The pedunculopontine nucleus (PPN) is a component of the brainstem Reticular Activating System (RAS), and is active during waking and paradoxical sleep. The PPN sends ascending cholinergic projections to the intralaminar thalamus, particularly the parafascicular nucleus (Pf). The Pf nucleus is part of the "non-specific" thalamocortical system that sends widespread projections to the cortex, and is thought to play a significant role in maintaining awareness and selective attention. Electrical stimulation of either the PPN or centrolateral (Cl)-Pf nuclei in vivo is known to produce arousal and gamma band activity in the cortical EEG. Gamma oscillations are evident in all Pf and PPN neurons and they are mediated by high threshold, voltage-dependent N- and P/Q- type calcium channels. Whole-cell patch clamp recordings were preformed in conjunction with high-speed calcium imaging on brainstem slices from 9 to 19 day old rat pups in order to visualize calcium oscillations and characterize calcium transients in the Pf and PPN in vitro. This age range was selected because it spans the developmental decrease in rapid eye movement (REM) sleep that occurs in the rat from birth to postnatal day 30. Calcium transients with oscillations were generated by depolarizing current ramps and were visualized with a specially designed high-speed imaging system. These studies determined that, 1) Both Pf and PPN cells manifested calcium transients with oscillations in both somatic and proximal dendritic regions in parallel with the electrical patch signal; 2) Fast imaging using single wavelength calcium indicators or novel ratiometric indicators were capable of recording peaks in calcium flux paralleling oscillations time-course in the electrical signal; 3) The mechanism behind both the imaged calcium oscillations and the parallel electrical oscillations was due to high threshold, voltage-dependent P/Q- and N-type calcium channels; 4) Different dendrites consist of oscillatory subdomains, with somatic oscillations representing summed oscillatory activity from the whole cell. In summary, these studies provide novel information about the role of high-threshold calcium channels in nuclei of the RAS involved in sleep-wake regulation and awareness, as well as useful new tools for investigating calcium signaling.
|Commitee:||Childs, Gwen, Hayar, Abdallah, Skinner, Robert, Urbano, Francisco|
|School:||University of Arkansas for Medical Sciences|
|Department:||Neurobiology and Developmental Science|
|School Location:||United States -- Arkansas|
|Source:||DAI-B 74/09(E), Dissertation Abstracts International|
|Keywords:||Calcium imaging, Calcium oscillations, Parafascicular nucleus, Pedunculopontine nucleus, Reticular activation|
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