Stress induced changes in transmitter release from sympathetic varicosities of the mouse vas deferens

Activation of the sympathetic nervous system is an important component of the response to stress, but the effects of prolonged stress on sympathetic neurotransmission have not been assessed. In the present study we have examined the effect of 3 to 10 days exposure to stress induced by frequent handling and sham injections on neurotransmitter release from sympathetic varicosities of the mouse vas deferens. DiOC2(5)-fluorescence was used to visualise the sympathetic varicosities so that extracellular electrodes could be placed over known numbers of varicosities to monitor transmitter release using electrophysiological techniques. The frequency of excitatory junction currents (EJCs) increased with increasing duration of exposure to stress. The mean and maximum EJC amplitude significantly increased by 107% and 43%, respectively after 10 days of exposure to stress. The density of sympathetic varicosities innervating smooth muscle of the mouse vas deferens was not changed throughout the duration of the exposure to stress. The findings from this study demonstrate that the efficacy of transmitter release from the sympathetic varicosities is altered by repeated exposure of mice to stressful stimuli, such as handling and sham injections. Since such procedures are routine in many pharmacological experiments, it is important that investigators are aware of these changes so that due consideration is given when interpreting the data obtained from animals treated in this way.