Excitatory effects of atrial natriuretic peptide on rat subfornical organ neurons in vitro

Atrial natriuretic peptide (ANP) was applied in the solution bathing the rat subfornical organ in vitro and the responses of 170 neurons recorded extracellularly. A significant change in firing rate was found in 20% of neurons tested at a concentration of 1 × 10 −10 M. At higher concentrations 45% of neurons responded. The response was usually a brief excitation. Tests of a range of concentrations on each of 6 neurons showed the maximal excitation was attained at 5 × 10 −9 M. The excitatory responses were generally (41/51) not affected by synaptic blockade indicating a direct action of ANP. The excitatory effect of ANP upon subfornical neurons can be contrasted with the generally inhibitory effect of changes in osmotic pressure. Neurons excited by ANP also responded to 5% osmotic pressure changes in the proportions (28/43) expected from the known response rate to osmotic pressure changes (66%). The commonest pattern of response (16/28) was excitation by hyper-osmotic solutions and inhibition by hypo-osmotic solutions.