bluuebunny/crossref_metadata_2025 huggingface dataset:
The supramammillary nucleus contributes to associative EPSP‐spike potentiation in the rat dentate gyrus in vivo
Authors: Nakanishi Kosuke , Saito Hiroshi , Abe Kazuho
Published: March 2003

The supramammillary nucleus (SUM) of the hypothalamus sends neural projections to the hippocampus and is supposed to be involved in learning and memory. To test the possibility that SUM afferents modulate hippocampal functions, we investigated the effect of electrical stimulation of the SUM on the induction of long‐term potentiation (LTP) at medial perforant path (PP)–granule cell synapses in the dentate gyrus (DG) of anaesthetized rats. High‐frequency stimulation of the SUM (100 pulses at 100 Hz) alone did not change PP–DG field potentials. However, when the SUM stimulation was applied simultaneously with weak tetanic stimulation of the PP (20 pulses at 20 Hz) which alone did not induce any potentiation, it produced a long‐lasting potentiation of the population spike, without an accompanying increase in the population excitatory postsynaptic potential (EPSP). The EPSP‐spike (E‐S) potentiation induced by pairing SUM and PP stimulation was abolished by lesions of the fimbria–fornix, a major pathway of SUM afferents. SUM stimulation applied 1 s before or after PP stimulation failed to produce E‐S potentiation, and SUM stimulation augmented PP–DG field potentials during tetanic stimulation. Furthermore, the E‐S potentiation was abolished by blocking GABAergic neurotransmission with picrotoxin. These results suggest that coactivation of SUM and PP inputs produces a long‐lasting increase of granule cell excitability by modulating GABAergic inhibition. SUM afferents may contribute to associative memory processing by modulating hippocampal excitability.
Role of GAP‐43 in mediating the responsiveness of cerebellar and precerebellar neurons to axotomy
Authors: Wehrlé Rosine , Caroni Pico , Sotelo Constantino , Dusart Isabelle
Published: March 2003

To determine whether the competence for axonal sprouting and/or regeneration in the cerebellar system correlates with GAP‐43 expression, we have studied GAP‐43 mRNA and protein expression in the postlesioned cerebellum and inferior olive. Purkinje cells transiently express GAP‐43 during their developmental phase (from E15 to P5 in the rat) which consists of fast axonal growth and the formation of the corticonuclear projection. Adult Purkinje cells, which in control adult rats do not express GAP‐43, are extremely resistant to the effects of axotomy but cannot regenerate axons. However, a late and protracted sprouting of axotomized Purkinje cells occurs spontaneously and correlates with a mild expression of GAP‐43 mRNA. In contrast, inferior olivary neurons, despite their high constitutive expression of GAP‐43, do not sprout but retract their axons and die after axotomy. Furthermore, mature Purkinje cells in cerebellar explants of transgenic mice that overexpress GAP‐43 do not regenerate after axotomy, even in the presence of a permissive substrate (cerebellar embryonic tissue) and, contrary to the case in wild‐type mice, they do not survive in the in vitro conditions and undergo massive cell death. These results show that the expression of GAP‐43 is not only associated with axonal growth, but also with neuronal death.
The D2 receptor is critical in mediating opiate motivation only in opiate‐dependent and withdrawn mice
Authors: Dockstader Colleen L. , Rubinstein Marcelo , Grandy David K. , Low Malcolm J. , Van Der Kooy Derek
Published: March 2003

According to the dual systems model for opiate reward, dopamine mediates opiate motivation when an animal is in a deprived motivational state (i.e. opiate‐dependent and in withdrawal) and not when an animal is in a nondeprived state (i.e. previously drug‐naive). To determine the role of the D2 dopamine receptor subtype in mediating opiate motivation, we examined the behaviour of N5 congenic D2 receptor knockout mice and their wild‐type siblings in opiate‐naive and opiate‐dependent and withdrawn place conditioning paradigms. Opiate‐naive D2 receptor knockout mice demonstrated acquisition of morphine‐conditioned place preference but failed to acquire place preference when conditioned in the deprived state. We propose that D2 receptor function is critical in mediating the motivational effects of opiates only when the animal is in an opiate‐dependent and withdrawn motivational state. These findings also underscore the important influence of the genetic background to a given phenotype, as evidenced by the observation that increasing the allelic contribution from the 129/SvJ strain abolishes morphine place preference in C57BL/6 wild‐type mice.
GABAA receptors in the ventral tegmental area control bidirectional reward signalling between dopaminergic and non‐dopaminergic neural motivational systems
Authors: Laviolette Steven R. , Van Der Kooy Derek
Published: March 2003

In the midbrain ventral tegmental area (VTA), both dopaminergic and nondopaminergic neural substrates mediate various behavioural reward phenomena. VTA GABAergic neurons are anatomically positioned to influence the activity of both the mesolimbic dopamine system and nondopamine efferents from the VTA. In order to examine the possible functional role of VTA GABAA receptors in neural reward processes, we performed discrete, bilateral microinjections of the GABAA receptor agonist, muscimol, or the GABAA receptor antagonist, bicuculline, into the VTA. Using a fully counterbalanced, unbiased conditioned place‐preference paradigm, we demonstrate that activation of VTA GABAA receptors, with the GABAA receptor agonist muscimol (5–50 ng/µL), or inhibition of VTA GABAA receptors, with the GABAA receptor antagonist bicuculline (5–50 ng/µL), both produce robust rewarding effects. Furthermore, these rewarding effects can be pharmacologically dissociated: blockade of dopamine receptors with a dopamine receptor antagonist, α‐flupenthixol (0.8 mg/kg; i.p.), or concurrent activation of VTA GABAB receptors with a GABAB receptor agonist, baclofen (70 ng/µL), blocked the rewarding properties of the GABAA receptor agonist, but had no effect on the rewarding properties of the GABAA receptor antagonist. These results suggest that, within the VTA, a single GABAA receptor substrate controls bidirectional reward signalling between dopaminergic and nondopaminergic brain reward systems.
P2Y receptor‐mediated inhibition of voltage‐activated Ca2+ currents in PC12 cells
Authors: Vartian Nina , Boehm Stefan
Published: March 2003

