bluuebunny/crossref_metadata_2025 huggingface dataset:
Locomotor‐like movements evoked by leg muscle vibration in humans
Authors: Gurfinkel V. S. , Levik Yu. S. , Kazennikov O. V. , Selionov V. A.
Published: March 2003

We attempted to elicit automatic stepping in healthy humans using appropriate afferent stimulation. It was found that continuous leg muscle vibration produced rhythmic locomotor‐like stepping movements of the suspended leg, persisting up to the end of stimulation and sometimes outlasting it by a few cycles. Air‐stepping elicited by vibration did not differ from the intentional stepping under the same conditions, and involved movements in hip and knee joints with reciprocal electromyogram (EMG) bursts in corresponding flexor and extensor muscles. The phase shift between evoked hip and knee movements could be positive or negative, corresponding to ‘backward’ or ‘forward’ locomotion. Such an essential feature of natural human locomotion as alternating movements of two legs, was also present in vibratory‐evoked leg movements under appropriate conditions. It is suggested that vibration evokes locomotor‐like movements because vibratory‐induced afferent input sets into active state the central structures responsible for stepping generation.
Eph receptor–ligand interactions are necessary for guidance of retinal ganglion cell axons in vitro
Authors: Ciossek Thomas , Monschau Bruno , Kremoser Claus , Löschinger Jürgen , Lang Susanne , Müller Bernhard K. , Bonhoeffer Friedrich , Drescher Uwe
Published: March 2003

Previous results of an in vitro guidance test, the stripe assay, have demonstrated the presence of a repulsive axon guidance activity for temporal retinal axons in the posterior part of the vertebrate optic tectum. Ephrin‐A5 and Ephrin‐A2 are ligands for the EphA subfamily of Eph receptor tyrosine kinases, which are expressed in overlapping gradients in the posterior part of the tectum. When recombinantly expressed, both proteins have been shown to guide retinal ganglion cell axons in the stripe assay. While these results suggest that Ephrin‐A5 and Ephrin‐A2 form part of the posterior repulsive guidance activity, they do not elucidate whether they are necessary components. Here we report that soluble forms of the ligands at nanomolar concentrations completely abolish this repulsive activity. Similar results were obtained with the soluble extracellular domain of EphA3, which is a receptor for Ephrin‐A2 and Ephrin‐A5, but not with the corresponding domain of EphB3, a receptor for the transmembrane class of Eph ligands. These experiments show that the repulsive axon guidance activity seen in the stripe assay is mediated by Ephrin‐A ligands.
The constructive nature of vision: direct evidence from functional magnetic resonance imaging studies of apparent motion and motion imagery
Authors: Goebel Rainer , Khorram‐Sefat Darius , Muckli Lars , Hacker Hans , Singer Wolf
Published: March 2003

Echoplanar functional magnetic resonance imaging was used to monitor activation changes of brain areas while subjects viewed apparent motion stimuli and while they were engaged in motion imagery. Human cortical areas MT (V5) and MST were the first areas of the ‘dorsal’ processing stream which responded with a clear increase in signal intensity to apparent motion stimuli as compared with flickering control conditions. Apparent motion of figures defined by illusory contours evoked greater activation in V2 and MT/MST than appropriate control conditions. Several areas of the dorsal pathway (V3A, MT/MST, areas in the inferior and superior parietal lobule) as well as prefrontal areas including FEF and BA 9/46 responded strongly when subjects merely imagined moving stimuli which they had seen several seconds before. The activation during motion imagery increased with the synaptic distance of an area from V1 along the dorsal processing stream. Area MT/MST was selectively activated during motion imagery but not during a static imagery control condition. The comparison between the results obtained with objective motion, apparent motion and imagined motion provides further insights into a complex cortical network of motion‐sensitive areas driven by bottom‐up and top‐down neural processes.
Retrograde degeneration of thalamic neurons in the mediodorsal nucleus after neonatal and adult aspiration lesions of the medial prefrontal cortex in the rat. Implications for mechanisms of functional recovery
Authors: Van Eden C. G. , Rinkens A. , Uylings H. B. M.
Published: March 2003

The behavioural consequences of neonatal lesions of the frontal cortex are limited as compared with similar lesions performed in adulthood. The present study has investigated, using unbiased quantitative methods with randomized systematic sampling, the total neuronal cell numbers in the mediodorsal nucleus of the thalamus after aspiration lesions of the medial prefrontal cortex performed in neonatal and in adult rats. It was found that the reduction in total cell numbers after neonatal prefrontal cortex lesions was similar to that found after adult cortex lesions. In neonatally lesioned animals the neuronal cell density was significantly increased by 13%, whereas in adult lesioned animals it was unchanged. On the other hand, the volume of the mediodorsal nucleus was reduced by 27% in neonatally, and 20% in adult lesioned animals. Total neuronal cell number of the mediodorsal nucleus was significantly decreased in neonatally as well as in adult lesioned rats, by 14% and 21%, respectively. These findings are discussed in the light of the previously proposed role of the thalamus as a neural substrate of functional sparing after neonatal cortical lesions.
Changes in the expression of protease‐activated receptor 1 and protease nexin‐1 mRNA during rat nervous system development and after nerve lesion
Authors: Niclou Simone P. , Suidan Hana S. , Pavlik Alfred , Vejsada Richard , Monard Denis
Published: March 2003

