Neural and Physiological Correlates of Prosocial Behavior: Temporoparietal Junction Activity in 3-Year-Old Children.

Although the development of prosocial behavior has been widely studied from the behavioral aspect, the neural mechanisms underlying prosocial behavior in the early stages of development remain unclear. Therefore, this study investigated the neural mechanisms underlying the emergence of prosocial behavior in 3-year-old children. Brain activity in the medial pFC and right TPJ (rTPJ) and facial expression activity, which are related to the ability to infer others' mental states (mentalizing), during the observation of prosocial and antisocial scenes were measured using functional near-infrared spectroscopy and electromyography, respectively. Subsequently, the children's helping and comforting behaviors toward an experimenter were assessed to examine prosocial behavioral tendencies. A correlation analysis revealed that the children who showed stronger activity levels in the rTPJ while observing prosocial scenes had more immediate helping behaviors toward others than those who did not show stronger response levels. Moreover, the amount of facial expression activity correlated with prosocial behavior, including both helping and comforting behaviors. These results suggest that the development of mentalizing ability and the social evaluation of others' actions, mediated by the rTPJ, contributes to the emergence of prosocial behavior.

Inter-brain synchrony during mother-infant interactive parenting in 3-4-month-old infants with and without an elevated likelihood of autism spectrum disorder.

Maternal bonding for mammalian infants is critical for their survival. Additionally, it is important for human infants' development into social creatures. However, despite the ample neurobiological evidence of attachment for the mother's brain, the interplay of this system in infants is poorly understood. We aimed to identify the neural substrates of synchrony in mothers and infants under three interactive conditions and compare the differences between groups with (n = 16) and without (n = 71) an elevated likelihood of autism spectrum disorder by examining the inter-brain synchrony between mothers and their 3-4-month-old infants. Mother-infant hyperscanning with functional near-infrared spectroscopy was performed during breastfeeding and while each of the mother and experimenter was holding the infants. The results showed almost no group differences, with both groups demonstrating the strongest inter-brain coupling for breastfeeding. The cerebral foci underlying these couplings differed between mothers and infants: the ventral prefrontal cortex, focusing on the right orbitofrontal cortex, in the mother and the left temporoparietal junction in the infant were chiefly involved in connecting the two brains. Furthermore, these synchronizations revealed many significant correlations with behavioral measures, including subsequent language development. The maternal reward-motivational system and the infant's elementary mentalization system seem to underlie mother-infant coupling during breastfeeding.

Low-grade serous carcinoma detected from intraoperative peritoneal washings: Cytological findings and detection of KRAS mutation.

BACKGROUND: Low-grade serous carcinoma (LGSC) of the ovary, which is extremely rare tumor, has better prognosis than high-grade serous carcinoma (HGSC). Genetic backgrounds of those are different, so that LGSC usually shows KRAS or BRAF mutation, whereas HGSC does not show such mutations. Since treatment strategies of those are different, differential pathological diagnosis between LGSC and HGSC is very important. CASE: We report a case of LGSC that was diagnosed by both cytological findings and genetic analysis using small amount cells from cytological specimen. The 30-year-old Japanese woman with bilateral ovarian tumors underwent salpingo-oopherectomy. The peritoneal washing cytologic specimen and touched cytologic specimen from the tumor included non-complex clusters with psammoma bodies composed of tumor cells with mild to moderate atypia and without bizarre nuclei. The ovarian tumor was histologically diagnosed as LGSC. The genetic analysis that was done using exfoliated cells from peritoneal washings specimen by idensy™, detected KRAS mutation at codon 12/13. CONCLUSION: The genetic investigation using cytological specimen as well as characteristic cytological findings were useful to make differential diagnosis between LGSC and HGSC.

Trastuzumab deruxtecan (DS-8201) in patients with HER2-expressing metastatic colorectal cancer (DESTINY-CRC01): a multicentre, open-label, phase 2 trial.

