Calcitonin gene-related peptide immunoreactivity in the hippocampus and its relationship to cellular changes following exposure to trimethyltin

Loss of APOBEC1 RNA-editing function in microglia exacerbates age-related CNS pathophysiology

Microglia (MG), a heterogeneous population of phagocytic cells, play important roles in central nervous system (CNS) homeostasis and neural plasticity. Under steady-state conditions, MG maintain homeostasis by producing antiinflammatory cytokines and neurotrophic factors, support myelin production, and remove synapses and cellular debris, as well as participating in "cross-correction," a process that supplies neurons with key factors for executing autophagy-lysosomal function. As sentinels for the immune system, MG also detect "danger" signals (pathogenic or traumatic insult), become activated, produce proinflammatory cytokines, and recruit monocytes and dendritic cells to the site of damage through a breached blood-brain barrier or via brain lymphatics. Failure to effectively resolve MG activation can be problematic and can lead to chronic inflammation, a condition proposed to underlie CNS pathophysiology in heritable brain disorders and age-related neurodegenerative and cognitive decline. Here, we show that APOBEC1-mediated RNA editing occurs within MG and is key to maintaining their resting status. Like bone marrow-derived macrophages, RNA editing in MG leads to overall changes in the abundance of edited proteins that coordinate the function of multiple cellular pathways. Conversely, mice lacking the APOBEC1 editing function in MG display evidence of dysregulation, with progressive age-related signs of neurodegeneration, characterized by clustering of activated MG, aberrant myelination, increased inflammation, and lysosomal anomalies that culminate in behavioral and motor deficiencies. Collectively, our study identifies posttranscriptional modification by RNA editing as a critical regulatory mechanism of vital cellular functions that maintain overall brain health.

Role of α-CGRP in the regulation of neurotoxic responses induced by kainic acid in mice

Kainic acid (KA) is an excitatory and neurotoxic substance. The role of α-calcitonin gene-related peptide (α-CGRP) in the regulation of KA-induced hippocampal neuronal cell death was investigated in the present study. The intracerebroventricular (i.c.v.) administration with KA (0.07 μg) increased hippocampal α-CGRP mRNA level in ICR mice. The α-CGRP mRNA level began to increase at 1h, reached at maximal level at 6 and 12h, and returned to the control level by 24h after i.c.v. administration with KA. In addition, KA-induced hippocampal CA3 neuronal death in C57BL6 (wild type) group was more pronounced compared to KA-induced hippocampal CA3 pyramidal cell death in α-CGRP knock-out (KO) group. Furthermore, sumatriptan, a CGRP releasing inhibitor, significantly protected the pyramidal cell death in CA3 hippocampal region induced by KA administered i.c.v. in ICR mice. Our results suggest that α-CGRP may play an important role in the regulation of KA-induced pyramidal cell death in CA3 region of the hippocampus.

Structural plasticity of the adult brain: how animal models help us understand brain changes in depression and systemic disorders related to depression

The brain interprets experiences and translates them into behavioral and physiological responses. Stressful events are those which are threatening or, at the very least, unexpected and surprising, and the physiological and behavioral responses are intended to promote adaptation via a process called “allostasis. ” Chemical mediators of allostasis include cortisol and adrenalin from the adrenal glands, other hormones, and neurotransmitters, the parasympathetic and sympathetic nervous systems, and cytokines and chemokines from the immune system. Two brain structures, the amygdala and hippocampus, play key roles in interpreting what is stressful and determining appropriate responses. The hippocampus, a key structure for memories of events and contexts, expresses receptors that enable it to respond to glucocorticoid hormones in the blood, it undergoes atrophy in a number of psychiatric disorders; it also responds to stressors with changes in excitability, decreased dendritic branching, and reduction in number of neurons in the dentate gyrus. The amygdala, which is important for “emotional memories, ” becomes hyperactive in posttraumatic stress disorder and depressive illness, in animal models of stress, there is evidence for growth and hypertrophy of nerve cells in the amygdala. Changes in the brain after acute and chronic stressors mirror the pattern seen in the metabolic, cardiovascular, and immune systems, that is, short-term adaptation (allostasis) followed by long-term damage (allostatic load), eg, atherosclerosis, fat deposition obesity, bone demineralization, and impaired immune function. Allostatic load of this kind is seen in major depressive illness and may also be expressed in other chronic anxiety and mood disorders.

