Local cerebral glucose utilization in controlled graded levels of hyperglycemia in the conscious rat

Local cerebral glucose utilization assayed by the [14C]deoxyglucose ([14C]DG) method and calculated by means of its operational equation with values for the rate constants and lumped constant determined in rats under physiological conditions remains relatively stable with variations in arterial plasma glucose concentration within the normoglycemic range. Large changes in arterial plasma glucose level may, however, significantly alter the values of these constants and lead to artifactual results. Values for the lumped constant have been measured and reported for a wide range of arterial plasma glucose concentrations ranging from hypoglycemia to hyperglycemia in the rat (Schuier et al., 1981; Suda et al., 1981; Pettigrew et al., 1983). In the present study we have redetermined the rate constants in rats with arterial plasma glucose levels clamped at approximately 350, 450, and 550 mg/dl (i.e., 19, 25, and 31 mM) by a glucose clamp technique. The rate constants for the transport of DG from plasma to brain, K1*, and its phosphorylation in tissue, k3*, were found to decline with increasing plasma glucose levels, while the rate constant for its transport back from brain to plasma, k*2, remained relatively unchanged from its value in normoglycemia. These rate constants were used together with the previously determined values for the lumped constants to calculate local rates of cerebral glucose utilization in three groups of rats in which arterial plasma glucose levels were clamped at approximately 350, 450, and 550 mg/dl (i.e., 19, 25, and 31 mM). Average glucose utilization in the brain as a whole was unchanged in hyperglycemia from the values calculated in normoglycemic rats with the standard normal set of constants. Changes in the rate of glucose utilization were found, however, in the hypothalamus, globus pallidus, and amygdala during hyperglycemia.

Local cerebral glucose utilization non-selectively elevated in rapid eye movement sleep of the fetus

The [14C]deoxyglucose method for measuring local cerebral glucose utilization was employed in an effort to identify regions of the brain which participate in the increased neuronal activity of rapid eye movement (REM) sleep. The study was conducted in near term fetal sheep in which REM periods are of sufficient duration to obtain reliable data with this method. Neither the postulated executive centers of REM sleep nor those structures in the brainstem known to participate in the electrical activity peculiar to this sleep phase were found to have selectively elevated rates of glucose utilization. Rather, these regions shared equally with virtually all other structures in having rates higher than those which accompany non-REM sleep.

Selective alterations in cerebral metabolism within the mesocorticolimbic dopaminergic system produced by acute cocaine administration in rats

The 2-[14C]deoxyglucose method was used to examine the effects of acute intravenous administration of cocaine on local cerebral glucose utilization in rats. These effects were correlated with the effects of cocaine on locomotor activity assessed simultaneously in the same animals. At the lowest dose of cocaine, 0.5 mg/kg (1.47 mumol/kg), alterations in glucose utilization were restricted to the medial prefrontal cortex and nucleus accumbens. Metabolic activity at 1.0 mg/kg (2.9 mumol/kg) was altered in these structures, but in the substantia nigra reticulata and lateral habenula as well. The selectivity of cocaine's effects at low doses demonstrates the particular sensitivity of these structures to cocaine's actions in the brain. In contrast, 5.0 mg/kg (14.7 mumol/kg) produced widespread changes in glucose utilization, particularly in the extrapyramidal system. Only this dose significantly increased locomotor activity above levels in vehicle-treated controls. Rates of glucose utilization were positively correlated with locomotor activity in the globus pallidus, substantia nigra reticulata, and subthalamic nucleus, and negatively correlated in the lateral habenula.

Effects of leukocytic pyrogen (interleukin-1) on local cerebral glucose utilization in rats with and without premedication with indomethacin or dexamethasone

Changes in body temperature were recorded in freely moving rats given phosphate-buffered saline or leukocytic pyrogen (interleukin-1) while the animals were in an infant incubator maintained at 25.5 +/- 0.5 degrees C. The leukocytic pyrogen increased body temperature by at least 1 degree C within 1 h. This rise in temperature was prevented by premedication with indomethacin (10 mg/kg) but not dexamethasone (0.5 mg/kg) given 15 min before the leukocytic pyrogen. Local rates of glucose utilization were measured in 47 regions of the central nervous system. In none of the regions previously reported to have an increased rate of glucose utilization associated with an ambient temperature of 32.5 degrees C (McCulloch et al., 1982b) was an increase found in the present experiments. It was concluded that the intensity of the changes in local cerebral glucose utilization in response to the fever caused by the leukocytic pyrogen was insufficient to be measured. Neither indomethacin nor dexamethasone caused remarkable changes in rates of local glucose utilization.

