Recovery of function is associated with increased spine density in cortical pyramidal cells after frontal lesions and/or noradrenaline depletion in neonatal rats

Noradrenergic antagonists mitigate amphetamine-induced recovery

Brain injury, including that due to stroke, leaves individuals with cognitive deficits that can disrupt daily aspect of living. As of now there are few treatments that shown limited amounts of success in improving functional outcome. The use of stimulants such as amphetamine have shown some success in improving outcome following brain injury. While the pharmacological mechanisms for amphetamine are known; the specific processes responsible for improving behavioral outcome following injury remain unknown. Understanding these mechanisms can help to refine the use of amphetamine as a potential treatment or lead to the use of other methods that share the same pharmacological properties. One proposed mechanism is amphetamine's impact upon noradrenaline (NA). In the current, study noradrenergic antagonists were administered prior to amphetamine to pharmacologically block α- and β-adrenergic receptors. The results demonstrated that the blockade of these receptors disrupted amphetamines ability to induce recovery from hemispatial neglect using an established aspiration lesion model. This suggests that amphetamine's ability to ameliorate neglect deficits may be due in part to noradrenaline. These results further support the role of noradrenaline in functional recovery. Finally, the development of polytherapies and combined therapeutics, while promising, may need to consider the possibility that drug interactions can negate the effectiveness of treatment.

Effects of Sex and Mild Intrainsult Hypothermia on Neuropathology and Neural Reorganization following Neonatal Hypoxic Ischemic Brain Injury in Rats

Hypoxia ischemia (HI) is a recognized risk factor among late-preterm infants, with HI events leading to varied neuropathology and cognitive/behavioral deficits. Studies suggest a sex difference in the incidence of HI and in the severity of subsequent behavioral deficits (with better outcomes in females). Mechanisms of a female advantage remain unknown but could involve sex-specific patterns of compensation to injury. Neuroprotective hypothermia is also used to ameliorate HI damage and attenuate behavioral deficits. Though currently prescribed only for HI in term infants, cooling has potential intrainsult applications to high-risk late-preterm infants as well. To address this important clinical issue, we conducted a study using male and female rats with a postnatal (P) day 7 HI injury induced under normothermic and hypothermic conditions. The current study reports patterns of neuropathology evident in postmortem tissue. Results showed a potent benefit of intrainsult hypothermia that was comparable for both sexes. Findings also show surprisingly different patterns of compensation in the contralateral hemisphere, with increases in hippocampal thickness in HI females contrasting reduced thickness in HI males. Findings provide a framework for future research to compare and contrast mechanisms of neuroprotection and postinjury plasticity in both sexes following a late-preterm HI insult.

Prenatal exposure to bisphenol A impacts neuronal morphology in the hippocampal CA1 region in developing and aged mice

Bisphenol A (BPA), a widely used raw component of polycarbonate plastics and epoxy resins, has been reported to induce developmental neurotoxicity in offspring born to dams exposed to low doses of BPA; however, the toxicity mechanism remains elusive. To study the effects of in utero BPA exposure on neuronal morphology, we studied spine density and dendritic growth in the hippocampal CA1 of aged mice and developing mice prenatally exposed to low doses of BPA. Pregnant mice were orally administered BPA at a low dose of 0, 40, or 400 μg/kg body weight/day on gestational days 8.5–17.5/18.5. Mouse progenies were euthanized at 3 weeks or 14 months, and their brains were analyzed for dendritic arborization of GFP-expressing neurons or spine densities of Golgi-stained neurons in the hippocampal CA1. Regardless of the dose, in utero BPA exposure reduced spine densities in the hippocampal CA1 of the 14-month-old mice. In the developing brain from the 3-week-old mice born to dams exposed to BPA at a dose of 400 μg/kg body weight/day, overall length and branching number of basal dendrites but not apical dendrites were decreased. In utero low doses of BPA exposure disrupts hippocampal CA1 neuronal morphology during development, and this disruption is believed to persist in adulthood.

MicroRNA-9 controls dendritic development by targeting REST

MicroRNAs (miRNAs) are conserved noncoding RNAs that function as posttranscriptional regulators of gene expression. miR-9 is one of the most abundant miRNAs in the brain. Although the function of miR-9 has been well characterized in neural progenitors, its role in dendritic and synaptic development remains largely unknown. In order to target miR-9 in vivo, we developed a transgenic miRNA sponge mouse line allowing conditional inactivation of the miR-9 family in a spatio-temporal-controlled manner. Using this novel approach, we found that miR-9 controls dendritic growth and synaptic transmission in vivo. Furthermore, we demonstrate that miR-9-mediated downregulation of the transcriptional repressor REST is essential for proper dendritic growth.

