Cell death and neuronal recruitment in the high vocal center of adult male canaries are temporally related to changes in song

Adult male canaries modify their song every year. Most of these changes occur during late summer and early fall, after the end of the breeding season, and in late winter, immediately before the onset of the next breeding season. The high vocal center (HVC) is an important nucleus in the brain pathway that controls this learned behavior. New neurons continue to be added to the HVC of adult male canaries, where they replace older neurons that have died. The present report describes the monthly incidence of cell death and neuronal addition in the HVC of such birds. Different groups of 1- to 2-year-old male canaries were treated with [3H]thymidine, a marker of cell birth, during each month of the year and killed 27 days later. The ratio of 3H-labeled neurons to all neurons in the HVC showed seasonal peaks and troughs. This ratio was highest in October and March. Peaks in the ratio of pycnotic (dying) HVC cells to all neurons in HVC preceded the peaks in the ratio of 3H-labeled neurons. We suggest that seasonal peaks in cell loss and neuronal recruitment in HVC are related to endocrine changes and that all three play a role in the seasonality of song modification.

Song learning in birds: the relation between perception and production

The vocal control system of oscine songbirds has some perplexing properties--e.g. laterality, adult neurogenesis, neuronal replacement--that are not predicted by common views of how vocal learning takes place. Similarly, we do not understand the relation between the direct pathway for the control of learned song and the recursive pathway necessary for song learning. Some of the paradoxes of the vocal system of birds may disappear once the relation between the perception and production of learned vocalizations is better understood. To some extent, perception and production may be two closely related states of a same system.

Control of cell number in the developing visual system. II. Effects of partial tectal ablation

The effects of potential excess innervation on cell survival in the superior colliculus and related structures during the period of normally occurring cell death was examined. A unilateral, partial lesion of the superficial layers of the superior colliculus on the day of birth, which results in a compression of the retinotectal map into the remaining area, was the manipulation used to produce the potential excess innervation. Cell density was reduced in the tectal fragment early in development, consistent with hyperinnervation, but had returned to normal by the end of the period of normally occurring cell death. The overall incidence of cell degeneration in the remaining partial colliculus was not different from the undamaged contralateral colliculus or from normal, though there was evidence of a transitory depression and later elevation of cell loss. Cell loss in the retina contralateral to the lesion was increased in the late part of the period of normal cell loss and there were fewer cells in the retinal ganglion cell layer at maturity. The amount of the cell loss in the retina was small compared to the amount of target removal. These results suggest that the survival of neurons with branching axons does not sensitively reflect target availability.

Differential effects of lesions in three limbic areas on ultrasound production and lordosis by female hamsters

Ultrasound production and lordosis were examined in ovariectomized, hormone-primed female hamsters before and after sham operations or bilateral electrolytic lesions in the lateral septum/bed nucleus, corticomedial amygdala, or lateral habenula. During 2-min exposures to synthetic ultrasounds and 1-min exposures to stimulus males, females with corticomedial amygdala lesions exhibited reduced ultrasound rates and lordosis durations. Following lesions in the lateral septum/bed nucleus, females showed significant increases in ultrasound rates with no pre- to postoperative change in lordosis. Ablations of the lateral habenula had no effect on calling but were associated with shorter lordosis durations. These results demonstrate that two reproductive behaviors, ultrasound production and lordosis, are differentially affected, depending on lesion placement within the limbic system. In turn, these differences demonstrate that the neural mechanisms for two elements of a single major class of behavior can be quite distinct, both in terms of the likelihood that particular brain areas will be involved and in the nature of their involvement.

Differential effects of lesions in three limbic areas on ultrasound production and lordosis by female hamsters

Ultrasound production and lordosis were examined in ovariectomized, hormone-primed female hamsters before and after sham operations or bilateral electrolytic lesions in the lateral septum/bed nucleus, corticomedial amygdala, or lateral habenula. During 2-min exposures to synthetic ultrasounds and 1-min exposures to stimulus males, females with corticomedial amygdala lesions exhibited reduced ultrasound rates and lordosis durations. Following lesions in the lateral septum/bed nucleus, females showed significant increases in ultrasound rates with no pre- to postoperative change in lordosis. Ablations of the lateral habenula had no effect on calling but were associated with shorter lordosis durations. These results demonstrate that two reproductive behaviors, ultrasound production and lordosis, are differentially affected, depending on lesion placement within the limbic system. In turn, these differences demonstrate that the neural mechanisms for two elements of a single major class of behavior can be quite distinct, both in terms of the likelihood that particular brain areas will be involved and in the nature of their involvement.