Development of a histologically validated segmentation protocol for the hippocampal body.

BACKGROUND: Recent findings have demonstrated that hippocampal subfields can be selectively affected in different disease states, which has led to efforts to segment the human hippocampus with in vivo magnetic resonance imaging (MRI). However, no studies have examined the histological accuracy of subfield segmentation protocols. The presence of MRI-visible anatomical landmarks with known correspondence to histology represents a fundamental prerequisite for in vivo hippocampal subfield segmentation. In the present study, we aimed to: 1) develop a novel method for hippocampal body segmentation, based on two MRI-visible anatomical landmarks (stratum lacunosum moleculare [SLM] & dentate gyrus [DG]), and assess its accuracy in comparison to the gold standard direct histological measurements; 2) quantify the accuracy of two published segmentation strategies in comparison to the histological gold standard; and 3) apply the novel method to ex vivo MRI and correlate the results with histology. METHODS: Ultra-high resolution ex vivo MRI was performed on six whole cadaveric hippocampal specimens, which were then divided into 22 blocks and histologically processed. The hippocampal bodies were segmented into subfields based on histological criteria and subfield boundaries and areas were directly measured. A novel method was developed using mean percentage of the total SLM distance to define subfield boundaries. Boundary distances and subfield areas on histology were then determined using the novel method and compared to the gold standard histological measurements. The novel method was then used to determine ex vivo MRI measures of subfield boundaries and areas, which were compared to histological measurements. RESULTS: For direct histological measurements, the mean percentages of total SLM distance were: Subiculum/CA1 = 9.7%, CA1/CA2 = 78.4%, CA2/CA3 = 97.5%. When applied to histology, the novel method provided accurate measures for CA1/CA2 (ICC = 0.93) and CA2/CA3 (ICC = 0.97) boundaries, but not for the Subiculum/CA1 (ICC = -0.04) boundary. Accuracy was poorer using previous techniques for CA1/CA2 (maximum ICC = 0.85) and CA2/CA3 (maximum ICC = 0.88), with the previously reported techniques also performing poorly in defining the Subiculum/CA1 boundary (maximum ICC = 0.00). Ex vivo MRI measurements using the novel method were linearly related to direct measurements of SLM length (r2 = 0.58), CA1/CA2 boundary (r2 = 0.39) and CA2/CA3 boundary (r2 = 0.47), but not for Subiculum/CA1 boundary (r2 = 0.01). Subfield areas measured with the novel method on histology and ex vivo MRI were linearly related to gold standard histological measures for CA1, CA2, and CA3/CA4/DG. CONCLUSIONS: In this initial proof of concept study, we used ex vivo MRI and histology of cadaveric hippocampi to develop a novel segmentation protocol for the hippocampal body. The novel method utilized two anatomical landmarks, SLM & DG, and provided accurate measurements of CA1, CA2, and CA3/CA4/DG subfields in comparison to the gold standard histological measurements. The relationships demonstrated between histology and ex vivo MRI supports the potential feasibility of applying this method to in vivo MRI studies.

In vivo diffusion tensor imaging and histopathology of the fimbria-fornix in temporal lobe epilepsy.

While diffusion tensor imaging (DTI) has been extensively used to infer micro-structural characteristics of cerebral white matter in human conditions, correlations between human in vivo DTI and histology have not been performed. Temporal lobe epilepsy (TLE) patients with mesial temporal sclerosis (MTS) have abnormal DTI parameters of the fimbria-fornix (relative to TLE patients without MTS) which are presumed to represent differences in axonal/myelin integrity. Medically intractable TLE patients who undergo temporal lobe resection including the fimbria-fornix provide a unique opportunity to study the anatomical correlates of water diffusion abnormalities in freshly excised tissue. Eleven patients with medically intractable TLE were recruited (six with and five without MTS) for presurgical DTI followed by surgical excision of a small specimen of the fimbria-fornix which was processed for electron microscopy. Blinded quantitative analysis of the microphotographs included axonal diameter, density and area, cumulative axon membrane circumference, and myelin thickness and area. As predicted by DTI the fimbria-fornix of TLE patients with MTS had increased extra-axonal fraction, and reduced cumulative axonal membrane circumference and myelin area. Consistent with the animal literature, water diffusion anisotropy over the crus of the fimbria-fornix was strongly correlated with axonal membranes (cumulative membrane circumference) within the surgical specimen (approximately 15% of what was analyzed with DTI). The demonstration of a correlation between histology and human in vivo DTI, in combination with the observation that in vivo DTI accurately predicted white matter abnormalities in a human disease condition, provides strong validation of the application of DTI as a noninvasive marker of white matter pathology.

