An in vitro experimental study on the relationship between pulsatile tinnitus and the dehiscence/thinness of sigmoid sinus cortical plate

Pulsatile tinnitus (PT), characterized as pulse-synchronous, is generally objective. Sigmoid sinus (SS) venous sound is widely suggested to be a possible sound source of PT. The dehiscence and thinness of SS cortical plate (CP) was commonly reported as PT pathology in previous studies, but lack quantitative or biomechanical analysis. In this study, it was aimed to quantify the relationship between venous sound and CP dehiscence/thinness using in vitro experiment. The in vitro models of SS and CP were established based on 3D-printing, with the developed pulsatile venous flow in the SS model. The generated sound signal and the vibration response at the dehiscent/thinned area were analyzed. The sound signal generated in the normal-sized dehiscence model was pulse-synchronous within 100-–400 Hz, which had similar acoustic characteristics as the clinical PT sounds. It was concluded that the pulsatile venous sound is produced at TS-SS junction in case of CP dehiscence. The CP, even a thinned one can effectively diminish the venous sound and sound-generating pulsatile vibration at TS-SS junction. The CP dehiscence would induce pulse-synchronous and high pressure venous sound, as well as pulse-synchronous vibration above 20 Hz, regardless of the dehiscence size. On the contrary, the CP thinness would not induce obvious venous sound or pulsatile vibration above 20 Hz.     

Cerebral perfusion pressure in giraffe: modelling the effects of head-raising and -lowering

Loss of consciousness caused by positional changes of the head results from reduced cerebral blood flow (CBF). CBF is related to cerebral perfusion pressure (CPP). CPP is the difference between mean arterial pressure (MAP) at the head and intracranial pressure (ICP). The positional change of the giraffe head between ground level and standing upright is the largest of all animals yet loss of consciousness does not occur. We have investigated the possibility that an increase in CPP protects giraffe from fainting, using a mechanical model that functioned as an anatomical U-tube. It consisted of a rigid ascending “carotid” limb, a collapsible “brain” tube drained by a rigid, “vertebral venous plexus” (VVP) tube, and a collapsible “head” tube drained by a collapsible tube representing the “jugular vein”. The descending tubes could be rotated relative to the “carotid” tube to be horizontal, or at 30°, 45°, and 60° to the vertical to simulate changes in head position. Pressure at the top of the “carotid” tube was intracranial MAP, at the top of the “VVP” tube was ICP, and the difference CPP. In the simulated “head-up” position and a fluid flow rate of 4 L min⁻¹, CPP was ∼170 mmHg. With the VVP tube horizontal, CPP fell from ∼170 to 45 mmHg, but increased to ∼67 mmHg at 30° “down”, to ∼70 mmHg at 45° “down” and to ∼75 at 60° “down”. The fall in CPP in the head-down positions resulted from a decrease in viscous resistance in, and dissipation of pressure to, the “head” and “jugular” tubes. These data provide an estimate of cranial pressure changes in giraffe during positional changes of the head, and suggest that an increase in CPP plays a significant role in maintaining CBF during head-raising and that it may be an important mechanism for preventing fainting in giraffe.     

Body and brain temperature coupling: the critical role of cerebral blood flow

Direct measurements of deep-brain and body-core temperature were performed on rats to determine the influence of cerebral blood flow (CBF) on brain temperature regulation under static and dynamic conditions. Static changes of CBF were achieved using different anesthetics (chloral hydrate, CH; α-chloralose, αCS; and isoflurane, IF) with αCS causing larger decreases in CBF than CH and IF; dynamic changes were achieved by inducing transient hypercapnia (5% CO₂ in 40% O₂ and 55% N₂). Initial deep-brain/body-core temperature differentials were anesthetic-type dependent with the largest differential observed with rats under αCS anesthesia (ca. 2°C). Hypercapnia induction raised rat brain temperature under all three anesthesia regimes, but by different anesthetic-dependent amounts correlated with the initial differentials—αCS anesthesia resulted in the largest brain temperature increase (0.32 ± 0.08°C), while CH and IF anesthesia lead to smaller increases (0.12 ± 0.03 and 0.16 ± 0.05°C, respectively). The characteristic temperature transition time for the hypercapnia-induced temperature increase was 2–3 min under CH and IF anesthesia and ~4 min under αCS anesthesia. We conclude that both, the deep-brain/body-core temperature differential and the characteristic temperature transition time correlate with CBF: a lower CBF promotes higher deep-brain/body-core temperature differentials and, upon hypercapnia challenge, longer characteristic transition times to increased temperatures.     