BACKGROUND: HER2 amplification has been identified in 2-3% of patients with colorectal cancer, although there are currently no approved HER2-targeted therapies for colorectal cancer. We aimed to study the antitumour activity and safety of trastuzumab deruxtecan (an antibody-drug conjugate of humanised anti-HER2 antibody with topoisomerase I inhibitor payloads) in patients with HER2-expressing metastatic colorectal cancer. METHODS: DESTINY-CRC01 is an open-label, phase 2 study that recruited patients from 25 clinics and hospitals in Italy, Japan, Spain, the UK, and the USA. Eligible patients had centrally confirmed HER2-expressing metastatic colorectal cancer that had progressed on two or more previous regimens (HER2-targeted therapies other than trastuzumab deruxtecan permitted), were aged 18 years or older (≥20 years in Japan), had an Eastern Cooperative Oncology Group score of 0 or 1, and had RAS and BRAFV600E wild-type tumours. Patients were enrolled into one of three cohorts by HER2 expression level: cohort A (HER2-positive, immunohistochemistry [IHC] 3+ or IHC2+ and in-situ hybridisation [ISH]-positive), cohort B (IHC2+ and ISH-negative), or cohort C (IHC1+). Patients received 6·4 mg/kg trastuzumab deruxtecan intravenously every 3 weeks until disease progression, unacceptable adverse events, withdrawal of consent, or death. The primary endpoint was confirmed objective response rate in cohort A by independent central review which was assessed in the full analysis set and safety was assessed in the safety analysis set. Both the full analysis set and the safety analysis set included all patients who received one or more doses of trastuzumab deruxtecan. This ongoing trial is registered with ClinicalTrials.gov, number NCT03384940. FINDINGS: Between Feb 23, 2018, and July 3, 2019, 78 patients were enrolled in the study (53 in cohort A, seven in cohort B, and 18 in cohort C), all of whom received at least one dose of study drug. For the 53 (68%) patients with HER2-positive tumours (cohort A), a confirmed objective response was reported in 24 (45·3%, 95% CI 31·6-59·6) patients after a median follow-up of 27·1 weeks (IQR 19·3-40·1). Grade 3 or worse treatment-emergent adverse events that occurred in at least 10% of all participants were decreased neutrophil count (17 [22%] of 78) and anaemia (11 [14%]). Five patients (6%) had adjudicated interstitial lung disease or pneumonitis (two grade 2; one grade 3; two grade 5, the only treatment-related deaths). INTERPRETATION: Trastuzumab deruxtecan showed promising and durable activity in HER2-positive metastatic colorectal cancer refractory to standard treatment, with a safety profile consistent with that reported in previous trastuzumab deruxtecan trials. Interstitial lung disease and pneumonitis are important risks requiring careful monitoring and prompt intervention. FUNDING: Daiichi Sankyo.

Misleading Focal Clinical, Neurophysiologic, and Imaging Features in 2 Children With Generalized Epilepsy Who Underwent Invasive Electroencephalographic (EEG) Monitoring.

Children and adults with genetic generalized epilepsy may have focal clinical seizure symptoms as well as electroencephalographic (EEG) findings. This may pose a diagnostic challenge to clinicians, especially when concomitant focal neuroimaging findings exist and the epilepsy is medically refractory. We sought to highlight the challenges that clinicians may face through the description of 2 children with suspected genetic generalized epilepsy who had both focal seizure symptoms and EEG/neuroimaging findings and underwent invasive EEG monitoring. Ultimately, invasive monitoring failed to demonstrate a focal origin for the seizures in both cases, and instead confirmed the presence of genetic generalized epilepsy. We demonstrate that ≥3-Hz generalized monomorphic spike and waves are less likely to represent secondary bilateral synchrony, that focal neuroimaging findings may not always be causal and that repeated hyperventilation is an essential activation procedure for genetic generalized epilepsy.

