Haloperidol administration in humans lowers plasma nerve growth factor level: evidence that sedation induces opposite effects to arousal

Molecular foundations of chiropractic therapy

Background and aim: Alternative medicine is a broad term used to encompass different therapies, including chiropractic. Chiropractic was called “a science of healing without drugs” by its founder, David Daniel Palmer. It is based on the idea that the body has a powerful self-healing ability and that there is a relationship between body structure and function that affects health. In particular, chiropractic assumes that the nervous system controls the human body through nerves branching from the vertebral column and spinal cord. Researchers do not fully understand how chiropractic therapies affect pain, but chiropractic is widely used today to treat chronic pain, such as back pain. Different studies with animal models have demonstrated that chiropractic therapies mediate neuroplasticity, specifically through modulation of neurotrophins. No studies have yet been published on interaction between neurotrophin gene polymorphisms and chiropractic treatment. Methods: We searched PubMed with the following keywords: chiropractic, neuroplasticity, neurotrophin gene polymorphism for a panorama of on the molecular mechanisms of chiropractic therapy. Results: From the material collected, we identified a set of genes and some functional polymorphisms that could be correlated with better response to chiropractic therapy. Conclusions: Further association studies will be necessary to confirm hypotheses of a correlation between single nucleotide polymorphisms in specific genes and better response to chiropractic therapy. (www.actabiomedica.it)

A meta-analysis of peripheral blood nerve growth factor levels in patients with schizophrenia

Neurotrophins particularly brain-derived neurotrophic factor (BDNF) and nerve growth factor (NGF) are crucial modulators in the neurodevelopment and maintenance of central and peripheral nervous systems. Neurotrophin hypothesis of schizophrenia (SCZ) postulated that the changes in the brains of SCZ patients are the result of disturbances of developing processes involving neurotrophic factors. This hypothesis was mainly supported by the abnormal regulation of BDNF in SCZ, especially the decreased peripheral blood BDNF levels in SCZ patients validated by several meta-analyses. However, the regulation of NGF in SCZ remains unclear because of the inconsistent findings from the clinical studies. Therefore, we undertook, to the best of our knowledge, the first systematic review with a meta-analysis to quantitatively summarize the peripheral blood NGF data in SCZ patients compared with healthy control (HC) subjects. A systematic search of Pubmed, PsycINFO and Web of Science identified 13 articles encompassing a sample of 1693 individuals for the meta-analysis. Random-effects meta-analysis showed that patients with SCZ had significantly decreased peripheral blood levels of NGF when compared with the HC subjects (Hedges's g=-0.633, 95% confidence interval (CI)=-0.948 to -0.318, P<0.001). Subgroup analyses revealed reduced NGF levels both in serum (Hedges's g=-0.671, 95% CI=-1.259 to -0.084, P=0.025) and plasma (Hedges's g=-0.621, 95% CI=-0.980 to -0.261, P<0.001) of the patients, and in drug-free (Hedges's g=-0.670, 95% CI=-1.118 to -0.222, P=0.003) and medicated (Hedges's g=-0.357, 95% CI=-0.592 to -0.123, P=0.003) patients with SCZ. Furthermore, meta-regression analyses showed that age, gender and sample size had no moderating effects on the outcome of the meta-analysis, whereas disease severity might be a confounding factor for the meta-analysis. These results demonstrated that patients with SCZ are accompanied by the decreased peripheral blood NGF levels, strengthening the clinical evidence of an abnormal neurotrophin profile in the patients with SCZ.

Peripheral blood nerve growth factor levels in major psychiatric disorders

Nerve growth factor (NGF) plays crucial roles in promoting neural growth and survival, and mediating synaptic and morphological plasticity. Several studies investigated the correlation between peripheral NGF levels and major psychiatric disorders, including schizophrenia (SCZ), major depressive disorder (MDD) and bipolar disorder (BPD); however, the findings were inconsistent. This meta-analysis sought to investigate blood NGF levels in patients with psychiatric disorders compared with healthy subjects and examined potential effects of blood fraction, medication and disease status. A total of 21 eligible studies, encompassing 1342 patients suffering from psychiatric disorders and 1225 healthy subjects, were enrolled in the present meta-analysis. No obvious publication bias was observed either for SCZ, MDD or BPD by the Begg's test (P > 0.05). Random-effects meta-analysis showed that SCZ (Z = 2.14, P = 0.033, SMD = -1.08, 95% CI = -2.07 to -0.09) and MDD (Z = 2.57, P = 0.010, SMD = -0.61, 95% CI = -1.08 to -0.14) patients had significantly reduced NGF levels, compared with healthy controls. Notably, this decrease was enhanced in un-medicated patients of SCZ (P = 0.004) and medicated or chronic patients of MDD (P < 0.001). No significant difference of NGF levels was observed between BPD patients and controls (P > 0.05). These results supported an association between the reduction of NGF levels and psychiatric disorders. It remains unclear whether the change of NGF levels is a prerequisite for its function in psychiatric disorders development or merely an epiphenomenon unrelated to the pathophysiologic mechanisms.

