The objective of this review article is to summarize current knowledge of blood flow and perfusion-related parameters, which usually go hand in hand and in turn define the cellular metabolic microenvironment of human malignancies. A compilation of available data from the literature on blood flow, oxygen and nutrient supply, and tissue oxygen and pH distribution in human tumors is presented. Whenever possible, data obtained for human tumors are compared with the respective parameters in normal tissues, isotransplanted or spontaneous rodent tumors, and xenografted human tumors. Although data on human tumors in situ are scarce and there may be significant errors associated with the techniques used for measurements, experimental evidence is provided for the existence of a compromised and anisotropic blood supply to many tumors. As a result, O2-depleted areas develop in human malignancies which coincide with nutrient and energy deprivation and with a hostile metabolic microenvironment (e.g., existence of severe tissue acidosis). Significant variations in these relevant parameters must be expected between different locations within the same tumor, at the same location at different times, and between individual tumors of the same grading and staging. Furthermore, this synopsis will attempt to identify relevant pathophysiological parameters and other related areas future research of which might be most beneficial for designing individually tailored treatment protocols with the goal of predicting the acute and/or long-term response of tumors to therapy.

https://cancerres.aacrjournals.org/content/canres/49/23/6449.full.pdf

Blood Flow, Oxygen and Nutrient Supply, and Metabolic Microenvironment of Human Tumors: A Review

In this paper, we consider the domain of executive functions (EFs) and their possible role in developmental psychopathologies. We first consider general theoretical and measurement issues involved in studying EFs and then review studies of EFs in four developmental psychopathologies: attention deficit hyperactivity disorder (ADHD), conduct disorder (CD), autism, and Tourette syndrome (TS). Our review reveals that EF deficits are consistently found in both ADHD and autism but not in CD (without ADHD) or in TS. Moreover, both the severity and profile of EF deficits appears to differ across ADHD and autism. Molar EF deficits are more severe in the latter than the former. In the few studies of more specific EF tasks, there are impairments in motor inhibition in ADHD but not in autism, whereas there are impairments in verbal working memory in autism but not ADHD. We close with a discussion of implications for future research.

Executive Functions and Developmental Psychopathology

• To evaluate dorsolateral prefrontal cortex (DLPFC) physiology and function simultaneously, 20 medication-free patients with chronic schizophrenia and 25 normal controls underwent three separate xenon Xe 133 inhalation procedures for determination of regional cerebral blood flow (rCBF): first at rest, then while performing an automated version of the Wisconsin Card Sort (WCS), a DLPFC-specific cognitive test, and while peforming a simple number-matching (NM) test. During rest, patients had significantly reduced relative, but not absolute, rCBF to DLPFC. During NM, no specific region differentiated patients from controls. During WCS, however, both absolute and relative rCBF to DLPFC significantly distinguished patients from controls. While controls showed a clear increase in DLPFC rCBF, patients did not. The changes were regionally specific, involving only DLPFC. Furthermore, in patients, DLPFC rCBF correlated positively with WCS cognitive performance, suggesting that the better DLPFC was able to function, the better patients could perform. Autonomic arousal measures, the pattern of WCS errors, and results of complementary studies suggest that the DLPFC finding is linked to regionally specific cognitive function and is not a nonspecific epiphenomenon.

Physiologic dysfunction of dorsolateral prefrontal cortex in schizophrenia. I. Regional cerebral blood flow evidence.

The purpose of this review is to extend the existing application of the frontal lobe hypothesis of cognitive aging beyond the limited work on inhibitory control (F. N. Dempster, 1992) to include memory processes supported by the prefrontal cortex. To establish a background for this analysis, I review existing models of prefrontal cortex function and present a synthesized model that includes a general function of temporal integration, supported by 4 specific processes: prospective memory, retrospective memory, interference control, and inhibition of prepotent responses. I found the frontal lobe hypothesis to perform well, with the exception of an inability to account for age-related declines in item recall and recognition memory, possibly a result of age-related declines in medial temporal function.

An application of prefrontal cortex function theory to cognitive aging.

The sections in this article are:


1
Essence of Prefrontal Function: Regulation of Behavior by Representational Knowledge
11
Subdivisions of Prefrontal Cortex

12
Global Nature of Prefrontal Syndrome in Humans

13
Animal Model for Prefrontal Function in Humans

14
Delayed-Response Tests and Varying Interpretations of Their Functional Significance

15
Distractability and Perseveration: Secondary Consequences of Basic Defect in Representational Memory

16
Representational Memory in Wisconsin Card Sort and Other Diagnostic Tests of Prefrontal Function in Humans

17
Localization of Delayed-Response Function: Principal Sulcus

18
Circuit Basis of Visuospatial Functions




2
Accessing and “On-Line” Processing of Representations in Visuospatial Domain: Parietal-Prefrontal Connections
21
Visuospatial Representational Memory in Humans

