The retirement rate due to multiple sclerosis has decreased since 1995- A retrospective study in a Finnish central hospital.

BACKGROUND: Multiple sclerosis (MS) is the most common cause of non-traumatic neurological disability affecting young adults during their best working years. Previous studies have shown that approximately two-thirds of patients with MS (PwMS) are unable to retain employment in the long term, and many retire soon after the diagnosis. However, it is not known, how the rate of retirement has changed over the decades, especially after the introduction of disease modifying therapies (DMTs). The year 1995 was selected as a division point because DMTs have been increasingly available ever since. OBJECTIVE: To evaluate the change in retirement rate due to MS and to present risk factors for early retirement. METHODS: A retrospective survey of all PwMS treated at the Department of Neurology, Kanta-Häme Central Hospital, Finland between 1978 and 2015, was conducted. The population was divided into two groups: those diagnosed before year 1995 and those diagnosed thereafter. A Kaplan-Meier analysis was performed to evaluate the time from diagnosis to beginning of a pension in both groups. Crude incidence rates, incidence rate differences as well as age and multivariable adjusted Cox proportional hazard regression analysis were calculated for all pension predictors collected. RESULTS: A total of 484 PwMS were identified, 140 of whom were diagnosed before the year 1995 and 344 after. Actual retirement rates were 88 (63%) before the year the year 1995 and 111 (32%) after, respectively. The hazard for disability pension diminished in PwMS diagnosed after the year 1995 compared to those diagnosed before, HR 0.41 (95% confidence interval 0.31-0.55). The median time from diagnosis to retirement was 8.3 years in the group diagnosed before year 1995 and 11.1 years in the group diagnosed later. Male sex and age were statistically significant risk factors in relapsing-remitting MS, HR for male sex 1.8 (95% confidence interval 1.18-2.75) and for age 1.1 (95% confidence interval 1.07-1.12). Only age was a risk factor in progressive MS with HR 1.09 (95% confidence interval 1.07-1.11). In subgroup of relapsing-remitting MS, not using disease modifying therapies was a statistically significant risk factor, HR 1.89 (95% confidence interval 1.19-3.01). CONCLUSION: The rate of retirement due to MS in Finland has decreased significantly since 1995 and the median time from diagnosis to retirement has become longer. Not using disease modifying therapies for relapsing remitting MS was identified as one risk factor for losing ability to work prematurely.

Elastase-2 Knockout Mice Display Anxiogenic- and Antidepressant-Like Phenotype: Putative Role for BDNF Metabolism in Prefrontal Cortex.

Several pieces of evidence indicate that elastase-2 (ELA2; chymotrypsin-like ELA2) is an alternative pathway to the generation of angiotensin II (ANGII). Elastase-2 knockout mice (ELA2KO) exhibit alterations in the arterial blood pressure and heart rate. However, there is no data on the behavioral consequences of ELA2 deletion. In this study, we addressed this question, submitting ELA2KO and wild-type (WT) mice to several models sensitive to anxiety- and depression-like, memory, and repetitive behaviors. Our data indicates a higher incidence of barbering behavior in ELA2KO compared to WT, as well as an anxiogenic phenotype, evaluated in the elevated plus maze (EPM). While a decrease in locomotor activity was observed in ELA2KO in EPM, this feature was not the main source of variation in the other parameters analyzed. The marble-burying test (MBT) indicated increase in repetitive behavior, observed by a higher number of buried marbles. The actimeter test indicated a decrease in total activity and confirmed the increase in repetitive behavior. The spatial memory was tested by repeated exposure to the actimeter in a 24-h interval. Both ELA2KO and WT exhibited decreased activity compared to the first exposure, without any distinction between the genotypes. However, when submitted to the cued fear conditioning, ELA2KO displayed lower levels of freezing behavior in the extinction session when compared to WT, but no difference was observed during the conditioning phase. Increased levels of BDNF were found in the prefrontal cortex but not in the hippocampus of ELA2KO mice compared to WT. Finally, in silico analysis indicates that ELA2 is putatively able to cleave BDNF, and incubation of the purified enzyme with BDNF led to the degradation of the latter. Our data suggested an anxiogenic- and antidepressant-like phenotype of ELA2KO, possibly associated with increased levels of BDNF in the prefrontal cortex.

Neuronal plasticity and neurotrophic factors in drug responses.

