Coexpression of neurotrophins and their receptors in neurons of the central nervous system

Cardiopulmonary bypass for total aortic arch replacement surgery: A review of three techniques

One treatment for acute type A aortic dissection is to replace the ascending aorta and aortic arch with a graft during circulatory arrest of the lower body, but this is associated with high mortality and morbidity. Maintaining the balance between oxygen supply and demand during circulatory arrest is the key to reducing morbidity and is the primary challenge during body perfusion. The aim of this review is to summarize current knowledge of body perfusion techniques and to predict future development of this field. We present three perfusion techniques based on deep hypothermic circulatory arrest (DHCA): DHCA alone, DHCA with selective cerebral perfusion, and DHCA with total body perfusion. DHCA was first developed to provide a clear surgical field, but it may contribute to stroke in 4%–15% of patients. Antegrade or retrograde cerebral perfusion can provide blood flow for the brain during circulatory arrest, and it is associated with much lower stroke incidence of 3%–9%. Antegrade cerebral perfusion may be better than retrograde perfusion during longer arrest. In theory, blood flow can be provided to all vital organs through total body perfusion, which can be implemented via either arterial or venous systems, or by combining retrograde inferior vena caval perfusion with antegrade cerebral perfusion. However, whether total body perfusion is better than other techniques require further investigation in large, multicenter studies. Current techniques for perfusion during circulatory arrest remain imperfect, and a technique that effectively perfuses the upper and lower body effectively during circulatory arrest is missing. Total body perfusion should be systematically compared against selective cerebral perfusion for improving outcomes after circulatory arrest.

Functional expression of TrkB receptors on interneurones and pyramidal cells of area CA3 of the rat hippocampus

The dentate gyrus and hippocampal area CA3 region of the mammalian brain contains the highest levels of brain-derived neurotrophic factor (BDNF) and its canonical membrane receptor, tropomyosin-related kinase B (TrkB). Therefore, the present study examines the expression and physiological responses triggered by activation of TrkB on hippocampal area CA3 interneurones and pyramidal cells of the rat hippocampus. Triple immunolabelling for TrkB, glutamate decarboxylase 67, and the calcium-binding proteins parvalbumin, calbindin or calretinin confirms the somatic expression of TrkB in all CA3 sublayers. TrkB-positive interneurones with fast-spiking discharge are restricted to strata oriens and lucidum, whereas regular-spiking interneurones are found in the strata lucidum, radiatum and lacunosum-moleculare. Activation of TrkB receptors with 7,8-dihydroxyflavone (DHF) modulates amplitude and frequency of spontaneous synaptic currents recorded from CA3 interneurones. Furthermore, the isolated excitatory postsynaptic currents (EPSC) of CA3 interneurones evoked by the mossy fibres (MF) or commissural/associational (C/A) axons, show input-specific synaptic potentiation in response to TrkB stimulation. On CA3 pyramidal cells, stimulation with DHF potentiates the MF synaptic transmission and increases the MF-EPSP - spike coupling. The latter exhibits a dramatic increase when picrotoxin is bath perfused after DHF, indicating that local interneurones restrain the excitability mediated by activation of TrkB. Therefore, we propose that release of BDNF on area CA3 reshapes the output of this hippocampal region by simultaneous activation of TrkB on GABAergic interneurones and pyramidal cells.

Activity Regulates Cell Death within Cortical Interneurons through a Calcineurin-Dependent Mechanism

We demonstrate that cortical interneurons derived from ventral eminences, including the caudal ganglionic eminence, undergo programmed cell death. Moreover, with the exception of VIP interneurons, this occurs in a manner that is activity-dependent. In addition, we demonstrate that, within interneurons, Calcineurin, a calcium-dependent protein phosphatase, plays a critical role in sequentially linking activity to maturation (E15-P5) and survival (P5-P20). Specifically, embryonic inactivation of Calcineurin results in a failure of interneurons to morphologically mature and prevents them from undergoing apoptosis. By contrast, early postnatal inactivation of Calcineurin increases apoptosis. We conclude that Calcineurin serves a dual role of promoting first the differentiation of interneurons and, subsequently, their survival.

Agomelatine alleviates neuronal loss through BDNF signaling in the post-status epilepticus model induced by kainic acid in rat

Recently, we have reported that while agomelatine (Ago) is unable to prevent development of epilepsy it exerts a strong neuroprotective and anti-inflammatory response in the KA post-status epilepticus (SE) rat model. In the present study, we aimed to explore whether the brain-derived neurotrophic factor (BDNF) in the hippocampus is involved in the neuroprotective effect of Ago against the KA-induced SE and epileptiform activity four months later in rats. Lacosamide (LCM) was used as a positive control. The EEG-recorded seizure activity was also evaluated in two treatment protocols. In Experiment#1, Ago given repeatedly at a dose of 40 mg/kg during the course of SE was unable neither to modify EEG-recorded epileptiform activity nor the video- and EEG-recorded spontaneous seizures four months later compared to LCM (50 mg/kg). However, both Ago and LCM inhibited the expression of BDNF in the mossy fibers and also prevented neuronal loss in the dorsal hippocampal and the piriform cortex after SE. In Experiment#2, acute injection of Ago and LCM on epileptic rats, characterized by high seizure rates, did not prevent EEG-recorded paroxysmal events while only LCM decreased either absolute or relative powers of gamma (28-60 Hz) and high (HI) (60-120 Hz) frequency bands to baseline in the frontal and parietal cortex, respectively. Our results suggest that the protection against neuronal loss in specific limbic regions and overexpressed BDNF in the mossy fibers resulting from the repeated treatment with Ago and LCM, respectively, during SE is not a prerequisite for alleviation of epileptogenesis and development of epilepsy. In addition, a reduction of gamma and HI bands in the frontal and parietal cortex is not associated with EEG-recorded paroxysmal events after acute injection of LCM.

Combined therapy involving electroacupuncture and treadmill exercise attenuates demyelination in the corpus callosum by stimulating oligodendrogenesis in a rat model of neonatal hypoxia-ischemia

We investigated whether electroacupuncture (EA) and treadmill (TM) exercise improve behaviors related to motor and memory dysfunction in a cerebral palsy-like rat model via activation of oligodendrogenesis. A neonatal hypoxia-ischemia model was created using Sprague-Dawley rats (P7), and these underwent EA stimulation and treadmill training from 3 to 5weeks after hypoxia-ischemia induction. EA treatment was delivered via electrical stimulation (2Hz, 1mA) at two acupoints, Baihui (GV20) and Zusanli (ST36). Behavioral tests showed that EA alleviated motor dysfunction caused by hypoxia-ischemia on a rotarod test, and TM exercise alleviated motor and memory dysfunction seen on cylinder and passive avoidance tests. Combined therapy with EA and TM exercise showed synergistic effects on the cylinder, rotarod, and catwalk tests. TM exercise significantly restored corpus callosum thickness, and combined therapy with EA and TM restored myelin basic protein (MBP) levels in this region. While EA stimulation only increased activation of cAMP-response element binging protein (CREB) in oligodendrocytes of the corpus callosum, TM exercise increased newly generated oligodendrocyte progenitor cells or oligodendrocytes via activation of CREB. Synergistic effects on oligodendrogenesis were also observed by the combined therapy. Furthermore, the combined therapy induced mature brain-derived neurotrophic factor (BDNF) expression in the cerebral cortex. These results demonstrate that combined therapy with EA and TM exercise may restore myelin components following neonatal hypoxia-ischemia via upregulation of oligodendrogenesis involving CREB/BDNF signaling, which subsequently improves motor and memory function. Therefore, combined therapy with EA and TM exercise offers another treatment option for functional recovery from injuries caused by neonatal hypoxia-ischemia, such as cerebral palsy.

NTRK2 (TrkB gene) variants and temporal lobe epilepsy: A genetic association study

OBJECTIVE

The NTRK2 gene encodes a member of the neurotrophic tyrosine kinase receptor family known as TrkB. It is a membrane-associated receptor with signaling and cellular differentiation properties that has been involved in neuropsychiatric disorders, including epilepsy. We report here the frequencies of NTRK2 allele variants in patients with temporal lobe epilepsy (TLE) compared to controls without epilepsy and explore the impact of these polymorphisms on major clinical variables in TLE.

