Yasushi Nakatani

Abnormality of circadian rhythm accompanied by an increase in frontal cortex serotonin in animal model of autism.

Several clinical reports have indicated that autistic patients often show disturbance of the circadian rhythm, which may be related to dysfunction of the serotonergic system in the brain. Using rats exposed prenatally to valproic acid (VPA) as an animal model of autism, we examined locomotor activity and feeding under a reversed 12-h light/dark cycle, and found disturbance of the circadian rhythm characterized by frequent arousal during the light/sleep phase. In addition, measurement of brain serotonin (5-HT) level using in vivo microdialysis showed that the brain 5-HT level in VPA-exposed rats was significantly higher than that in control rats. These results suggest that a higher brain 5-HT level might be responsible for the irregular sleep/awake rhythm in autism.

Augmented brain 5-HT crosses the blood–brain barrier through the 5-HT transporter in rat

The present study re‐evaluated an existing notion that serotonin (5‐hydroxytryptamine; 5‐HT) could not cross the brain to the circulating blood via the blood–brain barrier (BBB). To elevate brain 5‐HT alone, 5‐hydroxytryptophan (5‐HTP; 30–75 mg/kg) was administrated intravenously to anaesthetized rats that had undergone gastrointestinal and kidney resections along with liver inactivation (organs contributing to increasing blood 5‐HT after 5‐HTP administration). A microdialysis method and HPLC system were used to determine the brain 5‐HT levels in samples collected from the frontal cortex. Blood 5‐HT levels were determined from whole blood, not platelet‐poor plasma, collected from the central vein. We found that blood 5‐HT levels showed a significant augmentation whenever brain 5‐HT levels were significantly elevated after the administration of 5‐HTP in those rats with the abdominal surgical procedures. This elevation was abolished after pretreatment with a selective serotonin reuptake inhibitor (fluoxetine; 10 mg/kg i.v.), although brain 5‐HT levels remained augmented. These results indicate that augmented brain 5‐HT can cross the BBB through the 5‐HT transporter from the brain to the circulating blood.

Activation of the anterior prefrontal cortex and serotonergic system is associated with improvements in mood and EEG changes induced by Zen meditation practice in novices

To gain insight into the neurophysiological mechanisms involved in Zen meditation, we evaluated the effects of focused attention (FA) on breathing movements in the lower abdomen (Tanden) in novices. We investigated hemodynamic changes in the prefrontal cortex (PFC), an attention-related brain region, using 24-channel near-infrared spectroscopy during a 20-minute session of FA on Tanden breathing in 15 healthy volunteers. We found that the level of oxygenated hemoglobin in the anterior PFC was significantly increased during FA on Tanden breathing, accompanied by a reduction in feelings of negative mood compared to before the meditation session. Electroencephalography (EEG) revealed increased alpha band activity and decreased theta band activity during and after FA on Tanden breathing. EEG changes were correlated with a significant increase in whole blood serotonin (5-HT) levels. These results suggest that activation of the anterior PFC and 5-HT system may be responsible for the improvement of negative mood and EEG signal changes observed during FA on Tanden breathing.

Ventral prefrontal cortex and serotonergic system activation during pedaling exercise induces negative mood improvement and increased alpha band in EEG.

This study evaluates a possible involvement of the prefrontal cortex (PFC) and serotonergic (5-HT) system in psychiatric and electroencephalography (EEG) changes during and after pedaling exercise (PE). The subjects performed PE for 15 min using a cycle ergometer. PE rate was kept at 60 rpm, and the work load (93+/-5.4 W) was decided for each subject before the experiment based on a Rating of Perceived Exertion of 12-13 for self-selected exercise intensity. Cerebral oxygenation in the PFC was assessed by concentration changes in oxygenated hemoglobin (oxyHb) using 24-channel near-infrared spectroscopy. We found that PE evoked a significant increase in oxyHb levels in the ventral PFC during PE as compared with that in the dorsal PFC. Subjects had a feeling of reduced negative mood accompanied by a tendency of increased vigor-activity after PE, as assessed by the Profile of Mood States (POMS) questionnaire. Because the ventral PFC is associated with mood state, we hypothesized that the observed mood changes may have been induced by the activation of the ventral PFC. As for EEG changes during and after PE, we found a significant increase in the relative powers of high-frequency alpha bands (10-13 Hz) during and after PE. A significant increase in whole blood 5-HT level was obtained after PE. Because cortical attenuation would be caused by the 5-HT-induced inhibition of the basal forebrain, we hypothesized that the observed EEG changes are linked with the increased blood 5-HT level or an augmentation of the 5-HT system in the brainstem.

