Arvicanthis Niloticus Research Articles

Retinorecipient areas in the diurnal murine rodent Arvicanthis niloticus: A disproportionally large superior colliculus

The Nile grass rat (Arvicanthis niloticus) has a high proportion of cone photoreceptors (∼30-40%) compared with that in the common laboratory mouse and rat (∼1-3%) and may prove a preferable murine model with which to study cone-driven information processing in retina and primary visual centers. However, other than regions involved in circadian control, little is known about the retinorecipient structures in this rodent. We undertook a detailed analysis of the retinal projections as revealed after intravitreal injection of the anterograde tracer cholera toxin subunit B. Retinal efferents were evaluated in 45 subcortical structures. Contralateral projections were always dominant. Major contralateral inputs consisted of the suprachiasmatic nucleus, dorsolateral geniculate nucleus (dLGN), intergeniculate leaflet, ventral geniculate nucleus (magnocellular part), lateroposterior thalamic nucleus, all six pretectal nuclei, superficial layers of the superior colliculus (SC), and the main nuclei of the accessory optic system. Terminals from the contralateral eye were also localized in an unnamed field rostromedial to the dLGN as well as in the subgeniculate thalamic nucleus. Ipsilateral inputs were found mainly in the suprachiasmatic nucleus, dLGN, intergeniculate leaflet, internal sector of the magnocellular part of the ventral geniculate nucleus, olivary pretectal nucleus, and SC optic layer. Retinal afferents were not detected in the basal forebrain or the dorsal raphe nucleus. Morphometric measurements revealed that the superficial layers of the SC are disproportionately enlarged relative to other retinorecipient regions and brain size compared with rats and mice. We suggest that this reflects the selective projection of cone-driven retinal ganglion cells to the SC.

Microarray Studies on the Effects of Palm Fruit Juice in Diabetic Nile Rats

The Nile rat (NR) models diet‐induced human type 2 diabetes (T2DM). In previous experiments (Brit J Nutr 106:1664, 2011), palm fruit juice (PFJ) blocked T2DM in male NR, while untreated rats exhibited advanced disease stages. The molecular mechanisms whereby PFJ exerts anti‐diabetic effects are unknown, prompting microarray gene expression analysis. Livers were obtained from NR undergoing 4 diet plans: hiCHO alone (diabetic control), 4800ppm resveratrol (RES) in food, 4800ppm PFJ in food, or 1500ppm PFJ in drinking water. Compared to hiCHO (most diabetic), hepatic liver gene expression profiles were enhanced for RES and PFJ‐food, while PFJ‐water gene expression changes were subtler. Random blood glucose was lowered (p<0.05) in both PFJ groups, but only slightly by RES (n.s.). Compared to hiCHO, PFJwater had 17 genes up‐regulated, 29 down‐regulated. PFJ‐food had 71 genes up‐regulated, 108 down‐regulated. RES had 90 genes upregulated, 76 down‐regulated. As a preliminary observation, the insulin signaling pathway, especially phosphatidylinositol (PI) 3‐ kinase, was significantly down‐regulated by PFJ‐food and RES, PFJ‐water being less marked. PI 3‐kinase has been reported to suppress glucose‐stimulated insulin secretion (Diabetes 51:87, 2002), suggesting PFJ and RES may modulate this activity in NRs to favor insulin secretion.Funding source: Foster Biomed Res Lab and the Malaysian Palm Oil Board

Prevention of type 2 diabetes in the Nile rat by palm fruit juice

Diet‐related metabolic disorders are on the rise globally, and plant‐derived antioxidants may moderate these conditions. Palm fruit juice (PFJ) contains unique polyphenols with biological impact against various chronic diseases (Brit J Nutr 106:1664, 2011), including type 2 diabetes (T2DM) and metabolic syndrome in the Nile rat (NR). To examine these relationships, 84 male Wildtype NR were fed diabetogenic diets, as lab chow (#5020) or semipurified diets (CHO:fat:protein %En=70:10:20 or 40:43:17), in 4 experiments, with PFJ provided as a drink or mixed into the diet up to 1800ppm (GAE equiv). Body wt as well as random and fasting glucose were assessed for up to 6mo along with terminal organ weights, insulin, and plasma lipids to quantify T2DM. PFJ decreased blood glucose in all 4 experiments, and the anti‐diabetogenic effect correlated with polyphenol intake. PFJ was effective both as a drink and mixed into the diet, exerting positive effects on circulating insulin and liver, kidney and pancreas weight, without any observed negative effects. Data suggest mechanisms of preventing hyperglycemia may include reduced intestinal glucose absorption and/or stimulation of insulin secretion by protecting against ROS to preserve mitochondrial function (see related abstracts).Funding source: Foster Biomed Res Lab and the Malaysian Palm Oil Board

