Water transport in invertebrate peripheral nerve fibers

Osmotic and diffusion permeabilities (P_f and P_d) of invertebrate nerve fibers to tritiated water were measured to determine what water flux studies could reveal about "the nerve membrane" and to directly test the possibility of active transport of water into or out of invertebrate nerve fibers. P_f/P_d ratios for lobster walking leg nerve fibers were found to be about 20 ± 7 at 14°C. P_d measurements were made for squid giant axons at 25°C. and found to yield a value of 4 x 10^–4 cm.^–1 sec.^–1. When combined with the data of D. K. Hill for P_f, a P_f/P_d ratio of 21 ± 5 is obtained. These P_f/P_d ratios correspond to "effective pore radii" of about 16 ± 4 angstrom units, according to theories developed by Koefoed-Johnsen and Ussing and independently by Pappenheimer and his colleagues. Variations of water flux ratios with temperatures were studied and apparent activation energies calculated for both diffusion experiments and osmotic filtration experiments using the Arrhenius equation, and found to be close to 3 to 5 cal. per mole of water transferred. Cyanide (5 x 10^–3 molar) and iodoacetate (1 x 10^–3 molar) poisoned lobster leg nerve fibers showed no appreciable change in diffusion or osmotic filtration water effluxes. Caution in interpreting these proposed channels as simple pores was emphasized, but the possibility that such channels exist and are related to ionic flow is not incompatible with electrophysiological data.     

THE SIZE OF PORES IN COLLODION MEMBRANES

By the application of Poiseuille''s law to the rate of flow of water through collodion membranes, it is calculated that the membranes used had pore radii of the order of 0.3 to 2 x 10^–6 cm. On the same basis the number of pores per sq. cm. appears to vary from 270 x 10¹⁰ to 7 x 10¹⁰, decreasing with increase in pore size. Reasons are given for preferring these figures for the radii to figures, 100 times as large, which were calculated by others. Microscopic examination of the membranes, with dark-field illumination, indicates that they are made up of solid granules or filaments of collodion much less than 1 x 10^–4 cm. in thickness.     

ELECTRON BOMBARDMENT OF BIOLOGICAL MATERIALS : II. THE RATE OF DEATH OF FUNGUS SPORES BOMBARDED IN VACUUM WITH CATHODE RAY BEAMS FROM 4 KV.–15 KV.

A study has been undertaken of the rate of inactivation of spores of the ascomycete fungus Aspergillus niger when bombarded in vacuum, with homogeneous beams of cathode rays of energies from 4 to 15 electron kv. and current densities of 1 x 10^–7 to 3 x 10^–6 amperes per square cm. These velocities and densities are in the range of those of showers of secondary electrons produced in biological materials irradiated with moderately soft x-rays, and so may be made to serve as quantitative indicators of the mechanics of x-ray action. Four qualitative effects are described.     

THE APPARENT DISTORTION OF BRIEF RECTANGULAR ELECTRICAL STIMULI IN NERVE

If it is assumed that the kinetics of the process of excitation in nerve is given by dp/dt = KI – kp, I being the actual exciting component of the current, p the state of excitation, and K and k constants, it is necessary to postulate that on application of a rectangular stimulus of voltage, V, the current, I, undergoes a transient exponential variation, usually a decrease, in order that the integral of the differential equation (above) may fit the strength-duration data in V and t. This hypothesis is substantiated by data by Sakamoto on single fibers of the sciatic nerve of the frog. The time constant of the postulated current transient is of the order of 10^–4 sec. for single fibers and of the order of 10^–5 sec. or less in the sciatic nerve trunk. The latter value is about the same as that found by Cole in the same tissue by purely physical measurements. Some criticisms by Rushton (1934) are discussed.     

Osmosis in Cortical Collecting Tubules : ADH-Independent Osmotic Flow Rectification

