bluuebunny/crossref_metadata_2025 huggingface dataset:
Regulation of acetylcholine release by muscarinic receptors at the mouse neuromuscular junction depends on the activity of acetylcholinesterase
Authors: Minic Jasmina , Molgó Jordi , Karlsson Evert , Krejci Eric
Published: March 2003

Muscarinic acetylcholine receptors (mAChRs) play an important role in regulating the release of acetylcholine (ACh) in various tissues. We used subtype‐specific antibodies and a fluorescent‐labelled muscarinic toxin to demonstrate that mammalian neuromuscular junction expresses mAChR subtypes M1 to M4, and that localization of all subtypes is highly restricted to the innervated part of the muscle. To elucidate the roles of the mAChR subtypes regulating ACh release, we measured the mean quantal content of endplate potentials in isolated mouse phrenic–hemidiaphragm preparations in which release was reduced by a low Ca2+/high Mg2+ medium. Muscarine decreased evoked ACh release in normal junctions but, depending on the concentration, reduced or increased transmitter release in collagen Q‐deficient junctions completely lacking acetylcholinesterase (AChE). Both effects were also seen in normal junctions when AChE was inhibited by various doses of fasciculin‐2. Block of mAChRs by atropine had no effect on evoked release at normal junctions, but decreased release at junctions lacking AChE. The muscarine‐elicited depression of ACh release in normal junctions was completely abolished by pertussis toxin or methoctramine pretreatment, but was not affected by muscarinic toxin MT‐3, thus indicating the involvement of the M2 mAChR. The muscarine‐induced increase of ACh release in AChE‐deficient junctions was not affected by pertussis toxin, but was completely blocked by MT‐7, a specific M1 mAChR antagonist. Our results show that the M1 and M2 mAChRs have opposite presynaptic functions in modulating quantal ACh release, and that regulation of release by the two receptor subtypes depends on the functional state of AChE at the neuromuscular junction.
Glucocorticoids interact with the basolateral amygdala β‐adrenoceptor–cAMP/cAMP/PKA system in influencing memory consolidation
Authors: Roozendaal Benno , Quirarte Gina L. , McGaugh James L.
Published: March 2003

Infusion of a β‐adrenoceptor antagonist into the basolateral nucleus of the amygdala (BLA) blocks memory enhancement induced by systemic or intra‐BLA administration of a glucocorticoid receptor (GR) agonist. As there is evidence that glucocorticoids interact with the noradrenergic signalling pathway in activating adenosine 3′,5′‐cyclic monophosphate (cAMP), the present experiments examined whether glucocorticoids influence the β‐adrenoceptor–cAMP system in the BLA in modulating memory consolidation. Male, Sprague–Dawley rats received bilateral infusions of atenolol (a β‐adrenoceptor antagonist), prazosin (an α1‐adrenoceptor antagonist) or Rp‐cAMPS (a protein kinase A inhibitor) into the BLA 10 min before inhibitory avoidance training and immediate post‐training intra‐BLA infusions of the GR agonist, RU 28362. Atenolol and Rp‐cAMPS, but not prazosin, blocked 48‐h retention enhancement induced by RU 28362. A second series of experiments investigated whether a GR antagonist alters the effect of noradrenergic activation in the BLA on memory consolidation. Bilateral intra‐BLA infusions of the GR antagonist, RU 38486, administered 10 min before inhibitory avoidance training completely blocked retention enhancement induced by α1‐adrenoceptor activation and attenuated the dose–response effects of post‐training intra‐BLA infusions of clenbuterol (a β‐adrenoceptor agonist). However, the GR antagonist did not alter retention enhancement induced by post‐training intra‐BLA infusions of 8‐Br‐cAMP (a synthetic cAMP analogue). These findings suggest that glucocorticoids influence the efficacy of noradrenergic stimulation in the BLA on memory consolidation via an interaction with the β‐adrenoceptor–cAMP cascade, at a locus between the membrane‐bound β‐adrenoceptor and the intracellular cAMP formation site.
The anabolic androgenic steroid, nandrolone decanoate, increases the density of Fos‐like immunoreactive neurons in limbic regions of guinea‐pig brain
Authors: Johansson‐Steensland Pia , Nyberg Fred , Chahl Loris
Published: March 2003

The increased abuse of anabolic androgenic steroids is a major concern because of physiological and psychological side‐effects. In some individuals they induce dramatic behavioural changes such as increased aggression, anxiety and depression. The mechanisms behind these behavioural changes are still poorly understood. In order to obtain information on the brain regions affected by anabolic androgenic steroids, the distribution of neurons containing c‐Fos, the protein product of the immediate early gene c‐fos, and Fos‐related antigens was studied following chronic treatment of guinea‐pigs with a high dose of nandrolone decanoate (15 mg/kg i.m. daily for 14 days). The behaviour of the guinea‐pigs was monitored for 1 h each day. Animals treated with nandrolone exhibited a significantly greater incidence of biting behaviour during the 14 day treatment period than vehicle‐treated animals. A significantly greater density of c‐Fos and Fos‐related antigen‐positive neurons was found in the central nucleus of the amygdala, and of Fos‐related antigen‐positive neurons in the frontal cortex, the shell of the nucleus accumbens and the supraoptic nucleus in nandrolone‐treated animals than in vehicle controls. Therefore, nandrolone induced Fos in brain regions involved in stress, behavioural responses and reward. The increased Fos expression in these limbic brain regions is of particular interest in relation to the behavioural changes reported in humans who abuse anabolic androgenic steroids and the abuse potential of these drugs.
Nitric oxide‐dependent damage to neuronal mitochondria involves the NMDA receptor
Authors: Stewart V. C. , Heslegrave A. J. , Brown G. C. , Clark J. B. , Heales S. J. R.
Published: March 2003

