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Positron emission tomography (PET) imaging of the 18kDa translocator protein (TSPO) has been used to investigate whether microglial activation, an indication of neuroinflammation, is evident in the brain of adults with schizophrenia. Interpretation of these studies is confounded by potential modulatory effects of antipsychotic medication on microglial activity. In the first such study in antipsychotic-free schizophrenia, we have used [11C](R)-PK11195 PET to compare TSPO availability in a predominantly antipsychotic-naïve group of moderate-to-severely symptomatic unmedicated patients (n=8), similarly symptomatic medicated patients with schizophrenia taking risperidone or paliperidone by regular intramuscular injection (n=8), and healthy comparison subjects (n=16). We found no evidence for increased TSPO availability in antipsychotic-free patients compared to healthy controls (mean difference 4%, p=0.981). However, TSPO availability was significantly elevated in medicated patients (mean increase 88%, p=0.032) across prefrontal (dorsolateral, ventrolateral, orbital), anterior cingulate and parietal cortical regions. In the patients with schizophrenia, TSPO availability was also strongly correlated with negative symptoms measured using the Positive and Negative Syndrome Scale across all the brain regions investigated (r=0.651-0.741). We conclude that the pathophysiology of schizophrenia is not associated with microglial activation in the 2-6 year period following diagnosis. The elevation in the medicated patients may be a direct effect of the antipsychotic, although this study cannot exclude treatment resistance and/or longer illness duration as potential explanations. It also remains to be determined whether it is present only in a subset of patients, represents a pro- or anti-inflammatory state, its association with primary negative symptoms, and whether there are significant differences between antipsychotics.

Positron emission tomography (PET) imaging of the 18 kDa translocator protein (TSPO) has been used to investigate whether microglial activation, an indication of neuroinflammation, is evident in the brain of adults with schizophrenia. Interpretation of these studies is confounded by potential modulatory effects of antipsychotic medication on microglial activity. In the first such study in antipsychotic-free schizophrenia, we have used [

Properties of the cells (TE-CFU) that give rise within four to six days to transient endogenous erythropoietic spleen colonies in irradiated mice have been investigated. The results obtained indicate that (1) erythropoietic maturation within such colonies is highly erythropoietin-dependent, (2) the population size of TE-CFU is not erythropoietin-dependent, (3) initial exposure to a high dose of erythropoietin followed by continuing exposure to lower doses is required for maximal efficiency of colony formation by TE-CFU, (4) successful transplantation of TE-CFU has not been achieved, but they appear among the progeny of transplanted hemopoietic cells, (5) TE-CFU are defective in mice of genotype W/Wv. These findings are consistent with the view that the TE-CFU assay detects a class of early erythropoietin-sensitive progenitor cells committed to erythropoietic diffferentiation, rather than "abortive" colony formation by pluripotent stem cells.

Previous studies have shown that erythroid precursors at sequential stages of differentiation along the red cell pathway can be distinguished by differences in the size and maturation kinetics of the colonies to which they give rise in vitro. Using criteria based on these two parameters, it is thus possible to identify three distinct erythroid progenitor cell populations in the mouse, known as day 8 BFU- E, day 3 BFU-E, and CFU-E. These cell types have now been shown to differ in a number of other respects, including progenitor cell size, sensitivity to cycle-active agents, response to plethora, and effects of the W/Wv genotype. In addition, a comparison of the differences found between day 8 BFU-E and day 3 BFU-E on one hand and those distinguishing day 3 BFU-E and CFU-E on the other provides support for the view that early erythropoietic cell differentiation involves a series of changes that take place long before competence to synthesize hemoglobin becomes manifest.

