Neuron-Radial Glial Cell Communication via BMP/Id1 Signaling Is Key to Long-Term Maintenance of the Regenerative Capacity of the Adult Zebrafish Telencephalon

The central nervous system of adult zebrafish displays an extraordinary neurogenic and regenerative capacity. In the zebrafish adult brain, this regenerative capacity relies on neural stem cells (NSCs) and the careful management of the NSC pool. However, the mechanisms controlling NSC pool maintenance are not yet fully understood. Recently, Bone Morphogenetic Proteins (BMPs) and their downstream effector Id1 (Inhibitor of differentiation 1) were suggested to act as key players in NSC maintenance under constitutive and regenerative conditions. Here, we further investigated the role of BMP/Id1 signaling in these processes, using different genetic and pharmacological approaches. Our data show that BMPs are mainly expressed by neurons in the adult telencephalon, while id1 is expressed in NSCs, suggesting a neuron-NSC communication via the BMP/Id1 signaling axis. Furthermore, manipulation of BMP signaling by conditionally inducing or repressing BMP signaling via heat-shock, lead to an increase or a decrease of id1 expression in the NSCs, respectively. Induction of id1 was followed by an increase in the number of quiescent NSCs, while knocking down id1 expression caused an increase in NSC proliferation. In agreement, genetic ablation of id1 function lead to increased proliferation of NSCs, followed by depletion of the stem cell pool with concomitant failure to heal injuries in repeatedly injured mutant telencephala. Moreover, pharmacological inhibition of BMP and Notch signaling suggests that the two signaling systems cooperate and converge onto the transcriptional regulator her4.1. Interestingly, brain injury lead to a depletion of NSCs in animals lacking BMP/Id1 signaling despite an intact Notch pathway. Taken together, our data demonstrate how neurons feedback on NSC proliferation and that BMP1/Id1 signaling acts as a safeguard of the NSC pool under regenerative conditions.

HVC microlesions do not destabilize the vocal patterns of adult male zebra finches with prior ablation of LMAN

The songs of adult male zebra finches (Taeniopygia guttata) arise by an integration of activity from two neural pathways that emanate from the telencephalic nucleus HVC (proper name). One pathway descends directly from HVC to the vocal premotor nucleus RA (the robust nucleus of the arcopallium) whereas a second pathway descends from HVC into a basal ganglia circuit (the anterior forebrain pathway, AFP) that also terminates in RA. Although HVC neurons that project directly to RA outnumber those that contribute to the AFP, both populations are distributed throughout HVC. Thus, partial ablation (microlesion) of HVC should damage both pathways in a proportional manner. We report here that bilateral HVC microlesions in adult male zebra finches produce an immediate loss of song stereotypy from which birds recover, in some cases within 3 days. The contribution of the AFP to the onset of song destabilization was tested by ablating the output nucleus of this circuit (LMAN, the lateral magnocellular nucleus of the anterior nidopallium) prior to bilateral HVC microlesions. Song stereotypy was largely unaffected. Together, our findings suggest that adult vocal production involves nonproportional integration of two streams of neural activity with opposing effects on song--HVC's direct projection to RA underlies production of stereotyped song whereas the AFP seems to facilitate vocal variation. However, the rapid recovery of song in birds with HVC microlesions alone suggests the presence of dynamic corrective mechanisms that favor vocal stereotypy.

A study on mRNA expressions of fibronectin in dermal and cerebral wound healing for wound age estimation

We investigated mRNA expressions of fibronectin for wound age estimation during dermal and cerebral wound healing. Fibronectin mRNA expressions in the injured skin peaked at 8h post-injury. The expressions were detected in endothelial cells before and after injury, whereas they were detectable in the epidermal cells at 1-240 h, in fibroblasts at 1-72 h, in neutrophils and macrophages at 8-72 h, respectively. However, the expressions in epidermal cells became relatively weak in the subacute phase. Fibronectin mRNA expressions of the injured cerebrum increased after the intervention and peaked at 48 h, whereas there was a slight decrease during 24h post-injury. Although fibronectin mRNA was seen exclusively in the endothelial cells of the intact cerebrum, it was also detected in astrocytes during wound healing. From these findings, it was considered that fibronectin played an important role in dermal and cerebral wound healing. Expression of fibronectin mRNA was considered to indicate the acute phase of dermal wound healing, and the subacute phase of cerebral wound healing.

