Distribution of ionotropic glutamate receptor subunit mRNAs in the rat hypothalamus

The excitatory amino acid neurotransmitter glutamate participates in the control of most (and possibly all) neuroendocrine systems in the hypothalamus. This control is exerted by binding to two classes of membrane receptors, the ionotropic and metabotropic receptor families, which differ in their structure and mechanisms of signal transduction. To gain a better understanding about the precise sites of action of glutamate and the subunit compositions of the receptors involved in the glutamatergic neurotransmission in the hypothalamus and septum, in situ hybridization was used with 35S-labeled cRNA probes for the different ionotropic receptor subunits, including glutamate receptor subunits 1-4 (GluR1-GluR4), kainate-2, GluR5-GluR7, N-methyl-D-aspartate (NMDA) receptor 1 (NMDAR1), and NMDAR2A-NMDAR2D. The results showed that subunits of alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionate-preferring, kainate-preferring, and NMDA-preferring receptor subunits are distributed widely but heterogeneously and that the GluR1, GluR2, kainate-2, NMDAR1, NMDAR2A, and NMDAR2B subunits are the most abundant in the hypothalamus. Thus, GluR1 subunit mRNA was prominent in the lateral septum, preoptic area, mediobasal hypothalamus, and tuberomammillary nucleus, whereas kainate-2 subunit mRNA was abundant in the medial septum-diagonal band, median and anteroventral preoptic nuclei, and supraoptic nuclei as well as the magnocellular portion of the posterior paraventricular nucleus. Regions that contained the highest levels of NMDAR1 subunit mRNA included the septum, the median preoptic nucleus, the anteroventral periventricular nucleus, and the supraoptic and suprachiasmatic nuclei as well as the arcuate nucleus. Together, the extensive distribution of the different GluR subunit mRNAs strengthen the view that glutamate is a major excitatory neurotransmitter in the hypothalamus. The overlap in the distribution of the various subunit mRNAs suggests that many neurons can express GluR channels that belong to different families, which would allow a differential regulation of the target neurons by glutamate.     

Use of catechol‐O‐methyltransferase inhibition to minimize L‐3,4‐dihydroxyphenylalanine‐induced dyskinesia in the 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine‐lesioned macaque

L‐3,4‐dihydroxyphenylalanine (L‐DOPA)‐induced dyskinesia is a complication of dopaminergic treatment in Parkinson's disease. Lowering the L‐DOPA dose reduces dyskinesia but also reduces the antiparkinsonian benefit. A therapy that could enhance the antiparkinsonian action of low‐dose L‐DOPA (LDl) without exacerbating dyskinesia would thus be of considerable therapeutic benefit. This study assessed whether catechol‐O‐methyltransferase (COMT) inhibition, as an add‐on to LDl, might be a means to achieve this goal. Cynomolgus macaques were administered 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine. Dyskinesia was established by chronic treatment with L‐DOPA. Two doses of L‐DOPA were identified – high‐dose L‐DOPA (LDh), which provided good antiparkinsonian benefit but was compromised by disabling dyskinesia, and LDl, which was sub‐threshold for providing significant antiparkinsonian benefit, without dyskinesia. LDh and LDl were administered in acute challenges in combination with vehicle and, for LDl, with the COMT inhibitor entacapone (5, 15 and 45 mg/kg). The duration of antiparkinsonian benefit (ON‐time), parkinsonism and dyskinesia were determined. The ON‐time after LDh was ～170 min and the ON‐time after LDl alone (～98 min) was not significantly different to vehicle (～37 min). In combination with LDl, entacapone significantly increased the ON‐time (5, 15 and 45 mg/kg being ～123, ～148 and ～180 min, respectively). The ON‐time after LDl/entacapone 45 mg/kg was not different to that after LDh. However, whereas the percentage ON‐time that was compromised by disabling dyskinesia was ～56% with LDh, it was only ～31% with LDl/entacapone 45 mg/kg. In addition to the well‐recognized action of COMT inhibition to reduce wearing‐OFF, the data presented suggest that COMT inhibition in combination with low doses of L‐DOPA has potential as a strategy to alleviate dyskinesia.     

