Contralateral Neurons Research Articles

Neural circuits for peristaltic wave propagation in crawling Drosophila larvae: analysis and modeling.

Drosophila larvae crawl by peristaltic waves of muscle contractions, which propagate along the animal body and involve the simultaneous contraction of the left and right side of each segment. Coordinated propagation of contraction does not require sensory input, suggesting that movement is generated by a central pattern generator (CPG). We characterized crawling behavior of newly hatched Drosophila larvae by quantifying timing and duration of segmental boundary contractions. We developed a CPG network model that recapitulates these patterns based on segmentally repeated units of excitatory and inhibitory (EI) neuronal populations coupled with immediate neighboring segments. A single network with symmetric coupling between neighboring segments succeeded in generating both forward and backward propagation of activity. The CPG network was robust to changes in amplitude and variability of connectivity strength. Introducing sensory feedback via “stretch-sensitive” neurons improved wave propagation properties such as speed of propagation and segmental contraction duration as observed experimentally. Sensory feedback also restored propagating activity patterns when an inappropriately tuned CPG network failed to generate waves. Finally, in a two-sided CPG model we demonstrated that two types of connectivity could synchronize the activity of two independent networks: connections from excitatory neurons on one side to excitatory contralateral neurons (E to E), and connections from inhibitory neurons on one side to excitatory contralateral neurons (I to E). To our knowledge, such I to E connectivity has not yet been found in any experimental system; however, it provides the most robust mechanism to synchronize activity between contralateral CPGs in our model. Our model provides a general framework for studying the conditions under which a single locally coupled network generates bilaterally synchronized and longitudinally propagating waves in either direction.

Asymmetric neurotransmitter release enables rapid odour lateralization in Drosophila

In Drosophila, most individual olfactory receptor neurons (ORNs) project bilaterally to both sides of the brain1,2. Having bilateral rather than unilateral projections may represent a useful redundancy. However, bilateral ORN projections to the brain should also compromise the ability to lateralize odors. Nevertheless, walking or flying Drosophila reportedly turn toward their more strongly stimulated antenna3-5. Here we show that each ORN spike releases ~40% more neurotransmitter from the axon branch ipsilateral to the soma, as compared to the contralateral branch. As a result, when an odor activates the antennae asymmetrically, ipsilateral central neurons begin to spike a few milliseconds before contralateral neurons, and ipsilateral central neurons also fire at a 30-50% higher rate. We show that a walking fly can detect a 5% asymmetry in total ORN input to its left and right antennal lobes, and can turn toward the odor in less time than it requires the fly to complete a stride. These results demonstrate that neurotransmitter release properties can be tuned independently at output synapses formed by a single axon onto two target cells with identical functions and morphologies. Our data also show that small differences in spike timing and spike rate can produce reliable differences in olfactory behavior.

Transsynaptic inhibition of spinal transmission by A2 botulinum toxin.

Type A botulinum toxin blocks not only ACh release from motor nerve terminals but also central synaptic transmission, including glutamate, noradrenaline, dopamine, ATP, GABA and glycine. Neurotoxins (NTXs) are transported by both antero- and retrogradely along either motor or sensory axons for bidirectional delivery between peripheral tissues or the CNS. A newly developed type A2 NTX (A2NTX) injected into one rat foreleg muscle was transported to the contralateral muscle. This finding was consistent with the NTX traveling retrogradely via spinal neurons and then transsynaptically through motor neurons to the contralateral motor neurons within the spinal cord and on to the soleus muscle. In the present study we found that toxin injection into the rat left soleus muscle clearly induced bilateral muscle relaxation in a dose-dependent fashion, although the contralateral muscle relaxation followed the complete inhibition of toxin-injected ipsilateral muscles. The toxin-injected ipsilateral muscle relaxation was faster and stronger in A2NTX-treated rats than A1LL (BOTOX). A1LL was transported almost equally to the contralateral muscle via neural pathways and the bloodstream. In contrast, A2NTX was mainly transported to contralateral muscles via the blood. A1LL was more successfully transported to contralateral spinal neurons than A2NTX. We also demonstrated that A1LL and A2NTX were carried from peripheral to CNS and vice versa by dual antero- and retrograde axonal transport through either motor or sensory neurons.

