Pheromonal communication: vomeronasal organ or main olfactory epithelium?
Házi dolgozat
Cikkolvasó szeminárium
Kiss Georgina
SZIE-ÁOTK Alkalmazott Zoológus Szak
2008/09. oszi félév
The basic of the mammalian lifestyle is the maternal care, which led to the
complex social systems. The animals can use different cues to recognize individuals
from the same species, which cues can give informations due to the visual recognition
or vocal cues, but for most mammals the olfaction is the dominant sense to detect
these informations. So we can say that their behaviour is influenced by chemosensory
signals, called pheromones. The older definition of pheromones came from Karlson
and Luscher in 1959: „substances, which are secreted to the outside by
an individual and received by a second individual of the same species, in which
they release a mental process”. In recent studies this definition has
changes, like that a pheromone is detected by the vomeronasal organ (VNO), it
is non-volatile and detection is unconsciously [Kelliher 2007.]. In addition
there is differences between the four groups of the pheromones: the primer pheromones
can initate physiological responses that can be long lasting, for instance the
chemical cues in the male urine can induce puberty and make changes in the oestrus
cycle in female mice. The releaser pheromones can activate an immediate response,
which is usually behavioural, for instance the response in sows for the androsteron
is an immobile mating pose. The signaler pheromones give social informations
about the releaser, for instance the reproductive status, location in the hierarchy
or either individual identity. The modulator pheromones make changes in behaviour
indirectly, for instance these are important to decide whether the individual
feel sympathy to an other individual or not.
The dual olfactory system in which the VNO and the main olfactory epithelium
(MOE) are appear to be evolved in the common anchestor of amphibians and tetrapods
[Swaney and Keverne 2008.]. In amphibians the requirements of the detection
of pheromones are different from the terrestrial animals, of course, because
they spend the bigger or the whole part of their life in water. The key to detect
the pheromones in water is that the pheromones must be soluble in water, so
it appears that the amphibian pheromones are polar proteins or peptides. In
mammals the VNO is lined just with microvillar receptor neurons and the MOE
just with ciliated receptor neurons, while the amphibian VNO is lined with microvillar
receptor neurons, and in salamanders the MOE is lined with ciliated receptor
neurons and with a mixture of ciliated and microvillar receptor neurons in the
other amphibians which can leave the water for shorter or longer periods. In
addition fishes have no VNO, and their MOE is lined with a mixture of ciliated
and microvillar receptor neurons. Despite the lack of the VNO in fishes, the
expression of the receptor shows similarity with mammals: the olfactory-like
receptors are expressed in ciliated neurons and the vomeronasal-like receptors
are expressed in microvillar neurons. These changes in the evolution of the
receptor neurons suggest that the VNO evolved in the common aquatic anchestor
of amphibians and amniotes, and it is not an adaptation to life in land. This
suggest is underpined by the fact that the amphibians have the same dual olfactory
system with the other tetrapods, and the neural pathways of the VNO appear to
be the same, too.
The terrestrial mammals use volatile molecules to communicate and recognize
each other [Brennan and Kendrick 2006.]. The complex social odours are detected
by the MOE, and there is a strong argument that the individuality signals depend
on the individual genotype through the MHC class I proteins. For instance the
mice can take differences between the urines of different mice, and humans can
discriminate the odours from different individuals. The VNO has been shown to
convey the information about the MHC class I protein ligands, for instance in
the pregnancy block effect in mice. Selective lesions of the VNO stopped this
effect, while the lesions of the MOE did not make changes in behaviour in this
effect. In the male mice urine there are other important proteins, for instance
lipocains, which are dependent from the testosterone, and take an advertisment
about the presence of a reproductivly active male. So these proteins act role
in male aggressive behaviour and regulating the female reproductive behaviour,
including the indication the puberty and synchronization of the oestrus cycle.
The complex odours contain volatile and relatively non-volatile compounds, and
the MOE appears to detect the volatile signals, while the VNO detect the non-volatile
signals. This fact means that the VNO and the MOE are specialized for detecting
different types of stimuli, but recent studies show that there is overlap in
the chemosignals are detected by both of the VNO and the MOE. Learning the odours
can be started in the uterus, which can be underpined with separating the oversprings
from the mother after the birth for a few hours. Mice and hamsters can choose
after it their mother and as adults they choose a mate from an other MHC class,
which effect appears to be dependent from the MOE and the releasing of the noradrenaline
in the main olfactory bulb (MOB). The ewe’s and the sheeps have to use
more punctual cues and detecting to take differences between the individuals,
because the lambs stand up immediately after the birth. The sheeps need about
2-4 weeks to learn which ewe is their mother, but because of the sheeps try
to suckle from other ewes, the ewes have to learn in a shorter time, that which
sheep is their’s, because of the decrease of lost energy. They need just
2-4 hours to learn the odours of their newborn lambs, which is dependent the
hormonal changes after the birth and the vaginocerval stimulation, which increases
to release the noradrenalin in the MOB. In contrast the pregnancy block effect
and to recognize that which male they mated with are depend on the VNO in female
mice, although the luteotropic effect of male explosure is mediated by the MOE
in the following 7 days after mating. It suggests, that there is synergistically
processes between the VNO and the MOE.
While most mammals have the dual olfactory systems, there is no VNO in marine
mammals, bats, catarrhine primates [Swaney and Keverne 2008.]. The lack of the
VNO in marine mammals is maybe because of the constitution of the habitat they
live in: maybe they can detect so difficulty the soluble pheromones in the water
filled with ions and other soluble chemicals, in contrast the amphibians, which
live in clear freshwater. The VNO-lacking in bats is may the result of their
special locator organ, and the habitat of air. In catarrhine primates the inactivation
become from the occur of the trichomacy, which led to use vision cues not the
olfaction in the social life. Instead the humans have no functional VNO, there
is some effects led to controversy. For instance the odours of a woman who is
in ovulatory phase in the oestrus cycle have been shown to make changes in the
oestrus cycle in other women, or women usually choose a man from different MHC
class.
References:
K.R. Kelliher 2007: The combined role of the main olfactory and vomeronasal systems in social communication in mammals. Hormones and Behaviour vol 52. 561-570
P.A. Brennan and K.M. Kendrick 2006.: Mammalian social odours: attraction and individual recognition. Phil. Trans. R. Soc. B. vol 361. 2061-2078.
W.T. Swaney and B.K. Keverne 2008.: The evolution of pheromonal communication.
Behavioural Brain Research, doi:10.1016/j.bbr.2008.09.039.