Acute administration of methylphenidate differentially affects cortical processing of emotional facial expressions in attention-deficit hyperactivity disorder children as studied by functional near-infrared spectroscopy.

Significance: It has been reported that children with attention-deficit hyperactivity disorder (ADHD) have impairment in the recognition of angry but not of happy facial expressions, and they show atypical cortical activation patterns in response to facial expressions. However, little is known about neural mechanisms underlying the impaired recognition of facial expressions in school-aged children with ADHD and the effects of acute medication on their processing of facial expressions. Aim: We aimed to investigate the possibility that acute administration of methylphenidate (MPH) affects processing of facial expressions in ADHD children. Approach: We measured the hemodynamic changes in the bilateral temporo-occipital areas of ADHD children observing the happy and angry facial expressions before and 1.5 h after MPH or placebo administration in a randomized, double-blind, placebo-controlled, crossover design study. Results: We found that, regardless of medication, happy expressions induced increased oxyhemoglobin (oxy-Hb) responses in the right inferior occipital region but not in the superior temporal region. For angry expressions, oxy-Hb responses increased after MPH administration, but not after placebo administration, in the left inferior occipital area, whereas there was no significant activation before MPH administration. Conclusions: Our results suggest that (1) ADHD children consistently recruit the right inferior occipital regions to process happy expressions and (2) MPH administration to ADHD children enhances cortical activation in the left inferior occipital regions when they process angry expressions.

Hemodynamic response to familiar faces in children with ADHD.

BACKGROUND: School-age children with attention deficit hyperactivity disorder (ADHD) have difficulties in interpersonal relationships, in addition to impaired facial expression perception and recognition. For successful social interactions, the ability to discriminate between familiar and unfamiliar faces is critical. However, there are no published reports on the recognition of familiar and unfamiliar faces by children with ADHD. METHODS: We evaluated the neural correlates of familiar and unfamiliar facial recognition in children with ADHD compared to typically developing (TD) children. We used functional near-infrared spectroscopy (fNIRS) to measure hemodynamic responses on the bilateral temporal regions while participants looked at photographs of familiar and unfamiliar faces. Nine boys with ADHD and 14 age-matched TD boys participated in the study. fNIRS data were Z-scored prior to analysis. RESULTS: During familiar face processing, TD children only showed significant activity in the late phase, while ADHD children showed significant activity in both the early and late phases. Additionally, the boys with ADHD did not show right hemispheric lateralization to familiar faces. CONCLUSIONS: This study is the first to assess brain activity during familiar face processing in boys with ADHD using fNIRS. These findings of atypical patterns of brain activity in boys with ADHD may be related to social cognitive impairments from ADHD.

Differences in the Pattern of Hemodynamic Response to Self-Face and Stranger-Face Images in Adolescents with Anorexia Nervosa: A Near-Infrared Spectroscopic Study.

There have been no reports concerning the self-face perception in patients with anorexia nervosa (AN). The purpose of this study was to compare the neuronal correlates of viewing self-face images (i.e. images of familiar face) and stranger-face images (i.e. images of an unfamiliar face) in female adolescents with and without AN. We used near-infrared spectroscopy (NIRS) to measure hemodynamic responses while the participants viewed full-color photographs of self-face and stranger-face. Fifteen females with AN (mean age, 13.8 years) and 15 age- and intelligence quotient (IQ)-matched female controls without AN (mean age, 13.1 years) participated in the study. The responses to photographs were compared with the baseline activation (response to white uniform blank). In the AN group, the concentration of oxygenated hemoglobin (oxy-Hb) significantly increased in the right temporal area during the presentation of both the self-face and stranger-face images compared with the baseline level. In contrast, in the control group, the concentration of oxy-Hb significantly increased in the right temporal area only during the presentation of the self-face image. To our knowledge the present study is the first report to assess brain activities during self-face and stranger-face perception among female adolescents with AN. There were different patterns of brain activation in response to the sight of the self-face and stranger-face images in female adolescents with AN and controls.

Hemodynamic response of children with attention-deficit and hyperactive disorder (ADHD) to emotional facial expressions.