The present experiments were designed to evaluate the effects of varying the osmolality of luminal solutions on the antidiuretic hormone (ADH)-independent water and solute permeability properties of isolated rabbit cortical collecting tubules. In the absence of ADH, the osmotic water permeability coefficient (cm s^–1) P_f^l→b, computed from volume flows from hypotonic lumen to isotonic bath, was 20 ± 4 x 10^–4 (SEM); the value of P_f^b→l in the absence of ADH, computed from volume flows from isotonic bath to hypertonic lumen, was 88 ± 15 x 10^–4 cm s^–1. We also measured apparent urea permeability coefficients (cm s^–1) from ¹⁴C-urea fluxes from lumen to bath (P_DDurea^l→b) and from bath to lumen (P_DDurea^b→l). For hypotonic luminal solutions and isotonic bathing solutions, P_DDurea^l→b was 0.045 ± 0.004 x 10^–4 and was unaffected by ADH. The ADH-independent values of P_DDurea^l→b and P_urea^b→l were, respectively, 0.216 ± 0.022 x 10^–4 cm s^–1 and 0.033 ± 0.002 x 10^–4 cm s^–1 for isotonic bathing solutions and luminal solutions made hypertonic with urea, i.e., there was an absolute increase in urea permeability and asymmetry of urea fluxes. Significantly, P_DDurea^l→b did not rise when luminal hypertonicity was produced by sucrose; and, bathing fluid hypertonicity did not alter tubular permeability to water or to urea. We interpret these data to indicate that luminal hypertonicity increased the leakiness of tight junctions to water and urea but not sucrose. Since the value of P_f^b→l in the absence of ADH, when tight junctions were open to urea, was approximately half of the value of P_f^l→b in the presence of ADH, when tight junctions were closed to urea, we conclude that tight junctions are negligible paracellular shunts for lumen to bath osmosis with ADH. These findings, together with those in the preceding paper, are discussed in terms of a solubility-diffusion model for water permeation in which ADH increases water solubility in luminal plasma membranes.     

THE ACTIVATION OF STARFISH EGGS BY ACIDS : II. THE ACTION OF SUBSTITUTED BENZOIC ACIDS AND OF BENZOIC AND SALICYLIC ACIDS AS INFLUENCED BY THEIR SALTS.

1. Comparison of the rates of activation of unfertilized starfish eggs in pure solutions of a variety of parthenogenetically effective organic acids (fatty acids, carbonic acid, benzoic and salicylic acids, chloro- and nitrobenzoic acids) shows that solutions which activate the eggs at the same rate, although widely different in molecular concentration, tend to be closely similar in C_H. The dissociation constants of these acids range from 3.2 x 10^–7 to 1.32 x 10^–3. 2. In the case of each of the fourteen acids showing parthenogenetic action the rate of activation (within the favorable range of concentration) proved nearly proportional to the concentration of acid. The estimated C_H of solutions exhibiting an optimum action with exposures of 10 minutes (at 20°) lay typically between 1.1 x 10^–4 M and 2.1 x 10^–4 M (pH = 3.7–3.96), and in most cases between 1.6 x 10^–4 M and 2.1 x 10^–4 M (pH = 3.7–3.8). Formic acid (C_H = 4.2 x 10^–4 M) and o-chlorobenzoic acid (C_H = 3.5 x 10^–4 M) are exceptions; o-nitrobenzoic acid is ineffective, apparently because of slow penetration. 3. Activation is not dependent on the penetration of H ions into the egg from without, as is shown by the effects following the addition of its Na salt to the solution of the activating acid (acetic, benzoic, salicylic). The rate of activation is increased by such addition, to a degree indicating that the parthenogenetically effective component of the external solution is the undissociated free acid. Apparently the undissociated molecules alone penetrate the egg freely. It is assumed that, having penetrated, they dissociate in the interior of the egg, furnishing there the H ions which effect activation. 4. Attention is drawn to certain parallels between the physiological conditions controlling activation in the starfish egg and in the vertebrate respiratory center.     

THE ELECTRICAL CONDUCTIVITY OF SODIUM AND POTASSIUM GUAIACOLATES IN GUAIACOL

The data of the author and Uhlig, and new data, on the conductivity of sodium and of potassium guaiacolates in guaiacol at 25° have been computed with an improved conductance equation which is valid to somewhat higher concentrations than the equations formerly used. The new constants are, Λ₀ = 9.0, K = 2.8 x 10^–5 for sodium guaiacolate and Λ₀ = 9.5, K = 3.4 x 10^–5 for potassium guaiacolate.     