METHODS

A case-control study comparing the frequencies of the NTRK2 gene polymorphisms beween 198 TLE Caucasian patients and 200 matching controls without epilepsy. In a second step, the impact of allelic variation on major clinical and electroencephalographic epilepsy variables was evaluated in the group of TLE patients. The following polymorphisms were determined by testing different regions of the NTRK2 gene: rs1867283, rs10868235, rs1147198, rs11140800, rs1187286, rs2289656, rs1624327, rs1443445, rs3780645, and rs2378672. To correct for multiple correlations the level of significance was set at p<0.01.

RESULTS

Patients with TLE showed a statistical trend for increase of the T/T genotype in rs10868235 compared to control (O.R.=1.90; 95%CI=1.17-3.09; p=0.01). Homozygous patients for the A allele in rs1443445 had earlier mean age at onset of seizures, p=0.009 (mean age of 16.6 versus 22.4years). We also observed that the T allele in rs3780645 was more frequent in patients who needed polytheraphy for seizure control than in patients on monotherapy, (O.R.=4.13; 95%CI=1.68-10.29; p=0.001). This finding may reflect an increased difficulty to obtain seizure control in this group of patients. No additional differences were observed in this study.

CONCLUSIONS

Patients with epilepsy showed a trend for a difference in rs10868235 allelic distribution compared to controls without epilepsy. NTRK2 variability influenced age at seizure onset and the pharmacological response to seizure control. As far as we know, this is the first study showing an association between NTKR2 allelic variants in human epilepsy. We believe that further studies in this venue will shade some light on the molecular mechanisms involved in epileptogenesis and in the clinical characteristics of epilepsy.

A neural model of normal and abnormal learning and memory consolidation: adaptively timed conditioning, hippocampus, amnesia, neurotrophins, and consciousness

How do the hippocampus and amygdala interact with thalamocortical systems to regulate cognitive and cognitive-emotional learning? Why do lesions of thalamus, amygdala, hippocampus, and cortex have differential effects depending on the phase of learning when they occur? In particular, why is the hippocampus typically needed for trace conditioning, but not delay conditioning, and what do the exceptions reveal? Why do amygdala lesions made before or immediately after training decelerate conditioning while those made later do not? Why do thalamic or sensory cortical lesions degrade trace conditioning more than delay conditioning? Why do hippocampal lesions during trace conditioning experiments degrade recent but not temporally remote learning? Why do orbitofrontal cortical lesions degrade temporally remote but not recent or post-lesion learning? How is temporally graded amnesia caused by ablation of prefrontal cortex after memory consolidation? How are attention and consciousness linked during conditioning? How do neurotrophins, notably brain-derived neurotrophic factor (BDNF), influence memory formation and consolidation? Is there a common output path for learned performance? A neural model proposes a unified answer to these questions that overcome problems of alternative memory models.

BDNF trafficking and signaling impairment during early neurodegeneration is prevented by moderate physical activity

Physical exercise can attenuate the effects of aging on the central nervous system by increasing the expression of neurotrophins such as brain-derived neurotrophic factor (BDNF), which promotes dendritic branching and enhances synaptic machinery, through interaction with its receptor TrkB. TrkB receptors are synthesized in the cell body and are transported to the axonal terminals and anchored to plasma membrane, through SLP1, CRMP2 and Rab27B, associated with KIF1B. Retrograde trafficking is made by EDH-4 together with dynactin and dynein molecular motors. In the present study it was found that early neurodegeneration is accompanied by decrease in BDNF signaling, in the absence of hyperphosphorylated tau aggregation, in hippocampus of 11 months old Lewis rats exposed to rotenone. It was also demonstrated that moderate physical activity (treadmill running, during 6 weeks, concomitant to rotenone exposure) prevents the impairment of BDNF system in aged rats, which may contribute to delay neurodegeneration. In conclusion, decrease in BDNF and TrkB vesicles occurs before large aggregate-like p-Tau are formed and physical activity applied during early neurodegeneration may be of relevance to prevent BDNF system decay.

Expression of Brain-derived Neurotrophic Factor and Tyrosine Kinase B in Cerebellum of Poststroke Depression Rat Model

Background:

The pathophysiology of poststroke depression (PSD) remains elusive because of its proposed multifactorial nature. Accumulating evidence suggests that brain-derived neurotrophic factor (BDNF) plays a key role in the pathophysiology of depression and PSD. And the cerebellar dysfunction may be important in the etiology of depression; it is not clear whether it also has a major effect on the risk of PSD. This study aimed to explore the expression of BDNF and high-affinity receptors tyrosine kinase B (TrkB) in the cerebellum of rats with PSD.

Methods:

The rat models with focal cerebral ischemic were made using a thread embolization method. PSD rat models were established with comprehensive separate breeding and unpredicted chronic mild stress (UCMS) on this basis. A normal control group, depression group, and a stroke group were used to compare with the PSD group. Thirteen rats were used in each group. Immunohistochemistry and reverse transcription-polymerase chain reaction (RT-PCR) for detecting the expression of BDNF and TrkB protein and mRNA in the cerebellum were used at the 29^th day following the UCMS.

Results:

Compared with the normal control group and the stroke group, the number of BDNF immunoreactive (IR) positive neurons was less in the PSD group (P < 0.05). Furthermore, the number of TrkB IR positive cells was significantly less in the PSD group than that in the normal control group (P < 0.05). The gene expression of BDNF and TrkB in the cerebellum of PSD rats also decreased compared to the normal control group (P < 0.05).

Conclusions:

These findings suggested a possible association between expression of BDNF and TrkB in the cerebellum and the pathogenesis of PSD.

The BDNF Valine 68 to Methionine Polymorphism Increases Compulsive Alcohol Drinking in Mice That Is Reversed by Tropomyosin Receptor Kinase B Activation

BACKGROUND

The valine 66 to methionine (Met) polymorphism within the brain-derived neurotrophic factor (BDNF) sequence reduces activity-dependent BDNF release and is associated with psychiatric disorders in humans. Alcoholism is one of the most prevalent psychiatric diseases. Here, we tested the hypothesis that this polymorphism increases the severity of alcohol abuse disorders.

METHODS

We generated transgenic mice carrying the mouse homolog of the human Met66BDNF allele (Met68BDNF) and used alcohol-drinking paradigms in combination with viral-mediated gene delivery and pharmacology.

RESULTS

We found that Met68BDNF mice consumed excessive amounts of alcohol and continued to drink despite negative consequences, a hallmark of addiction. Importantly, compulsive alcohol intake was reversed by overexpression of the wild-type valine68BDNF allele in the ventromedial prefrontal cortex of the Met68BDNF mice or by systemic administration of the tropomyosin receptor kinase B agonist, LM22A-4.

CONCLUSIONS

Our findings suggest that carrying this BDNF allele increases the risk of developing uncontrolled and excessive alcohol drinking that can be reversed by directly activating the BDNF receptor, tropomyosin receptor kinase B. Importantly, this work identifies a potential therapeutic strategy for the treatment of compulsive alcohol drinking in humans carrying the Met66BDNF allele.

Mononuclear cells from the cord blood and granulocytecolony stimulating factor-mobilized peripheral blood: is there a potential for treatment of cerebral palsy?

