Cyclin-dependent kinase 5-deficient mice demonstrate novel developmental arrest in cerebral cortex

The cerebral cortex of mice with a targeted disruption in the gene for cyclin-dependent kinase 5 (cdk5) is abnormal in its structure. Bromodeoxyuridine labeling reveals that the normal inside-out neurogenic gradient is inverted in the mutants; earlier born neurons are most often found superficial to those born later. Despite this, the early preplate layer separates correctly and neurons with a normal, pyramidal morphology can be found between true marginal zone and subplate. Consistent with their identity as layer VI corticothalamic neurons, they can be labeled by DiI injections into thalamus. The DiI injections also reveal that the trajectories of the cdk5(-/-) thalamocortical axons are oblique and cut across the entire cortical plate, instead of being oriented tangentially in the subcortical white matter. We propose a model in which the cdk5(-/-) defect blocks cortical development at a heretofore undescribed intermediate stage, after the splitting of the preplate, but before the migration of the full complement of cortical neurons.     

Cortical gray matter volume deficits in schizophrenia: a replication

We sought to replicate an earlier finding of widespread deficit in cortical gray matter in schizophrenia by testing new samples of 22 schizophrenic patients and 27 controls between the ages of 21-46 years. Brain values for both patients and controls were standardized against age and head size norms derived from a larger control group (n = 73) spanning a wider age range (21-70). Compared to the new age-matched controls, the new schizophrenic sample showed a deficit in gray matter volume affecting the cortex as a whole and enlargement of the lateral and third ventricles. Thus, widespread cortical gray matter deficit is a replicable feature of the brain dysmorphology of schizophrenia in young to middle-aged men.     

The development of parvalbumin and calbindin-D28k immunoreactive interneurons in kitten visual cortical areas

Calbindin-D and parvalbumin are calcium binding proteins which are found in non-overlapping subpopulations of GABA-ergic interneurons in mammalian neocortex. We studied the development of these calcium-binding proteins in interneurons of cat striate and extrastriate cortical areas which have differing patterns of connectivity and follow different developmental timetables. We examined primary visual areas 17 and 18, secondary visual area 19, medial lateral suprasylvian and lateral suprasylvian areas (MLS and LLS) and association areas 7 and the splenial visual area from the day of birth (P0) through P101. Parvalbumin-immunoreactive (ir) interneurons followed the inside-out pattern of maturation of cortical laminae. They were located only in infragranular layers at the earliest ages and were not observed in the overlying cortical plate. At 3 weeks of age, when cortical lamination is mature, parvalbumin stained cells were found in all cortical layers except layer I. The number of stained secondary and tertiary dendrites in the parvalbumin-ir interneuronal population decreased with age. This change was associated with a shift in the molecular weight of parvalbumin detected on Western blots. During the first postnatal week, the area 17/18 border contained more parvalbumin-ir neurons than other visual areas. The developmental pattern of calbindin staining differed considerably from the parvalbumin staining pattern. Very few calbindin-ir interneurons were seen in area 17 during the first 2 weeks of life. In lateral cortical areas, calbindin-ir neurons were located in cortical plate, infragranular layers of cortex and white matter/subplate. Calbindin-ir neurons increased in supragranular layers of secondary cortical areas by P7 and in area 17 by P20. In the mature cortex, the calbindin staining pattern was bilaminar, with a dense band of calbindin-ir cells in layer II and a second band in layers V-VI. There was no difference in the distribution of calbindin-ir neurons among visual areas at maturity.     

