To map changes in neuronal activity in the brains of Dahl salt-sensitive (Dahl S) vs. salt-resistant (Dahl R) rats by high-sodium diet, we used immunohistochemical detection of Fra-like proteins as a marker for long-term neuronal activation. Compared with Dahl R rats during regular sodium intake, Dahl S rats showed modestly higher expression of Fra-like immunoreactivity (Fra-LI) in the supraoptic nucleus, anterior hypothalamic area (AHA), central gray, and nucleus of solitary tract (NTS) at 5,6, and 9 wk of age but clearly elevated Fra-LI in the magnocellular part of the paraventricular nucleus (PVN) at 6 wk of age (but not at 5 and 9 wk). In the median preoptic nucleus (MnPO) Fra-LI was lower at 9 wk of age and no differences were observed in the parvocellular PVN and subfornical organ in Dahl S vs. Dahl R rats on regular sodium intake. Compared with Dahl S rats on a regular-sodium diet, Dahl S rats on a high-sodium diet from 4 to 9 wk of age had significantly increased blood pressure and experienced transient activation of magnocellular PVN and MnPO and virtually no changes in the activity of the parvocellular PVN, AHA, and NTS. In contrast, Dahl R rats showed marked activation in the magnocellular PVN after 1 and 2 wk on a high-sodium diet compared with Dahl R rats on a regular-sodium diet. The present study demonstrates that Dahl S rats show differential activation of brain areas participating in regulation of osmotic and cardiovascular homeostasis during development of sodium-sensitive hypertension.