Thrombin causes profound metabolic and morphological changes in cultured neural cells via activation of the thrombin receptor, also called protease‐activated receptor 1 (PAR1). PAR1 mRNA is present in the rat brain, but the role of this receptor in the nervous system remains elusive. The expression of PAR1 and the potent thrombin inhibitor protease nexin‐1 (PN‐1) was investigated in the developing rat brain and spinal cord and after peripheral nerve lesion. As seen by in situ hybridization, the PAR1 mRNA signal in the late embryonic and early postnatal nervous system was widespread, but generally of low intensity whereas in the adult it was more pronounced and confined to particular neuronal cells. These include the mesencephalic dopaminergic neurons, several thalamic and brainstem nuclei, the mitral cells in the olfactory bulb and the Purkinje cells in the cerebellum. In the spinal cord, PAR1 mRNA was abundant in motoneurons and a particularly high expression was detected in the preganglionic neurons of the autonomic nervous system. High PAR1 mRNA expression was also found in the dorsal root ganglia. Interestingly, strong immunoreactivity for the protease inhibitor PN‐1 was present in spinal motoneuron cell bodies, although its transcript was undetectable there. In response to sciatic nerve transection, the signal intensity of PAR1 mRNA as seen by Northern analysis increased in the proximal and the distal part of the lesioned nerve and in the denervated muscle, whereas the PN‐1 mRNA signal strongly increased only in the distal part of the nerve but remained unchanged in the proximal part and in the muscle. After facial nerve transection, PAR1 mRNA expression substantially decreased in facial motoneurons. No PAR1 transcript was detected in reactive astrocytes. Similar to PAR1, PN‐1 mRNA which was expressed in interneurons within the facial nucleus was also decreased following facial nerve transection.
Inhibition of ischaemic hippocampal neuronal death in primates with cathepsin B inhibitor CA‐074: a novel strategy for neuroprotection based on ‘calpain–cathepsin hypothesis’
Authors: Yamashima Tetsumori , Kohda Yukihiko , Tsuchiya Katsuhiro , Ueno Takashi , Yamashita Junkoh , Yoshioka Tohru , Kominami Eiki
Published: March 2003

Although Cornu Ammonis (CA) 1 neurons of the hippocampus are known to be vulnerable to transient ischaemia, the mechanism of ischaemic neuronal death is still unknown, and there are very few strategies to prevent neuronal death at present. In a previous report we demonstrated μ‐calpain activation at the disrupted lysosomal membrane of postischaemic CA1 neurons in the monkey undergoing a complete 20 min whole brain ischaemia. Using the same experimental paradigm, we observed that the enzyme activity of the lysosomal protease cathepsin B increased throughout the hippocampus on days 3–5 after the transient ischaemia. Furthermore, by immunocytochemistry cathepsin B showed presence of extralysosomal immunoreactivity with specific localization to the cytoplasm of CA1 neurons and the neuropil of the vulnerable CA1 sector. When a specific inhibitor of cathepsin B, the epoxysuccinyl peptide CA‐074 (C18H29N3O6) was intravenously administered immediately after the ischaemic insult, ≈ 67% of CA1 neurons were saved from delayed neuronal death on day 5 in eight monkeys undergoing 20 min brain ischaemia: the extent of inhibition was excellent in three of eight and good in five of eight monkeys. The surviving neurons rescued by blockade of lysosomal activity, showed mild central chromatolysis and were associated with the decreased immunoreactivity for cathepsin B. These observations indicate that calpain‐induced cathepsin B release is crucial for the development of the ischaemic neuronal death, and that a specific inhibitor of cathepsin B is of potential therapeutic utility in ischaemic injuries to the human CNS.
The expression of Huntingtin‐associated protein (HAP1) mRNA in developing, adult and ageing rat CNS: implications for Huntington's disease neuropathology
Authors: Page Keith J. , Potter Laurence , Aronni Silvia , Everitt Barry J. , Dunnett Stephen B.
Published: March 2003

Using radioactivein situhybridization, we have mapped the expression of Huntingtin‐associated protein (HAP1) mRNA in rat brain at developmental stages (E12–E19, P0–P21), in adult rats (3 months) and in ‘aged’ (19–21 months) rats. Using two pairs of 45mer oligonucleotide probes specific for HAP1A and a probe which recognizes regions of both the HAP1A and HAP1B mRNA sequences (panHAP1), we find that the expression of HAP1 mRNA is specific to the CNS and restricted predominantly to anatomically connected limbic structures, particularly the amygdala (medial and corticomedial nuclei), the hypothalamus (arcuate, preoptic, paraventricular and lateral hypothalamic area), bed nucleus of the stria terminalis (BNST) and the lateral septal nuclei. HAP1 mRNA was detected in embryos at E12 and displayed a prevalent distribution in the developing limbic structures by E15. In aged, 19–21‐months‐old, rats there is a downregulation of HAP1 mRNA expression across all CNSlociwhere HAP1 was previously abundant. The lowest levels of HAP1 mRNA expression corresponded with the areas of greatest pathological cell loss in Huntington's disease (HD); the caudate putamen, globus pallidus and neocortex. These observations support the suggestion that HAP1 plays an important role in the neuropathology of HD.
Local nitric oxide synthase activity in a model of neuropathic pain
Authors: Levy Dan , Zochodne Douglas. W.
Published: March 2003

A local inflammatory reaction may play an important role in the development of neuropathic pain following peripheral nerve injury. One important participant in the inflammatory response of injured peripheral nerve may be nitric oxide (NO). In this work, we examined physiological and morphological evidence for nitric oxide synthase (NOS) activation in the chronic constriction injury model of neuropathic pain in rats. Physiological evidence of local NO action was provided by studying NO‐mediated changes in local blood flow associated with the injury site. Immunohistochemistry was used to localize isoforms of NOS that might generate NO.

