Possible nuclear protein kinase regulation of homologous ribonucleic acid polymerases from small dense nuclei of mouse brain during morphine tolerance-dependence. Involvement of cyclic 3',5'-adenosine monophosphate

Neuronal phosphoproteins. Mediators of signal transduction

This article summarizes some of our knowledge concerning intracellular protein phosphorylation pathways in nerve cells. It also summarizes, very briefly, recent direct experimental evidence involving intracellular injection of protein kinases, protein kinase inhibitors, and substrates, indicating that protein phosphorylation mediates the actions of a variety of neurotransmitters on their target cells. Finally, it summarizes in somewhat greater detail the results of studies of three different types of substrate proteins that appear to regulate different types of biological responses in nerve cells: synapsin I, a substrate protein present in virtually all nerve terminals, which appears to regulate neurotransmitter release from those nerve terminals; the acetylcholine receptor, the phosphorylation of which regulates its rate of desensitization in the presence of acetylcholine; and DARPP-32, the phosphorylation of which converts it into a very potent phosphoprotein phosphatase inhibitor that may be involved in the regulation by the neuromodulator dopamine of the effects of the neurotransmitter glutamate. The identification and characterization of additional neuronal phosphoproteins can be expected to lead to the clarification of numerous additional molecular mechanisms by which signal transduction is carried out in nerve cells.

Alteration of RNA synthesis in vitro in intact cerebral cortex nuclei induced by convulsions in seizure-susceptible El mice

We examined the effects of convulsive seizures on in vitro RNA synthesis by cerebral cortex nuclei in El mice. The rate of incorporation of [3H]uridine-5'-triphosphate by intact nuclei during seizures was decreased to 47.4% compared with the rate during the interictal period, but gradually recovered. During the 30-min period after onset of seizures, the rate of RNA synthesis was significantly lower in El mice than in identically stimulated ddY mice. Seizures in El mice had no effect on liver RNA synthesis, suggesting that the alteration of RNA polymerase activity is specific to the brain. Analysis of gel electrophoresis of polyadenylated RNA synthesized in the presence of ammonium sulphate revealed a marked decrease in high-molecular weight RNA species 15 min after seizures in El mice compared with the pattern in nonstimulated ddY mice. This shift from high- to low-molecular weight RNA species was not attributable to RNase activity, but it appeared to be related RNA polymerase.

Synapsin I, a phosphoprotein associated with synaptic vesicles: possible role in regulation of neurotransmitter release

The data presented here provide evidence that the study of neuronal phosphoproteins can lead to the identification of previously unknown proteins and that these proteins may play important roles in neuronal communication. Specifically, in the case of synapsin I, direct evidence has been obtained that this phosphoprotein is involved in regulating neurotransmitter release. A tentative explanation of the results obtained in the micro-injection studies is as follows: synapsin I, in the dephosphostate, is bound to the cytoplasmic surface of synaptic vesicles and inhibits the ability of the vesicle to interact with the plasma membrane; increases in intracellular calcium activate calmodulin kinase II which in turn phosphorylates synapsin I and the phosphorylated synapsin I dissociates from the synaptic vesicle thus removing a constraint on the release of neurotransmitter. Clearly, more studies need to be done to rigorously test this hypothesis. Nevertheless these studies of synapsin I suggest that the study of previously unknown phosphoproteins will lead to the elucidation of previously unknown regulatory processes in neurons.

Protein phosphorylation and neuronal function

Studies in the past several years have provided direct evidence that protein phosphorylation is involved in the regulation of neuronal function. Electrophysiological experiments have demonstrated that three distinct classes of protein kinases, i.e., cyclic AMP-dependent protein kinase, protein kinase C, and CaM kinase II, modulate physiological processes in neurons. Cyclic AMP-dependent protein kinase and kinase C have been shown to modify potassium and calcium channels, and CaM kinase II has been shown to enhance neurotransmitter release. A large number of substrates for these protein kinases have been found in neurons. In some cases (e.g., tyrosine hydroxylase, acetylcholine receptor, sodium channel) these proteins have a known function, whereas most of these proteins (e.g., synapsin I) had no known function when they were first identified as phosphoproteins. In the case of synapsin I, evidence now suggests that it regulates neurotransmitter release. These studies of synapsin I suggest that the characterization of previously unknown neuronal phosphoproteins will lead to the elucidation of previously unknown regulatory processes in neurons.

Effect of naloxone and D-met2-pro5-enkephalinamide treatment on the DNA synthesis in the developing rat brain

Effects of a single dose of naloxone and of D-Met2-Pro5-enkephalinamide on the DNA synthesis in the forebrain, hypothalamus and cerebellum of 11 day old female rats were studied. As an index of DNA synthesis the rate of incorporation of 3H-thymidine into DNA was measured 30 min after a sc. injection of 40 muCi/100 g b.w.. A time dependent effect of naloxone administration on cerebral DNA synthesis was observed. In the forebrain at 1 and 3 hrs after naloxone injection an increased rate of 3H-thymidine incorporation into DNA was found followed by a marked decrease at 9 and 12 hrs. The effect in the hypothalamus was similar but the initial increase at 1 hr was absent. On cerebellar DNA synthesis naloxone had no effect. The administration of D-Met2-Pro5-enkephalinamide resulted in a marked reduction in the labelling of cerebral and hypothalamic DNA between 1 to 12 hrs. Except a decrease at 1 hr no effect was found in the cerebellum.