Release of exogenously-supplied and endogenous serotonin from tissue slices of Hymenolepis diminuta

The release of exogenously-supplied [3H]serotonin and of endogenous serotonin from H. diminuta tissue slices was studied using high [K+] depolarization. The release of [3H]serotonin was not calcium-dependent or magnesium-antagonized. While high-magnesium antagonism of endogenous serotonin release was inconclusive, this release was calcium-dependent. These findings suggest that, while exogenous serotonin is not taken into and released from nervous tissue, endogenous serotonin appears to be released from nervous tissue in a neurotransmitter-like manner.