 Sciatic nerve injury associated with behavioural evidence of neuropathic pain had substantial rises in local blood flow. The NOS inhibitor NG‐nitro‐l‐arginine methyl ester (L‐NAME), but not NG‐nitro‐d‐arginine methyl ester (D‐NAME), reversed the hyperaemia in a dose‐dependent fashion proximal to the constriction at 48 h and distally at 14 days post‐operation when applied systemically or topically. Aminoguanidine, a NOS inhibitor with relatively greater selectivity for the inducible NOS (iNOS) isoform, reversed nerve hyperaemia distal to the constriction only at 14 days. NOS‐like immunoreactivity of the neuronal and endothelial isoforms was identified just proximal to the constriction at 48 h. iNOS‐like immunoreactivity was observed at 7 and 14 days at the constriction and distal sites, respectively.

 This work provides evidence for local NOS expression and NO action in the chronic constriction injury model of neuropathic pain. NO has local physiological actions that include vasodilatation of microvessels and that may be important in the development of pain sensitivity.
Initially expressed early rat embryonic GABAA receptor Cl– ion channels exhibit heterogeneous channel properties
Authors: Serafini Ruggero , Ma Wu , Maric Dragan , Maric Irina , Lahjouji Fatiha , Sieghart Werner , Barker Jeffery L.
Published: March 2003

We have studied the earliest expression of GABA‐induced Cl– channels in the rat embryonic dorsal spinal cord (DSC) using in situ hybridization, immunocytochemistry, flow cytometry and electrophysiology. At embryonic day 13 (E13) cells in the dorsal region are still proliferating. In situ hybridization consistently showed transcripts encoding only three GABAa receptor subunits (α4, β1 and γ1); immunocytochemistry both in tissue sections and in acutely isolated cells in suspension demonstrated the expression of the corresponding proteins and also revealed staining for other subunits (α2, α3, β3, γ2). In patch‐recordings performed in cells acutely isolated from the dorsal cord, responses to GABA were detected in 356 out of 889 cells. GABA‐evoked responses, which often displayed the opening of a few channels, were mediated by Cl– ions, were inhibited by bicuculline and picrotoxin, and potentiated by benzodiazepines. Taken together, these observations indicate that Cl– channels likely involve GABAa type receptors. Fluctuation analysis revealed channel kinetics consisting of three exponential components (τs: ≈ 1, 9 and 90 ms) and a wide variety of inferred unitary conductance values, ranging between 4 and 40 pS. A comparison of these results with observations in other, later embryonic cell types and recombinant receptors suggests that most of the earliest E13 DSC GABAa receptors may include α3 subunit. These GABAa receptor Cl– channels may be activated physiologically as both GABA synthesizing enzymes and GABA are present in the E13 dorsal cord.
Direct evidence of cubic difference tone propagation by intracochlear acoustic pressure measurements in the guinea‐pig
Authors: Avan Paul , Magnan Pascal , Smurzynski Jacek , Probst Rudolf , Dancer Armand
Published: March 2003

The fine tuning mechanisms involved in the normal processing of sound in the cochlea are non‐linear, hence combination tones are generated inside the cochlea when a pair of low‐level pure tones with neighbouring frequencies f1 and f2 is used as a stimulus. Their detection as sounds in the ear canal proves that they undergo backward propagation in the cochlea and through the middle ear, and the non‐invasive measurement of the combination tone at 2f1–f2, called the cubic difference tone (CDT), has become a routine method of monitoring cochlear function. In order to gain information on the hypothetical places where CDTs are generated, on their intracochlear levels and propagation velocities, direct measurements of CDT pressure waves were carried out in scala vestibuli and tympani of the first and second turn of the guinea‐pig cochlea. Cubic difference tones at

2f1–f2 varied from 0.75 to 9 kHz and were measured with a miniature piezoresistive transducer. Its high sensitivity allowed the detection of CDTs whenever their levels exceeded 5 dB SPL in the ear canal, i.e. 40 dB SPL (re: 20 μPa) inside the cochlea. The levels of CDTs were similar in scala vestibuli of the first and second turn. Phase comparisons between measurements at 2f1–f2 in the first and second turn allowed determination of the place where the CDT phase was minimum. It provided an estimation of the generation site of the CDT, which appeared to be close to the place tuned to f2 for stimulus levels lower than 70 dB SPL. Forward and backward travel times from one turn to the other were assessed at several frequencies, and both values were shorter than 0.2 ms. In contrast, the overall ‘round‐trip’ delay of CDTs, measured in the ear canal, was about five times larger, suggesting that local filtering processes rather than propagation delays account for the overall CDT delay.
Spectral characteristics of sleep EEG in chronic insomnia
Authors: Merica H. , Blois R. , Gaillard J. ‐M.
Published: March 2003

