Hippocampal and striatal M1‐muscarinic acetylcholine receptors are down‐regulated following bilateral vestibular loss in rats

Permanent vestibular loss has detrimental effects on the hippocampus, resulting in a disruption to spatial learning and memory, hippocampal theta rhythm and place cell field spatial coherence. Little is known about the vestibular system‐related hippocampal cholinergic transmission. Since the pharmacological blockade of muscarinic acetylcholine (ACh) receptors within the hippocampus produces deficits in learning and memory, we hypothesized that ACh receptors may at least partly support the integration of vestibular input. Consequently, we examined the expression of M₁ muscarinic ACh receptors in the hippocampus at 7 and 30 days following bilateral vestibular lesions (BVL) in rats using autoradiography. Animals were divided into sham (n = 12) and BVL (n = 11) groups. BVL animals received intratympanic injections of sodium arsanilate (30 mg/0.1 ml) under isoflurane anesthesia and sham animals received the same volume of saline. Analysis of the brain tissue revealed a significant reduction in the number of M₁ receptors throughout the hippocampus and striatum at 30 days (P ≤ 0.0001), but not at 7 days following BVL. This suggests that the changes in learning and memory seen following vestibular damage may be in part due to the loss of M₁ muscarinic receptors in the hippocampus and striatum. © 2016 Wiley Periodicals, Inc.     

Regional and subcellular distribution of HDAC4 in mouse brain

Histone deacetylases (HDACs) are part of a system that links epigenetic control of gene expression to a variety of environmental stimuli. Some HDACs, including HDAC4, shuttle between the cytoplasm and nucleus in response to physiological cues such as calcium signaling. HDAC4 mRNA is enriched in the brain, but the regional and subcellular protein expression pattern of HDAC4 is not known. Here we show that HDAC4 is more highly expressed in some brain regions than in others. HDAC4 is present in the perikaryial cytoplasm of most neurons but its nuclear localization is variable. In some areas, such as the dentate gyrus, nuclear expression is not detectable, whereas in other areas some neuronal nuclei contain HDAC4 immunoreactivity whereas others do not. In the cytoplasm, HDAC4 immunoreactivity is punctate. Some of these puncta are present in dendritic spines where the strongest immunoreactivity is associated with the postsynaptic density. These data demonstrate that the regional and subcellular distribution of HDAC4 is heterogeneous and raise the possibilities that HDAC4 acts on nonhistone substrates in dendritic spines or that it shuttles between spine and nucleus to coordinate synaptic activity with gene expression. J. Comp. Neurol. 518:722–740, 2010. © 2009 Wiley‐Liss, Inc.     

Negative correlation between grey matter in the hippocampus and caudate nucleus in healthy aging

Neurobiological changes that occur with aging include a reduction in function and volume of the hippocampus. These changes were associated with corresponding memory deficits in navigation tasks. However, navigation can involve different strategies that are dependent on the hippocampus and caudate nucleus. The proportion of people using hippocampus‐dependent spatial strategies decreases across the lifespan. As such, the decrease in spatial strategies, and corresponding increase in caudate nucleus‐dependent response strategies with age, may play a role in the observed neurobiological changes in the hippocampus. Furthermore, we previously showed a negative correlation between grey matter in the hippocampus and caudate nucleus/striatum in mice, young adults, and in individuals diagnosed with Alzheimer's disease. As such, we hypothesized that this negative relationship between the two structures would be present during normal aging. The aim of the current study was to investigate this gap in the literature by studying the relationship between grey matter in the hippocampus and caudate nucleus of the striatum, in relation to each other and to navigation strategies, during healthy aging. Healthy older adults (N = 39) were tested on the Concurrent Spatial Discrimination Learning Task (CSDLT), a virtual radial task that dissociates between spatial and response strategies. A regression of strategies against structural MRIs showed for the first time in older adults that the response strategy was associated with higher amounts of grey matter in the caudate nucleus. As expected, the spatial strategy correlated with grey matter in the hippocampus, which was negatively correlated with grey matter in the caudate nucleus. Interestingly, a sex difference emerged showing that among older adult response learners, women have the least amount of grey matter in the hippocampus, which is a known risk for Alzheimer's disease. This difference was absent among spatial learners. These results are discussed in the context of the putative protective role of spatial memory against grey matter loss in the hippocampus, especially in women.     

