Parvalbumin-, calbindin-, and calretinin-immunoreactive hippocampal interneuron density in autism.

BACKGROUND: There has been a long-standing interest in the possible role of the hippocampus in autism and both postmortem brain and neuroimaging studies have documented varying abnormalities in this limbic system structure. AIMS: This study investigates the density of subsets of hippocampal interneurons, immunostained with the calcium binding proteins, calbindin (CB), calretinin (CR) and parvalbumin (PV) to determine whether specific subpopulations of interneurons are impacted in autism. MATERIALS AND METHODS: Unbiased stereological techniques were used to quantify the neuronal density of these immunoreactive subpopulations of gamma-aminobutyric acid-ergic (GABAergic) interneurons analyzed in the CA and subicular fields in postmortem brain material obtained from five autistic and five age-, gender- and postmortem interval-matched control cases. RESULTS: Results indicate a selective increase in the density of CB-immunoreactive interneurons in the dentate gyrus, an increase in CR-immunoreactive interneurons in area CA1, and an increase in PV-immunoreactive interneurons in areas CA1 and CA3 in the hippocampus of individuals with autism when compared with controls. DISCUSSION/CONCLUSIONS: Although our sample size is small, these findings suggest that GABAergic interneurons may represent a vulnerable target in the brains of individuals with autism, potentially impacting upon their key role in learning and information processing. These preliminary findings further suggest the need for future more expanded studies in a larger number of postmortem brain samples from cases of autism and controls.

MRI measures of temporoparietal regions show differential rates of atrophy during prodromal AD.

BACKGROUND: MRI studies have demonstrated differential rates of atrophy in the entorhinal cortex and hippocampus during the prodromal phase of Alzheimer disease (AD). The current study was designed to determine whether a broader set of temporoparietal regions show differential rates of atrophy during the evolution of AD. METHODS: Sixteen regions of interest (ROIs) were analyzed on MRI scans obtained at baseline and follow-up in 66 subjects comprising three groups: controls = individuals who were cognitively normal at both baseline and follow-up; nonconverters = subjects with mild cognitive impairment (MCI) at both baseline and follow-up; converters had MCI at baseline but had progressed to AD at follow-up. RESULTS: Annualized percent change was analyzed with multivariate analysis of variance (MANOVA), covaried for age. The MANOVA demonstrated an effect of group (p = 0.004). Post hoc comparisons demonstrated greater rates of atrophy for converters vs nonconverters for six ROIs: hippocampus, entorhinal cortex, temporal pole, middle temporal gyrus, fusiform gyrus, and inferior temporal gyrus. Converters showed differentially greater rates of atrophy than controls in five of the same ROIs (and inferior parietal lobule). Rates of change in clinical status were correlated with the atrophy rates in these regions. Comparisons between controls and nonconverters demonstrated no differences. CONCLUSION: These results demonstrate that temporoparietal regions show differential rates of atrophy on MRI during prodromal Alzheimer disease (AD). MRI data correlate with measures of clinical severity and cognitive decline, suggesting the potential of these regions of interest as antemortem markers of prodromal AD.

Birthdates and number of neurons in the serotonergic raphe nuclei in the rat with prenatal protein malnutrition.

The effect of prenatal protein deprivation on timing of neurogenesis and on number of neurons generated in the serotonergic dorsal (DR) and median raphe (MR) nuclei of the rat was studied. These neurons are of interest because their neurogenesis occurs during the period of malnutrition and their axonal projections participate in the earliest stages of brain development. In this study, dams were maintained on a 25% casein diet or a 6% casein diet 5 weeks prior to mating and throughout pregnancy. At birth, all pups were cross-fostered to dams on a 25% casein diet. Bromodeoxyuridine, a thymidine analog that is incorporated into nuclear deoxyribonucleic acid during the cell cycle synthetic phase, was used as a marker of neurogenesis. Bromodeoxyuridine was administered on either embryonic day 11, 12, 13 or 14. On postnatal day 30, serial sections of raphe nuclei were processed with bromodeoxyuridine immunocytochemistry to determine the number of raphe cells generated on each day and with Nissl stain to determine the total number of cells generated. There were no significant differences between the two diet groups in timing of generation or in total number of cells generated, indicating that neurogenesis of these early generated neurons appears unaffected by concomitant protein deprivation.

