Effects of variations in local reinforcement rate on local response rate in variable interval schedules.

Rats trained to lever press for sucrose were exposed to variable-interval schedules in which (i) the probability of reinforcement in each unit of time was a constant, (ii) the probability was high in the first ten seconds after reinforcement and low thereafter, (iii) the probability was low for ten seconds and high thereafter, (iv) the probability increased with time since reinforcement, or (v) the probability was initially zero and then increased with time since reinforcement. All schedules generated similar overall reinforcement rates. A peak in local response rate occurred several seconds after reinforcement under those schedules where reinforcement rate at this time was moderate or high ([i], [ii], and [iv]).

In vitro studies of elastin metabolism.

Neonatal pig and rat aortas were studied for their ability to synthesize elastin in an in vitro situation. Smooth muscle cells from the rat aorta produced excellent multilayered cultures and produced soluble elastin (tropoelastin), insoluble elastin, and small amounts of collagen. BAPN proved to be toxic to these cells, adversely affecting the level of extracellular protein production.

Epidural narcotics in volunteers: sensitivity to pain and to carbon dioxide.

Tolerance to pain and sensitivity to rising concentrations of inhaled carbon dioxide were measured before and after administration of methadone, 5 mg, or hydromorphone, 0.5 mg, by the intravenous route and by epidural injection in the lumbar or upper thoracic region in 5 subjects. Tolerance to periosteal pressure, cutaneous electrical stimulation and the cold pressor response to ice-water immersion were measured in both upper and lower limbs.

Variation in Food Microbiological Tests Used to Evaluate Analyst Performance.

Procedures for evaluating analyst performance in state and federal milk and food laboratory quality assurance programs depend on the estimates of variation for the methods used. The total components of variance for a method consist of replicate error, among-analysts variance, and analyst-sample interaction components. Eleven methods were evaluated in this study.

Linkage conservation of homologous esterase loci in fish (Cyprinodontoidei: Poeciliidae).

Homologies among esterase isozymes in fish in the poeciliid genera Poeciliopsis and Xiphophorus are proposed. Esterase homologies are based on their tissue distributions and inhibition and substrate properties. The five esterases include two carboxylesterases, one eserine sulfate-sensitive esterase, and two esterases resistant to inhibition, one of which reacts only with acetate esters.

Intermolecular cross-links in collagen of human placenta.

1. There are four reducible cross-links in human placenta collagen. The principal one is dehydrodihydroxylysinorleucine.

Inflammatory fibrous histiocytoma in the left upper abdomen with a leukemoid blood picture.

A case of inflammatory fibrous histiocytoma arising in the left hypochondrium, which presented with a leukemoid reaction and was initially diagnosed as chronic neutrophilic leukemia, is described. The difficulty of interpreting the hematological findings, especially as the spleen appeared to be enlarged, is discussed. The tendency of this highly malignant group of tumors to cause a systemic granulocytosis is commented upon and attention is drawn to the lack of satisfactory treatment.

Effect of an episode of severe malnutrition and age on lactose absorption by recovered infants and children.

The degree of which the ability to absorb lactose can be regained after recovery from an acute episode of severe malnutrition is in doubt. Lactase activity was indirectly assessed by means of a standard lactose tolerance test (2 g lactose per kilogram of body weight) in 71 Peruvian Mestizo infants and children (age 5 to 55 months) who had suffered such an episode. All were studied just before discharge after several months of hospital rehabilitation, during which linear growth and weight gain had accelerated and signs of significant malabsorption of other nutrients had disappeared.

Alkaline hydrolysis of 1,3-dimethylphenobarbital.

The reaction of 1,3-dimethylphenobarbital (I) with 0.02-0.32 M KOH in aqueous methanol was studied.

Genetic dissection of clonally inherited genomes of poeciliopsis. I. Linkage analysis and preliminary assessment of deleterious gene loads.

Theoretical considerations suggest that a high load of deleterious mutations should accumulate in asexual genomes. An ideal system for testing this hypothesis occurs in the hybrid all-female fish Poeciliopsis monacha-lucida. The hybrid genotype is retained between generations by an oogenetic process that transmits only a nonrecombinant haploid monacha genome to their ova.

Influence of a pulp and paper mill effluent on aspects of distribution, survival and feeding of Nipigon Bay, Lake Superior, larval fish.

Surface distribution of Nipigon Bay larval fish was characterized by high abundance, between 500 and 2100 larval fish/10,000 m3 near shore, particularly in proximity to the pulp and paper mill effluent discharge, and low abundance, less than 100/10,000 m3 away from shore. Static bioassay indicated that approximately 60% effluent concentration was intolerable to the natural mixed larval fish community. No wood fibre was found among stomach contents and no difference was apparent in stomach contents of fish caught in influenced and uninfluenced areas.

Regulation of function of transplanted parathyroid glands in man.

The results of studies performed in nine patients who had undergone successful parathyroidectomy and gland transplantation are presented. Transplantation of parathyroid tissue to the forearm, performed for therapeutic reasons, provided a unique opportunity to sample parathyroid gland effluent and to assess secretory function in vivo. The relationship of calcium to immunoreactive parathyroid hormone (iPTH) release was studied during calcium and ethylenediamine tetraacetic acid (EDTA) infusions as well as dialysis against a low calcium bath (low calcium dialysis) in patients with chronic renal failure.

Effects of food deprivation and reinforcement magnitude on conditioned suppression.

In Experiment I, the responding of rats lever pressing on a variable-interval schedule for sucrose solution was partially suppressed by a variable duration conditioned stimulus followed by shock. When food deprivation was increased, response rates during and before the conditioned stimulus increased monotonically. Varying the concentration of sucrose across blocks of sessions or from session to session in a semi-random sequence had little effect on response rates either before or during the conditioned stimulus.

Genetic analysis of natural populations of Poeciliopsis monacha: Allozyme inheritance and pattern of mating.

The genetic bases of seven polymorphic enzymes in Poeciliopsis monacha have been demonstrated through the analysis of allelic segregation in presumed heterozygotes captured in natural populations. Tests of linkage among loci revealed a significant association between two loci, Ldh-1 and Idh-2. Evidence for multiple insemination was detected in 23 percent of the females examined.