Slitrk2 deficiency causes hyperactivity with altered vestibular function and serotonergic dysregulation.

SLITRK2 encodes a transmembrane protein that modulates neurite outgrowth and synaptic activities and is implicated in bipolar disorder. Here, we addressed its physiological roles in mice. In the brain, the Slitrk2 protein was strongly detected in the hippocampus, vestibulocerebellum, and precerebellar nuclei-the vestibular-cerebellar-brainstem neural network including pontine gray and tegmental reticular nucleus. Slitrk2 knockout (KO) mice exhibited increased locomotor activity in novel environments, antidepressant-like behaviors, enhanced vestibular function, and increased plasticity at mossy fiber-CA3 synapses with reduced sensitivity to serotonin. A serotonin metabolite was increased in the hippocampus and amygdala, and serotonergic neurons in the raphe nuclei were decreased in Slitrk2 KO mice. When KO mice were treated with methylphenidate, lithium, or fluoxetine, the mood stabilizer lithium showed a genotype-dependent effect. Taken together, Slitrk2 deficiency causes aberrant neural network activity, synaptic integrity, vestibular function, and serotonergic function, providing molecular-neurophysiological insight into the brain dysregulation in bipolar disorders.

Standardization of [F-18]FDG PET/CT for response evaluation by the Radiologic Society of North America-Quantitative Imaging Biomarker Alliance (RSNA-QIBA) profile: preliminary results from the Japan-QIBA (J-QIBA) activities for Asian international multicenter phase II trial.

PURPOSE: In an Asian international multicenter phase II trial conducted in patients with peripheral T-cell lymphoma (PTCL), [F-18]FDG-PET/CT was used for evaluation of the therapeutic response. Standardization of the PET/CT scanners was necessary before patient enrollment. We therefore standardized the scanners by phantom tests based on the profile approved by the Quantitative Imaging Biomarkers Alliance (QIBA) of Radiological Society of North America (RSNA). MATERIALS AND METHODS: The tests were conducted on 12 scanners in 12 facilities in compliance with the QIBA Profile and used National Electrical Manufacturers Association (NEMA) International Electrotechnical Commission (IEC) body phantoms. We measured three parameters (standardized uptake value [SUV], resolution and noise) and adjusted the imaging parameter values. The indexes recommended in the Japanese Society of Nuclear Medicine (JSNM) guideline were also evaluated. RESULTS: In a total of 12 facilities, 6 facilities required no change in imaging conditions and 6 facilities required changes in imaging parameters. After revision, the three measurements (SUV, resolution and noise) met QIBA criteria at all sites, but 10 of the 12 scanners did not meet JSNM criteria. CONCLUSION: We standardized imaging conditions using phantoms as required in the RSNA-QIBA profile for response evaluation by [F-18]FDG PET/CT images in a multicenter study.

Post-training cerebellar cortical activity plays an important role for consolidation of memory of cerebellum-dependent motor learning.

Adaptation of mouse horizontal optokinetic response (HOKR) eye movement provides an experimental model for cerebellum-dependent motor learning. Our previous study revealed that the memory trace of HOKR adaptation is initially encoded in the cerebellar flocculus after hours of optokinetic training, and transferred to the vestibular nuclei to be consolidated to long-term motor memory after days of training [28]. To reveal how the cerebellar cortex operates in the transfer of the memory trace of adaptation, we examined the effects of shutdown of the cerebellar cortex after daily training. Three groups of mice received 1h of optokinetic training daily for 4 days, and showed similar amounts of adaptation after the end of 1h of training throughout 4 days. However, in the mice which daily received bilateral floccular muscimol infusion under gas anesthesia in the post-training period, consolidation of memory of the adaptation was markedly impaired, compared with the control mice which daily received bilateral floccular Ringer's solution infusions under gas anesthesia or those which daily received only gas anesthesia. These results are consistent with the studies of the effects of inactivation of cerebellar cortex on the consolidation of motor memory of rabbit eyeblink conditioning [2,4,18], and suggest that the post-training cerebellar cortex activity play an important for the consolidation of motor memory of HOKR adaptation.

Role of cerebellar cortical protein synthesis in transfer of memory trace of cerebellum-dependent motor learning.

We developed a new protocol that induces long-term adaptation of horizontal optokinetic response (HOKR) eye movement by hours of spaced training and examined the role of protein synthesis in the cerebellar cortex in the formation of memory of adaptation. Mice were trained to view 800 cycles of screen oscillation either by 1 h of massed training or by 2.5 h to 8 d of training with 0.5 h to 1 d space intervals. The HOKR gains increased similarly by 20-30% at the end of training; however, the gains increased by 1 h of massed training recovered within 24 h, whereas the gains increased by spaced training were sustained over 24 h. Bilateral floccular lidocaine microinfusions immediately after the end of training recovered the gains increased by 1 h of massed training but did not affect the gains increased by 4 h of spaced training, suggesting that the memory trace of adaptation was transferred from the flocculus to the vestibular nuclei within 4 h of spaced training. Blockade of floccular protein synthesis, examined by bilateral floccular microinfusions of anisomycin or actinomycin D 1-4 h before the training, impaired the gains increased by 4 h of spaced training but did not affect the gains increased by 1 h of massed training. These findings suggest that the transfer of the memory trace of adaptation occurs within 4 h of spaced training, and proteins synthesized in the flocculus during training period may play an important role in memory transfer.

