| Abstract No.: | B-B2070 |
| Country: | Canada |
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| Title: | HIPPOCAMPAL-STRIATAL OSCILLATIONS UNDER VARIOUS PHARMACOLOGICAL AGENTS: INTERACTIONS REVEALED BY GRANGER CAUSALITY ANALYSIS |
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| Authors/Affiliations: | 1 Calvin Young*; 1 Jesse Jackson; 1 Brian Bland;
1 University of Calgary, AB, Canada
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| Content: | Objectives: The function of neural oscillations remains unclear despite decades of research. In recent years, much evidence indicate that brain oscillations may serve the underlying function of spike timing and through different frequencies, coordinate neuronal excitability across many brain areas that is crucial for function. Recent studies have revealed behavioural-dependent synchronization of oscillatory activities at the theta (4-12 Hz) range between the hippocampus (HPC) and extra-HPC structures such as the amygdala, neocortex, and the striatum (STR). These studies have provided correlative evidence that coupling of oscillatory activities are crucial for certain aspects of observable behaviour. In particular, HPC-STR theta coupling has been observed to occur just prior and during the stimulus discrimination phase of a cued-choice task and persists through the consumption of reward, although both structures display theta oscillations throughout the task (DeCoteau et al., 2007). In our laboratory, we have also demonstrated HPC-STR theta coupling during an active avoidance task. In addition, the electrical stimulation of the posterior hypothalamic nucleus (PH), is able to elicit and synchronize HPC and STR theta oscillations (Jackson et al., submitted). In the current study, the relationship between HPC and STR theta oscillations was investigated by autoregressive modeling based on the principles of Granger causality.
Materials and Methods: Sections of data from behavioural immobility during baseline and the intraperitoneal injection of saline (1 ml/kg), atropine sulphate (ATSO4, 50 mg/kg), haloperidol (HALO, 3 mg/kg) and urethane (URE, 2 g/kg) were analyzed using directed coherence (DCOH), directed transfer function (DTF) and short-time DTF (STDTF).
Results: The DCOH and DTF reveals that the HPC may drive theta oscillations in the STR with the involvement of a common source. The injection of saline increased the HPC->STR DTF, whereas all other pharmacological manipulations decreased it. None of the manipulations significantly changed DTF values in the direction of STR->HPC. Also, electrical stimulation of the PH appears to synchronize HPC-STR theta oscillations through HPC-mediated actions on the STR, as demonstrated by STDTF. Finally, STDTF also suggests that high voltage spindle (HVS) activity in the STRat the same frequencies as theta oscillations does not originate from the HPC. In fact, HVS in the STR appear to “drive” HPC rhythmic activity, indicating cortical and/or thalamic involvement in eliciting HPC theta during STR HVS.
Conclusion: Systemic injections of ATSO4, HALO and URE decreased HPC->STR theta driving without changing the theta driving in the opposite direction or the overall direction of the driving. Therefore, it appears HPC and STR theta oscillations during immobility are mediated by the HPC. HPC entrainment of STR single unit activities may have a prominent role in determining STR theta activities. STR HVS may have a thalamo-cortical origin, which may also elicit oscillatory activity in the HPC.
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