Coordinated Spine Pruning and Maturation Mediated by Inter-Spine Competition for Cadherin/Catenin Complexes.

Dendritic spines are postsynaptic compartments of excitatory synapses that undergo dynamic changes during development, including rapid spinogenesis in early postnatal life and significant pruning during adolescence. Spine pruning defects have been implicated in developmental neurological disorders such as autism, yet much remains to be uncovered regarding its molecular mechanism. Here, we show that spine pruning and maturation in the mouse somatosensory cortex are coordinated via the cadherin/catenin cell adhesion complex and bidrectionally regulated by sensory experience. We further demonstrate that locally enhancing cadherin/catenin-dependent adhesion or photo-stimulating a contacting channelrhodopsin-expressing axon stabilized the manipulated spine and eliminated its neighbors, an effect requiring cadherin/catenin-dependent adhesion. Importantly, we show that differential cadherin/catenin-dependent adhesion between neighboring spines biased spine fate in vivo. These results suggest that activity-induced inter-spine competition for ß-catenin provides specificity for concurrent spine maturation and elimination and thus is critical for the molecular control of spine pruning during neural circuit refinement.

An increase in dendritic plateau potentials is associated with experience-dependent cortical map reorganization.

The organization of sensory maps in the cerebral cortex depends on experience, which drives homeostatic and long-term synaptic plasticity of cortico-cortical circuits. In the mouse primary somatosensory cortex (S1) afferents from the higher-order, posterior medial thalamic nucleus (POm) gate synaptic plasticity in layer (L) 2/3 pyramidal neurons via disinhibition and the production of dendritic plateau potentials. Here we address whether these thalamocortically mediated responses play a role in whisker map plasticity in S1. We find that trimming all but two whiskers causes a partial fusion of the representations of the two spared whiskers, concomitantly with an increase in the occurrence of POm-driven N-methyl-D-aspartate receptor-dependent plateau potentials. Blocking the plateau potentials restores the archetypical organization of the sensory map. Our results reveal a mechanism for experience-dependent cortical map plasticity in which higher-order thalamocortically mediated plateau potentials facilitate the fusion of normally segregated cortical representations.

Dual-Component Structural Plasticity Mediated by αCaMKII Autophosphorylation on Basal Dendrites of Cortical Layer 2/3 Neurones.

Sensory cortex exhibits receptive field plasticity throughout life in response to changes in sensory experience and offers the experimental possibility of aligning functional changes in receptive field properties with underpinning structural changes in synapses. We looked at the effects on structural plasticity of two different patterns of whisker deprivation in male and female mice: chessboard deprivation, which causes functional plasticity; and all deprived, which does not. Using 2-photon microscopy and chronic imaging through a cranial window over the barrel cortex, we found that layer 2/3 neurones exhibit robust structural plasticity, but only in response to whisker deprivation patterns that cause functional plasticity. Chessboard pattern deprivation caused dual-component plasticity in layer 2/3 by (1) increasing production of new spines that subsequently persisted for weeks and (2) enlarging spine head sizes in the preexisting stable spine population. Structural plasticity occurred on basal dendrites, but not apical dendrites. Both components of plasticity were absent in αCaMKII-T286A mutants that lack LTP and experience-dependent potentiation in barrel cortex, implying that αCaMKII autophosphorylation is not only important for stabilization and enlargement of spines, but also for new spine production. These studies therefore reveal the relationship between spared whisker potentiation in layer 2/3 neurones and the form and mechanisms of structural plasticity processes that underlie them.SIGNIFICANCE STATEMENT This study provides a missing link in a chain of reasoning that connects LTP to experience-dependent functional plasticity in vivo We found that increases in dendritic spine formation and spine enlargement (both of which are characteristic of LTP) only occurred in barrel cortex during sensory deprivation that produced potentiation of sensory responses. Furthermore, the dendritic spine plasticity did not occur during sensory deprivation in mice lacking LTP and experience-dependent potentiation (αCaMKII autophosphorylation mutants). We also found that the dual-component dendritic spine plasticity only occurred on basal dendrites and not on apical dendrites, thereby resolving a paradox in the literature suggesting that layer 2/3 neurones lack structural plasticity in response to sensory deprivation.

