Mismatch between BDNF mRNA and protein expression in the developing visual cortex: the role of visual experience

Activity-based anorexia animal model: a review of the main neurobiological findings

BACKGROUND

The genesis of anorexia nervosa (AN), a severe eating disorder with a pervasive effect on many brain functions such as attention, emotions, reward processing, cognition and motor control, has not yet been understood. Since our current knowledge of the genetic aspects of AN is limited, we are left with a large and diversified number of biological, psychological and environmental risk factors, called into question as potential triggers of this chronic condition with a high relapse rate. One of the most valid and used animal models for AN is the activity-based anorexia (ABA), which recapitulates important features of the human condition. This model is generated from naïve rodents by a self-motivated caloric restriction, where a fixed schedule food delivery induces spontaneous increased physical activity.

AIM

In this review, we sought to provide a summary of the experimental research conducted using the ABA model in the pursuit of potential neurobiological mechanism(s) underlying AN.

METHOD

The experimental work presented here includes evidence for neuroanatomical and neurophysiological changes in several brain regions as well as for the dysregulation of specific neurochemical synaptic and neurohormonal pathways.

RESULTS

The most likely hypothesis for the mechanism behind the development of the ABA phenotype relates to an imbalance of the neural circuitry that mediates reward processing. Evidence collected here suggests that ABA animals show a large set of alterations, involving regions whose functions extend way beyond the control of reward mechanisms and eating habits. Hence, we cannot exclude a primary role of these alterations from a mechanistic theory of ABA induction.

CONCLUSIONS

These findings are not sufficient to solve such a major enigma in neuroscience, still they could be used to design ad hoc further experimental investigation. The prospect is that, since treatment of AN is still challenging, the ABA model could be more effectively used to shed light on the complex AN neurobiological framework, thus supporting the future development of therapeutic strategies but also the identification of biomarkers and diagnostic tools. Anorexia Nervosa (AN) is a severe eating disorder with a dramatic effect on many functions of our brain, such as attention, emotions, cognition and motion control. Since our current knowledge of the genetic aspects behind the development of AN is still limited, many biological, psychological and environmental factors must be taken into account as potential triggers of this condition. One of the most valid animal models for studying AN is the activity-based anorexia (ABA). In this model, rodents spontaneously limit food intake and start performing increased physical activity on a running wheel, a result of the imposition of a fixed time schedule for food delivery. In this review, we provide a detailed summary of the experimental research conducted using the ABA model, which includes extended evidence for changes in the anatomy and function of the brain of ABA rodents. The hope is that such integrated view will support the design of future experiments that will shed light on the complex brain mechanisms behind AN. Such advanced knowledge is crucial to find new, effective strategies for both the early diagnosis of AN and for its treatment.

Expression of brain-derived neurotrophic factor in the lateral geniculate body of monocular form deprivation amblyopic kittens

PURPOSE

The present study compared the expression of brain-derived neurotrophic factor (BDNF) in the lateral geniculate body between form deprivation amblyopia kittens and normal kittens to examine the significance of BDNF in the lateral geniculate body in the pathogenesis of amblyopia.

METHODS

Twenty kittens were divided into control group (n = 10) and deprivation group (n = 10). A black opaque eye mask was placed to cover the right eye of the deprivation group. Pattern visual-evoked potentials (PVEPs) were detected weekly in all kittens .After the kittens in the deprivation group developed monocular amblyopia, the lateral geniculate bodies of all kittens were removed. The expression of BDNF in the lateral geniculate body of the two groups was compared by immunohistochemistry and Western blotting.

RESULTS

The latency of the P100 wave in the right eye of the deprivation group was longer than that of the left eye and that of the right eye of the control group (p < 0.05), and the amplitude decreased (p < 0.05). The number and average optical density of BDNF-positive cells in the deprivation group were lower than those in the control group (p < 0.05), and the expression of BDNF in the deprivation group was lower than that in the control group (p < 0.05).

CONCLUSIONS

The expression of BDNF in the lateral geniculate body of the amblyopic kittens decreased, and the decrease in BDNF promoted the development of amblyopia. These results demonstrate that BDNF in the lateral geniculate body plays an important role in visual development.

Uncovering a critical period of synaptic imbalance during postnatal development of the rat visual cortex: role of brain-derived neurotrophic factor

KEY POINTS

With daily electrophysiological recordings and neurochemical analysis, we uncovered a transient period of synaptic imbalance between enhanced inhibition and suppressed excitation in rat visual cortical neurons from the end of the fourth toward the end of the fifth postnatal weeks. The expression of brain-derived neurotrophic factor (BDNF), which normally enhances excitation and suppresses inhibition, was down-regulated during that time, suggesting that this may contribute to the inhibition/excitation imbalance. An agonist of the BDNF receptor tropomyosin-related kinase B (TrkB) partially reversed the imbalance, whereas a TrkB antagonist accentuated the imbalance during the transient period. Monocular lid suture during the transient period is more detrimental to the function and neurochemical properties of visual cortical neurons than before or after this period. We regard the period of synaptic imbalance as the peak critical period of vulnerability, and its existence is necessary for neurons to transition from immaturity to a more mature state of functioning.

ABSTRACT

The mammalian visual cortex is immature at birth and undergoes postnatal structural and functional adjustments. The exact timing of the vulnerable period in rodents remains unclear. The critical period is characterized by inhibitory GABAergic maturation reportedly dependent on brain-derived neurotrophic factor (BDNF). However, most of the studies were performed on experimental/transgenic animals, questioning the relationship in normal animals. The present study aimed to conduct in-depth analyses of the synaptic and neurochemical development of visual cortical neurons in normal and monocularly-deprived rats and to determine specific changes, if any, during the critical period. We found that (i) against a gradual increase in excitation and inhibition with age, a transient period of synaptic and neurochemical imbalance existed with suppressed excitation and enhanced inhibition at postnatal days 28 to 33/34; (ii) during this window, the expression of BDNF and tropomyosin-related kinase B (TrkB) receptors decreased, along with glutamatergic GluN1 and GluA1 receptors and the metabolic marker cytochrome oxidase, whereas that of GABAA Rα1 receptors continued to rise; (iii) monocular deprivation reduced both excitatory and inhibitory synaptic activity and neurochemicals mainly during this period; and (iv) in vivo TrkB agonist partially reversed the synaptic imbalance in normal and monocularly-deprived neurons during this time, whereas a TrkB antagonist accentuated the imbalance. Thus, our findings highlight a transitory period of synaptic imbalance with a negative relationship between BDNF and inhibitory GABA. This brief critical period may be necessary in transitioning from an immature to a more mature state of visual cortical functioning.

Visualizing changes in brain-derived neurotrophic factor (BDNF) expression using bioluminescence imaging in living mice

Brain-derived neurotrophic factor (BDNF) plays a fundamental role in expressing various neural functions including memory consolidation. Alterations of BDNF levels in the brain are associated with neurodegenerative and neuropsychiatric disorders. Therefore, it is important to understand how levels of BDNF are controlled. Recently we generated a novel transgenic mouse strain, termed the Bdnf-Luciferase transgenic (Bdnf-Luc Tg) mouse, to monitor changes in Bdnf expression. In the present study, we detected the bioluminescence signal from living Bdnf-Luc Tg mice after intraperitoneal administration of d-luciferin. Despite high levels of Bdnf expression in the brain, it was difficult to detect a signal from the brain region, probably because of its poorly penetrable (short-wavelength) bioluminescence. However, we could detect the changes in the bioluminescence signal in the brain region using a luciferin analogue generating a near-infrared wavelength of bioluminescence. We also found a strong correlation between increases in body weight and bioluminescence signal in the abdominal region of Tg mice fed a high-fat diet. These results show that changes in Bdnf expression can be visualized using living mice, and that the Tg mouse could be a powerful tool for clarification of the role of Bdnf expression in pathophysiological and physiological conditions.

