bluuebunny/crossref_metadata_2025 huggingface dataset:
Selective GABAergic innervation of thalamic nuclei from zona incerta
Authors: Barthó P. , Freund T. F. , Acsády L.
Published: March 2003

Thalamocortical circuits that govern cortical rhythms and ultimately effect sensory transmission consist of three major interconnected elements: excitatory thalamocortical and corticothalamic neurons and GABAergic cells in the reticular thalamic nucleus. Based on the present results, a fourth component has to be added to this scheme. GABAergic fibres from an extrareticular diencephalic source were found to selectively innervate relay cells located mainly in higher‐order thalamic nuclei. The origin of this pathway was localized to zona incerta (ZI), known to receive collaterals from corticothalamic fibres. First‐order nuclei were innervated only in zones showing a high density of calbindin‐positive neurons. The large GABA‐immunoreactive incertal terminals established multiple contacts preferentially on the proximal dendrites of relay cells via symmetrical synapses with multiple release sites. The distribution, ultrastructural characteristics and postsynaptic target selection of extrareticular terminals were similar to type II muscarinic acetylcholine receptor‐positive boutons, which constituted up to 49% of all GABAergic terminals in the posterior nucleus. This suggests that a significant proportion of the GABAergic input into certain thalamic territories involved in higher‐order functions may have extrareticular origin. Unlike the reticular nucleus, ZI receives peripheral and layer V cortical input but no thalamic feedback; it projects to brainstem centres and has extensive intranuclear recurrent collaterals. This indicates that ZI exerts a conceptually new type of inhibitory control over the thalamus. The proximally situated, multiple active zones of ZI terminals indicate a powerful influence on the firing properties of thalamic neurons, which is conveyed to multiple cortical areas via relay cells which have widespread projections to neocortex.
Differential effects of acute and chronic exercise on plasticity‐related genes in the rat hippocampus revealed by microarray
Authors: Molteni Raffaella , Ying Zhe , Gómez‐Pinilla Fernando
Published: March 2003

Studies were performed to determine the effects of acute and chronic voluntary periods of exercise on the expression of hippocampal genes. RNAs from rodents exposed to a running wheel for 3, 7 and 28 days were examined using a microarray with 1176 cDNAs expressed primarily in the brain. The expression of selected genes was quantified by Taqman RT‐PCR or RNase protection assay. The largest up‐regulation was observed in genes involved with synaptic trafficking (synapsin I, synaptotagmin and syntaxin); signal transduction pathways (Ca2+/calmodulin‐dependent protein kinase II, CaM‐KII; mitogen‐activated/extracellular signal‐regulated protein kinase, MAP‐K/ERK I and II; protein kinase C, PKC‐δ) or transcription regulators (cyclic AMP response element binding protein, CREB). Genes associated with the glutamatergic system were up‐regulated (N‐methyl‐d‐aspartate receptor, NMDAR‐2A and NMDAR‐2B and excitatory amino acid carrier 1, EAAC1), while genes related to the gamma‐aminobutyric acid (GABA) system were down‐regulated (GABAA receptor, glutamate decarboxylase GAD65). Brain‐derived neurotrophic factor (BDNF) was the only trophic factor whose gene was consistently up‐regulated at all timepoints. These results, together with the fact that most of the genes up‐regulated have a recognized interaction with BDNF, suggest a central role for BDNF on the effects of exercise on brain plasticity. The temporal profile of gene expression seems to delineate a mechanism by which specific molecular pathways are activated after exercise performance. For example, the CaM‐K signal system seems to be active during acute and chronic periods of exercise, while the MAP‐K/ERK system seems more important during long‐term exercise.
Hippocampal long‐term depression as an index of spatial working memory
Authors: Nakao Kazuhito , Ikegaya Yuji , Yamada Maki K. , Nishiyama Nobuyoshi , Matsuki Norio
Published: March 2003

Long‐term potentiation (LTP), a form of synaptic plasticity in the hippocampus, is a cellular model for the neural basis of learning and memory, but few studies have investigated the contribution of long‐term depression (LTD), a counterpart of LTP. To address the possible relationship between hippocampal LTD and spatial performance, the spatial cognitive ability of a rat was assessed in a spontaneous alternation test and, thereafter, LTD in response to low‐frequency burst stimulation (LFBS) was monitored in the dentate gyrus of the same rat under anaesthesia. To enhance a divergence in the ability for spatial performance, some of the animals received fimbria–fornix (FF) transection 14 days before the experiments. LTD was reliably induced by application of LFBS to the medial perforant path of intact rats, while no apparent LTD was elicited in rats with FF lesions. The behavioural parameters of spatial memory showed a significant correlation with the magnitude of LTD. We found no evidence that the cognitive ability correlated with other electrophysiological parameters, e.g. basal synaptic responses, stimulus intensity to produce half‐maximal responses, paired‐pulse facilitation or paired‐pulse depression. These results suggest that the magnitude of LTD in the dentate gyrus serves as a reliable index of spatial cognitive ability, providing insights into the functional significance of hippocampal LTD.
Multiple‐site optical recording for characterization of functional synaptic organization of the optic tectum of rainbow trout
Authors: Kinoshita Masae , Ueda Risa , Kojima Satoshi , Sato Katsushige , Watanabe Masahiko , Urano Akihisa , Ito Etsuro
Published: March 2003