Neonatal Restriction of Tactile Inputs Leads to Long-Lasting Impairments of Cross-Modal Processing.

Optimal behavior relies on the combination of inputs from multiple senses through complex interactions within neocortical networks. The ontogeny of this multisensory interplay is still unknown. Here, we identify critical factors that control the development of visual-tactile processing by combining in vivo electrophysiology with anatomical/functional assessment of cortico-cortical communication and behavioral investigation of pigmented rats. We demonstrate that the transient reduction of unimodal (tactile) inputs during a short period of neonatal development prior to the first cross-modal experience affects feed-forward subcortico-cortical interactions by attenuating the cross-modal enhancement of evoked responses in the adult primary somatosensory cortex. Moreover, the neonatal manipulation alters cortico-cortical interactions by decreasing the cross-modal synchrony and directionality in line with the sparsification of direct projections between primary somatosensory and visual cortices. At the behavioral level, these functional and structural deficits resulted in lower cross-modal matching abilities. Thus, neonatal unimodal experience during defined developmental stages is necessary for setting up the neuronal networks of multisensory processing.

Whisker-related circuitry in the trigeminal nucleus principalis: Topographic precision.

Single whiskers are topographically represented in the trigeminal (V) nucleus principalis (PrV) by a set of cylindrical aggregates of primary afferent terminals and somata (barrelettes). This isomorphic pattern is transmitted to the thalamus and barrel cortex. However, it is not known if terminals in PrV from neighboring whiskers interdigitate so as to violate rules of spatial parcellation predicted by barrelette borders; nor is it known the extent to which higher order inputs are topographic. The existence of inter-whisker arbor overlap or diffuse higher order inputs would demand additional theoretical principles to account for single whisker dominance in PrV cell responses. In adult rats, first, primary afferent pairs responding to the same or neighboring whiskers and injected with Neurobiotin or horseradish peroxidase were rendered brown or black to color-code their terminal boutons. When collaterals from both fibers appeared in the same topographic plane through PrV, the percentage of the summed area of the two arbor envelopes that overlapped was computed. For same-whisker pairs, overlap was 5 ± 6% (mean ± SD). For within-row neighbors, overlap was 2 ± 5%. For between-row neighbors, overlap was 1 ± 4%. Second, the areas of whisker primary afferent arbors and their corresponding barrelettes in the PrV were compared. In the transverse plane, arbor envelopes significantly exceeded the areas of cytochrome oxidase-stained barrelettes; arbors often extended into neighboring barrelettes. Third, bulk tracing of the projections from the spinal V subnucleus interpolaris (SpVi) to the PrV revealed strict topography such that they connect same-whisker barrelettes in the SpVi and PrV. Thus, whisker primary afferents do not exclusively project to their corresponding PrV barrelette, whereas higher order SpVi inputs to the PrV are precisely topographic.

Deprivation-induced dendritic shrinkage might be oppositely affected by the expression of wild-type and mutated human amyloid precursor protein.

The physiological role of the amyloid precursor protein (APP) and its proteolytic fragments in the brain is associated with neuronal survival, neurite outgrowth, synaptic formation, and neuronal plasticity. However, malregulation of APP processing leads to disordered balance of fragments, which may results in opposite, degenerative neuronal effects. In the present study, we analyzed in vivo effects of the expression of wild-type or mutated human APP on afferent deprivation-induced changes of dendritic morphology. After vibrissectomy, expression of wild-type human APP prevented diameter shrinkage of dendritic segments as well as dendritic rarefaction of apical arbors. In contrast, mutant human APP expression exacerbated degenerative changes of deprived barrel neurons. Degradation of apical arbors was especially pronounced. Results demonstrate for the first time opposite effects of the expression of wild-type and mutated human APP on deprivation-induced dendritic restructuring in vivo.

Sensory lesioning induces microglial synapse elimination via ADAM10 and fractalkine signaling.

