Set Of Interneurons Research Articles

Distributed processing of load and movement feedback in the premotor network controlling an insect leg joint.

In legged animals, integration of information from various proprioceptors in and on the appendages by local premotor networks in the central nervous system is crucial for controlling motor output. To ensure posture maintenance and precise active movements, information about limb loading and movement is required. In insects, various groups of campaniform sensilla (CS) measure forces and loads acting in different directions on the leg, and the femoral chordotonal organ (fCO) provides information about movement of the femur-tibia (FTi) joint. In this study, we used extra- and intracellular recordings of extensor tibiae (ExtTi) and retractor coxae (RetCx) motor neurons (MNs) and identified local premotor nonspiking interneurons (NSIs) and mechanical stimulation of the fCO and tibial or trochanterofemoral CS (tiCS, tr/fCS), to investigate the premotor network architecture underlying multimodal proprioceptive integration. We found that load feedback from tiCS altered the strength of movement-elicited resistance reflexes and determined the specificity of ExtTi and RetCx MN responses to various load and movement stimuli. These responses were mediated by a common population of identified NSIs into which synaptic inputs from the fCO, tiCS, and tr/fCS are distributed, and whose effects onto ExtTi MNs can be antagonistic for both stimulus modalities. Multimodal sensory signal interaction was found at the level of single NSIs and MNs. The results provide evidence that load and movement feedback are integrated in a multimodal, distributed local premotor network consisting of antagonistic elements controlling movements of the FTi joint, thus substantially extending current knowledge on how legged motor systems achieve fine-tuned motor control.NEW & NOTEWORTHY Proprioception is crucial for motor control in legged animals. We show the extent to which processing of movement (fCO) and load (CS) signals overlaps in the local premotor network of an insect leg. Multimodal signals converge onto the same set of interneurons, and our knowledge about distributed, antagonistic processing is extended to incorporate multiple modalities within one perceptual neuronal framework.

Temporal Coding of Reward Value in Monkey Ventral Striatal Tonically Active Neurons.

The rostromedioventral striatum is critical for behavior dependent on evaluating rewards. We asked what contribution tonically active neurons (TANs), the putative striatal cholinergic interneurons, make in coding reward value in this part of the striatum. Two female monkeys were given the option to accept or reject an offered reward in each trial, the value of which was signaled by a visual cue. Forty-five percent of the TANs use temporally modulated activity to encode information about discounted value. These responses were significantly better represented using principal component analysis than by just counting spikes. The temporal coding is straightforward: the spikes are distributed according to a sinusoidal envelope of activity that changes gain, ranging from positive to negative according to discounted value. Our results show that the information about the relative value of an offered reward is temporally encoded in neural spike trains of TANs. This temporal coding may allow well tuned, coordinated behavior to emerge.SIGNIFICANCE STATEMENT Ever since the discovery that neurons use trains of pulses to transmit information, it seemed self-evident that information would be encoded into the pattern of the spikes. However, there is not much evidence that spike patterns encode cognitive information. We find that a set of interneurons, the tonically active neurons (TANs) in monkeys' striatum, use temporal patterns of response to encode information about the discounted value of offered rewards. The code seems straightforward: a sinusoidal envelope that changes gain according to the discounted value of the offer, describes the rate of spiking across time. This temporal modulation may provide a means to synchronize these interneurons and the activity of other neural elements including principal output neurons.

Refined parcellation of the nervous system by algorithmic detection of hidden features within communities.

The nervous system can be represented as a multiscale network comprised by single cells or ensembles that are linked by physical or functional connections. Groups of morphologically and physiologically diverse neurons are wired as connectivity patterns with a certain degree of universality across species and individual variability. Thereby, community detection approaches are often used to characterize how neural units cluster into such densely interconnected groups. However, the communities may possess deeper structural features that remain undetected by current algorithms. We present a scheme for refined parcellation of neuronal networks, by identifying local integrator units (LU) that are contained in network communities. An LU is defined as a connected subnetwork in which all neuronal connections are constrained within this unit, and can be formed for instance by a set of interneurons. Our method uses the Louvain algorithm to detect communities and participation coefficients to discriminate local neurons from global hubs. The sensitivity of the algorithm for discovering LUs with respect to the choice of community detection algorithm and network parameters was tested by simulations of different synthetic networks. The appropriateness of the algorithm for real-world scenarios was demonstrated on weighted and binary Caenorhabditis elegans connectomes. The detected LUs are distinctly localized within the worm body and clearly define functional groups. This approach provides a robust, observer-independent parcellation strategy that is useful for functional structure confirmation and potentially contributes to the current efforts in quantitative whole-brain architectonics of different species as well as the analysis of functional connectivity networks.

