Differential regulation of distinct phenotypic features of serotonergic neurons by bone morphogenetic proteins

Exploring the Therapeutic Effect of Neurotrophins and Neuropeptides in Neurodegenerative Diseases: at a Glance

Neurotrophins and neuropeptides are the essential regulators of peripheral nociceptive nerves that help to induce, sensitize, and maintain pain. Neuropeptide has a neuroprotective impact as it increases trophic support, regulates calcium homeostasis, and reduces excitotoxicity and neuroinflammation. In contrast, neurotrophins target neurons afflicted by ischemia, epilepsy, depression, and eating disorders, among other neuropsychiatric conditions. Neurotrophins are reported to inhibit neuronal death. Strategies maintained for "brain-derived neurotrophic factor (BDNF) therapies" are to upregulate BDNF levels using the delivery of protein and genes or compounds that target BDNF production and boosting BDNF signals by expanding with BDNF mimetics. This review discusses the mechanisms of neurotrophins and neuropeptides against acute neural damage as well as highlighting neuropeptides as a potential therapeutic agent against Parkinson's disease (PD), Huntington's disease (HD), Alzheimer's disease (AD), and Machado-Joseph disease (MJD), the signaling pathways affected by neurotrophins and their receptors in both standard and diseased CNS systems, and future perspectives that can lead to the potent application of neurotrophins and neuropeptides in neurodegenerative diseases (NDs).

Arsenic Induces Differential Neurotoxicity in Male, Female, and E2-Deficient Females: Comparative Effects on Hippocampal Neurons and Cognition in Adult Rats

We earlier reported that arsenic induced hippocampal neuronal loss, causing cognitive dysfunctions in male rats. This neuronal damage mechanism involved an altered bone morphogenetic protein (BMP2)/Smad and brain-derived neurotrophic factor (BDNF)/TrkB signaling. Susceptibility to toxicants is often sex-dependent, and hence we studied the comparative effects of arsenic in adult male and female rats. We observed that a lower dose of arsenic reduced learning-memory ability, examined through passive avoidance and Y-maze tests, in male but not female rats. Again, male rats exhibited greater learning-memory loss at a higher dose of arsenic. Supporting this, arsenic-treated male rats demonstrated larger reduction in the hippocampal NeuN and %-surviving neurons, together with increased apoptosis and altered BMP2/Smad and BDNF/TrkB pathways compared to their female counterparts. Since the primary female hormone, estrogen (E2), regulates normal brain functions, we next probed whether endogenous E2 levels in females offered resistance against arsenic-induced neurotoxicity. We used ovariectomized (OVX) rat as the model for E2 deficiency. We primarily identified that OVX itself induced hippocampal neuronal damage and cognitive decline, involving an increased BMP2/Smad and reduced BDNF/TrkB. Further, these effects appeared greater in arsenic + OVX compared to arsenic + sham (ovary intact) or OVX rats alone. The OVX-induced adverse effects were significantly reduced by E2 treatment. Overall, our study suggests that adult males could be more susceptible than females to arsenic-induced neurotoxicity. It also indicates that endogenous E2 regulates hippocampal BMP and BDNF signaling and restrains arsenic-induced neuronal dysfunctions in females, which may be inhibited in E2-deficient conditions, such as menopause or ovarian failure.

ActRIIB:ALK4-Fc alleviates muscle dysfunction and comorbidities in murine models of neuromuscular disorders

Patients with neuromuscular disorders suffer from a lack of treatment options for skeletal muscle weakness and disease comorbidities. Here, we introduce as a potential therapeutic agent a heterodimeric ligand-trapping fusion protein, ActRIIB:ALK4-Fc, which comprises extracellular domains of activin-like kinase 4 (ALK4) and activin receptor type IIB (ActRIIB), a naturally occurring pair of type I and II receptors belonging to the TGF-β superfamily. By surface plasmon resonance (SPR), ActRIIB:ALK4-Fc exhibited a ligand binding profile distinctly different from that of its homodimeric variant ActRIIB-Fc, sequestering ActRIIB ligands known to inhibit muscle growth but not trapping the vascular regulatory ligand bone morphogenetic protein 9 (BMP9). ActRIIB:ALK4-Fc and ActRIIB-Fc administered to mice exerted differential effects - concordant with SPR results - on vessel outgrowth in a retinal explant assay. ActRIIB:ALK4-Fc induced a systemic increase in muscle mass and function in wild-type mice and in murine models of Duchenne muscular dystrophy (DMD), amyotrophic lateral sclerosis (ALS), and disuse atrophy. Importantly, ActRIIB:ALK4-Fc improved neuromuscular junction abnormalities in murine models of DMD and presymptomatic ALS and alleviated acute muscle fibrosis in a DMD model. Furthermore, in combination therapy ActRIIB:ALK4-Fc increased the efficacy of antisense oligonucleotide M12-PMO on dystrophin expression and skeletal muscle endurance in an aged DMD model. ActRIIB:ALK4-Fc shows promise as a therapeutic agent, alone or in combination with dystrophin rescue therapy, to alleviate muscle weakness and comorbidities of neuromuscular disorders.

Transplantation of Fetal Kidney Cells: Neuroprotection and Neuroregeneration

Various trophic factors in the transforming growth factor-β (TGF-β) superfamily have been reported to have neuroprotective and neuroregenerative effects. Intracerebral administration of glial cell line-derived neurotrophic factor (GDNF) or bone morphogenetic proteins (BMPs), both members of the TGF-β family, reduce ischemia- or 6-hydroxydopamine (6-OHDA)-induced injury in adult rat brain. Because BMPs and GDNF are highly expressed in fetal kidney cells, transplantation of fetal kidney tissue could serve as a cellular reservoir for such molecules and protect against neuronal injury induced by ischemia, neurotoxins, or reactive oxygen species. In this review, we discuss preclinical evidence for the efficacy of fetal kidney cell transplantation in neuroprotection and regeneration models.

