Caffeine effects: interaction of drug and wheelrunning experience

Enhancement of hepatic tryptophan pyrrolase activity and decreases of open field locomotion following single and repeated administration of high doses of caffeine in rats

In view of a possible role of kynurenine in caffeine-induced anxiety syndrome, the effects of single and repeated administration of caffeine on hepatic tryptophan (T)-pyrrolase activity are investigated. Single administration of caffeine at doses of 80 mg/kg decreased open field locomotion and increased hepatic T-pyrrolase activity. Locomotor stimulating effects of 80 mg/kg caffeine, monitored in the home cages of rats, were attenuated following daily administration of caffeine for 5 days. Open field locomotor activity of rats and its caffeine-induced decrement were also attenuated following 5 daily administrations of caffeine on the 6th day. Basal levels of hepatic T-pyrrolase activity increased after 5 daily administrations of caffeine on the 6th day. Acute administration of caffeine did not further elevate hepatic T-pyrrolase activity in 5 day caffeine injected rats. Drug adjuvants decreasing hepatic T-pyrrolase activity may prove valuable for extending the clinical utility of caffeine.

Caffeine and the central nervous system: mechanisms of action, biochemical, metabolic and psychostimulant effects

Caffeine is the most widely consumed central-nervous-system stimulant. Three main mechanisms of action of caffeine on the central nervous system have been described. Mobilization of intracellular calcium and inhibition of specific phosphodiesterases only occur at high non-physiological concentrations of caffeine. The only likely mechanism of action of the methylxanthine is the antagonism at the level of adenosine receptors. Caffeine increases energy metabolism throughout the brain but decreases at the same time cerebral blood flow, inducing a relative brain hypoperfusion. Caffeine activates noradrenaline neurons and seems to affect the local release of dopamine. Many of the alerting effects of caffeine may be related to the action of the methylxanthine on serotonin neurons. The methylxanthine induces dose-response increases in locomotor activity in animals. Its psychostimulant action on man is, however, often subtle and not very easy to detect. The effects of caffeine on learning, memory, performance and coordination are rather related to the methylxanthine action on arousal, vigilance and fatigue. Caffeine exerts obvious effects on anxiety and sleep which vary according to individual sensitivity to the methylxanthine. However, children in general do not appear more sensitive to methylxanthine effects than adults. The central nervous system does not seem to develop a great tolerance to the effects of caffeine although dependence and withdrawal symptoms are reported.

Tolerance and sensitization to chronic and subchronic oral caffeine: effects on wheelrunning in rats

Twenty-four male Sprague-Dawley rats were tested for wheelrunning in conjunction with chronic (continuous) or subchronic (alternate day) oral caffeine administration. As expected, chronic administration led to complete tolerance to caffeine's locomotor stimulant effect, while subchronic administration produced sensitization. Results confirm earlier reports of enhanced stimulation with spaced administration of caffeine and tolerance with chronic administration.

Alteration of the effects of caffeine by prenatal stress

We examined the effect of prenatal stress exposure on sensitivity to caffeine using behavioral and physiological measures. Pregnant rats were handled 5 minutes daily from the 14th to 21st day of gestation. Male offspring were tested when 60 days of age in a modified open field apparatus 30 and 90 minutes after injection with caffeine (0, 10, 30 mg/kg). Caffeine increased crossover frequency and duration at the 10 mg/kg dose. Rearing frequency and duration were increased by the 10 mg/kg dose while the 30 mg/kg dose was ineffective. Gnawing was increased by caffeine, especially 90 minutes postinjection. Headpoke activity was decreased by caffeine treatment. Caffeine had no effect on defecation and urination. Gnawing activity was increased by caffeine in prenatally nonstressed animals, but was depressed in prenatally stressed animals. Prenatal stress increased sensitivity to caffeine on corner activity and rearing. The other measures were not affected differentially by prenatal stress exposure. Rectal temperature was depressed 0.75 degrees C in both prenatally stressed and nonstressed animals, by the 30 mg/kg dose of caffeine. Thus, our results indicate that prenatal stress affects sensitivity to caffeine in the adult offspring. However, the long-term effects of prenatal stress exposure are dependent on the measures employed.