A developmental redox dysregulation leads to spatio-temporal deficit of parvalbumin neuron circuitry in a schizophrenia mouse model

The fast-spiking parvalbumin (PV) interneurons play a critical role in neural circuit activity and dysfunction of these cells has been implicated in the cognitive deficits typically observed in schizophrenia patients. Due to the high metabolic demands of PV neurons, they are particularly susceptible to oxidative stress. Given the extant literature exploring the pathological effects of oxidative stress on PV cells in cortical regions linked to schizophrenia, we decided to investigate whether PV neurons in other select brain regions, including sub-cortical structures, may be differentially affected by redox dysregulation induced oxidative stress during neurodevelopment in mice with a genetically compromised glutathione synthesis (Gclm KO mice). Our analyses revealed a spatio-temporal sequence of PV cell deficit in Gclm KO mice, beginning with the thalamic reticular nucleus at postnatal day (P) 20 followed by a PV neuronal deficit in the amygdala at P40, then in the lateral globus pallidus and the ventral hippocampus Cornu Ammonis 3 region at P90 and finally the anterior cingulate cortex at P180. We suggest that PV neurons in different brain regions are developmentally susceptible to oxidative stress and that anomalies in the neurodevelopmental calendar of metabolic regulation can interfere with neural circuit maturation and functional connectivity contributing to the emergence of developmental psychopathology.

Stimulating effect of thyroid hormones in peripheral nerve regeneration: research history and future direction toward clinical therapy

Injury to peripheral nerves is often observed in the clinic and severe injuries may cause loss of motor and sensory functions. Despite extensive investigation, testing various surgical repair techniques and neurotrophic molecules, at present, a satisfactory method to ensuring successful recovery does not exist. For successful molecular therapy in nerve regeneration, it is essential to improve the intrinsic ability of neurons to survive and to increase the speed of axonal outgrowth. Also to induce Schwann cell phenotypical changes to prepare the local environment favorable for axonal regeneration and myelination. Therefore, any molecule that regulates gene expression of both neurons and Schwann cells could play a crucial role in peripheral nerve regeneration. Clinical and experimental studies have reported that thyroid hormones are essential for the normal development and function of the nervous system, so they could be candidates for nervous system regeneration. This review provides an overview of studies devoted to testing the effect of thyroid hormones on peripheral nerve regeneration. Also it emphasizes the importance of combining biodegradable tubes with local administration of triiodothyronine for future clinical therapy of human severe injured nerves. We highlight that the local and single administration of triiodothyronine within biodegradable nerve guide improves significantly the regeneration of severed peripheral nerves, and accelerates functional recovering. This technique provides a serious step towards future clinical application of triiodothyronine in human severe injured nerves. The possible regulatory mechanism by which triiodothyronine stimulates peripheral nerve regeneration is a rapid action on both axotomized neurons and Schwann cells.

Proximity of excitatory synapses and astroglial gap junctions in layer IV of the mouse barrel cortex

Neurons and astrocytes, the two major cell populations in the adult brain, are characterized by their own mode of intercellular communication--the synapses and the gap junctions (GJ), respectively. In addition, there is increasing evidence for dynamic and metabolic neuroglial interactions resulting in the modulation of synaptic transmission at the so-called "tripartite synapse". Based on this, we have investigated at the ultrastructural level how excitatory synapses (ES) and astroglial GJ are spatially distributed in layer IV of the barrel cortex of the adult mouse. We used specific antibodies for connexin (Cx) 30 and 43 to identify astroglial GJ, these two proteins are known to be present in the majority of astroglial GJ in the cerebral cortex. In electron-microscopic images, we measured the distance between two ES, between two GJ and between a GJ and its nearest ES. We found a ratio of two GJ per three ES in the hollow and septal areas. Taking into account the size of an astrocyte domain, the high density of GJ suggests the occurrence of reflexive type, i.e. GJ between processes of the same astrocyte. Interestingly, the distance between an ES and an astroglial GJ was found to be significantly lower than that between either two synapses or between two GJ. These observations indicate that the two modes of cell-to-cell communication are not randomly distributed in layer IV of the barrel cortex. Consequently, this feature may provide the morphological support for the recently reported functional interactions between neuronal circuits and astroglial networks.

Pathological reorganization of NMDA receptors subunits and postsynaptic protein PSD-95 distribution in Alzheimer's disease

In Alzheimer's disease (AD), synaptic alterations play a major role and are often correlated with cognitive changes. In order to better understand synaptic modifications, we compared alterations in NMDA receptors and postsynaptic protein PSD-95 expression in the entorhinal cortex (EC) and frontal cortex (FC; area 9) of AD and control brains. We combined immunohistochemical and image analysis methods to quantify on consecutive sections the distribution of PSD-95 and NMDA receptors GluN1, GluN2A and GluN2B in EC and FC from 25 AD and control cases. The density of stained receptors was analyzed using multivariate statistical methods to assess the effect of neurodegeneration. In both regions, the number of neuronal profiles immunostained for GluN1 receptors subunit and PSD-95 protein was significantly increased in AD compared to controls (3-6 fold), while the number of neuronal profiles stained for GluN2A and GluN2B receptors subunits was on the contrary decreased (3-4 fold). The increase in marked neuronal profiles was more prominent in a cortical band corresponding to layers 3 to 5 with large pyramidal cells. Neurons positive for GluN1 or PSD-95 staining were often found in the same localization on consecutive sections and they were also reactive for the anti-tau antibody AD2, indicating a neurodegenerative process. Differences in the density of immunoreactive puncta representing neuropile were not statistically significant. Altogether these data indicate that GluN1 and PSD-95 accumulate in the neuronal perikarya, but this is not the case for GluN2A and GluN2B, while the neuropile compartment is less subject to modifications. Thus, important variations in the pattern of distribution of the NMDA receptors subunits and PSD-95 represent a marker in AD and by impairing the neuronal network, contribute to functional deterioration.

Pre-existing astrocytes form functional perisynaptic processes on neurons generated in the adult hippocampus

The adult dentate gyrus produces new neurons that morphologically and functionally integrate into the hippocampal network. In the adult brain, most excitatory synapses are ensheathed by astrocytic perisynaptic processes that regulate synaptic structure and function. However, these processes are formed during embryonic or early postnatal development and it is unknown whether astrocytes can also ensheathe synapses of neurons born during adulthood and, if so, whether they play a role in their synaptic transmission. Here, we used a combination of serial-section immuno-electron microscopy, confocal microscopy, and electrophysiology to examine the formation of perisynaptic processes on adult-born neurons. We found that the afferent and efferent synapses of newborn neurons are ensheathed by astrocytic processes, irrespective of the age of the neurons or the size of their synapses. The quantification of gliogenesis and the distribution of astrocytic processes on synapses formed by adult-born neurons suggest that the majority of these processes are recruited from pre-existing astrocytes. Furthermore, the inhibition of astrocytic glutamate re-uptake significantly reduced postsynaptic currents and increased paired-pulse facilitation in adult-born neurons, suggesting that perisynaptic processes modulate synaptic transmission on these cells. Finally, some processes were found intercalated between newly formed dendritic spines and potential presynaptic partners, suggesting that they may also play a structural role in the connectivity of new spines. Together, these results indicate that pre-existing astrocytes remodel their processes to ensheathe synapses of adult-born neurons and participate to the functional and structural integration of these cells into the hippocampal network.

