Presynaptic transmitters and depolarizing influences regulate development of the substantia nigra in culture

Abstract

Recent evidence suggests that extracellular signals regulate neurotransmitter traits in brain catecholaminergic (CA) neurons as in the periphery. Development of the dopaminergic phenotype in the mouse substantia nigra (SN) was studied by monitoring tyrosine hydroxylase (TH), the rate-limiting enzyme in CA biosynthesis in vivo and in culture. Explants of SN were dissected from embryonic day 15 embryos and grown in culture for a week. To define the influence of depolarizing signals on central dopaminergic neurons, cultures were grown with the pharmacologic depolarizing agent veratridine. This treatment elicited a significant increase in TH enzyme activity, accompanied by elevated levels of enzyme protein. The increase in activity was prevented by TTX, suggesting that transmembrane Na+ influx was necessary for the rise in TH. A physiologic presynaptic agonist, substance P, also evoked a significant increase in TH activity; however, the coproduced tachykinin peptide, substance K (SK, neurokinin A) elicited a more dramatic rise. The SK effect was blocked by TTX, suggesting that the physiologic agonist was acting through the same mechanism as the pharmacologic agent veratridine. Immunoblot analysis revealed that SK elicited a parallel increase in TH enzyme protein. Our observations suggest that the novel peptide, SK, serves a physiological role in the regulation of TH in the striatonigral pathway.

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

“…In the present study, multiple veratridine stimulations increased DA release as compared with non‐stimulated control cultures. The increasing effect of multiple veratridine challenges may be explained by increased TH activity (Friedman et al. , 1988) due to increased phosphorylation of the enzyme (Witkovsky et al.…”

“…Treatment of primary cultures of mouse olfactory bulb with high KCl (40–50 m m ) for 48 h increases the number of TH + neurons at least twofold and causes alterations in neurite outgrowth (Cigola et al. , 1998), and long‐term treatment with low concentrations of veratridine enhances TH activity and protein expression in organotypic cultures of mouse ventral mesencephalon (Friedman et al. , 1988) and improves survival of dopaminergic neurons in rat primary mesencephalic cultures (Salthun‐Lassalle et al.…”

Substance P, Neurokinins A and B, and Synthetic Tachykinin Peptides Protect Mesencephalic Dopaminergic Neurons in Culture via an Activity-Dependent Mechanism

“…The effect of the tachykinin agonists might be simply to restore the expression of TH within neurons that contain undetectable amounts of the enzyme as they entered a premorbid state (Hirsch et al, 1988;Michel and Agid, 1996). Even though tachykinins were reported to stimulate TH protein expression (Friedman et al, 1988), this possibility is doubtful, because the tachykinin agonists failed to rescue the fraction of TH ϩ neurons that had already disappeared when initiation of the treatments was delayed. The observation that the pancaspase inhibitor Boc-D-FMK was also able to increase the number of DA neurons in this model system indicates that the tachykinins probably reversed an ongoing apoptotic process that is occurring spontaneously (Salthun-Lassalle et al, 2004).…”

Biochemistry of Information Storage in the Nervous System

“…We examined the SN in culture and found that depolarizing stimuli increased TH activity, and that this rise was attributable to an increase in TH enzyme protein, that is, was true enzyme induction (34). Moreover, in the case of the SN we were able to examine the effects of the physiologic presynaptic transmitters, because these had been identified; the SN appears to receive an excitatory SP-containing pathway from the striatum (35).…”