Subtle temporal delays of mothers' responses affect imitation learning in children: Mother-child interaction study.

The relationship between temporal contiguity of mothers' teaching behaviors and children's imitation learning was investigated. Participants (2-year-old children) observed their mothers' demonstration of using novel toys over a double television system under live and delayed conditions. The dyads normally interacted in the live condition, whereas they interacted with a 1-s time delay inserted between the children's actions and mothers' responses in the delayed condition. Then, the children were tested with identical toys. Results indicated that children's smiling responses and imitation performances were significantly decreased in the delayed condition compared with the live condition, although mothers' teaching approach did not differ between conditions. These results suggest that a subtle temporal delay in mothers' responses could affect young children's imitation learning.

A case of wild-type transthyretin amyloidosis associated with organizing pneumonia.

An 81-year-old man was referred to our hospital with bilateral multiple patchy opacities on chest radiography. His chief complaints were a few months' history of intermittent mild cough and slightly yellow sputum. Chest computed tomography (CT) showed non-segmental air-space consolidations with ground-glass opacities. Amyloid deposition with organizing pneumonia (OP) was seen in transbronchial lung biopsy (TBLB) specimens from the left S8. Three months later, the infiltration originally seen in the left lower lobe was remarkably diminished, and new infiltrations in the lingual and right lower lobes were detected on chest CT. Amyloid deposition with OP was seen in TBLB specimens from the left S4. Transthyretin was detected following immunohistochemical examination. The presence of wild-type transthyretin (ATTRwt) was proven using genetic analysis. The present report describes a rare case of ATTRwt amyloidosis associated with OP.

Pigeons (Columba livia) fail to connect dots in learning biological motion.

Biological motion point-light displays provide a powerful method for studying motion perception. Nonhuman animals are capable of discriminating point-light displays, but it remains unknown how they perceive biological motion in these displays. We trained two groups of pigeons to discriminate video stimuli using two different classification rules. The motion-congruent group was trained to discriminate full-detail and corresponding point-light displays of pigeons from full-detail and point-light displays of humans. The motion-incongruent group was trained to discriminate full-detail pigeons and point-light humans from the other displays. Both groups acquired the discrimination. When tested with novel displays, pigeons showed good transfer of learning. Transfer was poorest with the point-light displays in the motion-congruent group. The results indicate that the pigeons failed to make the connection between the full-detail displays and their point-light counterparts even when the common motion was available as a cue.

Randomized phase II trial of nimotuzumab plus irinotecan versus irinotecan alone as second-line therapy for patients with advanced gastric cancer.

BACKGROUND: This multicenter, randomized phase II trial was conducted to compare the efficacy and safety of nimotuzumab plus irinotecan (N-IRI) versus irinotecan alone (IRI) in patients with advanced gastric cancer (AGC) showing disease progression after previous 5-fluorouracil-based therapy. METHODS: Irinotecan-naive patients (n = 82) received N-IRI (nimotuzumab 400 mg weekly plus irinotecan 150 mg/m(2) biweekly) or IRI (irinotecan 150 mg/m(2) biweekly) until disease progression. The primary endpoint was progression-free survival (PFS), and the secondary endpoints were overall survival (OS), response rate (RR), safety, tolerability, and the correlation between efficacy and tumor epidermal growth factor receptor (EGFR) expression. RESULTS: Of 83 patients, 40 and 43 patients were randomly assigned to the N-IRI and IRI groups, respectively. In the N-IRI/IRI treatment group, median PFS was 73.0/85.0 days (P = 0.5668), and median OS and RR at 18 months were 250.5/232.0 days (P = 0.9778) and 18.4/10.3 %, respectively. Median PFS and OS in the EGFR 2+/3+ subgroups were 118.5/59.0 and 358.5/229.5 days, respectively. The RR was 33.3/0.0 % in the N-IRI/IRI treatment group. The incidence of grade 3 or higher adverse events was 77.5/64.3 %. No adverse events of grade 3 or higher skin rash or grade 3 or higher infusion-related reaction were reported. CONCLUSIONS: There was no superiority of N-IRI over IRI alone in terms of PFS in 5-fluorouracil-refractory AGC patients. However, N-IRI showed potential improvement in the EGFR 2+/3+ subgroup based on improved RR, PFS, and OS.

