Frontiers in Pharmacology
Why are menthol cigarettes more addictive?
Smokers of menthol cigarettes crave cigarettes more frequently, find it more difficult to quit smoking, and are more likely to become addicted. The traditional explanation for the effect of menthol is that it masks the harsh taste of tobacco and thus entices people to smoke more.
But Nadine Kabbani from George Mason University in the USA here review recent scientific findings and proposes an novel explanation: menthol may directly promote nicotine craving because it binds to a particular type of nicotinic receptor within nerve cells, the α7 nicotinic acetylcholine receptor, and impairs its response to nicotine. Furthermore, in the longer term, menthol seems to promote the expression of other nicotinic receptor genes in regions of the brain that process pleasure, reward, and addiction. Kabbani concludes that it is time to re-examine rules and regulations on menthol cigarettes.
Prof Nadine Kabbani
Department of Molecular Neuroscience
Krasnow Institute for Advanced Study
George Mason University, USA
Frontiers in Plant Science
A major evolutionary transition in the development of grasses
In many plants, flowers occur in inflorescences, clusters that develop through almost mathematical branching patterns. These patterns strongly impact the size and number of seeds and the success of pollination, which is why they are often conserved by natural selection over long evolutionary periods. But Elizabeth Kellogg from the University of Missouri, together with colleagues from Brazil, the UK, and Australia, here shows that around 40 million years ago there was an abrupt evolutionary transition in the branching pattern of inflorescences of cool-season grasses (subfamily Pooideae).
Through a series of Scanning Electron Microscopy images, Kellogg and colleagues show that inflorescences of most cool-season grasses grow in a "distichous" pattern, that is, in two opposite ranks of flower-bearing branches. Furthermore, this branching is oddly asymmetrical, with most branches forming on one side of the inflorescence. In contrast, inflorescences of most other grasses retain the ancestral arrangement of branches in a spiral, which is likewise retained in the inflorescences of the most basal genus of the cool-season grasses. The evolutionary innovation identified by Kellogg and colleagues helps to explain the great evolutionary success of this group, with contains approximately 3800 species spread across the Northern hemisphere, including important crops like wheat, barley, and oats.
Prof Elizabeth A. Kellogg
Department of Biology
University of Missouri, USA
Frontiers in Psychology
An inborn deficit causes children with dyscalculia to have an imprecise representation of numbers
Dyscalculia is a severe and persistent disability in learning arithmetic that is often highly selective, in that it can affect children with normal intellectual ability. Karin Landerl and her team at the University of Graz, Austria, investigated the development of numerical processing in elementary school children with dyscalculia and a control group with good arithmetic skills. Children from grades 2 through 4 were asked to repeatedly perform simple computer tasks, for example selecting the larger number or set of dots, counting dots, or placing numbers on a number line.
While the efficiency of numerical processing generally improved over time, children with dyscalculia showed marked and persistent deficits which were specific to the domain of number. Dyscalculic children also had particular difficulty to "subitize", that is, to enumerate between 1 and 3 dots as quickly as possible. Landerl and colleagues conclude a biologically driven deficit causes children with dyscalculia to have an imprecise internal representation of numbers, which explains these children's difficulty with the number line task.
Prof Karin Landerl
Department of Psychology
University of Graz, Austria
Frontiers in Psychiatry
Genetic variation in the oxytocin receptor has both positive and negative effects on human emotion
The hormone oxytocin which promotes pair bonding, maternal care, and reproductive behavior in mammals also regulates emotions. To have effects, oxytocin must bind to its receptor. Numerous studies have reported that persons with the nucleotide G (guanine) in a certain noncoding position of the oxytocin receptor gene tend to be more trustful, optimistic, and empathetic than persons with an A (adenine), although the underlying mechanism is poorly understood.
Robyn McQuaid, Opal McInnis, and colleagues from Carleton University, Ottawa, report that adults with G in one or both copies of the oxytocin receptor gene are also more likely to show depressive symptoms if they suffered from maltreatment (e.g. abuse or neglect) during childhood, possibly because they are more negatively affected by a breach in trust. The researchers conclude that the G variant of the oxytocin receptor gene is not always advantageous: persons with one or two copies of this variant may thrive in a positive social environment, but they are more affected by negative experiences in early life.
Robyn Jane McQuaid
Department of Neuroscience
Carleton University, Canada
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