Bilateral efferents from nucleus isthmi to the optic tectum in goldfish (Carassius auratus) are spatially restricted

The projection from nucleus isthmi (NI) to the optic tectum (OT) was investigated in the goldfish, Carassius auratus, by retrograde transport of biocytin applied at various sites in a tectal lobe. In previous studies, this projection is described as predominantly from the ipsilateral NI and maps topographically along the approximate rostrocaudal axis of both brain areas. However, the rostromedial tectal lobe, the tectal region representing the binocular visual field, receives afferents from both the ipsilateral and the contralateral NI. The contralateral isthmic neurons are found at the most caudal position in NI and are not topographic with the tectum. The bilateral projection from NI to the tectum may play a role in functions requiring the coordination of both eyes.

Bilateral Collicular Interaction: Modulation of Auditory Signal Processing in Amplitude Domain

In the ascending auditory pathway, the inferior colliculus (IC) receives and integrates excitatory and inhibitory inputs from many lower auditory nuclei, intrinsic projections within the IC, contralateral IC through the commissure of the IC and from the auditory cortex. All these connections make the IC a major center for subcortical temporal and spectral integration of auditory information. In this study, we examine bilateral collicular interaction in modulating amplitude-domain signal processing using electrophysiological recording, acoustic and focal electrical stimulation. Focal electrical stimulation of one (ipsilateral) IC produces widespread inhibition (61.6%) and focused facilitation (9.1%) of responses of neurons in the other (contralateral) IC, while 29.3% of the neurons were not affected. Bilateral collicular interaction produces a decrease in the response magnitude and an increase in the response latency of inhibited IC neurons but produces opposite effects on the response of facilitated IC neurons. These two groups of neurons are not separately located and are tonotopically organized within the IC. The modulation effect is most effective at low sound level and is dependent upon the interval between the acoustic and electric stimuli. The focal electrical stimulation of the ipsilateral IC compresses or expands the rate-level functions of contralateral IC neurons. The focal electrical stimulation also produces a shift in the minimum threshold and dynamic range of contralateral IC neurons for as long as 150 minutes. The degree of bilateral collicular interaction is dependent upon the difference in the best frequency between the electrically stimulated IC neurons and modulated IC neurons. These data suggest that bilateral collicular interaction mainly changes the ratio between excitation and inhibition during signal processing so as to sharpen the amplitude sensitivity of IC neurons. Bilateral interaction may be also involved in acoustic-experience-dependent plasticity in the IC. Three possible neural pathways underlying the bilateral collicular interaction are discussed.

Neural mechanism of binding amplitude information of echo sound with its frequency one in echolocating bat

Most species of bats making echolocation use the sound pressure level (SPL) and Doppler-shifted frequency of ultrasonic echo pulse to measure the size and velocity of target. The neural circuits for detecting these target features are specialized for amplitude and frequency analysis of the second harmonic constant frequency (CF2) component of Doppler-shifted echoes. The neuronal circuits involved in detecting these echo features have been well known [1]. In natural situation, large natural objects in environment, like bushes or trees, produce complex stochastic echoes, which can be characterized by the echo roughness. The echo signal reflecting from a target insect is embedded in the complex signal. Even in such an environment, bats can detect accurately the detailed information of flying insect. We consider here two questions: how the neural circuits bind amplitude and frequency information of echo sound, and how bat distinguishes target information from information of background signal. To address these issues, we developed a neural network model for detecting SPL amplitude and Doppler-shifted frequency of echo sound. The model contains two hemispheres, in each of which, the network model consists of cochlea (Ch), inferior colliculus (IC), and Doppler-shifted constant frequency (DSCF) processing area. The Ch network has a frequency map by which sound frequency is encoded. The model for detecting frequency information of echo sound was based on the model previously presented by us [2].The SPL amplitude is encoded in to firing rate of IC neurons. The IC neurons encode SPL amplitude by means of a balance between excitatory connection from contralateral Ch neurons and inhibitory connection from ipsilateral ones, and then combine the amplitude and frequency information of echo sound. The DSCF network has two types of sub-networks detecting AC and DC components of echo sound, which represent the information of target and background signals, respectively. We showed that in IC, the amplitude information of echo sound is encoded by integrating the outputs of ipsi and contralateral Ch neurons and then combined with the Doppler-shifted frequency information encoded by tonotopical map of Ch neurons. The accuracy of the amplitude and frequency information was improved in the DSCF area. The model reproduced well several experimental results observed in IC and DSCF neurons. We also showed that AC and DC components of echo signal are discriminated in the two sub-networks of DSCF. The discrimination ability is due to the difference in time constant between DSCF neurons in the two sub-networks.

