Uptake and storage of 5-hydroxydopamine in rat pineal nerves after electrical stimulation

The uptake and storage of 5-hydroxydopamine after electrical nerve stimulation was investigated in the rat pineal nerves. The drug was injected i.p. immediately after the stimulation of the afferent trunks of both superior cervical ganglia for 20 min, with sq pulses of 1 msec, 25 Hz and 25 V. The animals were killed by decapitation 10 and 30 min after the injection, fixed in glutaraldehyde-osmium tetroxide and processed for electron microscopy. The stimulation was performed under chloral hydrate anesthesia. Anesthetized non stimulated, stimulated-non injected and injected-non stimulated were used as controls. It was found that the storage of the false transmitter, whose presence is revealed by an intense osmiophilia in the synaptic vesicles, when tissues are fixed in glutaraldehyde osmium tetroxide, is significantly reduced in rats injected after stimulation. Evidence is reported supporting the concept that the uptake and the storage of the false transmitter are not prevented by previous nerve stimulation although they may be affected in some way.