Effects of vitamin A on formation of aminoacyl-tRNA

The melting temperature and hyperchromia of intestine mucosa tRNA preparations and the effect of inactivating factors on aminoacyl-tRNA-synthetase activity were studied at the stage of hypovitaminosis and under deep A-avitaminosis. It is shown that in the aminoacylation reaction, aminoacyl-tRNA-synthetase is a component more sensitive to vitamin A deficiency.     

Integrative properties of parietal cortex neurons of rabbits during the switching of heterogeneous classical conditioned reflexes

The impulsive activity of parietal cortex neurons of rabbits during the elaboration and specialisation of switching-over of alimentary and defensive conditioned reflexes has been studied. There are changes of parietal cortex neurons activity correlated with the stages of switching-over elaboration. The significant differences of the background neurons activity and neurons response to the conditional signal during alimentary and defensive conditioned reflexes have been established. The dominant motivation influences the neurons activity by modulation of background and conditioned activity of neurons. The integrative properties of neurons investigated in switching-over situation are revealed in their ability to summarize the excitation coming to the same sensory input with excitation from different motivational and reinforcement systems.     

Activity of premotor vestibular neurons in the alert cat

The activity of medial vestibular nucleus neurons projecting to the contralateral abducens nucleus (premotor vestibular neurons) has been recorded during spontaneous and vestibular induced eye movements in the alert cat. Recorded neurons were identified by their antidromic activation from the abducens nucleus and by the post-synaptic field potential induced in this nucleus. The activity of identified medial vestibular neurons increased significantly with horizontal eye position and velocity toward the contralateral side, and decreased abruptly during ipsilateral saccades. The activity of these neurons was also related to head velocity toward the ipsilateral side. The functional role and origin of eye position and velocity signals present in these vestibular neurons are discussed.     

Differential contribution of pacemaker properties to the generation of respiratory rhythms during normoxia and hypoxia

Pacemaker neurons have been described in most neural networks. However, whether such neurons are essential for generating an activity pattern in a given preparation remains mostly unknown. Here, we show that in the mammalian respiratory network two types of pacemaker neurons exist. Differential blockade of these neurons indicates that their relative contribution to respiratory rhythm generation changes during the transition from normoxia to hypoxia. During hypoxia, blockade of neurons with sodium-dependent bursting properties abolishes respiratory rhythm generation, while in normoxia respiratory rhythm generation only ceases upon pharmacological blockade of neurons with heterogeneous bursting properties. We propose that respiratory rhythm generation in normoxia depends on a heterogeneous population of pacemaker neurons, while during hypoxia the respiratory rhythm is driven by only one type of pacemaker.     

Changes in the protein level in rat hippocampal neurons during development of the alimentary conditioned reflex under normal conditions and after treatment with iproniazid

The protein content in neurons of areas CA-1 and CA-3 of the dorsal hippocampus has been determined by means of cytointerferometry in rats during elaboration of unlocal alimentary instrumental reflex (ULAIR) and local alimentary instrumental reflex (LAIR) on the background of increased and normal serotonine content in the brain. It has been found that during the ULAIR elaboration the hippocampal neurons react by an increase of dry mass, during the LAIR elaboration-by its decrease. Under condition of serotonine excess in the brain the changes of dry mass in hippocampal neurons during elaboration of the two reflexes are opposite to these observed during the ULAIR and LAIR elaboration with normal serotonine content.     

Effect of a cyclic enkephalin analog on the protein content in the hippocampal neurons of rats during the acquisition of a 2-way avoidance conditioned reflex

The protein content has been determined by means of cytointerferometry in neurons of fields CA-1 and CA-3 of the dorsal hippocampus in rats, which were trained in a conditioned reflex of two-way avoidance (CRTA) with the action of subcutaneously injected enkephalin cyclic analogue (ECA) in a dose 10 mkg. It has been found that after ECA injection the protein content in the neuronal nuclei of the hippocampal CA-3 field reduces. The acceleration of the CRTA elaboration occurring during the action of ECA is accompanied by a drastic increase of the protein content in the neuronal nuclei of the CA-3 field. The ECA administration to the rats of the active control groups to which were presented the same number of unpaired conditioned and unconditioned stimuli as during the CRTA elaboration also enhances the protein content in the neurons of the CA-3 field. The rats of all investigated groups in the neurons of the CA-1 field display no such significant shifts. The conclusion has been drawn that ECA produces a regulating influence on protein metabolism in hippocampal neurons depending on their functional state.     

