Role of the medial agranular cortex in unilateral spatial neglect.

Unilateral spatial neglect (USN) results from impaired attentional networks and can affect various sensory modalities, such as visual and somatosensory. The rodent medial agranular cortex (AGm), located in the medial part of the forebrain from rostral to caudal direction, is considered a region associated with spatial attention. The AGm selectively receives multisensory input with the rostral AGm receiving somatosensory input and caudal part receiving visual input. Our previous study showed slower recovery from neglect with anterior AGm lesion using the somatosensory neglect assessment. Conversely, the functional differences in spatial attention across the entire AGm locations (anterior, intermediate, and posterior parts) are unknown. Here, we investigated the relationship between the severity of neglect and various locations across the entire AGm in a mouse stroke model using a newly developed program-based analysis method that does not require human intervention. Among various positions of the lesions, the recovery from USN during recovery periods (postoperative day; POD 10-18) tended to be slower in cases with more rostral lesions in the AGm (r = - 0.302; p = 0.028). Moreover, the total number of arm entries and maximum moving speed did not significantly differ between before and after AGm infarction. According to these results, the anterior lesions may slowly recover from USN-like behavior, and there may be a weak association between the AGm infarct site and recovery rate. In addition, all unilateral focal infarctions in the AGm induced USN-like behavior without motor deficits.

Prevention of denervated muscle atrophy with accelerated nerve-regeneration by babysitter procedure in rat facial nerve paralysis model.

PURPOSE: The "babysitter" procedure is a reconstruction technique for facial nerve complete paralysis and uses the movement source from the healthy facial nerve with a cross-nerve graft. First, an end-to-side neurorrhaphy is performed between the affected facial nerve trunk and hypoglossal nerve for continuously delivering stimuli to the mimetic muscles for preventing the atrophy of mimetic muscles. Despite favorable clinical results, histological and physiological mechanisms remain unknown. This study attempted to establish a model for the "babysitter" procedure and find its efficacy in rats with facial nerve complete paralysis. MATERIALS AND METHODS: A total of 16 Lewis rats were used and divided into 2 groups; cross nerve graft (n = 8) and babysitter groups (n = 8). The facial nerve trunk was transected in both groups. Babysitter group underwent a two-stage procedure. Cross nerve graft group underwent only the transfer of nerve graft from the healthy side to affected side. The animals were assessed physiologically by compound muscle action potential (CMAP), and the regenerated nerve tissues were evaluated histopathologically at 13 weeks after surgery. RESULTS: Facial nucleus stained with retrograde tracers proved the re-innervation of affected facial muscle by the babysitter procedure. In CMAP, the amplitude of babysitter group was significantly higher than that of the cross-facial nerve graft group (p < .05). Histological examination found a significant difference in myelin g-ratio between two groups (p < .05). CONCLUSION: This study investigated the "babysitter" procedure for rat facial nerve palsy. Babysitter procedure shortened the denervation period without mimic muscle atrophy.

Adipose-derived stem cells and the stromal vascular fraction in polyglycolic acid-collagen nerve conduits promote rat facial nerve regeneration.

Adipose-derived stem cells (ADSCs) and the stromal vascular fraction (SVF) promote nerve regeneration. Biodegradable nerve conduits are used to treat peripheral nerve injuries, but their efficiencies are lower than those of autologous nerve grafts. This study developed biodegradable nerve conduits containing ADSCs and SVF and evaluated their facial nerve regenerating abilities in a rat model with a 7-mm nerve defect. SVF and ADSCs were individually poured into nerve conduits with polyglycolic acid-type I collagen as a scaffold (ADSCs and SVF groups). The conduits were grafted on to the nerve defects. As the control, the defect was bridged with polyglycolic acid-collagen nerve conduits without cells. At 13 weeks, after transplantation, the regenerated nerves were evaluated physiologically and histologically. The compound muscle action potential of the SVF group was significantly higher in amplitude than that of the control group. Electron microscopy showed that the axon diameter of the SVF group was the largest, followed by the ADSC group and control group with significant differences among them. The SVF group had the largest fiber diameter, followed by the ADSC group and control group with significant differences among them. The ADSC group had the highest myelin thickness, followed by the SVF group and control group with significant differences among them. Identical excellent promoting effects on nerve regeneration were observed in both the ADSC and SVF groups. Using SVF in conduits was more practical than using ADSCs because only the enzymatic process was required to prepare SVF, indicating that SVF could be more suitable to induce nerve regeneration.