T18. High dose phenobarbital is safe and effective treatment for SCN2A related epilepsy

Introduction Voltage-gated sodium channels play major role in neuronal excitability. Nav1.1, Nav1.2, Nav1.3 and Nav1.6 sodium channels found in the brain differ in α -subunits, encoded by SCN1A, SCN2A, SCN3A, and SCN8A genes respectively. NaV1.2 Channels is the only sodium channel expressed during early development at nodes of Ranvier and in the axon initial segment (AIS) in developing and mature neurons, particularly cortical glutamatergic pyramidal cells. NaV1.2 channel has relatively high exictation threshold. NaV1.2 is regulated developmentally by alternative splicing to produce ‘neonatal’ and ‘adult’ isoforms. ‘Neonatal’ form is less excitable than ‘adult’ conferring reduced neuronal excitability and seizure susceptibility. Most dominantly inherited missense genetic variants of NaV1.2 manifests as familial epilepsy while de novo mutations as severe epileptic encephalopathy, both have gain of function with increased excitability and lowered seizure threshold. Cortical pyramidal neurons AIS receives exclusively inhibitory GABA-ergic input from specific set of interneurons called chandelier cells. Methods A FT, WF child born via planned caesarian to a healthy 27 yr G2P2A0L2 with APGAR 8, 9 at 1, 5 min at OSH. On DOL 2, developed seizure manifested as chocking, left arm forced flexion with leftward head deviation, right arm extension evolve into whole body jerking with apnea. Ictal EEG documented left frontal-temporal onset focal seizure. She received two loading doses of Phenobarbital followed by maintenance of 5 mg/kg/day. At therapeutic level of 44 mcg/ml, seizures remained under controlled. On DOL 22, presented to OSH with right arm twitching. Random PHB level was 27.5 mcg/ml. She received load of PHB and Levetiracetam 20 mg/kg each. Seizures continued overnight leading to transfer to our institute. Patient physcial and neurologic exam was normal. Ictal EEG re-demonstrated left central onset rhythmic spike-wave seizure evolution pattern clinically manifesting wide-eyed gaze with right face and upper extremity clonic jerking. Patient received total dose of 40 mg/kg of levetiracetam without improvement. Later, two 10 mg/kg doses of PHB given at couple of hours interval stopped seizures. Maintenance dosing of PHB was increased to 6 mg/kg/day. PHB level obtained was 54.2mcg/ml. It was tolerated well without sedation, hypotonia or adverse effects. She has been weaned off PHB at 7 months of age and has been seizure free with normal development at 14 months of age. Gene DX Comprehensive Epilepsy Panel revealed pathogenic variant of the SCN2A gene (p. Val261Met). Results We described infant with de novo SCN2A mutation presenting as benign familial neonatal infantile epilepsy well controlled with high therapeutic phenobarbital level without experiencing adverse side effects. Conclusion Phenobarbital at very high therapeutic level exerted seizure control probably via inhibitory effects of Chanderlier cell counterbalancing increased excitability of genetic missense variant of NaV1.2 at the AIS.