Type II glucocorticoid receptor immunoreactivity in the mossy cells of the rat and the mouse hippocampus

Hippocampal principal neurons, granule and pyramidal cells, are known to express type II glucocorticoid receptors (GR) and it is believed that glucocorticoids (GC) mediate at least some of their effects through GR. Under conditions of severe stress and trauma, these principal cells are vulnerable to damage and this mechanism may be exacerbated by GR. The mossy cell, an excitatory dentate gyrus neuron, is also damaged following trauma, with over 50% reported loss in rats after kainate-induced seizures. However, it has not been determined if GC play any role in protecting or exacerbating damage to this important hippocampal cell type. In the present study, we have undertaken an evaluation of the presence of GR in mossy cells of the rat and mouse utilizing an immunocytochemical double-labeling technique. To identify mossy cells in the rat, we utilized an antibody to the glutamate receptor subunit 2/3 (GluR2/3). In addition to GluR2/3 antibodies, in the mouse, an antibody to the calcium-binding protein, calretinin (CR), to identify mossy cells was also employed. Our results show that GR immunoreactivity (IR) was colocalized with GluR2/3-IR in approximately 90% of the rat and the mouse mossy cells. In addition, GR-IR was identified in the CR-IR mossy cells in the mouse hippocampus, whereas the CR-IR interneurons of rat and mouse were negative for GR-IR. The presence of GR on mossy cells may indicate the ability of GC to mediate cellular activity of these cells.

Volumetric structural magnetic resonance imaging (MRI) of the rat hippocampus following kainic acid (KA) treatment

An in vivo MRI study employing a high field (7T) magnet and a T1- and T2-weighted imaging sequence with subsequent histopathological evaluations was undertaken to develop and evaluate MRI-based volumetric measurements in the rat. The brain structures considered were the hippocampus, the cingulate cortex, the retrosplenial granular cortex and the ventricles. Control (n=3) and kainic acid (KA; n=4) treated rats were scanned 10 days following the manifestation of stage four seizures. The MRI images exhibited anatomical details (125 microm in-plane resolution) that enabled volumetric analysis with high intra-rater reliability. Volumetric analysis revealed that KA-treated rats had significantly smaller hippocampi, and a significant increase in ventricular size. The cingulate cortex and the retrosplenial granular cortex did not differ in volume between the two groups. The histological observations supported the MRI data showing neuronal loss and neuronal degeneration in CA1 and CA3 of the hippocampus, which was accompanied by strong microglia activation. These data demonstrate a reliable and valid method for the measurement of the rat hippocampus in vivo using MRI with a high field magnet, thereby providing a useful tool for future studies of rodent models of neuro-degenerative diseases.

Selective alteration of calcitonin gene related peptide in hyperthermic brain injury. An experimental study in the rat brain using immunohistochemistry

The possibility that calcitonin gene related peptide (CGRP) participates in the pathophysiology of hyperthermic brain injury was examined in a rat model. The CGRP immunoreactivity was examined in several brain regions of control and 4 h heat stressed rats using immunohistochemistry. Subjection of animals to heat stress in a biological oxygen demand (BOD) incubator at 38 degrees C for 4 h resulted in a marked redistribution of CGRP immunoreactivity. Thus, in cerebral cortex, hippocampus, cerebellum, medulla and spinal cord the CGRP immunoreactivity was profoundly increased following heat stress. On the other hand in brain stem and pons, the CGRP activity is downregulated. These observations suggest that heat stress has the capacity to influence CGRP immunoreactivity and this redistribution of the peptide is somehow associated with the molecular mechanisms of thermal information processing system of the CNS in heat stress, not reported earlier.