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PPAR: a new pharmacological target for neuroprotection in stroke and neurodegenerative diseases.

PPARs (peroxisome-proliferator-activated receptors) are ligand-activated transcriptional factor receptors belonging to the so-called nuclear receptor family. The three isoforms of PPAR (alpha, beta/delta and gamma) are involved in regulation of lipid or glucose metabolism. Beyond metabolic effects, PPARalpha and PPARgamma activation also induces anti-inflammatory and antioxidant effects in different organs. These pleiotropic effects explain why PPARalpha or PPARgamma activation has been tested as a neuroprotective agent in cerebral ischaemia. Fibrates and other non-fibrate PPARalpha activators as well as thiazolidinediones and other non-thiazolidinedione PPARgamma agonists have been demonstrated to induce both preventive and acute neuroprotection. This neuroprotective effect involves both cerebral and vascular mechanisms. PPAR activation induces a decrease in neuronal death by prevention of oxidative or inflammatory mechanisms implicated in cerebral injury. PPARalpha activation induces also a vascular protection as demonstrated by prevention of post-ischaemic endothelial dysfunction. These vascular effects result from a decrease in oxidative stress and prevention of adhesion proteins, such as vascular cell adhesion molecule 1 or intercellular cell-adhesion molecule 1. Moreover, PPAR activation might be able to induce neurorepair and endothelium regeneration. Beyond neuroprotection in cerebral ischaemia, PPARs are also pertinent pharmacological targets to induce neuroprotection in chronic neurodegenerative diseases.

Brain↗

Assessment of intraspinal and intracranial conduction by P30 and P39 tibial nerve somatosensory evoked potentials in cervical cord, brainstem, and hemispheric lesions.

In routine recordings of tibial nerve somatosensory evoked potentials (SEPs), a global central conduction time is evaluated by measuring the interval between the segmental spinal N22 potential, recorded in the lumbar region, and the cortical P39 potential. In this study, we tested the reliability of the scalp far-field P30 potential, which originates in the vicinity of the cervico-medullary junction, in order to evaluate separately intraspinal and intracranial conduction in normal subjects and patients with cervical cord and intracranial lesions. P30 and cortical P39 potentials were studied in 23 healthy subjects and in 70 patients with cervical cord (n = 47), brainstem (n = 11) or hemispheric lesions (n = 12) selected on the basis of neuroimaging--computed tomography (CT) or magnetic resonance (MR)--findings. Median nerve SEPs were also recorded in all patients. Of the several montages tested to obtain the P30 potential, the Fpz-Cv6 derivation gave the highest signal-to-noise ratio; it permitted to obtain a P30 potential that peaked at 29.2 +/- 1.6 ms in all normal subjects. P30 abnormalities were observed only in patients with cervical or cervico-medullary lesions; these were associated with a normal P39 in only two of 33 abnormal recordings. Conversely, P30 was consistently normal in lesions situated above the cervico-medullary junction whether associated with normal, delayed, or reduced P39. P30 abnormalities were subclinical in 42% of abnormal recordings. All patients with normal tibial and median nerve SEPs on both sides had normal touch, joint, and vibration sensation in the four limbs. There was a strong correlation between tibial nerve P30 and median nerve P14 data in the whole series of patients; both potentials behaved similarly in all cases of intracranial supramedullary lesions. Combined abnormalities of P30 and P39 potentials thus indicate that conduction is impaired at the spinal level and proved to be particularly informative for detecting spinal cord dysfunction in patients with neuroimaging evidence of a narrowed cervical canal. Recording of abnormal N13, P14, or P30 potentials provided evidence of a cervical cord dysfunction in 66% of patients who had a suspected spondylotic myelopathy. Recording of tibial nerve P30 potential has proven to give reliable and useful information when a separate assessment of intraspinal and intracranial somatosensory conduction is needed; it merits inclusion, as does the upper limb N13 potential, in the evaluation of patients whose MR image indicates cervical canal narrowing.

Adolescent↗

Antisense knockdown of the glial glutamate transporter GLT-1 exacerbates hippocampal neuronal damage following traumatic injury to rat brain.