To investigate a possible therapeutic mechanism of cell therapy in the field of cerebral palsy using granulocyte-colony stimulating factor (G-CSF)-mobilized peripheral blood mononuclear cells (mPBMCs), we compared the expression of inflammatory cytokines and neurotrophic factors in PBMCs and mPBMCs from children with cerebral palsy to those from healthy adult donors and to cord blood mononuclear cells donated from healthy newborns. No significant differences in expression of neurotrophic factors were found between PBMCs and mPBMCs. However, in cerebral palsy children, the expression of interleukin-6 was significantly increased in mPBMCs as compared to PBMCs, and the expression of interleukin-3 was significantly decreased in mPBMCs as compared to PBMCs. In healthy adults, the expression levels of both interleukin-1β and interleukin-6 were significantly increased in mPBMCs as compared to PBMCs. The expression of brain-derived neurotrophic factors in mPBMC from cerebral palsy children was significantly higher than that in the cord blood or mPBMCs from healthy adults. The expression of G-CSF in mPBMCs from cerebral palsy children was comparable to that in the cord blood but significantly higher than that in mPBMCs from healthy adults. Lower expression of pro-inflammatory cytokines (interleukin-1β, interleukin-3, and -6) and higher expression of anti-inflammatory cytokines (interleukin-8 and interleukin-9) were observed from the cord blood and mPBMCs from cerebral palsy children rather than from healthy adults. These findings indicate that mPBMCs from cerebral palsy and cord blood mononuclear cells from healthy newborns have the potential to become seed cells for treatment of cerebral palsy.

Brain-derived neurotrophic factor modulates immune reaction in mice with peripheral nerve xenotransplantation

BACKGROUND

Brain-derived neurotrophic factor (BDNF) has been demonstrated to play an important role in survival, differentiation, and neurite outgrowth for many types of neurons. This study was designed to identify the role of BDNF during peripheral nerve xenotransplantation.

MATERIALS AND METHODS

A peripheral nerve xenotransplantation from rats to mice was performed. Intracellular cytokines were stained for natural killer (NK) cells, natural killer T (NKT) cells, T cells, and B cells and analyzed by flow cytometry in the spleen of the recipient mouse. Serum levels of related cytokines were quantified by cytometric bead array.

RESULTS

Splenic NK cells significantly increased in the xenotransplanted mice (8.47±0.88×10(7) cells/mL) compared to that in the control mice (4.66±0.78×10(7) cells/mL, P=0.0003), which significantly reduced in the presence of BDNF (4.85±0.87×10(7) cells/mL, P=0.0004). In contrast, splenic NKT cell number was significantly increased in the mice with xenotransplantation plus BDNF (XT + BDNF) compared to that of control group or of mice receiving xenotransplantation only (XT only). Furthermore, the number of CD3+ T cells, CD3+CD4+ T cells, CD3+CD4- T cells, interferon-γ-producing CD3+CD4+ T cells, and interleukin (IL)-17-producing CD3+CD4+ T cells, as well as CD3-CD19+ B cells, was significantly higher in the spleen of XT only mice compared to the control mice (P<0.05), which was significantly reduced by BDNF (P<0.05). The number of IL-4-producing CD3+CD4+ T cells and CD3+CD4+CD25+Foxp3+ T cells was significantly higher in the spleen of XT + BDNF mice than that in the spleen of XT only mice (P<0.05). Serum levels of IL-6, TNF-α, interferon-γ, and IL-17 were decreased, while IL-4 and IL-10 were stimulated by BDNF following xenotransplantation.

CONCLUSION

BDNF reduced NK cells but increased NKT cell accumulation in the spleen of xenotransplanted mice. BDNF modulated the number of splenic T cells and its subtype cells in the mice following xenotransplantation. These findings suggest that BDNF inhibits rejection of peripheral nerve following xenotransplantation by regulating innate as well as adaptive immune reaction.

Alcohol dependence-induced regulation of the proliferation and survival of adult brain progenitors is associated with altered BDNF-TrkB signaling

Effects of withdrawal from ethanol drinking in chronic intermittent ethanol vapor (CIE)-exposed dependent rats and air-exposed nondependent rats on proliferation and survival of progenitor cells in the hippocampus and the medial prefrontal cortex (mPFC) were investigated. Rats were injected with 5'-Bromo 2-deoxyuridine 72 h post-CIE to measure proliferation (2 h-old cells) and survival (29-day-old cells) of progenitors born during a time-point previously reported to elicit a proliferative burst in the hippocampus. Hippocampal and mPFC brain-derived neurotrophic factor (BDNF) and tropomyosin-related kinase B receptor (TrkB) expression were measured 3 h or 21d post-CIE to evaluate neurotrophic signaling during a time point preceding the proliferative burst and survival of newly born progenitors. CIE rats demonstrated elevated drinking compared to nondependent rats and CIE rats maintained elevated drinking following protracted abstinence. Withdrawal from CIE increased BDNF levels in the hippocampus and mPFC, and subsequently increased proliferation in the hippocampus and mPFC compared to nondependent rats and controls. Protracted abstinence from CIE reduced BDNF expression to control levels, and subsequently reduced neurogenesis compared to controls and nondependent rats in the hippocampus. In the mPFC, protracted abstinence reduced BDNF expression to control levels, whereas increased oligodendrogenesis in dependent rats compared to nondependent rats and controls. These results suggest a novel relationship between BDNF and progenitors in the hippocampus and mPFC, in which increased ethanol drinking may alter hippocampal and cortical function in alcohol dependent subjects by altering the cellular composition of newly born progenitors in the hippocampus and mPFC.

Corticostriatal BDNF and alcohol addiction

Growth factors, long studied for their involvement in neuronal development and plasticity, also regulate responses to drugs of abuse, including alcohol. This review details the intricate interaction between the Brain-Derived Neurotrophic Factor (BDNF) and alcohol, and provides evidence to suggest that corticostriatal BDNF signaling acts to keep alcohol drinking in moderation. Specifically, we describe studies in rodent models suggesting that moderate consumption of alcohol increases BDNF levels in the dorsal striatum, which in turn act to suppress alcohol intake by activating a Mitogen-Activated Protein Kinase (MAPK)-dependent genomic mechanism. We further provide data to suggest that alcohol intake levels escalate when the endogenous corticostriatal BDNF pathway becomes dysregulated. Finally, we summarize recent studies suggesting that specific microRNAs targeting BDNF mRNA in the medial prefrontal cortex (mPFC) regulate the breakdown of the protective corticostriatal BDNF pathway.

Long-delayed expression of the immediate early gene Arc/Arg3.1 refines neuronal circuits to perpetuate fear memory

Fear memories typically persist for long time periods, and persistent fear memories contribute to post-traumatic stress disorder. However, little is known about the cellular and synaptic mechanisms that perpetuate long-term memories. Here, we find that mouse hippocampal CA1 neurons exhibit biphasic Arc (also known as Arg3.1) elevations after fear experience and that the late Arc expression regulates the perpetuation of fear memoires. An early Arc increase returned to the baseline after 6 h, followed by a second Arc increase after 12 h in the same neuronal subpopulation; these elevations occurred via distinct mechanisms. Antisense-induced blockade of late Arc expression disrupted memory persistence but not formation. Moreover, prolonged fear memories were associated with the delayed, specific elimination of dendritic spines and the reactivation of neuronal ensembles formed during fear experience, both of which required late Arc expression. We propose that late Arc expression refines functional circuits in a delayed fashion to prolong fear memory.

Treatment with tianeptine induces antidepressive-like effects and alters the neurotrophin levels, mitochondrial respiratory chain and cycle Krebs enzymes in the brain of maternally deprived adult rats

Maternally deprived rats were treated with tianeptine (15 mg/kg) once a day for 14 days during their adult phase. Their behavior was then assessed using the forced swimming and open field tests. The BDNF, NGF and energy metabolism were assessed in the rat brain. Deprived rats increased the immobility time, but tianeptine reversed this effect and increased the swimming time; the BDNF levels were decreased in the amygdala of the deprived rats treated with saline and the BDNF levels were decreased in the nucleus accumbens within all groups; the NGF was found to have decreased in the hippocampus, amygdala and nucleus accumbens of the deprived rats; citrate synthase was increased in the hippocampus of non-deprived rats treated with tianeptine and the creatine kinase was decreased in the hippocampus and amygdala of the deprived rats; the mitochondrial complex I and II-III were inhibited, and tianeptine increased the mitochondrial complex II and IV in the hippocampus of the non-deprived rats; the succinate dehydrogenase was increased in the hippocampus of non-deprived rats treated with tianeptine. So, tianeptine showed antidepressant effects conducted on maternally deprived rats, and this can be attributed to its action on the neurochemical pathways related to depression.