Cytokine‐stimulated astrocytes produce nitric oxide, which can inhibit components of the mitochondrial respiratory chain. We have previously demonstrated that prolonged exposure (48 h) to rat astrocytic nitric oxide damages complexes II–III and IV of neighbouring rat neurons in coculture, resulting in neuronal death. Expanding on these observations, we have now shown that the NMDA receptor antagonist, MK‐801, prevents this damage, suggesting involvement of glutamate. We postulate that astrocyte‐derived nitric oxide stimulates release of neuronal glutamate. Indeed we demonstrate that neurons incubated with nitric oxide‐generating astrocytes display enhanced glutamate release. Furthermore, direct exposure to the nitric oxide donor, DETA‐NONOate resulted in a loss of activity of all the neuronal mitochondrial complexes, which was again prevented by MK‐801. Thus, nitric oxide, generated by both cytokine‐stimulated astrocytes and by a nitric oxide donor, causes activation of the NMDA receptor leading to damage to the neuronal mitochondrial respiratory chain. Glutamate exposure is known to damage the neuronal mitochondrial respiratory chain via neuronal nitric oxide synthase. Therefore, we propose that astrocyte‐derived nitric oxide is capable of eliciting neuronal glutamate release, which in turn activates the neuronal NMDA receptor and stimulates further formation of reactive nitrogen species via neuronal nitric oxide synthases, leading to mitochondrial damage and neuronal death. Our findings support the hypothesis that glutamate, reactive nitrogen species and mitochondrial dysfunction may have a role in the neurodegenerative process.
Physiological properties of central amygdala neurons: species differences
Authors: Dumont Éric C. , Martina Marzia , Samson Rachel D. , Drolet Guy , Paré Denis
Published: March 2003

The connections of limbic structures are remarkably constant across species. However, different species express fear in distinct ways. Because the central amygdaloid nucleus is considered an important mediator of fear responses, we compared the physiological properties of central amygdala neurons in guinea pigs, rats and cats using whole‐cell recordings in coronal slicesin vitro. In guinea pigs, most central medial and lateral neurons displayed an outward rectification that delayed firing onset in response to depolarizing current pulses (hence the designation late‐firing neurons). Late‐firing neurons were also prevalent in the lateral sector of the cat central nucleus. In contrast, late‐firing neurons were rare in the rat central nucleus and the cat central medial nucleus. There, most neurons generated Ni2+‐sensitive low‐threshold bursts of Na+spikes and/or displayed pronounced inward rectification in the hyperpolarizing direction. Species differences in passive properties were also observed, but they were mainly related to the relative prevalence of late‐firing cells. Indeed, late‐firing cells had a significantly lower input resistance and more negative membrane potential than other types of central neurons. Thus, there are marked species differences in the physiological properties of central neurons. Because the synaptic responsiveness of neurons is constrained by their physiological properties, our findings raise the possibility that the contrasting behavioural responsiveness observed across species is partly dependent on the species‐specific physiological properties of central neurons.
Ultrastructural evaluation of calcitonin gene‐related peptide immunoreactivity in the human cochlea and vestibular endorgans
Authors: Kong Wie‐Jia , Scholtz Arne W. , Kammen‐Jolly Keren , Glückert Rudolf , Hussl Burkhard , Von Cauvenberg Paul B. , Schrott‐Fischer Anneliese
Published: March 2003

Calcitonin gene‐related peptide (CGRP) is a neuropeptide widely distributed in the peripheral and central nervous system. Demonstrated in the efferent systems of the mammalian cochlea and vestibule, immunoreactive patterns of CGRP may vary by species. There is, however, no information in the literature investigating CGRP localization in the human cochlea. In the present study, the ultrastructural localization of CGRP immunoreactivity was evaluated in the human inner ear with immunoelectron microscopy. It was found that, in human cochlea, CGRP immunoreactivity was located in unmyelinated nerve fibres of the spiral lamina, inner spiral fibres beneath inner hair cells, tunnel spiral fibres, tunnel crossing fibres and outer radial fibres. In endorgans of human vestibule, CGRP immunoreactivity was located in vesiculated nerve fibres and bouton‐type nerve terminals which were seen to contact afferent nerve chalices surrounding type I sensory cells and afferent nerve fibres, or to form an en passant contact with afferent dendrites. CGRP immunoreactivity appeared to be confined to efferent systems in all cases. This study presents evidence that CGRP could serve a role in neurotransmission or neuroregulation in both cochlear and vestibular efferent systems of human.
Phosphorylation of GluR4 AMPA‐type glutamate receptor subunit by protein kinase C in cultured retina amacrine neurons
Authors: Carvalho Ana Luísa , Correia Susana , Faro Carlos J. , Duarte Carlos B. , Carvalho Arsélio P. , Pires Euclides M. V.
Published: March 2003