To map the functional synaptic organization over a wide area in the optic tectum, we directly monitored two‐dimensional propagation of postsynaptic depolarization evoked by firing of retinotectal afferents in optic tectum slices prepared from rainbow trout (Oncorhynchus mykiss), using a voltage‐sensitive dye and a photodiode array system. The postsynaptic responses to afferent stimulation first propagated in the stratum opticum and stratum fibrosum et griseum superficiale in an anterograde fashion in the afferents and then expanded vertically into the deep layers. This vertical propagation appeared to occur along a bundle‐like structure that corresponded well with a cluster of neurons whose somata are located in the stratum periventriculare. Pharmacological studies showed that these postsynaptic responses were mediated by ionotropic glutamate receptors. On the other hand, the optical signals appeared to consist of at least two components (a transient signal and a slow signal). The second transient signal summated with the first slow signal by paired stimulation, suggesting that the transient and slow signals originated from different cell types. Taken together, these results showed that the functional synaptic organization of the teleost optic tectum comprises of two depolarization‐signal propagating paths along a horizontal layer structure and a vertical bundle‐like structure and that these synaptic responses occur via glutamatergic transmission.
Adaptive loss of ultraviolet‐sensitive/violet‐sensitive (UVS/VS) cone opsin in the blind mole rat (Spalax ehrenbergi)
Authors: David‐Gray Z. K. , Bellingham J. , Munoz M. , Avivi A. , Nevo E. , Foster R. G.
Published: March 2003

In previous studies, fully functional rod and long‐wavelength‐sensitive (LWS) cone photopigments have been isolated from the eye of the subterranean blind mole rat (Spalax ehrenbergisuperspecies).Spalaxpossesses subcutaneous atrophied eyes and lacks any ability to respond to visual images. By contrast this animal retains the ability to entrain circadian rhythms of locomotor behaviour to environmental light cues. As this is the only known function of the eye, the rod and LWS photopigments are thought to mediate this response. Most mammals are dichromats possessing, in addition to a single rod photopigment, two classes of cone photopigment, LWS and ultraviolet‐sensitive/violet‐sensitive (UVS/VS) with differing spectral sensitivities which mediate colour vision. In this paper we explore whetherSpalaxis a dichromat and has the potential to use colour discrimination for photoentrainment. Using immunocytochemistry and molecular approaches we demonstrate thatSpalaxis a LWS monochromat.Spalaxlacks a functional UVS/VS cone photopigment due to the accumulation of several deleterious mutational changes that have rendered the gene nonfunctional. Using phylogenetic analysis we show that the loss of this class of photoreceptor is likely to have arisen from the visual ecology of this species, and is not an artefact of having an ancestor which lacked a functional UVS/VS cone photopigment. We conclude that colour discrimination is not a prerequisite for photoentrainment in this species.
Simultaneous intracerebral EEG recordings of early auditory thalamic and cortical activity in human
Authors: Yvert Blaise , Fischer Catherine , Guénot Marc , Krolak‐Salmon Pierre , Isnard Jean , Pernier Jacques
Published: March 2003

We describe documented simultaneous intracerebral auditory evoked potentials from the auditory cortex and medial geniculate body (MGB) of a human patient. The MGB response lasted > 300 ms, with an initial negativity at 13.5 ms (N13), two positive peaks P21 and P29, and two broader negativities N50 and N200. P21 and N50 amplitudes were strongest for lowest tone frequencies, suggesting possible MGB tonotopic organization. Thalamic peaks were strongly interlaced with cortical activities recorded in Heschl's gyri before 30 ms: N13 preceded the first cortical component by 3.5 ms, then P21 and P29 preceded and lagged, respectively, the following two cortical polarity reversals by 1.5–2 ms. This study provides new functional data on the human MGB, and supports a more complex than simply relay‐like role of the thalamus in sound perception.
GABAergic and glycinergic synapses onto neurokinin‐1 receptor‐immunoreactive neurons in the pre‐Bötzinger complex of rats: light and electron microscopic studies
Authors: Liu Ying‐Ying , Wong‐Riley Margaret T. T. , Liu Jin‐Ping , Jia Yi , Liu Hui‐Ling , Jiao Xi‐Ying , Ju And Gong
Published: March 2003

The pre‐Bötzinger complex (preBötC) in the ventrolateral medulla is thought to be the kernel for respiratory rhythm generation. Neurons in the preBötC contain intense neurokinin‐1 receptor (NK1R) immunoreactivity. Some of these neurons in the adult preBötC are presumed to be the pre‐inspiratory interneurons that are essential for generating respiratory rhythm in the neonate. Chloride‐mediated synaptic inhibition is critical for rhythmogenesis in the adult. The present study used immunofluorescence histochemistry and immunogold‐silver staining to determine the inhibitory synaptic relationship between glutamic acid decarboxylase (GAD)‐ or glycine transporter 2 (GlyT2)‐immunoreactive (ir) boutons and NK1R‐ir neurons in the preBötC of adult rats. Under the confocal microscope, we found that GAD‐ and GlyT2‐ir boutons were in close apposition to NK1R‐ir somas and dendrites in the preBötC. Under the electron microscope, GAD‐ and GlyT2‐ir terminals were in close apposition to NK1R‐ir somas and dendrites. Symmetric synapses were identified between GAD‐ or GlyT2‐ir terminals and NK1R‐ir neurons. A total of 51.6% GAD‐ir and 38.2% GlyT2‐ir terminals were found to contact or make synapses with NK1R‐ir profiles, respectively. GAD‐ and GlyT2‐ir terminals synapsed not only upon NK1R‐ir neurons but also upon NK1R immuno‐negative neurons. NK1R‐ir neurons received both symmetric (presumed inhibitory) and asymmetric (presumed excitatory) synapses. Thus, the present findings provide the morphological basis for inhibitory inputs to NK1R‐ir neurons in the preBötC, consistent with the suggestion that chloride‐mediated synaptic inhibition may contribute importantly to rhythm generation by controlling the membrane potential trajectory and resetting rhythmic bursting of the kernel neurons in the adult.
Flicker in the visual background impairs the ability to process a moving visual stimulus
Authors: Churan Jan , Ilg Uwe J.
Published: March 2003