To determine whether the spectral characteristics of the sleep electroencephalogram (EEG) of insomniacs differ from that of healthy subjects, we compared in each of the first four non‐rapid eye movement (NREM) and rapid eye movement (REM) episodes: (a) the time courses of absolute power, averaged over the subjects in each group, for the delta, theta, alpha, sigma and beta frequency bands; (b) the relationship between these time courses; and (c) the overnight trend of integrated power in each frequency band. The results show that NREM power, for all frequencies below the beta range, has slower rise rates and reaches lower levels in the insomniac group, whereas beta power is significantly increased. In REM, insomniacs show lower levels in the delta and theta bands, whereas power in the faster frequency bands is significantly increased. Thus, the pathophysiology of insomnia is characterized not only by the generally acknowledged slow wave deficiency, but also by an excessive hyperarousal of the central nervous system throughout the night, affecting both REM and NREM sleep. This hyperarousal is interpreted in terms of the neuronal group theory of sleep which provides a possible explanation for the discrepancies observed between subjective impressions and objective measures of sleep. Also, it is suggested that the progressive hyperpolarization of the thalamocortical neurons as sleep deepens is slower in the patient population and that this may explain the observed slow wave deficiency. The homeostatic control of slow wave activity, on the other hand, would appear to be intact in the patient population.
Enkephalin‐containing interneurons are specialized to innervate other interneurons in the hippocampal CA1 region of the rat and guinea‐pig
Authors: Blasco‐Ibáñez J. M. , Martínez‐Guijarro F. J. , Freund T. F.
Published: March 2003

Enkephalins are known to have a profound effect on hippocampal inhibition, but the possible endogenous source of these neuropeptides, and their relationship to inhibitory interneurons is still to be identified. In the present study we analysed the morphological characteristics of met‐enkephalin‐immunoreactive cells in the CA1 region of the rat and guinea‐pig hippocampus, their coexistence with other neuronal markers and their target selectivity at the light and electron microscopic levels.

 Several interneurons in all subfields of the hippocampus were found to be immunoreactive for met‐enkephalin. In the guinea‐pig, fibres arising from immunoreactive interneurons were seen to form a plexus in the stratum oriens/alveus border zone, and basket‐like arrays of boutons on both enkephalin‐immunoreactive and immunonegative cell bodies in all strata. Immunoreactive boutons always established symmetric synaptic contacts on somata and dendritic shafts.

 Enkephalin‐immunoreactive cells co‐localized GABA, vasoactive intestinal polypeptide and calretinin. Postembedding immunogold staining for GABA showed that all the analysed enkephalin‐immunoreactive boutons contacted GABAergic postsynaptic structures. In double‐immunostained sections, enkephalin‐positive axons were seen to innervate calbindin D28k‐, somatostatin‐, calretinin‐ and vasoactive intestinal polypeptide‐immunoreactive cells with multiple contacts. Based on these characteristics, enkephalin‐containing cells in the hippocampus are classified as interneurons specialized to innervate other interneurons, and represent a subset of vasoactive intestinal polypeptide‐ and calretinin‐containing cells.

 The striking match of ligand and receptor distribution in the case of enkephalin‐mediated interneuronal communication suggests that this neuropeptide may play an important role in the synchronization and timing of inhibition involved in rhythmic network activities of the hippocampus.
Induction of neurosteroid synthesis by NMDA receptors in isolated rat retina: a potential early event in excitotoxicity
Authors: Guarneri P. , Russo D. , Cascio C. , De Leo G. , Piccoli F. , Guarneri R.
Published: March 2003

Here we investigated the possible regulation of neurosteroidogenesis by N‐methyl‐d‐aspartic acid (NMDA) receptor activation and addressed the hypothesis that neurosteroid synthesis may be involved in acute excitotoxicity. In the isolated retina, exposure to NMDA modified pregnenolone and pregnenolone sulphate formation. This effect was dose and time dependent, the synthesis being increased by relatively moderate NMDA doses (1–100 μm) within 30 min exposure and reduced to its control value by 60 min or by raising drug concentrations. NMDA‐stimulated neurosteroid synthesis was blocked by (+)‐5‐methyl‐10,11‐dihydro‐5H‐dibenzo[a,d]cyclo‐hepten‐5,10‐imine hydrogen maleate (MK‐801) and 3(2‐carboxypiperazine‐4‐yl)propyl‐1‐phosphonic acid (CPP), depended on extracellular calcium and reproduced by glutamate. Lactate dehydrogenase (LDH) release and morphological analysis revealed that retinal cell viability was not significantly affected after 30 min exposure to 50 μm NMDA, but severe cell damage occurred by 60 min. When the GABAA (γ‐aminobutyric acid) receptor agonist muscimol (1–1000 μm), known to activate retinal neurosteroidogenesis, was added together with NMDA, no additional increase in neurosteroid synthesis was observed, and NMDA‐induced LDH release remained unchanged. However, exposure to a high concentration of muscimol alone (500 μm) provoked a similar degree of toxicity to NMDA. By contrast, bicuculline abolished the increase in neurosteroidogenesis and LDH release. Similarly, pretreatment with R (+)‐p‐aminoglutethimide (AMG), an inhibitor of cholesterol side‐chain cleavage cytochrome P450, attenuated acute retinal cell damage. The inhibitory nature of AMG on NMDA‐stimulated neurosteroidogenesis was confirmed in the observation that drug treatment reduced pregnenolone content and did not affect the bindings of [3H] MK‐801 and [3H] muscimol. The results demonstrate that NMDA receptors regulate neurosteroidogenesis through a transneuronal mechanism, which implies GABAA receptor activation. The early NMDA‐mediated stimulation of neurosteroid synthesis seems to play a critical role in acute excitotoxicity; consequently, its inhibition is likely to delay neuronal cell death.
GFRα‐3, a protein related to GFRα‐1, is expressed in developing peripheral neurons and ensheathing cells
Authors: Widenfalk Johan , Tomac Andreas , Lindqvist Eva , Hoffer Barry , Olson Lars
Published: March 2003