Ultradian Variation of Nerve Growth Factor Plasma Levels in Healthy and Schizophrenic Subjects

Some studies in animal models showed that several neurotrophins may be implicated in the regulation of light-dependent suprachiasmatic pacemaker and in other functions implicated in long-term memory acquisition during sleep. However, no data are known about the role played by NGF in ultradian regulation in humans. The aim of this study was to investigate whether or not there is a natural diurnal fluctuation during daytime in healthy and schizophrenic subjects with a normal light/dark cycle. In a sample of 33 subjects (10 male schizophrenics and 23 healthy subjects) an ELISA assay was used to study the ultradian NGF cycle in blood samples at 9.00, 13.00 and 20.00 hours. The study showed an ultradian rhythm of NGF in healthy subjects with a “V” trend: higher at 9:00 and 20:00 and lower at 13:00. We also show significant differences between male and female controls. No NGF ultradian rhythm among schizophrenic patients compared to healthy subjects was found. The results of this study lead to a rhythmic NGF regulation that appears altered in schizophrenics, where higher levels in the morning and lower levels in the evening were observed, compared to the controls, and support the hypothesis of a role played by NGF in schizophrenia.

Possible biomarkers modulating haloperidol efficacy and/or tolerability

Haloperidol (HP) is widely used in the treatment of several forms of psychosis. Despite of its efficacy, HP use is a cause of concern for the elevated risk of adverse drug reactions. adverse drug reactions risk and HP efficacy greatly vary across subjects, indicating the involvement of several factors in HP mechanism of action. The use of biomarkers that could monitor or even predict HP treatment impact would be of extreme importance. We reviewed the elements that could potentially be used as peripheral biomarkers of HP effectiveness. Although a validated biomarker still does not exist, we underlined the several potential findings (e.g., about cytokines, HP metabolites and genotypic biomarkers) which could pave the way for future research on HP biomarkers.

Nerve growth factor: basic studies and possible therapeutic applications

The nerve growth factor (NGF) belongs to a family of neurotrophic factors called neurotrophins. It was discovered as a molecule that stimulates the survival and maturation of developing neurons in the peripheral nervous system and has later been shown to protect adult neurons in the degenerating mammalian brain. Basic and clinical studies have been undertaken to use NGF as a therapeutic agent aimed at restoring and maintaining neuronal function in the central nervous system and to determine the mechanisms to safely deliver the molecule into the brain. Recent studies have also recognized that the role of NGF extends far beyond the horizon of nerve cells and even beyond the peripheral and central nervous system. Studies published from our laboratory have shown that topical application of NGF possesses a protective action on human pressure ulcer, corneal ulcer and glaucoma. Here, we will review these studies, supporting the therapeutic potential of NGF.

Mechanisms of antidepressant action: an integrated dopaminergic perspective

The molecular mechanisms that cause and maintain the major depressive disorder (MDD) are currently unknown. Consistently, antidepressant treatments are characterized by insufficient success rates. This causes high social costs and severe personal sufferings. In the present review we analyze some of the paradigms that are used to explain MDD, particularly from the perspective of the dopaminergic (DA) system. DA has been more classically associated with psychosis and substance abuse disorders, even though a role of DA in MDD has been proposed as well and some antidepressants with DA profile exist. In the present work, we review some of the molecular mechanisms that underpin MDD from the perspective of the dopaminergic system, in the hope of unifying some of the major theories of MDD - the monoaminergic, inflammatory, epigenetics, neurotrophin and anti-apoptotic theories. Several shared components of these theories are highlighted, partially accounted by the functions of the DA system (see supplementary video).