TMS of primary motor cortex with a biphasic pulse activates two independent sets of excitable neurones

BackgroundBiphasic pulses produced by most commercially available TMS machines have a cosine waveform, which makes it difficult to study the interaction between the two phases of stimulation. ObjectiveWe used a controllable pulse TMS (cTMS) device delivering quasi-rectangular pulse outputs to investigate whether monophasic are more effective than biphasic pulses. MethodsTemporally symmetric (“biphasic”) or highly asymmetric (“monophasic”) charge-balanced biphasic stimuli were used to target the hand area of motor cortex in the anterior-posterior (AP) or posterior-anterior (PA) initial current direction. ResultsWe observed the lowest motor thresholds and shortest motor evoked potential (MEP) latencies with initial PA pulses, and highest thresholds and longest latencies with AP pulses. Increasing pulse symmetry tended to increase threshold with a PA direction whereas it lowered thresholds and shortened latencies with an AP direction. Furthermore, it steepened the MEP input-output curve with both directions. Conclusions“Biphasic” TMS pulses can be viewed as two monophasic pulses of opposite directions, each stimulating a different set of interneurons with different thresholds (PA < AP). At threshold, the reverse phase of an initially PA pulse increases threshold compared with “monophasic” stimulation. At higher intensities, the reverse phase begins to activate AP-sensitive neurones and increase the effectiveness of stimulation above that of a “monophasic” PA pulse. “Biphasic” stimulation with initially AP pulses is dominated at threshold by activation produced by the lower threshold reverse (PA) phase. SignificanceThe effects of biphasic stimulation are best understood as the summed output of two independent sets of directionally selective neural populations.

Multiple sclerosis: Serum anti-CNS autoantibodies

Background: It is uncertain whether there are autoantibodies detectable by indirect immunofluorescence in the serum of patients with multiple sclerosis (MS). Objective: To determine whether there are anti-central nervous system (CNS) autoantibodies detectable by indirect immunofluorescence in the serum of MS patients. Methods: Sera and in some cases cerebrospinal fluid from 106 patients with multiple sclerosis, 156 patients with other neurological diseases, and 70 healthy control subjects were examined by indirect immunofluorescence using cryostat sections of rat cerebrum fixed by perfusion with paraformaldehyde. Results: Autoantibodies were detected that recognized more than 30 neuronal, glial, and mesodermal structures in 28 of 106 MS cases. Most were also detected in patients with other related and unrelated neurological diseases and several were also found in healthy controls. Novel anti-CNS autoantibodies recognizing particular sets of interneurons were detected in both normal controls and in subjects with CNS diseases. Interpretation: Serum anti-CNS autoantibodies of diverse specificities are common in MS patients. The same anti-CNS autoantibodies are not uncommon in patients with other neurological diseases. The findings provide no support for the proposition that myelin breakdown in MS is caused by exposure of intact myelin sheaths or oligodendrocytes to a pathogenic serum anti-myelin or anti-oligodendrocyte autoantibody.

Activation-dependent learning rule for GPCR localization - 5ht2AR regulation in prefrontal cortical neurons

