Electroencephalographic changes in the lateral septum complex following systemic administration of DES-TYR1 -α-endorphin,Des-Tyr1-γ-endorphin and haloperidol in rats

The influence of systemically administered Des-Tyr¹-α-endorphin (DTαE), Des-Tyr¹-γ-endorphin (DTγE) and haloperidol on electroencephalographic (EEG) activity of the lateral septum complex (LSC) and the frontal cortex was studied in male rats. DTαE (2 μg) significantly increased whereas DTγE (10 μg) significantly decreased the amounts of activity in the 5 Hz band. In addition, DTαE promoted production of 15 - 20 Hz activity, while DTγE decreased the amount of 20 - 30 Hz activity. EEG activity exhibited a marked variability which persisted throughout the recording session following administration of the peptides. Haloperidol markedly decreased the proportion of 10 - 15 Hz activity. The alterations in EEG of the frontal cortex were similar to those in LSC but less pronounced. The differences in the time course and frequency bands affected suggest that the effects of peptides and haloperidol on EEG activity of LSC are not mediated by the same mechanisms.     

Modulation by dopamine of population spikes in area CA1 hippocampal neurons elicited by paired stimulus pulses

Extracellular recording techniques were used to study the effects of dopamine on postactivation excitability of rat area CA1 hippocampal neurons maintained in vitro. Population spikes were elicited by delivery of conditioning and test stimulus pulses to afferent fibers. The interval between the conditioning and test volley was set to separate delivery of stimuli by 10 to 80 msec. The effect of superfusion or microtopical application of dopamine (DA) on population responses to test stimulus pulses was studied. When paired stimulus volleys, separated by brief intervals (up to 40 msec), were delivered to afferent fibers, paired-pulse suppression (PPS) was indicated by the amplitude of the population spike elicited by the test volley being smaller than that elicited by the conditioning volley. When paired volleys were separated by longer intervals (40 to 80 msec), the response elicited by the test volley was larger in amplitude than that elicited by the conditioning volley, indicating paired-pulse facilitation (PPF). Following exposure to DA, the amplitude of the population response elicited by the conditioning volley was larger than the amplitude before exposure to DA. This effect was long-lasting, enduring for tens of minutes. However, when the amplitude of the conditioning population response was held constant, the PPS was decreased, indicating disinhibition. It is suggested that dopamine produces a long-lasting attenuation of an intervening inhibitory influence onto CA1 pyramidal neurons.     

Biogeographical patterns and Rapoport's rule in southeastern Pacific benthic polychaetes of the Chilean coast

Recently three biogeographical units were identified along the Chilean coast (the Magellanic Province, an Intermediate Area, and the Peruvian Province), however few studies have focused on the factors and dynamic processes that formed these spatial units (e.g. Rapoport's rule and its causal mechanisms). In this study we used benthic polychaetes of the Chilean coast to evaluate patterns of latitudinal distribution and species richness, and the existence of the three main biogeographical provinces described for the Chilean coast. Additionally, we evaluated the latitudinal Rapoport effects and geometric constraint as a null hypothesis explaining the species richness distribution.
We found that benthic polychaete diversity increased towards southern latitudes. The cluster and ordination (non-metric MultiDimensional Scaling, nMDS) analyses of the distribution data, presented only two statistically significant (bootstrapping techniques) biogeographic provinces along the Chilean coast, with a break occurring between 41° and 42°S. While, our results did not support a latitudinal Rapoport effect, they did support the view that latitudinal Rapoport effects are a local phenomenon, occurring only for the Northeastern Pacific marine taxa. The relationship between latitudinal range extent and mean latitude indicated the existence of two hard boundaries at either extreme of the Chilean coast, limiting the geographical ranges of the species. However, geometric constraints tested using a Monte Carlo simulation approach showed a weak level of mid-domain effect on species richness. Finally, we propose that geometric constraint together with the geomorphology and historical characteristics of the Chilean coast explain the biogeographical patterns of benthic polychaete taxa in Chile.     

Potential interspecific competition and host specificity: hispine beetles on Heliconia

Abstract. 1. Adults of rolled-leaf hispine beetles (Chrysomelidae, Coleoptera) spend their lives in the scrolls formed by immature leaves of Heliconia (Heli-coniaceae, Monocotyledonae) in Tropical America. As many as eight hispine species can intermingle in the host scrolls at a single site. Scrolls of single host species are invariably occupied by adults of more than one hispine species, and as many as five species can simultaneously occupy one scroll.
2. I made virgin scrolls, which had never contained any insects, by growing leaves under the cover of plastic bags.
3. Thirty-seven combinations of single hispine and Heliconia species were experimentally created in the virgin scrolls, at two sites and in two seasons, in Costa Rica. Combinations included all abundant host species at the sites.
4. All beetles left all leaves of the twenty-eight unnatural beetle—host combinations, within 24 h. On the other hand, none of the nine natural combinations was completely abandoned within the experimental period.
5. Thus, host specificity is not broader in the absence of similar hispine species that might be competitors, and interspecies competition does not affect this obvious aspect of resource utilization for these phytophagous insects.     

Incorporation of biological information in cancer risk assessment: Example — Vinyl chloride

Vinyl chloride (VC) is used as an example to demonstrate how biological information can be incorporated into quantitative risk assessment. The information included is the pharmacokinetics of VC in animals and humans and the data-generated hypothesis that VC primarily affects the initiation stage of the multistage carcinogenesis. The emphasis in this paper is on the improvement of risk assessment methodology rather than the risk assessment of VC per se.Sufficient data are available to construct physiologically-based pharmacokinetic models for both animals and humans. These models are used to calculate the metabolized dose corresponding to exposure scenarios in animals and in humans.On the basis of the data on liver angiosarcomas and carcinomas in rats, the cancer risk per unit of metabolized dose is comparable, irrespective of routes (oral or inhalation) of exposure. The tumor response from an intermittent/partial lifetime exposure is shown to be consistent with that from a lifetime exposure when VC is assumed to affect the first (initiation) stage of the multistage carcinogenic process. Furthermore, the risk estimates calculated on the basis of animal data are shown to be consistent with the human experience.     

Characterization of circadian oscillations in alanine dehydrogenase activity in non-dividing populations of Euglena gracilis (z)

Possible factors that could generate the circadian oscillations in alanine dehydrogenase (EC 1.4.1.1.) activity observed in cultures of non-dividing Euglena gracilis (Z) have been examined in an effort to learn more about the basic timekeeping mechanism of biological clocks. No differences in K_m, pH optimum or electrophoretic mobility could be demonstrated between enzyme extracted from the minimum part of the 24-h oscillation in activity and that extracted from the maximum part. Also, no evidence for the presence of activators or inhibitors was found in mixing experiments. The effect of cycloheximide on the rhythm was examined; it was shown that the oscillation ceases in the presence of the inhibitor, but that if the inhibitor is removed after 12 h, the rhythm resumes with no apparent change in phase. Analyses of gel scans of enzyme preparations partially purified by (NH₄)₂SO₄ fractionation and polyacrylamide gel electrophoresis indicated that there was more alanine dehydrogenase protein present at the maximum part of the cycle than there was at the minimum part. In view of these and other data, an operational model of a circadian biological clock is discussed.