Olanzapine plus fluoxetine treatment increases Nt-3 protein levels in the rat prefrontal cortex

Evidence is emerging for a role for neurotrophins in the treatment of mood disorders. In this study, we evaluated the effects of chronic administration of fluoxetine, olanzapine and the combination of fluoxetine/olanzapine on the brain-derived-neurotrophic factor (BDNF), nerve growth factor (NGF), and neurotrophin-3 (NT-3) in the rat brain. Wistar rats received daily injections of olanzapine (3 or 6 mg/kg) and/or fluoxetine (12.5 or 25mg/kg) for 28 days, and we evaluated for BDNF, NGF and NT-3 protein levels in the prefrontal cortex, hippocampus and amygdala. Our results showed that treatment with fluoxetine and olanzapine alone or in combination did not alter BDNF in the prefrontal cortex (p=0.37), hippocampus (p=0.98) and amygdala (p=0.57) or NGF protein levels in the prefrontal cortex (p=0.72), hippocampus (p=0.23) and amygdala (p=0.64), but NT-3 protein levels were increased by olanzapine 6 mg/kg/fluoxetine 25mg/kg combination in the prefrontal cortex (p=0.03), in the hippocampus (p=0.83) and amygdala (p=0.88) NT-3 protein levels did not alter. Finally, these findings further support the hypothesis that NT-3 could be involved in the effect of treatment with antipsychotic and antidepressant combination in mood disorders.

Reduced NGF serum levels and abnormal P300 event-related potential in first episode schizophrenia

Nerve growth factor (NGF) plays a crucial role in central nervous system neuron plasticity. Low levels of serum NGF in schizophrenic patients suggest that the neurotrophin contributes to the pathogenesis of the disease. NGF is also thought to alter characteristics of event-related brain potential (ERP) components. The auditory-evoked P300 ERP component, considered an index of brain activity, has reduced amplitude in acute and chronic schizophrenia. This study evaluated the relationship among serum NGF levels, P300 characteristics, and Positive and Negative Symptom Scale (PANSS) scores in first episode, neuroleptic naive schizophrenic patients (N=30) and healthy controls (N=28). Serum NGF was measured by ELISA and P300 elicited using auditory oddball paradigm. Compared to control subjects, schizophrenic patients had significantly reduced serum NGF (p<0.001) and lower P300 amplitudes at Fz (p=0.003). Additionally, there was a positive correlation between serum NGF serum and P300 amplitude at Fz. No correlation was found between serum NGF or P300 characteristics and PANSS scores. These results suggest that the effects of NGF in schizophrenia are related not only to regulation of neurodevelopment, but also to the electrophysiological characteristics of nerve growth factor.

Antipsychotic drugs: comparison in animal models of efficacy, neurotransmitter regulation, and neuroprotection

Various lines of evidence indicate the presence of progressive pathophysiological processes occurring within the brains of patients with schizophrenia. By modulating chemical neurotransmission, antipsychotic drugs may influence a variety of functions regulating neuronal resilience and viability and have the potential for neuroprotection. This article reviews the current literature describing preclinical and clinical studies that evaluate the efficacy of antipsychotic drugs, their mechanism of action and the potential of first- and second-generation antipsychotic drugs to exert effects on cellular processes that may be neuroprotective in schizophrenia. The evidence to date suggests that although all antipsychotic drugs have the ability to reduce psychotic symptoms via D(2) receptor antagonism, some antipsychotics may differ in other pharmacological properties and their capacities to mitigate and possibly reverse cellular processes that may underlie the pathophysiology of schizophrenia.

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.

Differential effects of haloperidol and olanzapine on the expression of erythropoietin and its receptor in rat hippocampus and striatum

Compared with first-generation antipsychotics (FGAs), second-generation antipsychotics (SGAs) seem to be neuroprotective and trigger neuroplasticity. Because neuroplasticity is regulated by a variety of neurotrophic factors we studied differential effects of haloperidol (HAL, a FGA) and olanzapine (OLZ, a SGA) on temporal expression of erythropoietin (EPO), a potent neuroprotective factor and its receptor (EPOr) in rat brain. Rats (8-10/group) were treated with HAL or OLZ for 14 days (HAL-14 or OLZ-14) or 45 days (HAL-45 or OLZ-45). Animals were killed by decapitation or by perfusion to collect brains for immunoblotting and immunohistochemical analysis respectively. In hippocampus, the levels of both EPO and EPOr were significantly increased in HAL-14 (p < 0.001) and OLZ-14 (p < 0.001) groups. Their levels decreased in HAL-45 compared with levels in HAL-14 (EPO, p < 0.001; EPOr, p < 0.05), whereas the levels were further increased (EPO, p < 0.05) in OLZ-45 compared with OLZ-14. In striatum, the levels of both EPO and EPOr were unchanged in HAL-14 and EPO levels significantly decreased in HAL-45 (p < 0.05), whereas their levels were significantly increased in OLZ-14 and OLZ-45 compared with the vehicle-treated control (p < 0.001). Both EPO and EPOr were primarily expressed by neurons and endothelial cells. These data suggest that SGAs such as OLZ may have neuroprotective effects through expression of EPO that may be clinically relevant for long-term safe and beneficial management of psychotic patients.

