Increased glutamate-stimulated norepinephrine release from prefrontal cortex slices of spontaneously hypertensive rats.

Spontaneously hypertensive rats (SHR) have behavioral characteristics (hyperactivity, impulsiveness, poorly sustained attention) similar to the behavioral disturbances of children with attention-deficit hyperactivity disorder (ADHD). We have previously shown that dopaminergic and noradrenergic systems are disturbed in the prefrontal cortex of SHR compared to their normotensive Wistar-Kyoto (WKY) control rats. It was of interest to determine whether the underlying neural circuits that use glutamate as a neurotransmitter function normally in the prefrontal cortex of SHR. An in vitro superfusion technique was used to demonstrate that glutamate caused a concentration-dependent stimulation of [3H]norepinephrine release from rat prefrontal cortex slices. Glutamate (100 microM and 1 mM) caused significantly greater release of norepinephrine from prefrontal cortex slices of SHR than from control slices. The effect of glutamate was not mediated by NMDA receptors, since NMDA (10 and 100 microM) did not exert any effect on norepinephrine release and MK-801 (10 microM) did not antagonize the effect of 100 microM glutamate. These results demonstrate that glutamate stimulates norepinephrine release from rat prefrontal cortex slices and that this increase is enhanced in SHR. The results are consistent with the suggestion that the noradrenergic system is overactive in prefrontal cortex of SHR, the animal model for ADHD.

Physiological characteristics of rugby players including muscle glycogen content and muscle fibre composition.

There are few studies of the anthropomorphic and physiological characteristics of South African rugby players. Twenty-nine club rugby players were evaluated for body composition, maximal treadmill performance, muscle fibre composition and the muscle glycogen content, including the effects of carbohydrate-loading and playing a rugby match. The body composition and physiological characteristics of the players were similar to that previously reported for international players. Very high absolute values for maximum oxygen consumption (VO2 max) were measured in the forwards. Both backs and forwards had a preponderance of fast-twitch muscle fibres (57% and 53% respectively). Carbohydrate-loading increased pre-match muscle glycogen content but was unnecessary since severe muscle glycogen depletion did not occur during a match even in players on a normal mixed diet before competition. It is concluded that for forwards, a high absolute VO2 max, and for both backs and forwards a predominance of fast-twitch muscle fibres are pre-requisites for success in this sport. Pre-match carbohydrate-loading would appear to be necessary only when more than one match is to be played within 48 hours.