An effective strategy to reduce blood pressure after forest walking in middle-aged and aged people.

[Purpose] Forest walking may be effective for human health, but little information is available about effects of energy expenditure on blood pressure responses after forest walking. The aim of this study was to investigate the relationship between the activity energy expenditure and changes in blood pressure in individuals after forest walking. [Subjects] The subjects were 54 middle-aged and elderly people. [Methods] All subjects walked in the forest for approximately 90 min. Blood pressure, salivary amylase, and the Profile of Mood States were evaluated before and after forest walking, and activity energy expenditure was monitored throughout forest walking. Subjects were divided into two groups according to mean arterial pressure changes: a responder group (>5% decreases) and a nonresponder group (<5%). [Results] Forest walking significantly reduced the mean arterial pressure and improved the Profile of Mood States in both groups. Activity energy expenditure was related to changes in mean arterial pressure in the responder group, while this relation was not observed in the nonresponder group. Differential activity energy expenditure did not strongly affect improvement of the Profile of Mood States. [Conclusion] Greater walking-related greater activity energy expenditure might be required to accentuate physiological beneficial effects on in middle-aged and aged people. Furthermore, the forest environment per se can attenuate psychological stress.

Increased expression of ERp57/GRP58 is protective against pancreatic beta cell death caused by autophagic failure.

Autophagy is a tightly regulated self-digestion system. As in other cell types, autophagy plays an essential role in the homeostasis of pancreatic beta cells. However, the mechanisms involved in the deterioration of beta cell function caused by autophagic failure have not yet been fully elucidated. To gain insight into its mechanisms, we compared the protein expression of islets from beta cell-specific Atg7-deficient mice (Atg7(Δß-cell) mice) and their controls (Atg7(f/f) mice). Liquid chromatography/mass spectrometry after 1-dimensional electrophoresis identified the increased expression of ERp57/GRP58 in islets isolated from Atg7(Δß-cell) mice compared with those from Atg7(f/f) mice. The expression level of ERp57 was also elevated in rat insulinoma INS-1 cells by inducible knock-down of the atg7-gene. In Atg7 knock-down INS-1 cells, the suppression of ERp57 expression by siRNA resulted in an increase in the level of cleaved Caspase-3 protein and a decrease in the number of live cells. Furthermore, cell cycle analyses demonstrated that the suppressed expression of ERp57 increased the sub-G1 population. These data reveal that increased expression of ERp57 may contribute to the protection from beta cell death caused by autophagic failure.

Why don't plants have diabetes? Systems for scavenging reactive carbonyls in photosynthetic organisms.

In the present paper, we review the toxicity of sugar- and lipid-derived RCs (reactive carbonyls) and the RC-scavenging systems observed in photosynthetic organisms. Similar to heterotrophs, photosynthetic organisms are exposed to the danger of RCs produced in sugar metabolism during both respiration and photosynthesis. RCs such as methylglyoxal and acrolein have toxic effects on the photosynthetic activity of higher plants and cyanobacteria. These toxic effects are assumed to occur uniquely in photosynthetic organisms, suggesting that RC-scavenging systems are essential for their survival. The aldo-keto reductase and the glyoxalase systems mainly scavenge sugar-derived RCs in higher plants and cyanobacteria. 2-Alkenal reductase and alkenal/alkenone reductase catalyse the reduction of lipid-derived RCs in higher plants. In cyanobacteria, medium-chain dehydrogenases/reductases are the main scavengers of lipid-derived RCs.

