Pheromones as Chemical Substances - Essay Example

PHEROMONES Pheromones are chemical substances secreted externally by some animals that influence the physiology and behaviour of other animals of thesame species. The word 'pheromone' is derived from the Greek word pherein (to transport/carry) and hormone (stimulating/exciting substance). According to Kohl J., 1996, pheromones are social environmental chemical stimuli (e.g. odours) which are produced by one individual and detected by another individual of the same species. They exert their action at a sub- conscious level and the animal may not be aware that it is responding to an odour. Pheromonal communication elicits physiologic and behavioural changes in the subject affected. Pheromones were initially studied in insects, where they have an established role as proven by scientific research. Limited sensory development in insects as compared to mammals necessitates the presence of some communication mechanism by which they can exchange information. Pheromones are the substances which perform this function. The complex manner in which ants, termites, honey bees, bugs and other insects organise their daily life without any verbal communication is a definite clue to the presence of pheromones. All insects have a highly organised pattern of social interaction as well as a well defined reproductive pattern which are guided by pheromones. According to an online article by Pines Maya of the Howard Hughes Medical Institute, the first pheromone ever to be identified (in 1956) was a powerful sex attractant for silkworm moths. It was isolated over a span of twenty years by a team of German researchers. After removing certain glands at the tip of the abdomen of 500,000 female moths, they extracted the compound. Miniscule amounts of this compound elicited excitement in the male moths exhibited by fluttering of their wings. This clear sign that the males had sensed the attractant enabled the scientists to purify the pheromone. The compound was purified subsequently and was named "bombykol" for the silkworm moth, Bombyx mori from which it was extracted. There are enough visibly apparent instances of evidence of the existence of pheromones in our daily life when we observe insect behaviour. Bees and wasps home in to the precise location of their hives; ants leave a trail for others to follow, and the butterflies locate members of the opposite sex during flight. Pheromones are predominantly volatile compounds detected by the sense of smell but sometimes can be liquid contact chemicals (Gullan P.J. et al). They are secreted from the exocrine glands derived from the epidermal cells. Classification of pheromones in insects is based upon five categories of behaviour associated with sex, aggregation, spacing, trail forming and alarm. Sex pheromones are usually secreted during the breeding season by the female which attracts the males. Aggregation pheromones cause insects of both sexes to crowd around the source of the pheromone. Spacing pheromones are anti aggregation and are secreted to repel further arrivals of the species when a particular spot is saturated with the species or the food source is exhausted. Trail marking pheromones are volatile and short lived chemicals that evaporate within days unless reinforced. They are used by social insects like ants to mark the trail to the nest or food source. Alarm pheromones are volatile, non persistent compounds that are secreted by insects during aggression by a predator or any other calamity which may affect the nest. They induce protection behaviour by collection or aggregation of the affected species such as bees. The presence and significance of pheromones in higher species in the ecological order has been well documented but the role played by them in human beings has been full of claims, counterclaims and controversies. Social as well as sexual behaviour in the quadruped mammals is strongly influenced by the sense of smell. Territory marking is a prominent feature in animals like lions, tigers and dogs. Such animals can detect the presence of another male by the smell of urine from the marked trees and other physical objects. Sexual receptivity of females during their oestrus cycle is detected by the males by smell only, indicating towards the presence of pheromones. The sense of smell is highly developed in species such as dogs as compared to human beings. Human beings being at the top rung of the evolutionary ladder have done away with using and expressing the sense of smell as a social interaction due to the self imposed standards and restrictions of social and learned behaviour. Primitive human populations living in so called uncivilized parts of the world still use smell as an important sensory mechanism. The anatomical comparisons of the number of olfactory cells in man and animals such as dogs has undermined the importance of sense of smell in human beings to an extent that human beings have been made to believe that they are more 'visually active' creatures than the other species and the sense of smell is of secondary importance. But this fact is being proved wrong with increasing evidence of the importance of the sense of smell in human reproduction (Kohl J.V., et al, 2001). Recent studies have shown that olfaction plays a very important role in human reproductive biology and human reproductive biology in turn affects human behavior. The Hypothalamic- Hypophysis axis plays a crucial role in animal as well as human reproduction by playing a stellar role in the regulation of both male and female hormones. Human Anatomy Involved The nasal mucosa is functionally divided into