Axonal supercharged interpositional jump-graft with a hybrid artificial nerve conduit containing adipose-derived stem cells in facial nerve paresis rat model.

PURPOSE: Interpositional jump-graft (IPJG) technique with the hypoglossal nerve for supercharging can be applied in a facial nerve paresis case. In IPJG, an autologous nerve is required, and the donor site morbidity is unavoidable. Biodegradable nerve conduits are made from polyglycolic acid (PGA) and used recently without donor site complications after providing autologous grafts. Hybrid artificial nerve conduits with adipose-derived stem cells (ASCs) also attract attention as a nerve-regeneration enhancing agent. This study examined the effect of hybrid artificial nerve conduit on IPJG. MATERIALS AND METHODS: A total of 34 Lewis rats were used and divided into 4 groups by the bridge materials: autograft (n = 8), PGA nerve conduit (n = 8), hybrid PGA nerve conduit with ASCs (n = 8), and the nontreated control groups (n = 8). ASCs were collected from 2 rats and cultured. The animals were assessed physiologically and histopathologically at 13 weeks after surgery. RESULTS: In compound muscle action potential, the amplitude of hybrid PGA group (3,222 ± 1,779 µV) was significantly higher than that of PGA group (1,961 ± 445 µV, P < .05), and no significant difference between hybrid PGA and autograft group. All treated groups showed a myelinated nerve regeneration with double innervation in hypoglossal and facial nerve nuclei for vibrissal muscle. CONCLUSION: This study showed the effectiveness of IPJG with a hybrid PGA conduit especially in physiological examination.

Recent advances and applications of human brain models.

Recent advances in human pluripotent stem cell (hPSC) technologies have prompted the emergence of new research fields and applications for human neurons and brain organoids. Brain organoids have gained attention as an in vitro model system that recapitulates the higher structure, cellular diversity and function of the brain to explore brain development, disease modeling, drug screening, and regenerative medicine. This progress has been accelerated by abundant interactions of brain organoid technology with various research fields. A cross-disciplinary approach with human brain organoid technology offers a higher-ordered advance for more accurately understanding the human brain. In this review, we summarize the status of neural induction in two- and three-dimensional culture systems from hPSCs and the modeling of neurodegenerative diseases using brain organoids. We also highlight the latest bioengineered technologies for the assembly of spatially higher-ordered neural tissues and prospects of brain organoid technology toward the understanding of the potential and abilities of the human brain.

Cholinergic modulation of response gain in the primary visual cortex of the macaque.

ACh modulates neuronal activity throughout the cerebral cortex, including the primary visual cortex (V1). However, a number of issues regarding this modulation remain unknown, such as the effect and its function and the receptor subtypes involved. To address these issues, we combined extracellular single-unit recordings and microiontophoretic administration of ACh and measured V1 neuronal responses to drifting sinusoidal grating stimuli in anesthetized macaque monkeys. ACh was found to have mostly facilitatory effects on the visual responses, although some cases of suppressive effects were also seen. To assess the functional role of ACh, we further examined how ACh modulates the stimulus contrast-response function, finding that the response gain increased with the facilitatory effect. The response facilitation was completely or strongly blocked by atropine (At), a muscarinic ACh receptor (mAChR) antagonist, in almost all neurons (96% of cells), whereas any residual effect after At administration was fully removed by mecamylamine, a nicotinic AChR (nAChR) antagonist, suggesting a predominant role for mAChRs in this mechanism. Furthermore, we found no laminar distribution bias for the facilitatory modulation, although the relative contribution of mAChRs was smaller in layer 4C than in other layers. The suppressive effect was blocked completely by At. These results demonstrate that ACh plays an important role in visual information processing in V1 by controlling the response gain via mAChRs across all cortical layers and via nAChRs, mainly in layer 4C.

Distinct nociception processing in the dysgranular and barrel regions of the mouse somatosensory cortex.