DOI:http://dx.doi.org/10.7554/eLife.02755.001

Messages are sent back and forth in our brains by cells called neurons that connect to each other in complex networks. Neurons develop from stem cells in a complicated process that involves a number of different stages. In one of the final stages, tree-like structures called dendrites emerge from the neurons and connect with neighboring neurons via special junctions called synapses.

A group of small RNA molecules called microRNAs have roles in controlling the development of neurons. One microRNA, called miR-9, is abundant in the brain and is known to be involved in the early stages of neuron development. However, its role in the formation of dendrites and synapses remains unclear.

Giusti et al. studied this microRNA in mice. A length of DNA, coding for an RNA molecule that binds to miR-9 molecules and stops them performing their normal function, was inserted into the mice. These experiments showed that miR-9 is involved in controlling dendrite growth and synaptic function.

To enable a neuron to produce dendrites, miR-9 binds to and interferes with the RNA molecules that are needed to make a protein called REST. This protein is a transcription factor that switches off the expression of other genes so, in effect, miR-9 allows a set of genes that are needed for dendrite growth to be switched on.

The methodology developed by Giusti et al. could be used to study the functions of other microRNAs.

DOI:http://dx.doi.org/10.7554/eLife.02755.002

Embryonic pretreatment with bromodeoxyuridine blocks regeneration and functional recovery from perinatal medial frontal lesions in rats

Removal of the midline frontal cortex on postnatal day 10 is followed by apparent regeneration of the part of the lost cortex, correlated with substantial recovery of function in adulthood. The spontaneous regrowth of the medial frontal cortex after midline frontal lesions on postnatal day 10 was blocked by pretreatment with bromodeoxyuridine (BrdU) on embryonic days 11, 12, 13, 15, or 17. BrdU pretreatment on embryonic day 21 or postnatal day 10 did not block either functional recovery or cortical regrowth. These results demonstrate a teratological effect of BrdU and are consistent with the claim that functional recovery after midline frontal removal on postnatal day 10 is supported by the generation of new midline frontal tissue.

Hitting a moving target: Basic mechanisms of recovery from acquired developmental brain injury

Acquired brain injuries represent a major cause of disability in the pediatric population. Understanding responses to developmental acquired brain injuries requires knowledge of the neurobiology of normal development, age-at-injury effects and experience-dependent neuroplasticity. In the developing brain, full recovery cannot be considered as a return to the premorbid baseline, since ongoing maturation means that cerebral functioning in normal individuals will continue to advance. Thus, the recovering immature brain has to 'hit a moving target' to achieve full functional recovery, defined as parity with age-matched uninjured peers. This review will discuss the consequences of developmental injuries such as focal lesions, diffuse hypoxia and traumatic brain injury (TBI). Underlying cellular and physiological mechanisms relevant to age-at-injury effects will be described in considerable detail, including but not limited to alterations in neurotransmission, connectivity/network functioning, the extracellular matrix, response to oxidative stress and changes in cerebral metabolism. Finally, mechanisms of experience-dependent plasticity will be reviewed in conjunction with their effects on neural repair and recovery.

Postnatal binge-like alcohol exposure reduces spine density without affecting dendritic morphology in rat mPFC

Among the deficits associated with fetal alcohol syndrome (FAS), cognitive impairments are the most debilitating and permanent. These impairments, including deficits in goal-directed behavior, attention, temporal planning, and other executive functions, could result from damage to the prefrontal cortex (PFC), an area that has not been studied sufficiently in the context of FAS. Neuronal connectivity in this area, as measured by distribution of dendritic spines and the complexity of dendritic tree structure, can be influenced by exogenous variables other than alcohol, and the neuronal connectivity in other brain regions can be affected by alcohol exposure. The goal of this study was to determine whether binge-like alcohol exposure on postnatal days (PD) 4-9 affects dendritic spine density and other dendritic tree parameters in mPFC that could possibly underlie functional damage. Rats were intubated with alcohol [5.25 g/kg/day; alcohol exposed (AE)], sham intubated (SI), or remained with the mother (SC, suckle control) on PD 4-9. Animals were sacrificed between PD 26 and PD 30 and brains were processed for Golgi-Cox staining. Apical dendrite complexity and spine density were evaluated for layer III neurons in the mPFC using NeuroLucida software (MicroBrightField, Inc.). Spine density was significantly decreased in AE animals relative to SI and SC controls, but no differences in dendritic complexity were found across experimental groups. Our findings demonstrate that neonatal alcohol exposure has a persistent effect on the spine density in mPFC that can explain functional deficits in this cortical area.

