bluuebunny/crossref_metadata_2025 huggingface dataset:
Monoaminergic and Peptidergic Innervation of the Intermedio‐Lateral Horn of the Spinal Cord
Authors: Fuxe K. , Tinner B. , Bjelke B. , Agnati L. F. , Verhofstad A. , Steinbusch H. G. W. , Goldstein M. , Hersh L. , Kalia M.
Published: April 2006

In the rat the monoamine and neuropeptide innervation of the sympathetic visceral nuclei has been analysed using retrograde tracing and single and double immunolabelling procedures. When combined with tyrosine hydroxylase (TH), 5‐hydroxytryptamine (5‐HT) and enkephalin (ENK) immunocytochemistry, somata and dendrites of many preganglionic sympathetic neurons projecting to the coeliac ganglion visualized by retrograde tracing are found in close association with strands and plexa of strongly TH, 5‐HT or ENK immunoreactive (IR) nerve terminals, while others have only a minor association with strong TH, 5‐HT and ENK immunoreactivities, suggesting that a differential control of preganglionic sympathetic neurons is possible. Experiments with double immunolabelling procedures give further support to a direct innervation of preganglionic sympathetic neurons by TH, 5‐HT and ENK IR nerve terminals. In conclusion, the present results open up the possibility for differential regulation of the preganglionic sympathetic neurons according to the Sherringtonian concept of spatial occlusion and facilitation in a pool of motoneurons.
Activation of a K‐252b‐Sensitive Protein Kinase is Necessary for a Post‐Synaptic Phase of Long‐Term Potentiation in Area CA1 of Rat Hippocampus
Authors: Reymann K. G. , Davies S. N. , Matthies H. , Kase H. , Collingridge G. L.
Published: April 2006

K‐252b, a potent inhibitor of protein kinases blocked a late phase of long‐term potentiation (LTP) in area CA1 of rat hippocampal slices, resulting in decremental LTP. It also prevented the slowly developing increase in sensitivity of CA1 neurons to iontophoretically administered α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionic acid (AMPA) which was seen in control slices that exhibit nondecremental LTP. However, K‐252b applied 60–180 min after the induction of LTP had no effect on the potentiated synaptic and AMPA‐induced responses. A K‐252b‐sensitive protein kinase may therefore be involved in a slowly developing postsynaptic component of LTP.
Topographical and Synaptic Organization of the GABA‐Containing Pallidosubthalamic Projection in the Rat
Authors: Smith Y. , Bolam J. P. , von Krosigk M.
Published: April 2006

The anterograde transport of Phaseolus vulgaris‐leucoagglutinin (PHA‐L) was combined with postembedding immunocytochemistry for gamma‐aminobutyric acid (GABA) to study the topography, the synaptic organization and the neurotransmitter content of the pallidosubthalamic projection in the rat. After injections of PHA‐L in different parts of the globus pallidus a rich plexus of anterogradely labelled fibres and terminals was found in the ipsilateral subthalamic nucleus. The immunoreactive elements were distributed according to a mediolateral and rostrocaudal topography. Injections of PHA‐L restricted to the lateral two‐thirds of the globus pallidus gave rise to a massive anterograde labelling confined to the lateral half of the subthalamic nucleus. On the other hand, injections of PHA‐L strictly confined to the medial part of the globus pallidus resulted in anterograde labelling that occupied the ventromedial pole of the subthalamic nucleus. In some cases a few retrogradely labelled cells were found in the subthalamic nucleus after PHA‐L injections in the globus pallidus. The perikarya and the primary dendrites of these labelled cells were sometimes surrounded by anterogradely labelled terminals suggesting a close reciprocal connection between the globus pallidus and the subthalamic nucleus. Electron microscopic analysis of the PHA‐L‐labelled terminals revealed that they contain many mitochondria, numerous small round or slightly pleomorphic vesicles and occasionally one or two large dense core vesicles. They form symmetrical synaptic contacts predominantly with the proximal dendrites (39%) and less frequently with the perikarya (31%) and the distal dendrites (30%) of the subthalamic cells. Quantitative measurements showed that the pallidosubthalamic varicosities have a diameter ranging from 0.7 to 4.5 μm and a mean cross‐sectional area of 0.79 ± 0.26 μm2 (Mean ± SD). Postembedding immunocytochemistry for GABA revealed that the PHA‐L‐immunoreactive pallidosubthalamic axon terminals display GABA immunoreactivity. The results of our study demonstrate that the pallidosubthalamic projection is organized according to a mediolateral and rostrocaudal topography and that the proximal dendrites of the subthalamic cells are the major targets of the GABA‐immunoreactive pallidosubthalamic terminals. This suggests that the globus pallidus exerts a powerful control over the subthalamic cells through an inhibitory GABAergic pathway.
Long‐term Activation of Phosphoinositide Turnover Associated with Increased Release of Amino Acids in the Dentate Gyrus and Hippocampus Following Classical Conditioning in the Rat
Authors: Laroche S. , Negro C. Redini‐Del , Clements M. P. , Lynch M. A.
Published: April 2006

