High intensity exercise decreases global brain glucose uptake in humans

Physiological activation increases glucose uptake locally in the brain. However, it is not known how high intensity exercise affects regional and global brain glucose uptake. The effect of exercise intensity and exercise capacity on brain glucose uptake was directly measured using positron emission tomography (PET) and [¹⁸F]fluoro-deoxy-glucose ([¹⁸F]FDG). Fourteen healthy, right-handed men were studied after 35 min of bicycle exercise at exercise intensities corresponding to 30, 55 and 75% of     on three separate days. [¹⁸F]FDG was injected 10 min after the start of the exercise. Thereafter exercise was continued for another 25 min. PET scanning of the brain was conducted after completion of the exercise. Regional glucose metabolic rate (rGMR) decreased in all measured cortical regions as exercise intensity increased. The mean decrease between the highest and lowest exercise intensity was 32% globally in the brain (38.6 ± 4.6 versus 26.1 ± 5.0 μmol (100 g)⁻¹ min⁻¹, P < 0.001). Lactate availability during exercise tended to correlate negatively with the observed brain glucose uptake. In addition, the decrease in glucose uptake in the dorsal part of the anterior cingulate cortex (37% versus 20%, P < 0.05 between 30% and 75% of     ) was significantly more pronounced in subjects with higher exercise capacity. These results demonstrate that brain glucose uptake decreases with increase in exercise intensity. Therefore substrates other than glucose, most likely lactate, are utilized by the brain in order to compensate the increased energy needed to maintain neuronal activity during high intensity exercise. Moreover, it seems that exercise training could be related to adaptive metabolic changes locally in the frontal cortical regions.     

Relationship between personality trait and regional cerebral glucose metabolism assessed with positron emission tomography

There have been no studies systematically investigating relationships between biogenetic temperament dimensions and patterns of brain glucose metabolism. Nineteen healthy subjects were evaluated regarding the biogenetic temperament using Cloninger's Temperament and Character Inventory (TCI). In addition, [¹⁸F] fluorodeoxyglucose (FDG) positron emission tomography (PET) was used to measure regional brain glucose metabolism. Voxel-based correlation analysis was used to test correlations between regional brain glucose metabolism and scores on the TCI. We identified that each temperament dimension, such as Novelty Seeking, Harm Avoidance, and Reward Dependence, was significantly correlated with specific brain regions. The majority of correlations were observed in the areas of paralimbic regions and temporal lobes. The current study provides evidence linking each biogenetic temperament dimension with specific brain areas and provides a promising base for future personality research.     

Tacrine restores cholinergic nicotinic receptors and glucose metabolism in alzheimer patients as visualized by positron emission tomography

Three patients with Alzheimer's disease, a 68-year-old woman with mild dementia and 2 men (aged 64 and 72 years) with moderate dementia were treated orally with the cholinesterase inhibitor tacrine (tetrahydroaminoacridine), 80 mg daily, for several months. The patients were investigated using positron emission tomography (PET) prior to, and after 3 weeks and 3 months of treatment. The PET studies involved a multi-tracer system consisting of [¹⁸F]-fluoro-deoxy-glucose (¹⁸F-FDG) (tracer for glucose metabolism); ¹¹C-butanol (cerebral blood flow) and (S)(−)- and (R)(+)-[N-¹¹C-methyl]-nicotine (nicotinic receptors; cholinergic neural activity). Tacrine treatment increased the uptake of ¹¹C-nicotine to the brain. Significant reduced difference in uptake between the two enantiomers (S)(−)- and (R)(+)¹¹C-nicotine was observed in the frontal and temporal cortices after tacrine treatment in all three patients. The kinetic analysis indicated increased binding of (S)(−)¹¹C-nicotine in brain compatible with a restoration of nicotinic cholinergic receptors. The most pronounced effect was observed after 3 weeks and 3 months treatment in the patient with mild dementia. An increase in cerebral glucose utilization was found in the 68-year-old patient with mild dementia but also slightly in the 64-year-old man with moderate dementia when treated with tacrine for 3 months. Tacrine administration did not affect cerebral blood flow. The PET data obtained after 3 weeks of tacrine treatment was paralleled by improvement in neuropsychological performance. This study shows in vivo by PET neurochemical effects induced in brain by treatment with tacrine to Alzheimer patients. Intervention with tacrine in the early course of the disease might be necessary for clinical improvement.     