We report here the identification of a gene, termed GFRα‐3 (glial cell line‐derived neurotrophic factor family receptor alpha‐3), related to GFRα‐1 and GFRα‐2 (also known as GDNFR‐α and GDNFR‐β), and describe distribution of GDNFα‐3 in the nervous system and other parts of the mouse body during development and in the adult. GFRα‐3 in situ hybridization signals were found mainly in the peripheral nervous system, with prominent signals in developing dorsal root and trigeminal ganglia. Sympathetic ganglia were also positive. Developing nerves manifested strong GFRα‐3 mRNA signals, presumably generated by the Schwann cells. Olfactory ensheathing cells were also positive. Other non‐neuronal cells appearing positive during development included chromaffin cells in the adrenal gland and small clusters of cells in the intestinal epithelium. In the central nervous system no robust signals could be detected at any stage investigated with the present probes. Compared with the previously described GFRα‐1 and GFRα‐2 mRNAs, which are widely distributed in the central nervous system and peripheral organs, the expression of GFRα‐3 mRNA is much more restricted. The prominent expression in Schwann cells during development suggests a key role for GFRα‐3 in the development of the peripheral nervous system. As Schwann cells are known to lack expression of the transducing RET receptor, we propose that a possible function of GFRα‐3 during development could be to bind Schwann cell‐derived GDNF‐like ligands, thus presenting such molecules to growing axons.
Functional Ca2+ and Na+ channels on mouse Schwann cells cultured in serum‐free medium: regulation by a diffusible factor from neurons and by cAMP
Authors: Beaudu‐Lange Claire , Despeyroux Sophie , Marcaggi Païkan , Coles Jonathan A. , Amédée Thierry
Published: March 2003

Regulation of expression of functional voltage‐gated ion channels for inward currents was studied in Schwann cells in organotypic cultures of dorsal root ganglia from E19 mouse embryos maintained in serum‐free medium. Of the Schwann cells that did not contact axons, 46.5% expressed T‐type Ca2+ conductances (ICaT). Two days or more after excision of the ganglia, and consequent disappearance of neurites, ICaT were detectable in only 10.9% of the cells, and the marker 04 disappeared. On Schwann cells deprived of neurons, T‐ (but not L‐) type Ca2+ conductances were re‐induced by weakly hydrolysable analogues of cAMP, and by forskolin (an activator of adenylyl cyclase) after long‐term treatment (4 days). With CPT cAMP (0.1–2 mm), 8Br cAMP, db cAMP or forskolin (0.01 or 0.1 mm), the proportion of cells with ICaT was not significantly different from the proportion in the cultures with neurons. These agents also induced expression in some cells of tetrodotoxin‐resistant Na+ currents, which were rarely induced by neurons, but 04 was not re‐induced by cAMP analogue treatments that re‐induced ICaT. Inward currents (Ba2+ or Na+) were partly restored (P < 0.05) on Schwann cells cultured for 6–7 days beneath a filter bearing cultured neurons. In contrast, addition of neuron‐conditioned medium was ineffective. The results suggest that neurons activate, via diffusible and degradable factors, a subset of Schwann cell cAMP pathways leading to expression of ICaT, and activate additional non‐cAMP pathways that lead to expression of 04.
Calcium influx through N‐ and P/Q‐type channels activate apamin‐sensitive calcium‐dependent potassium channels generating the late afterhyperpolarization in lamprey spinal neurons
Authors: Wikström  , Manira A. El
Published: March 2003

Lamprey spinal neurons exhibit a fast afterhyperpolarization and a late afterhyperpolarization (AHP) which is due to the activation of apamin‐sensitive SK Ca2+‐dependent K+ channels (KCa) activated by calcium influx through voltage‐dependent channels during the action potential (Hill et al. 1992, Neuroreport, 3, 943–945). In this study we have investigated which calcium channel subtypes are responsible for the activation of the KCa channels underlying the AHP. The effects of applying specific calcium channel blockers and agonists were analysed with regard to their effects on the AHP. Blockade of N‐type calcium channels by ω‐conotoxin GVIA resulted in a significant decrease in the amplitude of the AHP by 76.2 ± 14.9% (mean ± SD). Application of the P/Q‐type calcium channel blocker ω‐agatoxin IVA reduced the amplitude of the AHP by 20.3 ± 10.4%. The amplitude of the AHP was unchanged during application of the L‐type calcium channel antagonist nimodipine or the agonist (±)‐BAY K 8644, as was the compound afterhyperpolarization after a train of 10 spikes at 100 Hz. The effects of calcium channel blockers were also tested on the spike frequency adaptation during a train of action potentials induced by a 100–200 ms depolarizing pulse. The N‐ and P/Q‐type calcium channel antagonists decreased the spike frequency adaptation, whereas blockade of L‐type channels had no effect. Thus in lamprey spinal cord motor‐ and interneurons, apamin‐sensitive KCa channels underlying the AHP are activated primarily by calcium entering through N‐type channels, and to a lesser extent through P/Q‐type channels.
Hyperpolarization induces a rise in intracellular sodium concentration in dopamine cells of the substantia nigra pars compacta
Authors: Knöpfel T. , Guatteo E. , Bernardi G. , Mercuri N. B.
Published: March 2003