Impairment and disability in 20 CIDP patients according to disease activity status

Twenty patients with chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) meeting the EFNS/PNS criteria were examined in order to assess differences/similarities between the various grading systems according to CIDP disease activity status (CDAS). A principal component (PC) analysis and the correlations between the following scores were performed: Neurological Symptom Score; MRC sum score; Neurological Impairment Score; Hammersmith Functional Motor Scale; Inflammatory Neuropathy Cause and Treatment (INCAT) Sensory Sum Score; Overall Disability Sum Score; INCAT Disability Score; Rasch-built Overall Disability Scale. Our analysis outlined two main sets of scales, with high influence in the top two PCs. The first PC that best explained the variability within the cohort consisted of CDAS, general disability scores and motor scores; these parameters were also strongly correlated amongst each other. The second PC explained less the variability and consisted mainly of sensory scores and disease duration; these parameters did not correlate with the scores of the first PC or with the CDAS. Our findings suggest separating screening for motor and sensory deficits when evaluating CIDP patients, as only the motor scores correlate with CDAS.

Increased postsynaptic density protein-95 expression in the frontal cortex of aged cognitively impaired rats

In the present work we studied synaptic protein concentrations in relation to behavioral performance. Long-Evans rats, aged 22-23 months, were classified for individual expression of place memory in the Morris water maze, in reference to young adults. Two main subgroups of aged rats were established: the Aged cognitively Unimpaired (AU) had search accuracy within the range (percent of time in training sector within mean ± 2 SEM) of young rats and the Aged cognitively Impaired (AI) rats had search accuracy below this range. Samples from the hippocampus and frontal cortex of all the AI, AU and young rats were analyzed for the expression of postsynaptic protein PSD-95 by Image J analysis of immunohistochemical data and by Western blots. PSD-95 expression was unchanged in the hippocampus, but, together with synaptophysin, was significantly increased in the frontal cortex of the AI rats. A significant correlation between individual accuracy (time spent in the training zone) and PSD-95 expression was observed in the aged group. No significant effect of age or PSD-95 expression was observed in the learning of a new position. All together, these data suggest that increased expression of PSD-95 in the frontal cortex of aged rats co-occurs with cognitive impairment that might be linked to functional alterations extending over frontal networks.

Early-life insults impair parvalbumin interneurons via oxidative stress: reversal by N-acetylcysteine

BACKGROUND

A hallmark of the pathophysiology of schizophrenia is a dysfunction of parvalbumin-expressing fast-spiking interneurons, which are essential for the coordination of neuronal synchrony during sensory and cognitive processing. Oxidative stress as observed in schizophrenia affects parvalbumin interneurons. However, it is unknown whether the deleterious effect of oxidative stress is particularly prevalent during specific developmental time windows.

METHODS

We used mice with impaired synthesis of glutathione (Gclm knockout [KO] mice) to investigate the effect of redox dysregulation and additional insults applied at various periods of postnatal development on maturation and long-term integrity of parvalbumin interneurons in the anterior cingulate cortex.

RESULTS

A redox dysregulation, as in Gclm KO mice, renders parvalbumin interneurons but not calbindin or calretinin interneurons vulnerable and prone to exhibit oxidative stress. A glutathione deficit delays maturation of parvalbumin interneurons, including their perineuronal net. Moreover, an additional oxidative challenge in preweaning or pubertal but not in young adult Gclm KO mice reduces the number of parvalbumin-immunoreactive interneurons. This effect persists into adulthood and can be prevented with the antioxidant N-acetylcysteine.

CONCLUSIONS

In Gclm KO mice, early-life insults inducing oxidative stress are detrimental to immature parvalbumin interneurons and have long-term consequences. In analogy, individuals carrying genetic risks to redox dysregulation would be potentially vulnerable to early-life environmental insults, during the maturation of parvalbumin interneurons. Our data support the need to develop novel therapeutic approaches based on antioxidant and redox regulator compounds such as N-acetylcysteine, which could be used preventively in young at-risk subjects.

Genetic dysregulation of glutathione synthesis predicts alteration of plasma thiol redox status in schizophrenia

Genetic studies have shown an association between schizophrenia and a GAG trinucleotide repeat (TNR) polymorphism in the catalytic subunit (GCLC) of the glutamate cysteine ligase (GCL), the key enzyme for glutathione (GSH) synthesis. The present study was aimed at analyzing the influence of a GSH dysregulation of genetic origin on plasma thiols (total cysteine, homocysteine, and cysteine-glycine) and other free amino acid levels as well as fibroblast cultures GSH levels. Plasma thiols levels were also compared between patients and controls. As compared with patients with a low-risk GCLC GAG TNR genotype, patients with a high-risk genotype, having an impaired GSH synthesis, displayed a decrease of fibroblast GSH and plasma total cysteine levels, and an increase of the oxidized form of cysteine (cystine) content. Increased levels of plasma free serine, glutamine, citrulline, and arginine were also observed in the high-risk genotype. Taken together, the high-risk genotypes were associated with a subgroup of schizophrenia characterized by altered plasma thiols and free amino acid levels that reflect a dysregulation of redox control and an increased susceptibility to oxidative stress. This altered pattern potentially contributes to the development of a biomarker profile useful for early diagnosis and monitoring the effectiveness of novel drugs targeting redox dysregulation in schizophrenia.

Differential damage in the frontal cortex with aging, sporadic and familial Alzheimer's disease

In order to understand relationships between executive and structural deficits in the frontal cortex of patients within normal aging or Alzheimer's disease, we studied frontal pathological changes in young and old controls compared to cases with sporadic (AD) or familial Alzheimer's disease (FAD). We performed a semi-automatic computer assisted analysis of the distribution of beta-amyloid (Abeta) deposits revealed by Abeta immunostaining as well as of neurofibrillary tangles (NFT) revealed by Gallyas silver staining in Brodman areas 10 (frontal polar), 12 (ventro-infero-median) and 24 (anterior cingular), using tissue samples from 5 FAD, 6 sporadic AD and 10 control brains. We also performed densitometric measurements of glial fibrillary acidic protein, principal compound of intermediate filaments of astrocytes, and of phosphorylated neurofilament H and M epitopes in areas 10 and 24. All regions studied seem almost completely spared in normal old controls, with only the oldest ones exhibiting a weak percentage of beta-amyloid deposit and hardly any NFT. On the contrary, all AD and FAD cases were severely damaged as shown by statistically significant increased percentages of beta-amyloid deposit, as well as by a high number of NFT. FAD cases (all from the same family) had statistically more beta-amyloid and GFAP than sporadic AD cases in both areas 10 and 24 and statistically more NFT only in area 24. The correlation between the percentage of beta-amyloid and the number of NFT was significant only for area 24. Altogether, these data suggest that the frontal cortex can be spared by AD type lesions in normal aging, but is severely damaged in sporadic and still more in familial Alzheimer's disease. The frontal regions appear to be differentially vulnerable, with area 12 having the less amyloid burden, area 24 the less NFT and area 10 having both more amyloid and more NFT. This pattern of damage in frontal regions may represent a strong neuroanatomical support for the deterioration of attention and cognitive capacities as well as for the presence of emotional and behavioral troubles in AD patients.