BMP signaling in axon regeneration

Neuronal competence to re-extend axons and a permissive environment that allows growth cone navigation are two major determinants for successful axon regeneration. Here, we review the roles of bone morphogenetic protein (BMP) signaling in mediating both neuronal and glial injury responses after CNS injury. BMPs can activate a pro-regenerative transcription program in neurons through Smad-mediated canonical pathway, or act locally on cytoskeleton assembly at distal axons via non-canonical pathways. Emerging evidence implicates retrograde BMP signalosomes in connecting the cytoskeletal and nuclear responses. In addition, BMP/Smad signaling modulates neurotrophin-mediated axonal outgrowth, and interacts with the epigenetic machinery to initiate epigenetic reprogramming for axon regeneration. Besides their influences on neurons, BMPs also regulate astrogliosis, inflammatory processes, and neural progenitor cell differentiation at the injury site, all of which can either positively or negatively modify the injury microenvironment. Lastly, an increasing number of BMP signaling partners, sensitizers, and downstream effectors collectively fine-tune the signaling intensity and spatiotemporal dynamics of BMP activity in an integrated signaling network during axon regeneration.

The cell-specific upregulation of bone morphogenetic protein-10 (BMP-10) in a model of rat cortical brain injury

Previous studies have suggested that bone morphogenetic protein-6 (BMP-6) has a pronounced upregulation in rat brains subjected to traumatic brain injury. Bone morphogenetic protein-10 (BMP-10) is a newly identified cardiac-specific peptide growth factor that belongs to the TGF-β superfamily. To elucidate the dynamic expression changes and cellular localization of BMP-10 during traumatic brain injury (TBI), we performed an acute traumatic brain injury model in adult rats. Western blot analysis, immunohistochemistry and RTPCR revealed that BMP-10 expression in impaired cerebral cortex was more strongly induced not only at protein level but also at mRNA level compared to that in normal group. Double immunofluorescence labeling suggested that BMP-10 was localized mainly in the cytoplasm of neurons, microglias, and astrocytes within 3 mm from the lesion site at day 3 post-injury. And there was a specific upregulation of BMP-10 in astrocytes following brain injury. Besides, co-localization of BMP-10 and proliferating cell nuclear antigen (PCNA) was detected in Glial fibrillary acidic protein (GFAP) (+) cells. We also examined the expression profiles of PCNA and GFAP whose change was correlated with the expression profiles of BMP-10 in the incised injury model used here. Another experiment in which astrocytes were treated with BMP-10 was also performed to confirm the relationship between the upregulation of BMP-10 and proliferation of astrocytes following TBI. Taken together, this is the first description of BMP-10 expression during the central nervous system (CNS) lesion and repair. Thus, the present data suggested that BMP-10 may be implicated in CNS pathophysiology after TBI. But, further studies are needed to understand the cell signal pathway which can direct the exact role of BMP-10 following traumatic brain injury.

Clustering by neurocognition for fine mapping of the schizophrenia susceptibility loci on chromosome 6p

Chromosome 6p is one of the most commonly implicated regions in the genome-wide linkage scans of schizophrenia, whereas further association studies for markers in this region were inconsistent likely due to heterogeneity. This study aimed to identify more homogeneous subgroups of families for fine mapping on regions around markers D6S296 and D6S309 (both in 6p24.3) as well as D6S274 (in 6p22.3) by means of similarity in neurocognitive functioning. A total of 160 families of patients with schizophrenia comprising at least two affected siblings who had data for eight neurocognitive test variables of the continuous performance test (CPT) and the Wisconsin card sorting test (WCST) were subjected to cluster analysis with data visualization using the test scores of both affected siblings. Family clusters derived were then used separately in family-based association tests for 64 single nucleotide polymorphisms (SNPs) covering the region of 6p24.3 and 6p22.3. Three clusters were derived from the family-based clustering, with deficit cluster 1 representing deficit on the CPT, deficit cluster 2 representing deficit on both the CPT and the WCST, and a third cluster of nondeficit. After adjustment using false discovery rate for multiple testing, SNP rs13873 and haplotype rs1225934-rs13873 on BMP6-TXNDC5 genes were significantly associated with schizophrenia for the deficit cluster 1 but not for the deficit cluster 2 or nondeficit cluster. Our results provide further evidence that the BMP6-TXNDC5 locus on 6p24.3 may play a role in the selective impairments on sustained attention of schizophrenia.

Differential effects of BMP signaling on parvalbumin and somatostatin interneuron differentiation

Several different populations of interneurons in the murine cortex, including somatostatin (SST)- or parvalbumin (PV)-expressing cells, are born in the ventral ganglionic eminences during mid-gestation and then migrate tangentially to the cortex. SST is expressed by some interneuron progenitors in the cerebral cortex and in migrating populations in the ventrolateral cortex at birth. However, PV (also known as PVALB) is not expressed by interneurons until the second postnatal week after reaching the cortex, suggesting that molecular cues in the cerebral cortex might be involved in the differentiation process. BMP4 is expressed at high levels in the somatosensory cortex at the time when the PV(+) interneurons differentiate. Treatment of cortical cultures containing interneuron precursors is sufficient to generate PV(+) interneurons prematurely and inhibit SST differentiation. Furthermore, overexpression of BMP4 in vivo increases the number of interneurons expressing PV, with a reduction in the number of SST(+) interneurons. PV(+) interneurons in the cortex express BMP type I receptors and a subpopulation displays activated BMP signaling, assessed by downstream molecules including phosphorylated SMAD1/5/8. Conditional mutation of BMP type I receptors in interneuron precursors significantly reduces the number of cortical PV(+) interneurons in the adult brain. Thus, BMP4 signaling through type I receptors regulates the differentiation of two major medial ganglionic eminence-derived interneuron populations and defines their relative numbers in the cortex.

Neuropeptides in depression: role of VGF

The monoamine hypothesis of depression is increasingly called into question by newer theories that revolve around changes in neuronal plasticity, primarily in the hippocampus, at both the structural and the functional levels. Chronic stress negatively regulates hippocampal function while antidepressants ameliorate the effects of stress on neuronal morphology and activity. Both stress and antidepressants have been shown to affect levels of brain-derived neurotrophic factor (BDNF) whose transcription is dependent on cAMP response element binding protein (CREB). BDNF itself has antidepressant-like actions and can induce transcription of a number of molecules. One class of genes regulated by both BDNF and serotonin (5-HT) are neuropeptides including VGF (non-acryonimic) which has a novel role in depression. Neuropeptides are important modulators of neuronal function but their role in affective disorders is just emerging. Recent studies demonstrate that VGF, which is also a CREB-dependent gene, is upregulated by antidepressant drugs and voluntary exercise and is reduced in animal models of depression. VGF enhances hippocampal synaptic plasticity as well as neurogenesis in the dentate gyrus but the mechanisms of antidepressant-like actions of VGF in behavioral paradigms are not known. We summarize experimental data describing the roles of BDNF, VGF and other neuropeptides in depression and how they may be acting through the generation of new neurons and altered synaptic activity. Understanding the molecular and cellular changes that underlie the actions of neuropeptides and how these adaptations result in antidepressant-like effects will aid in developing drugs that target novel pathways for major depressive disorders.

