Abnormalities of thalamic volume and shape detected in fetally irradiated rhesus monkeys with high dimensional brain mapping

A meta-analysis of deep brain structural shape and asymmetry abnormalities in 2,833 individuals with schizophrenia compared with 3,929 healthy volunteers via the ENIGMA Consortium

Schizophrenia is associated with widespread alterations in subcortical brain structure. While analytic methods have enabled more detailed morphometric characterization, findings are often equivocal. In this meta-analysis, we employed the harmonized ENIGMA shape analysis protocols to collaboratively investigate subcortical brain structure shape differences between individuals with schizophrenia and healthy control participants. The study analyzed data from 2,833 individuals with schizophrenia and 3,929 healthy control participants contributed by 21 worldwide research groups participating in the ENIGMA Schizophrenia Working Group. Harmonized shape analysis protocols were applied to each site's data independently for bilateral hippocampus, amygdala, caudate, accumbens, putamen, pallidum, and thalamus obtained from T1-weighted structural MRI scans. Mass univariate meta-analyses revealed more-concave-than-convex shape differences in the hippocampus, amygdala, accumbens, and thalamus in individuals with schizophrenia compared with control participants, more-convex-than-concave shape differences in the putamen and pallidum, and both concave and convex shape differences in the caudate. Patterns of exaggerated asymmetry were observed across the hippocampus, amygdala, and thalamus in individuals with schizophrenia compared to control participants, while diminished asymmetry encompassed ventral striatum and ventral and dorsal thalamus. Our analyses also revealed that higher chlorpromazine dose equivalents and increased positive symptom levels were associated with patterns of contiguous convex shape differences across multiple subcortical structures. Findings from our shape meta-analysis suggest that common neurobiological mechanisms may contribute to gray matter reduction across multiple subcortical regions, thus enhancing our understanding of the nature of network disorganization in schizophrenia.

BRAIN AND EYE AS POTENTIAL TARGETS FOR IONIZING RADIATION IMPACT: PART II - RADIATION CEREBRO/OPHTALMIC EFFECTS IN CHILDREN, PERSONS EXPOSED IN UTERO, ASTRONAUTS AND INTERVENTIONAL RADIOLOGISTS

BACKGROUND

Ionizing radiation (IR) can affect the brain and the visual organ even at low doses, while provoking cognitive, emotional, behavioral, and visual disorders. We proposed to consider the brain and the visual organ as potential targets for the influence of IR with the definition of cerebro-ophthalmic relationships as the «eye-brain axis».

OBJECTIVE

The present work is a narrative review of current experimental, epidemiological and clinical data on radiation cerebro-ophthalmic effects in children, individuals exposed in utero, astronauts and interventional radiologists.

MATERIALS AND METHODS

The review was performed according to PRISMA guidelines by searching the abstract and scientometric databases PubMed/MEDLINE, Scopus, Web of Science, Embase, PsycINFO, Google Scholar, published from 1998 to 2021, as well as the results of manual search of peer-reviewed publications.

RESULTS

Epidemiological data on the effects of low doses of IR on neurodevelopment are quite contradictory, while data on clinical, neuropsychological and neurophysiological on cognitive and cerebral disorders, especially in the left, dominant hemisphere of the brain, are nore consistent. Cataracts (congenital - after in utero irradiation) and retinal angiopathy are more common in prenatally-exposed people and children. Astronauts, who carry out longterm space missions outside the protection of the Earth's magnetosphere, will be exposed to galactic cosmic radiation (heavy ions, protons), which leads to cerebro-ophthalmic disorders, primarily cognitive and behavioral disorders and cataracts. Interventional radiologists are a special risk group for cerebro-ophthalmic pathology - cognitivedeficits, mainly due to dysfunction of the dominant and more radiosensitive left hemisphere of the brain, andcataracts, as well as early atherosclerosis and accelerated aging.

CONCLUSIONS

Results of current studies indicate the high radiosensitivity of the brain and eye in different contingents of irradiated persons. Further research is needed to clarify the nature of cerebro-ophthalmic disorders in different exposure scenarios, to determine the molecular biological mechanisms of these disorders, reliable dosimetric support and taking into account the influence of non-radiation risk factors.

