Tissue magnetic susceptibility mapping as a marker of tau pathology in Alzheimer's disease.

Alzheimer's disease is connected to a number of other neurodegenerative conditions, known collectively as 'tauopathies', by the presence of aggregated tau protein in the brain. Neuroinflammation and oxidative stress in AD are associated with tau pathology and both the breakdown of axonal sheaths in white matter tracts and excess iron accumulation grey matter brain regions. Despite the identification of myelin and iron concentration as major sources of contrast in quantitative susceptibility maps of the brain, the sensitivity of this technique to tau pathology has yet to be explored. In this study, we perform Quantitative Susceptibility Mapping (QSM) and T2* mapping in the rTg4510, a mouse model of tauopathy, both in vivo and ex vivo. Significant correlations were observed between histological measures of myelin content and both mean regional magnetic susceptibility and T2* values. These results suggest that magnetic susceptibility is sensitive to tissue myelin concentrations across different regions of the brain. Differences in magnetic susceptibility were detected in the corpus callosum, striatum, hippocampus and thalamus of the rTg4510 mice relative to wild type controls. The concentration of neurofibrillary tangles was found to be low to intermediate in these brain regions indicating that QSM may be a useful biomarker for early stage detection of tau pathology in neurodegenerative diseases.

Application of neurite orientation dispersion and density imaging (NODDI) to a tau pathology model of Alzheimer's disease.

Increased hyperphosphorylated tau and the formation of intracellular neurofibrillary tangles are associated with the loss of neurons and cognitive decline in Alzheimer's disease, and related neurodegenerative conditions. We applied two diffusion models, diffusion tensor imaging (DTI) and neurite orientation dispersion and density imaging (NODDI), to in vivo diffusion magnetic resonance images (dMRI) of a mouse model of human tauopathy (rTg4510) at 8.5months of age. In grey matter regions with the highest degree of tau burden, microstructural indices provided by both NODDI and DTI discriminated the rTg4510 (TG) animals from wild type (WT) controls; however only the neurite density index (NDI) (the volume fraction that comprises axons or dendrites) from the NODDI model correlated with the histological measurements of the levels of hyperphosphorylated tau protein. Reductions in diffusion directionality were observed when implementing both models in the white matter region of the corpus callosum, with lower fractional anisotropy (DTI) and higher orientation dispersion (NODDI) observed in the TG animals. In comparison to DTI, histological measures of tau pathology were more closely correlated with NODDI parameters in this region. This in vivo dMRI study demonstrates that NODDI identifies potential tissue sources contributing to DTI indices and NODDI may provide greater specificity to pathology in Alzheimer's disease.

In vivo imaging of tau pathology using multi-parametric quantitative MRI.

As the number of people diagnosed with Alzheimer's disease (AD) reaches epidemic proportions, there is an urgent need to develop effective treatment strategies to tackle the social and economic costs of this fatal condition. Dozens of candidate therapeutics are currently being tested in clinical trials, and compounds targeting the aberrant accumulation of tau proteins into neurofibrillary tangles (NFTs) are the focus of substantial current interest. Reliable, translatable biomarkers sensitive to both tau pathology and its modulation by treatment along with animal models that faithfully reflect aspects of the human disease are urgently required. Magnetic resonance imaging (MRI) is well established as a valuable tool for monitoring the structural brain changes that accompany AD progression. However the descent into dementia is not defined by macroscopic brain matter loss alone: non-invasive imaging measurements sensitive to protein accumulation, white matter integrity and cerebral haemodynamics probe distinct aspects of AD pathophysiology and may serve as superior biomarkers for assessing drug efficacy. Here we employ a multi-parametric array of five translatable MRI techniques to characterise the in vivo pathophysiological phenotype of the rTg4510 mouse model of tauopathy (structural imaging, diffusion tensor imaging (DTI), arterial spin labelling (ASL), chemical exchange saturation transfer (CEST) and glucose CEST). Tau-induced pathological changes included grey matter atrophy, increased radial diffusivity in the white matter, decreased amide proton transfer and hyperperfusion. We demonstrate that the above markers unambiguously discriminate between the transgenic group and age-matched controls and provide a comprehensive profile of the multifaceted neuropathological processes underlying the rTg4510 model. Furthermore, we show that ASL and DTI techniques offer heightened sensitivity to processes believed to precede detectable structural changes and, as such, provides a platform for the study of disease mechanisms and therapeutic intervention.