Neuronal activity of the external oculomotor nucleus during saccadic eye movement in the waking cat

The activity of antidromically identified abducens nucleus motoneurons and inter-nuclear neurons has been recorded during saccadic eye movements in the alert cat. The activity of these neurons has been demonstrated to be the sum of a velocity component proportional to eye velocity plus a position component proportional to instantaneous eye position during the movement. Results are discussed in relation to proposed models about the generation of saccadic eye movements.     

Neurophysiological analysis of efferent-afferent interaction of neurons of the parietal associate cortex in cats

Neuronal responses of the parietal associate cortex (field 5) was recorded in waking cat during electrical stimulation of the pyramidal tract axons and afferent stimulation. The electrical stimulation of the pyramid evoked marked responses in 39% of neurons. 87% of these neurons increased spike activity during sematic nociceptive stimulation, 61% of test neurons were activated by light or tonal stimulation. Neuronal activity was recorded during defensive conditioning to the pyramidal tract axons stimulation. It has been shown that conditioned stimulation of the pyramidal tract evoked plastic changes of responses in 66% of neurons of the parietal cortex. These data are discussed relative to the possible functional role of the efferent-afferent interaction to field 5.     

Human motor cortex excitability during the perception of others' action

Neuroscience research during the past ten years has fundamentally changed the traditional view of the motor system. In monkeys, the finding that premotor neurons also discharge during visual stimulation (visuomotor neurons) raises new hypotheses about the putative role played by motor representations in perceptual functions. Among visuomotor neurons, mirror neurons might be involved in understanding the actions of others and might, therefore, be crucial in interindividual communication. Functional brain imaging studies enabled us to localize the human mirror system, but the demonstration that the motor cortex dynamically replicates the observed actions, as if they were executed by the observer, can only be given by fast and focal measurements of cortical activity. Transcranial magnetic stimulation enables us to instantaneously estimate corticospinal excitability, and has been used to study the human mirror system at work during the perception of actions performed by other individuals. In the past ten years several TMS experiments have been performed investigating the involvement of motor system during others' action observation. Results suggest that when we observe another individual acting we strongly 'resonate' with his or her action. In other words, our motor system simulates underthreshold the observed action in a strictly congruent fashion. The involved muscles are the same as those used in the observed action and their activation is temporally strictly coupled with the dynamics of the observed action.     

Proctolin-immunoreactive neurons persist during metamorphosis of an insect: A developmental study of the ventral nerve cord of Tenebrio molitor(Coleoptera)

Summary Proctolin-immunoreactive neurons in all neuromers of the ventral nerve cord of Tenebrio molitor L. have been quantitatively demonstrated and mapped throughout metamorphosis. Each neuromer contains an anterior and a posterior group of neurons with light and dark staining properties as revealed by peroxidase-antiperoxidase labeling. Serial homologous subsets of dark staining neurons with central and peripheral projections have been identified and found to persist during morphogenetic changes from the larva to the adult. Most neurons maintain their topological and structural characteristics throughout metamorphosis. The identified proctolin-immunoreactive neurons exhibit structures similar to those described in other insect species; some may correspond known motoneurons.     

Histochemical and immunocytochemical study of the migration of neurons from the rat olfactory placode

Immunocytochemical and histochemical methods have been used to describe the neuronal population migrating from the rat olfactory placode and to analyze the spatio-temporal evolution of this neuronal migration during development. Several neuronal markers, such as binding to the lectin Ulex europaeus (UEA I) and the presence of neuron-specific enolase (NSE), olfactory marker protein (OMP), and luteinizing hormone-releasing hormone (LHRH), have been tested in order to determine whether migrating neurons originate from both the medial and the lateral parts of the placode and whether they all express LHRH. Our data show that a large population of differentiated migrating neurons can be identified with an antibody against NSE from the 14th day of gestation and with UEA I one day later. Migrating neurons are closely associated with both the vomeronasal axon fascicles emerging from the medial pit and the olfactory axons originating from the lateral pit. However, the neuron migration from the lateral pit appears to be more discrete than that from the medial pit. No LHRH immunoreactivity has been detected among neurons migrating from the lateral pit. Some neurons accompanying the olfactory axon fascicles exhibit a high level of maturation as shown by their OMP-positivity. Numerous neurons positive for both NSE and UEA I have also been observed within the presumptive olfactory nerve layer in early embryonic stages.     

