Dorsal LGN Research Articles

Single-cell and single-nucleus RNA-seq uncovers shared and distinct axes of variation in dorsal LGN neurons in mice, non-human primates, and humans.

Abundant evidence supports the presence of at least three distinct types of thalamocortical (TC) neurons in the primate dorsal lateral geniculate nucleus (dLGN) of the thalamus, the brain region that conveys visual information from the retina to the primary visual cortex (V1). Different types of TC neurons in mice, humans, and macaques have distinct morphologies, distinct connectivity patterns, and convey different aspects of visual information to the cortex. To investigate the molecular underpinnings of these cell types, and how these relate to differences in dLGN between human, macaque, and mice, we profiled gene expression in single nuclei and cells using RNA-sequencing. These efforts identified four distinct types of TC neurons in the primate dLGN: magnocellular (M) neurons, parvocellular (P) neurons, and two types of koniocellular (K) neurons. Despite extensively documented morphological and physiological differences between M and P neurons, we identified few genes with significant differential expression between transcriptomic cell types corresponding to these two neuronal populations. Likewise, the dominant feature of TC neurons of the adult mouse dLGN is high transcriptomic similarity, with an axis of heterogeneity that aligns with core vs. shell portions of mouse dLGN. Together, these data show that transcriptomic differences between principal cell types in the mature mammalian dLGN are subtle relative to the observed differences in morphology and cortical projection targets. Finally, alignment of transcriptome profiles across species highlights expanded diversity of GABAergic neurons in primate versus mouse dLGN and homologous types of TC neurons in primates that are distinct from TC neurons in mouse.

Distribution and development of molecularly distinct perineuronal nets in visual thalamus.

Visual information is detected by the retina and transmitted into the brain by retinal ganglion cells. In rodents, the visual thalamus is a major recipient of retinal ganglion cells axons and is divided into three functionally distinct nuclei: the dorsal lateral geniculate nucleus (dLGN), ventral LGN (vLGN), and intergeniculate leaflet. Despite being densely innervated by retinal input, each nucleus in rodent visual thalamus possesses diverse molecular profiles which underpin their unique circuitry and cytoarchitecture. Here, we combined large-scale unbiased proteomic and transcriptomic analyses to elucidate the molecular expression profiles of the developing mouse dLGN and vLGN. We identified several extracellular matrix proteins as differentially expressed in these regions, particularly constituent molecules of perineuronal nets (PNNs). Remarkably, we discovered at least two types of molecularly distinct Aggrecan-rich PNN populations in vLGN, exhibiting non-overlapping spatial, temporal, and cell-type specific expression patterns. The mechanisms responsible for the formation of these two populations of PNNs also differ as the formation of Cat315+ PNNs (but not WFA+ PNNs) required input from the retina. This study is first to suggest that cell type- and molecularly specific supramolecular assemblies of extracellular matrix may play important roles in the circuitry associated with the subcortical visual system and in the processing of visual information. OPEN SCIENCE BADGES: This article has received a badge for *Open Materials* because it provided all relevant information to reproduce the study in the manuscript. The complete Open Science Disclosure form for this article can be found at the end of the article. More information about the Open Practices badges can be found at https://cos.io/our-services/open-science-badges/. Cover Image for this issue: doi: 10.1111/jnc.14203.

Low-intensity repetitive transcranial magnetic stimulation improves abnormal visual cortical circuit topography and upregulates BDNF in mice.

