DISSOCIATION OF FOS-LIKE IMMUNOREACTIVITY IN LAMINA TERMINALIS AND MAGNOCELLULAR HYPOTHALAMIC NUCLEI INDUCED BY HYPERNATREMIA

Rats were given either slow (1 h) or rapid (10 min) intravenous infusi ons of either 6 or 12 mmol NaCl/kg body weight. Fos-like immunoreactiv ity (FLI) induced by the infusions was measured in several brain regio ns. The higher dose of NaCl induced FLI in structures of the lamina te rminalis, including organum vasculosum (OVLT) and subfornical organ (S FO), as well as in the magnocellular supraoptic (SON) and paraventricu lar hypothalamic (PVN) nuclei. The lower dose of hypertonic NaCl induc ed FLI in only the SON and PVN. Faster delivery of the solute load ten ded to amplify the FLI in SFO and OVLT. These data confirm and extend previous reports of osmotically-induced FLI in rat brain and demonstra te that the discrepancies between these studies result from different dosage regimens of NaCl. The data are discussed as they relate to the lamina terminalis as a primary osmosensitive region in brain.