Alcohol exposure during the first two trimesters-equivalent alters the development of corpus callosum projection neurons in the rat.

Children exposed prenatally to alcohol can display a variety of neural deficits, including an altered development of the corpus callosum (CC), the largest interhemispheric axon pathway in the brain. Furthermore, these children show functional abnormalities that are related to brain regions with significant numbers of CC connections. Little is known about how alcohol imparts influence on CC development, but one possible mechanism is by affecting the corpus callosum projection neurons (CCpn) directly. The purpose of this study was to quantify the effects of prenatal alcohol exposure on the number, size, and distribution of CCpn within the visual cortex. The visual cortex was selected specifically due to the many vision-related deficits noted in fetal alcohol exposed children and because the critical role of the CC in visual cortex development is well documented. Sprague-Dawley rat pups received one of four alcohol dosages during gestational days (G) 1-20, or reared as nutritional or untreated control animals. Each litter was categorized according to the peak blood alcohol concentration experienced. Pups were removed from each litter on days equivalent to G29, G36, G43, and G50, for histology and measurement. Callosal axons were labeled retrogradely to their CCpn using 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (DiI) and the CCpn were then examined using confocal laser scanning microscopy. Differences between alcohol-exposed and control animals were observed in CCpn cell body size, number, and location with the cortex. This was particularly true of animals exposed to high doses of alcohol. In addition, some trends of CCpn development were found to be unchanged as a result of prenatal alcohol exposure. The results demonstrate clear differences in the development of CCpn in the visual cortex between alcohol-exposed and control animals and suggest that this development is particularly affected in those animals exposed to high doses of alcohol.

Long-term alcohol exposure prior to conception results in lower fetal body weights.

BACKGROUND: It is well known that alcohol consumption during pregnancy can result in lower birth weight babies but many women stop consuming alcohol prior to conception as a part of pregnancy planning. The purpose of this study was to determine whether alcohol consumption prior to conception may also have an effect on fetal development. METHODS: Male and female C57BL/6J mice at 4, 6, or 8 weeks of age received either a single administration of alcohol (3.0 g/kg) via intragastric gavage (IG) each day for at least 60 days, or an isovolumetric IG administration of sterile water. After 60 treatment days, males and females within each age and treatment group were mated overnight. Females continued to receive daily alcohol treatments until conception. Males continued to receive treatments until all females were successfully mated. At conception, females were isolated and left undisturbed. On embryonic day 14, fetus number, size, and weight was determined. RESULTS: Maternal food consumption, body weight at conception, and delay to conception onset did not differ between the two treatment groups or among the three age groups. Fetal body weights did not differ among the three age groups. Fetuses from females treated with alcohol had lower body weights compared to those treated with water. Male treatments did not seem to affect fetal body weight. CONCLUSIONS: Fetal growth and development can be affected by alcohol consumption prior to the time of conception. Alcohol consumption prior to conception is a potential risk factor to fetal outcome and an important consideration for those females planning to have children.

Blood ethanol concentration profiles: a comparison between rats and mice.

It is important to select an appropriate model system for studies examining the mechanisms of ethanol-induced injury. The most common model systems use either mice or rats with ethanol administered by means of intragastric gavage or intraperitoneal injection, yet few studies have compared directly the blood ethanol concentration (BEC) profiles that result from each of these model systems. In the current study, Sprague-Dawley rats and C57BL/6J mice were given ethanol by means of intragastric gavage or intraperitoneal injection at 40 days of age. Blood samples were collected at consistent time intervals to determine BECs. Blood ethanol concentrations in mice were sharper, with a more rapid rise to a sharp peak BEC, followed by a relatively rapid decline. In contrast, rat BEC profiles showed an initial rapid rise, followed by a more gradual rise to peak concentrations, and, then, a relatively gradual decline. This difference was particularly evident in rats receiving ethanol intragastrically. The differences found in BEC profiles between rats and mice and between ethanol administration paradigms may yield differences in the extent or mechanism of damage induced by ethanol, an important consideration when selecting an appropriate model for the investigation of ethanol-induced tissue damage.