NGF but not GDNF or neurturin enhance acetylcholine tissue levels in striatal organotypic brain slices

Compulsive methamphetamine taking and abstinence in the presence of adverse consequences: Epigenetic and transcriptional consequences in the rat brain

Methamphetamine addiction is characterized by compulsive binges of drug intake despite adverse life consequences. A model of methamphetamine self-administration that includes contingent footshocks to constitute adverse consequences has helped to segregate rats that reduce or stop lever pressing for methamphetamine (sensitive) from those that continue to lever press for the drug (resistant) in the presence of negative outcomes. We have observed differential DNA hydroxymethylation and increased expression of potassium channel mRNAs in the nucleus accumbens of sensitive compared to resistant rats, suggesting a role of these channels in suppressing methamphetamine intake. There were also significant increases in nerve growth factor (NGF) expression and activation of its downstream signaling pathway (NGF-TrkA and p75NTR/MAPK signaling) in only the dorsal striatum of sensitive rats after a month of abstinence. In contrast, oxytocin mRNA expression was increased in only the nucleus accumbens of resistant rats compared to sensitive rats euthanized after that time. These results indicate that footshocks can differentiate two behavioral phenotypes with differential biochemical and epigenetic consequences in the ventral and dorsal striatum.

3D Organotypic Spinal Cultures: Exploring Neuron and Neuroglia Responses Upon Prolonged Exposure to Graphene Oxide

Graphene-based nanomaterials are increasingly engineered as components of biosensors, interfaces or drug delivery platforms in neuro-repair strategies. In these developments, the mostly used derivative of graphene is graphene oxide (GO). To tailor the safe development of GO nanosheets, we need to model in vitro tissue responses, and in particular the reactivity of microglia, a sub-population of neuroglia that acts as the first active immune response, when challenged by GO. Here, we investigated central nervous system (CNS) tissue reactivity upon long-term exposure to GO nanosheets in 3D culture models. We used the mouse organotypic spinal cord cultures, ideally suited for studying long-term interference with cues delivered at controlled times and concentrations. In cultured spinal segments, the normal presence, distribution and maturation of anatomically distinct classes of neurons and resident neuroglial cells are preserved. Organotypic explants were developed for 2 weeks embedded in fibrin glue alone or presenting GO nanosheets at 10, 25 and 50 μg/mL. We addressed the impact of such treatments on premotor synaptic activity monitored by patch clamp recordings of ventral interneurons. We investigated by immunofluorescence and confocal microscopy the accompanying glial responses to GO exposure, focusing on resident microglia, tested in organotypic spinal slices and in isolated neuroglia cultures. Our results suggest that microglia reactivity to accumulation of GO flakes, maybe due to active phagocytosis, may trim down synaptic activity, although in the absence of an effective activation of inflammatory response and in the absence of neuronal cell death.

Selective Activation of Striatal NGF-TrkA/p75NTR/MAPK Intracellular Signaling in Rats That Show Suppression of Methamphetamine Intake 30 Days following Drug Abstinence

BACKGROUND

The continuing epidemic of methamphetamine addiction has prompted research aimed at understanding striatal dysfunctions potentially associated with long-term methamphetamine use.

METHODS

Here, we investigated transcriptional and translational alterations in the expression of neurotrophic factors in the rat striatum at 30 days following methamphetamine self-administration and footshock punishment. Male Sprague-Dawley rats were trained to self-administer methamphetamine (0.1 mg/kg/injection, i.v.) or saline during twenty-two 9-hour sessions. Subsequently, rats were subjected to incremental footshocks for 13 additional methamphetamine self-administration sessions. This paradigm led to the identification of rats with shock-resistant and shock-sensitive phenotypes. Thirty days following the last footshock session, the dorsal striatum was dissected and processed for gene expression and protein analyses.

RESULTS

PCR arrays revealed significant differences in neurotrophins and their receptors between the 2 phenotypes. Brain-derived neurotrophic factor and nerve growth factor protein levels were increased in the dorsal striatum of both shock-resistant and shock-sensitive rats. However, neurotrophic receptor tyrosine kinase 1 phosphorylation and nerve growth factor receptor protein expression were increased only in the shock-sensitive phenotype. Moreover, shock-sensitive rats showed increased abundance of several phosphorylated proteins known to participate in Ras/Raf/MEK/ERK signaling cascade including cRaf, ERK1/2, MSK1, and CREB.

CONCLUSIONS

These findings support the notion that animals with distinct phenotypes for methamphetamine intake in the presence of adverse consequences also display differential changes in an intracellular signaling cascade activated by nerve growth factor-TrkA/p75NTR interactions. Thus, the development of pharmacological agents that can activate nerve growth factor-dependent pathways may be a promising therapeutic approach to combat methamphetamine addiction.