Orbito-cerebral penetrating knife-wound

An orbit-cerebral knife wound is described. Reasons for variation in outcome art discussed.

Spatial learning deficits after the development of dorsomedial telencephalon lesions in goldfish

The effects of lesions in the dorsal area of the caudal telencephalon (Carassius auratus) on the retention of spatial learning in goldfish were examined. The experimental paradigm was similar to the dry version of the Morris water maze for rodents. After being trained to reach a criterion, goldfish underwent surgery and were then retrained. In the retraining, dorsomedial lesions resulted in poor performance, while dorsolateral lesions did not. In a landmark task in which a small circular colored cue was set at a food location, dorsomedial lesions did not produce impairment during retraining. These results suggest that dorsomedial lesions selectively caused impairment in the retention of spatial learning.

The effects of L-arginine on cerebral hemodynamics after controlled cortical impact injury in the mouse

Traumatic brain injury (TBI) induces vascular changes that may influence neurological outcome by causing the brain to be more susceptible to secondary ischemic insults. In rat models of TBI, L-arginine administration has been shown to restore cerebral blood flow and improve neurological outcome. The purpose of this study was to determine if hypoperfusion occurs in a mouse model of TBI and if L-arginine administration has the same beneficial effects after injury in the mouse. C57BL6 mice were anesthetized with isoflurane, intubated and mechanically ventilated, and underwent a 3-m/sec, 1.5-mm deformation cortical impact injury. Five minutes after injury, L-arginine, 300 mg/kg, or saline were administered. Arterial blood pressure, intracranial pressure, and laser Doppler flow at the impact site were monitored for 3 h after the injury. The cerebral hemodynamic effects of the TBI induced by cortical impact injury were similar to that previously observed in rats. Intracranial hypertension, with ICP peaking at 46+/-2 mm Hg, and systemic hypotension both contributed to a reduction in CPP. In addition, LDF decreased significantly at the impact site. L-Arginine administration restored LDF to near baseline levels without increasing ICP. These studies demonstrate that cerebral hemodynamics can be measured in mouse models of TBI. The changes in cerebral hemodynamics are relatively simlar to those see in the rat model of cortical impact injury and suggest an important role for nitric oxide metabolism in the maintenance of cerebral blood flow following TBI.

The blood-brain barrier and cerebral angiogenesis: lessons from the cold-injury model

Brain injury is associated with an initial blood-brain barrier (BBB) breakdown, which can be life threatening. A second phase of BBB breakdown accompanies the angiogenesis occurring at the lesion margins. Studies of the molecular mechanisms involved in these processes are essential to determine targets for therapeutic intervention, as well as the time periods during which therapeutic intervention could ameliorate brain damage and thus improve the clinical outcome.

Effects of hypothermia on neonatal hypoxic-ischemic brain injury in the rat: phosphorylation of Akt, activation of caspase-3-like protease

Neuroprotective mechanisms of hypothermia have not been clearly established especially in the immature brain. To investigate the effect of hypothermia on cell death and cell survival signal pathways, we studied caspase-3-like activity and activation of Akt in a rat model of neonatal hypoxic-ischemic (H-I) brain injury. Seven-day-old rats underwent a combination of left common carotid artery ligation and exposure to 8% O(2) for 1-h (n=32). During recovery, the body temperature was reduced to 30 degrees C for 24 h in 16 animals, but was kept at 37 degrees C in 16 animals. Post-ischemic hypothermia was shown to diminish the caspase-3-like activity compared to normothermia at 6 and 24 h after H-I. Phospho-Akt was increased during the early reperfusion period after H-I in the normothermia group, but hypothermia rather decreased this enhanced phosphorylation of Akt following H-I. These results indicated that hypothermia may have some depressant effects on both cell death and cell survival signal pathways, and that Akt conceivably may not play a major role in the neuroprotective effect of hypothermia in the immature brain.