Exposure to extrinsic stressors, social defeat or bisphenol A, eliminates sex differences in DNA methyltransferase expression in the amygdala

Chemical and psychological stressors can exert long lasting changes in brain function and behaviour. Changes in DNA methylation have been shown to be an important mechanism mediating long lasting changes in neural function and behaviour, especially for anxiety-like or stress responses. In the present study, we examined the effects of either a social or chemical stressor on DNA methyltransferase (DNMT) gene expression in the amygdala, an important brain region modulating stress responses and anxiety. In adult California mice (Peromyscus californicus) that were naïve to social defeat, females had higher levels of Dnmt1 expression in punch samples of the central amygdala (CeA) than males. In addition, mice that underwent social defeat stress showed reduced Dnmt1 and Dnmt3a expression in the CeA of females but not males. A second study using more anatomically specific punch samples replicated these effects for Dnmt1. Perinatal exposure (spanning from periconception through lactation) to bisphenol A or ethinyl oestradiol (oestrogens in birth control pills) also abolished sex differences in Dnmt1 expression in the CeA but not the basolateral amygdala. These findings identify a robust sex difference in Dnmt1 expression in the CeA that is sensitive to both psychological and chemical stressors. Future studies should aim to examine the impact of psychological and chemical stressors on DNA methylation in the CeA and also investigate whether Dnmt1 may have an underappreciated role in plasticity in behaviour.

Combined cisplatin and aurora inhibitor treatment increase neuroblastoma cell death but surviving cells overproduce BDNF

Drug-resistance to chemotherapics in aggressive neuroblastoma (NB) is characterized by enhanced cell survival mediated by TrkB and its ligand, brain-derived neurotrophic factor (BDNF); thus reduction in BDNF levels represent a promising strategy to overcome drug-resistance, but how chemotherapics regulate BDNF is unknown. Here, cisplatin treatment in SK-N-BE neuroblastoma upregulated multiple BDNF transcripts, except exons 5 and 8 variants. Cisplatin increased BDNF mRNA and protein, and enhanced translation of a firefly reporter gene flanked by BDNF 5′UTR exons 1, 2c, 4 or 6 and 3′UTR-long. To block BDNF translation we focused on aurora kinases inhibitors which are proposed as new chemotherapeutics. NB cell survival after 24 h treatment was 43% with cisplatin, and 22% by cisplatin+aurora kinase inhibitor PHA-680632, while the aurora kinases inhibitor alone was less effective; however the combined treatment induced a paradoxical increase of BDNF in surviving cells with strong translational activation of exon6-3′UTR-long transcript, while translation of BDNF transcripts 1, 2C and 4 was suppressed. In conclusion, combined cisplatin and aurora kinase inhibitor treatment increases cell death, but induces BDNF overproduction in surviving cells through an aurora kinase-independent mechanism.

Summary: Cisplatin increases endogenous BDNF in MYCN-expanded neuroblastoma cells. Additional treatment with aurora kinase inhibitor PHA-680632 increases cell death but surviving cells overproduce BDNF, mainly by increased translation of exon 6.

BDNF rs6265 methylation and genotype interact on risk for schizophrenia

Epigenetic mechanisms can mediate gene-environment interactions relevant for complex disorders. The BDNF gene is crucial for development and brain plasticity, is sensitive to environmental stressors, such as hypoxia, and harbors the functional SNP rs6265 (Val(66)Met), which creates or abolishes a CpG dinucleotide for DNA methylation. We found that methylation at the BDNF rs6265 Val allele in peripheral blood of healthy subjects is associated with hypoxia-related early life events (hOCs) and intermediate phenotypes for schizophrenia in a distinctive manner, depending on rs6265 genotype: in ValVal individuals increased methylation is associated with exposure to hOCs and impaired working memory (WM) accuracy, while the opposite is true for ValMet subjects. Also, rs6265 methylation and hOCs interact in modulating WM-related prefrontal activity, another intermediate phenotype for schizophrenia, with an analogous opposite direction in the 2 genotypes. Consistently, rs6265 methylation has a different association with schizophrenia risk in ValVals and ValMets. The relationships of methylation with BDNF levels and of genotype with BHLHB2 binding likely contribute to these opposite effects of methylation. We conclude that BDNF rs6265 methylation interacts with genotype to bridge early environmental exposures to adult phenotypes, relevant for schizophrenia. The study of epigenetic changes in regions containing genetic variation relevant for human diseases may have beneficial implications for the understanding of how genes are actually translated into phenotypes.

Amitriptyline induces brain-derived neurotrophic factor (BDNF) mRNA expression through ERK-dependent modulation of multiple BDNF mRNA variants in primary cultured rat cortical astrocytes and microglia

A significant role of brain-derived neurotrophic factor (BDNF) has been previously implicated in the therapeutic effect of antidepressants. To ascertain the contribution of specific cell types in the brain that produce BDNF following antidepressant treatment, the effects of the tricyclic antidepressant amitriptyline on rat primary neuronal, astrocytic and microglial cortical cultures were examined. Amitriptyline increased the expression of BDNF mRNA in astrocytic and microglial cultures but not neuronal cultures. Antidepressants with distinct mechanisms of action, such as clomipramine, duloxetine and fluvoxamine, also increased BDNF mRNA expression in astrocytic and microglial cultures. There are multiple BDNF mRNA variants (exon I, IIA, IV and VI) expressed in astrocytes and microglia and the variant induced by antidepressants has yet to be elaborated. Treatment with antidepressants increased the expression of exon I, IV and VI in astrocyte and microglia. Clomipramine alone significantly upregulated expression of exon IIA. The amitriptyline-induced expression of both total and individual BDNF mRNA variants (exon I, IV and VI) were blocked by MEK inhibitor U0126, indicating MEK/ERK signaling is required in the expression of BDNF. These findings indicate that non-neural cells are a significant target of antidepressants and further support the contention that glial production of BDNF is crucial role in the therapeutic effect of antidepressants. The current data suggest that targeting of glial function could lead to the development of antidepressants with a truly novel mechanism of action.

Stress Modulation of Opposing Circuits in the Bed Nucleus of the Stria Terminalis

The anterior bed nucleus of the stria terminalis (BNST) has been recognized as a critical structure in regulating trait anxiety, contextual fear memory, and appetitive behavior, and is known to be sensitive to stress manipulations. As one of the most complex structures in the central nervous system, the intrinsic circuitry of the BNST is largely unknown; however, recent technological developments have allowed researchers to begin to untangle the internal connections of the nucleus. This research has revealed the possibility of two opposing circuits, one anxiolytic and one anxiogenic, within the BNST, the relative strength of which determines the behavioral outcome. The balance of these pathways is critical in maintaining a normal physiological and behavioral state; however, stress and drugs of abuse can differentially affect the opposing circuitry within the nucleus to shift the balance to a pathological state. In this review, we will examine how stress interacts with the neuromodulators, corticotropin-releasing factor, norepinephrine, dopamine, and serotonin to affect the circuitry of the BNST as well as how synaptic plasticity in the BNST is modulated by stress, resulting in long-lasting changes in the circuit and behavioral state.

