Glutamatergic Mechanisms in Glioblastoma and Tumor-Associated Epilepsy

The progression of glioblastomas is associated with a variety of neurological impairments, such as tumor-related epileptic seizures. Seizures are not only a common comorbidity of glioblastoma but often an initial clinical symptom of this cancer entity. Both, glioblastoma and tumor-associated epilepsy are closely linked to one another through several pathophysiological mechanisms, with the neurotransmitter glutamate playing a key role. Glutamate interacts with its ionotropic and metabotropic receptors to promote both tumor progression and excitotoxicity. In this review, based on its physiological functions, our current understanding of glutamate receptors and glutamatergic signaling will be discussed in detail. Furthermore, preclinical models to study glutamatergic interactions between glioma cells and the tumor-surrounding microenvironment will be presented. Finally, current studies addressing glutamate receptors in glioma and tumor-related epilepsy will be highlighted and future approaches to interfere with the glutamatergic network are discussed.

Dual signaling of Wamide myoinhibitory peptides through a peptide-gated channel and a GPCR in Platynereis

Neuropeptides commonly signal by metabotropic G-protein coupled receptors (GPCRs). In some mollusks and cnidarians, RFamide neuropeptides mediate fast ionotropic signaling by peptide-gated ion channels that belong to the DEG/ENaC family. Here we describe a neuropeptide system with a dual mode of signaling by both a peptide-gated channel and a GPCR. We identified and characterised a peptide-gated channel in the marine annelid Platynereis dumerilii that is specifically activated by Wamide myoinhibitory peptides derived from the same proneuropeptide. The myoinhibitory peptide-gated ion channel (MGIC) belongs to the DEG/ENaC family and is paralogous to RFamide-gated channels. Platynereis myoinhibitory peptides also activate a previously described GPCR, MAG. We measured the potency of all Wamides on both MGIC and MAG and identified peptides that preferentially activate one or the other receptor. Analysis of a single-cell transcriptome resource indicates that MGIC and MAG signal to distinct target neurons. The identification of a Wamide-gated channel suggests that peptide-gated channels are more diverse and widespread in animals than previously appreciated. The possibility of neuropeptide signaling by both ionotropic and metabotropic receptors to different target cells in the same organism highlights an additional level of complexity in peptidergic signaling networks.

Receiving the Synaptic Message

Ionotropic and metabotropic receptors differ in their speed of action, the variety of effects produced after ligand-binding, and in the number of types present in the nervous system. The participation of two ionotropic glutamate receptors in synaptic plasticity is thought to be the cellular basis of learning. The actions of acetylcholine on nicotinic acetylcholine receptors present at the neuromuscular junction are described. The pharmacological profile of the GABAA receptor, central to most neural functions, is introduced. The properties of metabotropic receptors that are coupled to G proteins, termed G protein-coupled receptors (GPCRs), are detailed. Three canonical second-messenger systems through which GPCRs act are briefly described. An introduction to clinical pharmacology focused on how drugs acting on muscarinic and adrenergic receptors produce peripheral and central psychotropic effects is provided. Finally, the role of connexins and gap junctions in myelination and hearing is introduced.

Seeing the evidence: learning from images in neuroscience

SummaryThe cover of this issue heralds a series of articles in which a visual image derived from cell biology or neuroscience is used to promote understanding of the biological mechanisms fundamental to psychiatry. ‘Images in neuroscience’ are intended to demonstrate the structures and mechanisms of the basic building blocks of brain function, including ionotropic and metabotropic receptors, second messenger systems, specialised ion channels, transmitter pathways, transporters, neuroglial function, and the complex mechanisms within cells that are being revealed, as new genetic associations for mental illness are discovered.