Adequate antipsychotic treatment normalizes serum nerve growth factor concentrations in schizophrenia with and without cannabis or additional substance abuse

Neurotrophins such as nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) are important for the development and maintenance of neuron function. Neurodevelopment is thought to be impaired in schizophrenia, and vulnerable schizophrenic brains may be more sensitive to toxic influences. Thus, cannabis as a neurotoxin (and other substances) may be more harmful to schizophrenic brains than to non-schizophrenic brains, when used chronically. In a previous study we demonstrated an earlier disease onset and significantly higher serum NGF concentrations in drug-naïve schizophrenic patients with previous long-term cannabis abuse than in schizophrenics without cannabis abuse or cannabis abusers without schizophrenia. We therefore investigated whether this difference is still observed after treatment. Serum NGF measured in 114 treated schizophrenic patients (schizophrenia alone, n=66; schizophrenia plus cannabis abuse, n=42; schizophrenia plus multiple substance abuse, n=6) no longer differed significantly among those groups and from the control groups (healthy controls, n=51; cannabis controls, n=24; multiple substance controls, n=6). These results were confirmed by an additional prospective study in 28 patients suffering from schizophrenia (S) or schizophrenia with cannabis abuse (SC). Previously elevated serum NGF levels in the drug-naïve state, also differing between the groups (S: 83.44+/-265.25 pg/ml; SC: 246.89+/-310.24 pg/ml, S versus SC: p=0.03) dropped to 10.72+/-14.13 pg/ml (S) and 34.19+/-38.96 pg/ml (SC) (S versus SC, p>0.05), respectively, after adequate antipsychotic treatment. We thus conclude that antipsychotic treatment leads to recovery of neural integrity, as indicated by renormalized NGF values.

Differential effects of long-term treatment with typical and atypical antipsychotics on NGF and BDNF levels in rat striatum and hippocampus

The results of mostly short-term treatment studies in human patients and animals suggest that second-generation antipsychotics (SGAs) such as risperidone (RISP) and olanzapine (OLZ) compared to first-generation antipsychotics (FGAs) such as haloperidol (HAL) and chlorpromazine (CPZ) have neuroprotective effects. The animal studies indicate that these effects are probably mediated through increased expression of neurotrophic factors such as nerve growth factor (NGF) and brain derived neurotrophic factor (BDNF). However, since antipsychotics are commonly used for very long-term treatment periods, particularly in schizophrenic patients, it is important to measure the effects of chronic administration of antipsychotic drugs on the aforementioned growth factors. This study determined the effects of 90- and 180-day treatments with two FGAs, HAL and CPZ, and two SGAs, RISP and OLZ, on the levels of NGF and BDNF protein in hippocampus and striatum of rat. Furthermore, since a preliminary study showed that 90-day treatment of HAL caused significant reductions in the expression of both NGF and BDNF the HAL-treated animals were then switched to SGAs for the next 90 days to assess the potential for restoration of trophic factor levels. After the 90-day treatment, NGF levels in the hippocampus were reduced by 60-70% with HAL or CPZ, and by only 25-30% with RISP or OLZ compared to levels with vehicle only. After the 180-day treatment, NGF levels were further reduced with HAL, RISP, and OLZ, but not with CPZ. The magnitude of the NGF decreases in the striatum was larger (70-90%) with all the antipsychotics compared to the hippocampus. However, the pattern of BDNF changes in the hippocampus differed significantly from the striatum after 90- or 180-day treatment with the antipsychotics. In hippocampus, compared to controls, BDNF levels remained unchanged with OLZ both after 90 and 180 days of treatment. Whereas, larger decreases in BDNF levels were observed with HAL or CPZ and intermediate decreases were observed with RISP after 90 days of treatment that continued to decline up to 180 days. Furthermore, switching HAL animals after 90 days of treatment to either RISP or OLZ for the next 90 days significantly restored levels of both NGF and BDNF in both the brain regions. These data indicate that SGAs compared to FGAs induce less deleterious effects on neurotrophic factor levels in the brain and may also offer ability to reverse the more pronounced negative effects of FGAs as well. These data may have significant clinical implications for long-term antipsychotic selection as well as the common practice of antipsychotic switchover.

