bluuebunny/crossref_metadata_2025 huggingface dataset:
On the Role of Galanin, Substance P and Other Neuropeptides in Primary Sensory Neurons of the Rat: Studies on Spinal Reflex Excitability and Peripheral Axotomy
Authors: Xu X.‐J. , Wiesenfeld‐Hallin Z. , Villar M. J. , Fahrenkrug J. , Hökfelt T.
Published: April 2006

The interaction of intrathecally (i.t.) applied galanin (GAL) with substance P (SP), calcitonin gene‐related peptide (CGRP), vasoactive intestinal polypeptide (VIP), somatostatin (SOM) and C‐fibre conditioning stimulation (CS) with regard to their effects on the spinal nociceptive flexor reflex was studied in decerebrate, spinalized, unanaesthetized rats with intact or sectioned sciatic nerves. SP, CGRP, VIP and SOM applied onto the surface of lumbar spinal cord or a brief CS train (1 Hz, 20 s) to the sural nerve facilitated the flexor reflex for several minutes in animals with intact or sectioned nerves. Pretreatment with GAL, which by itself had a biphasic effect on the flexor reflex in a dose‐dependent manner, antagonized the reflex facilitation induced by sural CS before and after sciatic nerve section. SP‐induced facilitation of the flexor reflex was antagonized by GAL in rats with intact sciatic nerves, but not after nerve section. In contrast, VIP‐induced reflex facilitation was antagonized by GAL only after sectioning of the sciatic nerve. GAL was effective in antagonizing the facilitatory effect of CGRP under both situations, but had no effect on SOM‐induced facilitation. A parallel immunohistochemical study revealed that after sciatic nerve section GAL‐like immunoreactivity (LI) and VIP‐LI are increased in the dorsal root ganglia and that these two peptides coexist in many cells. The present results indicate that GAL antagonizes the excitatory effect of some neuropeptides which exist in the spinal cord. This antagonism could explain the inhibitory effect of GAL on C‐fibre CS‐induced facilitation of the flexor reflex, which is presumably due to the release of some of these neuropeptides from the terminals of primary afferents. Furthermore, the interaction between GAL and other neuropeptides is altered by sciatic nerve section, paralleling changes in the levels of these neuropeptides in primary afferents and their pattern of coexistence after nerve section. It is proposed that SP and CGRP are important mediators of the spinal flexor reflex in intact rats. However, after axotomy VIP may replace SP in this capacity, paralleling the decrease in SP and marked increase in VIP levels. In general the study provides further support for involvement of peptides in sensory function.
Amoeboid Microglial Cells and not Astrocytes Synthesize TNF‐α in Swiss Mouse Brain Cell Cultures
Authors: Hetier Emmanuelle , Ayala Jésus , Bousseau Anne , Denèfle Patrice , Prochiantz Alain
Published: April 2006

The role of tumour necrosis factor (TNF‐α) in brain physiology and pathology has been the focus of several studies. However, the source of this lymphokine in the central nervous system and the regulation of its synthesis is still poorly understood. We have therefore used purified astrocytes and brain macrophages in culture to compare the abilities of these two cell types to synthesize TNF‐α and its mRNA. We find that, in the Swiss mouse, no significant TNF activity or TNF‐α mRNA are produced by astrocytes, even following activation with lipopolysaccharides (LPS). On the other hand, purified microglial cells express a cytotoxic activity able to kill TNF‐sensitive LM cells. Part of this activity is released into the culture medium and part remains bound to the membrane after mild paraformaldehyde treatment, demonstrating the existence in the culture of the soluble and membrane‐bound forms of TNF activity. The fact that amoeboid microglial cells, and not astrocytes, are the actual source of TNF in brain cultures was further demonstrated by Northern blot analysis and in situ hybridization using a TNF‐α specific oligonucleotide probe. The definition of the cell type which, in the CNS, is responsible for TNF synthesis will allow the regulation of this lymphokine to be analysed and opens the way for a better understanding of the interactions between amoeboid microglial cells and the other cell types which make up the nervous system.
Endothelin Induces a Rise of Inositol 1,4,5‐Trisphosphate, Inositol 1,3,4,5‐Tetrakisphosphate Levels and of Cytosolic Ca2+ Activity in Neural Cell Lines
Authors: Reiser Georg , Donié Frédéric
Published: April 2006

The mechanism of action of the vasoconstricting peptide endothelin was investigated in two neural cell lines. In rat glioma cells endothelin‐1 caused a biphasic rise in cytosolic Ca2+ activity. A large peak of 40 s duration was followed by another, however smaller, transient rise of comparable duration. In the absence of extracellular Ca2+ only the first peak was detected. Pretreatment with Ca2+ ionophores suppressed the Ca2+ response to endothelin. At the concentrations used the Ca2+ ionophores primarily deplete internal Ca2+ stores and prevent their refilling. Measurements of 45Ca2+ fluxes corroborate the conclusion that in the glioma cells endothelin induces firstly a release of Ca2+ from internal stores and subsequently a stimulation of Ca2+ entry. In neuronal cells (mouse neuroblastoma × rat glioma hybrid cells), endothelin caused a monophasic rise in cytosolic Ca2+ activity, most likely due to release from internal stores. In the glioma cells the concentrations of both inositol 1,4,5‐trisphosphate and inositol 1,3,4,5‐tetrakisphosphate were raised about 2.5‐fold for ca. 90 s after addition of endothelin. In the neuronal cells a shorter, smaller rise in inositololigophosphate concentrations was induced. Thus, endothelin seems to act as a neuropeptide activating phospholipase C and intracellular Ca2+.
Glucocorticoid Hormones Negatively Regulate Nerve Growth Factor Expression In Vivo and in Cultured Rat Fibroblasts
Authors: Lindholm Dan , Hengerer Bastian , Heumann Rolf , Carroll Patrick , Thoenen Hans
Published: April 2006

