Wednesday, December 3, 2008

On Hormonal and environmental control of neuroplasticity

Andrew Mora review's Christy Strand's seminar on neuroplasticity.

Nueroplasticity is an interesting concept that deals with changes in the brain due to experiences. In order to study neuroplasticity better, Dr. Christy Strand used hormonal and environmental cues to see how they would affect the brain. The specific region of the brain that Strand was interested in was called HVC (high vocal center in birds) and the size of this region of the brain was recorded before and after experiments. According to Strand, this region in birds is important in motoring song output, and is also involved in song learning. She asserted that testosterone, an important steroid that affects the brain, did in fact increase HVC volume, but was uncertain as to how the region got bigger. Did individual neurons get bigger? Was the density decreased? Or were there simply more neurons from new cells?

In order to test for the size of the HVC, Strand used bromodeoxyuridine (BrdU) which is a cell birth marker. She used house finches because they are very common throughout the US and they are great song birds to test for the HVC region. Besides using testosterone treatment for the birds, she also wanted to know the role of the photoperiod in increasing HVC growth. Her results indicated that testosterone treatment does affect HVC growth, that photoperiod alone might affect HVC growth, and that testosterone treatment does not affect the number of new HVC neurons, despite an increase in total neuron number. Her reasoning for this might be because of a natural turnover; that is, there is no new neurons being created, but there is a decrease in cell death. Corticosterone (a stress hormone) had no affect on HVC growth.

In another related experiment, Strand used rufus-winged sparrows to test environmental cues on HVC. She used these birds because they have a unique characteristic of beginning their breeding season after the first monsoon in southern Arizona and northern Mexico. Breeding season is important for HVC size because the birds are singing frequently when they are looking for a mate. According to strand, the testes of these birds are big in March, but only used in July when the first rain falls. Her results found that during breeding of these sparrows, HVC neuron number does not increase, and testosterone levels were not different on sampling dates. She did find that singing behavior increases during the breeding season, but was still unsure whether or not HVC affects singing behavior or if the reverse was true.

I particularly enjoyed the area of future research being done by Dr. Strand. She discussed that she will be experimenting with hormonal factors affecting neurogenesis and neuroplasticity in adult snakes and lizards. She will look at the affects of captivity on neurogenesis and affects of sex on neurogenesis. Instead of the HVC region she will look at the size of the medial cortex in adult rattlesnakes. I like this integration because it attempts to compare research done on birds with similar research done on reptiles. Hopefully we will see this work published soon.



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