Low‐glycemic index diets prevent type 2 diabetes in the Nile rat

The Nile rat (NR) is a novel model for type 2 diabetes (T2DM) and metabolic syndrome sensitive to metabolic stress from simple carbohydrates (CHO). Three experiments assessed the effects of a low‐glycemic index CHO (green lentils, GL) on T2DM. Expt 1 compared a GL diet directly with a semipurified hiCHO diet having identical %En from CHO:fat:protein (70:10:20). Expt 2 assessed reversibility of hyperglycemia by comparing a modCHO‐GL diet (45:25:30) to diabetogenic semipurified hiCHO (70:10:20) or lab chow (#5020) diets in 3 separate studies. Expt 3 examined young Nile rats “primed” from weaning for 7wks with the modCHO‐GL diet (45:25:30) before being challenged with stressful semipurified hiCHO (70:10:20) or modCHO (40:40:20) diets based on glucose and starch. 1. Compared to the hiCHO semipurified diet with the same macronutrient composition, the GL diet induced significantly less diabetes. 2. GL substantially reversed hyperglycemia, especially in young (<4mo) diabetic rats. 3.”Priming” rats with GL prior to hiCHO resulted in less severe diabetes compared to previous studies without priming. Positive influences on other metabolic parameters such as liver and kidney weight and plasma lipids also were observed. Since the NR mimics T2DM in humans, GL or components therein may represent a potentially useful adjunct for T2DM control in humans.Funding source: Foster Biomed Res Lab and the Malaysian Palm Oil Board

Pathology of the Nile rat developing type 2 diabetes

The Nile rat (NR) develops metabolic syndrome and type 2 diabetes (T2DM) in a manner similar to humans (NutrMetab 7: 29, 2010). To characterize the pathology of developing T2DM, relevant organs (pancreas, liver, kidney) were examined histopathologically. Immunohistochemical analyses of the pancreatic β cells were performed, as well. Fatty infiltration of the pancreas and hepatic steatosis were the most prevalent early lesions. Rats with advanced T2DM revealed a loss of pancreatic islet cells and insulin immunoreactivity. Hepatomegaly and discoloration were present macroscopically. This was confirmed as mid‐zonal to diffuse steatosis with microscopic foci of steatitis, accompanied by increased triglycerides and cholesterol esters. Hepatic steatosis was correlated with advancing T2DM, but was more pronounced in rats fed a modCHO/modFat diet compared to hiCHO/loFat rats, where clinical T2DM developed most rapidly. Selected chow‐fed diabetic rats >;1y of age with chronic hyperinsulinemia were found to have nodular hepatomas, not unlike non‐alcoholic steatohepatosis in humans. Histopathology of the kidney revealed the 4 stages of diabetic nephropathy described in humans, including early thickening of the glomerular basement membranes followed by thickening and increased interstitial fibrosis with end‐stage glomerular sclerosis.Funding source: Foster Biomed Res Lab and the Malaysian Palm Oil Board.

Depression-Like Responses Induced by Daytime Light Deficiency in the Diurnal Grass Rat (Arvicanthis niloticus)

