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Positive allosteric modulators (PAMs) of α5GABAA receptors (α5GABAARs) are emerging as potential therapeutics for a range of neuropsychiatric disorders. However, their role in memory processing of healthy animals is not sufficiently examined. We tested the effects of MP-III-022 (1 mg/kg, 2.5 mg/kg and 10 mg/kg), a PAM known to be selective for α5GABAARs and devoid of prominent side-effects, in different behavioral paradigms (Morris water maze, novel object recognition test and social novelty discrimination) and on GABRA5 expression in Wistar rats, 30 min and 24 h after intraperitoneal treatment administration. The lowest dose tested worsened short-term object memory. The same dose, administered two times in a span of 24 h, improved spatial and impaired object and, at a trend level, social memory. The highest dose had a detrimental effect on all types of long-term memory (object memory at a trend level) and short-term spatial memory, but improved short-term object and social memory. Distinct sets of expression changes were detected in both prefrontal cortex and two regions of the hippocampus, but the latter ones could be assessed as more consequential. An increase of GABRA5 mRNA in CA2 occurred in parallel with improvement of object and social, but impairment of spatial memory, while the opposite happened with a trend level change in CA1. Our study demonstrates the variability of the roles of the α5GABAAR based on its level of expression and localization, in dependence on the type and protocol of cognitive tasks, as well as the respective timing of pharmacological modulation and testing.

By decreasing glutamate transmission, mGlu4 receptor positive allosteric modulators (mGlu4-PAM), in combi-nation with levodopa (L-DOPA) may restore the synergy between glutamatergic and dopaminergic transmissions, thus maximizing the improvement of motor function in Parkinson's disease (PD). This study aimed to clarify the effects of foliglurax, a selective mGlu4-PAM, on the loss of bidirectional synaptic plasticity associated with L- DOPA-induced dyskinesia (LID). Behavioral assessments compared dyskinesia intensity in 6-hydroxydopamine (6-OHDA)-lesioned rats treated with L-DOPA or L-DOPA plus foliglurax. In slices from the same rats, patch -clamp techniques were used to examine electrophysiological differences in glutamatergic synapses, evaluating the EPSCs mediated by NMDA and AMPA receptors in striatal spiny projection neurons. High-frequency stim-ulation of corticostriatal fibers was used as long-term potentiation (LTP)-inducing protocol. Conversely, 15 min of low-frequency stimulation was applied to depotentiate LTP. The density of dendritic spines was measured in striatal slices in the same experimental conditions. Our results show that, in corticostriatal slices, foliglurax decreased spontaneous glutamatergic transmission in both sham-operated and 6-OHDA lesioned rats. When co -administered with L-DOPA in 6-OHDA-lesioned rats, foliglurax fully restored dendritic spine density in a dose -dependent manner. Moreover, this co-treatment rescued striatal bidirectional plasticity and attenuated the in-tensity of L-DOPA-induced dyskinesia. This is the first demonstration in an animal model of PD and dyskinesia that a mGlu4 PAM can restore striatal synaptic plasticity.

Transient receptor potential vanilloid 1 (TRPV1) ion channel is a nociceptor critically involved in pain sensation. Direct blockade of TRPV1 exhibits significant analgesic effects but also incurs severe side effects such as hyperthermia, causing failures of TRPV1 inhibitors in clinical trials. In order to selectively target TRPV1 channels that are actively involved in pain-sensing, peptidic positive allosteric modulators (PAMs) based on the high-resolution structure of the TRPV1 intracellular ankyrin-repeat like domain are de novo designed. The hotspot centric approach is optimized for protein design; its usage in Rosetta increases the success rate in protein binder design. It is demonstrated experimentally, with a combination of fluorescence resonance energy transfer (FRET) imaging, surface plasmon resonance, and patch-clamp recording, that the designed PAMs bind to TRPV1 with nanomolar affinity and allosterically enhance its response to ligand activation as it is designed. It is further demonstrated that the designed PAM exhibits long-lasting in vivo analgesic effects in rats without changing their body temperature, suggesting that they have potentials for developing into novel analgesics.