The release of amino acids and the hydrolysis of inositol phospholipids were examined in parallel in three hippocampal areas following classical conditioning. Paired or unpaired tone(CS) ‐ shock(US) presentations were given to animals engaged in a previously acquired food‐motivated lever‐pressing task. Conditioned suppression of lever‐pressing was the behavioural measure of conditioning. Twenty‐four hours after the last conditioning session, the dentate gyrus and areas CA3 and CA1 of the hippocampus were removed bilaterally from conditioned and pseudoconditioned animals, and slices cut and stored in liquid nitrogen for subsequent analysis. Crude synaptosomal pellets were prepared to investigate: (i) potassium‐stimulated release of preloaded [3H]glutamate and [14C]aspartate in the presence and absence of extracellular Ca2+; (ii) [3H]inositol labelling of phosphoinositides and inositol phosphates; and (iii) [14C]arachidonic acid labelling of 1,2‐diacylglycerol (1,2‐DG). Potassium‐stimulated, Ca2+‐dependent release of [3H]glutamate in synaptosomes prepared from the dentate gyrus and area CA3 was significantly greater in conditioned animals than in pseudoconditioned animals. In area CA1, K+‐stimulated, Ca2+‐dependent release of [14C]aspartate was significantly increased in conditioned animals. These results confirm in synaptosomes, and extend to a period of 24 h our previous report of an increased release of transmitter in the dentate gyrus and hippocampus associated with classical conditioning. In parallel with the increased release of amino acids, learning was associated with a significant increase in labelling of phosphoinositides and inositol phosphates by [3H]inositol and a significant increase in labelling of 1,2‐DG by [14C]arachidonic acid in the three hippocampal areas examined. It is suggested that a long‐lasting presynaptic activation of inositol lipid metabolism may contribute to the learning‐dependent increase in the capacity of hippocampal terminals to release transmitter and hence to the maintenance of a neurochemical trace which may, at least in part, underlie lasting changes in synaptic function built up during associative learning.
Memory for Places and the Region of the Mamillary Bodies in Rats
Authors: Saravis S. , Sziklas V. , Petrides M.
Published: April 2006

Rats with extensive lesions of the mamillary bodies and the immediately adjoining areas exhibited a severe impairment on two spatial memory tasks. In the first task, the animals had to retrieve food from each one of eight separate locations within the daily test session. In the second task, the animals were allowed to visit a particular location and retrieve food from it and, after a variable delay, they had to select between returning to the location they had already visited and a new location that now contained the food. Rats with lesions of the mamillary region were able to perform the task with minimal delay, but their performance was impaired as the delay increased. Finally, rats with mamillary lesions were not impaired in learning a visual discrimination task or its reversal. The results show that extensive damage in the mamillary region can lead to significant and long lasting spatial memory impairments.
Stimulus‐Dependent Neuronal Oscillations in Cat Visual Cortex: Inter‐Columnar Interaction as Determined by Cross‐Correlation Analysis
Authors: Engel Andreas K. , König Peter , Gray Charles M. , Singer Wolf
Published: April 2006

We have demonstrated previously that neurons in cat striate cortex, in response to their preferred stimuli, exhibit oscillatory responses in a frequency range of 40–60 Hz. Recently, we obtained evidence that such oscillatory responses can synchronize across columns. We have now performed an extensive analysis of this phenomenon for both unit and field potential responses. In addition, we studied the stimulus conditions leading to intercolumnar synchronization. We recorded both multi‐unit activity and local field potentials from area 17 of adult cats with arrays of several electrodes. Interelectrode distances ranged from 0.4 to 12 mm. For all pairs of unit (n = 200) and field potential (n = 174) recordings, we computed auto‐ and cross‐correlation functions. The modulation of the correlograms was quantified by fitting a damped sine wave (Gabor) function to the data. Cross‐correlation analysis of the unit data revealed that in 90 out of 200 cases the recorded cells established a constant phase‐relationship of their oscillatory responses. This occurred, on average, with no phase difference. If the receptive fields were nonoverlapping, we observed a synchronization primarily between cells with similar orientation preferences. Cells with overlapping receptive fields also showed a high incidence of synchronization if their orientation preferences were different. In this latter group, synchronization occurred even in cases where the stimulus was optimal for only one of the recording sites. Under conditions of monocular instead of binocular stimulation the oscillatory modulation of the responses was attenuated, but the cross‐correlogram still indicated a significant interaction. Similar effects were seen with the application of stationary instead of moving stimuli. A synchronization of oscillatory field potential responses was observed in 136 out of 174 paired recordings. At all distances investigated, the probability of synchronization of field potential responses was independent of the orientation preferences of the cells. However, the strength of interaction decreased with increasing spatial separation. Control experiments showed that the synchronization of field potential responses was not due to volume conduction. The results demonstrate that oscillatory responses at separate cortical sites can transiently synchronize. The probability and strength of synchronization are dependent on the spatial separation of the recorded cells and their orientation preferences. In addition, the cross‐columnar synchronization is influenced by features of the visual stimulus. It is suggested that this synchronization provides a mechanism for the formation of neuronal assemblies in the visual cortex.
Stimulus‐Dependent Neuronal Oscillations in Cat Visual Cortex: Receptive Field Properties and Feature Dependence
Authors: Gray Charles M. , Engel Andreas K. , König Peter , Singer Wolf
Published: April 2006