Repetitive transcranial magnetic stimulation (rTMS) is increasingly used as a treatment for neurological and psychiatric disorders. Although the induced field is focused on a target region during rTMS, adjacent areas also receive stimulation at a lower intensity and the contribution of this perifocal stimulation to network-wide effects is poorly defined. Here, we examined low-intensity rTMS (LI-rTMS)-induced changes on a model neural network using the visual systems of normal (C57Bl/6J wild-type, n = 22) and ephrin-A2A5(-/-) (n = 22) mice, the latter possessing visuotopic anomalies. Mice were treated with LI-rTMS or sham (handling control) daily for 14 d, then fluorojade and fluororuby were injected into visual cortex. The distribution of dorsal LGN (dLGN) neurons and corticotectal terminal zones (TZs) was mapped and disorder defined by comparing their actual location with that predicted by injection sites. In the afferent geniculocortical projection, LI-rTMS decreased the abnormally high dispersion of retrogradely labeled neurons in the dLGN of ephrin-A2A5(-/-) mice, indicating geniculocortical map refinement. In the corticotectal efferents, LI-rTMS improved topography of the most abnormal TZs in ephrin-A2A5(-/-) mice without altering topographically normal TZs. To investigate a possible molecular mechanism for LI-rTMS-induced structural plasticity, we measured brain derived neurotrophic factor (BDNF) in the visual cortex and superior colliculus after single and multiple stimulations. BDNF was upregulated after a single stimulation for all groups, but only sustained in the superior colliculus of ephrin-A2A5(-/-) mice. Our results show that LI-rTMS upregulates BDNF, promoting a plastic environment conducive to beneficial reorganization of abnormal cortical circuits, information that has important implications for clinical rTMS.

Degenerative alterations in the visual pathway after NMDA-induced retinal damage in mice

In the present study, intravitreal injection of N-methyl- d-aspartate (NMDA) into the left eye induced retinal damage (decreases in the number of retinal ganglion cells) at 1 day after the injection. At 7 days after the injection, atrophy of the optic tract was observed on the contralateral side, but not on the ipsilateral side. Number of neuronal nuclear specific protein (NeuN)-immunostained neurons were decreased in the contralateral dorsal LGN (dLGN) and contralateral ventral LGN-lateral (vLGN-l) at 90 and 180 days, respectively, after the injection. Furthermore, expressions of glial fibrillary acid protein (GFAP) were increased in the contralateral dLGN and contralateral vLGN-l at 7 and 30 days, respectively, and those of brain-derived neurotrophic factor (BDNF) were increased in the contralateral dLGN at 30 and 90 days and in the contralateral vLGN-l at 7 and 30 days. All NeuN-positive neuronal cells exhibited BDNF, whereas only some GFAP-positive astroglial cells exhibited BDNF. However, the contralateral ventral LGN-medial (vLGN-m) and ipsilateral LGN displayed no significant differences related to NeuN, GFAP, or BDNF immunohistochemistry. Taken together, these results indicate that time-dependent alterations occurred after the NMDA injection along the retinogeniculate pathway (from retina to LGN), and that the degree of damage in the LGN was region-dependent. In addition, the increased activated astroglial cells and expressions of BDNF in the damaged regions may play some roles in the cell-survival process of the LGN.

Early Retinal Activity and Visual Circuit Development

Does spontaneous retinal activity prior to vision play a role in the establishment of visual maps? In this issue of Neuron, two separate papers by Huberman et al. and Hooks and Chen demonstrate a role for early spontaneous retinal activity in the establishment of ocular dominance columns and synaptic refinement at retinogeniculate synapses.

Estimation of Local and Global Characteristics of Half-Tone Surfaces by the Cat's Lateral Geniculate Body

We investigated neuronal mechanisms in the cat's dorsal LGN that could carry information about the spatial brightness distribution across half-tone visual object surfaces. Stimuli were halftone spheres, cylinders, toroids, etc. We have found that geniculate neuronal structures describe and estimate both local and global characteristics of the brightness distribution on these surfaces. The search for local mechanisms of perception of half-tone surfaces revealed a new property of geniculate neurons: their sensitivity to changes in both the magnitude and vector direction of the spatial brightness gradient in the test stimulus. The quantitative estimation of gradient sensitivity in each case has been calculated by the formula: K=( Nmax- Nmin)/ Nmax, where Nmax is the number of spikes (in a 500 ms interval) in response to the preferred (and Nmin to the nonpreferred) gradient direction. The average value of K was 0.49 (range 0.15 – 0.95) for a mean brightness gradient of 2.7 cd m−2 deg−1. A ninefold decrease of the gradient reduced K by a factor of 6.5. The preferred direction of most (82%) neurons coincided with the radial direction from the centre of the receptive field to area centralis. The basis of this phenomenon probably lies in the influence of the spatial brightness gradient on spatiotemporal relations between excitatory and inhibitory processes in geniculate receptive fields. Global characteristics of the surface brightness distribution were represented in the population response of the neurons. The pattern of neuronal activity elicited in on-neurons and off-neurons in response to surface stimuli correlated with the isophot structure of the surface ( rav=0.86 for 23 cases). Therefore, separate descriptions of local and global brightness distributions originate at subcortical levels of the visual system.