A subclass of prefrontal gamma-aminobutyric acid axon terminals are selectively altered in schizophrenia

In the primate cerebral cortex, morphologically and functionally diverse classes of local circuit neurons containing the inhibitory neurotransmitter gamma-aminobutyric acid (GABA) differentially regulate the activity of pyramidal cells, the principal type of excitatory output neurons. In schizophrenia, GABA neurotransmission in the prefrontal cortex (PFC) appears to be disturbed but whether specific populations of GABA neurons are affected is not known. The chandelier class of GABA neurons are of particular interest because their axon terminals, which form distinctive arrays termed "cartridges," provide inhibitory input exclusively to the axon initial segment of pyramidal cells. Thus, chandelier cells are positioned to powerfully regulate the excitatory output of pyramidal neurons and, consequently, to substantially affect the patterns of neuronal activity within the PFC. In this study, an antibody directed against the GABA membrane transporter GAT-1 was used to label GABA axon terminals in postmortem human brains. The relative density of GAT-1-immunoreactive axon cartridges furnished by chandelier neurons was decreased by 40% in the PFC of schizophrenic subjects compared with matched groups of normal control and nonschizophrenic psychiatric subjects. In contrast, markers of the axon terminals of other populations of GABA neurons were not altered in the schizophrenic subjects. Furthermore, the density of GAT-1-immunoreactive axon cartridges was not altered in psychiatric subjects who had been treated with antipsychotic medications. The changes in GAT-1-immunoreactive axon cartridges of chandelier neurons in schizophrenia are likely to reflect altered information processing within the PFC and in its output connections to other brain regions and could contribute to the cognitive impairments seen in this disorder.     

Effective peer responses to impaired nursing practice

Subplate neurons, the first neurons of the cerebral cortex to differentiate and mature, are thought to be essential for the formation of connections between thalamus and cortex, such as the system of ocular dominance columns within layer 4 of visual cortex. To learn more about the requirement for subplate neurons in the formation of thalamocortical connections, we have sought to identify the neurotransmitters and peptides expressed by the specific class of subplate neurons that sends axonal projections into the overlying visual cortex. To label retrogradely subplate neurons, fluorescent latex microspheres were injected into primary visual cortex of postnatal day 28 ferrets, just prior to the onset of ocular dominance column formation. Subsequently, neurons were immunostained with antibodies against glutamate, glutamic acid decarboxylase (GAD-67), parvalbumin, neuropeptide Y (NPY), somatostatin (SRIF), or nitric oxide synthase (NOS). Retrograde labeling results indicate that the majority of subplate neurons projecting into the cortical plate reside in the upper half of the subplate. Combined immunostaining and microsphere labeling reveal that about half of cortically projecting subplate neurons are glutamatergic; most microsphere-labeled subplate neurons do not stain for GAD-67, parvalbumin, NPY, SRIF, or NOS. These observations suggest that subplate neurons can provide a significant glutamatergic synaptic input to the cortical plate, including the neurons of layer 4. If so, excitation from the axons of subplate neurons may be required in addition to that from lateral geniculate nucleus neurons for the activity-dependent synaptic interactions that lead to the formation of ocular dominance columns during development.     

Potency assay of diphtheria antitoxin in Vero cell microcultures

A slowly rising cortical potential shift with negative polarity following the imperative stimulus of a forewarned reaction time task, the 'post-imperative negative variation' (PINV), is regularly observed in schizophrenic patients but not in controls. The topography of the PINV suggests that it may originate in frontal cortical regions. We used a task designed to test two putative prefrontal cortical functions: working memory and processing of ambiguity. Nineteen patients with a chronic schizophrenic disorder and 19 control subjects matched for age, sex, and education participated in two experimental sessions. The EEG was recorded from frontal, central, temporal, and parietal leads over both hemispheres using a DC amplifier. PINV amplitudes were generally larger in patients than in controls. If the result of comparing physical features of the two successively presented stimuli (warning and imperative stimulus) was ambiguous rather than clear, an augmentation of the PINV amplitudes was seen in both groups. If this comparison required high rather than low involvement of working memory functions, PINV amplitudes were augmented in schizophrenic patients only. Scalp distribution of the PINV indicated a left-hemisphere fronto-central PINV maximum in patients, and a right-hemisphere predominance in controls, which was larger following ambiguous stimulus comparisons. These results suggest that ambiguity during the comparison of physical features of successively presented stimuli may be a general factor of the PINV in schizophrenic patients and healthy controls. Augmented involvement of working memory functions, presumably subserved by the prefrontal cortex, specifically affected the fronto-centrally predominant PINV in schizophrenic patients. This result is compatible with the hypothesis of prefrontal cortical dysfunctions in schizophrenia.     

