SummaryAstrocytes are particularly promising candidates for reprogramming into neurons, as they maintain some of the original patterning information from their radial glial ancestors. However, to which extent the position of astrocytes influences the fate of reprogrammed neurons remains unknown. To elucidate this, we performed stab wound injury covering an entire neocortical column, including the gray matter (GM) and white matter (WM), and targeted local reactive astrocytes via injecting FLEx switch (Cre-On) adeno-associated viral (AAV) vectors into mGFAP-Cre mice. Single proneural factors were not sufficient for adequate reprogramming, although their combination with the nuclear receptor-related 1 protein (Nurr1) improved reprogramming efficiency. Nurr1 and Neurogenin 2 (Ngn2) resulted in high-efficiency reprogramming of targeted astrocytes into neurons that develop lamina-specific hallmarks, including the appropriate long-distance axonal projections. Surprisingly, in the WM, we did not observe any reprogrammed neurons, thereby unveiling a crucial role of region- and layer-specific differences in astrocyte reprogramming.

En route from retina to cortex, visual information passes through the dorsolateral geniculate nucleus of the thalamus (dLGN), where extensive corticothalamic (CT) feedback has been suggested to modulate spatial processing. How this modulation arises from direct excitatory and indirect inhibitory CT feedback pathways remains enigmatic. Here we show that in awake mice, retinotopically organized cortical feedback sharpens receptive fields (RFs) and increases surround suppression in the dLGN. Guided by a network model indicating that widespread inhibitory CT feedback is necessary to reproduce these effects, we targeted the visual sector of the thalamic reticular nucleus (visTRN) for recordings. We found that visTRN neurons have large receptive fields, show little surround suppression, and exhibit strong feedback-dependent responses to large stimuli. These features make them an ideal candidate for mediating feedback-enhanced surround suppression in the dLGN. We conclude that cortical feedback sculpts spatial integration in dLGN, likely via recruitment of neurons in visTRN..

The neurotransmitter dopamine acts on the subventricular zone (SVZ) to regulate both prenatal and postnatal neurogenesis, in particular through D(3) receptor (D(3) R) subtype. In this study, we explored the cellular mechanism(s) underlying D(3) R-mediated cell proliferation and tested if systemic delivery of a D(3) R agonist would induce SVZ multipotent neural stem/precursor cell (NSC/NPC) proliferation in vivo. We found that treatment with the D(3) R agonist, 7-OH-DPAT, enhances cell proliferation in a dose-dependent manner in cultured SVZ neurospheres from wild-type, but not D(3) R knock-out mice. Furthermore, D(3) R activation also stimulates S-phase and enhances mRNA and protein levels of cyclin D1 in wild-type neurospheres, a process which requires cellular Akt and ERK1/2 signaling. Moreover, chronic treatment with low dose 7-OH-DAPT in vivo increases BrdU(+) cell numbers in the adult SVZ, but this effect was not seen in D(3) R KO mice. Additionally, we probed the cell type specificity of D(3) R agonist-mediated cell proliferation. We found that in adult SVZ, GFAP(+) astrocytes, type-B GFAP(+) /nestin(+) and type-C EGF receptor (EGFR(+) )/nestin(+) cells express D(3) R mRNA, but type-A Doublecortin (Dcx)(+) neuroblasts do not. Using flow cytometry and immunofluorescence, we demonstrated that D(3) R activation increases GFAP(+) type-B and EGFR(+) type-C cell numbers, and the newly divided Dcx(+) type-A cells. However, BrdU(+) /Dcx(+) cell numbers were decreased in D(3) R KO mice compared to wildtype, suggesting that D(3) R maintains constitutive NSC/NPCs population in the adult SVZ. Overall, we demonstrate that D(3) R activation induces NSC/NPC proliferation through Akt and ERK1/2 signaling and increases the numbers of type-B and -C NSC/NPCs in the adult SVZ.

