The most recent issue of Nature Neuroscience contains a truly amazing study by the Thomas Insel-group. Insel and his colleagues have for many years studied pair-formation in prairie voles. Earlier, they have demonstrated that dopamine transmission within the nucleus accumbens (Nacc) facilitates partner-preference formation (i.e., that the infusion of dopamine into Nacc makes male pairie voles seek out female mates). In this new paper, they demonstrate that the rostal shell of Nacc actually contains two different dopaminergic receptors that perform functionally different jobs. One type, called D2, facilitates the approach behavior associated with the formation of a pair-bond. The other, D1, maintains that bond, by antagonizing the activity of the D2-receptors. This “faithfulness” is expressed behaviourally by the male voles figthing off other female voles than the partner. Crucially, D1-receptors are upregulated after the pair-bond has been formed. In other words: the male vole’s brain changes with having a relationship – it, figuratively speaking, becomes faithful. Thus, the behavioural process of finding a mate, establishing a relationship and keeping it going depends upon a complicated molecular process in parts of the prairie vole’s reward system. This result opens at least two exiting new avenues of ressearch: (1) Will we find the same functional system in the human brain? What is the genetic reason for a vole having more or less D1-receptors, i.e. being able to form long lasting pair-bonds?
I personally wouldn’t be surprised if Insel one day receives the Nobel prize. Being the director of NIMH shouldn’t hurt!