Evidence for Modulation of DoDamine‐neuronal Function by Tachykinin NK₃ Receptor Stimulation in Gerbil Mesencephalic Cell Cultures

Abstract

Primary cultures of gerbil mesencephalon were used for studying the modulation exerted by tachykinin NK(3) receptor activation on the activity of dopamine (DA) neurons. Dopamine neurons were identified by their ability to take up [(3)H]DA in a nomifensine-dependent manner. Moreover, tyrosine hydroxylase immunohistochemistry revealed that these neurons accounted for 5-7% of the total cell population. The NK(3) receptor agonists, senktide (EC(50) = 0.58 nM) and [MePhe(7)]neurokinin B (EC(50) = 3 nM), increased spontaneous [(3)H]DA release in a concentration-dependent manner. In contrast, tested at a supramaximal concentration (IC(50) = 0.89 nM), neither septide nor substance P were found to affect [(3)H]DA release. The senktide-evoked [(3)H]DA release was not observed when extracellular Ca(2+) was chelated, but was unaffected by nomifensine. This indicates that this increase in [(3)H]DA outflow resulted more from an exocytotic process than from reversal of carrier-mediated DA uptake. Moreover, the senktide effect was unaffected by the Na+ channel blocker tetrodotoxin, a result suggesting a direct action of senktide on DA neurons. The non-peptide NK(3) receptor antagonist, SR 142801, shifted or blocked (IC(50) = 0.89 nM) the senktide-evoked [(3)H]DA release, while its (-)-antipode, SR 142806, was 80-fold less potent, in agreement with binding data. Selective antagonists for Nk1 (SR 140333) or Nk2 (SR 48968) receptors failed to reduce the senktide effect. Light scanning microscopic analysis of mesencephalic cells loaded with the Ca(2+) sensitive dye, fluo-3, showed that senktide induced a rise in cytosolic Ca(2+) in 8-10% of the cell population. The senktide-induced elevation in intracellular Ca(2+) was rapid in onset and transient (at 10-8 M) or more sustained with no further increase in fluorescence intensity (at 10(-7) M). The proportion of senktide-responsive cells was not significantly modified when extracellular Ca(2+) was chelated, but was reduced by 87% in the presence of SR 142801 and by 75% in cultures that were pre-treated with the DA neurotoxin 1-methyl-4-phenylpyridinium. The present study shows that enhancement of spontaneous [(3)H]DA release and intracellular Ca(2+) mobilization may be observed after NK(3) receptor stimulation and that both biochemical events are likely to occur in DA neurons.

In Vitro and In Vivo Characterization of the Non-peptide NK3 Receptor Antagonist SB-223412 (Talnetant): Potential Therapeutic Utility in the Treatment of Schizophrenia

“…The expression of NK 3 receptors in ventral mesencephalic DA cells and their apparent localization on dopaminergic cell bodies (Dam et al, 1990;Stoessl, 1994;Chen et al, 1998) was the first indication that these tachykinin receptors may be potential modulators of dopaminergic neurotransmission. Biochemical and electrophysiological studies with tachykinin receptor agonists provided supportive evidence (Humpel et al, 1991;Keegan et al, 1992;Bannon et al, 1986;Alonso et al, 1996) and the more recent development of selective, small molecule NK 3 receptor antagonists has confirmed this hypothesis. In this regard, the NK 3 receptor agonists senktide and the endogenous ligand NKB were demonstrated to stimulate dopaminergic cell firing in guinea pig slice preparations (Nalivaiko et al, 1997).…”

Neurokinin-3 receptor antagonists

“…Other evidence for the modulation of dopamine neuronal function by NK3 receptor stimulation has been recently reported in gerbil mesencephalic cell cultures. In this preparation, the selective NK3 receptor agonists, senktide and [MePhe 7 ]-NK-B, increased spontaneous dopamine release in a concentration-dependent manner; this effect was blocked by the potent NK3 receptor antagonist SR 142,801 [75]. Infusion of senktide by microdialysis in certain regions of the rat brain caused behavioural responses characteristic of the activation of dopaminergic pathways and this effect differed depending upon the age.…”

Neurokinin‐3 peptide instead of neurokinin‐1 synergistically exacerbates kainic acid‐inducing degeneration of neurons in the substantia nigra of mice

“…On the other hand, NK3 receptors are abundantly localized in the substantia nigra pars compacta (SNc), and co-expression of NK-3R with NMDA, a-amino-3-hydroxy-5-methyl-4-isoxazole-propionate/KA receptors was also detected in the nigral dopaminergic neurons (Chen et al 1998;Albers et al 1999;Wang et al 2005). Although it is known that NK3 regulate the neuronal activity and dopamine release (Humpel et al 1991;Bannon et al 1995;Alonso et al 1996), possible role of NK3 in neuronal survival remains to be delineated. Our previous data revealed that NK3 agonist enhanced phosphorylation level of NMDA receptors and motor symptoms in MPTP-treated PD mouse model (Wang et al 2005).…”

“…1991; Bannon et al. 1995; Alonso et al. 1996), possible role of NK3 in neuronal survival remains to be delineated.…”