Microglia rapidly respond to changes in neural activity and inflammation to regulate synaptic connectivity. The extracellular signals, particularly neuron-derived molecules, that drive these microglial functions at synapses remain a key open question. Here we show that whisker lesioning, known to dampen cortical activity, induces microglia-mediated synapse elimination. This synapse elimination is dependent on signaling by CX3CR1, the receptor for microglial fractalkine (also known as CXCL1), but not complement receptor 3. Furthermore, mice deficient in CX3CL1 have profound defects in synapse elimination. Single-cell RNA sequencing revealed that Cx3cl1 is derived from cortical neurons, and ADAM10, a metalloprotease that cleaves CX3CL1 into a secreted form, is upregulated specifically in layer IV neurons and in microglia following whisker lesioning. Finally, inhibition of ADAM10 phenocopies Cx3cr1-/- and Cx3cl1-/- synapse elimination defects. Together, these results identify neuron-to-microglia signaling necessary for cortical synaptic remodeling and reveal that context-dependent immune mechanisms are utilized to remodel synapses in the mammalian brain.

[NFLUENCE OF SPONTANEOUS PARTIAL SENSORY DEPRIVATION ON MALE C57BL/6N MICE BEHAVIOR].

Vibrissae loss associated with the peculiarities of the intragroup social interaction may be an important factor affecting the animals' performance in various behavioral tests. To evaluate the influence of spontaneous partial sensory deprivation as a consequence of the barbering activity of a cage mate, the battery of tests was conducted in male C57Bl/6N mice. The results indicate that the behavior of mice without vibrissae significantly differs from control animals in the tube, open field, social interaction and forced swim tests. Thus, the present findings suggest that vibrissae conditions have to be assessed before the inclusion of animals into experimental groups and/or further considered in data analysis.

Dissociating barrel development and lesion-induced plasticity in the mouse somatosensory cortex.

In the mouse somatosensory cortex, thalamocortical axons (TCAs) corresponding to individual whiskers cluster into restricted barrel domains during the first days of life. If whiskers are lesioned before that time, the cortical space devoted to the afferents from the damaged whisker shrinks and becomes occupied by thalamocortical afferents from neighboring unlesioned whiskers. This plasticity ends by postnatal day 3 (P3) to P4 when barrels emerge. To test whether TCA development and lesion-induced plasticity are linked, we used monoamine oxidase A knock-out (MAOA-KO) mice in which normal TCA development is halted by an excess of serotonin. Normal TCA development can be restored when serotonin levels are lowered by parachlorophenylalanine (PCPA). By varying the time of PCPA administration, we found that barrel development can be reinitiated until P11, although the emergence of TCA clusters becomes gradually slower and less complete. In mice in which barrels emerge 3 d later than the normal schedule, at P6 instead of P3, we examined lesion-induced plasticity. We find a progressive decline of the lesion-induced plasticity and a closure at P3, similar to normal mice, showing that this plasticity is not influenced by an excess of serotonin levels. Thus, in MAOA-KO mice, the emergence of barrel patterning can be delayed without a concomitant delay in lesion-induced plasticity, and the cortical space devoted to one whisker representation cannot be modified by the periphery once patterning is imprinted in the subcortical relays. We conclude that the closure of the lesion-induced plasticity period in the barrelfield is probably not determined at the cortical level.

Involvement of TRPV1 and TRPA1 in incisional intraoral and extraoral pain.

