Seeking the Amygdala: Novel Use of Diffusion Tensor Imaging to Delineate the Basolateral Amygdala.

The amygdaloid complex, including the basolateral nucleus (BLA), contributes crucially to emotional and cognitive brain functions, and is a major target of research in both humans and rodents. However, delineating structural amygdala plasticity in both normal and disease-related contexts using neuroimaging has been hampered by the difficulty of unequivocally identifying the boundaries of the BLA. This challenge is a result of the poor contrast between BLA and the surrounding gray matter, including other amygdala nuclei. Here, we describe a novel diffusion tensor imaging (DTI) approach to enhance contrast, enabling the optimal identification of BLA in the rodent brain from magnetic resonance (MR) images. We employed this methodology together with a slice-shifting approach to accurately measure BLA volumes. We then validated the results by direct comparison to both histological and cellular-identity (parvalbumin)-based conventional techniques for defining BLA in the same brains used for MRI. We also confirmed BLA connectivity targets using DTI-based tractography. The novel approach enables the accurate and reliable delineation of BLA. Because this nucleus is involved in and changed by developmental, degenerative and adaptive processes, the instruments provided here should be highly useful to a broad range of neuroimaging studies. Finally, the principles used here are readily applicable to numerous brain regions and across species.

Early life adversity in male mice sculpts reward circuits.

Early life adversity (ELA) comprises a wide variety of negative experiences during early life and has been linked to cognitive impairments, reduced experiences of pleasure (anhedonia), and other long-term consequences implying that ELA impacts the reward circuitry. In this study, we focused on the projections from the dorsal raphe (DR) to the ventral tegmental area (VTA) and on to the nucleus accumbens (NAcc), an important pathway within the reward circuit. We hypothesized that ELA alters connectivity within the DR-VTA-NAcc pathway, associated with deficient reward seeking behaviors in adulthood. We used the limited bedding and nesting model to induce ELA in mice and measured reward-related behaviors in adulthood using the three-chamber social interaction and sucrose preference tests. High resolution ex vivo diffusion tensor imaging (DTI) was acquired and processed for regional DTI metrics, including tractography to assess circuit organization. We found brain-wide changes in radial diffusivity (RD) and altered connectivity of the reward circuit in the ELA group. DR-VTA-NAcc circuit tractography and axial diffusivity (AD) along this tract exhibited dispersed organization where AD was increased in the VTA segment. Behaviorally, ELA elicited a social anhedonia-like phenotype in adulthood with decreased direct social approach and time spent with peers in the three-chamber task, and no overt differences in sucrose preference. Our findings suggest that reward circuits, assessed using DTI, are altered following ELA and that these changes may reflect enduring reward deficits.

A Novel Technique for Visualizing and Analyzing the Cerebral Vasculature in Rodents.

We introduce a novel protocol to stain, visualize, and analyze blood vessels from the rat and mouse cerebrum. This technique utilizes the fluorescent dye, DiI, to label the lumen of the vasculature followed by perfusion fixation. Following brain extraction, the labeled vasculature is then imaged using wide-field fluorescence microscopy for axial and coronal images and can be followed by regional confocal microscopy. Axial and coronal images can be analyzed using classical angiographic methods for vessel density, length, and other features. We also have developed a novel fractal analysis to assess vascular complexity. Our protocol has been optimized for adult rat, adult mouse, and neonatal mouse studies. The protocol is efficient, can be rapidly completed, stains cerebral vessels with a bright fluorescence, and provides valuable quantitative data. This method has a broad range of applications, and we demonstrate its use to study the vasculature in assorted models of acquired brain injury.

Corpus Callosum Vasculature Predicts White Matter Microstructure Abnormalities after Pediatric Mild Traumatic Brain Injury.

Emerging data suggest that pediatric traumatic brain injury (TBI) is associated with impaired developmental plasticity and poorer neuropsychological outcomes than adults with similar head injuries. Unlike adult mild TBI (mTBI), the effects of mTBI on white matter (WM) microstructure and vascular supply are not well understood in the pediatric population. The cerebral vasculature plays an important role providing necessary nutrients and removing waste. To address this critical element, we examined the microstructure of the corpus callosum (CC) following pediatric mTBI using diffusion tensor magnetic resonance imaging (DTI), and investigated myelin, oligodendrocytes, and vasculature of WM with immunohistochemistry (IHC). We hypothesized that pediatric mTBI leads to abnormal WM microstructure and impacts the vasculature within the CC, and that these alterations to WM vasculature contribute to the long-term altered microstructure. We induced in mice a closed-head injury (CHI) mTBI at post-natal day (P) 14; then at 4, 14, and 60 days post-injury (DPI) mice were sacrificed for analysis. We observed persistent changes in apparent diffusion coefficient (ADC) within the ipsilateral CC following mTBI, indicating microstructural changes, but surprisingly changes in myelin and oligodendrocyte densities were minimal. However, vascular features of the ipsilateral CC such as vessel density, length, and number of junctions were persistently altered following mTBI. Correlative analysis showed a strong inverse relationship between ADC and vessel density at 60 DPI, suggesting increased vessel density following mTBI may restrict WM diffusion characteristics. Our findings suggest that WM vasculature contributes to the long-term microstructural changes within the ipsilateral CC following mTBI.

The Impact of Prenatal Ethanol Exposure on Neuroanatomical and Behavioral Development in Mice.

BACKGROUND: In utero alcohol, or ethanol (EtOH), exposure produces developmental abnormalities in the brain of the fetus, which can result in lifelong behavioral abnormalities. Fetal alcohol spectrum disorders (FASD) is a term used to describe a range of adverse developmental conditions caused by EtOH exposure during gestation. Children diagnosed with FASD potentially exhibit a host of phenotypes including growth retardation, facial dysmorphology, central nervous system anomalies, abnormal behavior, and cognitive deficits. Previous research suggests that abnormal gene expression and circuitry in the neocortex may underlie reported disabilities of learning, memory, and behavior resulting from early exposure to alcohol (J Neurosci, 33, 2013, 18893). METHODS: Here, we utilize a mouse model of FASD to examine effects of prenatal EtOH exposure (PrEE), on brain anatomy in newborn (postnatal day [P]0), weanling (P20), and early adult (P50) mice. We correlate abnormal cortical and subcortical anatomy with atypical behavior in adult P50 PrEE mice. In this model, experimental dams self-administered a 25% EtOH solution throughout gestation (gestational days 0 to 19, day of birth), generating the exposure to the offspring. RESULTS: Results from these experiments reveal long-term alterations to cortical anatomy, including atypical developmental cortical thinning, and abnormal subcortical development as a result of in utero EtOH exposure. Furthermore, offspring exposed to EtOH during the prenatal period performed poorly on behavioral tasks measuring sensorimotor integration and anxiety. CONCLUSIONS: Insight from this study will help provide new information on developmental trajectories of PrEE and the biological etiologies of abnormal behavior in people diagnosed with FASD.