A transchromosomic rat model with human chromosome 21 shows robust Down syndrome features.

Progress in earlier detection and clinical management has increased life expectancy and quality of life in people with Down syndrome (DS). However, no drug has been approved to help individuals with DS live independently and fully. Although rat models could support more robust physiological, behavioral, and toxicology analysis than mouse models during preclinical validation, no DS rat model is available as a result of technical challenges. We developed a transchromosomic rat model of DS, TcHSA21rat, which contains a freely segregating, EGFP-inserted, human chromosome 21 (HSA21) with >93% of its protein-coding genes. RNA-seq of neonatal forebrains demonstrates that TcHSA21rat expresses HSA21 genes and has an imbalance in global gene expression. Using EGFP as a marker for trisomic cells, flow cytometry analyses of peripheral blood cells from 361 adult TcHSA21rat animals show that 81% of animals retain HSA21 in >80% of cells, the criterion for a "Down syndrome karyotype" in people. TcHSA21rat exhibits learning and memory deficits and shows increased anxiety and hyperactivity. TcHSA21rat recapitulates well-characterized DS brain morphology, including smaller brain volume and reduced cerebellar size. In addition, the rat model shows reduced cerebellar foliation, which is not observed in DS mouse models. Moreover, TcHSA21rat exhibits anomalies in craniofacial morphology, heart development, husbandry, and stature. TcHSA21rat is a robust DS animal model that can facilitate DS basic research and provide a unique tool for preclinical validation to accelerate DS drug development.

Netrin-4 regulates thalamocortical axon branching in an activity-dependent fashion.

Axon branching is remodeled by sensory-evoked and spontaneous neuronal activity. However, the underlying molecular mechanism is largely unknown. Here, we demonstrate that the netrin family member netrin-4 (NTN4) contributes to activity-dependent thalamocortical (TC) axon branching. In the postnatal developmental stages of rodents, ntn4 expression was abundant in and around the TC recipient layers of sensory cortices. Neuronal activity dramatically altered the ntn4 expression level in the cortex in vitro and in vivo. TC axon branching was promoted by exogenous NTN4 and suppressed by depletion of the endogenous protein. Moreover, unc-5 homolog B (Unc5B), which strongly bound to NTN4, was expressed in the sensory thalamus, and knockdown of Unc5B in thalamic cells markedly reduced TC axon branching. These results suggest that NTN4 acts as a positive regulator for TC axon branching through activity-dependent expression.

Latent TGF-ß binding protein-2 is essential for the development of ciliary zonule microfibrils.

Latent TGF-ß-binding protein-2 (LTBP-2) is an extracellular matrix protein associated with microfibrils. Homozygous mutations in LTBP2 have been found in humans with genetic eye diseases such as congenital glaucoma and microspherophakia, indicating a critical role of the protein in eye development, although the function of LTBP-2 in vivo has not been well understood. In this study, we explore the in vivo function of LTBP-2 by generating Ltbp2(-/-) mice. Ltbp2(-/-) mice survived to adulthood but developed lens luxation caused by compromised ciliary zonule formation without a typical phenotype related to glaucoma, suggesting that LTBP-2 deficiency primarily causes lens dislocation but not glaucoma. The suppression of LTBP2 expression in cultured human ciliary epithelial cells by siRNA disrupted the formation of the microfibril meshwork by the cells. Supplementation of recombinant LTBP-2 in culture medium not only rescued the microfibril meshwork formation in LTBP2-suppressed ciliary epithelial cells but also restored unfragmented and bundled ciliary zonules in Ltbp2(-/-) mouse eyes under organ culture. Although several reported human mutant LTBP-2 proteins retain normal domain structure and keep the fibrillin-1-binding site intact, none of these mutant proteins were secreted from their producing cells, suggesting secretion arrest occurred to the LTBP-2 mutants owing to conformational alteration. The findings of this study suggest that LTBP-2 is an essential component for the formation of microfibril bundles in ciliary zonules.

Critical period of experience-driven axon retraction in the pharmacologically inhibited visual cortex.