For the detection of a moving object, segregating the object from the background is a necessary first step. This segregation can be achieved by detection of differences in the spatial, temporal and spatio‐temporal properties of the object and background. Here we investigate how flicker influences the perception of a moving object in man and monkey, and we examine the neuronal responses in extrastriate medial temporal and medial superior temporal areas (MT and MST) of two rhesus monkeys. The performance of humans and monkeys in a direction discrimination task was impaired in the presence of flicker in the background compared to the static background condition. A similar effect was found in recordings from 155 single units in areas MT and MST during the discrimination task. The discriminability (d′) of the neuronal responses in preferred and nonpreferred directions was reduced by 33% on average in the presence of a flicker background compared to the static background. This reduction in discriminability was not caused by differences in variance of the neuronal activity for the two background conditions, but was due to a reduction of the difference between the activities in preferred and nonpreferred direction. This reduction in directional selectivity could be traced back to two different mechanisms: in 32 out of 155 neurons (21%), the decrease resulted from an increase in the response to the stimulus moving in the nonpreferred direction; in 62 out of 155 neurons (40%), the reduction in directional selectivity was due to a decrease in the response to the preferred direction. These results give deeper insights into how moving stimuli are processed in the presence of background flicker as present in natural visual scenes.
Change in bi‐directional plasticity at CA1 synapses in hippocampal slices taken from 6‐hydroxydopamine‐treated rats: the role of endogenous norepinephrine
Authors: Yang Hsiu‐Wen , Lin Yi‐Wen , Yen Chia‐De , Min Ming‐Yuan
Published: March 2003

The object of the present study is to investigate the role of endogenous adrenergic innervation in regulating bi‐directional synaptic plasticity in rat hippocampal CA1 synapses. The endogenous adrenergic system was eliminated by giving subcutaneous injection of 6‐hydroxydopamine (6‐OHDA) to rats immediately after birth, and the animals were killed for experiments at postnatal ages of 25–35 days. In hippocampal slices taken from 6‐OHDA‐treated animals, theta‐burst stimulation at 100 Hz failed to induce long‐term potentiation (LTP) at CA1 synapses. However, the induction of long‐term depression (LTD) by prolonged low frequency stimulation at 1 Hz was unaffected in slices from 6‐OHDA‐treated animals. Bath application of norepinephrine (NE) restored LTP to control levels and blocked LTD. This effect was mimicked by β‐ but not α‐adrenergic receptor agonists, i.e. by isoproterenol but not phenylephrine. The activators of adenylyl cyclase and protein kinase A (PKA), i.e. forskolin and 8‐bromoadenosine‐3′, 5′‐cyclic monophosphate, respectively, restored LTP in slices from 6‐OHDA‐treated animals. In addition, application of the D1/D5 receptor agonist, dihydrexidine, also restored LTP in slices from 6‐OHDA‐treated animals. These results suggest that physiologically the recruitment of catecholamine innervation may be important for induction of LTP at hippocampal CA1 synapses during tetanic stimulation, while it may not be essential for LTD induction by prolonged 1 Hz stimulation. The released NE and dopamine exert their role in modulating synaptic plasticity via activation of β‐adrenergic and D1/D5 receptors, respectively, which in turn increase the levels of cytoplasm adenosine‐3′,5′‐cyclic monophosphate and PKA.
Ephrin‐B3–EphA4 interactions regulate the growth of specific thalamocortical axon populations in vitro
Authors: Takemoto Makoto , Fukuda Tsuyoshi , Sonoda Rie , Murakami Fujio , Tanaka Hideaki , Yamamoto Nobuhiko
Published: March 2003

The role was studied of ephrin‐B3, a ligand of the Eph family of tyrosine kinase receptors, in the formation of cortical connectivity. In situ hybridization and immunohistochemistry showed that EphA4, a receptor of ephrin‐B3, was expressed in the lateral thalamus (visual and somaotosensory thalamus) of the developing rat brain, but not in the medial thalamic nuclei which project to the limbic cortex. Correspondingly, ephrin‐B3 was expressed strongly in the developing limbic cortex including amygdala, entorhinal cortex and hippocampus. To examine the action of ephrin‐B3 on thalamic axons, either lateral or medial thalamic explants were cultured on membranes obtained from ephrin‐B3‐expressing COS cells. Axonal growth was inhibited for cells from the lateral thalamus but not from the medial thalamus. These results suggest that ephrin‐B3 contributes to regional specificity by suppressing axonal growth of lateral thalamic neurons.
Chronic nicotine treatment changes the axonal distribution of 68 kDa neurofilaments in the rat ventral tegmental area
Authors: Sbarbati Andrea , Bunnemann Bernd , Cristofori Patrizia , Terron Andrea , Chiamulera Christian , Merigo Flavia , Benati Donatella , Bernardi Paolo , Osculati Francesco
Published: March 2003