Cellular mechanisms of activity-dependent BDNF expression in primary sensory neurons

Brain-derived neurotrophic factor (BDNF) is abundantly expressed by both developing and adult rat visceral sensory neurons from the nodose ganglion (NG) in vivo and in vitro. We have previously shown that BDNF is released from neonatal NG neurons by activity and regulates dendritic development in their postsynaptic targets in the brainstem. The current study was carried out to examine the cellular and molecular mechanisms of activity-dependent BDNF expression in neonatal rat NG neurons, using our established in vitro model of neuronal activation by electrical field stimulation with patterns that mimic neuronal activity in vivo. We show that BDNF mRNA (transcript 4) increases over threefold in response to a 4-h tonic or bursting pattern delivered at the frequency of 6 Hz, which corresponds to the normal heart rate of a newborn rat. No significant increase in BDNF expression was observed following stimulation at 1 Hz. The latter effect suggests a frequency-dependent mechanism of regulated BDNF expression. In addition to BDNF transcript 4, which is known to be regulated by activity, transcript 1 also showed significant upregulation. The increases in BDNF mRNA were followed by BDNF protein upregulation of a similar magnitude after 24h of stimulation at 6 Hz. Electrical stimulation-evoked BDNF expression was inhibited by pretreating neurons with the blocker of voltage-gated sodium channels tetrodotoxin and by removing extracellular calcium. Moreover, our data show that repetitive stimulation-evoked BDNF expression requires calcium influx through N-, but not L-type, channels. Together, our study reveals novel mechanisms through which electrical activity stimulates de novo synthesis of BDNF in sensory neurons, and points to the role of N-type calcium channels in regulating BDNF expression in sensory neurons in response to repetitive stimulation.

Memory and brain-derived neurotrophic factor after subchronic or chronic amphetamine treatment in an animal model of mania

Progression of bipolar disorder (BD) has been associated with cognitive impairment and changes in neuroplasticity, including a decrease in serum brain-derived neurotrophic factor (BDNF). However, no study could examine BDNF levels directly in different brain regions after repeated mood episodes to date. The proposed animal model was designed to mimic several manic episodes and evaluate whether the performance in memory tasks and BDNF levels in hippocampus, prefrontal cortex, and amygdala would change after repeated amphetamine (AMPH) exposure. Adult male Wistar rats were divided into subchronic (AMPH for 7 days) and chronic groups (35 days), mimicking manic episodes at early and late stages of BD, respectively. After open field habituation or inhibitory avoidance test, rats were killed, brain regions were isolated, and BDNF mRNA and protein levels were measured by quantitative real-time PCR and ELISA, respectively. AMPH impaired habituation memory in both subchronic and chronic groups, and the impairment was worse in the chronic group. This was accompanied by increased Bdnf mRNA levels in the prefrontal cortex and amygdala region, as well as reduced BDNF protein in the hippocampus. In the inhibitory avoidance, AMPH significantly decreased the change from training to test when compared to saline. No difference was observed between subchronic and chronic groups, although chronically AMPH-treated rats presented increased Bdnf mRNA levels and decreased protein levels in hippocampus when compared to the subchronic group. Our results suggest that the cognitive impairment related to BD neuroprogression may be associated with BDNF alterations in hippocampus, prefrontal cortex, and amygdala.

Pharmacological profile of brain-derived neurotrophic factor (BDNF) splice variant translation using a novel drug screening assay: a "quantitative code"

The neurotrophin brain-derived neurotrophic factor (BDNF) is a key regulator of neuronal development and plasticity. BDNF is a major pharmaceutical target in neurodevelopmental and psychiatric disorders. However, pharmacological modulation of this neurotrophin is challenging because BDNF is generated by multiple, alternatively spliced transcripts with different 5'- and 3'UTRs. Each BDNF mRNA variant is transcribed independently, but translation regulation is unknown. To evaluate the translatability of BDNF transcripts, we developed an in vitro luciferase assay in human neuroblastoma cells. In unstimulated cells, each BDNF 5'- and 3'UTR determined a different basal translation level of the luciferase reporter gene. However, constructs with either a 5'UTR or a 3'UTR alone showed poor translation modulation by BDNF, KCl, dihydroxyphenylglycine, AMPA, NMDA, dopamine, acetylcholine, norepinephrine, or serotonin. Constructs consisting of the luciferase reporter gene flanked by the 5'UTR of one of the most abundant BDNF transcripts in the brain (exons 1, 2c, 4, and 6) and the long 3'UTR responded selectively to stimulation with the different receptor agonists, and only transcripts 2c and 6 were increased by the antidepressants desipramine and mirtazapine. We propose that BDNF mRNA variants represent "a quantitative code" for regulated expression of the protein. Thus, to discriminate the efficacy of drugs in stimulating BDNF synthesis, it is appropriate to use variant-specific in vitro screening tests.

Expression of perineuronal nets, parvalbumin and protein tyrosine phosphatase σ in the rat visual cortex during development and after BFD

Abstract Purpose of the Study: Protein tyrosine phosphatase σ (PTPσ) acts as a neuronal receptor for chondroitin sulfate proteoglycans (CSPGs). CSPGs have inhibitory effects on experience-dependent plasticity and usually form lattice-like cell coatings that surround the parvalbumin (PV) interneurons in the visual cortex (VC). We investigated developmental changes and the effect of binocular form deprivation (BFD) on PTPσ, perineuronal nets (PNNs) and their tempo-spatial relationships with PV neurons in the VC.

MATERIALS AND METHODS

Double-immunostaining was used to observe the coexpression pattern of PNNs staining by biotinylated wisteria floribunda lectin (WFA) with PV neurons. The expression of PTPσ in the VC of Long Evans rats was detected by real-time quantitative PCR, immunohistochemistry and western blots. The changes in the number of PV/WFA/PTPσ labeled cells in layer IV of the VC and its proportion of PV neurons were examined during development and after BFD.

RESULTS

The expression of PV neurons wrapped by PNNs was increased, particularly in the first half of the critical period, and the ratio for PV neurons reached the highest level (over 75%) at adulthood, indicating that PNNs may play an important role in the maturation of PV neurons during the critical period. BFD decreased the density of PNNs and the percentage of PV neurons with PNNs. This result suggests that the number of PNNs surrounding PV neurons may be experience-dependent. Meanwhile, the CSPG receptor PTPσ was maintained at its lowest level during the critical period and could be modulated by BFD after the critical period. The percentage of PV/WFA/PTPσ-positive cells in PV population increased during development and reached its highest ratio at adulthood, which could also be reversed by BFD.

CONCLUSIONS

The changes in the coexpression of PNNs, PV and PTPσ provide valuable insights into the connection between CSPGs and PV neurons.

Upregulation of brain-derived neurotrophic factor expression in nodose ganglia and the lower brainstem of hypertensive rats

Hypertension leads to structural and functional changes at baroreceptor synapses in the medial nucleus tractus solitarius (NTS), but the underlying molecular mechanisms remain unknown. Our previous studies show that brain-derived neurotrophic factor (BDNF) is abundantly expressed by rat nodose ganglion (NG) neurons, including baroreceptor afferents and their central terminals in the medial NTS. We hypothesized that hypertension leads to upregulation of BDNF expression in NG neurons. To test this hypothesis, we used two mechanistically distinct models of hypertension, the spontaneously hypertensive rat (SHR) and the deoxycorticosterone acetate (DOCA)-salt rat. Young adult SHRs, whose blood pressure was significantly elevated compared with age-matched Wistar-Kyoto (WKY) control rats, exhibited dramatic upregulation of BDNF mRNA and protein in the NG. BDNF transcripts from exon 4, known to be regulated by activity, and exon 9 (protein-coding region) showed the largest increases. Electrical stimulation of dispersed NG neurons with patterns that mimic baroreceptor activity during blood pressure elevations led to increases in BDNF mRNA that were also mediated through promoter 4. The increase in BDNF content of the NG in vivo was associated with a significant increase in the percentage of BDNF-immunoreactive NG neurons. Moreover, upregulation of BDNF in cell bodies of NG neurons was accompanied by a significant increase in BDNF in the NTS region, the primary central target of NG afferents. A dramatic increase in BDNF in the NG was also detected in DOCA-salt hypertensive rats. Together, our study identifies BDNF as a candidate molecular mediator of activity-dependent changes at baroafferent synapses during hypertension.