Children with attention-deficit/hyperactivity disorder (ADHD) have difficulty recognizing facial expressions. They identify angry expressions less accurately than typically developing (TD) children, yet little is known about their atypical neural basis for the recognition of facial expressions. Here, we used near-infrared spectroscopy (NIRS) to examine the distinctive cerebral hemodynamics of ADHD and TD children while they viewed happy and angry expressions. We measured the hemodynamic responses of 13 ADHD boys and 13 TD boys to happy and angry expressions at their bilateral temporal areas, which are sensitive to face processing. The ADHD children showed an increased concentration of oxy-Hb for happy faces but not for angry faces, while TD children showed increased oxy-Hb for both faces. Moreover, the individual peak latency of hemodynamic response in the right temporal area showed significantly greater variance in the ADHD group than in the TD group. Such atypical brain activity observed in ADHD boys may relate to their preserved ability to recognize a happy expression and their difficulty recognizing an angry expression. We firstly demonstrated that NIRS can be used to detect atypical hemodynamic response to facial expressions in ADHD children.

Novel method to classify hemodynamic response obtained using multi-channel fNIRS measurements into two groups: exploring the combinations of channels.

Near-infrared spectroscopy (NIRS) in psychiatric studies has widely demonstrated that cerebral hemodynamics differs among psychiatric patients. Recently we found that children with attention-deficit/hyperactivity disorder (ADHD) and children with autism spectrum disorders (ASD) showed different hemodynamic responses to their own mother's face. Based on this finding, we may be able to classify the hemodynamic data into two those groups and predict to which diagnostic group an unknown participant belongs. In the present study, we proposed a novel statistical method for classifying the hemodynamic data of these two groups. By applying a support vector machine (SVM), we searched the combination of measurement channels at which the hemodynamic response differed between the ADHD and the ASD children. The SVM found the optimal subset of channels in each data set and successfully classified the ADHD data from the ASD data. For the 24-dimensional hemodynamic data, two optimal subsets classified the hemodynamic data with 84% classification accuracy, while the subset contained all 24 channels classified with 62% classification accuracy. These results indicate the potential application of our novel method for classifying the hemodynamic data into two groups and revealing the combinations of channels that efficiently differentiate the two groups.

Enhanced transglutaminase 2 expression in response to stress-related catecholamines in macrophages.

Transglutaminase 2 (TG2) is a multifunctional protein that contributes to inflammatory disease when aberrantly expressed. Although macrophages express TG2, the factor stimulating TG2 expression remains poorly characterized in these cells. In the present study, we examined the effects of the stress-related catecholamines adrenaline and noradrenaline on macrophage expression of TG2 in RAW264.7 murine macrophages and murine bone marrow-derived macrophages. Treatment with adrenaline markedly increased TG2 mRNA expression and increased TG2 protein levels. While the ß2-adrenoceptor-selective antagonist ICI 118,551 completely blocked adrenaline-induced TG2 mRNA expression, the ß2-adrenoceptor specific agonist salmeterol increased TG2 expression. Noradrenaline also increased TG2 mRNA expression at higher doses than the effective doses of adrenaline. The effect of adrenaline on TG2 mRNA expression was mimicked by treatment with the membrane-permeable cAMP analog 8-Br-cAMP. Thus, increased intracellular cAMP following stimulation of ß2-adrenoceptors appeared to be responsible for adrenaline-induced TG2 expression. Because stress events activate the sympathetic nervous system and result in secretion of the catecholamines, adrenoceptor-mediated increase in macrophage TG2 expression might be associated with stress-related inflammatory disorders.

Metaplastic regulation of the median raphe nucleus via serotonin 5-HT1A receptor on hippocampal synaptic plasticity is associated with gender-specific emotional expression in rats.

