Co-ordinating interneurones of the locust which convey two patterns of motor commands: their connexions with flight motoneurones.

1. Some flight motoneurones receive two superimposed rhythms of depolarizing synaptic potentials when the locust is not flying; a slow rhythm which is invariably linked to the expiratory phase of ventilation, and a fast rhythm with a period of about 50 ms which is similar to the wingbeat period in flight. 2. By recording simultaneously from groups of motoneurones, the synaptic potentials which underly these rhythms have been revealed in 30 flight motoneurones in the three thoracic ganglia. The inputs occur in elevator motoneurones and some depressors but are of lower amplitude in the latter. The inputs have not been found in leg motoneurones. 3. The rhythmic depolarizations are usually subthreshold but sum with sensory inputs to evoke spikes in flight motoneurones at intervals equal to or multiples of the wingbeat period in flight. 4. Both rhythms originate in the metathoracic ganglion and are mediated by the same interneurones. They can be adequately explained by supposing that there are two symmetrical interneurones which each make widespread connexions with left and right flight motoneurones in the three ganglia. 5. The slow rhythm is coded in the overall burst of interneurone spikes during expiration and the fast rhythm in the interval between the spikes of a burst.     

Co-ordinating interneurones of the locust which convey two patterns of motor commands: their connexions with ventilatory motoneurones.

1. The interneurones which make widespread connexions with flight motoneurones also synapse upon ventilatory motoneurones so that in all 50 motoneurones receive synapses. They influence three aspects of ventilation; (a) the closing and opening movements of the thoracic spiracles, (b) some aspects of abdominal pumping movements and (c) the recruitment of some motoneurones controlling head pumping. 2. The two closer motoneurones of a particular thoracic spiracle receive the same excitatory synaptic inputs (EPSPs) during expiration. The EPSPs match those in appropriate flight motoneurones. 3. The closer motoneurones of each thoracic spiracle whose somata are in the pro-, meso- or metathoracic ganglia all receive the same excitatory synaptic inputs. These inputs are an adequate explanation of the pattern of spikes in the closer motoneurones. Both the slow ventilatory and fast rhythms of synaptic potentials are expressed as spikes; the slow as the overall expiratory burst of spikes and the fast as the groups of spikes within that burst. This establishes a ventilatory function for the interneurones. All thoracic closer motoneurones therefore receive the same excitatory commands which will tend to synchronize the movements of each spiracle. 4. Spiracular opener motoneurones are inhibited during expiration, their IPSPs matching the EPSPs in flight or closer motoneurones. Therefore the interneurones have reciprocal effects on the antagonistic motoneurones of the spiracles. 5. The interneurones synapse upon some motoneurones which control the pumping movements of the abdomen and which have their somata in the metathoracic or first unfused abdominal ganglion. Motoneurones in four separate ganglia therefore receive inputs from these interneurones. 6. The interneurones also synapse upon motoneurones which control an auxiliary form of ventilation, head pumping.     

Flight motor patterns recorded in surgically isolated sections of the ventral nerve cord ofLocusta migratoria

Summary In the locust,Locusta migratoria, the pairs of connectives between the three thoracic ganglia and in the neck were transected in all possible combinations. Each of these preparations was tested for the production of rhythmic flight motor activity, with sensory input from the wing receptors intact and after deafferentation. The motor activity elicited in these preparations was characterized by intracellular recordings from motoneurons and electromyographic analyses.The motor patterns observed in locusts with either the neck or the pro-mesothoracic connectives severed (Figs. 2, 3, and 4) were very similar to the flight motor pattern produced by animals with intact connectives. The activity recorded in mesothoracic flight motoneurons of locusts with either only the meso-metathoracic connectives cut or both the meso-metathoracic and the neck connectives transected were similar to each other. Rhythmic motor activity could be observed in these preparations only as long as sensory feedback from the wing receptors was intact. These patterns were significantly different from the intact motor pattern (Figs. 5, 6, and 7). Similar results were obtained when the mesothoracic ganglion was isolated from the other two thoracic ganglia, although the oscillations produced under these conditions were weak (Fig. 8 upper). In the isolated metathorax no rhythmic flight motor activity could be recorded (Fig. 8 lower), even when wing afferents were intact.Considering the differences between the motor patterns observed in the various preparations these results suggest that the ganglia of the locust ventral nerve cord do not contain segmental, homologous flight oscillators which are coupled to produce the intact flight rhythm. Instead they support the idea that the functional flight oscillator network is distributed throughout the thoracic ganglia (Robertson and Pearson 1984). The results also provide further evidence that sensory feedback from the wing sense organs is necessary for establishing the correct motor pattern in the intact animal (Wendler 1974, 1983; Pearson 1985; Wolf and Pearson 1987 a).Abbreviations CPG central pattern generator - EMG electromyogram     

