Wilfried Dimpfel

Pharmacological modulation of cholinergic brain activity and its reflection in special EEG frequency ranges from various brain areas in the freely moving rat (Tele-Stereo-EEG)

Due to the electrochemical nature of the communication structure of the brain an intimate relationship between neurotransmitter activity on one side and field potentials (EEG) on the other side can be suspected. In order to learn more about this relationship pharmacological manipulation of the cholinergic transmitter system by means of agonistic and antagonistic receptor active drugs was used. Continuous recording of electrical activity from four selected brain areas (frontal cortex, hippocampus, striatum and reticular formation) in freely moving day-night converted Fisher rats was used (Tele-Stereo-EEG). Frequency analysis of telemetrically transmitted data and special definitions of frequency ranges were used to analyse the data from 45 min pre-drug and 180 min postdrug periods. Pharmacological modulation of brain activity by the selective nicotinic agonist metanicotine as well as the alpha 7 selective nicotinic antagonist methyllycaconitine revealed major changes in delta (1-4.5 Hz) and alpha2 (9-12.5 Hz) frequencies. In general blockade of the cholinergic system resulted in electrical power increases and activation in decreases. Unspecific modulation of cholinergic activity by using the cholinesterase inhibitors physostigmine, tacrine and galantamine led to alpha1 frequency (7-9.5 Hz) changes in addition to the delta and alpha2 changes. These three drugs produced a nearly identical pattern of frequency changes. Theta (4.75-6.75 Hz) and beta1 frequencies (12.75-18.5 Hz) changed to a lesser degree. A peculiar finding arose with respect to the effects of the antagonistic drugs scopolamine and biperiden since biperiden-besides the massive increase of delta and alpha1 power in common-induced a general decrease of alpha2 frequencies within all brain areas opposite to the effect of scopolamine. This special property of biperiden gives a plausible explanation for its efficacy in Parkinsonian patients since decreases of alpha2 waves in this model indicate enhancement of dopaminergic transmission [Dimpfel, W., Spüler, M., Koch, R., Schatton, W., 1987. Radioelectroencephalographic comparison of memantine with receptor-specific drugs acting on dopaminergic transmission in freely moving rats. Neuropsychobiology 18, 212-218]. Except for the effects of methyllycaconitine (p<10%) all results were statistically significant at least at the p<5% level. The results are best explained by assuming that electrical delta activity reflects cholinergic transmitter control followed by and closely linked to changes in dopaminergic transmission as indicated by additional concomitant changes in alpha2 electrical power.

Pharmacological Modulation of Dopaminergic Brain Activity and Its Reflection in Spectral Frequencies of the Rat Electropharmacogram

Background: Particular frequencies of electropharmacograms have been attributed to cholinergic, noradrenergic or dopaminergic mediated neurotransmission. This investigation deals with changes induced by L-DOPA or dopamine D2 receptor agonists. Method: Adult rats (day-night converted) were instrumented with four bipolar concentric semi-micro-electrodes into the frontal cortex, hippocampus, striatum and reticular formation. Field potentials were recorded during a pre-drug reference period followed by 4 h of recording thereafter. Data were transmitted wirelessly for spectral frequency analysis. Results: At low doses of L-DOPA (1–5 mg kg–1) and of the D2 agonists talipexole and quinpirole (0.1 mg kg–1), a delayed increase of delta and theta power was observed. Higher doses led to immediate stable decreases of alpha1, alpha2 and beta1 power as reported for dopamine D1 receptor agonists. Administration of the D2 blocker sulpiride (10–20 mg kg–1) resulted in increases of alpha2 power. Conclusion: A common denominator for changes of dopaminergic transmission could be seen in immediate changes of spectral alpha2 power. Delayed increases of delta and theta activity after low dosages of the medication are considered to originate from heterosynaptic, presynaptic D2 receptors sitting on cholinergic neurons. This pattern could explain daytime tiredness or sudden sleep attacks in Parkinson patients.

Different anticonvulsive effects of hesperidin and its aglycone hesperetin on electrical activity in the rat hippocampus in-vitro

This study investigated the possibility that hesperidin or hesperetin might interact directly with brain matter in a physiological manner. The effects of both compounds were followed in the in‐vitro hippocampus preparation by continuous superfusion in a concentration‐dependent manner in the presence of single stimuli and theta‐burst stimulation of the Schaffer Collaterals. Hesperidin increased the population spike response at a concentration up to 10 μm, especially after induction of long‐term potentiation, but attenuated it significantly at higher concentrations of up to 60 μm. Hesperetin only attenuated the response within the same concentration range. Modulation of the pyramidal cell response in the presence of tetraethylammonium (TEA) and pentylentetrazol on one hand and 4‐aminopyridine (4‐AP) and bicuculline on the other was influenced in a different way. Whereas hesperidin attenuated the response to 4‐AP and bicuculline but not to TEA or pentylentetrazol, hesperetin was able to attenuate the response to TEA and pentylentetrazol, but not to 4‐AP or bicuculline. This feature was reproduced and confirmed ex‐vivo after repetitive administration of hesperidin and hesperetin in‐vivo for one week (500 mg kg−1 orally) before in‐vitro testing against the challenging effects of 4‐AP and TEA. Since the action of hesperidin was sensitive to the presence of iberiotoxin, the involvement of a large conductance calcium‐dependent potassium channel might be assumed. In summary, the results provide the possibility for use of both compounds to control pathophysiological disturbances of brain excitability in drug abuse, migraine and epilepsy.