Embryonic assembly of auditory circuits: spiral ganglion and brainstem

During early development, peripheral sensory systems generate physiological activity prior to exposure to normal environmental stimuli. This activity is thought to facilitate maturation of these neurons and their connections, perhaps even promoting efficacy or modifying downstream circuitry. In the mammalian auditory system, initial connections form at embryonic ages, but the functional characteristics of these early neural connections have not been assayed. We investigated processes of embryonic auditory development using a whole-head slice preparation that preserved connectivity between peripheral and brainstem stations of the auditory pathway. Transgenic mice expressing fluorescent protein provided observation of spiral ganglion and cochlear nucleus neurons to facilitate targeted electrophysiological recording. Here we demonstrate an apparent peripheral-to-central order for circuit maturation. Spiral ganglion cells acquire action potential-generating capacity at embryonic day 14 (E14), the earliest age tested, and action potential waveforms begin to mature in advance of comparable states for neurons of the ventral cochlear nucleus (VCN) and medial nucleus of the trapezoid body (MNTB). In accordance, auditory nerve synapses in the VCN are functional at E15, prior to VCN connectivity with the MNTB, which occurs at least 1 day later. Spiral ganglion neurons exhibit spontaneous activity at least by E14 and are able to drive third-order auditory brainstem neurons by E17. This activity precedes cochlear-generated wave activity by 4 days and ear canal opening by at least 2 weeks. Together, these findings reveal a previously unknown initial developmental phase for auditory maturation, and further implicate the spiral ganglion as a potential controlling centre in this process.

Bilateral connectivity in the brainstem respiratory networks of lampreys

This study examines the connectivity in the neural networks controlling respiration in the lampreys, a basal vertebrate. Previous studies have shown that the lamprey paratrigeminal respiratory group (pTRG) plays a crucial role in the generation of respiration. By using a combination of anatomical and physiological techniques, we characterized the bilateral connections between the pTRGs and descending projections to the motoneurons. Tracers were injected in the respiratory motoneuron pools to identify pre-motor respiratory interneurons. Retrogradely labeled cell bodies were found in the pTRG on both sides. Whole-cell recordings of the retrogradely labeled pTRG neurons showed rhythmical excitatory currents in tune with respiratory motoneuron activity. This confirmed that they were related to respiration. Intracellular labeling of individual pTRG neurons revealed axonal branches to the contralateral pTRG and bilateral projections to the respiratory motoneuronal columns. Stimulation of the pTRG induced excitatory postsynaptic potentials in ipsi- and contralateral respiratory motoneurons as well as in contralateral pTRG neurons. A lidocaine HCl (Xylocaine) injection on the midline at the rostrocaudal level of the pTRG diminished the contralateral motoneuronal EPSPs as well as a local injection of 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) and (2R)-amino-5-phosphonovaleric acid (AP-5) on the recorded respiratory motoneuron. Our data show that neurons in the pTRG send two sets of axonal projections: one to the contralateral pTRG and another to activate respiratory motoneurons on both sides through glutamatergic synapses.