We have previously reported that the activity of α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazole propionate (AMPA) receptors is potentiated by protein kinase C (PKC) in cultured chick retina amacrine neurons, and that constitutive PKC activity is necessary for basal AMPA receptor activity (Carvalho et al., 1998). In this study, we evaluated the phosphorylation of the GluR4 subunit, which is very abundant in cultured amacrine neurons, to correlate it with the effects of PKC on AMPA receptor activity in these cells. 32P‐labelling of GluR4 increased upon AMPA receptor stimulation or cell treatment with phorbol 12‐myristate 13‐acetate (PMA) before stimulating with kainate. By contrast, phosphorylation of GluR4 was not changed when PKC was inhibited by treating the cells with the selective PKC inhibitor GF 109203X before stimulation with kainate. We conclude that GluR4 is phosphorylated upon PKC activation and/or stimulation of AMPA receptors in cultured amacrine cells. Additionally, AMPA receptor activation with kainate in cultured chick amacrine cells leads to translocation of conventional and novel PKC isoforms to the cell membrane, suggesting that PKC could be activated upon AMPA receptor stimulation in these cells.
Vasoactive intestinal polypeptide induces per1 and per2 gene expression in the rat suprachiasmatic nucleus late at night
Authors: Nielsen Henriette S. , Hannibal Jens , Fahrenkrug Jan
Published: March 2003

Circadian rhythms in behaviour and physiology generated by the suprachiasmatic nucleus (SCN) are entrained to the environmental light/dark cycle via the retinohypothalamic tract. How light is able to adjust the endogenous rhythm is not fully understood, but induction of the two clock genes per1 and per2 in the SCN is believed to be important for the adjustment. Recently, it was shown that vasoactive intestinal polypeptide (VIP), a neurotransmitter found in light‐responsive cells of the SCN, is able to phase shift the circadian rhythm similar to light. In the present study we show by means of an in vitro brain slice model and quantitative in situ hybridization histochemistry that VIP induces both per1 and per2 gene expression in the SCN during late subjective night (CT19). The signalling pathways responsible for the VIP signalling to the clock were investigated using inhibitors of protein kinase A and phospholipase C mediated signalling. Our results demonstrate that both pathways are involved in VIP induced per gene expression and suggest that VIP is important for light‐induced phase shift late at night.
Neural background of glucocorticoid dysfunction‐induced abnormal aggression in rats: involvement of fear‐ and stress‐related structures
Authors: Halász József , Liposits Zsolt , Kruk Menno R. , Haller József
Published: March 2003

Glucocorticoid hypofunction is associated with persistent aggression in some psychologically disordered human subjects and, as reported recently, induces abnormal forms of aggression in rats. Here we report on the effects of glucocorticoid hypofunction on aggression‐induced neural activation. Rats were adrenalectomized, and implanted with low‐release glucocorticoid pellets. After one week recovery, they were challenged by an unfamiliar intruder in their home‐cage. Neural activation was studied by c‐Fos protein immunocytochemistry. Aggressive encounters in controls induced c‐Fos activation in all brain areas relevant for the control of aggression (cortex, amygdala, septum, hypothalamus, periaqueductal grey and the locus coeruleus). Very intense c‐Fos activation was observed in the medial amygdala, the hypothalamic attack area and the periaqueductal grey matter which constitute a downward stimulatory stream that activates attack behaviour. The experimentally induced glucocorticoid hypofunction dramatically increased attacks targeted towards vulnerable parts of the opponent's body (mainly the head). This abnormal behaviour was not associated with changes in the activation of brain centres involved in the control of aggression. However, the activation of brain centres involved in both the stress response (the parvocellular part of the hypothalamic paraventricular nucleus) and fear reactions (central amygdala) were markedly increased. An acute glucocorticoid treatment abolished both behavioural and neural consequences of glucocorticoid hypofunction. Our data suggest that glucocorticoid hypofunction‐induced abnormal forms of aggressiveness are related to increased sensitivity to stressors and fear‐eliciting stimuli. This assumption is supported by the finding that fearful situations induce attack patterns in intact rats that are similar to those induced by glucocorticoid hypofunction.
Cortico‐hippocampal APP and NGF levels are dynamically altered by cholinergic muscarinic antagonist or M1 agonist treatment in normal mice
Authors: Seo Hyemyung , Ferree Andrew W. , Isacson Ole
Published: March 2003

To determine whether altered cholinergic neurotransmission can modify the long‐term secretion of amyloid precursor protein (APP), endogenous levels of APP and nerve growth factor (NGF), we administered a selective M1 muscarinic receptor agonist (RS86) or the muscarinic antagonist, atropine, for 7 days in vivo into young adult mice (C57BL/6j). The levels of NGF and total APP in the hippocampus, frontal cortex, striatum, parietal cortex and cerebrospinal fluid (CSF) were examined by ELISA and Western blot. We found that this repeated i.m. administration of M1 receptor agonist resulted in decreased total APP levels in the hippocampus, frontal cortex and parietal cortex, and increased secreted α‐APPs levels in the CSF. M1 agonist treatment also resulted in decreased NGF levels in the hippocampus and CSF. These effects of the M1 muscarinic agonist could be blocked by atropine, which by itself elevated tissue levels of total APP. Interestingly, we found that the decrease of total APP in the hippocampus and striatum after M1 agonist treatment inversely correlated with the change in NGF levels. These data suggest that a sustained increased cholinergic, M1‐mediated neurotransmission will enhance secretion of α‐APPs in CSF and adaptively reduce the levels of total APP and NGF in the corticohippocampal regions of normal mice. The dynamic and adaptive regulation linking total APP and NGF levels in normal adult mice is relevant for understanding the pathophysiology of conditions with cholinergic and APP related pathologies, like Alzheimer's disease and Down's syndrome.
Learning the invariance properties of complex cells from their responses to natural stimuli
Authors: Einhäuser Wolfgang , Kayser Christoph , König Peter , Körding Konrad P.
Published: March 2003

