A Seminar On

Pheromones and Reproduction

CONTENTS

• Introduction• Types of pheromones• Role of pheromones in fish Reproduction• Role of pheromone in amphibian Reproduction• Role of pheromone in reptiles Reproduction• Role of pheromone in birds Reproduction• Role of pheromone in mammalian Reproduction• Role of pheromone in human Reproduction• Conclusion

Introduction

• The term Pheromone was introduced by Karlson and luscher in 1959.It derives from greek word( pherein=to carry;Harman=to excite).Pheromones are also called as “ecto hormones”as they are chemical messengers that are emitted into the environment from the body where they can activate specific physiological or behavioural response in the other individual of the same species.

• According to McClintock pheromones can be divided into two classes:• Firstly Signal pheromones produce short term behavioral changes and seems to act as

attractants and repellents.• Secondly primer pheromones produce long lasting changes in the behavior by their activation

of the hypothalamus-pitutary-adrenal(HPA) axis.• In particular it is assume that primer pheromones triggers the secretions of GnRH from the

hypothalamus ,which in turn triggers the secretions of gonadotropins(LH,FSH) from the pituitary gland.

Types of pheromones

Bruce (1970) had recognized following three types of main pheromones:1. Releaser pheromones:-These pheromones induce immediate and reversible

behavioural responses mediated directly by the central nervous system through first acting on neurohumoral pathways.these are used mainly in recognition of species members ,sex,sexual status,aggression,ejection of milk,etc.

• Examples of releaser pheromones:These are represented by sex attractant,trail and

alarm substances of insects,fish,tods,mammals etc.• In mammals releaser pheromones is present in the urine and foot pads.In mice,urine of

the male contain releaser pheromone for attracting females.• In other animals such as dog,deer,horse and sheep etc.,urine contains releaser

pheromones which help to elicit sexual attraction and arousal.Vaginal secretions of sheep hamster and rhesus monkey act as releaser pheromone.

2. Primer pheromone:-These pheromones evoke a long term endocrine or physiological response in the receivers mediated by neuroendocrine pathway or through direct effects on target organs.• Examples of primer pheromones:The common example of primer pheromones

are those involved in suppression and induction of estrous cycle,termination of pregnancy and sexual maturation cycle.

3. Imprinting pheromones:These pheromones act at critical period of developmental age and cause permanent change in the adult bahaviour .Such pheromones are found in some rodents like mice and rats.

Pheromones and Reproduction in Fish

• It has long been known that fish commonly employ pheromones to coordinate many aspects of their reproductive biology,only in past two decades has it become apparent that many of these cues derived from ,or are closely related to hormones and other essential body metabolites.Studies of olfactory function show that many bile acids,sex steroids and prostaglandins are detected by fish ,providing compelling evidence that fish commonly employ these chemicals as pheromones.

• Hormonal pheromones contains unmodified hormones,hormonal precursoes and their metabolites.Almost all reproductive pheromones identified in fish are hormonal pheromones.

• Current model for hormonal pheromone studies: Most recent hormonal pheromone research involved three groups of fish: the gold fish and related carps within the subtribe Cyprini, the salmonidae, and perciform species.

• In Gold fish: In gold fish the timing of spawning is controlled by female ,in which increase plasma concentration in late vitellogenesis primes responsiveness to exogenous fectors that induce ovulation and thus initiates a cascade of events that syncronise behavioral changes within and between the sexes.During the approximately15-hour period between onset of the luteinizing hormone surge and completion of spawning ,female sequentially release a preovulatory steroid hormonal pheromone and a postovulatory prostaglandin based hormonal pheromone , both of which induce distinct and dramatic primer and releaser effects on males.

• Female Recrudescence Pheromone :Female goldfish undergoing vitellogenesis release a recrudescent pheromone that attracts males.

• Female Preovulatory Steroid Pheromone:The preovulatory pheromone is a dynamic mixture whose multiple effects on males change with the shifting ratios of its three principle components 17,20beta-dihydroxy-4-pregnen-3-one (1720betaP); 17,20beta-dihydroxy-4-pregnen-3-one-20-sulfate (1720betaP-S); and androstenedione (AD).

• The preovulatory pheromone 17,20β-P increases a male reproductive performance by increasing both his behavioral competitiveness and the quantity and quality of his releasable sperm .