Brain plasticity and recovery from early cortical injury

There is a general view that early brain damage leads to a far better outcome than damage later in life. Although there is a grain of truth to this idea, the reality is far more complex. We have identified a set of nine principles that underlie behavioral and anatomical changes after neonatal cortical injury as well as describing a variety of pre- and postnatal factors that modulate brain and behavioral plasticity after neonatal cortical lesions.

A chronic treatment with CDP-choline improves functional recovery and increases neuronal plasticity after experimental stroke

Chronic impairment of forelimb and digit movement is a common problem after stroke that is resistant to therapy. Although in the last years some studies have been performed to increase the efficacy of rehabilitative experience and training, the pharmacological approaches in this context remain poorly developed. We decided to study the effect of a chronic treatment with CDP-choline, a safe and well-tolerated drug that is known to stabilize membranes, on functional outcome and neuromorphological changes after stroke. To assess the functional recovery we have performed the staircase reaching test and the elevated body swing test (EBST), for studying sensorimotor integration and asymmetrical motor function respectively. The treatment with CDP-choline, initiated 24 h after the middle cerebral artery occlusion (MCAO) and maintained during 28 days, improved the functional outcome in both the staircase test (MCAO+CDP=87.0+/-6.6% pellets eaten vs. MCAO+SAL=40.0+/-4.5%; p<0.05) and the EBST (MCAO+CDP=70.0+/-6.8% vs. MCAO+SAL=88.0+/-5.4%; contralateral swing p<0.05). In addition, to study potential neuronal substrates of the improved function, we examined the dendritic morphology of layer V pyramidal cells in the undamaged motor cortex using a Golgi-Cox procedure. The animals treated with CDP-choline showed enhanced dendritic complexity and spine density compared with saline group. Our results suggest that a chronic treatment with CDP-choline initiated 24 h after the insult is able to increase the neuronal plasticity within noninjured and functionally connected brain regions as well as to promote functional recovery.

Neonatal handling alters brain organization but does not influence recovery from perinatal cortical injury

Handling rat pups by removing them from the nest during the preweaning period has been shown to influence brain and behavioral development. The authors hypothesized that handling rats with perinatal (Day 4) medial frontal cortex removals might attenuate behavioral deficits and reverse dendritic atrophy associated with such an injury. On the day after surgery, pups were removed from the nest for 15 min, 3 times per day until weaning. Animals were tested as adults in the Morris water task and on skilled reaching. Handled animals showed no improvement in behavioral performance. The handling procedure led to a decrease in dendritic length in parietal cortex, but spine density was unchanged. No therapeutic advantage was observed following the preweaning handling of brain-injured rats.

Prefrontal lesions and attentional skills in childhood

Despite the potential impact on development, few studies have examined the influence of prefrontal lesions occurring prior to maturation of the central nervous system. This study investigates the effect of prefrontal lesions in general, as well as the impact of lesion laterality, with respect to attentional abilities. The sample comprised 36 children with prefrontal lesions and 40 healthy controls. Attentional function was assessed across four domains: selective, shifting and divided attention, and processing speed. Group mean performances for children with prefrontal lesions indicated global attentional deficits, with greatest difficulties for "higher-order" skills including shifting and divided attention. Children with left prefrontal lesions performed similarly to controls, with a specific deficit characterized by difficulties with on-line processing of auditory-verbal information. Right prefrontaj lesions were primarily associated with impairments in day-to-day executive functions, including reduced monitoring, poor shifting attention and disinhibition. Children with bilateral prefrontal lesions performed worse than controls on tasks requiring greater cognitive resources. These results provide evidence of the important role played by prefrontal cortex in the development of attentional skills, and the particular role of the right prefrontal cortex. The pattern of attention deficits observed following early prefrontal lesions suggests some lateralization of function within the frontal lobes, even during childhood.

The effects of decompression and exogenous NGF on compressed cerebral cortex

Using a rat epidural bead implantation model, we found that compression alone could reduce the overall and individual layer thicknesses of cerebral cortex with no apparent cell death. The dendritic lengths and spine densities of layer II/III and V pyramidal neurons started to decrease within 3 days of compression. Decompression for 14 days resulted in near complete to partial recovery of the cortical thickness and of the dendritic lengths of layer II/III and V pyramidal neurons, depending on the duration of the preceding compression. The recoverability was better following short (3-day) than long (1- or 3-month) periods of compression. The loss of dendritic spines nevertheless persisted. An intraventricular infusion of NGF was performed after decompressing the lesions following 3 days of cortical compression, and this increased the recovery of the spines but not the dendritic length of the cortical pyramidal neurons, nor did it alter the recovery of the cortical thickness. NGF also promoted the increase of the dendritic spines, but not the dendritic length of the cortical pyramidal neurons of normal animals. In short, the data show that a few days of compression alone can cause permanent cortical damage. Exogenous NGF, if applied topically, may restore the dendritic spine density of cortical neurons subjected to compression.