Measurement of local cerebral blood flow with [14C]iodoantipyrine in the mouse

Local cerebral blood flow was measured in the mouse by means of the [14C]iodoantipyrine method. This method has been previously used in the monkey, dog, cat, and rat, but its application to small mammals such as the mouse requires special attention to potential sources of error. The small size of the mouse brain requires special attention to the rapid removal and freezing of the brain to minimize effects of postmortem diffusion of tracer in the tissue. Because of the relatively low diameter/length ratios of the catheters needed for arterial sampling in small animals, substantial errors can occur in the determination of the time course of the [14C]iodoantipyrine concentration in the arterial blood unless corrections for lag time and dead space washout in the catheter are properly applied. Local cerebral blood flow was measured in seven awake mice with appropriate care to minimize these sources of error. The values were found to vary from 48 ml/100 g/min in the corpus callosum to 198 ml/100 g/min in the inferior colliculus. The results demonstrate that the [14C]iodoantipyrine method can be used to measure local cerebral blood flow in the mouse and that the values in that species are, in general, somewhat higher than those in the rat.

Local glucose utilization of the brain and pineal gland during stimulation of the cervical sympathetic trunk

The quantitative autoradiographic 2-[14C]deoxyglucose method was employed to map the metabolic activity of the superior cervical ganglion and the entire brain during unilateral electrical stimulation of the cervical sympathetic trunk in the urethane-anesthetized rat. Stimulation of the cervical sympathetic trunk increased glucose utilization in the ipsilateral superior cervical ganglion (+95%) but did not produce side-to-side differences in glucose utilization in any of the brain structures examined in this study. Compared to the control nonstimulated animals, the rate of glucose metabolism in the pineal gland was increased 71% following stimulation of the cervical sympathetic trunk. The pineal gland was the only brain region out of 87 structures examined in which glucose utilization was increased by electrical stimulation of its sympathetic innervation.

Stimulation of matrix formation in rabbit chondrocyte cultures by ascorbate. 2. Characterization of proteoglycans

The effect of ascorbate on the proteoglycans synthesized by rabbit articular chondrocytes was studied in first- and third-passage cultures for 12 and 26 days total duration, respectively. L-Ascorbate (0.2 mM) was added daily to half of the flasks after attachment of the cells. The cultures were labeled with Na2[35S]O4 or [14C]-glucosamine and [3H]-proline. Proteoglycans were isolated from the media and pericellular matrices by dissociative extraction and associative density gradient centrifugation. There was a large decline in the amount of proteoglycan synthesized between early and late cultures. Ascorbate increased the DNA content, amount of radiosulfate incorporated into glycosaminoglycans per microgram of DNA, and the proportion of labeled proteoglycan in the pericellular fraction of both short- and long-term cultures. The proteoglycans of the media and matrices of all cultures, with and without ascorbate, eluted as aggregates under associative column chromatographic conditions. The proteoglycans of 26-day cultures exhibited a higher degree of polydispersity in size than those of the short-term culture and contained small amounts of keratan (2-5%) and dermatan sulfate (4-8%) as assessed by keratanase and chondroitinase digestions, respectively. The effect of ascorbate, therefore, was to increase the amount of proteoglycan formed and to direct it into matrix deposition rather than to alter its quality.

Metabolic mapping of the oculomotor system in MPTP-induced parkinsonian monkeys

The quantitative autoradiographic 2-[14C]deoxyglucose method was used to map the distribution of alterations of local cerebral metabolic rate for glucose (lCMRGlc) in the oculomotor system of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-(MPTP)-induced parkinsonian monkeys. The lCMRGlc was decreased in the frontal eye fields and in the paralamellar mediodorsal thalamus in the parkinsonian monkeys as compared to normal controls. No changes in lCMRGlc were observed in other areas of the oculomotor system. L-Dopa therapy reversed the oculomotor symptoms in these monkeys, as well as the decrease of lCMRGlc in the frontal eye fields and the paralamellar mediodorsal thalamus. Because the frontal eye fields are known to be involved in the initiation of voluntary saccades, these findings suggest a functional anatomical basis for the oculomotor deficits in Parkinson's disease.

Effect of fusarochromanone and T-2 toxin on articular chondrocytes in monolayer culture

The effect of fusarochromanone and T-2 toxin on DNA synthesis and radio-sulfate incorporation by rabbit articular chondrocytes was studied in monolayer culture. T-2 toxin reduced DNA more than 50% at 5 x 10(-9) M; fusarochromanone caused small but progressive decrements over a range of 5 x 10(-8) to 10(-6) M. These actions are not specific for chondrocytes. The findings lend no support to the hypothesis that fusarochromanone, at least in unmodified form, is the etiologic agent in Kashin-Beck disease.