Neurons in primary visual cortex are typically classified as either simple or complex. Whereas simple cells respond strongly to grating and bar stimuli displayed at a certain phase and visual field location, complex cell responses are insensitive to small translations of the stimulus within the receptive field [Hubel & Wiesel (1962)J. Physiol. (Lond.), 160, 106–154; Kjaer et al. (1997)J. Neurophysiol., 78, 3187–3197]. This constancy in the response to variations of the stimuli is commonly called invariance. Hubel and Wiesel's classical model of the primary visual cortex proposes a connectivity scheme which successfully describes simple and complex cell response properties. However, the question as to how this connectivity arises during normal development is left open. Based on their work and inspired by recent physiological findings we suggest a network model capable of learning from natural stimuli and developing receptive field properties which match those of cortical simple and complex cells. Stimuli are drawn from videos obtained by a camera mounted to a cat's head, so they should approximate the natural input to the cat's visual system. The network uses a competitive scheme to learn simple and complex cell response properties. Employing delayed signals to learn connections between simple and complex cells enables the model to utilize temporal properties of the input. We show that the temporal structure of the input gives rise to the emergence and refinement of complex cell receptive fields, whereas removing temporal continuity prevents this processes. This model lends a physiologically based explanation of the development of complex cell invariance response properties.
Effects of water on cortical excitability in humans
Authors: Müller Viktor , Birbaumer Niels , Preißl Hubert , Braun Christoph , Lang Florian
Published: March 2003

The effects of water on cortical excitability, measured using magnetoencephalographic recordings, were investigated in a sample of 19 healthy volunteers in a double‐blind, placebo experiment comparing water with saline solution. Spontaneous magnetoencephalogram as well as auditory‐evoked magnetic fields were recorded before and after the drinking of 750 mL water (9 subjects) or saline solution (10 subjects) and during and after hyperventilation following the drinking conditions. Hyperventilation was used to enhance the hypothesized synchronizing effect of water on spontaneous magnetoencephalographic activity. In addition, the magnetic fields were measured during a dichotic listening task under attended and unattended conditions. The prediction, that intake of water, because of induced cell swelling, will increase neuronal excitability and lead to an increased synchronization of the spontaneous magnetoencephalogram during hyperventilation was confirmed. Hyperventilation induced an increase of spectral power in all frequency bands particularly theta and delta power after water drinking. Furthermore, there was an increase of magnetic mismatch negativity (MMNm) amplitude in attended conditions and a simultaneous decrease in unattended conditions after water drinking. N1m (magnetic N1 wave) revealed significant changes during experimental conditions: increase after drinking and decrease after hyperventilation in both groups. MMNm for attended conditions showed a high positive correlation with osmolality changes (difference in the mol solute per kg water before and after drinking); N1m and PNm (magnetic processing negativity) as well as MMNm for unattended conditions showed significant correlations with subjective ratings of thirst and mood state.
Novel expression of AMPA‐receptor subunit GluR1 on mossy cells and CA3 pyramidal neurons in the human epileptogenic hippocampus
Authors: Eid Tore , Kovacs Ilona , Spencer Dennis D. , De Lanerolle Nihal C.
Published: March 2003

Previous immunocytochemical investigations performed in our laboratory on the human hippocampus surgically resected for the treatment of mesial temporal lobe epilepsy (MTLE) have demonstrated an increased expression of the AMPA‐receptor subunit GluR1 on neurons in the hilus and area CA3. Light microscopically, many of these neurons exhibited peculiar filamentous extensions and grape‐like excrescences that protruded from their somata and proximal dendrites, suggesting that these neurons may be mossy cells and CA3 pyramidal neurons, respectively. The present electron microscopic study was carried out to further characterize these cells. The filamentous extensions were identified as dendrites from which spines often protruded, and the grape‐like excrescences represented clusters of closely associated dendrites and spines. A variety of synapses were formed by the GluR1‐positive profiles. These arrangements ranged from simple contacts between a single unlabelled axon terminal and a single labelled postsynaptic element, to complex contacts involving multiple unlabelled axon terminals and labelled postsynaptic elements. Many of the axon terminals involved in these arrangements were mossy fibre boutons. Thus, a large proportion of the GluR1‐positive neurons were identified as hilar mossy cells and CA3 pyramidal neurons, cells hitherto thought to be absent or greatly reduced in the MTLE hippocampus. Taken together, these data suggest the presence of a highly efficient excitatory circuit involving AMPA receptors, mossy cells and CA3 pyramidal neurons in the sclerotic hippocampus. Such a circuit could be critically involved in the genesis and maintenance of temporal lobe epilepsy.
Crossed unilateral lesions of temporal lobe structures and cholinergic cell bodies impair visual conditional and object discrimination learning in monkeys
Authors: Barefoot H. C. , Baker H. F. , Ridley R. M.
Published: March 2003