Activation of 5-HT2 receptors enhances the release of acetylcholine in the prefrontal cortex and hippocampus of the rat

The role of 5-HT2 receptors in the regulation of acetylcholine (ACh) release was examined in the medial prefrontal cortex and dorsal hippocampus using in vivo microdialysis. The 5-HT(2A/2C) agonist +/-1-(2,5-dimethoxy-4-iodophenyl) -2- aminopropane hydrochloride (DOI) (1 and 2 mg/kg, i.p.) significantly increased the extracellular concentration of ACh in both brain regions, and this response was attenuated in rats treated with the 5-HT(2A/2B/2C) antagonist LY-53,857 (3 mg/kg, i.p.). Treatment with LY-53,857 alone did not significantly alter ACh release in either brain region The 5-HT(2C) agonist 6-chloro-2-(1-piperazinyl)-pyrazine) (MK-212) (5 mg/kg, i.p.) significantly enhanced the release of ACh in both the prefrontal cortex and hippocampus, whereas the 5-HT2 agonist mescaline (10 mg/kg, i.p.) produced a 2-fold increase in ACh release only in the prefrontal cortex. Intracortical, but not intrahippocampal, infusion of DOI (100 microM) significantly enhanced the release of ACh, and intracortical infusion of LY-53,857 (100 microM) significantly attenuated this response. These results suggest that the release of ACh in the prefrontal cortex and hippocampus is influenced by 5-HT2 receptor mechanisms. The increase in release of ACh induced by DOI in the prefrontal cortex, but not in the hippocampus, appears to be due to 5-HT2 receptor mechanisms localized within this brain region. Furthermore, it appears that the prefrontal cortex is more sensitive than the dorsal hippocampus to the stimulatory effect of 5-HT2 agonists on ACh release.     

Learning new sequential stepping patterns requires striatal plasticity during the earliest phase of acquisition

Animals including humans execute motor behavior to reach their goals. For this purpose, they must choose correct strategies according to environmental conditions and shape many parameters of their movements, including their serial order and timing. To investigate the neurobiology underlying such skills, we used a multi‐sensor equipped, motor‐driven running wheel with adjustable sequences of foothold pegs on which mice ran to obtain water reward. When the peg patterns changed from a familiar pattern to a new pattern, the mice had to learn and implement new locomotor strategies in order to receive reward. We found that the accuracy of stepping and the achievement of water reward improved with the new learning after changes in the peg‐pattern, and c‐Fos expression levels assayed after the first post‐switch session were high in both dorsolateral striatum and motor cortex, relative to post‐switch plateau levels. Combined in situ hybridization and immunohistochemistry of striatal sections demonstrated that both enkephalin‐positive (indirect pathway) neurons and substance P‐positive (direct pathway) neurons were recruited specifically after the pattern switches, as were interneurons expressing neuronal nitric oxide synthase. When we blocked N‐methyl‐D‐aspartate (NMDA) receptors in the dorsolateral striatum by injecting the NMDA receptor antagonist, D‐2‐amino‐5‐phosphonopentanoic acid (AP5), we found delays in early post‐switch improvement in performance. These findings suggest that the dorsolateral striatum is activated on detecting shifts in environment to adapt motor behavior to the new context via NMDA‐dependent plasticity, and that this plasticity may underlie forming and breaking skills and habits as well as to behavioral difficulties in clinical disorders.     