Gene silencing of TNF-alpha in a murine model of acute colitis using a modified cyclodextrin delivery system.

Inflammatory bowel disease (IBD) is a chronic relapsing inflammation of the gastrointestinal tract. The cytokine TNF-alpha (TNF-α) plays a pivotal role in mediating this inflammatory response. RNA interference (RNAi) holds great promise for the specific and selective silencing of aberrantly expressed genes, such as TNF-α in IBD. The aim of this study was to investigate the efficacy of an amphiphilic cationic cyclodextrin (CD) vector for effective TNF-α siRNA delivery to macrophage cells and to mice with induced acute-colitis. The stability of CD.siRNA was examined by gel electrophoresis in biorelevant media reflecting colonic fluids. RAW264.7 cells were transfected with CD.TNF-α siRNA, stimulated with lipopolysaccharide (LPS) and TNF-α and IL-6 responses were measured by PCR and ELISA. Female C57BL/6 mice were exposed to dextran sodium sulphate (DSS) and treated by intrarectal administration with either CD.siRNA TNF-α or a control solution. In vitro, siRNA in CD nanocomplexes remained intact and stable in both fed and fasted simulated colonic fluids. RAW264.7 cells transfected with CD.TNF-α siRNA and stimulated with LPS displayed a significant reduction in both gene and protein levels of TNF-α and IL-6. CD.TNF-α siRNA-treated mice revealed a mild amelioration in clinical signs of colitis, but significant reductions in total colon weight and colonic mRNA expression of TNF-α and IL-6 compared to DSS-control mice were detected. This data indicates the clinical potential of a local CD-based TNF-α siRNA delivery system for the treatment of IBD.

Differential effects of NMDA antagonists on high frequency and gamma EEG oscillations in a neurodevelopmental model of schizophrenia.

Neuroanatomical, electrophysiological and behavioural abnormalities following timed prenatal methylazoxymethanol acetate (MAM) treatment in rats model changes observed in schizophrenia. In particular, MAM treatment on gestational day 17 (E17) preferentially disrupts limbic-cortical circuits, and is a promising animal model of schizophrenia. The hypersensitivity of this model to the NMDA receptor antagonist-induced hyperactivity has been proposed to mimic the increase in sensitivity observed in schizophrenia patients following PCP and Ketamine administration. However, how this increase in sensitivity in both patients and animals translates to differences in EEG oscillatory activity is unknown. In this study we have shown that MAM-E17 treated animals have an increased response to the hyperlocomotor and wake promoting effects of Ketamine, PCP, and MK801 but not to the competitive antagonist SDZ 220,581. These behavioural changes were accompanied by altered EEG responses to the NMDAR antagonists, most evident in the gamma and high frequency (HFO) ranges; altered sensitivity of these neuronal network oscillations in MAM-exposed rats is regionally selective, and reflects altered interneuronal function in this neurodevelopmental model.

Symptomatic and neuroprotective effects following activation of nigral group III metabotropic glutamate receptors in rodent models of Parkinson's disease.

