Reduced sensorimotor reactivity following traumatic brain injury in rats

The present study examined sensorimotor reactivity in rats following traumatic brain injury (TBI). Moderate injury was induced with midline fluid percussion in some of the rats. Others received identical surgery, but were not injured (sham-injured rats), or received neither surgery nor injury (naive rats). All rats were evaluated in acoustic and/or tactile startle procedures. At 8 days post-injury, the sensorimotor reactivity of TBI rats to acoustic stimuli was severely reduced compared to that of sham-injured rats. This TBI-induced deficit was enduring (> 30 days). In a separate experiment, greater sensorimotor reactivity was observed with tactile (vs. acoustic) stimulation in both TBI and naive rats, although startle amplitudes for the TBI rats were lower than control levels for both types of stimuli. These results suggest that sensorimotor reactivity is altered by TBI and that the startle procedure is a promising method for investigation of information processing alterations following TBI.     

Diffuse axonal injury due to traumatic brain injury alters inhibition of imitative response tendencies

It is well known that traumatic brain injury particularly affects the frontal lobes. Consequently, patients often suffer from executive dysfunction and behavioral disturbances. Accordingly, our study aimed at investigating patients after traumatic brain injury with two tasks involving different functional processes and structural networks supported by the frontal lobes. Two paradigms were applied: the Stroop color-word task and a task in which subjects had to inhibit imitative response tendencies. We selected a patient group solely with diffuse axonal injury, as this type of injury is homogenous and is correlated with cognitive dysfunction more than focal contusions. To evaluate long-term effects most relevant for rehabilitation, we selected a patient group whose brain injuries dated back several years. Our results show that patients with diffuse axonal injury inhibited imitative responses more successfully than control subjects, whereas executive processes examined with the Stroop task were unaltered. Interestingly, impairments were tightly correlated both with the length of the post-traumatic amnesia predicting outcome in traumatic brain injury and with behavioral disturbances. Impairments in the imitation-inhibition task may indicate alterations in an anterior frontomedian neural network even years after traumatic brain injury.     

Neuronal MCP-1 expression in response to remote nerve injury.

Direct injury of the brain is followed by inflammatory responses regulated by cytokines and chemoattractants secreted from resident glia and invading cells of the peripheral immune system. In contrast, after remote lesion of the central nervous system, exemplified here by peripheral transection or crush of the facial and hypoglossal nerve, the locally observed inflammatory activation is most likely triggered by the damaged cells themselves, that is, the injured neurons. The authors investigated the expression of the chemoattractants monocyte chemoattractant protein MCP-1, regulation on activation normal T-cell expressed and secreted (RANTES), and interferon-gamma inducible protein IP10 after peripheral nerve lesion of the facial and hypoglossal nuclei. In situ hybridization and immunohistochemistry revealed an induction of neuronal MCP-1 expression within 6 hours postoperation, reaching a peak at 3 days and remaining up-regulated for up to 6 weeks. MCP-1 expression was almost exclusively confined to neurons but was also present on a few scattered glial cells. The authors found no alterations in the level of expression and cellular distribution of RANTES or IP10, which were both confined to neurons. Protein expression of the MCP-1 receptor CCR2 did not change. MCP-1, expressed by astrocytes and activated microglia, has been shown to be crucial for monocytic, or T-cell chemoattraction, or both. Accordingly, expression of MCP-1 by neurons and its corresponding receptor in microglia suggests that this chemokine is involved in neuron and microglia interaction.     

Cell activation and inflammatory response following traumatic axonal injury in the rat

In a rat model of traumatic brain injury cell activation was characterized immunohistochemically from 2 h up to 2 weeks. Reactive astrocytosis became apparent perivascularly and in the grey matter within 4h after trauma. Increased OX42 immunoreactivity indicated microglial activation in cortex and hippocampus as early as 4 h, whereas up-regulation of MHC class II (OX6) was evident in white matter tracts at 24 h. Although macrophage (ED1) numbers increased in the meninges and perivascularly, brain infiltration appeared marginal. Accumulation of lymphocytes and granulocytes was not observed. Our results show that traumatic axonal injury induces a rapid and sustained glial activation in the absence of leukocyte infiltration. Thus, cell activation following diffuse trauma strongly differs from that found after focal brain damage, awaiting further functional characterization.     