Enhanced activation of NMDA receptor responses at the immature retinogeniculate synapse

The maturation of retinogeniculate excitatory transmission and intrathalamic inhibition was studied in slices of the dorsal LGN obtained from ferrets during the first 2 postnatal months. Response to optic tract stimulation at neonatal ages consisted of slow EPSPs lasting several hundred milliseconds. Application of the NMDA receptor antagonist D-(-)-2-amino-5-phosphonovaleric acid (D-APV) during the first 2 postnatal weeks resulted in EPSPs that were reduced in peak amplitude and dramatically curtailed in duration, indicating that NMDA receptors participate strongly in retinogeniculate transmission at the immature synapse. Gradually, EPSPs became shorter in duration such that after the second postnatal week, the retinogeniculate EPSPs were only a few milliseconds in duration. At this late stage of development responses were remarkably less affected by application of D-APV. These changes in contribution of NMDA receptors to retinogeniculate transmission were found to be due to the development of strong IPSPs, the result of gradual maturation of activation of GABAergic inhibition. Indeed, application of bicuculline methiodide to block GABAA receptor-mediated IPSPs strongly enhanced the NMDA component of the EPSPs in more mature cells. The voltage dependence and kinetics of NMDA-induced excitatory postsynaptic currents (NMDA EPSCs) were characterized by voltage-clamp recordings after blocking AMPA/kainate receptors with 6-cyano-7-nitroquinoxaline-2,3-dione and GABAA receptors wit' bicuculline methiodide. The voltage dependence of the NMDA EPSCs remained unaltered with age. During the first postnatal month the kinetic properties of the NMDA EPSCs also remained unaltered, but a reduction in EPSC duration was observed within the following weeks, well after the critical period of anatomical reorganization.(ABSTRACT TRUNCATED AT 250 WORDS)

Developmental changes in electrophysiological properties of LGNd neurons during reorganization of retinogeniculate connections

Changes in electrophysiological properties of neurons in the ferret dorsal LGN (LGNd) were studied during early postnatal life, a critical developmental period when changes occur in morphology, connectivity, and response properties of LGNd neurons. Using the patch-clamp technique to obtain whole-cell recordings from cells maintained as in vitro slices of thalamus, several distinctive properties were observed in the immature LGNd. Relatively low resting membrane potentials were present that became more negative during the first 2 postnatal weeks. In addition, immature neurons exhibited high input resistances that decreased during early postnatal development. At all ages postnatally, neurons were capable of generating a train of Na(+)-dependent action potentials in response to intracellular injection of a depolarizing current pulse. Moreover, immature neurons resembled older cells in that little spike frequency adaptation was present during a train of action potentials. Action potential activity in immature neurons was nevertheless distinctive in several respects: (1) during the first 2-3 postnatal weeks action potentials became shorter in duration and larger in amplitude; (2) during the same period, thresholds for generation of action potentials changed in conjunction with the changes in resting membrane potential, becoming more negative; and (3) plots of frequency versus injected current revealed that thresholds for generation of trains of action potentials were reached with intracellular injection of lower current levels at earlier ages. These findings raise the possibility that relatively weak ionic currents generated at immature synapses have unexpectedly strong effects on the young LGNd neuron.(ABSTRACT TRUNCATED AT 250 WORDS)

Modulation of visually evoked responses in units of the ventral lateral geniculate nucleus of the rat by somatic stimuli

Single unit activity was recorded from the ventral part of the lateral geniculate nucleus (vLGN) in rats anaesthetized with urethane. Most of the cells located laterally in the nucleus were excited by light. The studied vLGN neurones did not respond to electrical stimulation of the tail, but about half of them changed their response to light significantly when the light flash was paired with the electrical stimulation. When the tail stimulus preceded the light, the changes consisted in a pronounced facilitation of flash-evoked activity. When the electrical stimulus was applied after the flash in a forward conditioning paradigm, facilitations were less pronounced and responses of some neurones were suppressed. These results are in contrast to those of similar experiments on the dorsal LGN, neurones of which were mainly facilitated by the conditioning paradigm. Thus, light-evoked activity of ventral geniculate cells can be enhanced by arousal-related processes.

