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From birdsong to neurodegenerative diseases
1/27/14

In birds, singing behaviour is controlled by steroid hormones. Testosterone is essential for learning to sing but also in order to sing as an adult. Previous studies have revealed brain structures controlling song in birds and the influence of testosterone and of the singing behaviour itself on the size of these structures. Professor Jacques Balthazart, from the GIGA Neurosciences at the University of Liege (Department of Biomedical and Preclinical Sciences / Biology of Sexual Differentiation), and his colleagues at the Johns Hopkins University (Baltimore MD, USA) have shown that in canaries, testosterone acts on different areas of the brain to control song and neurogenesis: it acts on the nucleus HVC to control the quality and structure of the song, and on the preoptic area to modulate the motivation to sing. In turn, singing induces an increase in neuroplasticity, i.e. the brain’s ability to restructure the connections between neurons and replace them. The hope is therefore to be able to transpose the mechanisms of plasticity observed in canaries to humans. "In the very long term”, Jacques Balthazart observes, “the idea is that if we manage to create neurogenesis or promote greater neurogenesis in the human brain, we will be able to counter, and even cure neurodegenerative diseases, or manage to repair, at least partly, traumatic brain damage".

While birds sing to attract females, they also use song to defend their territory. Therefore, there is a sexual and aggressive component in song, a behaviour controlled at least in part by the preoptic area of the brain (a part of the hypothalamus traditionally associated with the control of sexual behaviour). The study of birdsong therefore opens the door to understanding how sex hormones (such as testosterone) influence behaviour.

“Here, the idea was to see whether, by implanting testosterone into the preoptic area, we could induce song in castrated animals, which no more have endogenous testosterone. We already knew through other experiments that if we destroy this preoptic area, song and sexual behaviour disappear. In this case, we wanted to perform the opposite manipulation, which is far more specific", explains Professor Jacques Balthazart from the GIGA Neurosciences unit at the University of Liège.

A brain for all seasons?

But why this interest for the brains of songbirds? “I have been working on the hormonal control of behaviour for 40 years and, within this framework, I have been focusing on two main areas of research: one concerning the control of male behaviour, based on the Japanese quail, and the other on the plasticity of the brain of songbirds”, specifies Jacques Balthazart, who has been working for this research with Gregory Ball and Beau Alward from the Johns Hopkins University in Baltimore, USA. This research is part of a major international project that has been running for more than 25 years, funded by the Belgian Science Policy and the American NIH (National Institutes of Health).

The research carried out by these two teams drew on the work of Fernando Nottebohm, Rockfeller University, New York. In the 1970s, Nottebohm wanted to understand the controls of birdsong and, in particular, the neural circuits involved in this activity. In 1975-76, he identified the motor circuit that allows birds to sing and, in particular, a network of interconnected brain nuclei (RA, the robust nucleus of the arcopallium; and HVC, formerly called the high vocal centre), which testosterone acts upon in the context of song activation in the canary.SCS Volume The telencephalic nucleus HVC  does, in fact, play a key role in learning and producing song. Fernando Nottebohm saw that there was a well-differentiated compact group of neurons that only exists in songbirds. He then studied the volume of this group of neurons and observed that it varied with the seasons under the effect of testosterone”, he continues.

These structures therefore have a whole series of extremely interesting properties: on the one hand, they are sexually differentiated (they are more voluminous in the male, who sings, than in the female, who does not sing, allowing us to link behavioural differences with cerebral differences), and there is a seasonal plasticity (the nuclei are two to three times bigger in the spring when the birds sing and reproduce, than in winter).

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