The possible role of neurotrophins in the pathogenesis and therapy of schizophrenia

The pathogenesis of schizophrenia may be ascribed to early maldevelopment of brain tissue. Neurotrophins are a group of dimeric proteins that affect the development of the nervous system in all vertebrates' species. Since neurotrophins, as well as other growth factors, play a crucial role in neurodevelopment, they are plausible candidates of taking part in the pathophysiology of schizophrenia. In line with this hypothesis, accumulating preclinical and clinical data indicate that dysfunctions of nerve growth factor (NGF), brain derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3) may contribute to impaired brain development, neuroplasticity and synaptic "dysconnectivity" leading to the schizophrenic syndrome, or at least some of its presentations. This article reviews the functions of neurotrophins in the complex process of normal brain development, and their possible relevance to the neuropathology and neuropharmacology of schizophrenia. Further research in this area may bring about novel pharmacological therapeutic strategies to this chronic debilitating disorder.

Differential effects of typical and atypical antipsychotics on nerve growth factor and choline acetyltransferase expression in the cortex and nucleus basalis of rats

Previously we reported that chronic exposure to haloperidol (HAL), but not the atypical antipsychotics risperidone (RISP) or clozapine (CLOZ), resulted in reductions in brain choline acetyltransferase (ChAT) immunoreactivity and impaired water maze task performance in rats. In the present study, we compared the effects of these antipsychotic drugs on the expression of nerve growth factor (NGF) as well ChAT the in the rat cortex and nucleus basalis of Meynert (NBM) in an effort to determine the underlying mechanism for the differential drug effects observed previously. We also evaluated the effects of these compounds in a crossover design to evaluate specific neurochemical consequences of switching between typical and atypical antipsychotics, a common practice observed in the clinical setting. Male Wistar rats (250-300 g) were exposed to HAL (2.0 mg/kg/day), RISP (2.5 mg/kg/day), or CLOZ (20 mg/kg/day) for 45 days or a pre-treatment regimen consisting of administering either RISP/HAL (i.e., RISP followed by HAL) or CLOZ/HAL, or a post-treatment regimen consisting of administering: HAL/RISP or HAL/CLOZ. The duration of each treatment in the crossover study was also 45 days. NGF and ChAT immunoreactivity were measured by quantitative immunohistochemistry in some sub-cerebral cortical regions and NBM after drug exposures. NGF protein was also measured by an enzyme-linked ImmunoSorbent assay (ELISA) in rat sensorimotor cortex. The results indicated that HAL (but not RISP or CLOZ) significantly reduced NGF levels in some sub-cortical regions and ChAT immunoreactivity in both cortex and NBM. However, pre-treatment with CLOZ prevented the HAL-associated decreases in NGF and ChAT, while post-treatment with either RISP or CLOZ (i.e., after the administration of HAL) appeared to restore NGF and ChAT to control levels. These data indicate that antipsychotic drugs exert dissimilar effects on the levels of NGF and ChAT in the brain, which may contribute to their differential effects on cognitive function. The crossover data further suggest that certain atypical antipsychotic drugs (e.g., clozapine) may have the potential to prevent or reverse the deleterious effects of HAL on important neurochemical substrates of cognitive function.

Neurotrophic factors and CNS disorders: findings in rodent models of depression and schizophrenia

Nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) are proteins involved in neuronal survival and plasticity of dopaminergic, cholinergic and serotonergic neurons in the central nervous system (CNS). Loss of neurons in specific brain regions has been found in depression and schizophrenia, and this chapter summarizes the findings of altered neurotrophins in animal models of those two disorders under baseline condition and following antidepressive and antipsychotic treatments. In a model of depression (Flinders sensitive line/Flinders resistant line; FSL/FRL rats), increased NGF and BDNF concentrations were found in frontal cortex of female, and in occipital cortex of male 'depressed' FSL compared to FRL control rats. Using the same model, the effects of electroconvulsive stimuli (ECS) and chronic lithium treatment on brain NGF, BDNF and glial cell line-derived neurotrophic factors were investigated. ECS and lithium altered the brain concentrations of neurotrophic factors in the hippocampus, frontal cortex, occipital cortex and striatum. ECS mimic the effects of electroconvulsive therapy (ECT) that is an effective treatment for depression and also schizophrenia. Since NGF and BDNF may also be changed in the CNS of animal models of schizophrenia, we investigated whether treatment with antipsychotic drugs (haloperidol, risperidone, and olanzapine) affects the constitutive levels of NGF and BDNF in the CNS. Both typical and atypical antipsychotic drugs altered the regional brain levels of NGF and BDNF. Other studies also demonstrated that these drugs differentially altered neurotrophin mRNAs. Overall, these studies indicate that alteration of brain level of NGF and BDNF could constitute part of the biochemical alterations induced by antipsychotic drugs.