Involvement of the suboesophageal and thoracic ganglia in the control of antennal movements in crickets

In crickets (Gryllus campestris, Gryllus bimaculatus) the contribution of the suboesophageal ganglia (SOG) and thoracic ganglia to the generation of antennal movements during visual tracking, walking and flight was investigated by the transection of connectives. Transection of one circumoesophageal connective abolished the movements and postures of the antenna ipsilateral to the lesion, while the contralateral antenna behaved normally. Simple antennal reflexes remained. Transection of one neck connective reduced fast components of antennal movements during tracking and walking. During flight the ipsilateral antenna could not be maintained in a prolonged forward position. Antennal movements during tracking and walking appeared normal after transection of one connective between pro- and mesothoracic ganglia. However, the antennal flight posture required uninterrupted connections between brain and mesothoracic ganglion. The ablation of more posterior ganglia had no effect on the antennal behaviours investigated. Recordings from an antennal motor nerve revealed a unilateral net excitation relayed via the SOG to the brain. Two ascending interneurones with activity closely correlated with antennal movements are candidates for such a relay function. The data show that the brain is not sufficient to generate antennal movements and postures as integral parts of several behaviours. The SOG and the thoracic ganglia are required in addition. Accepted: 12 March 1997     

Ocellar interneurones in the blowfly Calliphora erythrocephala: Morphology and central projections

Summary The morphology and central projections of first-order ocellar interneurones were analysed in the blowfly, Calliphora erythrocephala after cobalt and horseradish-peroxidase labelling. Three classes of interneurones can be distinguished on the basis of axon diameters: large, medium and small neurones. In total there are 12 large, 10 medium and an unknown number of small interneurones. These interneurones connect the fused first-order ocellar neuropil (underlying the three ocelli) with various areas of the central nervous system. The large neurones terminate in three subregions of the posterior slope (ocellar foci); the medium neurones arborise in several regions of the lateral protocerebrum, in the posterior slope, the lobula, the ventral medulla, and in the pro- and mesothoracic ganglia. The thin fibers arborise in all the above regions (except in the thoracic ganglia), and in addition in the neuropil dorsal to the oesophagus and antero-ventral to posterior slope (tritocerebrum). The anatomy of the ocellar pathway in C. erythrocephala is compared with those in other studied insects. Possible interactions between ocellar interneurones and other pathways are discussed.     

Locust flight behavior after hemisection of individual thoracic ganglia: evidence for hemiganglionic premotor centers

Summary The flight behavior of locusts with hemisected mesothoracic or metathoracic ganglia was observed in unrestrained animals and monitored electromyographically in tethered animals. Animals with hemisected mesothoracic ganglia were able to initiate and carry out free flight. Hemisection of the mesothoracic ganglion caused no significant changes in the pattern of flight muscle firing; both intra- and intersegmental coordination of flight muscle activity were retained (Figs. 3, 4). Additional transection of one meso-metathoracic connective altered the pattern of flight muscle firing but did not abolish rhythmic activity (Fig. 8). Deafferentation of the thoracic ganglia in animals with hemisected mesothoracic ganglia resulted in rhythmically coordinated motor activity (Fig. 5) which was indistinguishable from that shown by deafferented animals with all ganglia intact. Hemisection of the metathoracic ganglion resulted in an abnormal pattern of flight muscle firing. However, a basic rhythmicity of motor activity was still present (Fig. 6). The implications of these results for rhythm generation and motor coordination in the flight control system of the locust are discussed.     