Further studies on the electrodiagnosis of diabetic peripheral polyneuropathy using discriminant function analysis

BACKGROUND: According to the D2 dopamine receptor hypothesis of schizophrenia, there is an increased number of D2 receptors in the brains of schizophrenic patients than in those of healthy controls. We tested this hypothesis in 13 newly admitted neuroleptic-naive schizophrenic patients and 10 healthy volunteers using positron emission tomography. METHOD: The quantification of striatal D2 dopamine receptor density (Bmax) and affinity (Kd) was done using an equilibrium model described for raclopride labeled with carbon 11. RESULTS: No statistically significant alterations were found in D2 receptor densities or affinities between the patient and control groups. However, a subgroup of four patients with a relatively high striatal D2 dopamine density was identified. Two patients, especially, had D2 dopamine densities almost twice as high as the mean control Bmax value. The Kd values also tended to be higher in this subset of patients than in the controls. No consistent striatal D2 dopamine receptor laterality was observed in schizophrenic patients or controls. However, an association of high D2 dopamine density in the left striatum and the mass of raclopride injected in the scan with low-specific radioactivity was observed in patients but not in controls. CONCLUSIONS: There are no general changes in D2 dopamine receptor Bmax or Kd values in neuroleptic-naive schizophrenics, but there may be a subgroup of patients with aberrant striatal D2 dopamine receptor characteristics in vivo.     

Differential distribution of tyrosine hydroxylase fibers on small and large neurons in layer II of anterior cingulate cortex of schizophrenic brain

A series of recent postmortem investigations of the anterior cingulate cortex in schizophrenic brain have suggested that there may be a loss and/or impairment of inhibitory interneurons in layer II. It has been postulated that changes of this type could secondarily result in a relative increase of dopaminergic inputs to GABAergic interneurons. To test this hypothesis, an immunoperoxidase technique was developed to extensively and reliably visualize tyrosine hydroxylase-immunoreactive (TH-IR) varicose fibers in human postmortem cortex. This method has been applied to the anterior cingulate (ACCx; Brodmann area 24) and prefrontal (PFCx: Brodmann area 10) cortices from a cohort of 15 normal control and 10 schizophrenic cases. The number of TH-IR varicosities in contact with large neurons (LN), small neurons (SN), and neuropil (NPL) was blindly analyzed using a computer-assisted microscopic technique. There was no significant difference in density of TH-IR varicosities in apposition with either LN or SN cell bodies observed in either ACCx or PFCx of schizophrenics when compared to normal controls. The density of varicosities was significantly reduced in NPL of layers V and VI in ACCx, but 2 neuroleptic-free cases did not show this change, suggesting that these decreases of TH-IR varicosities may be related to antipsychotic effects on corticostriatal projection cells in this region. When the density of TH-IR varicosities on SNs was compared to that observed on LNs, both groups showed a higher density on SNs. In ACCx, this pattern was much more pronounced for the schizophrenic group, particularly in layer II where the density on SNs was three times higher than that for LNs (P = 0.01). Unlike the changes in layer V, this latter change in layer II showed no relationship to neuroleptic exposure. There was a positive correlation between age and the density of TH-IR varicosities on SNs of layer II in ACCx; however, the patients were younger than the controls and would have been expected to show a lower density, rather than a higher one, if age considerations had accounted for the group differences. Overall, the results reported here suggest that there are no gross differences in the distribution of TH-IR varicosities in various laminae of the dorsolateral prefrontal cortex. In the anterior cingulate region, however, there may be a significant shift in the distribution of TH-IR varicosities from large neurons to small neurons that occurs selectively in layer II of schizophrenic subjects. Using size criteria, the majority of small neurons are likely nonpyramidal, while the majority of large neurons are predominantly pyramidal in nature. Taken together with other accumulating evidence of preferential abnormalities in this lamina of the cingulate region, the findings reported here are consistent with a model of schizophrenia in which a subtle "miswiring" of ventral tegmental inputs may result in a relative, though not absolute, hyperdopaminergic state with respect to an impaired population of GABAergic interneurons.     

