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

Effects of a Single Dose of X-Ray Irradiation on MMP-9 Expression and Morphology of the Cerebellum Cortex of Adult Rats

Although radiation is a strategy widely used to inhibit cancer progression, which includes those of the neck and head, there are still few experimental reports on radiation effects in the cerebellum, particularly on the morphology of its cortex layers and on the Matrix metalloproteinases' (MMPs') expression, which, recently, seems to be involved in the progression of some mental disorders. Therefore, in the present study, we evaluated the morphology of the cerebellum close to the expression of MMP-9 from 4 up to 60 days after a 15-Gy X-ray single dose of X-ray irradiation had been applied to the heads of healthy adult male rats. The cerebellum of the control and irradiated groups was submitted for an analysis of cell Purkinje count, nuclear perimeter, and chromatin density using morphometric estimatives obtained from the Feulgen histochemistry reaction. In addition, immunolocalization and estimative for MMP-9 expression were determined in the cerebellar cortex on days 4, 9, 14, 25, and 60 after the irradiation procedure. Results demonstrated that irradiation produced a significant reduction in the total number of Purkinje cells and a reduction in their nuclear perimeter, along with an increase in chromatin condensation and visible nuclear fragmentation, which was also detected in the granular layer. MMP-9 expression was significantly increased on 4, 9, and 14 days, being detected around the Purkinje cells and in parallel fibres at the molecular layer. We conclude that the effects of a single dose of 15-Gy X-ray irradiation in the cerebellum were an increase in MMP-9 expression in the first 2 weeks after irradiation, especially surrounding the Purkinje cells and in the molecular layers, with morphological changes in the Purkinje cell and granular cell layers, suggesting a continuous cell loss throughout the days evaluated after irradiation.

Structure–Function Decoupling: A Novel Perspective for Understanding the Radiation-Induced Brain Injury in Patients With Nasopharyngeal Carcinoma

Radiation-induced functional and structural brain alterations are well documented in patients with nasopharyngeal carcinoma (NPC), followed by radiotherapy (RT); however, alterations in structure–function coupling remain largely unknown. Herein, we aimed to assess radiation-induced structure–function decoupling and its importance in predicting radiation encephalopathy (RE). We included 62 patients with NPC (22 patients in the pre-RT cohort, 18 patients in the post-RT-RE_+ve cohort, and 22 patients in the post-RT-RE_–ve cohort). A metric of regional homogeneity (ReHo)/voxel-based morphometry (VBM) was used to detect radiation-induced structure–function decoupling, which was then used as a feature to construct a predictive model for RE. Compared with the pre-RT group, patients in the post-RT group (which included post-RT-RE_+ve and post-RT-RE_–ve) showed higher ReHo/VBM coupling values in the substantia nigra (SN), the putamen, and the bilateral thalamus and lower values in the brain stem, the cerebellum, the bilateral medial temporal lobes (MTLs), the bilateral insula, the right precentral and postcentral gyri, the medial prefrontal cortex (MPFC), and the left inferior parietal lobule (IPL). In the post-RT group, negative correlations were observed between maximum dosage of RT (MDRT) to the ipsilateral temporal lobe and ReHo/VBM values in the ipsilateral middle temporal gyrus (MTG). Moreover, structure–function decoupling in the bilateral superior temporal gyrus (STG), the bilateral precentral and postcentral gyri, the paracentral lobules, the right precuneus and IPL, and the right MPFC exhibited excellent predictive performance (accuracy = 88.0%) in identifying patients likely to develop RE. These findings show that ReHo/VBM may be a novel effective imaging metric that reflects the neural mechanism underlying RE in patients with NPC.

Unbiased Stereological Estimates of Dopaminergic and GABAergic Neurons in the A10, A9, and A8 Subregions in the Young Male Macaque

The ventral midbrain is the primary source of dopamine- (DA) expressing neurons in most species. GABA-ergic and glutamatergic cell populations are intermixed among DA-expressing cells and purported to regulate both local and long-range dopamine neuron activity. Most work has been conducted in rodent models, however due to evolutionary expansion of the ventral midbrain in primates, the increased size and complexity of DA subpopulations warrants further investigation. Here, we quantified the number of DA neurons, and their GABA-ergic complement in classic DA cell groups A10 (midline ventral tegmental area nuclei [VTA] and parabrachial pigmented nucleus [PBP]), A9 (substantia nigra, pars compacta [SNc]) and A8 (retrorubral field [RRF]) in the macaque. Because the PBP is a disproportionately expanded feature of the A10 group, and has unique connectional features in monkeys, we analyzed A10 data by dividing it into 'classic' midline nuclei and the PBP. Unbiased stereology revealed total putative DA neuron counts to be 210,238 ± 17,127 (A10 = 110,319 ± 9649, A9 = 87,399 ± 7751 and A8 = 12,520 ± 827). Putative GABAergic neurons were fewer overall, and evenly dispersed across the DA subpopulations (GAD67 = 71,215 ± 5663; A10 = 16,836 ± 2743; A9 = 24,855 ± 3144 and A8 = 12,633 ± 3557). Calculating the GAD67/TH ratio for each subregion revealed differential balances of these two cell types across the DA subregions. The A8 subregion had the highest complement of GAD67-positive neurons compared to TH-positive neurons (1:1), suggesting a potentially high capacity for GABAergic inhibition of DA output in this region.

Cross-translational models of late-onset cognitive sequelae and their treatment in pediatric brain tumor survivors

Pediatric brain tumor treatments have a high success rate, but survivors are at risk of cognitive sequelae that impact long-term quality of life. We summarize recent clinical and animal model research addressing pathogenesis or evaluating candidate interventions for treatment-induced cognitive sequelae. Assayed interventions encompass a broad range of approaches, including modifications to radiotherapy, modulation of immune response, prevention of treatment-induced cell loss or promotion of cell renewal, manipulation of neuronal signaling, and lifestyle/environmental adjustments. We further emphasize the potential of neuroimaging as a key component of cross-translation to contextualize laboratory research within broader clinical findings. This cross-translational approach has the potential to accelerate discovery to improve pediatric cancer survivors' long-term quality of life.

A Systematic Review of Brainstem Contributions to Autism Spectrum Disorder

Autism spectrum disorder (ASD) is a neurodevelopmental disorder that affects one in 66 children in Canada. The contributions of changes in the cortex and cerebellum to autism have been studied for decades. However, our understanding of brainstem contributions has only started to emerge more recently. Disruptions of sensory processing, startle response, sensory filtering, sensorimotor gating, multisensory integration and sleep are all features of ASD and are processes in which the brainstem is involved. In addition, preliminary research into brainstem contribution emphasizes the importance of the developmental timeline rather than just the mature brainstem. Therefore, the purpose of this systematic review is to compile histological, behavioral, neuroimaging, and electrophysiological evidence from human and animal studies about brainstem contributions and their functional implications in autism. Moreover, due to the developmental nature of autism, the review pays attention to the atypical brainstem development and compares findings based on age. Overall, there is evidence of an important role of brainstem disruptions in ASD, but there is still the need to examine the brainstem across the life span, from infancy to adulthood which could lead the way for early diagnosis and possibly treatment of ASD.