Effect of Neurexan on the pattern of EEG frequencies in rats

Stress-related disorders, such as mild anxiety, nervousness, and insomnia, are widespread among the population. For example, the prevalence of anxiety disorders and insomnia reaches 16.6% and 26%, respectively[1, 2]. Currently used medications include benzodiazepines and serotonin-specific reuptake inhibitors. However, these medications can be accompanied by considerable adverse effects, such as cognitive impairment and dependency[3‐5]. For the treatment of stress-related disorders, self-medication is often practiced, and there is a strong association between stress and alcohol consumption[6], leading to the known potential consequences for physical and psychological health.

Clinical studies have documented that complementary and alternative medicine effectively treats stress-related disorders, such as sleep disturbance and anxiety-related conditions, without serious adverse effects[7, 8]. For example, Neurexan is a multicomponent drug constituted of highly diluted natural, mainly plant, extracts. It is recommended to treat mild sleep disturbances and agitated conditions[9].

The effectiveness of the single components of Neurexan (passiflora incarnata [Passiflora], avena sativa coffea arabica, and zincum isovalerianicum) has been demonstrated in human and animal studies. Three randomized controlled trials demonstrated the anxiolytic efficacy of Passiflora as monotherapy[10, 11] and as part of an herbal combination[12]. Animal studies demonstrated the sedative effects of avena sativa[13] and increased sleep intensity by diluted preparations of coffea cruda[14]. In a retrospective analysis, a potential beneficial effect of zincum isovalerianicum in patients with restless legs syndrome could be observed[15].

Although these components are less concentrated in Neurexan than in the reference drugs tested in the previously mentioned studies, Neurexan is effective for the treatment of moderate insomnia and nervousness. In two observational studies, Neurexan was demonstrated as a well-tolerated alternative to conventional valeriana officinalis (Valeriana)–based therapies for the treatment of moderate insomnia and nervousness[16, 17].

As a multicomponent medication, Neurexan presumably acts on different targets, and the resulting net effect on the central nervous system has not been characterized. During the past decade, electroencephalography (EEG) has provided surrogate measures of drug efficacy of psychoactive drugs. The EEG signature obtained from the spectra of oscillation frequencies may differ between baseline and experimental conditions. Therefore, an EEG signature might be seen as a biomarker[18].

Biomarkers are increasingly used to both predict the clinical response to treatment and characterize the mechanism of action[19]. For instance, changes of EEG signatures observed after administration of experimental compounds can be assigned to the interference of drugs with certain neurotransmitter systems, such as the cholinergic, dopaminergic, and noradrenergic systems[20‐23]. Moreover, different drug categories, such as antidepressive, anticonvulsive, analgesic, neuroleptic, stimulatory, narcotic, sedative, and hallucinogenic drugs, result in a reproducible and disease-specific EEG signature. Therefore, unknown compounds could be classified into distinct drug categories by discriminant analysis of EEG data[24]. More important, the conservation of brain structure and neurobiological features across mammalian species allows the translatability of results[18].

In this report, we asked if the multicomponent, low-dose medication Neurexan induces an EEG signature that explains its calming effects. To answer this question, we characterized the effect of different doses of Neurexan on the EEG of four rat brain areas during 5-hour experiments.

The dose–response relationship between Neurexan and EEG signatures revealed a predominant effect on δ-, θ-, and α2-waves in the frontal cortex and reticular formation (Figure1). Changes of spectral frequencies were analyzed between 185 and 245 minutes after oral administration of a single dose of Neurexan. Although changes of spectral frequencies were observed at each dosage (0.25, 0.5, or 1 tablet), most significant changes were found with 0.5 tablets of Neurexan. At this concentration, δ-, θ-, and α2-waves were significantly changed in the frontal cortex when compared with vehicle control (Figure1A). Moreover, δ-, θ-, and α2-waves and, in addition, α1- and β1-waves were significantly altered in the reticular formation (Figure1D). In the hippocampus, only δ-waves were significantly affected by treatment with 1 tablet of Neurexan (Figure1B). Between 185 and 245 minutes, no significant change of spectral frequencies could be observed in the striatum (Figure1C).

Over time, 0.5 tablets of Neurexan significantly changed most spectral frequencies in the frontal cortex, reticular formation, and striatum when compared with vehicle control. Effects were predominantly observed on δ- and θ-waves (Figure2). In the frontal cortex, δ- and θ-waves persistently and significantly increased during the third to fourth hour and during the fourth to fifth hour after administration, respectively (Figure2A). In the reticular formation, δ- and θ-waves significantly increased during the third to fifth hour and, in addition, during the first hour after administration (Figure2D). Other spectral frequencies were only transiently affected by Neurexan. In the frontal cortex and reticular formation, α1-, α2-, and β1-waves were significantly increased at single experimental intervals. In the striatum, changes of θ-waves reached significance at two experimental intervals (third and fifth hours, Figure2C), whereas no significant changes were observed in the hippocampus at this dosage (Figure2B).

Taken together, Figures1 and2 demonstrate that even a single dose of Neurexan significantly modulated the EEG signature of several brain areas when compared with vehicle control. The EEG changes predominantly affected δ-, θ-, and, to a minor extent, α2-waves in the frontal cortex and reticular formation.