Protective effect of bone morphogenetic protein-6 on neurons from H2O2 injury

Bone morphogenetic protein-6 (BMP6) is a member of the TGF-beta superfamily. Expression of BMP6 and its receptors are increased when brain tissues of adult rats are injured, suggesting that BMP6 may have a neuroprotective function in the physiologic response to neurological damage. This research investigates the molecular mechanisms supporting a neuroprotective effect of BMP6 in neural cells traumatized by H(2)O(2). We demonstrate that presence of BMP6 either before or after H(2)O(2)-induced injury protects the cultured primary cortical cells from apoptosis. However, molecular mechanisms mediating the protective effects of either pre- or post-treatment with BMP6 are different. Cells pre-treated with BMP6 have attenuated MAPK activity induced by H(2)O(2), whereas the MAPK activity in cells post-treated with BMP6 remains unchanged. Further, pharmacological inhibitors of MAPKs, PD98059 and SB203580, block the protective effect of BMP6 in the cells pre-treated with BMP6 but not in the cells post-treated with BMP6. The protective effect of post-treatment with BMP6 appears to be mediated through regulation of p53 and Bax molecules, evidenced by decreased mRNA levels after BMP6 treatment. Taken together, these data suggest BMP6 protect cortical cells against oxidation stress induced by H(2)O(2) via two different mechanisms, where (1) pre-treatment with BMP6 acts through MAPK pathway and (2) post-treatment with BMP6 works by down-regulating p53 and Bax.

Modulation of electrically evoked serotonin release in cultured rat raphe neurons

Electrically evoked release of serotonin (5-HT) and its modulation via 5-HT autoreceptors and alpha(2)-heteroreceptors was studied in primary cell cultures prepared from the embryonic (ED 15) rat mesencephalic brain region comprising the raphe nuclei. Cultures were grown for up to 3 weeks on circular glass coverslips. They developed a dense network of non-neuronal and neuronal cells, some of which were positive for tryptophan hydroxylase. To measure 5-HT release, the cultures were pre-incubated with [(3)H]5-HT (in the presence of the selective noradrenaline reuptake inhibitor oxaprotiline [1 micromol/L]), superfused with modified Krebs-Henseleit medium containing 6-nitroqipazine [1 micromol/L] and electrically stimulated using two conditions. Condition A: 360 pulses, 3 Hz, 0.5 ms, 90 mA, or condition B: 4 pulses 100 Hz, 0.5 ms, 90 mA (a condition which diminishes interactions with endogenously released transmitters during ongoing stimulation). After only 1 week in culture, the electrically evoked overflow of [(3)H] was Ca(2+) dependent and tetrodotoxin sensitive, suggesting an action-potential-induced exocytotic release of 5-HT. Using stimulation condition A in cultures grown for 2 weeks, both basal and evoked 5-HT release were strongly enhanced by methiotepine (1 micromol/L) but unaffected by the 5-HT(1B) autoreceptor agonist CP-93, 129 (1 micromol/L) and the alpha(2)-adrenoceptor agonist UK-14, 304 (1 micromol/L). Conversely, using stimulation condition B, not only CP-93, 129 (IC(50) 8.1 +/- 1.4 nmol/L) and UK-14, 304 (IC(50) 14.9 +/- 1.6 nmol/L) had inhibitory effects on cells grown for 2 weeks, but also the 5-HT(1A) agonist 8-hydroxy-2-(di-n-propylamino)tetralin. In conclusion, we describe for the first time electrically evoked release of 5-HT from primary cultures of fetal raphe cells and its modulation via 5-HT(1B) and 5-HT(1A) auto- and alpha(2)-heteroreceptors. Such cultured raphe cells may represent a suitable model to study expression and development of presynaptic receptors on serotonergic neurons in-vitro.

Bone morphogenetic protein-6 is expressed early by activated astrocytes in lesions of rat traumatic brain injury

We have analyzed early expression of bone morphogenetic protein-6 in rat brains subjected to traumatic brain injury. Bone morphogenetic protein-6 was expressed in neurons of the hippocampus and cortex in normal adult rat brains. A pronounced expression of bone morphogenetic protein-6 in astroglia located to the lesion became obvious 48 h postinjury. Bone morphogenetic protein-6(+) glia were distributed around the lesion, thus demarcating the injured tissue from normal brain. Double labeling by immunohistochemistry revealed that the major glial sources for bone morphogenetic protein-6 were reactive astrocytes and few ED1(+) or W3/13(+) cells co-expressed bone morphogenetic protein-6. Furthermore, bone morphogenetic protein-6 expression in neurons located to hippocampus and cortex of the lesioned hemisphere was up-regulated 3 days postinjury. In conclusion, this is the first description of bone morphogenetic protein-6 expression in traumatic brains. Our data suggest that bone morphogenetic protein-6 might be involved in astrogliosis and neuron protection following traumatic brain injury.

Rapid up-regulation of the neuronal serotoninergic phenotype by brain-derived neurotrophic factor and cyclic adenosine monophosphate: relations with raphe astrocytes

Up-regulation of the neuronal serotoninergic phenotype in relation to astrocytic population was studied in primary cultures of rat embryonic rostral raphe. Short treatments (18 hr at day in vitro 4) with brain-derived neurotrophic factor (BDNF) or dibutyryl-cAMP (dBcAMP) increased the number of serotoninergic neurons by approximately 80% and approximately 40%, respectively, and markedly enhanced the branching (by 11-fold and 5-fold, respectively) and total length (by 4-fold and 2.5-fold, respectively) of their neurites. Concomitantly, under BDNF treatment, the astrocyte population was decreased by half and became mostly protoplasmic-like. In contrast, dBcAMP treatment also reduced the astrocytic cell density (by one-third) but induced a stellate morphology. Similar short treatment with the astrocyte-derived S100beta factor induced no modification of the serotonin (5-HT) neuronal phenotype nor of astrocytes morphology. Both BDNF- and cAMP-induced effects were abolished by simultaneous treatment with the specific tyrosine kinase inhibitor genistein, suggesting a role for the high-affinity BDNF receptor tyrosine kinase (TrkB). These data suggest that BDNF and cAMP, but not S100beta, rapidly induce both an up-regulation of the 5-HT neuronal phenotype and modifications of the neighboring astrocytes in a TrkB-dependent manner.