Reduced Midbrain Dopamine Neuron Number in the Adult Non-human Primate Brain after Fetal Radiation Exposure

Early gestation is a neurodevelopmental period that is especially vulnerable to environmental insult and one in which neurogenesis features prominently. Prenatal perturbation during early gestation has been linked to neuropsychiatric illnesses such as autism and schizophrenia, and severe environmental insult during this period can result in profound mental impairment. Midbrain dopamine neurons are generated during early gestation and play a key role in the motor, cognitive and reward circuitries implicated in neuropsychiatric disease and addiction. This study examined the impact of curtailing neurogenesis in early gestation on neuron number in the midbrain dopamine group, i.e., the substantia nigra and contiguous ventral tegmental area. Rhesus macaque monkeys were exposed in utero on embryonic days 39-41 to x-irradiation (3-4 exposures of 50 cGy over 3-7 days totalling <200 cGy) and allowed to mature to full adulthood. Stereologic cell counts of tyrosine hydroxylase-positive neurons in the midbrain dopamine group were performed in adult monkeys, as were measurements of somal size. Mean total neuron number in the irradiated monkeys was significantly reduced on average by 33% compared to that of the control group. Somal size did not differ between the groups, suggesting that the integrity of survivor populations was not impacted. Reduced midbrain dopamine neuron number in fetally irradiated, adult monkeys indicates that radiation exposure during the critical period of neurogenesis results in an enduring reduction of this population and underscores the susceptibility of early neurodevelopmental processes to irreversible damage from environmental exposures.

Motor stereotypies and cognitive perseveration in non-human primates exposed to early gestational irradiation

A number of psychiatric illnesses have been associated with prenatal disturbance of brain development, including autism, attention deficit hyperactivity disorder, and schizophrenia. Individuals afflicted with these disorders exhibit both repetitive motor and cognitive behavior. The potential role that environmental insult to the developing brain may play in generating these aberrant behaviors is unclear. Here we examine the behavioral consequences of an early gestational insult in the non-human primate. Rhesus macaques were exposed to x-irradiation during the first trimester of development to disrupt neurogenesis. The behavior of five fetally irradiated monkeys (FIMs) and five control monkeys (CONs) was observed as they matured from juvenile (1.5 years) to adult ages (4-5 years). Home-cage behavior was indistinguishable in the two groups. In the testing cage, circling was prevalent in both groups at juvenile ages, persisting to adulthood in three of the five FIMs. One FIM executed a ritualized motor sequence marked by semi-circling and undulating head movements. Seven macaques (4 FIMs, 3 CONs) were tested on a spatial Delayed Alternation (DA) task as adults. Perseverative errors and non-perseverative errors were recorded in early stages of the testing, at the 0 delay interval. While performing DA, FIMs made more errors of perseveration than CONs yet the number of total errors committed did not differ between groups. The presence of motor stereotypies and cognitive perseveration in fetally irradiated non-human primates suggests that environmental insult to the embryonic brain may contribute to repetitive motor and cognitive behaviors in neuropsychiatric diseases.

Distinct abnormalities of the primate prefrontal cortex caused by ionizing radiation in early or midgestation

Prenatal exposure of the brain to environmental insult causes different neurological symptoms and behavioral outcomes depending on the time of exposure. To examine the cellular bases for these differences, we exposed rhesus macaque fetuses to x-rays during early gestation (embryonic day [E]30-E42), i.e., before the onset of corticogenesis, or in midgestation (E70-E81), when superficial cortical layers are generated. Animals were delivered at term (~E165), and the size and cellular composition of prefrontal association cortex (area 46) examined in adults using magnetic resonance imaging (MRI) and stereologic analysis. Both early and midgestational radiation exposure diminished the surface area and volume of area 46. However, early exposure spared cortical thickness and did not alter laminar composition, and due to higher cell density, neuron number was within the normal range. In contrast, exposure to x-rays at midgestation reduced cortical thickness, mainly due to elimination of neurons destined for the superficial layers. A cell-sparse gap, observed within layer III, was not filled by the later-generated neurons destined for layer II, indicating that there is no subsequent replacement of the lost neurons. The distinct areal and laminar pathology consequent to temporally segregated irradiation is consistent with basic postulates of the radial unit hypothesis of cortical development. In addition, we show that an environmental disturbance inflicted in early gestation can induce subtle cytoarchitectonic alterations without loss of neurons, such as those observed in schizophrenia, whereas midgestational exposure causes selective elimination of neurons and cortical thinning as observed in some forms of mental retardation and fetal alcohol syndrome.