Gender differences in psychiatric disorders are considered to be associated with the serotonergic (5-HTergic) system; however the underlying mechanisms have not been clearly elucidated. In this study, possible involvement of the median raphe nucleus (MRN)-hippocampus 5-HTergic system in gender-specific emotional regulation was investigated, focusing on synaptic plasticity in rats. A behavioral study using a contextual fear conditioning (CFC) paradigm showed that the females exhibited low anxiety-like behavior. Extracellular 5-HT levels in the hippocampus were increased by CFC only in the males. Long-term potentiation (LTP) in the hippocampal CA1 field was suppressed after CFC in the males, which was mimicked by the synaptic response to MRN electrical stimulation. In the MRN, 5-HT immunoreactive cells significantly increased in the females compared with those in the males. Pretreatment with the 5-HT1A receptor agonists tandospirone (10 mg/kg, i.p.) and 8-OH DPAT (3 mg/kg, i.p.) significantly suppressed LTP induction in the males. Synaptic responses to CFC and 5-HT1A receptor interventions were not observed in the females. These results suggest that the metaplastic 5-HTergic mechanism via 5-HT1A receptors in the MRN-hippocampus pathway is a key component for gender-specific emotional regulation and may be a cause of psychiatric disorders associated with vulnerability or resistance to emotional stress.

Subanalgesic ketamine enhances morphine-induced antinociceptive activity without cortical dysfunction in rats.

PURPOSE: Ketamine, a noncompetitive N-methyl-D-aspartate receptor antagonist, has been used for the treatment of cancer pain as an analgesic adjuvant to opioids. However, ketamine is known to produce psychotomimetic side effects including cognitive impairments under a high-dose situation, presumably as the result of cortical dysfunction. Here, we investigated whether low-dose ketamine was useful as an analgesic adjuvant to morphine for pain control, focusing on frontocortical function. METHODS: To assess the analgesic effects of ketamine with or without morphine, we performed behavioral and histochemical experiments, using the hot plate test and c-Fos expression analysis in rats. The effect on cortical function was also determined by prepulse inhibition (PPI) of the acoustic startle and evoked potentials in the hippocampal CA1-medial prefrontal cortex (mPFC) synapses as measures of synaptic efficacy. RESULTS: Coadministration of ketamine as a subanalgesic dose significantly enhanced intraperitoneal morphine-induced antinociceptive response, which was measured as the increased reaction latency in the hot plate test. In addition, the noxious thermal stimulus-induced c-Fos expression in the ventrolateral periaqueductal gray matter was significantly suppressed by concomitant ketamine and morphine. In contrast, the subanalgesic dose of ketamine did not impair PPI and synaptic efficacy in the mPFC. CONCLUSION: The present results indicate that the morphine-induced analgesic effect is enhanced by a concomitant subanalgesic dose of ketamine without affecting cortical function. Our findings possibly support the clinical notion that low-dose ketamine as an analgesic adjuvant has therapeutic potential to reduce opioid dosage, thereby improving the quality of life in cancer pain patients.

Synaptic modulation via basolateral amygdala on the rat hippocampus-medial prefrontal cortex pathway in fear extinction.

The present study elucidated the functional role of modulatory effects of basolateral amygdala (BLA) on synaptic transmission in the rat hippocampus-medial prefrontal cortex (mPFC) pathway, compared with the hippocampal dentate gyrus (DG). Exposure to conditioned fear stress (CFS) or prior BLA activation enhanced tetanus-induced long-term potentiation (LTP) in DG. A similar synaptic response was found by low frequency stimulation (LFS) prior to tetanus. In mPFC, they did not affect LTP, but prior BLA activation, as well as pretreatment with the N-methyl-d-aspartate (NMDA)-receptor antagonist MK-801 (0.1 mg/kg, i.p.), suppressed LFS-primed LTP. This BLA-mediated synaptic pattern was mimicked by synaptic changes observed in the fear extinction process; prior BLA activation suppressed the synaptic potentiation responsible for extinction retrieval and attenuated decreases in fear-related freezing behavior. These data suggest that LFS-primed LTP in mPFC is related to the neural basis of extinction. Extinction-related synaptic potentiation did not occur in a juvenile stress model that exhibited extinction deficit. In addition, LFS-primed LTP was suppressed in this model, which was reversed by the NMDA-receptor agonist d-cycloserine (15 mg/kg, i.p.). These findings suggest that modulatory effects of BLA on synaptic function in the hippocampus-mPFC pathway play a significant role in fear extinction in rats.

Facilitation of fear extinction by the 5-HT(1A) receptor agonist tandospirone: possible involvement of dopaminergic modulation.