Effects of omega-3 dietary supplement in prevention of positive, negative and cognitive symptoms: a study in adolescent rats with ketamine-induced model of schizophrenia

Omega-3 has shown efficacy to prevent schizophrenia conversion in ultra-high risk population. We evaluated the efficacy of omega-3 in preventing ketamine-induced effects in an animal model of schizophrenia and its effect on brain-derived neurotrophic factor (BDNF). Omega-3 or vehicle was administered in Wistar male rats, both groups at the 30th day of life for 15days. Each group was split in two to receive along the following 7days ketamine or saline. Locomotor and exploratory activities, memory test and social interaction between pairs were evaluated at the 52nd day of life. Prefrontal-cortex, hippocampus and striatum tissues were extracted right after behavioral tasks for mRNA BDNF expression analysis. Bloods for serum BDNF were withdrawn 24h after the end of behavioral tasks. Locomotive was increased in ketamine-treated group compared to control, omega-3 and ketamine plus omega-3 groups. Ketamine group had fewer contacts and interaction compared to other groups. Working memory and short and long-term memories were significantly impaired in ketamine group compared to others. Serum BDNF levels were significantly higher in ketamine plus omega-3 group. There was no difference between groups in prefrontal-cortex, hippocampus and striatum for mRNA BDNF expression. Administration of omega-3 in adolescent rats prevents positive, negative and cognitive symptoms in a ketamine animal model of schizophrenia. Whether these findings are consequence of BDNF increase it is unclear. However, this study gives compelling evidence for larger clinical trials to confirm the use of omega-3 to prevent schizophrenia and for studies to reinforce the beneficial role of omega-3 in brain protection.

Protocadherin 11X/Y a human-specific gene pair: an immunohistochemical survey of fetal and adult brains

Protocadherins 11X and 11Y are cell adhesion molecules of the δ1-protocadherin family. Pcdh11X is present throughout the mammalian radiation; however, 6 million years ago (MYA), a reduplicative translocation of the Xq21.3 block onto what is now human Yp11 created the Homo sapiens-specific PCDH11Y. Therefore, modern human females express PCDH11X whereas males express both PCDH11X and PCDH11Y. PCDH11X/Y has been subject to accelerated evolution resulting in human-specific changes to both proteins, most notably 2 cysteine substitutions in the PCDH11X ectodomain that may alter binding characteristics. The PCDH11X/Y gene pair is postulated to be critical to aspects of human brain evolution related to the neural correlates of language. Therefore, we raised antibodies to investigate the temporal and spatial expression of PCDH11X/Y in cortical and sub-cortical areas of the human fetal brain between 12 and 34 postconceptional weeks. We then used the antibodies to determine if this expression was consistent in a series of adult brains. PCDH11X/Y immunoreactivity was detectable at all developmental stages. Strong expression was detected in the fetal neocortex, ganglionic eminences, cerebellum, and inferior olive. In the adult brain, the cerebral cortex, hippocampal formation, and cerebellum were strongly immunoreactive, with expression also detectable in the brainstem.

Expression of the dopaminergic D1 and D2 receptors in the anterior cingulate cortex in a model of neuropathic pain

BACKGROUND

The anterior cingulate cortex (ACC) has been related to the affective component of pain. Dopaminergic mesocortical circuits, including the ACC, are able to inhibit neuropathic nociception measured as autotomy behaviour. We determined the changes in dopamine D1 and D2 (D1R and D2R) receptor expression in the ACC (cg1 and cg2) in an animal model of neuropathic pain. The neuropathic group had noxious heat applied in the right hind paw followed 30 min. later by right sciatic denervation. Autotomy score (AS) was recorded for eight days and subsequently classified in low, medium and high AS groups. The control consisted of naïve animals.A semiquantitative RT-PCR procedure was done to determine mRNA levels for D1R and D2R in cg1 and cg2, and protein levels were measured by Western Blot.

RESULTS

The results of D1R mRNA in cg1 showed a decrease in all groups. D2R mRNA levels in cg1 decreased in low AS and increased in medium and high AS. Regarding D1R in cg2, there was an increase in all groups. D2R expression levels in cg2 decreased in all groups. In cg1, the D2R mRNA correlated positively with autotomy behaviour. Protein levels of D2R in cg1 increased in all groups but to a higher degree in low AS. In cg2 D2R protein only decreased discretely. D1R protein was not found in either ACC region.

CONCLUSIONS

This is the first evidence of an increase of inhibitory dopaminergic receptor (D2R) mRNA and protein in cg1 in correlation with nociceptive behaviour in a neuropathic model of pain in the rat.

Changes in the serotonergic system and in brain-derived neurotrophic factor distribution in the main olfactory bulb of pcd mice before and after mitral cell loss

The serotonergic centrifugal system innervating the main olfactory bulb (MOB) plays a key role in the modulation of olfactory processing. We have previously demonstrated that this system suffers adaptive changes under conditions of a lack of olfactory input. The present work examines the response of this centrifugal system after mitral cell loss in the Purkinje cell degeneration (pcd) mutant mice. The distribution and density of serotonergic centrifugal axons were studied in the MOB of control and pcd mice, both before and after the loss of mitral cells, using serotonin (5-HT) and 5-HT transporter immunohistochemistry. Studies of the amount of 5-HT and its metabolite, 5-hydroxyindole acetic acid (5-HIAA), were performed by means of high-performance liquid chromatography (HPLC), and the relative amounts of brain-derived neurotrophin factor, BDNF, and its major receptor, tropomyosin-related kinase B (TrkB), were measured by Western blot. Our study revealed that the serotonergic system develops adaptive changes after, but not before, mitral cell loss. The lack of the main bulbar projection cells causes a decrease in the serotonergic input received by the MOB, whereas the number of serotonergic cells in the raphe nuclei remains constant. In addition, one of the molecules directly involved in serotonergic sprouting, the neurotrophin BDNF and its main receptor TrkB, underwent alterations in the MOBs of the pcd animals even before the loss of mitral cells. These data indicate that serotonergic function in the MOB is closely related to olfactory activity and that mitral cell loss induces serotonergic plastic responses.

Structural dynamics of synapses in vivo correlate with functional changes during experience-dependent plasticity in visual cortex

The impact of activity on neuronal circuitry is complex, involving both functional and structural changes whose interaction is largely unknown. We have used optical imaging of mouse visual cortex responses and two-photon imaging of superficial layer spines on layer 5 neurons to monitor network function and synaptic structural dynamics in the mouse visual cortex in vivo. Total lack of vision due to dark-rearing from birth dampens visual responses and shifts spine dynamics and morphologies toward an immature state. The effects of vision after dark rearing are strongly dependent on the timing of exposure: over a period of days, functional and structural changes are temporally related such that light stabilizes spines while increasing visually driven activity. The effects of long-term light exposure can be partially mimicked by experimentally enhancing inhibitory signaling in the darkness. Brief light exposure, however, results in a rapid, transient, NMDA-dependent increase of cortical responses, accompanied by increased dynamics of dendritic spines. These findings indicate that visual experience induces rapid reorganization of cortical circuitry followed by a period of stabilization, and demonstrate a close relationship between dynamic changes at single synapses and cortical network function.

