Developmentally expressed Ca(2+)-sensitive adenylyl cyclase activity is disrupted in the brains of type I adenylyl cyclase mutant mice

The type I Ca(2+)-sensitive adenylyl cyclase has been implicated in several forms of synaptic plasticity in vertebrates. Mutant mice in which this enzyme was inactivated by targeted mutagenesis show deficient spatial memory and altered long term potentiation (Wu, Z. L., Thomas, S. A., Villacres, E. C., Xia, Z., Simmons, M. L., Chavkin, C., Palmiter, R. D., and Storm, D. R. (1995) Proc. Natl Acad Sci. U. S. A. 92, 220-224). Long term potentiation in the CA1 region of the rat hippocampus develops during the first 2 weeks after birth and reaches maximal expression at postnatal day 15 with a gradual decline at later stages of development. Here we report that Ca(2+)-stimulated adenylyl cyclase activity in rat hippocampus, cerebellum, and cortex increases significantly between postnatal days 1-16. This increase appears to be due to enhanced expression of type I adenylyl cyclase rather than type VIII adenylyl cyclase, the other adenylyl cyclase that is directly stimulated by Ca2+ and calmodulin. Type I adenylyl cyclase mRNA in the hippocampus increased 7-fold during this developmental period. The developmental expression of Ca(2+)-stimulated adenylyl cyclase activity in mouse brain was attenuated in mutant mice lacking type I adenylyl cyclase. Changes in expression of the type I adenylyl cyclase during the period of long term potentiation development are consistent with the hypothesis that this enzyme is important for neuroplasticity and spatial memory in vertebrates.

[The pathologic myocardial change caused by intracoronary ethyl alcohol injection and its mechanism]

Intracoronary chemical injection to ablate ventricular tachycardia is a new method. Through experiments in 22 dogs, we studied the pathologic change of the myocardium and its mechanism following intracoronary injection of 96% ethyl alcohol. All dogs receiving ethyl alcohol injection displayed myocardial necrosis, and most of them presented thrombus in the coronary branch. The pathologic change in the acute period may have resulted from direct ethyl alcohol damage, and that in the late period may have resulted from both direct damage and thrombus caused by arterial damage.

Electrophysiologic follow-up in dogs receiving intracoronary ethyl alcohol injection

96% ethyl alcohol was injected into a diagonal branch of the left anterior descending coronary artery of 10 out of 12 anesthetized dogs, and saline solution was injected in the remaining 2. After chest closure, the dogs were subjected to ambulatory monitoring (H) during days 1, 2, 3 and 7. The electrophysiologic study (EPS) and signal-averaged electrocardiography. (SA-ECG) were performed before the injection and again at day 7 after injection. H failed in one dog which died of ventricular fibrillation. In the other 9 dogs that received alcohol injection, H showed frequent ventricular premature and ventricular tachycardia (VT) after injection; six of the 9 dogs sustained VT, which was not inducible by EPS. VT was not found in 2 control dogs receiving saline solution injection. The SA-ECG showed no ventricular late potentials in dogs receiving alcohol injection. Post-ablation ventricular arrhythmia (including VT) occurred after intracoronary ethyl alcohol injection in all dogs. Arrhythmogenicity markedly declined during the first 3 days and almost completely disappeared on day 7 after ablation. There was no evidence in favor of reentry as the mechanism of these arrhythmias. Enhanced automaticity was considered as the mechanism for ventricular arrhythmia.

[The experimental ablation of ventricular tachycardia in dogs with intracoronary ethyl alcohol injection]

In 15 anesthetized dogs, a diagonal branch of the left anterior descending coronary artery was cannulated. Localized ventricular tachycardia (VT) was induced by injecting aconitine solution into the left ventricular wall perfused by the cannulated diagonal branch. In 6 untreated control dogs, VT lasted 17.6 +/- 8.3 minutes, 3 of them degenerated into ventricular fibrillation. The VTs were eliminated in 8 of the 9 dogs (88.9%) 1.2 +/- 1.4 minutes after injection of 96% ethyl alcohol. The pathologic examination revealed that transmural myocardial necrosis was present in 7 of 9 dogs receiving alcohol injection. Fibrin or thrombus was present in the diagonal coronary branch in 5 dogs. The conclusion was that the intracoronary injection of 96% ethyl alcohol ablated aconitine-induced ventricular tachycardia effectively. This approach may become a promising new method to treat ventricular tachycardia or other arrhythmia.