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.     

Distribution of orexin-A immunoreactive neurons and their terminal networks in the brain of the rock hyrax, Procavia capensis

The present study describes the distribution of orexin-A immunoreactive neurons and terminal networks in relation to the previously described catecholaminergic, cholinergic and serotonergic systems within the brain of the rock hyrax, Procavia capensis. Adult female rock hyrax brains were sectioned and immunohistochemically stained with an antibody to orexin-A. The staining revealed that the neurons were mainly located within the hypothalamus as with other mammals. The orexinergic terminal network distribution also resembled the typical mammalian plan. High-density orexinergic terminal networks were located within regions of the diencephalon (e.g. paraventricular nuclei), midbrain (e.g. serotonergic nuclei) and pons (locus coeruleus), while medium density orexinergic terminal networks were evident in the telencephalic (e.g. basal forebrain), diencephalic (e.g. hypothalamus), midbrain (e.g. periaqueductal gray matter), pontine (e.g. serotonergic nuclei) and medullary regions (e.g. serotonergic and catecholaminergic nuclei). Although the distribution of the orexinergic terminal networks was typically mammalian, the rock hyrax did show one atypical feature, the presence of a high-density orexinergic terminal network within the anterodorsal nucleus of the dorsal thalamus (AD). The dense orexinergic innervation of the AD nucleus has only been reported previously in the Nile grass rat, Arvicanthis niloticus and Syrian hamster, Mesocricetus auratus, both diurnal mammals. It is possible that orexinergic innervation of the AD nucleus might be a unique feature associated with diurnal mammals. It was also noted that the dense orexinergic innervation of the AD nucleus coincided with previously identified cholinergic neurons and terminal networks in this particular nucleus of the rock hyrax brain. It is possible that this dense orexinergic innervation of the AD nucleus in the brain of the rock hyrax may act in concert with the cholinergic neurons and/or the cholinergic axonal terminals, which in turn may influence arousal states and motivational processing.     

Cellular location and major terminal networks of the orexinergic system in the brain of two megachiropterans

The present study describes the distribution of orexin-A immunoreactive neurons and their terminal networks in the brains of two species of megachiropterans. In general the organization of the orexinergic system in the mammalian brain is conserved across species, but as one of two groups of mammals that fly and have a high metabolic rate, it was of interest to determine whether there were any specific differences in the organization of this system in the megachiropterans. Orexinergic neurons were limited in distribution to the hypothalamus, and formed three distinct clusters, or nuclei, a main cluster with a perifornical location, a zona incerta cluster in the dorsolateral hypothalamus and an optic tract cluster in the ventrolateral hypothalamus. The nuclear parcellation of the orexinergic system in the megachiropterans is similar to that seen in many mammals, but differs from the microchiropterans where the optic tract cluster is absent. The terminal networks of the orexinergic neurons in the megachiropterans was similar to that seen in a range of mammalian species, with significant terminal networks being found in the hypothalamus, cholinergic pedunculopontine and laterodorsal tegemental nuclei, the noradrenergic locus coeruleus complex, all serotonergic nuclei, the paraventricular nuclei of the epithalamus and adjacent to the habenular nuclei. While the megachiropteran orexinergic system is typically mammalian in form, it does differ from that reported for microchiropterans, and thus provides an additional neural character arguing for independent evolution of these two chiropteran suborders.     

Distribution and morphology of catecholaminergic and serotonergic neurons in the brain of the highveld gerbil,Tatera brantsii

