Psychostimulants and G tolerance in rhesus monkeys: effects of oral modafinil and injected caffeine.
BACKGROUND
Caffeine and modafinil are psychostimulants that may be taken by fighter aircraft pilots to reduce fatigue. Fighter pilots are subjected to high positive G loads that reduce cerebral blood flow and consequently may induce G-LOC. The aim of the experiment was to determine whether these drugs may reduce tolerance to G stress.


METHODS
Seven adult male rhesus monkeys participated in the experiment. Five were equipped with ECoG and ECG wires and underwent two G tests (A and B). Each experiment consisted of five centrifuge runs. Before the runs, the monkeys received no drug (control) or were given either 7.5 mg x kg(-1) caffeine IM or 64 mg x kg(-1) modafinil PO or the corresponding vehicles. The runs were performed up to +13 Gz with an onset rate of 0.1 G x s(-1) (test A) or 3 G x s(-1) (test B). The run was ended when the electrical activity of one ECoG channel had disappeared (i.e., G-LOC).


RESULTS
In experiment A, drug administration had no significant effect. In experiment B, the injection of the caffeine-free solvent caused a delay in G-LOC compared with the control condition (no administration). Caffeine solvent also induced an increase in plasma osmolality.


CONCLUSIONS
Modafinil administration has no significant effect on the G tolerance of rhesus monkeys. Regarding caffeine, the drug seems to have caused the reverse effect compared with the solvent.


CONCLUSIONS
Caffeine and modafinil administration had no significant effect on the G-tolerance of rhesus monkeys when compared with controls. This result needs to be confirmed in humans.
Florence
Geneviève
G
Institut de Medecine Aerospatiale du Service de Santé des Armees, Brétigny sur Orge, France. gflorence@imassa.fr
Riondet
Laurent
L
Serra
André
A
Etienne
Xavier
X
Huart
Bruno
B
van Beers
Pascal
P
Bonneau
Dominique
D
Gomez-Merino
Danièle
D
Drogou
Catherine
C
Pradeau
Pascal
P
D000054:Acceleration; D000337:Aerospace Medicine; D000818:Animals; D001559:Benzhydryl Compounds / Q000494:pharmacology*; D002110:Caffeine / Q000494:pharmacology*; D000697:Central Nervous System Stimulants / Q000494:pharmacology*; D002498:Centrifugation; D002540:Cerebral Cortex / Q000187:drug effects / Q000502:physiology; D004569:Electroencephalography; D004585:Electrooculography; D005221:Fatigue / Q000209:etiology / Q000517:prevention & control*; D018471:Hypergravity; D008253:Macaca mulatta; D008297:Male; D000077408:Modafinil; D018709:Statistics, Nonparametric; D014474:Unconsciousness / Q000209:etiology / Q000517:prevention & control*
D001559:Benzhydryl Compounds; D000697:Central Nervous System Stimulants; D002110:Caffeine; D000077408:Modafinil