GABA receptor subunits in human auditory cortex in normal and stroke cases

GABA receptors are ubiquitous in the cerebral cortex and play a major role in shaping responses of cortical neurons. GABA(A) and GABA(B) receptor subunit expression was visualized by immunohistochemistry in human auditory areas from both hemispheres in 9 normal subjects (aged 43-85 years; time between death and fixation 6-24 hours) and in 4 stroke patients (aged 59-87 years; time between death and fixation 7-24 hours) and analyzed qualitatively for GABA(A) and semiquantitatively for GABA(B) receptor subunits. In normal brains, the primary auditory area (TC) and the surrounding areas TB and TA displayed distinct GABA(A) receptor subunit labeling with differences among cortical layers and areas. In postacute and chronic stroke we found a layer-selective downregulation of the alpha-2 subunit in the anatomically intact cerebral cortex of the intact and of the lesioned hemisphere, whereas the alpha-1, alpha-3 and beta-2/3 subunits maintained normal levels of expression. The GABA(B) receptors had a distinct laminar pattern in auditory areas and minor differences among areas. Unlike in other pathologies, there is no modulation of the GABA(B) receptor expression in subacute or chronic stroke.

Differential changes in synaptic proteins in the Alzheimer frontal cortex with marked increase in PSD-95 postsynaptic protein

We investigated how synaptic plasticity is related to the neurodegeneration process in the human dorsolateral prefrontal cortex. Pre- and postsynaptic proteins of Brodmann's area 9 from patients with Alzheimer's disease (AD) and age-matched controls were quantified by immunohistochemical methods and Western blots. The main finding was a significant increase in the expression of postsynaptic density protein PSD-95 in AD brains, revealed on both sections and immunoblots, while the expression of spinophilin, associated to spines, remained quantitatively unchanged despite qualitative changes with age and disease. Presynaptic protein alpha-synuclein indicated an increased immunohistochemical level, while synaptophysin remained unchanged. MAP2, a somatodendritic microtubule protein, as well as AD markers such as amyloid-beta protein and phosphorylated protein tau showed an increased expression on immunosections in AD. Altogether these changes suggest neuritic and synaptic reorganization in the process of AD. In particular, the significant increase in PSD-95 expression suggests a change in NMDA receptors trafficking and may represent a novel marker of functional significance for the disease.

Expression of brain-derived neurotrophic factor is not modulated by chronic mild stress in the rat hippocampus and amygdala

Accumulating evidence supports a role for brain-derived neurotrophic factor (BDNF) in depression. However, most of these studies have been performed in animal models that have a low face validity with regard to the human disease. Here, we examined the regulation of BDNF expression in the hippocampus and amygdala of rats subjected to the chronic mild stress (CMS) model of depression, a paradigm that induces anhedonia, a core symptom of depression. We found that exposure of rats to the CMS paradigm did not modulate BDNF mRNA expression in the hippocampus and amygdala. In addition, chronic administration of imipramine, which reversed CMS-induced anhedonia, did not alter BDNF mRNA expression in these limbic structures.

Does the physical disector method provide an accurate estimation of sensory neuron number in rat dorsal root ganglia?

The physical disector is a method of choice for estimating unbiased neuron numbers; nevertheless, calibration is needed to evaluate each counting method. The validity of this method can be assessed by comparing the estimated cell number with the true number determined by a direct counting method in serial sections. We reconstructed a 1/5 of rat lumbar dorsal root ganglia taken from two experimental conditions. From each ganglion, images of 200 adjacent semi-thin sections were used to reconstruct a volumetric dataset (stack of voxels). On these stacks the number of sensory neurons was estimated and counted respectively by physical disector and direct counting methods. Also, using the coordinates of nuclei from the direct counting, we simulate, by a Matlab program, disector pairs separated by increasing distances in a ganglion model. The comparison between the results of these approaches clearly demonstrates that the physical disector method provides a valid and reliable estimate of the number of sensory neurons only when the distance between the consecutive disector pairs is 60 microm or smaller. In these conditions the size of error between the results of physical disector and direct counting does not exceed 6%. In contrast when the distance between two pairs is larger than 60 microm (70-200 microm) the size of error increases rapidly to 27%. We conclude that the physical dissector method provides a reliable estimate of the number of rat sensory neurons only when the separating distance between the consecutive dissector pairs is no larger than 60 microm.

A glutathione deficit alters dopamine modulation of L-type calcium channels via D2 and ryanodine receptors in neurons

Synthesis of glutathione, a major redox regulator, is compromised in schizophrenia. We postulated that the resulting glutathione deficit via its effect on redox-sensitive proteins could contribute to dysfunction of some neurotransmitter systems in schizophrenia. We investigated whether a glutathione deficit, induced by a blocker of glutathione synthesis, L-buthionine-(S,R)-sulfoximine, affects intracellular pathways implicated in dopamine signaling in neurons, namely dopamine modulation of calcium responses to NMDA. Such a glutathione deficit changed the modulation of responses by dopamine, from enhanced responses in control neurons (likely via D1-type receptors) to decreased responses in low-glutathione neurons (via D2-type receptors). This difference in dopamine modulation was due to a different modulation of L-type calcium channels activated during NMDA stimulation: dopamine enhanced function of these channels in control neurons but decreased it in low-glutathione neurons. The effect of a glutathione deficit on dopamine signaling was dependent on the redox-sensitive ryanodine receptors (RyRs), whose function was enhanced in low-glutathione neurons. This suggests that enhanced RyRs in low-glutathione neurons strengthens intracellular calcium-dependent pathways following activation of D2-type receptors and causes a decrease in function of L-type channels. This represents a mechanism by which dopaminergic systems could be dysfunctional under conditions of impaired glutathione synthesis as in schizophrenia.

Postsynaptic density protein PSD-95 expression in Alzheimer's disease and okadaic acid induced neuritic retraction

In order to understand how plasticity is related to neurodegeneration, we studied synaptic proteins with quantitative immunohistochemistry in the entorhinal cortex from Alzheimer patients and age-matched controls. We observed a significant decrease in presynaptic synaptophysin and an increase in postsynaptic density protein PSD-95, positively correlated with beta amyloid and phosphorylated Tau proteins in Alzheimer cases. Furthermore, Alzheimer-like neuritic retraction was generated in okadaic acid (OA) treated SH-SY5Y neuroblastoma cells with no decrease in PSD-95 expression. However, in a SH-SY5Y clone with decreased expression of transcription regulator LMO4 (as observed in Alzheimer's disease) and increased neuritic length, PSD-95 expression was enhanced but did not change with OA treatment. Therefore, increased PSD-95 immunoreactivity in the entorhinal cortex might result from compensatory mechanisms, as in the SH-SY5Y clone, whereas increased Alzheimer-like Tau phosphorylation is not related to PSD-95 expression, as suggested by the OA-treated cell models.

The expansion of 300 CTG repeats in myotonic dystrophy transgenic mice does not induce sensory or motor neuropathy

Although many studies have been carried out to verify the involvement of the peripheral nervous system (PNS) in dystrophia myotonica (DM1) patients, the results remain controversial. The generation of DM1 transgenic mice displaying the human DM1 phenotype provides a useful tool to investigate the type and incidence of structural abnormalities in the PNS. In the present study, the morphological and morphometric analysis of semi-thin sections of sciatic and sural nerves, lumbar dorsal root ganglia (DRG) and lumbar spinal cords revealed that in DM1 transgenic mice carrying 300 CTG repeats, there is no change in the number and diameter of myelinated axons compared to wild type. Only a non-significant reduction in the percentage of thin myelinated axons was detected in electron micrographs of ultra-thin sciatic nerve sections. Analysis of the number of neurons did not reveal a loss in number of either sensory neurons in the lumbar DRG or motor neurons in the lumbar spinal cord in these DM1 mice. Furthermore, in hind limb muscle sections, stained with a neurofilament antibody and alpha-bungarotoxin, the intramuscular axon arborization appeared normal in DM1 mice and undistinguishable from that in wild-type mice. Moreover, in DM1 mice, there was no irregularity in the structure or an increase in the endplate area. Also statistical analysis did not show an increase in endplate density or in the concentration of acetylcholine receptors. Altogether, these results suggest that 300 CTG repeats are not sufficient to induce axonopathy, demyelination or neuronopathies in this transgenic mouse model.