The effect of preterm birth on thalamic and cortical development

Preterm birth is a leading cause of cognitive impairment in childhood and is associated with cerebral gray and white matter abnormalities. Using multimodal image analysis, we tested the hypothesis that altered thalamic development is an important component of preterm brain injury and is associated with other macro- and microstructural alterations. T₁- and T₂-weighted magnetic resonance images and 15-direction diffusion tensor images were acquired from 71 preterm infants at term-equivalent age. Deformation-based morphometry, Tract-Based Spatial Statistics, and tissue segmentation were combined for a nonsubjective whole-brain survey of the effect of prematurity on regional tissue volume and microstructure. Increasing prematurity was related to volume reduction in the thalamus, hippocampus, orbitofrontal lobe, posterior cingulate cortex, and centrum semiovale. After controlling for prematurity, reduced thalamic volume predicted: lower cortical volume; decreased volume in frontal and temporal lobes, including hippocampus, and to a lesser extent, parietal and occipital lobes; and reduced fractional anisotropy in the corticospinal tracts and corpus callosum. In the thalamus, reduced volume was associated with increased diffusivity. This demonstrates a significant effect of prematurity on thalamic development that is related to abnormalities in allied brain structures. This suggests that preterm delivery disrupts specific aspects of cerebral development, such as the thalamocortical system.

Necessity of hippocampal neurogenesis for the therapeutic action of antidepressants in adult nonhuman primates

Background

Rodent studies show that neurogenesis is necessary for mediating the salutary effects of antidepressants. Nonhuman primate (NHP) studies may bridge important rodent findings to the clinical realm since NHP-depression shares significant homology with human depression and kinetics of primate neurogenesis differ from those in rodents. After demonstrating that antidepressants can stimulate neurogenesis in NHPs, our present study examines whether neurogenesis is required for antidepressant efficacy in NHPs.

Materials/Methodology

Adult female bonnets were randomized to three social pens (N = 6 each). Pen-1 subjects were exposed to control-conditions for 15 weeks with half receiving the antidepressant fluoxetine and the rest receiving saline-placebo. Pen-2 subjects were exposed to 15 weeks of separation-stress with half receiving fluoxetine and half receiving placebo. Pen-3 subjects 2 weeks of irradiation (N = 4) or sham-irradiation (N = 2) and then exposed to 15 weeks of stress and fluoxetine. Dependent measures were weekly behavioral observations and postmortem neurogenesis levels.

Results

Exposing NHPs to repeated separation stress resulted in depression-like behaviors (anhedonia and subordinance) accompanied by reduced hippocampal neurogenesis. Treatment with fluoxetine stimulated neurogenesis and prevented the emergence of depression-like behaviors. Ablation of neurogenesis with irradiation abolished the therapeutic effects of fluoxetine. Non-stressed controls had normative behaviors although the fluoxetine-treated controls had higher neurogenesis rates. Across all groups, depression-like behaviors were associated with decreased rates of neurogenesis but this inverse correlation was only significant for new neurons in the anterior dentate gyrus that were at the threshold of completing maturation.

Conclusion

We provide evidence that induction of neurogenesis is integral to the therapeutic effects of fluoxetine in NHPs. Given the similarity between monkeys and humans, hippocampal neurogenesis likely plays a similar role in the treatment of clinical depression. Future studies will examine several outstanding questions such as whether neuro-suppression is sufficient for producing depression and whether therapeutic neuroplastic effects of fluoxetine are specific to antidepressants.