Hypothyroidism in the adult rat causes incremental changes in brain-derived neurotrophic factor, neuronal and astrocyte apoptosis, gliosis, and deterioration of postsynaptic density

BACKGROUND

Adult hypothyroidism is a highly prevalent condition that impairs processes, such as learning and memory. Even though tetra-iodothyronine (T(4)) treatment can overcome the hypothyroidism in the majority of cases, it cannot fully recover the patient's learning capacity and memory. In this work, we analyzed the cellular and molecular changes in the adult brain occurring with the development of experimental hypothyroidism.

METHODS

Adult male Sprague-Dawley rats were treated with 6-propyl-2-thiouracil (PTU) for 20 days to induce hypothyroidism. Neuronal and astrocyte apoptosis were analyzed in the hippocampus of control and hypothyroid adult rats by confocal microscopy. The content of brain-derived neurotrophic factor (BDNF) was analyzed using enzyme-linked immunosorbent assay (ELISA) and in situ hybridization. The glutamatergic synapse and the postsynaptic density (PSD) were analyzed by electron microscopy. The content of PSD proteins like tyrosine receptor kinase B (TrkB), p75, and N-methyl-D-aspartate receptor (NMDAr) were analyzed by immunoblot.

RESULTS

We observed that the hippocampus of hypothyroid adult rats displayed increased apoptosis levels in neurons and astrocyte and reactive gliosis compared with controls. Moreover, we found that the amount of BDNF mRNA was higher in the hippocampus of hypothyroid rats and the content of TrkB, the receptor for BDNF, was reduced at the PSD of the CA3 region of hypothyroid rats, compared with controls. We also observed that the glutamatergic synapses from the stratum radiatum of CA3 from hypothyroid rats, contained thinner PSDs than control rats. This observation was in agreement with a reduced content of NMDAr subunits at the PSD in hypothyroid animals.

CONCLUSIONS

Our data suggest that adult hypothyroidism affects the hippocampus by a mechanism that alters the composition of PSD, reduces neuronal and astrocyte survival, and alters the content of the signaling neurotrophic factors, such as BDNF.

Self-amplifying autocrine actions of BDNF in axon development

A critical step in neuronal development is the formation of axon/dendrite polarity, a process involving symmetry breaking in the newborn neuron. Local self-amplifying processes could enhance and stabilize the initial asymmetry in the distribution of axon/dendrite determinants, but the identity of these processes remains elusive. We here report that BDNF, a secreted neurotrophin essential for the survival and differentiation of many neuronal populations, serves as a self-amplifying autocrine factor in promoting axon formation in embryonic hippocampal neurons by triggering two nested positive-feedback mechanisms. First, BDNF elevates cytoplasmic cAMP and protein kinase A activity, which triggers further secretion of BDNF and membrane insertion of its receptor TrkB. Second, BDNF/TrkB signaling activates PI3-kinase that promotes anterograde transport of TrkB in the putative axon, further enhancing local BDNF/TrkB signaling. Together, these self-amplifying BDNF actions ensure stable elevation of local cAMP/protein kinase A activity that is critical for axon differentiation and growth.

Emerging themes in GABAergic synapse development

Glutamatergic synapse development has been rigorously investigated for the past two decades at both the molecular and cell biological level yet a comparable intensity of investigation into the cellular and molecular mechanisms of GABAergic synapse development has been lacking until relatively recently. This review will provide a detailed overview of the current understanding of GABAergic synapse development with a particular emphasis on assembly of synaptic components, molecular mechanisms of synaptic development, and a subset of human disorders which manifest when GABAergic synapse development is disrupted. An unexpected and emerging theme from these studies is that glutamatergic and GABAergic synapse development share a number of overlapping molecular and cell biological mechanisms that will be emphasized in this review.

Therapeutic hypothermia: critical review of the molecular mechanisms of action

Therapeutic hypothermia (TH) is nowadays one of the most important methods of neuroprotection. The events that occur after an episode of ischemia are multiple and hypothermia can affect the various steps of this cascade. The mechanisms of action of TH are varied and the possible explanation for the benefits of this therapy is probably the multiple mechanisms of action blocking the cascade of ischemia on many levels. TH can affect many metabolic pathways, reactions of inflammation, apoptosis processes, and promote neuronal integrity. To know the mechanisms of action of TH will allow a better understanding about the indications for this therapy and the possibility of searching for other therapies when used in conjunction with hypothermia will provide a therapeutic synergistic effect.

Deoxygedunin, a natural product with potent neurotrophic activity in mice

Gedunin, a family of natural products from the Indian neem tree, possess a variety of biological activities. Here we report the discovery of deoxygedunin, which activates the mouse TrkB receptor and its downstream signaling cascades. Deoxygedunin is orally available and activates TrkB in mouse brain in a BDNF-independent way. Strikingly, it prevents the degeneration of vestibular ganglion in BDNF −/− pups. Moreover, deoxygedunin robustly protects rat neurons from cell death in a TrkB-dependent manner. Further, administration of deoxygedunin into mice displays potent neuroprotective, anti-depressant and learning enhancement effects, all of which are mediated by the TrkB receptor. Hence, deoxygedunin imitates BDNF's biological activities through activating TrkB, providing a powerful therapeutic tool for treatment of various neurological diseases.

Intranasal delivery of neurotrophic factors BDNF, CNTF, EPO, and NT-4 to the CNS

Injury to the central nervous system (CNS) generally results in significant neuronal death and functional loss. In vitro experiments have demonstrated that neurotrophic factors such as brain-derived neurotrophic factor (BDNF), ciliary neurotrophic factor (CNTF), and neurotrophin-4/5 (NT-4/5) can promote neuronal survival. However, delivery to the injured CNS is difficult as these large protein molecules do not efficiently cross the blood-brain barrier. Intranasal delivery of 70 microg [(125)I]-radiolabeled BDNF, CNTF, NT-4, or erythropoietin (EPO) resulted in 0.1-1.0 nM neurotrophin concentrations within 25 min in brain parenchyma. In addition, not only did these neurotrophic factors reach the CNS, they were present in sufficient concentrations to activate the prosurvival PI3Kinase/Akt pathway, even where lower levels of neurotrophic factors were measured. Currently traumatic, ischemic and compressive injuries to the CNS have no effective treatment. There is potential clinical relevancy of this method for rescuing injured CNS tissues in order to maintain CNS function in affected patients. The intranasal delivery method has great clinical potential due to (1) simplicity of administration, (2) noninvasive drug administration, (3) relatively rapid CNS delivery, (4) ability to repeat dosing easily, (5) no requirement for drug modification, and (6) minimal systemic exposure.

Escalating ethanol intake is associated with altered corticostriatal BDNF expression

Alcoholism is a chronically relapsing condition, indicative of long-term neuronal adaptations maintaining the disease even after prolonged abstinence. Previously, we identified brain-derived neurotrophic factor (BDNF) in the dorsal striatum as the central mediator of a homeostatic mechanism which is activated by acute alcohol (ethanol) exposure and functions to decrease the sensitivity of rodents to ethanol-related behaviors. We hypothesized that extensive exposure to ethanol would result in dysregulation of this BDNF-mediated protective mechanism, accompanied by heightened ethanol intake. In this study, we demonstrate that while a single bout of ethanol intake increases BDNF mRNA expression in the dorsal striatum, this effect is no longer observed after 6 weeks of daily ethanol access. Additionally, 6 weeks of ethanol consumption decreases BDNF in the cortex, a main source of BDNF for the striatum. Importantly, these ethanol-induced changes in BDNF levels are not ameliorated by 2 weeks' abstinence. Together, these data suggest that the BDNF pathway, which is activated following a single bout of ethanol drinking, breaks down by the end of 6 weeks of access and does not recover its protective function after a 2-week deprivation period. These results suggest that the persistence of altered BDNF signaling may contribute to the inflexibility of addictive behaviors.