Association of immune responses and ischemic brain infarction in rat

Inflammation plays an important role in the pathogenesis of neurodegenerative diseases including ischemia. Occlusion of common carotid artery and middle cerebral artery has been used to produce focal ischemic lesions in the rat. Here, we examined the associations between immune reactions and postischemic brain infarction. Ischemia/reperfusion time-dependently caused brain infarction. The kinetics of inflammatory reactions in rat brain including inflammatory cell infiltration, edema formation, cytokines/chemokines and adhesion molecules production and matrix metalloproteinase activation were relevant to the progression of ischemic infarction. Differential induction profile after ischemia suggests that this activation might contribute to secondary brain damage in ischemic tissues. On the other hand, another possibility of this response is to trigger processes that mediate the neural regeneration after ischemic injury.

Protein S-100B: a serum marker for ischemic and infectious injury of cerebral tissue

The S-100B protein is released by injured astrocytes. After passage through a disintegrated blood-brain barrier (BBB) the molecule can be detected in the peripheral circulation. We investigated the association between the extent of brain injury and S-100B concentration in serum in cerebral injury caused by cerebral ischemia and cerebral fungal infection. Study I: The S-100B serum concentration was serially determined in 24 patients with ischemic stroke at 4, 8, 10, 24, 72 hours after the onset of symptoms. We observed that patients with brain lesions larger than 5 cm3 exhibited significantly increased serum levels of S-100B at 10, 24 and 72 hours compared to those with lesion volumes below 5 cm3. Furthermore, an association between S-100B serum concentration and neurological outcome was observed. Study II: In a mouse model of systemic fungal infection with Candida albicans we observed that serum levels of S-100B increased at day 1 after intravenous infection. At this time we could histologically demonstrate brain tissue injury by invading hyphae which had crossed the BBB. Furthermore, reactive astrogliosis was demonstrated by immunohistochemistry. On day 7 we found a significant decrease of S-100B serum level compared to day 1 and 4. This was associated with a demarcation of the fungi with leukocytes in brain tissue at this late phase of infection. No further invasion through the BBB was seen on day 7. In conclusion, serum levels of S-100B reflect the time course of tissue injury in cerebral ischemia and cerebral infection to a similar extent. Thus, S-100B may be a useful marker to assess cerebral tissue injury.

Cerebral white matter damage in the preterm infant: pathophysiology and risk factors

Based on clinical, epidemiologic, and experimental studies, the aetiology of white matter damage, specifically periventricular leukomalacia (PVL), is multifactorial and involves pre- and perinatal factors possibly including genetic factors, hypoxic-ischaemic insults, infection, excess cytokines, free radical production, increased excitatory amino acid release, and trophic factor deficiencies. The article summarizes research findings about the aetiology of white matter damage and cerebral palsy in preterm infants. The information is organized according to specific antecedents, for which we present epidemiological and neurobiological data. The most important prenatal factor appears to be intrauterine infection. We discuss the evidence supporting the hypothesis that the foetal inflammatory response contributes to neonatal brain injury and later developmental disability. We recently established an animal model of excitotoxic lesions in the developing mouse brain. Brain damage was induced by intra-cortical injections of ibotenate, a glutamatergic agonist. When administered on post-natal day 5 ibotenate induced the formation of white matter cysts. Our animal model could be used to further explore the mechanisms involved in the formation of PVL. Potentially preventive strategies will be discussed.

The effects of telencephalic lesions on visually mediated prey orienting behavior in the leopard frog (Rana pipiens). I. The effects of complete removal of one telencephalic lobe, with a comparison to the effects of unilateral tectal lobe lesions

