This thesis describes studies of the development of the circadian system in the Siberian hamster. It concentrates on the ontogeny of the photic entrainment system, the functionality of maternal-postnatal entrainment, and the role of dopaminergic mechanisms underlying circadian entrainment. The induction of the immediate early gene <I>c-fos </I>was used as a phase-dependant marker of cellular activation to study the ontogeny of a photic response in the suprachiasmatic nucleus (SCN). Induction of <I>c-fos </I>is correlated with light-induced phase shifts of the biological clock in the adult. These studies established that <I>c-fos </I>was first inducible by a light pulse on postnatal day (PD) 3, and that the number of cells expressing light-induced <I>c-fos </I>increased from PD3 to PD5. The innervations of the SCN by the retinohypothalamic tract (RHT) was examined using tract-tracing agents, and the growth of fibres into the SCN was correlated with the development of the light induced <I>c-fos</I> response. Previous studies indicate that glutamate is the principal neurotransmitter of the RHT and mediates light entrainment of the SCN, and is also associated with neuronal plasticity and synapse formation in other brain regions. The expression of NMDAR1 splice variants was studied at different developmental stages. It was discovered that the SCN expressed a conserved isoform throughout the postnatal period. Experiments were undertaken to establish the existence and relevance of maternal entrainment during the postnatal period. Mothers maintained in constant dark from early pregnancy produced litters with synchronised circadian rhythms of locomotor activity at weaning. This suggests that despite an absence of light-dark cues, the developing animals are entrained by maternally-derived cues. In a subsequent experiment, new-born litters fostered to mothers exposed to a reversed light-dark cycle established a maternal influence on the circadian phase of the pups.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:598668 |
| Date | January 1997 |
| Creators | Duffield, G. E. |
| Publisher | University of Cambridge |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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