Nociception, a somatic discriminative aspect of pain, is, like touch, represented in the primary somatosensory cortex (S1), but the separation and interaction of the two modalities within S1 remain unclear. Here, we show spatially distinct tactile and nociceptive processing in the granular barrel field (BF) and adjacent dysgranular region (Dys) in mouse S1. Simultaneous recordings of the multiunit activity across subregions revealed that Dys neurons are more responsive to noxious input, whereas BF neurons prefer tactile input. At the single neuron level, nociceptive information is represented separately from the tactile information in Dys layer 2/3. In contrast, both modalities seem to converge on individual layer 5 neurons of each region, but to a different extent. Overall, these findings show layer-specific processing of nociceptive and tactile information between Dys and BF. We further demonstrated that Dys activity, but not BF activity, is critically involved in pain-like behavior. These findings provide new insights into the role of pain processing in S1.

Surround suppression by high spatial frequency stimuli in the cat primary visual cortex.

Surround suppression is a phenomenon whereby stimulation of the extraclassical receptive field suppressively modulates the visual responses of neurons in the primary visual cortex (V1) (also known as area 17). It is known that surround suppression tunes to spatial frequencies (SFs) that are much lower and broader than the frequencies to which the classical receptive field tunes. In this study, we tested the effects of varying SFs on surround suppression by using a circular sinusoidal grating patch that covered both the classical receptive field and the extraclassical receptive field. Using area-summation tuning curves, we found high-SF-tuned surround suppression in the cat V1. This high-SF-tuned surround suppression causes the SF tuning to shift to low SF for large stimuli. By simulating a model neuron lacking a suppressive surround mechanism, we confirmed that these preferred SF shifts do not occur in the absence of surround suppression. We surmise that the high-SF-tuned suppression, which shifts the preferred SF according to size, functionally contributes to the scale-invariant processing of visual images in V1.

Facial nerve regeneration with bioabsorbable collagen conduits filled with collagen filaments: An experimental study.

INTRODUCTION: A bioabsorbable collagen conduit (Renerve™) filled with collagen filaments is currently approved as an artificial nerve conduit in Japan and is mainly used for connecting and repairing peripheral nerves after traumatic nerve injury. However, there are few reports on its applications for reconstructing and repairing the facial nerve. The present study evaluated the efficacy of the conduit on promoting nerve regeneration in a murine model with a nerve defect at the buccal branch of the facial nerve. METHODS: Under inhalational anesthesia and microscopic guidance, the buccal branch of the left facial nerve in an 8-week-old Lewis rat was exposed, and a 7 mm gap was created in the nerve. The gap was then connected with either the nerve conduits (NC group) or an autologous nerve graft (the autograft group). At 13 weeks after the procedure, we compared the histological and physiological regenerations in the both groups. RESULTS: We found compound muscle action potential amplitude is significantly larger in the autograft group (2.8 ± 1.4 mV) than in NC group (1.3 ± 0.5 mV) (p < 0.05). The number of myelinated fibers of the autograft group was higher (3634 ± 1645) than that of NC group (1112 ± 490) (p < 0.01). The fiber diameter of the autograft group (4.8 ± 1.9 µm) was larger than that of NC group (3.8 ± 1.4 µm) (p < 0.05). The myelin thickness of the autograft group was thicker than that of NC group (0.6 ± 0.3 µm vs. 0.4 ± 0.1 µm) (p < 0.05). G-ratio of the autograft group (0.74 ± 0.19) was lower than that of NC group (0.79 ± 0.10) (p < 0.05). CONCLUSION: This study demonstrated the efficacy of collagen nerve conduit for facial nerve reconstruction following nerve injury. However, the effectiveness of the conduit on the promotion of nerve regeneration was inferior to that of the autograft.

Ipsilesional spatial bias after a focal cerebral infarction in the medial agranular cortex: A mouse model of unilateral spatial neglect.