Thermal and mechanical hypersensitivity in the injured region is a common complication. Although it is well known clinically that thermal and mechanical sensitivity of the oral mucosa is different from that of the skin, the mechanisms underlying injured pain of the oral mucosa remain poorly understood. The transient receptor potential (TRP) vanilloid 1 (TRPV1) and TRP ankyrin 1 (TRPA1) in primary afferent neurons are known to contribute to pathological pain. Therefore, we investigated whether TRPV1 and/or TRPA1 contribute to thermal and mechanical hypersensitivity following oral mucosa or whisker pad skin incision. Strong heat and mechanical and cold hypersensitivity was caused in the buccal mucosa and whisker pad skin following incisions. On day 3 after the incisions, the number of TRPV1-immunoreactive (IR) and TRPA1-IR trigeminal ganglion (TG) neurons innervating the buccal mucosa and whisker pad skin was significantly increased, and the number of TRPV1/TRPA1-IR TG neurons innervating whisker pad skin, but not the buccal mucosa, was significantly increased. Administration of the TRPV1 antagonist, SB366791, to the incised site produced a significant suppression of heat hyperalgesia in both the buccal mucosa and whisker pad skin, as well as mechanical allodynia in the whisker pad skin. Administration of the TRPA1 antagonist, HC-030031, to the incised site suppressed mechanical allodynia and cold hyperalgesia in both the buccal mucosa and whisker pad skin, as well as heat hyperalgesia in the whisker pad skin. These findings indicate that altered expressions of TRPV1 and TRPA1 in TG neurons are involved in thermal and mechanical hypersensitivity following the buccal mucosa and whisker pad skin incision. Moreover, diverse changes in the number of TRPV1 and TRPA1 coexpressed TG neurons in whisker pad skin-incised rats may contribute to the intracellular interactions of TRPV1 and TRPA1 associated with whisker pad skin incision, whereas TRPV1 and TRPA1 expression in individual TG neurons is involved in buccal mucosa-incised pain.

Reassemblage of primary cell aggregates and modulation of subcortical connections in the thalamic relay nucleus: effects of vibrissal damage in the developing whisker-to-barrel pathway in the mouse.

To investigate the mechanisms underlying the reorganization of barrels in the whisker-tobarrel pathway, the facial vibrissae of mice were damaged by electrocauterization at alternate positions on either postnatal day 0 (P0) or P3, before or after the onset of cell aggregation in the thalamus and cortex. Animals were subsequently killed on P8, topographical changes were examined by cytochrome C oxidase histochemistry, and afferent connections were identified using DiI tracer. The cytoarchitecture was characterized with bisbenzimide counterstain. Regardless of when damage was done, the reorganized barreloids and barrels in the thalamus and cortex, respectively, were integrated in an array that represented the topography of undamaged vibrissae. In the brainstem, although the original framework of the array was preserved, defective cell aggregates remained, possibly still in contact with damaged vibrissae. During normal development, on P0 cell aggregates are formed only in the brainstem, and begin to be organized at the other levels of the pathway on P3. Therefore, when damage is induced on P3, the primary cell aggregates are replaced by new, possibly recombined, cell aggregates in the thalamus and cortex to represent the new peripheral topography. The presumably recombined aggregates indicate that cell reassemblage occurred between neighboring cell aggregates. Concomitant with these changes, afferent fibers originating in the brainstem and thalamus extended their terminal arborizations to delineate the new cell aggregates in the thalamus and cortex, respectively. These findings indicate that activity-dependent competitive interactions of afferents may play a crucial role in organizing the topography of cell aggregation and reassemblage in response to vibrissal damage at each level of the pathway.

Development and lesion induced reorganization of the cortical representation of the rat's body surface as revealed by immunocytochemistry for serotonin.