Fear extinction-based exposure treatment is an important component of psychotherapy for anxiety disorders such as posttraumatic stress disorder (PTSD). Recent studies have focused on pharmacological approaches combined with exposure therapy to augment extinction. In this study, we elucidated the therapeutic potential of the serotonin 1A (5-HT(1A) ) receptor agonist tandospirone compared with the effects of the N-methyl-D-aspartate partial agonist D-cycloserine (DCS), focusing on the possible involvement of dopaminergic mechanisms. We used a rat model of juvenile stress [aversive footshock (FS)] exposure during the third postnatal week (3wFS). The 3wFS group exhibited extinction deficit reflected in sustained fear-related behavior and synaptic dysfunction in the hippocampal CA1 field and medial prefrontal cortex (mPFC), which are responsible for extinction processes. Tandospirone administration (5 mg/kg, i.p.) before and after the extinction trials ameliorated both the behavioral deficit and synaptic dysfunction, i.e., synaptic efficacy in the CA1 field and mPFC associated with extinction training and retrieval, respectively, was potentiated in the tandospirone-treated 3wFS group. Extracellular dopamine release in the mPFC was increased by extinction retrieval in the non-FS control group. This facilitation was not observed in the 3wFS group; however, tandospirone treatment increased cortical dopamine levels after extinction retrieval. DCS (15 mg/kg, i.p.) also ameliorated the extinction deficit in the 3wFS group, but impaired extinction in the non-FS control group. These results suggest that tandospirone has therapeutic potential for enhancing synaptic efficacy associated with extinction processes by involving dopaminergic mechanisms. Pharmacological agents that target cortical dopaminergic systems may provide new insights into the development of therapeutic treatments of anxiety disorders, including PTSD.

Phase-dependent synaptic changes in the hippocampal CA1 field underlying extinction processes in freely moving rats.

Recent studies focus on the functional significance of a novel form of synaptic plasticity, low-frequency stimulation (LFS)-induced synaptic potentiation in the hippocampal CA1 area. In the present study, we elucidated dynamic changes in synaptic function in the CA1 field during extinction processes associated with context-dependent fear memory in freely moving rats, with a focus on LFS-induced synaptic plasticity. Synaptic transmission in the CA1 field was transiently depressed during each extinction trial, but synaptic efficacy was gradually enhanced by repeated extinction trials, accompanied by decreases in freezing. On the day following the extinction training, synaptic transmission did not show further changes during extinction retrieval, suggesting that the hippocampal synaptic transmission that underlies extinction processes changes in a phase-dependent manner. The synaptic potentiation produced by extinction training was mimicked by synaptic changes induced by LFS (0.5 Hz) in the group that previously received footshock conditioning. Furthermore, the expression of freezing during re-exposure to footshock box was significantly reduced in the LFS application group in a manner similar to the extinction group. These results suggest that LFS-induced synaptic plasticity may be associated with the extinction processes that underlie context-dependent fear memory. This hypothesis was supported by the fact that synaptic potentiation induced by extinction training did not occur in a juvenile stress model that exhibited extinction deficits. Given the similarity between these electrophysiological and behavioral data, LFS-induced synaptic plasticity may be related to extinction learning, with some aspects of neuronal oscillations, during the acquisition and/or consolidation of extinction memory.

Early postnatal stress alters extracellular signal-regulated kinase signaling in the corticolimbic system modulating emotional circuitry in adult rats.

