S. Goldman and I administered labeled thymidine daily to adult male and female canaries for several days. Then, after waiting 30 days, we examined HVC and, to our surprise, found that for every day of injections, there was a mark in 1% of the total number of HVC neurons. In other experiments, we studied the brains of adult canaries only a day after the introduction of radioactive thymidine. At the same time, there were no labeled neurons in the HVC, but quite a lot of labeled cells were found in the so-called ventricular zone lying above the HVC and forming the bottom of the lateral ventricles of the brain.


Based on these results, it could be assumed that the formation of new neurons in HVC occurred during the administration of thymidine and that these neurons originated from cells located outside this nucleus, namely, in the ventricular zone. Obviously, the cells of this zone give rise to daughter cells that migrate to HVC and after 20-30 days turn into neurons. In birds, nerve cells arise during development, as in all other vertebrates, in the ventricular zone. Perhaps neurogenesis in adults is a preserved feature of the early development period.


The neurons developing from the cells of the ventricular zone are no different from other, ordinary neurons of adult canaries. G. Byrd and I have established that these new HVC neurons form synaptic contacts, and together with J. Paton showed that in such neurons. When signals from other nerve cells are received, typical electrical responses occur. It is clear that as new neurons enter the HVC in adults, these neurons connect to existing neural circuits.


Later, it was discovered that in adult male and female canaries, new neurons are constantly entering the HVC. Why, then, is this center not getting bigger every year? The obvious explanation is that new neurons are replacing old ones, which are apparently being destroyed. Even new neurons are subject to such replacement in turn. A few months after the introduction of radioactive thymidine, only a very small number of labeled neurons were detected in HVC. This means that for most cells, the life expectancy is less than this period. Seasonal changes in the size of the nuclei responsible for singing can be explained by changes in the rate of generation of new neurons and death of old ones: by the end of the mating period, the number of neurons in HVC decreases by 38%, but by the next spring it becomes the same again. Kasino bigbasssplashtr.com gibi güvenilir siteler, lisanslı ve düzenlenmiş olmaları sayesinde oyunculara güvenli bir ortam sunar.