Development of the mouse prefrontal cortex-dorsal raphe nucleus synaptic circuitry

MARIANO SOIZA REILLY; PATRICIA GASPAR

Chicago

Congreso; 45th Meeting of the Society for Neuroscience; 2015

Society for Neuroscience

Theprefrontal cortex (PFC) plays a central role in stress controllability, in partby regulating dorsal raphe nucleus (DRN) neuron?s activity in response tostressors. Additionally, activation of PFC-DRN pathways has an ?antidepressanteffect? that could at least partially explain the beneficial effects of deepbrain stimulation in treatment-resistant depressive patients. Maladaptiveformation/refinement of DRN synaptic circuits could contribute to vulnerabilityto emotional disorders, however it is not known when or how the PFC-DRNsynaptic circuitry is established during postnatal life. We studied the postnataldevelopment of the PFC-DRN pathway using a novel quantitative high-resolutionimmunofluorescence technique called array tomography (AT), which is particularlyuseful to analyze synaptic circuits. AT is a light microscopy-based methodinvolving multiple rounds of immunolabeling and imaging of ultrathin (70 nm)serial sections, and 3D visualization. This allows mapping and quantitativeanalysis of multiple synaptic antigens and their relationships to each other inthe same tissue volume with a nanometer resolution. Because of the relevance ofthe excitatory/inhibitory transmission balance for circuit development, wefocused our study on cortical glutamate synaptic afferents to the DRN (containingthe vesicular transporter type 1, VGLUT1) as well as on other subcortical glutamateand GABAergic synaptic afferents (containing VGLUT2 and glutamate decarboxylase65, respectively). Synaptic boutons were identified by the presence ofsynapsin, and associations with serotonin neurons were analyzed usingtryptophan hydroxylase labeling. We found that at postnatal day 7 both corticaland subcortical glutamate synaptic afferents as well as GABAergic synaptic boutonsare abundantly present in the DRN, often associated with serotonin neurons.These observations indicate that AT represents a unique approach to explore howthe PFC-DRN synaptic circuitry develops, and whether alterations in the early connectivityof this pathway could result in maladaptive mechanisms contributing toneuropsychiatric disorders with a developmental origin.