Previously we have demonstrated that neurons in the striate cortex of lightly anaesthetized cats exhibit oscillatory responses at a frequency near 50 Hz in response to their preferred stimuli. Here we have used both single and multiple unit recording techniques to determine: (i) the receptive field properties and laminar distribution of cells exhibiting oscillatory responses; and (ii) the influence of changing stimulus properties on the temporal behaviour of the oscillatory responses. Oscillatory responses were detected and evaluated by computation of the autocorrelation function of the neuronal spike trains. We recorded oscillatory responses in 56% of the standard complex cells and in 12% and 11% of the simple and special complex cells. Cells exhibiting oscillatory responses were located primarily in supra‐ and infragranular layers. The oscillatory modulation amplitude of the autocorrelation function was enhanced by binocular stimulation (9 out of 16 cells) and reduced by combined stimulation with optimal and orthogonally orientated light bars (16 out of 21 cells). Changing stimulus orientation caused no change in the oscillation frequency of the sampled population of cells, while oscillation frequency increased monotonically with respect to stimulus velocity within the range of 1–12 degrees per second (10 out of 11 cells). The oscillatory modulation of the autocorrelation function increased as a function of stimulus length within the boundary of the cell's receptive field (11 out of 11 cells). In 6 out of these 11 cells, the responses did not show an oscillatory modulation if elicited by small moving spots of light. Moving stimuli were much more effective in evoking oscillatory responses than were stationary stimuli (19 out of 20 cells). In no instance, using either stationary or moving stimuli, was the phase of the oscillatory response synchronized with the stimulus. These results demonstrate functional heterogeneity among cells within striate cortex based on their temporal firing patterns and provide evidence that the temporal pattern of oscillatory cellular activity is influenced by changes in stimulus properties.
Ion Dependence and Receptor Mediation of Glutamate Toxicity in the Immature Rat Hippocampal Slice
Authors: Lehmann Anders , Jacobson Ingemar
Published: April 2006

Glutamate (glu) is a major excitatory transmitter and a toxin in the brain. In the present study, the immature rat hippocampal slice was used to determine the morphology, topography, ionic mediation and receptor specificity of glu toxicity. Slices were exposed to glu for 30 min, and the damage was evaluated after 3 h of recovery in regular medium. The effects on glu toxicity of changes of [Ca2+], [Cl‐] and [Na+] were determined. The receptor preference of glu was assessed by using the N‐methyl‐D‐aspartate (NMDA) antagonist MK‐801 and the kainate (KA)/quisqualate (QA) antagonist DNQX, alone or in combination. Further, to see whether glu produces cytotoxicity via osmolysis, the effects of hyperosmolal sucrose on glu toxicity were studied. Glu toxicity was similar to the previously described NMDA toxicity with regard to cytopathology, but differed in some aspects from that caused by KA and QA. The severity of the lesion was determined by the proximity of neurons to the incubation fluid, probably as a consequence of cellular accumulation of the amino acid. Omission of Ca2+ abolished glu toxicity in all neurons except the granule cells of the outer blade. This population was completely protected when Ca2+ was omitted and [Cl‐] was reduced. Elevation of [Ca2+] markedly aggravated the lesion caused by glu. Substitution of isethionate for Cl‐ worsened the glu‐induced damage, whilst the amino acid produced qualitatively different neuropathology when choline substituted for Na+. Apparently glu did not damage hippocampal nerve cells through an osmolytic mechanism as medium supplemented with 100 mM sucrose increased the toxicity of glu. Since the lesion produced by glu was more widespread in the presence of high [Ca2+], the effects of receptor antagonists were studied under this condition. MK‐801 inhibited glu toxicity whereas DNQX had no effect. Combination of MK‐801 and DNQX did not offer better protection than did MK‐801 alone. The results suggest that Ca2+ is the main (but not single) determinant of glu toxicity in the immature hippocampal slice. The ionic requirements of glu neurotoxicity are identical to those of NMDA, but differ from those of KA and QA. The notion that glu is a selective NMDA agonist in the present model was confirmed by the protection of MK‐801, and by the lack of an effect of DNQX. This is the first report demonstrating that the toxicity of glu is mediated by NMDA receptors in brain tissue which has developed normally. The findings indicate that specific blockade of NMDA receptors may be the most rational strategy in the prevention of glu‐related neuronal death occurring in certain neurological anomalies.
Activity‐Dependent Changes in Rat Ventral Horn Neurons in vitro; Summation of Prolonged Afferent Evoked Postsynaptic Depolarizations Produce a D‐2‐Amino‐5‐Phosphonovaleric Acid Sensitive Windup
Authors: Thompson S. W. N. , King A. E. , Woolf C. J.
Published: April 2006

The synaptic responses of lumbar ventral horn neurons including identified flexor motoneurons, to graded stimulation of peripheral nerves have been recorded in vitro in the young rat spinal cord‐hindlimb preparation. Single shock stimulation of low threshold myelinated afferents evoked short latency (< 20 ms) short duration (<1.0 s, 391 ± 42 ms n = 43 SEM) compositive mono‐ and polysynaptic potentials. Recruitment of both thinly myelinated (A delta) and unmyelinated (C) afferent fibres elicited a prolonged postsynaptic depolarization (> 1 s) in all cells. In the majority of cells (67.4%), this depolarization exceeded 4.0 s in duration (8.01 ± 0.4 s, n = 26, maximum 14 s). In the remainder, shorter responses were evoked (< 3.0 s, mean = 1.74 ± 0.4 s, n = 18). In those cells where the postsynaptic response to a single A delta or C fibre strength stimulus exceeded 4 s, low frequency (0.5–1.0 Hz) repetitive stimulation resulted in a temporal summation of the postsynaptic depolarizations, which generated a cumulatively increasing depolarization. This incrementing depolarization was sufficient in 33% of the cells to produce a progressive increase in spike discharge (windup). On cessation of the train of stimuli the depolarization decayed slowly (65 ± 27 s). The N‐methyl D‐aspartic acid (NMDA) receptor antagonist D‐2‐amino‐5‐phosphonovaleric acid (d‐APV) reduced the duration and amplitude of the prolonged postsynaptic depolarizations elicited by a single shock stimulation of small diameter afferents by 57% and 50% respectively. A smaller effect was produced on the low threshold afferent evoked early excitatory postsynaptic potentials (EPSP) (3% decrease in amplitude and 24% decrease in duration). In the presence of d‐APV the cumulatively incrementing depolarization produced by repetitive stimulation was substantially reduced and windup failed to occur. Activity‐dependent amplifications of primary afferent evoked responses in spinal neurons therefore involves a temporal summation of d‐APV sensitive prolonged postsynaptic depolarizations.
Re‐expression of Nerve Growth Factor Receptor after Axonal Injury Recapitulates a Developmental Event in Motor Neurons: Differential Regulation when Regeneration is Allowed or Prevented
Authors: Wood S. J. , Pritchard J. , Sofroniew M. V.
Published: April 2006

