Near-infrared monitoring of cerebral oxygen sufficiency. I. Spectra of cytochrome c oxidase

Near-infrared (NIR) difference spectra were obtained for oxidized cytochrome c oxidase of isolated mitochondria in vitro and of cerebral tissue in situ observed through scalp and skull. The broad peaks of maximal absorption observed in both were not inconsistent with the customary assignment of an 830 nm peak. However, the ratios of the intensity of the NIR band to that of the visible peak (605 nm), which we found to be identical for in-vitro and in-situ spectra, were consistently and significantly higher than those of the various purified enzyme preparations reported in the literature. In addition the half-band widths of our in-vitro and in-situ preparations were narrower. Haemoglobin spectra in the NIR obtained in clear and in highly light-scattering media showed almost total absence of band distortion in this spectral region, suggesting that the differences observed are not due to scattering effects. Anoxia and the specific oxidase inhibitors, cyanide and carbon monoxide, caused the expected disappearance of the band in both the mitochondria in vitro and the cerebrum in situ. The 830 nm band observed in intact, well-oxygenated animal preparations was therefore identified with the NIR absorption band of oxidized cytochrome c oxidase, notwithstanding the differences with the observations on purified preparations. This points to the possibility of developing instrumentation and techniques for the non-invasive monitoring of the redox state of cytochrome c oxidase as an index to cerebral oxygen sufficiency, i.e. adequate delivery and utilization of oxygen to and by brain tissue.     

Cytochromec oxidase deficiency in infancy

Summary Five children with early onset of muscle weakness, lactic acidosis and deficient cytochromec oxidase staining in the muscle biopsy were studied. By oximetric assay of the respiratory chain of isolated mitochondria, cytochromec oxidase deficiency was confirmed in four of the cases, while one case showed only a slight decrease of cytochromec oxidase activity but considerably reduced activity when assayed spectrophotometrically. The muscle biopsies exhibited mitochondrial structural abnormalities and lipid storage in the four cases with oximetrically confirmed cytochromec oxidase deficiency, while the biopsy of the case with markedly reduced activity of cytochromec oxidase only in the enzyme-histochemical and spectrophotometrical assays had normal morphology. The light microscopical staining of cytochromec oxidase in the four cases with oximetrically confirmed deficiency showed deficient staining of the enzyme in all extrafusal fibres in three cases but one of the cases had normal enzyme-histochemical activity of cytochromec oxidase in about 25% of the fibres. In two cases muscle spindles were included in the biopsy. The intrafusal fibres showed normal enzyme-histochemical activity of cytochromec oxidase. Ultrastructural examination of the enzyme distribution in two of the cases revealed great heterogeneity of the mitochondria. The structurally abnormal mitochondria were usually deficient of enzyme activity. The mitochondria of endothelial cells appeared to have normal activity. Immunohistochemical staining with polyclonal antibodies to cytochromec oxidase revealed presence of immunoreactive material corresponding to the localisation of mitochondria in all cases. The results show that enzyme-histochemical staining of cytochromec oxidase is a useful technique to reveal deficiency of the enzyme and to study the distribution of the deficiency within the tissue both at the light microscopical and ultrastructural levels. However, the results of one of the cases show that deficiency revealed by the enzyme-histochemical technique is not completely reliable. Oximetric studies on isolated mitochondria are necessary to confirm the suspected deficiency and to reveal combined defects of the respiratory chain.Supported by grants from the Swedish Medical Research Council (proj. 03X 585 and 07122), Barnhusfonden Göteborg L 174/87 and The First of May Flower Annual Campaign for Childrens Health     