The outflow tract of the heart in fishes: anatomy, genes and evolution

A large number of congenital heart defects associated with mortality in humans are those that affect the cardiac outflow tract, and this provides a strong imperative to understand its development during embryogenesis. While there is wide phylogenetic variation in adult vertebrate heart morphology, recent work has demonstrated evolutionary conservation in the early processes of cardiogenesis, including that of the outflow tract. This, along with the utility and high reproductive potential of fish species such as Danio rerio , Oryzias latipes etc. , suggests that fishes may provide ideal comparative biological models to facilitate a better understanding of this poorly understood region of the heart. In this review, the authors present the current understanding of both phylogeny and ontogeny of the cardiac outflow tract in fishes and examine how new molecular studies are informing the phylogenetic relationships and evolutionary trajectories that have been proposed. The authors also attempt to address some of the issues of nomenclature that confuse this area of research.     

A morphological study of the vertebral venous plexus and its connections in the Cape dune mole‐rat,Bathyergus suillus (Bathyergidae)

Bathyergus suillus are subterranean rodents found in the Western Cape of South Africa, where they inhabit sandy, humid burrows. Vertebral venous plexuses around the vertebral column have been implicated in aiding the maintenance of a constant central nervous system temperature via its connections with muscles and interscapular brown adipose tissue. The morphology of the vertebral venous plexuses and its connections in B.suillus were investigated. Frozen (n = 10) animals were defrosted; the venous system injected with latex and the vertebral venous plexuses, azygos‐ and intercostal veins dissected along the dorsal and ventral aspects of the vertebral column. Specimens (n = 4) were used for histological serial cross sections of the thoracic vertebrae. Veins drained from the interscapular brown adipose tissue to the external vertebral venous plexus, via a dorsal vein at the spinous process of T2 which might represent the “vein of Sulzer” described in rats. The intercostal veins cranial to the level of T8 drained directly into the ventral external vertebral venous plexus instead of into the azygos vein as seen in rats. The azygos vein was situated ventrally on the thoracic vertebral bodies in the median plane as opposed to most rodents that have a left sided azygos vein. The internal vertebral venous plexus consisted of two ventrolateraly placed longitudinal veins in the spinal epidural space. Veins from the forelimbs entered the internal vertebral venous plexus directly at the levels of C7 and T1 and have not been described in other rodents. Serial histological sections, revealed no regulatory valves in vessels leading toward the internal vertebral venous plexus, allowing blood to presumably move in both directions within the vertebral venous plexus. The vertebral venous plexus of B. suillus shows similarities to that of the rat but the vessels from the forelimbs draining directly into to the internal vertebral venous plexus and the position of the azygos vein and the intercostal veins draining into the external vertebral venous plexus are notable exceptions. J. Morphol., 2011. © 2010 Wiley‐Liss, Inc.     

Evaluation of cytotoxicity and immune modulatory activities of soyasaponin Ab: An in vitro and in vivo study

To improve the immune efficacy of protein subunit vaccines, novel adjuvants are needed to elicit a suitable protective immune response and to promote long term immunologic memory. In this work, soyasaponin Ab, a major constituent among group A soyasaponins in soybeans was purified and prepared from soy hypocotyls. The immunomodulatory effects of soyasaponin Ab both in vitro and in vivo were investigated, and its pro-immunomodulatory molecular mechanism was also studied. For in vitro assays, with mouse macrophage cell line RAW264.7 as the studying model, both cytotoxicity and immune stimulatory activity were investigated to evaluate the potential of soyasaponin Ab as the vaccine adjuvant. The results indicated that soyasaponin Ab could be significantly safer than Quillaja saponins (QS). Soyasaponin Ab showed no toxicities over the tested concentration ranges compared to QS. Soyasaponin Ab was proved able to promote releases of inflammatory cytokines like TNFα and IL-1β in a dose-dependent manner. Furthermore, NF-κB signalling was also activated by soyasaponin Ab effectively. In addition, with TLR4 gene expression of RAW264.7 cell inhibited by RNA interference, immune stimulatory effects by soyasaponin Ab dropped down significantly. On the other hand, the in vivo experiment results showed that anti-ovalbumin (OVA) IgG, IgG1, IgG2a, IgG2b were significantly enhanced by the soyasaponin Ab and QS groups (p < 0.05 or p < 0.01). The results suggested that compared to QS, soyasaponin Ab may represent a viable candidate for effective vaccine adjuvant. TLR4 receptor dependent pathway may be involved in immune stimulatory effects of soyasaponin Ab.     

