Abstracts

Rationale: Quantification of the spatio-temporal neuronal activity patterns underlying electrographic epileptic signatures is critical for decoding these abnormal dynamics. It requires an ability to simultaneously monitor extended tissue areas and the activity of individual cells with high temporal resolution. Presently we lack clear understanding of the mechanisms of these processes and how they are influenced by underlying circuitry or neuromodulatory afferents. The aim of the current study is to investigate the genesis, evolution and beta adrenergic receptor (?-AR) effects on emergent interictal and ictal-like activity in anatomically-distinct rodent brain preparations using concurrent electro-optical toolkit. Methods: To study epileptiform activity and its neuromodulation by norepinephrine-like agonists, we used transverse hippocampal and visual neocortical rat brain slices (P21-P30). In acute 4-Aminopyridine (4-AP; 50-100 M) seizure model, both structures generated electrographically similar interictal bursts (IBs) and ictal-like events, which were further modulated by ?-AR agonist isoproterenol (ISO, 10 M). Concurrent fast voltage-sensitive dye (Di-4ANNEPS and Di-8ANNEPS) imaging (MiCam Ultima-CMOS, 100x100 pixels; 0.5-1KHz) and extracellular or whole-cell recordings were performed. We analyzed sites of IB and ictal-like event origin, duration, velocity of propagation, power spectrum, and local and global synchronization dynamics (Brainvision and Matlab). Results: Both structures exhibited short duration (70-500msec) IBs and longer ictal-like events in the presence of 4-AP. Application of ISO significantly reduced the duration (hippocampus CA1: from 49 to 20 sec., n=9 slices; visual cortex layers II-III: 132 to 72 sec., n=4 slices) or completely blocked ictal-like events. In hippocampus, most of the IBs originated from dentate gyrus/CA3 border and propagated downstream the tri-synaptic pathway toward CA1 (n=6 slices; 120 IBs). In the VC, 46.7% of IBs originated in layers II/III, 11.5% in layer IV, 9% in layer V, and 25% in layer VI (349 optical bursts; n=6 slices). ISO left IB origin sites unchanged, but instead increased frequency of IBs, and confined the spatial extent of the IB activity in the hippocampus to 30-50% of that seen in 4-AP (measured using spatial activation maps, n=4 slices; 60 IBs). Velocity of IB propagation from the hippocampal CA3 to CA1 area showed a significant decrease (0.3m/s to 0.16m/s; n= 6 slices; 120 IBs). IB inter-event interval durations were more regular in 4-AP (on average 600-800msec), while in 4-AP ISO this interval was more variable (600-1500ms; n=3 slices, 58 bursts in 4-AP and 123 bursts in 4-AP ISO). Conclusions: Anatomically diverse architecture and modulatory inputs play important roles in patterning the spatio-temporal dynamics of epileptiform activity emergence and propagation. The effects of ISO indicate the existence of hyperexcitable, rhythmically irregular, and spatially desynchronized epileptic-like state mediated by ?-AR activation.