Factors involved in the determination of the neurotransmitter phenotype of developing neurons of the CNS: Applications in cell replacement treatment for Parkinson's disease

The developmental stages involved in the conversion of stem cells to fully functional neurons of specific neurotransmitter phenotype are complex and not fully understood. Over the past decade many studies have been published that demonstrate that in vitro manipulation of the epigenetic environment of the stem cells allows experimental control of final neuronal phenotypic choice. This review presents the evidence for the involvement of a number of endogenous neurobiochemicals, which have been reported to potently influence DAergic (and other neurotransmitter) phenotype expression in vitro. They act at different stages on the pathway to neurotransmitter phenotype determination, and in different ways. Many are better known for their involvement in other aspects of development, and in other biochemical roles. Their proper place, and precise roles, in neurotransmitter phenotype determination in vivo will no doubt be determined in the future. Meanwhile, considerable medical benefits are offered from producing large, long-term, viable cryostores of self-regenerating multipotential neural precursor cells (i.e., brain stem cells), which can be used for cell replacement therapies in the treatment of degenerative brain diseases, such as Parkinson's disease.

Bone morphogenetic protein 9 induces the transcriptome of basal forebrain cholinergic neurons

Basal forebrain cholinergic neurons (BFCN) participate in processes of learning, memory, and attention. Little is known about the genes expressed by BFCN and the extracellular signals that control their expression. Previous studies showed that bone morphogenetic protein (BMP) 9 induces and maintains the cholinergic phenotype of embryonic BFCN. We measured gene expression patterns in septal cultures of embryonic day 14 mice and rats grown in the presence or absence of BMP9 by using species-specific microarrays and validated the RNA expression data of selected genes by immunoblot and immunocytochemistry analysis of their protein products. BMP9 enhanced the expression of multiple genes in a time-dependent and, in most cases, reversible manner. The set of BMP9-responsive genes was concordant between mouse and rat and included genes encoding cell-cycle/growth control proteins, transcription factors, signal transduction molecules, extracellular matrix, and adhesion molecules, enzymes, transporters, and chaperonins. BMP9 induced the p75 neurotrophin receptor (NGFR), a marker of BFCN, and Cntf and Serpinf1, two trophic factors for cholinergic neurons, suggesting that BMP9 creates a trophic environment for BFCN. To determine whether the genes induced by BMP9 in culture were constituents of the BFCN transcriptome, we purified BFCN from embryonic day 18 mouse septum by using fluorescence-activated cell sorting of NGFR(+) cells and profiled mRNA expression of these and NGFR(-) cells. Approximately 30% of genes induced by BMP9 in vitro were overexpressed in purified BFCN, indicating that they belong to the BFCN transcriptome in situ and suggesting that BMP signaling contributes to maturation of BFCN in vivo.

Stroke and TGF-beta proteins: glial cell line-derived neurotrophic factor and bone morphogenetic protein

Recent studies have indicated that proteins in the transforming growth factor-beta superfamily alter damage induced by various neuronal injuries. Of these proteins, glial cell line-derived neurotrophic factor (GDNF) and bone morphogenetic protein-7 (BMP-7) have unique protective and regenerative effects in stroke animals. Delivery of GDNF or BMP-7 to brain tissue reduced cerebral infarction and improved motor functions in stroke animals. Pretreatment with these factors reduced caspase-3 activity and DNA fragmentation in the ischemic brain region, suggesting that antiapoptotic effects are involved. Beside the protective effects, BMP-7 given after stroke improves locomotor function. These regenerative effects of BMP-7 may involve the enhancement of dendritic growth and remodeling. In this review, we illustrate the neuroprotective and neuroregenerative properties of GDNF and BMP-7 and emphasize their therapeutic potential for stroke.

SVZa neural stem cells differentiate into distinct lineages in response to BMP4

Neural stem cells (NSCs) reside in the anterior portion of the forebrain subventricular zone (SVZa) and generate the progenitors which will differentiate into neurons, and via a tangential migratory pathway, known as the rostral migratory stream (RMS), migrate to the olfactory bulbs (OB). Bone morphogenetic proteins (BMPs) play significant roles in neural development at different stages and locations, but their roles have not been determined in the SVZa. To explore possible roles of BMPs in SVZa NSCs, BMP4 at various concentrations were tested for their capacity to induce SVZa NSCs. The expression of BMP4 was also examined in living cells using a reportor vector, in which the BMP4 promotor was conjugated with red fluorescent protein (RFP). In the meantime, the differentiation of SVZa NSCs was dynamically monitored by using reportor vectors of the Nestin enhancer and the promoters of TH and GFAP. In the OB, high expression of BMP4 was found using both promoter activity analysis and in situ hybridization. However, low BMP4 expression was found in the RMS and only moderate expression of BMP4 was displayed in the SVZa. The results also demonstrated that low concentrations (1-5 ng/ml) of BMP4 promoted the proliferation of SVZa NSCs but high concentrations (10-100 ng/ml) of BMP4 inhibited this proliferation. BMP4 enhanced neuron commitment before 4 days but inhibited it after 4 days. As the antagonist of BMP4, Noggin almost completely blocked all these BMP4 responses. Thus, our findings indicate that BMP4 promotes the exit from the cell cycle and triggers the differentiation of neuron progenitors in the OB. BMP4 also promotes the proliferation of the committed neuron progenitors in the RMS, but in the SVZa, BMP4 may facilitate the commitment of NSCs into astrocytes.

Bone morphogenetic proteins and neurotrophins provide complementary protection of septal cholinergic function during phosphatase inhibitor-induced stress

Cultures of embryonic rat septum were exposed for 24-48 h to 2-5 nm okadaic acid (OA), an inhibitor of pp1A and pp2A phosphatases. This stress killed approximately 75% of neurons. A neurotrophin (NT) combination (nerve growth factor and brain-derived neurotrophic factor, each 100 ng/mL) plus a bone morphogenetic protein (BMP6 or BMP7, 5 nm) reduced the death of both cholinergic and non-cholinergic neurons, and preserved choline acetyltransferase (ChAT) activity assayed 2-6 days post-stress. This NT + BMP combination preserved ChAT activity better than either NTs or BMPs alone, and was effective even if trophic factor addition was delayed until 12 h after stress onset. A general caspase inhibitor (qVD-OPH, 10 micro g/mL) also increased survival of stressed cholinergic neurons, but its protection of ChAT activity was shorter lived than that produced by the NT + BMP combination. Neither the NT + BMP combination nor the caspase inhibitor reduced the OA-induced increase in tau phosphorylation. These findings indicate that NTs and BMPs have synergistic protective effects against an OA stress, and suggest that at least some of these protective effects occur upstream of caspase activation.

