It is well known that psychotropic drugs can induce EEG alterations. Dose dependence seems established; however, there are no data concerning the impact of plasma levels. The authors investigated the influence of clozapine plasma levels on the frequency of EEG alterations. Data from 29 inpatients (18 male, 11 female, 31.7 +/- 10.2 years) receiving clozapine in a dose range between 25 and 600 mg were collected prospectively. There was no psychotropic or anticholinergic comedication. All patients had normal EEGs before taking clozapine. Fifteen patients showed pathological changes (group 2) and 14 no changes (group 1). Discriminant analysis showed that EEG changes are dependent on plasma levels (P = 0.0009, plasma levels in group 1 mean 81.6 ng/ml, +/- SD 64.6, in group 2 235.7 ng/ml, +/- 169.8). A total of 72.4% of the patients were correctly classified as having either pathological EEG changes or none by this analysis. Variables such as dose, age, sex, weight and duration of treatment were not statistically relevant. It can therefore be suggested that clozapine plasma levels are a valid indicator for the appearance of electrophysiological reactions.

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Seasonal affective disorder is a form of depression which recurs at the same time of the year. Exposure to bright artificial light at a dose of 2,500 lux is used to treat seasonal affective disorders. We exposed a pigmented (Brown Norway) and a nonpigmented (Sprague-Dawley) rat strain with bright artificial light for 21 days at two doses (2,500 and 6,100 lux) and analyzed dopamine, dihydroxyphenyl-acetic acid, 5-hydroxytryptamine (5-HT), and 5-hydroxyindole-acetic acid (5-HIAA) by high performance liquid chromatography (HPLC) and electrochemical detection in eight different brain regions. Furthermore, we measured tissue levels of substance P (SP), neurokinins (NK), vasoactive intestinal polypeptide (VIP), calcitonin gene-related peptide (CGRP), and neuropeptide Y (NPY) with radioimmunoassay. Our data obtained with light microscopy show that bright artificial light at both doses induced a massive destruction of photoreceptors in the retina of albino rats but not of the pigmented rat strain. Retinal lesion of photoreceptors resulted in increased tissue levels of all measured neuropeptides except SP in the hypothalamus and increased VIP in the ventral tegmental area/substantia nigra. Furthermore, increased 5-HT and 5-HIAA tissue levels were found in the ventral tegmental area/substantia nigra. In contrast, in the frontal cortex there was a significant reduction in 5-HIAA tissue levels and a decreased 5-HIAA/5-HT ratio, indicating decreased 5-HT metabolism. Light exposure of the pigmented rat strain revealed no changes in the measured biogenic amines and neuropeptides in any investigated brain region. Our data suggest that retinal lesion but not direct visual neurotransmission induced changes in neurotransmitters in some brain regions. We conclude that Brown Norway rats but not Sprague-Dawley rats are useful to study neurochemical effects of bright artificial light. However, Sprague-Dawley rats may be a useful tool to study biochemical mechanisms of photoreceptor damage by bright light.