Neurotrophic factors, particularly brain-derived neurotrophic factor (BDNF) and other members of the neurotrophin family, are central mediators of the activity-dependent plasticity through which environmental experiences, such as sensory information are translated into the structure and function of neuronal networks. Synthesis, release and action of BDNF is regulated by neuronal activity and BDNF in turn leads to trophic effects such as formation, stabilization and potentiation of synapses through its high-affinity TrkB receptors. Several clinically available drugs activate neurotrophin signaling and neuronal plasticity. In particular, antidepressant drugs rapidly activate TrkB signaling and gradually increase BDNF expression, and the behavioral effects of antidepressants are mediated by and dependent on BDNF signaling through TrkB at least in rodents. These findings indicate that antidepressants, widely used drugs, effectively act as TrkB activators. They further imply that neuronal plasticity is a central mechanism in the action of antidepressant drugs. Indeed, it was recently discovered that antidepressants reactivate a state of plasticity in the adult cerebral cortex that closely resembles the enhanced plasticity normally observed during postnatal critical periods. This state of induced plasticity, known as iPlasticity, allows environmental stimuli to beneficially reorganize networks abnormally wired during early life. iPlasticity has been observed in cortical as well as subcortical networks and is induced by several pharmacological and non-pharmacological treatments. iPlasticity is a new pharmacological principle where drug treatment and rehabilitation cooperate; the drug acts permissively to enhance plasticity and rehabilitation provides activity to guide the appropriate wiring of the plastic network. Optimization of iPlastic drug treatment with novel means of rehabilitation may help improve the efficacy of available drug treatments and expand the use of currently existing drugs into new indications.

Two cases of small bowel obstruction secondary to a swallowed potato.

Bowel obstruction due to bezoars (compaction of ingested material within the gastrointestinal tract) is a rare, but well documented occurrence. In this paper, we present two cases of potato-induced small bowel obstruction. Both patients were approximately 50 years old and had cerebral palsy and learning disabilities, respectively. They presented with abdominal pain and bilious vomiting, with no medical or surgical history. Diagnosis of small bowel obstruction was confirmed by CT prior to taking the patients to the operating theatre, where whole potatoes were found to be obstructing each patient's bowel lumen. Both patients underwent laparotomy with enterotomy and removal of the potato. They both made a good recovery. Through a literature review of bezoar-induced bowel obstruction, these cases highlight important diagnostic and management principles.

Neurotrophins and psychiatric disorders.

Increasing number of studies has during the last decade linked neurotrophic factors with the pathophysiology of neuropsychiatric disorders and with the mechanisms of action of drugs used for the treatment of these disorders. In particular, brain-derived neurotrophic factor BDNF and its receptor TrkB have been connected with the pathophysiology in mood disorders, and there is strong evidence that BDNF signaling is critically involved in the recovery from depression with both pharmacological and psychological means. Neurotrophins play a central role in neuronal plasticity and network connectivity in developing adult brain, and recent evidence links plasticity and network rewiring with mood disorders and their treatment. Therefore, neurotrophins should not be seen as happiness factors but as critical tools in the process where brain networks are optimally tuned to environment, and it is against this background that the effects of neurotrophins on neuropsychiatric disorders should be looked at.

Sleep homeostasis and depression: studies with the rat clomipramine model of depression.

Neonatal treatment of rat pups with clomipramine (CLI) has been shown to cause long-lasting and persistent depression-related behaviors and changes in sleep architecture and in brain-derived neurotrophic factor (BDNF) signaling in adult animals, producing an animal model of depression. However, the molecular mechanisms which mediate these effects of early-life CLI treatment on adult animals remain largely unknown. In order to characterize these further, we investigated in neonatally CLI-treated rats the sleep architecture as well as the extracellular and cellular levels of sleep regulators (nitric oxide, adenosine) and BDNF, respectively, in the basal forebrain (BF), i.e. the brain area which is implicated in sleep and depression. We found that CLI-treated rats exhibited a disturbed sleep architecture (REM sleep fragmentation was increased and NREM periods preceding REM were shorter) and reduced levels of BDNF and adenosine in the BF, whereas the levels of nitric oxide were elevated. Next, we examined sleep deprivation (SD)-induced homeostatic responses on sleep regulation and brain BDNF levels in CLI-treated rats. Compared to control rats, 3h of SD induced a smaller increase in the amount of NREM sleep during sleep recovery. At the molecular level, the normal homeostatic response was dissociated: the rise in the adenosine level was not accompanied by a rise in the nitric oxide concentration. Moreover, while BF BDNF levels decreased during SD in control rats, such a decline was not observed in CLI rats. Taken together, neonatal CLI treatment produces long-lasting functional changes in the sleep architecture and sleep regulation in adult rats, accompanied by dysregulated BDNF signaling in the BF.