Distribution of dopaminergic receptors in the primate cerebral cortex: Quantitative autoradiographic analysis using [H]raclopride, [H]spiperone and [H]SCH23390

A widespread distribution of dopamine D₁ receptors in the neocortex is well recognized. However, the presence of dopamine D₂ receptors in this structure has only recently been established [Martres et al. (1985) Eur. J. Pharmac.118, 211–219; Lidow et al. (1989) Proc. natn. Acad. Sci. U.S.A.86, 6412–6416]. In the present paper, a highly specific antagonist, [³H]raclopride, was used for autoradiographic determination of the distribution of D₂ receptors in 12 cytoarchitectonic areas of the frontal, parietal, and occipital lobes of the rhesus monkey. A low density of D₂-specific [³H]raclopride binding (1.5–4.0 fmol/mg tissue) was detected in all layers of all cortical areas studied. Throughout the entire cortex, the highest density of binding was consistently found in layer V. This is a unique distribution not observed so far for any other neurotransmitter receptor subtype in monkey cerebral cortex, including D₁ receptor. In addition, a comparison was made of the distribution of [³H]raclopride and [³H]spiperone, which has been commonly used in previous attempts to label cortical D₂ receptors. We found marked differences in the distribution of these two radioligands. In the prefrontal cortex, the pattern of [³H]spiperone binding in the presence of ketanserin resembled the combined distribution of 5-HT_ic serotoninergic and ₂-adrenergic sites as well as D₂ receptors. Thus, [³H]raclopride provides a better estimation of the D₂ receptor distribution than does [³H]spiperone. The distribution of D₂-specific binding of [³H]raclopride was also compared with the D₁-specific binding of [³H]SCH23390 in the presence of mianserin to block labeling to 5-HT₂ and 5-HT_IC sites. The density of D₁-specific [³H]SCH23390 binding was 10–20 times higher than that of D₂-speciflc [³H]raclopride binding throughout the cortex. The densities of both [³H]raclopride and [³H]SCH23390 binding sites display a rostral-caudal gradient with the highest concentrations in prefrontal and the lowest concentrations in the occipital cortex. However, the binding sites of these two ligands had different laminar distributions in all areas examined. In contrast to preferential [³H]raclopride binding in layer V, a bilaminar pattern of [³H]SCH23390 labeling was observed in most cytoarchitectonic areas, with the highest concentrations in supragranular layers I, II and IIIa and infragranular layers V and VI. Whereas [³H]raclopride binding was similar in all cytoarchitectonic areas, [³H]SCH23390 exhibited some region-specific variations in the primary visual and motor cortex.

The different regional and laminar distributions of D₁ and D₂ dopaminergic receptors indicates that they may subserve different aspects of dopamine function in the cerebral cortex.     

Distribution and postnatal ontogeny of adenosine A2A receptors in rat brain: comparison with dopamine receptors

In adult rat brain, adenosine A_2A receptors and dopamine D₂ receptors are known to be located on the same cells where they interact in an antagonistic manner. In the present study we wanted to examine when this situation develops and compared the postnatal ontogeny of the binding of the adenosine A_2A receptor agonist [³H]CGS 21680, the binding of the dopamine D₁ receptor antagonist [³H]SCH 23390 and the dopamine D₂ receptor antagonist [³H]raclopride.

