Microprobe studies of aluminum accumulation in association with human central nervous system disease

The neurofibrillary tangle, first described by Alzheimer in 1907, along with the senile plaque, represent the two principle neuropathologic lesions identified in the brains of patients with Alzheimer's disease. Aluminum salts inoculated into the central nervous system of certain experimental animals induces neurofilamentous lesions which are similar, but not identical to the neurofibrillary tangles seen in Alzheimer's disease. Although some reports provide evidence of increased amounts of aluminum in the brains of Alzheimer's disease victims, such bulk analysis studies have been difficult to replicate. Over the past several years we have approached this problem using a variety of microprobe techniques in order to determine the distribution of trace elements within individual nerve cells.Using scanning electron microscopy with X-ray spectrometry, we have identified accumulations of aluminum in the neurofibrillary tangle-bearing neurons of cases of Alzheimer's disease. Similar accumulations have been found in the brains of the indigenous natives of Guam who suffer from parkinsonism with dementia and from amyotrophic lateral sclerosis. Recent studies using laser microprobe mass analysis suggest that the predominance of aluminum identified within the parikaryon of neurofibrillary tangle-bearing neurons is located within the neurofibrillary tangle itself. Although this ongoing research still cannot ascribe a causal role for aluminum in the etiology and/or pathogenesis of the neurofibrillary tangle, the data suggest that certain environmental factors related to trace elemental constituents may play an important role in the formation of this type of cellular pathology.     

On the integration of individual foraging strategies with colony ergonomics in social insects: nectar-collection in honeybees

Summary We experimentally tested whether foraging strategies of nectar-collecting workers of the honeybee (Apis mellifera) vary with colony state. In particular, we tested the prediction that bees from small, fast growing colonies should adopt higher workloads than those from large, mature colonies. Queenright small colonies were set up by assembling 10 000 worker bees with approximately 4100 brood cells. Queenright large colonies contained 35 000 bees and some 14 500 brood cells. Thus, treatments differed in colony size but not in worker/brood ratios. Differences in workload were tested in the context of single foraging cycles. Individuals could forage on a patch of artificial flowers offering given quantities and qualities of nectar rewards. Workers of small colonies took significantly less nectar in an average foraging excursion (small: 40.1 ± 1.1 SE flowers; large: 44.8 ± 1.1), but spent significantly more time handling a flower (small: 7.3 ± 0.4 s ; large: 5.8 ± 0.4 s). When the energy budgets for an average foraging trip were calculated, individuals from all colonies showed a behavior close to maximization of net energetic efficiency (i.e., the ratio of net energetic gains to energetic costs). However, bees from small colonies, while incurring only marginally smaller costs, gained less net energy per foraging trip than those from large colonies, primarily as a result of prolonged handling times. The differences between treatments were largest during the initial phases of the experimental period when also colony development was maximally different. Our results are at variance with simple models that assume natural selection to have shaped behavior in a single foraging trip only so as to maximize colony growth. Offprint requests to: P. Schmid-Hempel     

The hydrolytic products of aluminum and their biological significance

The relative distribution of Al between its various organic and inorganic complexes dictates its mobility in the environment, bioavailability, and toxicity. In recent years, there has been significant progress made in understanding the differential bioavailability and toxicity of various chemical species of Al to plants and certain aquatic organisms. Far less information concerning chemical speciation and differential uptake and transport of Al in humans is available. Among the important inorganic complexes of interest are the hydrolyzed-Al species, particularly the nonequilibrium, metastable polynuclear complexes, which form readily, have a fairly wide stability range, and have been demonstrated toxic to plants and fish. In recent years²⁷Al NMR spectroscopy has provided significant direct information on the polynuclear complexes existing in a wide range of aqueous solutions. The [Al₁₂O₄(OH)_24+n(H₂O)_12–n]^(7–n)+ polynuclear complex is often found to be the predominant species in partially neutralized Al solutions and has recently been demonstrated to be more toxic to certain plants than the hexaaqua Al cation. It is also the principal component of Al-chlorohydrate, a highly soluble antiperspirant, present in many hydrolyzed Al solutions utilized in water and waste water treatment, and, as hypothesized herein, a primary constituent of many hydroxide gels utilized as antacids. This polynuclear has a wide pH stability range, reportedly forms copolynuclears with Si, and contains tetrahedrally coordinated Al within its structure, all features that may be relevant to the recently reported properties of Al associated with neuritic plaque cores.     

Parental investment decision rules and the Concorde fallacy

Summary Investment theory states that animals should base their parental investment decisions on expected benefits, and not on whether or not past investment will be wasted. Otherwise, they would comnit the Concorde fallacy. If reproduction has a cost, however, then past investment and expected benefits are necessarily confounded. Assuming a cost of reproduction, animals will be selected to maximize their remaining lifetime reproductive success, subject to a tradeoff between present and future reproduction (Williams' principle). We extend Williams' principle and develop an experimental design that would allow past investment and expected benefits to be varied independently. This design illustrates the importance of the value of the brood relative to the value of future reproduction.