Major depressive disorder (MDD) is the leading cause of disability worldwide and contributes importantly to the global burden of morbidity according to reports from the World Health Organization. Several types of antidepressant medications are used to treat moderate and severe depressive disorders although weeks or even months are required to produce clinical improvement. However, an estimated one third of the patients have inappropriate responses or no response at all to treatment. Hence, finding new, more efficient and rapid-acting antidepressant therapies is urgently needed. The discovery that ketamine produced rapid and sustained antidepressant effects has been the major breakthrough in the field of pharmacotherapy for MDD. Interestingly, studies with rodents have shown that the antidepressant-like effects of ketamine are dependent on the activation of AMPA receptors (AMPARs) because its behavioral action is blocked by AMPAR antagonists. Moreover, the removal of specific AMPAR subunits from birth results in behavioral and neurochemical characteristics relevant to depression. Taken together, these findings suggest that the stimulation of AMPARs may be a useful approach to treat MDD. Preclinical studies have reported that positive allosteric modulators (PAMs) – also known as ampakines or AMPAR potentiators – manifest antidepressant-like effects. These molecules bind allosterically to AMPARs and prolong the duration of AMPAR-mediated responses, theoretically without an overstimulation of excitatory transmission. In this chapter, we will review the most important preclinical data to date on the antidepressant-like effects of AMPA potentiators discussing their potential use as therapeutic tool in the clinic.

Transient receptor potential vanilloid 1 (TRPV1) ion channel is a nociceptor critically involved in pain sensation. Direct blockade of TRPV1 exhibits significant analgesic effects but also incurs severe side effects such as hyperthermia, causing failures of TRPV1 inhibitors in clinical trials. In order to selectively target TRPV1 channels that are actively involved in pain-sensing, peptidic positive allosteric modulators (PAMs) based on the high-resolution structure of the TRPV1 intracellular ankyrin-repeat like domain are de novo designed. The hotspot centric approach is optimized for protein design; its usage in Rosetta increases the success rate in protein binder design. It is demonstrated experimentally, with a combination of fluorescence resonance energy transfer (FRET) imaging, surface plasmon resonance, and patch-clamp recording, that the designed PAMs bind to TRPV1 with nanomolar affinity and allosterically enhance its response to ligand activation as it is designed. It is further demonstrated that the designed PAM exhibits long-lasting in vivo analgesic effects in rats without changing their body temperature, suggesting that they have potentials for developing into novel analgesics.

Major depressive disorder (MDD) is the leading cause of disability worldwide and contributes importantly to the global burden of morbidity according to reports from the World Health Organization. Several types of antidepressant medications are used to treat moderate and severe depressive disorders although weeks or even months are required to produce clinical improvement. However, an estimated one third of the patients have inappropriate responses or no response at all to treatment. Hence, finding new, more efficient and rapid-acting antidepressant therapies is urgently needed. The discovery that ketamine produced rapid and sustained antidepressant effects has been the major breakthrough in the field of pharmacotherapy for MDD. Interestingly, studies with rodents have shown that the antidepressant-like effects of ketamine are dependent on the activation of AMPA receptors (AMPARs) because its behavioral action is blocked by AMPAR antagonists. Moreover, the removal of specific AMPAR subunits from birth results in behavioral and neurochemical characteristics relevant to depression. Taken together, these findings suggest that the stimulation of AMPARs may be a useful approach to treat MDD. Preclinical studies have reported that positive allosteric modulators (PAMs) – also known as ampakines or AMPAR potentiators – manifest antidepressant-like effects. These molecules bind allosterically to AMPARs and prolong the duration of AMPAR-mediated responses, theoretically without an overstimulation of excitatory transmission. In this chapter, we will review the most important preclinical data to date on the antidepressant-like effects of AMPA potentiators discussing their potential use as therapeutic tool in the clinic.