Selective reduction of neuron number and volume of the mediodorsal nucleus of the thalamus in macaques following irradiation at early gestational ages

Neurons in the macaque brain arise from progenitors located near the cerebral ventricles in a temporally segregated manner such that lethal doses of ionizing irradiation, if administered over a discrete time interval, can deplete individual nuclei selectively. A previous study showed that neuron number in the dorsal lateral geniculate nucleus is reduced following early gestational exposure to x-irradiation (Algan and Rakic [1997] J. Comp. Neurol. 12:335-352). Here we examine whether similarly timed irradiation decreases neuron number in three associational thalamic nuclei: mediodorsal (MD), anterior, and pulvinar. Ten macaques were exposed to multiple doses of x-rays (total exposure (175-350 cGy) in early gestation (E33-E42) or midgestation (E70-E90); eight nonirradiated macaques were controls. Only the early-irradiated monkeys, not the midgestationally irradiated animals, exhibited deficits in whole-thalamic neuron (-15%) and glia numbers (-21%) compared with controls. Reduction of neuron number (-26%) and volume (-29%) was particularly pronounced in MD. In contrast, cell number and volume were not significantly decreased in the anterior or pulvinar nuclei following early gestational irradiation. Thus, reduced thalamic neuron number was associated specifically with irradiation in early gestation. Persistence of the thalamic neuronal deficit in adult animals indicates that prenatally deleted neurons had not been replenished during maturation or in adulthood. The selective reduction of MD neuron number also supports the protomap hypothesis that neurons of each thalamic nucleus originate sequentially from separate lines of neuronal stem cells (Rakic [1977a] J. Comp. Neurol. 176:23-52). The early gestationally irradiated macaque is discussed as a potentially useful model for studying the neurodevelopmental pathogenesis of schizophrenia.

Volume and neuron number of the lateral geniculate nucleus in schizophrenia and mood disorders

Subjects with schizophrenia show deficits in visual perception that suggest changes predominantly in the magnocellular pathway and/or the dorsal visual stream important for visiospatial perception. We previously found a substantial 25% reduction in neuron number of the primary visual cortex (Brodmann's area 17, BA17) in postmortem tissue from subjects with schizophrenia. Also, many studies have found reduced volume and neuron number of the pulvinar--the large thalamic association nucleus involved in higher-order visual processing. Here, we investigate if the lateral geniculate nucleus (LGN), the visual relay nucleus of the thalamus, has structural changes in schizophrenia. We used stereological methods based on unbiased principles of sampling (Cavalieri's principle and the optical fractionator) to estimate the total volume and neuron number of the magno- and parovocellular parts of the left LGN in postmortem brains from nine subjects with schizophrenia, seven matched normal comparison subjects and 13 subjects with mood disorders. No significant schizophrenia-related structural differences in volume or neuron number of the left LGN or its major subregions were found, but we did observe a significantly increased total volume of the LGN, and of the parvocellular lamina and interlaminar regions, in the mood group. These findings do not support the hypothesis that subjects with schizophrenia have structural changes in the LGN. Therefore, our previous observation of a schizophrenia-related reduction of the primary visual cortex is probably not secondary to a reduction in the LGN.

The thalamus and schizophrenia: current status of research

The thalamus provides a nodal link for multiple functional circuits that are impaired in schizophrenia (SZ). Despite inconsistencies in the literature, a meta analysis suggests that the volume of the thalamus relative to that of the brain is decreased in SZ. Morphometric neuroimaging studies employing deformation, voxel-based and region of interest methodologies suggest that the volume deficit preferentially affects the thalamic regions containing the anterior and mediodorsal nuclei, and the pulvinar. Postmortem design-based stereological studies have produced mixed results regarding volume and neuronal deficits in these nuclei. This review examines those aspects of thalamic circuitry and function that suggest salience to SZ. Evidence for anomalies of thalamic structure and function obtained from postmortem and neuroimaging studies is then examined and directions for further research proposed.