Monocular deprivation (MD) during the critical period reduces the visual cortical response to the deprived eye and causes the geniculocortical axons serving the deprived eye to retract. When MD is combined with a pharmacological inhibition of the visual cortex, the cortical neurons weaken their response to an open eye and the input axons serving the open eye retract. To determine whether the 2 types of ocular dominance (OD) plasticity reflect an experience-driven modification of neural circuits sharing the same developmental time course, we analyzed the OD plasticity in an inhibited visual cortex using cats at different ages. MD did not affect the OD distribution in the inhibited cortex of adults, confirming that the OD plasticity in the inhibited cortex represents a developmental plasticity. In developing animals, the OD plasticity in the inhibited cortex was observed at the late phase of the critical period (P40-46) but not at the early phase (P22-26). We found a retraction of input axons serving an open eye at the late phase, whereas those at the early phase were comparable to the axons of normal animals. Therefore, the maturation of visual circuits might include an experience-driven rearrangement of thalamocortical projections during the late phase of development.

Layer specific regulation of critical period timing and maturation of mouse visual cortex by endocannabinoids.

Plasticity during the critical period is important for the functional maturation of cortical neurons. While characteristics of plasticity are diverse among cortical layers, it is unknown whether critical period timing is controlled by a common or unique molecular mechanism among them. We here clarified layer-specific regulation of the critical period timing of ocular dominance plasticity in the primary visual cortex. Mice lacking the endocannabinoid synthesis enzyme diacylglycerol lipase-α exhibited precocious critical period timing, earlier maturation of inhibitory synaptic function in layers 2/3 and 4, and impaired development of the binocular matching of orientation selectivity exclusively in layer 2/3. Activation of cannabinoid receptor restored ocular dominance plasticity at the normal critical period in layer 2/3. Suppression of GABAA receptor rescued precocious ocular dominance plasticity in layer 4. Therefore, endocannabinoids regulate critical period timing and maturation of visual function partly through the development of inhibitory synaptic functions in a layer-dependent manner.

Phase advance of the light-dark cycle perturbs diurnal rhythms of brain-derived neurotrophic factor and neurotrophin-3 protein levels, which reduces synaptophysin-positive presynaptic terminals in the cortex of juvenile rats.

In adult rat brains, brain-derived neurotrophic factor (BDNF) rhythmically oscillates according to the light-dark cycle and exhibits unique functions in particular brain regions. However, little is known of this subject in juvenile rats. Here, we examined diurnal variation in BDNF and neurotrophin-3 (NT-3) levels in 14-day-old rats. BDNF levels were high in the dark phase and low in the light phase in a majority of brain regions. In contrast, NT-3 levels demonstrated an inverse phase relationship that was limited to the cerebral neocortex, including the visual cortex, and was most prominent on postnatal day 14. An 8-h phase advance of the light-dark cycle and sleep deprivation induced an increase in BDNF levels and a decrease in NT-3 levels in the neocortex, and the former treatment reduced synaptophysin expression and the numbers of synaptophysin-positive presynaptic terminals in cortical layer IV and caused abnormal BDNF and NT-3 rhythms 1 week after treatment. A similar reduction of synaptophysin expression was observed in the cortices of Bdnf gene-deficient mice and Ca(2+)-dependent activator protein for secretion 2 gene-deficient mice with abnormal free-running rhythm and autistic-like phenotypes. In the latter mice, no diurnal variation in BDNF levels was observed. These results indicate that regular rhythms of BDNF and NT-3 are essential for correct cortical network formation in juvenile rodents.

Salt and potassium intake evaluated with spot urine and brief questionnaires in combination with blood pressure control status in hypertensive outpatients in a real-world setting.

Reducing salt and increasing potassium intake are recommended lifestyle modifications for patients with hypertension. The estimated 24-h urinary salt excretion value from spot urine using Tanaka's formula and the salt check-sheet scores, questionnaire-based scores of salt intake, are practical indices of daily salt intake. However, few studies have evaluated salt intake with these methods in hypertensive outpatients. We examined salt and potassium intake with the spot urine method and the salt check-sheet scores of hypertensive outpatients in a multi-facility, real-world setting and examined whether the salt or potassium intake evaluated with these methods related to inadequate blood pressure control. Hypertensive outpatients from 12 medical facilities in the Okinawa prefecture were enrolled from November 2011 to April 2014 (n = 1559, mean age 63.9 years, 46% women). The mean blood pressure, urinary salt excretion value, urinary potassium excretion value, and total score on the salt check-sheet were 129/75 mmHg, 8.7 g/day, 1.6 g/day, and 10.4 points, respectively. The urinary salt excretion value and total score on the salt check-sheet but not urinary potassium excretion value were associated with inadequate blood pressure control (≥140/90 mmHg). Higher body mass index, estimated glomerular filtration rate, urinary potassium excretion value, total score on the salt check-sheet, and presence of inadequate blood pressure control were associated with high urinary salt excretion (≥10.2 g/day). In conclusion, hypertensive outpatients with high urinary salt excretion values estimated using Tanaka's formula or with high scores on the salt check sheet may be candidates for more intensive salt reduction guidance.

