IT has been suggested recently that animals such as the cat and dog, when warned of an impending emotional or exertional task, anticipate the task with centrally induced cardiovascular changes similar to those that take place during the emotion or exertion itself 1,2. Particular emphasis has been placed on muscle vasodilatation, preparatory to and independent of muscle contraction, mediated through sympathetic fibres supposed to be cholinergic, because the vasodilatation can be abolished by atropine 1,3. Most of the data on which the "preparatory pattern" hypothesis is based, however, have been obtained by electrical stimulation of certain regions in the hypothalamus or subthalamus, from which are evoked either cardiac changes similar to those during exercise but without concomitant muscle activity 2 or cardiovascular changes as well as manifestations of defence behaviour 1,4. It should be realized, however, that the most quoted experiment on unanaesthetized, naturally behaving animals that may be relevant to this hypothesis, is that by Abrahams et al. 5 which showed an increase in muscle venous temperature, blocked by atropine, when "alerting" was induced by various sensory stimuli. The evidence it provides, however, rests on unverified assumptions that the venous temperature increase accurately reflected muscle vasodilatation, that there was no muscle activity which could have provided a metabolic vasodilatation, and that the behaviour was one preparatory to exertion or emotion.
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