1. The mountainous highlands of south-western China, Chinese Tibet and north­-eastern Burma, consist of a high platform which projects southward from the Tibetan tableland. That platform lies along the foundations of the ancient Indo-Malayan mountains and athwart the eastern end of the Himalaya. It appears, on examination of a map, to have caused the eastern continuation of the Alpine-Himalayan Systems to have been diverted southward as the Burma and Malay Arcs. Further to the north­ east the tableland of east central Asia ends abruptly above the lowlands of eastern China. Its eastern front forms the Great Khingan Mountains, which have been regarded by the late Prince Kropotkin (1904, p. 333) as the continuation of the Himalaya. This view of the eastern prolongation of the Himalaya into central China has been also adopted by Archibald Little (1905, map opposite p. 19, and p. 209). The whole geography of south-western China and the adjacent lands is dominated by the inter­ action of mountain movements belonging to two far-distant periods. The older moun­tains, the Indo-Malayan, belong to the Hercynian group of earth movements, which happened toward the end of the Paleozoic Era. The younger mountain system, the Himalayan, is Kainozoic, and though its uplifts happened at intervals from Upper Eocene to Pliocene, its movements culminated in the Middle .Kainozoic, and were probably most important in the Oligocene and Miocene. The mountain plan of south­ eastern Asia has been considered as a combination of the mountain lines of Eurasia, which trend from W. and E., with the border chains of the Pacific, which cross at high angles the eastern end of the Asiatic mountains. The history of the Indian Ocean is incomplete, until it be known what was happening on its north-eastern side synchronous with the movements which made the rift-valleys of East Africa. Chinese Tibet is one of the critical areas for the solution of these problems, for it is opposite the eastern end of the Himalaya. This country has also attracted attention from the parallelism of the three great rivers which cross it.

A time course study of the sequential appearance of erythropoietin-dependent colonies and bursts (derived from CFU-E and BFU-E, respectively) was performed on mouse hemopoietic cells cultured in methyl cellulose containing 2-mercaptoethanol. A new type of small, short-lived burst was found to be apparent by the third day in culture. By the sixth day most of these bursts had lysed. At the same time, differentiating erythroblasts began to be detectable in the large, late appearing bursts described previously. These two types of burst, differing from each other and from CFU-E derived colonies both in their ultimate size and morphology, as well as in their time course of appearance and lysis, were compared in other ways. It was found that early burst formation required about 100 times more erythropoietin than that needed to stimulate CFU-E. On the other hand, early burst formation required less than one-quarter of the amount of erythropoietin needed to obtain the large, late appearing bursts. Comparison of the distribution of early burst progenitors relative to pluripotent stem cells (CFU-S) in individual spleen colonies gave a correlation coefficient that was also intermediate between that obtained comparing CFU-S with CFU-E and that obtained comparing CFU-S with the progenitors of late bursts. These results suggest that decreasing proliferative capacity is associated with progressively increasing erythropoietin responsiveness as primitive erythropoietic progenitors move from a position close to pluripotent stem cells through several differentiation steps to reach a stage just prior to the onset of detectable hemoglobin synthesis.

Differentiation in the hemopoietic system is a complex process involving a progression of changes that extend through many cell divisions. In the most mature hemopoietic cells, the results of differentiation can be visualized directly and morphologic criteria can therefore be used to determine the relative positions of cells in the terminal stages of blood cell production. Detection of earlier cell types has relied on the development of assay procedures that exploit the capacity of primitive hemopoietic cells to give rise to colonies of mature progeny under appropriate conditions in vivo or in culture. A variety of such colony assays now exist (1, 3, 10, 11, 13, 14, 16, 17), and their use has led to a conceptual model of the hemopoietic system which makes a distinction between pluripotent stem cells or spleen colony-forming units (CFU-s), and secondary progenitor cell types still capable of extensive proliferation but committed to differentiation along a single pathway (9). Examples of this latter class of progenitor have been identified for bopth the granulopoietic and erythropoietic pathways. These are the progenitors of the granulopoietic colonies and the progenitors of the large erythroid bursts detected by established in vitro assay procedures (1, 3, 13), historically referred to as CFU-c (originally the only “colony-forming unit in culture”) and BFU-e (“erythropoietin-dependent burst-forming unit”), respectively.