Neuropathology of progressive cognitive decline in chronically hypertensive rhesus monkeys.

Hypertension is an identified major risk factor for cerebrovascular disease, which is second only to Alzheimer's disease as a cause of dementia in the elderly. In addition, hypertension has been associated with a more subtle, progressive decline in cognitive function for which the neuropathology is not well understood. The present study was undertaken to explore this relationship in an experimental, nonhuman primate model, with hypertension produced by a coarctation of the thoracic aorta. Since prior studies with this model have shown a progressive decline in memory function, similar to that seen in human hypertension, as well as scattered microinfarcts in the cerebral white and gray matter, this study was designed to explore the relationship between these two. In addition to microinfarcts, the hypertensive monkeys with the highest arterial blood pressure also showed minute areas of focal gliosis without infarction. The number of these focal lesions showed a significant correlation with the severity of the hypertension, but not with the behavioral deficit. For four of these hypertensive monkeys, immunostaining demonstrated a pervasive, widespread activation of microglial cells and astroglial cells in the white matter as well as evidence of leaks in the blood-brain barrier, providing a more logical substrate for the cognitive decline.

Density and distribution of hippocampal neurotransmitter receptors in autism: an autoradiographic study.

Neuropathological studies in autistic brains have shown small neuronal size and increased cell packing density in a variety of limbic system structures including the hippocampus, a change consistent with curtailment of normal development. Based on these observations in the hippocampus, a series of quantitative receptor autoradiographic studies were undertaken to determine the density and distribution of eight types of neurotransmitter receptors from four neurotransmitter systems (GABAergic, serotoninergic [5-HT], cholinergic, and glutamatergic). Data from these single concentration ligand binding studies indicate that the GABAergic receptor system (3[H]-flunitrazepam labeled benzodiazepine binding sites and 3[H]-muscimol labeled GABA(A) receptors) is significantly reduced in high binding regions, marking for the first time an abnormality in the GABA system in autism. In contrast, the density and distribution of the other six receptors studied (3[H]-80H-DPAT labeled 5-HT1A receptors, 3[H]-ketanserin labeled 5-HT2 receptors, 3[H]-pirenzepine labled M1 receptors, 3[H]-hemicholinium labeled high affinity choline uptake sites, 3[H]-MK801 labeled NMDA receptors, and 3[H]-kainate labeled kainate receptors) in the hippocampus did not demonstrate any statistically significant differences in binding.

Age-related neuronal loss from the substantia nigra-pars compacta and ventral tegmental area of the rhesus monkey.

This study was undertaken to document the effect of age on the volume, number, and size of neurons in the substantia nigra pars compacta (SNpc), the paranigral (VTApn), and the parabrachial pigmentosus (VTApbp) nuclei of the VTA in behaviorally well-characterized rhesus monkeys. Using a point counting technique and unbiased stereological methods, we found no significant effects of age on the volume of these dopaminergic brain stem nuclei, but there was significant age-related loss of total number of neurons in the SNpc and VTApn. The loss of neurons in the SNpc was found to be greater for neurons measuring less than 200 microm2 in cross sectional area, a size corresponding to the small GABAergic neurons in this nucleus. Age-related loss of total number of neurons in the SNpc and VTApn showed significant correlations with impairment on the delay phase of the delayed non match to sample test (DNMS), in the VTApn with impaired performance on the delayed recognition span test (DRST), and in the SNpc with impaired performance on the spatial component of reversal tasks. These correlations suggest that the loss of neurons in the SNpc and VTApn in these old monkeys may contribute to these behavioral deficits.

Human immunodeficiency virus infection, inducible nitric oxide synthase expression, and microglial activation: pathogenetic relationship to the acquired immunodeficiency syndrome dementia complex.

