Evidence for serotonin synthesis, uptake, and release in dissociated rat sympathetic neurons in culture.

In the previous paper (Matsumoto et al., 1987), pharmacological evidence for secretion of serotonin (5-HT) by cultured sympathetic principal neurons was reported. Here, we present further evidence that 5-HT is a transmitter of some of these neurons under certain culture conditions, and can also be a "false" transmitter. Sympathetic principal neurons, dissociated from superior cervical ganglia (SCG) of newborn rats, were grown in cell culture. The presence of serotonin was demonstrated with high-performance liquid chromatography (HPLC), immunocytochemistry, and electrophysiological recording. Homogenates of cultures contained a substance that comigrated with authentic 5-HT in HPLC. A voltammogram for this substance was superimposed upon that for authentic 5-HT. When the cultures were examined with immunocytochemical staining, using the peroxidase-antiperoxidase technique, many neuronal processes contained 5-HT-like immunoreactive material. Many somata also contained 5-HT-like immunoreactivity when the neurons were grown in the presence of medium conditioned by heart cells (CM), but few somata stained above background in the absence of CM. Medium that contained a raised concentration of K+ (54 mM) or veratridine evoked Ca2+-dependent release of 5-HT, consistent with a neurotransmitter role for 5-HT in the cultures. In preliminary electrophysiological experiments on microcultures containing single sympathetic principal neurons and cardiac myocytes, a nonadrenergic excitatory (NAE) interaction was sometimes obtained after exposing the neurons to 100 microM 5-hydroxytryptophan. This interaction was sensitive to the serotonin blockers reserpine, methysergide, and gramine.(ABSTRACT TRUNCATED AT 250 WORDS)