Neurochemistry and Molecular Biology of Maternal Behavior

Conclusions

In the previous chapter, when describing the neuroanatomy of maternal behavior, we focussed on the circuitry that connects the sensory inputs for nurturing to the neural pathways for behavior by linking to centers for reward and for overcoming avoidance. The neurochemistry of maternal behavior appears to follow the same strategy, building on generic pathways with endocrine functions, and via the combined influences of gonadal steroids, pup stimuli, and experience, shaping these for maternal care. As we have seen, neuropeptides appear especially important in this process. Oxytocin and prolactin operate within discrete hypothalamic/limbic circuits and appear exquisitely sensitive to estrogen, suckling, and experience. These are neurochemical systems that are largely “targetregulated”, meaning that local changes in receptors confer highly specific changes in the response to endogenous peptides. As estrogen appearsto regulate these receptors, one can consider oxytocin (and perhaps prolactin) receptors as transducers of the steroid changes we described in Chapter 2. that is, we have two early steps in a multistep process: The steroid changes of pregnancy lead to local changes in brain neuropeptide receptors. The next steps are less clear. Increased oxytocin and prolactin neurotransmission appears necessary for maternal behavior, but what about increased dopamine release, changes in GABA or glutamate, or activation of fos B? Clearly, we are at the beginning of these studies with many leads but few links. Going forward, we will need to consider that (a) neuropeptide systems are notoriously species-specific (InseI & Young, 2000), (b) new candidates will likely emerge from gene discovery tools, and (c) neurotransmitters do not work in isolation, but via a combinatorial process that integrates thousands of signals in each neuron and perhaps millions of neurons for each circuit.