Firstly, changes in peripheral section of oxytocin and α-MSH, and changes in oxytocin and α-MSH neurone activity were studied in male rats during copulation. Intromission increased plasma concentration of both oxytocin and α-MSH and Fos expression in neurones in the SON and in the PVN and in the accurate nucleus was increased, confirming the similarities between oxytocin and α-MSH in their involvement in male sexual behaviour. The putative interaction between oxytocin and α-MSH was then investigated by studying at which central or peripheral level this interaction would occur. Oxytocin antagonist iv-injection had no effect on the increase of oxytocin and α-MSH secretion during intromission, suggesting that peripheral oxytocin does not regulate peripheral α-MSH secretion. However, oxytocin administered centrally to non-mating conscious rates decreased plasma α-MSH concentration, suggesting that central oxytocin may regulate α-MSH peripheral secretion. These studies therefore support an interaction between central oxytocin and α-MSH. Then, the effects of central α-MSH on oxytocin secretion and neuronal activity were investigated. Central administration of α-MSH induced Fos expression in magnocellular oxytocin neurones in the SON and in the PVN but had no effect on parvocellular oxytocin neurons in the PVN. Α-MSH directly administered onto the SON induced a strong increase in Fos expression in oxytocin neurones in the SON. These studies indicate that α-MSH modulates directly the activity on selected oxytocin neurones and that consequently, αMSH may regulate some specific oxytocin effects and not others. However, central administration of α-MSH decreased oxytocin secretion from the pituitary gland. This illustrates that Fos induction does not necessarily reflect excitation of the neurones. Finally, MC4R antagonist centrally administered reduced the Fos expression induced at intromission in magnocellular oxytocin neurones but had no effect on the Fos expression in the parvocellular neurones.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:642585 |
| Date | January 2005 |
| Creators | Caquineau, Céline |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/24143 |
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