Adaptation of Binaural Processing in the Adult Brainstem Induced by Ambient Noise

Interaural differences in stimulus intensity and timing are major cues for sound localization. In mammals, these cues are first processed in the lateral and medial superior olive by interaction of excitatory and inhibitory synaptic inputs from ipsi- and contralateral cochlear nucleus neurons. To preserve sound localization acuity following changes in the acoustic environment, the processing of these binaural cues needs neuronal adaptation. Recent studies have shown that binaural sensitivity adapts to stimulation history within milliseconds, but the actual extent of binaural adaptation is unknown. In the current study, we investigated long-term effects on binaural sensitivity using extracellular in vivo recordings from single neurons in the dorsal nucleus of the lateral lemniscus that inherit their binaural properties directly from the lateral and medial superior olives. In contrast to most previous studies, we used a noninvasive approach to influence this processing. Adult gerbils were exposed for 2 weeks to moderate noise with no stable binaural cue. We found monaural response properties to be unaffected by this measure. However, neuronal sensitivity to binaural cues was reversibly altered for a few days. Computational models of sensitivity to interaural time and level differences suggest that upregulation of inhibition in the superior olivary complex can explain the electrophysiological data.

Sympathetic premotor neurones project to and are influenced by neurones in the contralateral rostral ventrolateral medulla of the rat in vivo

The tonic activity of bulbospinal neurones in the rostral ventrolateral medulla (RVLM) is thought to underlie basal sympathetic nerve activity. A key research objective is to delineate the mechanisms that contribute to the firing of these neurones. In the current study we investigate the hypothesis that inputs arising in the contralateral RVLM converge on barosensitive bulbospinal neurones and contribute to their discharge pattern. Extracellular recordings were made from 24 barosensitive bulbospinal neurones in urethane anaesthetised, vagotomised and artificially ventilated rats during activation (glutamate or D,L-homocysteic acid microinjection, 50nl, 50mM, or monopolar electrical stimulation) or inhibition (microinjection of GABA receptor agonists muscimol or isoguvacine, 50nl, 10mM) of the contralateral RVLM. Chemical RVLM activation strongly increased (10/17) or inhibited (6/17) the spontaneous activity of neurones recorded in the contralateral RVLM. Electrical RVLM stimulation evoked a combination of short latency (median 6ms) inhibitory and longer latency (median 9.1ms, P<0.01) excitatory orthodromic responses in contralateral sympathetic premotor neurones and in some cases evoked antidromic action potentials that collided with spontaneous spikes. RVLM inhibition increased the discharge rate of sympathetic premotor neurones in the contralateral brainstem by 21±13% (P<0.05) and reduced the variability of unit firing by 37±12% (n=5, p<0.05). These findings indicate that sympathetic premotor neurones receive inhibitory and excitatory input from the contralateral RVLM, that inhibitory inputs predominate under baseline conditions, and that a population of sympathetic premotor neurones project to the contralateral RVLM in addition to their spinal targets.

Redundant information encoding in primary motor cortex during natural and prosthetic motor control

Redundant encoding of information facilitates reliable distributed information processing. To explore this hypothesis in the motor system, we applied concepts from information theory to quantify the redundancy of movement-related information encoded in the macaque primary motor cortex (M1) during natural and neuroprosthetic control. Two macaque monkeys were trained to perform a delay center-out reaching task controlling a computer cursor under natural arm movement (manual control, 'MC'), and using a brain-machine interface (BMI) via volitional control of neural ensemble activity (brain control, 'BC'). During MC, we found neurons in contralateral M1 to contain higher and more redundant information about target direction than ipsilateral M1 neurons, consistent with the laterality of movement control. During BC, we found that the M1 neurons directly incorporated into the BMI ('direct' neurons) contained the highest and most redundant target information compared to neurons that were not incorporated into the BMI ('indirect' neurons). This effect was even more significant when comparing to M1 neurons of the opposite hemisphere. Interestingly, when we retrained the BMI to use ipsilateral M1 activity, we found that these neurons were more redundant and contained higher information than contralateral M1 neurons, even though ensembles from this hemisphere were previously less redundant during natural arm movement. These results indicate that ensembles most associated to movement contain highest redundancy and information encoding, which suggests a role for redundancy in proficient natural and prosthetic motor control.

