Nozomu Matsumoto

Altered emotional behavioral responses in mice lacking brain-type fatty acid-binding protein gene

Brain‐type fatty acid‐binding protein (B‐FABP) belongs to a family of intracellular lipid‐binding proteins. B‐FABP exhibits a binding affinity to long‐chain fatty acids (FAs) whose effects on brain functions including development, emotion, learning and memory have been proposed. B‐FABP is localized in the ventricular germinal cells in embryonic brain and astrocytes in developing and mature brain of rodents. In the present study we generated the mouse harboring a null mutation in the B‐FABP gene and studied its phenotype. B‐FABP mutant mice exhibited the enhanced anxiety and increased fear memory as well as the decreased content of docosahexaenoic acid (DHA) in their brain during the neonatal period without detection of any histological changes in the brain. In the adult brain, B‐FABP was localized more numerously to the astrocytes in the amygdala and septal area than to those in the hippocampal area. Analysis of FA content in the amygdala of adult brain revealed that arachidonic and palmitic acids increased significantly in the mutant mice compared with wild‐type. Furthermore, the response of N‐methyl‐d‐aspartate receptor‐mediated current to DHA in isolated neurons from B‐FABP mutant brain was significantly decreased compared with that of wild‐type, while no significant differences were detected in behavioral responses related to the spatial learning/memory or in the hippocampal long‐term potentiation. These data indicate that B‐FABP is crucially involved in the fear memory and anxiety through its binding with FAs and/or its own direct effects on pertinent metabolism/signaling of FAs.

Presynaptic 5-HT3 receptor-mediated modulation of synaptic GABA release in the mechanically dissociated rat amygdala neurons

1 Nystatin‐perforated patch recordings were made from mechanically dissociated basolateral amygdala neurons with preserved intact native presynaptic nerve terminals to study the mechanism of 5‐HT3 receptor‐mediated serotonergic modulation of GABAergic inhibition. 2 The specific 5‐HT3 agonist mCPBG (1 μM) rapidly facilitated the frequency of GABAergic miniature inhibitory postsynaptic currents (mIPSCs) and this facilitation desensitized within 1 min. Tropisetron (30 nM), a specific 5‐HT3 antagonist, blocked the mCPBG effect. 3 mCPBG augmented mIPSC amplitude. However, no direct postsynaptic serotonergic currents were evoked by mCPBG. Neither GABA‐evoked current amplitude nor the kinetics of individual GABAergic mIPSCs were affected by mCPBG. Therefore, the augmentation is unlikely to be due to postsynaptic effects evoked by mCPBG. At higher concentrations mCPBG produced shorter‐duration facilitation of miniature events. 4 While mCPBG increased the mIPSC frequency in calcium‐containing solution with Cd2+, this increase was absent in Ca2+‐free external solution. It appears that the Ca2+ influx through voltage‐dependent calcium channels was not as crucial as that through 5‐HT3 receptors for synaptic GABA release. 5 When two pulses of mCPBG (each 1 μM, 1 min) were given, the response to the second pulse elicited full recovery when the interval between pulses was at least 9 min. Protein kinase A (PKA) activation by 8‐Br‐cAMP (300 μM) shortened and PKA inhibition by Rp‐cAMP (100 μM) prolonged the recovery time. PKA activity did not affect the time course of fast desensitization. 6 Our results suggest that a 5‐HT3‐specific agonist acts on presynaptic nerve terminals facilitating synaptic GABA release without postsynaptic effects. The facilitation requires calcium influx through presynaptic 5‐HT3 receptors. PKA modulates the recovery process from desensitization of presynaptic 5‐HT3 receptor‐mediated regulation of synaptic GABA release.