Seasonal Affective Disorder (SAD) is one of the most common mood disorders with depressive symptoms recurring in winter when there is less sunlight. The fact that light is the most salient factor entraining circadian rhythms leads to the phase-shifting hypothesis, which suggests that the depressive episodes of SAD are caused by misalignments between the circadian rhythms and the habitual sleep times. However, how changes in environmental lighting conditions lead to the fluctuations in mood is largely unknown. The objective of this study is to develop an animal model for some of the features/symptoms of SAD using the diurnal grass rats Arvichantis niloticus and to explore the neural mechanisms underlying the light associated mood changes. Animals were housed in either a 12∶12 hr bright light∶dark (1000lux, BLD) or dim light∶dark (50lux, DLD) condition. The depression-like behaviors were assessed by sweet-taste Saccharin solution preference (SSP) and forced swimming test (FST). Animals in the DLD group showed higher levels of depression-like behaviors compared to those in BLD. The anxiety-like behaviors were assessed in open field and light/dark box test, however no significant differences were observed between the two groups. The involvement of the circadian system on depression-like behaviors was investigated as well. Analysis of locomotor activity revealed no major differences in daily rhythms that could possibly contribute to the depression-like behaviors. To explore the neural substrates associated with the depression-like behaviors, the brain tissues from these animals were analyzed using immunocytochemistry. Attenuated indices of 5-HT signaling were observed in DLD compared to the BLD group. The results lay the groundwork for establishing a novel animal model and a novel experimental paradigm for SAD. The results also provide insights into the neural mechanisms underlying light-dependent mood changes.

Responses of brain and behavior to changing day-length in the diurnal grass rat (Arvicanthis niloticus)

Seasonal affective disorder (SAD) is a major depressive disorder that recurs in the fall and winter when day-length gets short. It is well accepted that day-length is encoded by the principal circadian clock located in the suprachiasmatic nucleus (SCN), but very little is known about day-length encoding in diurnal mammals. The present study utilized the grass rat, Arvicanthis niloticus, to investigate how the circadian system responds to photoperiodic changes in a diurnal mammal that shows day-length-dependent mood changes. The animals were initially housed in equatorial day-length (12h, EP) followed by either long (16h, LP) or short (8h, SP) photoperiods. The LP animals showed an expansion of the peak phase of the PER1 and PER2 rhythm in the SCN as well as an extended behavioral active phase. In contrast, the SP animals did not show any compression of their active phase nor a change in the peak duration of PER1 or PER2 expression, compared to those in EP. The results suggest that the circadian system in the diurnal grass rats is less responsive when day-length gets short compared to when it gets longer. The depression-like behaviors were assessed using sweet solution preference (SSP) and forced swimming test (FST). Animals in the SP group showed decreased SSP and increased immobility time in FST as compared to the EP group, suggesting a depressive phenotype. The present study serves as the first step toward exploring the role that the circadian system plays in SAD using a diurnal rodent model.

Cutaneous leishmaniasis in Al-Ahsa Oasis in Saudi Arabia and in Sudan: A comparative study

This is a comparative study of cutaneous leishmaniasis (CL) in the Eastern Province of the Kingdom of Saudi Arabia and Sudan. The disease in both countries is caused by Leishmania major of different syndromes and the vector is Phlebotomus papatasi. The animal reservoir host in Saudi Arabia is Psammomys obesus and the Nile rat in Sudan. The clinical manifestations are similar, but some forms encountered in Sudan were not seen in Saudi Arabia. The pathology, immunology, diagnosis and treatment of CL are discussed.

Acute Behavioral Responses to Light and Darkness in Nocturnal Mus musculus and Diurnal Arvicanthis niloticus

The term masking refers to immediate responses to stimuli that override the influence of the circadian timekeeping system on behavior and physiology. Masking by light and darkness plays an important role in shaping an organism's daily pattern of activity. Nocturnal animals generally become more active in response to darkness (positive masking) and less active in response to light (negative masking), and diurnal animals generally have opposite patterns of response. These responses can vary as a function of light intensity as well as time of day. Few studies have directly compared masking in diurnal and nocturnal species, and none have compared rhythms in masking behavior of diurnal and nocturnal species. Here, we assessed masking in nocturnal mice (Mus musculus) and diurnal grass rats (Arvicanthis niloticus). In the first experiment, animals were housed in a 12:12 light-dark (LD) cycle, with dark or light pulses presented at 6 Zeitgeber times (ZTs; with ZT0 = lights on). Light pulses during the dark phase produced negative masking in nocturnal mice but only at ZT14, whereas light pulses resulted in positive masking in diurnal grass rats across the dark phase. In both species, dark pulses had no effect on behavior. In the 2nd experiment, animals were kept in constant darkness or constant light and were presented with light or dark pulses, respectively, at 6 circadian times (CTs). CT0 corresponded to ZT0 of the preceding LD cycle. Rhythms in masking responses to light differed between species; responses were evident at all CTs in grass rats but only at CT14 in mice. Responses to darkness were observed only in mice, in which there was a significant increase in activity at CT 22. In the 3rd experiment, animals were kept on a 3.5:3.5-h LD cycle. Surprisingly, masking was evident only in grass rats. In mice, levels of activity during the light and dark phases of the 7-h cycle did not differ, even though the same animals had responded to discrete photic stimuli in the first 2 experiments. The results of the 3 experiments are discussed in terms of their methodological implications and for the insight they offer into the mechanisms and evolution of diurnality.

