Nuclear organization of orexinergic neurons in the hypothalamus of a lar gibbon and a chimpanzee.

Employing orexin-A immunohistochemical staining we describe the nuclear parcellation of orexinergic neurons in the hypothalami of a lar gibbon and a chimpanzee. The clustering of orexinergic neurons within the hypothalamus and the terminal networks follow the patterns generally observed in other mammals, including laboratory rodents, strepsirrhine primates and humans. The orexinergic neurons were found within three distinct clusters in the ape hypothalamus, which include the main cluster, zona incerta cluster and optic tract cluster. In addition, the orexinergic neurons of the optic tract cluster appear to extend to a more rostral and medial location than observed in other species, being observed in the tuberal region in the anterior ventromedial aspect of the hypothalamus. While orexinergic terminal networks were observed throughout the brain, high density terminal networks were observed within the hypothalamus, medial and intralaminar nuclei of the dorsal thalamus, and within the serotonergic and noradrenergic regions of the midbrain and pons, which is typical for mammals. The expanded distribution of orexinergic neurons into the tuberal region of the ape hypothalamus, is a feature that needs to be investigated in other primate species, but appears to correlate with orexin gene expression in the same region of the human hypothalamus, but these neurons are not revealed with immunohistochemical staining in humans. Thus, it appears that apes have a broader distribution of orexinergic neurons compared to other primate species, but that the neurons within this extension of the optic tract cluster in humans, while expressing the orexin gene, do not produce the neuropeptide.

Putative adult neurogenesis in palaeognathous birds: The common ostrich (Struthio camelus) and emu (Dromaius novaehollandiae).

In the current study, we examined adult neurogenesis throughout the brain of the common ostrich (Struthio camelus) and emu (Dromaius novaehollandiae) using immunohistochemistry for the endogenous markers PCNA which labels proliferating cells, and DCX, which stains immature and migrating neurons. The distribution of PCNA and DCX labelled cells was widespread throughout the brain of both species. The highest density of cells immunoreactive to both markers was observed in the olfactory bulbs and the telencephalon, especially the subventricular zone of the lateral ventricle. Proliferative hot spots, identified with strong PCNA and DCX immunolabelling, were identified in the dorsal and ventral poles of the rostral aspects of the lateral ventricles. The density of PCNA immunoreactive cells was less in the telencephalon of the emu compared to the common ostrich. Substantial numbers of PCNA immunoreactive cells were observed in the diencephalon and brainstem, but DCX immunoreactivity was weaker in these regions, preferentially staining axons and dendrites over cell bodies, except in the medial regions of the hypothalamus where distinct DCX immunoreactive cells and fibres were observed. PCNA and DCX immunoreactive cells were readily observed in moderate density in the cortical layers of the cerebellum of both species. The distribution of putative proliferating cells and immature neurons in the brain of the common ostrich and the emu is widespread, far more so than in mammals, and compares with the neognathous birds, and suggests that brain plasticity and neuronal turnover is an important aspect of cognitive brain functions in these birds.

The brain of the tree pangolin (Manis tricuspis). V. The diencephalon and hypothalamus.

The diencephalon (dorsal thalamus, ventral thalamus, and epithalamus) and the hypothalamus, play central roles in the processing of the majority of neural information within the central nervous system. Given the interactions of the diencephalon and hypothalamus with virtually all portions of the central nervous system, the comparative analysis of these regions lend key insights into potential neural, evolutionary, and behavioral specializations in different species. Here, we continue our analysis of the brain of the tree pangolin by providing a comprehensive description of the organization of the diencephalon and hypothalamus using a range of standard and immunohistochemical staining methods. In general, the diencephalon and hypothalamus of the tree pangolin follow the organization typically observed across mammals. No unusual structural configurations of the ventral thalamus, epithalamus, or hypothalamus were noted. Within the dorsal thalamus, the vast majority of typically identified nuclear groups and component nuclei were observed. The visual portion of the tree pangolin dorsal thalamus appears to be organized in a manner not dissimilar to that seen in most nonprimate and noncarnivore mammals, and lacks certain features that are present in the closely related carnivores. Within the ventral medial geniculate nucleus, a modular organization, revealed with parvalbumin neuropil immunostaining, is suggestive of specialized auditory processing in the tree pangolin. In addition, a potential absence of hypothalamic cholinergic neurons is suggestive of unusual patterns of sleep. These observations are discussed in an evolutionary and functional framework regarding the phylogeny and life history of the pangolins.

