Presence and properties of a circadian rhythm in the rabbit's electrocorticogram

Abstract

Rabbits that have been exposed for several weeks to a L12:D12 regimen exhibit afterwards, under constant circumstances and in steady darkness for 53 h, the presence of "programmed" circadian rhythms in the RMS value and spectral composition of their (computer-analysed) EEG's, in the RMS value of their electromyograms, and in skin temperature. For the occipital and frontal EEG's the RMS value attains its lowest level during a dip occurring about 3 h before the previous light on-moment and its maximum, which is 1.5 times the minimal value, during a peak at some 3 h before the previously occurring light off-transient. Similar changes occur in the power spectral densities of all frequencies between 0.5 cps and 40 cps, with the result that circadian changes in the spectral composition of the EEG, although present and having the same time course, are rather slight. The results are discussed in terms of the two-oscillator model for the central circadian mechanism.

Effects of bilateral cervical sympathectomy and subsequent blinding on properties and circadian changes of the rabbit's EEG

“…However, since the data for each frequency band represent its RMS values as a percentage of the RMS values of the EEG as a whole and it has already appeared that the latter shows marked circadian fluctuations, the absence of circadian changes in spectral composition actually signals the occurrence of equally marked rhythms in the RMS value for each of the 3 frequency bands, with identical time course and nearly the same amplitude. This is in full accordance with the results of previous experiments on 8 intact rabbits (Bobbert et al, 1985).…”

“…Power spectral density always diminished steeply with increase of frequency from 0.5 to 40 cps, often with a hump in the range of 5-7 cps as was previously described (Bobbert et al, 1985). The mean g's for the frequency bands comprising the lowest (0.5-4.5 cps), the medium (5.0-8.5 cps) and the 288 A. C. BOBBERT ET AL.…”

“…These were always started between 11.00 h and 11.30 h, i.e. shortly after the lights came on, when an animal was transferred to the experimental set-up and kept in a situation that has previously been described in full (Bobbert et al, 1985).…”

“…It appeared that in each experiment circadian fluctuations occurred in a of the EEG which were superimposed on non-circadian changes of the same. Since this was already extensively described before (Bobbert et al, 1985), it will not be discussed here any further. However, it is important to note that, when the animals were still intact or merely sympathectomized, the RMS value of the EEG attained its lowest level on the 2nd day of the experiments during the last 3 h before the previous light-on moment (at 11.00 h), and then rapidly increased to reach a fairly stable level that was kept up until the light-off moment of the previous LD regimen.…”

“…cervical sympathetic trunk (Bobbert and Brandenburg, 1982). Recently, it was found that a rhythm with "programmed" time course also occurs in the rabbit's electrocorticogram and, thus, in its electroencephalogram (Bobbert et al, 1985).…”