It's All in the Mind

How do physiological and molecular variation combine to create a range of motivational drives that becomes manifest as a range of behaviors? Champagne et al. report measurements of dopamine in the nucleus accumbens of female rats caring for (licking and grooming) their pups. This region of the brain is known to contribute to motivating behaviors, particularly those that are followed by reward, such as the consumption of food. The increase in dopamine preceded the initiation of licking and grooming acts by the mothers, and the size and duration of the dopamine signal correlated with the duration of the act. Furthermore, mothers previously scored as high or low in licking/grooming (greater than 1 standard deviation from the mean of a normally distributed group) exhibited consistently high or low scores in the dopamine signal and in the density of dopamine receptors in the shell of the nucleus accumbens. Taken together with earlier studies in this series, these results begin to establish a neurochemical basis for individual differences in maternal behavior.
J. Neurosci. 24, 4113 (2004).