BACKGROUND AND PURPOSE: Increased glutamatergic innervation of the substantia nigra pars reticulata (SNpr) and pars compacta (SNpc) may contribute to the motor deficits and neurodegeneration, respectively, in Parkinson's disease (PD). This study aimed to establish whether activation of pre-synaptic group III metabotropic glutamate (mGlu) receptors reduced glutamate release in the SN, and provided symptomatic or neuroprotective relief in animal models of PD. EXPERIMENTAL APPROACH: Broad-spectrum group III mGlu receptor agonists, O-phospho-l-serine (l-SOP) and l-2-amino-4-phosphonobutyrate (l-AP4), were assessed for their ability to inhibit KCl-evoked [(3)H]-d-aspartate release in rat nigral prisms or inhibit KCl-evoked endogenous glutamate release in the SNpr in vivo using microdialysis. Reversal of akinesia in reserpine-treated rats was assessed following intranigral injection of l-SOP and l-AP4. Finally, the neuroprotective effect of 7 days' supra-nigral treatment with l-AP4 was examined in 6-hydroxydopamine (6-OHDA)-lesioned rats. KEY RESULTS: l-SOP and l-AP4 inhibited [(3)H]-d-aspartate release by 33 and 44% respectively. These effects were blocked by the selective group III mGlu antagonist (RS)-alpha-cyclopropyl-4-phosphonophenylglycine (CPPG). l-SOP also reduced glutamate release in the SNpr in vivo by 48%. Injection of l-SOP and l-AP4 into the SNpr reversed reserpine-induced akinesia. Following administration above the SNpc, l-AP4 provided neurochemical, histological and functional protection against 6-OHDA lesion of the nigrostriatal tract. Pretreatment with CPPG inhibited these effects. CONCLUSIONS AND IMPLICATIONS: These findings highlight group III mGlu receptors in the SN as potential targets for providing both symptomatic and neuroprotective relief in PD, and indicate that inhibition of glutamate release in the SN may underlie these effects.

Divergent patterns of breakpoint reuse in Muroid rodents.

Multiple Genome Rearrangement (MGR) analysis was used to define the trajectory and pattern of chromosome rearrangement within muroid rodents. MGR was applied using 107 chromosome homologies between Mus, Rattus, Peromyscus, the muroid sister taxon Cricetulus griseus, and Sciurus carolinensis as a non-Muroidea outgroup, with specific attention paid to breakpoint reuse and centromere evolution. This analysis revealed a high level of chromosome breakpoint conservation between Rattus and Peromyscus and indicated that the chromosomes of Mus are highly derived. This analysis identified several conserved evolutionary breakpoints that have been reused multiple times during karyotypic evolution in rodents. Our data demonstrate a high level of reuse of breakpoints among muroid rodents, further supporting the "Fragile Breakage Model" of chromosome evolution. We provide the first analysis of rodent centromeres with respect to evolutionary breakpoints. By analyzing closely related rodent species we were able to clarify muroid rodent karyotypic evolution. We were also able to derive several high-resolution ancestral karyotypes and identify rearrangements specific to various stages of Muroidea evolution. These data were useful in further characterizing lineage-specific modes of chromosome evolution.

Induction of labour in nulliparous women with an unfavourable cervix: a randomised controlled trial comparing double and single balloon catheters and PGE2 gel.

OBJECTIVE: To compare the efficacy and patient satisfaction of three methods of labour induction (double balloon catheters, single balloon catheters and prostaglandin gel) in term nulliparous women with unfavourable cervices. DESIGN: Randomised controlled trial. POPULATION: A total of 330 nulliparous women with unfavourable cervices induced at term. METHODS: Three cervical ripening study arms were used: double balloon catheter (107 women); 16F Foley catheter (110 women) and PGE(2) gel (2 mg) (113 women). MAIN OUTCOME MEASURES: Caesarean section, induction to delivery interval, adverse reactions and patient satisfaction. RESULTS: There was no difference in caesarean delivery rates between groups (double balloon 43%, single balloon 36%, PGE(2) 37%, P = 0.567). The induction to delivery interval was longer in the double balloon group (median 24.5; 95% CI 23.7, 30.6 hours) than the single balloon (23.2; 20.8, 25.8 hours) or PGE(2) (23.8; 21.7, 26.8 hours) (P = 0.043). Uterine hyperstimulation occurred in 14% of the PGE(2) group with none occurring with mechanical cervical ripening. Cord blood gases were worse in the PGE(2) group: median arterial pH double balloon 7.26 (range 7.03-7.40); single balloon 7.26 (7.05-7.44); PGE(2) 7.25 (6.91-7.41) (P = 0.050). Cervical ripening with the single balloon catheter was associated with significantly less pain (pain score > or =4: double balloon 55%, single balloon 36%, PGE(2) 63%, P < 0.001). CONCLUSIONS: Labour induction in nullipara with unfavourable cervices results in high caesarean delivery rates. Although all methods in this study had similar efficacy, the single balloon catheter offers the best combination of safety and patient comfort.