Long-term prenatal hypoxia alters maturation of brain catecholaminergic systems and motor behavior in rats

In order to determine the influence of long-term prenatal hypoxia on the maturation of the brain catecholaminergic structures involved in motor and cognitive functions, pregnant rats were subjected to hypoxia (10% O2) from the 5th to 20th day of gestation. The in vivo activity of tyrosine hydroxylase (TH), the rate-limiting enzyme in catecholamine biosynthesis, was assessed, by accumulation of L-DOPA after i.p. administration of NSD-1015, in the motor cortex areas, the hippocampus, and the striatum at birth and at the 3rd, 7th, 14th, 21st, and 68th postnatal days. The motor reactivity to novelty and the circadian motor activity were measured at the 21st and 68th postnatal days. Exposure to prenatal hypoxia strongly altered the developmental pattern of in vivo TH activity in restricted noradrenergic terminals of the brain. In the 21-day-old prenatal hypoxic rats, the TH activity was reduced by 80% in the motor cortex areas and by 43% in the hippocampus, compared to control rats, while no differences could be detected in the striatum. Compared to control rats, the prenatal hypoxic pups exhibited a higher motor reactivity to novelty and a nocturnal motor hypoactivity at the 21st postnatal day. The neurochemical and behavioral alterations were no longer observed at the 68th postnatal day. The altered in vivo TH activity in the young rats might be part of the neural mechanisms contributing to the motor behavioral impairments induced by prenatal hypoxia. Long-term prenatal hypoxia could be linked to the development of psychopathologies that can be detected in infancy.

Noradrenergic mechanisms in neurodegenerative diseases: a theory

A deficiency in the noradrenergic system of the brain, originating largely from cells in the locus coeruleus (LC), is theorized to play a critical role in the progression of a family of neurodegenerative disorders that includes Parkinson's disease (PD) and Alzheimer's disease (AD). Consideration is given here to evidence that several neurodegenerative diseases and syndromes share common elements, including profound LC cell loss, and may in fact be different manifestations of a common pathophysiological process. Findings in animal models of PD indicate that the modification of LC-noradrenergic activity alters electrophysiological, neurochemical and behavioral indices of neurotransmission in the nigrostriatal dopaminergic system, and influences the response of this system to experimental lesions. In models related to AD, noradrenergic mechanisms appear to play important roles in modulating the activity of the basalocortical cholinergic system and its response to injury, and to modify cognitive functions including memory and attention. Mechanisms by which noradrenaline may protect or promote recovery from neural damage are reviewed, including effects on neuroplasticity, neurotrophic factors, neurogenesis, inflammation, cellular energy metabolism and excitotoxicity, and oxidative stress. Based on evidence for facilitatory effects on transmitter release, motor function, memory, neuroprotection and recovery of function after brain injury, a rationale for the potential of noradrenergic-based approaches, specifically alpha2-adrenoceptor antagonists, in the treatment of central neurodegenerative diseases is presented.

Efficacy of rehabilitative experience declines with time after focal ischemic brain injury

To maximize the effectiveness of rehabilitative therapies after stroke, it is critical to determine when the brain is most responsive (i.e., plastic) to sensorimotor experience after injury and to focus such efforts within this period. Here, we compared the efficacy of 5 weeks of enriched rehabilitation (ER) initiated at 5 d (ER5), ER14, or ER30 after focal ischemia, as judged by functional outcome and neuromorphological change. ER5 provided marked improvement in skilled forelimb reaching ability and ladder-rung- and narrow-beam-walking tasks and attenuated the stroke-induced reliance on the unaffected forepaw for postural support. ER14 provided improvement to a somewhat lesser extent, whereas recovery was diminished after ER30 such that motor function did not differ from ischemic animals exposed to social housing. To examine potential neural substrates of the improved function, we examined dendritic morphology in the undamaged motor cortex because our previous work (Biernaskie and Corbett, 2001) suggested that recovery was associated with enhanced dendritic growth in this region. ER5 increased the number of branches and complexity of layer V neurons compared with both social housing and control animals. Dendritic arbor after ER14 (although increased) and ER30 did not differ from those exposed to social housing. These data suggest that the poststroke brain displays heightened sensitivity to rehabilitative experience early after the stroke but declines with time. These findings have important implications for rehabilitation of stroke patients, many of whom experience considerable delays before therapy is initiated.

