Simultaneous response of brain electrical activity (EEG) and cerebral circulation (REG) to microwave exposure in rats.

The correlations between physiological modalities in microwave field-activated systemic or localized regulatory mechanisms with changes in the central nervous system (CNS) seem not to be identical. These problems are important because of the increased number of radiating appliances, e.g. portable radios and mobile telephones. In two series of experiments on anaesthetized rats (N = 40) (i) before and after 10 min, whole body exposures to 2.45 GHz CW microwaves, and (ii) during 30 min exposures to 4 GHz amplitude modulated (AM, 16 Hz) microwaves, the effects on the CNS were observed simultaneously with those on the cardiovascular system by quantitative polygraphic measurement. In acute experiments on rats, electroencephalograms (EEG), rheoencephalograms (REG) as an index of cerebral blood flow (CBF), brain tissue DC impedance and temperature and ECG were recorded simultaneously. The total power of EEG spectra increased after whole body 30 mW/cm2 2.45 GHz CW exposure for 10 min. No changes occurred at 10 mW/cm2. The CBF increased after 10 mW/cm2 exposure. The power of EEG delta (0.5-4 Hz) waves was increased by thermal level of brain localized 4 GHz CW exposure at 42 mW/g specific absorption rate (SAR) simultaneously with the REG amplitude as an index of cerebral blood flow. Amplitude modulation at 16 Hz and 8.4 mW/g SAR was associated with increased power of EEG beta (14.5-30 Hz) waves but changes in the CBF were not observed. CW radiation at 8.4 mW/g increased the cerebral blood flow, but did not change EEG spectra.

Intrinsic and synaptically generated delta (1-4 Hz) rhythms in dorsal lateral geniculate neurons and their modulation by light-induced fast (30-70 Hz) events.

Thalamocortical neurons of cat dorsal lateral geniculate nucleus were recorded under urethane anesthesia. Neurons were identified by antidromic invasion from the internal capsule and by orthodromic stimulation from the optic chiasm or light stimuli. An intrinsic oscillation within the frequency of sleep delta waves (1-4 Hz) was induced by hyperpolarizing current pulses triggering a rhythmic sequence of low-threshold spikes alternating with after hyperpolarizing potentials. The increased propensity to oscillation after blockage of inputs arising in the retina indicates that afferent synaptic drives interfere with the intrinsic oscillation of lateral geniculate cells. The relatively rare occurrence of this type of oscillation in impaled neurons, as compared with extracellular recordings in the same nucleus or to intracellular recordings in other dorsal thalamic nuclei, suggests that the interplay between the two intrinsic currents generating delta oscillation is particularly critical in lateral geniculate cells. Another type of delta oscillation was characterized by excitatory postsynaptic potentials which gave rise to action potentials or to low-threshold spikes at more depolarized or hyperpolarized levels, respectively. It is suggested that this rhythm reflects synaptic coupling by intranuclear recurrent axonal collaterals. Light stimulation induced fast (30-70 Hz) excitatory events that were blocked after lidocaine injections into the eye. In all tested cells, changes in the ambient luminosity of the experimental room blocked the intrinsic as well as the synaptic oscillation within the delta frequency. In some cells, this suppressing effect was associated with depolarization and increased firing rate. These results demonstrate different types of sleep delta oscillations in visual thalamic neurons and show that they are modulated not only by brainstem regulatory systems, but also by specific drives along the visual channel.