Peromyscus maniculatus--Mus musculus chromosome homology map derived from reciprocal cross species chromosome painting.

The Mus musculus and Rattus norvegicus genomes have been extensively studied, yet despite the emergence of Peromyscus maniculatus as an NIH model for genome sequencing and biomedical research much remains unknown about the genome organization of Peromyscines. Contrary to their phylogenetic relationship, the genomes of Rattus and Peromyscus appear more similar at the gross karyotypic level than either does to Mus. We set out to define the chromosome homologies between Peromyscus, Mus and Rattus. Reciprocal cross-species chromosome painting and G-band homology assignments were used to delineate the conserved chromosome homology map between P. maniculatus and M. musculus. These data show that each species has undergone extensive chromosome rearrangements since they last shared a common ancestor 25 million years ago (mya). This analysis coupled with an inferred homology map with Rattus revealed a high level of chromosome conservation between Rattus and Peromyscus and indicated that the chromosomes of Mus are highly derived.

Acute onset by 5-HT(6)-receptor activation on rat brain brain-derived neurotrophic factor and activity-regulated cytoskeletal-associated protein mRNA expression.

A number of previous studies have shown that chronic but not acute treatment with antidepressant drugs targeting the central 5-HT system, enhances mRNA expression for a number of genes including, brain-derived neurotrophic factor (BDNF) and the effector immediate early gene (IEG), activity-regulated, cytoskeletal-associated protein (Arc). The present study investigated the effects of 5-HT(6)-receptor activation on hippocampal and cortical levels of mRNA expression of BDNF and Arc in the rat. The selective 5-HT(6)-receptor agonist LY-586713 was administered acutely (0.1-10 mg/kg, s.c.) and mRNA levels of BDNF and Arc were measured 18 h later. Administration of LY-586713 caused a bell-shaped dose response on hippocampal BDNF mRNA expression, having no effect at 0.1 mg/kg, a significant up-regulation at 1 mg/kg and no effect at 10 mg/kg. The up-regulation in BDNF expression observed at 1 mg/kg was completely blocked by pre-treatment with the selective 5-HT(6)-receptor antagonist SB-271046 (10 mg/kg, s.c.). The effective dose (1 mg/kg) of LY-586713 on the induction of BDNF expression was also tested on Arc expression. Acute administration of LY-586713 at this dose caused marked increases of the Arc mRNA levels in cortical and hippocampal regions. These increases were also attenuated by SB-271046 (10 mg/kg) in all regions of the hippocampus, as well as the parietal cortex. However, in frontal cortical regions there was no attenuation by the antagonist. Moreover, SB-271046 alone increased Arc expression in these regions. The results presented here provide the first evidence for the involvement of the 5-HT(6) receptor in regulating BDNF and Arc mRNA expression, suggesting that LY-586713 has potential effects on neuronal plasticity. Overall, these findings suggest that, as opposed to more general 5-HT receptor activation by, for example, antidepressants, direct 5-HT(6)-receptor activation results in a more rapid rise in BDNF and Arc mRNA expression which does not require repeated administration.

Physical mapping of the IGF2 locus in the South American opossum Monodelphis domestica.