two areas - the respiratory region and the olfactory region (Kohl J.V., et al, 2001). The latter is made up of the sensory cells and is located on both sides of the upper nasal septum. The olfactory cells are highly specialized sensory cells with the ability to differentiate smells of a wide variety. The cells have docking areas or receptors composed of specialized protein molecules which bind with the aromatic compounds. Whenever an aroma is detected, the axons from these receptors carry the stimulus to the olfactory bulb. Sensory input is then projected to the olfactory lobe of the brain. The olfactory input is then projected via the thalamus to the neocortex and the limbic system in brain leading to conscious detection of the stimulus and its interpretation. Olfactory stimuli thus directly influence the neuroendocrinology of emotions. This is the reason due to which humans distinguish between pleasant and unpleasant smell. The emotional response is then elicited according to the nature of the smell. The vomeronasal organ (VNO) also known as Jacobson's organ is a special component of the olfactory system. It is located above the hard palate on both sides of the nasal septum and consists of a pair of blind ended tubes that open into the nasal cavity. Receptor cells in the epithelium of the mammalian vomeronasal organ have axons which extend to an accessory olfactory bulb that projects directly into the limbic system. It directly translates olfactory cues into neuroendocrine responses. However, according to Wang Z., et al (2007), the vomeronasal organ is non functional in adult humans and the pheromonal responses, if any, could be mediated through the main olfactory epithelium (MOE). The effect exerted by pheromones is under intensive research and it has been postulated that pheromones do have a role in triggering the human sexual responses by initiating neuro-endocrinological changes (Bigiani A., et al, 2005). Although there are nerve bundles running from the human VNO to the brain, it is still unclear whether they contain actual sensory neurons or just autonomic nerves. Unlike that in animals, the human VNO does not have an obvious sensory epithelium; however, it contains cells that are considered to be bipolar receptor neurons. The human VNO is thought to be stimulated by airborne chemicals, as opposed to stimuli dissolved in mucus. Discovery of pheromones Evidence of the role played by pheromones in human reproduction was first noticed by Martha McClintock in 1971 who published a study showing that the menstrual periods of women who lived together tend to converge on the same time every month. This report was followed up by intensive research for the next thirty years and it was found that the secretion of the armpits in women had something in it which triggered this synchronization. It was practically demonstrated by collecting fluid from a donor woman's underarms and applying it on the upper lip of another woman. The procedure affected the recipient's menstrual cycle. The exact chemical involved was not identifiable as yet but the finding triggered a new interest in the field and stimulated intensive research. The pheromones responsible for inducing menstrual synchrony were labelled as 'primer' pheromones which influence long term changes in hormone levels. The researchers then identified some components of human sweat and finally focussed their research on two compounds - androstadienone and estratetraenol. "The idea was that men produce androstadienone and that's a sex attractant to women, and women produce estratetraenol and that's a sex attractant to men," explained McClintock. The compounds were proven to affect the psychological state and brain functions of the recipients on exposure. The results were however erratic and the substances were considered to act as modulators rather than as releasers of some fixed responses, which depended upon the pre-existing psychological state of the subjects exposed to them. In studies conducted on androstenol, a putative human pheromone, women who were exposed to the compound exhibited significant submissive behaviour in the middle of their menstrual; cycle as against aggressive behaviour in controls (Benton D., 1982). However in a subsequent study by the same author in 1986, it was found that the compound did not produce any significant effect in sexual arousal. Intramuscular injection of boar androstenol in an animal study on gilts changed the secretory ovarian function during sexual maturation, suggesting a humoral rather than olfactory pathway of action (Stefa'czyk-Krzymowska S., et al, 2003). Gilts treated with boar pheromone had a higher total number of follicles > 3 mm in diameter and a lower index of atresia. In addition, androstenol-treated animals were characterized by higher concentrations of progesterone and estradiol than those of controls. In a human study, Wyart C. et al, 2007 found that by smelling a single component of male sweat, androstadienone, there was an increase in the cortisol hormone level, measured after collection from the saliva of women. The compound thus acts as a chemical signal affecting hormonal status in the opposite sex thereby satisfying the criterion for a putative pheromone. Androstadienone and Estratetraenol were both tested for their physiological effects on the autonomic nervous system in men and women in a study by Bensafi M., et al (2003). Androstadienone did increase arousal significantly in women only but Estratetraenol; the other putative pheromone did not produce any significant effect in either sex. The authors carried out a further study in 2004 on the role of