Serotonin (5-ht) through 5ht2A receptors increases neuronal excitability (the neuronal gain function) by blocking voltage-gated K+ channels (Kv1.5) [1]. 5ht2A receptors also reduce calcium influx and activate calcium from intracellular stores (Ca[i]) [2]. High agonist exposure generally decreases 5ht2A density through endocytosis [3], in contrast 5ht2A receptors are upregulated after 5-ht innervation loss or under low 5ht exposure [4]. Both adaptations usually requires increase of Ca[i] and/or PKC pathway activation. We want to understand the contribution of serotonin receptor and other GPCR regulation on neuronal plasticity by the differential expression level of these receptors and the conditions for their regulation. As a hypothesis to guide further research, we propose to use a learning rule for 5ht2A placement, such that receptor density (R) is decreased by high agonist, or increased by low agonist, but only in the presence of high internal calcium. ΔR = X5ht-5htmγCai/Caim Here [5ht]m is the average 5ht concentration, [Cai]m the average calcium concentration, 5ht is the actual concentration, x and γ are scaling factors. We further assume that [Cai] reflects the history of neuronal activation. This learning rule may now be used in a network of model neurons. Principal neurons in prefrontal cortex (PFC) are initialized with a random distribution of 5ht2A receptors linked to voltage-gated K+ channels to regulate neuronal excitability. The model contains glial cells as variable sinks or sources of glutamate, to stabilize network activation, and a set of interneurons which contain activating 5ht2a receptors [5]. Synaptic connectivity is initially random. The model is loaded with patterns which produce a characteristic recurrent neural representation, determined by the synaptic connectivity and the 5ht2A-regulated intrinsic gain functions [1]. The model is trained under 5ht stimulation of varying magnitudes. 5ht increases excitability of neurons in a dose-dependent manner, and the density of 5ht2A receptors affects the intrinsic gain functions. We can show that patterns that were learned under high serotonin contain neurons with decreased 5ht sensitivity. When similar patterns are re-eoncountered under average or low serotonin conditions, these (the overlapping) features will be suppressed. Since the relevant neurons have decreased response to serotonin, they also have decreased excitability. The model could be altered to use dendritic regions rather than neurons. Since 5ht memory affects neuronal excitability, we have intrinsically generated differences in firing rates that start to affect synaptic connectivity. This creates traces in synaptic connectivity independent of 5ht activation. If 5ht2AR memory is erased, the trace is still present. Synaptic connectivity also determines which neurons (dendritic regions) receive sufficient input to undergo 5ht-mediated plasticity. The transfer of memory between synaptic connectivity and G-protein coupled receptor (GPCR) localization is therefore a two-way process. Memory may be stored in different places at different times. The model is undoubtedly simplistic, since many co-regulations among GPCRs exist, which are cell-type specific and require detailed analysis. But it directly explains findings such as [6], where 5-HT2AR stimulation produces an increase in activity for preferred target locations and/or a reduction in activity for nonpreferred locations in a working memory task in PFC. Most importantly, it provides a unified starting point to understand the regulation of GPCR distribution as a method for pattern storage that is synergistic with but not identical to AMPA synaptic strengthening or weakening, and may play an as yet not well understood role in the maintenance of a synapse.

Parameter dependent changes in strength of phase locking in a stochastic simulated central pattern generator

Walking behavior is produced by an oscillatory network of neurons termed the spinal central pattern generator for locomotion (sCPG). The basic building block of this sCPG is a half-center oscillator composed of two mutually inhibitory sets of interneurons each controlling one of the two dominant phases of the locomotor cycle: flexion and extension. The identity and function of neurons making up the sCPG are currently poorly characterized [1].

Homophilic Binding of Dscam Isoforms

Nervous system function depends on the specificity of individual neuronal connections, which in turn involves recognition of cell surface molecules during neuronal development. Dscam , which encodes an immunoglobulin (Ig) superfamily cell adhesion molecule (Down syndrome cell adhesion molecule) implicated in Drosophila axonal pathfinding, can give rise to 38,016 protein isoforms that share a common domain structure but differ in three extracellular Ig domains (Ig2, Ig3, Ig7). Individual neurons express multiple isoforms, and different neurons express distinct sets of isoforms. Wojtowicz et al. overexpressed a single Dscam isoform in Drosophila midline cells and a set of interneurons whose axons cross the midline and found a marked reduction in the number of axons crossing the midline at the posterior commissure. Dscam isoforms showed homophilic binding in assays involving aggregation of fluorescent beads bound to Dscam extracellular domain-Fc chimeras, decorated beads binding to COS cells expressing Dscam, and pull-downs from extracts of Drosophila S2 cells expressing FLAG-tagged Dscam. Further, the aggregation assay indicated that different isoforms differed in the rate and extent of aggregation. However, different isoforms did not bind to each other. Binding specificity depended on all three variable Ig domains, and even isoforms that differed in only 7 to 12 amino acids of Ig7 showed little if any heterophilic binding. The authors suggest that this specificity of Dscam interaction could promote repulsive interactions between sister branches of the same axon that share their entire Dscam complement, whereas low levels of signaling from neurites that share only some isoforms could lead to adhesion. W. M. Wojtowicz, J. J. Flanagan, S. S. Millard, S. L. Zipursky, J. C. Clemens, Alternative splicing of Drosophila Dscam generates axon guidance receptors that exhibit isoform-specific homophilic binding. Cell 118 , 619-633. [Online Journal]