Differential effects of short- and long-term hyperhomocysteinaemia on cholinergic neurons, spatial memory and microbleedings in vivo in rats

Hyperhomocysteinaemia (HHcy) has been identified as a cardiovascular risk factor for neurodegenerative brain diseases. The aim of the present study was to investigate the effects of short (5 months) or long (15 months) HHcy in Sprague–Dawley rats in vivo. Short- and long-term HHcy differentially affected spatial memory as tested in a partially baited eight-arm radial maze. HHcy significantly reduced the number of choline acetyltransferase (ChAT)-positive neurons in the basal nucleus of Meynert and ChAT-positive axons in the cortex only after short-term but not long-term treatment, while acetylcholine levels in the cortex were decreased at both time points. Nerve growth factor (NGF) was significantly enhanced in the cortex only after 15 months of HHcy. HHcy did not affect cortical levels of amyloid precursor protein, beta-amyloid(1-42), tau and phospho-tau181 and several inflammatory markers, as well as vascular RECA-1 and laminin density. However, HHcy induced cortical microbleedings, as illustrated by intensive anti-rat IgG-positive spots in the cortex. In order to study the regulation of the key enzyme ChAT, organotypic rat brain slices were incubated with homocysteine, which induced a decline of ChAT that was counteracted by NGF treatment. In conclusion, our data demonstrate that chronic short- and long-term HHcy differentially caused memory impairment, cholinergic dysfunction, NGF expression and vascular microbleedings.

Hypercholesterolemia in rats impairs the cholinergic system and leads to memory deficits

Alzheimer's disease (AD) is a chronic brain disorder characterized by cognitive impairment, cholinergic dysfunction, inflammation, tau and beta-amyloid pathology and vascular damage. Recent studies have shown, that high cholesterol levels are linked to the pathology of AD. The aim of our present work was to study the effects of hypercholesterolemia in adult rats. Five months after 5% cholesterol-enriched diet plasma cholesterol levels and total weight were significantly enhanced compared to controls. Spatial memory was studied in an 8-arm radial maze and cholesterol-treated rats showed an impaired learning and long-term memory. Hypercholesterolemia significantly reduced the number of cholinergic neurons in the basal nucleus of Meynert and decreased acetylcholine levels in the cortex. Nerve growth factor was only slightly enhanced in the cortex of cholesterol-treated animals. Levels of amyloid precursor protein, beta-amyloid(1–42), as well as tau and phospho-tau 181 were significantly enhanced in the cortex of cholesterol-fed rats. Hypercholesterolemia markedly increased several cerebral inflammatory markers and enhanced microglial CD11b-like immunoreactivity. Vascular density, stained by RECA-1 was not changed. However, cholesterol induced cortical microbleedings illustrated by intensive anti-rat IgG-positive spots in the cortex. In conclusion, our data demonstrate that hypercholesterolemia in rats caused memory impairment, cholinergic dysfunction, inflammation, enhanced cortical beta-amyloid and tau and microbleedings, all indications, which resemble an AD-like pathology.

Differential effects of phencyclidine application on secretogranin II expression in organotypic slices of rat prefrontal cortex

Phencyclidine (PCP) is a non-competitive NMDA glutamate receptor antagonist that induces psychotomimetic effects in humans and experimental animals. Chronic PCP exposure elicits signs of persistently altered frontal brain activity and related behaviors which are also seen in patients with schizophrenia. Secretogranin II (sg II) belongs to the chromogranin family of proteins that exist in large dense core vesicles in nervous tissue. In the brain, 90% of sg II is processed to the small peptide secretoneurin. We previously detected differential effects of single-dose and subchronic PCP administration on sg II expression in the rat prefrontal cortex (PFC). In the present study, we applied PCP to organotypic PFC slices. PCP application for 28 h induced decreased tissue and culture medium secretoneurin content. In contrast, incubation with the adenylate cyclase activator forskolin caused significantly increased secretoneurin levels after 8 h. PCP for 4 h followed by 24 h without PCP resulted in increased culture medium secretoneurin content but no change in tissue levels. sg II mRNA expression was decreased after 28 h PCP application in cortical neurons. Immunohistochemical and TUNEL staining profiles indicated that the alterations were not due to neurodegeneration. PCP for 5 days changed neither the secretoneurin tissue or culture medium levels, nor the sg II mRNA expression. These results demonstrate that PCP modulates sg II expression in PFC tissue in the absence of afferent inputs and that the nature of these changes is dependent upon the duration of exposure to and/or withdrawal from PCP.

Nerve growth factor and cholinergic CNS neurons studied in organotypic brain slices. Implication in Alzheimer's disease?

