The development of fixed-ratio performance under the influence of ribonucleic acid

The transition from fixed-ratio 1 performance (every response reinforced) to fixed-ratio 30 performance (every thirtieth response reinforced) was studied in nine pigeons. These were divided into three treatment groups given daily oral doses of saline, or 250 mg/kg/day or 500 mg/kg/day of yeast ribonucleic acid. Detailed computer-assisted analyses of how fixed-ratio behavior develops revealed the following typical sequence. After the transition, the first few ratios typically were emitted without long interresponse times within the ratio. Steady responding then ceased, and numerous long interresponse times occurred, with no systematic relationship to ordinal position within the ratio. Gradually, a new pattern evolved, characterized by a consistently long post-reinforcement time, a border region of the next few interresponse times within which the mean interresponse time monotonically decreased, and short interresponse times within the last 80% of the ratio. Long interresponse times were eliminated from this last section of the ratio without regard to proximity to reinforcement. Various analytical procedures suggested that the final pattern can be conceived, in part, as the shaping of a reliable response topography. The group of three pigeons given 250 mg/kg/day of yeast ribonucleic acid responded at higher rates than the saline and 500 mg/kg/day groups. The latter group, in contrast to the saline and lower dose groups, which continued to increase their rates, reached a rate asymptote very early.

Adenosine 3'-5'-monophosphate in rat pineal gland: increase induced by light

Rats were maintained in alternating periods of 12 hours of light and 12 hours of darkness. The concentration of adenosine 3',5'-monophosphate in pineal gland was six times higher at the end of the light period than at the end of the period of darkness. This effect of light was abolished in blinded animals.

Terminal cross-linking of DNA strands by an enzyme system from Escherichia coli infected with bacteriophage T4

An enzyme system, purified 560-fold from Escherichia coli infected with bacteriophage T4, catalyzes the formation of a phosphodiester bond between the original 5'-phosphoryl end-group of a DNA strand and a 3'-hydroxyl group of the complementary strand. The product, a terminally cross-linked, spontaneously renaturable DNA duplex, has been characterized by chromatographic analysis, by sedimentation analysis, and by enzymatic digestion. Essential components of the enzyme system, which requires both ATP and Mg(++), include the T4-induced DNA ligase and a component found in extracts of uninfected E. coli, which is probably an exonuclease.

Fluttering of the mitral valve in aortic insufficiency

Thirty-five patients with clinical evidence of aortic insufficiency were studied by echocardiography. Eleven patients had characteristic diastolic fluttering of the mitral valve (30 to 40 Hz, maximal amplitude 4 mm). In five others the fluttering was classified as equivocal.

In a control group of 500 echocardiograms in patients without evidence of aortic insufficiency, there were three examples of equivocal fluttering. Atrial fibrillation also produces diastolic fluttering but of slower frequency.

Further observations on overt "mediating" behavior and the discrimination of time

When the lever-pressing behavior of five rats was maintained by a DRL schedule (reinforcement was scheduled only when a specified waiting time between successive responses was exceeded), collateral behavior developed that apparently served a mediating function. In two cases this behavior did not arise until the experimental environment included pieces of wood that the rats started to nibble. When collateral behavior first appeared, it was always accompanied by an increase in responses spaced far enough apart to earn reinforcement. If collateral behavior was prevented, the number of reinforced responses always decreased. Extinction of lever pressing extinguished the collateral behavior. Adding a limited-hold contingency to the schedule did not extinguish collateral behavior. It appears that the rat can better space its responses appropriately when concurrently performing some overt collateral activity. The amount of this activity apparently comes to serve as a discriminative stimulus. To assume the existence of internal events that serve as discriminative stimuli in temporal discriminations is, at least under some circumstances, unnecessary.