Motor neurons in the brainstem and spinal cord transiently express nerve growth factor receptors (NGFr) during development, but not in normal adult animals. In this study, NGFr was immunohistochemically identified in hypoglossal motor neurons after different types of peripheral axonal injury in adult rats. NGFr is re‐expressed in motor neurons 7 days after a nerve crush injury, and has disappeared again by 28 days. These times correspond, respectively, to the active phase of regeneration, and a time by which regeneration has largely been completed, as determined by electrical activation of tongue muscle twitch. In contrast, 7 days after nerve transection and ligation of the proximal stump to prevent regeneration, there is no re‐expression of NGFr, but 28 days after such treatment NGFr is present in a few neurons. By this time, neuroma formation has begun proximal to the end of the cut and ligated nerve. Together, these findings suggest that motor neurons transiently re‐express NGFr during regeneration and not in response to axonal transection per se. The signal triggering re‐expression thus seems more likely to be the introduction of a message from the site of injury, rather than the loss of a target‐derived message. Although the function of NGFr in developing and regenerating motor neurons is not known, its expression appears to be associated with periods of axonal growth and maturation.
Striatal NPY‐Containing Neurons Receive GABAergic Afferents and may also Contain GABA: An Electron Microscopic Study in the Rat
Authors: Vuillet J. , Goff L. Kerkerian‐Le , Kachidian P. , Dusticier G. , Bosler O. , Nieoullon A.
Published: April 2006

Dual labelling methods were applied to localize simultaneously neuropeptide Y (NPY) and glutamate decarboxylase (GAD) immunoreactivities on ultrathin sections of the rat caudate‐putamen (CP). By means of a double peroxidase‐anti‐peroxidase technique, using 3,3′‐diaminobenzidine and benzidine dihydrochloride as chromogens in animals with no colchicine pretreatment, GAD immunoreactivity was found to be present in terminals only whereas NPY immunoreactivity was detected in neurons displaying the features of aspiny type cells and processes. With this approach, we observed numerous synaptic associations of the symmetrical type between GAD‐immunoreactive (‐Ir) axonal boutons and NPY‐Ir cell bodies and dendrites. By combining immunoperoxidase and radioimmunocytochemical labelling in animals pretreated with colchicine, NPY was again detected in a single population of aspiny type neurons whereas GAD immunoreactivity was observed in neurons which could be classified as aspiny and spiny on the basis of their ultrastructural characteristics. All the cells of the aspiny type displaying clear‐cut NPY immunoreactivity were also found to be GAD‐positive. Some other neurons of both the aspiny and the spiny type were found to be immunoreactive to GAD alone. GAD/NPY dually labelled terminals were also observed and some axo‐axonic appositions between GAD‐ and NPY‐Ir terminals were also detected. All in all, these data show that NPY aspiny type neurons of the rat CP receive GABAergic afferents and provide morphological support for two hypotheses: that NPY is co‐localized with GABA in some cell bodies, dendrites and axons, and that presynaptic interactions may occur between NPY and GABAergic neuronal systems.
The Maturation of the Superior Collicular Map of Auditory Space in the Guinea Pig is Disrupted by Developmental Visual Deprivation
Authors: Withington‐Wray D. J. , Binns K. E. , Keating M. J.
Published: April 2006

In the normal guinea pig a map of auditory space appears, in the deeper layers of the superior colliculus, at 32 days after birth (DAB). The animal is unable to construct this collicular map of auditory space in the absence of developmental visual experience. Auditory receptive fields of animals dark‐reared from birth are typically large, occupying most of the contralateral hemifield. There is no topographic relationship between the collicular location of the recording electrode and the spatial position from which auditory stimuli elicit a maximal response. The fields of dark‐reared animals resemble, in their tuning parameters, the spatially undifferentiated fields typical of young postnatal normal guinea pigs. To investigate the time‐course during which visual experience is required for map emergence, animals received normal visual experience until either 18 or 26 DAB and were then dark‐reared until the terminal mapping experiment. Maps developed in neither group. Animals provided with a normal visual environment until 30 DAB, and then placed in the dark did, however, construct topographically organized spatial maps with discrete spatial receptive fields. Maps also failed to emerge in animals receiving normal visual experience both before and after a 4‐day period of visual deprivation between 26 and 30 DAB. We conclude that this 4‐day period, or part of it, constitutes a ‘crucial’ period during which visual experience is required for the normal elaboration of the collicular map of auditory space.
A Collection of cDNA Clones with Specific Expression Patterns in Mouse Brain
Authors: Kato Kikuya
Published: April 2006