The role of the DLPFC in inductive reasoning of MCI patients and normal agings: An fMRI study

Previous studies of young people have revealed that the left dorsolateral prefrontal cortex (DLPFC) plays an important role in inductive reasoning. An fMRI experiment was performed in this study to examine whether the left DLPFC was involved in inductive reasoning of MCI patients and normal agings, and whether the activation pattern of this region was different between MCI patients and normal agings. The fMRI results indicated that MCI patients had no difference from normal agings in behavior per-formance (reaction time and accuracy) and the activation pattern of DLPFC. However, the BOLD re-sponse of the DLPFC region for MCI patients was weaker than that for normal agings, and the func-tional connectivity between the bilateral DLPFC regions for MCI patients was significantly higher than for normal agings. Taken together, these results indicated that DLPFC plays an important role in inductive reasoning of agings, and the functional abnormity of DLPFC may be an earlier marker of MCI before structural alterations.     

Perfusion and molecular diffusion-weighted MR imaging of the brain: in vivo assessment of tissue alteration in cerebral ischemia

Summary.  The combined use of perfusion imaging (PI) and diffusion-weighted imaging (DWI) is opening a new window into the processes that occur during the first hours of ischemia. DWI detects changes in molecular diffusion associated with cytotoxic edema. PI characterizes the degree of regional hypoperfusion. Regions showing mismatches between DWI and PI, i.e. hypoperfused areas with normal diffusion behavior are considered potentially salvageable. We present results of 11 patients with an occlusion of the middle cerebral artery stem and spontaneous stroke evolution. Whereas the infarct was clearly visible on initial DWI and PI, surrounding tissue at risk of infarction was marked in all patients by an increased blood volume and transit time, but only in a subgroup (n = 3) where alteration were more pronounced this tissue at risk was progressively infarcted. These human DWI and PI data show alterations in the area of tissue at risk which correlates with infarct progression. Received June 29, 2001 Accepted August 6, 2001 Published online August 20, 2002     

Upregulation of cerebral cortical glutathione synthesis by ammonia in vivo and in cultured glial cells: the role of cystine uptake

Glutathione (GSH) is a major antioxidant in the brain and ammonia neurotoxicity is associated with oxidative stress. In this study, we show that intracerebral administration of ammonium chloride (“ammonia”, final concentration 5 mM) via a microdialysis probe, increases by 80% the glutathione content in cerebral cortical microdialysates, and tends to increase its content in striatal microdialysates. Treatment with ammonia in vitro dose-dependently increased the glutathione content in cultured cerebral cortical astrocytes and a C6 glioma cell line. Significant effects have been observed after 1 h (astrocytes) or 3 h (C6 cells) of exposure and were sustained up to 72 h of incubation. A gradual decrease of the GSH/GSSG ratio noted during 3 h (astrocytes) or 24 h (C6 cells) of exposure, was followed by an partial recovery after 24 h of incubation, the latter phase possibly reflecting increased availability of de novo synthesized glutathione. In our hands, cystine, the precursor for astrocytic glutathione synthesis, was transported to astrocytes almost exclusively by system X_AG⁻, while in C6 cells the transport engaged both system x_c⁻ (60% of uptake) and X_AG⁻ (40% of uptake). Ammonia in either cell type stimulated cystine uptake without changing the relative contribution of the uptake systems. The results are consistent with the concept of increased astrocytic glutathione synthesis as an adaptive response of the brain to ammonia challenge, and emphasize upregulation of cystine uptake as a factor contributing to this response.     