Haloperidol blocks the acquisition but not the retrieval of a conditioned sensitization to apomorphine

The dopamine agonist apomorphine (apo) elicits stereotyped pecking bouts in pigeons, a response which increases with successive apo injections. The present study sought, first, to confirm the hypothesis that this sensitization arises through a Pavlovian conditioning driven by both external and internal cues; and, secondly, to advance the hypothesis that during this learning the dopaminergic activation only initiates a process that probably ends in glutamatergic synapse modifications. The conditioned nature of the sensitization to apo was examined in two separate experiments that compared context contingent and context uncontingent apo treatments. The role of dopaminergic mechanisms in the acquisition, maintenance and retrieval of sensitization-conditioned pecking was examined by administering the dopamine antagonist haloperidol (hal) either before, during or after apo sensitization treatments. A contingency between context and apo was found to be essential for the acquisition and retrieval of apo-sensitized pecking. A pretreatment with hal did not curtail a subsequent sensitization to apo. When hal was co-administrated with apo it suppressed the initial pecking response to apo and blocked the acquisition of sensitized responding. A pecking response normally observed when apo-sensitized pigeons are challenged with saline (sal) in the same cage in which they were sensitized, was also absent. When hal was co-administered with apo after the sensitization was complete this led at first to an only partial apo response suppression. When treated with hal in the same cage, already sensitized pigeons responded much as if they had been challenged with sal. The sensitization induced by apo was thus blocked by hal co-administered during acquisition, but during the maintenance or retrieval phase hal did not impair a previously sensitized responding. It is concluded that when pigeons are sensitized to apo, dopaminergic mechanisms are implicated in initiating the neural modifications that underlie the conditioned sensitization, but that they themselves are not importantly altered.

Nerve growth factor in never-medicated first-episode psychotic and medicated chronic schizophrenic patients: possible implications for treatment outcome

Nerve growth factor (NGF) has been found to play a crucial role in the neuroplasticity of predominantly cholinergic neurons in brain development, and neuronal survival following brain injury, which reflect in cognitive performance. Wide ranges of neurodevelopmental abnormalities have been reported in schizophrenic patients, who also show poor cognitive performance. We report plasma NGF levels in never-medicated first-episode psychotic (FEP; N=24) and chronic medicated schizophrenic patients (N=24). NGF levels were determined in plasma by Enzyme-Linked ImmunoSorbent Assay (ELISA). Plasma NGF levels were significantly lower in both FEP and medicated chronic patients as compared to normal subjects (P<0.001). However, NGF levels were significantly higher in chronic schizophrenic patients, which were treated with antipsychotics as compared to FEP (P<0.05). Moreover, NGF levels in chronic patients treated with atypical antipsychotics were markedly higher as compared to patients treated with typical antipsychotics (P<0.05). Lower NGF levels in FEP patients at the onset of psychosis may have implications for the neurodevelopmental abnormalities. However, higher NGF levels in chronic patients treated with atypical antipsychotics may have implications for the treatment outcome.

Nerve growth factor levels in Parkinson disease and experimental parkinsonian rats

Nerve growth factor (NGF) is well established for its ability to promote growth and survival for specific neuronal populations. However, its participation in the pathogenesis of human nervous system disorders such as Parkinson's disease (PD) remains to be resolved. This study examined NGF levels in the serum of healthy persons, in patients with PD and in parkinsonian rats using a double site immune-enzymatic assay (EIA) with the murine 27/21 anti-beta-NGF monoclonal antibody. PD patients were divided in two groups according to the stages of the disease (Grade: I-II and Grade: III-IV of Hoenh and Yahr scale). NGF levels in parkinsonian rats showed significant (P<0.01) reductions when compared with serum from normal animals. The NGF levels in early states of the disease (Grade I-II) showed greater reductions (P<0.01) in comparison to those with advanced stages (Grade III-IV). We consider that alterations in NGF levels may reflect ongoing neurodegenerative processes in PD.