To search for inhibitory nucleotide receptors in the sympathoadrenal cell lineage of the rat, voltage‐activated Ca2+ currents were recorded in PC12 cells after differentiation with nerve growth factor. ADP and ATP, but not uridine nucleotides, reduced Ca2+ current amplitudes and slowed activation kinetics. This effect was mediated by GTP binding proteins, as it was abolished by intracellular GDPβS and after treatment with pertussis toxin. Furthermore, depolarizations preceding the activation of Ca2+ currents abolished the ADP‐induced slowing of activation kinetics and attenuated its inhibitory action on current amplitudes. The modulatory effect of ADP was neither altered in the presence of adenosine receptor antagonists, nor mimicked by agonists at these receptors. In addition, the action of ADP was antagonized by reactive blue 2, but not by suramin or PPADS. Nucleotides tested for their inhibitory action on Ca2+ currents displayed the following rank order of potency: 2‐methylthio‐ADP ≥ 2‐methylthio‐ATP >> ADPβS > ADP = ATP. When P2X receptors were blocked, the P2X agonists ATP and 2‐methylthio‐ATP still reduced Ca2+ currents. The P2Y1 receptor antagonists adenosine‐2’‐phosphate‐5’‐phosphate and adenosine‐3’‐phosphate‐5’‐phosphate did not alter the inhibitory action of ADP, whereas the Sp‐isomer of adenosine‐5’‐O‐(1‐thiotriphosphate) and 2’‐ and 3’‐O‐(4‐benzoylbenzoyl)‐ATP showed significant antagonistic activity. These results demonstrate that PC12 cells express an as yet unidentified P2Y receptor with pharmacological characteristics similar to those of P2Y1. As receptor‐dependent modulation of Ca2+ channels is a key event in presynaptic inhibition, this receptor may correspond to previously described presynaptic nucleotide receptors mediating autoinhibition of sympathetic transmitter release.
Adrenoreceptor‐mediated modulation of the spinal locomotor pattern during swimming in Xenopus laevis tadpoles
Authors: Fischer Hanno , Merrywest Simon D. , Sillar Keith T.
Published: March 2003

This study focused on the contribution of different adrenoreceptor subtypes to the modulation of fictive swimming activity in a relatively simple, yet intact, lower vertebrate system, the immobilized Xenopus laevis tadpole and explored their possible role in mediating the noradrenergic modulation of spinal motor networks. In Xenopus embryos, near the time of hatching, activation of α1 adrenoreceptors increased the duration of episodes of fictive swimming, whilst in larvae, 24 h after hatching, they were decreased. Activation of α2 adrenoreceptors, however, markedly reduced episode duration at both developmental stages. Cycle periods in both stages were increased by the activation of α1 and/or α2 receptor subclasses, whereas β adrenoreceptors were not apparently involved in the modulation of cycle periods or the duration of swim episodes. However, both β and α1 receptor activation decreased the intersegmental delay in the head‐to‐tail propagation of swimming activity, while α2 receptors did not influence these rostro‐caudal delays. Activation of neither α, nor β, receptor subclasses had any consistent effect on the duration of ventral motor bursts. Our findings suggest that noradrenergic modulation of the swim‐pattern generator in Xenopus tadpoles is mediated through the activation of α and β adrenoreceptors. In addition, activation of particular receptor subclasses might enable the selective modulation of either the segmental rhythm generating networks, the intersegmental coordination of those networks or control at both levels simultaneously.
Photoreceptor plasticity in reaggregates of embryonic chick retina: rods depend on proximal cones and on tissue organization
Authors: Rothermel Andrée , Layer Paul G.
Published: March 2003

Plasticity of photoreceptors and their integration into epithelial structures homologous to an outer nuclear layer (ONL), was investigated in embryonic chick retinal cell reaggregates by immunohistochemistry using an antibody specific for red plus green cones (RG‐cones) and an antibody for rods. If reaggregates are raised in the presence of pigmented epithelium (RPE), completely reconstructed, stratified retinal spheres are produced, where all rods and cones are integrated into an outer laminar ONL, similar to a normal retina. In the absence of RPE, ‘rosetted’ spheres form which contain internal rosettes homologous to an ONL. Only a minor fraction of cones and rods of ‘rosetted’ spheres are located within rosettes, while a larger fraction is diffusely displaced in nonorganized areas, thus, not contributing to an ONL‐like epithelium. In both types of spheres, the total percentage of RG‐cones was similar to the in vivo retina, indicating that expression of cones is autonomous. Following cones, after about one day, rods developed only within already existing RG‐cone clusters. Thereby, the ratio of rods to RG‐cones increases as the tissue organization decreases: for stratified spheres this ratio is, 0.50 (1 rod/2 cones; similar to mature retina); for rosettes, 0.74 (3 rods/4 cones) and for nonorganized areas, 1.09 (1 rod/1 cone) – a higher ratio under our conditions has never been detected. Thus, rod expression depends strictly on the presence of nearby cones; their relative numbers are distinctively adjusted according to the cytoarchitecture of the tissue environment. The biomedical implications of these findings are briefly discussed.
Effects of amyloid peptides on cell viability and expression of neuropeptides in cultured rat dorsal root ganglion neurons: a role for free radicals and protein kinase C
Authors: Ma Weiya , Zheng Wen‐Hua , Belanger Serge , Kar Satyabrata , Quirion Remi
Published: March 2003