BDNF and TrkB in the preterm and near-term ovine fetal brain and the effect of intermittent umbilical cord occlusion

We have determined the developmental change in immunoreactivity for brain-derived neurotrophic factor and its high-affinity tyrosine kinase receptor, TrkB, in the ovine fetal brain with advancing gestation and in response to intermittent umbilical cord occlusion, which might then contribute to adverse neurodevelopment. Fetal sheep (control and experimental groups at 0.75 and 0.90 of gestation) were studied over 4 days with umbilical cord occlusions performed in the experimental group animals by complete inflation of an occluder cuff for 90 seconds every 30 minutes for 3 to 5 hours each day. Animals were then euthanized and the fetal brains perfusion fixed and prepared for subsequent histology with the distribution of brain-derived neurotrophic factor and tyrosine kinase receptor immunoreactivity determined by immunohistochemistry. In the control group animals brain-derived neurotrophic factor immunoreactivity decreased in the gray matter, thalamus, and hippocampus but increased in the white matter, while tyrosine kinase receptor immunoreactivity decreased in all regions (most P < .01), with advancing gestation consistent with the developmental change from neurogenesis/gliagenesis to myelination over this time period. Intermittent umbilical cord occlusion as studied with severe but limited hypoxemia resulted in a variable decrease in brain-derived neurotrophic factor and tyrosine kinase receptor immunoreactivity for all brain regions in the preterm animals (most P < .01) when protein turnover is higher, but a selective increase in brain-derived neurotrophic factor immunoreactivity in the hippocampus of the near-term animals consistent with a heightened vulnerability for necrotic/apoptotic injury at this time. As such, brain-derived neurotrophic factor-tyrosine kinase receptor in the ovine fetal brain may be altered with intermittent hypoxic insults over the latter part of pregnancy with potential for longer term neurologic consequences.

Up-regulation of brain-derived neurotrophic factor by application of fibroblast growth factor-2 to the cut optic nerve is important for long-term survival of retinal ganglion cells

Application of basic fibroblast growth factor (FGF-2) to the optic nerve after axotomy promotes the survival of retinal ganglion cells (RGCs) in the frog Rana pipiens and results in a rapid up-regulation of brain-derived neurotrophic factor (BDNF) and TrkB synthesis by the RGCs. Here we investigate whether this up-regulation is maintained over the long term and whether it is required for FGF-2's survival effect. At 6 weeks after axotomy and FGF-2 treatment, we found more RGCs immunopositive for BDNF protein and higher intensity of BDNF and TrkB immunostaining, accompanied by increases in BDNF and TrkB mRNA in RGCs. Application of fluorescently labeled siRNA targeted against BDNF to the cut RGC axons showed that it was transported to the cell bodies. Axonal siRNA treatment eliminated the increases in BDNF immunostaining and mRNA that were induced by FGF-2 and had no effect on TrkB mRNA. This reduction in BDNF synthesis by siRNA greatly reduced the long-term survival effect of FGF-2 on RGCs. This, taken together with previous results, suggests that, although FGF-2 may initially activate survival pathways via ERK signaling, its main long-term survival effects are mediated via its up-regulation of BDNF synthesis by the RGCs.

Lack of effect of antipsychotics on BNDF and NGF levels in hippocampus of Wistar rats

Schizophrenia is a common and serious mental disorder, in which the majority of patients require long-term antipsychotic treatment. Several studies have suggested that schizophrenia is associated with decreased neurotrophins such as brain-derived neurotrophic factor (BDNF) and nerve growth factor (NGF). Investigation of the mechanisms of pharmacological agents that are used in the treatment of schizophrenia has been used to better understand the basis of the pathology associated with this mental illness. The present study aims to investigate the effect of chronic treatment with antipsychotics, named haloperidol (HAL), clozapine (CLO), olanzapine (OLZ) or aripiprazole (ARI) on BDNF and NGF levels in rat hippocampus. Adult male Wistar rats received daily injections of HAL (1.5 mg/kg), CLO (25 mg/kg), OLZ (2.5, 5 or 10 mg/kg) or ARI (2, 10 or 20 mg/kg), whereas control animals were given vehicle. BDNF and NGF levels were measured in rat hippocampus by sandwich-ELISA. The results showed that chronic administration of antipsychotics did not modify BDNF and NGF levels in rat hippocampus, suggesting that their therapeutic properties are not mediated by stimulation of these neurotrophins.

Presynaptic functional trkB receptors mediate the release of excitatory neurotransmitters from primary afferent terminals in lamina II (substantia gelatinosa) of postnatal rat spinal cord

A subset of primary sensory neurons produces BDNF, which is implicated in control of nociceptive neurotransmission. We previously localized full-length trkB receptors on their terminals within lamina II. To functionally study these receptors, we here employed patch-clamp recordings, calcium imaging and immunocytochemistry on slices from 8-12 days post-natal rats. In this preparation, BDNF (100-500 ng/mL) enhances the release of sensory neurotransmitters (glutamate, substance P, CGRP) in lamina II by acting on trkB receptors expressed by primary afferent fibers of the peptidergic nociceptive type (PN-PAFs). Effect was blocked by trk antagonist K252a or anti-trkB antibody clone 47. A pre-synaptic mechanism was demonstrated after (i) patch-clamp recordings where the neurotrophin induced a significant increase in frequency, but not amplitude, of AMPA-mediated mEPSCs, (ii) real time calcium imaging, where sustained application of BDNF evoked an intense response in up to 57% lamina II neurons with a significant frequency rise. Antagonists of ionotropic glutamate receptors and NK(1) receptors completely inhibited the calcium response to BDNF. Reduction of CGRP (a specific marker of PN-PAFs) and substance P content in dorsal horn following BDNF preincubation, and analysis of the calcium response after depletion with capsaicin, confirmed that the neurotrophin presynaptically enhanced neurotransmitter release from PN-PAFs. This is the first demonstration that trkB receptors expressed by PN-PAF terminals in lamina II are functional during postnatal development. Implications of this finding are discussed considering that BDNF can be released by these same terminals and microglia, a fraction of which (as shown here) contains BDNF also in unactivated state.

GDNF delivery for Parkinson's disease

The mainstays of Parkinson's disease (PD) treatment remain symptomatic, including initial dopamine replacement and subsequent deep brain stimulation, however, neither of these approaches is neuroprotective. Neurotrophic factors - proteins that activate cell signalling pathways regulating neuronal survival, differentiation, growth and regeneration - represent an alternative for treating dopaminergic neurons in PD but are difficult to administer clinically because they do not pass through the blood-brain barrier. Glial cell line-derived neurotrophic factor (GDNF) has potent neurotrophic effects particularly but not exclusively on dopaminergic neurons; in animal models of PD, it has consistently demonstrated both neuroprotective and neuroregenerative effects when provided continuously, either by means of a viral vector or through continuous infusion either into the cerebral ventricles (ICV) or directly into the denervated putamen. This led to a human PD study in which GDNF was administered by monthly bolus intracerebroventricular injections, however, no clinical benefit resulted, probably because of the limited penetration to the target brain areas, and instead significant side effects occurred. In an open-label study of continuous intraputamenal GDNF infusion in five patients (one unilaterally and four bilaterally), we reported excellent tolerance, few side effects and clinical benefit evident within three months of the commencement of treatment. The clinical improvement was sustained and progressive, and by 24-months patients demonstrated a 57 and 63% improvement in their off-medication motor and activities of daily living UPDRS subscores, respectively, with clear benefit in dyskinesias. The benefit was associated with a significant increase in putamenal 18F-dopa uptake on positron emission tomography (PET), and in one patient coming to autopsy after 43 months of unilateral infusion there was evident increased tyrosine hydroxylase immunopositive nerve fibres in the infused putamen. A second open trial in 10 patients using unilateral intraputamenal GDNF infusions has also demonstrated a greater than 30% bilateral benefit in both on- and off-medication scores at 24 weeks. Based on our 6-month results, a randomized controlled clinical trial was conducted to confirm the open-label results, however, GDNF infusion over 6-months did not confer the predetermined level of clinical benefit to patients with PD despite increased 18F-dopa uptake surrounding the catheter tip. It is possible that technical differences between this trial and the positive open label studies contributed to this negative outcome.