The present study elucidated whether early life stress alters the extracellular signal-regulated kinase (ERK) pathway that underlies fear retrieval and fear extinction based on a contextual fear conditioning paradigm, using a juvenile stress model. Levels of phospho-ERK (pERK), the active form of ERK, increased after fear retrieval in the hippocampal CA1 region but not in the medial prefrontal cortex (mPFC). ERK activation in the CA1 following fear retrieval was not observed in adult rats who received aversive footshock (FS) stimuli during the second postnatal period (2wFS), which exhibited low levels of freezing. In fear extinction, pERK levels in the CA1 were increased by repeated extinction trials, but they were not altered after extinction retrieval. In contrast, pERK levels in the mPFC did not change during extinction training, but were enhanced after extinction retrieval. These findings were compatible in part with electrophysiological data showing that synaptic transmission in the CA1 field and mPFC was enhanced during extinction training and extinction retrieval, respectively. ERK activation in the CA1 and mPFC associated with extinction processes did not occur in rats that received FS stimuli during the third postnatal period (3wFS), which exhibited sustained freezing behavior. The repressed ERK signaling and extinction deficit observed in the 3wFS group were ameliorated by treatment with the partial N-methyl-D-aspartate receptor agonist D-cycloserine. These findings suggest that early postnatal stress induced the downregulation of ERK signaling in distinct brain regions through region-specific regulation, which may lead to increased behavioral abnormalities or emotional vulnerabilities in adulthood.

Serotonin(1A) receptor-mediated synaptic response in the rat medial prefrontal cortex is altered by early life stress: in vivo and in vitro electrophysiological studies.

Serotonin (5-HT)(1A) receptors play a critical role in the 5-HTergic mechanism associated with fear memory. Previously we showed that adult rats exposed to early postnatal stress, i.e. footshock (FS) stress experienced during the second week (PND 14-18, 2W-FS), exhibited low levels of fear expression. The present study explored whether aversive stress exposure in the second and/or the third week (PND 21-25, 3W-FS) affects the function of cortical 5-HT(1A) receptors, using in vivo and in vitro experiments. A 5-HT(1A) receptor agonist, 8-OH-DPAT (0.5 mg/kg, i.p.), slightly decreased the evoked potential in the mPFC in Non-FS control and 3W-FS group. In contrast, the evoked potential increased after 8-OH-DPAT in the 2W-FS group. The in vitro experiment using patch-clamp recording showed that application of 8-OH-DPAT (10 microM) elicited membrane hyperpolarization of pyramidal neurons in the mPFC in the Non-FS and 3W-FS groups, whereas no changes in membrane potential were observed in the 2W-FS group. These results suggest that synaptic facilitation induced by 8-OH-DPAT resulted from functional changes in cortical 5-HT(1A) receptors. Thus, aversive stress exposure during the second postnatal period appears to cause persistent changes mediated via 5-HT(1A) receptors, presumably involving signal transduction regulating the development of synaptic connectivity underlying fear circuits.

L-arginine-induced current in portal venous smooth muscle cells.

In our previous report, we showed that L-arginine induced depolarization of smooth muscle cells of the rat portal vein with an increased contraction. To clarify the ionic mechanism of the membrane depolarization, the effect of L-arginine on the holding current was studied in freshly isolated smooth muscle cells of the rat portal vein. The whole-cell patch-clamp technique was used, with the membrane potential held at -60 mV. In the presence of Na+ in the perfusate, L-arginine 10 mM induced an inward current in about 50% of the cells. In Na+-deficient perfusate, L-arginine 10 mM increased the amplitude of the inward current in a Na+ concentration-dependent manner. BCH, an inhibitor of the Na+-dependent amino acid transporter, ceased the L-arginine-induced current. These results indicate that L-arginine induces an inward current via Na+-dependent mechanisms in rat portal venous smooth muscle cells.

Salivary chromogranin-A as a marker of psychological stress during a cognitive test battery in humans.

The purpose of the present study was to evaluate the salivary Chromogranin-A (CgA) response to the psychological stress induced by a cognitive test battery. The subjects were 14 healthy volunteers administered the cognitive test battery CogScreen Aeromedical Edition (CogScreen-AE). CogScreen-AE is a test of reaction time and fundamental cognitive ability in the assessment of aeroplane pilots. The subjects were given five batteries of the test (1st approximately 5th) on separate days with 2 week intervals. Saliva samples were collected at 20 min before the test (BASE), immediately before the test (PRE), in the middle of the test (MID), and 5 min after the test (POS) for each subject. The concentration of CgA was determined by enzyme-linked immunosorbent assay. ANOVA revealed a significant by time interaction (BASE, PRE, MID and POS) without a significant effect of battery interaction (1st, 2nd, 3rd, 4th and 5th). The CgA concentration increased at PRE (2.46 +/- 0.24 pmol.mg protein- 1) from BASE (1.19 +/- 0.10 pmol.mg protein- 1). CgA level remained increased in the MID (2.90 +/- 0.26 pmol.mg protein- 1) and remained high in the POS samples (2.81 +/- 0.23 pmol.mg protein- 1). Salivary CgA remained at basal levels during a control study over the same time course without exposure to CogScreen-AE. The changes in salivary CgA secretion as a result of exposure to a cognitive task may indicate psychological stress in humans.

