Main Research Findings

1. Researchers Murillo-Rodriguez et. Al were able to conclude that the mechanism of action through which modafinil works is closely related to the dopaminergic system. Additionally, they reported that the sleep-inducing endocannabinoid, ANA, could potentially block the wakefulness effects of modafinil.
2. The research team of Willie et. Al determined that there is a positive correlation between modafinil and orexin, a hypothalamic neuropeptide involved in sleep disorders. This conclusion is based on the results of immunohistochemistry that highlighter Fos-immunoreactive (Fos-IR) nuclei, as well as latency of the REM sleep duration .

Selected Data

1. The experimentation was conducted on male Wistar rats that were kept in typical lab conditions with food provided ad libitum. The rats were split into groups and anesthetized in order to prepare them for microdialysis experimentation. From there, either a placebo or a 10 μg/5 μl dose of modafinil were administered to the rats via cannula into a microdialysis probe. The animals were observed every hour after treatment for 4 hours and samples of the dialysates were collected. All samples were then subject to an analysis of dopamine levels.

A second group of rats was used to complete sleep lab testing. The test subjects of group two underwent the same cannula placement surgery as the first group of rats. However, the subjects in group two experienced electrode placement in order to track sleep patterns. The research team randomly determined which subjects would be receiving a placebo, ANA, or modafinil. The rats were then administered doses of either 10 μg/2.5 μl or 10 μg/5 μl of each compound. Following administration the rats were attached to the sleep-record system in order to record all EEG/EMG data that occurred during the 4 hour testing period [1].

2. The goal of the study was to determine how modafinil affects orexin knockout mice in comparison to wild-type mice. Both types of mice were split into groups and randomly decided which subject would receive a placebo and which would receive an active dose of modafinil. All mice were administered either a 10 mg/kg or 100 mg/kg dosage of the vehicle or of modafinil at 19:00 hours in order to eliminate any time-related behavioral changes. After modafinil was administered researchers observed EEG/EMG activity of the mice over the following 12 hour dark period and 12 hour light period. Following observation the mice were euthanized and brain samples were sectioned and prepared for immunostaining so results could be obtained via immunohistochemistry [2].

Discussion

1. Results of the study found that there was a significant increase in dopamine levels in the rat given 10 μg/5 μl doses of modafinil. This finding was accompanied by a noticeable decrease in levels of L-DOPA. The hourly analysis that was conducted on the rats reported that modafinil led to a steady improvement in dopamine levels. The enhancement of dopamine was mirrored by the diminishment of L-DOPA at similar doses.

Figure 1: Changes in dopamine and L-DOPA induced by modafinil, observed over the 4 hour testing period.

Results of the first part of the sleep lab study reported that the subjects administered a 10 μg/5 μl dose of modafinil experienced increased total wake time (TWT) and decreased slow wave sleep (SWS) and rapid eye movement sleep (REMS). These results allowed the researchers to confirm the thought that modafinil increases wakefulness. Over a 4 hour testing period the researchers observed that modafinil increased wakefulness one hour after injection and remained steady the remaining 3 hours. Modafinil decreased SWS after the very first injection and continued to steadily decline on an hourly basis. REMS was found to decrease after the first hour post-injection and remain steady for the remaining 3 hours.

Figure 2: The effects of modafinil on the sleep-wake cycle.

Approximately 15 minutes before the rats were injected with modafinil, the subjects were administered the endocannabinoid, ANA; a compound that has been shown to induce sleep. Overall, evidence shows that ANA increases total sleep time (TST) and decreases wakefulness. Researchers Murillo-Rodriguez et. AL found that by injecting ANA prior to modafinil, the reduction of TST and the wakefulness effects of modafinil were partially blocked [1].

Figure 3: Effects on wakefulness and total sleep time when modafinil and sleep-inducing endocannabinoid, ANA, are administered together.

2. Results of this study found that when the 10 mg/kg of either the vehicle or modafinil were given, there were slight changes to Fos-IR levels in various brain regions. However, none of the changes were considered statistically significant enough to be considered reliable data. On the other hand, the 100 mg/kg dose of modafinil led to a drastic increase in Fos expression in both wild-type and orexin-null mice, specifically in the pyriform, frontal, parietal, and cingulate cortices.

Figure 4: Visual representation of the increase in Fos expression in mice administered modafinil.

The research team also observed EEG/EMG activity during the 24 hours following treatment in order to observe any changes in the REM sleep cycle after modafinil administration. Mice given the vehicle experienced longer total REM sleep time, increased REM sleep duration, and decreased latency to REM sleep. The orexin-null mice that received modafinil were awake longer during the 12 hour dark period. That being said, the wild-type mice exhibited shorter REM sleep intervals. However, during the 12 hour light period, latency to REM sleep was decreased in both orexin-null and wild-type mice. Overall, the study concluded that during the 12 hour dark period, modafinil improved wakefulness in the orexin-null mice following administration of the compound. This indicates that there is a relationship between the wakefulness effects of modafinil and orexin neuropeptides [2].

Figure 5: Dose-dependent changes in modafinil-induced wakefulness

Conclusion

**LAB USE ONLY**
*This information is for educational purposes only and does not constitute medical advice. THE PRODUCTS DESCRIBED HEREIN ARE FOR RESEARCH USE ONLY. All clinical research must be conducted with oversight from the appropriate Institutional Review Board (IRB). All preclinical research must be conducted with oversight from the appropriate Institutional Animal Care and Use Committee (IACUC) following the guidelines of the Animal Welfare Act (AWA).

Citations

[1] Murillo-Rodríguez E, Haro R, Palomero-Rivero M, Millán-Aldaco D, Drucker-Colín R. Modafinil enhances extracellular levels of dopamine in the nucleus accumbens and increases wakefulness in rats. Behav Brain Res. 2007 Jan 25;176(2):353-7. doi: 10.1016/j.bbr.2006.10.016. Epub 2006 Nov 13. PMID: 17098298.

[2] Willie JT, Renthal W, Chemelli RM, Miller MS, Scammell TE, Yanagisawa M, Sinton CM. Modafinil more effectively induces wakefulness in orexin-null mice than in wild-type littermates. Neuroscience. 2005;130(4):983-95. doi: 10.1016/j.neuroscience.2004.10.005. PMID: 15652995.

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