Genome size and GC-percent in vertebrates as determined by flow cytometry: the triangular relationship

Cortical dysplasia is a broad category for an abnormal structure of the cerebrum due to a disorder of the normal developmental process for neocortex. We investigated the cortical dysplastic lesions which were surgically resected from 4 patients with intractable epilepsy. All cases showed a derangement of the cortical laminar structure and dysplastic changes in the neurons. In addition, 3 of them showed large round cells (balloon cells) in the deep cortex and subcortical white matter. Since each lesion showed slightly different features, we further examined the lesions immunohistochemically by using a panel of antibodies against cytoskeletal proteins to recognize and classify the cortical dysplastic lesions. An immunohistochemical study revealed marked abnormalities of the cytoskeletal structures of dysplastic neurons, bizarre glial cells and balloon cells. These cells showed an accumulation of either phosphorylated NF, MAP2 or GFAP in a distinct fashion. Ubiquitin immunoreactivity highlighted the extent of cortical dysplastic lesions. In a young patient, we also found the neuronal cytoplasmic lipofuscin deposition. It is thus considered that these diverse immunohistochemical appearances of cortical dysplasia may thus imply a different pathogenesis and they should therefore be classified based on the extent of histological abnormalities.     

Eye tracking dysfunction in schizophrenia: Characterization of component eye movement abnormalities, diagnostic specificity, and the role of attention.

To characterize oculomotor components and diagnostic specificity of eye tracking abnormalities in schizophrenia, we examined a large consecutively admitted series of psychotic patients and matched controls. The most common abnormality in schizophrenic patients was low gain (slow) pursuit eye movements (47% of cases). Pursuit and saccadic eye movement abnormalities were no more severe in schizophrenic Ss than in those with affective psychoses, except that high rates of catch-up saccades were unique to schizophrenic Ss (17% of cases). These findings indicate that impaired pursuit eye movements are a major cause of eye tracking impairments in schizophrenia, that tracking dysfunctions commonly occur in affective psychoses, and that markedly high rates of catch-up saccades during eye tracking may be specific to schizophrenia. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Establishment of patterned thalamocortical connections does not require nitric oxide synthase

Subplate neurons are early-generated neurons that project into the overlying neocortex and are required for the formation of ocular dominance columns. A subset of subplate neurons express nitric oxide synthase (NOS) and produce nitric oxide (NO), a neuronal messenger thought to be involved in adult hippocampal synaptic plasticity and also in the establishment of certain specific connections during visual system development. Here, we examine whether the NOS-containing subplate neurons are involved in ocular dominance column formation in the ferret visual system. Ocular dominance columns form in ferrets between postnatal day 35 (P35) and P60. NOS expression in the visual subplate is low at birth, increases to a maximum at the onset of ocular dominance column formation, and falls thereafter. Nevertheless, blockade of NOS with daily injections of nitroarginine from P14 to P56 fails to prevent the formation of ocular dominance columns, although NOS activity is reduced by >98%. To test further a requirement for NOS in the patterning of connections during CNS development, we examined the cortical barrels in the somatosensory system of mice carrying targeted disruptions of NOS that also received injections of nitroarginine; cortical barrels formed normally in these animals. In addition, barrel field plasticity induced by whisker ablation at birth was normal in nitroarginine-injected NOS knock-out mice. Thus, despite the dynamic regulation of NOS in subplate neurons, NO is unlikely to be essential for the patterning of thalamocortical connections either in visual or somatosensory systems.     