We investigated the effect of changes in membrane‐voltage on intracellular sodium concentration ([Na+]i) of dopamine‐sensitive neurons of the substantia nigra pars compacta in a slice preparation of rat mesencephalon. Whole‐cell patch‐clamp techniques were combined with microfluorometric measurements of [Na+]i using the Na+‐sensitive probe, sodium‐binding benzofuran isophthalate (SBFI). Hyperpolarization of spontaneously

active dopamine neurons (recorded in current‐clamp mode) caused the cessation of action potential firing accompanied by an elevation in [Na+]i. In dopamine neurons voltage‐clamped at a holding potential of −60 mV elevations of [Na+]i were induced by long‐lasting (45–60 s) voltage jumps to more negative membrane potentials (–90 to −120 mV) but not by corresponding voltage jumps to −30 mV. These hyperpolarization‐induced elevations of [Na+]i were depressed during inhibition of Ih, a hyperpolarization‐activated inward current, by Cs+. Hyperpolarization‐induced elevations in [Na+]i might occur also in other cell types which express a powerful Ih and might signal lack of postsynaptic activity.
Efferent‐mediated protection of the cochlear base from acoustic overexposure by low doses of lithium
Authors: Horner Kathleen C. , Higueret Denise , Cazals
Published: March 2003

Many studies on anaesthetized animals and a few on awake animals have suggested that the cholinergic olivocochlear efferent feedback to outer hair cells can participate in the protection of the cochlea from acoustic overexposure. Lithium is known to stimulate acetylcholine synthesis and release in the brain and it is likely to act similarly at the level of the cochlear efferent synapses. We demonstrate here that, in the awake guinea‐pig with a chronically implanted electrode on the round window of the cochlea, the temporary threshold shift induced by 1 minute exposure to different pure tones at around 90 dB sound pressure level (SPL) was reduced by as much as 40 dB, when exposure occurred after lithium treatment. The protection effect was not observed in anaesthetized animals. The effect was seen across the test frequency range of 6.4–12.5 kHz, suggesting that both ‘fast’ and ‘slow’ efferent effects are likely to be mediated by acetylcholine. Together our results provide new evidence that the olivocochlear efferents can provide a more efficient protection from acoustic overexposure when animals are awake.
The response of cat visual cortex to flicker stimuli of variable frequency
Authors: Rager Günter , Singer Wolf
Published: March 2003

We examined the possibility that neurons or groups of neurons along the retino‐cortical transmission chain have properties of tuned oscillators. To this end, we studied the resonance properties of the retino‐thalamo‐cortical system of anaesthetized cats by entraining responses with flicker stimuli of variable frequency (2–50 Hz). Responses were assessed from multi‐unit activity (MUA) and local field potentials (LFPs) with up to four spatially segregated electrodes placed in areas 17 and 18. MUA and LFP responses were closely related, units discharging with high preference during LFP negativity. About 300 ms after flicker onset, responses stabilized and exhibited a highly regular oscillatory patterning that was surprisingly similar at different recording sites due to precise stimulus locking. Fourier transforms of these steady state oscillations showed maximal power at the inducing frequency and consistently revealed additional peaks at harmonic frequencies. The frequency‐dependent amplitude changes of the fundamental and harmonic response components suggest that the retino‐cortical system is entrainable into steady state oscillations over a broad frequency range and exhibits preferences for distinct frequencies in the θ‐ or slow α‐range, and in the β‐ and γ‐band. Concomitant activation of the mesencephalic reticular formation increased the ability of cortical cells to follow high frequency stimulation, and enhanced dramatically the amplitude of first‐ and second‐order harmonics in the γ‐frequency range between 30 and 50 Hz. Cross‐correlations computed between responses recorded simultaneously from different sites revealed pronounced synchronicity due to precise stimulus locking. These results suggest that the retino‐cortical system contains broadly tuned, strongly damped oscillators which altogether exhibit at least three ranges of preferred frequencies, the relative expression of the preferences depending on the central state. These properties agree with the characteristics of oscillatory responses evoked by non‐temporally modulated stimuli, and they indicate that neuronal responses along the retino‐cortical transmission chain can become synchronized with precision in the millisecond range not only by intrinsic interactions, but also by temporally structured stimuli.
Melanocortin receptors and δ‐opioid receptor mediate opposite signalling actions of POMC‐derived peptides in CATH.a cells
Authors: René Frédérique , Muller André , Jover Emmanuel , Kieffer Brigitte , Koch Bernard , Loeffler Jean‐Philippe
Published: March 2003

The locus cœruleus is innervated by proopiomelanocortin (POMC)‐derived peptide immunoreactive fibres. The biological effects of α melanocyte‐stimulating hormone (αMSH) and β‐endorphin on second messengers (cAMP, inositol phosphates) and gene transcription were studied in the locus cœruleus‐derived cell line CATH.a.