Neurosphere-derived cells exert a neuroprotective action by changing the ischemic microenvironment

Background

Neurosphere-derived cells (NC), containing neural stem cells, various progenitors and more differentiated cells, were obtained from newborn C57/BL6 mice and infused in a murine model of focal ischemia with reperfusion to investigate if: 1) they decreased ischemic injury and restored brain function; 2) they induced changes in the environment in which they are infused; 3) changes in brain environment consequent to transient ischemia were relevant for NC action.

Methodology/Principal Findings

NC were infused intracerebroventricularly 4 h or 7 d after 30 min middle cerebral artery occlusion. In ischemic mice receiving cells at 4 h, impairment of open field performance was significantly improved and neuronal loss significantly reduced 7–14 d after ischemia compared to controls and to ischemic mice receiving cells at 7 d. Infusion of murine foetal fibroblast in the same experimental conditions was not effective. Assessment of infused cell distribution revealed that they migrated from the ventricle to the parenchyma, progressively decreased in number but they were observable up to 14 d. In mice receiving NC at 7 d and in sham-operated mice, few cells could be observed only at 24 h, indicating that the survival of these cells in brain tissue relates to the ischemic environment. The mRNA expression of trophic factors such as Insulin Growth Factor-1, Vascular Endothelial Growth Factor-A, Transforming Growth Factor-β1, Brain Derived Neurotrophic Factor and Stromal Derived Factor−1α, as well as microglia/macrophage activation, increased 24 h after NC infusion in ischemic mice treated at 4 h compared to sham-operated and to mice receiving cells at 7 d.

Conclusions/Significance

NC reduce functional impairment and neuronal damage after ischemia/reperfusion injury. Several lines of evidence indicate that the reciprocal interaction between NC and the ischemic environment is crucial for NC protective actions. Based on these results we propose that a bystander control of the ischemic environment may be the mechanism used by NC to rapidly restore acutely injured brain function.

Cerebrospinal fluid antimicroglial antibodies in Alzheimer disease: A putative marker of an ongoing inflammatory process

Immunocompetent microglia play an important role in the pathogenesis of Alzheimer's disease (AD). Antimicroglial antibodies in the cerebrospinal fluid (CSF) in clinically diagnosed AD patients have been previously recorded. Here, we report the results of the analysis of the CSF from 38 autopsy cases: 7 with definite AD; 14 with mild and 10 with moderate Alzheimer's type pathology; and 7 controls. Antimicroglial antibodies were identified in 70% of patients with definite AD, in 80% of patients with moderate and in 28% of patients with mild Alzheimer's type pathology. CSF antimicroglial antibodies were not observed in any of the control cases. The results show that CSF antimicroglial antibodies are present in the majority of patients with definite AD and also in cases with moderate Alzheimer's type changes. They may also indicate dysregulation of microglial function. Together with previous observations, these findings indicate that compromised immune defense mechanisms play an important role in the pathogenesis of AD.

Thyroid Hormone in Biodegradable Nerve Guides Stimulates Sciatic Nerve Regeneration: A Potential Therapeutic Approach for Human Peripheral Nerve Injuries

It has been already demonstrated that thyroid hormone (T3) is one of the most important stimulating factors in peripheral nerve regeneration. We have recently shown that local administration of T3 in silicon tubes at the level of the transected rat sciatic nerve enhanced axonal regeneration and improved functional recovery. Silicon, however, cannot be used in humans because it causes a chronic inflammatory reaction. Therefore, in order to provide future clinical applications of thyroid hormone in human peripheral nerve lesions, we carried out comparative studies on the regeneration of transected rat sciatic nerve bridged either by biodegradable P(DLLA-(-CL) or by silicon nerve guides, both guides filled with either T3 or phosphate buffer. Our macroscopic observation revealed that 85% of the biodegradable guides allowed the expected regeneration of the transected sciatic nerve. The morphological, morphometric and electrophysiological analysis showed that T3 in biodegradable guides induces a significant increase in the number of myelinated regenerated axons (6862 +/- 1831 in control vs. 11799 +/- 1163 in T3-treated). Also, T3 skewed the diameter of myelinated axons toward larger values than in controls. Moreover, T3 increases the compound muscle action potential amplitude of the flexor and extensor muscles of the treated rats. This T3 stimulation in biodegradable guides was equally well to that obtained by using silicone guides. In conclusion, the administration of T3 in biodegradable guides significantly improves sciatic nerve regeneration, confirming the feasibility of our technique to provide a serious step towards future clinical application of T3 in human peripheral nerve injuries.

Structural basis for map formation in the thalamocortical pathway of the barrelless mouse

Barrelless mice (BRL) homozygous for the BRL mutation that disrupts the gene coding for adenylyl cyclase type I on chromosome 11 lack spatial segregation of layer IV cortical cells and of the thalamocortical axons (TCAs) into barrel domains. Despite these morphological perturbations, a functional topographic map has been demonstrated. We reconstructed individual biocytin-injected TCAs from thalamus to barrel cortex in NOR (normal) and BRL mice to analyze to what extent the TCA arborization pattern and bouton distribution could explain the topographic representation of the whisker follicles. In BRL, the geometry of TCA is modified within layer IV as well as in infragranular layers. However, in both strains, the spatial distribution of TCA in layer IV reflects the spatial relationship of their cell bodies in the ventrobasal nucleus of the thalamus. The morphometric analysis revealed that TCAs of both strains have the same length, branch number, and number of axonal boutons in layer IV. However, in barrelless, the boutons are distributed within a larger tangential extent. Analysis of the distribution of boutons from neighboring thalamic neurons demonstrated the existence in layer IV of domains of high bouton density that in both strains equal the size and shape of individual barrels. We propose that the domains of high bouton density are at the basis of the whisker map in barrelless mice.

Glutathione deficit during development induces anomalies in the rat anterior cingulate GABAergic neurons: Relevance to schizophrenia

A series of studies in schizophrenic patients report a decrease of glutathione (GSH) in prefrontal cortex (PFC) and cerebrospinal fluid, a decrease in mRNA levels for two GSH synthesizing enzymes and a deficit in parvalbumin (PV) expression in a subclass of GABA neurons in PFC. GSH is an important redox regulator, and its deficit could be responsible for cortical anomalies, particularly in regions rich in dopamine innervation. We tested in an animal model if redox imbalance (GSH deficit and excess extracellular dopamine) during postnatal development would affect PV-expressing neurons. Three populations of interneurons immunolabeled for calcium-binding proteins were analyzed quantitatively in 16-day-old rat brain sections. Treated rats showed specific reduction in parvalbumin immunoreactivity in the anterior cingulate cortex, but not for calbindin and calretinin. These results provide experimental evidence for the critical role of redox regulation in cortical development and validate this animal model used in schizophrenia research.

