Postsynaptic long-term enhancement (LTE) by dopamine may be mediated by Ca2+ and calmodulin

Continuously infusing quinpirole decreases Ca2+/calmodulin-dependent phosphorylation in mouse striatum

Continuously administering the D2 dopamine agonist quinpirole to mice for 6 days produces an initial stereotypy that is reduced by 2 h and is absent from 3 h to the 6 day duration of the infusion. In an attempt to determine the biochemical correlates for this down-regulation of stereotypic behavior, the effects of continuously administering quinpirole on a number of biochemical parameters were measured in mouse corpus striatum. After 6 days of infusion with quinpirole, the striata were analyzed for D1 and D2 dopamine receptors, for the activities of several protein phosphorylation reactions which are thought to be involved in receptor activity and for the levels of calmodulin-binding proteins. Quinpirole decreased the D2 receptors in striatum and produced a small but statistically non-significant increase in D1 receptors, resulting in a significant increase in the ratio of D1 to D2 dopamine receptors. An examination of the effects of quinpirole on protein phosphorylation systems showed that the agonist failed to alter the activity of cyclic AMP-dependent protein kinase or protein kinase C but significantly decreased the Ca2+/calmodulin-dependent phosphorylation of striatal membranes. However, this decrease in Ca2+/calmodulin-dependent phosphorylation was not associated with changes in the levels of calmodulin-binding proteins. The results suggest that behavioral down-regulation following the continuous administration of a D2 dopamine agonist is associated with at least two biochemical events: a down-regulation of D2 dopamine receptors and a decrease of Ca2+/calmodulin-dependent phosphorylation of striatal membranes.

Potentiation of nicotinic transmission in the rat superior cervical sympathetic ganglion: effects of cyclic GMP and nitric oxide generators

The efficacy of nicotinic transmission in the rat superior cervical ganglion in vitro (24-26 degrees C) was estimated by extracellular recording of the postganglionic compound action potential response to stimulation of the preganglionic nerve at a slow rate (one shock every 60 s). Atropine (2 microM) was included to block muscarinic transmission, and hexamethonium (200-250 microM) was used to produce a submaximal response sensitive to potentiation and inhibition of nicotinic transmission. Upon exposure to 1-100 microM 8-bromo-guanosine 3',5'-cyclic monophosphate (8-Br-cGMP), nicotinic transmission was potentiated by 6 +/- 1% (n = 4) to 89 +/- 5% (n = 5) in a dose-dependent manner. 8-Bromo-adenosine 3',5'-cyclic monophosphate (8-Br-cAMP, 10-100 microM) also potentiated nicotinic transmission (3.8 +/- 0.3% (n = 3) to 43 +/- 4% (n = 3)). However, 8-Br-cGMP was at least 2-fold more effective than 8-Br-cAMP. Sodium nitroprusside (0.1 microM to 1 mM) and sodium azide (0.1-100 microM) were used to stimulate the formation of endogenous cGMP52. Nicotinic transmission was potentiated by these substances also. The response was increased by 3.4 +/- 0.7% (n = 4) to 32 +/- 2% (n = 5) upon exposure to 0.1-100 microM sodium nitroprusside, and by 5.5 +/- 0.9% (n = 3) to 18 +/- 4% (n = 4) upon exposure to 0.1-100 microM sodium azide. Ferricyanide ion (10-100 microM) appeared to be ineffective, as would be expected if the effect of nitroprusside was due to the nitric oxide rather than the cyanide or ferric moieties.(ABSTRACT TRUNCATED AT 250 WORDS)