• Female postovulatory prostaglandin pheromone:At ovulation plasma-luteinizing hormone dramatically decreases,release of the preovulaory steroid pheromone dramatically decreses and movement of ovulated eggs into the oviduct induces the synthesis of prostaglandin F2α that triggers spawning behavior .Coincidently, females begin to release the postovulatory pheromone that attracts the male to the female,triggers male courtship,and activates mechanism that further increase releasable milt stores.

Pheromones and Amphibians• In Urodales ,the most significant fector in sex recognition and courtship is chemical

communication through the products pheromones of various glands that exhibit a marked development during the reproductive period.Effects of chemosignals on sexual behavior have been documented for a wide variety of vertebrate species but very few pheromones have been chemically identified. Previously, we found a novel female-attracting Pheromone in the abdominal gland of the cloaca of the male red-bellied newt, Cynops pyrrhogaster . This pheromone designated sodefrin is the first amphibian pheromone.

• Hormonal effect on the Pheromone secretion: The effects of PRL, androgen, and PRL plus androgen on the sodefrin content in hypophysectomized and castrated red-bellied newts was investigated using an RIA for sodefrin. A combinationof PRL and androgen is known to elicit the structural development of various organs related to reproduction including the abdominal gland as well as the reproductive behavior. This observation is consistent with the finding that the treatment of C. pyrrhogaster males with PRL plus androgen enhances the release of female-attractant into the water.

A female-attracting pheromone in a tree frog, Litoria splendida

The skin glands of anurans have been known to secrete defence compounds including various types of bioactive peptides . In the magnificent tree frog, Litoria splendida sends out biologically active peptides from the parotoid and rostral glands. peptide content of secretions from the parotoid and rostral gland of male and female frogs every month for 3 years by HPLC and found one component that exists only in male secretions. This peptide comprised 25 amino acid residues. Behavioral test revealed that it attracts female frogs but not conspecific males or females of different species, L. caerulea. This peptide pheromone designated splendipherin increases in concentrations during the breeding season up to 1% of total peptide content of the glandular secretion.

Pheromones and Reptiles• The chemoreception system is heavily used by lizard and snake species because they

produce chemical secretions that are often deposited in urine, feces or substrate scents in order to attract mates . The chemicals in the scent or trailing marks of lizards and snakes may give information on sex, body size, or age, which can then be used by females to detect areas that are scent marked by preferred potential males . Scents are detected in two ways, through olfaction or airborne cues through the nostril or vomerolfaction where substrates are accessed through the forked tongue and vomeronasal system .

• The vomeronasal system is the driving force in sexual behavior of snakes . Chemical cues of snakes are often incapable of diffusing through air as they are large epidermal lipids therefore they must use tongue-flicking techniques to determine characteristics of potential mates.

Role in Mate ChoiceSnakesIn most species of snakes, sexual behavior is characterized by the male investigating the female with rapid tongue flicking to her dorsal surface. The male then presses his chin onto the female’s dorsal surface, rubbing forward towards her head while continuing to rapidly tongue-flick.The occurrence of these two behaviors simultaneously is characteristic of courtship and sex behavior. Noble (1937) first hypothesized that males detected an odor or pheromone in the skin of female garter snakes that elicited male courtship.

The nonvolatile long-chain saturated and monounsaturated methyl ketones identified are the sex pheromone of the redsided garter snake and these compounds elicit membrane responses from vomeronsasal sensory neurons . This is the first identified pheromone in Class Reptilia.

Birds and Pheromones• Birds generally have small olfactory bulbs and a

poorly developed sense of smell, and are considered to be the animals in which the chemosignals play the minimal role.

• Pheromonal signals serve as the primary basis for species-specific mating cues in many vertebrates, but in birds it is acoustic signals that play the most important role.

• Intraspecific chemosignals are known in some seabirds, especially burrow- or crevice-nesting auklets and petrels that breed in large colonies and are often nocturnal on land. Crested Auklets secrete a distinctive scent closely associated with courtship and important in sexual selection.

• Individually distinctive odours of petrels allow them to identify their own nest and can have a significant role in social relationships.

• Perception of scents is detected by the presence of the odorant receptors (ORs) located in the nasal epithelium, at the ciliated surface of olfactory sensory neurons, representing the initial step of a transduction cascade that leads to odor detection.