Current injection into interneurones of the terminal ganglion modifies turning behaviour of walking crickets

Ascending interneurones of the terminal ganglion of orthopterous insects are known to carry information on wind stimuli perceived by cercal receptors to thoracic and cephalic ganglia. Neurones of these anterior ganglia control evasive walking behaviour. We demonstrate that current injection into individual wind-sensitive local non-spiking interneurones and ascending giant interneurones of the terminal ganglion can influence the orientation behaviour of walking crickets. To induce a change of turning during “wind puff stimulation” by current injection into the lateral giant interneurone, its spike activity has to be modified by at least 100%. In 5 of 12 different types of non-spiking interneurones a moderate shift of the membrane potential results in a change of the mean speed of rotation and/or the frequency of turns. All preparations tested with different amounts of current injection showed a proportional change of turning frequency. Normally, the turning behaviour is evasive with respect to the wind source. During current injection this dependence is preserved, but the general orientation is readjusted. Taking into account known connections between some of these interneurones and ascending neurones the tested wind-sensitive local non-spiking interneurones of the terminal ganglion are likely to impose an offset on the mean direction of orientation controlled by cephalic and thoracic neuronal networks. Accepted: 3 September 1997     

Chemical phenotypes of intrinsic cardiac neurons in the newborn pig (Sus scrofa domesticus Erxleben, 1777)

Intrinsic cardiac neurons (ICNs) are crucial cells in the neural regulation of heart rhythm, myocardial contractility, and coronary blood flow. ICNs exhibit diversity in their morphology and neurotransmitters that probably are age-dependent. Therefore, neuroanatomical heart studies have been currently focused on the identification of chemical phenotypes of ICNs to disclose their possible functions in heart neural regulation. Employing whole-mount immunohistochemistry, we examined ICNs from atria of the newborn pigs (Sus scrofa domesticus) as ICNs at this stage of development have never been neurochemically characterized so far. We found that the majority of the examined ICNs (>60%) were of cholinergic phenotype. Biphenotypic neuronal somata (NS), that is, simultaneously positive for two neuronal markers, were also rather common and distributed evenly within the sampled ganglia. Simultaneous positivity for cholinergic and adrenergic neuromarkers was specific in 16.4%, for cholinergic and nitrergic—in 3.5% of the examined NS. Purely either adrenergic or nitrergic ICNs were observed at 13% and 3.1%, correspondingly. Purely adrenergic and nitrergic NS were the most frequent in the ventral left atrial subplexus. Similarly to neuronal phenotype, sizes of NS also varied depending on the atrial region providing insights into their functional implications. Axons, but not NS, positive for classic sensory neuronal markers (vesicular glutamate transporter 2 and calcitonin gene-related peptide) were identified within epicardiac nerves and ganglia. Moreover, a substantial number of ICNs could not be attributed to any phenotype as they were not immunoreactive for antisera used in this study. Numerous dendrites with putative peptidergic and adrenergic contacts on cholinergic NS contributed to neuropil of ganglia. Our observations demonstrate that intrinsic cardiac ganglionated plexus is not fully developed in the newborn pig despite of dense network of neuronal processes and numerous signs of neural contacts within ganglia.     

The central nervous control of the adductor behaviour of lamellibranch molluscs.

In Egeria radiata (L.) and Mutela dubia (Gmelin) decerebration does not result in tonus of the posterior adductor muscle and each species continues to exhibit its characteristic rapid and slow rhythms. Excitatory and inhibitory nerve pathways originating in the cerebral ganglia terminate on the visceral ganglia. The cerebral ganglia alone do not exhibit any rhythm; the anterior adductor muscle remains relaxed after excision of the visceral ganglia. The mid-dorsal and the anterior lobes of the visceral ganglia in Scrobicularia plana (Da Costa) control all adductor activity. Groups of potentials in the posterior adductor nerves originate from the different lobes and are separate physiological mechanisms.     

Distribution of NADPH-diaphorase-positive ascending interneurones in the crayfish terminal abdominal ganglion

Previous neuropharmacological studies have described the presence of a nitric oxide-cGMP signalling pathway in the crayfish abdominal nervous system. In this study we have analysed the distribution of putative nitric oxide synthase (NOS)-containing ascending interneurones in the crayfish terminal abdominal ganglion using NADPH-diaphorase (NADPHd) histochemistry. Ascending intersegmental interneurones were stained intracellularly using the fluorescent dye Lucifer yellow and the ganglia containing the stained interneurones subsequently processed for NADPHd activity. Fluorescence persisted throughout histochemical processing. These double-labelling experiments showed that 12 of 18 identified ascending interneurones were NADPHd positive. Thus many ascending interneurones that process mechanosensory signals in the terminal ganglion may contain NOS, and are themselves likely sources of NO which is known to modulate their synaptic inputs. Three clear relationships emerged from our analysis between the effects of NO on the synaptic inputs of interneurones, their output properties and their staining for NADPH-diaphorase. First were class 1 interneurones with no local outputs in the terminal ganglion, the NE type interneurones, which had sensory inputs that were enhanced by NO and were NADPHd positive. Second were class 1 interneurones with local and intersegmental output effects that had sensory inputs that were also enhanced by NO but were NADPHd negative. Third were class 2 interneurones with local and intersegmental outputs that had synaptic inputs that were depressed by the action of NO but were NADPHd positive. These results suggest that NO could selectively enhance specific synaptic connections and sensory processing pathways in local circuits.     

