotonergic andorexinergic systems and is extended to the GABAergic elements involved with these nuclei.Quantitative analysis of the cholinergic and noradrenergic nuclei of the pontine region and theorexinergic nuclei of the hypothalamus revealed that in comparison to other mammals, thenumbers of pontine cholinergic, noradrenergic and orexinergic neurons are markedly higher inthe harbour porpoise and minke whale than in other large-brained bihemispheric sleepingmammals previously examined. Furthermore, the diminutive telencephalic commissures (anteriorcommissure, corpus callosum and hippocampal commissure) along with an enlarged posteriorcommissure and supernumerary pontine cholinergic and noradrenergic neurons in cetaceansindicate that the control of unihemispheric slow wave sleep is likely to be a function ofinterpontine competition, facilitated through the posterior commissure, in response to unilateraltelencephalic input related to the drive for sleep. In addition, an expanded peripheral division ofthe dorsal raphe nuclear complex appears likely to play a role in the suppression of REM sleep incetaceans. Thus, this thesis provides several clues to the understanding of the neural control ofthe unusual sleep phenomenology present in cetaceans

[发布机构] University of the Witwatersrand