Strategies for graft immunomodulation in islet transplantation

BACKGROUND: The cortex of patients with schizophrenia exhibits a deficit in neuropil, but the nature and extent of cellular abnormalities remain unclear. To gain further insight into this abnormality, neuronal and glial somal size were analyzed in postmortem brains from 9 patients with schizophrenia, 10 normal (control) patients, and 7 patients with Huntington disease, the latter representing a known neurodegenerative disorder. METHODS: A 3-dimensional image analyzer was used to measure the perimeters of 10722 neuronal and 19913 glial profiles in Brodmann areas 9 and 17. Neurons and glia were classified by size and layer to assess specific vulnerabilities with respect to cortical architecture and circuitry. RESULTS: The schizophrenic prefrontal cortex was characterized by a downward shift in neuronal sizes accompanied by 70% to 140% per layer increases in the density of small neurons. In layer III only, a significant reduction in mean neuronal size was associated with a significant decrease in the density of very large neurons in sublayer Illc. Neither neuronal size in occipital area 17 nor glial size in prefrontal or occipital cortexes were reduced. In cortex with Huntington disease, neuronal degeneration was evidenced by concurrence of reduced neuronal size, decreased density of large neurons, and dramatic elevation in density of large glia. CONCLUSIONS: Distinct cytometric abnormalities support the hypothesis that neuronal degeneration in the prefrontal cortex is not a prominent feature of the neuropathological changes in schizophrenia, although an ongoing process in Huntington disease. Rather, schizophrenia appears to involve more subtle abnormalities, with the largest corticocortical projection neurons of layer IIIc expressing the greatest somal reduction.     

Analysis of a novel delta gene during the formation of cortical layers

The preplate is composed of earliest-generated neurons, including Cajal-Retzius cells and prospected subplate neurons which together play a critical role in the formation of cortical layers. Additionally, Notch and Delta have been identified as key components that mediate the lateral specification and fate of numerous cells during development. Here, we demonstrate that a divergent type of Delta (D113) is expressed transiently and specifically in a set of earliest generated neurons in the neural tube. Moreover, in developing cerebrum, D113 is specifically and transiently expressed in prospected subplate neurons. Thus, our results suggest that D113 mediates the specification of cell fate in the earliest stage of neurogenesis including the neurons that compose preplate, leading to the mechanism of genesis of cortical layers.     

Dysfunctional uterine bleeding

Alzheimer's disease (AD) is characterized by progressive dementia and distinct neuropathology at autopsy. In order to test the relationship between dementia severity and loss of brain volumes, we prospectively documented the neurological/medical health of 26 male and 26 female controls and AD cases, and evaluated a subset of controls and AD cases using the Mini Mental State Examination (MMSE). At autopsy, Consortium to Establish a Registry for Alzheimer's Disease (CERAD) criteria confirmed diagnoses in 33 AD cases and 19 controls, and using unbiased stereology we quantified total volumes of cortical gray matter, subcortical grey matter including white matter, and forebrain. For ages of death between 50 to 100 years, controls showed minor cortical atrophy in the absence of cognitive decline. Cortical atrophy in AD cases was 20 to 25% greater than that in controls; AD patients dying at older ages showed less severe cortical atrophy than those dying at younger ages. Across all AD cases there was a strong correlation between cognitive performance on the Mini Mental State Examination and cortical volume loss. These findings confirm fundamental differences in the temporal patterns of cortical volume loss in aging and AD, and support cortical degeneration as the primary basis for cognitive decline in AD.     