Scavenging systems for reactive carbonyls in the cyanobacterium Synechocystis sp. PCC 6803.

To elucidate the scavenging systems of sugar- and lipid-derived reactive carbonyls (RCs) in the cyanobacterium Synechocystis sp. PCC 6803 (S. 6803), we selected proteins from S. 6803 based on amino-acid (AA) sequence similarities with proteins from Arabidopsis thaliana, and characterized the properties of the GST-fusion proteins expressed. Slr0942 catalyzed the aldo-keto reductase (AKR) reaction scavenging mainly sugar-derived RCs, methylglyoxal (MG). Slr1192 is the medium-chain dehydrogenase/redutase (MDR). It catalyzed the AKR reaction scavenging several lipid-derived RCs, acrolein, propionaldehyde, and crotonaldehyde. Slr0315 is a short-chain dehydrogenase/redutase (SDR), and it catalyzed only the reduction of MG in the AKR reaction. Slr0381 catalyzed the conversion of hemithioacetal to S-lactoylglutahione (SLG) in the glyoxalase (GLX) 1 reaction. Sll1019 catalyzed the conversion of SLG to glutathione and lactate in the GLX2 reaction. GLX1 and GLX2 compose the glyoxalase system, which scavenges MG. These enzymes contribute to scavenging sugar- and lipid-derived RCs as scavenging systems.

Antihistamine effects on prefrontal cortex activity during working memory process in preschool children: a near-infrared spectroscopy (NIRS) study.

Histamine H1 receptor antagonists (antihistamines) are widely used for the treatment of allergic disorders in young children. This study examined the effects of antihistamine on prefrontal cortex activity in preschool children using near-infrared spectroscopy (NIRS), an emerging brain-imaging method suitable for psychological experiments, especially in young children. We examined the changes of oxygenated hemoglobin concentration in the prefrontal cortex while children performed a spatial working memory task, 3h after taking a first-generation antihistamine (ketotifen), second-generation antihistamine (epinastine), or placebo. Fifteen healthy preschool children (mean age, 5.5 years) participated. Ketotifen significantly impaired behavioral performance and cortical activation at the lateral prefrontal cortex in the working memory task, compared with epinastine and placebo. There were no sedative effects on neural response or behavioral performance after epinastine administration. This paper demonstrates for the first time differential sedation effects of first- and second-generation antihistamines on brain hemodynamic response in young children. Also discussed is the utility of the NIRS technique in neuropsychopharmacological studies of children.

Effects of sedative and nonsedative antihistamines on prefrontal activity during verbal fluency task in young children: a near-infrared spectroscopy (NIRS) study.

INTRODUCTION: Antagonists of histamine H(1) receptors (antihistamines) are widely used for the treatment of allergic disorders in children. These drugs' sedative effect on brain function, however, has been mostly examined in adults. OBJECTIVE: The objective of this study was to examine the effects of anitihistamines on prefrontal cortex activity in young children using near-infrared spectroscopy (NIRS), a novel brain-imaging method. MATERIALS AND METHODS: In 15 healthy children (mean age, 7.7 years), we examined changes of oxygenated hemoglobin concentration in the prefrontal cortex while they performed a verbal fluency task 3 h after taking a sedating antihistamine (ketotifen), nonsedating antihistamine (epinastine), or placebo. RESULTS: Ketotifen significantly impaired behavioral performance and cortical activation at the lateral prefrontal cortex compared with placebo. There were no sedative effects on neural response or behavioral performance after epinastine administration. CONCLUSIONS: NIRS revealed that sedating and nonsedating antihistamines exert differential effects on brain hemodynamic response in young children.

Longitudinal study of spatial working memory development in young children.

