Quantitative analysis of glutamatergic innervation of the mouse dorsal raphe nucleus using array tomography

Department of Anesthesiology, Perioperative, and Pain Medicine, Children's Hospital Boston, Boston, Massachusetts 02115, USA.
The Journal of Comparative Neurology (Impact Factor: 3.51). 12/2011; 519(18):3802-14. DOI: 10.1002/cne.22734
Source: PubMed

ABSTRACT Serotonin (5-hydroxytryptamine, 5-HT) containing neurons located in the dorsal raphe nucleus (DR) comprise the main source of forebrain 5-HT and regulate emotional states in normal and pathological conditions including affective disorders. However, there are many features of the local circuit architecture within the DR that remain poorly understood. DR neurons receive glutamatergic innervation from different brain areas that selectively express three different types of the vesicular glutamate transporter (VGLUT). In this study we used a new high-resolution imaging technique, array tomography, to quantitatively analyze the glutamatergic innervation of the mouse DR. In the same volumetric images, we studied the distribution of five antigens: VGLUT1, VGLUT2, VGLUT3, the postsynaptic protein PSD-95, and a marker for 5-HT cells, the enzyme tryptophan hydroxylase (TPOH). We found that all three populations of glutamatergic boutons are present in the DR; however, the density of paired association between VGLUT2 boutons and PSD-95 was ≈2-fold higher than that of either VGLUT1- or VGLUT3-PSD-95 pairs. In addition, VGLUT2-PSD-95 pairs were more commonly found associated with 5-HT cells than the other VGLUT types. These data support a prominent contribution of glutamate axons expressing VGLUT2 to the excitatory drive of DR neurons. The current study also emphasizes the use of array tomography as a quantitative approach to understand the fine molecular architecture of microcircuits in a well-preserved neuroanatomical context.

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    Frontiers in Neural Circuits 08/2014; 8:105. DOI:10.3389/fncir.2014.00105
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    ABSTRACT: The dorsal raphe nucleus (DR) controls forebrain serotonin neurotransmission to influence emotional states. GABA neurotransmission in the DR has been implicated in regulating sleep/wake states and influencing anxiety and aggression. To gain insight into how GABA regulates DR activity, we analyzed the organization of both GABA and glutamate axons in the rat DR using a high-resolution immunofluorescence technique, array tomography, as well as EM. This analysis revealed that a third or more of GABA-containing axons are organized in synaptic triads with a glutamatergic axon and a common postsynaptic target. Electrophysiological recordings showed that GABA has the capacity to presynaptically gate glutamate release in the DR through a combination of GABA-A and GABA-B receptor-mediated effects. Thus, GABA-glutamate synaptic triads are a common feature of the network architecture of the DR with the potential to regulate excitation of the nucleus.
    Proceedings of the National Academy of Sciences 09/2013; DOI:10.1073/pnas.1304505110

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