Ribonuclease A mutant His119 Asn: the role of histidine in catalysis

BACKGROUND: We wished to investigate central serotonergic function in untreated schizophrenia. METHOD: Thirteen drug-naive, DSM-III-R schizophrenic patients were compared with sex, race, age, weight and menstrual phase matched controls. Plasma prolactin and cortisol responses to a specific serotonergic probe, d-fenfluramine, were measured along with BPRS ratings. RESULTS: Prolactin responses were enhanced in schizophrenic patients compared to controls (P < 0.05) and were correlated positively with BPRS items for depression, anxiety and guilt. Baseline cortisol was also raised in those with schizophrenia (P < 0.001). CONCLUSIONS: Central serotonergic tone may be raised in acute, drug-naive schizophrenia and may be associated with the presence of affective symptomatology.     

Scaling of cortical neuron density and white matter volume in mammals

A prior scaling model, based on repeating cortical units, whose number and size increase with brain size, gave discrete exponents for cortical thickness (1/9), outer (visible) surface area (2/3), folded cortical surface area (8/9) and cortical volume (1), each as a function of brain volume. These exponents are in reasonable agreement with a diversity of empirical data (Prothero, 1997). Rockel et al. (1980) reported that neuron number, assayed in a narrow column across cortex (pia to white matter) is invariant over several differing brain regions and species. Since cortical thickness scales, empirically, as about the 1/9 power of brain volume, their data imply that neuron line density (across cortex) scales with an exponent of about -1/9. Rockel et al. (1980) also urged that cortical neuron surface density is invariant. This extrapolation implies that neuron volume density scales, like line density, as the -1/9 power of brain volume, in marked disparity with the data of Haug (1987) and Tower (1954). The present model assumes an invariant number of neurons per repeating unit. Thus neuron number, assayed across cortical thickness, is independent of brain size, in accord with Rockel et al. (1980). The model predicts that neuron line density (in any direction) scales as the -1/9 power of brain volume. Now neuron volume density scales as the -1/3 power of brain volume, in reasonable agreement with the results of Haug (1987) and Tower (1954). For white matter, I assume that mean axon length scales with brain diameter (exponent of 1/3). The number of white matter axons scales in proportion to the number of repeating units (exponent of 2/3). Given an invariant size distribution of white matter axons, white matter volume thus scales with an exponent of one, in reasonable accord with Haug (1970).     

Prenatal development of nicotinamide adenine dinucleotide phosphate-diaphorase activity in the human hippocampal formation

Nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) histochemistry was used to study the development of the neurons metabolizing nitric oxide in the prenatal human hippocampal formation. Strongly reactive non-pyramidal neurons appeared in small numbers in the subplate at 15 weeks, and rapidly increased in this layer, as well as the cortical plate-derived layers between 17 and 24 weeks. The marginal zone also had a few NADPH-d cells at 15 weeks. The pattern of these darkly reactive cells stabilized by 28 weeks, with the somata distributed mostly at the border of the cortex and white matter in the entorhinal cortex and subiculum, or the alveus in Ammon's horn. Moderately stained non-pyramidal neurons appeared in the dentate gyrus by 17 weeks, and increased in this region and Ammon's horn up to 28 weeks. Small, lightly reactive non-pyramidal neurons were first seen by 32 weeks and increased in number by term. They were mainly distributed in layers II/III of the entorhinal cortex and stratum pyramidale of the subiculum and Ammon's horn. NADPH-d positive fibers in the marginal zone were mostly thin and developed between 20 and 28 weeks. In other cortical layers, thick processes from the darkly stained NADPH-d neurons appeared first, then fine fibers appeared more numerous, especially after 28 weeks. NADPH-d processes that arose from non-pyramidal cells were frequently apposed to blood vessels, including those in the hippocampal fissure. In addition, NADPH-d reactivity was also present in pyramidal and granule cells, but this staining was most pronounced between 15 and 24 weeks. The results show three types of distinctly stained NADPH-d interneurons in the fetal human hippocampal formation with different developmental courses and morphology. Also, hippocampal principal neurons transiently express NADPH-d at early fetal ages. Our data correlated with other findings suggest that nitric oxide may play a role in neuronal development in the hippocampal formation by modulating neuronal differentiation and maturation, and regulating blood supply.