Sciatic nerve transection leads to an up‐regulation of nerve growth factor (NGF) production in non‐neuronal cells surrounding the axons. The lesion‐mediated increase in NGF‐mRNA levels in the nerve can be blocked by pretreating the animals with the synthetic glucocorticoid dexamethasone. Dexamethasone also reduces NGF‐mRNA levels in cultured sciatic fibroblasts stimulated with fetal calf serum or interleukin‐1. In order to study at which level glucocorticoids down‐regulate NGF expression, sciatic fibroblasts where transfected with a construct in which a reporter gene (chloramphenicol acetyltransferase) is expressed under the control of the NGF promotor. The results demonstrated that dexamethasone effectively represses NGF gene transcription. Deletion experiments showed that a 162 nucleotide promotor region mediates the glucocorticoid hormone suppression of NGF expression. The negative regulation of NGF synthesis by glucocorticoids is a factor to be considered in the treatment of patients with peripheral nerve lesions.
Feedback Inhibition of Ca2+ Currents by Dopamine in Glomus Cells of the Carotid Body
Authors: Benot A. R. , López‐Barneo J.
Published: April 2006

The effect of dopamine on the voltage‐dependent ionic channels of enzymatically dispersed glomus cells from rabbit carotid bodies was studied. Whole‐cell currents were recorded on isolation with patch electrodes and dopamine applied to the bath solution. Dopamine at nanomolar concentrations produced a reversible attenuation of the calcium current whereas sodium and potassium currents remained unaltered. Dopamine inhibition of Ca2+ current was observed in all cells tested (n= 48) and at a saturating concentration (1μM) the average reduction was of 40 ± 6.5% (n= 8). The effect of dopamine was probably caused by a decrease in the number of channels activatable on depolarization since it did not modify the voltage‐dependent parameters of the current. These results indicate that dopamine, which is the major transmitter secreted by glomus cells, regulates further transmitter release by feedback inhibition of Ca2+ channels.
Opposed Behavioural Outputs of Increased Dopamine Transmission in Prefrontocortical and Subcortical Areas: A Role for the Cortical D‐1 Dopamine Receptor
Authors: Vezina P. , Blanc G. , Glowinski J. , Tassin J.‐P.
Published: April 2006

The possibility that the dopaminergic neurons innervating the medial prefrontal cortex (mPFC) can inhibit locomotor behaviour has been suggested in several studies. The evidence remains indirect, however, because the manipulations tested aimed exclusively at permanently depleting mPFC dopamine. Here we demonstrate in rats that acute increases in dopamine transmission in this site by local injections of amphetamine inhibit the known locomotor‐activating effects of amphetamine in the nucleus accumbens (N.Acc). Further, intra‐mPFC injections of the D‐1 dopamine receptor antagonist SCH‐23390, but not other dopamine antagonists with greater affinities for noradrenergic, serotonergic and D‐2 dopamine receptors, enhanced the locomotion induced by intra‐N.Acc. amphetamine. These findings provide direct evidence for the inhibition of locomotor activity by mPFC dopamine and suggest that it is acting at D‐1 dopamine receptors in this site.
Binocular Interactions in the Lateral Suprasylvian Visual Area of Strabismic Cats Following Section of the Corpus Callosum
Authors: Di Stefano M. , Lepore F. , Ptito M. , Bédard S. , Marzi C. A. , Guillemot J. P.
Published: April 2006

Visually responsive neurons have been recorded in the lateral suprasylvian area (LSA) of cats raised with either a convergent or a divergent strabismus. In contrast to areas 17 and 18, where many studies have documented a profound loss of binocularly activated neurons following early strabismus, in the LSA the majority of cells could still be binocularly driven. Acute or chronic section of the splenium of the corpus callosum reduced but did not abolish binocularity in the LSA. We propose that the widespread callosal connections, the large size of the receptive fields and the peculiar internal circuitry of the LSA all concur in permitting the maintenance of binocular coding in spite of early misalignment of the eyes.
Ca2+ Mobilization in Cultured Rat Cerebellar Cells: Astrocytes are Activated by t‐ACPD
Authors: de Barry Jean , Ogura Akihiko , Kudo Yoshihisa
Published: April 2006

Using primary rat cerebellar cell cultures we observed that trans‐1‐amino‐cyclopentyl‐1, 3‐dicarboxylic acid (t‐ACPD) was able to induce an increase in intracellular [Ca2+] in different cell types. This response was not abolished by external Ca2+ withdrawal, indicating that t‐ACPD triggered the release of intracellularly stored Ca2+. In neurons the t‐ACPD response was monophasic and inhibited by L‐2‐amino‐4‐phosphonobutyrate (APB). In astrocytes, characterized by their immunoreactivity to antisera to glial fibrillary acidic protein and S‐100 protein, the response was oscillatory and resistant to APB application. These results suggest the presence of glutamate metabotropic receptor subtypes in the mammalian brain.
Topographical Aspects of Intracortical Excitation and Inhibition Contributing to Orientation Specificity in Area 17 of the Cat Visual Cortex
Authors: Wörgötter Florentin , Eysel U. T.
Published: April 2006