This study longitudinally compared activity in the frontal cortex during a spatial working memory task between 5-year-old and 7-year-old children using near-infrared spectroscopy. Eight children participated in this study twice, once at 5 years and once at 7 years of age. Behavioral analysis showed that older children performed the working memory task more precisely and more rapidly than younger children. Near-infrared spectroscopy analysis showed that right hemisphere dominance was observed in older children, whereas no hemispheric difference was apparent in younger children. Children with strengthened lateralization showed improved performance from 5 to 7 years. We therefore offer the first demonstration of the developmental changes in frontal cortical activation during spatial working memory tasks during the preschool period.

Inspection of the activator binding site for 4-alpha-glucanotransferase in porcine liver glycogen debranching enzyme with fluorogenic dextrins.

Recently, we found that alpha-, beta- and gamma-cyclodextrins accelerated the 4-alpha-glucanotransferase action of porcine liver glycogen debranching enzyme (GDE) on Glcalpha1-4Glcalpha1-4Glcalpha1-4(Glcalpha1-4Glcalpha1-4Glcalpha1-4Glcalpha1-6)Glcalpha1-4Glcalpha1-4Glcalpha1-4Glcalpha1-4GlcPA (B5/84), and proposed the presence of an activator binding site in the GDE molecule. In liver cells, the structures of alpha-glucans proximal to the site GDE acts are not cyclodextrins, but glycogen and its degradation products. To estimate the structural characteristics of intrinsic activators and to inspect the features of the activator binding site, we examined the effects of four fluorogenic dextrins, (Glcalpha1-6)(m)Glcalpha1-4(Glcalpha1-4)(n)GlcPA (B5/51, m = 1, n = 3; B6/61, m = 1, n = 4; B7/71, m = 1, n = 5; G6PA, m = 0, n = 4), on the debranching of B5/84 by porcine liver GDE. The GDE 4-alpha-glucanotransferase removed the maltotriosyl residue from the maltotetraosyl branch of B5/84, producing Glcalpha1-4Glcalpha1-4Glcalpha1-4(Glcalpha1-6)Glcalpha1-4Glcalpha1-4Glcalpha1-4Glcalpha1-4GlcPA (B5/81). In the presence of G6PA, the removed maltotriosyl residue was transferred to G6PA to give Glcalpha1-4Glcalpha1-4Glcalpha1-4Glcalpha1-4Glcalpha1-4Glcalpha1-4Glcalpha1-4Glcalpha1-4GlcPA (G9PA). In the absence of G6PA, the removed maltotriosyl residue was transferred to water. B7/71, B6/61 and B5/51 did not undergo any changes by the GDE, but they accelerated the action of the 4-alpha-glucanotransferase in removing the maltotriosyl residue. Of the four fluorogenic dextrins examined, B6/61 most strongly accelerated the 4-alpha-glucanotransferase action. The activator binding site is likely to be a space that accommodates the structure of Glcalpha1-6Glcalpha1-4Glcalpha1-4Glcalpha1-4Glcalpha1-4Glc.

Strategy of auditory discrimination of scale in Java sparrows: they use both "imagery" and specific cues.

We examined whether Java sparrows use imagery of auditory stimuli (imagery is a subject's mental representation of a stimulus by which the subject's behaviour may be governed under stimulus control even in the absence of the physical stimulus). Three types of ascending tone sequences were used. In the intact scale, sequence tones were played in ascending order. In the intact-masked scale, part of the sequence was masked by noise but the remaining scale was identical with the intact scale, whereas in the violated scale, the sequence could be heard as if tones were played slowly (Experiment 1) or quickly (Experiment 2). Subjects were divided into two groups: one group was trained to respond to the intact and intact-masked scales and to suppress response to the violation scale (imagery-positive group). The contingency was reversed for the other (violation-positive) group. In Experiment 1, all the birds acquired discrimination, but successful transfer to novel stimuli was observed only in the imagery-positive group, suggesting that the imagery of the tone sequence was used as a discriminative cue. Experiment 2 confirmed that the stimulus duration was a discriminative cue for both groups, suggesting that the birds also acquired discrimination using only specific cues.