Monoamine Release during Unihemispheric Sleep and Unihemispheric Waking in the Fur Seal.

STUDY OBJECTIVES: Our understanding of the role of neurotransmitters in the control of the electroencephalogram (EEG) has been entirely based on studies of animals with bilateral sleep. The study of animals with unihemispheric sleep presents the opportunity of separating the neurochemical substrates of waking and sleep EEG from the systemic, bilateral correlates of sleep and waking states. METHODS: The release of histamine (HI), norepinephrine (NE), and serotonin (5HT) in cortical and subcortical areas (hypothalamus, thalamus and caudate nucleus) was measured in unrestrained northern fur seals (Callorhinus ursinus) using in vivo microdialysis, in combination with, polygraphic recording of EEG, electrooculogram, and neck electromyogram. RESULTS: The pattern of cortical and subcortical HI, NE, and 5HT release in fur seals is similar during bilaterally symmetrical states: highest in active waking, reduced in quiet waking and bilateral slow wave sleep, and lowest in rapid eye movement (REM) sleep. Cortical and subcortical HI, NE, and 5HT release in seals is highly elevated during certain waking stimuli and behaviors, such as being sprayed with water and feeding. However, in contrast to acetylcholine (ACh), which we have previously studied, the release of HI, NE, and 5HT during unihemispheric sleep is not lateralized in the fur seal. CONCLUSIONS: Among the studied neurotransmitters most strongly implicated in waking control, only ACh release is asymmetric in unihemispheric sleep and waking, being greatly increased on the activated side of the brain. COMMENTARY: A commentary on this article appears in this issue on page 491.

Organization and number of orexinergic neurons in the hypothalamus of two species of Cetartiodactyla: a comparison of giraffe (Giraffa camelopardalis) and harbour porpoise (Phocoena phocoena).

The present study describes the organization of the orexinergic (hypocretinergic) neurons in the hypothalamus of the giraffe and harbour porpoise--two members of the mammalian Order Cetartiodactyla which is comprised of the even-toed ungulates and the cetaceans as they share a monophyletic ancestry. Diencephalons from two sub-adult male giraffes and two adult male harbour porpoises were coronally sectioned and immunohistochemically stained for orexin-A. The staining revealed that the orexinergic neurons could be readily divided into two distinct neuronal types based on somal volume, area and length, these being the parvocellular and magnocellular orexin-A immunopositive (OxA+) groups. The magnocellular group could be further subdivided, on topological grounds, into three distinct clusters--a main cluster in the perifornical and lateral hypothalamus, a cluster associated with the zona incerta and a cluster associated with the optic tract. The parvocellular neurons were found in the medial hypothalamus, but could not be subdivided, rather they form a topologically amorphous cluster. The parvocellular cluster appears to be unique to the Cetartiodactyla as these neurons have not been described in other mammals to date, while the magnocellular nuclei appear to be homologous to similar nuclei described in other mammals. The overall size of both the parvocellular and magnocellular neurons (based on somal volume, area and length) were larger in the giraffe than the harbour porpoise, but the harbour porpoise had a higher number of both parvocellular and magnocellular orexinergic neurons than the giraffe despite both having a similar brain mass. The higher number of both parvocellular and magnocellular orexinergic neurons in the harbour porpoise may relate to the unusual sleep mechanisms in the cetaceans.

Distribution of orexinergic neurons and their terminal networks in the brains of two species of African mole rats.

The distribution of orexinergic cell bodies and terminal networks within the brains of two species of African mole rat (Cape-dune mole rat--Bathyergus suillus and highveld mole rat--Cryptomys hottentotus) were identified using immunohistochemistry for orexin-A. The aim of the study was to investigate possible differences in the nuclear complement and terminal distribution of this system by comparing those of the mole rats to published studies of other rodents and mammals. The wild-caught mole rats used in this study live a subterranean lifestyle and are well known for their regressed visual system, which may lead to the prediction of differences in the distribution of the cell bodies and the terminal networks; however, we found that both species of mole rat displayed orexinergic nuclei limited to the hypothalamus in regions similar to those previously reported for other rodent and mammalian species. No immunoreactive neurons could be identified, in either species of mole rat within the anterior hypothalamic paraventricular nucleus, as has been reported for Murid rodents. The terminal networks, while remaining similar between the species, are more strongly expressed in the Cape-dune mole rat than in the highveld mole rat.