Intracortical mechanisms contributing to orientation and direction specificity were investigated with a method of local cortical inactivation. Single‐unit activity was recorded in area 17 of the anaesthetized cat while a small volume of cortical tissue 400–2900 μm lateral to the recorded cell was inactivated by γ‐aminobutyric acid (GABA) microiontophoresis. Cells were stimulated with moving bars of variable orientation and changes of the response were monitored. Recording and inactivation sites were histologically verified. Statistically significant changes in orientation tuning during GABA‐induced remote inactivation were observed in 80 of 145 cells (55%), and consisted in a reduced orientation specificity due to either increased (36%) or decreased (19%) responses. Increases of responses were more pronounced for the non‐optimal orientations. This effect mainly occurred with GABA application at distances around 500 μm and is interpreted as loss of inhibition. Reduced orientation specificity as a result of decreasing response mainly to the optimal orientation was interpreted as loss of excitation. This effect most frequently occurred with inactivation at distances around 1000 μm. Loss of inhibition was also elicited from a distance of 1000μm; such inhibition, however, affected only directionality, without inducing changes in orientation tuning. For several cells at distances <1000 μm from the inactivation site a temporal sequence consisting of a change in direction specificity followed by a reduction of orientation specificity, and finally by direct GABAergic inhibition of the cell under study, could be induced with gradually increasing ejecting currents. The results indicate that excitation and inhibition originating from populations of neurons at different horizontal distances differentially contribute to direction and orientation specificity of a given visual cortical cell.
Long Survival of Retinal Ganglion Cells in the Cat After Selective Crush of the Optic Nerve
Authors: Cottee Lynne J. , FitzGibbon T. , Westland K. , Burke W.
Published: April 2006

In each of four cats gentle pressure was applied to one optic nerve by means of an inflatable cuff in order to disrupt the largest axons (Y fibres) and so produce a conduction block in them. It has previously been shown that this technique, as used by us, causes Wallerian degeneration in the fibres posterior to the site of application of the pressure (the crush site). The optic nerves and retinas in these cats were examined 2–2.8 years later. The optic nerves were prepared for electron microscopy and the retinas were flat‐mounted. Here we report an average 90% loss of large axons (>5 μm diameter) in the nerve posterior to the crush site. However, in the part of the nerve anterior to the crush site there was only a 33% loss and in the retina only a 57.5% reduction in the number of neurons of soma diameter >25 μm (i.e. alpha cells, the cell bodies of the Y neurons). These last two sets of values were significantly different, suggesting that the retinal ganglion cells had shrunk relatively more than the axons. Thus, the crushing technique has effectively axotomized almost all the Y fibres but, in spite of this, about half of the alpha retinal ganglion cells have survived this particular form of axotomy, with their axons intact at least for some distance into the optic nerve. This long survival raises the possibility that these neurons may have regenerated axons which have found targets and thus ensured their survival.
Outward Currents in Rat Entorhinal Cortex Stellate Cells Studied with Conventional and Perforated Patch Recordings
Authors: Eder C. , Ficker E. , Gündel J. , Heinemann U.
Published: April 2006

We have studied outward currents of neurons acutely isolated from superficial layers of the entorhinal cortex with whole‐cell patch‐clamp recordings. If cells were held more negative than ‐50 mV, depolarizing voltage commands activated a transient A‐type current together with a sustained outward current. Both currents were sensitive to 4‐aminopyridine, while only the sustained current was blocked by tetraethylammonium. The sustained outward current showed a considerable rundown in amplitude over prolonged recording periods. At the same time its half‐maximal inactivation shifted from ‐74 to ‐ 114 mV. Nystatin perforated patch recordings were used to minimize these perfusion effects. Under such conditions the amplitude and the steady‐state inactivation properties of the sustained outward current remained stable for more than 1 h. Pharmacological investigations revealed that only a small part of the sustained outward current could be attributed to a calcium‐activated potassium current. Therefore most of the rundown has to be due to changes in the delayed rectifier outward current. These results may suggest that the delayed rectifier current is under considerable metabolic control.
The Identification and Localization of the Guanine Nucleotide Binding Protein G0 in the Auditory System
Authors: Canlon Barbara , Homburger Vincent , Bockaert Joël
Published: April 2006

The identification of guanine nucleotide binding proteins (G proteins) in guinea‐pig tissues was assessed by the adenosine diphosphate‐ribosylation of the α subunit by Bordetella pertussis toxin using [α32P] nicotinamide adenine dinucleotide as the substrate followed by sodium dodecyl sulphate ‐ polyacrylamide gel electrophoresis and autoradiography. Three tissues (inferior colliculus, neuroblastoma cells, and the organ of Corti) contained G0α (39 kD), as well as Gi2α (40 kD) and Gi1α and/or Gi3α (41 kD). The stria vascularis and the VIIIth nerve contained mainly Gi2α, Gi1α and/or Gi3α, but G0α was barely detectable. A purified preparation of outer hair cells from the organ of Corti contained all three pertussis toxin substrates including G0α, with the Gi2α (40 kD) subunit being the most prominent. The immunocytochemical localization of the G0α subunit was determined by light microscopy after incubating isolated outer hair cells, Hensen cells and the stria vascularis with affinity‐purified anti‐G0α antibodies. In hair cells a positive reaction was observed along the plasma membrane and around the perimeter of the cuticular plate (zona adherens). Positive reaction was also observed within the infracuticular network extending from the cuticular plate towards the nucleus in outer hair cells. Finally, the base of the outer hair cells also contained G0α. However, it is likely that the G0α that is present in this cell region is not within the hair cell itself, but rather in nerve terminals which remained attached during dissection.
Homocysteate, an Excitatory Transmitter Candidate Localized in Glia
Authors: Grandes Pedro , Do Kim Quang , Morino Patrizia , Cuénod Michel , Streit Peter
Published: April 2006

l‐Homocysteate, a sulphur‐containing l‐glutamate analogue has recently been proposed as a neurotransmitter candidate. However, the cellular localization of this excitatory amino acid remained to be determined. By means of immunocytochemistry, the localization of homocysteate was accomplished in the cerebellar cortex of rats. Cerebellar glia could be defined as the major store of this compound. Homocysteate, thus, may not be a classical neurotransmitter but rather a member of another class of intercellular messengers that might be termed ‘gliotransmitters’.
Differential Expression of the GABAA Receptor Complex in the Dorsal Thalamus and Reticular Nucleus: An Immunohistochemical Study in the Adult and Developing Rat
Authors: Bentivoglio Marina , Spreafico Roberto , Álvarez‐Bolado Gonzalo , Sánchez Marina P. , Fairén Alfonso
Published: April 2006