Expression of tryptophan 5-hydroxylase gene during sea urchin neurogenesis and role of serotonergic nervous system in larval behavior

Tryptophan 5-hydroxylase (TPH) is the rate-limiting enzyme in the biosynthesis of serotonin. cDNA cloning of TPH was carried out, and the occurrence of spatiotemporal transcription of TPH message was examined in larvae of the sea urchin, Hemicentrotus pulcherrimus (HpTPH), with in situ hybridization by using the tyramide signal amplification (TSA) technique and Northern hybridization. Based on deduced amino acids sequence of HpTPH, phylogenetically sea urchin locates at the closest position to vertebrates among invertebrates, and HpTPH had common conserved sequences in a catalytic domain. Initiation of HpTPH transcription occurred at the late gastrula stage exclusively in serotonin cells of apical ganglion (SAG) that was composed of a cluster of HpTPH-positive cells and the negative cells in between. In situ hybridization showed that the mRNA expression pattern was similar to the immunohistochemical localization of serotonin cells reported before (Bisgrove and Burke [1986] Dev. Growth Differ. 28:557-569; Yaguchi et al. [2000] Dev. Growth Differ. 42:479-488). p-Chlorophenylalanine (CPA), an irreversible inhibitor of TPH activity, considerably decreased serotonin content in the serotonin cells, whereas the HpTPH expression pattern and timing, and the extension of neurofibers from SAG cells were apparently unaffected, suggesting CPA exclusively perturbed synthesis of serotonin but not nervous system organization. CPA-treated larvae did not swim, despite the occurrence of ciliary beating in culture chamber, suggesting that proper serotonin synthesis is necessary for normal swimming of the larvae.

Retrograde Gbb signaling through the Bmp type 2 receptor wishful thinking regulates systemic FMRFa expression in Drosophila

Amidated neuropeptides of the FMRFamide class regulate numerous physiological processes including synaptic efficacy at the Drosophila neuromuscular junction (NMJ). We demonstrate here that mutations in wishful thinking (wit) a gene encoding a Drosophila Bmp type 2 receptor that is required for proper neurotransmitter release at the neuromuscular junction, also eliminates expression of FMRFa in that subset of neuroendocrine cells (Tv neurons) which provide the systemic supply of FMRFa peptides. We show that Gbb, a Bmp ligand expressed in the neurohemal organ provides a retrograde signal that helps specify the peptidergic phenotype of the Tv neurons. Finally, we show that supplying FMRFa in neurosecretory cells partially rescues the wit lethal phenotype without rescuing the primary morphological or electrophysiological defects of wit mutants. We propose that Wit and Gbb globally regulate NMJ function by controlling both the growth and transmitter release properties of the synapse as well as the expression of systemic modulators of NMJ synaptic activity.

TGF-betas and their roles in the regulation of neuron survival

Transforming growth factor-betas (TGF-betas) are a still growing superfamily of cytokines with widespread distribution and diverse biological functions. They fall into several subfamilies including the TGF-betas 1, 2, and 3, the bone morphogenetic proteins (BMPs), the growth/differentiation factors (GDFs), activins and inhibins, and the members of the glial cell line-derived neurotrophic factor family. Following a brief description of their general roles and signaling in development, maintenance of homeostasis, and disease, we shall focus on their distribution in the CNS and their involvement in regulating neuron survival and death.

Bone morphogenetic protein-6 is a neurotrophic factor for calbindin-positive striatal neurons

Bone morphogenetic proteins (BMPs) are a set of members of the transforming growth factor-beta superfamily recently described as promoting the differentiation of several neuronal populations within the basal ganglia. This study examined whether a member of this family, BMP-6, could exert neurotrophic effects on the neurons of the striatum, in which BMP-6 mRNA had been previously detected during development. Here we show that BMP-6 increases the number and differentiation of calbindin-positive neurons in vitro. Indeed, BMP-6 increased the total area, the perimeter, and the degree of arborization of this neuronal population. This trophic factor promoted dendritic growth without modifying axonal length or soma area. Furthermore, BMP-6 increased the number of glial fibrillary acidic protein-positive cells while decreasing the number of nestin-positive cells. The suppression of cell proliferation or glial development by the antimitotic fluorodeoxyuridine removed the effects on striatal neurons, suggesting the involvement of astroglial cells in the differentiation induced by BMP-6. The current results confirm the relevance of BMPs in the development of the striatum and emphasize the crucial importance of the trophic interaction between glial and neuronal cells.

Increased monoamine concentration in the brain and blood of fetal thalidomide- and valproic acid-exposed rat: putative animal models for autism

Autism is defined as a congenital neurodevelopmental disorder in which serotonergic dysfunction may be involved in its pathogenesis. One of the characteristic laboratory findings in autistic patients is hyperserotonemia, although its mechanism has not been elucidated to date because of difficulties in studying human patients. Recent reports have demonstrated that thalidomide or valproic acid exposure during early embryonic days (first trimester) in humans causes higher incidence of autism. Morphologic abnormalities found in autism (e.g. cerebellar anomalies, reduced motor neuron numbers) have been reported in animals administered with these teratogens prenatally, suggesting the possibility of the use of these animals as an experimental autistic model. In this study, we evaluated monoamine levels in the brain and blood of rats exposed to teratogens prenatally. Of the groups exposed to thalidomide on embryonic day (E)2, E4, E7, E9, and E11, a significant increase of hippocampal serotonin was only observed in the group exposed on E9. Furthermore, E9 thalidomide and valproic acid exposure both resulted in an increase of hippocampal serotonin, frontal cortex dopamine, and hyperserotonemia. These results thus indicate that two potentially autism-inducing teratogens, thalidomide and valproic acid, have the same effect on early monoamine system development in the brain and the blood, which may explain the pathogenesis of autism.

