Whole-brain circuit dissection in free-moving animals reveals cell-specific mesocorticolimbic networks

Abstract

The ability to map the functional connectivity of discrete cell types in the intact mammalian brain during behavior is crucial for advancing our understanding of brain function in normal and disease states. We combined designer receptor exclusively activated by designer drug (DREADD) technology and behavioral imaging with μPET and [ 18 F]fluorodeoxyglucose (FDG) to generate whole-brain metabolic maps of cell-specific functional circuits during the awake, freely moving state. We have termed this approach DREADD-assisted metabolic mapping (DREAMM) and documented its ability in rats to map whole-brain functional anatomy. We applied this strategy to evaluating changes in the brain associated with inhibition of prodynorphin-expressing (Pdyn-expressing) and of proenkephalin-expressing (Penk-expressing) medium spiny neurons (MSNs) of the nucleus accumbens shell (NAcSh), which have been implicated in neuropsychiatric disorders. DREAMM revealed discrete behavioral manifestations and concurrent engagement of distinct corticolimbic networks associated with dysregulation of Pdyn and Penk in MSNs of the NAcSh. Furthermore, distinct neuronal networks were recruited in awake versus anesthetized conditions. These data demonstrate that DREAMM is a highly sensitive, molecular, high-resolution quantitative imaging approach. IntroductionThe mammalian brain is a complex organ with billions of heterogeneous cells whose local and long-range functional connections regulate behavior and physiology. Traditional approaches used for mapping functional brain anatomy do not provide information on long-range, global (i.e., intact whole brain) circuits. Recently, optogenetics was coupled with in vivo functional MRI (fMRI) and allowed, for what we believe is the first time, assessment of functional anatomy of discrete cell types in living animals (1, 2). fMRI technology, however, relies on nonmolecular, indirect measures of neuronal activity (i.e., neurovascular coupling) and is limited in its applicability to anesthetized or immobilized animals. Importantly, a recent study showed that light delivery in the absence of optogenetic stimulation induced strong local fMRI responses in the stimulated site (3). To overcome these limitations, we combined designer receptor exclusively activated by designer drug (DREADD) technology (4), which allows remote in vivo control of cell-specific firing (5), together with behavioral imaging using μPET and [ 18 F]fluorodeoxyglucose (FDG) to measure regional brain glucose metabolism, which is a direct marker of brain function (6-9). This approach, termed DREADD-assisted metabolic mapping (DREAMM), was used to map functional brain anatomy associated with inhibiting the activity of prodynorphin-expressing (Pdyn-expressing) and of proenkephalin-expressing (Penk-expressing) medium spiny neurons (MSNs) in the medial nucleus accum-

Elucidation of The Behavioral Program and Neuronal Network Encoded by Dorsal Raphe Serotonergic Neurons

“…In contrast, decreases in FDG uptake were observed in the periaqueductal gray, anterior olfactory, and medial and central thalamic areas (MT and CT, respectively) ( Figure 5a). CNO was previously shown to be devoid of non-specific effects on FDG uptake (Michaelides et al, 2013). The specificity of DREAMM responses to the behaviors observed in the open field after acute hM3Dq activation were validated using both within-subject (scanned after vehicleadministered open-field sessions) and between-subject controls (Slc6a4-EGFP mice), which did not show changes in time spent in the center of the open field in response to acute DRN serotonin neuron activation.…”

“…Thirty minutes later, mice were anesthetized with 1.5% isoflurane, placed in a prone position on the bed of an R4 microPET rodent scanner (Siemens Medical Solutions), and scanned using a 20-min static acquisition protocol. Scanning procedures, image processing, and analysis were performed as previously described (Michaelides et al, 2010(Michaelides et al, , 2013.…”

“…In an effort to map profiles associated with acute and chronic DRN serotonin neuronal activation in the open field with regional brain responses, we used DREADD-assisted metabolic mapping (DREAMM), which enables whole-brain circuit dissection in response to cell-type-specific signaling manipulations in behaving rodents (Michaelides et al, 2013). Concurrent with a reduction in time spent in the center of the open field, DREAMM revealed that acute hM3Dq activation of DRN 5-HT neurons led to increased metabolic activity (ie, FDG uptake) in the cingulate cortex (Cg2), the right inferior colliculus (IC), the right piriform (Pir), and primary somatosensory (SC), and motor cortices (MC) (Figure 5a).…”

“…We discovered that short-and long-term activation of DRN 5-HT neurons induces both similar and divergent behavioral programs, which mimic multiple actions of antidepressant drugs. In parallel, we associated these behavioral changes with alterations in whole brain metabolic activity using a newly developed technology (eg, DREADD Assisted Metabolic Mapping (DREAMM); Michaelides et al, 2013;Michaelides and Hurd, 2015).…”

Impaired periamygdaloid-cortex prodynorphin is characteristic of opiate addiction and depression

“…This technique, entitled DREAMM, integrates viral-mediated designer receptors exclusively activated by designer drugs (DREADD) (26) and metabolic mapping using a direct marker of brain metabolism, [ 18 F]Fluorodeoxyglucose (FDG) and μPET imaging. (27).…”