Chronic pain caused by nerve injury and inflammation is more common in the elderly. However, mechanisms underlying this phenomenon are unclear. Higher sensitivity of sensory neurons to free radicals has been suggested as one possibility. The production of free radicals can be induced by various agents, including the highly toxic protein β‐amyloid (Aβ), which is found in higher amounts in the brains of Alzheimer's Disease patients. In dorsal root ganglion (DRG) cultures exposed to Aβ, we examined cellular toxicity and peptide expression, in particular calcitonin gene‐related peptide (CGRP), a peptide which is abundantly expressed by nociceptive afferents and is known to be involved in pain processes. Exposure of cultured rat DRG neurons to Aβ25−35 or Aβ1−40 (10 or 20 µm for 24–96 h) increased trypan blue‐stained cells in a concentration‐ and time‐dependent manner, thus, indicating cellular toxicity. These treatments also increased the number of CGRP immunoreactive (IR) neurons while decreasing the number of neuropeptide Y‐ and galanin‐IR neurons. The free radical scavenger, superoxide dismutase, attenuated both the toxicity and neuropeptide changes induced by Aβ, thus, suggesting that oxidative stress probably contributes to these effects. Exposure of cultured DRG neurons to Aβ also increased the number of protein kinase Cα (PKCα)‐IR neurons. The PKC inhibitors, chelerythrine chloride and Gö6976, significantly augmented Aβ‐induced cellular toxicity while attenuating the increases in CGRP‐and PKCα‐IR cells, supporting the notion of a protective role for PKC in Aβ insults. These in vitro data suggest that Aβ peptides may, in addition to causing neurotoxicity, regulate neuropeptide expression in primary afferents. This finding could be relevant to the higher incidence of neuropathic pain that occurs with ageing.
Stimulation of corticospinal tract regeneration in the chronically injured spinal cord
Authors: Ferguson Ian A. , Koide Tomoaki , Rush. Robert A.
Published: March 2003

Acute spinal cord injury models have proved popular in studies aimed at identifying factors capable of influencing axonal regeneration within the central nervous system. In these models, the test factors (e.g. graft tissues or cells, antibodies, growth factors, etc.) are typically administered at the time of spinal cord injury. In this study, we use a rat chronic spinal cord injury model to identify possible factors which can stimulate regeneration of the chronically lesioned corticospinal tract axons. We demonstrate that surgical grafting of segments of autologous, preligated sural nerve, into the syrinx, stimulates sprouting and regeneration of the corticospinal tract as evidenced by the presence of anterograde labelled corticospinal tract processes within the cavity walls two or more weeks after treatment. Regrowing corticospinal processes were not observed within control animals. The anterogradely labelled corticospinal tract axons were found exclusively within the central grey tissue comprising the cavity walls with no regrowing corticospinal process observed within the white matter. A similar pattern of regeneration was observed following injection into the cavity of a suspension of minced autologous preligated sural nerve. Evidence of corticospinal tract regeneration was seen when either wheat germ agglutinin–horseradish peroxidase or biotinylated–dextran was used as an anterograde tracer. These data demonstrate that the chronically injured cortical motor neurons retain the capacity to regenerate for extended periods and that regeneration can be stimulated using grafts of minced, preligated autologous peripheral nerve tissue.
Dorsal hippocampal lesions impair appetitive classical conditioning to localized cues
Authors: Bonardi Charlotte
Published: March 2003

Three experiments examined appetitive classical conditioning in rats with small electrolytic lesions of the dorsal hippocampus. In all the experiments, the reinforcer was food delivery and the conditioned response (CR) entry to the food tray; the three experiments differed in the nature of the conditioned stimulus (CS). When this was a small light located inside the food tray, conditioning was impaired in lesioned animals, but when the CS was a general increase in illumination, they learned at the same rate as controls. With a white noise as the CS, learning was significantly faster in lesioned subjects. These data demonstrate that lesions of the dorsal hippocampus can produce impairments in appetitive delay conditioning, but only with certain types of CS. It is suggested that deficits are found with CSs that are localized in space.
Odour‐evoked [Ca2+] transients in mitral cell dendrites of frog olfactory glomeruli
Authors: Delaney Kerry , Davison Ian , Denk Winfried
Published: March 2003