Inflammatory response associated with axonal injury to spinal motoneurons in newborn rats

Axonal injury in peripheral nerve results in massive motoneuron loss during development. The purpose of this study was to examine the response of phagocytic populations (brain macrophages, BMOs, versus microglia) after different types of axonal lesions (distal axotomy or avulsion) in newborn rats. The morphology, spatial location and activation state of these inflammatory cells were observed. Following spinal root avulsion, BMOs were signaled rapidly and specifically to the location of dying motoneurons in the spinal cord. A large number of BMOs were observed around the avulsed motoneurons on the lesioned side of the spinal cord 1 day following the lesion. These BMOs were large, round, and intensely stained by both antibodies against ED1 and OX-42. The number of BMOs decreased by 3 days and disappeared by 5 days after injury. At the same time, reactive microglia appeared in the lesioned area and rapidly reached the peak level by the 5th day following avulsion. These reactive microglia were medium in size with retracted cellular processes and were also intensely stained by both ED1 and OX-42 antibodies. The number and staining intensity of reactive microglia declined sharply by day 7 after the lesion. In contrast, after distal axotomy only microglia but not BMOs were observed in the lesioned area. These microglial cells were small in size with long and fine-branched processes. They were ED1-negative but OX-42-positive.     

Regionally distinct patterns of calpain activation and traumatic axonal injury following contusive brain injury in immature rats

Impact-induced head injury in infants results in acute focal contusions and traumatic axonal injury (TAI) that are associated with chronic holohemispheric cortical and white matter atrophy and may contribute to poor outcome in brain-injured children less than 4 years of age. Contusive brain trauma in postnatal day (PND) 11 or PND 17 rat pups, ages neurologically equivalent to a human infant and toddler, respectively, leads to cortical tissue loss and white matter atrophy which are associated with cognitive deficits. In adult models of brain trauma and in brain-injured humans, acute and sustained activation of the calpain family of calcium-activated neutral proteases has been implicated in neuronal death and TAI. PND 11 or PND 17 rat pups were subjected to closed head injury over the left hemisphere using the controlled cortical impact device and sacrificed at 6 h, 24 h or 3 days. Hemorrhagic contusions and tissue tears in the cortex and white matter were visible at 6 h, and neuronal loss was evident by 3 days. Calpain activation was observed in cell soma and dendrites of injured neurons at 6 h, and in degenerating dendrites and atrophic neurons at 24 h after injury at both ages. Axonal accumulation of amyloid precursor protein, indicative of TAI, was observed in the corpus callosum and lateral aspects of the white matter below the site of impact, and in the thalamus in PND 11 rats only. Intra-axonal calpain activation was observed to a limited extent in the corpus callosum and subcortical white matter tracts in both brain-injured PND 11 and PND 17 rats. Collectively, these results provide evidence that calpain activation may participate in neuronal loss in the injured cortex, but may not contribute to the pathogenesis of TAI following contusive brain trauma in the immature rat.     

Diffuse axonal injury and traumatic coma in the primate

Traumatic coma was produced in 45 monkeys by accelerating the head without impact in one of three directions. The duration of coma, degree of neurological impariment, and amount of diffuse axonal injury (DAI) in the brain were directly related to the amount of coronal head motion used. Coma of less than 15 minutes (concussion) occurred in 11 of 13 animals subjected to sagittal head motion, in 2 of 6 animals with oblique head motion, and in 2 of 26 animals with full lateral head motion. All 15 concussed animals had good recovery, and none had DAI. Conversely, coma lasting more than 6 hours occurred in none of the sagittal or oblique injury groups but was present in 20 of the laterally injured animals, all of which were severely disabled afterward. All laterally injured animals had a degree of DAI similar to that found in severe human head injury. Coma lasting 16 minutes to 6 hours occurred in 2 of 13 in the sagittal group, 4 of 6 in the oblique group, and 4 of 26 in the lateral group; these animals had less neurological disability and less DAI than when coma lasted longer than 6 hours. These experimental findings duplicate the spectrum of traumatic coma seen in human beings and include axonal damage identical to that seen in severe head injury in humans. Since the amount of DAI was directly proportional to the severity of injury (duration of coma and quality of outcome), we conclude that axonal damage produced by coronal head acceleration is a major cause of prolonged traumatic coma and its sequelae.     