Swim stress exaggerates the hyperactive mesocortical dopamine system in a rodent model of autism.

Several clinical reports have suggested that there is a hyperactivation of the dopaminergic system in people with autism. Using rats exposed prenatally to valproic acid (VPA) as an animal model of autism, we measured dopamine (DA) levels in samples collected from the frontal cortex (FC) using in vivo microdialysis and HPLC. The basal DA level in FC was significantly higher in VPA-exposed rats relative to controls. Since the mesocortical DA system is known to be sensitive to physical and psychological stressors, we measured DA levels in FC before, during, and after a 60-min forced swim test (FST). There were further gradual increases in FC DA levels during the FST in the VPA-exposed rats, but not in the control rats. Behavioral analysis during the last 10 min of the FST revealed a significant decrease in active, escape-oriented behavior and an increase in immobility, which is thought to reflect the development of depressive behavior that disengages the animal from active forms of coping with stressful stimuli. These results suggest that this rodent model of autism exhibits a hyperactive mesocortical DA system, which is exaggerated by swim stress. This abnormality may be responsible for depressive and withdrawal behavior observed in autism.

Corticotropin-releasing factor neurons in the hypothalamic paraventricular nucleus are involved in arousal/yawning response of rats.

Our previous studies have suggested that activation of the hypothalamic paraventricular (PVN) descending oxytocinergic projections is involved in the induction of yawning accompanied by an arousal response, but the possibility that neural systems other than the oxytocinergic system in the PVN also mediate the arousal/yawning response cannot be ruled out. We assessed the activity of corticotropin-releasing factor (CRF) neurons during yawning induced by the PVN stimulation in anesthetized, spontaneously breathing rats using double-staining for c-Fos and CRF. Yawning response was evaluated by monitoring an intercostals electromyogram as an index of inspiratory activity and a digastric electromyogram as an indicator of mouth opening. We also recorded the electrocorticogram (ECoG) to determine the arousal response during yawning. Microinjection of l-glutamate (2-5 nmol) into the PVN produced a frequent yawning accompanied by an arousal shift in the ECoG, and these behavioral effects were associated with a significant increase of c-Fos positive CRF neurons in the medial parvocellular subdivision of the PVN. In addition, a marked enhancement in the c-Fos expression was found in the both locus coeruleus (LC) and global area in the cortex when the frequency of yawning response was increased by the PVN stimulation, suggesting that the arousal response during yawning might be mediated by the activation of LC neurons. The present study suggests that an activation of CRF neurons in the PVN is responsible for the arousal response accompanied by yawning behavior.

Decreased blood serotonin in the premenstrual phase enhances negative mood in healthy women

The purpose of this study was to evaluate mechanisms underlying the action of selective serotonin reuptake inhibitors on the improvement of negative mood symptoms in premenstrual syndrome. We assessed relationships between serotonin (5-HT) levels in the brain (estimated from 5-HT concentrations in whole blood) and negative mood states during the premenstrual phase in 13 healthy women. Mood states were evaluated using the Profile of Mood States questionnaire. We also evaluated relationships between 5-HT and ovarian hormones (oestradiol and progesterone). A significant negative correlation was seen between 5-HT concentrations in whole blood and negative mood scores (tension–anxiety and fatigue) observed in the premenstrual phase. A significant positive correlation was observed between 5-HT and oestradiol in the premenstrual phase, but not in the follicular phase. These results suggest that healthy women with lower whole blood 5-HT concentrations in the premenstrual phase exhibit enhanced negative mood due to lower 5-HT concentrations at brain synapses, which may be caused in part by lower oestrogen concentration.