Recovery from infant medial frontal cortical lesions in rats is reversed by cortical lesions in adulthood

Previous studies have shown that when the medial prefrontal cortex (mPFC) is removed at 7-10 days of age there is a spontaneous filling of the lesion cavity and a nearly complete restitution of behaviour. In the current study animals received mPFC lesions on postnatal day 10 and on day 160 the tissue occupying the mPFC region was again removed. Behavioural performance on the Morris water task was compared to animals with either only day 10 mPFC lesions or only day 160 mPFC lesions. Rats with the combined day 10 and day 160 lesions or day 160 lesions were severely impaired at the task whereas the rats with only day 10 lesions showed complete recovery. An analysis of dendritic arborization in pyramidal neurons adjacent to the lesion showed increased dendritic arborization in the basilar fields in both the P10 groups but this was not associated with functional recovery in the animals with the two mPFC lesions. It thus appears that the tissue that filled in the mPFC lesions on day 10 was functional.

Environmental complexity has different effects on the structure of neurons in the prefrontal cortex versus the parietal cortex or nucleus accumbens

Complex housing has been used widely as a model of experience-dependent change. Animals housed in complex environments typically show synaptogenesis throughout the sensory and motor cortex as well as the striatum and hippocampus, and thus it is generally assumed that such changes are likely to be found throughout the cerebrum. The purpose of the present study was to determine whether persistent alterations of dendritic morphology would be found in two regions that had previously not been examined, namely, the medial prefrontal region (Cg3) and nucleus accumbens (NAcc). The results show that housing female rats in complex environments for 3.5 months increased dendritic arborization on medium spiny neurons in the NAcc and on pyramidal cells in the somatosensory cortex (Par 1), but not in Cg3. Environmental complexity increased spine density in all three areas, however. The failure to find increased dendritic length or branching in Cg3 was unexpected. Thus, the data suggest that complex housing may not engage prefrontal neurons in the same manner as neurons in sensory or motor areas. It appears that complex housing may not produce generalized changes in cerebral morphology. The data further suggest that it is prudent to measure both dendritic length and spine density in studies of experience-dependent effects on synaptic plasticity.

Dendritic morphology is altered in hippocampal neurons following prenatal compromise

Chronic placental insufficiency (CPI), a known cause of intrauterine growth restriction, can lead to structural alterations in the developing brain that might underlie postnatal neurological deficits. We have previously demonstrated significant reductions in the volumes of hippocampal neuropil layers in fetal guinea pig brains following experimentally induced growth restriction. To determine the components of the neuropil affected in the brains of growth restricted (GR) fetuses, the dendritic morphology of CA1 pyramidal neurons and dentate granule cells was examined. CPI was induced by unilateral uterine artery ligation in pregnant guinea pigs at midgestation (term approximately 67 days). Hippocampi from control and GR fetuses were stained using the Rapid Golgi technique and the growth and branching of the dendritic arbors were quantified using the Sholl method. In addition, the density of dendritic spines was determined on the apical arbors of each population. In GR brains (n = 7) compared to controls (n = 7), there was a reduction in dendritic elongation (p < 0.005) and an alteration in the branch point distribution in CA1 basal arbors, and a reduction both in the outgrowth (p < 0.05) and branch point number (p < 0.05) of CA1 apical arbors. Dentate granule cells from GR brains also demonstrated reduced dendritic outgrowth (p < 0.05). There was an increase in dendritic spine density in both neuronal populations; this might be due either to altered synaptic pruning or as a compensatory mechanism for reduced dendritic length. These findings demonstrate that a chronic prenatal insult causes selective changes in the morphology of hippocampal cell dendrites and may lead to alterations in hippocampal function in the postnatal period.

Protective effects of the alpha 2-adrenoceptor antagonist, dexefaroxan, against degeneration of the basalocortical cholinergic system induced by cortical devascularization in the adult rat

