Olfactory bulb organization and development in Monodelphis domestica (grey short‐tailed opossum)

The cyto- and chemoarchitecture of the olfactory bulb of two monotremes (shortbeaked echidna and platypus) was studied to determine if there are any chemoarchitectural differences from therian mammals. Nissl staining in conjunction with enzyme reactivity for NADPH diaphorase, and immunoreactivity for calcium binding proteins (parvalbumin, calbindin and calretinin), neuropeptide Y, tyrosine hydroxylase and non-phosphorylated neurofilament protein (SMI-32 antibody) were applied to the echidna. Material from platypus bulb was Nissl stained, immunoreacted for calretinin, or stained for NADPH diaphorase. In contrast to eutherians, no immunoreactivity for either the SMI-32 antibody or calretinin was found in the mitral or dispersed tufted cells of the monotremes and very few parvalbumin or calbindin immunoreactive neurons were found in the bulb of the echidna. On the other hand, immunoreactivity for tyrosine hydroxylase in the echidna was similar in distribution to that seen in therians, and periglomerular and granule cells showed similar patterns of calretinin immunoreactivity to eutherians. Multipolar neuropeptide Y immunoreactive neurons were confined to the deep granule cell layer and underlying white matter of the echidna bulb and NADPH diaphorase reactivity was found in occasional granule cells, fusiform and multipolar cells of the inner plexiform and granule cell layers, as well as underlying white matter. Unlike eutherians, no NPY immunoreactive or NADPH diaphorase reactive neurons were seen in the glomerular layer. The bulb of the echidna was comparable in volume to prosimians of similar body weight, and its constituent layers were highly folded. In conclusion, the monotreme olfactory bulb does not show any significant chemoarchitectural dissimilarities from eutheria, despite differences in mitral/tufted cell distribution.

Section: Tyrosine Hydroxylase Immunoreactivity In Monotreme and Therisupporting

confidence: 64%

Section: Introductionmentioning

confidence: 99%

Chemoarchitecture of the Monotreme Olfactory Bulb

Ashwell

2006

“…There may be significant differences between marsupials as to the functional state of sensory systems at birth and the contribution those senses make to behavior immediately after birth. Diprotodont marsupials may follow a more advanced timetable of olfactory development relative to polyprotodont marsupials [Lin et al, 1988;SchwanzelFukuda et al, 1988;Brunjes et al, 1992;Malun and Brunjes, 1996;Chuah et al, 1997;Couper Leo and Brunjes, 1999] so that they can make use of olfactory cues.…”

Section: Introductionmentioning

confidence: 99%

“…Considerable attention has been given to the study of the development of the olfactory system and its central projections in Ameridelphids such as Didelphis and Monodelphis [Lin et al, 1988;Schwanzel-Fukuda et al, 1988;Brunjes et al, 1992;Malun and Brunjes, 1996;Chuah et al, 1997;Couper Leo and Brunjes, 1999], but study of the development of the olfactory system in Australian diprotodont marsupials (including macropods and phalangerids) has been largely confined to the olfactory epithelium [Gemmell and Nelson, 1988;Gemmell and Rose, 1989]. Nothing is known at present about the timing of the anatomical development of central olfactory connections in Australian marsupials; particularly with regard to the possible role of olfaction in the critically important survival behavior of newborn tammars.…”

Section: Introductionmentioning

confidence: 99%

Development of the Olfactory System in a Wallaby <i>(Macropus eugenii)</i>

Ashwell¹,

Marotte

Cheng³

2008

We used carbocyanine dye tracing techniques in conjunction with hematoxylin and eosin staining, immunohistochemistry for GAP-43, and tritiated thymidine autoradiography to examine the development of the olfactory pathways in early pouch young tammar wallabies (Macropus eugenii). The overarching aim was to test the hypothesis that the olfactory system of newborn tammars is sufficiently mature at birth to contribute to the guidance of the pouch young to the nipple. Although GAP-43 immunoreactive fibers emerge from the olfactory epithelium and enter the olfactory bulb at birth, all other components of the olfactory pathway in newborn tammars are very immature at birth, postnatal day (P0). In particular, maturation of the vomeronasal organ and its projections to the accessory olfactory bulb appears to be delayed until P5 and the olfactory bulb is poorly differentiated until P12, with glomerular formation delayed until P25. The lateral olfactory tract is also very immature at birth with pioneer axons having penetrated only the most rostral portion of the piriform lobe. Interestingly, there were some early (P0) projections from the olfactory epithelium to the medial septal region and lamina terminalis (by the terminal nerve) and to olfactory tubercle and basal forebrain. The former of these is presumably serving the transfer of LHRH⁺ neurons to the forebrain, as seen in eutherians, but neither of these very early pathways is sufficiently robust or connected to the more caudal neuraxis to play a role in nipple finding. Tritiated thymidine autoradiography confirmed that most piriform cortex pyramidal neurons are generated in the first week of life and are unlikely to be able to contribute to circuitry guiding the climb to the pouch. Our findings lead us to reject the hypothesis that olfactory projections contribute to guidance of the newborn tammar to the pouch and nipple. It appears far more likely that the trigeminal pathways play a significant role in this behavior because the central projections of the trigeminal nerve are more mature at birth in this marsupial.

“…Measurements of structures were made with the aid of ImageJ 1.37v software. All olfactory system structures were identified by reference to published accounts of the anatomy of the olfactory pathways in these two species [Ashwell, 2006a, b;Ashwell and Phillips, 2006], marsupials [Brunjes et al, 1992;Malun and Brunjes, 1996;Chuah et al, 1997;Ashwell et al, 2008] and a reference work on the anatomy of olfactory regions in the rat [Shipley et al, 2004].…”

Section: Analysis Of Materialsmentioning

confidence: 99%

Development of the Olfactory Pathways in Platypus and Echidna

Ashwell

2011

The two groups of living monotremes (platypus and echidnas) have remarkably different olfactory structures in the adult. The layers of the main olfactory bulb of the short-beaked echidna are extensively folded, whereas those of the platypus are not. Similarly, the surface area of the piriform cortex of the echidna is large and its lamination complex, whereas in the platypus it is small and simple. It has been argued that the modern echidnas are derived from a platypus-like ancestor, in which case the extensive olfactory specializations of the modern echidnas would have developed relatively recently in monotreme evolution. In this study, the development of the constituent structures of the olfactory pathway was studied in sectioned platypus and echidna embryos and post-hatchlings at the Museum für Naturkunde, Berlin, Germany. The aim was to determine whether the olfactory structures follow a similar maturational path in the two monotremes during embryonic and early post-hatching ages or whether they show very different developmental paths from the outset. The findings indicate that anatomical differences in the central olfactory system between the short-beaked echidna and the platypus begin to develop immediately before hatching, although details of differences in nasal cavity architecture emerge progressively during late post-hatching life. These findings are most consistent with the proposition that the two modern monotreme lineages have followed independent evolutionary paths from a less olfaction-specialized ancestor. The monotreme olfactory pathway does not appear to be sufficiently structurally mature at birth to allow olfaction-mediated behaviour, because central components of both the main and accessory olfactory system have not differentiated at the time of hatching.