The distribution of the GABAA receptor/benzodiazepine receptor/chloride channel complex was investigated in the thalamus of the rat by means of immunohistochemistry in adulthood, as well as during embryonic and postnatal development, using a monoclonal antibody. In adults, the immunoreactivity for the GABAA receptor complex was intensely expressed by neuronal processes throughout the dorsal thalamus. Neuronal perikaryal membranes were frequently outlined by punctate immunostaining; cell bodies, intrathalamic fibre bundles and the internal capsule did not display immunoreactivity for the GABAA receptor. Regional differences in the expression of the receptor were consistently observed: the immunostaining was much lighter in the thalamic reticular nucleus than in the dorsal thalamic nuclei and, among the latter, the anteroventral nucleus and the ventral nuclear complex displayed the most intense immunopositivity. Immunostaining for the GABAA receptor was already expressed in embryos at E14, and was homogeneously distributed throughout the neuropil of the dorsal and ventral thalamic primordia. During the first two postnatal weeks, a regional differentiation of the immunopositivity was appreciable in the thalamus, with a progressive reduction in the reticular nucleus and a parallel increase in the dorsal thalamic structures. Immunoreactive neuronal perikarya were not observed in the thalamus at any developmental stage. The expression of the GABAA receptor complex appeared to have reached a mature configuration by the end of the third postnatal week. These findings indicate that in adults the GABAA receptor is differentially expressed by thalamic nuclear structures, including the reticular nucleus. Furthermore, the maturation of the receptor in the thalamus undergoes a rearrangement during the first postnatal weeks that results in a considerable regression within the reticular nucleus.
Development of Neurons and Glial Cells in Cerebral Cortex, Cultured in the Presence or Absence of Bioelectric Activity: Morphological Observations
Authors: Ramakers G. J. A. , Raadsheer F. C. , Corner M. A. , Ramaekers F. C. S. , van Leeuwen F. W.
Published: April 2006

Chronic blockade of bioelectric activity (BEA) has been shown to increase neuronal cell death in tissue culture, but the effects of this treatment on non‐neuronal cells have not been investigated. To determine which cell types are affected by chronic suppression of BEA, we investigated their morphological development in primary cultures of rat cerebral cortex, grown with or without the sodium channel blocker tetrodotoxin (TTX). Morphological development was monitored by phase‐contrast microscopy and by immunofluorescent staining of markers specific for neurons (NSE, MAP2, B‐50, and the 200 kD neurofilament protein), astrocytes (GFAP), oligodendrocytes (galactocerebroside), macrophages (ED‐1) and fibroblasts (fibronectin). Neurons in control cultures steadily increased in size and elaborated a dense network of axons and dendrites during the first 3 weeks. Astrocytes proliferated strongly and formed a ‘bottom‐layer’ on which other cells grew. Part of the astrocytes migrated into the peripheral area of the culture, but retracted to the centre after 14 days in vitro (DIV). Oligodendrocytes and macrophages also increased in number, but oligodendrocytes were completely lost by 28 DIV. After 3 weeks, axons that had grown into the periphery of the culture gradually retracted and/or degenerated, following the retracting astrocytes. Some of the neurons died after 21 DIV, but a large part persisted until 42 DIV. Upon TTX treatment from 5/6 DIV, cultures with few macrophages showed an increase in the proportion of necrotic nuclei at 14 and 21 DIV. The retraction of peripherally located fibres was accelerated by 3–4 days and their degeneration was augmented. Neuronal density decreased to zero between 21 and 42 DIV. Astrocytes showed a clear decrease in density from 28 DIV. Conversely, the density of macrophages was increased about two‐fold from 14 DIV. These results indicate that both neurons and glia are affected by chronic TTX treatment.
Absence of Nerve – muscle Interaction Influences the Survival of Developing Motoneurons
Authors: Burls A. , Subramaniam Krishnan , Lowrie M. B. , Vrbová G.
Published: April 2006

Following sciatic nerve crush at birth, ∼70% of motoneurons to the soleus and 60% of motoneurons to the tibialis anterior (TA) and to the extensor digitorum longus (EDL) die. However, following nerve injury at 5 days, there is negligible motoneuron death. We investigated whether the interaction between the nerve and its target during these 5 days is an important factor for the ability of the motoneuron to survive injury. Nerve‐muscle interaction was blocked shortly after birth by α‐bungarotoxin (BTX) and the effect on motoneuron survival after subsequent injury was examined. It was confirmed that sciatic nerve crush at 5 days produced no significant reduction in motoneuron numbers. However, if nerve crush was preceded by paralysis with α‐bungarotoxin, the number of surviving motoneurons after nerve injury at 5 days was substantially reduced. On the operated side only 43 ± 6.68% of the motoneurons of the soleus pool survived and even fewer, 14 ± 5.0%, in the TA and EDL pool. In a control group of animals paralysed with α‐bungarotoxin at birth but receiving no nerve crush, there was no appreciable reduction in the motoneuron numbers at 28 days in either motor pool. It is concluded that blocking of nerve‐muscle interaction by paralysis in early postnatal life reduces the motoneurons' ability to survive nerve injury later in life, and that this effect is more severe for the motoneurons to the TA and EDL than to the soleus.
Calcium Influx Induced by Stimulation of ATP Receptors on Neurons Cultured from Rat Dorsal Root Ganglia
Authors: Bouvier M. M. , Evans M. L. , Benham C. D.
Published: April 2006