Orexinergic signaling mediates light-induced neuronal activation in the dorsal raphe nucleus

Seasonal affective disorder (SAD), a major depressive disorder recurring in the fall and winter, is caused by the reduction of light in the environment, and its depressive symptoms can be alleviated by bright light therapy. Both circadian and monoaminergic systems have been implicated in the etiology of SAD. However, the underlying neural pathways through which light regulates mood are not well understood. The present study utilized a diurnal rodent model, Arvicanthis niloticus, to explore the neural pathways mediating the effects of light on brain regions involved in mood regulation. Animals kept in constant darkness received light exposure in early subjective day, the time when light therapy is usually applied. The time course of neural activity following light exposure was assessed using Fos protein as a marker in the following brain regions/cells: the suprachiasmatic nucleus (SCN), orexin neurons in the perifornical-lateral hypothalamic area (PF-LHA) and the dorsal raphe nucleus (DRN). A light-induced increase in Fos expression was observed in orexin neurons and the DRN, but not in the SCN. As the DRN is densely innervated by orexinergic inputs, the involvement of orexinergic signaling in mediating the effects of light on the DRN was tested in the second experiment. The animals were injected with the selective orexin receptor type 1 (OXR1) antagonist SB-334867 prior to the light exposure. The treatment of SB-334867 significantly inhibited the Fos induction in the DRN. The results collectively point to the role of orexin neurons in mediating the effects of light on the mood-regulating monoaminergic areas, suggesting an orexinergic pathway that underlies light-dependent mood fluctuation and the beneficial effects of light therapy.

Dim Light at Night Increases Immune Function in Nile Grass Rats, a Diurnal Rodent

With the widespread adoption of electrical lighting during the 20th century, human and nonhuman animals became exposed to high levels of light at night for the first time in evolutionary history. This divergence from the natural environment may have significant implications for certain ecological niches because of the important influence light exerts on the circadian system. For example, circadian disruption and nighttime light exposure are linked to changes in immune function. The majority of studies investigating the effects of light exposure and circadian disruption on the immune system use nocturnal rodents. In diurnal species, many hormones and immune parameters vary with secretion patterns 180° out of phase to those of nocturnal rodents. Thus, the authors investigated the effects of nighttime light exposure on immunocompetence in diurnal Nile grass rats (Arvicanthis niloticus). Rats were housed in either standard 14-h light (L):10-h dark (D) cycles with L ∼150 lux and D 0 lux or dim light at night (dLAN) cycles of LD 14:10 with L ∼150 lux and D 5 lux for 3 wks, then tested for plasma bactericidal capacity, as well as humoral and cell-mediated immune responses. Rats exposed to dLAN showed increased delayed-type hypersensitivity pinna swelling, which is consistent with enhanced cell-mediated immune function. dLAN rats similarly showed increased antibody production following inoculation with keyhole lymphocyte hemocyanin (KLH) and increased bactericidal capacity. Daytime corticosterone concentrations were elevated in grass rats exposed to nighttime dim light, which may have influenced immunological measures. Overall, these results indicate nighttime light affects immune parameters in a diurnal rodent. (Author correspondence: fonken.1@osu.edu)

An ecological study on rodents of natural vegetation and farm lands in Siltie, Central Ethiopia

