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M.a TERESA MIRAS PORTUGAL AN. R. ACAD. NAC. FARM.

pseudogen sin funcionalidad y por lo tanto el órgano vomeronasal es un vestigio
carente de función. Recientes estudios indican que la captación de feromonas en
primates se realiza a través del epitelio olfativo y el bulbo olfativo principal e in-
cluso en otros mamíferos esta estructura parece mediar en algunas respuestas es-
pecie específicas.

Palabras clave: Bulbo olfativo accesorio.—Canales TRPC2.—Diacilglicerol.—
Diacilglicerol quinasa.—Feromonas.—Lipocalinas.—Órgano vomeronasal.—Recep-
tores vomeronasales.—V1R.—V2R.

ABSTRACT

Mammalian pheromone receptors: survival and sexuality

In 1995 Catherine Dulac and Richard Axel discovered a new gene family
corresponding to the pheromone receptors. They were members of the seven
transmembrane helix coupled to G proteins. Since then, new genes have been
clonned and grouped according their sequence homology in two main families of
vomeronasal receptors the V1R and the V2R. They exhibit different distribution
pattern at the vomeronasal epithelium, where they are coupled to different G
proteins. The chemical nature of the mammalian pheromones is very diverse and
can associate with proteins called lipocalins to reach the vomeronasal organ. The
transduction mechanisms of pheromone receptors, V1R and V2R, require
respectively a Gi and a Go proteins, to further activate a phospholipase C, the
PLCß2. This enzyme hydrolyses the phosphatidyl inositol located at the plasma
membrane originating phosphatidylinositol triphosphate and diacylglycerol.
Diacylglycerol is an endogenous ligand that opens the TRPC2 channel (Transient
Receptor Potential Channel), allowing the entrance of cations, mostly Ca2+ y Na+.
The membrane depolarisation at the vomeronasal neuron originates the action
potential that is sent to the accessory olfactory bulb by the axon, which in a
different way as those from the main olfactory epithelia, do not organise the axonal
prolongations and reach the mitral neurones in a disperse way, without forming a
glomerular structure, afterwards the mitral cells send their axons to the limbic
system and other cerebral structures related to aggressive behaviour and mating.
It is relevant to underline that in monkeys from the old world and primates
including humans, the vomeronasal organ is only a vestigial structure without
function. The reason relies on the TRPC2 gene, which is a pseudo gene, without
physiological function. Recent experimental approaches have demonstrated that
the sensing of some pheromonal signals in these species, and also in mammals
with a functional vomeronasal organ, can be carried out by the main olfactory
epithelia through the main olfactory bulb. This structure being also connected to
the hypothalamus, where neurones releasing LHRH can control sexual behaviour.
These data confirm the broad possibilities of signalling through pheromones and
that much effort is still required to fully understand their possibilities.

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