Antonio V. Lorenzo

Inhibition of penicillin transport from the cerebrospinal fluid after intracisternal inoculation of bacteria.

The effect of intracisternal inoculation of bacteria on the choroid plexus system, which transports penicillin from cerebrospinal fluid (CSF) to blood, was studied in vitro and in vivo. Meningeal and choroid plexus inflammations as well as CSF pleocytosis were induced in rabbits with intracisternal inoculations of Hemophilus influenzae or Staphylococcus aureus. At various times after bacterial inoculation, the choroid plexuses of the inoculated rabbits were removed and incubated in artificial CSF containing [(14)C]penicillin. The ability of the choroid plexuses to accumulate pencillin in vitro was measured and was found to be depressed as compared with controls. This depression of choroid plexus uptake reversed with resolution of the inflammatory process. In vivo on the day after intracisternal inoculation of Hemophilus influenzae, a decrease in the disappearance of penicillin relative to inulin in the inoculated rabbits (as compared to the controls) was observed when [(14)C]penicillin and [(3)H]inulin were injected intraventricularly and cisternal CSF was sampled 2 h later. This decrease could not be explained by penicillin binding to the CSF exudate. However, the choroid plexus transport system for penicillin was only partially depressed in those inoculated rabbits with bacterially induced inflammation, since in vitro the choroid plexuses could still accumulate penicillin and in vivo CSF penicillin levels could be further increased with probenecid pretreatment. These results suggest that CSF penicillin levels are increased in this model due to three factors: a depression of active efflux of penicillin from the CSF, an increase in permeability to penicillin of inflamed meninges, and, less significantly, by CSF binding of penicillin.

AMINO ACID TRANSPORT BY CHOROID PLEXUS IN VITRO

Choroid plexus from mongrel cats was incubated from 1 to 120 min in artificial cerebrospinal fluid containing α‐amino[1‐14C]isobutyric acid. The uptake of α‐amino [1‐14C]isobutyric acid occurred against a concentration gradient, was saturable, dependent on metabolic energy, and inhibited by natural amino acids. These results indicate that a transport mechanism is present in choroid plexus which could serve to regulate amino acid concentration in the cerebrospinal fluid of animals.

The origin of myo-inositol in brain, cerebrospinal fluid and choroid plexus

UNBOUND myo-inositol (inositol) is present in brain, CSF and choroid plexus at concentrations higher than in plasma (SP~CTOR & LORENZO, 1975). In fasted rabbits, 68, 21. and 3% of the total unbound inositol in CP, CSF and brain, respectively, entered these structures from the plasma during an 18 h period (SPECTOR & LORENZO, 1975). The transport system for inositol from plasma into CP, CSF and brain could be saturated by increasing the plasma concentration of inositol; a locus of the inositol transport system appeared to be the CP (SPECTOR & LOR-

Cerebrospinal fluid formation and absorption and transport of iodide and sulfate from the spinal subarachnoid space

Abstract Numerous studies have demonstrated transport mechanisms within the cerebral ventricles which regulate the concentration of solutes within the cerebrospinal fluid (CSF) in vivo. Furthermore, studies of choroid plexus transport in vitro indicate that ependymal cells play a major role in these active regulatory mechanisms. Unfortunately, less attention has been given to the possibility that such mechanisms may exist in extraventricular compartments such as the spinal subarachnoid space (SSS). Ventriculo-lumbar, ventriculo-cisternal and cisternal-lumbar perfusions were performed in anesthetized cats to study bulk formation and absorption of spinal subarachnoid fluid (SSF), and the clearance of radioiodide and sulfate from the SSS. The results obtained are summarised in Table 4. Finally, the results indicate that non-ependymal tissues or cells are capable of actively transporting iodide from the SSF to blood. The probable locus of this transport mechanism and its relation to the “sink” hypothesis are discussed.

Changes in Blood-Brain Permeability during Pharmacologically induced Convulsions

Publisher Summary Disturbances of the normal functions of the “blood–brain barrier” are well known following a large variety of pathological stresses. Relatively less attention has been directed toward the transient alterations in solute exchange between blood and brain that may accompany less destructive stimuli. Such alterations may be significant in the pathogenesis of certain disorders of central nervous system function. In this chapter, experiments on temporary alterations in the entry of sulfate into brain were found to accompany pharmacologically-induced convulsions. Marked concomitant changes in brain surface pH, oxygen and carbon dioxide tensions were recorded by direct measurement during the convulsion. As a result of these observations, the influence of hypercapnia and acidosis on brain vascular permeability was studied in some detail. Sulfate and albumin were employed as indicators. The chapter mainly deals with: The effects of pharmacologically induced convulsions on the penetration of sulfate into cat brain, the effect of Metrazol on the penetration of albumin into cat brain and the effect of hypercapnia on the penetration of sulfate and albumin into the brain. As a conclusion, the chapter states that hypercarbia had a profound effect on vascular permeability in some regions of the brain while sparing others.