趋化因子MCP-1、MIP-1α在EAE小鼠脊髓中的表达

目的:研究单核细胞趋化蛋白(MCP)-1和巨噬细胞炎性蛋白(MIP)-1α与实验性自身免疫性脑脊髓炎(EAE)发病的关系。方法:用髓鞘少突胶质细胞糖蛋白_(35-55)多肽加福氏完全佐剂皮下注射免疫C57BL/6小鼠建立EAE模型,用免疫组织化学方法观察EAE小鼠发病后第0天(初期)、第7天(高峰期)及第30天(恢复期)脊髓中MCP-1、MIP-1α的表达的变化,并通过免疫组化染色标记星形胶质细胞及小胶质细胞,判断MCP-1、MIP-1α的细胞来源。结果: MCP-1、MIP-1α在EAE小鼠发病初期脊髓中有少量表达,发病高峰期表达增高,而恢复期无表达,MCP-1主要由星形胶质细胞产生,MIP-1α主要由小胶质细胞产生;对照组小鼠脊髓中则没有MCP-1、MIP-1α表达。结论:趋化因子MCP-1、MIP-1α在EAE小鼠CNS不同胶质细胞中表达,是EAE发病早期募集免疫反应细胞向CNS浸润的重要致炎性因子。     

GPR88 in A2A receptor‐expressing neurons modulates locomotor response to dopamine agonists but not sensorimotor gating

The orphan receptor, GPR88, is emerging as a key player in the pathophysiology of several neuropsychiatric diseases, including psychotic disorders. Knockout (KO) mice lacking GPR88 throughout the brain exhibit many abnormalities relevant to schizophrenia including locomotor hyperactivity, behavioural hypersensitivity to dopaminergic psychostimulants and deficient sensorimotor gating. Here, we used conditional knockout (cKO) mice lacking GPR88 selectively in striatal medium spiny neurons expressing A_2A receptor to determine neuronal circuits underlying these phenotypes. We first studied locomotor responses of A_2AR‐Gpr88 KO mice and their control littermates to psychotomimetic, amphetamine, and to selective D1 and D2 receptor agonists, SKF‐81297 and quinpirole, respectively. To assess sensorimotor gating performance, mice were submitted to acoustic and visual prepulse inhibition (PPI) paradigms. Total knockout GPR88 mice were also studied for comparison. Like total GPR88 KO mice, A_2AR‐Gpr88 KO mice displayed a heightened sensitivity to locomotor stimulant effects of amphetamine and SKF‐81297. They also exhibited enhanced locomotor activity to quinpirole, which tended to suppress locomotion in control mice. By contrast, they had normal acoustic and visual PPI, unlike total GPR88 KO mice that show impairments across different sensory modalities. Finally, none of the genetic manipulations altered central auditory temporal processing assessed by gap‐PPI. Together, these findings support the role of GPR88 in the pathophysiology of schizophrenia and show that GPR88 in A_2A receptor‐expressing neurons modulates psychomotor behaviour but not sensorimotor gating.     

Dynamics of production of MIP-1alpha, MCP-1 and MIP-2 and potential role of neutralization of these chemokines in the regulation of immune responses during experimental autoimmune neuritis in Lewis rats.