Biochemical quantification of total brain glycogen concentration in rats under different glycemic states

All (13)C NMR studies of brain glycogen to date relied on observing the incorporation of (13)C label into glycogen, and thus interpretation was potentially affected by changes in (13)C label turnover rates. The goal of this study was to quantify total brain glycogen concentration under conditions of hypoglycemia or normoglycemia using biochemical methods. Rats were sacrificed using a focused microwave fixation device. The results showed that metabolism of brain glycogen was Glc- and insulin-sensitive and that insulin-induced hypoglycemia promoted a gradual glycogenolysis. Moreover, we show that there are very mild effects of isoflurane and alpha-chloralose anesthesia on brain glycogen concentration. Altogether these results show that total brain glycogen serves as a substantial source of glucosyl units during insulin-induced moderate hypoglycemia and therefore may be neuroprotective. Finally we also conclude that previous interpretation of (13)C NMR spectroscopy data accurately reflected the changes in total brain glycogen content.

Glucose and lactate are equally effective in energizing activity-dependent synaptic vesicle turnover in purified cortical neurons

This study examines the role of glucose and lactate as energy substrates to sustain synaptic vesicle cycling. Synaptic vesicle turnover was assessed in a quantitative manner by fluorescence microscopy in primary cultures of mouse cortical neurons. An electrode-equipped perfusion chamber was used to stimulate cells both by electrical field and potassium depolarization during image acquisition. An image analysis procedure was elaborated to select in an unbiased manner synaptic boutons loaded with the fluorescent dye N-(3-triethylammoniumpropyl)-4-(4-(dibutylamino)styryl)pyridinium dibromide (FM1-43). Whereas a minority of the sites fully released their dye content following electrical stimulation, others needed subsequent K(+) depolarization to achieve full release. This functional heterogeneity was not significantly altered by the nature of metabolic substrates. Repetitive stimulation sequences of FM1-43 uptake and release were then performed in the absence of any metabolic substrate and showed that the number of active sites dramatically decreased after the first cycle of loading/unloading. The presence of 1 mM glucose or lactate was sufficient to sustain synaptic vesicle cycling under these conditions. Moreover, both substrates were equivalent for recovery of function after a phase of decreased metabolic substrate availability. Thus, lactate appears to be equivalent to glucose for sustaining synaptic vesicle turnover in cultured cortical neurons during activity.

Neuronal and nonneuronal quantitative BACE immunocytochemical expression in the entorhinohippocampal and frontal regions in Alzheimer's disease

In this study, we quantitatively investigated the expression of beta-site amyloid precursor protein cleaving enzyme (BACE) in the entorhinohippocampal and frontal cortex of Alzheimer's disease (AD) and old control subjects. The semiquantitative estimation indicated that the intensity of BACE overall immunoreactivity did not differ significantly between AD and controls, but that a significantly stronger staining was observed in the hippocampal regions CA3-4 compared to other regions in both AD patients and controls. The quantitative estimation confirmed that the number of BACE-positive neuronal profiles was not significantly decreased in AD. However, some degeneration of BACE-positive profiles was attested by the colocalization of neurons expressing BACE and exhibiting neurofibrillary tangles (NFT), as well as by a decrease in the surface area of BACE-positive profiles. In addition, BACE immunocytochemical expression was observed in and around senile plaques (SP), as well as in reactive astrocytes. BACE-immunoreactive astrocytes were localized in the vicinity or close to the plaques and their number was significantly increased in AD entorhinal cortex. The higher amount of beta-amyloid SP and NFT in AD was not correlated with an increase in BACE immunoreactivity. Taken together, these data accent that AD progression does not require an increased neuronal BACE protein level, but suggest an active role of BACE in immunoreactive astrocytes. Moreover, the strong expression in controls and regions less vulnerable to AD puts forward the probable existence of alternate BACE functions.

Topography of cortico-striatal connections in man: anatomical evidence for parallel organization

Tracing studies in non-human primates support the existence of several parallel neuronal circuits involving cerebral cortex, basal ganglia and thalamus. Distinct functional loops were proposed to underlie multiple aspects of normal and pathological behaviour in man. We present here the first anatomical evidence for separate corticostriatal systems in humans. Neural connections of the sensorimotor and prefrontal cortex to the striatum were studied in one human brain using the Nauta method for anterogradely degenerating axons. Axons originating from a lesion in the left sensorimotor cortex, including the face area, were found to terminate in the superolateral part of the ipsilateral putamen, forming a narrow band in its posterior part. Inside the band, the distribution of degenerating axons was inhomogeneous; high-density clusters of approximately 2.5 mm in diameter were separated by regions with less dense cortical projections. Axons originating from a small lesion in the fundus of the right superior frontal sulcus were found in the upper part of the ipsilateral caudate nucleus. The existence of discrete and anatomically segregated terminal patches originating from distinct cortical regions suggests parallel organization of cortico-striatal connections in man.

Differential expression of LMO4 protein in Alzheimer's disease

The molecular bases of late-onset and sporadic Alzheimer's disease (AD) still have to be unraveled. Among putative candidates for molecular variations in AD, we propose LMO4 protein, a transcription regulator, involved in multiple protein complexes. We investigated changes in LMO4 immunoreactivity in vulnerable brain regions of AD cases and controls of comparable age. Immunocytochemical analysis revealed a high level of LMO4 expression in the entorhinal cortex (EC) and in the CA1 hippocampal region of the control brains and a consistent decrease in the AD brains, correlated with the amount of neurofibrillary tangles (NFT) degenerating neurones and the severity of senile plaques deposition. The decrease in LMO4 immunoreactivity resulted both from weaker immunoreactive signals and from a loss of immunoreactive neurones. LMO4 immunocytochemical staining appeared not to be colocalized with NFT in a majority of neurones. Its expression was weak in the dentate gyrus and stronger in CA3-4, two regions with no or low numbers of NFT, but there was no decrease in AD compared to control cases. In the frontal cortex, the ventro-infero-median region (area 12) showed a greater LMO4 expression than the polar one (area 9), but no decrease in AD was observed. As LMO4 has been proposed to inhibit cellular differentiation, it can be hypothesized that a reduced expression is associated in EC and CA1 with attempts of diseased neurones to differentiate (e.g. compensatory neuritogenesis). Taken together, these data indicate that LMO4 protein is involved in the complexity of the disease phenotype, at least as a secondary factor.

Thyroid hormone reduces the loss of axotomized sensory neurons in dorsal root ganglia after sciatic nerve transection in adult rat

We have shown that a local administration of thyroid hormones (T3) at the level of transected rat sciatic nerve induced a significant increase in the number of regenerated axons. To address the question of whether local administration of T3 rescues the axotomized sensory neurons from death, in the present study we estimated the total number of surviving neurons per dorsal root ganglion (DRG) in three experimental group animals. Forty-five days following rat sciatic nerve transection, the lumbar (L4 and L5) DRG were removed from PBS-control, T3-treated as well as from unoperated rats, and serial sections (1 microm) were cut. The physical dissector method was used to estimate the total number of sensory neurons in the DRGs. Our results revealed that in PBS-control rats transection of sciatic nerve leads to a significant (P < 0.001) decrease in the mean number of sensory neurons (8743.8 +/- 748.6) compared with the number of neurons in nontransected ganglion (mean 13,293.7 +/- 1368.4). However, administration of T3 immediately after sciatic nerve transection rescues a great number of axotomized neurons so that their mean neuron number (12,045.8 +/- 929.8) is not significantly different from the mean number of neurons in the nontransected ganglion. In addition, the volume of ganglia showed a similar tendency. These results suggest that T3 rescues a high number of axotomized sensory neurons from death and allows these cells to grow new axons. We believe that the relative preservation of neurons is important in considering future therapeutic approaches of human peripheral nerve lesion and sensory neuropathy.