It has been hypothesized [Colpaert, F.C., 1994. In: Briley, M., Marien, M. (Eds.), Noradrenergic Mechanisms in Parkinson's Disease. CRC Press, Boca Raton, FL, pp. 225-254] that a deficiency in the noradrenergic system originating from the locus coeruleus is a decisive factor in the progression of central neurodegenerative disorders including Alzheimer's disease, and that treatments which boost noradrenergic transmission (e.g. via blockade of alpha(2)-adrenoceptors) could provide both symptomatic and trophic benefits against the disease. Studies in the rat in vivo demonstrating that the selective alpha(2)-adrenoceptor antagonist dexefaroxan increases acetylcholine release in the cortex, improves measures of cognitive performance and protects against excitotoxin lesions, support this concept. As a further test of the hypothesis, we investigated the effect of dexefaroxan in a rat model of unilateral cortical devascularization that induces a loss of the cortical cholinergic terminal network and a retrograde degeneration of the cholinergic projections that originate in the nucleus basalis magnocellularis. Lesioned and sham-operated rats received a 28-day subcutaneous infusion of dexefaroxan (0.63 mg/rat/day) or vehicle, delivered by osmotic minipumps implanted on the day of the cortical devascularization procedure. In lesioned rats, the dexefaroxan treatment was associated with a significantly higher number and size of vesicular acetylcholine transporter-immunoreactive boutons in comparison to the vehicle treatment; this effect was most marked within cortical layer V. Dexefaroxan also significantly reduced the atrophy of cholinergic neurons within the nucleus basalis magnocellularis. Dexefaroxan had no observable effect on any of these parameters in sham-operated cohorts. These results show that systemically administered dexefaroxan mitigates cholinergic neuronal degeneration in vivo, and provide further evidence for a therapeutic potential of the drug in neurodegenerative diseases such as Alzheimer's disease, where central cholinergic function is progressively compromised.

Overview of cortical plasticity and recovery from brain injury

The analysis of plastic changes in the nervous system is based on the assumption that the nervous system is not a static system but rather one that changes over time. Neural plasticity can be studied at many levels, beginning with behavior and then becoming progressively more microscopic by descending to the level of cerebral maps, synaptic organization, physiologic activities, molecular structure, and mitosis. This article considers each level in turn and then briefly describes how an understanding of the principles of plasticity can be used to initiate treatments for cerebral injury.

Noradrenergic innervation of the developing and mature visual and motor cortex of the rat brain: a light and electron microscopic immunocytochemical analysis

The noradrenergic (NA) innervation of the developing and adult visual and motor cortex of the rat was examined with light and electron microscopic immunocytochemistry by using antibodies against dopamine-beta-hydroxylase. At birth, NA fibers were present in both cortical areas, appearing as two tangential streams, one above and the other below the cortical plate. During the subsequent weeks, these two streams arborized gradually innervating all cortical layers. The adult pattern of distribution was attained by postnatal day 14, but the density of innervation, which was higher in the motor than in the visual cortex, appeared similar to the adult by the end of the third postnatal week. Electron microscopic analysis revealed that a low proportion of NA varicosities (the highest value was 12% in the adult motor cortex in single sections) were engaged in synaptic contact, throughout development, in both areas examined. The overwhelming majority of these synapses were symmetrical, involving predominantly small or medium dendrites. This evidence suggests that transmission by diffusion is the major mode of NA action in the developing and adult cerebral cortex. Noradrenaline released in the rare synaptic junctions may act mainly to reduce the activity of its cortical targets. The results altogether provide morphologic evidence for an involvement of noradrenaline in the development of the neocortex and, along with earlier data on the serotonergic system, indicate that the monoaminergic systems are endowed with a specific anatomic organization in various areas of the brain.

Environmental enrichment enhances recovery of function but exacerbates ischemic cell death

Prior exposure to brief 'conditioning' episodes of ischemia protects hippocampal CA1 neurons against a subsequent more severe ischemic insult. However, protected cells exhibit abnormal function and as survival times are extended this ischemic tolerance dissipates and cells begin to die. In this study, we sought to determine whether environmental enrichment could alter the above pattern of delayed cell death and functional impairment in a gerbil model of ischemic tolerance. Gerbils received either ischemic preconditioning, 5 min of ischemia without preconditioning or sham surgery. Three days after ischemia, gerbils were placed in either an enriched environment or standard laboratory housing. Open field habituation was assessed 3, 7, 10, 30 and 60 days after ischemia. Subsequently, animals were trained in two versions (win-shift and win-stay) of a T-maze task. Following behavioral testing, extracellular CA1 field potential amplitudes and CA1 cell counts were determined. Initial open field activity was significantly higher in all experimental groups compared to sham animals (P<0.001). By 60 days, enriched ischemic preconditioned and enriched ischemic gerbils were not different than shams whereas non-enriched, ischemic preconditioned and ischemic gerbils continued to have higher activity scores (P<0.05). Preconditioned and enriched ischemic animals learned the win-shift T-maze problem as quickly as shams while non-enriched ischemic gerbils were severely impaired compared with all other groups (P<0.001). Only the sham and enriched preconditioned groups readily acquired the win-stay paradigm. CA1 field potential amplitudes were lower (P<0.05) in ischemic than sham gerbils irrespective of treatment. Surprisingly, CA1 cell counts were significantly lower (P<0.01) in enriched versus non-enriched ischemic preconditioned animals. These data demonstrate that early, intensive intervention after ischemia can improve functional outcome but that this is accompanied by increased brain damage. Careful consideration needs to be given to the timing of rehabilitation after stroke and related types of brain injury.