The distribution, morphology and nuclear subdivisions of the putative catecholaminergic and serotonergic systems within the brain of the highveld gerbil were identified following immunohistochemistry for tyrosine hydroxylase and serotonin. The aim of the present study was to investigate possible differences in the complement of nuclear subdivisions of these systems when comparing those of the highveld gerbil with those of the laboratory rat. The highveld gerbil was chosen as it is relatively closely related to the laboratory rat, but the Gerbillinae and Murinae lineages diverged over 20 million years ago. Moreover, even though brain sizes are similar, the life history and phenotypes between these two species are substantially different. The gerbils used in the present study were caught from the wild, which is again another contrast to the laboratory rat. While these differences may lead to the prediction of significant differences in the nuclear complement of these systems, we found that all nuclei identified in both systems in the laboratory rat in several earlier studies had direct homologs in the brain of the highveld gerbil. Moreover, there were no additional nuclei in the brain of the highveld gerbil that are not found in the laboratory rat. The only discernable difference between the two species was a greater density and number of catecholaminergic neurons in the olfactory bulb of the highveld gerbil. Thus, the evolution of nuclear parcellation in these systems appears to demonstrate a form of phylogenetic constraint related to the order Rodentia.     

Distribution and morphology of catecholaminergic and serotonergic neurons in the brain of the highveld gerbil, Tatera brantsii

The distribution, morphology and nuclear subdivisions of the putative catecholaminergic and serotonergic systems within the brain of the highveld gerbil were identified following immunohistochemistry for tyrosine hydroxylase and serotonin. The aim of the present study was to investigate possible differences in the complement of nuclear subdivisions of these systems when comparing those of the highveld gerbil with those of the laboratory rat. The highveld gerbil was chosen as it is relatively closely related to the laboratory rat, but the Gerbillinae and Murinae lineages diverged over 20 million years ago. Moreover, even though brain sizes are similar, the life history and phenotypes between these two species are substantially different. The gerbils used in the present study were caught from the wild, which is again another contrast to the laboratory rat. While these differences may lead to the prediction of significant differences in the nuclear complement of these systems, we found that all nuclei identified in both systems in the laboratory rat in several earlier studies had direct homologs in the brain of the highveld gerbil. Moreover, there were no additional nuclei in the brain of the highveld gerbil that are not found in the laboratory rat. The only discernable difference between the two species was a greater density and number of catecholaminergic neurons in the olfactory bulb of the highveld gerbil. Thus, the evolution of nuclear parcellation in these systems appears to demonstrate a form of phylogenetic constraint related to the order Rodentia.     

Nuclear organization and morphology of cholinergic, putative catecholaminergic and serotonergic neurons in the brains of two species of African mole-rat

The distribution, morphology and nuclear subdivisions of the cholinergic, putative catecholaminergic and serotonergic systems within the brains of two species of African mole-rat (Cape dune mole-rat -Bathyergus suillus; highveld mole-rat -Cryptomys hottentotuspretoriae) were identified following immunohistochemistry for acetylcholinesterase, tyrosine hydroxylase and serotonin. The aim of the present study was to investigate possible differences in the complement of nuclear subdivisions of these systems by comparing those of the mole-rats to published studies of other rodents. The mole-rats used exhibit a major reduction of the visual system and live a subterranean lifestyle. These wild caught animals also have differing social systems, the Cape dune mole-rat is strictly solitary whereas the highveld mole-rat occurs in social familial units. While these differences, especially that of phenotype, may lead to the prediction of significant differences in the nuclear complement of these systems, we found that all nuclei identified in all three systems in the laboratory rat and other rodents had direct homologs in the brains of the mole-rats studied. There were no additional nuclei in the brains of the mole-rats that are not found in the laboratory rat or other rodents and vice versa. The mole-rats are phylogenetically distant from the laboratory rat, but are still part of the order Rodentia. We conclude that changes in the nuclear organization of the systems studied appear to demonstrate a form of constraint related to the phylogenetic level of the order.     