Existence of respiratory interneurons in the cervical spinal cord of the rabbit

A spinal "respiration" generator has been shown to fire phrenic motoneurones in rhythmic bursts. It is very likely driven through bulbo-spinal inspiratory neurones in intact preparations. Although no direct evidence for respiratory interneurones at the C4-C5 spinal levels has been obtained so far (except for Renshaw cells ), it is currently believed that only few inspiratory inputs to the phrenic motoneurones are transmitted monosynaptically from the medulla. We have tried here to record spinal interneuronal respiratory activities in decorticate, unanaesthetized, vagotomized and curarized rabbit preparations. Different functional categories of interneurones could be identified at the C4-C5 spinal levels: inspiratory and expiratory interneurons with various discharge patterns which rather well correspond to the functional categories of inspiratory and expiratory bulbo-spinal neurones described by Bianchi and Richter. In addition, multiunit inspiratory bursting could be followed over several 100 microns during each electrode penetration. The different categories of interneurones were encountered laterally from 700 to 1,000 microns, at depths ranging from 300 to 500 microns dorsally to the phrenic nucleus, down to the nucleus itself. These results indicate that part of the medullary inspiratory drive is channelled via spinal cord interneurones; they also suggest that an inhibition of phrenic motoneurones from the bulbo-spinal expiratory drive takes place via interneurones.     

Morphology and physiology of auditory and vibratory ascending interneurones in bushcrickets

Auditory/vibratory interneurones of the bushcricket species Decticus albifrons and Decticus verrucivorus were studied with intracellular dye injection and electrophysiology. The morphologies of five physiologically characterised auditory/vibratory interneurones are shown in the brain, subesophageal and prothoracic ganglia. Based on their physiology, these five interneurones fall into three groups, the purely auditory or sound neurones: S-neurones, the purely vibratory V-neurones, and the bimodal vibrosensitive VS-neurones. The S1-neurones respond phasically to airborne sound whereas the S4-neurones exhibit a tonic spike pattern. Their somata are located in the prothoracic ganglion and they show an ascending axon with dendrites located in the prothoracic, subesophageal ganglia, and the brain. The VS3-neurone, responding to both auditory and vibratory stimuli in a tonic manner, has its axon traversing the brain, the suboesophageal ganglion and the prothoracic ganglion although with dendrites only in the brain. The V1- and V2-neurones respond to vibratory stimulation of the fore- and midlegs with a tonic discharge pattern, and our data show that they receive inhibitory input suppressing their spontaneous activity. Their axon transverses the prothoracic ganglion, subesophageal ganglion and terminate in the brain with dendritic branching. Thus the auditory S-neurones have dendritic arborizations in all three ganglia (prothoracic, subesophageal, and brain) compared to the vibratory (V) and vibrosensitive (VS) neurones, which have dendrites almost only in the brain. The dendrites of the S-neurones are also more extensive than those of the V-, VS-neurones. V- and VS-neurones terminate more laterally in the brain. Due to an interspecific comparison of the identified auditory interneurones the S1-neurone is found to be homologous to the TN1 of crickets and other bushcrickets, and the S4-neurone also can be called AN2. J. Exp. Zool. 286:219-230, 2000.     