 RT‐PCR analysis revealed the presence of four MSH receptor subtypes (1, 3, 4 and 5). Activation of these receptors by diacetyl αMSH stimulated cAMP accumulation in a dose‐dependent manner (EC50: 4 × 10–9m). Diacetyl αMSH stimulated transcription from reporter genes driven by the c‐fos or tyrosine hydroxylase promoter. This effect was abolished when protein kinase A was inactivated with a dominant inhibitory mutant. RT‐PCR analyses revealed the presence of δ‐, but not μ‐and κ‐opioid receptor. Pharmacological analysis showed that β‐endorphin (EC50: 2.5 × 10–8m), but not N‐acetyl β‐endorphin, antagonized the biological effect of diacetyl αMSH on cAMP production and gene transcription.

 Since N‐acetylation regulates the biological activity of αMSH and β‐endorphin in an opposite manner, we propose a model where the rate of secretion dictated by the bioelectric activity of the presynaptic neuron modulates POMC‐derived peptide maturation and the resulting biological signal sensed by the postsynaptic plate.
Functional connectivity within the visual cortex of the rat shows state changes
Authors: van der Togt Chris , Lamme Victor A. F. , Spekreijse Henk
Published: March 2003

The aim of this study was to investigate the dynamics of the horizontal functional connectivity within the visual cortex during spontaneous activity or during visual stimulation. Two arrays of 16 electrodes were inserted in the visual cortex of a rat. From these electrodes a depth profile was obtained of the local spiking activity. The cross‐correlations between all electrodes were estimated. Three types of cross‐correlation peaks were identified and classified as;‘thin peaks’, ‘fast waves’ and ‘slow waves’. Partialization was applied, a mathematical method to reduce the amount of common input in correlations, and its effect on the three types of correlation peaks was studied. Slow waves were found to be the most vulnerable to partialization and thin peaks the least. From these observations it was concluded that the three types of peaks represent synchronous neuronal assemblies of different magnitude; slow waves large, fast waves intermediate and thin peaks assemblies composed of small numbers of neurons.

Large changes were observed in the types of cross‐correlations and their spatial distribution within the set of interarray combinations of electrodes. These changes were spontaneous, and could not be related to the visual stimulation. Two states were identified; the ‘thin‐peak’ state and the ‘slow‐wave’ state. The ‘thin‐peak’ state is interpreted as occurring at a light level of anaesthesia and is characterized by the presence of thin peaks in all combinations of electrodes. Thin peaks with the largest strength were found in the upper interarray electrode combinations. The ‘slow‐wave’ state is interpreted as occurring at a deep level of anaesthesia and is characterized by the presence of exclusively slow waves, which were limited mostly to the middle and lower interarray combinations of electrodes. Activation of the cortex is thus associated with the appearance of synchrony between small groups of neurons (thin peaks) which, in contrast to the slow‐wave state, include the upper layers of the cortex.
Mesolimbic dopaminergic mechanisms underlying individual differences in sugar consumption and amphetamine hyperlocomotion in Wistar rats
Authors: Sills Terrence L. , Onalaja Ava O. , Crawley Jacqueline N.
Published: March 2003

Individual differences within strains of rats have been demonstrated for dopamine‐mediated behaviours and responses to dopaminergic drugs. Differences in mesolimbic dopamine function may underlie individual differences in some of these behaviours, including sugar consumption and amphetamine hyperlocomotion. The present study addressed two potential mechanisms for these differences in dopamine‐mediated behaviours. The possibility of functional differences in dopamine receptor subtypes was tested in LOW and HIGH sugar feeders. LOW and HIGH feeders did not differ in their response to the partial D1 agonist SKF‐38393. The highest dose (2.5 mg/kg) of the D2 agonist quinpirole stimulated locomotor activity to a greater degree in a subset of HIGH sugar feeders as compared with LOW feeders. All doses of amphetamine induced a greater locomotor response in HIGH feeders as compared with LOW feeders, and HIGH feeders exhibited higher levels of extracellular dopamine in the nucleus accumbens than LOW feeders following exposure to sugar and treatment with amphetamine. These results support the interpretation that LOW and HIGH feeders exhibit differences in presynaptic nucleus accumbens dopamine function that account for the expression of individual differences in sugar consumption and response to amphetamine treatments. A subset of HIGH feeders may also exhibit greater D2 receptor function.
NMDA‐induced superoxide production and neurotoxicity in cultured rat hippocampal neurons: role of mitochondria
Authors: Sengpiel Bernd , Preis Elke , Krieglstein Josef , Prehn Jochen H. M.
Published: March 2003

Excitotoxic mechanisms are believed to be involved in the death of neurons after trauma, epileptic seizures and cerebral ischaemia. We investigated the role of mitochondrial superoxide production in excitotoxic cell death of cultured rat hippocampal neurons. Brief exposure to the selective glutamate agonist N‐methyl‐d‐aspartate (NMDA; 100–300 μm, 10 min) induced significant neuronal death, which was sensitive to cycloheximide (1 μm) and the caspase‐1 inhibitor, acetyl‐Tyr‐Val‐Ala‐Asp‐chloromethylketone (10 μm). Intracellular superoxide production was monitored semiquantitatively on sister cultures from the same platings using the oxidation‐sensitive probe, hydroethidine. Brief exposures to toxic NMDA concentrations induced significant increases in superoxide production which correlated with the degree of neuronal injury. However, subtoxic NMDA exposures also produced moderate, yet statistically significant increases in superoxide production. Both NMDA‐induced superoxide production and neurotoxicity were reduced by inhibition of mitochondrial electron transport using either sodium cyanide (1 mm), or a combination of rotenone (2 μm) and oligomycin (2 μm). The mitochondrial uncoupler carbonyl cyanide p‐trifluoromethoxy‐phenylhydrazone (FCCP, 1 μm) mimicked the effect of NMDA on mitochondrial superoxide production. Both NMDA‐induced superoxide production and neurotoxicity were potentiated by FCCP (1 μm). Exposure to FCCP alone (1–10 μm, 10 min), however, failed to produce any toxicity. Our data suggest that mitochondrial superoxide production per se is not sufficient to trigger the degeneration of cultured hippocampal neurons, but that manipulation of mitochondrial activity alters NMDA‐induced superoxide production and neurotoxicity.
Identification and characterization of a novel member of the fibroblast growth factor family
Authors: Greene J. M. , Li Y. L. , Yourey P. A. , Gruber J. , Carter K. C. , Shell B. K. , Dillon P. A. , Florence C. , Duan D. R. , Blunt A. , Ornitz D. M. , Ruben S. M. , Alderson R. F.
Published: March 2003