A combination of microspectrofluorimetry and single cell voltage‐clamp was used to examine the response to ATP of cultured neurons from rat dorsal root ganglia. ATP activated an inward current and a rise in internal calcium concentration that was dependent on the external calcium concentration and on the magnitude of the ATP‐induced current response. The response was not affected by prerelease of internal calcium stores with caffeine. The rise in internal calcium was increased at hyperpolarized membrane potentials as the calcium driving force was increased. These results demonstrate that the ATP‐gated channels in these cells can admit a significant amount of calcium in a physiological calcium gradient. This alternative calcium entry pathway could provide an internal calcium signal that is spatially distinct to that generated by voltage‐gated calcium entry.
Paradoxical Modulation of Nociception in Mice by Barbiturate Agonism and Antagonism: Is a GABA Site Involved in Nociception?
Authors: Carmody John , Knodler Leigh , Murray Stuart
Published: April 2006

In a battery of four acute and chronic nociceptive tests, the GABA antagonist picrotoxin produces a uniform and sustained analgesia in mice. By contrast, barbiturates which have been presumed to act at the same receptor produce mixed and paradoxical actions. At a standard time of 10 min after drug administration a convulsant barbiturate [5‐ethyl‐5‐(3′‐rnethyI‐but‐2′‐enyl)‐barbituric acid] produced analgesia in three tests but had no effect in the fourth; a pure hypnotic barbiturate (amylobarbitone) produced hyperalgesia in three tests but analgesia in the fourth; while the mixed hypnotic‐convulsant pentobarbitone produced hyperalgesia in two of the tests and was without any effect in the other two. There was no pattern in these results with respect to acute or chronic nociceptive tests. Surprisingly, with extended observation using the tail‐flick test both pentobarbitone and the pure hypnotic (amylobarbitone) gave early hyperalgesia followed by analgesia; the convulsant barbiturate gave only analgesia. The results suggest a role for GABAA receptors in the transmission of nociceptive information; they also suggest that barbiturates act at quite a different receptor.
C‐fos Induction in the Spinal Cord after Peripheral Nerve Lesion
Authors: Williams Simon , Evan Gerard , Hunt Stephen P.
Published: April 2006

Immunocytochemical localization of a product of the proto‐oncogene c‐fos, Fos protein, was used to map the activity of a subset of rat spinal neurons at 3 days, 3 weeks and 3 months following section of the sciatic nerve. In a well‐established experimental paradigm, the gene was induced by activation of primary afferent fibres with brief noxious sensory stimulation under anaesthetic. Central sciatic projections were demonstrated with isolectin B4 counterstain and GAP43 immunocytochemistry. In Rexed's lamina II of the spinal cord, in which there is somatotopic organization of afferent terminals, Fos‐positive neurons were largely restricted to the projection area of intact peripheral nerves. Three days after a sciatic nerve lesion, the number of Fos‐positive neurons in a cord region innervated by the saphenous nerve was similar to control levels, but was markedly increased by 3 weeks, remaining elevated at 3 months. Three weeks after sciatic nerve section the lectin stain in the area of sciatic representation had almost completely disappeared, and conversely GAP43 staining had greatly intensified. There was no evidence of invasion by Fos‐immunoreactive cells of the area of sciatic representation. After 3 months both the size and the intensity of the lectin gap, and of the corresponding area of increased GAP43 immunoreactivity, appeared reduced. Thus a peripheral nerve lesion was followed by a delayed increase in excitability of the spinal cord as assessed by c‐fos expression, so that greater numbers of second‐order neurons were activated by sensory stimulation of an adjacent intact nerve. These changes may be related to the sensory abnormalities which follow nerve damage.
Enkephalin Expression in Spinal Cord Neurons is Modulated by Drugs Related to Classical and Peptidergic Transmitters
Authors: Foster G. A. , Eiden L. E. , Brenneman D. E.
Published: April 2006

The effects of various neurotransmitter agonists and antagonists on the synthesis and release of methionine enkephalin (mENK) in neuronal cultures of mouse spinal cord and dorsal root ganglia have been measured. Blockade of electrical activity with tetrodotoxin between days 9 and 13 in culture caused a > 95% decrease in the number of mENK‐immunoreactive neurons. This effect was also seen upon the blockade of glycine and β‐adrenergic receptors with strychnine and propranolol, respectively, and stimulation of GABA receptors with muscimol. Stimulation of β‐adrenergic receptors with isoproterenol, or blockade of glutamate and GABA receptors with 2‐aminophosphonovalerate and strychnine, respectively, had a qualitatively opposite action on both the number of mENK‐immunoreactive neurons and enkephalin peptide levels measured by radioimmunoassay. Application of substance P also enhanced the mENK cell number. These data suggest that, at least in the spinal cord, characteristics other than the average level of impulse activity in the afferent input may be critical to the regulation of expression of mENK.
Chronic Epileptic Foci in Neocortex: In Vivo and In Vitro Effects of Tetanus Toxin
Authors: Brener Karin , Amitai Yael , Jefferys John G.R. , Gutnick Michael J.
Published: April 2006