Myelin facilitates the fast transmission of nerve impulses and provides metabolic support to axons. Differentiation of oligodendrocyte progenitor cells (OPCs) and Schwann cell (SC) precursors is critical for myelination during development and myelin repair in demyelinating disorders. Myelination is tightly controlled by neuron-glia communication and requires the participation of a wide repertoire of signals, including neurotransmitters such as glutamate, ATP, adenosine, or gamma-aminobutyric acid (GABA). GABA is the main inhibitory neurotransmitter in the central nervous system (CNS) and it is also present in the peripheral nervous system (PNS). The composition and function of GABA receptors (GABARs) are well studied in neurons, while their nature and role in glial cells are still incipient. Recent studies demonstrate that GABA-mediated signaling mechanisms play relevant roles in OPC and SC precursor development and function, and stand out the implication of GABARs in oligodendrocyte (OL) and SC maturation and myelination. In this review, we highlight the evidence supporting the novel role of GABA with an emphasis on the molecular identity of the receptors expressed in these glial cells and the possible signaling pathways involved in their actions. GABAergic signaling in myelinating cells may have potential implications for developing novel reparative therapies in demyelinating diseases.

Myelin facilitates the fast transmission of nerve impulses and provides metabolic support to axons. Differentiation of oligodendrocyte progenitor cells (OPCs) and Schwann cell (SC) precursors is critical for myelination during development and myelin repair in demyelinating disorders. Myelination is tightly controlled by neuron-glia communication and requires the participation of a wide repertoire of signals, including neurotransmitters such as glutamate, ATP, adenosine, or gamma-aminobutyric acid (GABA). GABA is the main inhibitory neurotransmitter in the central nervous system (CNS) and it is also present in the peripheral nervous system (PNS). The composition and function of GABA receptors (GABARs) are well studied in neurons, while their nature and role in glial cells are still incipient. Recent studies demonstrate that GABA-mediated signaling mechanisms play relevant roles in OPC and SC precursor development and function, and stand out the implication of GABARs in oligodendrocyte (OL) and SC maturation and myelination. In this review, we highlight the evidence supporting the novel role of GABA with an emphasis on the molecular identity of the receptors expressed in these glial cells and the possible signaling pathways involved in their actions. GABAergic signaling in myelinating cells may have potential implications for developing novel reparative therapies in demyelinating diseases.

Myelin facilitates the fast transmission of nerve impulses and provides metabolic support to axons. Differentiation of oligodendrocyte progenitor cells (OPCs) and Schwann cell (SC) precursors is critical for myelination during development and myelin repair in demyelinating disorders. Myelination is tightly controlled by neuron-glia communication and requires the participation of a wide repertoire of signals, including neurotransmitters such as glutamate, ATP, adenosine, or gamma-aminobutyric acid (GABA). GABA is the main inhibitory neurotransmitter in the central nervous system (CNS) and it is also present in the peripheral nervous system (PNS). The composition and function of GABA receptors (GABARs) are well studied in neurons, while their nature and role in glial cells are still incipient. Recent studies demonstrate that GABA-mediated signaling mechanisms play relevant roles in OPC and SC precursor development and function, and stand out the implication of GABARs in oligodendrocyte (OL) and SC maturation and myelination. In this review, we highlight the evidence supporting the novel role of GABA with an emphasis on the molecular identity of the receptors expressed in these glial cells and the possible signaling pathways involved in their actions. GABAergic signaling in myelinating cells may have potential implications for developing novel reparative therapies in demyelinating diseases.