Acute and chronic effects of citalopram on 5‐HT1A receptor—Labeling by [18F]MPPF and—Coupling to receptors‐G proteins

Selective serotonin reuptake inhibitors take several weeks to produce their maximal therapeutic antidepressant effect. This delay has been attributed to the gradual desensitization of somatodendritic serotonin 5‐HT_1A autoreceptors. We evaluated adaptive changes of 5‐HT_1A receptors after acute and chronic citalopram challenges in rat. Small animal positron emission tomography trial and quantitative ex vivo autoradiography studies using [¹⁸F]MPPF were employed, as well as in vitro 8‐OH‐DPAT‐stimulated [³⁵S]‐GTPγS binding assay. Additionally, 5‐HT_1A receptor knock‐out mice were used to assess the specificity of [¹⁸F]MPPF. Acute treatment with citalopram did not alter [¹⁸F]MPPF binding in dorsal raphe nucleus (DR), frontal cortex, or hippocampus. The absence of [¹⁸F]MPPF binding in the brain of 5‐HT_1A knock‐out mice demonstrates the specificity of MPPF for 5‐HT_1A receptor brain imaging, but the high affinity of [¹⁸F]MPPF compared to 5‐HT suggests that it would only be displaced by dramatic increases in extracellular 5‐HT. Chronic citalopram did not modify 5‐HT_1A receptor density in any of the brain regions studied. In addition, this treatment did not modify 8‐OH‐DPAT‐stimulated [³⁵S]‐GTPγS binding in DR, although a significant increase was observed in frontal cortex and hippocampus. [¹⁸F]MPPF appears to be an efficient radioligand to quantify specifically 5‐HT_1A receptor density in brain imaging. The delayed therapeutic efficacy of citalopram did not appear to be linked to either a downregulation of 5‐HT_1A receptors or to a 5‐HT_1A receptor‐G protein decoupling process in serotonergic neurons, but to increased functional sensitivity of postsynaptic 5‐HT_1A receptors. Synapse 63:106–116, 2009. ©2008 Wiley‐Liss, Inc.     

Connectivity of cone photoreceptor telodendria in the zebrafish retina

The connectivity amongst photoreceptors is critical to their function, as it underpins lateral inhibition and effective translation of stimuli into neural signals. Despite much work characterizing second‐order interneurons in the outer retina, the synapses directly connecting photoreceptors have often been overlooked. Telodendria are fine processes that connect photoreceptor pedicles. They have been observed in diverse vertebrate groups, yet their roles in vision remain speculative. Here, we visualize telodendria via fluorescent protein expression in photoreceptor subtypes. We characterized short wavelength cone telodendria in adult and larval zebrafish retina. Additionally, in the larval retina, we investigated rod telodendria and UV cone telodendria in mutant and transgenic retinas with altered complements of cone types. In the adult retina, telodendria are twice as abundant and branch almost twice as often on blue cones compared to UV cones. Pedicles of neighboring UV and blue cones typically converge into contiguous pairs, despite the regular spacing of their cell bodies. In contrast to adults, larval UV cone telodendria are more numerous (1.3 times) than blue cone telodendria. UV cone telodendria are not detectably affected by ablation of blue cones, and are reduced twofold in mutant larval retina with few UV cones. We thus saw no evidence that telodendria increase in number in the absence of their typical cellular neighbors. We also found that larval rod telodendria are less abundant than short wavelength cone telodendria. In summary, we describe the development and morphology of zebrafish photoreceptor synaptic connectivity toward appreciating the function of telodendria in visual signal processing.     

Perampanel,a selective,noncompetitive α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionic acid receptor antagonist,as adjunctive therapy for refractory partial‐onset seizures: Interim results from phase III,extension study 307

