Effects of sex steroids on spatial cognition in the zebra finch (Taeniopygia guttata)
dc.contributor.advisor
Healy, Susan
en
dc.contributor.advisor
Meddle, Simone
en
dc.contributor.advisor
Clayton, Nicky
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dc.contributor.author
Haggis, Olivia
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dc.date.accessioned
2011-01-26T10:33:15Z
dc.date.available
2011-01-26T10:33:15Z
dc.date.issued
2010
dc.description.abstract
It is well established in mammals that chronic, long-term elevations in sex steroids
are associated with improvements in spatial cognition. It is less clear the extent to
which short to medium term elevations in sex steroids improve spatial cognition and
change hippocampal morphology, particularly in birds. The avian hippocampus
expresses both androgen receptors (AR) and oestrogen receptor alpha (ERα) and
high levels of the enzyme aromatase that converts testosterone to oestrogen. I began
by comparing spatial cognition, hippocampal sex steroid receptor and aromatase
expression between males and females. There were no differences in spatial or
visual cognition or in hippocampal sex steroid receptor expression between the
sexes, although hippocampal aromatase mRNA expression was higher in males. I
then addressed the effects of acute and medium-term sex steroid treatment on spatial
cognition and hippocampal aromatase and sex steroid receptor expression. A single
treatment of testosterone 30 minutes or four hours prior to cognitive testing improved
spatial performance. Additionally, when testosterone and oestrogen were given daily
for five days spatial cognition in both sexes was improved. The testosterone-induced
improvement was blocked when testosterone was administered in conjunction with
the aromatase inhibitor fadrozole but not when administered with saline. These
findings suggest that spatial cognition is improved by an oestrogenic effect. Thirty
minutes following acute testosterone treatment, plasma testosterone levels,
hippocampal AR and ERα mRNA expression all increased. Five days of oestrogen
treatment increased plasma oestrogen levels, hippocampal ERα mRNA and Nmethyl-
D-aspartate (NMDA) receptor levels in males and females; all were
positively correlated with enhanced spatial cognition on day five of treatment.
Finally, I determined which genes were differentially expressed as a result of five
days of oestrogen treatment. Nineteen genes, identified as being involved in learning
and memory were differentially expressed in the hippocampus, eleven of which were
up-regulated and eight were down-regulated. Taken together these results
demonstrate that oestrogen can improve spatial cognition in birds. It is plausible that
oestrogen acts to improve spatial memory in the hippocampus through upregulation
of genes that control neurotransmitter release, reuptake and receptor levels.
en
dc.identifier.uri
http://hdl.handle.net/1842/4688
dc.language.iso
en
dc.publisher
The University of Edinburgh
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dc.subject
zebra finch
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dc.subject
spatial cognition
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dc.subject
steroids, sex
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dc.subject
avian hippocampus
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dc.subject
oestrogenic effect
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dc.title
Effects of sex steroids on spatial cognition in the zebra finch (Taeniopygia guttata)
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dc.type
Thesis or Dissertation
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dc.type.qualificationlevel
Doctoral
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dc.type.qualificationname
PhD Doctor of Philosophy
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