Ultrastructural localization of the high molecular weight proteins associated with in vitro-assembled brain microtubules

Microtubules isolated from brain extracts by in vitro assembly (1, 19, 23) are composed principally of two tubulins and two high molecular weight proteins (microtubule-associated proteins [MAPS] 1 and 2) (2,5,7,20). Recently, it was demonstrated that in vitro-assembled brain microtubules (neurotubules) are coated with filaments (5, 7) which are similar to the filaments attached to neurotubules in situ (4, 15, 21, 24, 25), and it was suggested that the filaments are composed of the higher molecular weight MAPs (5, 7, 12). In this study, microtubules were assembled in the presence and absence of the MAPs, and thin sections of the microtubules were examined by electron microscopy. The results show that the filaments only occur on microtubules assembled in the presence of the MAPs and it is therefore concluded that the filaments are composed of the high molecular weight MAP's.     

Isolated Brain Microvessels as In Vitro Equivalents of the Blood-Brain Barrier: Selective Removal by Collagenase of the A-System of Neutral Amino Acid Transport

On treatment with collagenase, brain microvessels, together with several protein components, lose some enzymatic activities such as alkaline phosphatase and gamma-glutamyltranspeptidase, whereas no change occurs in the activities of 5'-nucleotidase and glutamine synthetase. The energy-requiring "A-system" of polar neutral amino acid transport is also severely inactivated, whereas the L-system for the facilitated exchange of branched chain and aromatic amino acids is preserved. In the collagenase-digested microvessels, this leads to loss of the transtimulation effect of glutamine on the transport of large neutral amino acids, because such transtimulation is due to a cooperation between the A- and L-systems. By contrast, NH4+ maintains (and even enhances) its ability to stimulate the L-system of amino acid transport, presumably through glutamine synthesis within the endothelial cells.     

The Histochemical Detection of Thallium in Paraffin-Embedded Tissues by the Sulfide-Selenium-Silver Method

Thallium can be histochemically localized in formalin-fixed, paraffin-processed tissues by treating sections, after passing them through xylene and graded alcohols to water, with gaseous H₂S for 15 min and with 20% ammonium sulfide saturated with powdered selenium for 10 min. Sections are then washed, treated 10 min with 20% H₂O₂, and incubated in darkness for 20-30 min in the following mixture: 25% gum acacia, 10 ml; 2% hydroquinone in 5% citric acid, 1 ml; and 10% AgNO₃, 0.1 ml. Tissues and cells, which contain thallium, are demonstrated by small black granules of silver.