Sodium, Potassium, and Chloride Fluxes in Intercostal Muscle from Normal Goats and Goats with Hereditary Myotonia

In isolated bundles of external intercostal muscle from normal goats and goats with hereditary myotonia the following were determined: concentrations and unidirectional fluxes of Na⁺, K⁺, and Cl^-, extracellular volume, water content, fiber geometry, and core-conductor constants. No significant difference between the two groups of preparations was found with respect to distribution of fiber size, intracellular concentrations of Na⁺ or Cl^-, fiber water, resting membrane potential, or overshoot of action potential. The intracellular Cl^- concentration in both groups of preparations was 4 to 7 times that expected if Cl^- were distributed passively between intracellular and extracellular water. The membrane permeability to K (P_K) calculated from efflux data was (a) at 38°C, 0.365 x 10^-6 cm sec^-1 for normal and 0.492 x 10^-6 for myotonic muscle, and (b) at 25°C, 0.219 x 10^-6 for normal and 0.199 x 10^-6 for myotonic muscle. From Cl^- washout curves of normal muscle usually only three exponential functions could be extracted, but in every experiment with myotonic muscle there was an additional, intermediate component. From these data PP_cl could be calculated; it was 0.413 x 10^-6 cm sec^-1 for myotonic fibers and was 0.815 x 10^-6 cm sec^-1 for normal fibers. The resting membrane resistance of myotonic fibers was 4 to 6 times greater than that of normal fibers.     

AMPHOTERIC BEHAVIOR OF COMPLEX SYSTEMS : IV. NOTE ON THE ISOELECTRIC POINT AND IONIZATION CONSTANTS OF SULFANILIC ACID.

From the solubility minimum the value of the basic ionization constant of sulfanilic acid is shown to lie probably between the values 1.7 x 10^–15 and 3.2 x 10^–15. From solubility measurements the value of this same constant is shown to lie probably between 2.0 and 2.2 x 10^–15, and the isoelectric point of sulfanilic acid is thus at a cH of 0.056 or a pH of 1.25. From conductivity ratios the acid ionization constant of sulfanilic acid is shown to be 7.05 x 10^–4 at room temperature (21°C.). Calculations are made, from data published in preceding papers, of the ionization constants of glycine, K_a being 2.3 x 10^–10, and K_b being 2.2 x 10^–12.     

The relationship of sodium uptake,potassium rejection,and skin potential in isolated frog skin

1. Isolated surviving frog skin, when bathed with the same kind of diluted Ringer's solution on both sides, shows a negative correlation between net active salt uptake by the epithelium and spontaneous skin potential. Average values of 0.15 to 0.86 µeq. x hr.^–1 x cm.^–2 were measured and correlated with average skin potentials ranging from 107 to 25 mv. 2. Sodium uptake exceeded chloride uptake by about the same amount, irrespective of the height of the skin potential. 3. The same skins which exhibited a negative correlation between net uptake of sodium chloride and skin potential showed a positive correlation between net potassium rejection from the epithelium and skin potential, for voltages above 30 to 40 mv. In skins of voltages lower than this, potassium ions were taken up rather than rejected. Average values for rejection of +11.8 to –0.8 centi-µeq. x hr.^–1 x cm.^–2 were measured. 4. Net fluid uptake, associated with active uptake of sodium chloride, was small and occurred in the direction of the salt uptake. No dependence of net fluid uptake upon skin potential was observed. 5. Skins of winter frogs, pretreated with a commercial purified ACTH preparation, were less active than their respective controls with regard to uptake of sodium chloride. Rejection of potassium was the same in treated and untreated skins. Posterior pituitary factors, as possible contaminants, did not account for the effect of the ACTH preparation. 6. DOCA, DOC, and cortisone did not alter the normal correlation referred to under (1) and (3). 7. In interpreting the experimental results on theoretical grounds, it is suggested (a) that in normal skin, it is the variation in the electric conductance in skin of chloride ions which essentially, although not exclusively, determines the rate of net uptake of sodium chloride, (b) that a factor in the ACTH preparation used, possibly ACTH itself, may have lowered the electric conductance in skin of sodium ions either truly or apparently, (c) that potassium ions are treated by the skin primarily as passive ions. There is some indication that potassium ions are also actively taken up by the epithelium of skin.     

Current- and Voltage-Clamped Studies on Myxicola Giant Axons : Effect of tetrodotoxin

A new dissection procedure for preparing Myxicola giant axons for observation under voltage clamp is described. Preparation time is generally 40–45 min. 65–70% of the preparations attempted may be brought through the entire procedure, including insertion of the long internal electrode, and support an initial action potential amplitude of 100 mv or greater. Mean values for axon diameter, resting membrane potential, action potential amplitude, maximum peak inward transient current, and resting membrane resistance are 560 µ, —66.5 mv, 112 mv, 0.87 ma/cm² and 1.22 KΩ cm ² respectively. Cut branches do not seem to be a problem in this preparation. Behavior under voltage clamp is reasonably stable over several hours. Reductions in maximum inward transient current of 10% and in steady-state current of 5–10% are expected in the absence of any particular treatment. Tetrodotoxin blocks the action potential and both the inward and outward transient current, but has no effect on either the resting membrane potential or the steady-state current. This selective action of tetrodotoxin on the transient current is taken as an indication that this current component is probably carried by Na.     