Early olfactory involvement in Alzheimer's disease

BACKGROUND

In Alzheimer's disease (AD) the olfactory system, including the olfactory bulb, a limbic paleocortex is severely damaged. The occurrence of early olfactory deficits and the presence of senile plaques and neurofibrillary tangles in olfactory bulb were reported previously by a few authors. The goal of the present study was to analyze the occurrence of AD-type degenerative changes in the peripheral part of the olfactory system and to answer the question whether the frequency and severity of changes in the olfactory bulb and tract are associated with those of the cerebral cortex in AD.

MATERIAL AND METHODS

In 110 autopsy cases several cortical areas and the olfactory bulb and tract were analyzed using histo- and immunohistochemical techniques. Based on a semiquantitative analysis of cortical senile plaques, neurofibrillary tangles and curly fibers, the 110 cases were divided into four groups: 19 cases with severe (definite AD), 14 cases with moderate, 58 cases with discrete and 19 control cases without AD-type cortical changes.

RESULTS

The number of cases with olfactory involvement was very high, more than 84% in the three groups with cortical AD-type lesions. Degenerative olfactory changes were present in all 19 definite AD cases, and in two of the 19 controls. The statistical analysis showed a significant association between the peripheral olfactory and cortical degenerative changes with respect to their frequency and severity (P < 0.001). Neurofibrillary tangles and neuropil threads appear in the olfactory system as early as in entorhinal cortex.

CONCLUSION

The results indicate a close relationship between the olfactory and cortical degenerative changes and indicate that the involvement of the olfactory bulb and tract is one of the earliest events in the degenerative process of the central nervous system in AD.

Cerebral hypoperfusion generates cortical watershed microinfarcts in Alzheimer disease

BACKGROUND AND PURPOSE

The watershed cortical areas are the first to be deprived of sufficient blood flow in the event of cerebral hypoperfusion and will be the sites of watershed microinfarcts. Cerebral hypoperfusion is associated with Alzheimer disease (AD), but information regarding the occurrence of watershed cortical infarcts in AD is lacking.

METHODS

Brains of 184 autopsy cases (105 definite AD cases and 79 age-matched controls) were selected and analyzed by histochemical and immunohistochemical techniques. The 3-dimensional reconstruction of the whole cerebrum, with 3-mm spaced serial sections, was performed in 6 AD cases to study the intrahemispheric and interhemispheric distribution of the cortical microinfarcts.

RESULTS

A significant association (P=0.001) was found between the occurrence of watershed cortical infarcts and AD (32.4% versus 2.5% in controls). The microinfarcts were restricted to the watershed cortical zones. Congophilic angiopathy was revealed to be an important risk factor. Perturbed hemodynamic factors (eg, decreased blood pressure) may play a role in the genesis of cortical watershed microinfarcts.

CONCLUSIONS

In AD, cerebral hypoperfusion induces not only white matter changes but cortical watershed microinfarcts as well, further aggravating the degenerative process and worsening dementia. To prevent the formation of watershed cortical microinfarcts in AD, monitoring blood pressure and treating arterial hypotension are essential.

Differential effect of thyroid hormone deficiency on the growth of calretinin-expressing neurons in rat spinal cord and dorsal root ganglia

The development of spinal cord or dorsal root ganglia neurons expressing calretinin (CR) was studied in thyroid hormone-deficient rats. Immunocytochemical and morphometric analyses showed that the hypothyroidism induced a significant decrease in the number and size of immunoreactive neurons in the spinal cord, as well as stunted growth and arborization of the axons and dendrites. These alterations were observed at different embryonic ages and persisted during the whole postnatal life. In adult hypothyroid rats, the mean number of CR-positive neurons per spinal cord section (31.2 +/- 2.3 in laminae I and II and 30.5 +/- 5.5 in laminae III-X) was significantly decreased (P < 0.001 and P = 0.024, respectively) compared with adult normal rats (68.7 +/- 8.9 and 50.0 +/- 11.0, respectively). In the peripheral nervous system, hypothyroidism altered the growth of sensory neurons expressing CR protein mainly during embryonic life. In comparison with normal rats, hypothyroid embryonic animals showed not only reduced cell size but also a significantly decreased percentage of CR-positive neurons (6.6 +/- 0. 9% in normal, 2.1 +/- 0.3% in hypothyroid rats, P < 0.001). In contrast, although the size of neurons was reduced in hypothyroid young and adult rats, there was no reduction in the percentage of CR-positive neurons. These results showed that thyroid hormone deficiency altered differentially the development of neurons expressing CR protein in the central and peripheral nervous systems. This suggests that central and peripheral neurons are heterogeneous in their sensitivity to thyroid hormone.

Primary motor cortex involvement in Alzheimer disease

In Alzheimer disease (AD) the involvement of entorhinal cortex, hippocampus, and associative cortical areas is well established. Regarding the involvement of the primary motor cortex the reported data are contradictory. In order to determine whether the primary motor cortex is involved in AD, the brains of 29 autopsy cases were studied, including, 17 cases with severe cortical AD-type changes with definite diagnoses of AD, 7 age-matched cases with discrete to moderate cortical AD-type changes, and 5 control cases without any AD-type cortical changes. Morphometric analysis of the cortical surface occupied by senile plaques (SPs) on beta-amyloid-immunostained sections and quantitative analysis of neurofibrillary tangles (NFTs) on Gallyas-stained sections was performed in 5 different cortical areas including the primary motor cortex. The percentage of cortical surface occupied by SPs was similar in all cortical areas, without significant difference and corresponded to 16.7% in entorhinal cortex, 21.3% in frontal associative, 16% in parietal associative, and 15.8% in primary motor cortex. The number of NFTs in the entorhinal cortex was significantly higher (41 per 0.4 mm2), compared with those in other cortical areas (20.5 in frontal, 17.9 in parietal and 11.5 in the primary motor cortex). Our findings indicate that the primary motor cortex is significantly involved in AD and suggest the appearance of motor dysfunction in late and terminal stages of the disease.

Alzheimer disease: curly fibers and tangles in organs other than brain

The filamentous brain lesions that define Alzheimer disease (AD) consist of senile plaques and neurofibrillary tangles. Undulated pathological filaments--curly fibers or neuropil threads--also occur in the neuropil. Beta-amyloid precursor proteins are synthesized by many cells outside the central nervous system and recently, deposition of beta-amyloid-protein was reported to occur in non-neuronal tissues. In addition, increasing data claim the importance of chronic inflammation in the pathogenesis of AD. These observations suggest that AD may be a widespread systemic disorder. Here we report that pathological argyrophilic filaments with histochemical properties of amyloid showing striking morphological similarity to curly fibers and/or tangles accumulate not only in ependymal layer and in epithelial cells of choroid plexus, but also in several other organs (e.g. liver, pancreas, ovary, testis, thyroid) in AD. The ependyma, choroid plexus, and various organs of 39 autopsy cases were analyzed. In search of curly fiber and tangle-like changes in organs other than brain, 395 blocks from 21 different tissues of 24 AD cases, 5 cases with discrete or moderate AD-type changes, and 10 control cases were investigated. We found in non-neuronal cells "curly fibers" or "tangles" immunoreactive with antibodies to P component, Tau-protein, ubiquitin, fibronectin, and Apolipoprotein-E, but lacking immunoreactivity with antibodies to neurofilament proteins. Ultrastructurally they consist of densely packed straight and paired helical filaments and closely resemble neurofibrillary tangles and neuropil threads. These observations indicate that the formation of "curly fibers" and "tangles" is not unique to the central nervous system. The results suggest that AD might be a systemic disorder or that similar fibrillary changes to tangles and curly fibers may also be associated with other amyloidosis than beta-amyloidosis. Further investigations are necessary to understand the pathogenetic interest of these fibrillary changes outside the CNS.