Increased blood serotonin concentrations are correlated with reduced tension/anxiety in healthy postpartum lactating women

The serotonin (5-HT) system in the brain plays an important role in mood regulation. The postpartum period is considered a high-risk time for mood and anxiety disorders. We assessed changes in 5-HT levels in whole blood (as an indicator of brain 5-HT concentrations) and mood states before and after delivery in 28 healthy, lactating postpartum women. Mood states were evaluated using Profile of Mood States questionnaires (POMS). Measurements were done on the same day in early (first week) and late (third-fourth and sixth-seventh weeks) postpartum, and compared with those in the third trimester and in age-matched, healthy, non-pregnant women. Mean 5-HT concentrations were significantly higher and mean tension/anxiety scores of POMS were significantly lower in late (but not early) postpartum than in the third trimester or non-pregnant controls. 5-HT concentrations correlated with tension/anxiety in the third trimester and late postpartum, indicating an important role for the 5-HT system in the regulation of tension/anxiety in healthy postpartum women. The mechanism underlying the changes in the 5-HT system may be rapid inhibition induced by the marked decrease in estradiol after delivery and gradual excitation caused by lactation-induced brain oxytocin release during the postpartum period.

Light induces cortical activation and yawning in rats.

We examined the effects of light stimulation on cortical activation and yawning response in anesthetized, spontaneously breathing rats. Cortical activation was assessed by means of an electrocorticogram (ECoG) and yawning response was evaluated by monitoring an intercostal electromyogram as an index of inspiratory activity and a digastric electromyogram as an indicator of mouth opening. Light stimulation elicited an arousal shift in the ECoG to faster rhythms. This arousal response was followed by a single large inspiration with mouth opening, i.e. a yawning response. Higher light intensity significantly reduced the onset latency of the arousal/yawning response. Pretreatment with pyrilamine, an H1-histamine receptor antagonist, injected into the lateral ventricle blocked both the cortical activation and the yawning response induced by light stimulation, suggesting a role of brain histaminergic neurotransmission in modulating the light-induced arousal/yawning responses.

Meta-analysis of whole blood serotonin levels at resting state in healthy subjects

The synthesizing enzyme of acetylcholine, the choline acetyltransferase (ChAT) has two isoforms. In rat, immunoreactivity for the preferentially observed isoform in the peripheral nervous system, the peripheral ChAT (pChAT), was observed in enteric nervous system and also in neurons of the dorsal root ganglion (DRG). The purpose of the present study is to examine pChAT immunohistochemical staining of these two structures in the human. Human specimens, large or small intestine and DRG, obtained within 24 h postmortem at autopsy in Shiga University of Medical Science, were fixed by immersion in 4% paraformaldehyde in 0.1M phosphate buffer for 4 days at 4 ◦C, and then cryoprotected. Free-floating cryostat sections of 24 m in thickness were used for immunohistochemistry using an avidin-biotinperoxidase complex method. In human intestines and DRG, the pattern of distribution of pChAT immunostaining was similar to the pattern observed previously in rat. Positive staining was exclusively localized in neuronal cell bodies and fibers. In human large intestine, for instance, pChAT-positive somata were observed in the submucosal and intramural ganglionated plexuses. Networks of positive nerve fibers were found within the submucosa, the longitudinal and the circular muscle; varicoses could be observed. Co-localisation of pChAT staining with other cholinergic markers, the high affinity choline transporter and the vesicular acetylcholine transporter, was observed in nerves fibers. In human DRG, all neuronal somata appeared immunoreactive though varying in staining intensity. Small neurons were often stained very intensely, while medium-sized to large neurons exhibited moderate staining. Immunoreactive fibers were observed throughout the ganglion and extending toward the dorsal root. This study demonstrates a pChAT-like immunoreactivity in the human peripheral nervous system.