Ken Nakazawa

Hydrogen peroxide modulates whole cell Ca2+ currents through L-type channels in cultured rat dentate granule cells.

Modification of voltage-gated Ca(2+) channels by hydrogen peroxide, a membrane-permeable form of reactive oxygen species, in cultured dentate granule cells was examined using the whole cell patch clamp technique. Pretreatment with hydrogen peroxide (1 and 10 microM) for 2 h enhanced the Ca(2+) current without affecting its voltage dependence. The enhancement was completely cancelled by 1 mM glutathione, an antioxidant, and 2 microM nifedipine, an L-type Ca(2+) channel blocker. In contrast, the enhancement of the Ca(2+) current was not mimicked by pretreatment with 10 microg/ml tunicamycin, an endoplasmic reticulum stressor. These results suggest that oxidative stress induced by hydrogen peroxide selectively regulates the activity of L-type Ca(2+) channels.

Multifunctional Laryngeal Premotor Neurons: Their Activities during Breathing, Coughing, Sneezing, and Swallowing

To examine whether motor commands of two or more distinct laryngeal motor patterns converge onto a common premotor network, we conducted dual recordings from the laryngeal adductor motoneuron and its premotor neuron within the brainstem respiratory circuitry during fictive breathing, coughing, sneezing, and swallowing in decerebrate paralyzed cats. Expiratory neurons with an augmenting firing pattern (EAUG), whose action potentials evoked monosynaptic IPSPs in the adductor motoneurons, sharply fired during the expulsive phases of fictive coughing and sneezing, during which the adductor motoneurons transiently repolarized. In contrast, these premotor neurons were silent during the swallow-related hyperpolarization in adductor motoneurons. These results show that one class of medullary respiratory neuron, EAUG, is multifunctional and shared among the central pattern generators (CPGs) for breathing, coughing, and sneezing. In addition, although the CPGs underlying these three behaviors and the swallowing CPG do overlap, EAUG neurons are not part of the swallowing CPG and, in contrast to the other three behaviors, are not a source of inhibitory input to adductor motoneurons during swallowing.

Effects of perinatal exposure to low dose of bisphenol A on anxiety like behavior and dopamine metabolites in brain

Bisphenol A (BPA), an endocrine-disrupting chemical, is widely present in the environment. It has been reported that perinatal exposure to low doses of BPA that are less than the tolerable daily intake level (50μg/kg/day) affects anxiety-like behavior and dopamine levels in the brain. Although the dopaminergic system in the brain is considered to be related to anxiety, no study has reported the effects of low-dose BPA exposure on the dopaminergic system in the brain and on anxiety-like behavior using the same methods of BPA exposure. To investigate the relationship between alterations in anxiety-like behavior and changes in the dopaminergic system in the brain induced by BPA, we examined the effects of BPA on anxiety-like behavior using an open field test in juvenile and adult mice and measured DA and DOPAC levels and the DOPAC/DA ratio in the dorsal hippocampus (HIP), amygdala (AMY), and medulla oblongata (MED) using high-performance liquid chromatography (HPLC) in adult mice. In males, BPA decreased the time spent in the center area of the open field in both juveniles and adults. In addition, BPA increased DA levels in the dorsal HIP and MED and decreased the DOPAC/DA ratio in the dorsal HIP, AMY, and MED in adults. The activity of monoamine oxidase (MAO)-B, the enzyme that metabolizes DA into DOPAC, was reduced in the MED. In females, those changes were not observed. These results suggest that an increase in anxiety-like behavior induced by perinatal exposure to BPA may be related to decreases in DA metabolites in the brain, and there are sex differences in those BPA effects.

d-serine enhances extinction of auditory cued fear conditioning via ERK1/2 phosphorylation in mice

