For mice, getting teary-eyed conveys more than just sentiment. A non-volatile peptide secreted from the eyes of male mice elicits neuronal activity in the vomeronasal organ (VNO) of females, pointing to a new mode of chemical communication between mammals. Kazushige Touhara at the University of Tokyo's Department of Integrated Biosciences says that while most putative mammalian pheromones are volatile substances present in urine, mice also explore the facial region of other individuals during social encounters, which activates neuronal firing in the VNO.
To investigate the source of this activation, Touhara and coauthors measured VNO sensory neuronal activity in mice exposed to various candidate stimuli. Direct contact with adult males or their shaved fur induced a robust response in females. From here, the source was narrowed down to a peptide in secretions from the extraorbital lacrimal gland, which the researchers named exocrine gland secreting peptide (ESP).1 In situ hybridization located the ESP1 receptors on a subset of neurons in the V2R region of the female VNO.
"This is a beautiful story overall," says Frank Zufall at the University of Maryland's School of Medicine. All that it lacks, he suggests, are behavioral data, which Touhara says are in progress.