We measured Ca2+ concentration, [Ca2+], transients in mitral cell distal apical dendritic tufts produced by physiological odour stimulation of the olfactory epithelium and electrical stimulation of the olfactory nerve (ON) using two‐photon scanning and conventional wide‐field microscopy of Ca2+‐Green‐1 dextran in an in vitro frog nose–brain preparation. Weak or strong ON shock‐evoked fluorescence transients always had short latency with an onset 0–10 ms after the onset of the bulb local field potential, rapidly increasing to a peak of up to 25% fractional fluorescence change (ΔF/F) in 10–30 ms, were blocked by 10 µm CNQX, decaying with a time constant of about 1 s. With stronger ON shocks that activated many receptor axons, an additional, delayed, sustained AP5‐sensitive component (peak at ≈ 0.5 s, up to 40% ΔF/F maximum) could usually be produced. Odour‐evoked [Ca2+] transients sometimes displayed a rapid onset phase that peaked within 50 ms but always had a sustained phase that peaked 0.5–1.5 s after onset, regardless of the strength of the odour or the amplitude of the response. These were considerably larger (up to 150% ΔF/F) than those evoked by ON shock. Odour‐evoked [Ca2+] transients were also distinguished from ON shock‐evoked transients by tufts in different glomeruli responding with different delays (time to onset differed by up to 1.5 s between different tufts for the same odour). Odour‐evoked [Ca2+] transients were increased by AMPA‐kainate receptor blockade, but substantially blocked by AP5. Electrical stimulation of the lateral olfactory tract (5–6 stimuli at 10 Hz) that evoked granule cell feedback inhibition, blocked 60–100% of the odour‐evoked [Ca2+] transient in tufts when delivered within about 0.5 s of the odour. LOT‐mediated inhibition was blocked by 10 µm bicuculline.
The mammalian homologue of the novel peptide Bv8 is expressed in the central nervous system and supports neuronal survival by activating the MAP kinase/PI‐3‐kinase pathways
Authors: Melchiorri D. , Bruno V. , Besong G. , Ngomba R. T. , Cuomo L. , De Blasi A. , Copani A. , Moschella C. , Storto M. , Nicoletti F. , Lepperdinger G. , Passarelli F.
Published: March 2003

Previous studies have identified the mammalian homologue of Bv8 (mBv8), a small protein originally isolated from skin secretions of the frog, Bombina variegata. In situ hybridization showed that mBv8 RNA was widely expressed in the rodent CNS, with high levels being detected in layer II of the cerebral cortex, limbic regions, cerebellar Purkinje cells, and dorsal and ventral horns of the spinal cord. A similar pattern of distribution was found by examining the presence of mBv8 protein by immunocytochemistry. Addition of frog Bv8 to cultured cerebellar granule cells reduced the extent of apoptotic death induced by switching the growing medium from 25 to 5 mm K+. Bv8 could also protect cultured cortical neurons against excitotoxic death. Both effects were prevented by PD98059 and LY294002, which inhibit the mitogen‐activated protein kinase (MAPK) and phosphatidylinositol‐3‐kinase (PI‐3‐K) pathways, respectively. In cultured cerebellar granule cells, Bv8 stimulated both the MAPK and the PI‐3‐K pathways, as revealed by Western blot analysis of phosphorylated p44/p42 MAPKs and phosphorylated Akt, respectively. We conclude that mBv8 acts as an endogenous neurotrophic factor and supports neuronal survival through the activation of the MAPK/PI‐3‐K pathways.
Acute and long‐term changes in the mesolimbic dopamine pathway after systemic or local single nicotine injections
Authors: Ferrari R. , Le Novère N. , Picciotto M. R. , Changeux J. P. , Zoli M.
Published: March 2003

We have examined several neurochemical and behavioural parameters related to the function of the mesolimbic dopamine (DA) pathway in animals treated with nicotine following three modes of drug administration, i.e. systemic intraperitoneal injection, intra‐accumbens (Acb) infusion or intraventral tegmental area (intra‐VTA) microinjection. The present modes of systemic, intra‐Acb and intra‐VTA nicotine administration elicited comparable acute increases in dialysate DA levels from the Acb. The increase in extracellular DA levels was paralleled by a significant enhancement of locomotion in a habituated environment in the case of systemic or intra‐VTA nicotine administration, whereas unilateral or bilateral intra‐Acb nicotine infusion was ineffective, showing that accumbal DA increase is not sufficient to elicit locomotion in this experimental paradigm. Intra‐VTA, but not systemic or intra‐Acb, nicotine administration caused a long‐term (at least 24‐h) increase in basal dialysate DA levels from the Acb. In addition, significant increases in tyrosine hydroxylase (TH) and GluR1 (but not dopamine transporter or NR1) mRNA levels in the VTA were detected 24 h after intra‐VTA nicotine administration. Systemic nicotine injection caused only an increase in TH mRNA levels while intra‐Acb infusion did not modify any of the mRNAs tested. The long‐term increase in basal DA levels in the Acb and TH, and GluR1 mRNA levels in the VTA upon intra‐VTA nicotine microinjection indicates that even a single nicotine injection can induce plastic changes of the mesolimbic DA pathway.
Opposing roles for medial and central amygdala in the initiation of noradrenergic cell responses to a psychological stressor
Authors: Dayas C. V. , Day T. A.
Published: March 2003

Psychological stressors trigger the activation of medullary noradrenergic cells, an effect that has been shown to depend upon yet‐to‐be‐identified structures located higher in the brain. To test whether the amygdala is important in this regard, we examined the effects of amygdala lesions on noradrenergic cell responses to restraint, and also looked at whether any amygdala cells that respond to restraint project directly to the medulla. Ibotenic acid lesions of the medial amygdala completely abolished restraint‐induced Fos expression in A1 and A2 noradrenergic cells. In contrast, lesions of the central amygdala actually facilitated noradrenergic cell responses to restraint. Tracer deposits in the dorsomedial (but not ventrolateral) medulla retrogradely labelled many cells in the central nucleus of the amygdala, but none of these cells expressed Fos in response to restraint. These data suggest for the first time that the medial amygdala is critical to the activation of medullary noradrenergic cells by a psychological stressor whereas the central nucleus exerts an opposing, inhibitory influence upon noradrenergic cell recruitment. The initiation of noradrenergic cell responses by the medial amygdala does not involve a direct projection to the medulla. Accordingly, a relay through some other structure, such as the hypothalamic paraventricular nucleus, warrants careful consideration.
Comparative cytoarchitectonic analysis of the human and the macaque ventrolateral prefrontal cortex and corticocortical connection patterns in the monkey
Authors: Petrides M. , Pandya D. N.
Published: March 2003

