Dopamine release in organotypic cultures of foetal mouse mesencephalon: effects of depolarizing agents, pargyline, nomifensine, tetrodotoxin and calcium.

Organotypic mesencephalic cultures provide an attractive in vitro alternative to study development of the nigrostriatal system and pathophysiological mechanisms related to Parkinson's disease. However, dopamine (DA) release mechanisms have been poorly characterized in such cultures. We report here endogenous DA release (assessed by high-performance liquid chromatography) in organotypic cultures of foetal mouse (E12) midbrain following single or multiple challenges (1-h incubations) with high K(+) or veratridine in the presence or absence of pargyline, nomifensine, calcium and/or tetrodotoxin (TTX). Basal (i.e. spontaneous) DA release was only detected in the presence of pargyline and nomifensine (PN), and was highly dependent on calcium and sensitive to TTX. Basal DA release increased 2.4-fold between week 3 (1st DA release experiment) and week 4 in vitro (3rd DA release experiment), DA tissue levels increased 1.6-fold and DA release expressed as a percentage of total DA (medium + tissue contents) increased from 20% to 34% during this growth period in vitro. Co-treatments with high K(+) or veratridine did not cause major changes in percentages of DA release. Tyrosine hydroxylase activity was increased by high K(+), but not by the other drug treatments. The acute (single or multiple) treatments with depolarizing agents did not affect the survival of dopaminergic neurons, but chronic low-level veratridine treatments were toxic.