Sleep in the blind mole rat Spalax ehrenbergi

STUDY OBJECTIVES: The mole rat, Spalax ehrenbergi, is an interesting species for sleep because of its pronounced specialization to a fossorial life. These rodents spend most of their life-time underground, and are less exposed to many of the environmental stimuli and challenges that are common to non-fossorial rodents. A prominent adaptation is their blindness, which is due to an atrophy of the eyes. DESIGN: Continuous 24-h recordings of EEG, EMG and cortical temperature, and EEG spectral analysis were performed in six individuals caught in the wild and adapted to the laboratory for several months. SETTING: N/A. PATIENTS OR PARTICIPANTS: N/A. INTERVENTIONS: N/A. MEASUREMENTS AND RESULTS: Total sleep time (52% of recording time) and the amount of REM sleep (8% of recording time) in these subterranean rodents are in the range of values found in the laboratory rat, mouse and hamster recorded under similar conditions. In contrast to these species, the polyphasic sleep-wakefulness distribution in mole rats was more distinct. A predominance of sleep in the dark period was only minor and not present in all individuals, which resembles sleep in the guinea pig. As in all other mammals investigated, the daily time course of EEG slow-wave activity (SWA) in nonREM sleep closely followed the polyphasic sleep-wake pattern and the light-dark preference. The transitions from non REM sleep to REM sleep were characterized, as in other rodents, by a gradual increase in EEG activity in the theta and sigma frequency bands before the transition. However, the power surge in these frequencies massively exceeded that found in other rodents. This feature may be related to adaptations of the brain to the requirements of the subterranean habitat. CONCLUSIONS: It is remarkable that large ecological differences between species within the same order have relatively small effects on many sleep features. The time course of SWA confirmed its predictability on the basis of the previous sleep-wake history.     

Distribution and morphology of putative catecholaminergic and serotonergic neurons in the brain of the greater canerat, Thryonomys swinderianus

The distribution, morphology and nuclear subdivisions of the putative catecholaminergic and serotonergic systems within the brain of the greater canerat (sometimes spelt cane rat) were identified following immunohistochemistry for tyrosine hydroxylase and serotonin. The aim of the present study was to investigate possible differences in the complement of nuclear subdivisions of these systems when comparing those of the greater canerat with reports of these systems in other rodents. The greater canerat was chosen for investigation as it is a large rodent (around 2.7kg body mass) and has an average brain mass of 13.75g, more than five times larger than that of the laboratory rat. The greater canerats used in the present study were caught from the wild, which is again another contrast to the laboratory rat. While these differences, especially that of size, may lead to the prediction of significant differences in the nuclear complement of these systems, we found that all nuclei identified in both systems in the laboratory rat and other rodents in several earlier studies had direct homologs in the brain of the greater canerat. Moreover, there were no additional nuclei in the brain of the greater canerat that are not found in the laboratory rat or other rodents. It is noted that the locus coeruleus of the laboratory rat differs in appearance to that reported for several other rodent species. The greater canerat is phylogenetically distant from the laboratory rat, but still a member of the order Rodentia. Thus, changes in the nuclear organization of these systems appears to demonstrate a form of constraint related to the phylogenetic level of the order.     

Parvalbumin-positive basket interneurons in monkey and rat prefrontal cortex

Differences in the developmental origin and relative proportions of biochemically distinct classes of cortical neurons have been found between rodents and primates. In addition, species differences in the properties of certain cell types, such as neurogliaform cells, have also been reported. Consequently, in this study we compared the anatomical and physiological properties of parvalbumin (PV)-positive basket interneurons in the prefrontal cortex of macaque monkeys and rats. The somal size, total dendritic length, and horizontal and vertical spans of the axonal arbor were similar in monkeys and rats. Physiologically, PV basket cells could be identified as fast-spiking interneurons in both species, based on their short spike and high-frequency firing without adaptation. However, important interspecies differences in the intrinsic physiological properties were found. In monkeys, basket cells had a higher input resistance and a lower firing threshold, and they generated more spikes at near-threshold current intensities than those in rats. Thus monkey basket cells appeared to be more excitable. In addition, rat basket cells consistently fired the first spike with a substantial delay and generated spike trains interrupted by quiescent periods more often than monkey basket cells. The frequency of miniature excitatory postsynaptic potentials in basket cells was considerably higher in rats than that in monkeys. These differences between rats and monkeys in the electrophysiological properties of PV-positive basket cells may contribute to the differential patterns of neuronal activation observed in rats and monkeys performing working-memory tasks.     