Reduction of BDNF expression in Fmr1 knockout mice worsens cognitive deficits but improves hyperactivity and sensorimotor deficits.

Fragile X syndrome (FXS) is a common cause of inherited intellectual disability and a well-characterized form of autism spectrum disorder. As brain-derived neurotrophic factor (BDNF) is implicated in the pathophysiology of FXS we examined the effects of reduced BDNF expression on the behavioral phenotype of an animal model of FXS, Fmr1 knockout (KO) mice, crossed with mice carrying a deletion of one copy of the Bdnf gene (Bdnf(+/-)). Fmr1 KO mice showed age-dependent alterations in hippocampal BDNF expression that declined after the age of 4 months compared to wild-type controls. Mild deficits in water maze learning in Bdnf(+/-) and Fmr1 KO mice were exaggerated and contextual fear learning significantly impaired in double transgenics. Reduced BDNF expression did not alter basal nociceptive responses or central hypersensitivity in Fmr1 KO mice. Paradoxically, the locomotor hyperactivity and deficits in sensorimotor learning and startle responses characteristic of Fmr1 KO mice were ameliorated by reducing BNDF, suggesting changes in simultaneously and in parallel working hippocampus-dependent and striatum-dependent systems. Furthermore, the obesity normally seen in Bdnf(+/-) mice was eliminated by the absence of fragile X mental retardation protein 1 (FMRP). Reduced BDNF decreased the survival of newborn cells in the ventral part of the hippocampus both in the presence and absence of FMRP. Since a short neurite phenotype characteristic of newborn cells lacking FMRP was not found in cells derived from double mutant mice, changes in neuronal maturation likely contributed to the behavioral phenotype. Our results show that the absence of FMRP modifies the diverse effects of BDNF on the FXS phenotype.

A role for BDNF/TrkB signaling in behavioral and physiological consequences of social defeat stress.

Accumulating evidences underlie the importance of the interplay between environmental and genetic factors in contributing to the risk to develop mental illness. Brain-derived neurotrophic factor (BDNF) and its Tyrosine receptor kinase B (TrkB) receptor play a fundamental contribution to brain development and plastic adaptations to life events. In the present study, the potential for the BDNF/TrkB contribution in increasing vulnerability to negative social experiences was assessed by subjecting TrkB.T1 overexpressing mice to a chronic social defeat model. TrkB.T1 mice overexpress the dominant-negative truncated splice variant of TrkB receptor leading to decreased BDNF signaling. After repeated social defeat, mice were assessed in a longitudinal study for behavioral, physiological, endocrine and immune responses potentially related to psychiatric endophenotypes. TrkB.T1 overexpression corresponded to smaller changes in metabolic parameters such as body weight, food intake, feed efficiency and peripheral ghrelin levels compared with wild-type (wt) littermates following social defeat. Interestingly, 4 weeks after the last defeat, TrkB.T1 overexpressing mice exhibited more consistent social avoidance effects than what observed in wt subjects. Finally, previously unreported effects of TrkB mutations could be observed on lymphoid organ weight and on peripheral immune biomarker levels, such as interleukin-1α and regulated on activation, normal, T-cell expressed, and secreted (RANTES), thus suggesting a systemic role of BDNF signaling in immune function. In conclusion, the present data support a contribution of TrkB to stress vulnerability that, given the established role of TrkB in the response to antidepressant treatment, calls for further studies addressing the link between stress susceptibility and variability in drug efficacy.

Chronic antidepressant treatment selectively increases expression of plasticity-related proteins in the hippocampus and medial prefrontal cortex of the rat.