A comparison of the cytoarchitecture of the human and the macaque monkey ventrolateral prefrontal cortex demonstrated a region in the monkey that exhibits the architectonic characteristic of area 45 in the human brain. This region occupies the dorsal part of the ventrolateral prefrontal convexity just below area 9/46v. Rostroventral to area 45 in the human brain lies a large cortical region labelled as area 47 by Brodmann. The ventrolateral component of this region extending as far as the lateral orbital sulcus has architectonic characteristics similar to those of the ventrolateral prefrontal region labelled by Walker as area 12 in the macaque monkey. We designated this region in both the human and the monkey ventrolateral prefrontal cortex as area 47/12. Thus, area 47/12 designates the specific part of the zone previously labelled as area 47 in the human brain that has the same overall architectonic pattern as that of Walker's area 12 in the macaque monkey brain. The cortical connections of these two areas were examined in the monkey by injecting fluorescent retrograde tracers. Although both area 45 and area 47/12 as defined here had complex multimodal input, they could be differentiated in terms of some of their inputs. Retrograde tracers restricted to area 47/12 resulted in heavy labelling of neurons in the rostral inferotemporal visual association cortex and in temporal limbic areas (i.e. perirhinal and parahippocampal cortex). In contrast, injections of tracers into dorsally adjacent area 45 demonstrated strong labelling in the superior temporal gyrus (i.e. the auditory association cortex) and the multimodal cortex in the upper bank of the superior temporal sulcus.
Neuronal responses of the rat amygdala during extinction and reassociation learning in elementary and configural associative tasks
Authors: Toyomitsu Yuji , Nishijo Hisao , Uwano Teruko , Kuratsu Junichi , Ono Taketoshi
Published: March 2003

To investigate functional heterogeneity within the amygdala in appetitive conditioned instrumental behaviours, neuronal activity was recorded from the amygdala of behaving rats during learning and discrimination of conditioned sensory stimuli associated with or without reinforcement [sucrose solution, intracranial self‐stimulation (ICSS)]. Sensory stimuli included auditory (tone), visual (light) and configural (simultaneous presentation of tone and light) stimuli. The rat was trained to lick a spout protruded close to its mouth just after a conditioned sensory stimulus to obtain a reward. Of the 609 neurons recorded from the amygdala and amygdalostriatal transition area, 154 responded to one or more sensory stimuli. The 62 amygdalar neurons responded strongly to certain conditioned sensory stimuli associated with rewards. Of these 62 neurons, 45 were tested with the extinction trials. Responses of 31 neurons to conditioned stimuli were finally extinguished, and those of the remaining 14 were not extinguished. Furthermore, responses of 26 of these 31 neurons resumed in the relearning trials (plastic neurons), suggesting that these sensory responses were associative rather than just responses to physical properties of the stimuli. These plastic neurons were located mainly in the basolateral nucleus of the amygdala, and responses of the plastic neurons were correlated with behavioural responses. These results suggest that the basolateral nucleus is crucial in associative learning between sensory information and affective significance for behavioural outputs in appetitive conditioned instrumental behaviours.
Differential post‐transcriptional regulation of p21WAF1/Cip1 levels in the developing nervous system following γ‐irradiation
Authors: Herzog Karl‐Heinz , Braun Johann S. , Han Sung‐Ho , Morgan James I.
Published: March 2003

Radiation‐induced death in the developing brain is p53‐dependent. However, genetic studies indicate that the signalling pathways that couple irradiation to p53 expression can vary between different developing neural populations [Herzog et al. (1998)Science, 280, 1089–1091]. Here we establish that signalling downstream of p53 also exhibits brain region‐specific differences that are associated with the relative vulnerability of some cell populations to radiation‐induced killing in the mouse. Following γ‐irradiation, p53 and p21WAF1/cip1, but not Bax, protein levels increased in the developing cerebellum. In contrast, neither p21WAF1/cip1 nor Bax protein levels were elevated in the retina following irradiation, despite increased p53 expression. In the retina, p53 expression was associated with cells destined to die, whereas in the cerebellum, p53 was expressed in both radiation‐sensitive and radiation‐resistant neuroblasts of the external granule cell layer. Although p21WAF1/cip1 mRNA was expressed in all p53‐positive neuroblasts after irradiation, p21WAF1/cip1 protein was only detected in radiation‐resistant neuroblasts of the cerebellum. Thus, p21WAF1/cip1 was subject to post‐transcriptional regulation with p21WAF1/cip1 protein only accumulating in cells destined to survive irradiation. Nevertheless, p21WAF1/cip1 function was not essential for radiation resistance, as postmitotic neuroblasts in the external granule cell layer were spared in p21WAF1/cip1 knockout mice.
A dose‐dependent facilitation and inhibition of peripheral nerve regeneration by brain‐derived neurotrophic factor
Authors: Boyd J. G. , Gordon T.
Published: March 2003

