The African grass rat (*Arvicanthis niloticus*) is a herbivorous murine rodent inhabiting dry savanna, woodlands, and grasslands in Africa. As opposed to other rodent species that are nocturnal, NGRs are primarily diurnal (15). This unique behavior pattern has made them a valuable tool in the study of circadian rhythm.
Here, we will introduce some interesting facts about African grass rats, including their physical characteristics, habitat, behavior, and their role in scientific research.
Einblicke in die Welt der Grasratten / A Glimpse into the World of Grass Rats /
Physical Characteristics
The African grass rat is a medium-sized rodent. Its head and body can be about 16 to 20 centimeters long. Its tail is a bit shorter, around 12 to 17 centimeters. These rats usually weigh up to 200 grams.
The fur is rough. The top part of their fur is yellowish with black tips. They also have long yellow or orange hairs on their underside. You might notice a dark stripe running down their back. Their belly is whitish. The areas around their whiskers and eyes are often orange. Their legs are pink.
Key Features:
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- Size: Head and body length of 16-20 cm
- Weight: Up to 200 grams
- Fur: Rough, yellowish with black tips, orange underside hairs
- Markings: Dark stripe down the back, whitish belly
- Legs: Pink
A male greater cane rat in captive breeding program in Gabon.
Habitat and Distribution
African grass rats live in many countries across Africa. You can find them in places like Benin, Burkina Faso, Chad, Ethiopia, Ghana, Kenya, Niger, Nigeria, Senegal, Sudan, Tanzania, and Uganda. They also live in Algeria, Egypt, and Yemen.
These rats like to live in dry or moist savannas. They can also be found near farms, in gardens, and even in urban areas. They are quite adaptable!
Geographical Distribution:
- Africa: Benin, Burkina Faso, Chad, Ethiopia, Ghana, Kenya, Niger, Nigeria, Senegal, Sudan, Tanzania, Uganda, and more.
- Other Regions: Algeria, Egypt, Yemen
Geographical distribution of Sorghum in Africa, an environment where African Grass Rats are commonly found.
Behavior and Lifestyle
The animals live underground in burrows constructed in a central area with surface runways radiating outward. The African grass rat is a gregarious species that lives in underground burrows. These burrows have multiple entrances and run about 20 cm deep.
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African grass rats usually have babies between June and November. A female rat can give birth to 5 or 6 babies at a time. They can have babies at least 3 or 4 times a year.
A. are shorter than the outer two. A. . buff in the middle, and black at the tip. and pepper" effect. Relatively little is known about the mating structure of this species. 3.1 males. and presumed not to disperse. descended testes, indicating the capability of breeding. A. A. with females more often outnumbering males than vice-versa. is capable of breeding year-round under highly favorable conditions.
During the breeding season, gestation may take 18 to 25 days, averaging 23 days. have two equipotential ovaries and a duplex uterus. at 3 to 4 months. Comprehensive examination of parental care in this species is lacking.
Comprehensive examination of parental care in this species is lacking. have been observed to defend their young prior to weaning. from their natal nest, whereas males often disperse. may occur. A. Male parental care is not well-documented. infanticide, which is not uncommon in captive rodents.
Key Behaviors:
- Social Behavior: Gregarious, lives in underground burrows
- Burrows: Multiple entrances, approximately 20 cm deep
- Breeding Season: June to November
- Litter Size: 5-6 pups per litter
- Breeding Frequency: 3-4 times per year
Diet
A. will alter the intake ratio of food types. improve its competitive ability. A.
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These rodents are primarily diurnal. They acquire food close to the colonial burrow. The use of runways is for rapid escape from predators. A. may be preyed upon by a number of carnivorous African animals.
Dietary Habits:
- Herbivorous diet
- Acquire food close to their burrows
- Use runways for rapid escape from predators
African Grass Rats as a Model for Metabolic Syndrome
Metabolic syndrome (MetS) currently affects over a quarter of the population in developed countries, and its prevalence is rapidly rising (1). It is characterized by the variable coexistence of obesity, dyslipidemia, hyperinsulinemia or type 2 diabetes, and hypertension (2,3,4). MetS is associated with a marked increase in the risk for cardiovascular disease and atherosclerosis, both of which pose a major burden to the public health.
Scientists use African grass rats to learn about a health problem called Type 2 Diabetes. This is a condition where the body has trouble using sugar for energy. By studying these rats, scientists can understand how this condition develops. They look at things like how the rats' bodies handle sugar and fat.
The study of MetS has been hampered by the lack of appropriate models. Genetically engineered rodents have been generated to resemble various aspects of MetS (12,13,14). Such models may allow investigation of links between individual genes and certain components of MetS. However, the genetic manipulations in these models may be causally unrelated to the natural roots of the human disease.
