Does dendritic growth underly recovery from neonatal occipital lesions in rats

Nurturing the preterm infant brain: leveraging neuroplasticity to improve neurobehavioral outcomes

An intrinsic feature of the developing brain is high susceptibility to environmental influence-known as plasticity. Research indicates cascading disruption to neurological development following preterm (PT) birth; yet, the interactive effects of PT birth and plasticity remain unclear. It is possible that, with regard to neuropsychological outcomes in the PT population, plasticity is a double-edged sword. On one side, high plasticity of rapidly developing neural tissue makes the PT brain more vulnerable to injury resulting from events, including inflammation, hypoxia, and ischemia. On the other side, plasticity may be a mechanism through which positive experience can normalize neurological development for PT children. Much of the available literature on PT neurological development is clinically weighted and focused on diagnostic utility for predicting long-term outcomes. Although diagnostic utility is valuable, research establishing neuroprotective factors is equally beneficial. This review will: (1) detail specific mechanisms through which plasticity is adaptive or maladaptive depending on the experience; (2) integrate research from neuroimaging, intervention, and clinical science fields in a summary of findings suggesting inherent plasticity of the PT brain as a mechanism to improve child outcomes; and (3) summarize how responsive caregiving experiences situate parents as agents of change in normalizing PT infant brain development.

Environmental enrichment and the sensory brain: the role of enrichment in remediating brain injury

The brain's life-long capacity for experience-dependent plasticity allows adaptation to new environments or to changes in the environment, and to changes in internal brain states such as occurs in brain damage. Since the initial discovery by Hebb (1947) that environmental enrichment (EE) was able to confer improvements in cognitive behavior, EE has been investigated as a powerful form of experience-dependent plasticity. Animal studies have shown that exposure to EE results in a number of molecular and morphological alterations, which are thought to underpin changes in neuronal function and ultimately, behavior. These consequences of EE make it ideally suited for investigation into its use as a potential therapy after neurological disorders, such as traumatic brain injury (TBI). In this review, we aim to first briefly discuss the effects of EE on behavior and neuronal function, followed by a review of the underlying molecular and structural changes that account for EE-dependent plasticity in the normal (uninjured) adult brain. We then extend this review to specifically address the role of EE in the treatment of experimental TBI, where we will discuss the demonstrated sensorimotor and cognitive benefits associated with exposure to EE, and their possible mechanisms. Finally, we will explore the use of EE-based rehabilitation in the treatment of human TBI patients, highlighting the remaining questions regarding the effects of EE.

Neurophysiological properties of cells filling the neonatal medial prefrontal cortex lesion cavity

Removal of the medial prefrontal cortex (mPFC) of the rat during the initial 7-12 days of life results in spontaneous filling of lesion cavity that is accompanied by recovery of cognitive and motor functions. To date, it remains uncertain whether tissue filling the lesion cavity is actually supporting the functional improvement. In the present study, we examined whether spontaneous neuronal activity could be recorded in adulthood from the tissue that fills the lesion cavity. We recorded EEG and multiunit activity in adulthood from the mPFC and the motor cortex of rats that had received neonatal mPFC lesions on post-natal day 10 (P10) or their non-lesioned littermate controls. We found similarities in both the firing pattern and firing rate of cells from the filled-in region compared to that of controls, although the power associated with peak frequencies in the delta, alpha, and beta range in the EEG recorded from the filled-in region was lower compared to controls. Overall, our results suggest that the cells found in the lesion cavity have similar neurophysiological properties to those found in normal tissue and thus should be capable of at least partially supporting the observed recovery of function.

Proliferation dynamics of germinative zone cells in the intact and excitotoxically lesioned postnatal rat brain

BACKGROUND

The forebrain subventricular zone (SVZ)-olfactory bulb pathway and hippocampal subgranular zone (SGZ) generate neurons into adulthood in the mammalian brain. Neurogenesis increases after injury to the adult brain, but few studies examine the effect of injury on neural and glial precursors in the postnatal brain. To characterize the spatio-temporal dynamics of cell proliferation in the germinative zones, this study utilized a model of postnatal damage induced by NMDA injection in the right sensorimotor cortex at postnatal day 9. Dividing cell populations were labeled with 5-Bromodeoxyuridine (BrdU) in the intact and damaged postnatal brain. Identity of proliferating cells was determined by double immunolabeling with nestin, GFAP, NeuN and tomato lectin (TL).