Exercise intolerance due to cytochrome b mutation

Cytochrome b mutations are rare causes of exercise intolerance. We report an 18‐year‐old man with exercise intolerance since childhood, resting lactic acidosis, cytochrome c oxidase (COX)‐positive ragged‐red fibers, and isolated muscle complex III deficiency due to a heteroplasmic m.14849T>C mutation in cytochrome b. We review previously described patients carrying mutations in the same gene. COX‐positive ragged‐red fibers together with exercise intolerance and lactic acidemia provide a clue for the diagnosis of this rare mitochondrial disorder. Muscle Nerve, 2010     

Inhibition of type A and B monoamine oxidase by 6,7-dihydroxy-1,2,3,4-tetrahydroisoquinolines and their N-methylated derivatives

Summary 6,7-Dihydroxy-1,2,3,4-tetrahydroisoquinoline (norsalsolinol) and 1-methyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline (salsolinol), and their N-methylated derivatives were found to inhibit type A and B monoamine oxidase isolated from human brain synaptosomal mitochondria. N-Methyl-norsalsolinol, (R) and (S) enantiomer of salsolinol, and N-methyl-salsolinols inhibited type A monoamine oxidase competitively to the substrate, kynuramine, andR enantiomers were more potent inhibitors thanS enantiomers. The inhibition was reversible. Norsalsolinol induced positive cooperativity toward kynuramine. Both norsalsolinol and N-methyl-norsalsolinol inhibited type B oxidase non-competitively to the substrate, and their K₁ values were much higher than those to type A. Types of inhibition of type A monoamine oxidase depended on the enzyme sources. Inhibition of monoamine oxidase by 6,7-dihydroxy-1,2,3,4-tetrahydroisoquinolines is discussed in relation to their chemical structures.     

Early-onset encephalomyopathy associated with tissue-specific mitochondrial DNA depletion: A morphological,biochemical and molecular-genetic study

A male infant, born from consanguineous parents, suffered from birth with a progressive neuromuscular disorder characterized by psychomotor delay, hypotonia, muscle weakness and wasting, deep-tendon areflexia and spastic posture. High levels of lactic acid in blood and cerebrospinal fluid suggested a mitochondrial respiratory chain defect. Muscle biopsy revealed raggedred and cytochromec oxidase-negative fibres, lipid accumulation and dystrophic changes. Multiple defects of respiratory complexes were detected in muscle homogenate, but cultured fibroblasts, myoblasts and myotubes were normal. Southern blot analysis showed markedly reduced levels of mitochondrial DNA (mtDNA) in muscle, while lymphocytes, fibroblasts and muscle precursor cells were normal. Neither depletion of mtDNA nor abnormalities of the respiratory complexes were observed in innervated muscle fibres cultured for as long as 4 months. No mutations were observed in two candidate nuclear genes,mtTFA andmtSSB, retro-transcribed, amplified and sequenced from the proband's mRNA. Sequence analysis of the mtDNA D-loop and of the origin of replication of the mtDNA light strand failed to identify potentially pathogenic mutations of these replicative elements in the proband's muscle mtDNA. Our findings indicate that mtDNA depletion is due to a nuclear encoded gene and suggest that the abnormality underlying defective mtDNA propagation must occur after muscle differentiation in vivo.     

Is electrical coupling involved in the generation of posterior hypothalamic theta rhythm?

Data obtained in in vitro experiments and urethane anaesthetized animals have revealed that the mechanisms responsible for the generation of hippocampal cholinergic theta rhythm are specifically affected by the administration of broad spectrum gap junctions (GJs) blocker – carbenoxolone (CBX). The aim of this study was to examine the effect of GJs modulation on the production of posterior hypothalamic theta. Specifically, we were interested in evaluating whether CBX could attenuate the theta rhythm recorded from the supramammillary nucleus and posterior hypothalamic nuclei, in both in vitro and in vivo preparations. The data we obtained from in vitro and in vivo preparations demonstrated that the administration of CBX did not suppress cholinergically induced theta in posterior hypothalamic area (PHa) slices nor the theta rhythm observed in the PHa of urethane anaesthetized rats. Moreover, the application of trimethylamine, while very effective in the enhancement of hippocampal theta rhythm, did not produce any changes in theta oscillations observed in either in vitro or in vivo posterior hypothalamic area preparations. These data show that electrical coupling via GJs is not involved in theta rhythm generation in the PHa. Surprisingly, we observed a significant enhancement of theta activity in response to the carbenoxolone administration in both in vitro and in vivo PHa preparations. The theta rhythm enhancement detected in those experiments was attenuated by the application of spironolactone (mineralocorticoid receptors antagonist). We suggest that the observed excitatory effects of CBX on posterior hypothalamic oscillatory activity in the theta band could be mediated by mineralocorticoid receptors.     