The effects of parvocellular lateral geniculate lesions on the acuity and contrast sensitivity of macaque monkeys

The effects of ablating the visual pathway that passes through the parvocellular (dorsal) LGN were tested in 2 macaque monkeys by measuring acuity and both luminance and chromatic contrast sensitivity. Thresholds were tested monocularly before and after ibotenic acid was used to lesion parvocellular layers 4 and 6 of the contralateral geniculate. The injections were centered at the representation of 6 degrees in the temporal field on the horizontal meridian, and vision was tested with localized stimuli at this location. In addition, in one of the monkeys, a lesion was made in magnocellular layer 1 of the opposite geniculate, and the same thresholds were tested. Physiological and anatomical reconstructions demonstrated complete destruction of the target layers in 1 parvocellular lesions and in the magnocellular lesion, and sparing of the nontarget layers in the tested region. Parvocellular lesions caused a 3-4-fold reduction in visual acuity within the affected part of the visual field, while the magnocellular lesion did not affect acuity. Both luminance and chromatic contrast sensitivity, tested with stationary gratings of 2 c/degree, were severely reduced by parvocellular lesions, but not affected by the magnocellular lesion. However, when luminance contrast sensitivity was tested with 1 c/degree gratings, counterphase modulated at 10 Hz, it was reduced by both parvocellular and magnocellular lesions. This study demonstrates that the parvocellular pathway dominates chromatic vision, acuity, and contrast detection at low temporal and high spatial frequencies, while the magnocellular pathway may mediate contrast detection at higher temporal and lower spatial frequencies.

Magnocellular and parvocellular contributions to responses in the middle temporal visual area (MT) of the macaque monkey

Many lines of evidence suggest that the visual signals relayed through the magnocellular and parvocellular subdivisions of the primate dorsal LGN remain largely segregated through several levels of cortical processing. It has been suggested that this segregation persists through to the highest stages of the visual cortex, and that the pronounced differences between the neuronal response properties in the parietal cortex and inferotemporal cortex may be attributed to differential contributions from magnocellular and parvocellular signals. We have examined this hypothesis directly by recording the responses of cortical neurons while selectively blocking responses in the magnocellular or parvocellular layers of the LGN. Responses were recorded from single units or multiunit clusters in the middle temporal visual area (MT), which is part of the pathway leading to parietal cortex and thought to receive primarily magnocellular inputs. Responses in the MT were consistently reduced when the magnocellular subdivision of the LGN was inactivated. The reduction was almost always pronounced and often complete. In contrast, parvocellular block rarely produced striking changes in MT responses and typically had very little effect. Nevertheless, unequivocal parvocellular contributions could be demonstrated for a minority of MT responses. At a few MT sites, responses were recorded while magnocellular and parvocellular blocks were made simultaneously. Responses were essentially eliminated for all these paired blocks. These results provide direct evidence for segregation of magnocellular and parvocellular contributions in the extrastriate visual cortex and support the suggestion that these signals remain largely segregated through the highest levels of cortical processing.

