Caffeine and Central Noradrenaline: Effects on Mood, Cognitive Performance, Eye Movements and Cardiovascular Function

Abstract

There have been numerous studies on the effects of caffeine on behaviour and cardiovascular function. It is now important to clarify the mechanisms that underlie such effects, and the main objective of the present study was to investigate whether changes in central noradrenaline underlie some of the behavioural and cardiovascular effects of caffeine. This was examined using a clonidine challenge paradigm. Twenty-four healthy volunteers were assigned to one of four conditions: (i) clonidine/caffeine; (ii) clonidine/placebo; (iii) placebo/caffeine: (iv) placebo/placebo. Baseline measurements of mood, cognitive performance, saccadic eye movements and cardiovascular function were recorded. Subsequently, volunteers were given either clonidine (200 microg) or placebo and consumed coffee containing caffeine (1.5 mg/kg) or placebo. The test battery was then repeated 30 min, 150 min and 270 min later. A second cup of coffee (with the same amount of caffeine as the first) was consumed 120 min after the first cup. The results showed that clonidine reduced alertness, impaired many aspects of performance and slowed saccadic eye movements; caffeine removed many of these impairments. Both clonidine and caffeine influenced blood pressure (clonidine reduced it, caffeine raised it) but the effects appeared to be independent, suggesting that separate mechanisms were involved. In addition, there were some behavioural effects of caffeine that were independent of the clonidine effect (e.g. effects on speed of encoding of new information) and these may reflect other neurotransmitter systems (e.g cholinergic effects). Overall, the results suggest that caffeine counteracts reductions in the turnover of central noradrenaline. This mechanism may underlie the beneficial effects of caffeine seen in low alertness states.

Effects of caffeine on alertness as measured by infrared reflectance oculography

“…The reaction time results here are also comparable with studies of alert people showing improvements after caffeine administration (Lorist et al 1994;Smith et al 2003;and summarized in Vanderveen et al 2001).…”

“…The only other study that could be found regarding caffeine and ocular variables was one where clonidine was administered in order to lower arousal levels (Smith et al 2003). Interestingly, the caffeine was able to counteract the decreases shown in saccade velocity caused by clonidine (Smith et al 2003). It is possible that in these previous studies, the ocular variables measured were not sensitive enough to changes in alertness generally in order to demonstrate changes in alertness due to caffeine consumption.…”

“…Previously, caffeine has not effected pupil diameter, pupil contraction latency (Minzhong et al 2004), or blink rate (Horne and Reyner 1996) and only indicated trends towards increased saccade velocities (Minzhong et al 2004). The only other study that could be found regarding caffeine and ocular variables was one where clonidine was administered in order to lower arousal levels (Smith et al 2003). Interestingly, the caffeine was able to counteract the decreases shown in saccade velocity caused by clonidine (Smith et al 2003).…”

Cognitive Enhancement: Methods, Ethics, Regulatory Challenges

“…In the case of nicotine a complex interaction with attention and memory occurs (Warburton 1992;Newhouse et al 2004;Rusted et al 2005), while caffeine reduces tiredness (Lieberman 2001;Smith et al 2003;Tieges et al 2004). In more recent years, a wide array of drugs have been developed that affect cognition (Farah et al 2004).…”

Intake of stimulant foods is associated with development of parasomnias in children

“…The stimulant effects of caffeine are not due to direct actions on the central nervous system, but to indirect stimulation by inducing blockade of another neuromodulator, adenosine, which usually exerts a calming effect on brain and spinal cord neurons 22 . Caffeine increases the amount of adrenaline and noradrenaline secreted by the adrenal medulla 23 and increases central noradrenaline synthesis and turnover in the cerebral cortex, consequently exerting a stimulatory effect and boosting wakefulness 24 . In a U.S. study, 41% of school-aged children were found to consume at least one caffeinated beverage per day.…”