Effects of sedative and non-sedative H1 antagonists on cognitive tasks: behavioral and near-infrared spectroscopy (NIRS) examinations.

RATIONALE: It is well known that the newer H1-receptor antagonists elicit better performance of working memory and selective attention relative to the first generation drugs in this class. However, the neural correlates of the poorer performance associated with first-generation H1-receptor antagonists remain unknown. OBJECTIVES: This study examined the effects of first- and second-generation H1-receptor antagonists on neural correlates of cognitive tasks using near-infrared spectroscopy (NIRS), a novel method of brain imaging suitable for psychological experiments. MATERIALS AND METHODS: We measured the NIRS responses of 12 healthy volunteer subjects during the performance of working memory, selective attention, and visual perception tasks, 3 h after taking a first-generation antagonist (ketotifen), second-generation antagonist (epinastine), or placebo. We also measured subjective sleepiness by visual analogue scale (VAS) test. RESULTS: Cortical activation at the lateral prefrontal region increased during the performance of working memory and selective attention tasks in subjects receiving epinastine and placebo but not in those who took ketotifen. No significant difference was observed at the occipital region in the visual perception task among the three drug groups. VAS score and the behavioral performance during working memory and visual perception tasks indicated sedative effects of ketotifen consistent with the findings of previous studies. CONCLUSIONS: Our results suggest that the neural response for working memory and selective attention task was impaired by the administration of ketotifen in comparison with that of epinastine and placebo. The sedative effect in the neural response was not observed after epinastine administration.

Active site mapping of amylo-alpha-1,6-glucosidase in porcine liver glycogen debranching enzyme using fluorogenic 6-O-alpha-glucosyl-maltooligosaccharides.

Glycogen debranching enzyme (GDE) has two enzymatic activities, 4-alpha-glucanotransferase and amylo-alpha-1,6-glucosidase. Products with 6-O-alpha-glucosyl structures formed from phosphorylase limit dextrin by the 4-alpha-glucanotransferase activity are hydrolyzed to glucose by the amylo-alpha-1,6-glucosidase activity. Here, we probed the active site of amylo-alpha-1,6-glucosidase in porcine liver GDE using various 6-O-alpha-glucosyl-pyridylamino (PA)-maltooligosaccharides, with structures (Glcalpha1-4)(m)(Glcalpha1-6)Glcalpha1-4(Glcalpha1-4)(n)GlcPA (GlcPA, 1-deoxy-1-[(2-pyridyl)amino]-D-glucitol residue). Fluorogenic dextrins were prepared from 6-O-alpha-glucosyl-alpha-, beta-, or gamma-cyclodextrin through partial acid hydrolysis, followed by fluorescent tagging of the reducing-end residues of the hydrolysates and separation by gel filtration and reversed-phase HPLC. Porcine liver GDE hydrolyzed dextrins with the structure Glcalpha1-4(Glcalpha1-6)Glcalpha1-4Glc to glucose and the corresponding PA-maltooligosaccharides, whereas other dextrins were not hydrolyzed. Thus, substrates must have two glucosyl residues sandwiching the isomaltosyl moiety to be hydrolyzed. The rate of hydrolysis increased as m increased and reached maximum at m = 4. The rates were the highest when n = 1 but did not vary much with changes in n. Of the dextrins examined, Glcalpha1-4Glcalpha1-4Glcalpha1-4Glcalpha1-4(Glcalpha1-6)Glcalpha1-4Glcalpha1-4GlcPA (6(3)-O-alpha-glucosyl-PA-maltoheptaose) was hydrolyzed most rapidly, suggesting that it fits the best in the amylo-alpha-1,6-glucosidase active site. It is likely that the active site accommodates 6(2)-O-alpha-glucosyl-maltohexaose and that the interactions of seven glucosyl residues with the active site allow the most rapid hydrolysis of the alpha-1,6-glucosidic linkage of the isomaltosyl moiety.