Asenapine exerts distinctive regional effects on ionotropic glutamate receptor subtypes in rat brain

Asenapine, a new pyschopharmacologic agent being developed for the treatment of schizophrenia and bipolar disorder, has a unique human receptor binding signature with strong affinity for dopaminergic, α‐adrenergic, and, in particular, serotonergic receptors raising the possibility of interactions with glutamatergic receptors. Changes in ionotropic glutamate (Glu) N‐methyl‐D ‐aspartic acid (NMDA) receptors and 2‐amino‐3‐(3‐hydroxy‐5‐methyl‐isoxazol‐4‐yl)propionic acid (AMPA) receptors in rat forebrain regions were quantified after repeated administration of multiple doses of asenapine (0.03, 0.1, or 0.3 mg/kg, subcutaneous, twice/day) or vehicle for 4 weeks. Brain sections were collected from the medial prefrontal cortex (mPFC), dorsolateral frontal cortex, caudate putamen (CPu), nucleus accumbens (NAc), and hippocampus (HIP), and processed for in vitro receptor autoradiography. Four weeks of treatment with 0.03, 0.1, or 0.3 mg/kg of asenapine significantly (P < 0.01) decreased binding of [³H]MK‐801 to NMDA/MK‐801 modulatory sites in NAc (by 27%, 29%, and 26%, respectively), medial CPu (by 25%, 28%, and 24%), and lateral CPu (by 24%, 31%, and 26%). In contrast, the same doses of asenapine did not alter binding of [³H]glycine to NMDA/glycine modulatory sites in any of the brain regions examined. [³H]AMPA binding to AMPA receptors was selectively and significantly (P < 0.001) elevated in hippocampal CA₁ (41%) and CA₃ (40%) regions but only at the highest dose tested. These results indicate that chronic treatment with asenapine has region‐specific and dose‐dependent effects on ionotropic Glu‐receptor subtypes in rat forebrain, which might contribute to the unique psychopharmacologic properties of asenapine. Synapse 63:413–420, 2009. © 2009 Wiley‐Liss, Inc.     

激活大鼠右侧尾壳核重建双侧海马癫痫网络的细胞机制

目的　 探讨强直电刺激大鼠右侧尾壳核 (rightcaudateputamen ,RCPu)重建双侧海马 (hippocampus,HPC)癫痫电网络的细胞机制。 方法　 实验共用雄性SD大鼠 10 1只 ,体重 2 0 0～ 2 5 0g。急性强直电刺激 (6 0Hz ,2s,0 .4～ 0 .6mA)RCPu (acutetetanizationoftherightcaudateputamen ,ATRC)或右背HPC(acutetetanizationoftherightdorsalhippocampus,ATRDH) ,同步记录双侧前背HPC神经元单位放电 ,比较激活RCPu或RHPC时 ,神经通路长度对HPC癫痫电网络重建过程中单个神经元电活动的影响。 结果　(1)ATRC和ATRDH均能明显地调制单个HPC神经元的紧张式放电成为节律性爆发式放电。 (2 )ATRC引起的HPC爆发式单位放电串放电时程长[(6 5 0 .738± 5 6 .4 19)ms ,n =12 0 ]、串间隔短 [(interburstinginterval,IBI ,(772 .6 0 0± 4 6 .6 6 5 )ms,n =90 ) ;相反 ,ATRDH引起HPC的爆发式单位放电特征是串放电时程短 [(2 70 .6 12± 19.917)ms,n =12 3](T =6 .35 3,P <0 .0 0 1)、IBI长 [(1373.6 6 3± 12 1.2 36 )ms,n =10 3](T =4 .6 2 7P <0 .0 0 1)。 (3)ATRC诱发的海马细胞单位后放电时程长 [(7.0 6± 0 .776 )s,n =10 4 ]、潜伏期长 [(8.77± 1.2 31)trains ,n =30 ],而ATRDH诱发的单位后放电时程短 [(3.93± 0 .6     

Reduced Hippocampal Volume and Its Relationship With Verbal Memory and Negative Symptoms in Treatment-Naive First-Episode Adolescent-Onset Schizophrenia

Accumulating neuroimaging evidence has shown remarkable volume reductions in the hippocampi of patients with schizophrenia. However, the relationship among hippocampal morphometry, clinical symptoms, and cognitive impairments in schizophrenia is still unclear. In this study, high-resolution structural magnetic resonance imaging data were acquired in 36 patients with adolescent-onset schizophrenia (AOS, age range: 13–18 years) and 30 age-, gender-, and education-matched typically developing controls (TDCs). Hippocampal volume was assessed automatically through volumetric segmentation and measurement. After adjusting for total intracranial volume, we found reduced hippocampal volume in individuals with AOS compared with TDCs, and the hippocampal volume was positively correlated with verbal memory and negatively correlated with negative symptoms in AOS. In addition, mediation analysis revealed the indirect effect of hippocampal volume on negative symptoms via verbal memory impairment. When the negative symptoms were represented by 2 dimensions of deficits in emotional expression (EXP) and deficits in motivation and pleasure (MAP), the indirect effect was significant for EXP but not for MAP. Our findings provide further evidence of hippocampal volume reduction in AOS and highlight verbal memory impairment as a mediator to influence the relationship between hippocampal morphometry and negative symptoms, especially the EXP dimension of negative symptoms, in individuals with AOS.     