Comparative pharmacology of feeding in molluscs

1. This paper reviews the role of transmitters in identified neurons of gastropod molluscs in generating and modulating fictive feeding. 2. In Lymnaea and Helisoma the 3 phase rhythm is generated by sets of interneurons which use acetylcholine for the N1 (protraction) phase, glutamate for the N2 (rasp) phase interneurons. The N3 interneurons are likely to use several different transmitters, of which one is octopamine. 3. In all the species examined, serotonin (5-HT) is released from giant cerebral cells. Other amines, including dopamine and octopamine, are present in the buccal ganglia and all these amines activate or enhance feeding. 4. Nitric oxide (NO), mostly originating from sensory processes, can also activate fictive feeding, but (at least in Lymnaea) may also be released centrally from buccal (B2) and cerebral neurons (CGC). 5. The central pattern generator for feeding is also modulated by peptides including APGWamide, SCP(B) and FMRFamide. 6. There is increasing evidence that most of these transmitters/modulators act on feeding neurons through second messenger systems--allowing them to act as longer-lasting neuromodulators of the feeding network. 7. Many of the transmitters are used in similar ways by each of the gastropods examined so far, so that their function in the CNS seems to have been conserved through evolution.

Consistency of interneuronal group formation in response to stimulation of identified cells.

In crayfish stimulation of abdominal positioning interneurons (APIs) recruits other interneurons producing various abdominal movements. We investigated whether: (1) the same API from different preparations activated a similar number or group of interneurons, (2) different APIs activated different groups, and (3) repeated stimulation of an API consistently affected a similar set of interneurons. To quantify the similarities and differences of the recruited interneuronal groups we compared the number of interneurons affected, their firing frequencies, and motor outputs. Three types of APIs (Curly Q, L and T) were identified and each type was stimulated in three preparations. Our results showed that for the Curly Q and L cells, each cell type activated interneuronal groups that were statistically similar in number and firing frequency. The T cell activated interneuronal groups that were more variable. Some APIs generally provided a repeatable motor output; all did not. The interneuronal groups activated by the Curly Q, L and T cells were very different from each other. Repeated stimulation of one Curly Q cell affected similar although not identical sets of interneurons. These data suggest that repeated motor outputs could be produced by a similar but not identical group of cells.

Calretinin-immunoreactivity in organotypic cultures of the rat cerebral cortex: effects of serum deprivation

Calretinin, a calcium-binding protein, is expressed in a specific set of interneurons in the adult rat cortex. Although its role in development is not known with any degree of certainty, evidence in support of a neuroprotective function has been forthcoming. To test this hypothesis, we submitted organotypic cultures (interphase technique) of 4- to 6-day-old rat brain slices to nutritive stress by serum deprivation for 1-3 weeks. Cultures were immunolabelled either with an antiserum against calretinin or with an antibody against MAP2 (the latter being used to assess neuronal cell number). In control (serum-enriched) cultures, the pattern of development of calretinin immunoreactivity mimicked that evinced in vivo with respect to layer- and cell-type specificity, but the maturation process was retarded by about 1 week. In the experimental group, cultures were incubated for 1 week in the presence of serum and then transferred to serum-free medium for an additional 2 weeks. Tissue was characterized by necrotic foci, a marked decrease in neuronal cell number and a further retardation in the course of development of the calretinin immunoreactivity pattern. The proportion of calretinin-immunoreactive cells to total number of viable neurons was 16% in serum-free cultures as against 9% in serum-enriched ones, suggesting that cells expressing the calcium-binding protein exhibit a greater tenacity for survival under conditions of nutritive stress, and thereby supporting the contention that calretinin acts in a neuroprotective capacity.

Inputs to group II-activated midlumbar interneurones from descending motor pathways in the cat.