Peptide heterogeneity of GABAA/benzodiazepine receptors in bovine cerebral cortex and cerebellum

The GABA_A/benzodiazepine receptor complex has been purified from both bovine cerebral cortex and cerebellum by immunoaffinity chromatography on immobilized monoclonal antibody 62-3G1. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the purified receptor from either cerebral cortex or cerebellum revealed 3 main bands corresponding to 51 000, 55 000 and 57 000M_r silver-stained peptides In addition, a minor band corresponding to a 53 000M_r peptide was also found. The difference between the two receptor preparations were: (1) that the main silver-stained 55 000M_r subunit was present in a relative smaller quantity in cerebellum than in cerebral cortex, and (2 when the membrane-bound receptor was photoaffinity-labeled with [³H]flunitrazepam and subsequently immunoaffinity-purified, two photolabeled peptide bands of 51 000 and 57 000M_r were found in cerebral cortex while only the 51 000M_r photolabeled peptide was detected cerebellum following one-dimension sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Peptide maps of the 57 000M_r [³H]flunitrazepam photoaffinity-labeled peptide indicated that it was composed of two closely migrating photolabeled peptides of 55 000M_r and 57 000M_r 0899 Peptide mapping and deglycosylation experiments using the [³H]flunitrazepam photolabeled receptor suggested that the photolabeled peptides commonly present in cerebellum and cerebral cortex are qualitatively similar if not identical. The results suggest that there are subunits of some type(s) of GABA_AR/BZDR complex(es) which are more abundant in cerebral cortex than in cerebellum. Photoaffinity labeling with [³H]muscimol showed similar photolabeled peptides in both cerebral cortex and cerebellum: two main peptides of 54 000 and 57 000M_r wer photolabeled with [³H]muscimol to a similar extent in both receptor preparations. Following deglycosylation, the mobility shifts of the peptides that were photolabeled with [³H]flunitrazepam or [³H]muscimol were different, suggesting that the co-migrating 54 000 – 57 000M_r peptides that have high affinity binding sites for [³H]flunitrazepam or [³H]muscimol are different receptor subunits.     

Genotype to phenotype correlations in mitochondrial encephalomyopathies associated with the A3243G mutation of mitochondrial DNA

We studied 22 subjects carrying the A3243G point mutation of human mitochondrial DNA (mtDNA). In 14 cases the clinical phenotype was characterized by mitochondrial encephalomyopathy, lactic acidosis and stroke-like episodes (MELAS), while 8 patients had chronic progressive external ophthalmoplegia (CPEO). The proportion of A3243G heteroplasmy in muscle was determined by two methods: densitometry on a diagnostic restriction-fragment length polymorphism and solid-phase mini-sequencing. We found a highly significant inverse correlation between the percentage of A3243G mutation and the specific activity of complex 1, the respiratory complex with the highest number of mtDNA-encoded subunits, suggesting a direct effect of the mutation on mtDNA translation. No correlation was observed between the percentage of mutated mtDNA and the presence or absence of specific clinical features, such as stroke, ophthalmoplegia and diabetes mellitus. However, in the MELAS group the percentage of mutated mtDNA molecules was strongly correlated with the age of onset, while no such correlation was found in the CPEO group, suggesting a different time-dependent evolution of the mutation in the two groups. Finally, in contrast with other mtDNA mutations associated with ragged-red fibres (RRF), in both MELAS³²⁴³ and CPE0³²⁴³ we observed a high proportion of RRF that were positive to the histochemical reaction to cytochromec oxidase, a morphological feature that seems to be specific for the neuromuscular phenotypes associated with mutations affecting the tRNA^Leu(UUR) gene.     