Curly fiber and tangle-like inclusions in the ependyma and choroid plexus--a pathogenetic relationship with the cortical Alzheimer-type changes?

The question of whether thread- and tangle-like inclusions of the choroid plexus (known as Biondi inclusions) are related to the cortical lesions in Alzheimer disease (AD) has been debated for almost a century, yet remains unanswered. Recently beta-amyloid protein was biochemically isolated from the plexus, indicating a possible pathogenetic relationship between the degenerative changes of the cerebral cortex and those of the plexus. The goal of the present study was to analyze whether or not a significant correlation exists between the occurrence of the cortical AD-type changes and those in the ependyma and choroid plexus. In 292 consecutive autopsy cases several cortical areas, the ependyma, and the choroid plexus were analyzed to look for AD-type changes and Biondi inclusions using histochemical staining techniques and immunohistochemistry. A semiquantitative analysis of the density of cortical AD-type changes showed that of the 292 cases, 63 had severe cortical changes, 23 moderate changes, and 142 discrete changes. In 64 cases no plaques or neurofibrillary tangles were found. The number of cases with thread- and tangle-like elements in the plexus and ependyma was more than 96% in the 3 groups with cortical AD-type lesions, but low in the group without AD-type cortical changes (19%). The pathological argyrophilic filaments accumulating in the ependymal layer and plexus had histochemical properties of amyloid and were immunoreactive with antibodies to P component, ubiquitin, fibronectin and Tau protein. They did not react with antibodies to neurofilament proteins. Ultrastructurally, they consisted of densely packed straight and paired helical filaments and closely resembled neurofibrillary tangles and neuropil threads. The highly significant correlation (chi2, p = 0.001; R = 0.85) between the occurrence of AD-type changes in the cortex and those in ependyma and plexus suggests a pathogenetic relationship.

Quantitative distribution of parvalbumin, calretinin, and calbindin D-28k immunoreactive neurons in the visual cortex of normal and Alzheimer cases

The distribution of parvalbumin (PV), calretinin (CR), and calbindin (CB) immunoreactive neurons was studied with the help of an image analysis system (Vidas/Zeiss) in the primary visual area 17 and associative area 18 (Brodmann) of Alzheimer and control brains. In neither of these areas was there a significant difference between Alzheimer and control groups in the mean number of PV, CR, or CB immunoreactive neuronal profiles, counted in a cortical column going from pia to white matter. Significant differences in the mean densities (numbers per square millimeter of cortex) of PV, CR, and CB immunoreactive neuronal profiles were not observed either between groups or areas, but only between superficial, middle, and deep layers within areas 17 and 18. The optical density of the immunoreactive neuropil was also similar in Alzheimer and controls, correlating with the numerical density of immunoreactive profiles in superficial, middle, and deep layers. The frequency distribution of neuronal areas indicated significant differences between PV, CR, and CB immunoreactive neuronal profiles in both areas 17 and 18, with more large PV than CR and CB positive profiles. There were also significantly more small and less large PV and CR immunoreactive neuronal profiles in Alzheimer than in controls. Our data show that, although the brain pathology is moderate to severe, there is no prominent decrease of PV, CR and CB positive neurons in the visual cortex of Alzheimer brains, but only selective changes in neuronal perikarya.

Ontogeny of calretinin expression in rat dorsal root ganglia

The relationship between the expression of calretinin and the maturation level of peripheral sensory neurons was investigated by means of immunohistochemistry and immunoblot analysis. Our immunohistochemical results show that calretinin is expressed during two different developmental phases in rat dorsal root ganglia. The early phase lasts between embryonic days 11 and 14, when calretinin is detectable in the majority (75%) of the cells. A second phase starts at embryonic day 17 and lasts throughout the whole postnatal life, when calretinin is expressed only in a small proportion of the neurons (less than 8%). Between these two periods no calretinin is found in the ganglia. These changes in calretinin expression during embryonic development were confirmed by Western blot analysis. The early expression of calretinin in dorsal root ganglion cells suggests that calretinin may act as a calcium regulator until neurotrophins take over the precise tuning of intracellular calcium concentration.

Local administration of thyroid hormones in silicone chamber increases regeneration of rat transected sciatic nerve

Conflicting actions of the exogenous thyroid hormone on regenerating peripheral nerve have been reported. These contradictory results were probably due to daily intraperitoneal injections which induce a high concentration of thyroid hormone after administration. In our present study we adapted a technique which allows a local administration of thyroid hormones in a closed system. The effect of a single and local treatment with triiodothyronine (T3) on axonal growth across a gap between sectioned ends of sciatic nerve within silicone chambers was examined in Wistar rats. After nerve transection and surgical implantation, silicone chambers were filled with either a neutral pH solution of triiodothyronine dissolved in NaOH or with sterile solvent as control. Regeneration of the nerves was examined 2 to 8 weeks following the surgery. Early regeneration (4 weeks) was studied by morphological analysis of nerves which showed a significant difference between T3-treated and control groups. Morphometric analysis revealed: (1) a significant difference in the mean diameter of myelinated axons between T3-treated nerve (phi 3.80 +/- 0.22 microns) and control (phi 3.07 +/- 0.44 microns); (2) that T3 increased significantly (1.4-fold) the number of myelinated axons that grew into the middle and distal ends of regeneration chambers; (3) that ultrastructural analysis showed significantly higher percentage of myelinated axons per total axon population in T3-treated groups (38.8 +/- 5.9%) as compared to control (16.0 +/- 2.3%); and (4) that the myelinated axons had thicker myelin sheaths. The beneficial effects of T3 on regeneration, observed at 4 weeks, were sustained over a prolonged period of time. Thus, at 8 weeks of regeneration, the number, the mean diameter of myelinated axons, and the thickness of myelin sheaths remained significantly greater in T3-treated groups. Therefore, a single and local administration of thyroid hormone at the level of the transected sciatic nerve is sufficient to rapidly set off several mechanisms which, in turn, produce a stimulating and lasting effect on peripheral nerve regeneration. The beneficial effects of T3 upon injured peripheral nerve may have considerable therapeutic potential.

Dendritic reorientation and cytolamination during the development of the isthmo-optic nucleus in chick embryos

In the mature isthmo-optic nucleus (ION, source of efferents to the contralateral retina), the neuronal perikarya are generally described as being arranged in a single convoluted lamina surrounding a U-shaped region of neuropil, into which their highly polarized (unidirectional) dendritic arbors project perpendicularly. We find, however, that the details are more complicated than this description suggests, and are variable, as might be expected if the ION is self-organized through neuron-to-neuron interactions in development. The laminated conformation of the ION first appears at embryonic day (E) 14. Our previous experiments indicate that this involves the displacement of perikarya and is not due to sculpting by neuronal death. We here present a quantitative demonstration that the dendritic arbors reorient during the period of lamination. At E11, they are already highly polarized, but their directions are different from those in the adult, being mostly medio-rostro-ventral. Then, between E11 and E13, the arbors in the border region of the ION undergo major changes in their direction of polarization, projecting towards the center of the ION. The arbors within the core of the ION make more subtle changes. The dendritic reorganization seems to be intrinsically linked to the process of cytolamination, since the two events occur synchronously and disruption of either affects the other. Mechanisms are discussed; interaction with afferents is not responsible for lamination.