Interleukin-6 -174 and -572 genotypes and the volume of deep gray matter in preterm infants

Preterm infants have smaller cerebral and cerebellar volumes at term compared with term born infants. Perinatal factors leading to the reduction in volumes are not well known. IL-6 -174 and -572 genotypes partly regulate individual immunologic responses and have also been connected with deviant neurologic development in preterm infants. Our hypothesis was that IL-6 -174 and -572 genetic polymorphisms are associated with brain lesions and regional brain volumes in very low birth weight or in very preterm infants. DNA was genotyped for IL-6 -174 and -572 polymorphisms (GG/GC/CC). Study infants (n = 175) were categorized into three groups according to the most pathologic brain finding in ultrasound examinations until term. The brain MRI performed at term was analyzed for regional brain volumes. Analyzed IL-6 genotypes did not show statistically significant association with structural brain lesions. However, IL-6 -174 CC and -572 GG genotypes associated with reduced volume of one brain region, the combined volume of basal ganglia and thalami, both in univariate and in multivariate analyses (p = 0.009, 0.009, respectively). The association of IL-6 -174 and -572 genetic polymorphisms with smaller volumes in deep gray matter provides us new ways to understand the processes leading to neurologic impairments in preterm infants.

Primary visual cortex volume and total neuron number are reduced in schizophrenia

A number of studies that assessed the visual system in subjects with schizophrenia found impairments in early visual processing. Furthermore, functional imaging studies suggested changes in primary visual cortex activity in subjects with schizophrenia. Interestingly, postmortem studies of subjects with schizophrenia reported an increased density of neurons in the primary visual cortex (Brodmann's area 17, BA17). The observed changes in visual processing may thus be reflected in structural changes in the circuitry of BA17. To characterize the structural changes further we used stereological methods based on unbiased principles of sampling (Cavalieri's principle and the optical fractionator) to estimate the total volume and neuron number of BA17 in postmortem brains from 10 subjects with schizophrenia and 10 matched normal comparison subjects. In addition, we assessed cortical thickness. We found a marked and significant reduction in total neuron number (25%) and volume (22%) of BA17 in the schizophrenia group relative to the normal comparison subjects. In contrast, we found no changes in neuronal density or cortical thickness between the two groups. Subjects with schizophrenia therefore have a smaller cortical area allocated to primary visual perception. This finding suggests the existence of a schizophrenia-related change in cortical parcellation.

Advances in magnetic resonance imaging methods for the evaluation of bipolar disorder

This article reviews the current state of magnetic resonance imaging techniques as applied to bipolar disorder. Addressed are conventional methods of structural neuroimaging and recently developed techniques. This latter group comprises volumetric analysis, voxel-based morphometry, the assessment of T2 white matter hyperintensities, shape analysis, cortical surface-based analysis, and diffusion tensor imaging. Structural analysis methods used in magnetic resonance imaging develop exponentially, and now present opportunities to identify disease-specific neuroanatomic alterations. Greater acuity and complementarity in measuring these alterations has led to the generation of further hypotheses regarding the pathophysiology of bipolar disorder. Included in the summary of findings is consideration of a resulting neuroanatomic model. Integrative issues and future directions in this relatively young field, including multi-modal approaches enabling us to produce more comprehensive results, are discussed.

Whether ionizing radiation is a risk factor for schizophrenia spectrum disorders?

The neural diathesis-stressor hypothesis of schizophrenia, where neurobiological genetic predisposition to schizophrenia can be provoked by environmental stressors is considered as a model of the effects of exposure to ionizing radiation. Analysis of information from electronic databases (MEDLINE, PsycINFO, EMBASE, Current Contents, Elsevier BIOBASE) and hand-made search was carried out. There are comparable reports on increases in schizophrenia spectrum disorders following exposure to ionizing radiation as a result of atomic bombing, nuclear weapons testing, the Chernobyl accident, environmental contamination by radioactive waste, radiotherapy, and also in areas with high natural radioactive background. The results of experimental radioneurobiological studies support the hypothesis of schizophrenia as a neurodegenerative disease. Exposure to ionizing radiation causes brain damage with limbic (cortical-limbic) system dysfunction and impairment of informative processes at the molecular level that can trigger schizophrenia in predisposed individuals or cause schizophrenia-like disorders. It is supposed that ionizing radiation can be proposed as a risk factor for schizophrenia spectrum disorders. The hypothesis that ionizing radiation is a risk factor for schizophrenia spectrum disorders can be tested using data from the Chernobyl accident aftermath. Implementation of a study on schizophrenia spectrum disorders in Chernobyl accident victims is of significance for both clinical medicine and neuroscience.