Antidepressants protect against hippocampal volume loss in humans and reverse stress-induced atrophic changes in animals thus supporting the hypothesis that the pathophysiology of stress-related disorders such as depression involves reductions in neuronal connectivity and this effect is reversible by antidepressant treatment. However, it is unclear which brain areas demonstrate such alterations in plasticity in response to antidepressant treatment. The aim of the present study was to examine the effect of antidepressant treatment on the expression of three plasticity-associated marker proteins, the polysialylated form of nerve cell adhesion molecule (PSA-NCAM), phosphorylated cyclic-AMP response element binding protein (pCREB) and growth-associated protein 43 (GAP-43), in the rat brain. To this end, rats were treated either acutely (60 min) or chronically (21 days) with imipramine (30 and 15 mg/kg, respectively) and the expression of PSA-NCAM, pCREB, and GAP-43 was assessed using immunohistochemistry. Initial mapping revealed that chronic imipramine treatment increased expression of these plasticity-associated proteins in the hippocampus, medial prefrontal cortex and piriform cortex but not in the other brain regions examined. Since PSA-NCAM and pCREB are expressed in recently-generated neurons in the dentate gyrus, it is likely that chronic imipramine treatment increased their expression in the hippocampus at least partially by increasing neurogenesis. In contrast, since chronic imipramine treatment is not associated with neurogenesis in the medial prefrontal cortex, increased expression of PSA-NCAM and pCREB in the prelimbic cortex implicates changes in synaptic connectivity in this brain region. Acute treatment with imipramine increased the number of pCREB positive nuclei in the hippocampus and the prefrontal cortex but did not alter expression of GAP-43 or PSA-NCAM in any of the brain regions examined. Taken together, the results of the present study suggest that antidepressant treatment increases synaptic plasticity and connectivity in brain regions associated with mood disorders.

Exacerbated status epilepticus and acute cell loss, but no changes in epileptogenesis, in mice with increased brain-derived neurotrophic factor signaling.

Several studies suggest that brain-derived neurotrophic factor (BDNF) can exacerbate seizure development during status epilepticus (S.E.) and subsequent epileptogenesis in the adult brain. On the other hand, evidence exists for the protective effect of BDNF. To study this controversy, we induced S.E. with kainate in transgenic mice with increased BDNF signaling due to trkB overexpression. Transgenic mice experienced a more severe S.E. than wild type animals did. Furthermore, they had increased acute hippocampal neuronal loss when assessed at 48 h after S.E. The effect of trkB overexpression on the development of epilepsy, chronic neuronal death, mossy fiber sprouting, and neurogenesis were studied at 4.5 months after kainate-induced S.E. No differences were found in the rate of epileptogenesis, severity of epilepsy, or cellular markers of network reorganization between transgenic and wild type mice. No differences between genotypes were observed in TUC-4 staining, indicating no effect of trkB overexpression to immature neuron numbers. Instead, in Cresyl Violet-stained preparations, the highest density of neurons was found in untreated transgenic mice suggesting a favorable effect of trkB overexpression on the survival of neurons in the hippocampus. Our data support the role of BDNF and trkB signaling in seizure generation and acute cellular damage after S.E. Long-term outcome was not, however, exacerbated by trkB overexpression.

Synexpression analysis of ESTs in the rat brain reveals distinct patterns and potential drug targets.

The gene expression profiles of 146 novel ESTs were characterized in newborn and adult rat brains via radioactive in situ hybridization. Using Euclidean metrics and hierarchical clustering tools the brain expression profiles obtained clustered into seven synexpression groups. The groups were: I, non-detectable expression (68 ESTs); II, low expression in hippocampus (40 ESTs); III, low expression in adult, high expression in newborn (two ESTs); IV, medium expression throughout brain (31 ESTs); V, high expression throughout brain (three ESTs); VI, selective high expression in hippocampus, caudate and putamen (one EST); VII, selective high expression in hippocampus (one EST). Five ESTs were expressed in the striatum and three responded transcriptionally to neuroleptic and neuroprotective drug treatments, suggesting that this approach could be used to detect novel drug targets. These results provide a useful starting point to explore the functional genomics of genes without known functions forthcoming from various genome projects.

The neuroprotective agent memantine induces brain-derived neurotrophic factor and trkB receptor expression in rat brain.

Memantine is a medium-affinity uncompetitive N-methyl-d-aspartate receptor antagonist and has been clinically used as a neuroprotective agent to treat Alzheimer's and Parkinson's diseases. We have examined the effect of memantine (ip 5-50 mg/kg; 4 h) on the expression of brain-derived neurotrophic factor (BDNF) and trkB receptor mRNAs in rat brain by in situ hybridization. Memantine at a clinically relevant dose markedly increased BDNF mRNA levels in the limbic cortex, and this effect was more widespread and pronounced at higher doses. Effects of memantine on BDNF mRNA were also reflected in changes in BDNF protein levels. Moreover, memantine induced isoforms of the BDNF receptor trkB. Taken together, these data suggest that the neuroprotective properties of memantine could be mediated by the increased endogenous production of BDNF in the brain. These findings may open up new possibilities of pharmacologically regulating the expression of neurotrophic factors in the brain.

