Auditory-vocal cholinergic pathway in zebra finch brain.

The two main song control nuclei in the zebra finch forebrain, the higher vocal center (HVC) and the robust nucleus of the archistriatum (RA), receive cholinergic innervation from the ventral paleostriatum (VP) of the basal forebrain which may play a key role in song learning. By injecting two kinds of neuroanatomical tracers, we found that a topographically segregated pathway from nucleus ovoidalis (Ov) and nucleus dorsomedialis posterior thalami (DMP) to VP and further to RA and HVC. Ov is known as a major relay in the main ascending auditory pathway. The results suggest that cholinergic neurons in the VP which are responsible for song learning are regulated by auditory information from the Ov.

The studies on neurogenesis induced by brain injury in adult ring dove.

It was the first time demonstrated by us that the number of newborn neurons was increased after making lesion in forebrain of adult ring dove (Streptopelia risoria) by means of autoradiography and immunohistochemistry. Neurogenesis in the adult avian is restricted to the telencephalon. In doves with bilateral electrolytic lesion of nucleus ectostriatum (E), the mean number of proliferating cells in the lateral ventricular zone (LVZ) and newborn neurons in the forebrain increased by 1.95 times and 2.38 times respectively as compared with that in intact doves. The most remarkable increase of neurogenesis induced by nucleus ectostriatum lesions was found at the anterior-posterior level 3 (L3), where the lesion site was located. These results showed that the electrolytic brain lesion altered the distribution pattern of proliferating cells in the LVZ and resulted in increase of the number of newborn neurons in the non-VZ areas of forebrain. The changes in number and distribution pattern of proliferating cells in LVZ and newborn neurons in forebrain may be dependent on site of lesion. Studies on the relationship between proliferating cells in LVZ and newly generated neurons in non-VZ areas may help to understand the mechanism of brain plasticity and development.

Avian auditory pathways show met-enkephalin-like immunoreactivity.

Pathways associated with a recently defined region of the avian auditory thalamus, the shell of the nucleus ovoidalis (Ov), were examined for met-enkephalin immunoreactivity. The presence of enkephalin-like immunoreactive (ELI) perikarya within the medial margin of the inferior colliculus (ICM), afferent to the Ov shell, implicated ICM as a source of ELI fibers within the Ov shell and tract. The shell also contained ELI perikarya and its targets, including the ventromedial hypothalamus and caudoventral paleostriatal complex, were characterized by ELI fields. These data suggest that enkephalinergic auditory pathways, in parallel with traditionally recognized auditory projections, target regions of the avian basal forebrain.

[A study on location of vocalization centres in hawfinch (Coccothraustes coccothraustes)].

Vocal-control nuclei in hawfinch (Coccothraustes coccothraustes) were studied by HRP retrograde tracing and electrophysiological methods. Vocal control centres in hawfinch consist of four discrete nuclei. Hyperstriatum ventral, pars caudale (HVc) is the highest nucleus, with its efferent fibers projecting to the rubust nucleus of archistriatum (RA), which in turn projects to the nucleus intercollicularis (ICo) of midbrain and the nucleus intermedius (IM) of medulla oblongata IM innervating vocal organ (syrinx) also receives input from ICo. The both vocal control pathways are not strictly unilateral. ICo plays a relative independent role in vocal control. The stereotaxic coordinates for HVc RA, ICo, IM are tabulated in Table 2.