All three radioligands bound to the striatum at birth and this binding increased several-fold during the postnatal period. [³H]SCH 23390 binding developed first (mostly during the first week), followed by [³H]raclopride binding (first to third week) and [³H]CGS 21680 binding (only during second and third week). For all three radioligands the binding tended to decrease between 21 days and adulthood. This occurred earlier and was more pronounced in the globus pallidus than in the other examined structures. The increase in [³H]CGS 21680 binding from newborn to adult was mainly due to four-fold increase in the number of binding sites. The pharmacology of [³H]CGS 21680 binding to caudate–putamen was similar in newborn, one-week-old and adult animals, and was indicative of A_2A receptors. The binding was inhibited by guanylyl imidodiphosphate at all ages, indicating that A_2A receptors are G-protein-coupled already at birth. In contrast to the large increase in [³H]CGS 21680 binding, there was a decrease in the levels of A_2A messenger RNA during the postnatal period in the caudate–putamen. In cerebral cortex [³H]CGS 21680 bound to a different site than the A_2A receptor. From birth to adulthood cortical binding of [³H]CGS 21680 increased four-fold and that of the adenosine A₁ agonist [³H]cyclohexyladenosine 19-fold. During early postnatal development [³H]SCH 23390 binding was higher in deep than in superficial cortical layers, but this difference disappeared in adult animals. There was binding of both [³H]CGS 21680 and [³H]cyclohexyladenosine to the olfactory bulb, suggesting a role of the two adenosine receptors in processing of olfactory information. [³H]CGS 21680 binding was present in the external plexiform layer and glomerular layer, and increased during development, but the density of binding sites was about one tenth of that seen in caudate–putamen. [³H]cyclohexyladenosine showed a very different labelling pattern, resembling that observed with [³H]SCH 23390.

Postnatal changes in adenosine receptors may explain age-dependent differences in stimulatory caffeine effects and endogenous protection against seizures. Since A_2A receptors show a co-distribution with D₂ receptors throughout development, caffeine may partly exert such actions by regulating the activity of D₂ receptor-containing striatopallidal neurons     

Localization of the dopamine uptake complex using [3H]N-[1-(2-benzo(b)thiophenyl)cyclohexyl]piperidine ([3H]BTCP) in rat brain

[³H]N-[1-(2-Benzo(b)thiophenyl)cyclohexyl]piperidine ([³H]BTCP) is a novel phencyclidine derivative with considerable selectivity for dopamine uptake sites. [³H]BTCP was used to label dopamine uptake sites in vitro, in rat brain, and the regions containing these sites were visualized with an autoradiographic technique. The binding was found to be highest in the striatum, where > 90% of binding was specific. Furthermore, 6-hydroxydopamine lesions of the nigrostriatal pathway obliterated striatal [³H]BTCP binding ipsilaterally, whereas ibotenic acid injection into the caudate-putamen failed to significantly reduce [³H]BTCP binding in that structure. These results indicate that [³H]BTCP labels dopamine uptake sites in mammalian brain and that it can be employed for autoradiographic studies of this transport complex.     

Decreased density of beta-adrenergic and muscarinic cholinergic receptor sites in the vasa nervorum of aged rats

The pharmacological profile and the anatomical localization of beta-adrenergic and muscarinic cholinergic receptors of the vasa nervorum were studied in sections of sciatic nerve using radioreceptor binding and light microscope autoradiography techniques. Sprague—Dawley rats of 4 and 24 months of age were used. [³H]Dihydroalprenolol (DHA) and [³H]quinuclidinyl benzilate (QNB) were used to label beta-adrenergic and muscarinic cholinergic receptors, respectively. The ligands were bound to sections of rat sciatic nerve in a manner consistent with the labelling of beta-adrenergic or muscarinic cholinergic receptors in the 2 age groups investigated. The dissociation constant (K_d) values (about 1.37 nM for [³H]DHA and 0.75 nM for [³H]QNB) did not significantly change between 4- and 24-month-old rats. The maximum concentration of binding sites (B_max) for [³H]DHA was decreased by about 35% in 24 in comparison with 4-month-old rats. The B_max value autoradiogaphy revealed the development of specific silver grains in the medial layer of epineurial and perineurial arteries in sections of sciatic nerve exposed either to [³H]DHA or [³H]QNB. The number of silver grains developed in epineurial and perineurial arteries of rats of 24 months is significantly lower than in animals of 4 months. The above results suggest the occurrence of an age-dependent loss in the density of beta-adrenergic and muscarinic cholinergic receptors of vasa nervorum.     