The auditory pathway in cat corpus callosum

The cortical auditory fields of the two hemispheres are interconnected via the corpus callosum. We have investigated the topographical arrangement of auditory callosal axons in the cat. Following circumscribed biocytin injections in the primary (AI), secondary (AII), anterior (AAF) and posterior (PAF) auditory fields, labelled axons have been found in the posterior two-thirds of the corpus callosum. Callosal axons labelled by small individual cortical injections did not form a tight bundle at the callosal midsagittal plane but spread over as much as one-third of the corpus callosum. Axons originating from different auditory fields were roughly topographically ordered, reflecting to some extent the rostro-caudal position of the field of origin. Axons from AAF crossed on average more rostrally than axons from AI; the latter crossed more rostrally than axons from PAF and AII. Callosal axons originating in a discrete part of the cortex travelled first in a relatively tight bundle to the telo-diencephalic junction and then dispersed progressively. In conclusion, the cat corpus callosum does not contain a sector reserved for auditory axons, nor a strictly topographically ordered auditory pathway. This observation is of relevance to neuropsychological and neuropathological observations in man.

Changes in volume, surface estimate, three-dimensional shape and total number of neurons of the human primary visual cortex from midgestation until old age

Macroscopic features such as volume, surface estimate, thickness and caudorostral length of the human primary visual cortex (Brodman's area 17) of 46 human brains between midgestation and 93 years were studied by means of camera lucida drawings from serial frontal sections. Individual values were best fitted by a logistic function from midgestation to adulthood and by a regression line between adulthood and old age. Allometric functions were calculated to study developmental relationships between all the features. The three-dimensional shape of area 17 was also reconstructed from the serial sections in 15 cases and correlated with the sequence of morphological events. The sulcal pattern of area 17 begins to develop around 21 weeks of gestation but remains rather simple until birth, while it becomes more convoluted, particularly in the caudal part, during the postnatal period. Until birth, a large increase in cortical thickness (about 83% of its mean adult value) and caudorostral length (69%) produces a moderate increase in cortical volume (31%) and surface estimate (40%) of area 17. After birth, the cortical volume and surface undergo their maximum growth rate, in spite of a rather small increase in cortical thickness and caudorostral length. This is due to the development of the pattern of gyrification within and around the calcarine fissure. All macroscopic features have reached the mean adult value by the end of the first postnatal year. With aging, the only features to undergo significant regression are the cortical surface estimate and the caudorostral length. The total number of neurons in area 17 shows great interindividual variability at all ages. No decrease in the postnatal period or in aging could be demonstrated.

Visual cortex in Alzheimer's disease: occurrence of neuronal death and glial proliferation, and correlation with pathological hallmarks

Visual areas 17 and 18 were studied with morphometric methods for numbers of neurons, glia, senile plaques (SP), and neurofibrillary tangles (NFT) in 13 cases of Alzheimer's disease (AD) as compared to 11 controls. In AD cases, the mean neuronal density was significantly decreased by about 30% in both areas 17 and 18, while the glial density was increased significantly only in area 17. The volume of area 17 was unchanged in AD cases but its total number of neurons was decreased by 33% and its total number of glia increased by 45% compared to controls. In AD the number of SP was similar in areas 17 and 18, while that of NFT was significantly higher in area 18. The number of neurons with NFT was only 2% in area 17 and about 10% in area 18. The discrepancy between the loss of neurons and the amount of NFT suggests that neuronal loss can occur without passing through NFT degeneration. The deposition of SP was correlated with glial proliferation, but not with neuronal loss or neurofibrillary degeneration.

The mode of activation of a barrel column: response properties of single units in the somatosensory cortex of the mouse upon whisker deflection

Response properties of single units in the mouse barrel cortex were studied to determine the sequence in which the neurons that form a cortical column become activated by a single 'natural' stimulus. Mice (n = 11) were anaesthetized with urethane. For a total of 153 cells, grouped by cortical layer, responses to a standardized deflection of a single whisker were characterized using poststimulus time and latency histograms. Usually, for each unit, data were collected for stimulation of its principal whisker (PW; the whiskers corresponding to the barrel column in which the cell was located) and of the four whiskers surrounding the PW. In all layers, PW stimulation evoked responses at shorter latency than surround whisker stimulation. In layers II-III and IV a bimodal distribution of cells according to latency to PW stimulation was found. Statistical analysis indicated the presence of two classes of cells in each of these layers: 'fast' units (latency < 15 ms) and 'slow' units (latency > or = 15 ms). The great majority of cells in layers I, V and VI fired at latencies of > 20 ms to PW stimulation. In general, stimulation of surround whiskers evoked a smaller response than PW stimulation. The fast cells of layer IV showed the greatest response to PW stimulation (mean = 1.78 spikes/100 ms poststimulus). Their firing was maximal during the 10-20 ms poststimulus epoch, while the slow layer IV cells fired maximally during the 20-30 ms poststimulus epoch. Surround inhibition occurred in all layers within the first 10 ms after stimulus onset, during which period the fast cells are the most active ones, and are thus likely to be responsible for the surround inhibition. This notion is supported by an analysis of spike duration that showed that eight of the ten cells with a thin spike (supposed to be GABAergic; McCormick et al., J. Neurophysiol., 54, 782-806, 1985), had PW latencies of < 15 ms. We conclude that the activation of a barrel column is initially inhibitory in nature.

Synapses on motoneuron dendrites in the brachial section of the frog spinal cord: a computer-aided electron microscopic study of cobalt-filled cells

Cobalt-labelled motoneuron dendrites of the frog spinal cord at the level of the second spinal nerve were photographed in the electron microscope from long series of ultrathin sections. Three-dimensional computer reconstructions of 120 dendrite segments were analysed. The samples were taken from two locations: proximal to cell body and distal, as defined in a transverse plane of the spinal cord. The dendrites showed highly irregular outlines with many 1-2 microns-long 'thorns' (on average 8.5 thorns per 100 microns 2 of dendritic area). Taken together, the reconstructed dendrite segments from the proximal sites had a total length of about 250 microns; those from the distal locations, 180 microns. On all segments together there were 699 synapses. Nine percent of the synapses were on thorns, and many more close to their base on the dendritic shaft. The synapses were classified in four groups. One third of the synapses were asymmetric with spherical vesicles; one half were symmetric with spherical vesicles; and one tenth were symmetric with flattened vesicles. A fourth, small class of asymmetric synapses had dense-core vesicles. The area of the active zones was large for the asymmetric synapses (median value 0.20 microns 2), and small for the symmetric ones (median value 0.10 microns 2), and the difference was significant. On average, the areas of the active zones of the synapses on thin dendrites were larger than those of synapses on large calibre dendrites. About every 4 microns 2 of dendritic area received one contact. There was a significant difference between the areas of the active zones of the synapses at the two locations. Moreover, the number per unit dendritic length was correlated with dendrite calibre. On average, the active zones covered more than 4% of the dendritic area; this value for thin dendrites was about twice as large as that of large calibre dendrites. We suggest that the larger active zones and the larger synaptic coverage of the thin dendrites compensate for the longer electrotonic distance of these synapses from the soma.