Traumatic injury to rat brain induced by controlled cortical impact (CCI) results in chronic neuronal death in the hippocampus. In the normal brain, glutamate transporters actively clear the glutamate released synaptically to prevent receptor overactivation and excitotoxicity. Glutamate transporter 1 (GLT-1) is the most abundant and active glutamate transporter, which mediates the bulk of glutamate uptake. CCI injury significantly decreased GLT-1 mRNA (by 49-66%, P < 0.05) and protein (by 29-44%, P < 0.05) levels in the ipsilateral hippocampus, compared with either the respective contralateral hippocampus or the sham-operated control, 24-72 h after the injury. CCI injury in rats infused with GLT-1 antisense oligodeoxynucleotides (ODNs) exacerbated the hippocampal neuronal death and mortality, compared with the GLT-1 sense/random ODN-infused controls. At 7 days after the injury, hippocampal neuronal numbers were significantly lower in the CA1 (reduced by 32%, P < 0.05), CA2 (by 45%, P < 0.01), CA3 (by 68%, P < 0.01) and dentate gyrus (by 31%, P < 0.05) in GLT-1 antisense ODN-infused rats, compared with the GLT-1 sense/random ODN-infused controls. This study suggested a role for GLT-1 dysfunction in promoting the hippocampal neuronal death after traumatic brain injury.

ATP-Binding Cassette Transporters↗

Common efficacy of psychotropic drugs in restoring stress-induced impairment of prefrontal plasticity.

We recently investigated the effects of stress on synaptic plasticity in the prefrontal cortex, namely the prelimbic area or the apparent homologue of the primate subgenual prefrontal cortex in humans where most of the hippocampal terminal fields are localized. Exposure to an acute stress causes a remarkable and long-lasting inhibition of long term potentiation (LTP) in the frontal cortex evoked by stimulation of hippocampal outflow and this impairment is prevented by the glucocorticoid receptor antagonist mifepristone. Thus, the frontal cortex is also a target for glucocorticoids involved in the stress response. Current data show that antidepressants of various types, i.e., tianeptine and fluoxetine, at doses normally used in antidepressant testing, restore LTP impaired by prior acute stress. Interestingly, clozapine administered in a similar way after stress rapidly reverses the stress-induced impairment of LTP at doses which do not affect LTP alone. This stress paradigm highlights comorbidity for both etiology and treatment of psychiatric disorders like depression and schizophrenia. Restoring appropriate cognitive functions in circuits associated with dysfunctions in coping with stress may be proposed as a new systems-level approach to drug discovery and development. We are presently investigating the involvement of signalling molecules in producing these plastic changes.

Antidepressive Agents↗

Nitric oxide in the nasal airway: a new dimension in otorhinolaryngology.

The discovery that the gas nitric oxide (NO) is an important signaling molecule in the cardiovascular system earned its Nobel prize in 1998. NO has since been found to play important roles in a variety of physiologic and pathophysiologic processes in the body including vasoregulation, hemostasis, neurotransmission, immune defense, and respiration. The surprisingly high concentrations of NO in the nasal airway and paranasal sinuses has important implications for the field of otorhinolaryngology. NO provides a first-line defense against micro-organisms through its antiviral and antimicrobial activity and by its upregulation of ciliary motility. Nasal treatments such as polypectomy, sinus surgery, removal of hypertrophic adenoids and tonsils, and treatment of allergic rhinitis may alter NO output and, therefore, the microbial colonization of the upper airways. Nasal surgery aimed at relieving nasal obstruction may do the same but would also be expected to improve pulmonary function in patients with asthma and upper airway obstruction. NO output rises in a number of conditions associated with chronic airway inflammation, but not all of them. Concentrations are increased in asthma, allergic rhinitis, and viral respiratory infections, but reduced in sinusitis, cystic fibrosis, primary ciliary dysfunction, chronic cough, and after exposure to tobacco and alcohol. Therefore, NO, similar to several other inflammatory mediators, probably subserves different functions as local conditions dictate. At present, it seems that the measurement of NO in the upper airway may prove valuable as a simple, noninvasive diagnostic marker of airway pathologies. The objective of this review is to highlight some aspects of the origin, physiology, and functions of upper airway NO, and to discuss the particular methodological problems that result from the complex anatomy.