Toxoplasma gondii tachyzoites possess an unusual plasma membrane adenosine transporter

Nucleoside transport may play a critical role in successful intracellular parasitism by Toxoplasma gondii. This protozoan is incapable of de novo purine synthesis, and must salvage purines from the host cell. We characterized purine transport by extracellular T. gondii tachyzoites, focusing on adenosine, the preferred salvage substrate. Although wild-type RH tachyzoites concentrated [³H]adenosine 1.8-fold within 30 s, approx. half of the [³H]adenosine was converted to nucleotide, consistent with the known high parasite adenosine kinase activity. Studies using an adenosine kinase deficient mutant confirmed that adenosine transport was non-concentrative. [¹⁴C]Inosine, [¹⁴C]hypoxanthine and [³H]adenine transport was also rapid and non-concentrative. Adenosine transport was inhibited by dipyridamole (IC₅₀ approx. 0.7 μM), but not nitrobenzylthioinosine (15 μM). Transport of inosine, hypoxanthine and adenine was minimally inhibited by 10 μM dipyridamole, however. Competition experiments using unlabeled nucleosides and bases demonstrated distinct inhibitor profiles for [³H]adenosine and [¹⁴C]inosine transport. These results are most consistent with a single, dipyridamole-sensitive, adenosine transporter located in the T. gondii plasma membrane. Additional permeation pathways for inosine, hypoxanthine, adenine and other purimes may also be present.     

Segmental, coronal and subcellular distribution of 2-[I]iodomelatonin binding sites in the chicken spinal cord

Radioreceptor and autoradiography studies using chicken spinal cords demonstrated that the binding density of 2-[¹²⁵I]iodomelationin ([¹²⁵I]MEL) was significantly higher in the lumbar segment and the specific binding of [¹²⁵I]MEL was localized in the gray matter. Subcellularly, different densities of binding sites were localized in the following order: nuclear > microsomal > mitochondrial > cytosolic. Localization of [¹²⁵I]MEL binding sites in the dorsal gray matter of the chicken spinal cord suggests that melatonin plays a role in regulating the spinal cord functions which may associate with the modulation of temperature and pain transmission and/or visceral and autonomic functions.     

Localization of NADPH-diaphorase activity in the salt gland of the saltwater-acclimated Pekin duck

The pharmacological properties and the anatomical localisation of dopamine D₃ receptor were assessed in the rat cerebellar cortex using radioligand binding techniques associated with light microscope autoradiography and 7-[³H]hydroxy-N,N-di-n-propyl-2-aminotetralin (7-[³H]OH-DPAT) as a ligand. 7-[³H]OH-DPAT was specifically bound to sections of rat cerebellar cortex with a dissociation constant (K_d) of 0.5 nM and a maximum density of binding sites (B_max) of 97 ± 4 fmol/mg tissue. The rank order of potency of competitors of 7-[³H]OH-DPAT binding and the observation that guanosine triphosphate did not affect radioligand binding suggest the labelling of a dopamine D₃ receptor. 7-[³H]OH-DPAT binding sites are located mainly in the molecular layer and in lesser amounts in the Purkinje neuron layer, primarily within the cell body of Purkinje neurons. No specific accumulation of silver grains was observed in the granule neuron layer or in the white matter of the cerebellar cortex. The localisation of a putative dopamine D₃ receptor within Purkinje neurons suggests that this site may have functional relevance in the cerebellar cortex.     

Reduced density of dopamine D2-like receptors on peripheral blood lymphocytes in Alzheimer's disease

Clinical and pathological evidence points to an involvement of dopamine in Alzheimer's disease (AD). The present study was designed to assay dopamine D1-like and D2-like receptors on peripheral blood lymphocytes (PBL) in 20 patients with AD and in 25 healthy controls by radioligand binding assay techniques with [³H][R]-(+)-(−)chloro-2,3,4,5 tetrahydro-5-phenyl-1H-3-benzazepin-al-hemimaleate (SCH 23390) and [³H]7-hydroxy-N,N-di-n-propyl-2-aminotetraline (7OH-DPAT) as radioligands. The density of dopamine D1-like receptors and the affinity of [³H]SCH 23390 and [³H]7OH-DPAT binding to PBL were similar in both groups investigated. AD patients revealed a lower density of dopamine D2-like receptors on PBL than controls (P=0.0016). The pharmacological profile of [³H]SCH 23390 and [³H]7OH-DPAT binding to PBL was consistent with the labeling of dopamine D5 and D3 receptor subtypes, respectively. The reduced density of dopamine D2-like receptors on PBL is consistent with the observation of changes in the expression of D2-like receptors in dopaminergic brain areas in AD. Our findings support the hypothesis of an involvement of dopamine in AD, even in those patients with no evidence of Parkinsonism, behavioral abnormalities or psychosis.     

