Avoidance learning in rats: Genetic evidence for two distinct behavioral processes in the shuttle box.

Used an 8 * 8 diallel cross of rats (Roman high, low, and control avoidance; Maudsley reactive and nonreactive; Tryon maze bright and dull; and Wistar albino) to analyze sequentially a conditioned avoidance response (CAR) within a session of 30 trials. On early conditioning trials, the F1 hybrids scored fewer avoidances than the parental strains, whereas on later trials the hybrids were superior to parents. This finding was confirmed within a session of 100 trials in a 3 * 3 diallel and interpreted to mean that 2 distinct adaptive behavior patterns underlie shuttle-box CAR acquisition in rats. There appears to be a tendency to develop an adaptive inactivity or "freezing" behavior pattern and later, as conditioning proceeds, to develop an equally adaptive but more active behavior pattern of "fleeing." Implications for 2-process theories of avoidance conditioning are considered briefly. (20 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The influence of acute diazepam pretreatment on the action and disposition of [14C]pentobarbital in rats

Diazepam (DZP) pretreatment (100mg/kg, ip) of rats 6 h before pentobarbital administration (45 mg/kg, ip) prolonged the barbiturate-induced narcosis. The concentrations of [14C]pentobarbital and total pentobarbital derivatives in blood or brain showed no differences between control and DZP-pretreated animals. The brain and blood concentrations of pentobarbital, when measured at a time corresponding to the respective arousal times from pentobarbital narcosis, were lower in the DZP-pretreated group. These results indicate that acute DZP pretreatment increases the sensitivity of the rat brain to pentobarbital rather than inducing changes in the disposition of the barbiturate.     

Electron microscopic study of the rat submaxillary gland during development

Cytological changes in the submaxillary glands of rat embryos of the 14th-21st days of the intrauterine development and of 7-day-old rats were studied electron microscopically. The cytoplasm of the salivary gland primordium cells of the 14-day embryo was found to possess multiple polysomes, the canals of the granular cytoplasmic network (GCN) being solitary. The latter elongated in the process of embryonic development, and later predominant development of GCN was observed in basal portions of the acinar cells. At early stages of the gland development the GCN was often observed to approximate mitochindria. The laminar complex in the course of embryonic development enlarges its size and at later stages it has a well differentiated appearance in the acinar cells. Secretory inclusions make their appearance in the forming cells of acinuses long before birth, the composition of the embryo gland secretion being somewhat different from that of adult animals. Differentiation of acinuses and striated parts of the salivary tubules is well pronounced in the embryonic period while no signs of appearance of granular portions of the salivary tubules are observed both in light and electron microscopy either in embryos or in 1-week-old rats.     

Possible enzyme deficiency in bovine lymphosarcoma cells grown in vitro

A culture of bovine lymphosarcoma cells was unable to grow in HAT medium, suggesting that the cells were unable to use either exogenous hypoxanthine or exogenous thymidine. Further work showed that they were able to incorporate tritiated thymidine but not tritiated guanine. This indicated that failure to grow in HAT medium was due to the cells being deficient in the enzyme hypoxanthine guanine phosphoribosyl transferase which is responsible for incorporation of the bases hypoxanthine and guanine. This finding may have application in the therapy of bovine lymphosarcoma.     

Cancer and dysplasia of the post-hysterectomy vaginal cuff

The localization of delta5-3beta-hydroxysteroid dehydrogenase activity was demonstrated histochemically in the neonatal mouse ovary. Histochemical studies were also undertaken in an attempt to investigate the effects of gonadotropic deprivation from birth to age 7 or 14 days on the distribution of enzymatic activity. Between birth and the age of 2 weeks, delta5-3beta-hydroxysteroid dehydrogenase activity was observed in virtually all follicles. In the newborn mouse ovary, the activity was found in granulosa cells of follicles developing in the center of the organ. On the 14th day, the granulosa cells of some apparently normal follicles histochemically were relatively inert, while others, obviously atretic, demonstrated extensive, localized, diformazan granules. Deprivation of endogenous circulating gonadotropin by daily injections of anti-rat gonadotropin had specific effects on follicular development and histochemical patterns in animals deprived of gonadotropins for 14 days but not for only 7 days.     

Circadian responsiveness of the hypothalamic-pituitary axis

Five healthy men 25-38 years old were subjected to simultaneous composite intravenous stimulation tests of insulin hypoglycemia (0.1 U/kg), thyrotropin-releasing hormone (TRH, 100 mug), and luteinizing hormone-releasing hormone (LHRH, 50 mug) at weekly intervals to study the circadian responsiveness of the hypothalamic-adenohypophyseal axis at 0600, 1200, 1800, and 0000 hours. Blood sugar (BS), LH, follicle-stimulating hormone, TSH, prolactin, cortisol (C), growth hormone, and testosterone (T) levels were estimated before and after the administration of drugs. Comparisons were made between basal and delta values (difference between basal and peak or nadir levels) at different tests. Significant circadian variations in BS, GH, C, and, to a lesser extent PRL, responses were observed 0600 h basal and delta BS values were the lowest, delta BS was highest at 0000 h accompanied by maximal hypoglycemic symptoms; the delta values of both C and GH were significantly higher at 0600 h and 0000 h; highest mean delta PRL was observed at 0600; at 1800 h the basal plasma PRL level was maximum but the delta PRL was lowest. Plasma TSH, LH, and FSH responses did not show significant circadian variations. These results suggest that circadian variations are evident when stimuli act through central or hypothalamic mechanisms; however, direct stimulation of the adenohypophysis resulted in indentical responses at different periods tested.     

Oxygenation-linked subunit interactions in human hemoglobin: experimental studies on the concentration dependence of oxygenation curves

An experimental study on the concentration dependence of oxygenation curves for human hemoglobin has been carried out between 4 X 10(-8) M heme and 5 X 10(-4) M heme in 0.1 M tris(hydroxymehtyl)aminomethane hydrochloride, 0.1 M NaCl, 1 mM disodium ethylenediaminetetraacetic acid, pH 7.4, 21.5 degrees C. With decreasing hemoglobin concentration the curves show pronounced shifts in position and shape, consistent with dissociation of tetrameric hemoglobin into dimeric species of high affinity and low cooperativity. Combination of these data with independently determined values of dissociation constants for unliganded and fully liganded hemoglobin permits a resolution of the seven parameters necessary to define the linked binding and subunit association processes. The total oxygenation-linked subunit dissociation energy (6.34 kcal) was resolved into intersubunit contact energy changes between alphabeta dimers in tetrameric hemoglobin which accompany binding of the first, middle two, and last oxygen molecules. The resolution is accurate to within approximately +/-0.3 kcal. To within this limit the isolated dimers are found to bind oxygen noncooperatively and with the same affinity as isolated alpha and beta chains. Equally good fits to the data are obtained when dimers are slightly anticooperative. At least three major energetic states are apparently assumed by hemoglobin tetramers, with respect to the alpha1beta2 contact region, corresponding to (a) unliganded, (b) singly liganded, (c) triply and quadruply liganded species. The results do not establish whether these states may be assumed by a single molecule, or whether they arise as averages over a distrubution of conformational states. They do provide unequivocal evidence against a concerted transition at any particular binding step in a system with only two energetic states of tetramer (i.e., an all or none switchover between T and R states at a particular binding step).