Subcellular localization of fragile X mental retardation protein with the I304N mutation in the RNA-binding domain in cultured hippocampal neurons.

1. Fragile X syndrome, the most common form of inherited mental retardation, is caused by the lack or dysfunction of fragile X mental retardation protein (FMRP). The 1304N mutation in the RNA-binding domain of FMRP results in an exceptionally severe form of mental retardation. 2. We have investigated the subcellular localization of FMRP and its 1304N-mutated form in cultured hippocampal neurons and PC12 cells, using immunofluorescence microscopy. In PC12 cells, FMRP was predominantly localized to the cytoplasm and also to the processes after differentiation by NGF. 3. In cultured hippocampal neurons, granular labeling was detected along the neuronal processes. 4. Double-labeling with synaptophysin antibody revealed FMRP at synaptic sites in neurons. 5. The 1304N mutation did not appear to affect the transport of FMRP to dendrites or its localization at synaptic sites. Thus, FMRP is a synaptic protein and the severe phenotype observed in the patient with the 1304N mutation is not produced by alterations in dendritic transport.

Increased expression of neuronal Src and tyrosine phosphorylation of NMDA receptors in rat brain after systemic treatment with MK-801.

We have observed that systemic treatment with the uncompetitive N-methyl-D-aspartate (NMDA) receptor antagonist MK-801 increases Src expression and NMDA receptor phosphorylation in rat brain. A partial cDNA encoding rat neuronal Src was isolated and its sequence was used to design specific oligonucleotide probes. Systemically administered MK-801 (5 mg/kg for 4 h) increased by 28+/-4% mRNA expression of neuronal Src in the superficial layers of the parietal cortex. This effect was observed at doses as low as 0.2 mg/kg. A similar, although more modest, induction was observed 6 h after phencyclidine (15 mg/kg) administration, but not after high doses of memantine and ketamine. The MK-801-induced effect was not blocked by pretreatment with clozapine. Consistent with the increase in mRNA levels, cortical Src protein was increased to 186 +/- 24% of control 24 h after MK-801 treatment. Total cellular Src activity was also increased in parietal cortex homogenates 4 h after MK-801 (5 mg/kg). Moreover, MK-801 treatment (0.5 mg/kg and 5 mg/kg for 4 h) increased tyrosine phosphorylation, but not protein levels, of the NMDA receptor subunit NR2A. These results provide evidence for a contribution of Src and tyrosine phosphorylation of NMDA receptors in the pharmacological actions of uncompetitive NMDA receptor antagonists.

Uncompetitive antagonists of the N-methyl-D-aspartate (NMDA) receptors alter the mRNA expression of proteins associated with the NMDA receptor complex.

N-methyl-D-aspartate (NMDA) receptor function appears to be under complex control during physiological and pharmacological states. We have investigated the effects of acute administration of uncompetitive NMDA receptor antagonists on mRNA levels of NMDA receptor subunits and on molecules known to cluster or phosphorylate the receptor utilizing in situ hybridization on rat brain sections. A high dose (5 mg/kg; 4 hr) of dizocilpine (MK-801) decreased mRNA levels of NMDA receptor subunits NR2C and NR2B in the entorhinal and parietal cortices, respectively. MK-801 increased mRNA levels of synapse-associated protein-90/postsynaptic density-95 (SAP90/PSD-95) and a gamma-isoform of protein kinase C (PKCgamma) in cortical regions. Synapse-associated protein-97 (SAP97) mRNA levels were increased in the entorhinal cortex layer III after MK-801 or after relatively high doses of other uncompetitive NMDA receptor antagonists: phencyclidine (15 mg/kg; 6 hr) and memantine (50 mg/kg; 6 hr). Memantine also increased SAP97 mRNA expression in other cortical regions, but this effect was not observed with MK-801 or phencyclidine. NMDA receptor uncompetitive antagonists alter the expression of multiple receptor components and such events may ultimately play a role in adaptation or toxic responses.

Truncated trkB.T1 is dominant negative inhibitor of trkB.TK+-mediated cell survival.