Serotonin-immunoreactive brain interneurons persist during metamorphosis of an insect: a developmental study of the brain of Tenebrio molitor L. (Coleoptera)

Summary Serotonin-immunoreactive neurons in the brain of Tenebrio molitor L. have been demonstrated and mapped throughout metamorphosis. Most serotonin-immunoreactive brain neurons persist throughout metamorphosis; their fate can be followed during development because of their characteristic cell body locations and arborization patterns. The detailed morphology of the persisting neurons, however, changes during metamorphosis, probably to accommodate architectural changes of the different brain centers. Serotonin-immunoreactivity in the optic lobes allows a subset of neurons that is newly differentiated during metamorphosis to be identified. Phylogenetic homology of serotonin-immunoreactive brain interneurons of different insect species is discussed. The serotonin-immunoreactive brain neurons comprise a phylogenetically conserved neuronal population. Serial homologous abdomino-thoracic and brain serotonin-immunoreactive neurons were characterized, allowing a comparison of some basic structural features of these neurons.     

Reliable Activation of Immature Neurons in the Adult Hippocampus

Neurons born in the adult dentate gyrus develop, mature, and connect over a long interval that can last from six to eight weeks. It has been proposed that, during this period, developing neurons play a relevant role in hippocampal signal processing owing to their distinctive electrical properties. However, it has remained unknown whether immature neurons can be recruited into a network before synaptic and functional maturity have been achieved. To address this question, we used retroviral expression of green fluorescent protein to identify developing granule cells of the adult mouse hippocampus and investigate the balance of afferent excitation, intrinsic excitability, and firing behavior by patch clamp recordings in acute slices. We found that glutamatergic inputs onto young neurons are significantly weaker than those of mature cells, yet stimulation of cortical excitatory axons elicits a similar spiking probability in neurons at either developmental stage. Young neurons are highly efficient in transducing ionic currents into membrane depolarization due to their high input resistance, which decreases substantially in mature neurons as the inward rectifier potassium (Kir) conductance increases. Pharmacological blockade of Kir channels in mature neurons mimics the high excitability characteristic of young neurons. Conversely, Kir overexpression induces mature-like firing properties in young neurons. Therefore, the differences in excitatory drive of young and mature neurons are compensated by changes in membrane excitability that render an equalized firing activity. These observations demonstrate that the adult hippocampus continuously generates a population of highly excitable young neurons capable of information processing.     

Pharmacological activation/inhibition of the cannabinoid system affects alcohol withdrawal-induced neuronal hypersensitivity to excitotoxic insults

Cessation of chronic ethanol consumption can increase the sensitivity of the brain to excitotoxic damages. Cannabinoids have been proposed as neuroprotectants in different models of neuronal injury, but their effect have never been investigated in a context of excitotoxicity after alcohol cessation. Here we examined the effects of the pharmacological activation/inhibition of the endocannabinoid system in an in vitro model of chronic ethanol exposure and withdrawal followed by an excitotoxic challenge. Ethanol withdrawal increased N-methyl-D-aspartate (NMDA)-evoked neuronal death, probably by altering the ratio between GluN2A and GluN2B NMDA receptor subunits. The stimulation of the endocannabinoid system with the cannabinoid agonist HU-210 decreased NMDA-induced neuronal death exclusively in ethanol-withdrawn neurons. This neuroprotection could be explained by a decrease in NMDA-stimulated calcium influx after the administration of HU-210, found exclusively in ethanol-withdrawn neurons. By contrast, the inhibition of the cannabinoid system with the CB1 receptor antagonist rimonabant (SR141716) during ethanol withdrawal increased death of ethanol-withdrawn neurons without any modification of NMDA-stimulated calcium influx. Moreover, chronic administration of rimonabant increased NMDA-stimulated toxicity not only in withdrawn neurons, but also in control neurons. In summary, we show for the first time that the stimulation of the endocannabinoid system is protective against the hyperexcitability developed during alcohol withdrawal. By contrast, the blockade of the endocannabinoid system is highly counterproductive during alcohol withdrawal.     

