Alteration of electroconvulsive threshold by cerebrospinal fluid from cats tolerant to electroconvulsive shock

Daily electroconvulsive shocks for 22 days resulted in a progressive elevation of electroconvulsive threshold. When these shocks were discontinued, the thresholds returned to untreated levels in approximately 20 days. Cerebrospinal fluid collected from cats with elevated thresholds and repeatedly transferred to the ventricular space of untreated animals elevated the electroconvulsive threshold of the recipient. This finding demonstrates that a substance present in the cerebrospinal fluid of cats with elevated electroconvulsive threshold can alter the threshold of untreated animals.     

Effects of Long-Term Low Dietary Tryptophan Intake on Determinants of 5-Hydroxytryptamine Metabolisn in the Brains of Young Rats

Abstract: The relationship between plasma and brain tryptophan (TRP) concentrations and brain 5-hydroxytryptamine (5-HT) metabolism was studied in weanling rats fed diets containing either 0.4 g or 1.45 g TRP/ 100 g casein hydrolysate. Both groups gained weight comparably though food intakes were generally higher in the low-TRP group. Severe depletion of plasma total and free TRP and of brain TRP, 5-HT, and 5-hydrox-yindoleacetic acid (5-HIAA) occurred within 1 day of feeding the 0.4% TRP diet. Levels became stable after 7 days. The decreased brain TRP concentration of the rats on the 0.4% TRP diet did not cause a compensatory rise of the tryptophan hydroxylase (TRP OHase) activity in vitro. In the low-TRP group, neither plasma free TRP nor total TRP correlated significantly with brain TRP and although plasma TRP/large neutral amino acid (NAA) ratios (TRP/NAA) correlated significantly ( P < 0.05) with the time course of brain TRP, this statistical relationship depended almost completely on the variation of the TRP values alone. In the higher TRP group none of these correlations were significant. A plot of mean plasma free TRP versus brain TRP gave two distinct regression lines with similar slopes and corresponding to values before and after 7 days on the diet. The time course of brain 5-hydroxyindole concentrations did not parallel those of brain TRP and suggested that changes of TRP OHase activity also had an influence on 5-HT synthesis.     

A Glutaraldehyde-Dichromate-Silver Sequence for Differentiating Norepinephrine Cells from Epinephrine Cells in Neonatal and Adult Rats—Paraffin Sections

A glutaraldehyde-K₂Cr₂O₇ procedure intensified by silver staining enabled norepinephrine and epinephrine cells to be distinguished readily in paraffin sections of the adrenal glands of rats 8 days after birth. The technique involved fixation in 0.1 M cacodylate-buffered 5% glutaraldehyde (6-24 hr), treatment with 3.5% K₂Cr₂O₇ (6-12 hr) and routine preparation of paraffin sections. The sections were deparaffinised, brought to water and immersed in Fontana's solution (24 hr), prepared by adding concentrated NH₄OH drop by drop to 5% AgNO₃ until the precipitate formed just redissolved; more 5% AgNO₃ was then added until a permanent cloudiness just developed. After a rinse in distilled water, the sections were treated with 0.5% gold chloride (5 min) and Na₂S₂O₃ (5 min), then mounted in Depex. This sequence resulted in an intense black cytoplasmic colouration in norpinephrine-containing cells of both the adult and 8-day-old animals whereas epinephrine-containing cells remained colourless. The glutaraldehyde-K₂CrO₇ procedure, without intensification, gave very clear results in the adult: a yellow cytoplasmic colour in the norepinephrine cells with epinephrine cells colourless. A glutaraldehyde-OsO₄ sequence gave a less well defined separation of these cell types in the adult and failed to distinguish the cell types in the neonate.     

Proctolin degradation by membrane peptidases from nervous tissues of the desert locust (Schistocerca gregaria).

The hydrolysis of the insect neuropeptide proctolin (Arg-Tyr-Leu-Pro-Thr) by enzyme preparations from the nervous tissue of the desert locust (Schistocerca gregaria) was investigated. Neural homogenate degraded proctolin (100 microM) at neutral pH by cleavage of the Arg-Tyr and Tyr-Leu bonds to yield Tyr-Leu-Pro-Thr, Arg-Tyr and free tyrosine. Arg-Tyr was detected as a major metabolite when the aminopeptidase inhibitors amastatin and bestatin were present to prevent Arg-Tyr breakdown. Around 50% of the proctolin-degrading activity was isolated in a 30,000 g membrane fraction and was shown to be almost entirely due to aminopeptidase activity. The aminopeptidase had an apparent Km of 23 microM, a pH optimum of 7.0 and was inhibited by 1 mM-EDTA and amastatin [IC50 = 0.3 microM], but was relatively insensitive to bestatin, actinonin and puromycin. Phenylmethanesulphonyl fluoride (1 mM) and p-chloromercuriphenylsulphonic acid (1 mM) had no effect on this enzyme activity. Although the bulk of the Tyr-Leu hydrolytic activity was located in the 30,000 g supernatant, some weak activity was detected in a washed membrane preparation. This peptidase displayed a high affinity for proctolin (Km = 0.35 microM) and optimal activity at around pH 7.0. Synaptosome- and mitochondria-rich fractions were prepared from crude neural membranes. The aminopeptidase activity was concentrated in the synaptic-membrane preparation, whereas activity giving rise to Arg-Tyr was predominantly localized in the mitochondrial fraction. The subcellular localization of the membrane aminopeptidase is consistent with a possible physiological role for this enzyme in the inactivation of synaptically released proctolin.     

Characterization of siderophore-mediated iron transport inGeotrichum candidum,a non-siderophore producer

Summary Geotrichum candidum is capable of utilizing iron from hydroxamate siderophores of different structural classes. The relative rates of iron transport for ferrichrome, ferrichrysin, ferrioxamine B, fusigen, ferrichrome A, rhodotorulic acid, coprogen B, dimerium acid and ferrirhodin were 100%, 98%, 74%, 59%, 49%, 35%, 24%, 12% and 11% respectively. Ferrichrome, ferrichrysine and ferrichrome A inhibited [⁵⁹Fe]ferrioxamine-B-mediated iron transport by 71%, 68% and 28% respectively when added at equimolar concentrations to the radioactive complex. The inhibitory mechanism of [⁵⁹Fe]ferrioxamine B uptake by ferrichrome was non-competitive (K _i 2.4 M), suggesting that the two siderophores do not share a common transport system. Uptake of [⁵⁹Fe]ferrichrome, [⁵⁹Fe]rhodotorulic acid and [⁵⁹Fe]fusigen was unaffected by competition with the other two siderophores or with ferrioxamine B. Thus,G. candidum may possess independent transport systems for siderophores of different structural classes. The uptake rates of [¹⁴C]ferrioxamine B and⁶⁷Ga-desferrioxamine B were 30% and 60% respectively, as compared to [⁵⁹Fe]ferrioxamine B. The specific ferrous chelates, dipyridyl and ferrozine at 6 mM, caused 65% and 35% inhibition of [⁵⁹Fe]ferrioxamine uptake. From these results we conclude that, although about 70% of the iron is apparently removed from the complex by reduction prior to being transported across the cellular membrane, a significant portion of the chelated ligand may enter the cell intact. The former and latter mechanisms seem not to be mutually exclusive.