Rat electropharmacograms of the flavonoids rutin and quercetin in comparison to those of moclobemide and clinically used reference drugs suggest antidepressive and/or neuroprotective action

In order to be able to test single constituents of herbal plant extracts with respect to possible clinical usefulness, the model of local field potential analysis leading to the so-called electropharmacogram has been successfully used in rats to classify the effects of theanine and theogallin in the past. The present investigation aims at the prediction of efficacy and possible mechanisms of action of rutin and quercetin. Adult rats (day-night converted) were instrumented with four bipolar concentric electrodes into the frontal cortex, hippocampus, striatum and reticular formation. Field potentials were recorded during a pre-drug reference period of 45 min followed by oral administration of the particular test compound and 4h recording thereafter. Data were transmitted wirelessly to the computer for spectral frequency analysis. Rutin (5-80 mg/kg) as well as quercetin (5-40 mg/kg orally) produced similar electropharmacograms with dose dependent decreases of spectral alpha2 and beta1 frequencies within all brain areas. Peak effects were reached 4h after administration. The pattern of changes approached that obtained after 2.5mg/kg of moclobemide during the first hour as revealed by discriminant analysis in comparison to a large matrix of other drugs with known clinical indications. Data suggest antidepressant capabilities for rutin and quercetin with inhibition of monoamino oxidase at least as part of the mechanism of action. Both compounds should be tested clinically in patients with symptoms of depression.

Hyperexcitability of cultured central nervous system neurons caused by tetanus toxin.

Abstract Rat central nervous system was cultured 5 to 6 weeks and then exposed 5 to 8 h to 2 × 10 −8 g/ml tetanus toxin. Forty to fifty hours later intracellular recording revealed an increase of both resting membrane potential and amplitude of action potentials in poisoned neurons whereas input resistance and depolarizing threshold currents were significantly reduced. In addition a number of neurons exhibited tonic firing characteristics under the influence of tetanus toxin. These results suggest that tetanus toxin has postsynaptic effects under tissue culture conditions, which appear to shift the phasic discharge of these neurons to a more tonic response. Thus the presynaptic action demonstrated under in vivo conditions might not be the only possible origin of the clinical symptoms seen after tetanus intoxication.

Pharmacological classification of herbal extracts by means of comparison to spectral EEG signatures induced by synthetic drugs in the freely moving rat.

Herbal extracts targeting at the brain remain a continuous challenge to pharmacology. Usually, a number of different animal tests have to be performed in order to find a potential clinical use. Due to manifold possibly active ingredients biochemical approaches are difficult. A more holistic approach using a neurophysiological technique has been developed earlier in order to characterise synthetic drugs. Stereotactic implantation of four semi-microelectrodes into frontal cortex, hippocampus, striatum and reticular formation of rats allowed continuous wireless monitoring of field potentials (EEG) before and after drug intake. After frequency analysis (Fast Fourier Transformation) electric power was calculated for 6 ranges (delta, theta, alpha1, alpha2, beta1 and beta2). Data from 14 synthetic drugs - tested earlier and representative for different clinical indications - were taken for construction of discriminant functions showing the projection of the frequency patterns in a six-dimensional graph. Quantitative analysis of the EEG frequency pattern from the depth of the brain succeeded in discrimination of drug effects according to their known clinical indication (Dimpfel and Schober, 2003). Extracts from Valerian root, Ginkgo leaves, Paullinia seed, Hop strobile, Rhodiola rosea root and Sideritis scardica herb were tested now under identical conditions. Classification of these extracts based on the matrix from synthetic drugs revealed that Valerian root and hop induced a pattern reminiscent of physiological sleep. Ginkgo and Paullinia appeared in close neighbourhood of stimulatory drugs like caffeine or to an analgesic profile (tramadol). Rhodiola and Sideritis developed similar frequency patterns comparable to a psychostimulant drug (methylphenidate) as well to an antidepressive drug (paroxetine).

Source density analysis of the human EEG after ingestion of a drink containing decaffeinated extract of green tea enriched with L-theanine and theogallin.