RESULTS

In the control brain, grouped BrdU+ cells were observed in the Rostral Migratory Stream (RMS), SVZ and SGZ. Maximal proliferation was seen at P12, persisted until P23 and diminished by P49. After injury, a striking reduction in the number of BrdU+ cells was observed in the ipsilateral SVZ from 10 hours (58% decrease) until 14 days post-lesion (88% decrease). In contrast, an increase in grouped BrdU+ cells was seen in the striatum adjacent to the depleted SVZ. Significantly reduced numbers of BrdU+ cells were also seen in the RMS until 3 days post-lesion. No changes were noted in the SGZ. Both in controls and lesioned hemispheres, BrdU+ cells located in the germinal zones were mostly nestin positive and negative for GFAP, NeuN, and TL. In the SVZ area lining the ventricle, BrdU+/nestin+ cells were mainly located between TL+ ependyma and parenchymal GFAP+ astrocytes. After excitotoxicity, a decrease in the number and orientation of GFAP/nestin+ prolongations leaving the SVZ to the cortex, corpus callosum and striatum was noted until 5 days post-lesion.

CONCLUSION

Postnatal excitotoxic injury differentially affects proliferating cells in the germinative zones: no change is observed in the dentate gyrus whereas excitotoxicity causes a significant decrease in proliferating cells in the SVZ and RMS. Depletion of BrdU+ cells in the postnatal SVZ and RMS differs from previous studies after adult brain injury and may affect the SVZ-RMS migration and is suggestive of progenitor recruitment to injured areas.

Posterior neocortical (visual cortex) lesions in the rat impair matching-to-place navigation in a swimming pool: a reevaluation of cortical contributions to spatial behavior using a new assessment of spatial versus non-spatial behavior

In the face of contradictory findings on the role of visual cortex contributions to spatial behavior, the present study evaluated the ability of rats with primary visual cortex (Area 17) lesions to learn spatial problems in a swimming pool. Because the solution to any spatial learning problem consists of acquiring at least two primary elements of a task, task procedures and spatial learning, the study, in addition to assessing spatial ability on a place task, used two training/testing methods to identify the nature of the spatial impairment associated with visual cortex lesions. Non-spatial training consisted of learning to find a platform in the dark and spatial training consisted of a series of matching-to-place problems. The results confirmed that although rats with visual cortex lesions were impaired on place learning, the deficit was partially ameliorated by non-spatial training given following the lesion, and completely ameliorated by non-spatial training given before the lesion. Nevertheless, all visual cortex groups failed to show a quadrant preference on a probe trial and displayed a profound impairment in matching-to-place learning. This definitive demonstration that appropriate testing methods can reveal a failure in spatial behavior following visual cortex lesions is consistent with the idea that primary visual cortex is required in spatial navigation.

Posterior neocortical (visual cortex) lesions in the rat impair matching-to-place navigation in a swimming pool: a reevaluation of cortical contributions to spatial behavior using a new assessment of spatial versus nonspatial behavior

In the face of contradictory findings on the role of visual cortex contributions to spatial behavior, the present study evaluated the ability of rats with primary visual cortex (area 17) lesions to learn spatial problems in a swimming pool. Because the solution to any spatial learning problem consists of acquiring at least two primary elements of a task, task procedures and spatial learning, the study, in addition to assessing spatial ability on a place task, used two training/testing methods to identify the nature of the spatial impairment associated with visual cortex lesions. Non-spatial training consisted of learning to find a platform in the dark and spatial training consisted of a series of matching-to-place problems. The results confirmed that although rats with visual cortex lesions were impaired on place learning, the deficit was partially ameliorated by non-spatial training given following the lesion, and completely ameliorated by non-spatial training given before the lesion. Nevertheless, all visual cortex groups failed to show a quadrant preference on a probe trial and displayed a profound impairment in matching-to-place learning. This definitive demonstration that appropriate testing methods can reveal a failure in spatial behavior following visual cortex lesions is consistent with the idea that primary visual cortex is required in spatial navigation.

