Retention deficit for avoidance training in hypophysectomized rats: Time-dependent enhancement of retention performance with post-training ACTH injections

These experiments examined the effects of hypophysectomy on retention of avoidance training. In addition, the experiments examined the effects, on retention, of post-training ACTH injections administered to hypophysectomized rats. Rats were trained in a visual discriminated avoidance Y maze. Each rat received six training trials followed by six retraining trials the next day. Retention was measured by the number of correct choices during the retraining trials. When trained with a low-footshock intensity (0.8 mA), hypophysectomized rats showed retention performance which was significantly poorer than that of intact animals. There was no significant difference in performance when the animals were trained with a higher footshock intensity (1.4 mA), in part because of poorer retention performance of intact animals under these training conditions. Under both footshock conditions, a single post-training injection of ACTH enhanced later retention performance of hypophysectomized rats. This effect on memory was timedependent; injections delayed 2 or 6 hr after training did not significantly enhance retention. These findings are consistent with the view that hormonal responses to training may modulate later retention of the training experience.     

Spontaneous missense mutation of an immunoglobulin in a mouse myeloma cell line.

The characterisation of the alteration in amino acid sequence of the immuno globulin heavy chain of IF4, a charge mutant of the myeloma line MOPC 21, is described. This was achieved by comparing the sequence of mutant IF4 heavy chain with the known sequence of the wild type. The peptic fragment (Fab′)₂ from whole immunoglobulin, and all the ten CNBr fragments of MOPC 21 wild-type and mutant IF4 heavy chains, were identified and characterised. The only difference was in a tryptic peptide of the C-terminal CNBr fragment which had the same amino acid composition, but different electrophoretic mobilities. Thermolysin digestion products showed that asparagine 415 of wild-type heavy chain had been replaced by an aspartate in the mutant. Analysis of newly synthesized immunoglobulins from wild type and mutant showed the same charge difference, which did not seem therefore to result from deamidation.Fingerprints of the [³²P]mRNA of IF4 heavy chain were prepared. The T₁ ribonuclease oligonucleotide that includes the coding sequence for residue 415 in wild type was not found in mutant IF4.The mechanism is most likely a missense point mutation (A to G transition) in the MOPC 21 heavy chain structural cistron.     

beta-Endorphin: structure-activity relationships in the guinea pig ileum and opiate receptor binding assays.

The opiate activities of some derivatives and enzymatic digests of camel and human β-endorphin were determined in the guinea pig ileum and rat brain opiate receptor binding assays. Derivatives of β-endorphins altered within the amino-terminal five residues showed pronounced losses in activity. Anisylation of the C-terminal glutamic acid residue of β_h-endorphin produced only small reductions in activity. Chymotryptic digestion greatly weakened the opiate activities of β_h-endorphin, whereas carboxypeptidase A, tryptic and leucine aminopeptidase digests showed only small losses in potency. The C-terminus of β-endorphin appears to contribute little directly to opiate activity. Amino acid analysis and assay of the leucine aminopeptidase digests suggest that the larger potency of β-endorphin relative to Met-enkephalin may be a consequence of its greater resistance to exopeptidase attack.     

Synthesis of leucine enkephalin derivatives: structure-function studies

Nucleoli isolated from livers of rats injected intraperitoneally with one dose of thioacetamide had a five-fold increase in the rate of RNA synthesis $\text{in vitro}$ when compared with livers of rats treated with saline or CCl₄. The stimulation was maximal 24 hours after treatment and decreased to control values 73 hours after treatment. The enhanced level of nucleolar activity was maintained at that level when thioacetamide was injected daily. Along with the increase in the endogenous activity there was a 7-fold increase in the “free” RNA polymerase I activity determined by blocking the bound enzyme with actinomycin D (7). The nucleoli of the thioacetamide-treated rats offer a useful model of modulation of ribosomal gene function.     

Quantitative determination of carbamazepine and carbamazepine-10,11-epoxide in rat brain areas by multiple ion detection mass fragmentography.

A specific and sensitive method is described for the simultaneous determination of carbamazepineand carbamazepine-10,11-epoxide in biological specimens by combined gas chromatography-mass spectrometry. Cytenamide is used as the internal standard for quantitation. Kinetics of the distribution of the drug and its metabolite in plasma and in different areas of rat brain are reported. Determinations are possible at the nanogram level.     

An ultramicro method of amino acid analysis: application to studies of protein metabolism in cultured cells.

Analysis of the quantity and specific radioactivity of amino acids derived from intra-cellular pools, aminoacyl-transfer RNA, and protein hydrolysates of cultured cells has been achieved using a radiolabeled amino group ligand, dansyl chloride. Speeific activities of ¹⁴C- or ³H-labeled amino acids are calculated after reaction with appropriately labeled dansyl chloride of known specific activity. The quantity of amino acid is determined as a function of its diluting influence on a radioactive standard. The specific activity of as little as 2 pmol of amino acid can be measured using [¹⁴C]dansyl chloride the less sensitive of the two isotopic species available. Thus, cells from a single 60-mm culture dish provide sufficient material for analysis of both intracellular and transfer RNA amino acid pools, and one can easily analyze the amino acids in hydrolysates made from individual bands in polyacrylamide gels. The method offers significant improvement in speed, sensitivity, and economy over conventional methods of amino acid analysis and, because of its double-label design, gives accurate results with a minimum of technical expertise and no major equipment other than a scintillation counter.     

Modification of an essential arginine of carbamate kinase

Carbamate kinase from Streptococcus faecalis is inactivated by butanedione in borate buffer, which implies the presence of an essential arginine at the active site of the enzyme. The inactivation reaction is first order in [butanedione] and a replot of the inactivation rate data infers that one arginine is modified. The enzyme is protected against inactivation by ADP, ATP, the metal-nucleotides and carbamyl phosphate but not by carbamate. Amino acid analyses reveal that one of three arginines is modified by butanedione in the absence of protecting agents, and the binding of ADP to the enzyme prevents modification. Thus, analysis of the data suggest that (i) substrate binding to arginine and (ii) protein conformational changes at the active site are responsible for protection of an essential arginine against modification by butanedione.