Comparison between a generalized Newtonian model and a network-type multiscale model for hemodynamic behavior in the aortic arch: Validation with 4D MRI data for a case study

Blood is a complex fluid in which the presence of the various constituents leads to significant changes in its rheological properties. Thus, an appropriate non-Newtonian model is advisable; and we choose a Modified version of the rheological model of Phan-Thien and Tanner (MPTT). The different parameters of this model, derived from the rheology of polymers, allow characterization of the non-Newtonian nature of blood, taking into account the behavior of red blood cells in plasma. Using the MPTT model that we implemented in the open access software OpenFOAM, numerical simulations have been performed on blood flow in the thoracic aorta for a healthy patient. We started from a patient-specific model which was constructed from medical images. Exiting flow boundary conditions have been developped, based on a 3-element Windkessel model to approximate physiological conditions. The parameters of the Windkessel model were calibrated with in vivo measurements of flow rate and pressure. The influence of the selected viscosity of red blood cells on the flow and wall shear stress (WSS) was investigated. Results obtained from this model were compared to those of the Newtonian model, and to those of a generalized Newtonian model, as well as to in vivo dynamic data from 4D MRI during a cardiac cycle. Upon evaluating the results, the MPTT model shows better agreement with the MRI data during the systolic and diastolic phases than the Newtonian or generalized Newtonian model, which confirms our interest in using a complex viscoelastic model.     

Stimulation of natural killer cells by homoeopathic complexes: An in vitro and in vivo pilot study in advanced cancer patients

The present study was designed in order to evaluate the effects of five homoeopathic complex preparations on functional activity natural killer cells (NKCs) in advanced cancer patients. We examined the effects of Coenzyme Compositum®, Ubichinon Compositum®, Glyoxal Compositum®, Katalysatoren® and Traumeel® on the functional activity of NKCs. Experimental procedures included in vitro and in vivo trials. The in vitro trials were performed in NKCs isolated from 12 healthy volunteers (aged 44 ± 4 years) and incubated with the five homoeopathic complex preparations. The in vivo trials were performed in 15 advanced cancer patients (aged 55 ± 12 years) supplemented for 3 months with the homoeopathic preparations. All five homoeopathic preparations significantly increased the cytotoxic activity of the NKCs at the lowest NKCs/target cell ratio 12:1 (p < 0·05). The order of activity was: Ubichinon Compositum® > Glyoxal Compositum® > Katalysatoren® > Traumeel® > Coenzyme Compositum®. In the advanced cancer patients, the homoeopathic preparation significantly increased NKCs cytotoxic activity (p < 0·05). The homoeopathic complex preparations tested in this study can be used as an adjuvant immunotherapy in advanced cancer patients. Copyright © 2013 John Wiley & Sons, Ltd.     

The study of cerebral venous blood flow disturbance peculiarity in the norm and under the extravasal compression of brachiocephalic veins with the use of magnetic resonance venography and ultrasound duplex scanning

The MR-venography of the veins and brain venous sinuses, brachiocephalic veins an internal jugular veins duplex scanning have been performed in order to study the distinctions of cerebral venous hemodynamics of healthy people and the patients with venous encephalopathy caused by the extravasal compression of the brachiocephalic veins at the neck level and the superior sections of mediastinum. It has been revealed that the blood flow reducing in transverse brain sinuses occurs not only in the case of outflow disorder in the distal sections of the venous system, but also in norm. This reducing depends on anatomic constitution of confluens sinuum and the venous angle type of brachiocephalic veins. The three venous angle types of brachiocephalic veins have been distinguished: y-type, mu-type and Y-type. It has been registered that in case of the mu-type angle the blood flow can be reduced in norm due to peripheral resistance increase at the physiological bends of nearly a right angle type. The distinctions of hemodynamics in case of venous obstruction in contrast to arterial obstruction have been described. It has been registered that in case of outflow trouble in one of the internal jugular veins the speed and the volume of the blood flow in it are progressively reduced depending on the duration and the manifestation of compression. All this results in narrowing of the vein diameter from the affected side, and in compensatory distention of the diameter and increase of blood flow volume in the contralateral internal jugular vein, vertebral and external jugular veins, in succession.     

Interaction between hypertension and HSP70 variants increase the risk of cerebral ischemia in Chinese Han population: An association study