Several lines of evidence suggest that the N-methyl-D-aspartate (NMDA) receptor plays a significant role in fear conditioning and extinction. However, our knowledge of the role of D-serine, an endogenous ligand for the glycine site of the NMDA receptor, in fear extinction is quite limited compared to that of D-cycloserine, an exogenous partial agonist for the same site. In the current study, we examined the effects of D-serine on fear extinction and phosphorylation of extracellular signal-regulated kinase (ERK) in the hippocampus, basolateral amygdala (BLA), and medial prefrontal cortex (mPFC) during the process of fear extinction. Systemic administrations of D-serine (2.7 g/kg, i.p.) with or without the ERK inhibitor SL327 (30 mg/kg, i.p.) to C57BL/6J mice were performed before fear extinction in a cued fear conditioning and extinction paradigm. Cytosolic and nuclear ERK 1/2 phosphorylation in the hippocampus, BLA, and mPFC were measured 1h after extinction (E1h), 24h after extinction (E24h), and 1h after recall (R1h) by Western blotting. We found that D-serine enhanced the extinction of fear memory, and the effects of D-serine were reduced by the ERK phosphorylation inhibitor SL327. The Western blot analyses showed that D-serine significantly increased cytosolic ERK 2 phosphorylation at E1h in the hippocampus and cytosolic ERK 1/2 phosphorylation at R1h in the BLA. The present study suggested that D-serine might enhance fear extinction through NMDA receptor-induced ERK signaling in mice, and that D-serine has potential clinical importance for the treatment of anxiety disorders.

Micturition-related neuronal firing in the periaqueductal gray area in cats.

The midbrain periaqueductal gray (PAG) is the area promoting emotional motor responses, reproductive behaviors and analgesia. Recent studies suggest that neurons in the PAG may be crucial for regulating the micturition reflex in both experimental animals and humans. We examined single neuronal activities in the PAG and the adjacent area in response to isovolumetric spontaneous micturition reflexes in 20 supracollicular decerebrated cats. In total, 84 neurons were recorded in the PAG that were related to urinary storage/micturition cycles. Of the neurons recorded, the most common were tonic storage neurons (43%), followed by tonic micturition neurons (29%), phasic storage neurons (15%) and phasic micturition neurons (13%). In addition to the tonic/phasic as well as storage/micturition classification, the neurons showed diverse discharge patterns: augmenting, constant and decrementing, with the constant discharge pattern being most common. Of the 16 neurons located within the PAG that had similar discharge patterns to those just ventral to the PAG, the micturition neurons were distributed in a broader area, whereas the storage neurons seemed to be concentrated in the middle part of the PAG (P0-1, Horsley-Clarke coordinate). High-frequency stimulation (HFS; 0.2-ms duration, 100 Hz) applied in the PAG elicited inhibition of the micturition reflex. Effective amplitude of the electrical stimulation for evoking inhibitory responses was less than 50 microA. In conclusion, the results of the present study showed that HFS of the PAG inhibited the micturition reflex and there were micturition-related neuronal firings in the PAG in cats, suggesting that the PAG is involved in neural control of micturition.

Effects of subthalamic nucleus stimulation on the micturation reflex in cats

High frequency stimulation (HFS) of the subthalamic nucleus (STN) has been performed to reverse motor dysfunction in severe parkinsonian patients. Recent studies suggested that neural circuitry in the basal ganglia might regulate micturition function as well. In 15 adult male cats under ketamine anesthesia, in which spontaneous isovolumetric micturition reflex had been generated, we performed electrical stimulation and extracellular single unit recording in the STN. Electrical stimulation applied in the STN elicited inhibition of the micturition reflex. None of the responses was facilitatory. Effective amplitude of the electrical stimulation for evoking inhibitory responses was less than 50 microA, which gradually increased and exceeded 250 microA as the location of the stimulation exceeded an area of the STN. Effective frequency of the electrical stimulation with given stimulus intensity was 50 Hz and higher. Total 10 neurons were recorded in the STN that were related to urinary storage/micturition cycles. All neurons were tonically active throughout storage/micturition cycles with storage phase predominance, with almost constant firing activities during the storage phase. In conclusion, our results showed that HFS-STN inhibited the micturition reflex and there were micturition-related neuronal firings in the STN in cats, suggesting the STN may be involved in neural control of micturition. The results also provide an implication that clinical HFS-STN may alter urinary function in parkinsonian patients.

Synaptic origin of the respiratory-modulated activity of laryngeal motoneurons.

To determine the synaptic source of the respiratory-related activity of laryngeal motoneurons, spike-triggered averaging of the membrane potentials of laryngeal motoneurons was conducted using spikes of respiratory neurons located between the Bötzinger complex and the rostral ventral respiratory group as triggers in decerebrate, paralyzed cats. We identified one excitatory and two inhibitory sources for inspiratory laryngeal motoneurons, and two inhibitory sources for expiratory laryngeal motoneurons. In inspiratory laryngeal motoneurons, monosynaptic excitatory postsynaptic potentials were evoked by spikes of inspiratory neurons with augmenting firing patterns, and monosynaptic inhibitory postsynaptic potentials (IPSPs) were evoked by spikes of expiratory neurons with decrementing firing patterns and by spikes of inspiratory neurons with decrementing firing patterns. In expiratory laryngeal motoneurons, monosynaptic IPSPs were evoked by spikes of inspiratory neurons with decrementing firing patterns and by spikes of expiratory neurons with augmenting firing patterns. We conclude that various synaptic inputs from respiratory neurons contribute to shaping the respiratory-related trajectory of membrane potential of laryngeal motoneurons.