The South American opossum Monodelphis domestica has been a model organism for marsupials for many years and has recently been the subject of a large-scale genome sequencing effort that will provide the foundation for comparative studies of gene function and regulation. Genomic imprinting is one mechanism of gene regulation that has received increasing attention due to the impact of imprinting defects on development and disease. We have mapped the imprinted insulin-like growth factor II (IGF2) gene of M. domestica as a first step in understanding the regulatory mechanisms involved in genomic imprinting in this marsupial.

Evaluation of cellular uptake and gene transfer efficiency of pegylated poly-L-lysine compacted DNA: implications for cancer gene therapy.

Recent success in phase I/II clinical trials (Konstan, M. W.; Davis, P. B.; Wagener, J. S.; Hilliard, K. A.; Stern, R. C.; Milgram, L. J.; Kowalczyk, T. H.; Hyatt, S. L.; Fink, T. L.; Gedeon, C. R.; Oette, S. M.; Payne, J. M.; Muhammad, O.; Ziady, A. G.; Moen, R. C.; Cooper, M. J. Hum. Gene Ther. 2004, 15 (12), 1255-69) has highlighted pegylated poly-L-lysine (C1K30-PEG) as a nonviral gene delivery agent capable of achieving clinically significant gene transfer levels in vivo. This study investigates the potential of a C1K30-PEG gene delivery system for cancer gene therapy and evaluates its mode of cellular entry with the purpose of developing an optimally formulated prototype for tumor cell transfection. C1K30-PEG complexes have a neutral charge and form rod-like and toroid-like nanoparticles. Comparison of the transfection efficiency achieved by C1K30-PEG with other cationic lipid and polymeric vectors demonstrates that C1K30-PEG transfects cells more efficiently than unpegylated poly-L-lysine and compares well to commercially available vectors. In vivo gene delivery by C1K30-PEG nanoparticles to a growing subcutaneous murine tumor was also demonstrated. To determine potential barriers to C1K30-PEG gene delivery, the entry mechanism and intracellular fate of rhodamine labeled complexes were investigated. Using cellular markers to delineate the pathway taken by the complexes upon cellular entry, only minor colocalization was observed with EEA-1, a marker of early endosomes. No colocalization was observed between the complexes and the transferrin receptor, which is a marker for clathrin-coated pits. In addition, complexes were not observed to enter late endosomes/lysosomes. Cellular entry of the complexes was completely inhibited by the macropinocytosis inhibitor, amiloride, indicating that the complexes enter cells via macropinosomes. Such mechanistic studies are an essential step to support future rational design of pegylated poly-L-lysine vectors to improve the efficiency of gene delivery.

Nicotine, but neither the alpha4beta2 ligand RJR2403 nor an alpha7 nAChR subtype selective agonist, protects against a partial 6-hydroxydopamine lesion of the rat median forebrain bundle.

Although previous studies suggest nicotine protects against a 6-hydroxydopamine (6-OHDA)-induced lesion of the nigrostriatal tract in rats, it is not known whether functional motor recovery occurs or which nicotinic acetylcholine receptor (nAChR) subtypes mediate this effect. These issues were investigated by comparing the effects of the subtype-specific nAChR agonists, RJR2403 (alpha4beta2 preferring) and (R)-N-(1-azabicyclo[2.2.2.]oct-3-yl)(5-(2-pyridyl)thiopene-2-carboxamide (Compound A; alpha7-selective) and nicotine given 30 min prior to and daily for 14 days after a partial 6-OHDA lesion. In vehicle treated animals, 6-OHDA (6 microg) produced a 65 +/- 1.8% loss of striatal tyrosine hydroxylase (TH) immunoreactivity in the lesion versus intact hemisphere. This loss was reduced in animals treated with nicotine (0.6 and 0.8 mg kg(-1)), reaching significance at the higher dose (36.6 +/- 3.7% loss; P < 0.01 versus vehicle). Treatment with nicotine (0.6 and 0.8 mg kg(-1)) also significantly reduced the number of amphetamine-induced rotations compared to vehicle treatment. In contrast, treatment with RJR2403 (0.2 and 0.4 mg kg(-1)) or Compound A (10 and 20 mg kg(-1)) reduced neither the degree of amphetamine-induced rotations nor the loss of striatal TH immunoreactivity. These data suggest that whilst nicotine is neuroprotective in this partial lesion model, activation of neither the alpha4beta2 nor alpha7 subtypes alone is sufficient to provide protection.

