Table 1.

Nonapeptides and receptors that play a role in reproductive behaviour.

Molecule or structure	Description
Oxytocin	A nonapeptide associated with reproduction and social bonding. Thought to be most important in females.
Mesotocin	The bird/reptile homolog of oxytocin.
Isotocin	The anamniote homolog of oxytocin.
Arginine Vasopressin (AVP)	A nonapeptide associated with aggression, space use, and reproduction. Thought to be most important in males.
Arginine Vasotocin (AVT)	The non-mammalian homolog of AVP.
V1a	A cell membrane receptor for AVT and AVP that is commonly associated with social behaviour.
AVP circuit	A collection of neurons that project axons and deliver AVP or AVT to another set of neurons in a different region in the brain.

Note: Each nonapeptide is pleiotropic and has various physiological functions in other organ systems.