Effects of sex steroids on spatial cognition in the zebra finch (Taeniopygia guttata)

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

Zebra Finches and cognition

In spite of attracting significant attention as a model for song learning, sexual imprinting and mate-choice, there has been surprisingly little research on the general cognitive abilities of Zebra Finches (Taeniopygia guttata), from spatial memory and social learning to more complex tests of social cognition such as Theory of Mind. This is perhaps surprising given the logistical benefits of the species: they are fairly cheap to house and easy to maintain in the laboratory, and they can be readily bought or bred on demand and consequently large sample sizes are readily achievable. The explanation probably lies with the model market for cognition already being fully occupied by rats and pigeons, with decades of research into learning and memory in these species, whereas tests of more complex cognition have traditionally been conducted on primates and more recently extended to corvids, pigs and dogs. Although it is not clear whether Zebra Finches are going to be useful for examining the role of cognition in mate-choice, this species does seem to be a good choice for some tests of cognitive abilities, particularly given the existing neurobiological tools for examining the neural correlates of song learning and sexual imprinting in this species, and that much is already known about the neuroanatomy and connectivity of the Zebra Finch brain.</p