P.175 Direct Visualization of Thalamic Nuclei using 7 Tesla MRI and quantification in patients with temporal lobe epilepsy.

Background: Most individual thalamic nuclei cannot be directly visualized on routine clinical MRI. Stereotactic targeting techniques are indirect, relying on histological atlases and electrophysiological recording. We investigate whether high-field MRI can directly visualize the thalamic nuclei in vivo and allow for analysis of disease-related changes. Methods: Thirty-two healthy individuals were imaged with 7T MRI at a resolution of 0.7mm3. To obtain a high-resolution composite image, these were registered across subjects and averaged together. Three thalamic structures closely integrated in seizure propagation, the anterior thalamic nucleus (ATN), mammillothalamic tract (MTT), and centromedian nucleus (CM) were manually segmented in a subset of healthy subjects and patients with temporal lobe epilepsy (TLE). Results: There is sufficient resolution within the thalamus at 7T for visualization of the ATN, CM, and MTT. In the small subset of 5 controls and 5 TLE patients examined, there was no significant difference (p>0.05) in volume or mean T1map for the three thalamic sturctures of interest. Conclusions: MRI at 7T provides a method of direct visualization of thalamic nuclei, uncovering substructures not previously identifiable in vivo. These advances will enable quantitative analysis of disease-related changes to these structures and improved clinical targeting as demonstrated in this initial ‘proof-of-concept’ subset analysis.

Molecular Characterization of Superficial Layers of the Presubiculum During Development

The presubiculum, a subarea of the parahippocampal region, plays a critical role in spatial navigation and spatial representation. An outstanding aspect of presubicular spatial codes is head-direction selectivity of the firing of excitatory neurons, called head-direction cells. Head-direction selectivity emerges before eye-opening in rodents and is maintained in adulthood through neurophysiological interactions between excitatory and inhibitory neurons. Although the presubiculum has been physiologically profiled in terms of spatial representation during development, the histological characteristics of the developing presubiculum are poorly understood. We found that the expression of vesicular glutamate transporter 2 (VGluT2) could be used to delimit the superficial layers of the presubiculum, which was identified using an anterograde tracer injected into the anterior thalamic nucleus (ATN). Thus, we immunostained slices from mice ranging in age from neonates to adults using an antibody against VGluT2 to evaluate the VGluT2-positive area, which was identified as the superficial layers of the presubiculum, during development. We also immunostained the slices using antibodies against parvalbumin (PV) and somatostatin (SOM) and found that in the presubicular superficial layers, PV-positive neurons progressively increased in number during development, whereas SOM-positive neurons exhibited no increasing trend. In addition, we observed repeating patch structures in presubicular layer III from postnatal days 12. The abundant expression of VGluT2 suggests that the presubicular superficial layers are regulated primarily by VGluT2-mediated excitatory neurotransmission. Moreover, developmental changes in the densities of PV- and SOM-positive interneurons and the emergence of the VGluT2-positive patch structures during adolescence may be associated with the functional development of spatial codes in the superficial layers of the presubiculum.

Sudden confusion and cognitive decline due to acute infarction of the anterior thalamic nucleus (ANT) - a case report

A 76-year-old man presented with sudden behavioral changes and cognitive decline. His clinical presentation was characterized by impaired short-term memory, strange behavior, disorientation, impaired executive function, and withdrawal. MRI of the head showed an infarcted lesion in the right thalamus, confined to the anterior thalamic nucleus. According to the characteristics of the cognitive network and evidence from different clinical and experimental studies, infarction in this critical part of the anterior thalamic nucleus can cause disruption of basal ganglia-thalamo-prefrontal circuit, resulting in confusion and cognitive decline. The combination of clinical symptoms, neuroimaging and temporal findings led to the final diagnosis of strategic infarct vascular dementia (VaD) subtype (SIVaD).

The Role of Hippocampal Neurogenesis in ANT-DBS for LiCl-Pilocarpine-Induced Epileptic Rats

<b><i>Purpose:</i></b> Abnormal neurogenesis in the hippocampus after status epilepticus (SE) has been suggested as a key pathogeny of temporal lobe epilepsy. This study aimed to investigate the effect of deep brain stimulation of the anterior thalamic nucleus (ANT-DBS) on hippocampal neurogenesis in LiCl-pilocarpine-induced epileptic rats and to analyze its relationship with postoperative spontaneous recurrent seizures (SRS) and anxiety. <b><i>Method:</i></b> SE was induced by a systemic LiCl-pilocarpine injection in adult male rats. Rats in the DBS group underwent ANT-DBS immediately after successful SE induction. SRS was only recorded during the chronic stage. An elevated plus maze was used to evaluate the level of anxiety in rats 7, 28, and 60 days after SE onset. After the elevated plus-maze experiment, rats were sacrificed under anesthesia in order to evaluate hippocampal neurogenesis. Doublecortin (DCX) was used as a marker for neurogenesis. <b><i>Results:</i></b> During the chronic stage, SRS in rats in the DBS group were significantly decreased. The level of anxiety was increased significantly in rats in the DBS group 28 days after SE, while no significant differences in anxiety levels were found 7 and 60 days after SE. The number of DCX-positive cells in the hippocampus was significantly increased 7 days after SE and was significantly decreased 60 days after SE in all rats in which SE was induced. However, the number of DCX-positive cells in the DBS group was significantly lower than that in the other groups 28 days after SE. <b><i>Conclusions:</i></b> ANT-DBS may suppress SRS and increase the postoperative anxiety of epileptic rats by influencing hippocampal neurogenesis.