GABA transport by nerve ending fractions of cat brain.

Abstract— Nerve ending and mitochondrial fractions were prepared from cat cerebral cortex by differential and sucrose density gradient centrifugation. The isolated fractions were characterized morphologically and enzymatically and the nerve‐ending fraction was shown to be particularly rich in glutamate decarboxylase activity. The uptake of [3H] γ‐aminobutyric acid (GABA) was studied by trapping the particles on a Millipore filter.

Factors governing the composition of the cerebrospinal fluid

The inability to readily alter the level of compounds within the cerebrospinal fluid (CSF) following drastic alterations in plasma concentrations has given rise to the concept that solute concentration within the cerebrospinal fluid is closely regulated. It appears that various factors associated with material transfer between cerebrospinal fluid and surrounding tissue and metabolic processes within cells adjoining the CSF compartment are involved in the control of both endogenous and exogenous compounds within this fluid. Of considerable importance in the overall homeostasis are the specific transport mechanisms which facilitate the passage of hydrophilic substances across the membranes which separate the blood from the CSF (blood-CSF barrier) and, in part, act to regulate the concentration of these substances within the CSF. As determined from ventriculocisternal perfusion studies, as well as other types of blood-CSF equilibration studies, these processes can transport solutes from blood to CSF (influx transport process) as is the case for glucose, amino acids, vitamins and other compounds, or from CSF to blood (efflux transport process) as documented for amino acids, some vitamins, end-products of brain metabolism and certain drugs. Evidence accumulated from in vitro studies with the isolated choroid plexus indicates that the choroid plexuses are the primary locus for these transport processes within the ventricular cavities. Other experimental findings indicate that the pia-arachnoid membrane is probably one of the loci for these transport processes within the subarachnoid spaces.

A rapid method for the determination of salicylate binding by the use of ultrafilters

An ultrafiltration method that combines speed, simplicity, accuracy and precision was employed to measure plasma binding of salicylate. Human plasma, containing 1·0 and 0·1mm sodium salicylate, was ultrafiltered through membranes using 45 p.s.i. and slow rotational stirring. Salicylate was bound at these concentrations 13·1 and 4·4% respectively. This method, using membranes that quantitatively separate small molecules from plasma proteins, yields results comparable to those obtained by equilibrium dialysis.

TRANSPORT OF GABA FROM THE PERFUSED VENTRICULAR SYSTEM OF THE CAT

Abstract— The transport of GABA was studied in anaesthetized cats undergoing ventriculo‐cisternal perfusion with radioactive GABA. Steady‐state clearance of GABA from the CSF was greater than that of other amino acids previously studied, and was saturated at lower substrate concentrations, with an apparent Kt of 5·4 × 10‐5 M, after correcting for non‐saturable transport. GABA clearance was inhibited by the inclusion of taurine or β‐alanine in the perfusion fluid, but not by a number of the common neutral and acidic amino acids. Study of punch biopsies of brain tissue taken adjacent to the venticular system, at the completion of perfusions, showed accumulation of radioactive GABA in the tissue to values four times higher than those found in the perfusion fluid. Of the radioactivity which had been removed from the ventricular system, only 11 per cent remained in the brain at the completion of the perfusion. Excised cat choroid plexus showed a saturable uptake of GABA which was inhibited by inclusion of taurine, β‐alanine, or β‐guanidino propionic acid in the incubation medium.

The effect of anaesthetic agents on the cerebrospinal fluid clearance of 35S-sulphate and 125I-iodide

Abstract In recent years, use of the ventriculocisternal perfusion technique for the study of cerebrospinal fluid transport of substances has become prevalent. This report compares the effect of three anesthetic agents, commonly used in the laboratory, on the clearance of 35S-sulfate and 125I-iodide out of the CSF. When compared with chloralose, pentobarbital and (to a lesser extent) urethane inhibit the CSF clearance of these anions. In studies with isolated choroid plexus incubated in vitro, the accumulation of 125I-iodide was found to be significantly less in the choroid plexus obtained from the anesthetized than from the unanesthetized animal. These results suggest that the reduced CSF clearance observed in vivo was a result, at least in part, of inhibition of choroid plexus transport.