Major histocompatibility complex class II alleles and haplotypes and blood groups of four Amerindian tribes of Northern Colombia

MHC class II alleles and haplotypes were determined from unrelated individuals and families of the Arhuaco (n = 107), Kogi (n = 42), Arsario (n = 18), and Wayú (n = 88) tribes located in the northern part of Colombia. Class II DRB, DQA1, and DQB1 alleles were determined by PCR-SSO and PCR-RFLP based methods. Four haplotypes, [DRB1^*0407, DRB4^*0101, DQA1^*03, DQB1^*0302]; [DRB1^*0403, DRB4^*0101, DQA1^*03, DQB1^*0302]; [DRB1^*1402/1406, DRB3^*0101, DQA1^*0501, DQB1^*0301]; and [DRB1^*0802, DQA1^*0401, DQB1^*0402], were observed among these four tribes. In addition to these haplotypes, the Wayú Indians showed a frequency of 21.3% for the [DRB1^*1602, DRB5^*02, DQA1^*0501, DQB1^*0301] haplotype, 13.1% for the [DRB1^*0411, DRB4^*0101, DQA1^*03, DQB1^*0302] haplotype, and 8.1% for the [DRB^*0411, DRB4^*0101, DQA1^*03, DQB1^*0402] haplotype. Red cell antigen typing was used to calculate genetic admixture. The Kogi and Arsario showed no genetic admixture while the Arhuaco tribe showed admixture with genes of African origin and the Wayú showed admixture with Caucasians as well as genes of African origin. These findings were confirmed by the MHC class II allele and haplotype data obtained, as alleles and haplotypes of Caucasian and African origin were detected in the Wayú and Arhuaco and not in the Kogi or Arsario. These studies will be important in disease association and transplantation studies for Amerindian and Colombian populations and for correlating genetic traits with the anthropologic and linguistic data available in order to better understand the Amerindian populations.     

GABA enhances acetylcholine release from hippocampal nerve endings through a mechanism blocked by a GABA uptake inhibitor

The effect of γ-aminobutyric acid (GABA) on the release of [³H]acetylcholine ([³H]ACh) was investigated using superfused rat hippocampal synaptosomes. GABA enhanced the basal efflux of [³H]ACh. The effect of GABA was bicuculline-insensitive. Muscimol, (±)-baclofen or (−)-baclofen did not increase [³H]ACh release. The effect of GABA was counteracted by SK&F 89976 A (N-(4,4-diphenyl-3-butenyl)-nipecotic acid), a GABA uptake inhibitor. One possible interpretation of the results is that a GABA transport system is present on cholinergic terminals, suggesting that GABA and ACh may coexist in some rat hippocampus nerve endings. Another possibility is that the effect of GABA is mediated by a novel subtype of GABA receptor sensitive to SK&F 89976 A.     

Light-microscopic distribution and parasagittal organisation of muscarinic receptors in rabbit cerebellar cortex

