Ligand-gated ion channels involved in the modulation of synaptic strength are the AMPA, kainate, and NMDA glutamate receptors. Small molecules that potentiate AMPA receptor currents relieve cognitive deficits caused by neurodegenerative diseases such as Alzheimer’s disease and show promise in the treatment of depression. Previously, there has been limited understanding of the molecular mechanism of action for AMPA receptor potentiators. Here we present cocrystal structures of the glutamate receptor GluR2 S1S2 ligand-binding domain in complex with aniracetam [1-(4-methoxybenzoyl)-2-pyrrolidinone] or CX614 (pyrrolidino-1,3-oxazino benzo-1,4-dioxan-10-one), two AMPA receptor potentiators that preferentially slow AMPA receptor deactivation. Both potentiators bind within the dimer interface of the nondesensitized receptor at a common site located on the twofold axis of molecular symmetry. Importantly, the potentiator binding site is adjacent to the "hinge" in the ligand-binding core "clamshell" that undergoes conformational rearrangement after glutamate binding. Using rapid solution exchange, patch-clamp electrophysiology experiments, we show that point mutations of residues that interact with potentiators in the cocrystal disrupt potentiator function. We suggest that the potentiators slow deactivation by stabilizing the clamshell in its closed-cleft, glutamate-bound conformation.

Molecular adaptations are believed to contribute to the mechanism of action of antipsychotic drugs (APDs). We attempted to establish common gene regulation patterns induced by chronic treatment with APDs.

Responses to threat-related stimuli are influenced by conscious and unconscious processes, but the neural systems underlying these processes and their relationship to anxiety have not been clearly delineated. Using fMRI, we investigated the neural responses associated with the conscious and unconscious (backwardly masked) perception of fearful faces in healthy volunteers who varied in threat sensitivity (Spielberger trait anxiety scale). Unconscious processing modulated activity only in the basolateral subregion of the amygdala, while conscious processing modulated activity only in the dorsal amygdala (containing the central nucleus). Whereas activation of the dorsal amygdala by conscious stimuli was consistent across subjects and independent of trait anxiety, activity in the basolateral amygdala to unconscious stimuli, and subjects’ reaction times, were predicted by individual differences in trait anxiety. These findings provide a biological basis for the unconscious emotional vigilance characteristic of anxiety and a means for investigating the mechanisms and efficacy of treatments for anxiety.

Dopamine (DA) receptor-mediated signal transduction and gene expression play a central role in many brain disorders from schizophrenia to Parkinson’s disease to addiction. While trying to evaluate the role of L-type Ca2+ channels in dopamine D1 receptor-mediated phosphorylation of the transcription factor cyclic AMP response element-binding protein (CREB), we found that activation of dopamine D1 receptors alters the properties of L-type Ca2+ channel inhibitors and turns them into facilitators of Ca2+ influx. In D1 receptor-stimulated neurons, L-type Ca2+ channel blockers promote cytosolic Ca2+ accumulation. This leads to the activation of a molecular signal transduction pathway and CREB phosphorylation. In the absence of dopamine receptor stimulation, L-type Ca2+ channel blockers inhibit CREB phosphorylation. The effect of dopamine on L-type Ca2+ channel blockers is dependent on protein kinase A (PKA), suggesting that protein phosphorylation plays a role in this phenomenon. Because of the adverse effect of activated dopamine receptors on L-type Ca2+ channel blocker action, the role of L-type Ca2+ channels in the dopamine D1 receptor signal transduction pathway cannot be assessed with pharmacological tools. However, with antisense technology, we demonstrate that L-type Ca2+ channels contribute to D1 receptor-mediated CREB phosphorylation. We conclude that the D1 receptor signal transduction pathway depends on L-type Ca2+ channels to mediate CREB phosphorylation.

In contrast to our increasingly detailed understanding of how synaptic plasticity provides a cellular substrate for learning and memory, it is less clear how a neuron’s voltage-gated ion channels interact with plastic changes in synaptic strength to influence behavior. We find, using generalized and regional knockout mice, that deletion of the HCN1 channel causes profound motor learning and memory deficits in swimming and rotarod tasks. In cerebellar Purkinje cells, which are a key component of the cerebellar circuit for learning of correctly timed movements, HCN1 mediates an inward current that stabilizes the integrative properties of Purkinje cells and ensures that their input-output function is independent of the previous history of their activity. We suggest that this nonsynaptic integrative function of HCN1 is required for accurate decoding of input patterns and thereby enables synaptic plasticity to appropriately influence the performance of motor activity.

Addictive drugs such as amphetamine and cocaine stimulate the dopaminergic system, activate dopamine receptors and induce gene expression throughout the striatum. The signal transduction pathway leading from dopamine receptor stimulation at the synapse to gene expression in the nucleus has not been fully elucidated. Here, we present evidence that D1 receptor stimulation leads to phosphorylation of the transcription factor Ca2+ and cyclic AMP response element binding protein (CREB) in the nucleus by means of NMDA receptor-mediated Ca2+ signaling. Stimulation of D1 receptors induces the phosphorylation of Ser897 on the NR1 subunit by protein kinase A (PKA). This phosphorylation event is crucial for D1 receptor-mediated CREB phosphorylation. Dopamine cannot induce CRE-mediated gene expression in neurons transfected with a phosphorylation-deficient NR1 construct. Moreover, stimulation of D1 receptors or increase in cyclic AMP levels leads to an increase in cytosolic Ca2+ in the presence of glutamate, but not in the absence of glutamate, indicating the ability of dopamine and cyclic AMP to facilitate NMDA channel activity. The recruitment of the NMDA receptor signal transduction pathway by D1 receptors may provide a general mechanism for gene regulation that is fundamental for mechanisms of drug addiction and long-term memory.

Enkephalin modulates striatal function, thereby affecting motor performance and addictive behaviors. The proenkephalin gene is also used as a model to study cyclic AMP-mediated gene expression in striatal neurons. The second messenger pathway leading to proenkephalin expression demonstrates how cyclic AMP pathways are synchronized with depolarization. We show that cyclic AMP-mediated regulation of the proenkephalin gene is dependent on the activity of L-type Ca2+ channels. Inhibition of L-type Ca2+ channels blocks forskolin-mediated induction of proenkephalin. The Ca2+-activated kinase, Ca2+/calmodulin kinase, as well as the cyclic AMP-activated kinase, protein kinase A (PKA), are both necessary for the induction of the proenkephalin promoter. Similarly, both kinases are needed for the L-type Ca2+ channel-mediated induction of proenkephalin. This synchronization of second messenger pathways provides a coincidence mechanism that gates proenkephalin synthesis in striatal neurons, ensuring that levels are increased only in the presence of activated PKA and depolarization.