Purpose: To evaluate safety, tolerability, and seizure outcome data during long‐term treatment with once‐daily adjunctive perampanel (up to 12 mg/day) in patients with refractory partial‐onset seizures. Methods: Study 307 was an extension study for patients completing the double‐blind phase of three pivotal phase III trials (studies 304, 305, and 306). The study consisted of two phases: an open‐label treatment phase (including a 16‐week blinded conversion period and a planned 256‐week maintenance period) and a 4‐week follow‐up phase. Patients were blindly titrated during the conversion period to their individual maximum tolerated dose (maximum 12 mg/day). Adverse events (AEs) were monitored throughout the study and seizure frequency recorded. The interim data cutoff date for analyses was December 1, 2010. Key Findings: In total, 1,218 patients were enrolled in the study. At the interim cutoff date, 1,186 patients were in the safety analysis set; 1,089 (91.8%) patients had >16 weeks of exposure to perampanel, 580 (48.9%) patients had >1 year of exposure, and 19 (1.6%) patients had >2 years of exposure. At the interim analysis, 840 (70.8%) patients remained on perampanel treatment. The large majority of patients (n = 1,084 [91%]) were titrated to 10 mg or 12 mg/day. Median (range) duration of exposure was 51.4 (1.1–128.1) weeks. Treatment‐emergent AEs were reported in 87.4% of patients. The most frequent were dizziness (43.9%), somnolence (20.2%), headache (16.7%), and fatigue (12.1%). Serious AEs were reported in 13.2% of patients. In the intent‐to‐treat analysis set (n = 1,207), the frequency of all seizures decreased over the first 26 weeks of perampanel treatment in patients with at least 26 weeks of exposure to perampanel (n = 1,006 [83.3%]); this reduction was maintained in patients with at least 1 year of exposure (n = 588 [48.7%]). The overall median percent changes in seizure frequency in patients included in each 13‐week interval of perampanel treatment were ?39.2% for weeks 14–26 (n = 1,114), ?46.5% for weeks 40–52 (n = 731), and ?58.1% for weeks 92–104 (n = 59). Overall responder rates in patients included in each 13‐week interval of perampanel treatment were 41.4% for weeks 14–26 (n = 1,114), 46.9% for weeks 40–52 (n = 731), and 62.7% for weeks 92–104 (n = 59). During the blinded conversion period, the reduction in seizure frequency in patients previously randomized to placebo (?42.4%, n = 369) was similar to that in patients previously randomized to perampanel (?41.5%, n = 817). Significance: Consistent with pivotal phase III trials, these interim results demonstrated that perampanel had a favorable tolerability profile in patients with refractory partial‐onset seizures over the longer term. The decrease in seizure frequency was consistent and maintained in those patients over at least 1 year of perampanel exposure.     

Kampo therapy as an alternative to pharmacotherapy using antipsychotic medicines for behavioral and psychological symptoms of dementia (BPSD)

The behavioral and psychological symptoms of dementia (BPSD), including aggression, agitation, screaming, wandering, hallucinations, and delusions, occur in 50–90% of patients with dementia, and have a negative impact on the activity of daily living (ADL) of patients, as well as caregivers. Patients with severe BPSD often require management with antipsychotic medicines. However, an increased mortality rate has been reported in patients with dementia taking antipsychotic medicine and, thus, there is an urgent need to develop safer treatments for BPSD. Kampo medicines are an alternative to antipsychotic medicines and several Kampo medicines have been reported to be effective in the treatment of BPSD. Oren‐gedoku‐to has been reported to be effective for the treatment of irritability and sullenness in patients with vascular dementia, as well as improving excitement, depression, anxiety, and restlessness of patients with cerebrovascular lesions. Choto‐san has been reported to be effective in the treatment of delirium, insomnia, and hallucinations/delusions in patients with vascular dementia. Toki‐syakuyaku‐san has been reported to improve emotional lability, restlessness, and sleep disturbances in patients with dementia. Yokukan‐san has been reported to be effective for hallucinations, agitation/aggression, irritability/lability, and aberrant motor activity, as well as being effective in the treatment of visual hallucinations in patients with dementia with Lewy bodies (DLB). A multicenter randomized crossover study confirmed that Yokukan‐san is effective in the treatment of BPSD and is well‐tolerated. Kampo medicines do not induce extrapyramidal or anticholinergic symptoms and have no adverse effects on ADL or cognitive function. Thus, Kampo therapy is recommended for patients who cannot tolerate treatment with neuroleptics, patients who have extrapyramidal symptoms and gait disturbance, and patients with DLB. In future, to confirm the effectiveness of Kampo medicines in the treatment of BPSD, further studies, such as randomized control trials, are needed. In addition, basic studies are required to elucidate the processes by which Kampo medicines are metabolized, as well as any interactions between Western and Kampo medicines.