Monkeys with excitotoxic lesions of the CA1/subiculum region in the right hemisphere and with immunotoxic lesions of the cholinergic cells of the diagonal band in the left hemisphere were impaired on a visual conditional task. In this task, correct choice of one of two objects depends on which of two background fields both objects are presented against, irrespective of the spatial positions of the objects. They were not impaired on simple object or shape discrimination tasks. The pattern of impairments is the same as that seen after bilateral excitotoxic lesions of CA1/subiculum, implying that the diagonal band lesion disables the ipsilateral CA1/subiculum. It also argues that CA1/subiculum, sustained by its cholinergic input, is necessary for some forms of nonspatial conditional learning. Addition of an inferotemporal (IT) cortical ablation to the left hemisphere did not affect simple visual discrimination learning, although all the monkeys then failed to learn a new visual conditional task. This demonstrates that intact IT cortex in only one hemisphere is sufficient to sustain simple visual discrimination learning but implies that the cholinergic input and the inferotemporal cortical input to the hippocampus both contribute to visual conditional learning. The subsequent addition of an immunotoxic lesion of the basal nucleus of Meynert in the right hemisphere resulted in an additional impairment on a difficult shape discrimination. This argues that it is the cholinergic projection to the inferotemporal cortex, rather than to the rest of the cortex, which contributes to visual discrimination learning and memory.
Cortical representation of acoustic motion in the Rufous Horseshoe bat, Rhinolophus rouxi
Authors: Firzlaff U. , Schuller G.
Published: March 2003

Responses of neurons to apparent auditory motion in the azimuth were recorded in three different fields of auditory cortex of the rufous horseshoe bat. Motion was simulated using successive stimuli with dynamically changing interaural intensity differences presented via earphones. Seventy‐one percent of sampled neurons were motion‐direction‐sensitive. Two types of responses could be distinguished. Thirty‐four percent of neurons showed a directional preference exhibiting stronger responses to one direction of motion. Fifty‐seven percent of neurons responded with a shift of spatial receptive field position depending on direction of motion. Both effects could occur in the same neuron depending on the parameters of apparent motion. Most neurons with contralateral receptive fields exhibited directional preference only with motion entering the receptive field from the opposite direction. Receptive field shifts were opposite to the direction of motion. Specific combinations of spatiotemporal parameters determined the motion‐direction‐sensitive responses. Velocity was not encoded as a specific parameter. Temporal parameters of motion and azimuth position of the moving sound source were differentially encoded by neurons in different fields of auditory cortex. Neurons with a directional preference in the dorsal fields can encode motion with short interpulse intervals, whereas direction‐preferring neurons in the primary field can best encode motion with medium interpulse intervals. Furthermore, neurons with a directional preference in the dorsal fields are specialized for encoding motion in the midfield of azimuth, whereas direction‐preferring neurons in the primary field can encode motion in lateral positions. The results suggest that motion information is differentially processed in different fields of the auditory cortex of the rufous horseshoe bat.
Emergence of axons from distal dendrites of adult mammalian neurons following a permanent axotomy
Authors: Rose P. K. , MacDermid V. , Joshi M. , Neuber‐Hess M.
Published: March 2003

The distinctive features of axons and dendrites divide most neurons into two compartments. This polarity is fundamental to the ability of most neurons to integrate synaptic signals and transmit action potentials. It is not known, however, if the polarity of neurons in the adult mammalian nervous system is fixed or plastic. Following axotomy, some distal dendrites of neck motoneurons in the adult cat give rise to unusual processes that, at a light microscopic level, resemble axons (Rose, P.K. & Odlozinski, M., J. Comp. Neurol., 1998, 390, 392). The goal of the present experiments was to characterize these unusual processes using well‐established ultrastructural and molecular criteria that differentiate dendrites and axons. These processes were immunoreactive for growth‐associated protein‐43 (GAP‐43), a protein that is normally confined to axons. In contrast, immunoreactivity for a protein that is widely used as a marker for dendrites, microtubule‐associated protein (MAP)‐2a/b, could not be detected in the unusual distal arborizations. At the electron microscopic level, unusual distal processes contained dense collections of neurofilaments and were frequently myelinated. These molecular and structural characteristics are typical of axons and suggest that the polarity of adult neurons in the mammalian nervous system can be disrupted by axotomy. If this transformation in neuronal polarity is common to other types of neurons, axon‐like processes emerging from distal dendrites may represent a mechanism for replacing connections lost due to injury. Alternatively, the connections formed by these axons may be aberrant and therefore maladaptive.
Abnormal trafficking and subcellular localization of an N‐terminally truncated serotonin transporter protein
Authors: Ravary Anne , Muzerelle Aude , Darmon Michèle , Murphy Dennis L. , Moessner Rainald , Lesch K. Peter , Gaspar Patricia
Published: March 2003