Pheromones in Mammalian Reproduction

• Priming pheromones• In mammals priming pheromones play an important role in reproduction by influencing

the onset of puberty and timing of the estrus cycle,and by their ability to interfare with pregnancy.

• Acceleration of Puberty: Puberty must occur at an appropriate time in an individual development to promote maximum reproductive efficiency.In several species,priming pheromones have an important role in regulating the onset of puberty.This is shown to result from male stimulation.In most urine seems to convey the signal.

• Females placed in cages recently inhabited by males and in cages containing a resident male for lengths of time varying from 10 minutes to 24 hours showed accelerated puberty.The presence of male induced an earlier onset of puberty than to the chemical signal is required for the effect.

• Ovarian Cyclicity:Once puberty has been reached ,chemo signals continue to play a role in regulating ovarian function in several species. When female rats live together ,the onset of estrus becones synchronous.The synchrony of ovarian cycle in grouped rats was shown to result from pheromonal cpmmunication showed that females sharing a recirculated air supply show ovarian synchrony similar to grouped females. It shows that grouped females rat produce two cheomosignal,one that phase –advances ovulation and thus shortens the cycle, and one that delays ovulation and thereby lengthens the cycle.

• Pregnancy block :Even when pregnant ,the female mouse is still subject to pheromonal stimulation from a male. Work by bruce showed that a high proportion of new mated female mice separated from stud males and exposed to strange males terminate their pregnancy and promptly return to estrus. These block to pregnancy or the bruce effect is effective in twenty percent to eighty percent of females depending on strangeness of the male . Males of a different genetics strains induce the greatest block to pregnancy.

• Reason of block:The stud male fails to block pregnancy because the female has a memory of his odor. The intact vomeronasal organ is necessary for the pregnancy block effect. Neuroendocrine and endocrine changes associated with pregnancy block has been reviewed by Marchlewska-Koj. She summarizes evidence showing that pheromonal stimuli from an alien male decreases prolactin release

• which prevents corpus luteum formation and consequent

• a decreased the concentration of progesteron is the final link in the hormonal change of events resulting in failure of implantation.

Human Pheromones and Reproduction

• The main producers of human pheromones are the apocrine glands located in the axillae and pubic region. The high concentration of apocrine glands found in the armpits led to the term ‘axillary organ’, which is considered an independent ‘organ’ of human odour production.

• Apocrine glands develop in the embryo, but become functional only with the onset of puberty. At sexual maturation, they produce steroidal secretions derived from 16-androstenes ( androstenone and androstenol ) via testosterone, and as such, the concentrations of several 16-androstenes is significantly higher in males .

• Freshly produced apocrine secretions are odourless but are transformed into the odorous androstenone and androstenol by aerobic coryeform bacteria. In the vagina, aliphatic acids (referred to as copulins) are secreted and their odour varies with the menstrual cycle.

• Pheromone detection:In most mammals, a specialised region of the olfactory system called the vomeronasal organ (VNO), also referred to as ‘Jacobson’s organ’ is responsible for pheromone detection.The VNO is located above the hard palate on both sides of the nasal septum and it is lined with receptor cells whose axons project to the accessory olfactory bulb, which sends its projects to the hypothalamic nuclei . Pheromones can thus potentially influence sexual and reproductive behaviours and endocrine function via the HPA axis.

• In particular,it is assumed that primer pheromones trigger the secretion of GnRH from the hypothalamus, which in turn triggers the release of gonadotropins (LH, FSH) from the pituitary gland.

• These gonadotropins influence gonadal hormone secretion, e.g. follicle maturation in the ovaries in females, testosterone and sperm production in males.

• It is now possible to isolate and manufacture synthetic human pheromones and such compounds are often used in research as they are relatively easy to make, convenient to store, and easy to apply.

Conclusion Pheromones are referred to as ‘ecto-hormones’ as they are chemical messengers that are emitted into the environment from the body where they can then activate specific physiological or behavioural responses in other individuals of the same species. A specialised region of the olfactory system called the vomeronasal organ (VNO), also referred to as ‘Jacobson’s organ’ is responsible for pheromone detection in all vertebrates. It is lined with receptor cells whose axons project to the accessory olfactory bulb, which sends its projects to the hypothalamic nuclei . Pheromones can thus potentially influence sexual and reproductive behaviours and endocrine function via the HPA axis.