Nicotine mode of action

By binding to nicotinic acetylcholine receptors, nicotine increases the levels of several neurotransmitters - acting as a sort of "volume control". It is thought that increased levels of dopamine in the reward circuits of the brain are responsible for the euphoria and relaxation and eventual addiction caused by nicotine consumption.

Smells like Teen Spirit, or maybe lilac....

Did you know that the 2004 Nobel Prize was awarded to Richard Axel and Linda B. Buck for their discoveries of "odorant receptors and the organization of the olfactory system"?

There's a nice summary of their research on the Nobel website (this is the summary of the summary - check the link for the full version):

The sense of smell long remained the most enigmatic of our senses. The basic principles for recognizing and remembering about 10,000 different odours were not understood. This year's Nobel Laureates in Physiology or Medicine have solved this problem and in a series of pioneering studies clarified how our olfactory system works. They discovered a large gene family, comprised of some 1,000 different genes (three per cent of our genes) that give rise to an equivalent number of olfactory receptor types. These receptors are located on the olfactory receptor cells, which occupy a small area in the upper part of the nasal epithelium and detect the inhaled odorant molecules.

Each olfactory receptor cell possesses only one type of odorant receptor, and each receptor can detect a limited number of odorant substances. Our olfactory receptor cells are therefore highly specialized for a few odours. The cells send thin nerve processes directly to distinct micro domains, glomeruli, in the olfactory bulb, the primary olfactory area of the brain. Receptor cells carrying the same type of receptor send their nerve processes to the same glomerulus. From these micro domains in the olfactory bulb the information is relayed further to other parts of the brain, where the information from several olfactory receptors is combined, forming a pattern. Therefore, we can consciously experience the smell of a lilac flower in the spring and recall this olfactory memory at other times.

Golden Years Truly Are Golden

As I mentioned in class the AAAS website reported on a PNAS paper out online yesterday: A snapshot of the age distribution of psychological well-being in the United States

In contrast to other, similar, studies this one used a large sample with fewer questions. In fact the sample size was over a third of a million people!

Stone's team found that global well-being declines from the 20s to age 50, then increases steadily. Happiness and enjoyment also increase after age 50. Although sadness is fairly flat throughout the age groups, most negative feelings decline with age. Worry stays level until about 50, then drops. Anger falls steadily from the 20s; stress peaks in the 20s, starts a decline, then plummets after age 50. The patterns are almost identical for men and women, although women have more stress, worry more, and are sadder at all ages, despite reporting better global well-being than men at most ages. The findings make sense to anyone who has gotten out of their 20s, says Stone. "If you were to do a survey and say, 'How many of you would like to be 25 again?' you don't get a lot of takers," he says.

Hopefully this news is not too depressing to those of you looking at 25 from the other side!

Your inner fish

I just finished reading Neil Shubin's book 'Your Inner Fish.' It is a very easy and highly recommended read. We tend to focus on those areas where we have 'improved' on our fish-like ancestors (walking upright, doing pushups, inventing calculus etc) but what I found fascinating, and relevant to class today, was a discussion of olfaction (smelling) and how it's all been downhill since our aquatic past.

The human genome only contains about 23,000 protein-coding genes - which itself is an amazing fact. The other 98.5% of our genome consists of non-coding genes, regulatory sequences, introns and endogenous retrovirus sequences.

About 1,000 of those 23,000 protein-coding genes code for different odor receptors but less than half of them are functional in modern humans. Which says a lot about the importance of different senses in the evolution of humans from an aquatic ancestor (smell) to a terrestrial life (vision). Our evolutionary history is revealed in our genes.

Primate sperm competition: speed matters

Sperm cells from the sexually promiscuous chimpanzee and rhesus macaques swim faster and with greater force than those of gorillas. The surprise was how fast human sperm cells swim.

Bigger testes and semen displacement

A paper in PLoS One last month: Genetic Patterns of Paternity and Testes Size in Mammals

Also the subject of a news article in National Geographic: Bigger Testes Can Offer a Competitive Edge

When competition for females is fierce, males of some species have evolved bigger testes to trounce their rivals, a new study has confirmed.

Specifically, the research shows that testicle size matters in highly competitive animal societies in which females mate with many males or in which females live in groups ruled by an alpha male that must constantly defend his harem.

But that doesn't mean that females seek out more endowed males. Rather, the rivalry occurs after mating, as sperm battle inside the female.

Not surprisingly, males with larger testes produce more sperm—giving the male, so to speak, more bang for his buck.

Just how much all this applies to humans is always interesting to consider. Here's a curious paper with a lot more speculation than data: Semen Displacement as a Sperm Competition Strategy in Humans

We examine some of the implications of the possibility that the human penis may have evolved to compete with sperm from other males by displacing rival semen from the cervical end of the vagina prior to ejaculation. The semen displacement hypothesis integrates considerable information about genital morphology and human reproductive behavior, and can be used to generate a number of interesting predictions.