Truncated trkB.T1 (T1) neurotrophin receptor inhibits full-length trkB.TK+ (TK+) signaling. At least two possible mechanisms have been proposed for this action: T1 could trap the ligand or function as a dominant negative receptor. To differentiate between these possibilities we have studied survival of serum-deprived PC12-trkB cells stably expressing TK+. PC12-trkB cells were observed to display constitutive trkB kinase activity which leads to survival of a cell subpopulation in the absence of added brain-derived neurotrophic factor (BDNF) and serum. Exogenous BDNF significantly increased cell survival, and this increase was inhibited by BDNF neutralizing antibody. The antibody treatment had no effect on the constitutive TK+ activity. Transfected T1 completely inhibited survival by BDNF or constitutive trkB kinase activity in PC12-trkB cells similarly to tyrosine kinase inhibitor K252a. In addition, T1 coimmunoprecipitated with TK+ and inhibited its autophosphorylation by BDNF. These data suggest that truncated T1 inhibits TK+ signaling by dominant negative action.

trkB-receptor activation contributes to the kainate-induced increase in BDNF mRNA synthesis.

1. The expression of brain-derived neurotrophic factor (BDNF) mRNA is induced by neuronal activity through increased intracellular calcium. As BDNF also increases intracellular calcium levels through trkB activation, we have examined here whether BDNF also regulates the synthesis of its own mRNA. 2. Neurotrophin mRNA expression was induced with kainic acid administration in transgenic mice overexpressing the dominant-negative form of BDNF receptor trkB and wild-type littermates. 3. Kainate strongly induced BDNF mRNA expression in both genotypes, but the up-regulation was significantly lower in transgenic mice. 4. These data suggest that the synthesis of BDNF mRNA is at least partly mediated by BDNF release and the activation of trkB receptors. The present findings further suggest that the BDNF signaling system in brain is regulated by positive feedback.

A functional genomic study of the effects of antipsychotic agent chlorpromazine in PC12 cells.

Expression profiling using methods of functional genomics can be used to investigate changes in gene transcription induced by drug treatment, which may lead to discovery of new potential drug targets. Antipsychotic agents alleviate symptoms of schizophrenia but the mechanism behind their clinical efficacy is unclear. We have used the PC12 cell line as a model to characterize effects of the antipsychotic drug chlorpromazine on gene expression using high-density complementary DNA array filters prepared from a rat brain entorhinal cortex complementary DNA library. Chlorpromazine treatment positively regulated the expression of several clones, five of which were selected for further characterization. Northern blotting experiments confirmed the increased expression of these genes after chlorpromazine treatment. Sequencing revealed that two clones were cytochrome c oxidase and three were novel genes. Characterization of the function of these genes could increase our understanding of the mechanisms of action of antipsychotic drugs, and might be beneficial for the development of more effective agents.

Expression of c-Met in developing rat hippocampus: evidence for HGF as a neurotrophic factor for calbindin D-expressing neurons.

Hepatocyte growth factor-scatter factor (HGF) is expressed in different parts of the nervous system, and has been shown to exhibit neurotrophic activity. Here we show that c-Met, the receptor for HGF, is expressed in developing rat hippocampus, with the highest levels during the first postnatal weeks. To study the function of HGF, hippocampal neurons were prepared from embryonic rats and treated with different HGF concentrations. In these cultures, HGF increased the number of neurons expressing the 28-kDa calcium-binding protein (calbindin D) in a dose-dependent manner. The effect of HGF was larger than that observed with either brain-derived neurotrophic factor (BDNF) or neurotrophin-3 (NT-3), and cotreatment of the cultures with HGF and the neurotrophins was additive with respect to calbindin D neurons. Besides affecting the number of neurons, HGF significantly increased the degree of sprouting of calbindin D-positive neurons, suggesting an influence on neuronal maturation. BDNF and NT-3 stimulated neurite outgrowth of calbindin D neurons to a much smaller degree. In contrast to calbindin D neurons, HGF did not significantly increase the number of neurons immunoreactive with the neurotransmitter gamma-aminobutyric acid (GABA) in the hippocampal cultures. Immunohistochemical studies showed that c-Met-, calbindin D- and HGF-immunoreactive cells are all present in the dentate gyrus and partly colocalize within neurons. These results show that HGF acts on calbindin D-containing hippocampal neurons and increases their neurite outgrowth, suggesting that HGF plays an important role for the maturation and function of these neurons in the hippocampus.