Recovery from early cortical damage in rats. IX. Differential behavioral and anatomical effects of temporal cortex lesions at different ages of neural maturation

Rats were given lesions of the temporal association cortex on postnatal day 4 or 10, or in adulthood. Ninety days later they were trained on two visual tasks (visual-spatial navigation; horizontal-vertical stripes discrimination). Lesion animals were compared behaviorally and neuroanatomically to littermate sham control rats. The day 4 lesions produced a larger deficit in the navigation task than day 10 or adult lesions. There were no deficits in the discrimination task. Analysis of the brains showed that the day 4 lesions produced a smaller brain and thinner cortex than day 10 lesions. The day 10 lesions produced hypertrophy in the dendritic arborization of pyramidal cells in parietal cortex. The results are consistent with the general findings that perinatal cortical injury in rats produces more severe behavioral and morphological effects than similar lesions in the second week of life and that cortical lesions around day 10 lead to an increase in cortical synaptogenesis.

Role of the neocortex in the water maze task in the rat: a detailed behavioral and Golgi-Cox analysis

The role of the neocortex in acquisition of the water maze task was investigated with both detailed behavioral and anatomical analyses. The neocortical areas examined were: (1). primary visual and posterior parietal areas Oc1 and Oc2M, (2). parietal area Par1, and (3). prefrontal areas Cg1, Cg3, IL, and part of Fr2 of Zilles, 1985. In Experiment 1, the effects of lesions in these areas were examined separately in different groups of naive male hooded rats. Additional rats were given water maze strategy pretraining before receiving a lesion. Strategy pretraining was used to separate water maze strategy learning from spatial learning to evaluate the contribution of the neocortical areas to these two components of task acquisition. All groups of naive lesioned rats were impaired in the task. In contrast, corresponding groups of pretrained lesioned rats performed as well as controls on all behavioral measures. In Experiment 2, the same neocortical areas lesioned in Experiment 1 were examined with the Golgi-Cox method to determine whether water maze training was associated with changes in the dendritic arborization of neocortical pyramidal cells. Contrary to expectations, no anatomical changes that could be ascribed to the behavioral training were seen in the areas and cortical layers examined. The data suggest that (1). these areas contribute to water maze strategy learning in naive rats, (2). none of the areas are crucially required for spatial learning provided rats are familiar with the general behavioral strategies required in the task before the lesion is made, and (3). any changes in neuronal morphology that occur as a consequence of the training may be subtle and widely distributed.

Neuronal, astroglial and microglial cytokine expression after an excitotoxic lesion in the immature rat brain

Cytokines are important intercellular messengers involved in neuron-glia interactions and in the microglial-astroglial crosstalk, modulating the glial response to brain injury and the lesion outcome. In this study, excitotoxic lesions were induced by the injection of N-methyl-D-aspartate in postnatal day 9 rats, and the cytokines interleukin-1 beta (IL-1beta), interleukin-6 (IL-6), tumour necrosis factor alpha (TNFalpha) and transforming growth factor beta 1 (TGF-beta1) analysed by ELISA and/or immunohistochemistry. Moreover, cytokine-expressing glial cells were identified by means of double labelling with glial fibrillary acidic protein or tomato lectin binding. Our results show that both neurons and glia were capable of cytokine expression following different patterns in the excitotoxically damaged area vs. the nondegenerating surrounding grey matter (SGM). Excitotoxically damaged neurons showed upregulation of IL-6 and downregulation of TNFalpha and TGF-beta1 before they degenerated. Moreover, in the SGM, an increased expression of neuronal IL-6, TNFalpha and TGF-beta1 was observed. A subpopulation of microglial cells, located in the SGM and showing IL-1beta and TNFalpha expression, were the earliest glial cells producing cytokines, at 2-10 h postinjection. Later on, cytokine-positive glial cells were found within the excitotoxically damaged area and the adjacent white matter: some reactive astrocytes expressed TNFalpha and IL-6, and microglia/macrophages showed mild IL-1beta and TGF-beta1. Finally, the expression of all cytokines was observed in the glial scar. As discussed, this pattern of cytokine production suggests their implication in the evolution of excitotoxic neuronal damage and the associated glial response.