In this paper, we report studies aimed at characterizing the relationship between forebrain and midbrain systems involved in the control of prey orienting behavior in the leopard frog. In frogs, unilateral forebrain lesions, like unilateral tectal lobe lesions, have their most prominent effects in the contralateral monocular visual field. Such lesions produce partial reductions in response frequency in the binocular visual field as well. Similar sequelae follow unilateral tectal lobe removal. These findings suggest that the effects of unilateral forebrain removal can be largely attributed to removal of a facilitating influence on the tectal lobe on the same side of the brain. In the case of both forebrain and midbrain lesions, behavior was assayed not only in terms of the frequency with which animals responded to stimuli at various locations in the visual field (as is usually done) but also in terms of the latency of whatever responses were observed. A striking inverse relationship between response frequency and response latency was found, both in lesioned and in normal frogs. This relationship has not previously been noticed, doesn't appear to be an obvious consequence of any existing models of the neuronal circuitry underlying anuran orienting behavior, and is difficult to account for in terms of the time scales associated with axonal conduction times and synaptic delays. It may be easier to account for in terms of the responses to perturbation of large interacting systems of neurons, and this possibility seems worthy of further exploration.

The effects of telencephalic lesions on visually mediated prey orienting behavior in the leopard frog (Rana pipiens). II. The effects of limited lesions to the telencephalon

Unilateral removal of the telencephalon in the leopard frog, Rana pipiens, produces a contralateral deficit in visual prey orienting behavior [Patton and Grobstein, 1997]. In mammals, such deficits are most commonly associated with damage to the isocortex, a pallial derived structure. In contrast, we here report that in leopard frogs, lesions that remove substantial areas of one telencephalic lobe, including virtually the entire pallium, have no discernible effect on visual orienting behavior. Restricted lesions to the ventrocaudal telencephalon, however, produce an effect that closely resembles that produced by the complete removal of one telencephalic lobe. The 'critical area' that is both included in all lesions that are effective in producing a severe deficit and excluded from all ineffective lesions includes a portion of the caudal striatum. The striatum is known to play a significant role in anuran vision. It thus seems likely that the deficit produced by unilateral removal of the telencephalon in the leopard frog is due specifically to the removal of the caudal striatum. Unilateral lesions to the striatum have previously been shown to produce a contralateral deficit in visual orienting behavior in cats, and a role for the striatonigral pathway in the production of the visual orienting deficit that follows visual cortex lesions has been proposed. The current findings call attention to the possible general importance of the striatum in the control of vertebrate visual orienting behaviors.

The studies on neurogenesis induced by brain injury in adult ring dove

It was the first time demonstrated by us that the number of newborn neurons was increased after making lesion in forebrain of adult ring dove (Streptopelia risoria) by means of autoradiography and immunohistochemistry. Neurogenesis in the adult avian is restricted to the telencephalon. In doves with bilateral electrolytic lesion of nucleus ectostriatum (E), the mean number of proliferating cells in the lateral ventricular zone (LVZ) and newborn neurons in the forebrain increased by 1.95 times and 2.38 times respectively as compared with that in intact doves. The most remarkable increase of neurogenesis induced by nucleus ectostriatum lesions was found at the anterior-posterior level 3 (L3), where the lesion site was located. These results showed that the electrolytic brain lesion altered the distribution pattern of proliferating cells in the LVZ and resulted in increase of the number of newborn neurons in the non-VZ areas of forebrain. The changes in number and distribution pattern of proliferating cells in LVZ and newborn neurons in forebrain may be dependent on site of lesion. Studies on the relationship between proliferating cells in LVZ and newly generated neurons in non-VZ areas may help to understand the mechanism of brain plasticity and development.

[Significance of magnetic resonance imaging in diffuse axonal injury]

Advantages of magnetic resonance imaging (MRI) to computed tomography (CT) on a diagnosis of diffuse axonal injury (DAI) were discussed. Sixteen patients diagnosed as DAI defined by the criteria of Gennarelli were studied with CT and MRI. Lesions were demonstrated as high intensity areas on MRI of T2 weighted imaging (SE 2000/111) in all of the patients. These lesions were located only in a cerebral white matter in the cases of mild DAI, whereas in the cases of severe DAI located in a basal ganglia, corpus callosum, dorsal part of the brain stem as well as in the cerebral white matter. As for the findings of CT, these parenchymal lesions were not visualized in nine cases including six cases without any pathological findings. Our series suggest that MRI is superior to CT on the diagnosis of DAI and provides some information to evaluate the severity of DAI.