The time‐dependent decline in the ability of motoneurons to regenerate their axons after axotomy is one of the principle contributing factors to poor functional recovery after peripheral nerve injury. A decline in neurotrophic support may be partially responsible for this effect. The up‐regulation of BDNF after injury, both in denervated Schwann cells and in axotomized motoneurons, suggests its importance in motor axonal regeneration. In adult female Sprague–Dawley rats, we counted the number of freshly injured or chronically axotomized tibial motoneurons that had regenerated their axons 1 month after surgical suture to a freshly denervated common peroneal distal nerve stump. Motor axonal regeneration was evaluated by applying fluorescent retrograde neurotracers to the common peroneal nerve 20 mm distal to the injury site and counting the number of fluorescently labelled motoneurons in the T11–L1 region of the spinal cord. We report that low doses of BDNF (0.5–2 µg/day for 28 days) had no detectable effect on axonal regeneration after immediate nerve repair, but promoted axonal regeneration of motoneurons whose regenerative capacity was reduced by chronic axotomy 2 months prior to nerve resuture, completely reversing the negative effects of delayed nerve repair. In contrast, high doses of BDNF (12–20 µg/day for 28 days) significantly inhibited motor axonal regeneration, after both immediate nerve repair and nerve repair after chronic axotomy. The inhibitory actions of high dose BDNF could be reversed by functional blockade of p75 receptors, thus implicating these receptors as mediators of the inhibitory effects of high dose exogenous BDNF.
GDNF and NGF released by synthetic guidance channels support sciatic nerve regeneration across a long gap
Authors: Fine Eric G. , Decosterd Isabelle , Papaloïzos Michael , Zurn Anne D. , Aebischer Patrick
Published: March 2003

The present work was performed to determine the ability of neurotrophic factors to allow axonal regeneration across a 15‐mm‐long gap in the rat sciatic nerve. Synthetic nerve guidance channels slowly releasing NGF and GDNF were fabricated and sutured to the cut ends of the nerve to bridge the gap. After 7 weeks, nerve cables had formed in nine out of ten channels in both the NGF and GDNF groups, while no neuronal cables were present in the control group. The average number of myelinated axons at the midpoint of the regenerated nerves was significantly greater in the presence of GDNF than NGF (4942 ± 1627 vs. 1199 ± 431, P ≤ 0.04). A significantly greater number of neuronal cells in the GDNF group, when compared to the NGF group, retrogradely transported FluoroGold injected distal to the injury site before explantation. The total number of labelled motoneurons observed in the ventral horn of the spinal cord was 98.1 ± 23.4 vs. 20.0 ± 8.5 (P ≤ 0.001) in the presence of GDNF and NGF, respectively. In the dorsal root ganglia, 22.7% ± 4.9% vs. 3.2% ± 1.9% (P ≤ 0.005) of sensory neurons were labelled retrogradely in the GDNF and NGF treatment groups, respectively. The present study demonstrates that, sustained delivery of GDNF and NGF to the injury site, by synthetic nerve guidance channels, allows regeneration of both sensory and motor axons over long gaps; GDNF leads to better overall regeneration in the sciatic nerve.
Dose‐dependent rescue of axotomized rat retinal ganglion cells by adenovirus‐mediated expression of glial cell‐line derived neurotrophic factorin vivo
Authors: Schmeer Christian , Straten Guido , Kügler Sebastian , Gravel Claude , Bähr Mathias , Isenmann Stefan
Published: March 2003

Adult rat retinal ganglion cells undergo degeneration after optic nerve transection. Repeated intraocular injection of glial cell‐line derived neurotrophic factor (GDNF) has been shown to be efficient in enhancing retinal ganglion cell survival following optic nerve axotomy. In the present study we evaluated the potential survival‐promoting effect of adenovirally administered GDNF on axotomized retinal ganglion cells. A single intravitreal injection [7 × 107 plaque‐forming units (pfu) or 7 × 108 pfu] of an adenoviral vector expressing the rat GDNF gene from a cytomegalovirus promoter enhanced retinal ganglion cell survival 14 days after axotomy by 67 and 125%, respectively, when compared to control animals. Intraocular administration of the vector rescued 12.6 and 23%, respectively, of the retinal ganglion cells which would otherwise have died after axotomy. An increase in retinal GDNF protein and specific virally transduced GDNF mRNA expression was detected following intraocular vector application. Our data support previous findings showing that adenoviral delivery of neurotrophic factors to the vitreous body is a feasible approach for the prevention of axotomy‐induced retinal ganglion cell death in vivo and may constitute a relevant strategy for future treatment in traumatic brain injury and ensuing neurodegeneration.
Hypothalamic bHLH transcription factors are novel candidates in the regulation of energy balance
Authors: Nilaweera Kanishka N. , Ellis Claire , Barrett Perry , Mercer Julian G. , Morgan Peter J.
Published: March 2003

The basic helix–loop–helix transcription factors, neurological basic‐helix–loop–helix‐2 (Nhlh‐2), neurogenic differentiation‐1 (NeuroD‐1) and single minded‐1 (Sim‐1) could have roles in energy balance regulation, although supporting evidence is inconclusive. This study in mice provides further evidence that Nhlh‐2 and NeuroD‐1 are involved in energy balance regulation. In situ hybridization was used to study the expression of the genes in relation to physiological status and genetic background within hypothalamic nuclei that are involved in energy balance regulation. These studies show reduced expression of Nhlh‐2 mRNA in the arcuate (ARC) nucleus and NeuroD‐1 mRNA in the paraventricular (PVN) nucleus in obese ob/ob and 24 h food‐deprived mice relative to respective controls, suggesting regulation by leptin. Interestingly, Nhlh‐2 mRNA expression is reduced in obese db/db mice, whereas NeuroD‐1 remains unchanged, suggesting different mechanisms of regulation by leptin of these two genes. To study the role of leptin in the regulation of these genes, leptin was injected intraperitoneally in obese ob/ob mice and mRNA expression evaluated after 1 h or 4 h, or after twice‐daily injection for 7 days. None of these regimes restored Nhlh‐2 or NeuroD‐1 to wild‐type mRNA levels. These latter data suggest either that the regulation of the Nhlh‐2 and NeuroD‐1 genes by leptin is indirect or that the apparent leptin insensitivity of the gene expression reflects a developmental deficit that is a consequence of the phenotype of the obese ob/ob mice. The relationship between Nhlh‐2 and candidate energy balance‐related genes was studied by dual in situ hybridization. Nhlh‐2 mRNA was coexpressed in a subpopulation (30%) of ARC neurons expressing pro‐opiomelanocortin (POMC) mRNA, suggesting a potential functional relationship.
Haematopoietic progenitor cells from adult bone marrow differentiate into cells that express oligodendroglial antigens in the neonatal mouse brain
Authors: Bonilla Sonia , Alarcón Pedro , Villaverde Ramón , Aparicio Pedro , Silva Augusto , Martínez Salvador
Published: March 2003

