Scientists Decode Molecular Details Of Genetic Defect That Causes Autism

Using an animal model, brain researchers in Göttingen have examined the effects of mutations that cause autism in humans. These are mutations in the genes which carry the building instructions for proteins in the neuroligin family. The study published in the scientific journal Neuron (September 21, 2006) shows that neuroligins ensure that signal transmission between nerve cells functions. In the brain of genetically altered mice without neuroligins, the contact points at which the nerve cells communicate, the synapses, do not mature. The researchers assume that similar malfunctions are experienced by autistic patients.

Autism is one of the most common psychiatric illnesses. Around 0.5 percent of all young children have a syndrome belonging to the "autistic spectrum". The main symptoms of this developmental malfunction are delayed language development or no language development at all, disturbed social behaviour and repetitive behaviour patterns. In many patients, the disease is accompanied by mental disability. Autistic individuals exhibiting high intelligence or outstanding skills in a particular area, called "savants", such as the main character in the film "Rain Man", are rare.

Even up to the middle of the last century, exceptionally cold emotional behaviour on the part of the mother was given as the cause for autism. However, the "refrigerator mom" theory has now been refuted. The belief widely held in the 1990s that the measles, mumps and rubella vaccine could cause autism in small children has no scientific basis at all. Today, it is clear that genetic factors are the major cause of the illness. Studies of identical twins have been particularly convincing in demonstrating this fact - the probability that the identical twin of an autistic person will also be autistic lies between 80 and 95 percent.

In 2003, French geneticist Thomas Bourgeron showed in an investigation of families with several autistic children that mutations in the two genes NLGN3 and NLGN4X had lead to a complete loss of function in the genes and triggered autism in affected patients. Bourgeron’s work sent a shock wave through neuro-scientific institutes worldwide, as the a NLGN genes were not unknown. They are responsible for the creation of two proteins, neuroligin-3 and neuroligin-4, which are considered to play an important part in the structure of nerve cell contacts.

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Scientists Decode Molecular Details Of Genetic Defect That Causes Autism

Giant Jumping Rats' Numbers Get Big Bounce In Madagascar

Madagascar's giant jumping rats are less endangered than previously thought, new surveys suggest.

The rats, which can launch themselves three feet (a meter) into the air with their kangaroolike hind legs, were predicted in 2001 to become extinct on the African island by 2025.But several studies over a more extensive area of the nocturnal animal's habitat have found this forecast to be excessively pessimistic.

The new findings have led researchers to increase their population estimate for the rabbit-size rodents from 11,000 to around 33,000.

The data come from tallies of the animals' burrows and the results of camera traps—devices set to take a photograph each time a rat enters or exits its burrow.

Despite the revised population estimate, scientists warn that giant jumping rats still need the attention of continued conservation efforts.

"It's no reason to be complacent … because this absolutely incredible animal is restricted to such a tiny area," said John Fa, director of conservation science at England's Durrell Wildlife Conservation Trust, which conducted the surveys.

Rare, Unusual Animal

The giant jumping rat is found only in a fragmented region of dry, deciduous forest—just 154 square miles (400 square kilometers) in size—in an area of western Madagascar called Menabe. (See Madagascar map.)

A village splits the habitat in two, isolating a northern population of giant jumping rats from one further south.

Local people collect firewood and honey from the forest and occasionally start fires to clear land for agriculture.

Where this destruction is most acute, only thick-trunked baobab trees remain. The result is an emptier landscape of scrappy shrub and grassland where giant jumping rats have difficulty burrowing, Fa explains.

Giant Jumping Rats' Numbers Get Big Bounce In Madagascar

Top tips for avoiding a dog attack

Dog attacks are rare, but this weekend a five month-old child died when two Rottweilers grabbed hold of her at a pub in Leicester. Newsround interviewed vet Tricia Mundy from the Village Animal Hospital in Surrey, who gave us some top tips for avoiding dangerous dogs. Here's what you should do if you fear a dog might be about to attack you. Stand still Stay calm Face the dog Fold your arms Walk away calmly, facing the dog, but without making eye contact And remember, if a dog attacks a human, it's usually not because it is trying to "hunt". Tricia said it's often because the animal feels frightened, so dogs are usually more scared of us than we are of them.