Herein, we demonstrate that the low-dose medication Neurexan induces significant changes of rat EEG signatures. Neurexan-induced changes predominantly affect δ- and θ-waves in the frontal cortex and reticular formation, supporting the fact that Neurexan generally exhibits calming effects.

The rat EEG signature was significantly altered after a single oral administration of Neurexan when compared with vehicle control, thus characterizing Neurexan as psychoactive. Changes were observed in the reticular formation as early as during the first hour after administration. This immediate effect differentiates Neurexan from other plant-derived drugs against stress-related disorders that are effective as early as 3 hours after administration[29]. At later time points, EEG signatures of the frontal cortex and striatum, but not the hippocampus, were also affected by Neurexan.

After having established the principal evidence of dose- and time-dependent effects of Neurexan on the central nervous system, we found a predominant increase of δ- and θ-waves, supporting the calming effect of Neurexan in general. Earlier publications have demonstrated that pharmacological interference with neurotransmitter systems results in changes of distinct brain waves. Accordingly, changes of δ-waves correspond to interference with the cholinergic system[20]. The fact that enhancing cholinergic transmission in the reticular formation increases rapid eye movement sleep in several species[30‐32] might, therefore, contribute to an explanation of the beneficial effects of Neurexan on sleep disturbance[16]. According to previous studies[21, 33], Neurexan-induced changes of α2-waves can be interpreted as inactivation of the dopaminergic system, whereas increases of θ-waves could be related to interference with the norepinephrine α2 receptor, leading to sedation[22].

The effects on EEG signatures in rats have been demonstrated for several different synthetic and plant-derived psychoactive substances, and, more important, the same method of EEG recording was used in these studies[20, 24, 28]. We were, therefore, able to descriptively compare the net effects of Neurexan on six frequency bands in four rat brain areas with those of other substances. It might not be scientifically adequate to draw direct conclusions from these comparisons, but several similarities between Neurexan and Valeriana or Passiflora could be found (data not shown).

Both Valeriana and Passiflora are present in Neurexan, although at a far smaller concentration. Several clinical trials have demonstrated that Valeriana effectively treats insomnia mostly by reducing sleep latency and improving sleep quality. In two double-blind and placebo-controlled studies, single doses between 400 and 900 mg significantly improved sleep latency and sleep quality when compared with placebo[34, 35]. In two randomized, double-blind studies, the effects of Valeriana (600 mg/d) on insomnia were comparable to those of Oxazepam[36, 37]. Interestingly, a high dosage of Valeriana (1500 mg Valeriana in combination with 360 mg hops) particularly increased δ-waves in human subjects[38]. However, the concentration of Valeriana in Neurexan is far lower (0.6 mg valerianate of zinc D4 per tablet), but Neurexan has been as effective as Valeriana-based therapies for the treatment of mild to moderate insomnia[16]. Either highly diluted valerianate of zinc might be as effective as high-dose Valeriana or, more probably, the combination of valerian ate of zinc with other components of Neurexan synergistically mediates calming effects.

The second comparator drug generating a similar EEG signature such as Neurexan, Passiflora, exerts anxiolytic effects in mice[39, 40] and humans[10‐12]. In a double-blind, placebo-controlled trial, Passiflora has been as effective as benzodiazepine in eliminating anxiety symptoms[10]. Doses of 10 mg/kg body weight were effective in mice[39]. In our experiments, the reference drug Passiflora was applied at a dose of 100 mg/kg and predominantly increased θ-activity in the frontal cortex and striatum (data not shown). Likewise, 1200 mg of Passiflora extract strongly increased θ-waves and slightly increased δ-waves in patients with sleep disorders[41]. Concerning this influence on EEG activity, Neurexan containing low-dose Passiflora seems to be comparably effective as the high-dose comparator drug.

We recognize two major limitations of our study. First, the number of animals in our study was relatively small, but the sample size was sufficient to detect significant effects (P < 0.01) on the EEG signature in rats. Second, our results are rather descriptive and need to be correlated with the effects of Neurexan on human subjects, even if the translatability of results across mammalian species might be widely accepted[18]. However, one objective of our study was to demonstrate an effect of this low-dose and multicomponent medication on the central nervous system, providing a starting point for further research. Correlation with the effectiveness of Neurexan on moderate insomnia and nervousness has already been provided by two observational studies[16, 17]. Moreover, a double-blind, placebo-controlled trial is conducted to evaluate the psychophysiological effects of Neurexan on human subjects in more detail.

In summary, the current study demonstrated that the multicomponent, low-dose medication, Neurexan, influences neuronal activity in particular brain areas, thereby suggesting that the drug has calming effects. The similarity of Neurexan with other medications with known calming effects suggests that the combination of the lower concentrated components of Neurexan exerts an additive and synergistic effect on neuroactivity. It can be speculated that Neurexan has beneficial effects for patients with stress-related disorders. Moreover, this report demonstrates that EEG signatures are valid biomarkers for the psychoactivity of multicomponent, low-dose medications, such as Neurexan. The outcome gives guidance for further scientific investigations of that drug, to identify the working mechanism and its efficacy in more detail.