The regional expression of immune-mediated and neurotoxic events in the human immunodeficiency virus (HIV)-infected brain in relationship to the acquired immunodeficiency syndrome (AIDS) dementia complex (ADC) and brain pathology remains uncertain. The extent of gp41, inducible nitric oxide synthase (iNOS), and HLA-DR expression was examined in the frontal lobe and basal ganglia of 25 patients at varying stages of ADC. The expression of gp41 and iNOS was present predominantly in perivascular cells and most often in the basal ganglia. Staining for gp41 correlated significantly with iNOS in the basal ganglia, whereas the severity of staining for gp41 and iNOS in the basal ganglia and white matter was significantly greater in subjects with moderate to severe dementia compared with those with milder impairment. The degree of macrophage staining in the white matter and basal ganglia also correlated significantly with ADC severity and was more abundant than gp41 or iNOS staining, particularly in the white matter. Logistic regression analysis revealed that staining for iNOS and gp41 increased linearly with ADC severity and was significantly more abundant in the basal ganglia compared with the white matter. Double-immunolabeling studies colocalized iNOS predominantly to macrophage/microglia and to gp41-positive cells. The expression of iNOS and gp41 in the basal ganglia combined with immune activation contributes to the development and progression of the clinical syndrome.

Effect of Prenatal Protein Malnutrition on Birthdates and Number of Neurons in the Rat Locus Coeruleus.

The effect of prenatal protein deprivation on the timing of neurogenesis and on the number of neurons generated in the locus coeruleus of the rat was studied. These neurons are of interest as their axon projections are involved in the earliest stages of cerebral cortical development. Dams were maintained on a 25% casein diet or a 6% casein diet five weeks prior to mating and the diets continued throughout the pregnancy. At birth, all pups were cross-fostered to dams on a 25% casein diet. BrDU, a thymidine analog that is incorporated into the nuclear DNA during the synthetic phase of the cell cycle, was used as a marker of the generation period. It was administered intraperitoneally (25 mg/kg body weight) on embryonic day 10, 11, 12, 13, or 14. On postnatal day 30, the brain stems were processed with BrDU immunocytochemistry to determine the relative number of neurons generated on each day, and with Nissl stain to determine the total number of neurons generated in the two groups. There were no significant differences between the two diet groups in the timing of their generation or in the total number of neurons generated, indicating a preservation of neurogenesis of these early generated neurons in these malnourished rats.

Age-related neuronal loss in the nucleus centralis superior of the rhesus monkey.

The effect of age on the number of neurons in the nucleus centralis superior (NCS) was determined in 11 behaviorally tested rhesus monkeys of 7-32 years of age, There was a significant age-related decrease in both cell packing density and in the total number of neurons. This decrease in number of neurons appeared to effect two different populations of cell in the NCS, one of which corresponded in size to the serotonergic cells in this nucleus and the other to a smaller-sized cell. Comparisons of the changes in the cell packing density with behavioral testing, showed significant correlations with the overall test performance as well as with individual tests of memory function and of executive system functions. These findings suggest that neuronal loss in the NCS may play a significant role in mediating cognitive changes seen in normal aging.

Neurobiological bases of age-related cognitive decline in the rhesus monkey.

The rhesus monkey offers a useful model of normal human aging because when monkeys are tested on a battery of behavioral tasks that can also be used to evaluate cognition in humans, it is found that the monkeys undergo an age-related decline in several domains of cognitive function as do humans. In monkeys these changes begin at about 20 years of age. To determine what gives rise to this cognitive decline, we have examined several parameters in the brains of monkeys. Some parameters do not change with age. Examples of this are the numbers of neurons in the neocortex and hippocampal formation, and the numbers of synapses in the hippocampal formation. Changes in other parameters can be positively correlated with chronological age; examples of this are numbers of neuritic plaques, a decrease in the numbers of neurons in the striatally projecting pars compacta of the substantia nigra, and a decrease in the thickness of layer I in primary visual cortex. But the most interesting changes are those that correlate either with cognitive decline alone, or with both cognitive decline and chronological age. Among these are a breakdown in the integrity of myelin around axons, an overall reduction in the volume of white matter in the cerebral hemispheres, thinning of layer I in area 46 of prefrontal cortex, and decreases in the cell density in cortically projecting brain stem nuclei. To date then, our studies suggest that the cognitive declines evident in the rhesus monkey may be a consequence of changes in layer I and in the integrity of myelinated axons, rather than an age-related loss of cortical neurons or synapses, as has long been assumed.

Hippocampus in autism: a Golgi analysis.

Autism is a behaviorally defined syndrome in which neuropathological abnormalities have been identified in the limbic system and cerebellum. The morphology of hippocampal neurons in two cases of infantile autism was studied and compared to age-matched controls. CA4 neurons in autistic children were smaller in perikaryon area and dendritic branching of both CA4 and CA1 neurons was less than in controls. These findings are consistent with previous studies and suggest a curtailment in maturation in the pathogenesis of autism.