We report here that a truncated 5‐HTT protein is produced in the neurons of the raphe, in serotonin transporter (5‐HTT) knockout (KO) mice. The 5‐HTT gene has exon 2 deleted and we found that one main transcript, shortened by 450 bp, is produced in these KO mice. The mutated 5‐HTT protein is only recognized by antibodies against the C‐terminal portion of 5‐HTT. This protein is not functional as there is no high‐affinity serotonin uptake in 5‐HTT KO mice, in adults or during development. Conversely, low‐affinity serotonin uptake was detected in vitro, and in dopaminergic neurons of the substantia nigra in vivo. The truncated 5‐HTT, recognized by antibodies to the C‐terminus, is present exclusively in the somatodendritic compartment of the raphe neurons instead of being exported to axons. As shown with confocal and electron microscopy, the truncated 5‐HTT does not reach the plasma membrane and is essentially retained in the endoplasmic reticulum. However, this does not seem to trigger refolding or degradation responses, as no upregulation of the chaperone BiP or of the degradation signal ubiquitin was detected. Last, as observed in heterozygous mice, the presence of the truncated 5‐HTT protein, although produced in large quantities, does not disturb the normal trafficking of the wild‐type protein. This study therefore validates the 5‐HTT KO model despite the occurrence of an incomplete translation, and brings novel information on the in vivo 5‐HT uptake and cellular processing of an abnormal 5‐HTT protein.
Somatosensory cortical neuronal population activity across states of anaesthesia
Authors: Erchova Irina A. , Lebedev Mikhail A. , Diamond Mathew E.
Published: March 2003

Experiments were carried out to learn about changes in sensory cortical processing associated with different levels of anaesthesia. Traditionally this question has been addressed by studying single neurons. Because state changes are likely to influence the relationships between neurons, the present experiments were undertaken to investigate the spatial and temporal firing patterns distributed across cortex. Using 5 × 5 or 10 × 10 microelectrode arrays, spontaneous and stimulus‐evoked activity of multineuron clusters was recorded from rat somatosensory ‘barrel’ cortex (the whisker representation) during a light surgical stage of urethane anaesthesia, and after two supplemental doses of urethane which led to intermediate and deep levels of anaesthesia. At all depths of anaesthesia, spontaneously occurring action potentials at a single electrode tended to be clustered into ‘bursts.’ With increasing anaesthetic depth, bursts became more prominent and rhythmic, and increasingly synchronized between cortical barrel‐columns. Burst frequency decreased and fewer spikes occurred outside bursts, leading to a decrease in the overall spontaneous firing rate. The cortical territory engaged by individual whiskers contracted with increasing depth of anaesthesia, leading to the spatial segregation of whisker representations. At all stages of anaesthesia, whisker stimulation produced the maximal cortical response when delivered close to burst onset. These observations show that ongoing spontaneous activity modulates sensory response properties and makes peripheral tactile information accessible to a cortical territory whose size is determined by the phase of burst cycle. The possible significance of the cyclic cortical responsiveness encountered during urethane anaesthesia to cortical processing in awake rats is considered.
Modulation of secretion by the endoplasmic reticulum in mouse chromaffin cells
Authors: Rigual Ricardo , Montero Mayte , Rico Alberto J. , Prieto‐Lloret Jesús , Alonso María Teresa , Alvarez Javier
Published: March 2003

The endoplasmic reticulum (ER) has been suggested to modulate secretion either behaving as a Ca2+ sink or as a Ca2+ source in neuronal cells. Working as a Ca2+ sink, through ER‐Ca2+ pumping, it may reduce secretion induced by different stimuli. Instead, working as a Ca2+ source through the Ca2+ induced Ca2+ release (CICR) phenomenon, it may potentiate secretion triggered by activation of plasma membrane Ca2+ channels. We have previously demonstrated the presence of CICR in bovine chromaffin cells, but we now find that mouse chromaffin cells almost lack functional caffeine‐sensitive ryanodine receptors in the ER and, consistently, no CICR from the ER could be observed. In addition, inhibition of ER Ca2+ pumping with ciclopiazonic acid or thapsigargin strongly stimulated high‐K+‐evoked catecholamine secretion and cytosolic [Ca2+] ([Ca2+]c) transients. Surprisingly, 5 mm caffeine reduced high‐K+‐induced [Ca2+]c peaks but considerably potentiated secretion induced by high‐K+ stimulation. However, this potentiation was insensitive to ryanodine and additive to that induced by emptying the ER of Ca2+ with thapsigargin, suggesting that it is unrelated to the activation of ryanodine receptors. We conclude that, in mouse chromaffin cells, CICR is not functional and the ER strongly inhibits secretion by acting as a damper of the [Ca2+]c signal.
The neuronal α6 subunit forms functional heteromeric acetylcholine receptors in human transfected cells
Authors: Fucile Sergio , Matter Jean‐Marc , Erkman Linda , Ragozzino Davide , Barabino Benedetta , Grassi Francesca , Alemà Stefano , Ballivet Marc , Eusebi Fabrizio
Published: March 2003

We examine some of the biological and physiological properties of the avian α6 neuronal nicotinic acetylcholine receptor (nAChR) subunit. We show here that, beginning at embryonic day 5, α6 mRNA is abundantly expressed in the developing chick neuroretina, where it coexists with other nicotinic receptor subunit mRNAs such as α3, β2 and β4. In contrast, α6 mRNA is absent from the optic tectum and from the peripheral ganglia. Despite numerous efforts, the α6 subunit has long failed the critical test of functional reconstitution. Here we use patch‐clamp techniques and confocal laser microscopy to measure ACh‐activated currents and nicotine‐elicited Ca2+ transients in human BOSC 23 cells transfected with chick α6 in combination with other chick nAChR neuronal subunits. Heterologously expressed α6 and β4 subunits form functional heteromeric nAChRs, which are permeable to Ca2+ ions and blocked by the nicotinic antagonist methyllycaconitine (10 μm). Likewise, ACh elicits measurable currents in cells transfected with α6 and β2. Hill analysis of the dose–response curves in cells transfected with α3, β4 and α6 cDNAs, suggests the assembly of functional α3β4α6 receptor, with an apparent affinity for ACh threefold lower than α3β4. Our results indicate that α6‐containing nAChRs assemble in heterologous expression systems and are probably present in retinal cells.
Neural encoding of subject–object distance in a visual recognition system
Authors: Nicol  , Brown  , Horn
Published: March 2003