Region‐specific decreases of neurofilament proteins (NF) were described in the ventral tegmental area (VTA) of rats treated chronically with morphine, cocaine or alcohol. In a previous study, we demonstrated that NF levels were also changed in the VTA after chronic treatment with nicotine. The aim of this study was to clarify the submicroscopic basis of decreased immunoreactivity for NF‐68, NF‐160 and NF‐200, as determined by using NR4, BF10 and RT97 antibodies, respectively. Microdensitometric analysis of brain sections showed that immunoreactivity for all NF was reduced in the VTA of animals exposed chronically to nicotine (0.4 mg/kg per day, 6 days of treatment), when compared to rats exposed to saline. Reduction in immunoreactivity was significant for NF‐68 (P < 0.05), NF‐160 (P < 0.01) and NF‐200 (P < 0.05), showing a relative reduction of 34%, 42% and 38%, respectively, when compared to saline‐treated rats. No difference was observed for any of the NF under study when immunoreactivity measurements in the substantia nigra were compared. Ultrastructural analysis was applied to evaluate changes in NF‐68, NF‐160 and NF‐200 immunoreactivity in regions of the VTA that contain dopaminergic neurons following chronic nicotine treatment. At the electron microscopic level, no degenerative changes were found in neurons or glial cells of the VTA. With ultrastructural immunohistochemistry, evaluation of the homogeneity parameter of NF distribution showed a loss of homogeneity for NF‐68 linked to the nicotine treatment. In areas in which NF organization appeared well preserved, analysis of the numerical density of NF revealed no significant difference for NF‐68 (897/µm2 vs. 990/µm2), NF‐160 (970/µm2 vs. 820/µm2) and NF‐200 (1107/µm2 vs. 905/µm2) in nicotine‐treated rats when compared to saline‐treated rats. These results confirm that nicotine shares the same properties with cocaine and morphine in reducing NF in the VTA, a key brain structure of the rewards system, and that chronic nicotine treatment changes the axonal distribution of 68 kDa neurofilaments in the rat VTA.
Multiple determinants in voltage‐dependent P/Q calcium channels control their retention in the endoplasmic reticulum
Authors: Cornet Véronique , Bichet Delphine , Sandoz Guillaume , Marty Isabelle , Brocard Jacques , Bourinet Emmanuel , Mori Yasuo , Villaz Michel , De Waard Michel
Published: March 2003

Surface expression level of voltage‐dependent calcium channels is tightly controlled in neurons to avoid the resulting cell toxicity generally associated with excessive calcium entry. Cell surface expression of high voltage‐activated calcium channels requires the association of the pore‐forming subunit, Cavα, with the auxiliary subunit, Cavβ. In the absence of this auxiliary subunit, Cavα is retained in the endoplasmic reticulum (ER) through mechanisms that are still poorly understood. Here, we have investigated, by a quantitative method based on the use of CD8α chimeras, the molecular determinants of Cavα2.1 that are responsible for the retention, in the absence of auxiliary subunits, of P/Q calcium channels in the ER (referred to here as ‘ER retention’). This study demonstrates that the I–II loop of Cavα2.1 contains multiple ER‐retention determinants beside the β subunit association domain. In addition, the I–II loop is not the sole domain of calcium channel retention as two regions identified for their ability to interact with the I–II loop, the N‐ and C‐termini of Cavα2.1, also produce ER retention. It is also not an obligatory determinant as, similarly to low‐threshold calcium channels, the I–II loop of Cavα1.1 does not produce ER retention in COS7 cells. The data presented here suggests that ER retention is suppressed by sequential molecular events that include: (i) a correct folding of Cavα in order to mask several internal ER‐retention determinants and (ii) the association of other proteins, including the Cavβ subunit, to suppress the remaining ER‐retention determinants.
The essential nutrient pyrroloquinoline quinone may act as a neuroprotectant by suppressing peroxynitrite formation
Authors: Zhang Yumin , Rosenberg Paul A.
Published: March 2003

Pyrroloquinoline quinone (PQQ) is a redox active essential nutrient that can generate or scavenge superoxide depending on its microenvironment. PQQ has been shown previously to be neuroprotective in a rodent stroke model. Here we test whether PQQ interacts with reactive nitrogen species, known to be involved in the pathogenesis of stroke. Using rat forebrain neurons in culture, we determined that the toxicity of SIN‐1 was mediated by peroxynitrite and that PQQ could block this toxic action. However, PQQ could not block the toxicity of peroxynitrite itself. Both SIN‐1 and peroxynitrite caused ATP depletion, but only SIN‐1 evoked ATP depletion was blocked by PQQ. In a cell‐free system, PQQ blocked nitration of bovine serum albumin produced by SIN‐1, but potentiated peroxynitrite‐induced nitration. PQQ was unable to block ATP depletion and cell death induced by NO· donors (DEA/NO, DPT/NO and DETA/NO), indicating that it does not directly interact with nitric oxide, and suggesting that it acts as a superoxide scavenger. PQQ significantly potentiated cGMP accumulation evoked by SIN‐1, similar to the effect of superoxide dismutase (SOD). However, unlike SOD, which potentiated neurotoxicity induced by SIN‐1, PQQ blocked its toxicity, arguing against the possibility that PQQ functions simply as a SOD mimetic. Indeed, substantially less H2O2 was produced by the incubation of SIN‐1 with PQQ, when compared to SOD. These results suggest that PQQ scavenges superoxide without forming toxic levels of H2O2. Therefore, the protective effect of PQQ on stroke might be due, at least in part, to the suppression of peroxynitrite formation.
Potentiation of inhibitory glycinergic neurotransmission by Zn2+: a synergistic interplay between presynaptic P2X2 and postsynaptic glycine receptors
Authors: Laube Bodo
Published: March 2003