A new member of the fibroblast growth factor (FGF) family, FGF‐13, has been molecularly cloned as a result of high throughput sequencing of a human ovarian cancer cell library. The open reading frame of the novel human gene (1419 bp) encodes for a protein of 216 a.a. with a molecular weight of 22 kDa. The FGF‐13 sequence contains an amino‐terminal hydrophobic region of 23 a.a. characteristic of a signal secretion sequence. FGF‐13 is most homologous, 70% similarity at the amino acid level, to FGF‐8. Northern hybridization analysis demonstrated prominent expression of FGF‐13 in human foetal and adult brain, particularly in the cerebellum and cortex. In proliferation studies with BaF3 cells, FGF‐13 preferentially activates cell clones expressing either FGF receptor variant, 3‐IIIc or 4. The signal transduction pathways of FGF‐13 and FGF‐2 were compared in rat hippocampal astrocytes. The two FGFs induce an equivalent level of tyrosine phosphorylation of mitogen‐activated protein kinase (MAPK) and c‐raf activation. However, FGF‐13 is more effective than FGF‐2 in inducing the phosphorylation of phospholipase C‐gamma (PLC‐γ). Treatment of neuronal cultures from rat embryonic cortex with FGF‐13 increases the number of glutamic acid decarboxylase immunopositive neurons, the level of high‐affinity gamma‐aminobutyric acid (GABA) uptake, and choline acetyltransferase enzyme activity. The GABAergic neuronal response to FGF‐13 treatment is rapid with a significant increase occurring within 72 h. We have identified a novel member of the FGF family that is expressed in the central nervous system (CNS) and increases the number as well as the level of phenotypic differentiation of cortical neurons in vitro.
Serotonin is not synthesized, but specifically transported, in the neurons of the hypothalamic dorsomedial nucleus
Authors: Vanhatalo Sampsa , Soinila Seppo
Published: March 2003

A small group of neurons in the hypothalamic dorsomedial nucleus (DMN) have been reported to contain serotonin after pharmacological treatments enhancing brain serotonin levels. This study aimed at elucidating whether these neurons are able to synthesize serotonin de novo, and whether they possess a specific serotonin transport mechanism. Serotonin content in these neurons was raised by administration of l‐tryptophan and pargyline. Double immunostaining for serotonin and tryptophan hydroxylase (TpOH), the serotonin synthesizing enzyme, revealed that none of the serotonin‐containing neuronal somata expressed TpOH. Intracerebro‐

ventricular colchicine treatment did not result in TpOH‐IR in these neurons. Fluoxetine, a specific serotonin transport inhibitor, prevented the accumulation of serotonin in these neurons. The present results thus indicate that the serotonin‐containing DMN neurons are not able to synthesize serotonin. Instead, they take up exogenous serotonin via a specific serotonin transport mechanism. As serotonin and DMN are associated with various physiological functions, such as regulation of food intake and modulation of fear and anxiety, the mechanisms revealed in the present study may participate in these clinically important brain functions.
Effects of elevated levels of nerve growth factor on the septohippocampal system in transgenic mice
Authors: Kawaja Michael D. , Walsh Gregory S. , Tovich P. Ronald , Julien Jean‐Pierre
Published: March 2003

Elevating target‐derived levels of nerve growth factor (NGF) in peripheral organs of postnatal mammals is known to enhance the survival of postganglionic sympathetic neurons and to promote the terminal arborization of sympathetic axons within such NGF‐rich target tissues. Although increasing levels of NGF in the central nervous system can ameliorate cholinergic function of damaged and aged neurons of the medial septum, it remains undetermined whether the postnatal development of this neuronal population and their projections that innervate the hippocampus are likewise affected by elevated levels of target‐derived NGF. To address this question, the cholinergic septohippocampal pathway was examined in adult transgenic mice which display elevated levels of NGF protein production in the dorsal hippocampus during postnatal development. Adult transgenic mice possessed a cholinergic population of septal neurons ≈ 15% larger than that seen in age‐matched control animals. Despite increased numbers of cholinergic septal neurons, as well as elevated levels of hippocampal NGF, the density of cholinergic septal axons in the outer molecular layer of the hippocampal dentate gyrus of adult transgenic animals was comparable with that found in wild‐type controls. These results reveal that elevating levels of target‐derived NGF during postnatal development can increase the population size of the cholinergic septal neurons but does not alter their pattern of afferent innervation in the hippocampus of adult mice.