Faculty Bibliography

High-affinity binding of [3H]cocaine to membranes of mouse cerebral cortex is inhibited by Tris (hydroxymethyl) aminomethane, the buffer commonly used in receptor binding assays. This inhibition is not due to an effect of ionic strength in general. Comparison of binding in Tris buffer with that in sodium phosphate buffer indicates a more than 4-fold higher Kd in the former buffer, with no differences in the Bmax values

The anticonvulsant effect of either phenobarbital or dilantin was potentiated by exogenous glycine in DBA/2 audiogenic seizure mice and in 3-mercaptopropionic acid-induced seizures. In seizures caused by pentylenetetrazol, glycine potentiated the anticonvulsant effect of phenobarbital only slightly; in combination with dilantin, which was ineffective by itself, it did not have an effect. Valproic acid, in large doses, prevented 3-mercaptopropionic acid-induced seizures; glycine did not potentiate its effect. Glycine thus potentiates anticonvulsant effects, but only of some drugs and only in some of the seizure models. This suggests that the mechanism of the anticonvulsant effect of glycine is similar to that of some of the anticonvulsant drugs such as dilantin and different from others, and that this mechanism is not effective in all seizure models

Protein synthesis rates were measured (33 days postoperatively) in rats with portacaval shunts and in unoperated controls. In brain, no change in the rate of protein synthesis was evident in shunted rats. These data thus do not support the hypothesis that an inhibition of brain protein synthesis is a factor in the etiology of hepatic encephalopathy. The synthesis rate in forebrain at 82 days of age was 0.52%/h. Though brain wet weight was the same in both groups, rats with shunts grew relatively slowly, and their testicles probably decreased in weight. However, no inhibition of muscle, liver, or testicular protein synthesis could be detected. The mechanism of slower or negative growth in these tissues might thus involve an increase in the degradation rate, although a transient inhibition of synthesis at an earlier period is also possible

Previously we found close similarities between high-affinity binding sites for [3H]cocaine and those for [3H]imipramine in the mouse cerebral cortex in regard to their association with neuronal uptake of serotonin. In the present study we investigated whether the two ligands bind to the same site. The two ligands had the following high-affinity binding properties in common: localization in both synaptosomal and microsomal fractions; vulnerability to treatment with N-ethylmaleimide, trypsin, and phospholipase A2; and resistance to exposure to dithiothreitol. In contrast, cocaine binding in the cerebral cortex was more sensitive to heat inactivation than imipramine binding. In addition, the mechanism by which cocaine inhibited [3H]imipramine binding differed from that by which imipramine inhibited [3H]cocaine binding. These data suggest that the high-affinity binding sites for [3H]cocaine and [3H]imipramine in the cerebral cortex are distinct entities

[3H]Imipramine and [3H]cocaine were concentrated at membranes of liposomes prepared from phosphatidylcholine, cholesterol, and dicetylphosphate. This 'binding' has an apparent dissociation constant in the micromolar range and a density close to 2 pmol/micrograms of phosphatidylcholine. The potencies of various drugs in inhibiting the binding to liposomes correlated only weakly with those in inhibiting the high-affinity binding of [3H]imipramine and [3H]cocaine to brain membranes. However, there was a highly significant correlation between the potencies of drugs in inhibiting binding to liposomes and their lipophilic character, indicating the involvement of hydrophobic bonding. Although the amounts of phosphatidylcholine and cholesterol in brain preparations in assays for high-affinity binding to brain membranes were in the same range as those used in our assays with liposomes, the inhibition of the high-affinity binding to brain membranes was only weakly dependent upon the lipophilicity of the inhibiting drug. These results indicate that lipophilicity is but one of the factors in the complex binding interactions between lipophilic substances and integral brain membranes. In addition, the results are in agreement with the suggestion that phosphatidylcholine and cholesterol are not the primary sites of high-affinity binding [3H]imipramine and [3H]cocaine to brain membranes, although it cannot be ruled out that these lipids have different properties in natural biological membranes and in artificial liposome membranes

Administration of N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (NMPTP) (daily injections of 8 mg/kg for 5 days via tail vein) reduced [3H]dopamine uptake in striatal synaptosomes by 63% and reduced [3H]cocaine binding to striatal membranes by 61%. [3H]Cocaine binding was not affected in olfactory tubercle, suggesting a selective effect of NMPTP on the nigro-striatal but not on the mesolimbic dopaminergic system. The destruction of dopamine terminals in the striatum did not alter (up-regulate) [3H]spiroperidol binding. The results suggest that NMPTP causes a degenerative destruction of the striatal dopamine pathway and that NMPTP may be useful in developing a rodent model of Parkinson's disease

In adult mice cerebral puncture results in an inhibition of brain protein synthesis, as suggested previously by Dunn (1975). The inhibition is apparent within a few minutes but subsides by 15 min after puncture. The percent inhibition therefore depends on the length of time between the puncture and the measurement. Mice receiving a puncture were less active than controls, and a decrease in brain temperature was observed in these animals. The decrement is, however, too small to account for the inhibition of synthesis. Diphenylhydantoin had no effect on the inhibition. Cerebral puncture of young mouse (7-day-old) or rat (8-day-old) brain induced no inhibition of brain protein synthesis

As a first approximation of ribosomal concentration we have measured total RNA in some regions of the CNS at different ages and found that the rates of protein synthesis therein are directly proportional to the RNA content. This suggests that the 'RNA activity' remains unchanged during growth and that higher protein synthesis rates in young brain are due to higher content of ribosomal material