these two compounds by making the subjects sniff human sex-steroid derived compounds and found that the procedure resulted in modulation of mood, memory and autonomic nervous system function in specific behavioural contexts. Subjects were tested with Androstadienone, Estratetraenol, or a Control compound within four mood contexts: neutral, sexually aroused, sad and happy. These moods were successfully induced using selected film segments. During the neutral context, none of the compounds affected mood or autonomic nervous system function. However, compound effects were significantly increased within arousing contexts. During the sexually arousing context, both compounds increased sexual arousal. During the sad context, Androstadienone maintained positive mood in women and increased negative mood in men. Memory for events during the sad context was impaired by Androstadienone in women but not in men. Finally, effects of Androstadienone on physiology were observed during the sexually arousing context whereby Androstadienone increased skin temperature in both sexes but reduced abdominal respiration rate in men only. These findings lend support to a specific role for these compounds as pheromones. The study confirmed similar results obtained by Jacob S. et al (2001), when effects of these compounds on the autonomic physiological responses and mood were measured. Both androstadienone and estratetraenol raised the skin temperature of men's hands and lowered it in women. Likewise, each steroid increased skin conductance, with a significantly greater effect on women than men. Historical social patterns in animals as well as humans, their behaviour and biological activities clearly point towards the existence of pheromones which has been substantiated by research in the last thirty years. Putative pheromone compounds are under intensive scrutiny of the medical researchers with increasing evidence of their effects as chemical signals inducing hormonal changes in opposite sexes. The exact mechanisms however need further elucidation in order to lend credibility to the facts and develop therapeutic approaches in medical use of such compounds. The cosmetics industry has already started using pheromones in their products aimed at enticing the youth into buying them to enhance their sex appeal. Modern lifestyles have brought human populations farther from nature and into highly organized urban societies where animal instincts are frowned upon. Increased preoccupation with cleanliness, hygiene and the practice of daily baths using chemical detergents has a detrimental effect on natural human odours. This fact might be responsible for fewer roles of pheromones in context to human beings. The significance has only lately been recognised and studies need to be conducted on human populations in societies which are still in touch with nature and live in close contact with mother Earth. Certain tribes in underdeveloped parts of the world can be the prime targets for such studies. Sub human primates closest to human beings such as gorillas, baboons and monkeys still live in the wild and studies can be planned for observing their social patterns; material from their body secretions can be analyzed for the presence of putative pheromone like compounds and then extrapolated into human studies. References: Bensafi M, Brown WM, Tsutsui T, Mainland JD, Johnson BN, Bremner EA, Young N, Mauss I, Ray B, Gross J, Richards J, Stappen I, Levenson RW, Sobel N.2003 Dec Sex-steroid derived compounds induce sex-specific effects on autonomic nervous system function in humans. Behav Neurosci.;117(6):1125-34 Bensafi M, Brown WM, Khan R, Levenson B, Sobel N, 2004 Jun 4 Sniffing human sex- steroid derived compounds modulates mood, memory and autonomic nervous system function in specific behavioral contexts. Behav Brain Res.;152(1):11-22 Benton D. 1982 Nov-Dec 15(3-4) The influence of androstenol - a putative human pheromone - on mood throughout the menstrual cycle. Biol Psychol. ;:249-56 Benton D, Wastell V., 1986 Apr;22(2) Effects of androstenol on human sexual arousal. Biol Psychol. :141-7 Bigiani A, Mucignat-Caretta C, Montani G, Tirindelli R. 2005 Pheromone reception in mammals. Rev Physiol Biochem Pharmacol. ;154:1-35 Gullan P. J., Cranston P. S., McInnes Karina Hansen, 2004, The Insects: An Outline of Entomology Wiley-Blackwell - USA Kohl, J. 1996. Human pheromones: Mammalian olfactory, genetic, neuronal, hormonal and behavioral reciprocity, and human sexuality. Advances in Human Behavior and Evolution. http://psych.lmu.edu/ahbe.htm Kohl J. V., Atzmueller Michaela, Fink Bernhard & Grammer Karl: 2001;22 Human Pheromones: "Integrating Neuroendocrinology and Ethology" NEL VOL. 22 No. 5 Invited NEL Review, :309-321 Jacob S, Hayreh DJ, McClintock MK, 2001 Sep 1-15;74(1-2) Context-dependent effects of steroid chemosignals on human physiology and mood. Physiol Behav. :15-27 Pines Maya, A Secret Sense in the Human Nose: Pheromones and Mammals, A report fom the Howard Hughes Medical Institute, Available online at http://www.hhmi.org/senses/d230.html Stefa'czyk-Krzymowska S, Krzymowski T, Wasowska B, Jana B, S'omi'ski J, 2003 Nov;3(3) Intramuscular injections of male pheromone 5 alpha-androstenol change the secretory ovarian function in gilts during sexual maturation. Reprod Biol. :241- 57 Wang Z, Nudelman A, Storm DR, 2007 Jun;35(3) Are pheromones detected through the main olfactory epithelium' : Mol Neurobiol. :317-23 Wyart C, Webster WW, Chen JH, Wilson SR, McClary A, Khan RM, Sobel N., 2007 Feb 7;27(6) Smelling a single component of male sweat alters levels of cortisol in women. J Neurosci. :1261-5 Read More