Transposition and Intermingling of Galphai2 and Galphao afferences into single vomeronasal glomeruli in the Madagascan lesser Tenrec Echinops telfairi.

The vomeronasal system (VNS) mediates pheromonal communication in
mammals. From the vomeronasal organ, two populations of sensory
neurons, expressing either Galphai2 or Galphao proteins, send
projections that end in glomeruli distributed either at the rostral
or caudal half of the accessory olfactory bulb (AOB), respectively.
Neurons at the AOB contact glomeruli of a single subpopulation. The
dichotomic segregation of AOB glomeruli has been described in
opossums, rodents and rabbits, while Primates and Laurasiatheres
present the Galphai2-pathway only, or none at all (such as apes,
some bats and aquatic species). We studied the AOB of the
Madagascan lesser tenrec Echinops telfairi (Afrotheria:
Afrosoricida) and found that Galphai2 and Galphao proteins are
expressed in rostral and caudal glomeruli, respectively. However,
the segregation of vomeronasal glomeruli at the AOB is not
exclusive, as both pathways contained some glomeruli transposed
into the adjoining subdomain. Moreover, some glomeruli seem to
contain intermingled afferences from both pathways. Both the
transposition and heterogeneity of vomeronasal afferences are
features, to our knowledge, never reported before. The organization
of AOB glomeruli suggests that synaptic integration might occur at
the glomerular layer. Whether intrinsic AOB neurons may make
synaptic contact with axon terminals of both subpopulations is an
interesting possibility that would expand our understanding about
the integration of vomeronasal pathways.