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A comparative analysis of the distribution of immunoreactive orexin A and B in the brains of nocturnal and diurnal rodents.

Nixon JP, Smale L - Behav Brain Funct (2007)

Bottom Line: The orexins (hypocretins) are a family of peptides found primarily in neurons in the lateral hypothalamus.However, the present study shows significant species differences in the distribution of orexin cell bodies and in the density of orexin-IR fibers in some regions.Finally, we note previously undescribed populations of orexin-positive neurons outside the lateral hypothalamus in three of the four species examined.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Zoology, Michigan State University, 203 Natural Science Building, East Lansing, MI 48824-1115, USA. nixon049@umn.edu

ABSTRACT

Background: The orexins (hypocretins) are a family of peptides found primarily in neurons in the lateral hypothalamus. Although the orexinergic system is generally thought to be the same across species, the orexins are involved in behaviors which show considerable interspecific variability. There are few direct cross-species comparisons of the distributions of cells and fibers containing these peptides. Here, we addressed the possibility that there might be important species differences by systematically examining and directly comparing the distribution of orexinergic neurons and fibers within the forebrains of species with very different patterns of sleep-wake behavior.

Methods: We compared the distribution of orexin-immunoreactive cell bodies and fibers in two nocturnal species (the lab rat, Rattus norvegicus and the golden hamster, Mesocricetus auratus) and two diurnal species (the Nile grass rat, Arvicanthis niloticus and the degu, Octodon degus). For each species, tissue from the olfactory bulbs through the brainstem was processed for immunoreactivity for orexin A and orexin B (hypocretin-1 and -2). The distribution of orexin-positive cells was noted for each species. Orexin fiber distribution and density was recorded and analyzed using a principal components factor analysis to aid in evaluating potential species differences.

Results: Orexin-positive cells were observed in the lateral hypothalamic area of each species, though there were differences with respect to distribution within this region. In addition, cells positive for orexin A but not orexin B were observed in the paraventricular nucleus of the lab rat and grass rat, and in the supraoptic nucleus of the lab rat, grass rat and hamster. Although the overall distributions of orexin A and B fibers were similar in the four species, some striking differences were noted, especially in the lateral mammillary nucleus, ventromedial hypothalamic nucleus and flocculus.

Conclusion: The orexin cell and fiber distributions observed in this study were largely consistent with those described in previous studies. However, the present study shows significant species differences in the distribution of orexin cell bodies and in the density of orexin-IR fibers in some regions. Finally, we note previously undescribed populations of orexin-positive neurons outside the lateral hypothalamus in three of the four species examined.

No MeSH data available.


Suprachiasmatic nucleus. Photomicrographs of orexin A fibers around the suprachiasmatic nucleus (SCN) of the Long-Evans rat (A), grass rat (B), Syrian hamster (C), and degu (D). 3V: third ventricle; OC: optic chiasm. Scale bar = 200 μm.
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Figure 9: Suprachiasmatic nucleus. Photomicrographs of orexin A fibers around the suprachiasmatic nucleus (SCN) of the Long-Evans rat (A), grass rat (B), Syrian hamster (C), and degu (D). 3V: third ventricle; OC: optic chiasm. Scale bar = 200 μm.

Mentions: In all species examined, OXA- and OXB-IR fibers extended from the lateral hypothalamus throughout much of the brain. These fibers were moderately to densely distributed throughout much of the hypothalamus, with the exception of the zona incerta, where fiber density was low, and the suprachiasmatic (Figure 9) and medial mammilary nuclei, which exhibited little to no orexin fibers in any species. Several species differences were observed. First, differences in fiber density were seen in the main regions in which we saw substantial differences in the distribution of labeled cells. In the hamster PeF, fiber density was reduced in comparison with the other species, and in the LE rat and grass rat, many OXA fibers were also present in the magnocellular Pa and SO. Orexin B fibers in all species and OXA fibers in the hamster and degu were moderate to low in the Pa and SO. Second, in the degu, a very dense network of OXA and OXB fibers was present in the VMH (Figure 10D), but in the other species fiber densities in this region were moderate to low. The OXA and OXB fiber complex in the degu VMH was the single most densely distributed network of orexin fibers in this animal. Third, in the hamster, OXA- and OXB-IR fibers in the lateral mammillary nucleus (LM) were fairly dense, while in the other three species fibers in the LM were sparse (Figure 11).