Darkness reduces BDNF expression in the visual cortex and induces repressive chromatin remodeling at the BDNF gene in both hippocampus and visual cortex

Neuronal activity regulates the expression of brain-derived neurotrophic factor (BDNF) in brain. In darkness, reduced neuronal activity in the visual cortex markedly decreases total BDNF transcription level in adult rats. Epigenetic mechanisms are crucially involved in the regulation of gene expression in response to environmental stimuli. In this study, we examined the effect of 1 week of light deprivation (LD) on the activity-dependent changes in BDNF expression from different promoters in the visual cortex and hippocampus. We analyzed the correlation between the chromatin state of Bdnf promoters, exon-specific transcripts levels, and total protein levels in light-deprived rats and in rats reared under normal light-dark cycle. We found that 1 week of LD significantly reduced Bdnf mRNA and protein in the visual cortex but not in the hippocampus. However, epigenetic analysis revealed that LD increased histone-3 methylation and DNA methylation at the Bdnf promoter IV in both the visual cortex and hippocampus. These data highlight the spatial differences in signaling pathways that lead to the BDNF expression in response to diminished ambient light.

Molecular mechanisms of experience-dependent plasticity in visual cortex

A remarkable amount of our current knowledge of mechanisms underlying experience-dependent plasticity during cortical development comes from study of the mammalian visual cortex. Recent advances in high-resolution cellular imaging, combined with genetic manipulations in mice, novel fluorescent recombinant probes, and large-scale screens of gene expression, have revealed multiple molecular mechanisms that underlie structural and functional plasticity in visual cortex. We situate these mechanisms in the context of a new conceptual framework of feed-forward and feedback regulation for understanding how neurons of the visual cortex reorganize their connections in response to changes in sensory inputs. Such conceptual advances have important implications for understanding not only normal development but also pathological conditions that afflict the central nervous system.

Androgen-dependent regulation of brain-derived neurotrophic factor and tyrosine kinase B in the sexually dimorphic spinal nucleus of the bulbocavernosus

Castration of adult male rats causes the dendrites of androgen-sensitive motoneurons of the spinal nucleus of the bulbocavernosus (SNB) to retract. Brain-derived neurotrophic factor (BDNF), via activation of tyrosine receptor kinase B (trkB), has been implicated in mediating androgen effects on SNB dendrites. We used in situ hybridization to demonstrate that SNB motoneurons in gonadally intact adult male rats contain mRNA for both BDNF and trkB. Two weeks after gonadectomy, both transcripts were significantly decreased in SNB motoneurons but not in the non-androgen-responsive motoneurons of the adjacent retrodorsolateral nucleus (RDLN). In a second experiment, target perineal and foot muscles of SNB and RDLN motoneurons, respectively, were injected with the retrograde tracer Fluorogold, and then immunocytochemistry was performed to examine the distribution of BDNF and trkB proteins in SNB and RDLN motoneurons and their glutamatergic afferents. Confocal analysis revealed that gonadectomy induces a loss of BDNF protein in SNB dendrites but not in RDLN dendrites. Testosterone treatment of castrates prevented the loss of BDNF from SNB dendrites. Confocal analysis also revealed trkB protein in SNB and RDLN dendrites and in their glutamatergic afferents. Gonadectomy had no discernable effect on trkB protein in SNB or RDLN motoneurons or in their glutamatergic afferents. These results suggest that androgen maintains a BDNF-signaling pathway in SNB motoneurons that may underlie the maintenance of dendritic structure and synaptic signaling.

Molecular, cellular, and functional characterizations of pituitary adenylate cyclase-activating polypeptide and its receptors in the cerebellum of New and Old World monkeys

The neuropeptide pituitary adenylate cyclase-activating polypeptide (PACAP) exerts trophic activities during cerebellar development, and a neuroprotective effect of PACAP has been demonstrated in pathological conditions such as stroke. However, all these data have been obtained in rodents, and neuroprotective effects of PACAP in primates remain unknown. Because of their evolutionary relationships with humans, monkeys represent powerful models for validating the therapeutic interest in PACAP. The objective of the present study was to characterize PACAP and its receptors in the cerebellum of two nonhuman primates. RT-PCR and in situ hybridization experiments revealed that PACAP is expressed in the cerebellum by Purkinje cells. Via immunohistochemistry, PACAP was detected in Purkinje cells and radial glial fibers. With regard to PACAP receptors, PAC1-R and VPAC1-R were detected by RT-PCR. In situ hybridization revealed a strong expression of PAC1-R and VPAC1-R in the granule cell layer (GCL), and VPAC1-R was also expressed in the Purkinje cell layer. A high density of PACAP binding sites was visualized in the GCL and the Purkinje cell layer. Competition studies indicated that, in the GCL, PACAP induced complete displacement of [(125)I]PACAP27 binding, whereas vasoactive intestinal polypeptide (VIP) was a weak competitor. In contrast, in the Purkinje cell layer, both PACAP and VIP displaced [(125)I]PACAP27 binding. Measurement of cAMP levels showed that PACAP is a powerful activator of adenylyl cyclase, whereas VIP is about 100-fold less potent. Altogether, these observations constitute the first demonstration of a functional PACAPergic system in monkey cerebellum. They strongly suggest that neuroprotective effects of PACAP can be transposed to primates, including human.

Active versus passive cocaine administration: differences in the neuroadaptive changes in the brain dopaminergic system

There is considerable evidence that chronic exposure to cocaine is associated with low striatal dopamine D2 receptor availability. In the present study we wished to determine whether neuroadaptive changes in densities of D2 receptors were due to direct pharmacological actions of cocaine or they reflected motivational states that were present when cocaine injection depended on active drug-seeking behavior and whether these changes were related to the actual expression of D2 mRNA. To achieve this goal we utilized a "yoked" procedure in which rats were tested simultaneously in groups of three, with only one rat actively self-administering cocaine while the other two received yoked injections of either cocaine or saline. Only passively administered cocaine produced a decrease in dopamine D2 receptor levels in the anterior and central regions of caudate/putamen, and both the shell and core of the nucleus accumbens, as measured by in vitro quantitative autoradiography. In contrast, examination of D2 receptor gene expression using in situ hybridization analysis revealed that there was an increase in D2 receptor mRNA levels in the ventral tegmental area of rats actively self-administered cocaine. We conclude that the reductions in striatal D2 receptor densities may be related to the chronic administration of cocaine per se and not to the motivated process of reinforced responding. Our results also suggest that increases in D2 receptor mRNA levels in limbic regions do not necessarily result in increased receptor densities and these changes likely reflect motivational states that were present when cocaine injection dependent on active drug self-administration.

Developmental changes of neurotrophin mRNA expression in the layers of rat visual cortex

Neurotrophins are essential factors for the structural, neurochemical and functional maturation of the brain including developmental and adult plasticity. Northern blots and polymerase chain reaction revealed the expression of neurotrophin 4 (NT4), neurotrophin 3 (NT3), brain-derived neurotrophic factor (BDNF) and nerve growth factor (NGF) in the cortex. The cellular producers of NT3 and BDNF have been characterized by anatomical methods as being mostly pyramidal, and the tyrosine kinase B (TrkB) receptor is expressed by many cortical neurons. However, these methods have so far failed to identify the cells producing NT4 and NGF mRNA. These factors are much lower in expression than, e.g. BDNF, and apparently remain below detection levels of in situ hybridization. Given their specific actions on cell types and afferent systems, knowledge about the producing cell types is highly desirable. To narrow down on the producing cell types, we quantified by reverse transcriptase-polymerase chain reaction (RT-PCR) the developmental changes of BDNF, NT3, NT4, NGF and TrkB mRNA expression in total visual cortex lysates, and in the cortical layers dissected by tangential cryostat sectioning. We found dramatic changes in laminar expression of NT3 and NGF, mild changes of NT4, and no changes of BDNF and TrkB mRNA. For instance, NT3 is important early on for thalamocortical axons, and we found transient peaks of NT3 mRNA expression first in layer VI, then in layer IV. NT4 mRNA was in layers IV and VI, suggesting NT4 protein production in thalamorecipient layers, but peak expression gradually shifted to upper layers as did NGF expression. The layer-specific developmental expression shifts of neurotrophin mRNAs correlate with morphogenetic processes.