The divalent cation zinc is known to modulate chloride currents carried by native and recombinant mammalian glycine receptors (GlyRs). To unravel the effect of Zn2+ on glycinergic neurotransmission, inhibitory postsynaptic currents (IPSC) of rat spinal neurons grown in culture were analysed in the absence and presence of Zn2+. Low concentrations of Zn2+ (0.5 and 5 µm) augmented the mean amplitude of miniature IPSCs by ≈ 40% over values obtained in the absence of zinc, whereas higher concentrations of Zn2+ (50 µm) significantly decreased mean amplitude values. Remarkably, low concentrations of Zn2+ also significantly increased the mean frequency of miniature IPSCs. This effect was blocked by the P2X receptor antagonists PPADS and suramin, indicating the presence of Zn2+‐sensitive presynaptic P2X receptors on glycinergic terminals. Immunostaining with antibodies against different P2X receptor subtypes revealed that P2X2 receptors partially colocalize with the GlyR. Potentiating concentrations of Zn2+ also affected the kinetics of miniature and evoked IPSCs by significantly prolonging their decay time constants. Electrophysiological analysis of heterologously expressed glycine transporters (GlyT) revealed for GlyT2 zero, and for GlyT1 a modest (< 20%), reduction of glycine uptake in the presence of 5 µm Zn2+, indicating that prolongation of glycinergic IPSCs by Zn2+ is not due to inhibition of glycine removal from the synaptic cleft. Together, these results suggest that Zn2+ is a potent modulator of glycinergic synaptic transmission which increases in a synergistic manner the agonist affinity of both presynaptic P2X2 receptors and postsynaptic GlyRs.
Characterization of large conductance Ca2+‐activated K+ channels in cerebellar Purkinje neurons
Authors: Womack Mary D. , Khodakhah Kamran
Published: March 2003

We investigated the role of large conductance, calcium‐activated potassium channels (BK channels) in regulation of the excitability of cerebellar Purkinje neurons. Block of BK channels by iberiotoxin reduced the afterhyperpolarization of spontaneous action potentials in Purkinje neurons in acutely prepared cerebellar slices. To establish the conditions required for activation of BK channels in Purkinje neurons, the dependence of BK channel open probability on calcium concentration and membrane voltage were investigated in excised patches from soma of acutely prepared Purkinje cells. Single channel currents were studied under conditions designed to select for potassium currents and in which voltage‐activated currents were largely inactivated. Micromolar calcium concentrations activated channels with a mean single channel conductance of 266 pS. BK channels were activated by both calcium and membrane depolarization, and showed no sign of inactivation. At a given calcium concentration, depolarization over a 60‐mV range increased the mean open probability (PO) from < 0.1 to > 0.8. Increasing the calcium concentration shifted the voltage required for half maximal activation to more hyperpolarized potentials. The apparent affinity of the channels for calcium increased with depolarization. At −60 mV the apparent affinity was ≈35 µm decreasing to ≈3 µM at +40 mV. These results suggest that BK channels are unlikely to be activated at resting membrane potentials and calcium concentrations. We tested the hypothesis that Purkinje cell BK channels may be activated by calcium entry during individual action potentials. Significant BK channel activation could be detected when brief action potential‐like depolarizations were applied to patches under conditions in which the sole source of calcium was flux across the plasma membrane via the endogenous voltage‐gated calcium channels. It is proposed that BK channels regulate the excitability of Purkinje cells by contributing to afterhyperpolarizations and perhaps by shaping individual action potentials.
Glucocorticoids alter calcium conductances and calcium channel subunit expression in basolateral amygdala neurons
Authors: Karst Henk , Nair Suresh , Velzing Els , Rumpff‐van Essen Lisette , Slagter Eelco , Shinnick‐Gallagher Patricia , Joëls Marian
Published: March 2003

Glucocorticoid hormones, which are released in high amounts after stress, enter the brain where they bind to intracellular receptors that are abundant in limbic areas, in particular the hippocampus and amygdala nuclei. Behavioural studies indicate that glucocorticoids modulate learning and memory processes via receptors in the hippocampus and amygdala. So far, the effects of glucocorticoids on amygdala neurons have not been investigated at the cellular and molecular level. We report here that in vitro application of glucocorticoids for 20 min increases 1–4 h later the amplitude of sustained, high‐voltage‐activated calcium currents in principal neurons of the basolateral amygdala. In contrast, the transient, low‐voltage‐activated currents were decreased. We examined whether these functional changes in calcium conductance were accompanied by transcriptional regulation of calcium channel subunits. Analysis of the RNA – collected after recording and then linearly amplified – revealed that glucocorticoid‐mediated increases in sustained calcium currents are associated with a parallel shift in the relative expression of the α1 subunit constituting the pore of the sustained, high‐voltage‐activated (L‐type) calcium channel. These data indicate that glucocorticoids, probably by selectively targeting genes encoding calcium channel subunits, largely alter the calcium influx into basolateral amygdala neurons. These actions could modify amygdala network function and thus contribute to the behavioural effects exerted by the stress hormones via the basolateral amygdala.
Anatomical and functional correlation of the endomorphins with mu opioid receptor splice variants
Authors: Abbadie C. , Rossi G. C. , Orciuolo A. , Zadina J. E. , Pasternak G. W.
Published: March 2003

The present study characterizes the relationship between the endogenous mu opioid peptides endomorphin‐1 (EM‐1) and endomorphin‐2 (EM‐2) and several splice variants of the cloned mu opioid receptor (MOR‐1) encoded by the mu opioid receptor gene (Oprm). Confocal laser microscopy revealed that fibers containing EM‐2‐like immunoreactivity (‐LI) were distributed in close apposition to fibers showing MOR‐1‐LI (exon 4‐LI) and to MOR‐1C‐LI (exons 7/8/9‐LI) in the superficial laminae of the lumbar spinal cord. We also observed colocalization of EM‐2‐LI and MOR‐1‐LI in a few fibers of lamina II, and colocalization of EM‐2‐LI and MOR‐1C‐LI in laminae I–II, and V–VI. To assess the functional relevance of the MOR‐1 variants in endomorphin analgesia, we examined the effects of antisense treatments that targeted individual exons within the Oprm1 gene on EM‐1 and EM‐2 analgesia in the tail flick test. This antisense mapping study implied mu opioid receptor mechanisms for the endomorphins are distinct from those of morphine or morphine‐6β‐glucuronide (M6G).
Differential involvement of cortical muscarinic and NMDA receptors in short‐ and long‐term taste aversion memory
Authors: Ferreira G. , Gutiérrez R. , De la Cruz V. , Bermúdez‐Rattoni F.
Published: March 2003