Unilateral spatial neglect is a disorder of higher brain function that occurs after a brain injury, such as stroke, traumatic brain injury, brain tumor, and surgical procedures etc., and leads to failure to attend or respond to stimuli presented to the side contralateral to the lesioned cerebral hemisphere. Because patients with this condition often have other symptoms due to the presence of several brain lesions, it is difficult to evaluate the recovery mechanisms and effect of training on unilateral spatial neglect. In this study, a mouse model of unilateral spatial neglect was created to investigate whether the size of the lesion is related to the severity of ipsilesional spatial bias and the recovery process. Focal infarction was induced in the right medial agranular cortex (AGm) of mice via photothrombosis. After induction of cerebral infarction, ipsilesional spatial bias was evaluated for 9 consecutive days. The major findings were as follows: (1) unilateral local infarction of the AGm resulted in ipsilateral bias during internally guided decision-making; (2) the lesion size was correlated with the degree of impairment rather than slight differences in the lesion site; and (3) mice with anterior AGm lesions experienced lower recovery rates. These findings suggest that recovery from ipsilesional spatial bias requires neural plasticity within the anterior AGm. This conditional mouse model of ipsilesional spatial bias may be used to develop effective treatments for unilateral spatial neglect in humans.

FoxG1 regulates the formation of cortical GABAergic circuit during an early postnatal critical period resulting in autism spectrum disorder-like phenotypes.

Abnormalities in GABAergic inhibitory circuits have been implicated in the aetiology of autism spectrum disorder (ASD). ASD is caused by genetic and environmental factors. Several genes have been associated with syndromic forms of ASD, including FOXG1. However, when and how dysregulation of FOXG1 can result in defects in inhibitory circuit development and ASD-like social impairments is unclear. Here, we show that increased or decreased FoxG1 expression in both excitatory and inhibitory neurons results in ASD-related circuit and social behavior deficits in our mouse models. We observe that the second postnatal week is the critical period when regulation of FoxG1 expression is required to prevent subsequent ASD-like social impairments. Transplantation of GABAergic precursor cells prior to this critical period and reduction in GABAergic tone via Gad2 mutation ameliorates and exacerbates circuit functionality and social behavioral defects, respectively. Our results provide mechanistic insight into the developmental timing of inhibitory circuit formation underlying ASD-like phenotypes in mouse models.

Enriched expression of serotonin 1B and 2A receptor genes in macaque visual cortex and their bidirectional modulatory effects on neuronal responses.

To study the molecular mechanism how cortical areas are specialized in adult primates, we searched for area-specific genes in macaque monkeys and found striking enrichment of serotonin (5-hydroxytryptamine, 5-HT) 1B receptor mRNA, and to a lesser extent, of 5-HT2A receptor mRNA, in the primary visual area (V1). In situ hybridization analyses revealed that both mRNA species were highly concentrated in the geniculorecipient layers IVA and IVC, where they were coexpressed in the same neurons. Monocular inactivation by tetrodotoxin injection resulted in a strong and rapid (<3 h) downregulation of these mRNAs, suggesting the retinal activity dependency of their expression. Consistent with the high expression level in V1, clear modulatory effects of 5-HT1B and 5-HT2A receptor agonists on the responses of V1 neurons were observed in in vivo electrophysiological experiments. The modulatory effect of the 5-HT1B agonist was dependent on the firing rate of the recorded neurons: The effect tended to be facilitative for neurons with a high firing rate, and suppressive for those with a low firing rate. The 5-HT2A agonist showed opposite effects. These results suggest that this serotonergic system controls the visual response in V1 for optimization of information processing toward the incoming visual inputs.

Layer-specific sensory processing impairment in the primary somatosensory cortex after motor cortex infarction.

Primary motor cortex (M1) infarctions sometimes cause sensory impairment. Because sensory signals play a vital role in motor control, sensory impairment compromises the recovery and rehabilitation of motor disability. However, the neural mechanism of the sensory impairment is poorly understood. We show that sensory processing in mouse primary somatosensory cortex (S1) was impaired in the acute phase of M1 infarctions and recovered in a layer-specific manner in the subacute phase. This layer-dependent recovery process and the anatomical connection pattern from M1 to S1 suggested that functional connectivity from M1 to S1 plays a key role in the sensory processing impairment. A simulation study demonstrated that the loss of inhibition from M1 to S1 in the acute phase of M1 infarctions could impair sensory processing in S1, and compensation for the inhibition could recover the temporal coding. Consistently, the optogenetic activation of M1 suppressed the sustained response in S1. Taken together, we revealed how focal stroke in M1 alters the cortical network activity of sensory processing, in which inhibitory input from M1 to S1 may be involved.

