The forebrain of the blind cave fish Astyanax hubbsi (Characidae). II. Projections of the olfactory bulb.
The primary subdivisions of the telencephalon of a characidian, Astyanax hubbsi, were extensively described and this subsequent study elucidates the organization of the secondary olfactory system based on horseradish peroxidase (HRP) and carbocyanine dye (DiI) tracing techniques. Both methods yielded similar results. Two fiber bundles project from the olfactory bulbs into the ventral rostral telencephalon: the medial olfactory tract (tom), embedded in the white matter of the ventral telencephalon (V), which gives rise to a dorsal (tom-d) and a ventral (tom-v) branch, and the lateral olfactory tract (tol). Running caudally, fibers of the tom-v synapse both ipsi- and contralaterally, after decussation in the ventral part of the anterior commissure, identified as the interbulbar commissure of Goldstein, in the medial terminal field of V, and in the preoptic terminal field. The dorsal branch (tom-d) projects bilaterally to a complex pattern of terminal fields, including the medial terminal field in V, the central terminal field in the dorsomedial forebrain (Dm), the caudal part of the lateral terminal field in the dorsoposterior telencephalon (Dp), and, finally, a hypothalamic terminal field at the lateral edge of the posterior nucleus tuberis. In addition, some fibers of tom-d and tom-v reach into the contralateral olfactory bulb. Here, both nerve terminals and cells were stained in the olfactory nucleus. The lateral olfactory tract (tol) runs along the lateral edge of the external sulcus forming a horizontal band. Extensive terminals were identified bilaterally in the lateral terminal field, which uniformly covers the medial and caudal parts of the dorsal hemispheres (Dc, Dl and Dp). Fibers decussate prominently in the dorsal part of the anterior commissure. A small number of projections, which join the stria medullaris, protrude into the diencephalon, decussate in the habenular commissure, and turn rostrally back into the telencephalon to synapse in the caudal part of the contralateral terminal field. These features resemble a simple bauplan of olfactory fiber connections in actinopterygian brains and further indicate that substantial parts of the telencephalon are not dominated by olfactory inputs.
Riedel
G
G
Institut für Zoologie III, Abteilung Biophysik, Universität Mainz, Germany.
Krug
L
L
D000818:Animals; D003623:Dark Adaptation / Q000502:physiology*; D004292:Dominance, Cerebral / Q000502:physiology; D005399:Fishes / Q000033:anatomy & histology*; D009412:Nerve Fibers / Q000648:ultrastructure; D009830:Olfactory Bulb / Q000033:anatomy & histology*; D009833:Olfactory Pathways / Q000033:anatomy & histology; D016548:Prosencephalon / Q000033:anatomy & histology*; D012683:Sensory Deprivation / Q000502:physiology*; D013687:Telencephalon / Q000033:anatomy & histology