Humans↗

Effects of vitamin E deficiency on autonomic neuroeffector mechanisms in the rat caecum, vas deferens and urinary bladder.

1. Modified sucrose-gap, standard organ-bath techniques and transmitter release studies were used to examine neuromuscular transmission in the caecum, vas deferens and urinary bladder in normal rats and in rats maintained for 12 months on a diet free of vitamin E. 2. In the caecum circular muscle, non-adrenergic, non-cholinergic inhibitory junction potentials were absent from 48 and 15% of preparations from vitamin E-deficient and control animals, respectively. Cholinergic excitatory junction potentials were absent from 83 and 8% of vitamin E-deficient and control preparations, respectively. Responses to applied noradrenaline (0.1-30 microM), alpha,beta-methylene ATP (3-100 microM) and acetylcholine (0.1-30 microM) were attenuated or absent in vitamin E-deficient tissues. Responses to applied KCl were similar in both groups. Release of [3H]noradrenaline or endogenous acetylcholine could not be evoked from vitamin E-deficient tissues. 3. In contrast, in isolated preparations of the vas deferens and urinary bladder, neuromuscular transmission by adrenergic, cholinergic and purinergic components were unaffected by long-term vitamin E deficiency. 4. In conclusion, vitamin E deficiency causes dysfunction of autonomic neuroeffector mechanisms in the smooth muscle of the rat caecum, at both a pre- and postjunctional level. The lesions in autonomic transmission mechanisms brought about by long-term vitamin E deficiency were found only in the caecum; no changes in sympathetic neuromuscular transmission were observed in the vas deferens, or in parasympathetic neuromuscular transmission in the urinary bladder.

Adenosine Triphosphate↗

Dopamine, the prefrontal cortex and schizophrenia.

Dysfunction of the prefrontal cortex (PFC) in schizophrenia has been suspected based on observations from clinical, neuropsychological and neuroimaging studies. Since the PFC receives a dense dopaminergic innervation, abnormalities of the mesocortical dopamine system have been proposed to contribute to the pathophysiology of schizophrenia. In this review, aspects of the anatomy, physiology and pharmacology of the mesencephalic-frontal cortical dopamine system as they may relate to schizophrenia are described, and evidence for altered dopaminergic neurotransmission in the frontal cortex of schizophrenic patients is presented.

Antipsychotic Agents↗

The recurrent mossy fiber pathway of the epileptic brain.

The dentate gyrus is believed to play a key role in the pathogenesis of temporal lobe epilepsy. In normal brain the dentate granule cells serve as a high-resistance gate or filter, inhibiting the propagation of seizures from the entorhinal cortex to the hippocampus. The filtering function of the dentate gyrus depends in part on the near absence of monosynaptic connections among granule cells. In humans with temporal lobe epilepsy and in animal models of temporal lobe epilepsy, dentate granule cells form an interconnected synaptic network associated with loss of hilar interneurons. This recurrent mossy fiber pathway mediates reverberating excitation that can reduce the threshold for granule cell synchronization. Factors that augment activity in this pathway include modest increases in [K+]o; loss of GABA inhibition; short-term, frequency-dependent facilitation (frequencies of 1-2 Hz); feedback activation of kainate autoreceptors; and release of zinc from recurrent mossy fiber boutons. Factors that diminish activity include short-term, frequency-dependent depression (frequencies < 1 Hz); feedback activation of type II metabotropic glutamate receptors; and the potential release of GABA, neuropeptide Y, adenosine, and dynorphin from recurrent mossy fiber boutons. The axon sprouting and reactive synaptogenesis that follow seizure-related brain damage can also create or strengthen recurrent excitation in other brain regions. These changes are expected to facilitate participation of these regions in seizures. Thus, reactive processes that are often considered important for recovery of function after most brain injuries probably contribute to neurological dysfunction in epilepsy.

Animals↗

Elevated thalamic dopamine: possible link to sensory dysfunctions in schizophrenia.