Retinal projections in the ground squirrel (Citellus tridecemlineatus)

The retinal projections of the thirteen-lined ground squirrel were determined by tracing anterograde transport of intravitreally injected horseradish peroxidase (HRP) or wheat-germ conjugated horseradish peroxidase (WGA-HRP). Label was seen in the suprachiasmatic nucleus and adjacent anterior hypothalamic area, the accessory optic system (the medial, dorsal, and lateral terminal nuclei), the dorsal and ventral lateral geniculate nuclei, the intergeniculate leaflet, the pretectal nuclei (the anterior, posterior, and olivary pretectal nuclei and the nucleus of optic tract), and the superior colliculus. Most of these structures were labeled bilaterally, with dense contralateral label and sparse ipsilateral label, a pattern typical for animals with laterally placed eyes. However, the suprachiasmatic nucleus and the nucleus of the optic tract received input only from the contralateral eye. In contrast to previous degeneration studies, the sensitive HRP tracers (in conjunction with cytochrome-oxidase reactivity) revealed an elaborate organization within the lateral geniculate nucleus (dorsal LGN, ventral LGN, and intergeniculate leaflet) that is consistent with existing organizational schemes for other mammalian species.

The innervation density of serotonergic (5-HT) fibers varies in different subdivisions of the cat lateral geniculate nucleus complex.

The innervation density of serotonin (5-HT)-immunoreactive fibers, identified using an antibody to 5-HT, was found to differ in the 4 subdivisions of the cat lateral geniculate nucleus complex (LGN). The mean density (fiber length per unit area) of anti-5-HT-stained fibers was highest in the ventral LGN (0.062 micron per micron 2), moderate in the medial interlaminar nucleus (MIN) and the parvicellular C laminae of the dorsal LGN (0.039-0.040 per micron 2), and lowest in the A and magnocellular C laminae of the dorsal LGN (0.020 per micron 2). The fiber density in MIN was particularly dense along the medial edge of the nucleus, a region called the geniculate wing. The heaviest serotonin innervation is thus found in geniculate structures receiving input from W-type retinal ganglion cells and lightest in structures receiving X and Y input.

Development of glutamic acid decarboxylase immunoreactivity in the cat's lateral geniculate nucleus

The development of glutamic acid decarboxylase (GAD) immunoreactivity in the cat's dorsal LGN was studied during fetal and postnatal life. In the adult, inhibitory interactions within the LGN are known to be mediated by GABA. Here we have used an antiserum to GAD, the rate-limiting synthetic enzyme for GABA, to examine the development of the anatomical substrate for this inhibitory system. The pattern of immunostaining observed in the adult cat LGN was similar to that reported by Fitzpatrick et al. (1984), with heavily stained somata and proximal dendrites located within the LGN layers and the adjacent perigeniculate nucleus (PGN). The LGN also contained a complex array of terminal staining. In development, specific staining was seen about 2 weeks before birth and was confined to PGN somata and, to a lesser extent, to somata located in the future ventral C-layers. A similar pattern of immunostaining was seen using GABA antiserum. Not until birth did the A-layers of the LGN show appreciable staining of both somata and terminals; however, even then the pattern of immunostaining was far from mature. Furthermore, excessive numbers of PGN neurons appeared to stain. By 5 weeks after birth, the intensity of both soma and terminal staining within the A-layers of the LGN increased substantially relative to that of the PGN and ventral C-layers. The first glomerular clusters of terminal staining could also be seen, and the number of stained PGN neurons had diminished to levels similar to those seen in the adult. The pattern of immunostaining was almost adultlike by 2 months after birth, except within the C-complex, where the staining did not yet show the distinct difference in staining intensity present in the adult between dorsal layer C and ventral layers C1 and C2. The final adult pattern of GAD immunoreactivity appeared by 3 months after birth. These results suggest that during fetal life the PGN and ventral C-layers of the LGN may supply the first source of GABA-mediated inhibition to the nucleus, with the major portion of the inhibition supplied by intrinsic LGN neurons arising postnatally. Thus, PGN neurons may provide part of the anatomical substrate for the inhibitory interactions seen physiologically during late fetal development (Shatz and Kirkwood, 1984). Finally, the relatively late appearance of the adultlike pattern of GAD immunostaining suggests that intrageniculate inhibitory circuitry continues to develop well after birth.