1. Connections from descending motor pathways to group II-activated interneurones in the midlumbar segments of the spinal cord have been examined by intracellular recording. Interneurones, many of which had axonal projections to the hindlimb motor nuclei, were tested for inputs from rubro-, reticulo-, vestibulo- or corticospinal fibres. 2. Of 138 cells, 113 were monosynaptically excited by electrical stimulation of at least one of the descending motor pathways. Monosynaptic excitation from reticulo-, vestibulo- and rubrospinal pathways was common. Monosynaptic corticospinal EPSPs were identified in fewer neurones. 3. Convergent monosynaptic inputs from pathways which descend in the ventrolateral and ventral funiculi were common. Although few neurones with monosynaptic input from the corticospinal tract were identified, most also had monosynaptic rubrospinal input. In contrast, few neurones (4.3%) had convergent monosynaptic input both from pathways in the dorsolateral funiculus and from fibres in the ventral/ventrolateral funiculi. 4. The patterns of convergence from the different descending motor pathways differ from the patterns expected if the descending connections were distributed independently. Thus there is a significant segregation between rubrospinal and reticulo- or vestibulospinal inputs, and a significant association of reticulo- and vestibulospinal inputs. 5. Since descending motor pathways make monosynaptic connections with most group II-activated midlumbar neurones, many of which project to the hindlimb motor nuclei, some of these neurones provide a disynaptic pathway for the supraspinal control of hindlimb movements. The distribution of descending connections is consistent with the hypothesis that pathways descending in the dorsal part of the lateral funiculus and those descending in the ventrolateral or ventral funiculi contact different sets of interneurones.

Response dynamics and directional properties of nonspiking local interneurons in the cockroach cercal system

The response properties and directional receptive fields of nonspiking local interneurons in the cercal system of the cockroach are described. Wind-evoked responses were recorded intracellularly, and then analyzed by means of the Wiener kernel method in which a Gaussian white noise signal was used as a stimulus. Cross-correlation between the response and the white noise signal produced first- (linear) and second-order (nonlinear) kernels that were used to define input-output characteristics of the interneurons. Three sets of interneurons were distinguished on the basis of kernel analysis. First, responses in interneurons 101, 107, 111, and 203 were characterized predominantly by a differentiating first-order kernel, which suggests a linear relationship to the stimulus. The amplitude and waveform of the kernel changed with the change in stimulus angle, indicating that these four cells are directionally sensitive. Second, responses in interneurons 102 and 103 were also directionally sensitive but highly nonlinear. The first-order kernel was biphasic, whereas the second-order kernel had an elongated depolarizing peak on the diagonal. The response dynamics were accounted for by a cascade of two filters, a linear band-pass filter and a static nonlinear filter, in which the nonlinearity is a signal compression (or a rectification). Third, responses in interneurons 104 and 201 consist largely of the second-order nonlinear component. The second-order kernel, which had an elongated depolarizing peak or a hyperpolarizing valley on the diagonal, did not show any directional preference. The second-order nonlinearity was dynamic, and could be modeled by a band-pass linear filter-static nonlinearity-low-pass linear filter cascade, where the static nonlinearity is a full-wave rectification. The band-pass filter would simply reflect the mechanical property of cercal hair sensilla, whereas the low-pass filter represents the transfer at synapses between the cercal afferents and the interneurons. The nonlinear response thus explains the difference in the directional sensitivity while the differentiating first-order kernel explains the velocity sensitivity of the interneurons. We show that 101 and 107 respond most preferentially to wind from the left versus right, whereas 102, 103, 111, and 203 respond to wind from the front versus rear. Thus, it is suggested that there are two subsystems responding maximally to wind displacement along two coordinate directions, one for the longitudinal direction and the other for the transverse direction. On the other hand, the full-wave-rectifier nonlinear interneurons are omnidirectional, and thus suggested to code simply the power of the wind displacement.

The Posture of the Abdomen during Locust Flight: Regulation by Steering and Ventilatory Interneurones

ABSTRACT Tethered flying locusts (Locusta migratoria) make correctional steering movements with the abdomen when stimulated with a moving artificial horizon and integrated wind jet, simulating deviation from a straight course. Neurones in the metathoracic and first abdominal neuromeres of the metathoracic ganglion have been characterized morphologically and physiologically. The selective stimulation of these cells causes movements of the abdomen. One group of neurones responds directionally to visually perceived horizon movements and is excited by wind on the head. Some of these neurones are rhythmically activated at the flight frequency while others receive tonic drive from the flight oscillator. Electrical depolarization results in bending of the abdomen; the direction of this movement is always compatible with compensatory steering. Interneurones which are active during the expiration phase of ventilation also contribute to the posture of the abdomen in flight. They are not visually responsive but their selective inhibition at the onset of flight activity helps to bring the abdomen into flight posture. Some of these Interneurones are modulated at the flight frequency. The efficiency of cooperation between different sets of Interneurones in producing behavioural patterns and the signficance of single neurone stimulation are discussed.