运动过程的网络逻辑——从离子通道到动物行为

为了揭示神经网络在脊椎动物运动中所行使的内在功能,作者开发了七鳃鳗这种低等脊椎动物模型。在这套系统中,不仅可以了解到运动模式生成网络以及激活此网络的命令系统,同时还可以在运动中研究方向控制系统和变向控制系统。七鳃鳗的神经系统有较少的神经元,而且运动行为中的不同运动模式可以由分离的神经系统所引发。模式生成神经网络包括同侧的谷氨酸能中间神经元和对侧的抑制性甘氨酸能中间神经元。网络中的突触连接、细胞膜特性和神经递质都也已经被鉴定。运动是由脑干区域的网状脊髓神经元所引起,而这些神经元又是被问脑和中脑分离的一些运动命令神经元群所控制。因此,运动行为最初是由这两个“运动核心”所启动。而这两个运动核心被基底神经节调控,基底神经节即时地做出判断是否允许下游的运动程序启动。在静止情况下基底神经节的输出核团维持对下游不同运动核心的抑制作用,反之则去除抑制活化运动核心。纹状体和苍白球被认为是这个运动抉择系统的主要部件。根据“霍奇金一贺胥黎”模型神经元开发了这套网络模型,不同的细胞具有各自相应的不同亚型的钠、钾、钙离子通道和钙依赖的钾通道。每个模型神经元拥有86个不同区域模块以及其对应的生物学功能,例如频率控制、超极化等等。然后根据已有实验证据,利用突触将不同的模型神经元相连。而系统中的10000个神经元大致和生物学网络上的细胞数量相当。突触数量为760000。突触类型有AMPA、NMDA、glycine型。有了这样大规模的模型,不仅可以模拟肌节与肌节之间的神经网络,还可以模拟到由基底神经节开始的行为起始部分。此外,这些网络模拟还被用于一个神经机械学模型来模拟包含有推进和方向控制部分的真实运动。     

Gradual adjustment of circaseptan-circadian blood pressure and heart rate rhythms after a trans-9-meridian flight.

Circadian and circaseptan adjustment of blood pressure and heart rate after a transmeridian flight by a family of four was relatively fast, but it was not abrupt; it was not completed during the first week in the new setting. Gradual changes continued for the ensuing three weeks. The circadian and circaseptan rhythm characteristics and their adjustment in particular differed among variables in the husband: the circadian component of heart rate adjusted more rapidly than that of blood pressure. The adjustment also differed among two members of the family. A new phenomenon, namely a difference in circadian rhythm adjustment between husband and wife, is also described herein: the wife's circadian rhythm in blood pressure advanced by 9 hours within the 4-week span of recording following a 9-hour advance in living routine (after a 9-zone transmeridian flight); since both schedule and rhythm moved in the same direction (albeit not at the same rate), the behavior may be dubbed concursive. By contrast, the husband delayed to achieve the same adjustment: his behavior was anticursive. The phenomenon of a difference in direction of adjustment for different variables in the same subject has been described earlier as polarity, now qualified as intra-individual polarity, to separate it from the precedent of an intrafamilial or more broadly inter-individual polarity or partitioning, reported apparently for the first time and dubbed 'cursion'.     

Patterned synaptic drive to locust flight motoneurons after hemisection of thoracic ganglia

Intracellular recordings were carried out on locust flight motoneurons after hemisection of individual thoracic ganglia. With the exception of minimal surgical manipulations, the animals were intact and able to perform tethered flight. Analysis of the synaptic drive recorded in the motoneurons during flight motor activity revealed the extent to which ganglion hemisection influenced the premotor rhythm generating network.

Localization of octopaminergic neurones in insects

This paper reviews data on the localization of octopaminergic neurones revealed by immunocytochemistry in insects, primarily the locusts Schistocerca gregaria and Locusta migratoria, cricket Gryllus bimaculatus, and cockroach Periplaneta americana. Supporting evidence for their octopaminergic nature is mentioned where available. In orthopteran ventral ganglia, the major classes of octopamine-like immunoreactive (-LI) neurones include: (1) efferent dorsal and ventral unpaired median (DUM, VUM) neurones; (2) several intersegmentally projecting DUM interneurones in the suboesophageal ganglion; other DUM interneurones are probably GABAergic; (3) a pair of anterior median cells in the prothoracic ganglion; (4) a single pair of ventral cells in most thoracic and some other ganglia; these appear to be plurisegmentally projecting interneurones. Eight categories of octopamine-LI neurones occur in the orthopteran brain. The basic projections of three types are described here: one class project to the optic lobes to form wide field projections. Another type descends to cross into the tritocerebral commissure and may invade the contralateral brain hemisphere. A further class is the median neurosecretory cells with axons in the nervi corpori cardiaci I. Available data for the honey bee Apis mellifera and moth Manduca sexta indicate that the octopamine-LI cell types found in orthopterans also occur in holometabolous insects. Immunocytochemical evidence suggests that some octopaminergic DUM cells contain an FMRFamide-related peptide and the amino acid taurine as putative cotransmitters.     