Selective effects of kainic acid on diencephalic neurons

Injections of kainic acid (KA) into the lateral hypothalamus (LH) produce neuronal loss in this region without apparent damage to medial forebrain bundle fibers passing through the area. Cellular destruction is not limited to the LH; the neuronal loss in the thalamic reticular nucleus, the subthalamic nucleus and zona incerta is more extensive than that in the LH. Since all of the nuclei of ventral thalamic origin except the ventral lateral geniculate nucleus (VLGN) were destroyed by LH injections of KA, we sought to determine whether this nucleus also is sensitive to KA. Injections directly into the VLGN produce total neuronal loss here as well as in the thalamic reticular nucleus, zona incerta and subthalamic nucleus. Other areas showing cell loss are the dorsal LGN, medial geniculate, lateral portion of the ventrobasal complex and midline thalamic nuclei. Injections of KA into medial hypothalamus adjacent to the suprachiasmatic nucleus produced no neuronal degeneration. In addition, no neuronal loss was noted in medial hypothalamic nuclei lying adjacent to areas of LH in which KA was injected. Therefore, the sensitivity of diencephalic nuclei appears to range from highly sensitive regions such as derivatives of ventral thalamus and midline thalamic nuclei to regions of moderate sensitivity such as the LH, geniculate nuclei and ventrobasal thalamic nucleus, to regions resistant to KA toxicity such as the suprachiasmatic nucleus and other nuclei and areas of medial hypothalamus.

Selective effects of kainic acid on diencephalic neurons

Injections of kainic acid (KA) into the lateral hypothalamus (LH) produce neuronal loss in this region without apparent damage to medial forebrain bundle fibers passing through the area. Cellular destruction is not limited to the LH; the neuronal loss in the thalamic reticular nucleus, the subthalamic nucleus and zona incerta is more extensive than that in the LH. Since all of the nuclei of ventral thalamic origin except the ventral lateral geniculate nucleus (VLGN) were destroyed by LH injections of KA, we sought to determine whether this nucleus also is sensitive to KA. Injections directly into the VLGN produce total neuronal loss here as well as in the thalamic reticular nucleus, zona incerta and subthalamic nucleus. Other areas showing cell loss are the dorsal LGN, medial geniculate, lateral portion of the ventrobasal complex and midline thalamic nuclei. Injections of KA into medial hypothalamus adjacent to the suprachiasmatic nucleus produced no neuronal degeneration. In addition, no neuronal loss was noted in medial hypothalamic nuclei lying adjacent to areas of LH in which KA was injected. Therefore, the sensitivity of diencephalic nuclei appears to range from highly sensitive regions such as derivatives of ventral thalamus and midline thalamic nuclei to regions of moderate sensitivity such as the LH, geniculate nuclei and ventrobasal thalamic nucleus, to regions resistant to KA toxicity such as the suprachiasmatic nucleus and other nuclei and areas of medial hypothalamus.

Morphological and functional effects of visual deprivation on the rabbit visual system

Evidence from studies on the cat suggest that many of the adverse effects of suturing one eyelid are not simply a consequence of reduced visual pattern stimulation, but in large part may be due to unbalanced competitive interaction between projections from the two eyes. The rabbit provides an opportunity for testing the effects of visual deprivation in a system nearly free from binocular synaptic competition. Its visual system has a large monocular projection that includes the central retina. Seven rabbits were reared with monocular lid-suture and trained on brightness, pattern, and form discriminations. They learned these tasks as readily with the deprived eye as with the normal eye. Single-unit recordings were carried out in nine rabbits raised with either monocular or binocular lid-suture. Receptive field properties of cells in the large monocular segment of the visual cortex and in the superior colliculus appeared qualitively normal and the various receptive field types were seen in their normal proportions. Quantitative histological measurements were made on cells in the monocular segment of the dorsal lateral geniculate nuclei of seven rabbits. Monocular lid-suture for 3–5 mo produced no changes in cell size in the dorsal LGN, while deprivation for 10–15 mo produced a small (less than 10%) but statistically significant reduction in size. Monocular enucleation, by contrast, produced a large (26.6%) decrease in cell size and total volume of this nucleus (54.5%). These results, as well as other data available from rabbit and other species with largely crossed visual systems, are discussed in relation to the hypothesis that the principal effects of lid-suture are a consequence of competitive interaction between the two eyes.