Bone morphogenetic proteins BMP-6 and BMP-7 have differential effects on survival and neurite outgrowth of cerebellar granule cell neurons

The bone morphogenetic proteins (BMPs) play an inductive role in the generation of cerebellar granule cells embryonically. Therefore, we chose to look at their effects on cerebellar granule cell survival and differentiation postnatally. The cells express mRNA for both BMP-6 and BMP-7, as well as for the receptors BMPRIA and BMPRII, demonstrating that the postnatal cells have the ability to form the heterodimer receptors needed to respond to BMPs. BMP-7 promotes cell survival, with a maximal effect at 10 ng/ml, whereas tenfold more BMP-6 is needed: Both were active over the course of 8 days in culture. In addition, both BMPs were able to protect the neurons against death from induced apoptosis (exposure to serum-free, low-potassium medium) or exposure to glutamate. However, only BMP-6 could stimulate neurite outgrowth, measured with a neurofilament ELISA, an effect that was seen over the first 6 days in culture. These results, taken together with others in the literature, suggest that the BMPs have strong neurotrophic effects that are both neuron specific and BMP specific.

Upregulation of acetylcholine synthesis by bone morphogenetic protein 9 in a murine septal cell line

Previous studies showed that bone morphogenetic protein 9 (BMP-9) induces the expression of choline acetyltransferase and the vesicular acetylcholine (ACh) transporter, and upregulates ACh synthesis in cultured primary neurons from embryonic mouse septum [I. López-Coviella, B. Berse, R. Krauss, R.S. Thies, J.K. Blusztajn, Induction and maintenance of the neuronal cholinergic phenotype in the central nervous system by BMP-9. Science 289 (2000) 313-316]. In the present studies we investigated the effects of BMP-9 on ACh synthesis in the cholinergic mouse SN56T17 septal cell line. BMP-9 increased ACh synthesis in these cells up to 2.5-fold in a time- and dose-dependent, saturable manner. The maximal effect of BMP-9 was observed after a 3-day treatment and the median effective concentration of BMP-9 was 0.5 ng/ml. These data show that SN56T17 cells are a useful model for studies of the effects of BMPs on the cholinergic phenotype.

Brain-derived neurotrophic factor (BDNF) mediates bone morphogenetic protein-2 (BMP-2) effects on cultured striatal neurones

Bone morphogenetic proteins are members of the transforming growth factor-beta superfamily that have multiple functions in the developing nervous system. One of them, bone morphogenetic protein-2 (BMP-2), promotes the differentiation of cultured striatal neurones, enhancing dendrite growth and calbindin-positive phenotype. Bone morphogenetic proteins have been implicated in cooperative interactions with other neurotrophic factors. Here we examined whether the effects of BMP-2 on cultured striatal neurones are mediated or enhanced by other neurotrophic factors. BMP-2 had a cooperative effect with low doses of brain-derived neurotrophic factor or neurotrophin-3 (but not with other neurotrophic factors such as glial cell line-derived neurotrophic factor, neurturin or transforming growth factor-beta 2) on the number of calbindin-positive striatal neurones. Moreover, BMP-2 induced phosphorylated Trk immunoreactivity in cultured striatal neurones, suggesting that neurotrophins are involved in BMP-2 neurotrophic effects. The addition of TrkB-IgG or antibodies against brain-derived neurotrophic factor abolished the effects of BMP-2 on the number and degree of differentiation of calbindin-positive striatal neurones. Indeed, BMP-2 treatment increased brain-derived neurotrophic factor protein levels in treated cultures media and BDNF immunocytochemistry revealed that this neurotrophin was produced by neuronal cells. Taken together, these results indicate that brain-derived neurotrophic factor mediates the effects of BMP-2 on striatal neurones.

Induction of a dopaminergic phenotype in cultured striatal neurons by bone morphogenetic proteins

In the present study, we examined whether the bone morphogenetic proteins (BMPs), which are important in the developmental specification of transmitter type in certain classes of neurons, might also play a role in signaling the differentiation of a dopaminergic (DA) phenotype. We found that BMP-2, -4 and -6 were each capable of inducing, in a dose and time dependent manner, moderate levels of the DA enzyme tyrosine hydroxylase (TH) in cultured neurons from the mouse embryonic striatum. In contradistinction to other TH-inducing agents, BMPs initiated de novo TH expression without the required synergy of exogenous growth factors or co-activating substances and in neurons presumably aged (E16) beyond the critical period for induction. However, the appearance of TH in induced cells was short-lived (24 h) and could not be prolonged by repeated supplementation with the BMPs. Inhibitors of the mitogen-activated protein kinase (MAPK/ERK) signaling pathway, PD98059 and apigenin, did not prevent TH induction by BMP-4, as they did other TH inducing agents, indicating that the MAPK/ERK pathway does not mediate BMPs effects on TH expression. We conclude that BMP-2, -4 and -6 can be added to the expanding inventory of agents capable of inducing TH, making them potentially important in the specification of a DA phenotype in stem/precursor cells for the treatment of Parkinson's disease.

Bone morphogenetic protein-5 (BMP-5) promotes dendritic growth in cultured sympathetic neurons

BACKGROUND

BMP-5 is expressed in the nervous system throughout development and into adulthood. However its effects on neural tissues are not well defined. BMP-5 is a member of the 60A subgroup of BMPs, other members of which have been shown to stimulate dendritic growth in central and peripheral neurons. We therefore examined the possibility that BMP-5 similarly enhances dendritic growth in cultured sympathetic neurons.

RESULTS

Sympathetic neurons cultured in the absence of serum or glial cells do not form dendrites; however, addition of BMP-5 causes these neurons to extend multiple dendritic processes, which is preceded by an increase in phosphorylation of the Smad-1 transcription factor. The dendrite-promoting activity of BMP-5 is significantly inhibited by the BMP antagonists noggin and follistatin and by a BMPR-IA-Fc chimeric protein. RT-PCR and immunocytochemical analyses indicate that BMP-5 mRNA and protein are expressed in the superior cervical ganglia (SCG) during times of initial growth and rapid expansion of the dendritic arbor.

CONCLUSIONS

These data suggest a role for BMP-5 in regulating dendritic growth in sympathetic neurons. The signaling pathway that mediates the dendrite-promoting activity of BMP-5 may involve binding to BMPR-IA and activation of Smad-1, and relative levels of BMP antagonists such as noggin and follistatin may modulate BMP-5 signaling. Since BMP-5 is expressed at relatively high levels not only in the developing but also the adult nervous system, these findings suggest the possibility that BMP-5 regulates dendritic morphology not only in the developing, but also the adult nervous system.

Bone morphogenetic protein-6 reduces ischemia-induced brain damage in rats

BACKGROUND AND PURPOSE

Bone morphogenetic protein-6 (BMP6) and its receptors are expressed in adult and fetal brain. Receptors for BMP6 are upregulated in adult brain after injury, leading to the suggestion that BMP6 is involved in the physiological response to neuronal injury. The purpose of this study was to determine whether there was a neuroprotective effect of BMP6 in vivo and in vitro.