DNA repair by articular chondrocytes. V. O6 methylguanine-acceptor protein activity in resting and cultured rabbit and human chondrocytes

The level of O6-methylguanine acceptor protein activity was examined in rabbit and human articular chondrocytes of different ages. The activity per microgram of DNA in rabbit chondrocytes was 5-fold lower than in humans. There was no age-dependent decrease in the activity of resting or cultured chondrocytes of either species. The values for resting cells were comparable to those of cultured cells. The lack of age-related differences in methyltransferase activity, in contrast to nucleotide excision repair [Mech. Ageing Dev. 32 (1985) 39-55], indicates that separate repair systems behave differently with respect to chronological aging. The methyl transferase activity may be more essential for survival of articular chondrocytes and therefore more highly conserved with age.

Effects of antidromic stimulation of the ventral root on glucose utilization in the ventral horn of the spinal cord in the rat

Electrical stimulation of the proximal stump of the transected sciatic nerve increased glucose utilization in the ventral horn of the spinal cord, with the greater increase in Rexed's lamina IX. Antidromic stimulation of the ventral root, however, did not change glucose utilization in the ventral horn. These results suggest that the axon terminals and not the cell bodies are the sites of enhanced metabolic activity during increased electrical activity in these elements.

Local cerebral metabolic effects of L-dopa therapy in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced parkinsonism in monkeys

The quantitative 2-deoxy[14C]glucose autoradiographic method was used to map the distribution of alterations in local cerebral glucose utilization that accompanies clinically effective chronic L-dopa therapy of rhesus monkeys made parkinsonian by the administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). This pattern of changes was compared to the effects of a similar treatment regimen in normal monkeys. L-Dopa (100 mg with 10 mg carbidopa) was administered orally to normal and parkinsonian monkeys 3 times daily for 60-120 days prior to measurement of local cerebral glucose utilization. In parkinsonian monkeys treated with L-dopa, signs and symptoms of parkinsonism were controlled or suppressed, and widespread increases in glucose utilization were seen throughout the brain. Cerebral metabolic activity was increased both in areas rich in dopaminergic receptors, such as the caudate and putamen, and in nondopaminergic areas involved in motor functions. In many structures the rates of glucose utilization in L-dopa-treated parkinsonian monkeys were increased to levels that far exceeded rates measured in normal monkeys. In sharp contrast, similar treatment with L-dopa in normal monkeys had little if any effect on local cerebral glucose utilization. L-Dopa, then, appears to have an action in animals with selective lesions of the substantia nigra pars compacta produced by MPTP that is distinctly different from its effects in the normal monkey.

Effects of insulin on local cerebral glucose utilization in the rat

The effects of hyperinsulinemia on local cerebral glucose utilization were studied by the quantitative autoradiographic 2-[14C]deoxyglucose method in normal conscious rats under steady-state normoglycemic conditions. Hyperinsulinemia and a steady state of normoglycemia were achieved and maintained during the experimental period by a continuous intravenous (i.v.) infusion of insulin given simultaneously with a programmed i.v. infusion of D-glucose. Hyperinsulinemia under normoglycemic conditions did not change the average rate of glucose utilization in the brain as a whole, but significant increases in local glucose utilization were found selectively in the ventromedial, dorsomedial, and anterior hypothalamic nuclei. The results suggest that a known anatomical pathway linking the dorsomedial and anterior nuclei with the ventromedial nucleus of the hypothalamus may be physiologically activated in response to hyperinsulinemia.

Osteoarthritis as a remodeling process

Osteoarthritic remodeling involves intimately related events in 3 compartments of the joint surface: the cartilage, osteochondral junction, and capsular tissues. Despite common wisdom, it is difficult to identify abnormalities confined to the cartilage. This places theoretical constraints on what can be accomplished by antiproteases in the treatment of degenerative joint disease.

Changes in local cerebral glucose utilization associated with Parkinson's syndrome induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) in the primate

The quantitative 2-[14C]deoxyglucose autoradiographic method was used to map the pattern of alterations in local cerebral glucose utilization associated with the Parkinsonian syndrome induced by the administration of the neurotoxin, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), to rhesus monkeys. Monkeys treated with the neurotoxin exhibited both behavioral symptoms (e.g. akinesia, rigidity, flexed posture, and eyelid closure) and neuropathological changes (degeneration of the cells of the substantia nigra pars compacta) that closely paralleled those in human Parkinson's disease. Glucose utilization was significantly reduced in the pars compacta of the substantia nigra and in the subthalamus, and increased in the external segment of the globus pallidus. Outside the basal ganglia reductions in glucose utilization were limited to the mediodorsal nucleus of the thalamus, frontal eye fields, and ventral tegmental area. The results of these studies indicate that the profound functional and behavioral deficits in MPTP-induced Parkinson's syndrome are the consequences of highly selective functional changes in a few cerebral structures, mainly within the basal ganglia.