Effect of prenatal protein deprivation on postnatal granule cell generation in the hippocampal dentate gyrus.

The effect of prenatal malnutrition, produced by protein deprivation, on postnatal neurogenesis of granule cells in the fascia dentata of the rat hippocampal formation was examined by injecting tritiated thymidine on P8 and P15 and sacrificing the pups on P30, or by injecting on P30 and sacrificing on P90. The number of labeled granule cells was significantly decreased in prenatally malnourished rats injected on P8, and unaffected in those injected on P15. In contrast, the number of labeled granule cells in prenatally malnourished rats was significantly increased in animals injected in P30. The study shows that prenatal malnutrition significantly alters the postnatal pattern of granule cell neurogenesis in rat hippocampal formation and that the effect persists despite nutritional rehabilitation at birth.

The effects of cocaine exposure prior to and during pregnancy in rats fed low or adequate protein diets.

Sprague-Dawley rats were fed a diet of low protein content (6% casein), an isocaloric diet of adequate protein content (25% casein), or a laboratory chow diet for 5 weeks prior to mating and throughout pregnancy. Within each diet group, rats received either cocaine (30 mg/kg IP two times per week prior to mating and 30 mg/kg or 40 mg/kg SC daily from days 3 to 18 of pregnancy) or saline injections. Cocaine produced a greater reduction in food intake during pregnancy in the malnourished group compared with the other two diet groups. The effect of cocaine on food intake was minimal in chow-fed rats. Weight gain in pregnancy was reduced by cocaine in a dose-dependent manner, and by malnutrition. Both prenatal cocaine and malnutrition impaired skeletal maturation of the pups, but there was no additive effect of the two insults on this measure. Litter size was significantly reduced by the 40 mg/kg, but not by the 30 mg/kg dose of cocaine across all diet groups. Consequently, the 40 mg/kg dose of cocaine proved to be fetotoxic in this model. Birth weight was significantly reduced by prenatal malnutrition but not by prenatal cocaine. Gestation length was unaffected by either insult. Hence, the ability to detect a diet x drug interaction was dependent upon the variable being measured.

Pervasive neuroanatomic abnormalities of the brain in three cases of Rett's syndrome.

Rett's syndrome (RS) is a clinically defined disorder that appears to be unique to girls and is characterized by apparent cognitive and motor skill loss early in life. We report our findings in the brains of three girls with RS, which were studied in comparison with age-matched controls by means of gapless serial section. Reduced neuronal cell size and increased cell-packing density were present throughout the cortical and subcortical regions of the brain in all cases without evidence of active degeneration. These observations appear to be consistent with a curtailment of development. Further, the degree of abnormality in each case correlates more closely with the clinical presentation of the patient at the time of death than with the age of the patient or duration of symptoms.

Microscopic observations of the brain in Rett syndrome.

Rett syndrome (RS) is a clinically defined disorder which appears to be unique to females and which is associated with apparent loss of cognitive and motor skills early in life. Using the technique of gapless serial section, microscopic analysis of the brains from three cases of RS and identically processed age-matched controls was conducted to determine the nature and extent of cerebral abnormality in this disorder. Small neuronal cell size and increased cell packing density were observed throughout the brain in all three cases, without evidence of gliosis or active degeneration. These findings are consistent with a curtailment of brain development which may begin before birth. Further, the brain abnormalities in RS appear to be more diffuse than previously appreciated and are in accord with the widespread neurological symptoms characteristic of this disorder.

Prenatal malnutrition effect on pyramidal and granule cell generation in the hippocampal formation.

The effects of prenatal malnutrition produced by protein deprivation on the neurogenesis of granule and pyramidal cells in the rat hippocampal formation was investigated by injecting pregnant rats with tritiated thymidine on E12, E16, or E20 and sacrificing the pups on P30. Granule cell neurogenesis was significantly decreased in the pups injected on E20, but not in E12 or E16 groups. There was no effect on the generation of pyramidal cells at the times noted, indicating a differential effect of prenatal malnutrition on the generation of these two different neuronal types in the hippocampal formation.