The neurons within the segmented hindbrain of the early chick embryo have been mapped with the neuronal tracers HRP and fluorescent lysinated dextran. We have categorised neurons according to their axonal pathways and have then compared rhombomeres with respect to the number and class of neurons present. The results indicate that most rhombomeres are similar in that they contain the same set of basic neuronal types but differ in that particular neuronal types are more abundant in some rhombomeres than others. The data support the concept that the hindbrain develops according to ‘variations on a segmental theme’ rather than ‘each segment is unique’. Many of the cell types occupy distinct mediolateral domains that are probably established by both the differential migration of some neuronal classes and the spatial segregation of distinct precursors. The caudal rhombomeres 7 and 8 are exceptional in that they do not have the full set of basic neuronal types and also contain two additional medial cell types that are not present rostrally. The mechanisms that may generate the regional diversity apparent in the more mature hindbrain are discussed.

Reference

Burns
F. R.
,
von Kannen
S.
,
Guy
L.
,
Raper
J. A.
,
Kamholz
J.
,
Chang
S.
(
1991
)
DM-GRASP, a novel immunoglobulin superfamily axonal surface protein that supports neurite extension.
Neuron
7
,
209
220
Doe
C. Q.
,
Goodman
C. S.
(
1985
)
Early events in insect neurogenesis. The role of cell interactions and cell lineage in the determination of neuronal precursor cells.
Dev. Biol
111
,
206
219
Fraser
S.
,
Keynes
R.
,
Lumsden
A.
(
1990
)
Segmentation in the chick embryo hindbrain is defined by cell lineage restrictions.
Nature
344
,
431
435
Glover
J. C.
,
Petursdottir
G.
(
1988
)
Pathway specificity of reticulospinal and vestibulospinal projections in the 11-day chicken embryo.
J. Comp. Neurol
270
,
25
38
Glover
J. C.
,
Petursdottir
G.
(
1991
)
Regional specificity ofdeveloping reticulospinal, vestibulospinal and vestibulo-ocular projections in the chicken embryo.
J. Neurobiol
22
,
352
376
Guthrie
S.
,
Lumsden
A.
(
1992
)
Motor neuron pathfinding following rhombomere reversals in the chick hindbrain.
Development
114
,
663
673
Hannemann
E.
,
Trevarrow
B.
,
Metcalfe
W. K.
,
Kimmel
C. B.
,
Westerfield
M.
(
1988
)
Segmental pattern of development of the hindbrain and spinal cord of the zebrafish embryo.
Development
103
,
49
58
Holt
C. E.
,
Bertsch
T. W.
,
Ellis
H. M.
,
Harris
W. A.
(
1988
)
Cellular determination in the Xenopus retina is independent of lineage and birth date.
Neuron
1
,
15
26
Kimmel
C. B.
,
Powell
S. L.
,
Metcalfe
W. K.
(
1982
)
Brain neurons which project to the spinal cord in young larvae of the zebrafish.
J. Comp. Neurol
205
,
112
127
Kuwada
J. Y.
,
Goodman
C. S.
(
1985
)
Neuronal determination during embryonic development of the grasshopper nervous system.
Dev. Biol
110
,
114
126
Lumsden
A.
(
1990
)
The cellular basis of segmentation in the developing hindbrain.
Trends Neurosci
13
,
329
335
Lumsden
A.
,
Keynes
R.
(
1989
)
Segmental patterns of neuronal development in the chick hindbrain.
Nature
337
,
424
428
Marshall
H.
,
Nonchev
S.
,
Sham
M.H.
,
Muchamore
I.
,
Lumsden
A.
,
Krumlauf
R.
(
1992
)
Retinoic acid alters the hindbrain Hox code and induces transformation of rhombomeres 2/3 into a 4/5 identity.
Nature
360
,
737
741
McConnell
S. K.
,
Kaznowski
C. E.
(
1991
)
Cell cycle dependence of laminar determination in developing neocortex.
Science
254
,
282
285
Mendelson
B.
(
1986
)
Development of reticulospinal neurons of the zebrafish. I. Time of origin.
J. Comp. Neurol
251
,
160
171
Mendelson
B.
(
1986
)
Development of reticulospinal neurons of the zebrafish. II. Early axonal outgrowth and cell body position.
J. Comp. Neurol
251
,
172
184
Metcalfe
W. K.
,
Mendelson
B.
,
Kimmel
C. B.
(
1986
)
Segmental homologies among reticulospinal neurons in the hindbrain of the zebrafish larvae.
J. Comp. Neurol
251
,
147
159
Moody
S. A.
,
Heaton
M. B.
(
1981
)
Morphology of migrating trigeminal neuroblasts as revealed by horseradish peroxidase retrograde labelling techniques.
Neuroscience
6
,
1707
1723
Nordlander
R. H.
,
Baden
S. T.
,
Ryba
T. M. J.
(
1985
)
Development of early brainstem projections to the tail spinal cord in Xenopus.
J. Comp. Neurol
231
,
519
529
Petursdottir
G.
(
1990
)
Vestibulo-ocular projections in the 11-day chicken embryo: pathway specificity.
J. Comp. Neurol
297
,
283
297
Rovainen
C.
(
1967
)
Physiological and anatomical studies on large neurons of the central nervous system of the sea lamprey (Petromyzon marinus) Muller and Mauthner cells.
J. Neurophysiol
30
,
1024
1042
Trevarrow
B.
,
Marks
D. L.
,
Kimmel
C. B.
(
1990
)
Organisation of hindbrain segments in the zebrafish embryo.
Neuron
4
,
669
679
Van Mier
P.
,
ten Donkelaar
H. J.
(
1984
)
Early development of the descending pathways from the brain stem to the spinal cord in Xenopus laevis.
Anat. Embryol
170
,
259
306
Walsh
C.
,
Cepko
C. L.
(
1992
)
Widespread dispersion of neuronal clones across functional regions of the cerebral cortex.
Science
255
,
434
440
Wetts
R.
,
Fraser
S. E.
(
1988
)
Multipotent precursors can give rise to all major cell groups of the frog retina.
Science
239
,
1142
1145
Windle
W. F.
,
Austin
M. F.
(
1936
)
Neurofibrillar development in the central nervous system of chick embryos up to 5 days incubation.
J. Comp. Neurol
63
,
431
463
This content is only available via PDF.