Top tips for avoiding a dog attack

Rats Careful Deliberators

Rats, like humans, contemplate problems by carefully weighing the costs and benefits of a situation before making decisions, according to a new study on Wistar rats, a rodent developed for research.

The study is the first to demonstrate that a non-human animal creates a desired ratio, or standard, to decide between options requiring varying levels of effort and that yield different rewards.

A person buying a new car, for example, must weigh the cost and the effort needed to make payments versus the value of the car. Rats, and likely all rodents, do something similar, only under a lot more pressure.

"In its natural habitat, rats are facing the problem that little is under their control, so they are facing various levels and forms of uncertainty all the time," said Ruud van den Bos, who led the research. "For instance, the quality and amount of food items at patches varies over time and between different patches, thus benefits are not always the same."

Van den Bos, a scientist in the Faculty of Veterinary Medicine at Utrecht University in The Netherlands, added, "The amount of energy spent to obtain these different items varies during the different foraging sessions, as sometimes it's cold, sometimes it's hot, sometimes it rains, sometimes sudden obstacles are present after heavy storms, etc."

Van den Bos and his team attempted to duplicate such challenges by manipulating barriers in a T-shaped maze that rats explored. Rats entered at the bottom of the "T," which connected two arms.

At the end of each arm was a chamber filled with treats. One side had a low reward — one sugar pellet — while the other side had three to five sugar pellets.

Rats that wanted the higher rewards had to climb steep barriers. It would be like placing a person's favorite dessert behind a Marines-type training wall that would have to be scaled before the individual could nosh. The researchers varied the size of the barrier and the amount of reward on that side to see how the rodents would react.

At first the rats went for the easy pickings, but when they determined more sweets were available on the other side of the maze, they exerted additional effort, but only after a certain point. When the pain yielded too little gain, they stuck with the tiny treat.

Findings have been accepted for publication in the journal Behavioral Brain Research.

Rats Careful Deliberators

The Mexica / Aztecs

The term, Aztec, is a startlingly imprecise term to describe the culture that dominated the Valley of Mexico in the fifteenth and sixteenth centuries. Properly speaking, all the Nahua-speaking peoples in the Valley of Mexico were Aztecs, while the culture that dominated the area was a tribe of the Mexica (pronounced "me-shee-ka") called the Tenochca ("te-noch-ka"). At the time of the European conquest, they called themselves either "Tenochca" or "Toltec," which was the name assumed by the bearers of the Classic Mesoamerican culture. The earliest we know about the Mexica is that they migrated from the north into the Valley of Mexico as early as the twelfth century AD, well after the close of the Classic Period in Mesoamerica. They were a subject and abject people, forced to live on the worst lands in the valley. They adopted the cultural patterns (called Mixteca-Pueblo) that originated in the culture of Teotihuacán, so the urban culture they built in the fifteenth and sixteenth centuries is essentially a continuation of Teotihuacán culture.

As stated in the section on the Toltecs, the peoples of Mesoamerica distinguished between two types of people: the Toltec (which means "craftsman"), who continued Classic urban culture, and the Chichimec, or wild people, who settled Mesoamerica from the north. The Mexica were, then, originally Chichimec when they migrated into Mexico, but eventually became Toltecs proper.

The history of the Tenochca is among the best preserved of the Mesoamericans. They date the beginning of their history to 1168 and their origins to an island in the middle of a lake north of the Valley of Mexico. Their god, Huitzilopochtli, commanded them on a journey to the south and they arrived in the Valley of Mexico in 1248. According to their history, the Tenochca were originally peaceful, but their Chichimec ways, especially their practice of human sacrifice, revolted other peoples who banded together and crushed their tribe. In 1300, the Tenochcas became vassals of the town of Culhuacan; some escaped to settle on an island in the middle of the lake. The town they founded was Tenochtitlan, or "place of the Tenochcas."

The Mexica / Aztecs