An ecological study on species composition, distribution, relative abundance and habitat association of rodents was conducted in Siltie natural vegetation and nearby farmlands during July 2008 - March 2009. Five habitat types, three from natural and two from agricultural fields were randomly selected based on representation of the main vegetation zones. In each habitat type, one representative grid was selected for live trapping. In addition, rodents were also snap-trapped from these habitats. A total of 562 captures was made in 2940 live-trap nights and 87 in 1200 snap-trap nights. Species of small mammals trapped were Mastomys natalensis (33.3%), Arvicanthis dembeensis (23.0%), Mastomys erythroleucus (12.1%), Stenocephalemys albipes (8.4%), Desmomys harringtoni (6.0%), Mus mahomet (5.9%) , Tatera robusta (5.1%) , Lophuromys flavopunctatus (2.8%) , Rattus rattus (2.5%) and Arvicanthis niloticus (0.9%). The trap success varied significantly from habitat to habitat. Population density of rodents was high in the bush land and forest habitats. Plant matters were the most common food items revealed from the stomach contents of snap-trapped individuals. A. dembeensis , M. Mahomet , D. harringtoni and M. natalensis were recorded as major pests in the study area. Breeding was seasonal for most of the species trapped. The number of embryos varied both within and among species.An ecological study on species composition, distribution, relative abundance and habitat association of rodents was conducted in Siltie natural vegetation and nearby farmlands during July 2008 - March 2009. Five habitat types, three from natural and two from agricultural fields were randomly selected based on representation of the main vegetation zones. In each habitat type, one representative grid was selected for live trapping. In addition, rodents were also snap-trapped from these habitats. A total of 562 captures was made in 2940 live-trap nights and 87 in 1200 snap-trap nights. Species of small mammals trapped were Mastomys natalensis (33.3%), Arvicanthis dembeensis (23.0%), Mastomys erythroleucus (12.1%), Stenocephalemys albipes (8.4%), Desmomys harringtoni (6.0%), Mus mahomet (5.9%) , Tatera robusta (5.1%) , Lophuromys flavopunctatus (2.8%) , Rattus rattus (2.5%) and Arvicanthis niloticus (0.9%). The trap success varied significantly from habitat to habitat. Population density of rodents was high in the bush land and forest habitats. Plant matters were the most common food items revealed from the stomach contents of snap-trapped individuals. A. dembeensis , M. Mahomet , D. harringtoni and M. natalensis were recorded as major pests in the study area. Breeding was seasonal for most of the species trapped. The number of embryos varied both within and among species.

Positive outcomes of oil palm phenolics on degenerative diseases in animal models

It is well established that plant phenolics elicit various biological activities, with positive effects on health. Palm oil production results in large volumes of aqueous by-products containing phenolics. In the present study, we describe the effects of oil palm phenolics (OPP) on several degenerative conditions using various animal models. OPP reduced blood pressure in a NO-deficient rat model, protected against ischaemia-induced cardiac arrhythmia in rats and reduced plaque formation in rabbits fed an atherogenic diet. In Nile rats, a spontaneous model of the metabolic syndrome and type 2 diabetes, OPP protected against multiple aspects of the syndrome and diabetes progression. In tumour-inoculated mice, OPP protected against cancer progression. Microarray studies on the tumours showed differential transcriptome profiles that suggest anti-tumour molecular mechanisms involved in OPP action. Thus, initial studies suggest that OPP may have potential against several chronic disease outcomes in mammals.

Comparison of Area 17 Cellular Composition in Laboratory and Wild-Caught Rats Including Diurnal and Nocturnal Species

In this study we examine the size of primary sensory areas in the neocortex and the cellular composition of area 17/V1 in three rodent groups: laboratory nocturnal Norway rats (Long-Evans; Rattus norvegicus), wild-caught nocturnal Norway rats (R. norvegicus), and laboratory diurnal Nile grass rats (Arvicanthis niloticus). Specifically, we used areal measures of myeloarchitecture of the primary sensory areas to compare area size and the isotropic fractionator method to estimate the number of neurons and nonneurons in area 17 in each species. Our results demonstrate that the percentage of cortex devoted to area 17 is significantly greater and the percentage of cortex devoted to S1 is significantly smaller in the diurnal Nile grass rat compared with the nocturnal Norway rat groups. Further, the laboratory rodent groups have a greater percentage of cortex devoted to auditory cortex compared with the wild-caught group. We also demonstrate that wild-caught rats have a greater density of neurons in area 17 compared to laboratory-reared animals. However, there were no other clear cellular composition differences in area 17 or differences in the percentage of brain weight devoted to area 17 between nocturnal and diurnal rats. Thus, there are differences in primary sensory area size between diurnal versus nocturnal and laboratory versus wild-caught rat groups and cellular density between wild-caught and laboratory rat groups. Our results demonstrate that the differences in the size and cellular composition of cortical areas do not fit with what would be expected based on brain scaling differences alone, and have a consistent relationship with lifestyle and sensory morphology.

