Electrophysiologically identified presynaptic mechanisms underlying amylinergic modulation of area postrema neuronal excitability in rat brain slices

Abstract

Amylin, which is co-secreted together with insulin by pancreatic beta cells, is considered to be an important peptide hormone involved in the control of feeding behavior and energy homeostasis. Although the area postrema has been implicated to be a primary target of amylin, there are no studies of the mechanisms by which amylin may alter the excitability of area postrema neurons. To investigate the mechanism for amylinergic modulation of neuronal excitability, we performed perforated patch-clamp recordings from area postrema neurons in rat brainstem slices. Amylin-induced changes in excitatory responses, such as increases in the frequency of mEPSCs (miniature excitatory postsynaptic currents) and changes in the amplitude distribution of mEPSCs, were found in cells not displaying the hyperpolarization-activated cation current (Ih). Area postrema cells displaying Ih did not respond to amylin application. Inhibitory responses to amylin were never encountered. Bath application of CNQX (AMPA type glutamate receptor antagonist) abolished the effects of amylin. Depolarization of cells during amylin application was sufficient at 1μM to cause action potential discharge by responding cells. We conclude that amylin receptors are located mostly on presynaptic glutamatergic terminals connecting to the area postrema neurons not displaying Ih and amylin concentrations can increase glutamate release enough to cause cell firing. Modulation of amylinergic activity may offer a novel target to influence food intake and obesity.