METHODS

Lactate dehydrogenase and microtubule-associated protein-2 (MAP-2) activities were used to determine the protective effect of BMP6 against H(2)O(2) in primary cortical cultures. The neuroprotective effects of BMP6 were also studied in chloral hydrate-anesthetized rats. BMP6 or vehicle was injected into right cerebral cortex before transient right middle cerebral artery (MCA) ligation. Animals were killed for triphenyl-tetrazolium chloride staining, caspase-3 immunoreactivity and enzymatic assays, and TUNEL assay. A subgroup of animals were used for locomotor behavioral assays.

RESULTS

Application of H(2)O(2) increased lactate dehydrogenase activity and decreased the density of MAP-2(+) neurons in culture. Both responses were attenuated by BMP6 pretreatment. Complementary in vivo studies showed that pretreatment with BMP6 increased motor performance and generated less cerebral infarction induced by MCA ligation/reperfusion in rats. Pretreatment with BMP6 did not alter cerebral blood flow or physiological parameters. There was decreased ischemia-induced caspase-3 immunoreactivity, caspase-3 enzymatic activity, and density of TUNEL-positive cells in ischemic cortex in BMP6-treated animals.

CONCLUSIONS

BMP6 reduces ischemia/reperfusion injury, perhaps by attenuating molecular events underlying apoptosis.

Bone morphogenetic protein-2, but not bone morphogenetic protein-7, promotes dendritic growth and calbindin phenotype in cultured rat striatal neurons

Bone morphogenetic proteins are members of the transforming growth factor-beta superfamily. They are widely expressed in the mammalian nervous system, where they exert trophic effects on several neuronal populations. We studied the neurotrophic activity of bone morphogenetic protein-2 and bone morphogenetic protein-7 (also called osteogenic protein-1) on cultured striatal cells, previously shown to express bone morphogenetic protein ligands and receptors. Our results indicate that only bone morphogenetic protein-2 promoted the differentiation of GABAergic neurons, especially of the calbindin-positive subpopulation, the subset of projecting striatal neurons that degenerates in Huntington's disease. Bone morphogenetic protein-2 increased the area, perimeter and degree of arborization of GABAergic neurons, promoting calbindin phenotype without altering proliferation or apoptosis. In contrast, neither bone morphogenetic protein-2 nor -7 affected striatal cholinergic interneurons. However, they both increased the number of glial fibrillary acidic protein-positive cells. Suppression of glial proliferation with 5-fluorodeoxyuridine did not abolish bone morphogenetic protein-2 effects on the differentiation of striatal neurons, ruling out an indirect mechanism through astrocytes. In conclusion, our results show that bone morphogenetic protein-2 promotes the differentiation of cultured GABAergic striatal neurons, suggesting that bone morphogenetic proteins are involved in the development of the striatum.

Bone morphogenetic proteins (BMP6 and BMP7) enhance the protective effect of neurotrophins on cultured septal cholinergic neurons during hypoglycemia

The effects of two bone morphogenetic proteins (BMP6, BMP7), alone and in combination with neurotrophins, were tested on cultures of embryonic day 15 rat septum. A week-long exposure to BMP6 or BMP7 in the optimal concentration range of 2-5 n M increased the activity of choline acetyltransferase (ChAT) by 1.6-2-fold, in both septal and combined septal-hippocampal cultures. The increase in ChAT activity reached significance after 4 days and continued to increase over an 11-day exposure. Under control culture conditions neither BMP significantly altered the number of cholinergic neurons, and BMP effects on ChAT activity were less than linearly additive with those of nerve growth factor. The effects of BMPs and BMP + neurotrophin combinations were also assayed under two stress conditions: low-density culture and hypoglycemia. In low-density cultures BMPs and BMP + neurotrophin combinations preserved ChAT activity more effectively than neurotrophins alone. During 24 h hypoglycemic stress, BMPs alone did not preserve ChAT activity, but BMP + neurotrophin combinations preserved ChAT activity much more effectively than neurotrophins alone. These results demonstrate that BMP6 and BMP7 enhance ChAT activity under control and low-density stress conditions, and that during a hypoglycemic stress their trophic effect requires and complements that exerted by neurotrophins.

Epigenetic regulation of human bone morphogenetic protein 6 gene expression in prostate cancer

Bone morphogenetic proteins (BMPs), belonging to the transforming growth factor-beta (TGF-beta) superfamily, are multifunctional molecules that regulate bone induction and organ development. Among BMPs, BMP-6 has been shown to be overexpressed in prostate cancer and is speculated to be associated with bone-forming skeletal metastasis. We investigated the regulatory mechanism of the BMP-6 gene expression in prostate cancer cell lines DU-145, LNCaP, PC-3, and PC-3M with regard to the methylation status of the CpG island in the 5' flanking region of the human BMP-6 gene. By sequence-specific analysis of methylated cytosines, we show here that the methylation status of the CpG loci around the Sp1 site of the BMP-6 promoter is related to its steady-state expression and an alternative splicing of messenger RNA (mRNA) in prostate cancer cell lines. Furthermore, a study of clinical cases of benign and malignant prostate lesion by in situ hybridization showed that BMP-6 expression was high at both primary and secondary sites in cases of advanced cancer with metastasis. Demethylation of the CpG loci around the Spl binding site was shown in cases with high BMP-6 expression by sequencing analysis of the methylated cytosine from paraffin-embedded materials. Our results suggested that during cancer progression, besides inactivation of tumor suppressor genes by hypermethylation, activation of certain genes like BMP-6 by selective demethylation was a common epigenetic event giving a variable character to the invading and metastasizing cancer cells.