A total of 950 cDNA clones were randomly selected from mouse cerebellar cDNA libraries, and of these, about 130 clones were found to correspond to mRNAs which were expressed unequally between the cerebellum and other parts of mouse brain. Their distribution patterns in adult mouse brain were analysed by in situ hybridization, and eight clones were found restricted to specific regions of the brain, including four clones specific to cerebellar granule cells and one clone specific to Purkinje cells. Another 27 clones were preferentially expressed in a diverse, but distinctive subpopulation of brain cells. Among them seven clones were especially abundant in specific nuclei, and three in specific fibre bundles. These clones will be useful in defining new subpopulations of brain cells characterized by different gene expression.
Insulin and Neuroparsin Promote Neurite Outgrowth in Cultured Locust CNS
Authors: Vanhems Elisabeth , Delbos Marline , Girardie Josiane
Published: April 2006

Organotypic cultures of locust embryo central nervous system (CNS) were used to study the influence of hormonal factors on neurite outgrowth. Explants from the third thoracic ganglion (embyronic day 9) were grown in a serum‐free medium and exposed to insulin, neuroparsin, a recently characterized insect neurohormone, somatostatin and two insect hormones: 20‐hydroxyecdysone and juvenile hormone. These hormonal factors were tested either alone or in several combinations. In our culture system both insulin and neuroparsin promoted extensive neurite outgrowth. Their effects were quantitatively similar. Somatostatin had no effect on neurite formation, but was a growth factor for glial cells. 20‐hydroxyecdysone was a required factor for glial cell and neurite survival. Juvenile hormone did not have any observable effects in this culture system. When insulin was added in combination with 20‐hydroxyecdysone the stimulation of neurite outgrowth exceeded that seen when insulin was added alone. A similar enhancement was observed with the combination of neuroparsin and 20‐hydroxyecdysone. We conclude that in locusts: (i) insulin can be implicated as a neurotrophic factor as in vertebrates; and (ii) neuroparsin, a locust neurohormone, can also be characterized as a neurotrophic factor for the locust. Moreover, both neurohormones interact synergistically with the steroid hormone 20‐hydroxyecdysone to enhance neurite growth.
Effect of Glutamate and lonomycin on the Release of Arachidonic Acid, Prostaglandins and HETEs from Cultured Neurons and Astrocytes
Authors: Oomagari Kiyoshi , Buisson Bruno , Dumuis Aline , Bockaert Joël , Pin Jean‐Philippe
Published: April 2006

The release of arachidonic acid (ArA) metabolites from mouse neurons and astrocytes in primary culture has been studied in response to ionomycin or glutamate stimulation. Cells were preincubated with [3H] ArA for 24 h and the radioactivity released was examined by HPLC. In striatal, cortical and hippocampal neurons, glutamate and ionomycin strongly stimulated the release of ArA, but neither prostaglandins (PGs) nor hydroxyeicosatetraenoic acids (HETEs) could be detected. If they were released, these latter compounds represented < 0.02% of the amount of ArA. In contrast, in astrocyte cultures, ionomycin (but not glutamate) strongly stimulated the release of PGs and HETEs as well as ArA. Reversed‐ and straight‐phase HPLC analysis revealed the presence of PGD2, PGE2, PGF2α, 12‐hydroxyheptadeca‐5, 8,10‐trienoic acid (HHT) and HETEs (15‐HETE, 11‐HETE and 5‐HETE). Indomethacin inhibited the release of PGs and HHT, but also that of 11‐ and 15‐HETE, indicating that these two HETEs may be produced through the cyclooxygenase pathway. Metabolism of [3H]ArA was also examined in cellular homogenates. Although > 50% of the [3H]ArA was metabolized to PGF2α, PGE2, PGD2, HHT, 15‐ and 11‐HETE in cultured astrocyte homogenates, no [3H]ArA metabolism could be detected in cultured striatal neuron homogenates. Moreover, neuronal homogenates did not inhibit the metabolism of [3H]ArA observed in either astrocyte or platelet homogenates. These results indicate that central neurons in primary culture possess very low lipoxygenase and cyclooxygenase activities. They emphasize the need to identify the cellular source of ArA metabolites in the brain, particularly when considering the multiple new messenger roles proposed for these molecules, such as that of retrograde messengers involved in synaptic plasticity phenomena.
Developmentally Regulated Expression of HDNF/NT‐3 mRNA in Rat Spinal Cord Motoneurons and Expression of BDNF mRNA in Embryonic Dorsal Root Ganglion
Authors: Ernfors Patrik , Persson Hakan
Published: April 2006