Striatal dopamine level increases in the urinary storage phase in cats : An in vivo microdialysis study

Parkinsons disease is a common neurodegenerative disease that shows not only movement disorder, but also profound urinary dysfunction. Bladder hyperactivity is the major urodynamic abnormality. Therefore, the basal ganglia have been thought to modulate the micturition reflex. In six male adult cats under ketamine anesthesia, in which spontaneous isovolumetric micturition reflexes had been generated, we measured levels of striatal dopamine, in micturition and storage phases, using in vivo microdialysis. The striatal dopamine level significantly increased in the storage phase as compared with that in the micturition phase. It is suggested that striatal dopamine may inhibit the micturition reflex via the dopamine D1 receptor-GABAergic direct striatal output pathway, and that disruption of this pathway may be what leads to bladder hyperactivity in patients with Parkinsons disease.

Effects of aripiprazole on MK-801-induced prepulse inhibition deficits and mitogen-activated protein kinase signal transduction pathway

Based on NMDA hypofunction hypothesis for negative symptoms and cognitive deficits in schizophrenia, MK-801-induced animal models of schizophrenia may help us understand the different effects between typical and atypical antipsychotics. On the other hand, the mitogen-activated protein kinase (MAPK) signaling pathways may participate in antipsychotic actions. The aim of this study was to investigate the effects of aripiprazole on MK-801-induced prepulse inhibition (PPI) disruption and MAPK phosphorylation in mice. To clarify the effects of aripiprazole on MK-801-induced PPI disruption, we measured PPI of 51 ddY male mice after aripiprazole was administered 15 min prior to the injection of MK-801, and measured activation of cytosol and nuclear MAPK phosphorylation by western blotting. Aripiprazole (4.0 mg/kg) significantly reversed the MK-801 (0.15 mg/kg)-induced PPI deficits. Pretreatment of aripiprazole (40 mg/kg) had a tendency to suppress MK-801 (1.0 mg/kg)-induced pMEK/MEK (Ser218/222) activation. In addition, aripiprazole treatment showed a significant decrease of pERK/ERK. Our data suggested that aripiprazole may reverse MK-801-induced PPI deficits through regulation of MAPK phosphorylation in the same way as the atypical antipsychotic drug, clozapine.

Effects of electrical stimulation of the raphe area on the micturition reflex in cats

The raphe nucleus has a variety of physiological functions, including emotion, regulation of skeletal muscle motoneurons, spinal transmission of nociceptive signals, sleep, respiration, gastric motility, and cardiovascular function. Recent evidence has shown that centrally administered serotonin has modulatory effects on micturition function, and that decreased brain serotonin might underlie depression and an overactive bladder. We applied high-frequency stimulation (HFS; 0.2-ms duration, 100 Hz) in the raphe nucleus and the adjacent midline area in 20 supracollicular decerebrate cats, which mostly elicited inhibition of the micturition reflex. The effective amplitude of the electrical stimulation for evoking inhibitory responses was less than 50 muA. We also examined single neuronal activities in the raphe nucleus in response to isovolumetric spontaneous micturition reflexes. In total, 79 neurons were recorded in the raphe nucleus that were related to urinary storage/micturition cycles. Of the neurons recorded, the most common were tonic storage neurons (48%), followed by tonic micturition neurons (28%), phasic storage neurons (18%), and phasic micturition neurons (6%). In addition to the tonic/phasic as well as storage/micturition classification, the neurons showed diverse discharge patterns: augmenting, constant and decrementing, with the constant discharge pattern being most common. Among neurons in the raphe nucleus, the neurons with a decrementing discharge pattern were concentrated in the rostral portion, whereas the augmenting and constant neurons existed diffusely. The storage and micturition neurons were intermingled in the rostral portion, whereas they were separate in the caudal portion. In conclusion, the results of the present study indicate that HFS of the raphe area inhibits the micturition reflex and that there are micturition-related neuronal firings in the raphe area in cats, suggesting that the raphe nucleus is involved in neural control of micturition.