Layer 6 Corticothalamic Neurons Activate a Cortical Output Layer, Layer 5a

Kim, Juhyun; Matney, Chanel J.; Blankenship, Aaron G.; Hestrin, Shaul; Brown, Solange P.

doi:10.1523/jneurosci.1325-14.2014

Cited by 136 publications

(197 citation statements)

References 42 publications

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“…For the success of these experiments, it is essential to label the majority of ipRGCs, and hence we injected a high dose of tamoxifen that led to the labeling of hundreds of ipRGCs in the retina. This synaptophysin-tdTomato protein was shown to localize to presynaptic terminals (27) and was confirmed here by colocalizing tdTomato with Vglut2 staining (Fig. S10 A and B).…”

Section: Retinal Projections To the Scn: Identification Of Postsynaptsupporting

confidence: 72%

Architecture of retinal projections to the central circadian pacemaker

Fernandez

Chang

Hattar

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

128

134

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The suprachiasmatic nucleus (SCN) receives direct retinal input from the intrinsically photosensitive retinal ganglion cells (ipRGCs) for circadian photoentrainment. Interestingly, the SCN is the only brain region that receives equal inputs from the left and right eyes. Despite morphological assessments showing that axonal fibers originating from ipRGCs cover the entire SCN, physiological evidence suggests that only vasoactive intestinal polypeptide (VIP)/ gastrin-releasing peptide (GRP) cells located ventrally in the SCN receive retinal input. It is still unclear, therefore, which subpopulation of SCN neurons receives synaptic input from the retina and how the SCN receives equal inputs from both eyes. Here, using single ipRGC axonal tracing and a confocal microscopic analysis in mice, we show that ipRGCs have elaborate innervation patterns throughout the entire SCN. Unlike conventional retinal ganglion cells (RGCs) that innervate visual targets either ipsilaterally or contralaterally, a single ipRGC can bilaterally innervate the SCN. ipRGCs form synaptic contacts with major peptidergic cells of the SCN, including VIP, GRP, and arginine vasopressin (AVP) neurons, with each ipRGC innervating specific subdomains of the SCN. Furthermore, a single SCNprojecting ipRGC can send collateral inputs to many other brain regions. However, the size and complexity of the axonal arborizations in non-SCN regions are less elaborate than those in the SCN. Our results provide a better understanding of how retinal neurons connect to the central circadian pacemaker to synchronize endogenous circadian clocks with the solar day.melanopsin | circadian | suprachiasmatic nucleus | non-image-forming functions | ipRGCs T he suprachiasmatic nucleus (SCN) houses a central pacemaker that orchestrates circadian (circa: "about" and diem: "day") behaviors that cycle with a period close to 24 h. This endogenous clock is self-sustained even in the complete absence of external stimuli, but can be entrained to the light/dark cycle of the solar day in a process defined as circadian photoentrainment (1). In mammals, phototransduction solely occurs in the retina (2). Retinal ganglion cells (RGCs) are projection neurons of the retina that send light information to brain targets (3). Although the majority of RGCs project to brain areas involved in object tracking and image formation, some RGCs also innervate non-image-forming brain regions to influence circadian activity, sleep, the pupillary light response, mood, and learning functions (4).Recent studies showed that a small subpopulation of RGCs expresses a photopigment called melanopsin (Opn4), making these cells intrinsically photosensitive (ip)RGCs (5-7). It is now known that there are at least five different ipRGC subtypes (M1-M5) (8, 9). Using genetic tracing techniques, it was shown that ipRGCs send projections to non-image-forming centers in the brain, including the SCN, which receives retinal input predominantly from M1 ipRGCs (10-12) and to a lesser extent from M2 ipRGCs (12). The SCN is a smal...

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Section: Retinal Projections To the Scn: Identification Of Postsynaptsupporting

confidence: 72%

Architecture of retinal projections to the central circadian pacemaker

Fernandez

Chang

Hattar

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

128

134

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“…These connections are weak and show paired pulse facilitation [58,59]. Similar unreliable connections showing paired pulse EPSP facilitation have also been found in rat barrel cortex for connections onto both L4 spiny neurons and L5A pyramidal cells; all EPSPs at these connections showed a fast time course indicative of proximal synaptic contacts [49,60]. Corticothalamic L6A-L5A connections (activated by light-induced activation of ChR2) were substantially stronger than CT L6A-L4 connections.…”

Section: Layersupporting

confidence: 65%

“…4.2c) suggests that these neurons form synaptic connections with L4 spiny neurons [56,57]. This has been demonstrated for visual cortex [58,59] and very recently also for barrel cortex [49,60].…”

