12 January 2016

Short Takes About Organs In Organisms

* As long suspected, there are distinct patterns of methylation in the epigenome for tissues for each of the major kinds of organs in a person.  And, we have reached a point where scientists can now read those methylation patterns.

* It turns out that taste buds are a subclass of a larger category of organs in the body that analyze the chemical content of molecules presented to them, which appear throughout the body.  The results of the taste and smell organs reach our conscious brain, but, for example, something very like taste buds in our kidneys are used to determine if it is correctly filtering our blood so that only stuff that should be removed from the body ends up in urine.

* Scientists suspected that they had discovered a previously undetected human organ in the 1990s. This discovery was put to use in clinical applications that in 2013 were published and shows a new treatment for high blood pressure.
Removing one of the tiniest organs in the body has shown to provide effective treatment for high blood pressure. . . . The carotid body -- a small nodule (no larger than a rice grain) found on the side of each carotid artery -- appears to be a major culprit in the development and regulation of high blood pressure. . . . Normally, the carotid body acts to regulate the amount of oxygen and carbon-dioxide in the blood. They are stimulated when oxygen levels fall in your blood as occurs when you hold your breath. This causes a dramatic increase in breathing and blood pressure until blood oxygen levels are restored. This response comes about through a nervous connection between the carotid body and the brain. . . . "Despite its small size the carotid body has the highest blood flow of any organ in the body. Its influence on blood pressure likely reflects the priority of protecting the brain with enough blood flow."
The journal article reference is: McBryde, et al., "The carotid body as a putative therapeutic target for the treatment of neurogenic hypertension.", Nature Communications (2013); 4 DOI: 10.1038/ncomms3395

* In mammals, the vomeronasal organ is the one popularly associated with receiving chemical communications from other individuals, particularly chemicals known as pheromones.  While there is some dispute regarding the issue, it appears that the weight of the evidence indicates that adult humans generally have at least one vomeronasal organ, in the form a a "pit" partway down at least one side of your nose (there is no disagreement that the organ is found in the same location in embryos).
Numerous reports of a structure identified as the VNO in the nasal septum in adult humans agree that it is a blind ending diverticulum in the septal mucosa opening via a depression (the VNO pit) into the nasal cavity ∼2 cm in from the nostril.
The connection between the VNO pit and chemical communication among humans isn't firmly established empirically, but there is very good circumstantial evidence to suggest that this is the mechanism.
There is fairly clear evidence for chemical communication among humans. The most notable example is a trend towards synchronization of menstrual cycles in women who live together (McClintock, 1971). Stern and McClintock have recently deduced the presence of two substances that can mediate this response when extracts of skin secretions are placed on the upper lip (Stern and McClintock, 1998). Thus, the signals are most likely to be airborne chemicals. The trend towards synchronization arises from either shortening or lengthening of the cycle by secretions produced at different phases of the donor’s cycle [but see the comment by Whitten (Whitten, 1999)]. The substances involved are unknown and although the effect does appear to be chemosensory, there is no evidence that it is due to vomeronasal sensory input.
Another data point which has been attributed to chemical communication through pheromones, but could instead be due to subconscious awareness of subtle visual cues, comes from studies which have found that men at strip clubs consistent prefer performers and tip them better, when performers are not on hormonal contraceptives and at the most fertile stage of their menstrual cycle, over other performers.

There is likewise suggestive evidence that VNO input should be largely a subconscious one.
Whether any of these findings are evidence for human pheromones is a different question. None of them meet the test for pheromone communication proposed below, i.e. evidence that the communication is beneficial (in the evolutionary sense) to both sender and receiver. The subjects in these studies had no conscious perception of odor stimulation, which could be a feature of vomeronasal input although not a sine qua non for pheromonal communication. The suggestion that vomeronasal input might be unconscious (Lloyd-Thomas and Keverne, 1982) comes in part from observations of vomeronasal system connections in the rodent brain. There are close connections with the amygdala and limbic system (Halpern, 1987; Meredith, 1991), the seat of emotional, hormonal and autonomic control, but there are only indirect connections with the cerebral cortex, generally considered to be the site of consciousness. The main olfactory system in general has good connections with cerebral cortex, but also has connections to the amygdala.
It is also worth noting that pheromones (a term that has more strict and less strict definitions, but at a minimum facilitate chemical communication between animals of the same type) need not always involve the VNO, even though they often do.
Whatever the definition of pheromone, there is no evidence that pheromones are necessarily detected by the VNO. Several recent examples in animals with well-developed VNOs make this clear. The response of newborn rabbits to the mother’s nipple (Hudson and Distel, 1986), referred to above, and the standing response of a receptive female pig to the male’s pheromone (Dorries et al., 1997) both depend on the main olfactory system. The recognition of newborn lambs by ewes also appears to depend on the main olfactory system (Levy et al., 1995), although a vomeronasal contribution has also been reported (Booth and Katz, 2000). Thus, even if an authentic pheromone response were to be documented in humans, that would not be evidence for a functional VNO.
The attraction of the VNO is the synthetic (or naturally harvested and purified) pheromones present an attractive and quite straightforward and non-invasive way to unconsciously influence people's behavior, and alternatively, at least a way of better understanding a possibly rich medium of unconscious communication (although the adult human VNO does clearly seem to be less developed than in many other kinds of mammals, like our olfactory system generally).

* There are some organs found in other kinds of animals that are not found in humans.  Some of the most interesting include spinnerets in spiders, and "the ampullae of lorenzini." These are found "in many fish and sharks, it allows them to sense electrical signals in the water emitted (usually) by other living organisms. This gives them a 'sixth sense' which allows them to find prey that is hiding underground or in the dark. It also is what prevents them from constantly running into the transparent glass of an aquarium."

Frogs have a third eyelid and can use their skin to breathe. We are also learning a lot about regeneration in amphibians, although the fact that this ability seems to be an ancestral state that was lost in less basal vertebrate species suggests that we proceed with caution as this ability apparently came with serious evolutionary costs.

* Some of the more interesting questions about the future of biotechnology come under the heading of "transhumanism", basically, redesigning the human body so that it can do something better or differently than ordinary humans.  This could involve adding a new organ not found in ordinary humans, or perhaps simply a new localized area or organ within the brain that confers some new mental capacity.

We increasingly understand how our complex human anatomy works in great detail at every level from gross anatomy to the chemical level, and can increasingly read the DNA and epigenetic codes that cause the human body to form itself in this way.  For example, while we've know the letters of the genetic code and some of its overall structure for decades, we are starting to now understand the "grammar" of the genetic code.  While in some respects, DNA is harder to understand than we might have naively hoped, many aspects of DNA seem to be uniform across all living things, so like most languages and sciences, once mastered, our knowledge may have broad applicability to unanticipated situations.

With new tools for DNA modification like CRISPR, and even less invasive tools the can modify epigenetic signals, it isn't unthinkable that we could start to write the codes that make our bodies in some way that would create a "transhuman" deliberately, although overconfidence of a type demonstrated in centuries of neuromedical missteps and fads, suggests strongly that hubris will produce unexpected consequences on more than one occasion, as well as raising serious professional ethical issues.  But, in the end, professional ethics never seems to be sufficient to prevent scientific breakthroughs in the long run.

No comments: