Arachidonic acid metabolites as mediators of somatostatin-induced increase of neuronal M-current

Article Abstract:

M-current is a type of current carried across the membrane of nerve cells by potassium ions; M-current is time- and voltage-dependent during voltage changes, and persists when the normal voltage across the membrane is slightly reduced. Examining the electrophysiology of M-current in cells of the hippocampus, researchers have found that it is affected by two complementary control systems. Muscarinic receptors, which bind acetylcholine, reduce M-current, while receptors for somatostatin increase M-current. Further research has identified an unusual mechanism for the augmentation of M-current by somatostatin that apparently involves the enzyme phospholipase A2. This is inferred by the fact that two drugs, quinacrine and 4-bromophenacyl bromide, which inhibit phospholipase A2, also interfere with the affect. Phospholipase A2 produces arachidonic acid, which may be converted into leukotrienes by other enzymes. It has been recognized that leukotrienes are manufactured in various parts of the brain, but this is the first example of biochemical responses to somatostatin which might produce such an effect. The authors suggest that the existence of two complementary systems for the control of M-current, mediated by two biochemically distinct processes, may make possible the sensitive biasing of membrane current and neuronal activity. (Consumer Summary produced by Reliance Medical Information, Inc.)

Neurophysiology, Electrophysiology, Hippocampus (Brain), Leukotrienes

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The LDL receptor pathway delivers arachidonic acid for eicosanoid formation in cells stimulated by platelet-derived growth factors

Article Abstract:

Low-density lipoproteins (LDL) are well known for their role in the regulation of cholesterol within the body, and high levels of LDL cholesterol carry an increased risk for heart disease. However, LDLs also are involved in the synthesis and regulation of prostaglandins, which are important mediators of inflammation and immunological reactions. The body cannot manufacture prostaglandins without substances such as linoleic acid derived from the diet. Research has now shown that, not only do the LDLs carry the raw materials for prostaglandin synthesis, but they also play a role in the regulation of the process. The lipoproteins, which are laden with fatty raw materials, bind to cells via the LDL receptor. This molecule then initiates the uptake of the LDL and the fats into the cell. The presence of the raw material on the LDL stimulates the initiation of synthesis of prostaglandins in the presence of platelet-derived growth factor, a substance involved in wound healing. However, as the cell digests the LDL it has incorporated, fragments appear to inhibit PDH synthase, an important enzyme of prostaglandin synthesis. Therefore, the LDL and receptor complex play a role in both the stimulation and inhibition of prostaglandin synthesis. (Consumer Summary produced by Reliance Medical Information, Inc.)

Prostaglandins, Growth factors, Low density lipoproteins

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A cortical neuropeptide with neuronal depressant and sleep-modulating properties

Article Abstract:

Cortistatin is a neuropeptide that depresses neuronal electrical activity and induces low-frequency waves in the cerebral cortex. The peptide is structurally similar to somatostatin but is produced by a different gene. Cortistatin controls the hippocampal neuron activity and sleep physiology in a manner different from that of somatostatin. An uncharacterized receptor in the peptide may be responsible for the effects.

Hypnotics and sedatives, Neuropeptides, Central nervous system depressants, Sleep substances

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