J. Zawilska, J. Rosiak, M. Berezińska
Mar 1, 2003
Citations
0
Influential Citations
7
Citations
Quality indicators
Journal
Journal of Neural Transmission
Abstract
Summary. This study examined the in vivo activity of L-745,870 at dopamine (DA) D4 receptors, using the chick retina as a model system. In dark-adapted retinas of various vertebrates, including hen, DA acting via D4 receptors suppresses melatonin content and activity of serotonin N-acetyltransferase (AA-NAT, a key regulatory enzyme in melatonin synthesis). Systemic administration to chicks of quinpirole (0.1 mg/kg), a high affinity agonist of D3/D4-DA receptors, potently decreased the nighttime AA-NAT activity of the retina. The quinpirole-evoked decline in the enzyme activity was attenuated by L-745,870 (0.1–10 nmol/eye). In addition to this action, L-745,870 given to chicks either directly into the eye (0.03–10 nmol/eye) or intraperitoneally (0.5–5 mg/kg) decreased the nighttime AA-NAT activity of the retina in a dose-dependent manner. The suppressive effect of L-745,870 on retinal AA-NAT activity was blocked by 2-chloro-11-(4-methylpiperazino)dibenz[b,f]oxepin, an antagonist of D4-DA receptors, but was not affected by raclopride, an antagonist of D2/D3-DA receptors. Altogether these results indicate that in chicks L-745,870, the potent putative D4-DA receptor antagonist, behaves in vivo as a partial D4 agonist.