Effects of caffeine and nicotine on open-field exploration

Changes in sensitivity of response distributions to changing reinforcement ratios during exposure to ephedrine, caffeine, and ephedrine-caffeine combinations

Changes in the sensitivity of response distributions to changes in reward distribution (reinforcer distribution sensitivity) were examined when rats were exposed to low and moderate doses of caffeine, ephedrine, and caffeine-ephedrine combinations. The data show significant decreases in sensitivity in response distributions to changes in reward schedule values during exposure to caffeine and ephedrine/caffeine combinations, whereas ephedrine alone resulted in overmatching comparable with baseline and NaCl conditions. Rats treated either with 3.0-mg/kg or 10.0-mg/kg doses of caffeine and all combinations of ephedrine at doses of 1.8 or 5.6 mg/kg with caffeine at 3.0 or 10.0 mg/kg showed reduced sensitivity in response distributions to differences in reinforcement schedule ratios. In contrast, when rats were exposed to ephedrine at 1.8 or 5.6 mg/kg, they maintained or increased the degree of overmatching. Although reinforcer distribution sensitivity was altered, drug exposure did not significantly affect the absolute rates of responding. Bias varied after exposure to caffeine, ephedrine, and their combinations, but not systematically. Finally, whereas the estimates of goodness of fit (r2) to the matching equation showed some decreases during drug exposure, these were neither statistically significant nor correlated with drug dose. These results suggest differential effects of ephedrine and caffeine on the sensitivity of response distributions to changes in reinforcement ratio distributions, with deleterious effects of caffeine and ephedrine/caffeine combinations.

Effects of caffeine- and sugar-free beverages on psychomotor performance

Two cola beverages containing caffeine stimulated rope jumping more than beverages without caffeine; sugar content of the beverages did not appear to affect rope jumping by 36 college men.

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.

Effects of caffeine, L-phenylisopropyladenosine and their combination on local cerebral blood flow in the rat

The quantitative [14C]iodoantipyrine autoradiographic method was applied to study the effects of acute administration of caffeine and L-phenylisopropyladenosine (LPIA) separately or in combination on local cerebral blood flow in the rat. After the injection of caffeine, cerebral blood flow rates were decreased in 13 out of the 61 structures studied, mainly in motor and auditory areas. The administration of LPIA induced a general decrease in local cerebral blood flow, which was significant in only 4 regions. The combined administration of caffeine and LPIA induced decreases in blood flow rates in 17 brain areas, motor, limbic and hypothalamic structures and increases in 3 limbic regions. The results confirm previous data on the effect of caffeine on cerebral circulation. The consequences of LPIA administration on blood flow may originate partly from peripheral effects and may also be the reflection of the reduction in the energy demand of the brain. Finally, LPIA also seems to be able to modulate caffeine effects on local cerebral blood flow when injected simultaneously with caffeine.

Nicotine-induced tail-tremor and drug effects

Tail-tremor induced by repeated and daily administration (0.5 mg/kg SC x 6 times/day) of nicotine as well as effects of various drugs on this response were investigated in Wistar strain male rats. Daily administration of nicotine in doses of 0.5 mg/kg SC caused tail-tremors to appear beginning on the 3rd day. Tail-tremor induced by the first injection of each day gradually increased with the daily injections, however, the heightened effect of this first injection at the beginning of each day decreased during the day upon repeated administration of 6 times/day at 2-hr intervals. Basically, tail-tremor appeared about 5 min after SC administration of nicotine and reached a peak approximately 7-9 min after injection, declining to zero afterwards. Different drugs showed various effects on this response. While mecamylamine (0.5 and 1.0 mg/kg IP) abolished nicotine-induced tail-tremor, arecoline (0.5 and 1.0 mg/kg IP), atropine (2.5 and 5.0 mg/kg IP), scopolamine (1.0 and 2.0 mg/kg IP) and hexamethonium (0.5 and 1.0 mg/kg IP) showed no such effects. Furthermore, physostigmine (0.1 mg/kg IP) actually potentiated this action. These results suggest that tail-tremor induced by nicotine may be mediated through central nicotine receptor system.

Effects of caffeine and doxapram perfusion on local cerebral glucose utilization in conscious rats

The quantitative autoradiographic 2-[14C]deoxyglucose method was used to measure the effects of a continuous infusion of the respiratory stimulants, caffeine or doxapram, 18 mg/kg per h, on local cerebral glucose utilization in the adult male rat. Local cerebral glucose utilization was measured in 54 cerebral structures from different systems. Caffeine induced widespread increases in energy metabolism, resulting in a significant increase in glucose utilization in 25 structures out of the 54 studied. These increases were distributed within all systems studied, sensory, extrapyramidal motor, limbic and hypothalamic systems. In addition, caffeine induced a non-significant, 10-15%, increase in local cerebral glucose utilization in central respiratory areas. Doxapram infusion did not change the rates of glucose utilization in any of the structures. The rates of local cerebral glucose utilization were significantly lower after doxapram than after caffeine exposure in five cerebral areas, among which were three central respiratory areas. The results confirm the absence of side-effects of doxapram as compared to caffeine when used as respiratory stimulant, especially in neonates. These results also favor a preferentially central action of caffeine on respiratory areas and a more peripheral action of doxapram on chemoreceptors, at least at therapeutic levels.