BDNF regulation in the rat dorsal vagal complex during stress-induced anorexia

The dorsal vagal complex (DVC) is the satiety reflex-integrating center of adult mammals. Immobilization stress (IS) is known to elicit anorexia and to up-regulate BDNF expression in adult rat forebrain; intra-DVC delivery of BDNF was shown to elicit anorexia. Therefore, we addressed here whether IS would increase BDNF signaling in rat DVC by using PCR and western-blot on microdissected tissue extracts. Significant variations of BDNF expression in DVC after IS include exon V mRNA increase at 3 h, decreases of both protein and exon III mRNA at 24 h, and exon I mRNA decrease at 72 h. At the receptor level, IS elicited a highly significant induction of both full-length and truncated-1 TrkB mRNAs at 24 h after IS. In vivo recruitment of BDNF signaling in DVC during stress thus differs from hypothalamus, the relevance of which to anorexia is discussed.

“Let There be Light!” pigeon eggs are regularly exposed to light during breeding

Light stimulation before hatching initiates the emergence of avian visual lateralisation. Since several studies show that birds benefit from being lateralised, we can conjecture that their clutch is being exposed to light during breeding. We tested this assumption in pigeons with a semi-natural setup where the animals were systematically recorded using a movement detection system throughout their breeding period. The results show that pigeon pairs perform their relieves in a regular way by abandoning their clutch for a mean of about 55 s at approximately every 43 min. Thus, the developing visual pathways are repetitively stimulated by light for cumulatively over 3h before the breeding period ends. It becomes apparent that both the duration as well as the repetitions of light stimulation play a crucial role in the onset of visual asymmetry.

What is the biological significance of BDNF mRNA targeting in the dendrites? Clues from epilepsy and cortical development

The neurotrophin brain-derived neurotrophic factor (BDNF) is a regulatory factor of several, partially contrasting, aspects of the biology of neural cells, including survival, growth, differentiation, and cell death. Regulation of the local availability of BDNF at distinct subcellular domains such as the cell soma, dendrites, axons, and spines appears to be the key to conferring spatial and temporal specificity of the different effects elicited by this neurotrophin. This article reviews recent findings in the context of epileptogenesis and visual cortex maturation that showed that different BDNF messenger RNA (mRNA) transcripts are localized at different subcellular locations in hippocampal and cortical neurons. It also reviews findings demonstrating that strong depolarizing stimuli, both in vitro and in vivo, elicit accumulation of BDNF mRNA and protein in the distal dendrites through a signaling pathway involving the activation of the N-methyl-D-aspartate and tyrosine kinase B receptors and an intracellular increase in Ca2+ concentration. Finally, this article proposes that the regulation of the delivery of BDNF mRNA and protein to the different subcellular domains--particularly the dendritic compartment--may represent a fundamental aspect of the processes of cellular and synaptic morphological rearrangements underlying epileptogenesis and postnatal development of the visual cortex.

Effects of food restriction on synthesis and expression of brain-derived neurotrophic factor and tyrosine kinase B in dentate gyrus granule cells of adult rats

We have previously found that the dendritic trees of dentate gyrus granule cells are selectively vulnerable to food restriction but there are reorganizational morphological events that minimize functional impairments. As the neurotrophin brain-derived neurotrophic factor (BDNF) and the cognate receptor tyrosine kinase B (TrkB) are involved in the maintenance of the structure of dendritic trees, we thought of interest to verify if there are alterations in its synthesis and expression in granule cells. To investigate this issue, 2-month-old rats were submitted to 40% caloric restriction for 6 months and compared to controls fed ad libitum. The numbers of granule cells containing BDNF and TrkB proteins were estimated from immunostained sections and the respective mRNA levels of individual neurons evaluated using nonradioactive in situ hybridization. After dietary treatment there was a 15% reduction of BDNF-immunoreactive granule cells with no changes of the number of TrkB-immunostained neurons. No alterations were found in the levels of BDNF and TrkB mRNAs of individual granule cells. As caloric restriction extends the lifespan of animals, the restrictive dietary regimens are generally regarded as beneficial to the organisms, but the present results suggest that caution is needed when extrapolating to some neuronal populations.

Reduction of GFAP induced by long dark rearing is not restricted to visual cortex

A key component of the astrocyte cytoskeleton is the glial fibrillary acidic protein (GFAP), which plays an essential role in neuron/astrocyte interactions. Environmental conditioning, such as visual experience manipulation, can affect neuronal and/or glial plasticity in specific brain areas. Previous work from our laboratory showed that short light deprivation throughout the period of GFAP maturation does not influence the expression profile of GFAP in mouse visual cortex; however, it was strong enough to affect neuronal phenotype. It was suggested that visual experience controls the maturation of the neuronal circuitry in this brain area. Therefore, to see whether the modifications of neuronal activity induced by light deprivation affect the maintenance of normal astrocytic phenotype, the dark rearing protocol was extended until the adult life. GFAP-immunoreactive cells were dramatically affected, showing an 80% decrease in number. In addition, GFAP protein level exhibited a 50% reduction, while its mRNA remained unaffected. Besides the visual cortex, two other areas of the brain not directly involved in vision, the hippocampus and the motor cortex, were chosen as internal controls. Unexpectedly, also in these areas, astrocytes were affected by light deprivation. The present results show that lack of visual experience for long periods of time deeply affects glial phenotype not only in visual areas but also in brain regions not directly involved in sensory processing.

Photic inhibition of TrkB/Ras activity in the pigeon's tectum during development: impact on brain asymmetry formation

Asymmetric photic stimulation during embryonic or post-hatch development induces a functional lateralization of the pigeon's visual system, which is accompanied by left-right differences in tectal cell sizes. The intracellular membrane-anchored GTPase Ras can be activated by a number of upstream mechanisms including binding of brain-derived neurotrophic factor to its specific TrkB receptor. Ras activity plays an important morphogenetic role in neurons and therefore might also be involved in the asymmetric differentiation of tectal cells. To investigate the role of Ras, we determined the relative levels of activated Ras and of signalling active phospho-TrkB in tecta of light- and dark-incubated pigeons and combined this with an immunohistochemical detection of Ras-GTP and TrkB receptors. While Ras activation levels did not differ between light- and dark-incubated pigeons during embryonic development, directly after hatching Ras activity was significantly decreased in the stronger stimulated left tectum of light-incubated animals. This was accompanied by lower levels of TrkB phosphorylation. Immunohistochemical staining revealed Ras-GTP-positive cell bodies within the efferent cell layer. These cells were TrkB-positive and developed enlarged soma sizes within the right tectum during the first week after hatching. This association suggests asymmetric Ras activation to be involved in the asymmetric differentiation of the efferent cells as a result of asymmetric TrkB signalling. Because asymmetric light exposure occurs only during embryonic development, the observed transient asymmetric inhibition of TrkB/Ras activity after hatching may reflect differential embryonic maturation of tectal inhibitory circuits leading to a functional superiority of the right eye in the adult organism.

The exercise-induced expression of BDNF within the hippocampus varies across life-span

Voluntary exercise increases hippocampal brain-derived neurotrophic factor (BDNF) expression in young animals. In this investigation we examined the induction of BDNF protein in the hippocampus of young (2 months), late middle-aged (15 months) and old (24 months) animals over 4 weeks of exercise. Average running distances decreased with age, with the old animals also maintaining a constant level of activity over time, whereas the other groups tended to increase their average running distance. All animals demonstrated a biphasic profile of BDNF protein induction, with a significant (P<0.05) increase after 1 week of exercise followed by a decrease to near sedentary levels at 2 weeks. After this, BDNF protein levels increased significantly (P<0.05), as compared to baseline, primarily only in the young animals. In whole hippocampal homogenates, only particular BDNF mRNA exons were significantly (P<0.05) changed as a result of exercise, with the largest induction occurring in young animals. BDNF protein induction may, therefore, not be directly correlated with significant mRNA changes. Exercise may represent a therapeutic tool for disorders which involve a decrease in BDNF.