Cerebral infarction has become one of the leading diseases and a major mortality factor around the world. Atherosclerosis is recognized as one of the important causes of ischemic stroke. Recently, accumulating evidences have indicated that the anti-inflammatory and anti-apoptotic functions of the HSP70 family play an important role in cerebral ischemia. However, the association between HSP70 SNPs and ischemic stroke was also not well established. We chose 101 cases of cerebral ischemia and 100 healthy people from the Chinese Han population as our study subjects, and PCR-RFLP was employed to analyze HSP70 polymorphisms: HSP70-1+190G/C, HSP70-2+1267A/G and HSP70-hom+2437T/C. There were no significant differences in + 1267A/G allele or genotype frequencies between patients with stroke and healthy controls. However, genotypes of + 190CG and + 2437TT were differentially distributed between the patients and controls. A significant difference of T allele distribution in the HSP70-hom+2437T/C site was observed. Logistic regression analysis indicated that genotypes of + 190CG, + 2437TT and T allele in HSP70-hom were risk factors of ischemic stroke. Moreover, the study has formulated that the interactions between hypertension and + 190CG or + 2437TT may increase the risks of ischemic stroke. The results from this study have suggested a clinical indicator for assessing the possibilities of cerebral stroke, and supply basis to clinicians to give precaution to people who are at risk of stroke.     

The effect of chlorpromazine on SCE frequency in human chromosomes: An in vitro and in vivo study

Schizophrenic patients who were receiving, or who had received chlorpromazine showed SCE levels similar to those in a normal control population. Of 8 normal individuals whose lymphocytes were exposed in vitro to chlorpromazine (0.05–2.00 μg/ml) for two cell cycles, 4 showed a significant increase in SCE, 3 showed no increase and 1 a decrease compared with untreated lymphocytes. Lymphocytes from a further 8 donors treated with 2.0 μg/ml chlorpromazine prior to mitogen stimulation (G₀ lymphocytes) showed a similar SCE response. Only 3 of the 8 donors showed a significant increase in SCEs over the baseline level. When proliferating lymphocytes were exposed to chlorpromazine 38 h after culture initiation and prior to the addition of BrdUrd to the culture medium, metaphase chromosomes from only 3 of the 8 individuals studied showed increased levels of exchange. These results indicate that chlorpromazine can induce SCEs in vitro but that there is considerable variation in SCE response among individuals. Furthermore, our data emphasises the importance of using more than 1 or 2 donors when analysing SCE response in human chromosomes.     

The effect of ethanol on erythrocyte carbonic anhydrase isoenzymes activity: An in vitro and in vivo study

The ethanol is a widely consumed as sedative-hypnotic drug throughout the world. In this study, the effects of ethanol were investigated on carbonic anhydrase (CA) enzyme activities both in vitro in human erythrocyte and in vivo in Sprague-Dawley rat erythrocyte. For in vitro study, the human carbonic anhydrase-I (HCA-I) and -II (HCA-II) are purified by Sepharose 4B–L-tyrosine-sulphanilamide affinity chromatography. In vivo CA enzyme activity was determined colorimetrically by using CO₂-hydration method of Wilbur and Anderson. Rat blood samples were taken from each rat before and after the ethanol administration at different times (1 h, 3 h, and 5 h). Rat erythrocyte CA activity was significantly inhibited by pharmacological dosage of the ethanol (2 mL.kg^{? 1}) for up to 3 h (p < 0.001) following intraperitoneally administration. The ethanol showed in vitro inhibitory effects on HCA-I and HCA-II hydratase activity, determined by colorimetrically using the CO₂-hydratase method. The inhibitor concentrations causing up to 50% inhibition (IC₅₀) were 2.09 M for HCA-I (r²:0.9273) and 1.83 M for HCA-II (r²:9749). In conclusion, it was demonstrated that carbonic anhydrase enzyme in erythrocytes was significantly inhibited by the ethanol both in in vitro and in vivo.     

The effect of isosorbide dinitrate on uterine and ovarian blood flow in cycling and early pregnant mares: A pilot study

Poor uterine perfusion has been proposed as a cause of infertility in mares. The objective of this study was to investigate the effect of isosorbide dinitrate (ISDN), a nitric oxide donor, on uterine and ovarian blood flow resistance during diestrus and early pregnancy in mares. Six Trotter mares, aged 7 to 14 years, were examined daily during the first 11 days of three diestrous periods, and five of those mares were also examined during the first 11 days of two pregnancies. Six mares randomly received a placebo, a low dose (30 mg, ISDN30), or a high dose of ISDN (60 mg, ISDN60) through three nonconsecutive cycles. The treatments were administered orally, every 12 hours from Day 1 to 11 of the cycle (Day 0 = ovulation). Five of the 6 mares received a placebo or 60 mg of ISDN orally every 12 hours from Day 1 to 11 of pregnancy. The mares were short cycled on Day 12 of each trial. Transrectal color Doppler was used to determine blood flow resistance semiquantitatively and expressed as pulsatility index. Mean pulsatility index of both uterine arteries combined and of the dominant (ipsilateral to the CL) ovarian artery was lower (treatment effects: P ≤ 0.01; time effects: P ≤ 0.002) in mares receiving 30 mg or 60 mg of ISDN compared with placebo-treated mares. Blood flow resistance in the dominant ovarian artery was lower in ISDN-treated pregnant mares than in placebo-treated pregnant and cycling mares (treatment effect: P = 0.04; time effect: P = 0.003). Isosorbide dinitrate increases uterine and ovarian perfusion in cycling mares and ovarian perfusion in early pregnant mares. Further studies are needed to investigate these effects in relation to fertility of the mare.     

