Sentence:  A state of parasympathetic `` tuning '' of the hypothalamus induced experimentally causes not only an increase in the parasympathetic reactivity this structure to direct and reflexly induced stimuli , but leads also to an autonomic reversal : a stimulus <WSD>acting</WSD> sympathetically under control conditions elicits in this state of tuning a parasympathetic response ! 
Meaning of the word marked with <WSD> tags:  behave in a certain manner; show a certain behavior; conduct or comport oneself