The supraoptic nucleus (SON) of the hypothalamus is an important integrative brain structure that co-ordinates responses to perturbations in water balance and regulates maternal physiology through the release of the neuropeptide hormones vasopressin and oxytocin into the circulation. Both dehydration and lactation evoke a dramatic morphological remodelling of the SON, a process known as function-related plasticity. We hypothesise that some of the changes seen in SON remodelling are mediated by differential gene expression, and have thus used microarrays to document global changes in transcript abundance that accompany chronic dehydration in female rats, and in lactation. In situ hydridisation analysis has confirmed the differential expression of 3 of these genes, namely Tumour necrosis factor induced protein 6, Gonadotrophin inducible transcription factor 1 and Ornithine decarboxylase antizyme inhibitor 1. Comparison of differential gene expression patterns in male and female rats subjected to dehydration and in lactating rats has enabled the identification of common elements that are significantly enriched in gene classes with particular functions. Two of these are related to the requirement for increased protein synthesis and hormone delivery in the physiologically stimulated SON (translation initiation factor activity and endoplasmic reticulum-Golgi intermediate compartment respectively), whilst others are consistent with concept of SON morphological plasticity (collagen fibril organisation, extracellular matrix organization and biogenesis, extracellular structure organization and biogenesis and homophilic cell adhesion). We suggest that the genes co-ordinately regulated in the SON as a consequence of dehydration and lactation form a network that mediates the plastic processes operational in the physiologically activated SON.