DELTA ACTIVITY AND NEURONAL ENSEMBLES IN THE RAT VENTROBASAL THALAMUS

 

Topchiy I.A.,  Rector D.M.

 

Department of VCAPP, Washington State University, Pullman, WA, USA

A.B.Kogan Research Institute for Neurocybernetics, Rostov-on-Don, Russia

topchiy2001@yahoo.com

 

Delta-activity during slow-wave sleep is generated at the thalamic and cortical level and originates from both single thalamic cells and their groups (or clusters) (Steriade, Dossi Nunez, 1991; Dossi, Nunez, Steriade, 1992). According the cluster structure of the thalamic nuclei, different clusters generate delta-waves independently, but can also be synchronized by the reticular nucleus or recurrent cortical pathways (Steriade, McCormick, Sejnowski, 1993). In rodents investigators have questioned the existence of local circuits, which would produce independent local synchronization of neuronal groups in the ventrobasal thamus (McAllister, Wells, 1981). We recorded activity of thalamic unit ensembles in rats in relation to delta-waves to ascertain whether different neuronal groups can be synchronized by local networks.

Experiments were carried out upon Sprague-Dawley rats under ketamine/xyazine anesthesia. Unit activity and slow fiels potentials were registered from thalamic n. VPL and n. VPM, using a 16-channel single shank silicon probe (1 cm)  with 100 mkm site spacing and 13 mkm site diameter. Data were filtered between 0.1 Hz and 3 kHz. EEG was extracted by applying a 0.1-4 Hz IIRC Butterworth filter for delta activity and unit data extracted by applying a 300 Hz-3 kHz ARC filter.

Recording from both nuclei showed similarity (grouping) of delta-waves and correlation of neuronal activity in several sites synchronized within separate clusters of neurons in the ventrobasal thalamus. Regular synchronized bursting activity of units fired with periodicity of delta-band (0.5-0.6/s) has been revealed. The majority of neuronal activity occurred during the delta-waves` negative slope and formed a definite discharge pattern.

Slow (<1 Hz) waves, modulated delta-activity were found with similarity and synchronicity within the neighboring cites and different phase characteristics between groups of cites.

Thus,  the globally controlled neuronal discharges, synchronized in delta-waves  and unit discharges locally synchronized within groups, reated to the definite phase of delta-wave has been revealed. In order to investigate the origin of this synchronization, further studies are required.

Supported by: NIMH 60263, an SRS Junior Faculty Award and a Beckman Foundation Young Investigator Award.