Orexinergic bouton density is lower in the cerebral cortex of cetaceans compared to artiodactyls

The species of the cetacean and artiodactyl suborders, which constitute the order Cetartiodactyla, exhibit very different sleep phenomenology, with artiodactyls showing typical bihemispheric slow wave and REM sleep, while cetaceans show unihemispheric slow wave sleep and appear to lack REM sleep. The aim of this study was to determine whether cetaceans and artiodactyls have differently organized orexinergic arousal systems by examining the density of orexinergic innervation to the cerebral cortex, as this projection will be involved in various aspects of cortical arousal. This study provides a comparison of orexinergic bouton density in the cerebral cortex of twelve Cetartiodactyla species (ten artiodactyls and two cetaceans) by means of immunohistochemical staining and stereological analysis. It was found that the morphology of the axonal projections of the orexinergic system to the cerebral cortex was similar across all species, as the presence, size and proportion of large and small orexinergic boutons were similar. Despite this, orexinergic bouton density was lower in the cerebral cortex of the cetaceans studied compared to the artiodactyls studied, even when corrected for brain mass, neuron density, glial density and glial:neuron ratio. Results from correlational and principal component analyses indicate that glial density is a major determinant of the observed differences between artiodactyl and cetacean cortical orexinergic bouton density.     

Nuclear organization and morphology of cholinergic, putative catecholaminergic and serotonergic neurons in the brain of the Cape porcupine (Hystrix africaeaustralis): increased brain size does not lead to increased organizational complexity

The distribution, morphology and nuclear organization of the cholinergic, putative catecholaminergic and serotonergic systems within the brain of the Cape porcupine (Hystrix africaeaustralis) were identified following immunohistochemistry for choline acetyltransferase, tyrosine hydroxylase and serotonin. The aim of the present study was to investigate possible differences in the complement of nuclear subdivisions of these systems in the Cape porcupine in comparison with previous studies of these systems in other rodents. The Cape porcupine is the largest rodent in which these systems have been examined and has an adult body mass of 10-24kg and an average brain mass of approximately 37g, around 15 times larger than the laboratory rat. The Cape porcupines were taken from the wild and while these differences, especially that of mass, may lead to the prediction of a significant difference in the nuclear organization or number within these systems, all the nuclei observed in all three systems in the laboratory rat and in other rodents had direct homologues in the brain of the Cape porcupine. Moreover, there were no additional nuclei in the brain of the Cape porcupine that are not found in the laboratory rat or other rodents studied and vice versa. It is noted that the medial septal nucleus of the Cape porcupine appeared qualitatively to have a reduced number of neurons in comparison to the laboratory rat and other rodents. The locus coeruleus of the laboratory rat differs in location to that observed for the Cape porcupine and several other rodent species. The Cape porcupine is distantly related to the laboratory rat, but still a member of the order Rodentia; thus, changes in the organization of these systems appears to demonstrate a form of constraint related to the phylogenetic level of the order.     

Analysis of gamasid mites (Acari: Mesostigmata) associated with the Asian house rat, Rattus tanezumi (Rodentia: Muridae) in Yunnan Province, Southwest China

During a survey lasting from 1990 to 2008, we captured 4,113 Asian house rats, Rattus tanezumi Temminck 1844 (Rodentia: Muridae) from 28 counties of Yunnan Province in Southwestern China. From these rats, a total of 19,304 gamasid mites (Acari: Mesostigmata) were collected and identified as comprising 50 different species. The species diversity of gamasid mites from this single rat species is higher than that reported previously from multiple hosts within a given geographical region. Of the 50 mite species, 31 species belonged to ectoparasites and 19 species belonged to free-living mites. The species diversity of the mites from rats trapped outdoors was much higher than from rats trapped indoors. The parameter K from the negative binomial distribution was used to measure the spatial distribution patterns of the dominant mite species and revealed that all the mites had an aggregated distribution among the rat hosts. Most mite species showed a predominantly female-biased population structure with many more females than males.     