Stress and nerve growth factor: findings in animal models and humans

Stress is elicited by environmental, social or pathological conditions occurring during the life of animals and humans that determine changes in the nervous, endocrine and immune systems. In the present review, we present data supporting the hypothesis that stress-related events both in animal models and humans are characterized by modifications of endogenous nerve growth factor (NGF) synthesis and/or utilization. Stress inducing alteration in NGF synthesis and/or utilization appears to be more severe during neurogenesis and in early postnatal life. However, NGF endogenously released during stress may promote remodeling of damaged tissues following acute and/or chronic stressful events.

Prenatal exposure to methylazoxymethanol acetate in the rat alters neurotrophin levels and behavior: considerations for neurodevelopmental diseases

We did a single injection of methylazoxymethanol acetate (MAM) in pregnant rats on gestational day (GD) 11 or 12 to investigate the long-lasting effects of early entorhinal cortex (EC) and hippocampus maldevelopment on behavior, brain nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) levels, and the neurotrophin receptor p75 and choline acetyltransferase (ChAT) immunoreactivity. Adult animals treated with MAM had compromised EC development and showed changes in locomotion and displacement activities. In addition, rats treated on GD 12 had increased concentration of NGF and BDNF in the EC and hippocampus if compared to control rats. Prenatal MAM administration did not affect significantly p75 and ChAT distribution in the EC and septum. Results are discussed in reference to the neurodevelopmental hypothesis of psychiatric disorders.

Data and hypotheses on the role of nerve growth factor and other neurotrophins in psychiatric disorders

Nerve growth factor (NGF) was discovered and characterized for its role on the growth, differentiation and maintenance of specific neurons of the peripheral nervous system. Subsequent studies revealed that NGF is synthesized and released within the central nervous system and exerts a trophic and functional role on basal forebrain cholinergic neurons; it is involved in a protective role following brain insults induced by an epileptic status, seizure, as well as surgical and chemical lesions.More recently our collaborative studies provided evidence that NGF is implicated in neurobehavioral response including cerebral alterations associated with psychiatric disorders. In this brief review, ongoing and emerging data are presented and discussed.

Brain-derived neurotrophic factor and tyrosine kinase receptor TrkB in rat brain are significantly altered after haloperidol and risperidone administration

The antipsychotics haloperidol and risperidone are widely used in the therapy of schizophrenia. The former drug mainly acts on the dopamine (DA) D(2) receptor whereas risperidone binds to both DA and serotonin (5HT) receptors, particularly in the neurons of striatal and limbic structures. Recent evidence suggests that neurotrophins might also be involved in antipsychotic action in the central nervous system (CNS). We have previously reported that haloperidol and risperidone significantly affect brain nerve growth factor (NGF) level suggesting that these drugs influence the turnover of endogenous growth factors. Brain-derived neurotrophic factor (BDNF) supports survival and differentiation of developing and mature brain DA neurons. We hypothesized that treatments with haloperidol or risperidone will affect synthesis/release of brain BDNF and tested this hypothesis by measuring BDNF and TrkB in rat brain regions after a 29-day-treatment with haloperidol or risperidone added to chow. Drug treatments had no effects on weight of brain regions. Chronic administration of these drugs, however, altered BDNF synthesis or release and expression of TrkB-immunoreactivity within the brain. Both haloperidol and risperidone significantly decreased BDNF concentrations in frontal cortex, occipital cortex and hippocampus and decreased or increased TrkB receptors in selected brain structures. Because BDNF can act on a variety of CNS neurons, it is reasonable to hypothesize that alteration of brain level of this neurotrophin could constitute one of the mechanisms of action of antipsychotic drugs. These observations also support the possibility that neurotrophic factors play a role in altered brain function in schizophrenic disorders.

Studies in animal models and humans suggesting a role of nerve growth factor in schizophrenia-like disorders

Neurotrophic factors, such as nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF), are known to play a crucial role in growth, differentiation and function in a variety of brain neurons during development and in adult life. We have recently shown that environmental changes, aggressive behavior and anxiety-like responses alter both circulating and brain basal NGF levels. In the present review, we present data obtained using animal models which suggest that neurotrophic factors, particularly NGF and BDNF, might be implicated in mechanism(s) leading to a condition associated with schizophrenic-like behaviors. The hypothesis that neurotrophins of the NGF family can be implicated in some maldevelopmental aspects of schizophrenia is supported by findings indicating that the constitutive levels of NGF and BDNF are affected in schizophrenic patients.