Sensory-processing dysfunctions, deficit states, and the combinations of seemingly disparate behavioral symptoms of schizophrenia are addressed with regard to a common thread--the possibility of dysfunctional processing in the thalamus. Recent views of the connectional neuroanatomy and electrical activity of thalamus are examined. A hypothesis is presented in which disturbances in the timing and phasic neuronal activity of the thalamus and, especially, its connections with other brain regions may result in many of the behavioral manifestations of schizophrenia. It is suggested that neurotransmitter or other chemical imbalances might produce such thalamic disturbances. Experimental findings of enhanced dopamine content in the thalami of schizophrenic patients are reported. Several varieties of distributional patterns of this elevated dopamine are shown and evaluated.

Brain Mapping↗

Pathogenesis of methylazoxymethanol-induced lesions in the postnatal mouse cerebellum.

Previous studies have shown that methylazoxymethanol acetate (MAM) and methylazoxymethanol glucoside (cycasin) cause destruction of differentiation cells in the postnatal mouse cerebellum. The major features of the resulting architectural disarray were Purkinje cell misalignment and granule cell deletion along with cerebellar dysfunction. Although it was clear from a number of studies that destruction of differentiation cells in the immediate postnatal period was the primary lesion, several important facets of the pathellular response to the injury was incompletely described. The relationship of the cellular response to the subsequent pathological alterations was not completely evaluated. Also, the presence of unattached Purkinje cell dendritic spine postsynpatic sites suggested that their development had occurred without presynaptic parallel fiber terminal differentiation. The possibility of early synaptogenesis and degeneration was not, however, completely ruled out.

Animals↗

5-HT(1A) receptor dysfunction in female patients with schizophrenia.

BACKGROUND: Serotonin (5-HT)(1A) receptors are of interest in the pathophysiology of schizophrenia (SCH) and the mechanism of action of atypical antipsychotic drugs. To test the hypothesis that 5-HT(1A) receptor responsivity is significantly different in patients with SCH compared to normal control subjects, the neuroendocrine study was performed using ipsapirone (IPS), a 5-HT(1A) partial agonist, as a probe. METHODS: Ipsapirone 0.5 mg/kg, p.o. or placebo were administered, in random order, to patients with SCH (n = 43; 32 male) and normal controls (n = 33; 21 male). Blood samples for plasma cortisol and body temperature were obtained from 30 min before to 180 min after administration of IPS or placebo. RESULTS: Female normal control subjects had markedly greater increases in plasma cortisol following IPS than did male control subjects. The placebo response-corrected plasma cortisol response to IPS was significantly blunted in female SCH compared to female normal control subjects (p =.0001). The IPS-stimulated plasma cortisol response in male SCH did not differ from that of male normal control subjects or female SCH. There were no significant differences in the IPS-induced hypothermia in men and women or between patients with SCH and normal control subjects. Behavioral responses to IPS, including nausea, dizziness, irritability, and feeling less well, did not differ between groups. CONCLUSIONS: These results suggest that the post-synaptic 5-HT(1A) receptor mediated endocrine response is diminished in female SCH compared to female normal control subjects, possibly secondary to an abnormality in intracellular signal transduction mechanism.

Adult↗

Neonatal toluene exposure alters N-methyl-D-aspartate receptor subunit expression in the hippocampus and cerebellum in juvenile rats.

Recent evidence indicates that toluene is a non-competitive inhibitor of N-methyl-d-aspartate (NMDA) receptor-mediated synaptic currents. The NMDA receptor plays a major role in neuronal development and differentiation. The present study characterized the long-term effects of toluene exposure during synaptogenesis on the expression of NMDA receptor subunits (NR1, NR2A and NR2B). Neonatal rats were administered toluene (500 mg/kg, ip) daily over postnatal days (PN) 4-9. The expression of NMDA receptor subunits in rat brain was measured on PN 30. Western blot analysis demonstrated that toluene exposure significantly increased NR2A expression in the hippocampus and cerebellum. Immunohistochemical results indicated that the increased NR2A expression is mainly in hippocampal CA1-stratum oriens, CA1-stratum radiatum, CA1-lacunosm molecular, CA2- stratum oriens, and dentate gyrus-molecular layer and the cerebellar Purkinje cell layer, respectively. In contrast, the levels of NR2B in the toluene-exposed rats were decreased in the molecular layer. These results suggest that the region-specific changes in the expression of NMDA receptor subunits may be related to the neurobehavioral dysfunction following toluene exposure during synaptogenesis.