Peripheral facial nerve lesion induced long-term dendritic retraction in pyramidal cortico-facial neurons

Little evidence is available concerning the morphological modifications of motor cortex neurons associated with peripheral nerve injuries, and the consequences of those injuries on post lesion functional recovery. Dendritic branching of cortico-facial neurons was characterized with respect to the effects of irreversible facial nerve injury. Twenty-four adult male rats were distributed into four groups: sham (no lesion surgery), and dendritic assessment at 1, 3 and 5 weeks post surgery. Eighteen lesion animals underwent surgical transection of the mandibular and buccal branches of the facial nerve. Dendritic branching was examined by contralateral primary motor cortex slices stained with the Golgi-Cox technique. Layer V pyramidal (cortico-facial) neurons from sham and injured animals were reconstructed and their dendritic branching was compared using Sholl analysis. Animals with facial nerve lesions displayed persistent vibrissal paralysis throughout the five week observation period. Compared with control animal neurons, cortico-facial pyramidal neurons of surgically injured animals displayed shrinkage of their dendritic branches at statistically significant levels. This shrinkage persisted for at least five weeks after facial nerve injury. Irreversible facial motoneuron axonal damage induced persistent dendritic arborization shrinkage in contralateral cortico-facial neurons. This morphological reorganization may be the physiological basis of functional sequelae observed in peripheral facial palsy patients.

Spinal glycinergic and GABAergic neurons expressing C-FOS after capsaicin stimulation are increased in rats with contralateral neuropathic pain

There is increasing evidence that pain transmission on one side of the body is influenced by a painful state on the other side. We have investigated this phenomenon by studying the activation pattern (using C-fos labeling) of spinal glycinergic and GABAergic (Gly/GABA) neurons after capsaicin injection in the ipsilateral hind paw of rats that were preconditioned with an acute or chronic pain stimulus in the contralateral hind paw or rats that were not preconditioned (control). For this purpose, fluorescent in situ hybridization with GlyT2 and GAD67 mRNA probes was combined with fluorescent C-fos immunohistochemistry. Rats were preconditioned with acute (capsaicin, Complete Freund's Adjuvant (CFA) 1.5 h), chronic inflammatory (CFA 20 h and 4 days), neuropathic (spared nerve injury (SNI) 2 weeks), or control pain stimuli (saline 20 h and 4 days; sham-SNI 2 weeks). We found that after capsaicin injection in rats preconditioned with CFA inflammation (4 days), sham-SNI or with SNI neuropathic pain, the numbers (27 ± 3, 21 ± 2, and 21 ± 2, respectively) and percentages (55% ± 4, 43% ± 2, and 42% ± 2, respectively) of C-fos activated neurons that were Gly/GABA increased significantly as compared with control (10 ± 1 and 25% ± 2). The increase in the total number of C-fos activated Gly/GABA neurons was present primarily in the superficial dorsal horn (laminae I and II; control: 9%; CFA 4 days: 56%; SNI 2 weeks: 42%). This increase in C-fos activation of Gly/GABA neurons occurred without significant changes in the total number of C-fos activated neurons, and without any significant changes in the mechanical thresholds in the hind paws after capsaicin injection. The results showed that one-sided chronic pain, especially inflammation, significantly increases the C-fos activation pattern of spinal Gly/GABA neurons on the other side of the spinal cord. This further underlines the existence of a dynamic interaction between ipsi- and contralateral spinal neurons in the processing of nociceptive information.

Monocular eye position specificity in the oculomotor neural integrator

Background The oculomotor neural integrator (NI) is a conceptual neuronal mechanism that maintains eye position after each scanning saccade without visual feedback in the dark. Saccades are triggered by an impulse-like activity of brain stem burst neurons that, similar to a mathematical function, must be integrated to produce a step-like motor command. The impulseand step-like signals are combined in motor neurons to produce a rapid saccadic eye movement followed by a stable eye position. In the Laplace domain, a perfect integrator is described as 1/s and an imperfect one as 1/(s+a) with a positive a being “leaky” and a negative a, “unstable”. Experimentally, the NI was found to be modifiable by using visual feedback paradigms to imitate either ‘leaky’ or ‘unstable’ behaviors [1]. In goldfish, neurons exhibiting a highly correlated NI activity have been found in the hindbrain Area I [1]. A recent study demonstrated 3 types of neurons in Area I: ipsilateral (37%), conjugate (59%), and contralateral (4%) [2]. The ipsiand contralateral neurons increased their firing rate when the ipsiand contralateral eye positions changed in the temporal and nasal direction, respectively. By contrast, the conjugate neurons did not distinguish between the eyes and fired in both cases. This finding predicts that if the visual feedback paradigm would be applied exclusively to either a nasal or temporal hemi-field of one eye, the effect of training would not be confined to the trained hemi-field.

