Very slow oscillatory activities in lateral geniculate neurons of freely moving and anesthetized rats

In urethane anesthetized rats many lateral geniculate neurons display a strong very slow oscillatory behavior in the range of 0.025-0.01 Hz. One of the aims of the present study was to determine whether very slow oscillatory activity in this range can also be obtained in barbiturate anesthetized and in awake animals, respectively. Although very slow oscillations were found in geniculate neurons both during awakeness and during anesthesia, significant differences in peak frequencies of oscillations under the three experimental conditions (barbiturate, urethane, awake) were demonstrated. In addition, we have tested the influence of glutamate antagonists and GABA agonists as well as antagonists on the very slow oscillatory activity in urethane anesthetized rats. Very slow oscillatory activity which could be blocked by the continuous illumination of the eyes was re-induced by iontophoresis of NMDA and non-NMDA glutamate antagonists. GABA(A) as well as GABA(B) agonists also caused a significant re-induction of very slow oscillatory activity under light conditions. In the dark, muscimol, a GABA(A) agonist, significantly enhanced the very slow oscillatory activity, i.e. muscimol either induced it or reduced the frequency of very slow oscillations. For the whole sample, GABA antagonists did not have a significant influence on the very slow oscillatory activity. Autocorrelation analysis based on the spike interval histograms and determination of the spectrum of autocorrelograms revealed the significance of periodicity.