Immunocytochemistry with an antiserum directed against serotonin (5-HT) was used to assess the development of the representation of the body surface in the rat's primary somatosensory cortex (S-I). Within 1 hour of birth (P-O), 5-HT-positive fibers were present in the marginal zone, the cortical plate, and developing layers V and VI. Immunoreactivity in the marginal zone consisted of a thin band of coarse fibers oriented parallel to the pia. Only a small number of isolated fibers were visible in the cortical plate. A denser network of both coarse and fine fibers could be seen in presumptive layers V and VI. By the first hour of P-I, 5-HT-positive axons in the deeper cortical plate were organized into a crude representation of the rat's body surface. At this age, aggregates of fibers corresponding to the head, lower jaw, trunk, and forepaw could be clearly distinguished. These regions of dense 5-HT immunoreactivity consisted primarily of fine caliber axons that had invaded the lower part of the cortical plate. Dense aggregates of fine caliber axons were also visible in developing layers V and VI. Coarse 5-HT-positive fibers were visible in all layers, but they did not appear to contribute to the pattern that corresponded to the body surface. By the first hour of P-2, the map of the body surface in S-I was more refined and a row-related organization of 5-HT-immunoreactive fibers was visible in the portion of the cortex representing the vibrissa pad. The laminar distributions of coarse and fine caliber serotoninergic axons at this age were essentially the same as on P-I. By P-2.5 (60 hours after birth), patches of 5-HT-positive fibers corresponding to individual vibrissa follicles were clearly evident. These consisted of dense aggregates of fine caliber axons that were centered in presumptive layer IV, but which also extended above and below this lamina. Over the next 3 days, the pattern continued to mature. By P-4, dense 5-HT labelling was also visible in the secondary somatosensory cortex (S-II). By the beginning of P-5, clusters of fibers corresponding to more rostral facial hairs and individual digits within the forepaw representation could also be discerned. By P-12, the differential distribution of 5-HT fibers in S-I was no longer visible. Thus, immunocytochemistry for serotonin showed a representation in S-I homeomorphic with the body surface prior to the age at which it can be discerned with other methods thought to reveal thalamocortical axons. Transection of the infraorbital nerve (ION) on the day of birth altered the organization of the vibrissal representation in the contralateral cortex from the earliest age at which it could be detected by 5-HT immunocytochemistry in normal animals. However, the departure from the normal organization was gradual. Row-related organization was clearly visible in the cortices of rats sacrificed on P-3, but not in those of rats that were killed on P-5. These results suggested that the organization of the 5-HT innervation of the cortex may be guided by thalamic afferents and further that some aspects of this guidance persist, albeit temporarily, after ION transection on P-0. The 5-HT immunoreactivity that we observed in the developing somatosensory cortex was not contained in thalamocortical axons. Unilateral electrocautery of the ventrobasal thalamus on P-4 did not reduce the density or alter the pattern of the 5-HT innervation of the cortex in rats that were examined on P-6.

Experience-dependent regulation of synaptic zinc is impaired in the cortex of aged mice.

Zinc plays an important role in synaptic signaling in the mammalian cerebral cortex. Zinc is sequestered into presynaptic vesicles of subpopulations of glutamatergic neurons and is released by depolarization, in a calcium-dependent manner. As the majority of mechanisms that have been suggested to participate in experience-dependent alterations in synaptic strength in the cerebral cortex implicate signaling by glutamate, it stands to reason that zincergic signaling might also be crucial. Here we show that synaptic zinc is rapidly and dynamically modulated in relation to alterations in sensory input and that this response is highly age-dependent. Juvenile, adult, and aged mice were subjected to whisker removal and levels of staining for synaptic zinc in deprived and non-deprived cortical barrels were quantitatively assessed at post-deprivation times ranging from 3 h to 21 days. In the first 12 h, zinc levels increased slightly, but significantly, in all groups. At later time points, zinc levels increased robustly (23%) in the youngest group by 24 h and remained elevated through 7 days. By contrast, deprivation-induced changes in zinc staining in aged animals, achieved their maximal levels at 12 h (approximately 10%) and steadily declined thereafter. Adult animals revealed a biphasic, intermediate change with time. In all age groups, levels of zinc staining returned to baseline by 21 days after whisker plucking. However, only in juvenile and adult mice did we observe that the level of zinc staining in deprived barrel hollows, was correlated with the length of whiskers as they regrew. Our data suggest that alterations in the regulation of synaptic zinc may be involved with decrements of synaptic plasticity that accompany senescence.

Regulation of growth-associated protein 43 (GAP-43) messenger RNA associated with plastic change in the adult rat barrel receptor complex.

