Effects of L-methionine-DL-sulphoximine on the assimilation of newly fixed NH3, acetylene reduction and heterocyst production in Anabaena cylindrica.

The addition of exogenous L-methionine-DL-sulphoximine (MSO) to N₂-fixing cultures of the blue-green alga Anabaena cylindrica results in over half of the newly fixed NH₃ being released into the medium. MSO also inhibits glutamine synthetase (GS) activity, has negligible effect on alanine dehydrogenase activity, and glutamate dehydrogenase activity under N₂-fixing conditions is negligible. In the presence of MSO, intracellular pools of glutamate and glutamine decrease, those of aspartate and alanine + glycine show little change, and the NH₃ pool increases. MSO alleviates the inhibitory effect of exogenous NH₄⁺ on nitrogenase synthesis and heterocyst production. The results suggest that in N₂-fixing cultures of A. cylindrica the primary NH₃ assimilating pathway involves GS, and probably glutamate synthase (GOGAT), and that the repressor of nitrogenase synthesis and heterocyst production is not NH₄⁺ but is GS, GOGAT, or a product of their reactions.     

Pyruvate and nitrogenase activity in cell-free extracts of the blue-green alga Anabaena cylindrica

When extracts of $\text{Anabaena cylindrica}$ are prepared in the absence of dithionite, they catalyze pyruvate-dependent acetylene reduction, a reaction not observable in assays containing dithionite. Ferredoxin and coenzyme-A, but not NADP and ferredoxin-NADP reductase, are required for maximal pyruvate-dependent activity. These acetylene-reducing extracts do not exhibit NADP-pyruvate dehydrogenase activity. However, pyruvate:ferredoxin oxidoreductase is present at levels of activity sufficient to support the $\text{in vitro}$ rate of pyruvate-supported acetylene reduction. These $\text{in vitro}$ data support earlier $\text{in vivo}$ evidence that pyruvate:ferredoxin oxidoreductase transfers electrons from pyruvate to nitrogenase in $\text{A. cylindrica}$.     

Connections between descending visual interneurons and metathoracic motoneurons in the locust

Summary Connections between the four DMD neurons and metathoracic motoneurons in the locustSchistocerca were examined by recording extracellularly from the interneurons in the pro-mesothoracic connectives and intracellularly from seventeen motoneurons. A DIMD or DCMD spike causes an EPSP in the fast extensor tibiae motoneuron, which can be modified by changing the membrane potential. The EPSP always follows spikes at frequencies up to 200 Hz and with a latency of 0.9 ms, suggesting that the connections are monosynaptic and chemically mediated. EPSPs from the DIMD or DCMD arrive at the same time, their axons having the same conduction velocity, and appear simultaneously in the fast extensor tibiae motoneurons on both sides of the ganglion. There is spatial and temporal summation between the inputs but on no occasion did the motoneurons spike. Three inhibitory neurons are depolarized by DMD inputs and may on occasion spike, but it is not known whether these connections are direct. Similarly the slow excitatory motoneuron to the anterior coxal adductor muscle is hyperpolarized by DMD input. Other leg, flight or ventilatory motoneurons examined received no inputs from the DMD neurons. The connections shown are consistent with the hypothesis that the DMD neurons are in some way involved with initiation of a jump, but to achieve this must act synergistically with other inputs. This work was supported in part by USPHS grant No. NS 09404-03 to C.H.F.R. Dr. Rowell wishes to thank Dr. J. Phillipson for the use of facilities in the Oxford Department of Zoology during sabbatical leave.     