Impaired auditory-vestibular functions and behavioral abnormalities of Slitrk6-deficient mice.

A recent study revealed that Slitrk6, a transmembrane protein containing a leucine-rich repeat domain, has a critical role in the development of the inner ear neural circuit. However, it is still unknown how the absence of Slitrk6 affects auditory and vestibular functions. In addition, the role of Slitrk6 in regions of the central nervous system, including the dorsal thalamus, has not been addressed. To understand the physiological role of Slitrk6, Slitrk6-knockout (KO) mice were subjected to systematic behavioral analyses including auditory and vestibular function tests. Compared to wild-type mice, the auditory brainstem response (ABR) of Slitrk6-KO mice indicated a mid-frequency range (8-16 kHz) hearing loss and reduction of the first ABR wave. The auditory startle response was also reduced. A vestibulo-ocular reflex (VOR) test showed decreased vertical (head movement-induced) VOR gains and normal horizontal VOR. In an open field test, locomotor activity was reduced; the tendency to be in the center region was increased, but only in the first 5 min of the test, indicating altered adaptive responses to a novel environment. Altered adaptive responses were also found in a hole-board test in which head-dip behavior was increased and advanced. Aside from these abnormalities, no clear abnormalities were noted in the mood, anxiety, learning, spatial memory, or fear memory-related behavioral tests. These results indicate that the Slitrk6-KO mouse can serve as a model of hereditary sensorineural deafness. Furthermore, the altered responses of Slitrk6-KO mice to the novel environment suggest a role of Slitrk6 in some cognitive functions.

Lipid signaling in cytosolic phospholipase A2alpha-cyclooxygenase-2 cascade mediates cerebellar long-term depression and motor learning.

In this study, we show the crucial roles of lipid signaling in long-term depression (LTD), that is, synaptic plasticity prevailing in cerebellar Purkinje cells. In mouse brain slices, we found that cPLA(2)alpha knockout blocked LTD induction, which was rescued by replenishing arachidonic acid (AA) or prostaglandin (PG) D(2) or E(2). Moreover, cyclooxygenase (COX)-2 inhibitors block LTD, which is rescued by supplementing PGD(2)/E(2). The blockade or rescue occurs when these reagents are applied within a time window of 5-15 min following the onset of LTD-inducing stimulation. Furthermore, PGD(2)/E(2) facilitates the chemical induction of LTD by a PKC activator but is unable to rescue the LTD blocked by a PKC inhibitor. We conclude that PGD(2)/E(2) mediates LTD jointly with PKC, and suggest possible pathways for their interaction. Finally, we demonstrate in awake mice that cPLA(2)alpha deficiency or COX-2 inhibition attenuates short-term adaptation of optokinetic eye movements, supporting the view that LTD underlies motor learning.

Dual involvement of G-substrate in motor learning revealed by gene deletion.

In this study, we generated mice lacking the gene for G-substrate, a specific substrate for cGMP-dependent protein kinase uniquely located in cerebellar Purkinje cells, and explored their specific functional deficits. G-substrate-deficient Purkinje cells in slices obtained at postnatal weeks (PWs) 10-15 maintained electrophysiological properties essentially similar to those from WT littermates. Conjunction of parallel fiber stimulation and depolarizing pulses induced long-term depression (LTD) normally. At younger ages, however, LTD attenuated temporarily at PW6 and recovered thereafter. In parallel with LTD, short-term (1 h) adaptation of optokinetic eye movement response (OKR) temporarily diminished at PW6. Young adult G-substrate knockout mice tested at PW12 exhibited no significant differences from their WT littermates in terms of brain structure, general behavior, locomotor behavior on a rotor rod or treadmill, eyeblink conditioning, dynamic characteristics of OKR, or short-term OKR adaptation. One unique change detected was a modest but significant attenuation in the long-term (5 days) adaptation of OKR. The present results support the concept that LTD is causal to short-term adaptation and reveal the dual functional involvement of G-substrate in neuronal mechanisms of the cerebellum for both short-term and long-term adaptation.

Impaired cerebellar development and function in mice lacking CAPS2, a protein involved in neurotrophin release.