Mice lacking ganglioside GM3 synthase exhibit complete hearing loss due to selective degeneration of the organ of Corti

The ganglioside GM3 synthase (SAT-I), encoded by a single-copy gene, is a primary glycosyltransferase for the synthesis of complex gangliosides. In SAT-I null mice, hearing ability, assessed by brainstem auditory-evoked potentials (BAEP), was impaired at the onset of hearing and had been completely lost by 17 days after birth (P17), showing a deformity in hair cells in the organ of Corti. By 2 months of age, the organ of Corti had selectively and completely disappeared without effect on balance or motor function or in the histology of vestibule. Interestingly, spatiotemporal changes in localization of individual gangliosides, including GM3 and GT1b, were observed during the postnatal development and maturation of the normal inner ear. GM3 expressed in almost all regions of cochlea at P3, but at the onset of hearing it distinctly localized in stria vascularis, spiral ganglion, and the organ of Corti. In addition, SAT-I null mice maintain the function of stria vascularis, because normal potassium concentration and endocochlear potential of endolymph were observed even when they lost the BAEP completely. Thus, the defect of hearing ability of SAT-I null mice could be attributed to the functional disorganization of the organ of Corti, and the expression of gangliosides, especially GM3, during the early part of the functional maturation of the cochlea could be essential for the acquisition and maintenance of hearing function.

Role of presynaptic 5-HT1A and 5-HT3 receptors in modulation of synaptic GABA transmission in dissociated rat basolateral amygdala neurons.

Serotonin (5-HT) is considered to play a significant role in anxiety-related behaviors in animals through actions on the amygdaloid complex. To evaluate this role from the point of neurotransmitter release regulation, nystatin-perforated patch recording was employed on mechanically dissociated basolateral amygdala neurons containing functional synaptic boutons. GABAAergic miniature inhibitory postsynaptic currents (mIPSCs) were pharmacologically separated. In subsets of neurons, 8-OH-DPAT (1 microM), a specific 5-HT1A agonist, continuously inhibited mIPSC frequency without effects on mIPSC amplitude. By comparison, mCPBG (1 microM), a specific 5-HT3 agonist, transiently facilitated mIPSC frequency without effects on mIPSC amplitude. Together these results suggest the presynaptic existence of both 5-HT receptor subtypes. In these neurons, application of 8-OH-DPAT and its subsequent removal still suppressed mCPBG-induced responses on mIPSCs. This suppression was not caused by a reduction of presynaptic 5-HT3 receptor affinities to mCPBG and was completely eliminated by pretreatment with N-ethylmaleimide, a pertussis toxin sensitive GTP-binding protein inhibitor. In the neurons exhibiting presynaptic modulation with mCPBG but not 8-OH-DPAT, such suppression by exposure to 8-OH-DPAT was not observed. In conclusion, activation of presynaptic 5-HT1A receptors inhibited mIPSC frequency and at the same time suppressed, via a G-protein-mediated mechanism, the transient facilitation of mIPSC frequency produced by activation of presynaptic 5-HT3 receptors.

Medical Navigation System for Otologic Surgery Based on Hybrid Registration and Virtual Intraoperative Computed Tomography

An image-guided surgical system for otologic surgery was developed and clinically evaluated. With reliable hybrid registration, real-time patient movement compensation and virtual intraoperative computed tomography imaging have been originally proposed. In contrast to the commercially available systems that mainly use 2-D images for pointing probes, in this system, the surgical drill position is navigated and displayed in the 3-D space with real-time surface rendering. In a temporal bone model study, the navigation accuracy was 1.12 plusmn 0.09 mm with regard to the target registration error. Initial clinical evaluation of the proposed method was performed in five cochlea implantation surgeries. Accurate insertion of the electrodes into the cochlea was achieved, and the facial nerve was protected from injury in all surgeries. The proposed method could be applied to various surgeries for accurate targeting and protection of critical organs.