Domestic chicks follow a familiar (imprinted) object when it recedes. In behaving, imprinted chicks with no experience of objects at different distances, neuronal activity was recorded from the intermediate and medial part of the hyperstriatum ventrale (IMHV), a brain region crucial for the recognition memory underlying imprinting. We found that (i) some neurones responded equivalently, irrespective of the subject–object distance d (d‐invariant); (ii) other neurones responded differently at different values of d (d‐sensitive); (iii) these response types were found in monocular chicks and in chicks with both eyes exposed; (iv) the action potential shape of d‐invariant neurones was different from that of other neurones and (v) the spontaneous firing rate of some neurones was correlated with locomotor activity. Taken together with previous findings, the results raise the possibility that IMHV has a major role to play in the sensory and motor‐control aspects of imprinting in addition to its mnemonic functions.
Characterization of the multisynaptic neuronal control of the rat pineal gland using viral transneuronal tracing
Authors: Larsen  , Enquist  , Card
Published: March 2003

Knowledge of the polysynaptic pathway conveying photic information to the pineal gland is based upon studies employing lesions, knife cuts and classical tracers. In the present investigation we used viral transneuronal tracing to re‐examine the organization of this circuitry. This was accomplished by injecting a neurotropic alpha herpesvirus (pseudorabies virus) into the gland and localizing viral antigen in infected neurones at various postinoculation intervals. This approach is based upon the demonstrated ability of this virus to invade axon terminals, replicate in neurones and pass retrogradely through a multisynaptic circuit. Immunohistochemical localization of viral antigen revealed the progressive appearance of infected neurones in the superior cervical ganglion (SCG), intermediolateral nucleus of the upper thoracic spinal cord (IML), parvicellular subdivisions of the hypothalamic paraventricular nucleus (PVN), and the suprachiasmatic nucleus (SCN). Other infected cell groups known to project to the IML also became infected. Infection of the PVN reproducibly involved neurones in the dorsal, medial and lateral parvicellular subdivisions and preceded the appearance of infected neurones in the SCN and other regions of hypothalamus. Topographic analysis of virus infected neurones within the SCN revealed differential infection of SCN subdivisions that suggested topography in the projection of the SCN to the PVN. Removal of the SCG eliminated infection within the aforementioned circuitry and revealed a parasympathetic innervation from the sphenopalatine ganglion. The data provide further detail on the cellular identity and synaptology of neural circuitry controlling the rhythmic secretion of melatonin by the rat pineal gland.
Prenatal differentiation of mouse vomeronasal neurones
Authors: Tarozzo  , Cappello  , De Andrea  , Walters  , Margolis  , Oestreicher  , Fasolo
Published: March 2003

The vomeronasal organ (VNO) subserves basic chemosensory functions in rodents, mainly related to sexual behaviour. In order to understand early stages of the VNO structural maturation, we have undertaken an immunocytochemical analysis of the VNO of fetal mice.

 Our results demonstrate that Olfactory Marker Protein (OMP), a marker of differentiated chemosensory cells, is already expressed in vomeronasal neurones and their fibres projecting to the accessory olfactory bulb during the last week of gestation. However, in contrast to the adult, where its expression is restricted to the medial sensory neuronal component of the VNO, during fetal development OMP is also present in cells located in the lateral non‐sensory epithelial component. Some other markers of nasal chemosensory neurones, such as GAP‐43/B‐50, Protein Gene Product 9.5 (PGP 9.5) and carnosine are also transiently expressed in this ectopic site.

 These results indicate that (i) significant morphological and biochemical maturation of the VNO is achieved before birth; (ii) transient cell populations, sharing the biochemical profile of the vomeronasal chemosensory receptors, occur in ectopic areas during fetal development.
Synaptic clustering of GABAC receptor ρ‐subunits in the rat retina
Authors: Koulen Peter , Brandstätter Johann Helmut , Enz Ralf , Bormann Joachim , Wässle Heinz
Published: March 2003

