Chemosensitive neurons within the area postrema of the rat

It is demonstrated that some neurons within the area postrema, if not all, are responsive to glucose or sodium ions applied topically by means of microelectro-osmotic techniques. Glucose-responsive neurons displayed a marked decrease in the discharge rate in response to the topical application of glucose. Two different types of sodium-responsive neurons were observed; one was characterized by increasing the frequency of the discharges responding to microiontophoretic application of Na+, while the other showed the opposite response by decreasing the discharge rate in response to the same stimulation. They may serve enteroceptors in response to changes in the glucose or sodium concentrations of cerebrospinal fluid (CSF) or blood.