Localization of hypocretin-like immunoreactivity in the brain of the diurnal rodent, Arvicanthis niloticus

The neuropeptide hypocretin (HCRT, also called orexin) acts in the brain to increase arousal and inhibit REM sleep. There is also substantial evidence that disruption of the hypocretin system results in narcolepsy. The distribution of HCRT + fibers in nocturnal animals is consistent with its role in arousal; fibers are concentrated in brain areas important in arousal and the inhibition of REM sleep. The distribution of HCRT-like immunoreactive (HCRT +) cells and fibers has been described in nocturnal but not diurnal rodents. We therefore examined the anatomical distribution of HCRT + cells and fibers in the diurnal murid rodent Arvicanthis niloticus (unstriped Nile grass rat). Arvicanthis niloticus were perfused and brain sections were collected through the forebrain and midbrain and processed for HCRT immunocytochemistry. Hypocretin-like immunopositive cell bodies were located in the lateral hypothalamus, dorsomedial hypothalamus, and perifornical area. The densest staining for HCRT + neuronal fibers was seen in the paraventricular thalamic nucleus, the locus coeruleus, and the raphe nuclei. The distribution of HCRT + cells and fibers is consistent with that found in other rodents such as rats and Syrian hamsters. Although the pattern of HCRT-like immunostaining for cells and fibers is similar in nocturnal rodents and diurnal A. niloticus, it will be important to compare the pattern of HCRT release, as well as activity of HCRT cells, between nocturnal and diurnal species.     

Immunocytochemical characterization of the pregeniculate nucleus and distribution of retinal and neuropeptide Y terminals in the suprachiasmatic nucleus of the Cebus monkey

Circadian rhythms generated by the suprachiasmatic nucleus (SCN) are modulated by photic and non-photic stimuli. In rodents, direct photic stimuli reach the SCN mainly through the retinohypothalamic tract (RHT), whereas indirect photic stimuli are mainly conveyed by the geniculohypothalamic tract (GHT). In rodents, retinal cells form a pathway that reaches the intergeniculate leaflet (IGL) where they establish synapses with neurons that express neuropeptide Y (NPY), hence forming the GHT projecting to the SCN. In contrast to the RHT, which has been well described in primates, data regarding the presence or absence of the IGL and GHT in primates are contradictory. Some studies have suggested that an area of the pregeniculate nucleus (PGN) of primates might be homologous to the IGL of rodents, but additional anatomical and functional studies on primate species are necessary to confirm this hypothesis. Therefore, this study investigated the main histochemical characteristics of the PGN and the possible existence of the GHT in the SCN of the primate Cebus, comparing the distribution of NPY immunoreactivity, serotonin (5-HT) immunoreactivity and retinal terminal fibers in these two structures. The results show that a collection of cell bodies containing NPY and serotonergic immunoreactivity and retinal innervations are present within a zone that might be homologous to the IGL of rodents. The SCN also receives dense retinal innervations and we observed an atypical distribution of NPY- and 5-HT-immunoreactive fibers without regionalization in the ventral part of the nucleus as described for other species. These data may reflect morphological differences in the structures involved in the regulation of circadian rhythms among species and support the hypothesis that the GHT is present in some higher primates (diurnal animals).     

Comparative morphology and morphometry of alveolar macrophages from six species

Pulmonary alveolar macrophages (PAM) were collected from normal, healthy mice, rats, dogs, cynomolgus monkeys, chimpanzees, and humans and evaluated for morphologic and morphometric characteristics. The PAM of mice, rats, and dogs were morphologically similar and had statistically similar frequency distributions for size. The cell size distribution or these three species was relatively homogeneous. The PAM of nonhuman primates and humans were morphologically heterogenous with sometimes prominent cytoplasmic vacuolation, irregular cell outlines, and increased numbers of multinucleated cells as compared to the PAM of rodents and dogs. The mean size of human PAM was statistically greater than that for all other species evaluated, including nonhuman primates. These data indicate that significant differences in PAM morphology and size exist among species.     

