Modulation of synaptic transmission by presynaptic receptors in the cerebral cortex

Lead Research Organisation: MRC Anatomical Neuropharmacology Unit

Abstract

Synaptic transmission is the process by which nerve cells signal to one another. At chemical synapses a cleft of extracellular space separates presynaptic and postsynaptic neurons and a change in the membrane voltage of the presynaptic cell leads to the release of chemical messengers (neurotransmitters) from its nerve terminals. The transmitter diffuses across the synaptic cleft and binds to specific proteins (receptors) on the postsynaptic membrane. The receptors carry out an effector function within the target cell, usually opening ion channels through which current flows activating or inhibiting the postsynaptic neuron. Interestingly, receptors are present not only in the postsynaptic membrane, but also in the presynaptic membrane, strategically placed close to the sites where the transmitter is released. Therefore, the activation of presynaptic receptors powerfully controls the amount of transmitter released and in this way modulates the communication between neurons. Many neuroactive drugs including useful medicines selectively interact with presynaptic receptors and therefore their study is of considerable clinical interest. Current work is directed towards better understanding of the functional diversity of expression of presynaptic receptors in cortical and sub-cortical areas of the brain by using in vitro approaches that allow high resolution of analysis.

Technical Summary

The information transfer from one neuron to another is modulated by specific receptors present at presynaptic axon terminals. Main goals of my programme are: (i) Elucidate the mechanisms of neuronal communication amongst neurons of the hippocampus and amygdala, in both normal and neuropathological conditions; (ii) Discover novel cellular and molecular mechanisms of receptor-mediated modulation of transmitter release; (iii) Analyse the action of presynaptic GABAB receptors and metabotropic glutamate receptors II/III, at synapses between the entorhinal cortex and hippocampus, and hippocampal interneurons.||Although synaptic vesicles are proven to be biochemically rather uniform, some differences in the expression of specific presynaptic proteins between glutamatergic and GABAergic synapses have begun to emerge. Therefore, we believe that distinct sets of synapses are endowed with a specific set of presynaptic proteins associated with the release machinery and are uniquely affected by presynaptic neuromodulators. Furthermore, we investigate the net physiological output induced by activation of receptors expressed at different membrane domains of GABAergic cells of the hippocampus and amygdala. At a cellular level of analysis, bearing in mind the importance of understanding the role of specific classes of neurons embedded in defined neuronal networks, we also examined the cellular integration of short and long range excitatory and inhibitory inputs.||We use electrophysiological techniques and recording from single neurons and from synaptically-coupled pairs of neurons. Synaptic strength is compared in control and after manipulations of presynaptic function including: a) modulation of the electrical activity of the pre- and postsynaptic cells, b) genetic expression or inhibition, kinase- and toxin-mediated stimulation or inhibition, receptor-ligand activation or inhibition. Combined physiological, pharmacological and anatomical approaches is used in most projects. Following the neuropharmacological experiments, the slices containing the recorded neurones labelled with dyes are fixed and processed for correlated light and electron microscope techniques, in order to identify the cell types recorded and the ultrastructural localisation of the presynaptic receptors tested physiologically. Two main in vitro preparations are used: acute slices of hippocampus and amygdala, and hippocampal organotypic slice cultures, which are long-term surviving explants developing a tissue organisation close to that observed in situ.||This work provides a high-resolution analysis of the divergence of the expression of different presynaptic ligand-gated channels and release machinery associated proteins at different cortical synapses. Importantly, a deeper understanding of presynaptic receptor physiology and neuropharmacology of GABAergic synapses will hopefully lead to a new generation of innovative drugs useful for the treatment of epilepsy, depression and anxiety disorders, and also to more accurately targeted therapeutic approaches.

Publications

10 25 50
 
Description MRC Collaborative Project Grant (Probing presynaptic receptor function with two-photon uncaging, two-photon Ca2+ imaging and two-photon photobleaching)
Amount £440,000 (GBP)
Funding ID G0600368 
Organisation Medical Research Council (MRC) 
Sector Public
Country United Kingdom
Start  
 
Description Marie Curie Contract MEIF-CT-2006-024841
Amount £109,207 (GBP)
Organisation Marie Sklodowska-Curie Actions 
Sector Charity/Non Profit
Country Global
Start 08/2006 
End 07/2008
 
Description GAD-65 transgenic mice 
Organisation Hungarian Academy of Sciences (MTA)
Department Institute of Experimental Medicine
Country Hungary 
Sector Academic/University 
PI Contribution Electrophysiology and anatomy of GAD-65 green fluorescent protein positive neurons of the amygdala.
Collaborator Contribution Generation of GAD-65 green fluorescent protein mice where GABAergic cells to visualise GABAergic cells under fluorescent illumination.
Impact PMID: 17916608
 
Description SNAP-25 
Organisation Medical Research Council (MRC)
Department MRC Functional Genomics Unit
Country United Kingdom 
Sector Academic/University 
PI Contribution Electrophysiological analysis of the snap-25 mutants.
Collaborator Contribution Molecular, anatomical, functional and behavioral analysis of the brain in the presynaptic proteins snap-25 mutants.
Impact PMID: 17283335
Start Year 2006
 
Description amygdala interneurons_2 
Organisation University of Münster
Department Institute of Physiology I
Country Germany 
Sector Academic/University 
PI Contribution Electrophysiology and anatomy of neurons of rodent amygdala.
Collaborator Contribution Anatomy, immunohistochemistry and electron microscopy of neurons of rodent amygdala.
Impact PMID: 17916608 PMID: 25972162 PMID: 26402610
 
Description amygdala interneurons_2 
Organisation University of Washington
Department Department of Pharmacology
Country United States 
Sector Academic/University 
PI Contribution Electrophysiology and anatomy of neurons of rodent amygdala.
Collaborator Contribution Anatomy, immunohistochemistry and electron microscopy of neurons of rodent amygdala.
Impact PMID: 17916608 PMID: 25972162 PMID: 26402610
 
Description calcium imaging 
Organisation University College London
Department Institute of Neurology
Country United Kingdom 
Sector Academic/University 
PI Contribution Electrophysiological, pharmacological and anatomical results.
Collaborator Contribution Name of the collaborators: Prof. D Kullmann, Prof. DA Rusakov. Two photon calcium imaging of selected hippocampal neurons, such as dentate granule cells and GABAergic cells, in control and during pharmacological treatments.
Impact PMID: 18596171 PMID: 19052205
 
Description hippocampal interneurons 
Organisation University of Oxford
Department MRC Anatomical Neuropharmacology Unit
Country United Kingdom 
Sector Academic/University 
PI Contribution Anatomy and electrophysiology of hippocampal GABAergic cells in vitro.
Collaborator Contribution Anatomy and electrophysiology of hippocampal GABAergic cells in vivo.
Impact PMID: 18367092
 
Description Science open days 
Form Of Engagement Activity Participation in an open day or visit at my research institution
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Schools
Results and Impact I participate and in one year organised (2009) to the Science open day held annually at the MRC, Anatomical Neuropharmacology Unit, Oxford. Typical visit includes: 5-8 schools, 50-120 pupils, 6-14 teachers. The pupils are given opportunity in hands on experience.

Positive feedback from schools and participants.
Year(s) Of Engagement Activity 2006,2007,2008,2009,2010,2011,2012,2013,2014,2015