Raphe neuron as a synaptic hub during development revealed by high-resolution anatomy

GASPAR P; ARGAÑARAZ C*; ARGAÑARAZ C*; ADJIMANN T*; SOIZA REILLY M; ADJIMANN T*; SOIZA REILLY M; GASPAR P

Buenos Aires

Congreso; Latin-American Society for Developmental Biology; 2019

LASDB

The dorsal raphe nucleus (DRN) contains most of brain neurons that synthesize serotonin. This neurotransmitter modulates a wide repertoire of physiological processes including cardiovascular and respiratory functions, sleep, cognition, stress responses and locomotion. Maladaptive changes in the DRNcircuit development could contribute to vulnerability to psychiatric disorders. However, how DRN synaptic circuits are assembled during postnatal development remains poorly understood. We studied the ontogeny of synaptic afferents that modulates DRN neuron´s activity using the high-resolution immunofluorescence technique arraytomography (ATom). ATom involves immunolabeling and imaging of 70 nm serial-sections and 3D reconstruction, allowing quantitative analysis of multiple antigens inthe same tissue volume. Since the excitatory/inhibitory ratio has a role in circuit development, we studied glutamate and GABA synaptic inputs onto DRN neurons. We labeled cortical (VGLUT1+) and subcortical (VGLUT2+) glutamate synapses and GABAergic synapses (GAD65). Synaptic boutons were identified by synapsin labeling, jointly to the presence of postsynaptic protein partners (PSD-95 or gephyrin for glutamate and GABA boutons, respectively). We found that glutamate and GABAergic synapses are abundantly present in the DRN as early as at postnatal day 7. This study highlights the use of ATom to explore developmental circuit alterations contributing to psychiatric disorders with an early origin.