Pre- and postsynaptic ATP-sensitive potassium channels during metabolic inhibition of rat hippocampal CA1 neurons

Presynaptic and postsynaptic membrane activities during experimental metabolic inhibition were analysed in mechanically dissociated rat hippocampal neurons using nystatin‐perforated and conventional whole‐cell patch clamp recordings. NaCN, an inhibitor of mitochondrial ATP synthesis, induced an outward current across the postsynaptic soma membrane. This current was blocked by tolbutamide, a sulfonylurea, which blocks ATP‐sensitive K+ (KATP) channels. The presynaptic effect of metabolic inhibitors such as NaCN, NaN3, or glucose‐free solution was to increase the frequency of GABAergic miniature inhibitory postsynaptic currents (mIPSCs). Tolbutamide had no effect on this increase in mIPSC frequency induced by metabolic inhibition. Diazoxide, a KATP channel opener, evoked a similar somatic outward current in a dose‐dependent manner. In addition, diazoxide decreased the frequency of mIPSCs in a dose‐dependent fashion. Both these pre‐ and postsynaptic effects of diazoxide were reversed by tolbutamide, suggesting the existence of KATP channels on both pre‐ and postsynaptic membranes. These results confirm the presence of KATP channels on both the pre‐ and postsynaptic membranes but indicate that the channels have significantly different sensitivities to metabolic inhibition.

A minimally invasive registration method using surface template-assisted marker positioning (STAMP) for image-guided otologic surgery.

OBJECTIVE: A new, minimally invasive registration method was developed for image-guided otologic surgery. We utilized laser-sintered template of the patients bone surface to transfer the virtual markers to the patients bone intraoperatively and eliminated the necessity for preoperative marker positioning or additional CT scan. STUDY DESIGN: Simulation surgeries and clinical application. SUBJECTS AND METHODS: We measured registration errors in 10 trials using replicas and six ear surgeries (two cochlear implant insertions, four translabyrinthine acoustic tumor removals). RESULTS: The target registration errors varied among the surgical targets. Errors were less than 1 mm near the cochlear implant insertion target both in phantom study and in actual surgeries. CONCLUSION: Our newly developed method reduced the preoperative procedures for patients but did not reduce the accuracy in cochlear implant surgery. Our method would be a useful image-guided surgery method in the field of otology, where both accuracy and noninvasiveness are required.

Spontaneous miniature outward currents in mechanically dissociated rat Meynert neurons.

1 Spontaneous miniature outward currents (SMOCs) were observed in mechanically dissociated rat Meynert neurons using nystatin perforated patch recordings under voltage‐clamp conditions. 2 SMOCs were blocked by apamin, a selective blocker of small conductance Ca2+‐activated K+ (SK) channels, but not by blockers for other types of Ca2+‐activated K+ channel. 3 Ryanodine (10‐100 μm) reduced both the amplitude and frequency of SMOCs. Caffeine (1 mm) increased the SMOC frequency. Blockers of the sarco/endoplasmic reticulum Ca2+‐ATPase completely abolished SMOCs, indicating a requirement for functioning sarco/endoplasmic reticulum (SR/ER) Ca2+ stores. 4 Both Cd2+‐containing and Ca2+‐free solutions partially inhibited SMOC frequency, a result which suggests that Ca2+ influx contributes to, but is not essential for, SMOC generation. 5 Thus, SMOCs are SK currents linked to ryanodine‐ and caffeine‐sensitive SR/ER Ca2+ stores, and are only indirectly influenced by extracellular Ca2+ influx. The development of this new, minimally invasive mechanical dissociation method has revealed that SMOCs are common in native CNS neurons.

Warning navigation system using real-time safe region monitoring for otologic surgery

AbstractPurpose We developed a surgical navigation system that warns the surgeon with auditory and visual feedback to protect the facial nerve with real-time monitoring of the safe region during drilling. Methods Warning navigation modules were developed and integrated into a free open source software platform. To obtain high registration accuracy, we used a high-precision laser-sintered template of the patient’s bone surface to register the computed tomography (CT) images. We calculated the closest distance between the drill tip and the surface of the facial nerve during drilling. When the drill tip entered the safe regions, the navigation system provided an auditory and visual signal which differed in each safe region. To evaluate the effectiveness of the system, we performed phantom experiments for maintaining a given safe margin from the facial nerve when drilling bone models, with and without the navigation system. The error of the safe margin was measured on postoperative CT images. In real surgery, we evaluated the feasibility of the system in comparison with conventional facial nerve monitoring. Results The navigation accuracy was submillimeter for the target registration error. In the phantom study, the task with navigation (