Prevalence and distribution of adnexal findings suggesting endometriosis in patients with MR diagnosis of adenomyosis.

The purpose of this investigation was to establish the prevalence and distribution of MR findings associated with pelvic endometriosis in patients with a MRI diagnosis of adenomyosis. Retrospective review of the pelvic MRI in 59 patients (age 32-54 years, mean 42 years) who met strict MRI criteria for adenomyosis was performed. T1 weighted fat saturated and T2 weighted images in these patients were reviewed for the presence or absence of T1 bright signal suggesting endometriosis in any of nine locations (uterine serosa, right and left ovary, right and left fallopian tube, right and left broad ligament, and right and left pelvic side wall). 20 (20/59) patients (34%), showed characteristic MRI features associated with endometriosis. A total of 54 sites of involvement were identified (uterine serosa n = 17, ovaries n = 14, broad ligaments n = 10, fallopian tubes n = 8, pelvic side walls n = 5) in 20 patients with an average of 2.7 sites per patient. Implants (n = 43) were more common than endometriomas (n = 11). Endometriomas occurred most often in the ovaries (ovaries n = 9, broad ligament n = 2) whereas implants were seen on all locations (uterine serosa n = 17, ovaries n = 5, broad ligaments n = 8, fallopian tubes n = 8, pelvic side walls n = 5). One third of patients with adenomyosis diagnosed by MRI also had MRI findings of endometriosis, with serosal implants being the most common finding. Imaging protocols should routinely include T1 weighted fat saturated imaging sequences in order to detect coexistent endometriosis in patents undergoing pelvic MRI for the diagnosis of adenomyosis.

Chronic pre-treatment with nicotine enhances nicotine-evoked striatal dopamine release and alpha6 and beta3 nicotinic acetylcholine receptor subunit mRNA in the substantia nigra pars compacta of the rat.

Whilst local intrastriatal infusion of nicotine consistently elicits striatal dopamine release, systemic administration often fails to do so. Since chronic nicotine administration is known to result in desensitisation-induced upregulation of nicotinic acetylcholine receptors (nAChRs), the present study investigated whether chronic pre-treatment could enhance the response to systemic nicotine and, if so, whether increases in specific nAChR subunit mRNA levels in the substantia nigra pars compacta (SNc) may underlie this effect. In vivo microdialysis studies in male Sprague-Dawley rats revealed that following 4 days pre-treatment with nicotine (0.8 mg kg(-1)s.c.), local intrastriatal nicotine infusion (3 mM) elicited significantly higher dopamine efflux compared to vehicle pre-treated controls (peak release: 1273 +/- 199% basal versus 731 +/- 113% basal), whereas systemic nicotine challenge (0.8 mg kg(-1)s.c.) elicited no response. In contrast, following 8 days pre-treatment with nicotine (0.8 mg kg(-1)s.c.), systemic nicotine challenge (0.8 mg kg(-1)s.c.) now produced significantly higher dopamine efflux than that of vehicle pre-treated controls (147 +/- 30% basal versus 91 +/- 5% basal). Eight days pre-treatment with nicotine also significantly elevated the levels of alpha6 (approximately 55%) and beta3 (approximately 43%) nAChR subunit mRNA in the SNc, suggesting that up-regulation of these nAChR subunit genes in the nigrostriatal tract may contribute to the enhanced nicotine-evoked striatal dopamine release.

Fluoxetine-induced change in rat brain expression of brain-derived neurotrophic factor varies depending on length of treatment.