Ca2+-dependent activator protein for secretion 2 (CAPS2/CADPS2) is a secretory granule-associated protein that is abundant at the parallel fiber terminals of granule cells in the mouse cerebellum and is involved in the release of neurotrophin-3 (NT-3) and brain-derived neurotrophic factor (BDNF), both of which are required for cerebellar development. The human homolog gene on chromosome 7 is located within susceptibility locus 1 of autism, a disease characterized by several cerebellar morphological abnormalities. Here we report that CAPS2 knock-out mice are deficient in the release of NT-3 and BDNF, and they consequently exhibit suppressed phosphorylation of Trk receptors in the cerebellum; these mice exhibit pronounced impairments in cerebellar development and functions, including neuronal survival, differentiation and migration of postmitotic granule cells, dendritogenesis of Purkinje cells, lobulation between lobules VI and VII, structure and vesicular distribution of parallel fiber-Purkinje cell synapses, paired-pulse facilitation at parallel fiber-Purkinje cell synapses, rotarod motor coordination, and eye movement plasticity in optokinetic training. Increased granule cell death of the external granular layer was noted in lobules VI-VII and IX, in which high BDNF and NT-3 levels are specifically localized during cerebellar development. Therefore, the deficiency of CAPS2 indicates that CAPS2-mediated neurotrophin release is indispensable for normal cerebellar development and functions, including neuronal differentiation and survival, morphogenesis, synaptic function, and motor learning/control. The possible involvement of the CAPS2 gene in the cerebellar deficits of autistic patients is discussed.

Low dose beta-emitter source induces sexual reproduction instead of fragmentation in an earthworm, Enchytraeus japonensis.

We examined whether background radiation, or radiation at a slightly higher level, plays a role in the reproduction of a terrestrial earthworm. Enchytraeus japonensis a recently described terrestrial oligochaete, reproduces asexually by fragmentation and subsequent regeneration. Following radiation exposure in which the worms were subjected to a 32P beta-emitter source at 15 times the background dose rate (4.5 microGy/h), a statistically significant decrease in the number of fragmentations was observed as compared with the sham controls. At that time, in a stained preparation with haematoxylin and eosin (HE), sexual reproduction occurred instead of asexual fragmentation, and mature oocytes were observed in the body of grown worms. However, increasing the radiation dose rate by 30 microGy/h resulted in the complete disappearance of the radiation-induced effects, i.e., fragmentation again occurred after 14 h. The results of this study indicate that a lower dose of radiation may be essential to achieve sexual reproduction, inducing an inhibition of fragmentation (asexual reproduction), but at higher, more cytotoxic doses of radiation these effects are negated.

Marked depression of time interval between fertilization period and hatching period following exposure to low-dose X-rays in zebrafish.

In recent years there has been growing concern over the stimulating effects of very low-dose X-rays. Our laboratory had observed that zebrafish irradiated with low-dose X-rays tended to emerge earlier than sham controls. This observation led us to quantitatively examine the effects of low-dose X irradiation on a series of stages of development in the zebrafish. The embryos were fertilized simultaneously in vitro and incubated at an optimal temperature without crowding. Following exposure of the cleavage period (1.5 h after fertilization) to 0.025-Gy X-rays, the duration to hatching was slightly shorter than that of the sham controls. This tendency was increased when the X-ray exposure occurred during the blastula period (3.5 h). In these embryos, the duration to hatching decreased significantly by an average of 6 h sooner than for sham controls. No differences in duration to hatching were seen when irradiation was given during either the zygote period (45 min) or the segmentation period (12 h). On the contrary, upon exposure to 0.5-Gy X-rays during the blastula period, the duration to hatching increased significantly relative to that of sham controls. These results suggest that the radiation-induced early hatching effect is observed for low doses of X-rays.

Parental exposure to low-dose X-rays in Drosophila melanogaster induces early emergence in offspring, which can be modulated by transplantation of polar cytoplasm.

In recent years there has been growing concern over the biological effects of low-dose X-rays, but few studies have addressed this issue. Our laboratory had observed flies (Drosophila melanogaster) irradiated with low-dose X-rays tend to emerge earlier than normal flies. This observation led us to quantitatively examine the effects of low-dose X-irradiation on development in the fly. Following exposure of prepupal (day 5) flies to 0.5 Gy X-rays, the time to emergence was slightly shorter than in the sham controls. This tendency was increased when the X-ray exposure came during the pupal stage (day 7). In these flies, the time to eclosion decreased significantly, by an average of 30 h sooner than sham controls. A further experiment examined whether such radiation effects could be observed in the unexposed F1 generation of exposed individuals. Greater radiation effects on early F1 emergence were seen when the time between exposure and mating was 3 days, indicating an effect on early spermatid development. Early F1 emergence was also observed after exposure of female flies to X-rays during late previtellogeny. Furthermore, rapid emergence could be induced in the F1 embryos of unexposed parents by transferring the polar cytoplasm (precursor cells of the germ cell line) from F1 embryos of exposed flies. These results show that radiation-induced effects can be transmitted to the next generation through the germ cell line.