Abstract Source density analysis of EEG recordings from 12 healthy human volunteers was used in a randomized, placebo controlled cross over study to investigate the change in physiological parameters after ingestion of a soft drink containing green tea extract enriched with L-theanine and theogallin. EEG was recorded 1, 2, 3 and 4 h after ingestion during different recording conditions. Visually evoked P300 potentials were recorded every hour in addition to the EEG recordings. Analysis of the data revealed a general attenuation of electrical delta power under the condition of eyes open during the first hour (statistically significant at p < 0.01). During a reading test increases of delta and theta power were observed at frontal electrode sites starting with the second hour after administration, significant at the third and fourth hour (p < 0.04) in comparison to placebo. These changes indicate a higher level of mental performance. Increases of beta1 power starting with the second hour indicated a higher degree of relaxation. However, no statistical significance was reached. Analysis of visually evoked P300 waves revealed a decrease in latency at the last hour (statistical significance p < 0.04) as well as increases of amplitudes at the electrode position Cz (from the first to the third hour, statistically not significant). This type of result in general suggests an improvement of attention. Thus, decaffeinated extract of green tea still has a stimulating effect despite the lack of caffeine presumably due to its high content in L-theanine and theogallin as found in preclinical experiments.

Theogallin and l-theanine as active ingredients in decaffeinated green tea extract: II. Characterization in the freely moving rat by means of quantitative field potential analysis

The model Tele‐Stereo‐EEG (continuous recording of intracerebral field potentials in the freely moving rat to produce an electropharmacogram) has been used to see if l‐theanine‐ and theogallin‐enriched decaffeinated green tea extract would change electrical brain activity after oral administration, to provide proof of access of active components to the brain via the blood‐brain barrier. Baseline recording (45 min) was followed by a 5‐h recording session after oral ingestion of the extract or single components: l‐theanine, theogallin and quinic acid, a suggested metabolite of theogallin. Power spectra from Fast Fourier Transformed (FFT) field potential changes were divided into six frequency bands (delta, theta, alpha1, alpha2, beta1 and beta2). No effects could be measured using a saline solution for control purposes. Oral administration of 75 mg kg−1 total extract led to power decreases mainly in delta and alpha2 frequencies during the first hour. This pattern has been observed in the presence of stimulatory synthetic compounds. Oral administration of 30 mg kg−1 l‐theanine led to power decreases of nearly all frequencies, being more pronounced during the second and following hours in comparison with the first hour. Ingestion of 20 mg kg−1 theogallin also showed a power decreasing effect on cortical activity. Its possible metabolite quinic acid (10 mg kg−1, p.o.) also produced decreases in delta, alpha2 and beta1 frequencies. Measurement of motion resulted in an increase during the first hour in the presence of theogallin and l‐theanine. A tendential decrease was observed in the presence of l‐theanine during the last hour at its presumably highest plasma levels. The results with the administration of the total extract provided evidence for the maior involvement of l‐theanine and theogallin (or its presumable metabolite quinic acid) in its action, since no other active compounds were present in the extract. These compounds could be classified by comparison with reference drugs using discriminant analysis as being antidepressive and cognition enhancing, respectively. The extract appeared among those drugs having stimulatory effects.

Neurophysiological characterization of a functionally active drink containing extracts of ginkgo and ginseng by source density analysis of the human EEG.

Abstract Functional food products should provide scientifically proven beneficial effects in healthy subjects. The highly sensitive method of EEG recording from healthy human volunteers was used in a randomized, placebo controlled crossover study to investigate the effects of a change in physiological parameters after ingestion of a total of 750 ml of a softdrink containing 0.232 g of ginseng and 2 g of ginkgo extract, both produced by water extraction. Application of a random, placebo controlled crossover design was done with 10 healthy male volunteers. EEG recordings were performed 1, 2, 3 and 4 h under the conditions of 10 min eyes open, 5 min eyes closed and 5 min reading short stories. Auditory P300 potentials were recorded every hour in addition to the EEG recordings. Source density analysis of the data revealed an attenuation of circadian induced electrical delta power decreases under the condition of eyes open and closed recording from centro-parieto-occipital electrode positions. During a reading test even absolute increases of delta power were observed at these electrode sites. These changes were statistically significant at p < 2% for the second hour (eyes open and reading) and are interpreted to indicate a higher degree of emotional well-being. Decreases in latency (from 333.9 to 321.3 ms) as well as increases of amplitude (from 2.07 to 3.95 μV) of the auditory P300 potential at the electrode position Pz point to a possible improvement of attention, however, the difference did not reach statistical significance.

Differential distribution of gangliosides in nerve-cell cultures

Summary1.The continuous tumor-cell lines Neuro 2a, NB41/A3, and C6 were compared with regard to ganglioside synthesis. In the two neuroblastoma lines a very high rate of synthesis of GM2 could be observed, whereas the glioma line C6 showed a high prevalence of synthesizing GM3. None of them produced GD1b or GT1b. [For nomenclature, see the proposal of Svennerholm (1963).]2.Primary cultures appeared to be very similar to nervous tissuein vivo, containing essentially all the major brain gangliosides in comparable amounts.3.Treatment of primary cultures with the neurotoxins kainic acid and hydroxydopamine showed a decrease in neurons as measured by125I-labeled tetanus toxin binding concomitant with a selective loss of GT1b, GD1b, GD1a, and GM1 but not GM3.4.It is concluded that the ganglioside GM3 is confined mainly to nonneuronal cells, whereas the other four gangliosides mentioned are normal constituents of the neuronal membrane.