Recent studies on the effects of intrafloccular injections of muscarinic agonists and antagonists on compensatory eye movements in rabbit, indicate that muscarinic receptors may play a modulatory role in the rabbit cerebellar circuitry. It was previously demonstrated by Neustadt et al. (1988), that muscarinic receptors in rabbit cerebellar cortex are distributed into alternating longitudinal zones of very high and very low receptor density. In the present study, the zonal and cellular distribution of muscarinic receptors in the rabbit cerebellar cortex is investigated in detail using in vitro ligand autoradiography with the non-selective high-affinity antagonist [³H]quinuclidinyl benzilate (QNB), and the M2-specific antagonist [³H]AF-DX384, and immunocytochemistry with a monoclonal antibody specific for the cloned m2 muscarinic receptor protein. [³H]QNB and [³H]AF-DX384 binding sites and m2-immunoreactivity had similar overall distributions: dense labeling occurred in the dendritec arbors of a subset of Purkinje cells that are organized into parasagittal bands. A high level of muscarinic receptor labeling was also observed in a thin substratum of the molecular layer immediately above the Purkinje cell layer of the vestibulo-cerebellar lobules, i.e. the nodulus, the ventral uvula and the flocculus. Labeling in this stratum was associated with densely packed fibres, which were putatively identified as parallel fibres. Also Golgi cells, which were localized in part in the molecular layer, and a subset of mossy fibre rosettes, primarily concentrated in lobule VI, were immunoreactive for the m2 receptor. The parasagittal bands of labeled Purkinje cell dendrites were most prominent in the anterior lobe (lobules I–V), in crus 1 and 2, in the flocculus, the ventral paraflocculus and the rostral folium of the nodulus. In other lobules, only infrequent Purkinje cells contained muscarinic receptors. The parasagittal organisation of muscarinic receptors differed from that of zebrin I, a Purkinje cell-specific protein which is often used as a marker of parasagittal parcelation of the cerebellar cortex. In the anterior lobe, however, there was a partial correspondence between muscarinic receptor and zebrin I bands. In the flocculus the distribution of muscarinic-receptor-positive Purkinje cells was related to the distinct white matter compartments as revealed with acetylcholinesterase (AChE) histochemistry. Muscarinic receptor-containing Purkinje cells were located primarily in the floccular zone 1, which is implicated in the control of eye movements about a horizontal axis. In order to relate the distribution of muscarinic receptor labeling to that of cholinergic nerve terminals, [³H]QNB binding sites and sodium-dependent [³H]hemicholinium-3 binding were compared. Sodium-dependent [³H]hemicholinium-3 binding sites mainly occurred in the granule cell layer of the vestibulo-cerebellum, which corresponds well with the distribution of the acetylcholine synthesizing enzyme, choline acetyltransferase (ChAT). However, sodium-dependent [³H]hemicholinium binding complemented, rather than co-localized with, muscarinic receptors which were primarily distributed in the molecular layer of the lobules of the vestibulo-cerebellar lobules. Their functional significance is puzzling, since their distribution does not correspond to that of markers of cholinergic innervation.     

Quantitative autoradiography of dopamine D2 sites in rat caudate-putamen: Localization to intrinsic neurons and not to neocortical afferents

Dopamine D₂ receptors, labeled with [³H]spiroperidol or [³H]sulpiride, show a lateral-to-medial gradient in the caudate-putamen, with a more than two-fold greater density laterally than medially. It has been thought that D₂ receptors are located on at least two neuronal elements of the caudate-putamen, neurons intrinsic to this structure and axons whose cell bodies reside in the cortex. As a first step in establishing what neuronal elements underlie this heterogeneous organization of D₂ receptors, we took advantage of quantitative autoradiography to examine the association of these receptors with those elements. The present findings show that the D₂ sites are almost exclusively located on neurons whose somata reside in the caudate-putamen and are not located on terminals of corticostriatal axons. A detailed comparison of the distribution of histochemically identified acetylcholinesterase neurons with that of D₂ receptors in serially adjoining sections suggests a common organizational pattern.

The density of [³H]spiroperidol sites in rat caudate-putamen was determined after unilateral injection of the neurotoxin quinolinic acid into this structure or after ablation of neocortical regions. Quantification of the tissue damage was achieved by acetylcholinesterase histochemistry (following diisopropylfluoro-phosphate treatment), as well as by thionin and luxol fast staining of sections adjacent to those used for [³H]spiroperidol autoradiography. In identically treated animals, biochemical determination of the extent of tissue damage was made utilizing assays for high-affinity [³H]choline and [³H]glutamate uptake in the caudate-putamen. In quinolinic acid-injected rats, the density of D₂ sites was decreased by 90–95% at the site of complete loss of large acetylcholinesterase-positive neurons. Other animals, given ablations of specific neocortical fields (medial prefrontal, motor, somatosensory) or of the entire parietal-frontal cortex of one hemisphere, showed no loss of caudate-putamen D₂ sites unless the cortical ablation caused accompanying damage of the caudate-putamen. In the caudate-putamen of all animals there was a close correspondence between the D₂ sites and the striatal neurons (and processes) that show strong acetylcholinesterase reactivity.

We suggest that the caudate-putamen topography of D₂ sites is based largely on the internal organization of this structure and may preferentially involve acetylcholine-containing intrinsic neurons.     