Distribution of bone morphogenetic protein and bone morphogenetic protein receptor transcripts in the rodent nervous system and up-regulation of bone morphogenetic protein receptor type II in hippocampal dentate gyrus in a rat model of global cerebral ischemia

Bone morphogenetic proteins belong to the transforming growth factor-beta superfamily and act through serine/threonine kinase type I and type II receptors such as bone morphogenetic protein receptor type I and type II. In order to further understand the roles that these factors exert in the nervous system, we have examined the expression pattern of seven bone morphogenetic proteins and bone morphogenetic protein receptor type I and II transcripts in the brain and spinal cord of rodent. Whereas bone morphogenetic protein receptor type I expression was low in rat brain, in situ hybridization studies performed with specific digoxigenin-labelled riboprobes revealed the presence of bone morphogenetic protein receptor type II-positive cells throughout the brain, with a notable localization in dopaminergic cells of the substantia nigra. Bone morphogenetic protein receptor type II transcripts were also expressed by large motoneuron-like cells located in the ventral horn of the spinal cord and by sensory neurons of dorsal root ganglia. In addition, we observed a significant up-regulation of bone morphogenetic protein receptor type II in the granule cells of the dentate gyrus 48 h after transient global cerebral ischemia in rat suggesting that modulation of this receptor intervenes during neuronal plasticity or repair that occur upon brain injury. Among the potential ligands for this receptor, bone morphogenetic protein-6 and bone morphogenetic protein-7 were expressed in meninges and the choroid plexus, while bone morphogenetic protein-4-expressing cells were spatially and temporally regulated in myelinated structures during development and in the adult suggesting its expression in oligodendrocytes. These data clearly indicate that besides their roles in bone and embryonic tissues, bone morphogenetic proteins and their receptors may have also important functions in adult neural tissues.

Serotonin uptake and release mechanisms in developing cultures of rat embryonic raphe neurons: age- and region-specific differences

The development of serotonergic neurons of the rat raphe was followed in primary neuronal cell cultures taken at embryonic days embryonic day 13 and embryonic day 14 from three different raphe sub-groups, topographically defined with respect to their position to the isthmus as rostral (R1), intermediate (R2) and caudal (R3). In neurons cultivated from embryonic day 13 raphe serotonin, immunoreactivity was detected after only two days in vitro in the rostral R1 and the intermediate R2 sub-groups. Within two weeks of cultivation the number of serotonergic neurons as well as the dendritic branching continuously increased in all three sub-groups. In cultures obtained from embryonic day 13 raphe a specific uptake of [3H]serotonin could not be detected during the first days in vitro. Specific uptake as well as regulated serotonin release, however, was clearly discernible in these cultures after nine days in vitro, indicating developmental differentiation of the initially immature serotonergic neurons in culture. In contrast, serotonergic neurons obtained from the three raphe sub-groups at embryonic day 14 took up and released [3H]serotonin, as early as after two days in culture. Basal as well as stimulated serotonin release was diminished when preincubating the cells with tetanus toxin, which cleaves synaptobrevin thereby blocking exocytosis. Our data indicate that the differential development of serotonergic neurons in the various raphe sub-groups in vivo is also sustained in culture. The differences observed when comparing neurons from embryonic days 13 and 14 suggest that a short time-period of about 24h appears to be crucial for the developmental upregulation of serotonin uptake, storage and release.

Brain-derived neurotrophic factor and trkB are essential for cAMP-mediated induction of the serotonergic neuronal phenotype

Serotonergic neurons in the central nervous system are crucial in the control of autonomic functions and behavior. Mechanisms by which development and maintenance of the serotonergic transmitter phenotype is regulated include activation of protein kinase A (PKA). Using cultures established from the E14 rat raphe we show here that forskolin (10 microM) increases numbers of neurons expressing tryptophan hydroxylase (TpOH), the key enzyme of serotonin synthesis, and uptake of the false serotonergic transmitter 5, 7-dihydroxytryptamine (5,7-DHT). As shown by short-term treatments the effect is due to phenotype induction rather than survival. To begin to understand downstream or parallel signaling pathways required for the PKA-mediated induction of serotonergic markers, we have studied the putative implication of brain-derived neurotrophic factor (BDNF) and its receptor trkB. Treatment of raphe neurons with forskolin induced BDNF mRNA assayed by competitive RT-PCR. Moreover, trkB-IgG receptor bodies fully prevented the forskolin-induced numerical increase in TpOH- and 5,7-DHT-positive cells suggesting an implication of a TrkB-activated pathway. TrkC-IgG had no effect. K252b, a specific inhibitor of trk kinase activity likewise abolished the induction of serotonergic markers by forskolin. In turn, the inductive effect of BDNF on serotonergic markers was blocked by KT5720, a specific inhibitor of PKA. Taken together, these data suggest that co-activation of cAMP- and trkB-dependent signaling pathways plays a crucial role in the regulation of the serotonergic neuronal phenotype.

Induction and maintenance of the neuronal cholinergic phenotype in the central nervous system by BMP-9

Bone morphogenetic proteins (BMPs) have multiple functions in the developing nervous system. A member of this family, BMP-9, was found to be highly expressed in the embryonic mouse septum and spinal cord, indicating a possible role in regulating the cholinergic phenotype. In cultured neurons, BMP-9 directly induced the expression of the cholinergic gene locus encoding choline acetyltransferase and the vesicular acetylcholine transporter and up-regulated acetylcholine synthesis. The effect was reversed upon withdrawal of BMP-9. Intracerebroventricular injection of BMP-9 increased acetylcholine levels in vivo. Although certain other BMPs also up-regulated the cholinergic phenotype in vitro, they were less effective than BMP-9. These data indicate that BMP-9 is a differentiating factor for cholinergic central nervous system neurons.

Sequential activation of the 5-HT1(A) serotonin receptor and TrkB induces the serotonergic neuronal phenotype

Serotonin (5-HT) is an important factor controlling survival, differentiation, and plasticity of neurons in serotonergic target regions of the brain and has been implicated in major psychiatric and autonomic disorders. Relatively little is known, however, of factors controlling differentiation and plasticity of developing and adult 5-HT neurons. We show now that 5-HT, the 5-HT1(A) receptor, brain-derived neurotrophic factor (BDNF), and its receptor, trkB, form an auto/paracrine loop for the regulation of the serotonergic phenotype. Serotonin applied to cultures from E14 rat raphe increased numbers of neurons expressing serotonergic markers in a dose-dependent manner. Agonists of the 5-HT1(A) receptor, BP-554 and 8-OH-DPAT, but not agonists of the 5-HT1(B) and 5-HT1(D) receptors, mimicked this effect, while the specific 5-HT1(A) antagonist, WAY-100635, inhibited it. Serotonin also increased BDNF mRNA and protein in embryonic raphe cultures. Induction of serotonergic markers by serotonin was suppressed by a trkB-IgG fusion protein but not by trkC-IgG. Taken together, our data indicate that serotonin acts on 5-HT1(A) autoreceptors, causing up-regulation of BDNF, which activates trkB to promote serotonergic phenotype-specific markers.