This laboratory has utilised a number of arterially perfused in situ preparations for studying brainstem-spinal cord regulation of both the cardiovascular and respiratory systems (Chizh et al. 1998; Pickering et al. 2003; Potts et al. 2005). In this study, we have tested the integrity of hypothalamic structures in regulating sympathetic activity in a decorticate arterially perfused rat preparation. Male Wistar rats (70-90 g) were anaesthetised deeply with halothane and decorticated; the thalamus was destroyed also. Animals were arterially perfused with a Ringer solution containing Ficoll (1.25%) at 31°C. Recordings of phrenic (PNA) and lumbar sympathetic nerve activities (LSNA) as well as heart rate and perfusion pressure were monitored. In order to test the integrity of hypothalamic structures, changes in perfusate osmolality were made. Following a switch from an isotonic Ringer solution (e.g. 290 mOsmol/kg/water) to a hyperosmotic perfusate (320 mOsmol/kg/water) for 40 s, we observed an increase in LSNA (78±36%, n=8), which persisted until the isotonic perfusate was reintroduced. To demonstrate a potential role for hypothalamic structures in mediating this sympathoexcitation to increased osmolaltiy, we transected the neuraxis at the precollicular level. After the transection the sympathoexcitation evoked with the hyperosmotic perfusate was reduced in both magnitude and duration (10±5%, n=3). In conclusion, we have demonstrated that the arterially perfused decorticate preparation demonstrates appropriate responses to salt loading as seen in vivo (Scrogin et al. 1999) and that these responses are likely dependent on hypothalamic structures. We suggest that this preparation is a promising model for future studies for understanding hypothalamic and brainstem mechanisms of homeostatic regulation of blood pressure and volume.