Frontal cortex and response suppression in the rat

Parts of the rat's neocortex were mapped for sites where electrical stimulation, square waves at 10/sec, will suppress a bar-press response for food. Effective sites were found in the frontal pole and over most of the frontal dorsolateral cortex. Within these regions the strongest inhibitory influences were at sites in the frontal pole and adjacent frontal cortex, and at sites along the midline. These data generally agree with results of previous cortical ablation studies, but they suggest that inhibitory processes are more widespread in the dorsolateral cortex than these studies indicated.     

Skeletal uptake of 99mTc-diphosphonate in relation to local bone blood flow

The right/left ratios of tibial uptake of 99mTc-diphosphonate (EHDP) and relative blood flow (based on microsphere distribution) were determined in control rats and rats with a ligated right femoral artery or a healing right tibial fracture. Correlation between 99mTc-EHDP uptake and relative blood flow was highly significant (r=0.917; P less than 0.0001) for relative flow ratios less than 1.7. When the ratio was greater than 1.7, there was little further increase in 99mTc-EHDP uptake. Ligation of the femoral artery in rats with healing fractures resulted in a more marked reduction of blood flow than of 99mTc-EHDP uptake. These results suggest that regional bone blood flow is a major determinant of 99mTc-EHDP uptake, though changes in regional tracer extraction efficiency are also important.     

Esculin hydrolysis by Streptococcus dysgalactiae

In a mastitis control program based on eradication of intramammary infection, it is important to differentiate streptococci. According to earlier reports, Streptococcus dysgalactiae was unable to hydrolyze esculin. Preliminary data from the present study indicated that under optimal conditions, some strains of S dysgalactiae were capable of esculin hydrolysis. In a study of 45 strains of S dysgalactiae, 55.5% were able to hydrolyze esculin. In the past, these organisms would probably have been identified as Streptococcus uberis. Streptococcus dysgalactiae is more sensitive to antibiotics than S uberis, and the infection is easier to eradicate from infected glands.     

Nitrous oxide analgesia: reversal by naloxone and development of tolerance

The objective of this study was to characterize further the nature of nitrous oxide analgesia and to establish if tolerance to nitrous oxide occurs. Methods for studying the analgesic action of a gas are described. In mice, nitrous oxide is analgesic in the phenylquinone and acetic acid abdominal constriction tests. Aspirin and very high doses of alcohol are also active in these tests; however, only nitrous oxide-induced analgesia is antagonized by narcotic antagonists. These data indicate the mechanism of action of nitrous oxide analgesia differs from that of the other two drugs. Nitrous oxide produced a dose-related analgesic response in rats (ED50, 67%) as measured by the tail-flick method. Naloxone, 5 to 30 mg/kg, also antagonized nitrous oxide analgesia in rats. Lower doses of the antagonist were not effective. Tolerance developed to the effects of nitrous oxide in both rats and mice after prolonged exposure. These data lend support to the hypothesis that nitrous oxide and opiates have a significant pharmacologic resemblance and may ultimately produce similar molecular events in the brain leading to the relief of pain.     

Effect of several cholinomimetic and anticholinesterase substances on the somatic musculature of the nematode Ascaris suum

On the basis of discrete concentration--effect curves, quantitative evaluation of the effect of acetylcholine, propionylcholine, suberylcholine and carbacholine upon the strips of the spinal muscle of Ascaris was made. Anticholinesterase drugs, eserine and phosphacol, exhibit weak potentiation of the effect of acetycholine (by 2--6 times). The results obtained are discussed in relation to cholinoreceptive properties of muscles in higher animals.     

The serological diagnosis of bovine brucellosis: an evaluation of the complement fixation, serum agglutination and rose bengal tests

In a collaborative investigation in which 4 laboratories took part, the Rose Bengal Test (RBT), Serum Agglutination Test (SAT) and 4 different Complement Fixation (CFT) techniques were evaluated in selected cattle for the diagnosis of bovine brucellosis, by comparing the results they gave with the bacteriological examination of a selection of lymph nodes taken from the same animals at slaughter. The RBT correctly classified all but 1 of 79 culture-positive cattle, but was more often positive in culture-negative animals than the other tests. The RBT may be most useful as a screen test. 11% of the culture-positive cattle had SAT titres below 100 iu and almost 4% of them had less than 30 iu. However, the SAT was more effective in cattle vaccinated with the 45/20 vaccine. The CFT, in 1 of 4 techniques used, identified all of the culture-positive cattle at a serum dilution of 1/4 or above and was considered to be far superior to the SAT as a diagnostic test, except perhaps in cattle vaccinated with the 45/20 vaccine.