Influence of copper on the early post-implantation mouse embryo: An in vivo and in vitro study

Summary Female mice were injected intravenously with copper sulphate on either the 7th day (early egg cylinder stage of development), the 8th day (late egg cylinder stage), or the 9th day (early somite stage of development), and examined on the 10th day of gestation. Injection on the 7th day was found to be embryo-lethal; when females were injected on the 8th day, the majority of the surviving embryos exhibited anomalies of the neural tube and/or the heart, while injection on the 9th day resulted in a very low incidence of anomalies. The most common malformations seen on the 10th day involved failure of closure of the neural tube in the head region of the embryo, and various types of anomalies of cardiac rotation and shape. When additional females injected on the 8th day were examined on the 12th day, a high proportion of the fetuses examined had developed exencephaly.A further group of embryos from untreated females were explanted on the 9th day and cultured in vitro in various concentrations of copper sulphate. The lowest levels tested had little obvious effect on neural tube closure. Intermediate doses resulted in, retarded and anomalous embryonic development, while the highest levels employed resulted in neural tube and cardiac anomalies similar to those produced in vivo.The results demonstrate both the direct toxic effect of copper on embryonic development and that the stage of embryonic development at the time of exposure determines both the nature and the extent of the effect.     

The hyporheic zone: Hydrogeological and geochemical study of a stream in the pyrenees mountains

The hydrogeological and geochemical characteristics of the hyporheic zone were studied for a year on a 30 m² site within a stream in the Pyrenees Mountains. This included the drawing of potentiometric maps, measuring hydraulic conductivity and porosity, and the monthly analysis of major chemical elements in water samples. Use of the combined data led to the clarification of certain aspects of the characteristics, functioning and development of the hyporheic zone. Even though the area studied lies in a zone of groundwater recharge, the direct vertical exchange between surface- and groundwater does not seem to be determinant in the potentiometric and chemical development of the area. However, the state of reserves, which can be reduced or reconstituted, seems to play an essential role in flow dynamics, and thus of the chemistry of this area. Flow dynamics in the hyporheic zone apparently are of the longitudinal-transversal type, related to the local stream morphology. The results show how difficult it is to define the hyporheic zone in a structural sense, even though the zone represents an entity that is clearly characterized by specific and identifiable dynamics.     

Characterization of non-lymphoid cells in the white pulp of the mouse spleen: An in vivo and in vitro study

Summary Non-lymphoid cells (marginal metallophils, follicular immunecomplex-retaining cells, interdigitating cells), which are present in certain areas of the white pulp in the mouse spleen were characterized by means of (immuno)enzyme histochemical techniques, carbon uptake and experiments with lethal X-irradiation. Marginal metallophils are clearly present at the inner border of the marginal zone and show a very strong, E-600 sensitive, non-specific esterase (NSE) activity. Follicular immune-complex-retaining cells show a weak and diffuse NSE activity and no carbon uptake as shown by the combined application of an immunohistoperoxidase technique (for the demonstration of immune complexes), enzyme histochemistry (for NSE activity) and carbon uptake (for phagocytosis). Interdigitating cells show a distinct focus of NSE activity in the cytoplasm, weak carbon uptake and high radiation sensitivity. Demonstration of NSE activity is useful for the identification of the different non-lymphoid cells in the white pulp of the mouse spleen. It is suggested that the in vitro observed dendritic cells of Steinman and Cohn (1973) belong to the mononuclear phagocyte system, as transitional cells are encountered with cytological features of both dendritic cells and macrophages. These in vitro dendritic cells (or a portion of them) are probably similar to the interdigitating cells.Abbreviations HRP horseradish peroxidase - IDC interdigitating cells - PALS periarteriolar lymphocytic sheath - NSE non-specific esterase