The effects of lime and phosphorus on the function of wheat roots in acid top soils and subsoils

Two wheat varieties with differing aluminium tolerance were grown in pots of acid soil. Liming did not change significantly the amounts of chemically extractable P and K, but caused improved vegetative growth, increased inflow of P and K and reduced uptake of Al. Without lime, roots had a higher content and concentration of P than shoots; liming reversed this. Without lime the sensitive variety with a shorter root length had an Al inflow ten times that of the tolerant one: tolerance involves a mechanism for exlcuding Al. The inflow of P per unit inflow of Al (mol ratio) without lime was three times greater for the tolerant variety which therefore has more P to counteract the effects of Al. The same varieties were grown in two-layer soil columns, with a low P status and a limed topsoil and acid subsoil. Liming the subsoil improved plant growth but this was still restricted by low P availability. Addition of P to the topsoil caused good growth regardless of subsoil acidity: root growth increased in both layers and P (labelled with³²P) taken up from the topsoil was translocated to roots in the subsoil. This P inactivated root Al and allowed the roots to grow and take up more P from the acid subsoil with however a reduction in inflow. The sensitive variety was affected more by the acid subsoil and low P availability, had a similar ability to translocate P to subsoil roots but could not attain the growth rate of the tolerant wheat even with P and lime.     

Stimulation of [3H]Dopamine Release by Nicotine in Rat Nucleus Accumbens

Abstract: The mesolimbic system of the brain has been shown to be involved in the reward properties of a number of agents. It is possible that release of monoamines by nicotine in this brain area could be related to the pleasurable aspects related to cigarette smoking. In this investigation, the effect of nicotine on the release of [³H]dopamine in the nucleus accumbens of the rat was studied. It was shown that nicotine produced a concentration-dependent increase in [³H]dopamine release at concentrations of 0.1 μ M and above. The increase in release was found to be almost completely calcium dependent. The nicotine-induced release was only partially blocked by the nicotinic antagonists hexamethonium and d -tubocurarine. A number of cholinergic agonists, as well as other compounds, were tested for their capacity to mimic the effect of nicotine. At equimolar concentrations there was, at most, only 50% of the activity of nicotine. The results of this study demonstrate that nicotine stimulates the release of dopamine in the nucleus accumbens at concentrations similar to those in the blood of cigarette smokers. This suggests that the release of mono-amines in specific nuclei of the mesolimbic system may be an important determinant of the desire to smoke cigarettes.     

The ontogeny of sex differences in the behavior of patas monkeys

Many studies of sex differences in primates have been based on small experimental groups of peers in which only a limited range of social behavior could be expressed. In addition, the first few months of life are often the focus of such studies, with relatively little attention paid to older juveniles. In this study, 11 male and 9 female juvenile patas monkeys, living in a captive social group with all age-sex classes available, were observed between 1 and 4 years of age. A subset of seven patas monkeys was also observed between birth and 1 year of age. Here, we report the development of sex differences in independence, play, grooming, positioning behavior, and aggression over the juvenile period. Juvenile male patas monkeys played more and in longer bouts than females, but wrestling (rough-and-tumble play) was not more common among males. There were few differences in behaviors directed to male and female juveniles by other group members. Distinct differences emerged only in the behaviors of the juveniles themselves, with females being more active participants in social and aggressive interactions than males. In general, sex differences in patas monkeys show a mixture of patterns, some of which are predictive of adult sex differences and some of which appear to be specific to the particular demands of the juvenile period in this species     

Brain and serum levels of choline and lecithin resulting from longterm administration

Choline and phosphatidylcholine tissue concentrations were examined in mice treated with long-term (18–22 month) dietary choline enrichment, choline deficiency, or phosphatidylcholine enrichment. There were no significant differences found in choline levels among the dietary groups in any of the tissues examined: plasma, erythrocytes, cortex, hippocampus, and striatum. In contrast, the concentration of phosphatidylcholine in both the choline enriched and phosphatidylcholine enriched groups were significantly increased in the cortex, compared to the choline deficient group, and in the striatum, compared to control. No differences in phosphatidylcholine concentration were found in the hippocampus or plasma between any of the dietary groups. These results are in contrast to the reported effects of acute or short-term choline and phosphatidylcholine treatment and indicate that there may be differences between the effects of short-term and long-term administration on the blood and brain levels of choline and phosphatidylcholine.