Effects of perfusion flow rate, prostaglandin F2α, phenylephrine, and serotonin on isolated, perfused brains of spontaneously hypertensive rats

Effects of perfusion flow rate and three vasoconstrictors, phenylephrine, prostaglandin F_2α (PGF_2α) and serotonin, on isolated, perfused brain preparations of spontaneously hypertensive (SHR) and normotensive Wistar-Kyoto rats (WKY) were investigated. The basal perfusion pressure of the cerebral vascular beds at a flow rate of 2.5 ml/min was 48 ± 3mm Hg(n = 11) in SHR and 32 ± 2mm Hg(n = 12)in WKY(P < 0.005). The perfusion pressures at all flow rates tested (2.5−6.5 ml/min) in SHR were significantly greater than those in WKY. Concentration-perfusion pressure curves for the vasoconstrictors showed that the brain vascular bed was much more reactive to sertonin compared with phenylephrine and PGF_2α. EC₅₀ values (−logM) for serotonin in the perfused brains of SHR and WKY were 7.0 ± 0.06 (n = 10)and6.5 ± 0.06 (n = 11), respective (P < 0.01). There were no differences in EC₅₀ values for phenylephrine or PGF_2α between SHR and WKY. Exogenous serotonin and phenulephrine caused significantly greater maximal vasoconstrictor responses in SHR compared with WKY, while the pressor response to PGF_2α was very weak and no significant difference between SHR and WKY preparations was observed. These results indicate that cerebral vascular beds in SHR exhibit higher cerebrovascular resistance than those in WKY, and that reactivity and sensitivity to serotonin and reactivity to phenylephrine in SHR rats are enhanced to a greater extent compared to WKY.     

The genes for schizophrenia: Finally a breakthrough?

A number of susceptibility genes for schizophrenia have recently been identified. They have engendered excitement because replicate studies have attained greater consistency than in the past. In this review, we outline gene mapping methods, and briefly review their strengths and challenges. We also evaluate peer-reviewed genetic association studies that have implicated six selected genes: catechol-O-methyl transferase (COMT), neuregulin I (NRGI), dysbindin (DTNBPI), regulator of G-protein signaling 4 (RGS4), andG72 and D-amino-acid oxidase (DAAO). The available supporting evidence is variable. Though credible evidence is available for all of these genes, it is strongest forNRGI andDTNBPI. Further studies, particularly exhaustive analyses of all polymorphisms at each locus, meta-analyses, and investigations of the likely function of risk alleles (variants) are desirable.     

Cerebral postischemic hypoperfusion is mediated by ETA receptors

Effect of ETA-receptor antagonist, BQ123, on postischemic hypoperfusion in the presence or absence of nitric oxide synthetase inhibitor,Nω-nitro-l-arginine (NLA), was investigated in Mongolian gerbils. BQ123 given prior to ischemia reversed the early incomplete recovery of cerebral blood flow observed with NLA without affecting the late postischemic hypoperfusion. Additional postischemic administration of BQ123 also reversed (P < 0.01) the late postischemic hypoperfusion seen in NLA-,Nω-nitro-d-arginine methyl ester- or Ringer's-treated animals.     