Nerve growth factor (NGF) is a potent growth factor for cholinergic neurons. The aim of the present study was to investigate if NGF affects cholinergic neurons of the basal nucleus of Meynert (nBM) in organotypic brain slices. In single nBM slices cholinergic neurons rapidly degenerated when incubated without NGF. The number of remaining neurons was rescued by NGF application at any time point. When nBM slices were co-cultured with a cortex slice the number of cholinergic neurons was significantly increased pointing to a trophic influence of the cortex. Incubation with acetylcholine precursors did not affect the survival of cholinergic neurons. There was no significant difference when postnatal day 3 or day 10 nBM slices were cultured. In conclusion, NGF is the most potent growth factor for cholinergic neurons and is a promising candidate for treating Alzheimers disease, however, the delivery of NGF to the brain must the solved.

Nestin expression persists in astrocytes of organotypic slice cultures from rat cortex

Nestin is an intermediate filament protein typical for neural precursor cells that is down-regulated in the post-natal rodent brain. Re-expression of nestin has been observed in reactive astrocytes after injury. In this study, organotypic slice cultures from rat cortex were examined for expression of nestin and glial fibrillary acidic protein between 2 and 8 weeks in culture. Immunoreactivity for nestin and glial fibrillary acidic protein was seen in astrocytes which persisted throughout the observation period. Immunofluorescence double labeling showed widespread co-localization of nestin and glial fibrillary acidic protein. Image analysis revealed that levels of nestin-immunoreactivity plateaued after 5 weeks in culture. By comparison nestin immunoreactivity was absent from glial cells of the cortex in mature rats. These immunohistochemical findings of a persistent expression of nestin in glial cells of organotypic slice culture of the rat cortex indicate a different time course of glial maturation in vitro. This difference could be related to the altered trophic stimulation in vitro; differences in neuronal maturation, activity or survival; slow degeneration of the vasculature; or intrinsic properties of astrocytes.

Nerve growth factor and glial cell line-derived neurotrophic factor restore the cholinergic neuronal phenotype in organotypic brain slices of the basal nucleus of Meynert

Loss of cholinergic neurons is found in the medial septum and nucleus basalis of Meynert in Alzheimer's disease. Recent observations suggest that cholinergic neurons down-regulate their phenotype and that growth factors may rescue cholinergic neurons. The aim of this study was to investigate whether cholinergic neurons of the basal nucleus of Meynert can be cultured in rat organotypic slices, and if nerve growth factor and glial cell line-derived neurotrophic factor can rescue the cholinergic phenotype. In the organotypic slices, glial cells, GABAergic and cholinergic neurons were visualized using immunohistochemistry. The number of cholinergic neurons was found to be very low in slices cultured without exogenous nerve growth factor. Analysis of nerve growth factor tissue levels by enzyme-linked immunosorbent assay revealed very low endogenous tissue levels. When slices were incubated with 100ng/ml nerve growth factor during the initial phase of culturing, a stable expression of choline acetyltransferase was found for up to several weeks. After eight weeks in culture with nerve growth factor or two to three weeks after nerve growth factor withdrawal, numbers of detected cholinergic neurons decreased. Neurons incubated with nerve growth factor displayed a significantly enlarged cell soma compared to neurons without growth factors. In cultures incubated for up to nine weeks, it was also found that glial cell line-derived neurotrophic factor was capable of restoring the cholinergic phenotype. The low-affinity p75 and high-affinity trkA receptors, as well as the glial cell line-derived neurotrophic factor receptor GFRalpha-1, could be visualized in slices using immunohistochemistry. In conclusion, it is shown that, in the axotomized organotypic slice model, the number of cholinergic neurons is decreased, but can be partly restored by nerve growth factor and glial cell line-derived neurotrophic factor.

Striatal preprotachykinin mRNA levels are regulated by stimulatory agents and dopamine D1 receptor manipulation in rodent organotypic slice cultures

We have utilized an organotypic slice culture system to determine factors which directly influence the expression of striatal preprotachykinin (PPT) mRNA. Striatal slices were generated from 3-day-old male rat pups and cultured on Millicell-CM inserts in serum-containing media. Under these conditions, striatal PPT mRNA levels fell significantly (-55.7+/-6.2%) in slices cultured for 2 days in vitro (2DIV) as compared to slices placed in culture for 3 h (0DIV). However, striatal PPT mRNA expression did not decline further in 4DIV cultured slices (-59.6+/-7.1%). When 2DIV slices were exposed to combined high potassium (K(+), 10 mM) and forskolin (10 microM) stimulation for 3 h, PPT mRNA levels were increased within areas of the brain normally associated with tachykinin production. Application of the dopamine (DA) D1 receptor agonist SKF-38393 (10 microM) at 2DIV for 3 h also increased (+162.9+/-28.9%) PPT mRNA expression, but increases were localized within the striatum. SKF-38393-stimulated increases were completely blocked by the D1 antagonist SCH-23390 (10 microM), which alone had no effect on mRNA levels. However, a 3-h incubation with SKF-38393 on 0DIV slice cultures did not affect PPT mRNA expression whereas SCH-23390 decreased PPT message levels (-24.5+/-5.4%). These findings indicate that tachykinin gene expression is inducible within slice culture preparations and that the maintenance of normal striatal PPT mRNA levels depends on DA D1 receptor tone.