THE SOLUBILITY OF TYROSINE IN ACID AND IN ALKALI

Measurements have been made of the solubility at 25°C. of tyrosine in hydrochloric acid and in sodium hydroxide solutions varying from 0.001 to 0.05 M, and also in distilled water. The pH of the saturated solutions was measured with the hydrogen electrode. The following values for the ionization constants of tyrosine have been obtained from the measurements: k_b = 1.57 x 10^–12, k_a1 = 7.8 x 10^–10, k_a2 = 8.5 x 10^–11. The changes in solubility with pH can be satisfactorily explained by the use of these ionization constants.     

Long-Term Effect of Agricultural Reclamation on Soil Chemical Properties of a Coastal Saline Marsh in Bohai Rim,Northern China

Over the past six decades, coastal wetlands in China have experienced rapid and extensive agricultural reclamation. In the context of saline conditions, long-term effect of cultivation after reclamation on soil chemical properties has not been well understood. We studied this issue using a case of approximately 60-years cultivation of a coastal saline marsh in Bohai Rim, northern China. The results showed that long-term reclamation significantly decreased soil organic carbon (SOC) (−42.2%) and total nitrogen (TN) (−25.8%) at surface layer (0–30 cm) as well as their stratification ratios (SRs) (0–5 cm:50–70 cm and 5–10 cm:50–70 cm). However, there was no significant change in total phosphorus (TP) as well as its SRs under cultivation. Cultivation markedly reduced ratios of SOC to TN, SOC to TP and TN to TP at surface layer (0–30 cm) and their SRs (0–5 cm:50–70 cm). After cultivation, electrical conductivity and salinity significantly decreased by 60.1% and 55.3% at 0–100 cm layer, respectively, suggesting a great desalinization. In contrast, soil pH at 20–70 cm horizons notably increased as an effect of reclamation. Cultivation also changed compositions of cations at 0–10 cm layer and anions at 5–100 cm layer, mainly decreasing the proportion of Na⁺, Cl⁻ and SO₄ ²⁻. Furthermore, cultivation significantly reduced the sodium adsorption ratio and exchangeable sodium percentage in plow-layer (0–20 cm) but not residual sodium carbonate, suggesting a reduction in sodium harm.     

Muscle Contraction during Hyperpolarizing Currents in the Crab

Isolated muscle fibers from the motor legs of the crab Trichodactilus dilocarcinus were submitted to strong hyperpolarizing currents of varied intensities which produced tension during the current pulse. Threshold for tension was obtained with intensities of about 0.2 x 10^–5 A, changing E_m to ca. –150 mV (starting from a resting potential ofca. –80 mV). At the closure of the anodic square pulse, a second phase of tension usually appeared superimposed upon the one obtained during hyperpolarization. The first phase of tension increased with the increase of Ca⁺⁺ concentration in the bath. Sr⁺⁺ produced the same type of mechanical output as Ca⁺⁺. When added to the normal Ca⁺⁺ concentration, Ba⁺⁺ and Mn⁺⁺ in low concentrations (up to 21.5 mM) also increased the tension of this phase, but at higher concentrations they blocked both phases while Mg⁺⁺ did not alter the tension. Of all the divalent cations employed, only Sr⁺⁺ is capable of developing tension as a substitute for Ca⁺⁺ in the external media. Procaine administered in a dosage (5 x 10^–3 W/V)which would suppress the contracture due to caffeine (10 mM), did not modify the tension developed during the hyperpolarization. The preceding data indicate that the Ca⁺⁺ required for tension during hyperpolarization comes from sites which would differ from those usually postulated for tension due to depolarization in the muscle fibers of other crustaceans (American crayfish). Furthermore, the external source of Ca⁺⁺ appears to be one mainly implicated in the induction of tension due to inward current pulses.     