The function of the D3 dopamine (DA) receptor remains ambiguous largely because of the lack of selective D3 receptor ligands. To investigate the function and intracellular signaling of D3 receptors, we established a PC‐12/hD3 clone, which expresses the human D3 DA receptor in a DA producing cell line. In this model, we find that the D3 receptor functions as an autoreceptor controlling neurotransmitter secretion. Pre‐treatment with 3,6a,11, 14‐tetrahydro‐9‐methoxy‐2 methyl‐(12H)‐isoquino[1,2‐b] pyrrolo[3,2‐f][1,3] benzoxanzine‐1‐carboxylic acid, a D3 receptor preferring agonist, dose‐dependently suppressed K+‐evoked [3H]DA release in PC‐12/hD3 cells but not in the control cell line. This effect was prevented by D3 receptor preferring antagonists GR103691 and SB277011‐A. Furthermore, activation of D3 receptors significantly inhibits forskolin‐induced cAMP accumulation and leads to transient increases in phosphorylation of cyclin‐dependent kinase 5 (Cdk5), dopamine and cAMP‐regulated phosphoprotein of Mr 32 000 and Akt. Because we observed differences in Cdk5 phosphorylation as well as Akt phosphorylation after DA stimulation, we probed the ability of Cdk5 and phosphatidylinositol‐3 kinase (PI3K) to influence DA release. Cdk5 inhibitors, roscovitine, or olomoucine, but not the PI3K inhibitor wortmannin, blocked the D3 receptor inhibition of DA release. In a complimentary experiment, over‐expression of Cdk5 potentiated D3 receptor suppression of DA release. Pertussis toxin, 3‐[(2,4,6‐trimethoxyphenyl)methylidenyl]‐indolin‐2‐one and cyclosporine A also attenuated D3 receptor‐mediated inhibition of DA release indicating that this phenomenon acts through Gi/oα and casein kinase 1, and phosphatase protein phosphatase 2B (calcineurin), respectively. In support of previous data that D3 DA receptors reduce transmitter release from nerve terminals, the current results demonstrate that D3 DA receptors function as autoreceptors to inhibit DA release and that a signaling pathway involving Cdk5 is essential to this regulation.

20En route from retina to cortex, visual information travels through the dorsolateral geniculate nucleus of the thalamus (dLGN), where extensive cortico-thalamic (CT) feedback has been suggested to modulate spatial processing. How this modulation arises from direct excitatory and indirect inhibitory CT feedback components remains enigmatic. We show that in awake mice topographically organized cortical feedback modulates spatial integration in dLGN by sharpening receptive fields (RFs) and increasing surround suppression. Guided by a network model revealing wide-scale inhibitory CT feedback necessary to reproduce these effects, we targeted the visual sector of the thalamic reticular nucleus (visTRN) for recordings. We found that visTRN neurons have large receptive fields, show little surround suppression, and have strong feedback-dependent responses to large stimuli, making them an ideal candidate for mediating feedback-enhanced surround suppression in dLGN. We conclude that cortical feedback sculpts spatial integration in dLGN, likely via recruitment of neurons in visTRN. 21 24 object recognition 1, 2 , inference of depth and 3D structure from 2D images 3, 4 and semantic segmentation 5, 6 . Inspired by the 25 early visual system, these deep convolutional neural networks process visual information feedforward through a hierarchy of 26 layers. These layers each contain small computational units that, similar to real neurons operating within their receptive field 27 (RF), are applied to small patches of the image and during learning acquire selectivity for certain visual features. Remarkably, 28 such feature maps found in artificial networks resemble those of real neurons 7-9 , and the activity of various layers along the 29 artificial feedforward hierarchy can predict responses of real neurons in various cortical visual areas 2,[9][10][11] . Besides providing a 30 framework for machine vision, the feedforward architecture is also powerful for biological vision, where the initial feedforward 31 sweep contains a significant amount of information, sometimes sufficient to drive perception [12][13][14] . 32 So why then, is feedback such a prominent and ubiquitous motif in the brain, where descending projections generally 33 tend to outnumber ascending afferents? For instance, most inputs to primary sensory cortical areas do not come from primary 34 thalamus, but from higher-order structures 15 . The same principle applies to cortico-thalamic (CT) communication: relay cells 35 in the dorsolateral geniculate nucleus (dLGN) of the thalamus receive only 5-10% of their synaptic inputs from retinal afferents, 36 whereas 30% originate from L6 cortico-thalamic (L6CT) pyramidal cells of primary visual cortex (V1) 16 . 37Similar to a lack of general consensus regarding the function of cortico-cortical feedback 17, 18 , how CT feedback influences 38 the representation of visual information remains poorly understood. Despite massive cortical input, dLGN RFs closely resemble 39 retinal RFs rather than cortical ones [19][20...