Experimental autoimmune neuritis (EAN) is an inflammatory autoimmune demyelinating disease of the peripheral nervous system (PNS) and represents an animal model of Guillain-Barré syndrome (GBS), which is a major inflammatory demyelinating disease of the PNS in humans. In the present study, the dynamics of the expression of the chemokines macrophage inflammatory protein-1alpha (MIP-1alpha), MIP-2 and monocyte chemotactic protein-1 (MCP-1) were determined in the sciatic nerves of EAN rats. Additionally, the effect of neutralizing antibodies against MIP-1alpha, MIP-2 and MCP-1 on the clinical course of EAN and the chemokine expression was investigated. The maximum of MIP-1alpha positive cells in the sciatic nerves was seen on day 14 post immunization (p.i.) correlating with the development of severe clinical signs. Administration of an anti-MIP-1alpha antibody suppressed the clinical signs of EAN and inhibited inflammation and demyelination in the sciatic nerve. Peak numbers of MCP-1 positive cells in the sciatic nerves were detected on day 7 p.i. Administration of an anti-MCP-1 antibody caused a delay of onset of EAN. However, 4 of the 6 EAN rats receiving the anti-MCP-antibody showed the same degree of inflammatory cell infiltration and demyelination in the sciatic nerves as sham-treated EAN rats, whereas only 2 EAN rats had less inflammation and demyelination. The numbers of MIP-2 positive cells reached a maximum on day 21 p.i. Anti-MIP-2 antibody failed to suppress the clinical signs of EAN and the inflammation and demyelination in the sciatic nerves. Only administration of the anti-MIP-1alpha antibody resulted in a significant reduction in the number of chemokine (MIP-1alpha)-positive cells and ED1-positive macrophages in the sciatic nerves. The present results demonstrate that MIP-1alpha and MCP-1 may play a role in the immunopathogenesis of EAN, and that MIP-1alpha induced trafficking of inflammatory cells can be inhibited by immunoneutralization. Further elucidation of the regulation and coordination of MIP-1alpha and MCP-1 production may lead to new therapeutic approaches to GBS in humans.     

Adrenalectomy further suppresses the NT-3 mRNA response to traumatic brain injury but this effect is not reversed with corticosterone

Fluid percussion injury (FPI) and in situ hybridisation were used to evaluate the expression of NT-3 mRNA in the hippocampus after traumatic brain injury (TBI) in adrenal-intact and adrenalectomised rats (with or without corticosterone replacement). FPI and adrenalectomy independently significantly reduced the expression of NT-3 mRNA in the dentate gyrus (DG) and CA2 region. The effects of adrenalectomy in the CA2 region were partially reversed with corticosterone. In adrenalectomised animals undergoing FPI, a further significant decrease in NT-3 mRNA was observed in the DG, but this was not reversed by corticosterone. Glucocorticoids may, therefore, play a role in the basal regulation of NT-3 in the hippocampus, but the role of glucocorticoids in the modulation of the NT-3 response to TBI is unclear.     

Phosphorylated MAP1B is induced in central sprouting of primary afferents in response to peripheral injury but not in response to rhizotomy

A peripheral nerve lesion induces sprouting of primary afferents from dorsal root ganglion (DRG) neurons into lamina II of the dorsal horn. Modifications of the environment in consequence to the axotomy provide an extrinsic stimulus. A potential neuron-intrinsic factor that may permit axonal sprouting is microtubule-associated protein 1B (MAP1B) in a specific phosphorylated form (MAP1B-P), restricted to growing or regenerating axons. We show here that both in rat and mouse, a sciatic nerve cut is rapidly followed by the appearance of MAP1B-P expression in lamina II, increasing to a maximum between 8 and 15 days, and diminishing after three months. Evidence is provided that sprouting and induction of MAP1B-P expression after peripheral injury are phenomena concerning essentially myelinated axons. This is in accordance with in situ hybridization data showing especially high MAP1B-mRNA levels in large size DRG neurons that give rise to myelinated fibers. We then employed a second lesion model, multiple rhizotomy with one spared root. In this case, unmyelinated CGRP expressing fibers do indeed sprout, but coexpression of MAP1B-P and CGRP is never observed in lamina II. Finally, because a characteristic of myelinated fibers is their high content in neurofilament protein heavy subunit (NF-H), we used NF-H-LacZ transgenic mice to verify that MAP1B-P induction and central sprouting were not affected by perturbing the axonal organization of neurofilaments. We conclude that MAP1B-P is well suited as a rapidly expressed, axon-intrinsic marker associated with plasticity of myelinated fibers.     