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.

Phase preference for the display of activity is associated with the phase of extra-suprachiasmatic nucleus oscillators within and between species

Many features of the suprachiasmatic nucleus (SCN) are the same in diurnal and nocturnal animals, suggesting that differences in phase preference are determined by mechanisms downstream from the SCN. Here, we examined this hypothesis by characterizing rhythmic expression of Period 1 (PER1) and Period 2 (PER2) in several extra-SCN areas in the brains of a diurnal murid rodent, Arvicanthis niloticus (grass rats). In the shell of the nucleus accumbens, dorsal striatum, piriform cortex, and CA1 of the hippocampus, both PER1 and PER2 were rhythmic, with peak expression occurring at ZT10. PER1 in the dentate gyrus also peaked at ZT10, but PER2 was arrhythmic in this region. In general, these patterns are 180° out of phase with those reported for nocturnal species. In a second study, we examined inter-individual differences in the multioscillator system of grass rats. Here, we housed grass rats in cages with running wheels, under which conditions some individuals spontaneously adopt a day active (DA) and others a night active (NA) phase preference. In the majority of the extra-SCN regions sampled, the patterns of PER1 and PER2 expression of NA grass rats resembled those of nocturnal species, while those of DA grass rats were similar to the ones seen in grass without access to running wheels. In contrast, the rhythmic expression of both PER proteins was identical in the SCN and ventral subparaventricular zone (vSPZ) of DA and NA animals. Differences in the phase of oscillators downstream from the SCN, and perhaps the vSPZ, appear to determine the phase preference of particular species, as well as that of members of a diurnal species that show voluntary phase reversals. The latter observation has important implications for the understanding of health problems associated with human shift work.

Nutritional correlates and dynamics of diabetes in the Nile rat (Arvicanthis niloticus): a novel model for diet-induced type 2 diabetes and the metabolic syndrome

BackgroundThe prevalence of Metabolic Syndrome and related chronic diseases, among them non-insulin-dependent (type 2) diabetes mellitus, are on the rise in the United States and throughout the world. Animal models that respond to environmental stressors, such as diet, are useful for investigating the outcome and development of these related diseases.ObjectiveWithin this context, growth and energy relationships were characterized in the Nile rat, an exotic African rodent, as a potential animal model for diet-induced type 2 diabetes mellitus and Metabolic Syndrome.MethodsCompiled data from several studies established the relationship between age, body weight gain (including abdominal adiposity), food and water consumption, and blood glucose levels as determinants of diabetes in male and female Nile rats. Glucose Tolerance Testing, insulin, HbA1c, blood pressure measurements and plasma lipids further characterized the diabetes in relation to criteria of the Metabolic Syndrome, while diet modification with high-fat, low-fiber or food restriction attempted to modulate the disease.ResultsThe Nile rat fed lab chow demonstrates signs of the Metabolic Syndrome that evolve into diet-induced non-insulin-dependent (type 2) diabetes mellitus characterized by hyperinsulinemia with rising blood glucose (insulin resistance), abdominal adiposity, and impaired glucose clearance that precedes increased food and water intake, as well as elevated HbA1c, marked elevation in plasma triglycerides and cholesterol, microalbuminuria, and hypertension. Males are more prone than females with rapid progression to diabetes depending on the challenge diet. In males diabetes segregated into early-onset and late-onset groups, the former related to more rapid growth and greater growth efficiency for the calories consumed. Interestingly, no correlation was found between blood glucose and body mass index (overall adiposity) in older male Nile rats in long term studies, whereas blood glucose and the perirenal fat pad, as well as liver and kidney weight, were positively related to early-onset diabetes. Rats weaned early (4-5 wks) and challenged with a high-fat Western-type diet developed diabetes faster, and body fat accumulation was more apparent, whereas food restriction curtailed it.ConclusionThe Nile rat fed typical rodent diets develops hyperinsulinemia that precedes hyperglycemia (insulin resistance) leading to diet-induced type 2 diabetes associated with hypertriglyceridemia, hypercholesterolemia, and hypertension. Dietary modulation affected growth rate (weight gain and central adiposity) to impact disease progression. This rodent model represents a novel system of gene-diet interactions affecting energy utilization that can provide insight into the prevention and treatment of the type 2 diabetes and Metabolic Syndrome.