STUDIES ON CELL METABOLISM AND CELL DIVISION : III. OXYGEN CONSUMPTION AND CELL DIVISION OF FERTILIZED SEA URCHIN EGGS IN THE PRESENCE OF RESPIRATORY INHIBITORS

1. The effects of a number of respiratory inhibiting agents on the cell division of fertilized eggs of Arbacia punctulata have been determined. For eggs initially exposed to the reagents at 30 minutes after fertilization at 20°C., the levels of oxygen consumption prevailing in the minimum concentrations of reagents which produced complete cleavage block were (as percentages of the control): In 0.4 per cent O₂-99.6 per cent N₂, 32; in 0.7 per cent O₂-99.3 per cent CO, 32; in 1.6 x 10^–4 M potassium cyanide, 34; in 1 x 10^–3 M phenylurethane, 70; in 4 x 10^–3 M 5-isoamyl-5-ethyl barbituric acid, 20; in 3 x 10^–4 M iodoacetic acid, 53. 2. The carbon monoxide inhibition of oxygen consumption and cell division was reversed by light. The percentage inhibition of oxygen consumption by carbon monoxide in the dark is described by the usual mass action equation with K, the inhibition constant, equal to approximately 60, as compared to values of 5 to 10 for yeast and muscle. In 20 per cent O₂-80 per cent CO in the dark there was a slight stimulation of oxygen consumption, averaging 20 per cent. 3. Spectroscopic examination of fertilized and unfertilized Arbacia eggs reduced by hydrosulfite revealed no cytochrome bands. The thickness and density of the egg suspension was such as to indicate that, if cytochrome is present at all, the amount in Arbacia eggs is extremely small as compared to that in other tissues having a comparable rate of oxygen consumption. 4. Three reagents poisoning copper catalyses, potassium dithio-oxalate (10^–2 M), diphenylthiocarbazone (10^–4 M), and isonitrosoacetophenone (2 x 10^–3 M) produced no inhibition of division of fertilized Arbacia eggs. 5. These results indicate that the respiratory processes required to support division in the Arbacia egg may perhaps differ in certain essential steps from the principal respiratory processes in yeast and muscle.     

POLARIZATION AND ELECTRON MICROSCOPE STUDY OF FROG NERVE AXOPLASM

1. The submicroscopic organization of nerve axons from R. pipiens and R. catesbiana has been studied by means of polarizing and electron microscopes. 2. In measurements on a series of 85 fresh myelinated axons from which the sheaths had been removed average values were obtained for the total birefringence, +2.5 x 10^–4, the form birefringence, +1.4 x 10^–4, and the refractive index of the oriented component, 1.523. The average partial volume occupied by axially oriented filaments was computed to be 0.69 per cent. 3. Electron micrographs of fixed myelinated axons demonstrate an average of 93 axially oriented neuroprotofibrils per square micron of cross-section. The neuroprotofibrils are approximately 90 A in diameter, of indefinite length, and occupy a computed partial volume of 0.59 per cent. 4. Mitochondria, neuroprotofibrils, endoplasmic reticulum, and dense particles are seen in electron micrographs of both myelinated and unmyelinated nerve axons. 5. It is concluded that the neuroprotofibrils are present in the living nerve, that they play an important but undetermined role in nerve function, and that these structures are not an artifact of osmium tetroxide fixation.     

THE BEHAVIOR OF THE NUCLEIC ACIDS DURING THE EARLY DEVELOPMENT OF THE SEA URCHIN EGG (ARBACIA)

The authors wish to correct an error in the paper "The behavior of the nucleic acids during the early development of the sea urchin egg (Arbacia)" (J. Gen. Physiol., 1947–48, 31, 203). Owing to an oversight, the figures for the amounts of various P fractions in a single Arbacia egg have been erroneously expressed in γ x 10^–3 units (Tables I and II, page 205; the last two lines of page 206). The figures should have been expressed in γ x 10^–5 units. Thus, the fertilized Arbacia egg contains an average of 20 γ x 10^–5 ribonucleic acid P and 0.7 to 1 γ x 10^–5 desoxyribonucleic acid P.     

PERMEABILITY OF ERYTHROCYTES TO RADIOACTIVE POTASSIUM

The diffusion coefficients for the exchange of potassium across the membrane of erythrocytes of humans, rats, and rabbits have been determined by the use of artificially radioactive potassium, both into and out of the erythrocytes both in vitro and in vivo. The diffusion coefficients found in minutes^–1 were 0.2 to 0.25 x 10^–3 for human, 0.32 to 0.665 x 10^–3 for rabbits, and 1.0 x 10^–3 for rat erythrocytes. Rabbit erythrocytes appear to be more permeable in vivo. Reasons are advanced to explain the failure of earlier workers to demonstrate appreciable exchange of potassium in erythrocytes.     