Age Factors↗

AAEE Minimonograph #33: electrodiagnostic approach to defects of neuromuscular transmission.

Clinical testing for neuromuscular dysfunction is supported by an extensive amount of excellent basic information about normal and abnormal subcellular physiology and ultrastructure. This information provides an essential frame of reference for describing the rationale of single-fiber electromyography (SFEMG). SFEMG in turn helps to explain the more conventional clinical testing of neuromuscular function by repetitive nerve stimulation (RNS). Electrical findings in myasthenia gravis, Lambert-Eaton myasthenic syndrome, and botulinum intoxication are discussed from the subcellular level via the cellular level (SFEMG) to the integrated responses of whole muscle (RNS) as a rational means of understanding the technique of clinical repetitive nerve stimulation.

Electromyography↗

Optimization of chronic stress paradigms using anxiety- and depression-like behavioral parameters.

Chronic stress is a risk factor for psychiatric illnesses, such as anxiety and depression disorders. To understand the underlying mechanism regarding how chronic stress triggers such psychiatric dysfunctions, restraint-based chronic stress models have been attempted in the past. However, total durations of repeated restraint stress and the evaluation time points used after the last restraint application vary from experiment to experiment. One reason for these methodological heterogeneities is related to considerable ambiguity concerning the definition of chronic stress, particularly in animal models. In the present study, we used behavioral traits, anxiety and depression, as stress-assessment parameters that meet operationally useful requirements for the definition of the chronic stress state. We demonstrate that restraint treatment for 2 or 8 hr daily for 14 days is enough to produce anxiety- and depression-like behaviors, whereas a 2 hr-10 days restraint was marginally effective. cDNA microarray analysis identified 34 genes in the hippocampus and 72 genes in the amygdala with expression levels that were up- or down-regulated by >2.0-fold. Among the wide range of genes identified in this analysis, genes required for energy metabolism, signal transduction, transcription, synaptic plasticity, and remodeling of the brain architecture were notable. Our results suggest that the psychiatric criteria of anxiety and depression can be used as chronic stress-assessment parameters and that a restraint stress paradigm consisting of restraint treatment for 2 or 8 hr daily for 14 days could be used as a prototype paradigm for chronic stress studies.

Amygdala↗

The canine as an animal model of human aging and dementia.

The aged canine displays many features that make it an excellent model for studying the progression of pathology in brain aging and linking these findings to learning, memory and other cognitive functions. Canines develop extensive beta-amyloid deposition within neurons and their synaptic fields, which appears to give rise to senile plaques. These plaques are primarily of the early diffuse subtype. Aged canines also exhibit accumulations of lipofuscin, cerebral vascular changes, dilation of the ventricles, and cytoskeletal changes. Neurofibrillary tangles (NFTs) are not present in the aged canine. Thus, the aged canine brain provides a suitable model for studying early degeneration normally considered to be pre-Alzheimer's. This supposition is also supported by behavioral data. We have found that the extent of beta-amyloid deposition correlates with a decline in select measures of cognitive function. These data provide the first evidence of a correlation between beta-amyloid accumulation and cognitive decline in the absence of NFTs. We summarize four lines of evidence that support using the aged canine as a model of human aging: (a) Aged canines develop aspects of neuropathology similar to that observed in aged humans; (b) Veterinarians have observed that many canines exhibit a clinical syndrome of age-related cognitive dysfunction; (c) Aged canines are deficient on a variety of neuropsychological tests of cognitive function; (d) The level of beta-amyloid accumulation correlates with cognitive dysfunction in the canine. These data indicate that the aged canine is a particularly useful model for studying age-related cognitive dysfunction (ARCD), early neuronal changes associated with aging, and the initial stages of senile plaque formation.

Aging↗

Age-related sympathetic ganglionic neuropathology: human pathology and animal models.

