Catecholaminergic cell groups and vocal communication in male songbirds.
The nucleus intercollicularis (ICo) region of the midbrain has been shown to concentrate testosterone and to be involved in the neural control of avian vocal behavior. The present study investigated the possible role of the ICo region in the androgen-dependent courtship behavior of male ring doves, with the use of radio-frequency lesion and intracranial hormone-implant techniques. In the first experiment, bilateral lesions in the ICo region reduced nest-cooing but did not specifically alter other courtship behavior of males tested with stimulus females. No effect on gonadal state could be discerned. In a second experiment, unilateral 30-ga. implants containing crystalline testosterone propionate (TP) or cholesterol (C) were placed in the ICo region or in other parts of midbrain of castrated male doves. The TP implants activated nest-cooing when placed in the ICo region only. Other behaviors were not elicited or not selectively affected by TP implants. Diffusion from the implant was probably not responsible for the elicitation of nest-cooing, since the weights of the peripheral steroid-sensitive tissues of males implanted with TP and C did not differ and since many sites near, but not in, the ICo region were ineffective. These data demonstrate the importance of the ICo region in the expression of nest-cooing, vocal courtship behavior, in the male ring dove. Furthermore, the facilitation of certain vocal courtship behavior by hormonal stimulation is in line with the suggestion that the central gray/ICo/torus semicircularis regions of the vertebrate brain are analogous in their mediation of vocalizations.