STAT3 and NFkappaB activation precedes glial reactivity in the excitotoxically injured young cortex but not in the corresponding distal thalamic nuclei

In this study we evaluated the activation of the cytokine and growth factor responsive transcription factors signal transducer and activator of transcription 3 (STAT3) and nuclear factor kappa B (NFkappaB) after different grades of neural damage in the immature rat brain using double immunocytochemical techniques and electron microscopy. Following neocortical N-methyl-D-aspartate induced excitotoxic cell death, both these transcription factors are mainly activated in astrocytes, although microglia, endothelial cells, and neurons show transient activation at specific times and locations. Interestingly, activation of both transcription factors is only observed in cortical areas affected by severe tissue damage, neuronal degeneration, and blood-brain barrier (BBB) disruption. In contrast, the milder glial response occurring in the distal thalamus is not preceded by immunocytochemically detectable STAT3 and NFkappaB activation, although microglial response, astroglial hypertrophy, and glial fibrillary acidic protein (GFAP) overexpression do occur. In the cortex, astrocytes show STAT3 and NFkappaB activation already at 2 to 4 hours post-lesion, preceding cell hypertrophy and GFAP upregulation, and being maintained in the long-term formed glial scar. STAT3 and NFkappaB activation in microglial cells is protracted and observed at 10 to 24 hours post-lesion. The early activation of both transcription factors in astroglial cells could contribute to the changes in gene expression leading to astrogliosis and the release of signalling molecules which may contribute to the subsequent activation of these transcription factors in microglial cells.

Primary cortical glial reaction versus secondary thalamic glial response in the excitotoxically injured young brain: microglial/macrophage response and major histocompatibility complex class I and II expression

The excitatory amino acid analog, N-methyl-D-aspartate, was injected intracortically into nine-day-old rats. Resulting axon-sparing lesions in the developing sensorimotor cortex, which secondarily affect thalamic neurons that become deprived of cortical targets, provide an experimental model for the study of the glial response in distantly affected areas. The microglial/macrophage response was studied using tomato lectin histochemistry and major histocompatibility complex I and II immunocytochemistry. Blood-brain barrier integrity was evaluated. In the cortical lesion site, where blood-brain barrier breakdown occurs, the rapid microglial response was restricted to the degenerating area. Microglial changes were first seen at 4 h post-injection, peaking at days 3-5. Reactive microglia changed morphology, increased tomato lectin binding and expressed major histocompatibility complex I. Additionally, some cells expressed major histocompatibility complex II. In the secondarily affected thalamus, the microglial response was not as pronounced as in the cortex, was first seen at 10 h post-injection and peaked at days 3-5. Reactive microglia showed a bushy morphology, were intensely lectin positive and expressed major histocompatibility complex I. The exceptional response of the nine-day-old brain to cortical lesions makes this model an interesting tool for studying the implications of microglial major histocompatibility factor expression in still enigmatic processes such as wound healing and plasticity.

Possible regeneration of rat medial frontal cortex following neonatal frontal lesions

The experiments described here show that the cavity left by midline frontal cortex removals at 10 days of age (P10) fills in with neural tissue. Similar changes are not found at earlier and later ages. This neuronal filling is blocked by prior pretreatment by administration of Bromodeoxyuridine (BrdU) on embryonic day 13. Administration of BrdU following the P10 lesion does not interfere with regrowth. Subsequent immunohistochemical staining for BrdU demonstrates the regrown area to be composed of newly generated cells. which include pyramidal and nonpyramidal neurons. Injections of a retrograde tracer into the striatum or posterior parietal cortex shows that the new neurons have connections similar to those of undamaged brains. The regrowth of this tissue is correlated with recovery of function in a test of forelimb use. Thus, the mammalian brain, during some privileged postnatal stages of growth. is capable of extensive reorganization that includes regeneration of lost neurons. These results are discussed in relation to the proximity of the lesion to the stem cells in the lateral ventricle and their postnatal migrational activities.

A method for vibratome sectioning of Golgi-Cox stained whole rat brain

A method for impregnating the whole rat brain with Golgi-Cox stain and sectioning with the vibratome is described. The method is simple, inexpensive and provides good resolution of dendrites and spines.