Age-related increase in oxidized proteins in mouse synaptic mitochondria

Since it has been proposed that oxidized protein accumulation plays a critical role in brain aging, we have investigated their contents in synaptic mitochondria from five age groups of mice. Protein carbonyl content in synaptic mitochondria showed a significant positive correlation with age (r = 0.95, P = 0.01). A linear inverse relationship was observed between protein carbonyl content and complex IV/complex I ratio (which was used as an index of imbalance between mitochondrial respiratory complexes) in synaptic mitochondria in the five age groups (r = −0.99, P < 0.001). We suggest that age-related accumulation of oxidized proteins in synaptic mitochondria may be the result of an age-dependent increase in reactive oxygen species generation because of a disarrangement of mitochondrial oxidative phosphorylation.     

Impairment of the nitric oxide/cyclic GMP pathway in cerebellar slices prepared from thehph-1 mouse

In this study, the effect of tetrahydrobiopterin deficiency on the nitric oxide/cGMP pathway has been investigated in cerebellar slices derived from thehph-1 mouse. This animal displays a partial deficiency of tetrahydrobiopterin. Basal levels of cGMP were significantly reduced (−29.5%) in thehph-1 mouse cerebellum compared to controls. Following kainate stimulation (500 μM) cGMP levels increased in both control andhph-1 preparations but were again significantly lower (−29.1 %) in thehph-1 mouse. Exposure of slices to the nitric oxide donors,S-nitroso-N-acetylpenicillamine andS-nitroso-glutathione, revealed no difference in cGMP accumulation between the two groups. These findings suggest that the cerebellar nitric oxide/cGMP pathway may be impaired in partial tetrahydrobiopterin deficiency states due to diminished nitric oxide formation.     

Prostaglandin E2 may induce hyperthermia through EP1 receptor in the anterior wall of the third ventricle and neighboring preoptic regions

We have previously reported that intracerebroventricular injection of prostaglandin E₂ (PGE₂) induces hyperthermia possibly through EP₁ receptors in the rat. In the present study, to determine the sites in the brain where PGE₂ induces hyperthermia through EP₁ receptors, we microinjected an EP₁ receptor agonist, 17-phenyl-ω-trinor PGE₂ (17-Ph-PGE₂, 100 ng) into different sites in the rat brain and observed the colonic temperature (T_co) for 2 h in a 23±1°C environment. Responsive sites where 17-Ph-PGE₂ (100 ng) produced a rise in the T_co of more than 1.1°C within 60 min after injection were found in the medial preoptic area, the subchiasmatic portion of the median preoptic nucleus, the anterior wall of the third ventricle (A3V) and the ventral portion of the diagonal band of Broca. Among these sites, the A3V was the most responsive. In contrast, microinjection of neither butaprost (an EP₂ agonist, 100 ng) nor M&B28767 (an EP₃ agonist, 100 ng) into these four sites had any effect on the T_co. Intracerebroventricular pretreatment with SC-19220 (an EP₁ antagonist, 100 μg) inhibited the rise in the T_co which was induced by microinjection of PGE₂ (50 ng) into the A3V. These results thus suggest that PGE₂ induces hyperthermia by stimulating EP₁ receptors in the A3V and the neighboring preoptic region.     

The anti-amnesic effects of sigma1 (σ1) receptor agonists confirmed by in vivo antisense strategy in the mouse

The sigma₁ (σ₁) receptor cDNA was recently cloned in several animal species, including the mouse. In order to firmly establish the implication of σ₁ receptors in memory, a phosphorothioate-modified antisense oligodeoxynucleotide (aODN) targeting the σ₁ receptor mRNA and a mismatched analog (mODN) were administered intracerebroventricularly for 3 days in mice. Scatchard analyses of in vitro (+)-[³H]SKF-10,047 binding to σ₁ sites showed that B_max values were significantly decreased in the hippocampus (−58.5%) and cortex (−38.1%), but not in the cerebellum, of aODN treated mice, as compared to saline- or mODN-treated animals. In vivo binding levels were also significantly decreased after aODN treatment in the hippocampus and cortex but not in the cerebellum. The anti-amnesic effects of the selective σ₁ agonists PRE-084 or SA4503 were evaluated against the learning impairments induced by dizocilpine or scopolamine, respectively, using spontaneous alternation behavior and passive avoidance task. The anti-amnesic effects of PRE-084 or SA4503, observed after saline- or mODN-treatment, were blocked after aODN administration. These observations bring a molecular basis to the modulatory role of σ₁ receptors in memory processes.     

