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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.


Centrolateral nucleus. Photomicrographs of orexin A fibers in the centrolateral nucleus (CL) of the Long-Evans rat (A), grass rat (B), Syrian hamster (C), and degu (D). Note higher density of orexin fibers in the degu CL in comparison with the other three species. LV: lateral ventricle; PV: paraventricular thalamic nucleus, MHb: medial habenular nucleus; LHb: lateral habenular nucleus. Scale bar = 300 μm.
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Figure 13: Centrolateral nucleus. Photomicrographs of orexin A fibers in the centrolateral nucleus (CL) of the Long-Evans rat (A), grass rat (B), Syrian hamster (C), and degu (D). Note higher density of orexin fibers in the degu CL in comparison with the other three species. LV: lateral ventricle; PV: paraventricular thalamic nucleus, MHb: medial habenular nucleus; LHb: lateral habenular nucleus. Scale bar = 300 μm.

Mentions: In contrast to the dense networks of OXA and OXB fibers in the hypothalamus, orexin fibers were sparse or absent throughout much of the thalamus. The majority of orexin projections to the thalamus targeted midline structures, most notably the paraventricular thalamic nucleus (PV), which received dense or very dense orexin projections in all four species. In all species examined, projections of OXA or OXB fibers to lateral regions of the thalamus were most dense in the intergeniculate leaflet (IGL) (Figure 12); other lateral or ventral thalamic nuclei received little to no orexin input. Although the pattern of orexin innervation in the thalamus was fairly consistent, the degu differed from most or all of the other species examined in several regions. First, dense orexin fibers were present in the degu centrolateral (CL) and paracentral nuclei (PC) (Figure 13D). In the other three species, orexin fibers in these nuclei were mostly sparse or absent, although the LE rat did exhibit moderate innervation in the PC (Figure 13A). In contrast, the opposite pattern was observed in the xiphoid nucleus (Xi), which contained sparse fibers in the degu and dense orexin innervation in the other three species (Figure 14).


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)

Centrolateral nucleus. Photomicrographs of orexin A fibers in the centrolateral nucleus (CL) of the Long-Evans rat (A), grass rat (B), Syrian hamster (C), and degu (D). Note higher density of orexin fibers in the degu CL in comparison with the other three species. LV: lateral ventricle; PV: paraventricular thalamic nucleus, MHb: medial habenular nucleus; LHb: lateral habenular nucleus. Scale bar = 300 μm.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 13: Centrolateral nucleus. Photomicrographs of orexin A fibers in the centrolateral nucleus (CL) of the Long-Evans rat (A), grass rat (B), Syrian hamster (C), and degu (D). Note higher density of orexin fibers in the degu CL in comparison with the other three species. LV: lateral ventricle; PV: paraventricular thalamic nucleus, MHb: medial habenular nucleus; LHb: lateral habenular nucleus. Scale bar = 300 μm.
Mentions: In contrast to the dense networks of OXA and OXB fibers in the hypothalamus, orexin fibers were sparse or absent throughout much of the thalamus. The majority of orexin projections to the thalamus targeted midline structures, most notably the paraventricular thalamic nucleus (PV), which received dense or very dense orexin projections in all four species. In all species examined, projections of OXA or OXB fibers to lateral regions of the thalamus were most dense in the intergeniculate leaflet (IGL) (Figure 12); other lateral or ventral thalamic nuclei received little to no orexin input. Although the pattern of orexin innervation in the thalamus was fairly consistent, the degu differed from most or all of the other species examined in several regions. First, dense orexin fibers were present in the degu centrolateral (CL) and paracentral nuclei (PC) (Figure 13D). In the other three species, orexin fibers in these nuclei were mostly sparse or absent, although the LE rat did exhibit moderate innervation in the PC (Figure 13A). In contrast, the opposite pattern was observed in the xiphoid nucleus (Xi), which contained sparse fibers in the degu and dense orexin innervation in the other three species (Figure 14).

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.