Investigation of the effect of testosterone on the increase in the size of the RA nucleus in adult birds

In 1981, T. de Vogd and I (who worked at Rockefeller University) investigated the effect of testosterone on the increase in RA size in adult birds (as for HVC, it is not yet known how testosterone causes an increase in its size). I have already mentioned that most RA neurons send axons to the motor neurons of the nuclei of the hyoid nerves innervating the syrinx. Many other types of relatively short appendages called dendrites extend from the bodies of RA neurons; in male canaries, their length is always longer than in females. However, when we injected testosterone into the females, the dendrites began to grow and soon became the same as in the males; as they grew, the dendrites established additional connections (synapses) with other nerve cells.


A bird's song can be characterized by the number of different sounds, or syllables. At the stage of a plastic song, the canary has not yet developed a stereotype and often adds new syllables. This stage is preceded by a decrease in testosterone levels in the blood. When the hormone level is high and the bird is at the stage of stable song, new syllables in its repertoire appear only very rarely.


The formation and seasonal fluctuations in the size of HVC and RA nuclei in adult male canaries, as well as significant changes in the size of these nuclei occurring in adult females under the influence of testosterone, suggest that when a bird learns to sing, not some subtle changes occur in its brain, but a significant restructuring of neural circuits.. Seasonal and hormone-induced changes in the size of the nuclei responsible for singing were so unusual for the brains of adult vertebrates that my colleagues and I asked a "seditious" question: can these changes always be explained by the restructuring of connections between the same neurons, the number of which remains unchanged in the brain after puberty?


It is quite easy to determine whether new cells are being born. The fact is that if a cell is going to undergo a division process, then new DNA must be synthesized in it — the substance from which genes are built and which is located mainly in the nucleus. Therefore, if an animal is injected with radiolabeled thymidine (a precursor to DNA), it will accumulate in the nuclei of those cells that are preparing for division. When dividing such a labeled cell, the nucleus of each of the two daughter cells should contain half of the total amount of labeled DNA. Thus, each of the daughter cells will also be labeled. Sign up on the 1xBet platform using the 1xbet promo code your account gives you a welcome bonus worth up to 130$. 1xBet is available in over 100 countries, including Canada, Ireland, India, Nigeria, Pakistan, and South Africa. Making it one of the most accessible bookmakers in the world.