Adenosine A(2A) receptors are required for normal BDNF levels and BDNF-induced potentiation of synaptic transmission in the mouse hippocampus

Brain-derived neurotrophic factor (BDNF), a member of neurotrophin family, enhances synaptic transmission and regulates neuronal proliferation and survival. Both BDNF and its tyrosine kinase receptors (TrkB) are highly expressed in the hippocampus, where an interaction with adenosine A(2A) receptors (A(2A)Rs) has been recently reported. In the present paper, we evaluated the role of A(2A)Rs in mediating functional effects of BDNF in hippocampus using A(2A)R knock-out (KO) mice. In hippocampal slices from WT mice, application of BDNF (10 ng/mL) increased the slope of excitatory post-synaptic field potentials (fEPSPs), an index of synaptic facilitation. This increase of fEPSP slope was abolished by the selective A(2A) antagonist ZM 241385. Similarly, genetic deletion of the A(2A)Rs abolished BDNF-induced increase of the fEPSP slope in slices from A(2A)R KO mice The reduced functional ability of BDNF in A(2A)R KO mice was correlated with the reduction in hippocampal BDNF levels. In agreement, the pharmacological blockade of A(2)Rs by systemic ZM 241385 significantly reduced BDNF levels in the hippocampus of normal mice. These results indicate that the tonic activation of A(2A)Rs is required for BDNF-induced potentiation of synaptic transmission and for sustaining a normal BDNF tone in the hippocampus.

Investigating the neurobiology of music: brain-derived neurotrophic factor modulation in the hippocampus of young adult mice

It has been shown that music might be able to improve mood state in people affected by psychiatric disorders, ameliorate cognitive deficits in people with dementia and increase motor coordination in Parkinson patients. Robust experimental evidence explaining the central effects of music, however, is missing. This study was designed to investigate the effect of music on brain neurotrophin production and behavior in the mouse. We exposed young adult mice to music with a slow rhythm (6 h/day; mild sound pressure levels, between 50 and 60 db) for 21 consecutive days. At the end of the treatment, mice were tested for passive avoidance learning and then killed for analysis of brain-derived neurotrophic factor (BDNF) and nerve growth factor with enzyme-linked immunosorbent assay (ELISA) in selected brain regions. We found that music-exposed mice showed increased BDNF, but not nerve growth factor in the hippocampus. Furthermore, we observed that music exposure significantly enhanced learning performance, as measured by the passive avoidance test. Our results demonstrate that exposure to music can modulate the activity of the hippocampus by influencing BDNF production. Our findings also suggest that music exposure might be of help in several central nervous system pathologies.

BDNF/ TrkB interaction regulates migration of SVZ precursor cells via PI3-K and MAP-K signalling pathways

Neuroblasts born in the subventricular zone (SVZ) migrate along the rostral migratory stream, reaching the olfactory bulb (OB) where they differentiate into local interneurons. Several extracellular factors have been suggested to control specific steps of this process. The brain-derived neurotrophic factor (BDNF) has been demonstrated to promote morphological differentiation and survival of OB interneurons. Here we show that BDNF and its receptor TrkB are expressed in vivo throughout the migratory pathway, implying that BDNF might also mediate migratory signals. By using in vitro models we demonstrate that BDNF promotes migration of SVZ neuroblasts, acting both as inducer and attractant through TrkB activation. We show that BDNF induces cAMP response element-binding protein (CREB) activation in migrating neuroblasts via phosphatidylinositol 3-kinase (PI3-K) and mitogen-activated protein kinase (MAP-K) signalling. Pharmacological blockade of these pathways on SVZ explants significantly reduces CREB activation and impairs neuronal migration. This study identifies a function of BDNF in the SVZ system, which involves multiple protein kinase pathways leading to neuroblast migration.

A local reduction in cortical GABAergic synapses after a loss of endogenous brain-derived neurotrophic factor, as revealed by single-cell gene knock-out method

To address questions of whether brain-derived neurotrophic factor (BDNF) released from active excitatory neurons acts locally only on GABAergic presynaptic terminals contacting these neurons or generally also on GABAergic terminals contacting other inactive neurons, we developed a single-cell gene knock-out method in organotypic slice culture of visual cortex of floxed BDNF transgenic mice. A biolistic transfection of Cre recombinase with green fluorescence protein (GFP) plasmids to layer II/III of the cortex resulted in loss of BDNF in a single neuron or a small number of neurons, which expressed GFP at 13-14 d in vitro. Analysis with in situ hybridization and immunohistochemistry confirmed that neurons expressing GFP lacked BDNF mRNA and protein, respectively. Analysis with immunohistochemistry using antibody against GABA synthesizing enzyme showed that the number of GABAergic terminals on the soma of BDNF knock-out neurons was smaller than that of neighboring control neurons. Morphological analysis indicated that there was no significant difference in the soma size and branch points and length of dendrites between the BDNF knock-out and control neurons. Recordings of miniature IPSCs (mIPSCs) showed that the frequency of mIPSCs of BDNF knock-out neurons was lower than that of control neurons, although the amplitude was not significantly different, suggesting the smaller number of functional GABAergic synapses on whole the BDNF knock-out neuron. The present results suggest that BDNF released from postsynaptic target neurons promotes the formation or proliferation of GABAergic synapses through its local actions in layer II/III of visual cortex.

A BDNF infusion into the medial prefrontal cortex suppresses cocaine seeking in rats

The medial prefrontal cortex (mPFC) is critical for reinstatement of cocaine seeking and is the main source of brain-derived neurotrophic factor (BDNF) to striatal regions of the brain relapse circuitry. To test the hypothesis that BDNF in the mPFC regulates cocaine-seeking behavior, rats were trained to press a lever for cocaine infusions (0.2 mg/inf, 2 h/day) paired with light+tone conditioned stimulus (CS) presentations on 10 consecutive days. After the last self-administration session, rats received a single infusion of BDNF (0.75 microg/0.5 microL/side) into the mPFC; this manipulation produced protracted effects on cocaine-seeking behavior (non-reinforced lever pressing). BDNF pretreatment administered after the last session attenuated cocaine seeking 22 h later and, remarkably, it also blocked cocaine-induced suppression of phospho-extracellular-regulated kinase and elevated BDNF immunoreactivity in the nucleus accumbens. The same pretreatment also suppressed cocaine-seeking behavior elicited by response-contingent CS presentations after 6 days of forced abstinence or extinction training, as well as a cocaine challenge injection (10 mg/kg, i.p.) after extinction training. However, BDNF infused into the mPFC had no effect on food-seeking behavior. Furthermore, BDNF infused on the sixth day of abstinence failed to alter responding, suggesting that the regulatory influence of BDNF is time limited. The suppressive effects of BDNF infused into the mPFC on cocaine seeking indicate that BDNF regulates cortical pathways implicated in relapse to drug seeking and that corticostriatal BDNF adaptations during early abstinence diminish compulsive drug seeking.

In vivo brain-derived neurotrophic factor release and tyrosine kinase B receptor expression in the supraoptic nucleus after osmotic stress stimulus in rats

Brain-derived neurotrophic factor (BDNF) is a member of the neurotrophin family involved in plasticity and neuroprotective processes. In recent years, we have reported the presence of BDNF mRNA in the supraoptic nucleus (SON) as well its sensitivity to osmotic stress. The rat SON is a relatively homogenous nucleus mainly consisting of magnocellular soma with their dendritic processes. BDNF may be released from dendrites to the extracellular space to stimulate tyrosine kinase (Trk) B receptors which are hypothetically present on these subcellular SON compartments. The main goal of this work was thus to study the presence and the in vivo BDNF-IR release from SON using the push-pull perfusion technique following systemic (i.p.) or local (within the SON) osmotic stimulation. BDNF was detected by immunocytochemistry and its release was measured by immunological assay (ELISA). Likewise, TrkB receptor localization in the SON-mRNA and their respective proteins-were studied by in situ hybridization and immunohistofluorescence techniques, respectively. Phosphorylation of CREB was detected by immunohistofluorescence. We present here direct evidence of in vivo dendritic BDNF release from SON which is highly sensitive to osmotic stress. The osmotic response latency period clearly depends on the mode of stimulus application (210 min for i.p. route vs. 15 min for intra-SON administration). The fact that BDNF is released as a very rapid peak when osmotic stimulation is locally applied is strong evidence in favor of an intra-SON origin of this secretion. Osmotic stress also increased phosphorylated cAMP response element binding protein immunoreactivity in the SON. In addition, we show in control rats that truncated forms of tyrosine kinase B receptor 2 mRNA represent the most abundant messenger in the SON as compared with brain-derived neurotrophic factor full-length catalytic receptor or truncated forms of tyrosine kinase B receptor 1 mRNA. In conclusion, it is likely that BDNF and their receptors are involved in neuronal plasticity changes induced by osmotic stress in the SON.