Accelerated outgrowth in cross-facial nerve grafts wrapped with adipose-derived stem cell sheets.

In this study, we devised a novel cross-facial nerve grafting (CFNG) procedure using an autologous nerve graft wrapped in an adipose-derived stem cell (ADSC) sheet that was formed on a temperature-responsive dish and examined its therapeutic effect in a rat model of facial palsy. The rat model of facial paralysis was prepared by ligating and transecting the main trunk of the left facial nerve. The sciatic nerve was used for CFNG, connecting the marginal mandibular branch of the left facial nerve and the marginal mandibular branch of the right facial nerve. CFNG alone, CFNG coated with an ADSC suspension, and CFNG wrapped in an ADSC sheet were transplanted in eight rats each, designated the CFNG, suspension, and sheet group, respectively. Nerve regeneration was compared histologically and physiologically. The time to reinnervation, assessed by a facial palsy scoring system, was significantly shorter in the sheet group than in the other two groups. Evoked compound electromyography showed a significantly higher amplitude in the sheet group (4.2 ± 1.3 mV) than in the suspension (1.7 ± 1.2 mV) or CFNG group (1.6 ± 0.8 mV; p < .01). Toluidine blue staining showed that the number of myelinated fibers was significantly higher in the sheet group (2,450 ± 687) than in the suspension (1,645 ± 659) or CFNG group (1,049 ± 307; p < .05). CFNG in combination with ADSC sheets, prepared using temperature-responsive dishes, promoted axonal outgrowth in autologous nerve grafts and reduced the time to reinnervation.

Tonic GABAergic Inhibition Is Essential for Nerve Injury-Induced Afferent Remodeling in the Somatosensory Thalamus and Ectopic Sensations.

Peripheral nerve injury induces functional and structural remodeling of neural circuits along the somatosensory pathways, forming the basis for somatotopic reorganization and ectopic sensations, such as referred phantom pain. However, the mechanisms underlying that remodeling remain largely unknown. Whisker sensory nerve injury drives functional remodeling in the somatosensory thalamus: the number of afferent inputs to each thalamic neuron increases from one to many. Here, we report that extrasynaptic γ-aminobutyric acid-type A receptor (GABAAR)-mediated tonic inhibition is necessary for that remodeling. Extrasynaptic GABAAR currents were potentiated rapidly after nerve injury in advance of remodeling. Pharmacological activation of the thalamic extrasynaptic GABAARs in intact mice induced similar remodeling. Notably, conditional deletion of extrasynaptic GABAARs in the thalamus rescued both the injury-induced remodeling and the ectopic mechanical hypersensitivity. Together, our results reveal a molecular basis for injury-induced remodeling of neural circuits and may provide a new pharmacological target for referred phantom sensations after peripheral nerve injury.

Corrigendum to "Dedifferentiated fat cells in polyglycolic acid-collagen nerve conduits promote rat facial nerve regeneration" [Regen Ther 11 (2019) 240-248].

[This corrects the article DOI: 10.1016/j.reth.2019.08.004.].

Surround suppression sharpens orientation tuning in the cat primary visual cortex.

In the primary visual cortex (V1), the response of a neuron to stimulation of its classical receptive field (CRF) is suppressed by concurrent stimulation of the extraclassical receptive field (ECRF), a phenomenon termed 'surround suppression'. It is also known that the orientation tuning of V1 neurons becomes sharper as the size of the stimulus increases beyond the CRF. However, there have been few quantitative investigations of the relationship between sharpening of orientation tuning and surround suppression. We examined this relationship in 73 V1 neurons recorded from anesthetized and paralysed cats using sinusoidal grating patches as stimuli. We found that sharpening of orientation tuning was significantly correlated with the strength of surround suppression for large stimuli that cover both CRF and ECRF. Furthermore, simulation analysis using a variety of tuning widths and most suppressive orientation of orientation-tuned surround suppression demonstrated that broadly orientation-tuned surround suppression sharpens orientation tuning for large gratings without shift in optimal orientation. Our findings suggest that one of the functional roles of surround suppression in V1 is enhancement of orientation discrimination for large and uniformly patterned objects.