The Effects of Early Lead Exposure on the Brains of Adult Rhesus Monkeys: A Volumetric MRI Study

Little is known about direct effects of exposure to lead on central nervous system development. We conducted volumetric MRI studies in three groups of 17-year-old rhesus monkeys: (1) a group exposed to lead throughout gestation (n = 3), (2) a group exposed to lead through breast milk from birth to weaning (n = 4), and (3) a group not exposed to lead (n = 8). All fifteen monkeys were treated essentially identically since birth with the exception of lead exposure. The three-dimensional MRI images were segmented on a computer workstation using pre-tested manual and semi-automated algorithms to generate brain volumes for white matter, gray matter, cerebrospinal fluid, and component brain structures. The three groups differed significantly in the adjusted (for total brain size) volumes of the right cerebral white matter and the lateral ventricles. A significant reduction was noted in right cerebral white matter in prenatally exposed monkeys as compared to controls (p = 0.045). A similar reduction was detected in the white matter of the contralateral hemisphere; however, this difference did not achieve statistical significance (p = 0.143). Prenatally exposed monkeys also had larger right (p = 0.027) and left (p = 0.040) lateral ventricles. Depending on the timing of exposure during development, lead may exhibit differential effects with resultant life-long alterations in brain architecture.

Direct and indirect effects of fetal irradiation on cortical gray and white matter volume in the macaque

BACKGROUND

Schizophrenia is associated with reductions in thalamic neuronal number and cortical gray matter volume. Exposure of nonhuman primates to x-irradiation in early gestation has previously been shown to decrease thalamic volume and neuronal number. Here we examine whether early gestational irradiation also results in cortical volume reduction.

METHODS

High-resolution, T1-weighted magnetic resonance scans were collected in adult monkeys 1) exposed to irradiation during the early gestational period (E33-E42) corresponding to thalamic neurogenesis, 2) irradiated in midgestation (E70-81) during neocortical neurogenesis, and 3) not exposed to irradiation. Cortical gray matter and white matter volumes were derived via manual segmentation; frontal and nonfrontal volumes were distinguished via sulcal landmarks.

RESULTS

Monkeys irradiated in early gestation exhibited a trend reduction in nonfrontal gray matter volume (17%) and significant reductions in white matter volume in frontal (26%) and nonfrontal (36%) lobes. Monkeys irradiated in midgestation had smaller gray (frontal: 28%; nonfrontal: 22%) and white matter (frontal: 29%; nonfrontal: 38%) volumes.

CONCLUSIONS

The cortical deficits observed in midgestationally irradiated monkeys are consistent with a reduction in cortical neuronal number. Cortical volume reductions following early gestational irradiation may be secondary to reduced thalamic neuronal number and therefore model the thalamocortical pathology of schizophrenia.

Craniofacial dysmorphogenesis in fetally irradiated nonhuman primates: implications for the neurodevelopmental hypothesis of schizophrenia

BACKGROUND

Craniofacial abnormalities arising from gestational disturbances have been documented in some schizophrenic patients. Reduction of thalamic neurons, a key feature of the neuropathology of schizophrenia, could also have a prenatal origin via disruption of thalamic neurogenesis. This study investigates whether craniofacial dysmorphology and thalamic neuron loss might be associated manifestations of a disruption in embryonic development.

METHODS

Thalamic neurons were deleted by exposing fetal macaques to x-rays during thalamic genesis (E33-42). Another group of macaques was irradiated after thalamic genesis (E70-81). Body, head, and facial measurements were obtained from the early irradiated (EX), late irradiated (LX), and control animals at adulthood.

RESULTS

Head width, distance between outer eye edges, and ear width were smaller in EX macaques compared with control animals. The LX macaques exhibited only reduced ear width compared with control animals.

CONCLUSIONS

These findings indicate that certain features of thalamic neuropathology and craniofacial dysmorphogenesis observed in schizophrenic patients may have a common etiology.