Reorganization of pericruciate cortical projections to the spinal cord and dorsal column nuclei after neonatal or adult cerebral hemispherectomy in cats

This is a quantitative study of changes in distribution and density of terminals of the corticospinal tract in the cervical spinal cord and dorsal column nuclei (DCN) in cats with left cerebral hemispherectomy performed neonatally or in adulthood. Kittens received hemispherectomy at a mean of 12.1 postnatal days and were compared, as adults, to adult-lesioned cats of similar survival time. All animals, including controls, received injections of [3H]leucine-proline and were sacrificed 5 days later. Injection sites and terminal fields were reconstructed from autoradiography-processed tissue. The label filled comparable extents of areas 4 gamma and 3a of the right cerebral cortex. Coronal sections from upper and lower cervical cord levels, and from the brainstem (cuneate and gracile nuclei) were studied. Computer-image processing procedures were used to count labeled particles from multiple sites of the dorsal horn and DCN, bilaterally. In the spinal cord of intact and adult-hemispherectomized cats, most terminals were found in lamina VI, and adjacent laminae V and VII contralateral to the injection side. The major finding was that neonatal-lesioned cats showed a significant increase in axon terminals in areas ipsilateral to the injection. The topography of distribution of the novel terminals was similar to that in the contralateral side and the originating fibers appeared to have crossed the midline from that side. A similar reorganization occurred in the gracile nucleus where, in intact and adult-lesioned cats, the cortical terminals also predominated in the side contralateral to the injection. In contrast, neonatal-lesioned animals showed a significant increase in terminal density ipsilateral to the cortical injection. These findings are discussed as an alternative mechanism for postlesion remodeling of the corticospinal tract in animals with the pyramidal crossing completed at the time of birth.

[Surgical tactics in contusions of the cerebral hemispheres]

The author conducted complex examination of 540 patients who were operated on for brain contusion. Comparison of the clinical and instrumental findings with the pathomorphological changes in the brain (disclosed during operation or autopsy) revealed the structural features of contusion foci of convex and pole-basal localization which were factors underlying the three-dimensional enlargement of the affected brain lobe in cases of increasing perifocal edema. The results of surgical management were analysed according to the character of the contusion foci, the extent of traumatic softening of the white matter in the zone of the contusion, and the volume of surgical debridement of the foci. It is concluded that decompression of the brain can be accomplished by removing massive convex and pole-basal contusion foci penetrating the deep layers of the cerebral hemispheres; the volume of surgical debridement of contusion foci is determined by their macrostructure and the size of the zone of white matter softening.

Recovery of function after neonatal or adult hemispherectomy in cats: I. Time course, movement, posture and sensorimotor tests

Cats with removal of the left hemitelencephalon (hemispherectomy) as neonates (n = 12) or in adulthood (n = 14), were compared using a battery of 16 neurological and behavioral tests given when they were young adults (kittens) or at least 5 months after the lesion (adults). The neonatal-lesioned subjects grew normally and performed markedly and significantly better than adult-lesioned cats in 13 tests covering the wide range of movement, posture and sensory functions which were assessed. None of the animals recovered tactile placing of the right forelimb or a normal vision in the right visual field. However, the overall recovery was outstanding for all cats such that the neonatal-lesioned were hard to differentiate from intact controls in their spontaneous, daily activities. Because the lesions were similar in the two age-at-lesion groups, and since numerous functions were followed for prolonged, comparable postlesion time, we conclude that, after hemispherectomy in the cat, there definitely is greater functional recovery if the lesion is sustained early in life. We propose that the enhanced recovery of function in neonatal-lesioned cats is largely due to the extensive anatomical reorganization which we have demonstrated in ongoing studies, and which contrasts with a lesser remodeling in adult-lesioned cats.

Computed tomography in child abuse and cerebral contusion

Cerebral contusion is considered to be the lesion leading to neurological sequelae of mental retardation and cerebral palsy in abused children. This has been difficult to document other than at autopsy or craniotomy by previously available techniques. Acute contusion or hemorrhage presumably secondary to contusion is readily documented by computed tomography (CT). We are reporting the cases of four children with alleged or suspected abuse and CT evidence of cerebral contusion. The contusion has been found both with and without external evidence of head injury.