title: Control of Amygdala Circuits by 5-HT Neurons via 5-HT and Glutamate Cotransmission.
abstract: The serotonin (5-HT) system and the amygdala are key regulators of emotional behavior. Several lines of evidence suggest that 5-HT transmission in the amygdala is implicated in the susceptibility and drug treatment of mood disorders. Therefore, elucidating the physiological mechanisms through which midbrain 5-HT neurons modulate amygdala circuits could be pivotal in understanding emotional regulation in health and disease. To shed light on these mechanisms, we performed patch-clamp recordings from basal amygdala (BA) neurons in brain slices from mice with channelrhodopsin genetically targeted to 5-HT neurons. Optical stimulation of 5-HT terminals at low frequencies (≤1 Hz) evoked a short-latency excitation of BA interneurons (INs) that was depressed at higher frequencies. Pharmacological analysis revealed that this effect was mediated by glutamate and not 5-HT because it was abolished by ionotropic glutamate receptor antagonists. Optical stimulation of 5-HT terminals at higher frequencies (10-20 Hz) evoked both slow excitation and slow inhibition of INs. These effects were mediated by 5-HT because they were blocked by antagonists of 5-HT2Aand 5-HT1Areceptors, respectively. These fast glutamate- and slow 5-HT-mediated responses often coexisted in the same neuron. Interestingly, fast-spiking and non-fast-spiking INs displayed differential modulation by glutamate and 5-HT. Furthermore, optical stimulation of 5-HT terminals did not evoke glutamate release onto BA principal neurons, but inhibited these cells directly via activation of 5-HT1Areceptors and indirectly via enhanced GABA release. Collectively, these findings suggest that 5-HT neurons exert a frequency-dependent, cell-type-specific control over BA circuitry via 5-HT and glutamate co-release to inhibit the BA output.SIGNIFICANCE STATEMENTThe modulation of the amygdala by serotonin (5-HT) is important for emotional regulation and is implicated in the pathogenesis and treatment of affective disorders. Therefore, it is essential to determine the physiological mechanisms through which 5-HT neurons in the dorsal raphe nuclei modulate amygdala circuits. Here, we combined optogenetic, electrophysiological, and pharmacological approaches to study the effects of activation of 5-HT axons in the basal nucleus of the amygdala (BA). We found that 5-HT neurons co-release 5-HT and glutamate onto BA neurons in a cell-type-specific and frequency-dependent manner. Therefore, we suggest that theories on the contribution of 5-HT neurons to amygdala function should be revised to incorporate the concept of 5-HT/glutamate cotransmission.
authors.affiliation: Department of Pharmacology, University of Oxford, Oxford, OX1 3QT United Kingdom.
authors.forename: Ayesha
authors.identifier: 0000-0002-8348-1799
authors.initials: A
authors.lastname: Sengupta
authors.affiliation: Medical Research Council Brain Network Dynamics Unit, Department of Pharmacology, University of Oxford, Oxford, OX1 3TH United Kingdom.
authors.forename: Marco
authors.identifier: 0000-0002-7005-3453
authors.initials: M
authors.lastname: Bocchio
authors.affiliation: Department of Experimental Psychology, University of Oxford, Oxford, OX1 3UD United Kingdom.
authors.forename: David M
authors.initials: DM
authors.lastname: Bannerman
authors.affiliation: Department of Pharmacology, University of Oxford, Oxford, OX1 3QT United Kingdom, trevor.sharp@pharm.ox.ac.uk marco.capogna@biomed.au.dk.
authors.forename: Trevor
authors.identifier: 0000-0001-7434-9713
authors.initials: T
authors.lastname: Sharp
authors.affiliation: Medical Research Council Brain Network Dynamics Unit, Department of Pharmacology, University of Oxford, Oxford, OX1 3TH United Kingdom, trevor.sharp@pharm.ox.ac.uk marco.capogna@biomed.au.dk.|Department of Biomedicine, University of Aarhus, 8000 Aarhus C, Denmark, and.|The Danish Research Institute of Translational Neuroscience (DANDRITE), Nordic EMBL Partnership for Molecular Medicine, Department of Biomedicine, University of Aarhus, 8000 Aarhus C, Denmark.
authors.forename: Marco
authors.identifier: 0000-0002-2742-5485
authors.initials: M
authors.lastname: Capogna
mesh_terms: D000679:Amygdala / Q000166:cytology*; D000818:Animals; D000831:Animals, Newborn; D000075402:Channelrhodopsins; D018683:Excitatory Amino Acid Agents / Q000494:pharmacology; D005260:Female; D018756:GABA Antagonists / Q000494:pharmacology; D018698:Glutamic Acid / Q000378:metabolism*; D008164:Luminescent Proteins / Q000235:genetics / Q000378:metabolism; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D009415:Nerve Net / Q000187:drug effects / Q000502:physiology*; D009474:Neurons / Q000378:metabolism*; D010879:Piperazines / Q000494:pharmacology; D011725:Pyridines / Q000494:pharmacology; D011985:Receptors, Serotonin / Q000378:metabolism; D012701:Serotonin / Q000378:metabolism* / Q000494:pharmacology; D012702:Serotonin Antagonists / Q000494:pharmacology; D050486:Serotonin Plasma Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism; D009435:Synaptic Transmission / Q000187:drug effects / Q000235:genetics
chemical_list: D000075402:Channelrhodopsins; D018683:Excitatory Amino Acid Agents; D018756:GABA Antagonists; D008164:Luminescent Proteins; D010879:Piperazines; D011725:Pyridines; D011985:Receptors, Serotonin; D012702:Serotonin Antagonists; D050486:Serotonin Plasma Membrane Transport Proteins; C493231:Slc6a4 protein, mouse; D012701:Serotonin; D018698:Glutamic Acid; C090413:N-(2-(4-(2-methoxyphenyl)-1-piperazinyl)ethyl)-N-(2-pyridinyl)cyclohexanecarboxamide
keywords: amygdala; electrophysiology; interneuron; optogenetics; serotonin; synaptic transmission