22
Spatial-Mnemonic Nature of Delayed-Response Deficit: Domain-Specific Memory Loss

23
Topography of Representational Memory in Prefrontal Cortex

24
Electrophysiological Evidence of Spatial-Mnemonic Processes in Principal Sulcus

25
Parietal-Prefrontal Connectivity

26
Columnar and Laminar Framework for Feedforward and Feedback Mechanisms

27
Functional Significance of Parietal-Prefrontal Collaboration




3
Long-Term Memory and “Off-Line” Processing: Prefrontal-Limbic Connections
31
Role of Hippocampus in Spatial Memory

32
Multiple Connections Between Principal Sulcus and Hippocampal Formation

33
Quadripartite Neural Network: Parietal-Temporal-Cingulate-Prefrontal Circuit

34
Limbic Contribution to Spatial Memory




4
Response Initiation and Inhibition: Projections to Striatum, Tectum, Thalamus, and Premotor Cortex
41
Motor-Control Functions of Prefrontal Cortex

42
Cortical-Striatal Pathway and Related Feedback Loops

43
Cortical-Tectal Pathway

44
Thalamic-Cortical Systems

45
Prefrontal-Premotor Connections: Anterior Supplementary Motor Cortex Relays

46
Functional Speculations




5
Modulatory Mechanisms: Brain Stem Catecholamine Projections
51
Activation of Cognitive Machinery

52
Concentration and Synthesis of Catecholamines in Primate Cortex

53
Brain Stem Innervation of Prefrontal Cortex

54
Delayed-Response Deficits and Recovery Produced by Catecholamine Loss and Replacement in Prefrontal Cortex

55
Circuit Basis for Neuromodulation in Principal Sulcus




6
Multiple Subsystems of Prefrontal Cortex: Unity or Diversity of Function
61
Unity or Diversity of Prefrontal Function

62
Frontal Eye Fields

63
Inferior Convexity

64
Orbital Prefrontal Cortices

65
Problem of Integration




7
Diseases Affecting Prefrontal Cortex
71
Schizophrenia: Loss of Corticocortical Processing and Regulation of Behavior by Representational Knowledge

72
Wernicke-Korsakoff Syndrome: Loss of Thalamocortical and Brain Stem Modulatory Mechanisms

73
Huntington's Chorea and Parkinson's Disease: Loss of Prefrontal-Striatal Mechanisms and Initiation or Inhibition of Motor Response

74
Overview of Neurobiology of Disease




8
Summary

Circuitry of Primate Prefrontal Cortex and Regulation of Behavior by Representational Memory

The finding in schizophrenic patients of a reversal of the normal frontal to posterior pattern of brain metabolic activity with positron emission tomography (PET) is of interest, but its relevance to psychopathology is unknown. Using PET, the authors studied 21 patients with chronic schizophrenia and 21 age- and sex-matched control subjects. Although eight of the 21 patients and only one of the control subjects showed a relatively lower anteroposterior metabolic gradient, no clinical correlates of this finding were noted. In addition, cerebral atrophy, as determined by CAT scan, was not associated with this aberrant metabolic pattern.

Clinical correlates of decreased anteroposterior metabolic gradients in positron emission tomography (PET) of schizophrenic patients

The cerebral metabolic rate for glucose, as measured with positron emission tomography and fluorine-18-labeled 2-deoxy-D-glucose, was significantly higher in four healthy young subjects with trisomy 21 syndrome (Down's syndrome) than the mean rate in healthy young controls. The rate of cerebral glucose utilization in the frontal lobe of a 51-year-old subject with Down's syndrome was significantly lower than the rate in the young subjects with this syndrome, but approximated the rate in middle-aged controls. Thus glucose utilization by the brain appears to be excessive in young adults with Down's syndrome but may decline with age in some brain regions.

https://science.sciencemag.org/content/sci/221/4612/781.full.pdf

Down's Syndrome in Adults: Brain Metabolism

Positron emission tomography (PET) was employed to examine time-dependent changes in blood-brain barrier (BBB) permeability to (68Ga)ethylenediaminetetraacetate (EDTA) in the rhesus monkey, following reversible barrier opening by intracarotid infusion of a hypertonic mannitol solution. The PET technique, when combined with measurements of plasma radioactivity, provided a quantitative measure of the cerebrovascular permeability-area product (PA) at different times following mannitol infusion. Hypertonic mannitol treatment reversibly increased PA to (68Ga)EDTA more than 10-fold; much of the barrier effect was over by 10 min after mannitol treatment. The results show that PET can be used to measure transient changes in BBB integrity in specific brain regions, under in vivo, noninvasive conditions.

https://journals.sagepub.com/doi/pdf/10.1038/jcbfm.1984.48

R. M. Kessler

Papers

Clinical correlates of decreased anteroposterior metabolic gradients in positron emission tomography (PET) of schizophrenic patients

Down's Syndrome in Adults: Brain Metabolism

Measurement of blood-brain barrier permeability with positron emission tomography and [68Ga]EDTA.

Gilles de la tourette syndrome: studies with the fluorine-18-labeled fluorodeoxyglucose positron emission tomographic method.

18f-2-fluoro-2-deoxyglucose positron emission tomography of human cerebral gliomas