Stem cells are self‐renewable, pluripotent cells that, in adult life, proliferate by a characteristic asymmetric division in which one daughter cell is committed to differentiation whereas the other remains a stem cell. These cells are also characterized by their ability to differentiate into various cell types under heterotopic environmental influences. In the present study, we have explored the potential of adult haematopoietic bone marrow cells to differentiate into cells of oligodendroglial lineage under physiological, active myelinating conditions. We present evidence of generation of cells expressing oligodendroglial specific markers from a bone marrow subpopulation enriched on adult haematopoietic progenitor cells (CD117+) in vivo after intracerebral transplantation into the neonatal mouse brain. Our results suggest that adult bone marrow cells have the capacity to undergo differentiation from haematopoietic to oligodendroglial cells and add support the validity of bone marrow transplants as an alternative treatment for demyelinating diseases of the CNS including Multiple Sclerosis.
NMDA receptors and PSD‐95 are found in attachment plaques in cerebellar granular layer glomeruli
Authors: Petralia Ronald S. , Wang Ya‐Xian , Wenthold Robert J.
Published: March 2003

N‐methyl‐d‐aspartate (NMDA) receptors mediate long‐term changes in excitatory synapses in response to glutamate release. In the cerebellar granular layer, most glutamatergic synapses are formed between mossy terminals and granule cell dendrites, which together with some other components, make up complex glomerular structures. Glomeruli contain numerous attachment plaques (or puncta adherentia), which are sites of adhesion between cells. These structures are found mainly between granule cell dendrites, and probably help maintain the integrity of glomeruli. Attachment plaques contain adhesive proteins such as cadherins. In this study, we show that NMDA receptors are common at these attachment plaques, in addition to being found at synapses. We used four different antibodies to the NMDA receptor subunit, NR1, and another to NR2A/B. In contrast, labelling for an α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionate (AMPA) glutamate receptor antibody was seen only in a few attachment plaques, although AMPA receptors were seen frequently at glomerular synapses. We also show that substantial levels of the NMDA receptor‐associated protein, PSD‐95, are found in both synapses and attachment plaques. One way that NMDA receptors mediate changes in synapses is through effects on synaptic cadherins, which change their adhesive properties in response to NMDA receptor activation and consequently may alter synaptic function. The presence of NMDA receptors in attachment plaques suggests that these receptors mediate changes in the adhesive properties of these plaques, similar to this function in synapses.
Decreased BDNF signalling in transgenic mice reduces epileptogenesis
Authors: Lähteinen Sari , Pitkänen Asla , Saarelainen Tommi , Nissinen Jari , Koponen Eija , Castrén Eero
Published: March 2003

Brain derived neurotrophic factor (BDNF) has been suggested to be involved in epileptogenesis. Both pro‐ and antiepileptogenic effects have been reported, but the exact physiological role is still unclear. Here, we investigated the role of endogenous BDNF in epileptogenesis by using transgenic mice overexpressing truncated trkB, a dominant negative receptor of BDNF. After induction of status epilepticus (SE) by kainic acid, the development of spontaneous seizures was monitored by video‐EEG system. Hilar cell loss, and the number of neuropeptide Y immunoreactive cells were studied as markers of cellular damage, and mossy fibre sprouting was investigated as a plasticity marker. Our results show that transgenic mice had significantly less frequent interictal spiking than wild‐type mice, and the frequency of spontaneous seizures was lower. Furthermore, compared to wild‐type animals, transgenic mice had less severe seizures with later onset and mortality was lower. In contrast, no differences between genotypes were observed in any of the cellular or plasticity markers. Our results suggest that transgenic mice with decreased BDNF signalling have reduced epileptogenesis.
In vivo activation and nuclear translocation of phosphorylated glycogen synthase kinase‐3β in neuronal apoptosis: links to tau phosphorylation
Authors: Elyaman W. , Terro F. , Wong N. S. , Hugon J.
Published: March 2003

The roles of glycogen synthase kinase‐3β (GSK‐3β) and tau phosphorylation were examined in seven‐day‐old rats injected with the NMDA receptor antagonist (MK801) that is known to induce neuronal apoptosis. Immunoblot and immunohistochemical analysis of brain samples demonstrated a site‐specific increase in tau phosphorylation associated with the relocalization of the protein to the nuclear/perinuclear region of apoptotic neurons. In addition, a tau 32‐kDa fragment was detected, suggesting that tau was a target of intracellular proteolysis in MK801‐treated brains. The proteolytically modified form of tau has reduced ability to bind to microtubules. GSK‐3β kinase assay and immunoblottings of active (tyrosine‐216) and inactive (serine‐9) forms of GSK‐3β revealed a rapid and transient increase in the kinase activity. Lithium chloride, a GSK‐3β inhibitor, prevented tau phosphorylation suggesting that tau phosphorylation is mediated by the activation of GSK‐3β. Confocal microscopy using double labelling of tau and GSK‐‐3β revealed that the activation of GSK‐3β in neurons was associated with early (2 h) nuclear translocation of tyrosine‐216 GSK‐3β. The execution phase of neuronal apoptosis was accompanied by a selective phosphorylation of serine‐9 and dephosphorylation of tyrosine‐216 GSK‐3β. These findings demonstrate that in vivo, GSK‐3β kinase activation and nuclear translocation are early stress signals of neuronal apoptosis.
Integration of calcium signals by calmodulin in rat sensory neurons
Authors: Milikan Jacob M. , Carter Tom D. , Horne John H. , Tzortzopoulos Athanasios , Török Katalin , Bolsover Stephen R.
Published: March 2003

