Effect of anaesthetics on the sympathetic reflex

i) In the awake animal, neither a late response nor a silent period could be evoked from the tibial nerve. Somatic afferentation with impulse trains failed to inhibit efferent sympathetic activity. On the other hand, vagal afferentation had an inhibitory action also in the awake animal. In the awake animal, the excitatory processes are dominant. ii) Urethan anaesthesia did not influence the sympathetic nervous processes; the reflex response were practically the same as in the awake animal. iii) Chloralose anaesthesia altered the sympathetic reflex observable in the awake animal. Somatic afferentation of low threshold voltage already elicited a late response and a silent period; in addition, a high degree of summation ability of silent periods was apparent. Thus, chloralose anaesthesia seems to raise the excitatory level of the sympathetic centres in the direction of inhibition. iv) Combined chloralose+urethan anaesthesia, under which investigations are usually performed, was seem to affect the reactivity of the sympathetic centres in the same way as did chloralose anaesthesia.