Glial cell line-derived neurotrophic factor (GDNF) is a proliferation factor for rat C6 glioma cells: evidence from antisense experiments

Growth factors play an important role in proliferation and differentiation of malignant brain gliomas in humans. Glial cell line-derived neurotrophic factor (GDNF) has been shown recently to be highly expressed in human glioblastomas and in rat glial cell lines B49 and C6. The aim of the present study was to knockdown GDNF, its receptor GFR-alpha1, and the related family member persephin by using antisense oligonucleotides and to observe the effects on cell proliferation. To enhance cellular uptake into C6 glioma cells, 15-mer phosphorothioate oligonucleotides were complexed with the cationic lipid Lipofectamine. The complex was applied for 3 x 12 hours to C6 glioma cells, and cells were allowed to recover for 24 hours after each transfection and then analyzed. This protocol markedly reduced GDNF and GFR-alpha1 protein levels in C6 glioma cells compared with control oligonucleotides. Knockdown of C6 cells with GDNF and GFR-alpha1 but not with persephin antisense oligonucleotides significantly decreased the number of C6 glioma cells and also inhibited the incorporation of bromodeoxyuridine as a sign of reduced DNA synthesis. In conclusion, it is shown that GDNF but not persephin is a potent proliferation factor for rat glioma cells. Knockdown of GDNF using antisense oligonucleotides complexed with lipids as carriers may be useful in gene therapeutic approaches in vitro and possibly also in vivo.

Chronic repetitive transcranial magnetic stimulation enhances c-fos in the parietal cortex and hippocampus

Repetitive transcranial magnetic stimulation (rTMS) is a novel non-invasive method with anti-depressant properties. However, the mechanism of activation on the cellular level is unknown. Twelve hours after the last chronic rTMS treatment (14 days, once per day, 20 Hz, 10 s, 75% machine output, the transcription factor c-fos was markedly increased in neurons in layers I-IV and VI of the parietal cortex and in few scattered neurons in the hippocampus of Sprague-Dawley rats. The cortical activation was not blocked by the NMDA antagonist MK-801. The increase of c-fos was not paralleled by an increased glial response and activation of cortical growth factors. Thus, it is concluded that chronic rTMS differentially activates parietal cortical layers and this might be involved in mediating anti-depressant activity in other brain areas.

The effect of streptozotocin-induced diabetes mellitus on substance P and calcitonin gene-related peptide expression in the rat trigeminal ganglion

Substance P (SP) and calcitonin gene-related peptide (CGRP) constitute the main sensory peptides in the trigeminal ganglion (TG). The objective of this study was to characterize peptidergic changes in the streptozotocin-induced diabetes mellitus rat model both quantitatively and qualitatively. Diabetes mellitus was induced by a single intraperitoneal injection of streptozotocin (65 mg/kg) and the levels of SP and CGRP were measured by means of radioimmunoassay (RIA) in a time-dependent manner. Peptide immunoreactivities were characterized by high pressure liquid chromatography (HPLC). The expression of both neuropeptides was examined 5 weeks after streptozotocin injection using in situ hybridization with 35S-labelled oligonucleotides. Saline-injected rats served as controls. SP was significantly decreased in the diabetic rat TG, i.e. , a 44.6% (+/-10.9) decrease after 1 week, 40.2% (+/-11.8) after 3 weeks and 72.3% (+/-14.6) after 5 weeks. CGRP was decreased only after 5 weeks (19.6% decrease +/-3.9), whereas at later stages, both peptide levels returned to normal values. HPLC revealed one major peak coeluting with the synthetic peptides. By using in situ hybridization, a significantly increased signal of both peptide-encoding mRNAs was found (43.8%), which seems to act to restore a diabetes-associated depletion of neuropeptides in the diabetic rat TG. The decreased SP- and CGRP levels in the diabetic rat TG reflect a diabetes-associated deficit which may be clinically relevant. Diabetes mellitus is associated with a variety of ocular complications, even corneal complications, including decreased corneal sensitivity, which in many ways resemble those after interruption of the normal trophic innervation of the eye. Our results point to reduced availability of neuropeptides for corneal innervation and may thus support the idea of a partial loss of trophic influences from the trigeminal nerve in diabetics.