We have used the fluorescently labelled calmodulin TA‐CaM to follow calmodulin activation during depolarization of adult rat sensory neurons. Calcium concentration was measured simultaneously using the low affinity indicator Oregon Green BAPTA 5N. TA‐CaM fluorescence increased during a 200‐ms depolarization but then continued to increase during the subsequent 500 ms, even though total cell calcium was falling at this time. In the next few seconds TA‐CaM fluorescence fell, but to a new elevated level that was then maintained for several tens of seconds. During a train of depolarizations that evoked a series of largely independent calcium changes TA‐CaM fluorescence was in contrast raised for the duration of the train and for many tens of seconds afterwards. The presence of a peptide corresponding to the calmodulin binding domain of myosin light chain kinase significantly increased the depolarization‐induced TA‐CaM fluorescence increase and slowed the subsequent fall of fluorescence. We interpret the slow recovery component of the TA‐CaM signal as reflecting the slow dissociation of calcium–calmodulin–calmodulin binding protein complexes. Our results show that after brief electrical activity calmodulin's interaction with calmodulin binding proteins persists for approximately one minute.
Activation of extracellular signal‐regulated kinases 1 and 2 by depolarization stimulates tyrosine hydroxylase phosphorylation and dopamine synthesis in rat brain
Authors: Lindgren Niklas , Goiny Michel , Herrera‐Marschitz Mario , Haycock John W. , Hökfelt Tomas , Fisone Gilberto
Published: March 2003

Production of dopamine is regulated via phosphorylation of tyrosine hydroxylase (TH), the rate‐limiting enzyme in the synthesis of catecholamines. Here we have used a preparation of rat striatal slices to examine the involvement of two mitogen‐activated protein kinases (MAPKs), extracellular signal‐regulated protein kinases 1 and 2 (ERK1/2), in the depolarization‐dependent regulation of TH phosphorylation and dopamine synthesis. Depolarization with elevated KCl (45 mm) caused an increase in the phosphorylation state and, thereby, activation of ERK1/2. The same stimulus also increased TH phosphorylation at Ser19, Ser31 and Ser40 (measured using site‐ and phospho‐specific antibodies) and TH activity [measured as 3,4‐dihydroxyphenylalanine (DOPA) accumulation]. A MAPK/ERK kinase inhibitor, PD098059, decreased the basal levels of phospho‐ERK1/2 and prevented the increase in ERK1/2 phosphorylation induced by depolarization. PD098059 also decreased both basal and depolarization‐induced phosphorylation of TH at Ser31 and reduced the increase in Ser40 phosphorylation induced by high potassium, but did not affect Ser19 phosphorylation. PD098059 alone inhibited basal TH activity and decreased the accumulation of DOPA induced by depolarization. These data provide evidence for the involvement of ERK1/2 in the regulation of the state of phosphorylation of TH at Ser31 and Ser40 and a correlation between ERK1/2‐dependent phosphorylation of TH and stimulation of dopamine synthesis in the brain.
Cross‐modal neuroplasticity in neonatally enucleated hamsters: structure, electrophysiology and behaviour
Authors: Izraeli Ruth , Koay Gimseong , Lamish Meyrav , Heicklen‐Klein Alice J. , Heffner Henry E. , Heffner Rickye S. , Wollberg Zvi
Published: March 2003

Potential auditory compensation in neonatally bilaterally enucleated Syrian hamsters was explored anatomically, electrophysiologically and behaviourally. Gross morphology of the visual cortex appeared normal and no obvious cytoarchitectural malformation was discerned. However, enucleation induced a significant increase in the spontaneous firing rate of visual cortex cells. Further, auditory stimuli elicited field potentials and single unit responses in the visual cortex of enucleated, but not normal, animals. About 63% of the cells isolated in the visual cortex of 16 enucleated hamsters responded to at least one type of auditory stimulus. Most of the responses were less vigorous and less time‐locked than those of auditory cortex cells, and thresholds were typically higher. Projection tracing with WGA–HRP disclosed reciprocal connections between the visual cortex and the dorsal lateral geniculate nucleus in both intact and enucleated animals. However, in the enucleated animals retrogradely labelled cells were also found in the inferior colliculus, the major midbrain auditory nucleus. Behaviourally determined auditory sensitivity across the hearing range did not differ between enucleated and intact hamsters. Minimum audible angle, as determined by a conditioned suppression task, ranged from around 17 to 22°, with no significant difference between normal and enucleated animals. The two groups also did not differ with regard to the direction of their unconditioned head orientating response to intermittent noise. However, the enucleated animals showed a more vigorous response and were slower to habituate to the noise. These results show that bilateral enucleation of newborn hamsters results in auditory activation of visual targets, in addition to the typical activation of the intact auditory pathway. Behaviourally it appears that enucleated hamsters, compared with their normal littermates, are slower to habituate in their response to an unexpected source of sound.