Thyroid hormone level is associated with the frequency and severity of Guillain–Barré syndrome

Objective: Guillain–Barré syndrome (GBS) is a neurodegenerative and inflammatory demyelination disorder, and oxidative stress is concerned with the pathogenesis of the disease. Also, we found that thyroid hormone level is correlated to the oxidative and antioxidant status in previous studies. Our study was aimed to find the possible relationship between the frequency and severity of GBS and thyroid hormone levels. Materials and methods: We measured serum levels of thyroid-stimulating hormone (TSH), free thyroxine (FT₄) and free triiodothyronine (FT₃) in 238 individuals, including 90 GBS, 44 multiple sclerosis and 104 healthy controls. Results: Our findings demonstrate that the patients with GBS had lower TSH and higher FT_4, FT₄/FT₃ than healthy controls in the normal range. Furthermore, it was also shown in our study that TSH levels in patients with GBS were correlated with disease severity measured by the Hughes Functional Grading Scale. Conclusion: Lower TSH, higher FT₄ and FT₄/FT₃ stand for the oxidative status and are associated with the incidence and severity of GBS.     

Dopamine denervation leads to an increase in the intramembrane interaction between adenosine A2 and dopamine D2 receptors in the neostriatum

We have previously found, in striatal membrane preparations from young (2 months old) rats, that stimulation of adenosine A₂ receptors (with the selective adenosine A₂ agonist CGS 21680) increases the dissociation constants of high- (K_h) and low-affinity (K_l) dopamine D₂ binding sites (labelled with the selective dopamine D₂ antagonist [³H]raclopride) without changing the proportion of high affinity binding sites (R_h). In the present study in striatal preparations from adult (6 months old) rats, it was found that in addition to the increase in both K_h and K_l values, stimulation of adenosine A₂ receptors is associated with an increase in R_h. These result suggest that, in the adult rat, adenosine A₂ stimulation may inhibit the behavioural effects induced by dopamine D₂ stimulation both by decreasing the affinity and the transduction of dopamine D₂ receptors. We have also studied the intramembrane A₂-D₂ receptor interaction in an experimental model of Parkinson's disease, namely in rats with a unilateral 6-OH-dopamine-induced lesion of the nigro-striatal dopamine pathway. It was found that a unilateral dopamine denervation is associated with a higher density of striatal dopamine D₂ receptors in the order of 20%, without any change in their affinity compared with the unlesioned neostriatum. Furthermore, the density (B_max values) of dopamine D₂ receptors in the contralateral neostriatum was significantly higher (about 20%) than in the striatum from native animals. This finding suggests that an unilateral dopamine denervation also induces compensatory long-lasting changes of dopamine D₂ receptors in the contralateral neostriatum. In addition to the hightened sensitivity to dopamine agonists, it is known that the dopamine denervated striatum is more sensitive to adenosine antagonists like methylxanthines. If the adenosine A₂-dopamine D₂ interaction is the main mechanism of action mediating the central effects of methylxanthines, the dopamine denervation might also potentiate this interaction, i.e., dopamine D₂ receptors could be not only more sensitive to dopamine but also to adenosine A₂ receptor activation. Our results support this hypothesis, since membrane preparations from the denervated neostriatum are more sensitive to the effect of CGS 21680 on dopamine D₂ receptors. Thus a low dose of CGS 21680 (3 nM), which is not effective in membrane preparations from the neostriatum of naive animals, is still effective in membranes from the denervated neostriatum. These results underline the potential antiparkinsonian activity of adenosine A₂ antagonists.     