Increased amyloid beta-peptide (1-40) level in brain of streptozotocin-induced diabetic rats

The aims of the study were to investigate whether the level of amyloid β-peptide (Aβ) (1–40) was increased in brain of diabetic rats and whether the increase was associated with dysfunction of P-glycoprotein at the blood–brain barrier. A diabetes-like condition was induced by single administration of 65 mg/kg streptozotocin via i.p. injection. Aβ (1–40) levels in brain of the diabetic rats were measured using an enzyme linked immunosorbent assay (ELISA) kit. The in vivo brain-to-blood efflux and blood-to-brain influx transport of [¹²⁵I]-labeled human amyloid-β-peptide (hAβ) (1–40) were measured using the brain efflux index and brain permeability coefficient-surface area product, respectively. [¹⁴C]inulin served as a reference compound. The results showed that Aβ (1–40) levels significantly increased in temporal cortex and hippocampus of the diabetic rats. The brain remaining percentage of [¹²⁵I]hAβ (1–40) in diabetic rats significantly increased at 30 min after intracerebral microinjection, accompanied by decrease of the brain efflux index. Pretreatment of P-glycoprotein inhibitors verapamil or cyclosporin A significantly increased the brain remaining percentage of [¹²⁵I]hAβ (1–40). The brain permeability coefficient-surface area product of [¹²⁵I]hAβ (1–40) was increased in diabetic rats, accompanied by increased Aβ (1–40) levels in plasma. The present study demonstrated that a diabetic state could increase Aβ (1–40) levels in brain, which might be explained, at least in part, by the decline in brain-to-blood efflux of Aβ (1–40) due to deficient cerebral P-glycoprotein function in diabetic rats.     

Pharmacological stimulation reveals recombinant human nerve growth factor-induced increases of in vivo hippocampal cholinergic function measured in rats with partial fimbrial transections.

The present study determined the effects of chronic recombinant human nerve growth factor administration [1 μg given intracerebroventricularly q.i.d. (every other day) for three weeks] on in vivo hippocampal cholinergic function in adult rats with unilateral partial fimbrial transections. Partial fimbrial transections did not significantly alter the levels of endogenous acetylcholine or [²H₄]acetylcholine in the hippocampus due to functional compensation by surviving cholinergic terminals. In animals chronically treated with nerve growth factor, the levels of endogenous choline, endogenous acetylcholine, [²H₄]choline and [²H₄]acetylcholine accumulated in the hippocampus on the lesioned side were not significantly different from those on the contralateral unlesioned side or from values measured in animals treated with cytochrome c, a control protein. However, changes in cholinergic parameters induced by the partial lesions or recombinant human nerve growth factor treatment became manifest when animals were challenged using pharmacological agents such as pentylenetetrazole or pilocarpine given after lithium chloride pretreatment. First, in nerve growth factor-treated animals administered the general stimulant pentylenetetrazole (10 mg/kg) 2 min prior to measuring in vivo cholinergic parameters, we observed a significant increase in the hippocampal content of [²H₄]choline in both lesioned and unlesioned hippocampi. The magnitude of the increase was significantly higher on the lesioned compared to the unlesioned side. Although chronic recombinant human nerve growth factor treatment induced increases of hippocampal [²H₄]choline levels, there were no concomitant increases in the level of [²H₄]acetylcholine. Second, in nerve growth factor-treated animals administered lithium chloride (3 mmol/kg) 20 h prior to pilocarpine (30 mg/kg), we observed a significant enhancement of the content of endogenous acetylcholine in the hippocampus of the lesioned side. Partial fimbrial transections also reduced in vitro cholinergic parameters reflecting endogenous acetylcholine levels in hippocampal slices. The content of endogenous acetylcholine in the slices was decreased by approximately 50% and chronic nerve growth factor treatment significantly elevated this value to approximately non-lesioned control values. Similarly, reductions in spontaneous and veratridine-evoked release of endogenous acetylcholine induced by partial fimbrial transections were counteracted by recombinant human nerve growth factor treatment.

These findings demonstrate that chronic recombinant human nerve growth factor treatment effectively enhances the in vivo and in vitro synthesis, storage and release of endogenous acetylcholine. The results from the in vivo studies suggest that recombinant human nerve growth factor-induced differences in functional performance of hippocampal neurons may only be manifest during behavioral and/or pharmacological stimulation.     