Plastic change occurs in the adult rat barrel receptor complex following peripheral deafferentation by removal of facial vibrissae (vibrissectomy) and can be prevented by prior depletion of brain norepinephrine. Growth-associated protein (GAP-43, B50, F1, pp46), a marker for synaptic reorganization, increases in the barrel cortex of adult rats following both peripheral and central deafferentation. Here we followed changes in GAP-43 mRNA expression in the barrel receptor system following vibrissectomy. Adult rats had unilateral total vibrissectomy with sparing of the central (C3) vibrissa. By in situ hybridization, GAP-43 mRNA first increased at 24h (9%, P < 0.05) in the ipsilateral trigeminal complex. Levels remained elevated (up to 25% of the unlesioned side) over the next 6 days, decreased to 88% at 7 days and returned to control levels at 14 days. Contralateral barrel cortex levels of GAP-43 mRNA increased by 14% at 4-5 days remained elevated through 7 days and returned to control levels by 14 days. Increased GAP-43 mRNA levels 6 days after vibrissectomy were reproduced by complete transection of the infraorbital nerve and were blocked by depletion of brain norepinephrine. No change occurred in ventrobasal thalamus GAP-43 mRNA at any time. Dot blot and Northern blot hybridizations of GAP-43 mRNA after vibrissectomy showed a 43% increase in the ipsilateral trigeminal complex and a 16% increase in the contralateral barrel cortex at 3 days and an 84% increase in ipsilateral trigeminal and 50% increase in contralateral barrel cortex GAP-43 mRNA at 6 days, respectively. Thus, deafferentation-induced plasticity in the barrel pathway depends upon norepinephrine and is associated with increase in both GAP-43 mRNA and protein suggesting that this may involve a structural change.

Neonatal electrolytic lesions of the basal forebrain stunt plasticity in mouse barrel field cortex.

Previous studies have shown that neonatal electrolytic lesions of basal forebrain cholinergic projections in mice lead to a transient cholinergic depletion of neocortex and to permanent alterations in cortical cytoarchitecture and in cognitive performance. The present study examines whether neonatal electrolytic lesions of the basal forebrain modify neocortical plasticity. Using cytochrome oxidase histochemistry, we compared cross-sectional areas of individual barrels in the barrel field of four groups of postnatal day 8 (P8) old mice that on P1 received either (1) right electrolytic lesions of the basal forebrain, (2) left C row 1-4 whisker follicle ablations, (3) combined lesion treatments or (4) ice anesthesia only. The size of barrels in basal forebrain lesioned animals was not significantly different from controls. However, the plastic response to whisker removal was compromised in basal forebrain lesioned animals. An index of plasticity, the ratio of row D/row C areas, was reduced significantly in the combined nBM lesioned/follicle ablation group. Compared to whisker-lesioned mice, the expansion in rows B and D and the shrinkage in the lesioned row C area were diminished in the combined treatment group. The present findings correspond to those from a study of rats injected with a cholinergic immunotoxin [Cereb. Cortex 8 (1998) 63]. These results suggest that cholinergic inputs play a role in regulating plasticity as well as in the morphogenesis of mouse sensory-motor cortex.

Ethanolic extract of Astragali radix and Salviae radix prohibits oxidative brain injury by psycho-emotional stress in whisker removal rat model.

Myelophil, an ethanolic extract of Astragali Radix and Salviae Radix, has been clinically used to treat chronic fatigue and stress related disorders in South Korea. In this study, we investigated the protective effects of Myelophil on a whisker removal-induced psycho-emotional stress model. SD rats were subjected to whisker removal after oral administration of Myelophil or ascorbic acid for consecutive 4 days. Whisker removal considerably increased total reactive oxygen species in serum levels as well as cerebral cortex and hippocampal regions in brain tissues. Lipidperoxidation levels were also increased in the cerebral cortex, hippocampus regions, and brain tissue injuries as shown in histopathology and immunohistochemistry. However, Myelophil significantly ameliorated these alterations, and depletion of glutathione contents in both cerebral cortex and hippocampus regions respectively. Serum levels of corticosterone and adrenaline were notably altered after whisker removal stress, whereas these abnormalities were significantly normalized by pre-treatment with Myelophil. The NF-κB was notably activated in both cerebral cortex and hippocampus after whisker removal stress, while it was efficiently blocked by pre-treatment with Myelophil. Myelophil also significantly normalizes alterations of tumor necrosis factor-α, interleukin (IL)-1ß, IL-6 and interferon-γ in both gene expressions and protein levels. These results suggest that Myelophil has protective effects on brain damages in psycho-emotional stress, and the underlying mechanisms involve regulation of inflammatory proteins, especially NF-κB modulation.

Sensory-related neural activity regulates the structure of vascular networks in the cerebral cortex.