Aging related changes in determinants of muscle force generating capacity: A comparison of muscle aging in men and male rodents

Human aging is associated with a progressive decline in skeletal muscle mass and force generating capacity, however the exact mechanisms underlying these changes are not fully understood. Rodents models have often been used to enhance our understanding of mechanisms of age-related changes in human skeletal muscle. However, to what extent age-related alterations in determinants of muscle force generating capacity observed in rodents resemble those in humans has not been considered thoroughly. This review compares the effect of aging on muscle force generating determinants (muscle mass, fiber size, fiber number, fiber type distribution and muscle specific tension), in men and male rodents at similar relative age. It appears that muscle aging in male F344*BN rat resembles that in men most; 32–35-month-old rats exhibit similar signs of muscle weakness to those of 70–80-yr-old men, and the decline in 36–38-month-old rats is similar to that in men aged over 80 yrs. For male C57BL/6 mice, age-related decline in muscle force generating capacity seems to occur only at higher relative age than in men. We conclude that the effects on determinants of muscle force differ between species as well as within species, but qualitatively show the same pattern as that observed in men.     

Morphological characteristics and electrophysiological properties of CA1 pyramidal neurons in macaque monkeys

Little is known about the morphological characteristics and intrinsic electrophysiological properties of individual neurons in the nonhuman primate hippocampus. We have used intracellular recording and biocytin-labeling techniques in the in vitro hippocampal slice preparation to provide quantitative evaluation of the fundamental morphological and intrinsic electrophysiological characteristics of macaque monkey CA1 pyramidal neurons. These neurons have previously been studied in the rat in our laboratory. Monkey CA1 pyramidal neurons have an average soma volume of 3578 microm3, 4.71 basal dendrites with 53 terminal branches for a dendritic length of about 10,164 microm, 1.13 apical dendrites with 47 terminal branches for a dendritic length of about 10,678 microm. In comparison, rat CA1 pyramidal neurons have an average soma volume of 2066 microm3, 3.35 basal dendrites with 29 terminal branches for a dendritic length of about 4,586 microm, 1.43 apical dendrites with 62 terminal branches for a dendritic length of about 8,838 microm. The basic intrinsic electrophysiological properties of CA1 pyramidal cells are similar in monkeys and rats. Monkey CA1 pyramidal neurons have a resting membrane potential of about -62 mV (rat: -62 mV), an input resistance of 35 MOmega (rat: 34-49 MOmega), a rheobase of 0.17 nA (rat: 0.12-0.20 nA) and an action potential amplitude of 83 mV (rat: 71-89 mV). Although morphological differences such as the increased dendritic length may translate into differences in neural processing between primates and rodents, the functional significance of these morphological differences is not yet clear. Quantitative studies of the primate brain are critical in order to extrapolate information derived from rodent studies into better understanding of the normal and pathological function of the human hippocampus.     

Variations in the intralobular distribution of copper in the livers of copper-loaded rats in relation to the pathogenesis of copper storage diseases

There are differences in the hepatic intralobular distribution of copper in copper storage related diseases which may be of pathogenetic significance. Male rats fed a high copper diet (1500 ppm) for 16 weeks were killed at intervals in an attempt to compare copper distribution in their livers with those in human, canine and ovine copper toxicosis. Copper was found to accumulate almost exclusively in the periportal and mid-zones of the rat liver lobules and was associated with progressive pathological changes which included focal and periportal degeneration and necrosis. This pattern of copper distribution contrasts markedly with the centrilobular retention reported in familial canine copper toxicosis and chronic copper poisoning in sheep which suggests that, in these conditions, a secretory deficiency may be less important than a metabolic zonal defect of intracellular copper metabolism. The pathological changes observed in copper-loaded rats have a different micro-anatomical localization from those in dogs and sheep, but show similarities to the early changes reported in the latter species and indicate the possibility of a similar cellular lesion.