Elastase-induced hydrolysis of synthetic solid substrates: poly(ester-urea-urethane) and poly(ether-urea-urethane)

Human neutrophil elastase (HNE) and porcine pancreatic elastase (PPE) were incubated with two radiolabelled model poly(urethane)s, a poly(ester-urea-urethane) containing [¹⁴C]toluene diisocyanate ([14C]TDI), poly(caprolactone) (PCL) and ethylenediamine (ED), and a poly(ether-urea-urethane) containing [¹⁴C]TDI, poly(tetramethylene oxide) (PTMO) and ED. Ten-fold more radioactive carbon was released when PPE was incubated with [¹⁴C]TDI/PCL/ED than when HNE was used. The PPE-induced radioactive carbon release was significantly reduced by a specific elastase inhibitor. Ten-fold less radioactive carbon was released when [¹⁴ was incubated with PPE as compared to [¹⁴C]TDI/PCL/ED. Since neutrophils, which contain elastolytic activity, are present during the inflammatory response, the stability of biomaterials used in implanted devices may be affected.     

Drug‐induced cardiomyopathy: Characterization of a rat model by [18F]FDG/PET and [99mTc]MIBI/SPECT

BackgroundDrug‐induced cardiomyopathy is a significant medical problem. Clinical diagnosis of myocardial injury is based on initial electrocardiogram, levels of circulating biomarkers, and perfusion imaging with single photon emission computed tomography (SPECT). Positron emission tomography (PET) is an alternative imaging modality that provides better resolution and sensitivity than SPECT, improves diagnostic accuracy, and allows therapeutic monitoring. The objective of this study was to assess the detection of drug‐induced cardiomyopathy by PET using 2‐deoxy‐2‐[¹⁸F]fluoro‐D‐glucose (FDG) and compare it with the conventional SPECT technique with [^99mTc]‐Sestamibi (MIBI).MethodsCardiomyopathy was induced in Sprague Dawley rats using high‐dose isoproterenol. Nuclear [¹⁸F]FDG/PET and [^99mTc]MIBI/SPECT were performed before and after isoproterenol administration. [¹⁸F]FDG (0.1 mCi, 200‐400 µL) and [^99mTc]MIBI (2 mCi, 200‐600 µL) were administered via the tail vein and imaging was performed 1 hour postinjection. Isoproterenol‐induced injury was confirmed by the plasma level of cardiac troponin and triphenyltetrazolium chloride (TTC) staining.ResultsIsoproterenol administration resulted in an increase in circulating cardiac troponin I and showed histologic damage in the myocardium. Visually, preisoproterenol and postisoproterenol images showed alterations in cardiac accumulation of [¹⁸F]FDG, but not of [^99mTc]MIBI. Image analysis revealed that myocardial uptake of [¹⁸F]FDG reduced by 60% after isoproterenol treatment, whereas that of [^99mTc]MIBI decreased by 45%.ConclusionWe conclude that [¹⁸F]FDG is a more sensitive radiotracer than [^99mTc]MIBI for imaging of drug‐induced cardiomyopathy. We theorize that isoproterenol‐induced cardiomyopathy impacts cellular metabolism more than perfusion, which results in more substantial changes in [¹⁸F]FDG uptake than in [^99mTc]MIBI accumulation in cardiac tissue.     

Role of lactate in the brain energy metabolism: revealed by Bioradiography

To elucidate the role of lactate in the brain, we used a novel method, 'Bioradiography', in which the dynamic process could be followed in living slices by use of positron-emitter-labeled compounds and imaging plates. We studied the incorporation of 2-[18F]fluoro-2-deoxy-D-glucose ([18F]FDG) into rat brain slices incubated in oxygenated Krebs-Ringer solution. Under the glucose-free condition, [18F]FDG uptake rate in the cerebral cortex decreased with time and plateaued within 350 min but the addition of 5 mM lactate made the [18F]FDG uptake linear. When an inhibitor of the lactate transporter, 0.5 mM alpha-cyano-4-hydroxycinnamate (4-CIN) was applied to the glucose-free solution, the uptake rate decreased. Under the normal glucose condition, [18F]FDG uptake linearly increased for 6 h, but when 10 mM lactate was applied, the uptake rate decreased. In contrast, when 0.5 mM 4-CIN was applied to the normal glucose solution, [18F]FDG uptake rate increased. These results suggest that exogenous and endogenous lactate can substitute for glucose in the brain.