In conditioned taste aversion, an animal avoids a taste previously associated with toxic effects, and this aversive memory formation requires an intact insular cortex. In this paper, we investigated the possible differential involvement of cholinergic and glutamatergic receptors in the insular cortex in short‐term memory (STM) and long‐term memory (LTM) of taste aversion in rats. Taste aversion was induced by intraperitoneal administration of lithium chloride (a malaise‐inducing drug) 15 min after experience with an unfamiliar taste. In order to test STM and LTM of taste aversion, taste stimulus was again presented 4 h and 72 h after lithium injection, respectively. During the acquisition, microinjection of the muscarinic antagonist, scopolamine, in the insular cortex before, but not after, the presentation of the new taste, abolished STM as well as LTM. Blockade of the NMDA receptor, in the insular cortex, by AP5 before, but not after, the presentation of the taste stimulus, impaired LTM but left STM intact. Moreover, when injected 1 h after malaise induction (i.e., during taste–illness association), AP5 disrupted both STM and LTM. These results suggest that activation of muscarinic receptors in the insular cortex is involved in the acquisition of taste memory, whereas NMDA receptors participate in taste memory consolidation. These data demonstrate that different neurochemical mechanisms subserve different memory phases. NMDA receptors are also probably involved in processing the visceral input, thus allowing subsequent taste–illness association. This indicates that in the same cortical area the same neurotransmitter system can be involved in distinct processes: taste memory consolidation vs. taste–illness association.
Consequences of amygdala kindling and repeated withdrawal from ethanol on amphetamine‐induced behaviours
Authors: Ripley Tamzin L. , Dunworth Sarah J. , Stephens David N.
Published: March 2003

It has been shown previously that chronic ethanol treatment in mice leads to accelerated behavioural sensitization to psychomotor stimulants [Manley & Little (1997) J. Pharmacol. Exp. Ther., 281, 1330–1339], whilst repeated experience of ethanol withdrawal sensitizes pathways underlying seizure activity (Becker & Hale (1993) Alcohol Clin. Exp. Res., 17, 94–98]. The aim of the current experiment was to investigate the consequences of repeated withdrawal from ethanol on amphetamine‐induced behaviours in the rat and compare this with animals with electrical kindling of the amygdala, a procedure that has been shown to enhance alcohol withdrawal seizures [Pinel et al. (1975) Can. J. Neurol. Sci., 2, 467–475]. For the kindling experiments, electrodes were surgically implanted in the left basolateral amygdala and were stimulated daily at the afterdischarge threshold until a criterion of three consecutive stage 5 seizures was reached. Fully kindled rats showed a marginally significant reduction in sensitivity to the locomotor stimulant effects of acute amphetamine compared with sham and partially kindled rats which had experienced subthreshold stimulation of the amygdala. Sham and partially kindled rats sensitized readily to the locomotor activating effects of amphetamine (0.125 mg/kg) following repeated treatments, but the fully kindled rats did not. Fully kindled rats also failed to show place preference conditioning to amphetamine (0.5 mg/kg). Rats, withdrawn three times from chronic ethanol (liquid‐diet), kindled more quickly to PTZ (30 mg/kg, i.p.) than rats with the same overall exposure to ethanol (24 days) followed by a single withdrawal or control animals. However, there was no difference in the locomotor stimulating effects of acute amphetamine (0.25–1 mg/kg, i.p.), the rate of sensitization to amphetamine (0.125 mg/kg, i.p.) or amphetamine induced conditioned place preference (1 mg/kg, i.p.). These observations suggest that, in rats, repeated withdrawal from a relatively mild chronic ethanol treatment modulates neuronal systems that may also be involved in PTZ‐induced kindling but not those involved in either the acute stimulant effects of amphetamine or behavioural sensitization or appetitive conditioning following repeated amphetamine administration. Behavioural changes following amygdala kindling differed from those following repeated ethanol withdrawal, suggesting that withdrawal kindling from a mild ethanol treatment differs in its effects from amygdala kindling.
In the rat, exogenous melatonin increases the amplitude of pineal melatonin secretion by a direct action on the circadian clock
Authors: Bothorel Béatrice , Barassin Stéphane , Saboureau Michel , Perreau Stéphanie , Vivien‐Roels Berthe , Malan André , Pévet Paul
Published: March 2003