Learning abilities, NGF and BDNF brain levels in two lines of TNF-alpha transgenic mice, one characterized by neurological disorders, the other phenotypically normal

In this study we used two lines of transgenic mice overexpressing tumor necrosis factor alpha (TNF-alpha) in the central nervous system (CNS), one characterized by reactive gliosis, inflammatory demyelination and neurological deficits (Tg6074) the other showing no neurological or phenotypical alterations (TgK3) to investigate the effect of TNF-alpha on brain nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) levels and learning abilities. The results showed that the amount of NGF in the brain of Tg6074 and TgK3 transgenic mice is low in the hippocampus and in the spinal cord, increases in the hypothalamus of Tg6074 and showed no significant changes in the cortex. BDNF levels were low in the hippocampus and spinal cord of TgK3. BDNF increased in the hypothalamus of TgK3 and Tg6074 while in the cortex, BDNF increased only in Tg6074 mice. Transgenic mice also had memory impairments as revealed by the Morris Water Maze test. These findings indicate that TNF-alpha significantly influences BDNF and NGF synthesis, most probably in a dose-dependent manner. Learning abilities were also differently affected by overexpression of TNF-alpha, but were not associated with inflammatory activity. The possible functional implications of our findings are discussed.

Prenatal methylazoxymethanol acetate alters behavior and brain NGF levels in young rats: a possible correlation with the development of schizophrenia-like deficits

It has been hypothesized that a deleterious key contribution to schizophrenia (SZ) development is a failure of migration and setting of young neurons into their appropriate cortical target sites, particularly in the entorhinal cortex (EC). To test this hypothesis in an animal model, we injected, in pregnant rats, on gestational day (GD) 9, or 10, or 11, or 12, the antimitotic compound methylazoxymethanolacetate (MAM) known to cause EC neuronal loss. We investigated whether or not EC disruption during prenatal development is able to affect behavior, including memory and learning, and brain nerve growth factor (NGF). Prenatally MAM treated young rats didn't display gross behavioral changes in social interaction, open-field and novel object investigation tests. By contrast, GD11 and GD12 MAM treated rats had a retardation in passive avoidance acquisition, while, in GD12 animals, pain sensitivity was reduced. GD12 animals also showed increased NGF in the EC and remaining cortex. MAM treated animals showed no changes in paw NGF or substance P levels suggesting that the altered nociceptive response is not related to local downregulation of these two molecules. The possibility that these behavioral and biochemical alterations might be associated with the onset of SZ is discussed.

TNF-alpha expressed in the brain of transgenic mice lowers central tyroxine hydroxylase immunoreactivity and alters grooming behavior

Tumor necrosis factor-alpha (TNF-alpha) is a cytokine involved in a wide range of biological effects both in physiological and non-physiological conditions. It is also produced in the central nervous system (CNS) where it has been implicated in reparative processes after traumatic injuries and in CNS demyelination, neurodegeneration and inflammation. Using transgenic mice (Tg-m) expressing TNF-alpha specifically in the CNS, we showed that the overexpression of this cytokine reduced tyroxine hydroxylase immunoreactivity (TH-ir) in the caudate-putamen and in the dorsomedial hypothalamic areas and impaired grooming behavior. We also showed that this behavior is increased following anti-nerve growth factor injection. These findings support the hypothesis, proposed by others, that TNF-alpha is involved in the degenerative processes which occur in Parkinson's disease.

The expanding role of nerve growth factor: from neurotrophic activity to immunologic diseases

Numerous studies published in the last 10-15 years have shown that nerve growth factor (NGF), a polypeptide originally discovered in connection with its neurotrophic activity, also acts on cells of the immune system. NGF has been found in various immune organs including the spleen, lymph nodes, and thymus, and cells such as mast cells, eosinophils, and B and T cells. The circulating levels of NGF increase in inflammatory responses, in various autoimmune diseases, in parasitic infections, and in allergic diseases. Stress-related events both in animal models and in man also result in an increase of NGF, suggesting that this molecule is involved in neuroendocrine functions. The rapid release of NGF is part of an alerting signal in response to either psychologically stressful or anxiogenic conditions in response to homeostatic alteration. Thus, the inflammation and stress-induced increase in NGF might alone or in association with other biologic mediators induce the activation of immune cells during immunologic insults. A clearer understanding of the role of NGF in these events may be useful to identify the mechanisms implicated in certain neuroimmune and immune dysfunctions.