Upregulation of annexins I, II, and V after traumatic spinal cord injury in adult rats

The posttraumatic inflammatory reaction contributes to progressive tissue damage after spinal cord injury (SCI). Annexins, a family of structurally related calcium- and phospholipid-binding proteins, have potent anti-inflammatory effects by inhibiting the activity of phospholipase A(2) (PLA(2)), a key enzyme responsible for inflammation and cytotoxicity. We investigated spatiotemporal expression of annexins I, II, and V after a contusive SCI using the New York University impact device (a 10-g rod, height 12.5 mm) in adult rats. Western blot analysis revealed that annexin I expression increased at 3 days after injury, peaked at 7 days (1.75-fold above the baseline level; P < 0.01), started to decline at 14 days, and returned to the baseline level at and beyond 28 days post-injury. The expression of annexin II started to increase at 3 days, reached its maximal level at 14 days (2.73-fold; P < 0.01), remained at a high level up to 28 days, and then declined to the basal level by 56 days after injury. Annexin V expression started at 3 days, reached its maximal level at 7 days (1.61-fold; P < 0.05) and remained at this level until 56 days after injury. RT-PCR results confirmed expression of all three annexins at the mRNA level after SCI. Immunohistochemistry and immunofluorescence double-labeling analyses revealed that increased annexins I, II, and V were localized in neurons and glial cells. The present study thus revealed increased expression of the three annexin isoforms after moderate contusive SCI. The precise role of annexins in posttraumatic inflammation and neuroprotection after SCI remains to be determined.     

The effects of cyclosporin-A on axonal conduction deficits following traumatic brain injury in adult rats

Immunophilin ligands, including cyclosporin-A (CsA), have been shown to be neuroprotective in experimental models of traumatic brain injury (TBI) and to attenuate the severity of traumatic axonal injury. Prior studies have documented CsA treatment to reduce essential components of posttraumatic axonal pathology, including impaired axoplasmic transport, spectrin proteolysis, and axonal swelling. However, the effects of CsA administration on axonal function, following TBI, have not been evaluated. The present study assessed the effects of CsA treatment on compound action potentials (CAPs) evoked in corpus callosum of adult rats following midline fluid percussion injury. Rats received a 20 mg/kg bolus of CsA, or cremaphor vehicle, at either 15 min or 1 h postinjury, and at 24 h postinjury CAP recording was conducted in coronal brain slices. To elucidate how injury and CsA treatments affect specific populations of axons, CAP waveforms generated largely by myelinated axons (N1) were analyzed separately from the CAP signal, which predominantly reflects activity in unmyelinated axons (N2). CsA administration at 15 min postinjury resulted in significant protection of CAP area, and this effect was more pronounced in N1, than in the N2, CAP component. This treatment also significantly protected against TBI-induced reductions in high-frequency responding of the N1 CAP signal. In contrast, CsA treatment at 1 h did not significantly protect CAPs but was associated with atypical waveforms in N1 CAPs, including decreased CAP duration and reduced refractoriness. The present findings also support growing evidence that myelinated and unmyelinated axons respond differentially to injury and neuroprotective compounds.     