Injection of 0.2–3.0 ng of tetanus toxin into rat parietal neocortex resulted in permanent (> 7 months) changes in the local circuit properties of this tissue. It caused excessive synchronization of neuronal activity. This was seen as spontaneous paroxysmal field potentials and/or evoked all‐or‐none population burst discharges. Such activity was recorded widely over the parietal and temporal areas of both the injected and the contralateral hemispheres from as little as 16 h after injection up to the maximum survival time of 7 months. Several observations suggest that the speed with which the hypersynchronous activity spread to the opposite hemisphere reflects transport of the toxin through corticocortical axons, and consequent blockade of synaptic inhibition. However, from what is known of the half life of the peptide in brain, it is unlikely that the persistent, widespread distribution of epileptiform discharge several months after injection was due to the continued presence of toxin. Thus, intracortical application of tetanus toxin provides a good experimental model of chronic focal epilepsies, and raises fundamental questions regarding the long term regulation of local circuit properties in the neocortex.
Specific Reinnervation of Lesioned Mouse Striatum by Grafted Mesencephalic Dopaminergic Neurons
Authors: Zuddas Alessandro , Corsini Giovanni U. , Barker Jeffery L. , Kopin Irwin J. , di Porzio Umberto
Published: April 2006

Selective lesions of the dopaminergic nigrostriatal system and embryonic neuron grafts were used to study the mechanism by which exogenous neurons can restore transmitter function and to examine CNS development and plasticity. C57BL mice treated with acetaldehyde/1‐methyl‐4‐phenyl‐1,2,3,6‐tetra‐hydropyridine show irreversible loss of substantia nigra dopaminergic neurons. Implants of embryonic mesencephalic dopaminergic neurons functionally reinnervate the striatum and form a dense network of fibres; ∼20% of the implanted dopaminergic cells survive for several months. However, dopaminergic fibre outgrowth and mesencephalic graft development appear lower in control, non‐lesioned, animals. Moreover, implants of embryonic hypothalamic dopaminergic neurons show little or no survival. These results indicate that interactions between embryonic and adult neurons are selective. We suggest that this specificity may be sustained by the action of still unknown trophic and/or tropic factors, possibly produced by the lesioned striatum and by putative inhibitory mechanisms of cell migration and neuritic outgrowth.
Functional Connections Formed by Saphenous Nerve Terminal Sprouts in the Dorsal Horn Following Neonatal Sciatic Nerve Section
Authors: Shortland Peter , Fitzgerald Maria
Published: April 2006

The rostrocaudal distribution of saphenous nerve inputs into the lumbar dorsal horn from L2 to L6 has been investigated in urethane anaesthetized rats whose left sciatic nerve was cut and ligated at birth. In normal cord, electrical stimulation of the saphenous nerve evoked dorsal horn spikes in L2 to caudal L4. Few or no spikes were evoked in L5. After neonatal sciatic nerve section, saphenous nerve stimulation evoked spikes throughout segments L2 to L6. Dorsal horn cell receptive fields were also altered following neonatal sciatic nerve section. A somatotopic map of the lumbar enlargement in normal rats was constructed from the receptive fields (RFs) of adjacent dorsal horn cells. Cells with RFs in the saphenous skin region were concentrated in L3 and rostral L4 and very few were found in L5. After neonatal sciatic nerve section, however, a substantial number of cells with low threshold saphenous skin RFs were also found in caudal L4 and throughout L5. These results show that the central saphenous nerve terminal sprouts that grow into the sciatic terminal region following neonatal sciatic nerve section (Fitzgerald, 1985, J. Comp. Neurol., 240, 414–422; Fitzgerald et al., 1990, J. Comp. Neurol., 300, 370–385) form functional connections. This results in dorsal horn cells that are not normally influenced by saphenous nerve inputs developing substantial low threshold RFs in saphenous nerve skin regions.
Interaction of Noradrenergic and Cholinergic Agonists with Ligands Increasing K‐conductance of Guinea Pig Hippocampal Neurons, in vitro
Authors: Bijak M. , Misgeld U. , Müer W.
Published: April 2006

Single electrode current clamp and voltage clamp recordings were employed to study the effects of noradrenergic agonists and a cholinergic agonist (carbachol, Cch) on the resting membrane potential of CA3 neurons in guinea pig hippocampal slices. Stimulation of muscarinic and β‐adrenergic receptors depolarized, and stimulation of α1‐adrenergic receptor hyperpolarized, CA3 neurons but the membrane potential changes were small. Hyperpolarizations or outward currents induced by baclofen, adenosine or serotonin (5‐HT) were strongly potentiated by α‐noradrenergic agonists and suppressed by Cch at concentrations ten times lower than those having any direct effects on membrane potential. Both the enhancement of the baclofen‐induced hyperpolarization by phenylephrine and its suppression by Cch were pronounced at low concentrations of baclofen, but diminished at higher concentrations. The modulatory effects persisted after blockade of sodium spikes by tetrodotoxin and after blockade of fast inhibitory and excitatory synaptic transmission by picrotoxin and 6‐cyano‐7‐nitroquinoxaline‐2,3‐dione. Our data suggest that, through the postsynaptic interaction with ligands activating potassium conductance, noradrenergic and muscarinic receptor stimulation can exert a stronger inhibitory and excitatory effect on CA3 pyramidal neurons at their resting membrane potential than would be expected from the changes in membrane potential induced by these neuromodulators on their own.
The Projections of Mitral Cells from Small Local Regions of the Olfactory Bulb: An Anterograde Tracing Study Using PHA‐L (Phaseolus vulgaris Leucoagglutinin)
Authors: Buonviso N. , Revial M. F. , Jourdan F.
Published: April 2006

