SEXUAL DIMORPHISM OF SONG CONTROL NUCLEUS RA IN THE FOREBRAIN OF SONGBIRD (LONCHURA STRIATA)

摘要

Songbirds exhibit some of the most extreme sex dimorphism in the brain of all vertebrates. The mechanisms that control this sexual dimorphism are poorly understood. By using histological and neural tract- tracing methods, we studied the development of the sexual dimorphism of a forebrain nucleus involved in the song control, the robust nucleus of the archistriatum (RA) of songbird, Striated mannikin ( Lonchura striata ). We found: (1) The outline of RA could be first distinguished from its surroundings around 5 days post- hatch (D5) in both female and male birds. From D5 to 45, the RA volume increased gradually. The growth in RA volume was occurred significantly during D5 to 25 ( P 0. 05). During development the RA volume for females became smaller and smaller after D45, whereas the RA volume for males continuously increased. As a result, the RA volume in females was only one third of that in males at D120; (2) There was no significant difference in the neuron size in the RA between the sexes during D5 to D35 ( P >0. 05). At D5 the neurons size of RA in both females and males remains essentially the same, 15. 7 μ m ² ± 5. 2 μ m ² . However, the neuron sizes in RA were 5. 6 and 5. 5 times larger at D45 than their sizes at D5, respectively, for the males and the females. The neuron size in RA for both females and males no longer increased after D45. The larger neurons with 80 μ m ² cell size in RA disappeared gradually after D 45 and they were nearly absent in females by D120. The neuron size was 109 μ m ² ± 5. 2 μ m ² in male RA and 60. 9 μ m ² ± 10. 0 μ m ² in female RA at D120, respectively. The neuron size in RA was nearly two times larger in males than in females at D120; (3) The neuron density in RA decreased from 1. 18 × 10. 5 to 1. 98 × 10. 4 per mm ³ and from 1. 21 × 10. 5 to 1. 17 × 10. 4 per mm ³ , respectively, for the females and the males during D5 to D120. Before D45 the RA neuron density in both sexes was not significantly different, however, after D45 the RA neuron density was larger in females than in males; (4) By using Nissl staining, the apoptotic neurons were observed. The apoptotic neurons were easily seen especially in the female RA during D45 to D60. The numbers of apoptotic neurons were 19. 4 ± 8. 0 per mm ³ at D45 and (17. 9 ± 8. 2) × 10. 3 per mm ³ at D60 in the female RA. Compared to the features of normal neurons, the size of apoptotic neurons became smaller and shape became crimpy. There a few granules (apoptotic bodies) appeared in the nucleus stained darkly and distributed uniformly in apoptotic neurons. Apart from apoptotic bodies, the other parts of apoptotic neurons were almost not stained by Nissl substance. For a normal neuron, however, there was only a big pale nucleus with one or two dark nucleolus. The cytoplasm could be stained with blue by Nissl substance. Glia were as large as the apoptotic neurons. Like normal neurons, they have only one or two dark nucleolus. However, an apoptotic neuron contains a few apoptotic bodies. These made the apoptotic neurons easily be distinguished from other neurons or glia in the RA. Although the neuronal apoptosis appeared from D5 to D80, the most obvious apoptotic stage distributed from D45 to D60. The apoptotic neurons were almost not observed in the adult female and male RA. From D35 to D80, apoptotic RA neurons were significantly increased in females than in males ( P <0. 05); (5) At D5, no labeled fibers were found within RA from injections of BDA (biotinylated dextran amine) into the lateral magonocellular nucleus of anterior neostriatum (LMAN). However, RA was labeled from the injection into LMAN at D15. This result suggested that the connections between RA and LMAN sh