Recent studies indicate that brain-derived neurotrophic factor (BDNF) may be implicated in the clinical action of antidepressant drugs. Repeated (2-3 weeks) administration of antidepressant drugs increases BDNF gene expression. The onset of this response as well as concomitant effects on the corresponding BDNF protein is however, unclear. The present study investigated the effects of acute and chronic administration of the selective serotonin reuptake inhibitor, fluoxetine (10mg/kg p.o.), upon regional rat brain levels of BDNF mRNA and protein expression. To improve the clinical significance of the study, fluoxetine was administered orally and mRNA and protein levels were determined ex vivo using the techniques of in situ hybridisation histochemistry and immunocytochemistry respectively. Direct measurement of BDNF protein was also carried out using enzyme-linked immunosorbent assay (ELISA). Four days of once daily oral administration of fluoxetine induced decreases in BDNF mRNA (hippocampus, medial habenular and paraventricular thalamic nuclei). Whilst 7 days of treatment showed a non-significant increase in BDNF mRNA, there were marked and region-specific increases following 14 days of treatment. BDNF protein levels remained unaltered until 21 days of fluoxetine treatment, when the numbers of BDNF immunoreactive cells were increased, reaching significance in the pyramidal cell layer of CA1 and CA3 regions of Ammon's horn (CA1 and CA3) but not in the other sub-regions of the hippocampus. Indicative of the highly regional change within the hippocampus, the ELISA method failed to demonstrate significant up-regulation at 21 days, measuring levels of BDNF protein in the whole hippocampus. In contrast to the detected time dependent and biphasic response of the BDNF gene, activity-regulated, cytoskeletal-associated protein (Arc) mRNA showed a gradual increase during the 14-day course of treatment. The results presented here show that BDNF is expressed differentially depending on length of fluoxetine administration, which could contribute in explaining the slow onset of antidepressant activity observed with selective serotonin reuptake inhibitors.

The adenosine A2A antagonist KF17837 reverses the locomotor suppression and tremulous jaw movements induced by haloperidol in rats: possible relevance to parkinsonism.

Recent evidence indicates that adenosine A2A receptors modulate the activity of striatal neurons, and that antagonists of this receptor may have actions in various animal models related to motor function. Four experiments were conducted to study the effects of systemic injections of the adenosine A2A antagonist KF17837 on the behavioral effects produced by repeated administration of the dopamine (DA) antagonist haloperidol. In the first two experiments, it was shown that repeated 0.5 mg/kg haloperidol severely suppressed open-field locomotor activity, and that KF17837 (0.0-20.0 mg/kg) did not significantly increase open-field locomotor activity. The third experiment demonstrated that injections of KF17837 (0.0-20.0 mg/kg) completely reversed the suppression of locomotion induced by haloperidol, and also increased rearing behavior in haloperidol-treated rats. Previous research has reported that haloperidol induces tremulous jaw movements that have many of the characteristics of parkinsonian tremor. The fourth experiment demonstrated that i.p. injections of KF17837 (0.0-20.0 mg/kg) also suppressed haloperidol-induced tremulous jaw movements. Taken together, the results of these experiments indicate that adenosine A2A antagonism can reverse the locomotor suppression and tremulous movements induced by DA antagonism. This profile of activity is consistent with the hypothesis that antagonism of adenosine A2A receptors can result in an antiparkinsonian effect in animal models.

Differences in the BOLD fMRI response to direct and indirect cortical stimulation in the rat.