Interhemispherically dynamic representation of an eye movement-related activity in mouse frontal cortex.

Cortical plasticity is fundamental to motor recovery following cortical perturbation. However, it is still unclear how this plasticity is induced at a functional circuit level. Here, we investigated motor recovery and underlying neural plasticity upon optogenetic suppression of a cortical area for eye movement. Using a visually-guided eye movement task in mice, we suppressed a portion of the secondary motor cortex (MOs) that encodes contraversive eye movement. Optogenetic unilateral suppression severely impaired contraversive movement on the first day. However, on subsequent days the suppression became inefficient and capability for the movement was restored. Longitudinal two-photon calcium imaging revealed that the regained capability was accompanied by an increased number of neurons encoding for ipsiversive movement in the unsuppressed contralateral MOs. Additional suppression of the contralateral MOs impaired the recovered movement again, indicating a compensatory mechanism. Our findings demonstrate that repeated optogenetic suppression leads to functional recovery mediated by the contralateral hemisphere.

Dedifferentiated fat cells in polyglycolic acid-collagen nerve conduits promote rat facial nerve regeneration.

INTRODUCTION: Polyglycolic acid (PGA) nerve conduits, an artificial biodegradable nerve regeneration-inducing tube currently used in clinical practice, are effective in regenerating peripheral nerves. Dedifferentiated fat (DFAT) cells differentiate into various cells including adipocytes, osteoblasts, chondrocytes, skeletal muscle cells, and myofibroblasts, when cultured in appropriate differentiation-inducing conditioned culture medium. This study made a hybrid artificial nerve conduit by filling a PGA conduit with DFAT cells, applied the conduit to a rat facial nerve defect model, and investigated the facial nerve regenerative ability of the conduit. METHODS: Under inhalational anesthesia, the buccal branch of the facial nerve in Lewis rats was exposed, and a 7-mm nerve defect was created. PGA nerve conduits were filled with DFAT cells, which were prepared from rat subcutaneous adipose tissue with type I collagen as a scaffold, and then grafted into the nerve defect sites in rats with a microscope (DFAT group) (n = 10). In other rats, PGA artificial nerve conduits alone were similarly grafted into the nerve defect sites (the control group) (n = 10). Reinnervation was confirmed at 13 weeks postoperatively by a retrograde tracer, followed by histological and physiological comparative studies. RESULTS: The mean number of myelinated fibers was significantly higher in DFAT group (1605 ± 806.23) than in the control group (543.6 ± 478.66). Myelin thickness was also significantly lager in DFAT group (0.57 ± 0.17 µm) than in the control group.(0.46 ± 0.14 µm). Although no significant difference was found in the amplitude of compound muscle action potential (CMAP) between DFAT group (2.84 ± 2.47 mV) and the control group (0.88 ± 0.56 mV), whisker motion was lager in DFAT group (9.22° ± 0.65°) than in the control group (1.9° ± 0.84°). CONCLUSIONS: DFAT cell-filled PGA conduits were found to promote nerve regeneration in an experimental rat facial nerve defect model.

Receptive field properties of cat perigeniculate neurons correlate with excitatory and inhibitory connectivity to LGN relay neurons.

The cat perigeniculate nucleus (PGN) is a visual sector of the thalamic reticular nucleus that consists of GABAergic neurons. It receives excitatory axon-collateral input from relay neurons of the dorsal lateral geniculate nucleus (LGN) to which it provides inhibitory input. Thus, it is usually argued that the PGN works as feedback inhibition to the LGN. At the single neuron level, however, this circuit can also provide lateral inhibition. Which inhibition dominates in the visual circuit of the thalamus has yet to be well characterized. In this study, we conducted cross-correlation analysis of single spike trains simultaneously recorded from PGN and LGN neurons in anesthetized cats. For 12 pairs of functionally connected PGN and LGN neurons with overlapped receptive fields (RF), we quantitatively compared RF properties including the spatial frequency (SF) and temporal frequency (TF) tunings of each neuron. We found the SF and TF tunings of PGN neurons and LGN neurons were similar when there was only excitatory input from the LGN neuron to the PGN neuron, but different when the PGN neuron returned inhibitory inputs back, suggesting the circuit between PGN and LGN neurons works as lateral inhibition for these properties.