Arboreal Squirrels Have a Segregated Vomeronasal System With a Regressed Type 2 Receptor (V2R)-Domain.

Area of Science:

• Neuroscience
• Olfactory System Research
• Mammalian Chemosensation

Background:

• The vomeronasal system (VNS) detects species-specific chemicals using V1R and V2R receptors coupled with Gαi2 and Gαo proteins, respectively.
• Mammalian VNS organization varies, with rodents typically exhibiting segregated V1R/Gαi2 and V2R/Gαo neuron projections to the accessory olfactory bulb (AOB).
• California ground squirrels are an exception, showing a V1R/Gαi2 AOB, deviating from typical rodent segregated patterns.

Purpose of the Study:

• To investigate the VNS organization in arboreal squirrels (Pallas's and Eurasian red squirrels).
• To compare the distribution of V1R/Gαi2 and V2R/Gαo expressing neurons in squirrel AOBs.
• To determine if V2R expression is reduced in the Sciuridae family.

Main Methods:

• Immunohistochemical analysis of accessory olfactory bulbs (AOBs) from Pallas's and Eurasian red squirrels.
• Utilized antibodies against Gαi2 and Gαo proteins to identify receptor expression domains.
• Examined the vomeronasal nerve (VNL), glomerular (GL), external cellular (ECL), and internal cellular (ICL) layers of the AOB.

Main Results:

• Both Gαi2- and Gαo-positive regions were detected in the VNL and GL of all studied squirrels.
• Squirrels can likely detect nonvolatile cues via V2R, similar to other rodents.
• A significant portion of the AOB corresponded to the V1R/Gαi2 domain, indicating unequal V1R/Gαi2 and V2R/Gαo domain sizes.

Conclusions:

• The VNS of Pallas's and Eurasian red squirrels exhibits a predominantly V1R/Gαi2 organization.
• V2R expression appears reduced in the squirrel family Sciuridae.
• This study highlights a unique VNS organization within rodents, impacting pheromone detection and communication strategies.