Northern blot analysis was used to demonstrate high levels of hippocampus‐derived neurotrophic factor/ neurotrophin‐3 (HDNF/NT‐3) mRNA in the embryonic day (E) 13–14 and 15–16 spinal cord. The level decreased at E18–19 and remained the same until postnatal day (P) 1, after which it decreased further to a level below the detection limit in the adult. In situ hybridization revealed that the NT‐3 mRNA detected in the developing spinal cord was derived from motoneurons and the decrease seen at E18–19 was caused by a reduction in the number of motoneurons expressing NT‐3 mRNA. The distribution of NT‐3 mRNA‐expressing cells in the E15 spinal cord was very similar to the distribution of cells expressing choline acetyltransferase or nerve growth factor receptor (NGFR) mRNA. Moreover, a striking similarity between the developmentally regulated expression of NT‐3 and NGFR mRNA was noted in spinal cord motoneurons. A subpopulation of all neurons in the dorsal root ganglia expressed brain‐derived neurotrophic factor (BDNF) mRNA from E13, the earliest time examined, to adulthood. These results are consistent with a trophic role of NT‐3 for proprioceptive sensory neurons innervating the ventral horn, and imply a local action of BDNF for developing sensory neurons within the dorsal root ganglia.
L‐Homocysteate Preferentially Activates N‐methyl‐D‐aspartate Receptors to CA1 Rat Hippocampal Neurons
Authors: Provini L. , Ito S. , Ben Ari Y. , Cherubini E.
Published: April 2006

Intracellular recordings and current and single‐electrode voltage‐clamp techniques were used to study the membrane responses of CA1 pyramidal neurons to bath application of L‐homocysteic acid (L‐HC) in the rat hippocampal slice preparation. In control artificial cerebrospinal fluid (ACSF), L‐HC (25 ‐ 250 μM) depolarized the membrane and induced a burst‐like firing pattern. Both the membrane depolarization and the burst firing were blocked by the N‐methyl‐D‐aspartic acid (NMDA) receptor antagonists D‐(‐)‐2‐amino‐5‐phosphonovaleric acid (AP‐5, 50 μM), D‐(‐)‐2‐amino‐7‐phosphonoheptanoic acid (AP‐7, 50 μM) and (±)‐3‐(2‐carboxy‐pipera‐zin‐4‐yl)‐propyl‐1‐phosphonic acid (CPP, 20 μM). In ACSF containing tetrodotoxin (1 μM), L‐HC (100–300 μM) induced at resting membrane potential a depolarization which was associated with a small increase in input conductance. These effects were unaffected by 6‐cyano‐7‐nitroquinoxaline‐2, 3‐dione (CNQX, 10–20 μM) but were fully blocked by AP‐5, AP‐7 (50 μM) and CPP (10–20 μM). In voltage‐clamp experiments, L‐HC induced slow inward currents which were voltage‐dependent between ‐ 70 and ‐ 30 mV and reversed polarity near 0 mV. The L‐HC‐induced inward current was unaffected by CNQX (10–20 μM) but was strongly reduced by AP‐5 or AP‐7 (50 μM). The L‐HC‐induced inward current was temperature‐dependent. Between ‐60 and ‐70 mV, its amplitude increased by 320% when the temperature was lowered from 33 to 22°C. The L‐HC‐induced current was also potentiated by the specific L‐HC uptake blocker β‐p‐chlorophenylglutamate (Chlorpheg, 0.5–2 mM). These data suggest that L‐HC preferentially activates NMDA receptors in CA1 hippocampal neurons.
Lesions of the Cerebral Cortex and Caudate‐Putamen Enhance GABA Function in the Rat Superior Colliculus
Authors: Kilpatrick I. C. , Neal J. W. , Pearson R. C. A. , Powell T. P. S.
Published: April 2006

Unilateral lesions of the rat frontal cortex were made either alone or in combination with the caudate‐putamen in order to examine (a) their morphological influence on the substantia nigra and (b) their neurochemical influence on GABA function in the superior colliculus. One to two months following the combined lesion, neuronal somata in the ipsilateral pars reticulata of the substantia nigra were clearly hypertrophied (+ 30%). Morphological changes in the substantia nigra were not evident contralateraly or in animals bearing only cortical lesions. One to two months following cortex‐only lesions, no significant alterations in tectal GABA concentration were observed. However, the combined lesion induced elevations of GABA within both the medial and lateral sectors of the intermediate and deep layers of the superior colliculus. This effect was restricted to the ipsilateral side and was most pronounced in lateral sectors. The vast majority of GABA released from superfused control tectal slices by a depolarizing stimulus (35 mM KCI) was calcium‐dependent. Such evoked GABA release from ipsilateral tectal slices was significantly reduced (‐25%) by unilateral lesions of the substantia nigra, a structure that is known to provide GABA‐containing inputs to the tectum. In contrast, cortical lesions alone significantly enhanced the evoked tectal GABA release (+ 66%), although their influence was again confined to the ipsilateral side. Combined lesions of the cerebral cortex and caudate‐putamen significantly enhanced the evoked GABA release from tectal slices in both hemispheres but the changes were most marked ipsilaterally (+ 147%). It is suggested that the hypertrophy of GABA‐containing nigrotectal somata seen after removal of corticostriatal, corticotectal and in particular GABA‐containing striatonigral fibres may reflect concomitant increases in GABA synthesis within and/or sprouting of nigrotectal terminals.
The Effects of NMDA Antagonists on Neuronal Activity in Cat Spinal Cord Evoked by Acute Inflammation in the Knee Joint
Authors: Schaible Hans‐Georg , Grubb Blair D. , Neugebauer Volker , Oppmann Maria
Published: April 2006

