Actions of isoproterenol on amygdalar neurons in vitro

The effects of isoproterenol (Iso) on neuronal excitability and synaptic transmission were investigated in slices of rat amygdala using intracellular recording technique. Most basolateral amygdala (BLA) neurons fired rapid action potentials which slowed or accommodated in response to a long-duration depolarizing current pulse. The end of depolarizing pulse was followed by an after-hyperpolarization (AHP). Superfusion of Iso (15 microM) reversibly blocked both the AHP and accommodation resulting in more action potential firing. Forskolin, a direct activator of adenylyl cyclase, mimicked the effect of Iso suggesting the involvement of cyclic adenosine-3',5'-monophosphate (c-AMP). Iso also produced a long-lasting enhancement of excitatory postsynaptic potential (EPSP). Pretreatment of the slices with propranolol completely prevented the effect of Iso confirming the mediation by beta-adrenergic receptors. These results suggest that the combined blockade of AHP and persistent potentiation of EPSP together form the cellular basis for the memory-enhancing effect of Iso in the amygdala.