Mechanism of neuronal coordination of the rhythmic activities of developing flight muscles and a neurosecretory cell population in the silkmoth, Bombyx mori

Ultradian rhythmic firing activity (period of 40-90 min) of a population of neurosecretory cells (NSCs) producing FXPRLamide peptides in the subesophageal ganglion (SG) of the silkmoth, Bombyx mori, is closely coordinated with periodically occurring electrical activity of developing flight muscles (FMs) during metamorphosis. To examine neuronal mechanisms and pathways that mediate the coordination of the NSC and flight motor systems, the ventral nerve cord (VNC) or circumesophageal connectives were transected. Transection of the VNC between the SG and thoracic ganglia greatly shortened the period of activity rhythm of the FMs (5-15 min) with no effect on the rhythmicity of NSCs. Bilateral transsection of the circumesophageal connectives between the brain and SG abolished the rhythmic activity of NSCs, thereby suggesting that the coordination of the two systems may be mediated by a common oscillatory mechanism in the brain. Further, bisection of the brain in the midline failed to abolish the ultradian rhythmicity of FMs. Thus, each brain hemisphere may have an ultradian oscillator that activates the NSC system in the SG, and modulates the short-period oscillation of the flight motor system located in the thoracic ganglia.     

Analysis of the Neural Network Regulating the Cardio-Renal System in the Central Nervous System of Helix pomatia L.

In the central nervous system of Helix pomatia 22 cells takingpart in the regulation of the cardio-renal system have beenidentified. These cells are scattered throughout the visceraland right parietal ganglia. Among identified cells sensory,motor, and interneurons were found and the hierarchical characterof the network was stated. The network regulating heart activitywas found to be of the over-guaranteed, convergent type, wherethe inputs predominate and the outputs form independent, parallelpathways, being coordinated by interneurons. This neural networkcan be divided into two levels: collectors and coordinators,which are responsible for the conduction or analysis of theafferent inputs, respectively. The localization of identifiedcells was studied by intracellular and retrograde injectionof CoCl₂. Primary sensory cells were found to be bipolar, motoneuronesand interneurones were unipolar or pseudo-unipolar with richarborization within the ganglia. Interneuron V21 showed a phasic or tonic pattern of firing.The phasic activity of the neuron V21 appeared as a burst correlatedwith the individual heartbeats. The tonic pattern of firingwas caused by activation of various inputs of the cardio-renalsystem and led always to the stopping of the heartbeat. Thenetwork regulating the heartbeat was organized around the interneurones.In the activity pattern of the interneurones the origin of theinput was not distinguishable; however, on the middle levelof the system it can be verified. These cells play a role inthe storage of information originating Irom various receptorareas. According to this the regulatory network can be dividedinto subsystems.     

Histochemistry of nitric oxide synthase in the nervous system

Summary Nitric oxide synthase, which generates the physiological messenger molecule nitric oxide, and its associated NADPH diaphorase (NADPHd) activity are distributed throughout selective neuronal populations of the central and peripheral nervous system. Considerable evidence has been accumulated to indicate that NADPHd activity labels cells lacking neuronal nitric oxide synthase, i.e., the specificity of the reaction has to be considered for the reliable detection of the enzyme in neuronal but also non-neuronal tissue. In the present review, critical aspects of nitric oxide synthase visualization in neurones, using its NADPHd activity, are discussed. Furthermore, the organization of the central and peripheral nitric oxide synthase-containing neuronal systems is described. Nitric oxide synthase is present in local cortical and striatal neurones, hypothalamic magnocellular neurones, mesopontine cholinergic neurones, cerebellar interneurones, preganglionic sympathetic and parasympathetic neurones, neurones in parasympathetic autonomic and enteric ganglia and primary viscero-afferent neurones. Finally, injury-related alterations in nitric oxide synthase activity are briefly outlined. In this respect, the histochemistry of nitric oxide synthase may represent a valuable marker for neurochemical, if not structural, alterations observed in neural diseases, regeneration and transplantation.     

Effects of gravity, hypergravity and microgravity on vestibular neurones of the crab

Recordings were made from identified balancing system interneurones using implanted electrodes in crabs oscillated at 0.3 Hz during bouts of Parabolic flight. Repeatable non stabilized patterns of response firing were seen in head up and head down interneurones. During the hypergravity phases, the ratio of firing frequencies in the two directional categories of interneurones was altered showing that hypergravity produced effects normally seen during tilting of the crab, implying greater bending of the sensory thread hairs. During microgravity, firing levels remained low and constant or changed slowly towards initial firing levels.