Systematic studies of the autonomic nervous system of human subjects and development of well-defined animal models have begun to substantially improve our understanding of the pathogenesis of autonomic dysfunction in aging and may eventually provide strategies for intervention. Neuropathological studies of the sympathetic ganglia of aged human subjects and rodent models have demonstrated that neuroaxonal dystrophy involving intraganglionic terminal axons and synapses is a robust, unequivocal and consistent neuropathological finding in the aged sympathetic nervous system of man and animals. Quantitative studies have demonstrated that markedly swollen argyrophilic dystrophic axon terminals develop in the prevertebral superior mesenteric (SMG) and coeliac, but to a much lesser degree in the superior cervical ganglia (SCG) as a function of age, sex (males more than females) and diabetes. Dystrophic axons were immunoreactive for neuropeptide Y, tyrosine hydroxylase, dopamine-beta-hydroxylase, trkA and p75NTR, an immunophenotype consistent with their origin from postganglionic sympathetic neurons, and contained large numbers of highly phosphorylated neurofilaments or tubulovesicular elements. The sympathetic ganglia of aged rodents also showed the hallmark changes of neuroaxonal dystrophy as a function of age and location (many more in the SMG than in the SCG). Plasticity-related synaptic remodeling could represent a highly vulnerable target of the aging process. The fidelity of animal models to the neuropathology of aged humans suggests that similar pathogenetic mechanisms may be involved in both and that therapeutic advances in animal studies may have human application.

Aging↗

Triiodothyronine administration reverses vitamin A deficiency-related hypo-expression of retinoic acid and triiodothyronine nuclear receptors and of neurogranin in rat brain.

Recent studies have revealed that retinoids play an important role in the adult central nervous system and cognitive functions. Previous investigations in mice have shown that vitamin A deficiency (VAD) generates a hypo-expression of retinoic acid (RA, the active metabolite of vitamin A) receptors and of neurogranin (RC3, a neuronal protein involved in synaptic plasticity) and a concomitant selective behavioural impairment. Knowing that RC3 is both a triiodothyronine (T3) and a RA target gene, and in consideration of the relationships between the signalling pathways of retinoids and thyroid hormones, the involvement of T3 on RA signalling functionality in VAD was investigated. Thus, the effects of vitamin A depletion and subsequent administration with RA and/or T3 on the expression of RA nuclear receptors (RAR, RXR), T3 nuclear receptor (TR) and on RC3 in the brain were examined. Rats fed a vitamin A-deficient diet for 10 weeks exhibited a decreased expression of RAR, RXR and TR mRNA and of RC3 mRNA and proteins. RA administration to these vitamin A-deficient rats reversed only the RA hypo-signalling in the brain. Interestingly, T3 is able to restore its own brain signalling simultaneously with that of vitamin A and the hypo-expression of RC3. These results obtained in vivo revealed that one of the consequences of VAD is a dysfunction in the thyroid signalling pathway in the brain. This seems of crucial importance since the down regulation of RC3 observed in the depleted rats was corrected only by T3.

Animals↗

Nucleation-dependent polymerization is an essential component of amyloid-mediated neuronal cell death.

Accumulating evidence suggests that amyloid protein aggregation is pathogenic in many diseases, including Alzheimer's disease. However, the mechanisms by which protein aggregation mediates cellular dysfunction and overt cell death are unknown. Recent reports have focused on the potential role of amyloid oligomers or protofibrils as a neurotoxic form of amyloid-beta (Abeta) and related amyloid aggregates. Here we describe studies indicating that overt neuronal cell death mediated by Abeta(1-40) is critically dependent on ongoing Abeta(1-40) polymerization and is not mediated by a single stable species of neurotoxic aggregate. The extent and rate of neuronal cell death can be controlled by conditions that alter the rate of Abeta polymerization. The results presented here indicate that protofibrils and oligomeric forms of Abeta most likely generate neuronal cell death through a nucleation-dependent process rather than acting as direct neurotoxic ligands. These findings bring into question the use of the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide formazan assay (MTT assay) as a reporter of Abeta-mediated neuronal cell death and suggest that diffusible Abeta protofibrils and oligomers more likely mediate subtle alterations of synaptic function and long-term potentiation rather than overt neuronal cell death. These results have been extended to Abeta(1-42), the non-Abeta component of Alzheimer's disease amyloid plaques, and human amylin, suggesting that nucleation-dependent polymerization is a common mechanism of amyloid-mediated neuronal cell death. Our findings indicate that ongoing amyloid fibrillogenesis may be an essential mechanistic process underlying the pathogenesis associated with protein aggregation in amyloid disorders.

Amyloid↗