The effect of exogenous melatonin on pineal melatonin synthesis was studied in the rat in vivo. Daily melatonin profiles were measured by transpineal microdialysis over 4 consecutive days in rats maintained on a 12‐h light : 12‐h dark schedule (LD 12 : 12). Curve‐fitting was used to determine the amplitude of the peak of melatonin production, and the times of its onset (IT50) and offset (DT50). A subcutaneous injection of melatonin (1 mg/kg) at the onset of darkness (ZT12) induced an advance of IT50 on the second day after the treatment, in 50% of the animals kept in LD. When the animals were switched to constant darkness, the treatment caused no detectable advance of IT50, while 70% of individuals showed a significant delay in DT50 2 days after the injection. Locally infusing the drug by reverse microdialysis into the suprachiasmatic nuclei (SCN) failed to enhance the shift in melatonin onset. Following subcutaneous melatonin injection, a significant increase (≈ 100%) in melatonin peak amplitude was observed. This increase persisted over 2 days and occurred only when the melatonin was applied at ZT12, but not at ZT6, 17 or 22. The effect was also observed when the drug was infused directly into the SCN, but not into the pineal. Thus, the SCN are the target site for the effect of exogenous melatonin on the amplitude of the endogenous melatonin rhythm, with a similar window of sensitivity as its phase‐shifting effect on the pacemaker.
Passive avoidance training enhances cell proliferation in 1‐day‐old chicks
Authors: Dermon C. R. , Zikopoulos B. , Panagis L. , Harrison E. , Lancashire C. L. , Mileusnic R. , Stewart M. G.
Published: March 2003

One‐day‐old domestic chicks were injected i.p. with bromodeoxyuridine (BrdU) before training on a one‐trial passive avoidance task where the aversive experience was a bead coated with a bitter tasting substance, methyl anthranilate (MeA). Animals were tested 24 h later; those avoiding (if MeA‐trained) or pecking if water (W)‐trained (which they peck appetitively), along with a group of untrained naïve chicks, were used to determine cell proliferation either 24 h or 9 days post BrdU injection. In all three groups, BrdU positive cells were identified sparsely throughout the forebrain but labelling was pronounced around ventricular zone (VZ) surfaces at both 24 h and 9 days post‐BrdU‐injection. Double immunolabelling with neuronal specific antibodies, to either NeuN, or β‐tubulin III, confirmed that most BrdU labelled cells appeared to be neurons. Unbiased stereological analysis of labelled cells in selected forebrain areas 24 h post BrdU injection showed a significant MeA‐training induced increase in labelled cells in both the dorsal VZ surface bordering the intermediate and medial hyperstriatum ventrale (IMHV) and the tuberculum olfactorium (TO). By 9 days post‐BrdU‐injection, there was a significantly greater number of BrdU labelled cells in MeA‐trained birds within the IMHV, lobus parolfactorius (LPO) and TO. These results demonstrate that avoidance training in 1‐day‐old chicks has a marked effect on cell proliferation, in the LPO and IMHV, regions of the chick previously identified as a key loci of memory formation, and in a second region (TO), which has olfactory functions, but has not been previously investigated in relation to avoidance learning.
Postnatal innervation of the rat superior colliculus by axons of late‐born retinal ganglion cells
Authors: Dallimore Elizabeth J. , Cui Qi , Beazley Lyn D. , Harvey Alan R.
Published: March 2003

Rat retinal ganglion cells (RGCs) are generated between embryonic day (E) 13 and E19. Retinal axons first reach the superior colliculus at E16/16.5 but the time of arrival of axons from late‐born RGCs is unknown. This study examined (i) whether there is a correlation between RGC genesis and the timing of retinotectal innervation and (ii) when axons of late‐born RGCs reach the superior colliculus. Pregnant Wistar rats were injected intraperitoneally with bromodeoxyuridine (BrdU) on E16, E18 or E19. Pups from these litters received unilateral superior colliculus injections of fluorogold (FG) at ages between postnatal (P) day P0 and P6, and were perfused 1–2 days later. RGCs in 3 rats from each BrdU litter were labelled in adulthood by placing FG onto transected optic nerve. Retinas were cryosectioned and the number of FG, BrdU and double‐labelled (FG+/BrdU+) RGCs quantified. In the E16 group, the proportion of FG‐labelled RGCs that were BrdU+ did not vary with age, indicating that axons from these cells had reached the superior colliculus by P0/P1. In contrast, for the smaller cohorts of RGCs born on E18 or E19, the proportion of BrdU+ cells that were FG+ increased significantly after birth; axons from most RGCs born on E19 were not retrogradely FG‐labelled until P4/P5. Thus there is a correlation between birthdate and innervation in rat retinotectal pathways. Furthermore, compared to the earliest born RGCs, axons from late‐born RGCs take about three times longer to reach the superior colliculus. Later‐arriving axons presumably encounter comparatively different growth terrains en route and eventually innervate more differentiated target structures.
Identification and comparative analysis of differentially expressed proteins in rat striatum following 6‐hydroxydopamine lesions of the nigrostriatal pathway: up‐regulation of amyloid precursor‐like protein 2 expression
Authors: Shen Yan , Yu Yi , Guo Hong , Tang Zhongshu , Yu Fu‐Shin X. , Zhou Jiawei
Published: March 2003