Dark Rearing Promotes the Recovery of Visual Cortical Responses but Not the Morphology of Geniculocortical Axons in Amblyopic Cat.

Monocular deprivation (MD) of vision during early postnatal life induces amblyopia, and most neurons in the primary visual cortex lose their responses to the closed eye. Anatomically, the somata of neurons in the closed-eye recipient layer of the lateral geniculate nucleus (LGN) shrink and their axons projecting to the visual cortex retract. Although it has been difficult to restore visual acuity after maturation, recent studies in rodents and cats showed that a period of exposure to complete darkness could promote recovery from amblyopia induced by prior MD. However, in cats, which have an organization of central visual pathways similar to humans, the effect of dark rearing only improves monocular vision and does not restore binocular depth perception. To determine whether dark rearing can completely restore the visual pathway, we examined its effect on the three major concomitants of MD in individual visual neurons, eye preference of visual cortical neurons and soma size and axon morphology of LGN neurons. Dark rearing improved the recovery of visual cortical responses to the closed eye compared with the recovery under binocular conditions. However, geniculocortical axons serving the closed eye remained retracted after dark rearing, whereas reopening the closed eye restored the soma size of LGN neurons. These results indicate that dark rearing incompletely restores the visual pathway, and thus exerts a limited restorative effect on visual function.

Experience-driven axon retraction without binocular imbalance in developing visual cortex.

Refinement of the neural circuit during brain maturation is regulated by experience-driven neural activity. In the mammalian visual cortex, monocular visual deprivation (MD) in the early postnatal life causes a significant loss of cortical responses to a deprived eye and the retraction of input axons serving the deprived eye. A competitive interaction between inputs serving both eyes has been supposed to underlie the effects of MD because the loss of cortical response is much weaker when both eyes are deprived of vision. Also, the input axons do not retract after binocular deprivation. Here, we report that uncorrelated activity between presynaptic and postsynaptic neurons can solely lead to the retraction of geniculocortical axons in the absence of activity imbalance between two inputs. We analyzed the morphology of geniculocortical axons in a pharmacologically inhibited visual cortex of animals with normal vision and of binocularly deprived animals. In the normal vision animals, the axonal arbors in the inhibited cortex showed robust retraction. On the other hand, the arbors in binocularly deprived animals remained mostly intact. These results suggest that a homosynaptic associative mechanism, rather than a heterosynaptic competition between inputs, may play an important role in experience-driven axon retraction.

The Influence of Illumination Color on the Subjective Visual Recognition of Biological Specimens.

BACKGROUND: Visual examination by the naked eye is integral to medical diagnosis and surgery. The illumination in conditioned color is widely used for visual inspection in the industry but has not been introduced to the biomedical context. The color that can enhance the visual recognition of individual tissues is still unknown. Therefore, we carried out a visual recognition experiment on biological specimens to determine the subjective preference for illumination color based on questionnaires. METHODS: Twenty healthy subjects were asked to compare the visual recognizability of several rat tissues between the illuminations in test colors and white. The rats were anesthetized, and the femoral vein and abdominal cavity were exposed. Seven tissues were selected for a visual recognition test. Illumination was generated using a multi-color LED light. The subjects observed the tissues under the illuminations of white and one of the test colors alternately and reported which illumination is suitable for visual recognition using a questionnaire. RESULTS: The analysis of the questionnaires showed that the blue test color was more effective than white illumination in the visual recognition of fine structures such as the branching of blood vessels and nerves, and red illumination disturbed the visual recognizability of the same tissues. On the other hand, the red but not the blue illumination improved the visual recognizability of the vein beneath the intact skin. As to the recognition of individual tissues in the abdominal cavity, the white illumination gave a better visual recognizability compared to every other test color. CONCLUSION: This study shows that the illumination color influences the visual recognition of biological specimens and the adequate color for the visual recognition of specific tissue parts is distinct among biological specimens. Using the lighting system to make fine adjustments to the illumination color may be useful in medical diagnosis and surgery.