Functional MRI (fMRI) exploits a relationship between neuronal activity, metabolism, and cerebral blood flow to functionally map the brain. We have developed a model of direct cortical stimulation in the rat that can be combined with fMRI and used to compare the hemodynamic responses to direct and indirect cortical stimulation. Unilateral electrical stimulation of the rat hindpaw motor cortex, via stereotaxically positioned carbon-fiber electrodes, yielded blood oxygenation level-dependent (BOLD) fMRI signal changes in both the stimulated and homotypic contralateral motor cortices. The maximal signal intensity change in both cortices was similar (stimulated = 3.7 +/- 1.7%; contralateral = 3.2 +/- 1.0%), although the response duration in the directly stimulated cortex was significantly longer (48.1 +/- 5.7 sec vs. 19.0 +/- 5.3 sec). Activation of the contralateral cortex is likely to occur via stimulation of corticocortical pathways, as distinct from direct electrical stimulation, and the response profile is similar to that observed in remote (e.g., forepaw) stimulation fMRI studies. Differences in the neuronal pool activated, or neurovascular mediators released, may account for the more prolonged BOLD response observed in the directly stimulated cortex. This work demonstrates the combination of direct cortical stimulation in the rat with fMRI and thus extends the scope of rodent fMRI into brain regions inaccessible to peripheral stimulation techniques.

The role of neuronal nicotinic acetylcholine receptors in acute and chronic neurodegeneration.

In the last five years there has been a rapid explosion of publications reporting that neuronal nicotinic acetylcholine receptors (nAChRs) play a role in neurodegenerative disorders. Furthermore, there is a well-established loss of nAChRs in post-mortem brains from patients with Alzheimer's disease, Parkinson's disease and a range of other disorders. In the present review we discuss the evidence that nicotine and subtype selective nAChR ligands can provide neuroprotection in in vitro cell culture systems and in in vivo studies in animal models of such disorders. Whilst in vitro data pertaining to a protective effect of nicotine against nigral neurotoxins like MPTP is less robust, most studies agree that nicotine is protective against glutamate and beta-amyloid toxicity in various culture systems. This effect appears to be mediated by alpha7 subtype nAChRs since the protection is blocked by alpha-bungarotoxin and is mimicked by alpha7 selective agonists. In vivo studies indicate that alpha7 receptors play a critical role in protection from cholinergic lesions and enhancing cognitive function. The exact subtype involved in the neuroprotectant effects seen in animal models of Parkinson's disease is not clear, but in general broad spectrum nAChR agonists appear to provide protection, while alpha4beta2 receptors appear to mediate symptomatic improvements. Evidence favouring a protectant effect of nicotine against acute degenerative conditions is less strong, though some protection has been observed with nicotine pre-treatment in global ischaemia models. A variety of cellular mechanisms ranging from the production of growth factors through to inactivation of toxins and antioxidant actions of nicotine have been proposed to underlie the nAChR-mediated neuroprotection in vitro and in vivo. In summary, although the lack of subtype selective ligands has hampered progress, it is clear that in the future neuronal nAChR agonists could provide functional improvements and slow or halt the progress of several crippling degenerative diseases.

Olanzapine activates the rat locus coeruleus: in vivo electrophysiology and c-Fos immunoreactivity.

BACKGROUND: Activation of central noradrenergic pathways by atypical antipsychotics has been hypothesized to play a role in their efficacy in treating the negative symptoms and cognitive impairment of schizophrenia. Because acute administration of the atypical antipsychotic olanzapine has been shown to increase extracellular levels of norepinephrine in the medial prefrontal cortex, we examined the effects of olanzapine on the noradrenergic cells of the locus coeruleus (LC). METHODS: The effects of olanzapine (0.25-16 mg kg(-1), IV) on the firing rates and patterns of LC neurons were determined by extracellular, single-unit recordings in chloral hydrate-anaesthetized rats. The effects of olanzapine and clozapine on c-Fos expression in the LC, nucleus subcoeruleus part alpha (SubCA), and nucleus A5 (A5) were studied by immunohistochemistry. RESULTS: Olanzapine increased LC cell firing rates, de-regularized firing, and induced burst firing. Induction of c-Fos expression in the LC by olanzapine and clozapine was confirmed and was also found in the SubCA, but not in A5. CONCLUSIONS: Acute administration of olanzapine activates the noradrenergic neurons of the rat LC. This increased activity of LC neurons may play an important role in the efficacy of olanzapine and clozapine in treating both the negative symptoms and cognitive impairment observed in schizophrenic patients.