During neurodegenerative processes, cascades of degeneration and subsequent regeneration are triggered. However, the molecular nature of the factors involved in the neurodegeneration of the CNS remains largely unknown. In this study, the variations of protein expression in the striatum of adult Sprague–Dawley rats following 6‐hydroxydopamine lesions were investigated, in order to better understand the molecular events occurring in the denervated target tissue. The rat striatum, ipsilateral to the lesion was analysed by two‐dimensional gel electrophoresis followed by matrix assisted laser desorption/ionization‐time of flight mass spectrometry. Seven proteins were up‐regulated (188.1–750% compared to control) in response to the lesion: amyloid precursor‐like protein 2 (APLP2), kininogen, glucokinase, tropomyosin α chain, type brain‐1 and calpactin I light chain; whilst four proteins, neural epidermal growth factor‐like 2, minichromosome maintenance 6, and thyroid hormone receptor β‐2, were down‐regulated (to between 36% and 59% of levels in sham‐operated controls). Three proteins that did not match with available data in the SWISS‐PROT protein database were also determined. Immunohistochemical analysis demonstrated colocalization of APLP2 and tyrosine hydroxylase in the nigral neurons. Moreover, reduction of APLP2‐positive neurons in the substantia nigra pars compacta as well as the increases in the substantia nigra pars reticulata and in the striatum were observed. Furthermore, the conditioned medium of the Chinese hamster ovary cells over‐expressing APLP2‐751 (chondroitin sulphate‐modified), but not APLP2‐763 (nonchondroitin sulphate‐modified), was able to increase the number of the tyrosine hydroxylase‐positive neurons in fetal mesencephalic cultures. These results suggest that the expression of APLP2, a protein that has been thought to be associated with Alzheimer's disease, is up‐regulated in the striatum following dopaminergic denervation. They also support the view that chondroitin sulphate‐modified APLP2 protein may play an important role in the dopaminergic nigrostriatal system.
Zinc‐induced inhibition of protein synthesis and reduction of connexin‐43 expression and intercellular communication in mouse cortical astrocytes
Authors: Alirezaei Mehrdad , Mordelet Elodie , Rouach Nathalie , Nairn Angus C. , Glowinski Jacques , Prémont Joël
Published: March 2003

Zinc released from a subpopulation of glutamatergic synapses, mainly localized in the cerebral cortex and the hippocampus, facilitates or reduces glutamatergic transmission by acting on neuronal AMPA and NMDA receptors, respectively. However, neurons are not the only targets of zinc. In the present study, we provide evidence that zinc inhibits protein synthesis in cultured astrocytes from the cerebral cortex of embryonic mice. This inhibition, which reached 85% in the presence of 100 µm zinc, was partially and slowly reversible and resulted from the successive inhibition of the elongation and the initiation steps of the protein translation process. This was assessed by measuring the phosphorylation level of the elongation factor eEF‐2 and of the α subunit of the initiation factor eIF‐2. Due to the rapid turnover of connexin‐43 that forms junction channels in cultured astrocytes, the zinc‐induced decrease of protein synthesis led to a partial disappearance of connexin‐43, which was associated with an inhibition of the cellular coupling in the astrocytic syncitium. In conclusion, zinc not only inhibits protein synthesis in neurons, as previously demonstrated, but also in astrocytes. The resulting decrease in the intercellular communication between astrocytes should alter the function of surrounding neurons as well as their survival.
In vivo infusions of exogenous growth factors into the fourth ventricle of the adult mouse brain increase the proliferation of neural progenitors around the fourth ventricle and the central canal of the spinal cord
Authors: Martens David J. , Seaberg Raewyn M. , Van Der Kooy Derek
Published: March 2003

Stem cells isolated from the fourth ventricle and spinal cord form neurospheres in vitro in response to basic fibroblast growth factor (FGF2)+heparin (H) or epidermal growth factor (EGF)+FGF2 together. To determine whether these growth factor conditions are sufficient to induce stem cells within the fourth ventricle and spinal cord to proliferate and expand their progeny in vivo, we infused EGF and FGF2, alone or together, with or without H, into the fourth ventricle for 6 days via osmotic minipumps. Animals were injected with bromodeoxyuridine (BrdU) on days 4, 5 and 6 of infusion in order to label cells proliferating in response to the growth factors. Infusions of EGF+FGF2+H into the fourth ventricle resulted in the largest proliferative effect, a 10.8‐fold increase in the number of BrdU+ cells around the fourth ventricle, and a 33.5‐fold increase in the number of BrdU+ cells around the central canal of the spinal cord, as compared to vehicle infused controls. The majority of the cells were nestin+ after 6 days of infusion. Seven weeks post‐infusion, 22 and 30% of the number of BrdU+ cells induced to proliferate after 6 days of EGF+FGF2+H infusions were still detected around the fourth ventricle and central canal of the spinal cord, respectively. Analysis of the fates of the remaining cells showed that a small percentage of BrdU+ cells around the fourth ventricle and in the white matter of the spinal cord differentiated into astrocytes and oligodendrocytes. BrdU+ neurons were not found in the brainstem or in the grey matter of the cervical spinal cord 7 weeks post‐infusion. These results show that endogenous stem cells and progenitors around the fourth ventricle and central canal of the spinal cord proliferate in response to exogenously applied growth factors, but unlike in the lateral ventricle where they generate some new neurons, they only produce new astrocytes and oligodendrocytes at 7 weeks post‐infusion.
The cerebellum in action: a simulation and robotics study
Authors: Hofstötter Constanze , Mintz Matti , Verschure Paul F. M. J.
Published: March 2003

The control or prediction of the precise timing of events are central aspects of the many tasks assigned to the cerebellum. Despite much detailed knowledge of its physiology and anatomy, it remains unclear how the cerebellar circuitry can achieve such an adaptive timing function. We present a computational model pursuing this question for one extensively studied type of cerebellar‐mediated learning: the classical conditioning of discrete motor responses. This model combines multiple current assumptions on the function of the cerebellar circuitry and was used to investigate whether plasticity in the cerebellar cortex alone can mediate adaptive conditioned response timing. In particular, we studied the effect of changes in the strength of the synapses formed between parallel fibres and Purkinje cells under the control of a negative feedback loop formed between inferior olive, cerebellar cortex and cerebellar deep nuclei. The learning performance of the model was evaluated at the circuit level in simulated conditioning experiments as well as at the behavioural level using a mobile robot. We demonstrate that the model supports adaptively timed responses under real‐world conditions. Thus, in contrast to many other models that have focused on cerebellar‐mediated conditioning, we investigated whether and how the suggested underlying mechanisms could give rise to behavioural phenomena.