Numerous anatomical and electrophysiological studies have demonstrated a lack of simple point‐to‐point topographical relationships between the olfactory bulb and primary olfactory projection areas. They reveal instead, a complex pattern of divergence and convergence. Furthermore, several authors reported that a single mitral cell could project onto different widely spaced cortical regions of the olfactory cortex. In the present study, we attempted to label the projections of a few mitral cells so close together so that they might be assumed to be connected to the same glomerulus, and to determine if these cells had similar patterns of axonal projections. For this purpose small Phaseolus vulgaris leucoagglutinin (PHA‐L) injections were performed in the olfactory bulb of adult rats. We found that labelling two to five mitral cells, lying close together in the mitral cell layer, resulted in well‐delineated patches of labelled fibres in the cortex. The number of patches was not related to the number of labelled mitral cells but the fibre density in each patch increased with the number of PHA‐L filled somata in the olfactory bulb. We conclude that mitral cells lying close together in the mitral cell layer have similar patterns of axonal projections. Functional implications of such an organization in olfactory coding is discussed.
Characterization of a Voltage‐dependent Calcium Current in the Human Neuroblastoma Cell Line SH‐SY5Y During Differentiation
Authors: Toselli M. , Masetto S. , Rossi P. , Taglietti V.
Published: April 2006

In the presence of retinoic acid, cultured human neuroblastoma SH‐SY5Y cells grow processes indicative of neuronal differentiation. A voltage‐gated Ca current is already present in undifferentiated cells. A gradual increase of the Ca current density occurs during cell differentiation. According to kinetic and pharmacological properties, Ca currents in differentiated cells are indistinguishable from those elicitable in undifferentiated cells and resemble features of the high‐voltage activated currents present in mammalian neuronal cells. ω‐conotoxin strongly depresses high‐voltage activated currents, both in undifferentiated and in differentiated SH‐SY5Y cells. Interestingly, the Ca agonist Bay K 8644 is effective, albeit with great variability from cell to cell, only in differentiated cells and only when barium is the current carrier through the Ca channels. A diversity of high‐voltage activated Ca channels of distinct pharmacology has been recently observed in other kinds of neurons. This requires a redefinition of the role that voltage‐dependent Ca channel subtypes can play in mammalian neurons.
Spatio‐temporal Distribution of Epileptiform Potentials in the Hippocampal Slice: Recordings with Voltage‐sensitive Dyes
Authors: Albowitz Birgit , Kuhnt Ulrich
Published: April 2006

Voltage‐sensitive dyes and fast optical recording techniques were used to monitor the spatio‐temporal activity pattern of epileptiform potentials in hippocampal slices from guinea pigs. Epileptiform potentials were induced by adding 4‐aminopyridine to the bath solution and applying single pulse stimulation either to the stratum pyramidale of area CA3 or to the stratum radiatum of area CA1. Optical activity as well as intra‐ or extracellular electrical activity were recorded from area CA1. There was a good correlation between optical and intracellular records from the same site. The spatio‐temporal activity pattern of control and epileptiform potentials elicited by stimulation of CA1 was similar for the initial part of the potential. Then, epileptiform changes became apparent throughout the vertical extent of pyramidal neurons. Qualitative changes occurred in the stratum moleculare, reflecting activity of apical dendrites, such changes occurred even more strongly in the stratum oriens, reflecting activity of basal dendrites. The activity in the stratum oriens occurred relatively late, so that it cannot account for the initiation of epileptic discharges. It might, however, play an important role in the synchronization and spread of epileptiform potentials. The investigation of the horizontal distribution of potentials throughout the entire area CA1 indicates that different mechanisms are involved in the spread of epileptiform activity elicited by stimulation of CA1 and stimulation of CA3.
Mediodorsal Thalamic Lesions Impair Long‐Term Visual Associative Memory in Macaques
Authors: Gaffan D. , Watkins S.
Published: April 2006

Six cynomolgus monkeys (Macaca fascicularis) were trained to associate visual stimuli with the delivery of various amounts of food reward. The animals had to choose correctly between pairs of stimuli drawn from a population of 16. Four of these stimuli were associated with 0 reward pellets, four with 1 pellet, four with 2 pellets and four with 4 pellets. Mediodorsal thalamic lesions including the medial part of the mediodorsal nucleus, similar to those which are frequently seen in Korsakoff amnesia, produced a severe impairment in this task. The impairment was seen both in memory for the quantity of reward, as expressed in choices between 1‐pellet and 2‐pellet stimuli or choices between 2‐pellet and 4‐pellet stimuli, and also in memory for the qualitative absence or presence of reward, as expressed in choices between 0‐pellet and 1‐pellet stimuli. The deficit in this task establishes that mediodorsal thalamic lesions in monkeys can impair long‐term memory tasks, in addition to their known effects on several short‐term memory tasks. The contrast between the present results and those of previous experiments on visual long‐term memory in the monkey following mediodorsal thalamic lesions can be related to similar contrasts in studies of lesions in the amygdala, suggesting that the functions of these two structures are related.
NMDA Actions on Rat Abducens Motoneurons
Authors: Durand Jacques
Published: April 2006