Signaling mechanisms in mirror image pain pathogenesis.

It is now clear that a peripheral nerve lesion affects contralateral non-lesioned structures, and thus such a lesion can result in mirror image pain. The pathogenesis is still not exactly known, but there are some possible signaling pathways in the contralateral reaction of the nerve tissue after unilateral nerve injury. Potential signaling pathways of contralateral changes can be generally divided into humoral and neuronal mechanisms. Damage to peripheral nerves or spinal roots produces a number of breakdown products with development of an aseptic inflammatory reaction. Released immunomodulatory cytokines are believed to be transported via blood or cerebrospinal fluid into the contralateral part of the body affecting spinal roots, dorsal root ganglia or peripheral nerves. Because neurons are elements of a highly organized network, injury to the peripheral neuron results in signals that travel transneuronally into the central nervous system and affects the contralateral homonymous neurons. There is also evidence that spinal glia creates and maintain pathological pain. Additionally, there may be compensatory changes in behavior of animals with an impact on contralateral neurons, such as altered stance and motor performance or autonomic reflex changes. Although the transneuronal signaling pathway appears to be plausible, the humoral signaling pathway or other communication systems cannot be excluded at this time. Knowledge about these processes has clinical implications for the understanding of chronic neuropathic pain states, and, therefore, further studies will be necessary. Understanding signaling mechanisms in mirror image pain pathogenesis may provide novel therapeutic targets for the management of neuropathic pain.

Different Roles for Homologous Interneurons in Species Exhibiting Similar Rhythmic Behaviors

It is often assumed that similar behaviors in related species are produced by similar neural mechanisms. To test this, we examined the neuronal basis of a simple swimming behavior in two nudibranchs (Mollusca, Opisthobranchia), Melibe leonina and Dendronotus iris. The side-to-side swimming movements of Dendronotus [1] strongly resemble those of Melibe [2, 3]. In Melibe, it was previously shown that the central pattern generator (CPG) for swimming is composed of two bilaterally symmetric pairs of identified interneurons, swim interneuron 1 (Si1) and swim interneuron 2 (Si2), which are electrically coupled ipsilaterally and mutually inhibit both contralateral counterparts [2, 4]. We identified homologs of Si1 and Si2 in Dendronotus. (Henceforth, homologous neurons in each species will be distinguished by the subscripts (Den) and (Mel).) We found that Si2(Den) and Si2(Mel) play similar roles in generating the swim motor pattern. However, unlike Si1(Mel), Si1(Den) was not part of the swim CPG, was not strongly coupled to the ipsilateral Si2(Den), and did not inhibit the contralateral neurons. Thus, species differences exist in the neuronal organization of the swim CPGs despite the similarity of the behaviors. Therefore, similarity in species-typical behavior is not necessarily predictive of common neural mechanisms, even for homologous neurons in closely related species.

Inhibition in Superior Colliculus Neurons in a Brightness Discrimination Task?

Simultaneous recordings were collected from between two and four buildup neurons from the left and right superior colliculi in rhesus monkeys in a simple two-choice brightness discrimination task. The monkeys were required to move their eyes to one of two response targets to indicate their decision. Neurons were identified whose receptive fields were centered on the response targets. The functional role of inhibition was examined by conditionalizing firing rate on a high versus low rate in target neurons 90 ms to 30 ms before the saccade and examining the firing rate in both contralateral and ipsilateral neurons. Two models with racing diffusion processes were fit to the behavioral data, and the same analysis was performed on simulated paths in the diffusion processes that have been found to represent firing rate. The results produce converging evidence for the lack of a functional role for inhibition between neural populations corresponding to the two decisions.