Clonidine induced endothelium-dependent tonic contraction in circular muscle of the rat hepatic portal vein.

Clonidine, an alpha2-agonist, has been shown to be useful in the treatment of hepatic portal hypertension in cirrhosis. The mechanism has been attributed to a clonidine-induced decrease in sympathetic activity. While clonidine has been shown to stimulate the alpha2-adrenoceptors of blood vessels, there is limited knowledge of the effects of clonidine on the circular muscle of the hepatic portal vein which regulates its blood flow. To investigate clonidine-induced contraction of the circular muscle of the hepatic portal vein and to clarify the possible role of the endothelium in the contraction, we examined the effects of clonidine on the isometric contraction of endothelium-intact and -removed ring preparations of the rat hepatic portal vein. In endothelium-intact preparations, clonidine caused a concentration-dependent increase in the amplitude of contractions. Inhibition of NO synthesis with Nomega-nitro-L-arginine (L-NNA) elevated the resting tone, and increased the amplitude of the clonidine-induced contractions. Inhibition of cyclooxygenase by diclofenac did not change the amplitude of the clonidine-induced contractions observed both in the presence and absence of L-NNA. Application of a single concentration of clonidine induced a clear increase in amplitude of both twitch and tonic contractions. Twitch and tonic contractions induced by clonidine were inhibited by yohimbine. When the endothelium was damaged by sodium deoxycholate, tonic contractions induced by clonidine were completely suppressed, whereas the increase in twitch contractions was not influenced by chemical damage of the endothelium. Neither SKF-96365, a nonselective cation channel blocker, nor superoxide dismutase, a free radical scavenger, in the presence of catalase, changed the tonic contraction induced by clonidine. These results indicate that stimulation of alpha2-adrenoceptors enhanced twitch contractions and induced tonic contractions in the circular muscle of the rat hepatic portal vein, especially in the absence of NO. The latter, but not the former, occurs through an endothelium-dependent pathway.

Evidence for the involvement of the cyclooxygenase-metabolic pathway in diclofenac-induced inhibition of spontaneous contraction of rat portal vein smooth muscle cells.

The effects of diclofenac, a cyclooxygenase (COX) inhibitor, were investigated on spontaneous phasic contractions of longitudinal preparations of the rat portal vein. Diclofenac produced a concentration-dependent decrease in the amplitude of these spontaneous phasic contractions. Diclofenac (30 microM) decreased the amplitude of the spontaneous phasic increase in the F340/F380 ratio of Fura PE3, an indicator of intracellular Ca2+ concentration. It also reduced the number of action potentials in each burst discharge without changing the resting membrane potential of longitudinal smooth muscle cells. The extent of the distribution of Lucifer Yellow injected into a smooth muscle cell was decreased in the presence of diclofenac (30 microM). Both AH6809, a prostanoid EP receptor antagonist, and SQ22536, an adenylate cyclase inhibitor, decreased the amplitude of the spontaneous contractions. On the other hand, neither ozagrel, a thromboxane synthase inhibitor, nor SQ29548, a prostanoid TP receptor antagonist, significantly affected spontaneous contractions. These results indicate that diclofenac inhibits the amplitude of spontaneous contractions of the rat portal vein through inhibition of electrical activity, which may be related to an inhibition of the cyclooxygenase pathway.

Effects of L-arginine on spontaneous contraction of the rat portal vein.