In α‐chloralose‐anaesthetized, spinalized cats we examined the effects of NMDA antagonists on the discharges of 71 spinal neurons which had afferent input from the knee joint. These neurons were rendered hyperexcitable by acute arthritis in the knee induced by kaolin and carrageenan. They were located in the deep dorsal and ventral horn and some of them had ascending axons. The N‐methyl‐d‐aspartate (NMDA) antagonists ketamine and d‐2‐amino‐5‐phosphonovalerate (AP5), were administered ionophoretically, and ketamine was also administered intravenously. In some of the experiments the antagonists were tested against the agonists NMDA and quisqualate. The effects of the NMDA antagonists consisted of a significant reduction in the resting activity of neurons and/or the responses of the same neurons to mechanical stimulation of the inflamed knee. Intravenous ketamine was most effective in suppressing the resting and mechanically evoked activity in 25 of 26 neurons tested. Ionophoretically applied ketamine had a suppressive effect in 11 of 21 neurons, and AP5 decreased activity in 17 of 24 cells. The reduction in the resting and/or the mechanically evoked discharges was achieved with doses of the antagonists which suppressed the responses to NMDA but not those to quisqualate. These results suggest that NMDA receptors are involved in the enhanced responses and basal activity of spinal neurons induced by inflammation in the periphery.
The Effect of Calcium Channel Antagonists on Spontaneous and Evoked Epileptiform Activity in the Rat Neocortex In Vitro
Authors: Boulton Caroline L. , O'Shaughnessy Celestine T.
Published: April 2006

Calcium influx through voltage‐activated calcium channels may play a crucial role in the propagation and maintenance of seizure activity. We have examined the contribution of various types of calcium currents to epileptogenesis by studying the effects of various calcium channel blockers on epileptiform activity. N‐methyl‐d‐aspartate receptor‐mediated epileptiform activity was induced by removal of magnesium ions superfusing the cortex, or by low‐frequency stimulation of the underlying white matter. CoCl2, CdCl2 and ω‐conotoxin, acting at the N‐ and L‐type calcium channels, significantly reduced epileptiform activity. L‐channel antagonists nifedipine and verapamil, and the agonist BAY K 8644, increased spontaneous bursting in cortical wedges, but had no effect upon evoked activity. The T‐channel blocker NiCI2 had variable effects on epileptiform activity, whereas phenytoin consistently reduced such activity. These results suggest that calcium influx underlying epileptiform activity in the rat neocortex may occur at least partially via the activation of the N‐type calcium channel. However, contributions from other calcium channel types cannot be excluded.
Nerve Growth Factor Receptor‐immunoreactive Fibres Innervate the Reticular Thalamic Nucleus: Modulation by Nerve Growth Factor Treatment in Neonate, Adult and Aged Rats
Authors: Fusco M. , Bentivoglio M. , Vantini G. , Guidolin D. , Polato P. , Leon A.
Published: April 2006

Terminal arborizations expressing nerve growth factor receptor (NGF‐R) have been detected with immunohistochemistry in the reticular thalamic nucleus of neonate, adult and aged rats. Intracerebroventricular administration of nerve growth factor (NGF) resulted in a dramatic increase in NGF‐R immunoreactivity throughout the lifespan. This effect was paralleled by a concomitant increase in NGF‐R immunopositivity in the neurons of the basal forebrain, which was here demonstrated also in aged animals, thus indicating that the NGF‐R immunoreactivity within the reticular thalamic nucleus derives in all likelihood from cholinergic neuronal cell bodies of the basal forebrain. Our results demonstrate a prominent ability of NGF to up‐regulate its receptors within fibres innervating the reticular thalamic nucleus, and show that this up‐regulation of NGF‐R is maintained throughout the lifetime. Altogether this indicates that the reticular thalamic nucleus may represent a new, important site of action of endogenous NGF or NGF‐like molecules within the brain. In view of the crucial role played by the reticular thalamic nucleus in gating thalamocortical information, the autoregulation of NGF‐R in this structure may have important concomitants in both physiological and pathological conditions.
The Isolation and Identification of Spinal Neurons That Control Movement in the Xenopus Embryo
Authors: Dale Nicholas
Published: April 2006

A procedure for isolating spinal neurons of the Xenopus embryo has been devised. Using a variety of methods four of the eight previously described categories of neuron can be distinguished in vitro. Firstly, since many anatomical features of the neurons survived dissociation, sensory neurons and glycinergic inhibitory interneurons could be identified after isolation using anatomical criteria. Secondly, by selective labelling of the neurons in the intact spinal cord with fluorescein‐conjugated dextran amines prior to dissociation, three classes of isolated neuron could be identified: motoneurons, putative excitatory interneurons and, once again, inhibitory interneurons. The identity of the inhibitory interneurons has been confirmed using glycine immunocytochemistry. The physiological properties of the isolated neurons were similar to those of their in vivo counterparts. The dissociated neurons exhibited strong membrane accommodation and outward rectification, both of which could be blocked by the injection of Cs+ ions. The neurons also retained their receptors for the agonists N‐methyl‐d‐aspartate, kainate, quisqualate, glycine and GABA. Both the membrane properties and pharmacological sensitivity of the isolated neurons therefore appeared to be unaltered by the dissociation procedure. Thus the four classes of neuron from the Xenopus embryonic nervous system that can be identified after isolation constitute the basis for a valid model for detailed study of how the properties of individual neurons contribute to the functioning of the circuitry that underlies locomotor pattern generation in vertebrates.
An Organotypic Spinal Cord‐Dorsal Root Ganglion‐Skeletal Muscle Coculture of Embryonic Rat. I. The Morphological Correlates of the Spinal Reflex Arc
Authors: Spenger Christian , Braschler Urs Felix , Streit Jürg , Lüscher Hans‐Rudolf
Published: April 2006