Evaluation of Fluoro-Jade C Staining: Specificity and Application to Damaged Immature Neuronal Cells in the Normal and Injured Mouse Brain.

Fluoro-Jade C (FJC) staining is widely used for the specific detection of all degenerating mature neurons, including apoptotic, necrotic, and autophagic cells. However, whether FJC staining can detect degenerating immature neurons and neural stem/precursor cells remains unclear. In addition, some conflicting studies have shown that FJC and its ancestral dyes, Fluoro-Jade (FJ) and FJB, can label resting/activated astrocytes and microglia. In the present study, we examined the validity of FJC staining for the detection of neuronal cells in adult and embryonic mouse brains under normal and injured conditions. In the adult rodent subventricular zone (SVZ)-rostral migratory stream (RMS)-olfactory bulb (OB) system, apoptosis associated with neurogenesis occurs under normal conditions. Using this system, we detected FCJ positive (+) cells, some of which were doublecortin (DCX)(+) neuroblasts, in addition to neuronal nuclei (NeuN)(+) mature neurons. FJC negative (-) apoptotic cells expressing activated Caspase 3 were also observed, and a small number of FJC(+)/ionized calcium-binding adaptor molecule 1 (Iba1)(+) microglia and FJC(+)/glial fibrillary acidic protein (GFAP)(+) astrocytes were observed in the normal brain. Next, we analyzed embryonic brains, in which the apoptosis of neural stem/precursor cells was induced by the administration of N-ethyl-N-nitrosourea (ENU) or ethanol at embryonic day 14 or 10, respectively. In those brains, FJC(+) neural stem/precursor cells and neuroepithelial cells expressing SRY-related HMG-box 2 (Sox2) were observed. Surprisingly degenerating mesenchymal cells were also FJC(+). The present study indicates that FJC is a reliable marker for degenerating neuronal cells during all differentiation stages. However, FJC could also label degenerating non-neuronal cells under some conditions.

A phase advance of the light-dark cycle stimulates production of BDNF, but not of other neurotrophins, in the adult rat cerebral cortex: association with the activation of CREB.

Circadian variation in the expression of brain-derived neurotrophic factor (BDNF) indicates that BDNF is involved in the regulation of diurnal rhythms in a variety of biological processes. However, it is still unclear which brain regions alter their BDNF levels in response to external light input. Therefore, in selected brain regions of adult male rats, we investigated diurnal variation, as well as the effects of a single eight-hour phase advance of the light-dark cycle, on the levels of BDNF and of other neurotrophins. The cerebellum, hippocampus and cerebral cortex containing visual cortex (VCX) showed diurnal variation in BDNF protein levels and the VCX also in NT-3 levels. In the VCX and the region containing the entorhinal cortex and amygdala (ECX), BDNF protein levels were increased 12 h after the phase advance, while BDNF mRNA levels were increased significantly in the VCX and slightly in the ECX after 4 h. After one week, however, BDNF protein levels were reduced in eight brain regions out of 13 examined. BDNF levels in the ECX and VCX were significantly different between light rearing and dark rearing, while a hypothyroid status did not produce an effect. Cyclic AMP responsive element-binding protein (CREB), a transcription factor for BDNF, was greatly activated by the phase advance in the ECX and VCX, suggesting the existence of CREB-mediated pathways of BDNF synthesis that are responsive to external light input.

Effects of anesthesia on immunohistochemical detection of phosphorylated extracellular signal-regulated kinase in cerebral cortex.

During attempts to examine the phosphorylation status of extracellular signal-regulated kinase (ERK) in cerebral cortex immunohistochemically, we determined whether deep anesthesia for euthanasia disturbs the phosphorylation status of ERK, because the anesthesia might influence activity-dependent phosphorylation of ERK. We compared effects of short (2 and 5 min) and long (>10 min) anesthesia by pentobarbital on the immunoreactivity for phosphorylated ERK in the visual and entorhinal cortices of rat. The long anesthesia drastically reduced the density of phosphorylated ERK immunopositive cells to about 15% of the short anesthesia condition. The reduction was observed in all cortical regions. We found no significant difference in pERK immunoreactivity between 2 and 5 min groups. A reduction of similar degree was induced by long anesthesia with isoflurane. Even if a similar duration of anesthesia is given, the immunohistochemical results possibly contain a variation due to the individual difference in the sensitivity to the anesthetics. We demonstrated that the variation of pERK immunopositive cell density in the visual cortex was significantly reduced by normalizing the values to the density in the nonvisual area in the entorhinal cortex, thus enabling us to detect differences between animals under different visual conditions with higher sensitivity. Therefore, the variation could be reduced by calculating the ratio of immunoreactivity in the area of interest to that in other cortical area as reference.