Section: Layer 4 Serves To Distribute Intracortical Excitationmentioning

confidence: 64%

Synaptic Microcircuits in the Barrel Cortex

Radnikow

Feldmeyer

2015

Sensorimotor Integration in the Whisker System

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An elementary feature of sensory cortices is thought to be their organisation into functional signal-processing units called 'cortical columns'. These elementary units process sensory information arriving from peripheral receptors; they are vertically oriented throughout all cortical layers and contain several thousands of excitatory and inhibitory synaptic connections. To understand how sensory signals are transformed into electrical activity in the neocortex it is necessary to elucidate the spatial-temporal dynamics of cortical signal processing and the underlying neurons and synaptic 'microcircuits'.In the somatosensory barrel cortex there appears to be a structural correlate for the 'functional' cortical column. Therefore, it has become an attractive model system to study the synaptic microcircuitry in the neocortex. Although many synaptic connections in whisker-related cortical 'columns' have been characterised over the past years our knowledge is far from complete, in particular with respect to inhibitory connections. In this chapter we will summarise recent data on different excitatory and inhibitory synaptic connections in a whisker-related 'column' of the somatosensory cortex and try to outline their function in the neuronal network. This requires an appreciation of the diverse types of excitatory and inhibitory neurons and their function within cortical columns and beyond. When necessary, we will also discuss the synaptic input from and to subcortical structures, in particular the thalamus. However, we will not provide a detailed description of the functional mechanisms of these connections; this is beyond the scope of this chapter.

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“…Acute coronal brain slices (300 m thick) were generated for in vitro recording and optical stimulation largely as previously described (Brown and Hestrin, 2009a; Kim et al, 2014). After anesthetizing the mice (P24 -P105) with isoflurane, brains were isolated in an ice-cold sucrose solution composed of the following (in mM): 76 NaCl, 25 NaHCO 3 , 25 glucose, 75 sucrose, 2.5 KCl, 1.25 NaH 2 PO 4 , 0.5 CaCl 2 , 7 MgSO 4 , pH 7.3, 315 mOsm.…”

Section: Methodsmentioning

confidence: 99%

“…ChR2 was photoactivated as previously described (Kim et al, 2014). Briefly, a small circle of blue light (110 -315 m diameter) was focused onto the brain slice using a fiber optic cable (920 m diameter; Thorlabs) coupled to a blue LED (ϳ470 nm; Luminous) focused onto the focal plane of a camera port with a 10ϫ 0.3 numerical aperture lens.…”

Section: Methodsmentioning

confidence: 99%

Synaptic Organization of the Neuronal Circuits of the Claustrum

et al. 2016

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The claustrum, a poorly understood subcortical structure located between the cortex and the striatum, forms widespread connections with almost all cortical areas, but the cellular organization of claustral circuits remains largely unknown. Based primarily on anatomical data, it has been proposed that the claustrum integrates activity across sensory modalities. However, the extent to which the synaptic organization of claustral circuits supports this integration is unclear. Here, we used paired whole-cell recordings and optogenetic approaches in mouse brain slices to determine the cellular organization of the claustrum. We found that unitary synaptic connections among claustrocortical (ClaC) neurons were rare. In contrast, parvalbumin-positive (PV) inhibitory interneurons were highly interconnected with both chemical and electrical synapses. In addition, ClaC neurons and PV interneurons formed frequent synaptic connections. As suggested by anatomical data, we found that corticoclaustral afferents formed monosynaptic connections onto both ClaC neurons and PV interneurons. However, the responses to cortical input were comparatively stronger in PV interneurons. Consistent with this overall circuit organization, activation of corticoclaustral afferents generated monosynaptic excitatory responses as well as disynaptic inhibitory responses in ClaC neurons. These data indicate that recurrent excitatory circuits within the claustrum alone are unlikely to integrate across multiple sensory modalities. Rather, this cellular organization is typical of circuits sensitive to correlated inputs. Although single ClaC neurons may integrate corticoclaustral input from different cortical regions, these results are consistent with more recent proposals implicating the claustrum in detecting sensory novelty or in amplifying correlated cortical inputs to coordinate the activity of functionally related cortical regions.

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Layer 6 Corticothalamic Neurons Activate a Cortical Output Layer, Layer 5a

Cited by 136 publications

References 42 publications

Architecture of retinal projections to the central circadian pacemaker

Architecture of retinal projections to the central circadian pacemaker

Synaptic Microcircuits in the Barrel Cortex

Synaptic Organization of the Neuronal Circuits of the Claustrum

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