Direct determination of homovanillic acid release from the human brain, an indicator of central dopaminergic activity

The plasma concentration of the dopamine (DA) metabolite, homovanillic acid (HVA), is used as an indicator of central nervous system dopaminergic activity. Using percutaneously inserted catheters we were able to obtain blood samples simultaneously from the right and left internal jugular veins. Veno-arterial HVA plasma concentration differences combined with adjusted organ plasma flows were used, according to the Fick Principle, to determine the HVA overflow from the brain. The HVA overflow from the liver was also measured. HVA overflow from the brain represented 12% of the total body HVA production. A similar amount was released from the liver, illustrating the limited validity of peripheral plasma HVA measurements as an indicator of central dopaminergic activity. HVA release from the human brain displayed a degree of asymmetry, the overflow into the left internal jugular vein being 36% greater than that into the right. Cerebral venous blood flow scans indicated that cortical cerebral regions drained preferentially into the right internal jugular; by inference the higher HVA overflow on the left originated from dopamine-rich subcortical brain areas. Since HVA in plasma may arise from the metabolism of DA existing either as a neurotransmitter or a norepinephrine (NE) precursor we measured the internal jugular vein plasma concentrations of NE, and its metabolite dihydroxyphenylglycol (DHPG), to determine whether they displayed a similar pattern of release to HVA. The overflow of both NE and DHPG into the right internal jugular vein was approximately double that on the left. Since the overflow of HVA did not parallel that of NE and DHPG it may be inferred that the origin of much of the subcortically produced HVA is from dopaminergic neurons and not from the metabolism of precursor DA in noradrenergic neurones or cerebrovascular sympathetic nerves.     

Comparative study of conjugation between horseradish peroxidase and D-cytochrome b5. Incorporation into subcellular membranes

Horseradish peroxidase was conjugated to D-cytochrome b5 by three different two-step methods. The yield of conjugates based on the peroxidase enzymatic activity recovered after gel filtration was very low in the glutaraldehyde method, but higher in the N-succinimidyl 3-(2-pyridyldithio)propionate (SPDP) and periodate methods. The molecular size of the conjugates was analyzed by sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis. Monomeric conjugates were mostly formed via the glutaraldehyde and SPDP methods in the presence of appropriate molar ratios of proteins. Most of the conjugates formed via the periodate method were polymers. The conjugate preparations of the three methods could be incorporated into microsomal membranes. Conjugate polymers, however, appeared less able to be incorporated then monomers. There was a nonpreferential incorporation of free or conjugated D-cytochrome b5 contained in the conjugate preparation of the glutaraldehyde method. In conclusion, this study gives preference to the glutaraldehyde method for the preparation of conjugates that will subsequently be used as an in vivo marker of the D-cytochrome b5 incorporation into membranes.     

Phosphorus limitation in some tropical African lakes

Two of three Kenyan lakes studied between November 1979 and October 1980 have very short ³³PO₄ turnover times, indicating a high phosphorus (P) demand throughout the year. The P turnover time in Lakes Oloidien and Sonachi is as rapid as in the most P deficient temperate zone lakes. The third lake, Lake Naivasha, has a lower overall P demand and a wide seasonal range, with lowest demand between November 1979 and February 1980 when a P deficiency was unlikely. On an annual basis the Lake Naivasha status is, however, not statistically different from that recorded during the summer in Lake Memphremagog, a generally P-limited temperate zone lake. Lake Naivasha and Lake Oloidien fit well to the line of best fit for the Dillon-Rigler relationship relating total phosphorus (TP) and chlorophyll a derived in temperate zone lakes. Thus, temperate zone models predicting aspects of lake behaviour on the basis of TP may also be applicable to these two tropical lakes. Saline lake Sonachi had not only a short P turnover time but also responded dramatically to the fertilization of enclosures with P. However, it does not fit the TP-chla or the total nitrogen-chla plots from the temperate zone. This suggests that, in this saline lake at least, much of the TP is unavailable to the algae, with some of it in a particulate form that is readily extracted with boiling water. The epilimnetic N:P ratios also characterize lakes Oloidien and Sonachi lakes as highly P deficient and lake Naivasha as more moderately P limited. A single set of measurements in Winam Gulf (Lake Victoria) also showed a rapid P turnover time and thus P limitation, but as in lake Sonachi much of the TP was in a non-algal particulate form. Occasional measurements in three other hypertrophic and saline lakes suggest them to be primarily light limited on the basis of their very high photosynthetic cover. These findings support the hypothesis of a primary P limitation for those lakes not light limited, and contradicts literature suggestions that nitrogen is the primary limiting element in tropical lakes.     

Interpreting CARS images of tissue within the C–H‐stretching region

Single band coherent anti‐Stokes Raman scattering (CARS) microscopy is one of the fastest implementation of nonlinear vibrational imaging allowing for video‐rate image acquisition of tissue. This is due to the large Raman signal in the C—H‐stretching region. However, the chemical specificity of such images is conventionally assumed to be low. Nonetheless, CARS imaging within the C—H‐stretching region enables detection of single cells and nuclei, which allows for histopathologic grading of tissue. Relevant information such as nucleus to cytoplasm ratio, cell density, nucleus size and shape is extracted from CARS images by innovative image processing procedures. In this contribution CARS image contrast within the C—H‐stretching region is interpreted by direct comparison with Raman imaging and correlated to the tissue composition justifying the use of CARS imaging in this wavenumber region for biomedical applications. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Phytoplankton and its dynamics in two tropical lakes: a tropical and temperate zone comparison

Temporal patterns of phytoplankton biomass and community structure are described for two Kenyan lakes and subsequently compared with patterns reported in other tropical and temperate lakes. Lake Naivasha had a lower and more seasonally variable (10×) biomass, with a seasonal shift between diatoms and blue-greens, while the L. Oloidien biomass was less variable (3.7×) and dominated by blue-greens. Biomass and chlorophyll a were strongly correlated and in turn were coupled to the level of total phosphorus. A total of 143 and 94 taxa were described for L. Naivasha and L. Oloidien, respectively.The comparative analysis showed: a) a paucity of exclusively tropical species; b) that more than 30 percent of the species in two highly saline Kenyan lakes were also present in the two freshwater lakes; c) no evidence for a postulated decline of phytoplankton species abundance with latitude from the temperate zone to the tropics; d) that the low fraction of chrysophyte biomass in tropical lakes is a function of trophy rather than of latitude; e) that the fraction of chlorophyte biomass in tropical lakes is generally higher than in temperate lakes; f) that the proportion of nannoplankton in the two Kenyan freshwater lakes is not different from that in temperate lakes of the same trophy; g) that seasonal or annual biomass oscillations in the tropics are not systematically lower than in the temperate zone; h) evidence for large inter-year difference in the max.:min. biomass ratio in the only tropical lake (L. Naivasha) for which such data are available; i) that an average biomass ratio appears predictable for tropical lakes from the proportion of the sediment surface in contact with epilimnetic water. Overall, no evidence was found that the freshwater tropical phytoplankton composition or dynamics differ in any fundamental fashion from that observed in the temperate lakes during the summer.Contribution number 147 of the Limnology Research Centre, McGill University.