The goal of this project is to determine the underlying synaptic dysfunction in Tuberous Sclerosis Complex (TSC). Scope: TSC is a multi-system genetic disorder with central nervous system dysfunction as a defining factor. The most common clinical features are mental retardation, epilepsy, autism, anxiety and mood disorders. Fragile X syndrome (FXS), another form of inherited mental retardation and autism, shares many of the same molecular and clinical features. Much of the pathophysiology in FXS can be ameliorated through modulation of Group 1 metabotropic glutamate receptors (mGluRs). Since both disorders share key features suggests that they may also share common pathogenic mechanisms. Therefore, determined whether altered synaptic protein synthesis, plasticity and hippocampal-dependent behavior could be ameliorated through modulation of mGluR s in a mouse model of TSC. Major findings: Unlike in FXS where negative modulation of mGluR s has proven beneficial, we found that augmenting mGluR function either genetically or through application of an mGluR5 positive allosteric modulator (PAM) ameliorates several of the synaptic and hippocampal-dependent behavioral deficits observed in a mouse model of TSC. Significance: These results suggest that modulation of mGluR activity with PAMs may be a therapeutic intervention for several of the deficits observed in TSC., The original document contains color images.

The investigation of novel drug targets for treating cognitive impairments associated with neurological and psychiatric disorders remains a primary focus of study in central nervous system (CNS) research. Many promising new therapies are progressing through preclinical and clinical development, and offer the potential of improved treatment options for neurodegenerative diseases such as Alzheimer's disease (AD) as well as other disorders that have not been particularly well treated to date like the cognitive impairments associated with schizophrenia (CIAS). Among targets under investigation, cholinergic receptors have received much attention with several nicotinic agonists (alpha 7 and alpha 4 beta 2) actively in clinical trials for the treatment of AD, CIAS and attention deficit hyperactivity disorder (ADHD). Both glutamatergic and serotonergic (5-HT) agonists and antagonists have profound effects on neurotransmission and improve cognitive function in preclinical experiments with animals; some of these compounds are now in proof-of-concept studies in humans. Several histamine H3 receptor antagonists are in clinical development not only for cognitive enhancement, but also for the treatment of narcolepsy and cognitive deficits due to sleep deprivation because of their expression in brain sleep centers. Compounds that dampen inhibitory tone (e.g., GABA(A) alpha 5 inverse agonists) or elevate excitatory tone (e.g., glycine transporter inhibitors) offer novel approaches for treating diseases such as schizophrenia. AD and Down syndrome. In addition to cell surface receptors, intracellular drug targets such as the phosphodiesterases (PDEs) are known to impact signaling pathways that affect long-term memory formation and working memory. Overall, there is a genuine need to treat cognitive deficits associated with many neuropsychiatric conditions as well as an increasingly aging population.

The investigation of novel drug targets for treating cognitive impairments associated with neurological and psychiatric disorders remains a primary focus of study in central nervous system (CNS) research. Many promising new therapies are progressing through preclinical and clinical development, and offer the potential of improved treatment options for neurodegenerative diseases such as Alzheimer's disease (AD) as well as other disorders that have not been particularly well treated to date like the cognitive impairments associated with schizophrenia (CIAS). Among targets under investigation, cholinergic receptors have received much attention with several nicotinic agonists (alpha 7 and alpha 4 beta 2) actively in clinical trials for the treatment of AD, CIAS and attention deficit hyperactivity disorder (ADHD). Both glutamatergic and serotonergic (5-HT) agonists and antagonists have profound effects on neurotransmission and improve cognitive function in preclinical experiments with animals; some of these compounds are now in proof-of-concept studies in humans. Several histamine H3 receptor antagonists are in clinical development not only for cognitive enhancement, but also for the treatment of narcolepsy and cognitive deficits due to sleep deprivation because of their expression in brain sleep centers. Compounds that dampen inhibitory tone (e.g., GABA(A) alpha 5 inverse agonists) or elevate excitatory tone (e.g., glycine transporter inhibitors) offer novel approaches for treating diseases such as schizophrenia. AD and Down syndrome. In addition to cell surface receptors, intracellular drug targets such as the phosphodiesterases (PDEs) are known to impact signaling pathways that affect long-term memory formation and working memory. Overall, there is a genuine need to treat cognitive deficits associated with many neuropsychiatric conditions as well as an increasingly aging population.