The cytoarchitecture of a spinal cord‐dorsal root ganglion ‐ skeletal muscle tissue coculture system was investigated at the level of the light microscope using a number of different staining techniques. In these cultures central synapses between dorsal root ganglion (DRG) cells and interneurons in the ventral spinal cord and between DRG cells and motoneurons were visualized by parvalbumin immunostaining and by intracellular horseradish peroxidase (HRP) filling of DRG cells. Skeletal muscle fibres regenerated in vitro first into multinucleated myotubes, and around day 8 in vitro into well differentiated muscle fibres with regular cross‐striation. At the same time newly formed motor endplates could be visualized using acetylcholinesterase staining. The axons of motoneurons could be traced retrogradely by local application of HRP to the regenerated muscle fibres. The motor axons sometimes gave off collaterals reminiscent of Renshaw collaterals at about 300 μm from the axon hillock. Intracellular filling of motoneurons with HRP revealed that only a minority of the motoneurons within a culture had reached their appropriate target. Comparing the dendrograms of the motoneurons which had innervated muscles to those which had not suggested that motoneurons innervating muscle tissue had more complex dendritic trees and larger somata than those which did not innervate muscle tissue. Peripheral neurites of parvalbumin‐immunoreactive DRG cells coiling around regenerated muscle fibres could be demonstrated in these cultures. These probably correspond to that part of the sensory muscle spindle apparatus which developed in vivo. However, only a few of the several hundred DRG cells found in every culture were parvalbumin‐immunoreactive, suggesting that the actual number of la and II afferents within the population of DRG cells in culture is very small. This study demonstrates that all the neural elements necessary for the segmental spinal reflexes develop and can be maintained for several weeks in vitro.
An Organotypic Spinal Cord‐Dorsal Root Ganglion‐Skeletal Muscle Coculture of Embryonic Rat. II. Functional Evidence for the Formation of Spinal Reflex Arcs In Vitro
Authors: Streit Jürg , Spenger Christian , Lüscher Hans‐Rudolf
Published: April 2006

Electrical properties of motoneurons, muscle fibres and dorsal root ganglion (DRG) cells were studied in an organotypic coculture of embryonic rat spinal cord, dorsal root ganglia and skeletal muscle. The motoneurons were identified by their morphology and position in culture. Their size and input conductance were significantly larger than those of spinal interneurons. Intracellular current injection evoked action potentials in all motoneurons, but only evoked stable repetitive firing patterns in some. Excitability was correlated to somatic size and the rate of spontaneous excitatory input. It is suggested that the somatic growth and the increase in excitability is regulated by the excitatory afferents. The motoneurons showed spontaneous excitatory and inhibitory postsynaptic potentials and action potentials which disappeared with the application of various agents known to inhibit excitability or excitatory synaptic transmission. Excitatory and inhibitory postsynaptic potentials (EPSPs and IPSPs respectively) were distinguished by their shape, reversal potential and pharmacology. IPSPs could be depolarizing or hyperpolarizing in different cells. A higher percentage of cells with hyperpolarizing IPSPs was found in older cultures and in the presence of skeletal muscle, suggesting a reversal of the polarity of IPSPs with development. The spontaneous muscle contractions observed in the cultures could be due either to innervation, spontaneous oscillations of the membrane potential, or electrical coupling between neighbouring fibres. A small percentage of DRG cells showed spontaneous action potentials, all of which were found in cultures with spontaneous muscle contractions. The electrical stimulation of DRG afferents evoked mono‐ and polysynaptic EPSPs in motoneurons, endplate potentials and muscle contractions. The stimulation of the ventral horns evoked endplate potentials and muscle contractions via mono‐ or polysynaptic pathways. Together these results indicate that appropriate and functional contacts were established in the culture between myotubes and DRG cells, between DRG cells and motoneurons, and between motoneurons and muscle fibres.
Morphological Classification of Bipolar Cells of the Primate Retina
Authors: Boycott B. B. , Wässle H.
Published: April 2006

Bipolar cells were studied in Golgi‐Colonnier‐stained whole mounts of macaque monkey retinae. A piece of retina, at 6–7 mm eccentricity, was particularly well stained for the analysis of the different bipolar cell types. Many midget bipolar cells were encountered and the dichotomy into flat and invaginating midget bipolars was confirmed. Six types of diffuse cone bipolar cell are distinguished. They differ in their dendritic branching pattern, in the number of cones contacted–usually between five and ten–and in the shape and branching level of their axons. The size, shape and stratification of the axons were found to be the most reliable distinguishing features for classifying diffuse cone bipolar cells. The stratification of the axons in the inner plexiform layer (IPL), whether closer to the amacrine or ganglion cells, was used to name diffuse cone bipolar cells in the order DB1 to DB6. Blue cone and rod bipolar cells were confirmed as distinct types. Axon terminals of diffuse cone bipolars were found to tile their sublamina of the IPL in a territorial manner. From this the density of each type could be estimated, and it is shown that a single cone is likely to be in contact with as many as 15 individual diffuse bipolar cells, as well as two midget bipolars. The diffuse bipolar cells observed contact all the cone pedicles in their dendritic fields. It is, therefore, unlikely that they carry a chromatic signal into the inner retina. The presence of many midget bipolar cells, which make contact with one cone pedicle only, suggests that midget bipolars provide chromatic input to ganglion cells in peripheral retina as well as in the fovea. The data show that the P‐ and M‐cell pathways of the primate visual system are, to a significant extent, already anatomically discrete at the photoreceptor synapse.