Dissociation between CA3-CA1 synaptic plasticity and associative learning in TgNTRK3 transgenic mice

Neurotrophins and their cognate receptors might serve as feedback regulators for the efficacy of synaptic transmission. We analyzed mice overexpressing TrkC (TgNTRK3) for synaptic plasticity and the expression of glutamate receptor subunits. Animals were conditioned using a trace [conditioned stimulus (CS), tone; unconditioned stimulus (US), shock] paradigm. A single electrical pulse presented to the Schaffer collateral-commissural pathway during the CS-US interval evoked a monosynaptic field EPSP (fEPSP) at ipsilateral CA1 pyramidal cells. In wild types, fEPSP slopes increased across conditioning sessions and decreased during extinction, being linearly related to learning evolution. In contrast, fEPSPs in TgNTRK3 animals reached extremely high values, not accompanied with a proportionate increase in their learning curves. Long-term potentiation evoked in conscious TgNTRK3 was also significantly longer lasting than in wild-type mice. These functional alterations were accompanied by significant changes in NR1 and NR2B NMDA receptor subunits, with no modification of NR1(Ser 896) or NR1(Ser 897) phosphorylation. No changes of AMPA and kainate subunits were detected. Results indicate that the NT-3/TrkC cascade could regulate synaptic transmission and plasticity through modulation of glutamatergic transmission at the CA3-CA1 synapse.

Hippocampal mossy fiber sprouting and elevated trkB receptor expression following systemic administration of low dose domoic acid during neonatal development

We have previously reported that serial systemic injections of low-dose (subconvulsive) domoic acid (DOM) during early postnatal development produces changes in both behavior and hippocampal cytoarchitecture in aged rats (17 months) that are similar to those seen in existing animal models of temporal lobe epilepsy. Herein we report further hippocampal changes, consisting of mossy fiber sprouting and associated changes in the trkB receptor population in young adult (3 months) rats, and further, report that these changes show regional variation throughout the septo-temporal axis of the hippocampus. Groups of Sprague Dawley rat pups were injected daily from postnatal day 8-14 with either saline (n = 23) or 20 microg/kg DOM (n = 25), tested for key indicators of neonatal neurobehavioral development, and then left undisturbed until approximately 90 days of age, at which time brain tissue was removed, hippocampi were dissected, fixed and processed using either Timm's stain to visualize hippocampal mossy fiber sprouting (MFS) or trkB immunohistochemistry to visualize full length trkB receptors. Multiple sections from dorsal, mid, and ventral hippocampus were analyzed separately and all measures were conducted using image analysis software. The results indicate significant increases in MFS in the inner molecular layer in treated animals with corresponding changes in trkB receptor density. Further we identified significant increases in trkB receptor density in the hilus of the dentate gyrus and area CA3 and report increased mossy fiber terminal density in the stratum lucidum in treated rats. The magnitude of these changes differed between sections from dorsal, mid, and ventral hippocampus. We conclude that low dose neonatal DOM produces cytoarchitectural changes indicative of abnormal development and/or synaptic plasticity that are progressive with age and show regional variation within the hippocampal formation.

Immunohistochemical distribution of NGF, BDNF, NT-3, and NT-4 in adult rhesus monkey brains

Immunohistochemical distribution and cellular localization of neurotrophins was investigated in adult monkey brains using antisera against nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), and neurotrophin-4 (NT-4). Western blot analysis showed that each antibody specifically recognized appropriate bands of approximately 14.7 kDa, 14.2 kDa, 13.6 kDa, and 14.5 kDa, for NGF, BDNF, NT-3, and NT-4, respectively. These positions coincided with the molecular masses of the neurotrophins studied. Furthermore, sections exposed to primary antiserum preadsorbed with full-length NGF, BDNF, NT-3, and NT-4 exhibited no detectable immunoreactivity, demonstrating specificities of the antibodies against the tissues prepared from rhesus monkeys. The study provided a systematic report on the distribution of NGF, BDNF, NT-3, and NT-4 in the monkey brain. Varying intensity of immunostaining was observed in the somata and processes of a wide variety of neurons and glial cells in the cerebrum, cerebellum, hippocampus, and other regions of the brain. Neurons in some regions such as the cerebral cortex and the hippocampus, which stained for neurotrophins, also expressed neurotrophic factor mRNA. In some other brain regions, there was discrepancy of protein distribution and mRNA expression reported previously, indicating a retrograde or anterograde action mode of neurotrophins. Results of this study provide a morphological basis for the elucidation of the roles of NGF, BDNF, NT-3, and NT-4 in adult primate brains.

Brain-derived neurotrophic factor in the brain of Xenopus laevis may act as a pituitary neurohormone together with mesotocin

Brain-derived neurotrophic factor (BDNF), a member of the neurotrophin family, occurs abundantly in the brain, where it exerts a variety of neural functions. We previously demonstrated that BDNF also exists in the endocrine melanotroph cells in the intermediate lobe of the pituitary gland of the amphibian Xenopus laevis, suggesting that BDNF, in addition to its neural actions within the brain, can act as a hormone. In the present study, we tested whether BDNF, in addition to its neural and hormonal roles, can be released as a neurohormone from the neural pituitary lobe of X. laevis. By light immunocytochemistry, we show that BDNF is present in perikarya, in ventrolaterally projecting axons of the hypothalamic magnocellular nucleus and in the neural lobe of the pituitary gland, and that it coexists in these structures with the amphibian neurohormone, mesotocin. The neural lobe was studied in detail at the ultrastructural level. Two types of neurohaemal axon terminals were observed, occurring intermingled and in similar numbers. Type A is filled with round, moderately electron-dense secretory granules with a mean diameter of approximately 145 nm. Type B terminals contain electron-dense and smaller, ellipsoid granules (long and short diameter approximately 140 and 100 nm, respectively). BDNF is exclusively present in secretory granules of type A axon terminals. Double gold-immunolabelling revealed that BDNF coexists in these granules with mesotocin. Furthermore, we demonstrate in an superfusion study performed in vitro that mesotocin stimulates peptide release from the endocrine melanotroph cells. On the basis of these data, we propose that BDNF can act on these cells as a neurohormone.