Variability in the activity of respiratory chain enzymes in mitochondrial myopathies

Summary Four patients with mitochondrial abnormality had multiple muscle biopsies at several year intervals during which respiratory chain enzyme activities were shown to be quite variable. In three patients, progression of the disease paralleled the decrease in respiratory chain enzyme activity. In one patient, the clinical and pathological findings improved with age as is seen in the benign infantile form of cytochromec oxidase (CCO) deficiency. The variability in these mitochondrial disorders may result from the varied proportions of normal and abnormal mitochondria in the muscle cells in which the mitochondria are said to be randomly replicated from numerous mitochondrial DNA copies.This work was partially supported by a Grant-in-Aid for Scientific Research (No. 61570397) from the Ministry of Education, Science and Culture of Japan     

A single (−)-nicotine injection causes change with a time delay in the affinity of striatal D2 receptors for antagonist, but not for agonist, nor in the D2 receptor mRNA levels in the rat substantia nigra

The in vitro and in vivo effects of (−)-nicotine on dopamine D₂ receptors in the rat neostriatum have been studied using biochemical binding, in situ hybridization and immunocytochemistry. A single i.p. injection (1 mg/kg) of (−)-nicotine resulted in a reduction of theK_D value of the D₂ antagonist [³H]raclopride binding sites in rat neostriatal membrane preparations at 12 h without any significant change in theB_max value. This action of (−)-nicotine was counteracted by pretreatment 15 min earlier with the nicotine antagonist mecamylamine (1 mg/kg, i.p.). However, theK_D and theB_max values of the D₂ agonist [³H]NPA binding sites in the rat neostriatal membrane preparations were not significantly affected 0.5–48 h after a single i.p. injection with 1 mg/kg of (−)-nicotine. No significant change in neostriatal D₂ receptor mRNA levels was observed at any time interval after the (−)-nicotine injection. No significant change was observed in tyrosine hydroxylase (TH) immunoreactivity in either the substantia nigra or the neostriatum, nor in nigral TH mRNA levels during the time interval studied (4–24 h posttreatment). Furthermore, addition of low (10 nM) or high (1 μM) concentrations of (−)-nicotine in vitro to rat neostriatal membranes did not alter the characteristics of [³H]raclopride or [³H]NPA binding. These results indicate that a single (−)-nicotine injection can produce a selective and delayed increase in the affinity of D₂ receptors for the antagonist, but not for the agonist without modifying the levels of D₂ receptor mRNA, probably via the activation of central nicotinic receptors.     

Non‐invasive,dynamic imaging of murine intestinal motility

Background After intravenous (i.v.) administration, indocyanine green (ICG) is known to be secreted into bile from the liver via the biliary tracts, enabling fluorescent delineation of the intestine. In addition, ICG is a near‐infrared (NIR) excitable fluorophore, capable of providing exogenous contrast for rapid NIR fluorescence imaging. We sought to quantify the intestinal motility using dynamic NIR fluorescence imaging after injection of ICG. Methods C57BL6 mice were dynamically imaged immediately before and up to 24 h after i.v. and intradermal (i.d.) injection of 50 and 10 μL of ICG, respectively. Necropsy was also performed 1 h postinjection and the entire gastrointestinal tract was isolated and exposed for ex vivo fluorescence imaging. Key Results The secretion of ICG‐laden fluorescent bile into the duodenum was observed in vivo and confirmed in situ. Different patterns of the intestinal motility, such as peristaltic and segmental motions, were dynamically imaged in vivo. Our imaging data showed that the frequency of contractions ranged from 27 to 35 cycles min^?1 and the propagation velocity of peristaltic waves ranged from 0.82 ± 0.5 to 2.04 ± 1.12 cm s^?1. Conclusions & Inferences Dynamic NIR fluorescence imaging with injection of ICG can provide a method for diagnostic motility testing for intestinal motility disorders or dysfunction and for potential evaluation of therapeutic agents.