A functional MRI study of three motor tasks in the evaluation of stroke recovery

Functional brain imaging studies have provided insights into the processes related to motor recovery after stroke. The comparative value of different motor activation tasks for probing these processes has received limited study. We hypothesized that different hand motor tasks would activate the brain differently in controls, and that this would affect control-patient comparisons. Functional magnetic resonance imaging (MRI) was used to evaluate nine control subjects and seven patients with good recovery after a left hemisphere hemiparetic stroke. The volume of activated brain in bilateral sensorimotor cortex and four other motor regions was compared during each of three tasks performed by the right hand: index-finger tapping, four-finger tapping, and squeezing. In control subjects, activation in left sensorimotor cortex was found to be significantly larger during squeezing as compared with index-finger tapping. When comparing control subjects with stroke patients, patients showed a larger volume of activation in right sensorimotor cortex during index-finger tapping but not with four-finger tapping or squeezing. In addition, patients also showed a trend toward larger activation volume than controls within left supplementary motor area during index-finger tapping but not during the other tasks. Motion artifact was more common with squeezing than with the tapping tasks. The choice of hand motor tasks used during brain mapping can influence findings in control subjects as well as the differences identified between controls and stroke patients. The results may be useful for future studies of motor recovery after stroke.

Cortical plasticity and the development of behavior after early frontal cortical injury

It has been known for over 100 years that frontal lobe injury in children is often associated with considerably more functional recovery than after similar injury in adulthood. Systematic study of frontal cortical injury in laboratory animals has shown that this recovery is tightly tied to developmental age: There is a brief window of time during cortical development during which the brain is able to compensate. Simply being young is not sufficient because injury prior to this critical period leads to miserable behavioral outcomes. For humans, the least favorable time for cortical injury is likely at the end of the gestational period, perhaps including the 1st month or so of life whereas the most favorable time is around 1 to 2 years of age. In addition to age, the extent of behavioral recovery is influenced by age at assessment, the nature of the behavioral assessment, sex, and lesion size. Anatomical studies have shown that functional recovery following early cortical injury is correlated with a reorganization of remaining cortical circuitry, including increased dendritic arborization and increased spine density. Recovery, and the compensatory anatomical changes, can also be potentiated by application of different treatments including behavioral therapy, trophic factors, and neuromodulators. Finally, there is preliminary evidence in laboratory animals to suggest that it may be possible to induce neural regeneration in the injured brain and that the regenerated brain functions to support functional recovery.

Ectopic noradrenergic hyperinnervation does not functionally compensate for neonatal forebrain acetylcholine lesion

Adult rats who have undergone neonatal 192 IgG-saporin induced lesions of forebrain acetylcholine (ACH) neurons are normal on many behavioral tasks. In this study we determined whether ectopic hippocampal ingrowths, a documented consequence of these neonatal cholinergic lesions, functionally compensate for ACH denervation in these rats. Neonatal rats underwent systemic 6-hydroxydopamine (6-OHDA) injections on postnatal days (PND) 1-3 to prevent the ingrowths, and/or intraventricular 192 IgG-saporin injections on PND 7. The 192 IgG-saporin profoundly reduced basal forebrain p75 neurotrophin receptor (p75(NTR)) immunoreactive (IR) neurons. The 6-OHDA treatment abolished hippocampal and cortical dopamine-beta-hydroxylase (DBH) IR terminals, indicating the absence of normal norepinephrine (NE) innervation. Ectopic DBH IR and p75(NTR) IR varicosities which occurred in the hippocampus of 192 IgG-saporin treated rats were also eliminated by 6-OHDA treatment. Behavioral testing in adulthood indicated no effect of the treatments on the Morris water maze. 192 IgG-saporin treatment caused perseveration during delayed spatial alternation (DSA) and increased working but not reference memory errors on the radial arm maze (RAM). The 6-OHDA plus 192 IgG-saporin treated rats did not differ from the 192 IgG-saporin only rats on any task. These results indicate that ectopic hippocampal NE ingrowths do not functionally compensate for neonatal ACH lesions. Neonatal forebrain ACH lesion impairs working memory on the RAM but the absence of an effect on DSA contraindicates a basic dysfunction of short term memory. Despite severe combined neonatal loss of forebrain ACH and NE innervation, behavior is remarkably intact.