A comparative analysis of the distribution of immunoreactive orexin A and B in the brains of nocturnal and diurnal rodents.

Nixon JP, Smale L - Behav Brain Funct (2007)

Suprachiasmatic nucleus. Photomicrographs of orexin A fibers around the suprachiasmatic nucleus (SCN) of the Long-Evans rat (A), grass rat (B), Syrian hamster (C), and degu (D). 3V: third ventricle; OC: optic chiasm. Scale bar = 200 μm.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC1913054&req=5

Figure 9: Suprachiasmatic nucleus. Photomicrographs of orexin A fibers around the suprachiasmatic nucleus (SCN) of the Long-Evans rat (A), grass rat (B), Syrian hamster (C), and degu (D). 3V: third ventricle; OC: optic chiasm. Scale bar = 200 μm.
Mentions: In all species examined, OXA- and OXB-IR fibers extended from the lateral hypothalamus throughout much of the brain. These fibers were moderately to densely distributed throughout much of the hypothalamus, with the exception of the zona incerta, where fiber density was low, and the suprachiasmatic (Figure 9) and medial mammilary nuclei, which exhibited little to no orexin fibers in any species. Several species differences were observed. First, differences in fiber density were seen in the main regions in which we saw substantial differences in the distribution of labeled cells. In the hamster PeF, fiber density was reduced in comparison with the other species, and in the LE rat and grass rat, many OXA fibers were also present in the magnocellular Pa and SO. Orexin B fibers in all species and OXA fibers in the hamster and degu were moderate to low in the Pa and SO. Second, in the degu, a very dense network of OXA and OXB fibers was present in the VMH (Figure 10D), but in the other species fiber densities in this region were moderate to low. The OXA and OXB fiber complex in the degu VMH was the single most densely distributed network of orexin fibers in this animal. Third, in the hamster, OXA- and OXB-IR fibers in the lateral mammillary nucleus (LM) were fairly dense, while in the other three species fibers in the LM were sparse (Figure 11).

Bottom Line: The orexins (hypocretins) are a family of peptides found primarily in neurons in the lateral hypothalamus.However, the present study shows significant species differences in the distribution of orexin cell bodies and in the density of orexin-IR fibers in some regions.Finally, we note previously undescribed populations of orexin-positive neurons outside the lateral hypothalamus in three of the four species examined.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Zoology, Michigan State University, 203 Natural Science Building, East Lansing, MI 48824-1115, USA. nixon049@umn.edu

ABSTRACT

Background: The orexins (hypocretins) are a family of peptides found primarily in neurons in the lateral hypothalamus. Although the orexinergic system is generally thought to be the same across species, the orexins are involved in behaviors which show considerable interspecific variability. There are few direct cross-species comparisons of the distributions of cells and fibers containing these peptides. Here, we addressed the possibility that there might be important species differences by systematically examining and directly comparing the distribution of orexinergic neurons and fibers within the forebrains of species with very different patterns of sleep-wake behavior.

Methods: We compared the distribution of orexin-immunoreactive cell bodies and fibers in two nocturnal species (the lab rat, Rattus norvegicus and the golden hamster, Mesocricetus auratus) and two diurnal species (the Nile grass rat, Arvicanthis niloticus and the degu, Octodon degus). For each species, tissue from the olfactory bulbs through the brainstem was processed for immunoreactivity for orexin A and orexin B (hypocretin-1 and -2). The distribution of orexin-positive cells was noted for each species. Orexin fiber distribution and density was recorded and analyzed using a principal components factor analysis to aid in evaluating potential species differences.

Results: Orexin-positive cells were observed in the lateral hypothalamic area of each species, though there were differences with respect to distribution within this region. In addition, cells positive for orexin A but not orexin B were observed in the paraventricular nucleus of the lab rat and grass rat, and in the supraoptic nucleus of the lab rat, grass rat and hamster. Although the overall distributions of orexin A and B fibers were similar in the four species, some striking differences were noted, especially in the lateral mammillary nucleus, ventromedial hypothalamic nucleus and flocculus.

Conclusion: The orexin cell and fiber distributions observed in this study were largely consistent with those described in previous studies. However, the present study shows significant species differences in the distribution of orexin cell bodies and in the density of orexin-IR fibers in some regions. Finally, we note previously undescribed populations of orexin-positive neurons outside the lateral hypothalamus in three of the four species examined.

No MeSH data available.