Act locally and think globally: intracerebral testosterone implants induce seasonal-like growth of adult avian song control circuits - PubMed (original) (raw)

Act locally and think globally: intracerebral testosterone implants induce seasonal-like growth of adult avian song control circuits

Eliot A Brenowitz et al. Proc Natl Acad Sci U S A. 2002.

Abstract

There is pronounced seasonal plasticity in the morphology of the neural circuits that regulate song behavior in adult songbirds, primarily in response to changes in plasma testosterone (T) levels. Most song nuclei have androgen receptors. Afferent input from the telencephalic nucleus HVc (also known as the "high vocal center") is necessary for seasonal growth of the direct efferent target nuclei RA and area X. We asked here whether T-stimulated growth of HVc is sufficient to induce growth of its efferent nuclei. Intracerebral T implants were placed unilaterally near HVc or RA in photosensitive adult male white-crowned sparrows for one month. The T implant near HVc produced significant growth of the ipsilateral (but not contralateral) HVc, RA, and area X, and increased neuronal number in the ipsilateral HVc. The T implant near RA did not produce selective growth of ipsilateral RA, HVc, or area X. Intracerebral T implants did not elevate plasma T levels, nor did they stimulate growth of two peripheral androgen sensitive targets, the syrinx and the cloacal protuberance. These results suggest that seasonal growth of the adult song circuits results from T acting directly on HVc, which then stimulates the growth of RA and area X transynaptically.

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Figures

Fig 1.

Fig 1.

Simplified schematic sagittal view of the avian song control system showing the distribution of steroid receptors. Black arrows connect nuclei in the main descending motor circuit, and white arrows connect nuclei in the anterior forebrain circuit. DLM, Dorsolateral nucleus of the medial thalamus; lMAN, lateral portion of the magnocellular nucleus of the anterior neostriatum; nXIIts, the tracheosyringeal portion of the hypoglossal nucleus; RA, the robust nucleus of the archistriatum; syrinx, vocal production organ; V, lateral ventricle; X, area X of the parolfactory lobe.

Fig 2.

Fig 2.

The ratio of the mean volumes of song nuclei ipsilateral and contralateral to T implanted unilaterally near HVc or RA. The dashed horizontal line indicates a ratio of 1.0 expected if there was no difference in size between the ipsilateral and contralateral nuclei. *, Differences in volume between the ipsilateral and contralateral sides were significant (see Table 1).

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