Enhanced nucleus accumbens dopamine and plasma corticosterone stress responses in adult rats with neonatal excitotoxic lesions to the medial prefrontal cortex

The medial prefrontal cortex modulates the nucleus accumbens dopamine response to stress and has been implicated in feedback regulation of hypothalamic-pituitary-adrenal axis activation by stress. Here we report on the effects of bilateral neonatal (postnatal day 7) ibotenate-induced lesions to the medial prefrontal cortex on nucleus accumbens dopamine and neuroendocrine function in adult rats. Voltammetry was used to monitor the dopamine response to each of five, once-daily exposures to tail-pinch stress whereas alterations in neuroendocrine function were determined from the plasma corticosterone response to a single 20-min episode of restraint stress. Potential lesion-induced deficits in sensory-motor gating were assessed by measuring prepulse inhibition of the acoustic startle response before and after repeated stress. Our data show that each daily stress episode elicited larger and longer-lasting dopamine increases in prefrontal cortex-lesioned animals than in sham-lesioned controls. Furthermore, greater stress-induced elevations in plasma corticosterone were seen in lesioned animals than in their sham-lesioned counterparts. However, while repeated stress potentiated startle responses in animals of both groups, there was no effect of lesion on the amplitude or on prepulse inhibition of the startle response.Together, these findings indicate that neonatal prefrontal cortex damage can lead to changes in mesolimbic dopamine and neuroendocrine function during adulthood. They also add to a growing body of experimental and clinical evidence implicating abnormal prefrontal cortex neuronal development in the pathophysiology of schizophrenia and other disorders linked to central dopamine dysfunction.

Ovariectomy of adult rats leads to increased expression of astrocytic basic fibroblast growth factor in the ventral tegmental area and in dopaminergic projection regions of the entorhinal and prefrontal cortex

Changes in astrocytic function may underlie the neurochemical and morphological alterations in limbic and cortical areas after estrogen loss in adult females. We assessed whether increased expression of basic fibroblast growth factor (bFGF), an astrocytic response involved in injury-induced neuronal plasticity, occurs after ovariectomy. We examined bFGF immunoreactivity (IR) in ovariectomized rats with oil or estradiol benzoate (5 microgram every 4 d; Experiment 1) and in ovariectomized and intact animals (Experiment 2). In the ventral tegmental area (VTA), bFGF-IR and glial fibrillary acidic protein (GFAP)-IR were greater in ovariectomized animals than in animals with estrogen replacement. bFGF-IR in the VTA was greater in ovariectomized than in intact females. In the dorsal raphe, no differences between groups were found in GFAP-IR or bFGF-IR. In mesolimbic dopaminergic target areas within entorhinal cortex (Ent), prefrontal cortex, and nucleus accumbens, bFGF-IR was higher in Ent of ovariectomized animals 4 weeks after surgery in both experiments, but no differences were seen in nucleus accumbens or in an occipital cortical, control, area in either study. In Experiment 2, small increases in bFGF-IR were seen in the prefrontal cortex after ovariectomy. In the VTA and Ent, changes in bFGF-IR developed gradually, peaking at 4 weeks and waning at 40 weeks. Furthermore, increased dendritic arbor of Ent layer II/III pyramidal cells was found in ovariectomized females with the use of a modified Golgi-Cox staining procedure. These findings suggest that, within specific regions, ovariectomy induces astrocytic responses similar to those observed after injury that may affect neuronal chemistry and morphology.

Synaptic plasticity in cortical systems

Recent studies indicate that synapse addition and/or loss is associated with different types of learning. Other factors influencing synaptogenesis and synapse loss include neurotrophins, hormones, and the induction of long-term potentiation. An emerging view of synaptic plasticity suggests that local neurotrophin action and synaptically associated protein synthesis may promote synaptic remodelling and changes in receptor expression or activation.

Lesion-induced plasticity as a potential mechanism for recovery and rehabilitative training

Brain lesions not only cause a functional deficit in the lesion area, but also affect the structurally intact brain network connected to the lesion. In brain areas surrounding the lesion, as well as those remote from it, the structural and functional plasticity of the brain is increased because of an alteration of transmitter receptor expression and membrane properties of neurones. Within the penumbra of brain ischaemia, as well as after trauma, an additional perilesional dysfunctional zone is found that contributes to the neurological deficit. The lesion-induced plasticity can be used for adaptation, which also may restore function in the perilesional zone, if adequate rehabilitative training is performed.