Phosphorylation of ERK/MAP kinase is required for long-term potentiation in anatomically restricted regions of the lateral amygdala in vivo.

We have previously shown that the extracellular signal-regulated kinase/mitogen-activated protein kinase (ERK/ MAPK) is transiently activated in anatomically restricted regions of the lateral amygdala (LA) following Pavlovian fear conditioning and that blockade of ERK/MAPK activation in the LA impairs both fear memory consolidation and long-term potentiation (LTP) in the amygdala, in vitro. The present experiments evaluated the role of the ERK/MAPK signaling cascade in LTP at thalamo-LA input synapses, in vivo. We first show that ERK/MAPK is transiently activated/phosphorylated in the LA at 5 min, but not 15 or 60 min, after high-frequency, but not low-frequency, stimulation of the auditory thalamus. ERK activation induced by LTP-inducing stimulation was anatomically restricted to the same regions of the LA previously shown to exhibit ERK regulation following fear conditioning. We next show that intra-LA infusion of U0126, an inhibitor of ERK/MAPK activation, impairs LTP at thalamo-LA input synapses. Collectively, results demonstrate that ERK/MAPK activation is necessary for synaptic plasticity in anatomically defined regions of the LA, in vivo.

Memory consolidation of Pavlovian fear conditioning requires nitric oxide signaling in the lateral amygdala.

Nitric oxide (NO) has been widely implicated in synaptic plasticity and memory formation. In studies of long-term potentiation (LTP), NO is thought to serve as a 'retrograde messenger' that contributes to presynaptic aspects of LTP expression. In this study, we examined the role of NO signaling in Pavlovian fear conditioning. We first show that neuronal nitric oxide synthase is localized in the lateral nucleus of the amygdala (LA), a critical site of plasticity in fear conditioning. We next show that NO signaling is required for LTP at thalamic inputs to the LA and for the long-term consolidation of auditory fear conditioning. Collectively, the findings suggest that NO signaling is an important component of memory formation of auditory fear conditioning, possibly as a retrograde signal that participates in presynaptic aspects of plasticity in the LA.

Pavlovian fear conditioning regulates Thr286 autophosphorylation of Ca2+/calmodulin-dependent protein kinase II at lateral amygdala synapses.

Ca2+/calmodulin-dependent protein kinase II (CaMKII) plays a critical role in synaptic plasticity and memory formation in a variety of learning systems and species. The present experiments examined the role of CaMKII in the circuitry underlying pavlovian fear conditioning. First, we reveal by immunocytochemical and tract-tracing methods that alphaCaMKII is postsynaptic to auditory thalamic inputs and colocalized with the NR2B subunit of the NMDA receptor. Furthermore, we show that fear conditioning results in an increase of the autophosphorylated (active) form of alphaCaMKII in lateral amygdala (LA) spines. Next, we demonstrate that intra-amygdala infusion of a CaMK inhibitor, 1-[NO-bis-1,5-isoquinolinesulfonyl]-N-methyl-l-tyrosyl-4-phenylpiperazine, KN-62, dose-dependently impairs the acquisition, but not the expression, of auditory and contextual fear conditioning. Finally, in electrophysiological experiments, we demonstrate that an NMDA receptor-dependent form of long-term potentiation at thalamic input synapses to the LA is impaired by bath application of KN-62 in vitro. Together, the results of these experiments provide the first comprehensive view of the role of CaMKII in the amygdala during fear conditioning.

The group I metabotropic glutamate receptor mGluR5 is required for fear memory formation and long-term potentiation in the lateral amygdala.

The group I metabotropic glutamate receptor subtype mGluR5 has been shown to play a key role in the modulation of synaptic plasticity. The present experiments examined the function of mGluR5 in the circuitry underlying Pavlovian fear conditioning using neuroanatomical, electrophysiological, and behavioral techniques. First, we show using immunocytochemical and tract-tracing methods that mGluR5 is localized to dendritic shafts and spines in the lateral nucleus of the amygdala (LA) and is postsynaptic to auditory thalamic inputs. In electrophysiological experiments, we show that long-term potentiation at thalamic input synapses to the LA is impaired by bath application of a specific mGluR5 antagonist, 2-methyl-6-(phenyle-thynyl)-pyridine (MPEP), in vitro. Finally, we show that intra-amygdala administration of MPEP dose-dependently impairs the acquisition, but not expression or consolidation, of auditory and contextual fear conditioning. Collectively, the results of this study indicate that mGluR5 in the LA plays a crucial role in fear conditioning and in plasticity at synapses involved in fear conditioning.