Neuronal activity regulates the developmental expression and subcellular localization of cortical BDNF mRNA isoforms in vivo

Activity-dependent changes in BDNF expression have been implicated in developmental plasticity. Although its expression is widespread in visual cortex, developmental regulation of its different transcripts by visual experience has not been investigated. Here, we investigated the cellular expression of different BDNF transcripts in rat visual cortex during postnatal development. We found that transcripts I and II are expressed only in adults but III and IV are expressed from early postnatal stage. Total BDNF mRNA is expressed throughout the age groups. Transcripts III and IV show a differential intracellular localization, while former was detected only in cell bodies, latter is present both in cell bodies and dendritic processes. Inhibition of visual activity decreases the levels of exons, with exon IV transcript almost disappearing from dendrites. In vitro experiments also confirmed the above results, indicating activity-dependent regulation of different BDNF promoters with specific temporal and cellular patterns of expression in developing visual cortex.

Alpha7 but not alpha4 AChR subunit expression is regulated by light in developing primary visual cortex

In the present paper we analyzed the expression pattern of the alpha4 and alpha7 nicotinic acetylcholine receptor (nAChR) subunits in the rat visual cortex through postnatal development, to clarify whether their expression is developmentally regulated and whether eventual developmental changes are regulated by visual experience. We found that both alpha4 and alpha7 mRNA levels accumulate from postnatal day 12 (P12) before eye opening, to around P35. The immunohistochemical results indicated that both subunits are expressed throughout all cortical laminae, except layer I. Alpha4 subunit immunohistochemistry revealed significant increments in the number of positive cells in layers V and VI after eye opening. In the case of the alpha7 subunit, the number of immunoreactive cells increased in all cortical layers soon after eye opening, except in layer VI, matching the results found at the transcriptional level. In animals reared in darkness from P9 to P22, the relative amount of the alpha4 mRNA and the number of immunoreactive cells exhibited no changes. 3H-epibatidine binding experiments showed that the number of heteromeric nAChR subunits in dark-reared rats did not change with respect to age-matched controls, thus confirming the immunohistochemical results. The mRNA of the alpha7 subunit remained stable in dark-reared rats, whereas the number and distribution of immunoreactive cells changed. Moreover, the number of 125I alphabungarotoxin-binding nAChRs was significantly increased in dark-reared animals. These results indicate that visual cortex stimulation by visual input is an essential step for alpha7 nAChR normal expression, suggesting a possible role for these receptors in an experience-dependent fashion on the maturation of this cortical area.

Sigma1 receptor upregulation after chronic methamphetamine self-administration in rats: a study with yoked controls

RATIONALE

Sigma(1) receptors (Sig-1R) are implicated in behavioral sensitization, conditioned place preference, and cellular restructuring induced by psychostimulants. We previously reported that rats which actively self-administered methamphetamine for 5 weeks and were then withdrawn from methamphetamine for 24 h showed downregulation of dopamine D(2) autoreceptors (approximately 30%) in the midbrain and this was not seen in rats that passively received injections of methamphetamine or saline at the same time (yoked controls). Involvement of Sig-1R in the self-administration of psychostimulants, however, has never been reported.

OBJECTIVES

This study examined neuroadaptive changes in Sig-1R in the brains of rats self-administering methamphetamine.

METHODS

Three groups of rats were tested simultaneously 5 days per week, for 5 weeks (25 daily sessions). Two groups served as yoked controls and passively received an injection of either 0.1 mg/kg methamphetamine or saline (not contingent on responding) each time a response-contingent injection of 0.1 mg/kg methamphetamine was actively self-administered by the first group of rats. Protein and mRNA levels of Sig-1R were then measured by Western and Northern blottings, respectively.

RESULTS

There was a marked upregulation of Sig-1R proteins (50%) in the midbrain and altered levels of Sig-1R mRNA in the frontal cortex and hippocampus of rats that learned to actively self-administer methamphetamine, but not in yoked methamphetamine- or saline-control rats.

CONCLUSIONS

Neuroadaptive increases in Sig-1R seen in this study may contribute to the reinforcing effects of methamphetamine. This upregulation of Sig-1R may be mediated by increased protein kinase A activity due to downregulation of dopamine D(2) autoreceptors.

The timecourse of induction of brain-derived neurotrophic factor mRNA and protein in the rat hippocampus following voluntary exercise

In this study we examined the timecourse of induction of brain-derived neurotrophic factor (BDNF) mRNA and protein after 1, 3, 5, 7, 14 and 28 days of exercise in the rat. To measure the expression of mRNA for individual BDNF exons we utilized a semi-quantitative RT-PCR technique, while BDNF protein was assessed using commercial ELISA kits. We demonstrated that the distance run by animals increased significantly (P<0.05) after 4 weeks. BDNF protein was significantly (P<0.05) increased after 4 weeks of exercise, while the mRNA for individual BDNF exons increased significantly (P<0.05) over the timecourse (exon I after 1 and 28 days and exons II and V after 28 days). The Morris water maze was then utilized to demonstrate that 3 weeks of prior exercise enhanced the rate of learning on this task. Exercise, therefore, was shown to modulate BDNF induction in a time-dependent manner, and this may translate to improvements in neurotrophin-mediated tasks within the CNS.

A novel antipyretic action of 15-deoxy-Delta12,14-prostaglandin J2 in the rat brain

Fever is an important part of the host defense response, yet fever can be detrimental if it is uncontrolled. We provide the first evidence that 15-deoxy-Delta12,14-prostaglandin J2 (15d-PGJ2), an endogenous ligand for peroxisome proliferator-activated receptor gamma (PPARgamma), can attenuate the febrile response to lipopolysaccharide (LPS) in rats via an action on the brain. Furthermore, we show that PPARgamma is expressed in the hypothalamus, an important locus in the brain for fever generation. In addition, 15d-PGJ2 and its synthesizing enzyme (PGD2 synthase) were present in rat cerebrospinal fluid, and their levels were enhanced in response to systemic injection of LPS. The antipyretic effect of 15d-PGJ2 was associated with reduction in LPS-stimulated cyclooxygenase-2 expression in the hypothalamus but not in p44/p42 mitogen-activated protein kinase phosphorylation or in the expression of the PPARgamma. Thus it is likely that there is a parallel induction of an endogenous prostanoid pathway in the brain capable of limiting deleterious actions of the proinflammatory prostaglandin E2-dependent pathway.

Sleep deprivation effects on growth factor expression in neonatal rats: a potential role for BDNF in the mediation of delta power

The sleeping brain differs from the waking brain in its electrophysiological and molecular properties, including the expression of growth factors and immediate early genes (IEG). Sleep architecture and homeostatic regulation of sleep in neonates is distinct from that of adults. Hence, the present study addressed the question whether the unique homeostatic response to sleep deprivation in neonates is reflected in mRNA expression of the IEG cFos, brain-derived nerve growth factor (BDNF), and basic fibroblast growth factor (FGF2) in the cortex. As sleep deprivation is stressful to developing rats, we also investigated whether the increased levels of corticosterone would affect the expression of growth factors in the hippocampus, known to be sensitive to glucocorticoid levels. At postnatal days 16, 20, and 24, rats were subjected to sleep deprivation, maternal separation without sleep deprivation, sleep deprivation with 2 h recovery sleep, or no intervention. mRNA expression was quantified in the cortex and hippocampus. cFos was increased after sleep deprivation and was similar to control level after 2 h recovery sleep irrespective of age or brain region. BDNF was increased by sleep deprivation in the cortex at P20 and P24 and only at P24 in the hippocampus. FGF2 increased during recovery sleep at all ages in both brain regions. We conclude that cortical BDNF expression reflects the onset of adult sleep-homeostatic response, whereas the profile of expression of both growth factors suggests a trophic effect of mild sleep deprivation.