Automatic activation of positive but not negative attitudes after traumatic brain injury

This study investigated social judgment problems of an individual (AM) with bilateral frontal and temporal lobe damage including damage to the amygdala. We hypothesized that AM could automatically process positive, but not negative evaluative information and could process both types of evaluative information using controlled processing. In Phase 1 of Experiment 1 AM and controls were shown a series of words one at a time and were required to make good/bad judgments as quickly as possible. Results showed that AM was more likely than controls to rate words as good, and was significantly slower to make good/bad judgments of negatively, but not positively, evaluated words. In Phase 2 AM was shown a prime (positive or negative) then target (positive or negative) and instructed to evaluate whether the target word was good or bad. Results showed that AM responded more quickly when prime and target were both positive, but not when prime and target were both negative, whereas controls showed both types of priming. Experiment 2 determined whether AM's impaired processing of negative evaluative information could be abolished under controlled processing. AM was explicitly instructed to generate positive and negative connotations of a series of single words and given essentially unlimited time. Under these conditions, AM and controls did not differ significantly in their ability to generate positive versus negative connotations of words. In Experiment 3 AM and controls both showed normal semantic priming effects. The results are interpreted within the component process model of memory.     

IFNAR1 and IFNAR2 polymorphisms confer susceptibility to multiple sclerosis but not to interferon-beta treatment response

We investigated the role of three polymorphisms in the IFNAR1 (SNPs 18417 and -408) and IFNAR2 (SNP 11876) genes in multiple sclerosis (MS) susceptibility and in the IFNbeta treatment response in a group of 147 patients and 210 controls undergoing interferon therapy during the last 2 years. Only the 18417 and the 11876 SNPs showed an association with disease susceptibility (p=0.001 and 0.035, respectively) although no differential genotype distribution were observed between interferon responders and non-responder MS patients. No alteration of the expression level of IFNAR-1 was observed with respect to the -408 genotypes or to interferon treatment response. These data suggest a role for the IFNAR pathway in susceptibility to MS.     

Kindling of basolateral amygdala but not ventral hippocampus or perirhinal cortex disrupts sensorimotor gating in rats

The neural mechanisms mediating prepulse inhibition (PPI) appear to have relevance to neurological and psychiatric disorders. Patients with temporal lobe epilepsy exhibit psychotic symptoms and disrupted PPI, therefore the present experiments examined the consequences of seizures induced by kindling on PPI. Rats were chronically implanted with an electrode into the basolateral amygdala, perirhinal cortex, or ventral hippocampus and stimulated twice daily until 3 fully generalized, class 5 seizures were elicited. Kindling of basolateral amygdala, but not perirhinal cortex or ventral hippocampus, disrupted PPI when testing began 2min, but not 48h, following the elicitation of the third class 5 seizure. Startle amplitudes were unaffected by kindling. These results suggest that the anatomical origin of seizures is an important factor in determining their potentially disruptive effects on PPI.     

Detection of traumatic axonal injury with diffusion tensor imaging in a mouse model of traumatic brain injury

Traumatic axonal injury (TAI) is thought to be a major contributor to cognitive dysfunction following traumatic brain injury (TBI), however TAI is difficult to diagnose or characterize non-invasively. Diffusion tensor imaging (DTI) has shown promise in detecting TAI, but direct comparison to histologically-confirmed axonal injury has not been performed. In the current study, mice were imaged with DTI, subjected to a moderate cortical controlled impact injury, and re-imaged 4-6 h and 24 h post-injury. Axonal injury was detected by amyloid beta precursor protein (APP) and neurofilament immunohistochemistry in pericontusional white matter tracts. The severity of axonal injury was quantified using stereological methods from APP stained histological sections. Two DTI parameters - axial diffusivity and relative anisotropy - were significantly reduced in the injured, pericontusional corpus callosum and external capsule, while no significant changes were seen with conventional MRI in these regions. The contusion was easily detectable on all MRI sequences. Significant correlations were found between changes in relative anisotropy and the density of APP stained axons across mice and across subregions spanning the spatial gradient of injury. The predictive value of DTI was tested using a region with DTI changes (hippocampal commissure) and a region without DTI changes (anterior commissure). Consistent with DTI predictions, there was histological detection of axonal injury in the hippocampal commissure and none in the anterior commissure. These results demonstrate that DTI is able to detect axonal injury, and support the hypothesis that DTI may be more sensitive than conventional imaging methods for this purpose.