Changes in the number and erythropoietin sensitivity of erythropoietic progenitor cells (CFU-E or E) capable of erythropoietin-dependent colony formation in culture have been measured in mice subjected to a variety of manipulations known to affect erythropoiesis. Injection of erythropoietin into mice whose E levels had been reduced by transfusion-induced plethora stimulated a striking increase in this population within 24 hours in both spleen and marrow. Following irradiation and marrow transplantation E were found to regenerate in the spleen with a population doubling time of 6 hours. Evidence of erythropoietin-dependent stimulation of E in vivo under conditions of hemopoietic regeneration was also obtained, although substantial numbers of E were detected in both regenerating spleen and marrow of plethoric mice even without erythropoietin administration, In the same experiments comparable effects of erythropoietin on pluripotent stem cells or the progenitors of granulopoietic colonies in culture were not observed. Detailed studies of the dependence of colony formation on erythropoietin concentration in culture showed variations in erythropoietin sensitivity of E from normal, regenerating and plethoric, erythropoietin-stim-ulated spleen and marrow. This finding provides the basis for an extremely fine mechanism regulating the flow of erythropoietic differentiation at the level of the production of E. The number of E present in the marrow of untreated W/WV mice was normal, but their sensitivity to erythropoietin in culture was decreased to a similar extent as E from normal mice exposed to a heightened erythropoietic demand. Plethora had a more marked effect in reducing E numbers in W/WV mice than in +/ + controls and stimulation of E following subsequent erythropoietin administration was highly defective. The results of these studies provide further evidence that cells identified as E represent a stage of differentiation along the erythropoietic pathway that is several steps removed from pluripotent stem cells and support the view that erythropoiesis, granulopoiesis and stem cell self-renewal are regulated to a major degree by independent mechanisms.

Three assays for erythropoietic progenitor cells have been applied to mice of genotype f/f and to nearly congenic +/+ controls. When f/f mice were tested for their ability to generate transient endogenous erythroid spleen colonies 4-6 days after 800 rads and 10 units of erythropoietin, the numbers of such colonies detected were greatly reduced, although normal numbers of spleen colonies appeared at later times (9-12 days) postirradiation. In contrast, cells capable of erythropoietic colony formation in culture (CFU-E) were present within the normal range in both f/f spleen and marrow and their sensitivity to erythropoietin in culture was the same as that found previously for CFU-E in the marrow and spleen of +/+ mice. Transfusion-induced plethora reduced the number of CFU-E in marrow to a similar extent in both f/f and +/+ mice; likewise, subsequent administration of 10 units of erythropoietin induced a rapid return in the number of marrow CFU-E in both genotypes. In the spleen, CFU-E numbers were approximately three-fold lower in f/f mice in each group. These results support the view that the 5 day assay for transient endogenous spleen colonies detects cells (TE-CFU) that are different from both CFU-E and pluripotent stem cells (CFU-S), although possibly overlapping to some extent with the immediate progenitors of CFU-E. The results also indicate that the generation or maturation of TE-CFU represents a primary site of expression of the f/f defect.

The differentiated state of mouse erythropoietic progenitor cells (CFU-E), detected by their ability to form erythropoietin-dependent colonies in vitro, has been investigated. Transfusion-induced plethora was found to reduce the population size of CFU-E in both spleen and femoral marrow, which indicates that a significant number of CFU-E arise by differentiation processes that are themselves erythropoietin-dependent. Individual spleen colonies were found to be heterogeneous in their content of CFU-E, and the numbers of CFU-E per colony were not correlated either positively or negatively with the numbers of granulocyte-macrophage progenitors (CFU-C) present in the same colonies. The absence of a negative correlation between CFU-E and CFU-C indicates that the erythropoietic and granulopoietic pathways of differentiation are not mutually exclusive within individual spleen colonies. The numbers of CFU-E per spleen colony were also found to vary independently of the numbers of pluripotent stem cells (CFU-S) per colony; in contrast, as found previously, the numbers of CFU-C and CFU-S per colony were positively correlated. These results indicate that more randomizing events separate CFU-E from CFU-S than separate CFU-C from CFU-S, and are consistent with the view that CFU-E occupy a position on the erythropoietic pathway of differentiation that is more remote from the pluripotent stem cells than is the corresponding position of CFU-C on the granulopoietic pathway.

The increase in splenic plaque-forming cell (PFC) responsiveness which occurs in mice following the injection of a primary dose of 108 sheep red blood cells was measured using the spleen cell transfer system. As for grafts of normal spleen cells, the peak direct (19S) and indirect (7S) responses obtained with grafts of primed spleen cells were found to be related to the number of cells transferred in a near-parabolic fashion. Splenic direct PFC responsiveness as measured by the regression defining the corresponding graft-response relationship was increased about five times 4 weeks after priming; focus-forming capacity was also increased by a similar factor. At the same time indirect PFC responsiveness was increased almost twenty times. These results are discussed in terms of antigen-induced changes in the populations of PFC precursors and antigen-reactive auxiliary cells in the spleen.