Role of the lateral paragigantocellular nucleus in the network of paradoxical (REM) sleep: an electrophysiological and anatomical study in the rat

The lateral paragigantocellular nucleus (LPGi) is located in the ventrolateral medulla and is known as a sympathoexcitatory area involved in the control of blood pressure. In recent experiments, we showed that the LPGi contains a large number of neurons activated during PS hypersomnia following a selective deprivation. Among these neurons, more than two-thirds are GABAergic and more than one fourth send efferent fibers to the wake-active locus coeruleus nucleus. To get more insight into the role of the LPGi in PS regulation, we combined an electrophysiological and anatomical approach in the rat, using extracellular recordings in the head-restrained model and injections of tracers followed by the immunohistochemical detection of Fos in control, PS-deprived and PS-recovery animals. With the head-restrained preparation, we showed that the LPGi contains neurons specifically active during PS (PS-On neurons), neurons inactive during PS (PS-Off neurons) and neurons indifferent to the sleep-waking cycle. After injection of CTb in the facial nucleus, the neurons of which are hyperpolarized during PS, the largest population of Fos/CTb neurons visualized in the medulla in the PS-recovery condition was observed in the LPGi. After injection of CTb in the LPGi itself and PS-recovery, the nucleus containing the highest number of Fos/CTb neurons, moreover bilaterally, was the sublaterodorsal nucleus (SLD). The SLD is known as the pontine executive PS area and triggers PS through glutamatergic neurons. We propose that, during PS, the LPGi is strongly excited by the SLD and hyperpolarizes the motoneurons of the facial nucleus in addition to local and locus coeruleus PS-Off neurons, and by this means contributes to PS genesis.     

Expression and function of the neurotransmitter serotonin during development of the Helisoma nervous system

Exogenous serotonin has been shown to evoke a neuron-selective inhibition of neurite outgrowth and synaptogenesis in identified Helisoma neurons in vitro. We demonstrate here that serotonin is present in the embryonic nervous system of Helisoma and can act as a regulator of neuronal development in vivo. Serotonin-like immunoreactivity was first observed in neurons at an early stage of nervous system development (E20). Throughout embryogenesis, the number of serotonin-immunoreactive neurons increased in a stereotypic pattern that was unique for each type of ganglion. Strikingly, the number of serotonin-immunoreactive neurons continued to increase throughout adult life. Transient perturbation of endogenous serotonin levels during embryogenesis had profound effects on the development of specific identified neurons. Embryos treated with 5,7-dihydroxytryptamine and raised to maturity showed aberrations in neuronal morphology, neuronal dye coupling, and strength of electrical synaptic connections. These effects were restricted to neurons known to be sensitive to the growth-inhibitory effects of serotonin in vitro. These results support the hypothesis that neurotransmitters are an important class of regulatory factors during normal development of the nervous system.     

DUM neurons in locust flight: a model system for amine-mediated peripheral adjustments to the requirements of a central motor program

In both vertebrates and invertebrates, multiple effects of biogenic amines on neuromuscular transmission, muscle contraction kinetics and metabolism have been described. Nevertheless, it is not yet known whether and how these different effects work in concert during the performance of a specific behavior. In the locust flight system, the biogenic amine octopamine is released as a neurohormone into the haemolymph, and also delivered directly onto specific target muscles by individually identified dorsal unpaired median neurons. Determining the connectivity of these neurons and their activation during behavior, we show for the first time that different types of dorsal unpaired median neurons are differentially connected to certain components of the flight circuitry. During flight, all types of pterothoracic dorsal unpaired median neurons innervating flight muscles receive inhibitory inputs from tegula proprioceptive afferents and from the central flight circuitry, whereas all other types of dorsal unpaired median neurons are excited by wind-sensitive pathways and by the central pattern generator. Considering the results of other studies which investigated metabolic effects of octopamine, we propose a model in which the differential activation of dorsal unpaired median neurons during flight may lead to an adequately controlled release or removal of octopamine to adjust metabolic processes to the requirements of a specific motor program. Accepted: 24 February 1999     

