Power spectrum analysis of EEG synchronization following application of serotonin to area postrema

The role of serotonin and of the area postrema in synchronization of the neocortical electroencephalogram (EEG) was investigated in the present studies by observing the effects of different drugs (serotonin, norepinephrine, acetylcholine, and Xylocaine) applied topically at the site of the area postrema in cats. Using Fast Fourier Spectral analysis and power density spectra techniques it was found that serotonin increased the low frequency components and decreased the high frequency components in the cortical EEG. Application of serotonin to the floor of the fourth ventrical 6 mm rostral to the area postrema never produced EEG synchronizing effects. Xylocaine applied directly to the area postrema, as well as lesions of this region, decreased the low frequency components of the EEG while norepinephrine and acetylcholine produced variable effects. These results indicate that a serotonergic-sensitive mechanism, which induces EEG synchronization, exists in the region of the area postrema. This research was supported by N.I.M.H. Grants 0221 and 10625.     

Amplitude and spectral quantification of the effects of morphine on the cortical EEG of the rat

The effect of systemically administered morphine sulfate on the cortical EEG of the rat was studied using direct visual scoring procedures and spectral and amplitude distribution analysis techniques. The EEG effect was found to be dose-dependent, i.e., as higher doses of morphine were administered morphine-induced spindles or spike-like activity progressively increased and were eventually replaced by a highly synchronized EEG. In quantifying these EEG patterns, using spectral analysis, distinct frequency spectra were found for morphine-induced spindles and epochs of high voltage low frequency (HVLF) activity. The power in the 5-7 Hz frequency band was found to be a good indicator of the duration of the morphine effect since the value of this index was elevated during the time course of the drug effect. In addition, amplitude distribution methods revealed the sensitivity of two specific measures to the EEG changes induced by morphine. Values of standard amplitude followed closely the degree of EEG synchronization while kurtosis proved sensitive enough to follow the effect of specific doses of morphine sulfate.     

Effect of chronic protein malnutrition on non-specific thalamo-cortical evoked potentials in the rat

Cortical incremental responses to repetitive thalamic stimulation were studied in normal and protein malnourished rats. The rate of cortical incrementation ipsilateral to the thalamic site of stimulation varied as a function of stimulus repetition rate but was unaffected by dietary treatment. The waveform of the ipsilateral response likewise was unaffected by protein malnutrition and a characteristic positive-negative-positive response was observed. In the cortex contralateral to thalamic stimulation, seven of eight malnourished animals exhibited a surface positive peak, in some cases quite prominent, at a latency at which seven of eight normals exhibited a prominent surface negativity. These results are discussed in relation to reported effects of malnutrition on sensory evoked potentials.     

Locus coeruleus-to-dorsal raphe input examined by electrophysiological and morphological methods

In order to examine the hypothesis that the locus coeruleus (LC) projects directly to the nucleus raphe dorsalis (DR), electrical stimulation was applied to the LC of rats while recording from single neurons in the region of the DR. Slow firing units of the DR were not influenced by the stimulation, although faster firing units in the nearby substantia grisea centralis (SGC) were. These latter cells become oscillatory in their firing rates during LC stimulation. In parallel studies a retrograde transport technique was employed to obtain morphological evidence regarding projections to DR. Placements of horseradish peroxidase precisely in the DR resulted in very sparse labeling in the LC, although positive transport occurred to other areas. The results indicate that the LC does not project directly to slow firing DR neurons, but does influence faster firing cells in the region of the SGC, probably by complex routes. Suggestions are made for the integration of these findings with earlier fluorescence studies.     

Protein malnutrition in rats: response of brain amines and behavior to foot shock stress.

The changes in regional brain levels of serotonin, 5-hydroxyindoleacetic acid, and norepinephrine following an acute shock stress to the feet were examined in adult rats which had been fed a protein-poor diet or a normal diet during the developmental period and adulthood. Regional brain levels of the amines and 5-hydroxyindolacetic acid showed little change in normal rats following up to 90 min of shock, whereas depletions of up to 50% occurred in chronically protein malnourished rats. These neurochemical changes in the chronically malnourished rats were pronounced in the diencephalon and in the midbrain-pons-medulla brain regions. Normal rats which were switched in adulthood to the low protein diet showed minimal decreases in brain amine and 5-hydroxyindoleacetic acid levels following foot shock. This suggests that the effects observed in the chronically malnourished rats reflect a developmental interaction and were not due to the diet being administered at the time of testing. Behavioral measures of reactivity to foot shock, however, did not reveal marked diet related effects. Possible reasons for the differences in the behavioral vs. central neurochemical responses to foot shock are discussed. The results regarding the amine and 5-hydroxyindoleacetic acid levels demonstrate that the brains of chronically protein malnourished rats do not compensate to the same extent as the brains of normal rats (or normal rats switched to a low protein diet at adulthood) for the effects of an acute stress.