Intracellular recordings were made from rat abducens motoneurons in vivo during local extracellular micro‐ionophoretic application of N‐methyl‐d‐aspartate (NMDA) and NMDA receptor antagonists. Typical NMDA responses, at a resting potential of –60 mV, consisted of a slow depolarization with an apparent increase in membrane resistance, bursts of action potentials followed by stable repetitive firing, lonophoretic applications of aminophosphonovalerate (APV), kynurenate or MK801 reduced or blocked the NMDA‐induced responses. The NMDA responses were voltage‐dependent. NMDA responses induced by short (< 30 s) NMDA application pulses were blocked by hyperpolarizing the neuron. Long duration (> 30 s) NMDA applications induced rhythmic plateau potentials in hyperpolarized abducens motoneurons. The rhythmic depolarizations (15–30 mV) were modulated in both frequency and duration by current injection. They were abolished by further hyperpolarization or replaced by stable repetitive firing when hyperpolarization was removed. Our data show that NMDA receptors are present in rat abducens motoneurons and may be involved in the induction of rhythmic activities. The voltage‐dependent blockade of somatic NMDA receptor‐associated ion channels by cell hyperpolarization may be important for these oscillations. It is suggested that the rhythmic behaviour is due to the activation of dendritic NMDA receptors.
Innervation of Entorhinal Principal Cells by Neurons of the Nucleus Reuniens Thalami. Anterograde PHA‐L Tracing Combined with Retrograde Fluorescent Tracing and Intracellular Injection with Lucifer Yellow in the Rat
Authors: Wouterlood Floris G.
Published: April 2006

The innervation of dendrites of identified entorhinal principal cells by fibres originating in the nucleus reuniens thalami was studied in the rat. The lectin Phaseolus vulgaris‐leucoagglutinin (PHA‐L, anterograde tracer) was injected into the nucleus reuniens and the fluorescent dye Fast Blue (retrograde tracer) into the hippocampus. After survival, perfusion‐fixation and the preparation of brain slices, entorhinal neurons retrogradely labelled with Fast Blue were intracellularly injected with the dye Lucifer yellow to introduce a specific marker into their dendrites. The transported PHA‐L and the injected Lucifer yellow were visualized through dual peroxidase immunohistochemistry. Varicosities on PHA‐L labelled reuniens fibres abut ascending and descending Lucifer yellow‐filled secondary dendrites of multipolar and pyramidal principal entorhinal neurons that possess either spiny or sparsely spiny dendrites, but they do not appose the perikarya of these cells. In the electron microscope, PHA‐L labelled boutons in the entorhinal cortex were observed forming asymmetrical synaptic contacts with dendritic spines (50%) or shafts (50%). The results indicate that direct thalamic input occurs on dendrites of neurons in the entorhinal cortex which project to the hippocampus.
Immunohistochemistry of c‐fos in Mouse Brain During Postnatal Development: Basal Levels and Changing Response to Metrazol and Kainate Injection
Authors: Sakurai‐Yamashita Yasuko , Sassone‐Corsi Paolo , Gombos Giorgio
Published: April 2006

Levels and cellular distribution of FOS, the product of c‐fos (onco)gene, were studied by immunohistochemistry during the development of mouse brain at rest and after the administration of convulsants. Basal FOS immunoreactivity became detectable only after postnatal day 20 (P20). Metrazol and kainate at the appropriate doses induced convulsions at all ages but, in both cases, FOS accumulated in limbic areas (particularly in the dentate gyrus) only after a certain age: P20 for kainate and P30 for Metrazol. Surprisingly, considering the different molecular targets of Metrazol and kainate, respectively, and the different type of convulsions elicited, the cell groups in the limbic areas in which FOS increased were the same in the two cases. These results suggest that both drugs produced FOS increase by finally activating the same circuit. During ontogeny, the ability to accumulate FOS, which appears after P20, could be the sign of the attained maturity of signal transduction mechanisms in the cells of the hippocampal formation; endogenous signals originating from the activity of the nervous system increase the basal FOS levels and exogenous signals (i.e. like those given, probably locally, by kainate) further increase these levels. Metrazol manifests its capability to induce FOS accumulation only at later ages. We suggest that this occurs because the Metrazol target is probably distant from the hippocampal region and thus the maturity of a nerve pathway(s) is also required for c‐fos induction.
Properties of a High‐threshold Voltage‐activated Calcium Current in Rat Cerebellar Granule Cells
Authors: De Waard M. , Feltz A. , Bossu J. L.
Published: April 2006

Postmitotic cerebellar granule cells, maintained for 5–6 days in Dulbecco's modified essential medium supplemented with 25 mM KCl, have been studied in whole‐cell recording conditions to characterize calcium currents. With 10 mM Ba2+ as the divalent charge carrier, and using a pipette solution highly buffered for Ca2+ (30 mM EGTA, 100 mM HEPES–Tris, pH 7.2), only a high‐threshold voltage‐activated barium current was recorded from a holding potential of – 90 mV. The addition of 1 mM ATP to the pipette medium allowed stable recording for an average duration of 10 min, compatible with pharmacological studies of the barium current. Ninety‐six per cent of the current was half‐inactivated at low negative holding potential (‐76 mV). A total block of current was obtained with 1 μM Cd2+. Sixty‐three per cent of the mean current was abolished by 3 μM ω‐conotoxin (ω‐CgTx; Ki= 10 nM for a 15 min application), but individual cells showed either full sensitivity to this toxin or incomplete sensitivity. Seventy‐eight per cent of the mean current was also abolished by 10 μM nicardipine but with a higher Ki, of 0.5 μM. After exposure to ω‐CgTx, BAY K 8644 had no effect on the remaining current, though it was suppressed by nicardipine. No sensitivity to diltiazem, desmethoxyverapamil or flunarizine could be detected. Our major conclusion is that at least half of the channels have a mixed pharmacology, showing sensitivity to both ω‐CgTx and dihydropyridine antagonists.