Identification of NeuN immunopositive cells in the adult mouse subventricular zone.

In the adult rodent subventricular zone (SVZ), there are neural stem cells (NSCs) and the specialized neurogenic niche is critical to maintain their stemness. To date, many cellular and noncellular factors that compose the neurogenic niche and markers to identify subpopulations of Type A cells have been confirmed. In particular, neurotransmitters regulate adult neurogenesis and mature neurons in the SVZ have been only partially analyzed. Moreover, Type A cells, descendants of NSCs, are highly heterogeneous and more molecular markers are still needed to identify them. In the present study, we systematically classified NeuN, commonly used as a marker of mature and immature post-mitotic neurons, immunopositive (+) cells within the adult mouse SVZ. These SVZ-NeuN+ cells (SVZ-Ns) were mainly classified into two types. One was mature SVZ-Ns (M-SVZ-Ns). Neurochemical properties of M-SVZ-Ns were similar to those of striatal neurons, but their birth date and morphology were different. M-SVZ-Ns were generated during embryonic and early postnatal stages with bipolar peaks and extended their processes along the wall of the lateral ventricle. The second type was small SVZ-Ns (S-SVZ-Ns) with features of Type A cells. They expressed not only markers of Type A cells, but also proliferated and migrated from the SVZ to the olfactory bulb. Furthermore, S-SVZ-Ns could be classified into two types by their spatial locations and glutamic acid decarboxylase 67 expression. Our data indicate that M-SVZ-Ns are a new component of the neurogenic niche and S-SVZ-Ns are newly identified subpopulations of Type A cells.

Substrate specificity of a chimera made from Xenopus SGLT1-like protein and rabbit SGLT1.

To characterize the sugar translocation pathway of Na(+)/glucose cotransporter type 1 (SGLT1), a chimera was made by substituting the extracellular loop between transmembrane domain (TM) 12 and TM13 of Xenopus SGLT1-like protein (xSGLT1L) with the homologous region of rabbit SGLT1. The chimera was expressed in Xenopus oocytes and its transport activity was measured by the two-microelectrode voltage-clamp method. The substrate specificity of the chimera was different from those of xSGLT1L and SGLT1. In addition the chimera's apparent Michaelis-Menten constant (K(m)) for myo-inositol, 0.06 mM, was about one fourth of that of xSGLT1L, 0.25 mM, while the chimera's apparent K(m) for d-glucose, 0.8 mM, was about one eighth of that of xSGLT1L, 6.3 mM. Our results suggest that the extracellular loop between TM12 and TM13 participates in the sugar transport of SGLT1.

Neuroprotective effect of transcorneal electrical stimulation on the acute phase of optic nerve injury.

PURPOSE: Traumatic optic neuropathy often induces a loss of vision that proceeds rapidly within several hours, together with retinal ganglion cell death, in a much slower time course. Electrical stimulation has previously been shown to rescue injured retinal ganglion cells from cell death. The present study tests whether transcorneal electrical stimulation could preserve visual function after an optic nerve crush. METHODS: Transcorneal electrical stimulation was given immediately after a calibrated optic nerve crush. We measured visually evoked potentials (VEPs) in the visual cortex of rats before and immediately after the optic nerve crush and after the transcorneal stimulation to estimate an extent of damage and effects of stimulation in individual animals. In addition, the retinal axons were labeled with a fluorescent anterograde tracer to determine whether the transcorneal electrical stimulation can protect the retinal axons from degeneration. RESULTS: The optic nerve crush was made at an intensity that does not allow a spontaneous recovery of VEP for 1 week. The transcorneal stimulation immediately increased VEP amplitude impaired by the optic nerve crush, and this augmentation was often preserved after 1 week. In the stimulated animals, a larger amount of retinal axons projected centrally beyond the crushed region in comparison to the unstimulated animals. CONCLUSIONS: Transcorneal electrical stimulation would restore the functional impairment of optic nerve by traumatic injury at a very early stage and protect retinal axons from the ensuing degeneration.