Neural circuits mediating visual flight control in flies. II. Separation of two control systems by microsurgical brain lesions

The role of 2 sets of interneurons in the optic lobes of blowflies in visual course control was studied by means of brain lesions. The first set comprises the cells HS and H2, which respond to global horizontal motion. The second set are the FD-cells, which respond selectively to local horizontal motion. All these cells are output neurons of the third optic ganglion of flies and are thought to be coupled via descending neurons to the flight motor system. In 2 series of experiments specific cells of these 2 sets were inactivated by microsurgical brain lesions L1 and L2 respectively. The effects of the lesions on visual course control were tested by measuring the yaw torque responses of the animals in restrained flight before and after the operation. The flies were stimulated in these tests with monocular and binocular motion of periodic gratings moving in either the horizontal or the vertical direction. Lesion L1 in the right side of the brain inactivates the right HS-cells and the left H2- and FD-cells. This leads to a complete block of the response to binocular clockwise horizontal motion and a reduction of the response to monocular motion from front to back on the right side of the animal. Application of L1 also leads to a pronounced response to binocular motion from front to back not observed in normal animals. The response to monocular vertical motion is unaffected. Lesion L2 reduces all responses to monocular and binocular horizontal motion present in normal animals. The behavioral effects of the lesions are highly specific and consistent with predictions based on the well-known anatomical and physiological properties of the neural circuitry investigated. The results demonstrate directly that the HS-, H2-, and FD-cells control motion-induced steering maneuvers in flight.

GABA-like immunoreactivity of identified interneurons in the flight system of the locust, Locusta migratoria

The transmitter content of identified inhibitory interneurons in the flight system of the locust, Locusta migratoria, has been characterized using antibodies raised against protein-conjugated gamma aminobutyric acid. Identified flight neurons were filled with the fluorescent dye, Lucifer Yellow. Serial sections of dye-filled neurons were incubated with an antibody to gamma aminobutyric acid which was subsequently tagged with a fluorescent marker. Excitatory motoneurons to wing muscles and 13 flight interneurons (3 excitatory, 7 inhibitory, and 3 with unknown synaptic effect) were examined. Neither the moto-neurons nor any of the 3 excitatory interneurons contained immunoreactive material. Six of the 7 inhibitory interneurons did contain immunoreactive material. All the neurons which contained immunoreactive material and whose synaptic effect is known were inhibitory. We conclude that most of the inhibitory flight interneurons which have been described use gamma aminobutyric acid as their transmitter. Interestingly, at least 1 set of interneurons known to be inhibitory does not use gamma aminobutyric acid. We predict that the 2 interneurons which do contain immunoreactive material and whose synaptic effect is not yet known will be found to have inhibitory roles in the operation of the flight circuitry.

Neuronal organization of escape swimming inTritonia

1. Escape swimming behavior inTritonia diomedea consists of two major components: an initial reflexive withdrawal followed by a series of alternating ventral and dorsal flexions. The basic mechanism of generating motor neuron activity, therefore, switches from reflexive to centrally programmed. 2. Three classes of cerebral interneurons and some of their synaptic connections have been identified. 3. Reflexive withdrawal interneurons (RWI) receive direct input from sensory afferents and synapse with motoneurons in the pedal ganglion (DFN, VFN). This class of interneuron is excited during reflexive withdrawals and inhibited during the swim phase. 4. Swim interneurons (SI) are excited during reflexive withdrawals and burst during the swim phase. 5. The third set of interneurons (C2) are shown to be necessary for the normal initiation and maintenance of the cyclical swim phase. Activity in C2 neurons appears to retrigger the swim oscillator network cycle-by-cycle. 6. C2 neurons inhibit the RWI neurons during swimming thus freeing motoneurons to respond predominantly to inputs from the SI and C2 neurons. The switch from reflexive to programmed motor output is, therefore, mediated centrally by two identified C2 neurons.