Effects of exposure to a predator on behaviour and serotonergic neurotransmission in different brain regions of C57bl/6N mice

Clinical studies and animal models have provided evidence that stress and serotonin may play a role in the aetiology of psychiatric diseases such as depression and anxiety. In addition, reciprocal interactions between stress and serotonergic neurotransmission have been demonstrated. However, the relationships between stress, serotonin and behaviour are far from completely understood. In this integrative study, we aimed to elucidate the effect of the psychological stress model predator exposure on behaviour and serotonergic neurotransmission in mice. We used a high time-resolution microdialysis method to measure extracellular levels of serotonin (5-hydroxytryptamine, 5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) in the hippocampus, prefrontal cortex, lateral septum and caudate putamen of C57BL/6N [corrected] mice, before (08:30-10:30 h), during (10:30-11:00 h) and after exposure (11:00-14:00 h) to a rat. Detailed behavioural observations were also made. Rat exposure resulted in behavioural activation, with predominant risk-assessment activities, and in increases in hippocampal, cortical, septal but not striatal 5-HT and 5-HIAA. When rat exposure was repeated on the consecutive day, small behavioural differences and reductions in 5-HIAA levels, but no differences in the 5-HT response, as compared with the first exposure were observed. As increases in 5-HT often coincide with behavioural activation, it was particularly interesting to find that 5-HT also increased in periods when mice only made minor movements such as sniffing, and that an effect of predator stress was absent in the caudate putamen. Our results indicate that the presence of the rat leads to differential activation of serotonergic neurotransmission in higher brain structures, probably involved in the coping response to this potentially life-threatening situation.     

Sensitivity and Specificity of Memory Dysfunction in Schizophrenia: A Comparison With Major Depression

Fifty-three schizophrenic subjects were compared to 50 patients with major depression and 50 normal controls on measures of working memory, declarative memory and malingering. The schizophrenic group scored 1–2 SDs below controls on all measures, while depressive patients exposed only lesser deficits in working memory and free recall. The memory deficit of the schizophrenic subjects was disproportionately greater than their intellectual decline. Differences between clinical groups could not be explained by differences in IQ, clinical symptom load or demographic characteristics. This indicates that impaired memory is a particular sensitive symptom of schizophrenia and that the impairment is specific to the illness. Working memory failure was prominent in both clinical groups. The schizophrenic subjects displayed primarily an acquisition failure, while the depressed group showed retrieval difficulties.     

Neural Substrates of Psychotic Depression: Findings From the Global ECT-MRI Research Collaboration

Psychotic major depression (PMD) is hypothesized to be a distinct clinical entity from nonpsychotic major depression (NPMD). However, neurobiological evidence supporting this notion is scarce. The aim of this study is to identify gray matter volume (GMV) differences between PMD and NPMD and their longitudinal change following electroconvulsive therapy (ECT). Structural magnetic resonance imaging (MRI) data from 8 independent sites in the Global ECT-MRI Research Collaboration (GEMRIC) database (n = 108; 56 PMD and 52 NPMD; mean age 71.7 in PMD and 70.2 in NPMD) were analyzed. All participants underwent MRI before and after ECT. First, cross-sectional whole-brain voxel-wise GMV comparisons between PMD and NPMD were conducted at both time points. Second, in a flexible factorial model, a main effect of time and a group-by-time interaction were examined to identify longitudinal effects of ECT on GMV and longitudinal differential effects of ECT between PMD and NPMD, respectively. Compared with NPMD, PMD showed lower GMV in the prefrontal, temporal and parietal cortex before ECT; PMD showed lower GMV in the medial prefrontal cortex (MPFC) after ECT. Although there was a significant main effect of time on GMV in several brain regions in both PMD and NPMD, there was no significant group-by-time interaction. Lower GMV in the MPFC was consistently identified in PMD, suggesting this may be a trait-like neural substrate of PMD. Longitudinal effect of ECT on GMV may not explain superior ECT response in PMD, and further investigation is needed.