Early deprivation increases high-leaning behavior, a novel anxiety-like behavior, in the open field test in rats.

The open field test is one of the most popular ethological tests to assess anxiety-like behavior in rodents. In the present study, we examined the effect of early deprivation (ED), a model of early life stress, on anxiety-like behavior in rats. In ED animals, we failed to find significant changes in the time spent in the center or thigmotaxis area of the open field, the common indexes of anxiety-like behavior. However, we found a significant increase in high-leaning behavior in which animals lean against the wall standing on their hindlimbs while touching the wall with their forepaws at a high position. The high-leaning behavior was decreased by treatment with an anxiolytic, diazepam, and it was increased under intense illumination as observed in the center activity. In addition, we compared the high-leaning behavior and center activity under various illumination intensities and found that the high-leaning behavior is more sensitive to illumination intensity than the center activity in the particular illumination range. These results suggest that the high-leaning behavior is a novel anxiety-like behavior in the open field test that can complement the center activity to assess the anxiety state of rats.

Chronic Inactivation of the Orbitofrontal Cortex Increases Anxiety-Like Behavior and Impulsive Aggression, but Decreases Depression-Like Behavior in Rats.

The orbitofrontal cortex (OFC) is involved in emotional processing, and orbitofrontal abnormalities have often been observed in various affective disorders. Thus, chronic dysfunction of the OFC may cause symptoms of affective disorders, such as anxiety, depression and impulsivity. Previous studies have investigated the effect of orbitofrontal dysfunction on anxiety-like behavior and impulsive aggression in rodents, but the results are inconsistent possibly reflecting different methods of OFC inactivation. These studies used either a lesion of the OFC, which may affect other brain regions, or a transient inactivation of the OFC, whose effect may be restored in time and not reflect effects of chronic OFC dysfunction. In addition, there has been no study on the effect of orbitofrontal inactivation on depression-like behavior in rodents. Therefore, the present study examined whether chronic inactivation of the OFC by continuous infusion of a GABAA receptor agonist, muscimol, causes behavioral abnormalities in rats. Muscimol infusion inactivated the ventral and lateral part of the OFC. Following a week of OFC inactivation, the animals showed an increase in anxiety-like behavior in the open field test and light-dark test. Impulsive aggression was also augmented in the chronically OFC-inactivated animals because they showed increased frequency of fighting behavior induced by electric foot shock. On the other hand, chronic OFC inactivation reduced depression-like behavior as evaluated by the forced swim test. Additionally, it did not cause a significant change in corticosterone secretion in response to restraint stress. These data suggest that orbitofrontal neural activity is involved in the regulation of anxiety- and depression-like behaviors and impulsive aggression in rodents.

Long-term depression is not induced by low-frequency stimulation in rat visual cortex in vivo: a possible preventing role of endogenous brain-derived neurotrophic factor.

Low-frequency stimulation (LFS) at 1 Hz for 15 min is an effective protocol to induce homosynaptic long-term depression (LTD) in visual cortical slices. It is reported that LFS becomes ineffective when brain-derived neurotrophic factor (BDNF) is applied to slices. It is not known, however, whether such a protocol induces LTD in visual cortex in vivo, and whether endogenous BDNF has the same or similar action. To address these questions, we recorded field potentials of rat visual cortex evoked by stimulation of lateral geniculate nucleus, white matter, or cortical layer IV. We found that LFS did not induce LTD of cortical responses in vivo. To test the possibility that spontaneous activity from retinas would interfere with the induction of LTD, both eyes were removed or inactivated by tetrodotoxin. LTD was not induced in these conditions either. To test whether the difference in temperature between the two preparations is a factor for the discrepancy, the temperature of slices was increased from 31 to 37 degrees C. LTD was induced in slices at either temperature. Then, we hypothesized that endogenous BNDF and its receptors, TrkB, prevent the induction of LTD. To test this, we infused the cortex with an inhibitor of Trk receptor tyrosine kinases, anti-TrkB IgG1, anti-BDNF, and anti-neurotrophin 4/5 antibodies. LTD was induced when the BDNF-TrkB system was blocked. In slices, the level of phosphorylation of Trks was found to decrease with time. These results indicate that activation of TrkB signal pathway prevents LFS from inducing synaptic depression in visual cortex in vivo.