A rapid increase in the total number of cell surface functional GABAA receptors induced by brain-derived neurotrophic factor in rat visual cortex

The number of postsynaptic gamma-aminobutyric acid type A (GABAA) receptors is a fundamental determinant of the variability of inhibitory synaptic responses in the central nervous system. In rat visual cortex, [3H]SR-95531 binding assays revealed that brain-derived neurotrophic factor (BDNF), one of the neurotrophins, induced a rapid increase in the total number of cell surface GABAA receptors, through the activation of Trk B receptor tyrosine kinases. We also demonstrated that BDNF rapidly induced a sustained potentiation of GABAA receptor-mediated currents, using nystatin-perforated patch clamp recordings, in visual cortical layer 5 pyramidal neurons freshly isolated from P14 rats. The potentiation was caused by the activation of Trk B receptor tyrosine kinase and phospholipase C-gamma. In addition, intracellular Ca2+ was important for the potentiation of GABAA responses induced by BDNF. The selective increase in mean miniature inhibitory postsynaptic (mIPSC) current amplitude without effects on mIPSC time courses supports the idea that BDNF rapidly induces an increase in the total number of cell surface functional GABAA receptors in visual cortical pyramidal neurons. These results suggest that BDNF could alter the number of cell surface GABAA receptors in a region-specific manner.

Brain-derived neurotrophic factor stimulates energy metabolism in developing cortical neurons

Brain-derived neurotrophic factor (BDNF) promotes the biochemical and morphological differentiation of selective populations of neurons during development. In this study we examined the energy requirements associated with the effects of BDNF on neuronal differentiation. Because glucose is the preferred energy substrate in the brain, the effect of BDNF on glucose utilization was investigated in developing cortical neurons via biochemical and imaging studies. Results revealed that BDNF increases glucose utilization and the expression of the neuronal glucose transporter GLUT3. Stimulation of glucose utilization by BDNF was shown to result from the activation of Na+/K+-ATPase via an increase in Na+ influx that is mediated, at least in part, by the stimulation of Na+-dependent amino acid transport. The increased Na+-dependent amino acid uptake by BDNF is followed by an enhancement of overall protein synthesis associated with the differentiation of cortical neurons. Together, these data demonstrate the ability of BDNF to stimulate glucose utilization in response to an enhanced energy demand resulting from increases in amino acid uptake and protein synthesis associated with the promotion of neuronal differentiation by BDNF.

Dark-rearing decreases NR2A N-methyl-D-aspartate receptor subunit in all visual cortical layers

Maturation of the visual cortex is a visual experience-dependent process. It has been shown that visual input triggers changes in N-methyl-D-aspartate receptor (NMDAR) subunit expression in the visual cortex. However, no data are available on the layer distribution of these molecular changes. Here we describe the laminar distribution of the cells expressing the NMDAR subunits NR2A and NR2B in the rat primary visual cortex at postnatal day (P) 21 and 37 using anti-NR2A and anti-NR2B antibodies and a stereological method to count labelled neurons. The percentage of neurons expressing the NR2A subunit in the layers II-VI remained unchanged between P21 and P37 with a slight decrease in layer V. Dark-rearing from P21 to P37 induced a pronounced decrease of the staining intensity and a significant decrease in the percentage of NR2A-expressing neurons. The changes in NR2A expression caused by dark rearing occur at similar levels in layers II-VI. The percentage of NR2B-positive cells in the different cortical layers remains unchanged from P21 to P37. The NR2B pattern was not significantly affected by dark-rearing. Thusly, the expression of NR2A depends upon visual experience after P21.

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.

Activity-dependent change in the protein level of brain-derived neurotrophic factor but no change in other neurotrophins in the visual cortex of young and adult ferrets

Neurotrophins are suggested to play a role in activity-dependent plasticity of visual cortex during the critical period of postnatal development. Thus, the concentration of neurotrophins in the cortex is expected to change with development and/or with alteration in neuronal activities. To test this, we measured protein levels of nerve growth factor, brain-derived neurotrophic factor, neurotrophin-3 and neurotrophin-4/5 in visual cortex of young (postnatal day 38-46, at the peak of the critical period) and adult ferrets with two-site enzyme-immunoassay systems. Measurements were carried out also in somatosensory cortex, hippocampus and cerebellum as control. With development the level of brain-derived neurotrophic factor did not significantly change, while those of the other neurotrophins changed in the visual cortex. A blockade of visual inputs for 24 h by an injection of tetrodotoxin into both eyes significantly decreased brain-derived neurotrophic factor protein level in the visual cortex, but not in the other regions in both young and adult ferrets. On the other hand, no significant decrease was seen in the protein level of the other neurotrophins in the visual cortex of young and adult ferrets. A monocular injection of tetrodotoxin in young ferrets resulted in the reduction of brain-derived neurotrophic factor by approximately half that by binocular injection. The degree of the decrease in the contralateral cortex to the injected eye was significantly larger than that in the ipsilateral cortex, reflecting that the contralateral eye is dominantly represented in the cortex in ferrets. Blockade of cortical neuronal activities by a GABA(A) receptor agonist led to a remarkable reduction of brain-derived neurotrophic factor protein in the visual cortex. These results suggest that the level of brain-derived neurotrophic factor protein in visual cortex is regulated by activities of cortical neurons.

NR2A but not NR2B N-methyl-D-aspartate receptor subunit is altered in the visual cortex of BDNF-knock-out mice

1. Aim of the present paper is to study the expression of N-Methyl-D-Aspartate receptor (NMDAR) subunits NR2A and NR2B within mouse visual cortex. 2. To investigate the influence of neurotrophic factor of NGF family (neurotrophins) on NMDAR expression we used mutant mice carrying a deletion in the gene for brain-derived neurotrophic factor (BDNF), a well-known neurotrophin expressed in visual cortex. 3. Western blot and immunohistochemistry were performed at postnatal day P12-14, P21-23, and adulthood showing that both subunits change during postnatal development. 4. Absence of BDNF induced a reduction of NR2A level. This effect was specific since the other subunit investigated, NR2B, was not affected in mutant mice. 5. We conclude that endogenous BDNF modulates NMDAR expression in the developing visual cortex.

Effects of dark rearing on phosphorylation of neurotrophin Trk receptors

Total lack of visual experience (dark rearing, DR) is known to affect development of mammalian visual cortex (VC) and to prolong the critical period of visual cortical plasticity. Neurotrophins (NTs) have been proposed to play a relevant role in activity dependent processes important for the final shaping of cortical visual connections. Neurotrophin supply or antagonism of endogenous NT action profoundly affect visual cortical development and plasticity; in particular, exogenous supply of NTs counteracts DR effects on VC development. However, the effects of DR on NT expression are still debated and mounting evidence reports a mismatch between BDNF mRNA and protein expression in DR animals. To gain insight into the effects of DR on expression of nerve growth factor (NGF) and the functional state of NT signalling pathways, we assessed the phosphorylation state of Trk receptors in light-reared animals (LR), in dark-reared animals (DR), in DR animals briefly exposed to light and in DR animals with exogenous supply of NTs [NGF, brain-derived neurotrophic factor (BDNF) and NT-4] in the VC. We report that DR increases the expression of NGF but reduces the phosphorylation of TrkA and TrkB receptors with respect to LR; normal phosphorylation is rapidly rescued by a brief exposure to light. Exogenous supply of NGF, BDNF or NT4 in DR animals also rescues the phosphorylation of their receptors.