Kashin-Beck disease

Kashin-Beck disease is the most frequent rheumatologic problem of children in China. Although it is acquired environmentally and frequently leads to life-long crippling, the etiology remains an enigma.

A method for cytologic examination of cartilaginous lesions

Chondrocytes, dissociated from their matrix with trypsin and clostridial collagenase, retain their cytologic integrity. Successful preparations have been made from postmortem as well as surgical specimens. The method may lend itself to diagnosis of both neoplastic and developmental lesions.

Effects of insulin on hexose transport across blood-brain barrier in normoglycemia

The effects of insulin on 3-O-[14C]methylglucose transport across the blood-brain barrier (BBB) were studied in conscious rats under steady-state normoglycemic conditions. The [14C]methylglucose was infused intravenously at a constant rate, and animals were killed at various times between 5 and 30 min after the initiation of the infusion. The time course of the arterial plasma concentration of [14C]methylglucose was determined in timed arterial blood samples taken during the infusion. Local cerebral tissue concentrations of [14C]methylglucose at the time of killing were determined by quantitative autoradiography of brain sections. The rate constants for inward and outward transport of [14C]methylglucose across the BBB, K1, and k2, respectively, were estimated by a least-squares, best-fit of a kinetic equation to the measured time courses of plasma and tissue concentrations. K1 and k2 were reduced by an average of 24 and 31%, respectively, in gray matter and 7 and 16% in white matter from values estimated similarly in normal insulinemic control rats. The equilibrium distribution ratio, K1/k2, for [14C]methylglucose in brain increased by approximately 10-11% in the hyperinsulinemic animals. Because 3-O-[14C]methylglucose shares the same carrier that transports glucose and other hexoses across the BBB, these results suggest that hyperinsulinemia decreases the rate constants for transport but increases the distribution space for hexoses in brain. These effects are, however, quite small and are probably minor or negligible when compared with the major effects of insulin in other tissues.

Mseleni disease serum is not harmful to cultured chondrocytes

The origins of Mseleni disease, an acquired polyarticular degenerative joint disease, are unknown. We examined sera from 12 patients with the disease, 5 unaffected Mseleni residents, and 5 Durban residents. The effects of sera from the 12 patients with Mseleni disease on DNA or sulfated proteoglycan synthesis by cultured rabbit or human infant articular chondrocytes were no different from those of control sera. Cells derived from 2 children contained no stainable DR antigens; coculture had no impact on either of the above measures of cell function.

Local cerebral glucose utilization in the adult cretinous rat

Local rates of cerebral glucose utilization were determined in 5-month-old neonatally radiothyroidectomized and control (littermate) rats. Virtually all 48 brain regions examined in the thyroidectomized rats exhibited lower rates of glucose utilization than those of the controls with differences ranging from -24 to -58%. The decreases were particularly large in the cerebral cortex and throughout the auditory system. Altered patterns in the intrastructural distribution of rates of glucose utilization were seen in a number of regions and were particularly prominent in the hippocampus and inferior colliculus. Lesser changes were seen in hypothalamic regions involved in the synthesis of thyrotropin releasing hormone (TRH). The results indicate that the many structural, functional and biochemical abnormalities of cretinism are associated with widespread reductions in energy metabolism throughout the brain.

The effect of sodium selenite on chondrocytes in monolayer culture

The effect of sodium selenite on DNA and sulfated proteoglycan synthesis by cultured rabbit articular and growth plate chondrocytes was studied as an in vitro model for Kashin-Beck disease. The selenium content of a defined medium (DMEM, fibroblast growth factor, insulin, and dexamethasone) was below the limit of detection by isotope dilution mass spectrometry. The chondrocytes were viable in the Se-free basal medium. Selenite over a range of 5 X 10(-9) M to 5 X 10(-7) M had no stimulatory effect on DNA or sulfated proteoglycan synthesis by either type of chondrocyte or skin fibroblasts. Proliferation of bovine endothelial cells was enhanced by 5 X 10(-7) M Se. At Se concentrations of greater than or equal to 10(-6) M, there was progressive inhibition of cell growth and radiosulfate incorporation of the connective tissue cells; bovine endothelial cells were more resistant. Twice equimolar concentrations of vitamins C and E exerted no protective effect against the cytotoxicity of higher concentrations of Se. Se supplementation also failed to stimulate growth of human infant chondrocytes. The model enabled simulation of conditions of hyposelenosis below those encountered in nature. The data provide no evidence that chondrocytes have idiosyncratic requirements for Se, and do not support the hypothesis that Se deficiency is a major etiologic factor in Kashin-Beck disease.