Although morphological characteristics of mammalian olfactory bulb (OB) are well documented
in rodents (rat, mice), only one study has been performed in rabbit, which is also
commonly used in olfactory research. The study carried out by Allison and Warwick
in 1949 led to surprising results still quoted in recent literature. The present study
re-examined this question in young rabbit OB, while it was also conducted with rat
as control. In five animals of each species, areas and coordinates of glomeruli and
mitral profiles were measured in 10 coronal sections uniformly distributed along the
rostrocaudal axis of the OB, and a distribution-free stereological method was used
to compute values along this axis. For glomeruli, the estimated number was 4200 in
rat and 6300 in rabbit. While this estimation matched with those found in literature
in rat, it strikingly differed from the Allison and Warwick's value of 1900 only.
For mitral cell number, we found 59,600 while the preceding study found 45,000 only.
In contrast to the number of glomeruli, the mitral cell number in rat and rabbit were
very close. Indeed, results showed 56, 200 in rat. The results suggest that the numbers
of olfactory glomeruli and mitral cells has been previously underestimated in rabbit,
and that the number of glomeruli changes as a function of species. In addition, both
the results of the present study and reports in the literature suggest the number
of mitral cells to be rather similar in mouse, rat and rabbit. As a consequence, the
glomerular/mitral cell ratio is likely to varied in a wide range across species.
Copyright 1998 Elsevier Science B.V.