The effects of L-arginine on spontaneous contraction of endothelium-denuded longitudinal preparations of the rat portal vein were studied. L-arginine increased the frequency of spontaneous contraction concentration-dependently between 10 microM and 1 mM. Changes in contraction amplitude and duration were not remarkable. D-arginine had a negligible effect on spontaneous contraction. N(omega)-nitro-L-arginine (1 mM) did not affect spontaneous contraction or the response to L-arginine. Addition of N(G)-monomethyl-L-arginine (1 mM), l-lysine (1 mM) or N-ethymaleimide (0.1 mM) increased the frequency of spontaneous contractions and inhibited the effect of L-arginine. Glibenclamide (10 microM) did not affect spontaneous contraction or the response to L-arginine. Spontaneous increase in concentration of intracellular Ca2+, estimated as the ratio of Fura-PE3 fluorescence occurred synchronously with spontaneous contraction. Spontaneous increase in concentration of intracellular Ca2+ occurred more frequently in the presence of L-arginine (1 mM). L-arginine (1 mM) also increased the number of action potential bursts/min in the longitudinal smooth muscle layer. L-arginine (1 mM) also depolarized cell membranes. This study indicates that L-arginine increases the frequency of spontaneous contraction of longitudinal muscle in the rat portal vein by membrane depolarization through mechanisms that do not involve nitric oxide or the inhibition of ATP-sensitive K+ channels.

Reduced effect of caffeine on twitch contraction of oesophageal striated muscle from stroke-prone spontaneously hypertensive rats.

1. There are known differences in the sensitivity to caffeine between skeletal muscle (soleus) of normotensive Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHR). The present study was performed in order to examine differences in the effects of caffeine on twitch contraction between visceral striated muscle using the outer layer of the oesophagus from WKY rats and stroke-prone SHR (SHRSP). 2. Caffeine, at concentrations ranging from 0.3 to 10 mmol/L, exhibited potentiating effects on twitch contraction in preparations from both WKY rats and SHRSP. The potentiating effect of caffeine was markedly less prominent in preparations from SHRSP compared with preparations from WKY rats. 3. The rate of contraction and relaxation, the time to peak tension and 80% relaxation time were not significantly altered by caffeine at concentrations lower than 3 mmol/L in preparations from either strain. 4. With 10 mmol/L caffeine, the rate of relaxation was markedly reduced and the 80% relaxation time was prolonged, with no significant changes in the rate of contraction, in preparations from WKY rats. These changes were significantly smaller in preparations from SHRSP. 5. The duration of the action potential was greater in preparations from SHRSP than in preparations from WKY rats, although the membrane potential and the amplitude of the action potential were not significantly different between preparations from WKY rats and SHRSP. 6. Caffeine, at 10 mmol/L, prolonged the duration of the action potential in preparations from both strains. The effect of caffeine was not different between preparations from WKY rats and SHRSP. 7. The results of the present study suggest that caffeine augments release of Ca2+ from the sarcoplasmic reticulum (SR) at low concentrations and attenuates Ca2+ re-uptake at 10 mmol/L. Decreased reactivity of SR to caffeine may be a cause of the lesser potentiation of twitch contraction by caffeine in preparations from SHRSP.

Effects of flufenamic acid on smooth muscle of the carotid artery isolated from spontaneously hypertensive rats.

Endothelium-removed carotid artery strips from stroke-prone spontaneously hypertensive rats spontaneously developed a tonic myogenic contraction. Flufenamic acid reduced the resting tone observed during superfusion with Tyrode's solution, in a concentration-dependent manner. Flufenamic acid also inhibited contractions produced by high-K solutions in a concentration-dependent manner. The resting membrane potential of smooth muscle cells in the artery was around -32 mV, with occasional oscillatory potentials. Flufenamic acid hyperpolarized the membrane in a concentration-dependent manner. The voltage-dependent outward currents recorded in isolated cells with micropipettes filled with high-K+ solution (holding potential, -60 mV) were enhanced by flufenamic acid and inhibited by tetraethylammonium. When the recording micropipette was filled with high Cs to inhibit the K+-current, depolarizing step pulses evoked nifedipine-sensitive inward currents. Flufenamic acid inhibited the inward currents. These results indicate that flufenamic acid inhibits the spontaneous active tone of the carotid artery by inhibiting L-type Ca2+-channels and possibly by membrane hyperpolarization through activation of the voltage-dependent K+-channels.