Limits...
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.


Long-Evans rat. Line drawing of every 6th section through the region of the Long-Evans rat hypothalamus that contains orexin cells. Sections are ordered from rostral (A) to caudal (N). Filled circles indicate locations where both orexin A and orexin B neurons are found, while open circles indicate orexin A neurons only. 3V: third ventricle; SCN: suprachiasmatic nucleus; OC: optic chiasm; f: fornix; mt: mammillothalamic tract. Scale bar = 500 μm.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC1913054&req=5

Figure 5: Long-Evans rat. Line drawing of every 6th section through the region of the Long-Evans rat hypothalamus that contains orexin cells. Sections are ordered from rostral (A) to caudal (N). Filled circles indicate locations where both orexin A and orexin B neurons are found, while open circles indicate orexin A neurons only. 3V: third ventricle; SCN: suprachiasmatic nucleus; OC: optic chiasm; f: fornix; mt: mammillothalamic tract. Scale bar = 500 μm.

Mentions: In all animals examined, OXA- and OXB-IR cell bodies were present in the lateral hypothalamus (Figure 1). Within each species examined, the distribution of orexin-IR neurons was quite consistent, with little individual variation from one animal to the next. Although the distribution of orexin neurons differed among species, the majority of the orexin cells in all species were observed in the perifornical region (PeF) and lateral hypothalamic area (LHA). In the LE rat, grass rat and hamster, cell bodies immunoreactive for OXA were also found in the paraventricular hypothalamic nucleus (Pa), supraoptic nucleus (SO), and the supraoptic retrochiasmatic nucleus (SOR) (Figure 2, Figure 3). Orexin A-IR neurons in the Pa and SO were generally smaller and less intensely stained for OXA than were cells in the PeF. For all three species exhibiting orexin-IR neurons in the Pa and SO, the OXA-IR nuclei did not appear to represent nonspecific binding of the primary antibody, as preabsorption of the primary antibody with OXA blocking peptide supplied by the manufacturer reduced or eliminated OXA immunoreactivity in these nuclei (Figure 4). Preabsorption with blocking peptides reduced or eliminated both OXA and OXB immunoreactivity in the LH in all four species examined (not shown). No OXB-IR neurons were observed in Pa, SO, or SOR of any species. Orexin A and OXB cell body distribution in the LE rat, grass rat, degu and hamster are summarized in Table 1 and are depicted in Figures 5, 6, 7, and 8, respectively.


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)

Long-Evans rat. Line drawing of every 6th section through the region of the Long-Evans rat hypothalamus that contains orexin cells. Sections are ordered from rostral (A) to caudal (N). Filled circles indicate locations where both orexin A and orexin B neurons are found, while open circles indicate orexin A neurons only. 3V: third ventricle; SCN: suprachiasmatic nucleus; OC: optic chiasm; f: fornix; mt: mammillothalamic tract. Scale bar = 500 μm.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 5: Long-Evans rat. Line drawing of every 6th section through the region of the Long-Evans rat hypothalamus that contains orexin cells. Sections are ordered from rostral (A) to caudal (N). Filled circles indicate locations where both orexin A and orexin B neurons are found, while open circles indicate orexin A neurons only. 3V: third ventricle; SCN: suprachiasmatic nucleus; OC: optic chiasm; f: fornix; mt: mammillothalamic tract. Scale bar = 500 μm.
Mentions: In all animals examined, OXA- and OXB-IR cell bodies were present in the lateral hypothalamus (Figure 1). Within each species examined, the distribution of orexin-IR neurons was quite consistent, with little individual variation from one animal to the next. Although the distribution of orexin neurons differed among species, the majority of the orexin cells in all species were observed in the perifornical region (PeF) and lateral hypothalamic area (LHA). In the LE rat, grass rat and hamster, cell bodies immunoreactive for OXA were also found in the paraventricular hypothalamic nucleus (Pa), supraoptic nucleus (SO), and the supraoptic retrochiasmatic nucleus (SOR) (Figure 2, Figure 3). Orexin A-IR neurons in the Pa and SO were generally smaller and less intensely stained for OXA than were cells in the PeF. For all three species exhibiting orexin-IR neurons in the Pa and SO, the OXA-IR nuclei did not appear to represent nonspecific binding of the primary antibody, as preabsorption of the primary antibody with OXA blocking peptide supplied by the manufacturer reduced or eliminated OXA immunoreactivity in these nuclei (Figure 4). Preabsorption with blocking peptides reduced or eliminated both OXA and OXB immunoreactivity in the LH in all four species examined (not shown). No OXB-IR neurons were observed in Pa, SO, or SOR of any species. Orexin A and OXB cell body distribution in the LE rat, grass rat, degu and hamster are summarized in Table 1 and are depicted in Figures 5, 6, 7, and 8, respectively.

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.