Synaptic and intrinsic activation of GABAergic neurons in the cardiorespiratory brainstem network

GABAergic pathways in the brainstem play an essential role in respiratory rhythmogenesis and interactions between the respiratory and cardiovascular neuronal control networks. However, little is known about the identity and function of these GABAergic inhibitory neurons and what determines their activity. In this study we have identified a population of GABAergic neurons in the ventrolateral medulla that receive increased excitatory post-synaptic potentials during inspiration, but also have spontaneous firing in the absence of synaptic input. Using transgenic mice that express GFP under the control of the Gad1 (GAD67) gene promoter, we determined that this population of GABAergic neurons is in close apposition to cardioinhibitory parasympathetic cardiac neurons in the nucleus ambiguus (NA). These neurons fire in synchronization with inspiratory activity. Although they receive excitatory glutamatergic synaptic inputs during inspiration, this excitatory neurotransmission was not altered by blocking nicotinic receptors, and many of these GABAergic neurons continue to fire after synaptic blockade. The spontaneous firing in these GABAergic neurons was not altered by the voltage-gated calcium channel blocker cadmium chloride that blocks both neurotransmission to these neurons and voltage-gated Ca(2+) currents, but spontaneous firing was diminished by riluzole, demonstrating a role of persistent sodium channels in the spontaneous firing in these cardiorespiratory GABAergic neurons that possess a pacemaker phenotype. The spontaneously firing GABAergic neurons identified in this study that increase their activity during inspiration would support respiratory rhythm generation if they acted primarily to inhibit post-inspiratory neurons and thereby release inspiration neurons to increase their activity. This population of inspiratory-modulated GABAergic neurons could also play a role in inhibiting neurons that are most active during expiration and provide a framework for respiratory sinus arrhythmia as there is an increase in heart rate during inspiration that occurs via inhibition of premotor parasympathetic cardioinhibitory neurons in the NA during inspiration.     

Tonic inhibition of dorsal pontine neurons during the postural atonia produced by an anticholinesterase in the decerebrate cat.

1. Experiments performed in precollicular decerebrate cats indicate that neurons located in the caudal part of the locus coeruleus and locus subcoeruleus as well as in the surrounding reticular formation were greatly depressed during the cataplectic episodes induced by i.v. injection of 0.1 mg/kg of eserine sulphate. 2. These units actually showed a slow regular firing rate when the rigidity was present. Moreover their firing rate greatly decreased during the episodes of postural atonia produced by the anticholinesterase. In some instances a complete abolition of firing occurred during these episodes. The depression of unit discharge anticipated the onset of postural atonia and lasted throughout the episodes. 3. Some of the neurons described above responded with steady changes in their discharge rate to natural stimulation of macular labyrinthine receptors during postural rigidity. However, the response of these neurons to lateral tilts was suppressed during the episodes of postural atonia induced by the anticholinesterase, This and other arguments suggested that these units were tonically inhibited during the induced cataplectic episodes. 4. The time course of the rate deceleration shown by these neurons during transition from postural rigidity to muscular atonia represents a mirror image of the rate acceleration which affects most of the pontine reticular neurons located in the gigantocellular tegmental field (FTG) during the induced cataplectic episodes. These reciprocal rate relations suggest that a functional interaction exists between the two cell groups. In particular it is postulated that the pontine FTG neurons are self-excitatory and excitatory to the locus coeruleus neurons, while the last neurons may be self-inhibitory and inhibitory to FTG neurons. These findings can be related to previous observations showing that neurons located in the region of locus coeruleus undergo a rate deceleration during desynchronized sleep which mimics the time course of firing to the pontine reticular neurons. 5. In conclusion it appears that the decerebrate rigidity is present in so far as the cholinergic reticular neurons, which trigger the bulbospinal inhibitory system, are tonically inhibited by neurons located in the monoaminergic structures of the dorsolateral pontine tegmentum. On the other hand the suppression of the decerebrate rigidity ,which occurs during the cholinergically induced cataplectic episodes results from activation of the cholinergic reticular neurons, which escape tonic inhibition from monoaminergic structures.