BDNF up-regulates TrkB protein and prevents the death of CA1 neurons following transient forebrain ischemia

The neurotrophin family of growth factors, which includes Nerve Growth Factor (NGF), Brain-Derived Neurotrophic Factor (BDNF), Neurotrophin-3 (NT3) and Neurotrophin-4/5 (NT4/5) bind and activate specific tyrosine kinase (Trk) receptors to promote cell survival and growth of different cell populations. For these reasons, growing attention has been paid to the use of neurotrophins as therapeutic agents in neurodegeneration, and to the regulation of the expression of their specific receptors by the ligands. BDNF expression, as revealed by immunohistochemistry, is found in the pre-subiculum, CA1, CA3, and dentate gyrus of the hippocampus. Strong TrkB immunoreactivity is present in most CA3 neurons but only in scattered neurons of the CA1 area. Weak TrkB immunoreactivity is found in the granule cell layer of the dentate gyrus. Unilateral grafting of BDNF-transfected fibroblasts into the hippocampus resulted in a marked increase in the intensity of the immunoreaction and in the number of TrkB-immunoreactive neurons in the granule cell layer of the dentate gyrus, pre-subiculum and CA1 area in the vicinity of the graft. No similar effects were produced after the injection of control mock-transfected fibroblasts. Delayed cell death in the CA1 area was produced following 5 min of forebrain ischemia in the gerbil. The majority of living cells in the CA1 area at the fourth day were BDNF/TrkB immunoreactive. Unilateral grafting of control mock-transfected or BDNF fibroblasts two days before ischemia resulted in a moderate non-specific protection of TrkB-negative, but not TrkB-positive cells, in the CA1 area of the grafted side. This finding is in line with a vascular and glial reaction, as revealed, by immunohistochemistry using astroglial and microglial cell markers. This astroglial response was higher in the grafted side than in the contralateral side in ischemic gerbils, but no differences were seen between BDNF-producing and non-BDNF-producing grafts. However, grafting of BDNF-producing fibroblasts two days before ischemia significantly and specifically prevented nerve cells from dying in the CA1 area of the ipsilateral hippocampus. Cell survival was associated with increased TrkB immunoreactivity as the majority of living cells were TrkB immunoreactive. Thus, our results show that BDNF is able to up-regulate the expression of TrkB in control and pathological states, and that BDNF prevention of neuronal death following transient forebrain ischemia is associated with increased expression of its specific receptor.

Increased Expression of BDNF and Proliferation of Dentate Granule Cells After Bacterial Meningitis

Proliferation and differentiation of neural progenitor cells is increased after bacterial meningitis. To identify endogenous factors involved in neurogenesis, expression of brain-derived neurotrophic factor (BDNF), TrkB, nerve growth factor (NGF), and glial cell line-derived neurotrophic factor (GDNF) was investigated. C57BL/6 mice were infected by intracerebral injection of Streptococcus pneumoniae. Mice were killed 30 hours later or treated with ceftriaxone and killed 4 days after infection. Hippocampal BDNF mRNA levels were increased 2.4-fold 4 days after infection (p = 0.026). Similarly, BDNF protein levels in the hippocampal formation were higher in infected mice than in control animals (p = 0.0003). This was accompanied by an elevated proliferation of dentate granule cells (p = 0.0002). BDNF protein was located predominantly in the hippocampal CA3/4 area and the hilus of the dentate gyrus. The density of dentate granule cells expressing the BDNF receptor TrkB as well as mRNA levels of TrkB in the hippocampal formation were increased 4 days after infection (p = 0.027 and 0.0048, respectively). Conversely, NGF mRNA levels at 30 hours after infection were reduced by approximately 50% (p = 0.004). No significant changes in GDNF expression were observed. In conclusion, increased synthesis of BDNF and TrkB suggests a contribution of this neurotrophic factor to neurogenesis after bacterial meningitis.

The hematopoietic factor G-CSF is a neuronal ligand that counteracts programmed cell death and drives neurogenesis

G-CSF is a potent hematopoietic factor that enhances survival and drives differentiation of myeloid lineage cells, resulting in the generation of neutrophilic granulocytes. Here, we show that G-CSF passes the intact blood-brain barrier and reduces infarct volume in 2 different rat models of acute stroke. G-CSF displays strong anti-apoptotic activity in mature neurons and activates multiple cell survival pathways. Both G-CSF and its receptor are widely expressed by neurons in the CNS, and their expression is induced by ischemia, which suggests an autocrine protective signaling mechanism. Surprisingly, the G-CSF receptor was also expressed by adult neural stem cells, and G-CSF induced neuronal differentiation in vitro. G-CSF markedly improved long-term behavioral outcome after cortical ischemia, while stimulating neural progenitor response in vivo, providing a link to functional recovery. Thus, G-CSF is an endogenous ligand in the CNS that has a dual activity beneficial both in counteracting acute neuronal degeneration and contributing to long-term plasticity after cerebral ischemia. We therefore propose G-CSF as a potential new drug for stroke and neurodegenerative diseases.

BDNF function in adult synaptic plasticity: the synaptic consolidation hypothesis

Interest in BDNF as an activity-dependent modulator of neuronal structure and function in the adult brain has intensified in recent years. Localization of BDNF-TrkB to glutamate synapses makes this system attractive as a dynamic, activity-dependent regulator of excitatory transmission and plasticity. Despite individual breakthroughs, an integrated understanding of BDNF function in synaptic plasticity is lacking. Here, we attempt to distill current knowledge of the molecular mechanisms and function of BDNF in LTP. BDNF activates distinct mechanisms to regulate the induction, early maintenance, and late maintenance phases of LTP. Evidence from genetic and pharmacological approaches is reviewed and tabulated. The specific contribution of BDNF depends on the stimulus pattern used to induce LTP, which impacts the duration and perhaps the subcellular site of BDNF release. Particular attention is given to the role of BDNF as a trigger for protein synthesis-dependent late phase LTP--a process referred to as synaptic consolidation. Recent experiments suggest that BDNF activates synaptic consolidation through transcription and rapid dendritic trafficking of mRNA encoded by the immediate early gene, Arc. A model is proposed in which BDNF signaling at glutamate synapses drives the translation of newly transported (Arc) and locally stored (i.e., alphaCaMKII) mRNA in dendrites. In this model BDNF tags synapses for mRNA capture, while Arc translation defines a critical window for synaptic consolidation. The biochemical mechanisms by which BDNF regulates local translation are also discussed. Elucidation of these mechanisms should shed light on a range of adaptive brain responses including memory and mood resilience.

N-methyl-D-aspartic acid-induced and Ca-dependent neuronal swelling and its retardation by brain-derived neurotrophic factor in the epileptic hippocampus

Dentate granule cell (DGC) swelling was studied by imaging changes in light transmittance from hippocampal slices in the rat pilocarpine model of epilepsy and human epileptic specimens. Brief bath-application of N-methyl-D-aspartic acid (NMDA) induced swelling in the control rat DGC (physiological swelling). Physiological swelling was short-lasting, and rapidly recovered upon removal of NMDA. In contrast, the swelling induced in the pilocarpine-treated rat hippocampus and human epileptic hippocampus (epileptic swelling) was long-lasting, and often recovered slowly over an hour. Both types of swelling were blocked by the NMDA receptor (NMDAR) antagonist, D-APV, suggesting that they shared the same induction mechanism. However, the swellings differed in their sensitivity to a calcium chelator, 1.2-bis(2-aminophenoxy)ethane-N,N,N,N-tetra-acetate (BAPTA), and an endoplasmic reticulum (ER) Ca2+-ATPase inhibitor, thapsigargin (TG). BAPTA and TG affected only epileptic swelling, and physiological swelling was spared. This suggested that the NMDAR-induced epileptic swelling might involve an additional mechanism for its maintenance, likely recruiting ER Ca2+ stores. Brain-derived neurotrophic factor (BDNF) slightly attenuated physiological swelling, and blocked epileptic swelling. The present study suggests a functional link between the activation of NMDAR and a release of Ca2+ from internal stores during the induction of epileptic swelling, and a neuroprotective role of BDNF on the NMDAR-induced swelling in the epileptic hippocampus.

BDNF in schizophrenia, depression and corresponding animal models

Understanding the etiology and pathogenesis schizophrenia and depression is a major challenge facing psychiatry. One hypothesis is that these disorders are secondary to a malfunction of neurotrophic factors. Inappropriate neurotrophic support during brain development could lead to structural disorganisation in which neuronal networks are established in a nonoptimal manner. Inadequate neurotrophic support in adult individuals could ultimately be an underlying mechanism leading to decreased capacity of brain to adaptive changes and increased vulnerability to neurotoxic damage. Brain-derived neurotrophic factor (BDNF) is a mediator involved in neuronal survival and plasticity of dopaminergic, cholinergic, and serotonergic neurons in the central nervous system (CNS). In this review, we summarize findings regarding altered BDNF in schizophrenia and depression and animal models, as well as the effects of antipsychotic and antidepressive treatments on the expression of BDNF.