Genetic visualization with an improved GCaMP calcium indicator reveals spatiotemporal activation of the spinal motor neurons in zebrafish

Animal behaviors are generated by well-coordinated activation of neural circuits. In zebrafish, embryos start to show spontaneous muscle contractions at 17 to 19 h postfertilization. To visualize how motor circuits in the spinal cord are activated during this behavior, we developed GCaMP-HS (GCaMP-hyper sensitive), an improved version of the genetically encoded calcium indicator GCaMP, and created transgenic zebrafish carrying the GCaMP-HS gene downstream of the Gal4-recognition sequence, UAS (upstream activation sequence). Then we performed a gene-trap screen and identified the SAIGFF213A transgenic fish that expressed Gal4FF, a modified version of Gal4, in a subset of spinal neurons including the caudal primary (CaP) motor neurons. We conducted calcium imaging using the SAIGFF213A; UAS:GCaMP-HS double transgenic embryos during the spontaneous contractions. We demonstrated periodic and synchronized activation of a set of ipsilateral motor neurons located on the right and left trunk in accordance with actual muscle movements. The synchronized activation of contralateral motor neurons occurred alternately with a regular interval. Furthermore, a detailed analysis revealed rostral-to-caudal propagation of activation of the ipsilateral motor neuron, which is similar to but much slower than the rostrocaudal delay observed during swimming in later stages. Our study thus demonstrated coordinated activities of the motor neurons during the first behavior in a vertebrate. We propose the GCaMP technology combined with the Gal4FF-UAS system is a powerful tool to study functional neural circuits in zebrafish.

Encoding of Eye Position in the Goldfish Horizontal Oculomotor Neural Integrator

Monocular organization of the goldfish horizontal neural integrator was studied during spontaneous scanning saccadic and fixation behaviors. Analysis of neuronal firing rates revealed a population of ipsilateral (37%), conjugate (59%), and contralateral (4%) eye position neurons. When monocular optokinetic stimuli were employed to maximize disjunctive horizontal eye movements, the sampled population changed to 57, 39, and 4%. Monocular eye tracking could be elicited at different gain and phase with the integrator time constant independently modified for each eye by either centripetal (leak) or centrifugal (instability) drifting visual stimuli. Acute midline separation between the hindbrain oculomotor integrators did not affect either monocularity or time constant tuning, corroborating that left and right eye positions are independently encoded within each integrator. Together these findings suggest that the "ipsilateral" and "conjugate/contralateral" integrator neurons primarily target abducens motoneurons and internuclear neurons, respectively. The commissural pathway is proposed to select the conjugate/contralateral eye position neurons and act as a feedforward inhibition affecting null eye position, oculomotor range, and saccade pattern.

MicroRNA‐21 protects neurons from ischemic death

MicroRNAs are small RNAs that attenuate protein expression by complementary binding to the 3'-UTR of a target mRNA. Currently, very little is known about microRNAs after cerebral ischemia. In particular, microRNA-21 (miR-21) is a strong antiapoptotic factor in some biological systems. We investigated the role of miR-21 after stroke in the rat. We employed in situ hybridization and laser capture microdissection in combination with real-time RT-PCR to investigate the expression of miR-21 after stroke. In situ hybridization revealed that miR-21 expression was upregulated in neurons of the ischemic boundary zone, and quantitative real-time RT-PCR analysis revealed that stroke increased mature miR-21 levels by approximately threefold in neurons isolated from the ischemic boundary zone by laser capture microdissection as compared with homologous contralateral neurons 2 days (n = 4; P < 0.05) and 7 days (n = 3; P < 0.05) after stroke. In vitro, overexpression of miR-21 in cultured cortical neurons substantially suppressed oxygen and glucose deprivation-induced apoptotic cell death, whereas attenuation of endogenous miR-21 by antisense inhibition exacerbated cell death after oxygen and glucose deprivation. Moreover, overexpression of miR-21 in neurons significantly reduced FASLG levels, and introduction of an miR-21 mimic into 293-HEK cells substantially reduced luciferase activity in a reporter system containing the 3'-UTR of Faslg. Our data indicate that overexpression of miR-21 protects against ischemic neuronal death, and that downregulation of FASLG, a tumor necrosis factor-α family member and an important cell death-inducing ligand whose gene is targeted by miR-21, probably mediates the neuroprotective effect. These novel findings suggest that miR-21 may be an attractive therapeutic molecule for treatment of stroke.