Polyclonal antibodies which recognize the ρ‐subunits of the GABAC receptor were applied to sections of the rat retina. Strong punctate immunoreactivity was found in the inner plexiform layer (IPL), which was shown by electron microscopy to represent a clustering of the GABAC receptors at synaptic sites. During postnatal development diffuse ρ‐immunoreactivity was first observed at postnatal day P3. Distinct labelling of bipolar cells appeared at P7 and punctate, synaptic labelling was observed at P10. In order to show that the ρ‐immunoreactive puncta coincide with the axons of bipolar cells, double immunostainings of retinal sections with an antiserum against syntaxin 3 and with the ρ‐antiserum were performed. The experiments showed that ρ‐immunoreactive puncta are preferentially located on the axon terminals of rod and cone bipolar cells. In order to determine whether GABAC receptor ρ‐subunits coassemble with GABAA receptor subunits, double‐labelling experiments were performed with subunit specific antisera. Punctate, putative synaptic clustering was observed with all antisera applied, however, GABAC receptor expressing puncta did not coincide with GABAA receptor containing puncta. This suggests that there are no synaptic GABA receptors in the retina in which GABAA and GABAC receptor subunits are coassembled. Similar double‐labelling experiments were also performed to find out whether GABAC receptors and glycine receptors are colocalized. They were clustered at different synapses. This suggests that synaptic GABAC receptors consist of ρ‐subunits and are not coassembled with GABAA‐ or glycine‐receptor subunits.
Role of the cerebellum in reaching movements in humans. I. Distributed inverse dynamics control
Authors: Schweighofer Nicolas , Arbib Michael A. , Kawato Mitsuo
Published: March 2003

This study focuses on the role of the motor cortex, the spinal cord and the cerebellum in the dynamics stage of the control of arm movement. Currently, two classes of models have been proposed for the neural control of movements, namely the virtual trajectory control hypothesis and the acquisition of internal models of the motor apparatus hypothesis. In the present study, we expand the virtual trajectory model to whole arm reaching movements. This expanded model accurately reproduced slow movements, but faster reaching movements deviated significantly from the planned trajectories, indicating that for fast movements, this model was not sufficient. These results led us to propose a new distributed functional model consistent with behavioural, anatomical and neurophysiological data, which takes into account arm muscles, spinal cord, motor cortex and cerebellum and is consistent with the view that the central nervous system acquires a distributed inverse dynamics model of the arm. Previous studies indicated that the cerebellum compensates for the interaction forces that arise during reaching movements. We show here how the cerebellum may increase the accuracy of reaching movements by compensating for the interaction torques by learning a portion of an inverse dynamics model that refines a basic inverse model in the motor cortex and spinal cord.
Role of the cerebellum in reaching movements in humans. II. A neural model of the intermediate cerebellum
Authors: Schweighofer Nicolas , Spoelstra Jacob , Arbib Michael A. , Kawato Mitsuo
Published: March 2003

The cerebellum is essential for the control of multijoint movements; when the cerebellum is lesioned, the performance error is more than the summed errors produced by single joints. In the companion paper ( Schweighofer et al. 1998 ), a functional anatomical model for visually guided arm movement was proposed. The model comprised a basic feedforward/feedback controller with realistic transmission delays and was connected to a two‐link, six‐muscle, planar arm. In the present study, we examined the role of the cerebellum in reaching movements by embedding a novel, detailed cerebellar neural network in this functional control model. We could derive realistic cerebellar inputs and the role of the cerebellum in learning to control the arm was assessed.

This cerebellar network learned the part of the inverse dynamics of the arm not provided by the basic feedforward/feedback controller. Despite realistically low inferior olive firing rates and noisy mossy fibre inputs, the model could reduce the error between intended and planned movements. The responses of the different cell groups were comparable to those of biological cell groups. In particular, the modelled Purkinje cells exhibited directional tuning after learning and the parallel fibres, due to their length, provide Purkinje cells with the input required for this coordination task. The inferior olive responses contained two different components; the earlier response, locked to movement onset, was always present and the later response disappeared after learning. These results support the theory that the cerebellum is involved in motor learning.
A presynaptic N‐methyl‐d‐aspartate autoreceptor in rat hippocampus modulating amino acid release from a cytoplasmic pool
Authors: Breukel Alexandra I. M. , Besselsen Elly , Da Silva Fernando H. Lopes , Ghijsen Wim E. J. M.
Published: March 2003

A possible role of the N‐methyl‐d‐aspartate receptor (NMDA‐R) as a presynaptic autoreceptor was investigated using Percoll‐purified hippocampus nerve terminals (synaptosomes). This preparation contained only a neglectable amount of postsynaptic structures. Two main effects of NMDA were observed. First, NMDA dose‐dependently (10–100 μm) and in the absence of Mg2+, stimulated basal release of aspartate and glutamate, but not of GABA. MK801 (10 μm), an open NMDA‐R‐channel blocker, reduced this effect even below control levels, indicating endogenous NMDA‐R activation. By superfusing synaptosomes, which prevents a tonic receptor occupation, also basal GABA release was stimulated by NMDA. The NMDA‐induced potentiation of amino acid superfusate levels was blocked both by MK801 and Mg2+ (1 m
m), was slow in onset and returned to baseline after NMDA‐removal. The NMDA‐effect was also found in the absence of extracellular Ca2+, suggesting that amino acids were released from a non‐vesicular (cytoplasmic) pool. Secondly, in KCl‐depolarized synaptosomes exposed to 1 m
m Mg2+, NMDA did not affect the release of the amino acids. MK801, however, reduced the KCl‐evoked Ca2+‐independent release of aspartate and glutamate, but not of GABA.
l‐trans‐PDC, the selective inhibitor of the glutamate/aspartate transporter, prevented this MK801‐effect, suggesting a coupling between NMDA‐Rs and these transporters.

These data provide evidence for a presynaptic NMDA autoreceptor in rat hippocampus. We speculate on the role of this NMDA‐R to depolarize the presynaptic membrane by Na+‐entry, which may induce reversal of amino acid transporters and thereby releasing amino acids from a cytoplasmic pool.