Current status of research on rice yellow mottle Sobemovirus

Rice yellow mottle genus Sobemovirus is an important disease of rice worldwide. Although the virus attacks both upland and lowland rice cultivars, the latter are worse infected. The disease is spread by insect vectors belonging to the families Chrysomelidae, Coccinelidae, and Tettigonidae. It is also transmitted by domestic cattle (Bos spp.), donkeys (Asinus spp.), grass rats (Arvicanthis niloticus), weed species of the family Poaceae, debris, irrigation water and through mechanical inoculation. Six strains of the virus have been reported so far. Rice yellow mottle virus (RYMV) incidence ranges between 5 and 100% and yield losses vary from 20 to 100%. Effective management includes the use of resistant cultivars, control of insect vectors, good sanitation and integrated pest and production management. This paper reviews the current status of the virus, with emphasis on its geographical distribution, characteristics, strains, symptomatology, diagnosis, transmission, host range and management strategies.

An animal model of spontaneous metabolic syndrome: Nile grass rat

Metabolic syndrome (MetS) is a prevalent and complex disease, characterized by the variable coexistence of obesity, dyslipidemia, hyperinsulinaemia, and hypertension. The alarming rise in the prevalence of metabolic disorders makes it imperative to innovate preventive or therapeutic measures for MetS and its complications. However, the elucidation of the pathogenesis of MetS has been hampered by the lack of realistic models. For example, the existing animal models of MetS, i.e., genetically engineered rodents, imitate certain aspects of the disease, while lacking other important components. Defining the natural course of MetS in a spontaneous animal model of the disease would be desirable. Here, we introduce the Nile grass rat (NGR), Arvicanthis niloticus, as a novel model of MetS. Studies of over 1100 NGRs in captivity, fed normal chow, revealed that most of these animals spontaneously develop dyslipidemia (P<0.01), and hyperglycemia (P<0.01) by 1 yr of age. Further characterization showed that the diabetic rats develop liver steatosis, abdominal fat accumulation, nephropathy, atrophy of pancreatic islets of Langerhans, fatty streaks in the aorta, and hypertension (P<0.01). Diabetic NGRs in the early phase of the disease develop hyperinsulinemia, and show a strong inverse correlation between plasma adiponectin and HbA1c levels (P<0.01). These data indicate that the NGR is a valuable, spontaneous model for exploring the etiology and pathophysiology of MetS as well as its various complications.

PER2 rhythms in the amygdala and bed nucleus of the stria terminalis of the diurnal grass rat ( Arvicanthis niloticus)

The suprachiasmatic nucleus (SCN) of the hypothalamus is the central pacemaker that controls circadian rhythms in mammals. In diurnal grass rats ( Arvicanthis niloticus), many functional aspects of the SCN are similar to those of nocturnal rodents, making it likely that the difference in the circadian system of diurnal and nocturnal animals lies downstream from the SCN. Rhythms in clock genes expression occur in several brain regions outside the SCN that may function as extra-SCN oscillators. In male grass rats PER1 is expressed in the oval nucleus of the bed nucleus of the stria terminalis (BNST-ov) and in the central and basolateral amygdala (CEA and BLA, respectively); several features of PER1 expression in these regions of the grass rat brain differ substantially from those of nocturnal species. Here we describe PER2 rhythms in the same three brain regions of the grass rat. In the BNST-ov and CEA PER2 expression peaked early in the light period Zeitgeber time (ZT) 2 and was low during the early night, which is the reverse of the pattern of nocturnal rodents. In the BLA, PER2 expression was relatively low for most of the 24-h cycle, but showed an acute elevation late in the light period (ZT10). This pattern is also different from that of nocturnal rodents that show elevated PER2 expression in the mid to late night and into the early day. These results are consistent with the hypothesis that diurnal behavior is associated with a phase change between the SCN and extra-SCN oscillators.