Neurovascular interactions are essential for proper brain function. While the effect of neural activity on cerebral blood flow has been extensively studied, whether or not neural activity influences vascular patterning remains elusive. Here, we demonstrate that neural activity promotes the formation of vascular networks in the early postnatal mouse barrel cortex. Using a combination of genetics, imaging, and computational tools to allow simultaneous analysis of neuronal and vascular components, we found that vascular density and branching were decreased in the barrel cortex when sensory input was reduced by either a complete deafferentation, a genetic impairment of neurotransmitter release at thalamocortical synapses, or a selective reduction of sensory-related neural activity by whisker plucking. In contrast, enhancement of neural activity by whisker stimulation led to an increase in vascular density and branching. The finding that neural activity is necessary and sufficient to trigger alterations of vascular networks reveals an important feature of neurovascular interactions.

A system for delivering mechanical stimulation and robot-assisted therapy to the rat whisker pad during facial nerve regeneration.

Functional recovery is typically poor after facial nerve transection and surgical repair. In rats, whisking amplitude remains greatly diminished after facial nerve regeneration, but can recover more completely if the whiskers are periodically mechanically stimulated during recovery. Here we present a robotic "whisk assist" system for mechanically driving whisker movement after facial nerve injury. Movement patterns were either preprogrammed to reflect natural amplitudes and frequencies, or movements of the contralateral (healthy) side of the face were detected and used to control real-time mirror-like motion on the denervated side. In a pilot study, 20 rats were divided into nine groups and administered one of eight different whisk assist driving patterns (or control) for 5-20 minutes, five days per week, across eight weeks of recovery after unilateral facial nerve cut and suture repair. All rats tolerated the mechanical stimulation well. Seven of the eight treatment groups recovered average whisking amplitudes that exceeded controls, although small group sizes precluded statistical confirmation of group differences. The potential to substantially improve facial nerve recovery through mechanical stimulation has important clinical implications, and we have developed a system to control the pattern and dose of stimulation in the rat facial nerve model.

Regeneration of hair follicles is modulated by flightless I (Flii) in a rodent vibrissa model.

Regeneration of cells, tissues, and organs has long captured the attention of researchers for its obvious potential benefits in biomedical applications. Although mammals are notoriously poor at regeneration compared with many lower-order species, the hair follicle, paradoxically a defining characteristic of mammals, is capable of regeneration following partial amputation. To investigate the role of a negative regulator of wound healing, flightless I (Flii), on hair follicle regeneration, the bulbar region of vibrissae from rats as well as strains of mice expressing low (Flii(+/-)), normal (Flii(+/+)), and high (FLII(Tg/Tg)) levels of Flii were surgically amputated, and then allowed to regenerate in vivo. Macroscopic and histological assessment of the regeneration process revealed impaired or delayed regenerative potential in Flii(+/-) follicles. Regenerated follicles expressing high levels of Flii (FLII(Tg/Tg)) produced significantly longer terminal hair fibers. Immunohistochemical analysis was used to characterize the pattern of expression of Flii, as well as markers of hair follicle development and wound healing-associated factors during hair follicle regeneration. These studies confirmed that Flii appears to have a positive role in the regeneration of hair follicles, contrary to its negative influence on wound healing in skin.

Experience-dependent regulation of vesicular zinc in male and female 3xTg-AD mice.

In the mammalian cerebral cortex, zinc is an important modulator of synaptic transmission and conversely, plasticity. Zinc is also involved, in a sex-dependent manner, in the pathogenesis of Alzheimer's disease (AD), where substantial declines in plasticity may occur. To examine this relationship further, the regulation of vesicular zinc was examined after the induction of cortical plasticity through vibrissae plucking in male and female C57Bl/6 and 3xTg-AD mice at various age points. Female C57Bl/6 mice were found to have an elevated response compared to male C57Bl/6 mice through mid-adult ages, a sex-difference likely mediated by the differential regulation of vesicular zinc by the sex hormones. Male 3xTg-AD mice had a significantly greater zincergic response compared to C57Bl/6 mice, which is likely indicative of a compensatory mechanism utilized by the male 3xTg-AD mice to combat the decline in plasticity associated with the AD state. These results exemplify how the regulation of vesicular zinc may be a significant component in the progression of AD, especially regarding the sex-dependent element.