Melanopsin as a Sleep Modulator: Circadian Gating of the Direct Effects of Light on Sleep and Altered Sleep Homeostasis in Opn4−/− Mice

Light influences sleep and alertness either indirectly through a well-characterized circadian pathway or directly through yet poorly understood mechanisms. Melanopsin (Opn4) is a retinal photopigment crucial for conveying nonvisual light information to the brain. Through extensive characterization of sleep and the electrocorticogram (ECoG) in melanopsin-deficient (Opn4^−/−) mice under various light–dark (LD) schedules, we assessed the role of melanopsin in mediating the effects of light on sleep and ECoG activity. In control mice, a light pulse given during the habitual dark period readily induced sleep, whereas a dark pulse given during the habitual light period induced waking with pronounced theta (7–10 Hz) and gamma (40–70 Hz) activity, the ECoG correlates of alertness. In contrast, light failed to induce sleep in Opn4^−/− mice, and the dark-pulse-induced increase in theta and gamma activity was delayed. A 24-h recording under a LD 1-h1-h schedule revealed that the failure to respond to light in Opn4^−/− mice was restricted to the subjective dark period. Light induced c-Fos immunoreactivity in the suprachiasmatic nuclei (SCN) and in sleep-active ventrolateral preoptic (VLPO) neurons was importantly reduced in Opn4^−/− mice, implicating both sleep-regulatory structures in the melanopsin-mediated effects of light. In addition to these acute light effects, Opn4^−/− mice slept 1 h less during the 12-h light period of a LD 1212 schedule owing to a lengthening of waking bouts. Despite this reduction in sleep time, ECoG delta power, a marker of sleep need, was decreased in Opn4^−/− mice for most of the (subjective) dark period. Delta power reached after a 6-h sleep deprivation was similarly reduced in Opn4^−/− mice. In mice, melanopsin's contribution to the direct effects of light on sleep is limited to the dark or active period, suggesting that at this circadian phase, melanopsin compensates for circadian variations in the photo sensitivity of other light-encoding pathways such as rod and cones. Our study, furthermore, demonstrates that lack of melanopsin alters sleep homeostasis. These findings call for a reevaluation of the role of light on mammalian physiology and behavior.     

Variations in the FRA10AC1 Fragile Site and 15q21 Are Associated with Cerebrospinal Fluid Aβ1-42 Level

Proteolytic fragments of amyloid and post-translational modification of tau species in Cerebrospinal fluid (CSF) as well as cerebral amyloid deposition are important biomarkers for Alzheimer’s Disease. We conducted genome-wide association study to identify genetic factors influencing CSF biomarker level, cerebral amyloid deposition, and disease progression. The genome-wide association study was performed via a meta-analysis of two non-overlapping discovery sample sets to identify genetic variants other than APOE ε4 predictive of the CSF biomarker level (Aβ_1–42, t-Tau, p-Tau_181P, t-Tau:Aβ_1–42 ratio, and p-Tau_181P:Aβ_1–42 ratio) in patients enrolled in the Alzheimer’s Disease Neuroimaging Initiative (ADNI) study. Loci passing a genome-wide significance threshold of P < 5 x 10⁻⁸ were followed-up for replication in an independent sample set. We also performed joint meta-analysis of both discovery sample sets together with the replication sample set. In the discovery phase, we identified variants in FRA10AC1 associated with CSF Aβ_1–42 level passing the genome-wide significance threshold (directly genotyped SNV rs10509663 P _FE = 1.1 x 10⁻⁹, imputed SNV rs116953792 P _FE = 3.5 x 10⁻¹⁰), rs116953792 (P _one-sided = 0.04) achieved replication. This association became stronger in the joint meta-analysis (directly genotyped SNV rs10509663 P _FE = 1.7 x 10⁻⁹, imputed SNV rs116953792 P _FE = 7.6 x 10⁻¹¹). Additionally, we identified locus 15q21 (imputed SNV rs1503351 P _FE = 4.0 x 10⁻⁸) associated with CSF Aβ_1–42 level. No other variants passed the genome-wide significance threshold for other CSF biomarkers in either the discovery sample sets or joint analysis. Gene set enrichment analyses suggested that targeted genes mediated by miR-33, miR-146, and miR-193 were enriched in various GWAS analyses. This finding is particularly important because CSF biomarkers confer disease susceptibility and may be predictive of the likelihood of disease progression in Alzheimer’s Disease.