This report describes the systemic pathology in NGRs that matches all aspects of human MetS. Fed a conventional lab diet, NGRs spontaneously develop obesity, hyperglycemia, and hypertension.
Key Findings:
- NGRs spontaneously develop dyslipidemia and hyperglycemia by 1 year of age.
- Diabetic rats develop liver steatosis, abdominal fat accumulation, nephropathy, atrophy of pancreatic islets of Langerhans, fatty streaks in the aorta, and hypertension.
- Early-stage diabetic NGRs develop hyperinsulinemia and show an inverse correlation between plasma adiponectin and HbA1c levels.
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.
Metabolic Profile in NGRs:
To investigate the influence of age and gender on the development of MetS in NGRs, a cohort of 62 (38 female and 24 male) animals were divided into 4 groups. Rats < 10 mo were considered young (female, 5.7±0.1 mo, n=20; male, 6.1±0.3 mo, n=13), while rats ≥ 10 mo were considered aged (female, 12.7±0.5 mo, n=18; male, 12.6±0.3 mo, n=11).
The BW of the young male NGRs (98±6 g; n=13) was similar to that of the age-matched females (97±3 g; n=20; P=0.8). Nonfed BG in the older males (250±22 mg/dl; n=11) was significantly higher than in older females (163±31 mg/dl; n=18; P<0.05; Fig. 4A). Furthermore, nonfed BG was significantly higher in the older males than in younger males (157±38 mg/dl; n=13; P<0.05; Fig. 4A). Older female rats had higher nonfed BG than younger females, but the difference was not significant (P=0.19; Fig. 4A).
In line with the BG levels, HbA1c was significantly higher in the older male animals (11.0±0.8%; n=7) than in the age-matched female rats (7.8±0.8%; n=9; P<0.05; Fig. 4B). HbA1c in older male NGRs was significantly higher than in the younger males (7.8±0.8%; n=9; P<0.05), while HbA1c in the older (7.8±0.8%) and younger females (6.3±0.3%) was not statistically different (P=0.1) and tended to be lower than males (Fig.
To investigate lipid metabolism, plasma TG and TC were measured in the various groups. Plasma TG was significantly higher in young male NGRs (322±59 mg/dl; n=13) compared with the age-matched females (86±10 mg/dl; n=20; P<0.01; Fig. 4C), while the aged males (391±105 g/dl; n=11) had significantly higher plasma TG than females (149±20 mg/dl; n=18; P<0.05; Fig. 4C). Aged female rats had significantly higher plasma TG levels than young females (P<0.01; Fig. 4C). Plasma TC in young male rats (212±60 mg/dl; n=13) was significantly higher than in age-matched females (76±3 mg/dl; n=20; P<0.05; Fig. 4D). Aged male rats had higher TC (306±56 mg/dl; n=11) compared to age-matched females (163±19 mg/dl; n=18; P<0.05; Fig. 4D). Aged females had significantly higher TC than young females (P<0.01; Fig.
To investigate potential organ manifestations of the metabolic changes in NGRs, the visceral organs of normal and diabetic animals were examined macroscopically and histologically. Livers from nondiabetic rats appeared normal by both measures (Fig. 5A). By contrast, livers from diabetic NGRs were typically enlarged, with a pale, marble-like appearance (Fig. 5A and Table 1). When examined histologically, intracellular microvesicular fatty depositions were noted in the pericentral and midzonal areas of the hepatic lobules (Fig. 5B).
The lipid particles varied in size but appeared to be larger in the central areas compared to those in the midzonal or peripheral areas, suggesting a gradual confluence of the lipid droplets during the course of the disease. Electron microscopy revealed marked cytoplasmic lipid droplets, characteristic of microvesicular hepatic steatosis (Fig.
Histological analysis of livers from nondiabetic and diabetic NGRs.
Table: Metabolic Parameters in Young and Aged NGRs
| Parameter | Young Males | Young Females | Aged Males | Aged Females |
|---|---|---|---|---|
| Non-fed BG (mg/dl) | 157±38 | 97±3 | 250±22 | 163±31 |
| HbA1c (%) | 7.8±0.8 | 6.3±0.3 | 11.0±0.8 | 7.8±0.8 |
| Plasma TG (mg/dl) | 322±59 | 86±10 | 391±105 | 149±20 |
| Plasma TC (mg/dl) | 212±60 | 76±3 | 306±56 | 163±19 |
The African grass rat is a fascinating creature with a significant role in scientific research, particularly in the study of metabolic syndrome. Understanding its characteristics and behavior can provide valuable insights into both its natural history and its utility as a model organism.
